QUT GP P 628.530994 1

VOLUME 1. No. 2 SEPTEMBER ,1967

Journal of the Clean Air Society of Austral ia and New Zea land

incorporated 1966

The aim of the Society is to conserve clean air in Australia and

New Zealand.

EDITOR:

Graham J. Cleary

ASSOCIATE EDITORS:

E. Finsten R. Williams

H. Voss

The Journal of the Clean Air Society of Australia

& New Zealand Published Quarterly

SUBSCRIPTION:

75c single copy $2.50 per year

The Clean Air Society of Australia and

New Zealand

PRESIDENT:

Mr. J. G. Schroder

SECRETARY:

Dr. G. J. Cleary

P.O. Box 31, George St. North

Post Office Sydney

2000 Australia

Telephone: 27.8541

Wholly set up and printed by The Sydney & Melbourne Publishing Co. Pty. Ltd.. 29 Alberta Street,

Sydney, 2000. Tel. 61-4369

Vol. 1 No. 2 SEPTEMBER, 1967

TECHNICAL PAPERS

Technical aspects of a modern cement plant . . . . 7

by W. M. Gale

Some arguments suggesting a causative relationship

between air pollutants and lung cancer . . . . 15 by Graham J. Cleary

Emissions from large municipal incinerators and control

of air pollution 19

by N. Y. Kirov

FEATURES

Inaugural dinner and meeting of the Victorian

branch 6

—-Election of office bearers

Leichhardt Smoke Abatement Advisory Panel . . . . 13

People 13

July meeting of the New South Wales branch . . . . 18

Air pollution projects 18

—Dust control from cotton processing —Projects completed recently or in

the process of construction

The First Australian Refuse Disposal Conference . . 25

—Report by K. S. Basden

Inaugural Dinner and Meeting of the Victorian Branch

The Inaugural Dinner and Meeting of the Victorian Branch of the Clean Air Society of Australia and New Zealand took place on Tuesday, August 15, 1967.

The dinner was held in the Savoy Plaza, Spencer Street, Melbourne. Mr. John Schroder, Federal President of the Clean Air Society, arrived from Sydney to head the table of over 50 guests. Mr. Schroder was introduced to the guests by Mr. Hans Hartmann of the Gas and Fuel Corporation of Victoria. Mr. W. Gale, of Southern Portland Cement, New South Wales, accompanied Mr. Schroder to Mel-bourne as guest speaker.

Mr. Schroder made a short speech in which he thanked the guests for the enthusiasm and interest shown by the large number present.

The dinner ended at 8.15 p.m. and the party then repaired to the Shell Theatrette on the corner of Bourke

and William Streets. With the addition of a number of people who were not able to be present at the dinner, the attendance at the Inaugural Meeting was increased to 70.

The meeting commenced at 8.30 p.m. with Mr. Hartmann officially introducing the Federal President, Mr. J. Schroder, and the guest speaker, Mr. W. Gale. Mr. Hartmann then handed the meeting over to Mr. Schroder.

The Federal President opened his speech by welcoming the guests. He then went on to explain the con-stitution of the Society, its aims and powers. On terminating his speech, he called on Mr. Gale to present his paper on Air Pollution Problems in the Cement Industry. Mr. Gale's presentation was assisted by excellent slides depicting the effects of dust in the cement industry and the results of air pollution control. Slides showing

cement plants operated by computer control created a good deal of interest.

The election of members of the Victorian Branch Council was then held and the following office bearers were elected for the ensuing year:

President: Mr. H. Hartmann. Secretary/Treasurer: Mr. D. L.

Draper. Committee: Messrs. A. T. Nealis,

B. Judd, J. Maher, L. Clunn, N. C. Hawthorn, B. T. Gray, J. M. Mclver, S. H. White.

After the election, Mr. Schroder handed over the meeting to the Vic-torian President Mr. Hans Hartmann. Mr. Hartmann in closing the proceed-ings expressed his gratitude for the support which led to the formation of the Victorian Branch.

September, 1967—CLEAN AIR 6

Although the relative contribution of a number of possible causative factors is not known with certainty, it is a fact that the increase in lung cancer in the 20th Century has been substantial and in the second technical paper appearing in this issue the major arguments suggesting a causative relationship between air pollutants and lung cancer are examined.

The First Australian Refuse Disposal Conference which was held at the University of New South Wales on August 22-23 last, filled a most pressing need. The interest shown in the Conference can be gauged not only by the impressive number of people who were present but also by the full and at times almost-too-lively discussion which ensued. Professor Kirov and the other members of the Organising Committee are to be congratulated on a job well done.

Congratulations must also be extended to our Victorian members on the very successful dinner and inaugural meeting held in Melbourne during August. We now look forward to the forma-tion of other branches to help focus attention on the problems of air pollution control in other parts of Australia and New Zealand, thereby enabling a more balanced overall assessment of the position to be made.

Many members may not be aware that the Society was granted membership of the International Union of Air Pollution Prevention Associations recently. This is a major step forward in our progress. Not only does it give international recognition to our Society but it opens the way for an exchange of information on air pollution problems with the other member associations in the United States of America, Great Britain. Argentina. France. Japan and West Germany. Membership in the International Union will also enable us to play a full and active role in future International Air Pollution Congresses. The first of these was held in London in October, 1966, and the second is to be held in Washington in either 1969 or 1970.

TECHNICAL ASPECTS OF A MODERN CEMENT PLANT

IN addition Iron Oxide is required in small quantities as it has a

fluxing effect which reduces the tem-perature at which the chemical re-actions can take place.

Calcium Oxide is obtained from limestone. Silica and Alumina are obtained from clay or shale but if they are not in the correct proportions then they can be corrected for by the addition of sand or bauxite. Iron Oxide is obtained from iron ore, pyrites cinders or steelworks pre-cipitator flue dust.

Types of Portland cement These elements are mixed in various

proportions to produce several types of Portland Cement, four of which are produced at Berrima.

These are:

Type 'A' Ordinary—For general construc-tion purposes.

Type 'A' Category 'B'—Moderate heat of hydration and moderate sulphate resistance. Used for major structures by the Snowy Mountains Authority.

Type 'B' High Early Strength—High early strength concrete when it is essential to use the structure as soon as possible after pouring.

Type 'C' Low Heat—Low heat of hydration for mass concrete construction and high sulphate resistance. This is the only cement used by the M.W.S. and D.B. for the last 30 years.

Growth in cement consumption and plant size

At present the New South Wales consumption of cement is about 1,400,000 tons per annum and is expected to rise to 1,770,000 tons in 1972. Berrima's share is 410,000 tons and is expected to rise to 590,000 tons in 1972.

With increase in consumption and variety of cements there has come a great change in plant and equipment requirements.

Mr. W. Gale.

In 1929 when the Berrima Works first started operation there were two small kilns each of 10 ft diameter x 180 ft long. Another kiln was added in 1954 of much the same size. A fourth added in 1957 was 11 ft 2 ins. diameter x 236 ft long with a calcina-tor at the back end. The effect of the calcinator is to recover heat from the waste gases thereby improving the fuel economy. The output is also increased and is equivalent to that of a 11 ft 2 ins. x 440 ft kiln.

In 1964 when a fifth kiln was in-stalled it was 15 ft 3 ins. diameter and 560 ft long. The output of this kiln is greater than that of the four old kilns combined and to produce one ton of clinker it uses less coal. Also less raw materials are required because of the more efficient dust collecting system.

Similarly there have been great changes in the size of ball mills. For example the four old cement mills

at Berrima are each 7 ft diameter x 36 ft long. Two have 600 hp and two have 750 hp motors. The new cement mill commissioned in May, 1966, is 11 ft diameter x 34 ft long and has a 2,000 hp motor. Mills are being built presently in other plants with motors well over 3,000 hp.

This rapid increase in size is typical of the changes in the cement industry but only a foretaste of the progress that is being made else-where. At present, in USA and Japan, the use of computers as a process tool is becoming widespread. This is affecting equipment design, plant layout and operating methods. Within the next 10 years, and possibly within the next 5, we should see computers in Australian plants and the associated changes that they will bring.

Clean Air Act and modern plant design

Cement plants have a reputation as being dusty, dirty places making working conditions difficult and un-pleasant. The Clean Air Act legisla-tion has caused attention to be focused on the problem of dust suppression and this has to be taken into account in the design of new plant.

However other factors are also at work calling for cleaner conditions generally and these are tied up with the changes in size of plant items and to changing methods of plant opera-tion which will be referred to later as each section of plant is described.

Modern cement plants in the USA are very attractive with a great deal of attention paid to the lay-out. The result is an uncluttered plant which is clean and pleasant to look at.

The advent of sophisticated operat­ing tools, such as the computer, coupled with clean air legislation has provided a much needed impetus in the attitude towards plant operating conditions.

It is worth noting that even if com-puters, etc., could tolerate dirty un-pleasant conditions it is unlikely that such a plant could attract and hold men of the calibre required to run it.

Basic process Reduced to fundamentals the manu­

facture of cement involves three main stages. These are:— 1. The proportioning of the raw

materials and the grinding of them, in ball mills, to a certain size.

CLEAN AIR—September, 1967 7

By W. M. Gale, B.Sc, B.E., A.M.I.E. (Aust.)

Portland Cement is the name given to the group of cementitious materials derived from the chemical combination of the Oxides of Calcium, Silicon and Aluminium into a group of complex compounds. This group occurs in a relatively small region of the phase diagram drawn for these three elements and is distinguished by its very high Calcium content.

2. Burning of the materials from Stage 1 in a rotary kiln to form the compounds that constitute cement clinker.

3. The grinding of this clinker, together with approximately 5 per cent, of gypsum to produce cement. This grinding is also done with ball mills.

These are two principal processes for the making of cement clinker:—

1. Wet process The raw materials are ground with

the addition of water to the mills to produce a slurry which is fed to the rotary kiln. The main advantages of the wet process are:— (a) Lower grinding cost. (b) No dust problem in the raw

milling and reduced problem at the kilns.

(c) Easier blending to obtain exact raw mix.

(d) Slurry can be handled with centrifugal pumps.

(e) Slurry can be easily fed to the rotary kiln.

2. Dry process The raw materials are dried to

less than 1 per cent, moisture and then ground to a fine powder. Advan-tages of the dry process are:— (a) Lower fuel consumption. (b) No water supply required. Disadvantages are:— (a) Higher grinding costs. (b) Greater difficulty in blending the

raw materials. (c) Higher dust losses from all

sections of the raw grinding plant and also from the kiln.

Raw milling This involves the reduction in

particle size of the raw materials until 80-90 per cent, passes through a 180 mesh sieve. This was men­tioned earlier as Stage 1.

The actual reduction is carried out in ball mills which are horizontal rotating cylinders charged with steel media which can be either spherical or cylindrical in shape and range in size from 1¼ in. to 4 in. in diameter or in. diameter by in. long to 2 in. diameter by 2 in. long. The total weight of balls is in excess of 50 tons in a modern mill which can range in size up to 14 ft diameter and 40 ft long requiring over 3,000 hp to drive it.

In the wet process dust problems are minimised due to the product being a slurry. Some dust suppression equipment may be required in the

8

has to be paid to this stage can be gauged from Table 1 where a typical analysis of raw materials is given and also a typical analysis of the desired blended kiln feed.

At some plants in the United States rapid analysis is being carried out u s i n g X-ray analysers and attempts are being made to have these analysers control (by computers) the mixing of raw materials. The use of X-ray analysers would reduce the time delay, between taking a sample and taking corrective action, from a matter of hours under the present system to a matter of minutes, and, of course, if the sequence is automatic then this delay is reduced even further. Referring to Fig. 1, the Analyser would be placed between the materials heap and the raw mill.

Attempts at automatic analysis and control in the United States have met with varying degrees of success. The analysers are, at this stage, generally suspect and difficulties have not been resolved in automatically taking and preparing samples to produce con-sistent results but there is no doubt that X-ray on-stream analysis will be here in a few years as a reliable process tool.

This means that the analyser will probably be housed near the raw materials dump, i.e., out in the works area. Obviously such expensive equipment will require clean rooms with filtered air, and air condition­ing. But in order to decrease the probability of analyser failure due to dirt and dust it will be almost essential to pay careful attention to the raw materials stacking and re-covery system so that the air-borne dust in the region of the analyser is kept at a practical minimum.

This is an example of the coming need for increased cleanliness from the point of view of equipment re-quirements rather than from the more common health and aesthetic point of view.

Burning The raw materials are fed to the

kiln where they are progressively heated to:—

September, 1967—CLEAN AIR

sections handling the raw materials but this will depend on the free water content in the raw materials. If problems do arise these are in the nature of dust coming from transfer points on conveyors, etc. In this regard the problem is similar to that of handling cement clinker and is discussed later.

In the dry process the problem of dust around the raw mills is similar to that encountered around cement mills and this is also discussed later.

One of the problems in preparing kiln feed is in proportioning the raw materials to o b t a i n the desired accuracy of chemical composition.

For example the Calcium Carbon-ate content of the limestone received at the Berrima Works varies from 70-95 per cent, and has to be blended to 83.0±0.1 per cent., for ordinary cement.

Another complication occurs when the fuel is coal because the ash takes part in the reaction to form clinker due to the fact that ash comprises silica, alumina, iron and a trace of calcium. A typical analysis of a Berrima coal ash is set out in Table 1.

The amount of ash and its com-position has to be allowed for when the raw materials are being blended.

Some raw materials systems use comparatively rough control methods in the initial mixing and grinding of raw materials and then use more refined methods of blending to pro-duce kiln feeds of fairly constant quality.

Other systems involve accurate and frequent analysis with regard to the percentages of the basic oxides in the raw materials and the control of the proportioning of the raw materials to give the correct ratios of the basic oxides. The degree of attention that

1. drive off any moisture present. 2. liberate the carbon dioxide present

in the limestone. 3. to raise the mixture to 2,500 deg.

Fahr. at which temperature the various chemical reactions take place to form clinker.

The clinker is discharged into a cooler which is generally some type of travelling grate through which air is passed in order to cool the clinker. Part of this air is used as secondary air in burning the coal, oil or gas. This recovery of heat reduces the coal requirements and hence increases efficiency.

The quench cooling of clinker is also carried out because it improves the properties of the final cement.

The main points of interest in dust suppression on a rotary kiln are:— (1) At the exhaust gas discharge

end, which is also the feed inlet end. This is the end where the electrostatic precipitator is shown on Fig. 1.

(2) At the waste gas outlet on the cooler. This is not shown on Fig. 1.

(3) At pulverised coal leaks in the coal milling circuit.

Discussing these in turn the first one is also usually the point of major concern on a kiln.

At Berrima the volume of exhaust gas is approximately 275,000 cfm from the 560 ft kiln and the dust collected by the electrostatic pre-cipitator is normally about 5 tons per hour. The dust collected is fed back into the kiln by a conveyor and elevator arrangement. The flow is in-dicated by the dotted line in Fig. 1. A special system of scoops is pro-vided so that the dust can enter the rotary kiln and yet minimise air leak-age into the kiln at that point. In a wet process the performance of the electrostatic precipitator is greatly enhanced by the water vapour present with the exhaust gases. This water comes from the slurry.

Dry process kilns do not have this water in the feed and often it is necessary to add it as an aid to pre-cipitator operation.

Wet process kilns, and some dry process, have at the feed end a large quantity of chains which hang down inside the kiln and flop about as the kiln rotates. These chains increase the efficiency of heat transfer between the exhaust gases and feed.

This is called the "Chain Section" and can be over 100 ft long and contain up to 200 tons of chains. At Berrima it is 80 ft long and contains 85 tons. The chains, their con-dition and disposition greatly affect the dust load on the precipitator.

If everything is in a reasonable state then the exhaust gases have to follow a tortuous path through the chains as obviously they will intro-duce turbulence to the stream. This turbulence will cause the gas to follow paths which most of the dust particles can't follow. Some of these particles will get caught by the flow of kiln feed and continue down the kiln. This has the effect of reducing the precipitator load. As chains wear with use the dust burden usually rises.

At Berrima experience has shown that best operation occurs if the material coming from the chains has 8 to 10 per cent of moisture for a feed containing 36 per cent. water.

If for some reason the temperature of the gases reaching the chains be-comes too high it is found that the slurry dries out too quickly and somewhere deep in this section a plastic zone occurs and a ring can

CLEAN AIR—September, 1967 9

build up. This ring reduces the in­ternal diameter of the kiln with a subsequent increase in gas velocity through this restricted area. When this happens the dust burden becomes so great that the mechanical means for returning dust to the kiln does not have sufficient capacity and trucks have to be used to dump dust. This is a waste and is undesirable. Under these conditions the dust make could be 12 to 15 tph.

For a given exhaust gas tempera­ture the moisture content of material coming from the chains depends on the chain pattern. If this pattern is incorrect it can drop the moisture to zero and a result similar to kiln maloperation is achieved with an in­crease in the dust loss.

Some kilns use bag filters instead of precipitators but many operators are relucant to use them because of problems of high temperatures on both wet and dry process kilns and at low temperatures on wet process.

On a dry process kiln the exhaust temperature can easily reach 800 deg. Fahr. due to faulty operation. In addition a condition of after­burning can exist due to excess coal being fed into the kilns. This coal initially consumes all the oxygen available but burns at a later stage when oxygen again becomes available due to air leaks in seals and ducting. The temperature resulting from either of these causes is above the generally accepted level for bag filters.

In a wet process kiln the quantity of water vapour in the exhaust gases can be quite large. For each ton of coal burnt there can be over 1.5 tons of water in the exhaust gases. If the exhaust gas temperature falls too low and water settles out in the fibres of the bag filters then it is not long b e f o r e the filter is completely blocked.

One seaside plant overseas found that in operation they had to run with a greater slurry moisture than the design figure. This resulted in lower exhaust gas temperature than design and bag filter malfunction. The bag collectors had to be by-passed with the result that the plant was only allowed to operate while an offshore breeze existed. Otherwise the plant had to be shut down; an expensive business when it is realised that a kiln must operate continuously and takes 24 hours to settle down after a minor upset and up to a week if off for any length of time.

It is interesting to dwell on the quantity of dust recovered by dust

collectors. Calculated on, say, 8,000 hours annual availability a loss of 5 tons per hour, if uncollected, repre­sents 40,000 tons per annum lost.

This is, of course, not the whole story as in many cases the loss of material is loss of a wasting asset. In the case of cement, the cement works can only exist as long as the source of raw materials lasts.

The loss of raw materials can only be deplored in the strongest of terms.

From the point of view of plant maintenance dust losses are also to be avoided. In the case of a cement kiln each ton of dust lost still has to be ground. Using the case of Berrima, if 5 tons of dust was lost for each 50 tons of clinker produced then for each week a raw mill is operated at present it would have to operate another 12 hours.

Now ball mills of all types are a constant maintenance problem. The work is heavy with the result that little real maintenance can be done in an hour or two. Imagine how breakdown and maintenance problems are aggravated by plant operating 12 hours extra each week just to make up dust loss. How much worse in these plants where the dust loss is as much as 10 tons per hour for each 50 or less tons of clinker pro­duced?

No mention has been made of the capital cost of excess plant capacity required to produce this dust loss, but of course this is also a major con­sideration.

It is not so much a question of whether you can afford to have efficient dust collection as much as whether you can afford not to have it.

As stated previously the cooler is used to cool the clinker as it falls from the kiln. The Berrima cooler has two fans on each side which force approximately 160,000 cfm of cold air up through the bed of clinker. Of this some 40,000 cfm goes to the kiln to help burn the coal and the balance goes out through a mechanical dust collector fan and stack.

The particles of clinker picked up and entrained by the air are compara­tively large and readily collected mechanically.

Coal is burnt in the kiln as pulverised fuel. To achieve this at Berrima, coal is dried and ground in a ball mill until about 80 per cent passes through a 180 mesh sieve. Heat for drying is obtained by draw­ing hot air to the coal mill circuit from the cooler.

Referring to the circuit in Fig. 2 it can be seen that air coming out of the mill rises to the separator. Coarse oversize particles are removed and returned to the mill. Fine particles continue on and are re­moved in the cyclone. From the cyclone coal goes to the fine coal bin where it is stored until extracted by the weigh feeder and fed to the kiln burner pipe.

Air leaving the fine coal cyclone continues to the mill exhaust fan. From there some goes back to the mill and some goes to the forced draught fan and thence into the kiln as primary air. The amount taken as primary air is equal to the quantity drawn off from the cooler plus leaks around the system.

The interesting part of the design of this circuit is that it is under suction so that at joints, etc., air leaks in rather than pulverised coal being blown out and deposited upon rafters, girts, etc. In this respect the installation at Berrima has been very successful.

The values of the suction at various points are set out in Fig. 2.

With respect to coal or other flammable materials the reduction of build up on other items of plant, building members, etc., has another advantage b e s i d e s keeping the atmosphere clean and equipment pleasant to the eye. This advantage relates to the explosive hazard.

Most people are aware that fine coal or similar material will ignite spontaneously if allowed to build up to more than a few inches deep. This is of course a fire hazard in some situations. In steel buildings it may not be of much concern except for its unsightliness.

But what is not generally realised is that this dust build up is in fact a major potential explosion hazard. When an explosion occurs within a plant item, such as inside the coal milling circuit of Fig. 2, then this explosion usually only disrupts that plant item. This is serious enough and obviously to be avoided.

However the main danger comes from the dust which is dispersed from ledges, window sills, girders, etc. This dust becomes distributed throughout the whole working area or building containing the coal plant and if ignited by the primary explosion, which shook it loose, or a spark from damaged electrical equipment, then the whole building becomes one large bomb. This effect is the cause of the worst explosions in coal milling and similar plant. This subject is dealt

10 September, 1967—CLEAN AIR

with in more detail in "Crushing and Grinding"—A Bibliography printed by Her Majesty's Stationery Office. This includes a few pages summarising the literature and a list of references.

As indicated earlier the size of kilns has increased greatly in a short space of time. Reference was also made to computers. These are being widely used in the USA and coming more into vogue throughout the world.

One problem in operating a kiln is the long time delay between feed entering the kiln and being discharged from the other end. At Berrima the residence time in the big kiln is about two hours. Thus the effect of change in a variable may not be seen for a long time.

A computer can be used to provide feed forward control not possible with normal analogue controllers. Also it can compare the effect of changes in several variables at once and apply the most suitable correc­tion.

There are several advantages from the use of a computer. These are:— 1. Increased fuel economy. At

Berrima approximately 29 tons of coal are used to make 100 tons of clinker so that even small economies would have a sub­stantial return.

2. More uniform product. 3. Increased output. 4. Increased brick life. A kiln is

lined with bricks over almost its whole length. In the high tem­perature zones these bricks are protected by a coating formed between the brick and the com­ponents of clinker. If the kiln does not run under uniform conditions this coating breaks away and takes some brick with it. Thus to lengthen brick life it is necessary to increase uniformity of operation.

5. Decreased plant maintenance due to longer periods of steady run­ning conditions.

The use of computers requires clean air rooms and as previously mentioned this is more easily achieved if the dust blowing around outside is kept to a minimum.

A computer, while running the kiln or kilns, is also used to calculate the most economical ratios of raw

materials based on information from the X-ray analyser.

The next step, and this is also happening in the USA, is to centralise controls for the whole cement works in one room. Some plants have gone so far as to control every operation from quarry to cement silos from one point.

Obviously this calls for very high plant availability and reliability be­tween periods of scheduled main­tenance. This cannot be achieved without special attention to dust control.

Cement milling Mills can operate in open or closed

circuit. In open circuit the material com­

ing from the discharge end of the mill is product. In closed circuit this is not so. The mill discharge is taken to a separator where the product is separated and the oversize returned to the mill. Closed circuit is shown on Fig. 1.

At Berrima the new 2,000 hp cement mill is closed circuited.

Dust emission is controlled by the

CLEAN AIR—September, 1967 11

use of an electrostatic precipitator and a mechanical collector.

One problem in grinding dry is that most of the horsepower con­sumed appears as heat thus raising the temperature of the cement. If this temperature is not controlled it can affect the quality of cement by dehydrating the gypsum and this can produce false setting times.

In order to control cement tem­perature in the 2,000 hp mill, water, atomised by compressed air, is injected into the mill outlet. The rate of water injection is metered by a temperature controller. This tem­perature is sufficiently high that all water evaporates and cannot hydrate the cement.

Possible leakages of dust around the mill ends are controlled by keeping the mill under suction and drawing approximately 5,000 cfm through it.

This air is drawn up to the pre­cipitator and carries the water vapour with it.

Other sections of the mill circuit in which there is likely to be water vapour are also vented to the pre­cipitator.

The presence of water vapour improves the precipitator performance and can be readily shown by turning the water off.

Sections of the mill circuit which do not carry water vapour are kept under suction with air being taken to a bagfilter.

In assessing the benefit of the pre­cipitator it is not merely a question of determining the quantity of cement collected and saying that it has a sale price of so many dollars per ton and hence a certain value over a given period. There are other benefits be­sides these.

In cement it is desirable to have a reasonably uniform gradation in size between the acceptable upper limit in particle size and the lower limit.

The particles collected in the electrostatic precipitator, in general, come from the lower size fractions. Thus if it is not collected it leaves a gap at this end. This means that if a certain average particle size or surface area is to be achieved, and surface area is a very widely used control criteria, then the size of the larger particles must be reduced.

The result is that for a mill of a given horsepower the amount of feed to the mill has to be cut back. But this reduction is greater than the amount that could be collected so that the loss in mill output is greater

12

than the loss which would occur if dust collection was not used.

Silos Once the cement is ground it is

conveyed pneumatically to silos. In the industry this is referred to as "pumping".

By this means cement and other fine powders can be conveyed over half a mile or more. At Berrima the cement silos are about 200 yards from the mills.

The quantity of air required varies with the amount of material to be conveyed but is approximately 500 cfm.

At the discharge end of the line this 500 cfm can produce a dust problem. As the air and cement is discharged from the end of the pipe line the air escapes from the silo through any possible openings carry­ing with it small quantities of fine cement.

The result over a period is that the top of silos and adjacent buildings become covered with cement which is a nuisance and a waste when dry but also becomes a costly cleaning item if it gets wet.

In order to overcome this on the three new bulk silos at Berrima bag type dust collectors are installed in housings on top of the silos and the silos are vented through the dust collectors. The cement collected is discharged directly back into the silos.

Despatch The final handling of cement at the

works comes when it is placed in bags or bulk hoppers for despatch to the customer.

Each cement bag is filled through a hole in one of the top corners. This hole is self sealing when the bag is full.

The cement enters the bag through a nozzle on the bagging machine. When the bag weight reaches a pre­determined value the supply to the nozzle is cut off and the bag falls away from the machine. There is always a small amount of cement which dribbles out of the nozzle. This produces a dust, irritating to the operators and covering associated machinery. It can also detract from customer appeal by producing dirty bags.

This can be minimised by causing a down draft of air past the operator, who sits just above the level of the nozzles, and taking this air away to dust collectors. These collectors are usually of the cloth type.

In bulk loading dust nuisance is caused by the displacement of air as

the cement fills the trucks. At Berrima this is eliminated under the new bulk silos by breathing air from the trucks into the dust collecting system at the top of the silos.

Transfer points While mills and kilns are the in­

teresting items of plant, the works as a whole is a large materials handling system. Thus conveyors and elevators are an integral part of the system and each transfer point between repre­sent a potential dust nuisance.

On the new clinker handling system at Berrima bag type filters have been used to control dust at these points. It has been quite successful but it would appear that with fine clinker bag life is too short.

General comments on collectors

Dust collectors are one item of equipment which can introduce a high emotional factor into discussions if they do not achieve the expected results. Possibly this is so because a loss of 1 per cent, in collecting efficiency in a plant operating 24 hours a day, soon becomes obvious to all.

My observations, over the last seven years, of several different companies indicate that many installations as supplied do not give the performance of which they are capable because of minor engineering design defects which are costly and sometimes impossible to rectify once in situ.

Examples of this are:— 1. Insufficient study of the choice of

filter cloth in relation to material to be collected so that the build up of filter cake is too rapid.

2. Poor sealing between clean air and dirty air compartments particularly around the edges of bags.

3. Insufficient strength so that bags collapse under suction.

4. Insufficient slope on the sides of collecting hoppers so that they do not empty properly. Even if the sides are steep enough atten­tion has to be paid to valley angles because if these are too flat the materials will build up there and possibly arch, etc.

5. Poor finish of welded joints inside hoppers. This can cause build up.

6. Insufficient instrumentation. Each installation has certain variables which are absolutely essential to efficient operation. These variables should be instrumented so that they can be kept at the correct values and so that management can see that they are being main­tained.

The cement plant of the future will certainly be a much cleaner place to

September, 1967—CLEAN AIR

work than in the past both because of force of law and operational necessity. This will involve the use of all types of dust collectors supplied by many different firms.

Unfortunately my experience with pumps, fans, motors, turbines, boilers and dust collectors is such that I believe that very few installations meet the efficiencies claimed in tenders. Often it is difficult to prove the lower efficiency. For example in boilers it becomes very difficult to measure coal, water and steam accurately without costly provisions for this in the design stage. But operational experience often shows that these boilers have not achieved efficiencies claimed.

Since the plant operator cannot become an expert in dust collection he must rely on the experience of other operators. This information will be actively disseminated among man­agers and engineers throughout the cement industry at the periodic con­ferences held each year.

To avoid unfair criticism there will be need for equipment suppliers to put their best foot forward and while operators have the legal obliga­tion to get dust collectors to work, suppliers have the very real obliga­tion to make sure that all tenders are bona fide, that all data supplied by plant operators is as correct as it can be, that the application is correctly understood, and that they have vetted the installation into which their equip­ment is to be fitted so that they can be sure that it will work as designed.

LEICHHARDT SMOKE ABATEMENT ADVISORY PANEL

Leichhardt makes no claim to being the first Council to set up an air pollution control committee. New­castle City Council had a similar com­mittee in operation before Leichhardt, however, the latter claims to be the first and only Municipality in the State of New South Wales to enter the air pollution field, and Leichhardt is justly proud of its record in air pollution control.

The Committee came into existence on March 8, 1955, and has persuaded management of industries to take cor­rective action on air pollution prob­lems. It is interesting to note that in 1965 (returns are not available to date for 1966), a sum of 1895,496.00 was spent by industry on new installations and other improvements to plant. The result . . . a cleaner and brighter atmosphere.

Mr. B. Cook has been appointed General Manager, of Aerex (Aus­tralia) Company, his duties being to control all operations which specialise in air handling, including fans and air pollution control equipment. Mr. Keith Troy, Chief Engineer, also of Aerex (Australia) Company, has re­cently returned from a seven weeks tour of the United Kingdom, Germany and South Africa during which time he investigated new industrial pro­cesses, industrial fan and air pollution control applications.

Mr. B. C. Smith has recently been a p p o i n t e d Officer-in-Charge of Effluents and Emissions for the Cockle Creek and Newcastle Works of Sulphide Corporation Pty. Limited and Greenleaf Fertilisers Limited. Activities covered by these companies include Lead/Zinz smelting, Sulphuric Acid and Fertiliser manufacture. A graduate of the South Australian School of Mines, Mr. Smith joined Sulphide Corporation in 1951 as a Technical Officer. Following in­vestigational work in connection with the technical aspects of cement, acid and fertiliser manufacture, he was seconded as a Treatment Plant Super­visor to Territory Enterprises Pty. Limited at Rum Jungle in 1956. Returning to Cockle Creek in 1957, he was appointed Assistant Superinten­dent, Fertilisers, in 1958 and Superin­tendent, Fertiliser Despatch, in 1961.

Mr. B. C. Smith.

Mr. T. Mackay, formerly Develop-m e n t Superintendent, Australian Fertilisers Ltd., Port Kembla, has recently been appointed Research and Development Manager, ACF and Shirleys Pty. Ltd., Queensland. Mr. Mackay has been with Australian Fertilisers for the past 17 years and he was the company's representative on the Wollongong City Council's Air Pollution Advisory Committee.

Mr. T. R. Nossle, of Email Limited, Electrical Engineering Division has recently been appointed Sales Man­ager of the newly formed Chemical and Mechanical Special Products Department. T h i s Department specialises to a large extent in the application techniques of both in­dustrial and commercial o d o u r counteraction problems.

Mr. Van De Plasse, of the Allis-Chalmers Aust. Pty. Ltd. organisa­tion, has recently returned from a four months visit to United States of America during which time he in­vestigated current negotiations dealing with the new major Rope River Iron Ore Pelletising Project.

Dr. Werner Strauss, Head of the Department of Industrial Science at Melbourne University has just re­turned from an eight month overseas study leave. Most of this time was spent at Wcstinghouse Research and Development C e n t r e , Pittsburgh, where Dr. Strauss participated in the development of a high temperature control power station fuel cell, being concerned particularly with high tem­perature gas cleaning.

CLEAN AIR—September, 1967 13

think clearly..

Whether you're big or small with a dust collector installation.

A lot of people think we are only interested in the large prestige jobs and that we are too expensive for any but the larger Companies. This of course is far f rom the t ru th . We are keenly interested in both the large and small Companies. We have a complete engineering service and

can advise on all aspects of dust collection. We design, carry out tests, manufacture, install, set to work and even maintain plants. We can take the responsibility for a complete project.

MCPHERSONS LTD Dust & Fume Control Department 134 Ferrars St., Sth. Melbourne, Victoria. Also service in all States.

14 September. 1967—CLEAN AIR

Some Arguments Suggesting a Causative Relationship Between Air Pollutants

and Lung Cancer By Graham J. Cleary, Ph.D., Secretary, Clean Air Society

of Austra l ia and New Zealand

Abstract: A summary is given of the main presumptive, epidemiological, biological and chemical evidence suggesting a causative relationship between air pollutants and lung cancer.

Much has been written in recent years about the possible carcino­

genicity of a host of individual chemical compounds and gross ex­tracts, which are found in industrial situations, in automobile exhausts and in the atmosphere generally. Because workers new to this field run the risk of becoming enmeshed in this plethora of minutac the current paper presents a summary of the major arguments suggesting a causative relationship be­tween atmospheric pollutants and lung cancer.

Although the relative contribution of a number of causative factors is argued, it is an established fact that a substantial increase in primary lung cancer has taken place this century. In Switzerland for example a 32-field increase occurred between 1900 and 1952 while the population increased only 1.4 times and between 1920 and 1954 the incidence in England in­creased 3.8 times.1

In Australia the annual death rate in 1933 was 3.15 per 100,000 for males and 2.02 per 100,000 for females compared with rates of 27.9 and 4.2 respectively in I960.2 The figures for individual years are given in Table 1.

Many studies of environmental factors relating to the development of lung cancer have indicated that smoking, particularly of cigarettes, is an important cause. Other epidemio­logical studies have shown that workers in some occupations such as painting, metal working and black-smithing have a higher incidence of the disease3,4 although these occupa­tions have not contributed much to the overall increase.

Evidence for a causative relationship

(a) Presumptive evidence

Throughout the world, expanding industrialisation and the increasing number of motor vehicles in use have resulted in a steady increase in air

pollution even though coal consump­tion has decreased in many regions. Because the incidence of lung cancer, too, is increasing proportionately it may be stated that the increases in lung cancer and in air pollution have been parallel.

Also air pollutants, when inhaled, come into contact with the major bronchial tree, the region where lung cancer most commonly develops. The actual amount entering the lower respiratory passages and the retention time of these particles is difficult to estimate because of the protective mechanism of the upper respiratory system.5

Stocks6 found that 3, 4 benzopyrene measure either per unit weight of smoke or per unit volume of air was correlated significantly with lung cancer mortality, coefficients of 0.63 and 0.79 respectively being obtained. When the population density was held constant, however, partial coefficients of 0.28 and 0.29 were obtained, compared with the conventional five per cent, probability level of 0.48. At the same time, while 1, 12

bcnzopcrylene was correlated signi­ficantly with lung cancer (first order coefficients of 0.65 per unit weight of smoke and 0.85 per unit volume of air were obtained) when the popu­lation density was held constant the partial coefficients were 0.48 and 0.50 respectively. It was also found that while lung cancer and smoke density were highly correlated, lung cancer was also highly correlated with popu­lation density.

From these studies Stocks con­cluded that smoke density is an impor­tant factor in the excess of lung cancer found in large towns but that other factors such as the higher rate of cigarette smoking in towns could also contribute to the increase.

A characteristic of lung cancer mortality rates in any individual year is that they rise steadily up to a certain age then decline. However in "cohorts" of men born within the same decade it is found that lung cancer death rates within each cohort increase steadily with age, even in later life. Successive cohorts of men each have a higher death rate than that of the preceding cohort at the same attained age. Thus it may be argued that the rise in lung cancer death rates was produced by a causative a g e n t to which each successive cohort had been more heavily exposed.7 This presumptive evidence is true for air pollution and for cigarette consumption.

Suggestive evidence against air pollution being a major contribution to lung cancer is the larger incidence among males. In the United States of America in 1959-61, for example, the male to female ratios of lung cancer sufferers were 6.7 to 1 (whites) and 6.2 to 1 (non-whites)8 which parallel the Australian figure of 6.6 to l,2 but no conclusive evidence has been advanced to support or refute the contention that women are more resistant to lung cancer. Higher cigarette consumption by men and the predominately m a l e occupational exposure may account for at least part of the difference.7

(b) Epidemiological evidence Most of the studies suggesting that

air pollutants cause lung cancer are based upon evidence relating lung cancer incidence with the amount of pollution to which they are exposed.

Hammond9 showed that the lung cancer death rates for men in Great Britain was twice that for men in the United States while Dean2 found that the corresponding death rates for men or women in Australia were only one-third that in England and Wales for

CLEAN AIR—September, 1967 15

the period 1950 to 1961. As cigarette Table 2 compares the urban-rural consumption in the two areas was incidence and death rates for different roughly parallel the factors chiefly re­sponsible for the differences appeared

areas without relation to smoking habits. The morbidity for males in

to be climate and atmospheric pollu- Copenhagen, found by Clemmeson tion. and Nielsen10 to be five times that in

TABLE 2

Comparison of Urban:Rural Lung Cancer Incidence for di f ferent regions

w i t h no regard to smoking habits.

rural Denmark was outstanding as in no other study was the ratio found to be as high as 3:1. The mortality rate Sydney: Rest of New South Wales for males (1.93:1) was comparable with similar studies in the United States but the equivalent ratio for females was much higher in Sydney (1.93:1) than in the United States.

Stocks18 demonstrated that the mortality rate among urban non-smokers (Table 3) was from 14 to 163 per cent, higher than in mixed or urban areas. Similar studies were made by Hammond and Horn19 who determined lung cancer death rates for various sized communities, the results of which are shown in Table 4.

Urban-rural rates for separate categories of smoking habits were given by Stocks and Campbell20 in Table 5. They show an increased risk among lighter smokers in urban areas but less relative difference among heavier cigarette smokers. These find­ings were also supported by Mills'6

and by Stocks.18 This trend would appear to indicate that with a heavier intake of cigarettes, a stage is reached where consumption of cigarettes be­comes the predominant factor.

In the United States,'4 South Africa,21 New Zealand22 and Aus­tralia,2 immigrants from the United Kingdom have been shown to have higher lung cancer death rates than native-born men. Also immigrants from Norway have a lower rate than native-born Americans.23 As it has been found that the lung cancer mortality rates for all these migrants are intermediate b e t w e e n their countries of origin and destination these results strongly indicate an environmental factor such as air pollution in early life.

(c) Biological evidence

Passey24 in 1922 induced skin cancer in mice by painting them with an extract of soot taken from the flues of domestic stoves.

The presence of carcinogens in atmospheric soot samples was proven by Lciter, Shimpkin and Shear25 in 1942. They produced sarcomas in mice by subcutaneous injection of a benzene extract obtained from the atmospheric dust of eight cities in the United States. Extracts of atmospheric soot samples were also used to pro­duce sarcomas in mice by Kotin et al26

and by Shabad and co-workers.27

Murphy and Sturm28 in 1925 established that pulmonary tumours may also occur in mice painted with coal tar. A short time later Campbell29'30'31 produced pulmonary

16 September, 1967—CLEAN AIR

tumours in mice by exposing them to coal dust, exhaust gases from internal combustion engines, road dust and tobacco smoke. Extracts of soot from oil combustion and from solid fuel combustion were also shown by Shabad et al27 to produce skin and lung cancers in test animals.

Kotin et al showed that extracts from gasoline32 on diesel engines33

produced sarcomas and skin cancers in mice. This work was later con­firmed by Wynder and Hoffman34

for gasoline exhausts. In other work, Kotin and Falk35 produced pulmonary tumours in mice by exposing them to ozonised gasoline.

TABLE 3 Urban:Rural Lung Cancer Mor ta l i t y f o r Male

Non-Smokers, 35-74 years, 1952-195518.

Ratio, Areas Compared per cent.

Urban (Liverpool) : Rural (Nor th Wales) 227 Urban (Lancashire): Rural 114 Urban (Liverpool): M i x e d 263 Urban (Lancashire): M i x e d 132 M i x e d : Rural - 1 1 4

TABLE 4

Urban:Rural Mor ta l i t y Rates among Non-Smokers, Whi te Males 50-69 Years of A g e in nine States

of the Un i ted States, 1 9 5 2 - 1 9 5 5 " .

Lung Cancer Death Rate Per

100,000 men

14.7 9.3 4.7

0

Population Studied

Cities greater than 50,000 Cities 50,000-10,000 .... Suburban o r t o w n Rural

TABLE 5

Urban:Rural Lung Cancer Mor ta l i t y fo r Dif ferent Smoking Habits among Males 45-74 years in Nor th Wales (Rural) and L iverpool (Urban) 1952-

195420.

Ratio, Smoking Category per cent.

Non-Smokers 936 Pipe Smokers 349 Cigaret te Smokers

Light 341 Modera te 157 Heavy 109

(d) Chemical evidence As the carcinogenic polynuclear

hydrocarbons reported in atmospheric samples have also been identified in many samples of soot and tar, the established biological activity of the gross extracts could be attributed in a substantial degree to the carcinogenic potency of the polycyclic hydro­carbons present.

Because of this well over 2,000 polycyclic hydrocarbons have now been tested for carcinogenic activity on test animals. Table 6 shows the relative carcinogenic potency of the more common of these compounds which have been found in air, exhaust gases or extracted soot.

It should be pointed out that other carcinogenic organic substances such as epoxides and peroxy compounds and certain phenols and quinones may also be present in very small quantities associated with the particulate fraction of atmospheric soot.36 Of special in­terest are the epoxides, hydroperoxides and peroxides as it is possible that these could be formed by autoxida-tion or photo chemical oxidation of defines in the air. However, as pointed out by van Duuren36 study of the carcinogenicity of these com­pounds is chiefly of interest because they could yield information of the early stages in the metabolism of aromatic carcinogens.

TABLE 6

Relative Carcinogenic Potency of Polynuclear Hydrocarbons f o u n d in Atmospher ic Soot or Exhaust Gases, f r o m var ious sources37,38,.39,40,41

Carcinogenic Activity

3,4 Benzopyrene * * * 1,2,5,6 Dibenzanthracene * * * 3,4 Benzof luoranthene * * 10,11 Benzof luoranthene ** 1,2 Benzanthracene ** 1,12 Benzopery lene ** 1,2 Benzopyrene * Chrysene — Fluoranthene — Tr iphenylene — Anthan th rene — Perylene — Coronene — Anthracene — Fluorene — Phenanthrene —

Legend Strong Modera te . Weak Ni l

Extrapolation of biological tests to humans

The use of biological test data derived from test animals to support a proposed theory of carcinogenesis or to affirm or deny potency of a given chemical compound towards man must be evaluated carefully. For example, lack of carcinogenic potency implies such a lack only under the limited experimental con­ditions used. The position has been expounded by Shear and Leiter.42

". . . the statement to the effect that given compounds are non-carcinogenic does not necessarily mean that they are incapable of inducing malignant tumours; it means only that the com­pounds did not give rise to tumours under the conditions of certain experi­ments of restricted scope. For example the hundreds of such com­pounds which have been examined for potency . . . have, with few exceptions

been tested in mice only. The small number which were tested in several species of animals have given results which make it clear that there are pronounced differences in the response of different species to the action of compounds carcinogenic in the case of the mouse. Moreover, there is evidence that some compounds which were negative in the mouse can in­duce tumours in other species. . . ." Furthermore, in the mouse itself, it is now abundantly evident that different tissues respond differently to the same compound.

"The mode of administration may also influence the result markedly. The dose may be too high as well as too low, and the most effective dose for one compound is not necessarily the same as that for another closely related one. The solvent or vehicle may affect the results profoundly. Media of complex nature such as lard or sesame oil, may contain anti-carcinogens or cocarcinogens and even chemically homogeneous vehicles may give different results with the same dose of the same carcinogen administered to the same tissue of the mouse.

"Moreover, the sex of the animal is not without influence on the results. . . . It is also conceivable that the life span of the mouse is a factor. Since some compounds which were negative during the first year gave rise to tumours during the second year of the experiment, it is possible that some compound which gave negative results in the mouse might give positive re­sults if its life span were longer. Diet, too, may be an important factor. Thus the term "carcinogenic potency" is not to be considered as an invariable property inherent in a compound. . . . Conclusions regarding potency of any given compound should therefore be interpreted in the light of the data upon which they are based."

Other factors may become impor­tant. The type of human exposure and the d o s a g e are difficult to duplicate in an experimental animal.7

Also, Falk et al40 point out that certain lung irritants although them­selves non-carcinogenic, i n h i b i t normal physiological elimination of foreign material and hence increase the potential hazard by increasing the retention time.

The action of promoters and inhibitors is not clearly understood. Phenol, o—, m— and p—cresol and 2, 4 dimethyl phenol have been shown to accelerate tumour production over a wide range of carcinogenic and weakly carcinogenic polycyclic hydro-

CLEAN AIR—September, 1967 17

i

AIR POLLUTION PROJECTS carbons.43 Alternatively the produc­tion of tumours by certain carcinogens has been largely or sometimes com­pletely inhibited by the action of closely r e l a t e d partially reduced hydrocarbons. For example dihydro — 1 , 2, 5, 6 dibenzanthracene and hexahydro—1, 2, 5, 6 dibenzan­thracene completely inhibited the pro­duction of tumours by 1, 2, 5, 6 dibenzanthracene on mice when ad­ministered in the molar ratios of 15 parts inhibitor to I part carcinogen.40

A much lower level of inhibition was found for the simpler polycyclic hydrocarbons phenanthrene and 1, 2 benzanthracene with 1, 2, 5, 6 dibenz­anthracene and then only with a very large excess of the inhibitor.40

References 1 Nicks, R. M e d . J. Aust. (1960) 26 , 997.

2 Dean, G. M e d . J. Aust. (1960) 26 , 1003.

3 Breslow, L, Hoagl in , L, Rasmussen, G., and Abrams, H. K. A m . J. Public Health (1954), 44 , 171 .

4 Wynder , E. L, and Graham, E. A. A .M.A. Arch. Industr . H y g . (1951) 4 ,221 .

5 Blacklock, J. W. , Kennaway, E. L, Lewis, G. M. , and U rquha r t , M. E. Brit. J. Cancer (1954) 8, 40 .

6 Stocks, P. Int. J. A i r Pol l . (1958) 1, 1.

7 Wynder , E. L, and Hammond , E. C. Cancer (1962) 15 , 79 .

8 " S m o k i n g and Hea l t h " Report of the Adv isory Commi t tee to the Surgeon General o f the Publ ic Hea l th Service. U.S. Public Health Service Pub l ica t ion No. 1103 (undated) p. 133.

9 H a m m o n d , E. C. Brit. M. J. (1958) 2, 649.

lO Q e m m e s o n , J . , and Nie lson, A. Acta Unio. In ternat . Cotnra Cantrurn (1952); 8, 140.

11 Lancaster, H. O. M e d . J . Aust . (1960) 26, 1006.

12 Ho f fman , E. F., and Gi l l i am, A. G. U.S. Public Health Repor t (1954) 69, 1033.

13 G r i s w o l d , M. H., Wi lder , C.S., Cut ler, S. J . , and Pol lack , J. S. Cancer in Connect icut 1939-1 9 5 1 . Connec t icu t State Department of Health Publ ica t ion (1955).

14 Mancuso , T. F., MacFarlane, E. M. , and Porter-f i e ld , J . D. A m . J. Pub. Health (1955) 45. 5a.

15 Levin, M. L., Haenszel, W. , Carrol l , B. E., Ge rha rd t , P. R., Kandy, V. H., and I. N., G r a h a m , S. C. J. Nat. Cancer Inst. (1960) 24, 1243.

16 Mi l l s , C. A. A m . J. M e d . Sc. (1960) 239, 316. 17 Mi l l s , C. A . , and Porter, M. Cancer Res. (1957)

17, 9 8 1 .

18 Stocks, P. Brit ish Empire Cancer Campaign,

A n n u a l Report cover ing the year 1957, Lon­

d o n , Eng land.

19 H a m m o n d , E. C, and Horn , D. J.A.M.A. (1958)

166, 1159.

20 Stocks, P., and Campbel l , J. M. Brit. M. J.

(1955) 2 , 923 .

21 Dean, G. Brit . M. J. (1959) 2, 852.

22 Eastcott, D. F. Lancet (1956) 1, 37.

23 Haenszel , W. J. J. Nat. Cancer Inst. (1961) 26,

37 .

24 passey, R. D. Brit . Med. J. (1922) 2, 1112.

25 Leiter, J . , Sh imk in , M., and Shear, M. J. Nat. Cancer Inst. (1942) 3, 155.

26 Kot in , P. Cancer Res. (1956) 16, 375.

A recent and unusual dust control project is associated with the Aus­tralian c o t t o n growing industry centred in the Ord River area. The dust control system is used to control and reclaim trash cotton and other waste produced during the operation of cotton processing gins.

Six control hood and dust convey­ing ducting systems have been in­stalled, all terminating at a common centralised reclamation unit which is in the form of a battery of 14 involute type cyclones.

The application is believed to be the first of its kind in this growing Australian industry, the complete control plant being designed in Aus­tralia by Messrs. MacDonald, Wagner & Priddle with cyclone research and supply carried out by Aerex (Aust.) Company.

A number of other projects have been completed or are in the process of construction in Australia, some of these being: Iron ore crushing station dust control

27 Shabad, L. M. Internat. J. A i r Pol lu t ion (1960) 3 , 2 2 1 .

28 M u r p h y , J. B., and Sturm, E. J. Exp. M e d . (1925) 42, 693.

29 Campbe l l , J. A. Brit. J. Exper. Path. (1936)

17, 146.

30 Campbel l , J. Brit J. Exp. Path. (1934) 15, 287.

31 Campbel l , J. Brit. J. Exp. Path. (1939) 20 , 122.

32 Kot in , P., Falk, H. L., and Thomas, M. A .M.A . A r ch . Industr . Hyg . (1954) 9, 164.

33 Kot in , P., Falk, H. L, and Thomas, M. A .M .A . A rch . Industr . Hyg . (1955) 1 1 , 113.

34 Hof fman, D., and Wynder , E. L. Cancer (1962) 15, 93.

35 Kot in , P., and Falk, H. L. Cancer (1956) 9, 910. 36 Van Duuren, B. L. Symposium on Analysis of

Carcinogenic A i r Pollutants (1962) p. 135 Nat ional Cancer Inst i tute Monograph No. 9.

37 Katz, M. , and Monkman , J. L. Proceedings of the Clean A i r Conference held at the Uni­vers i ty of New South Wales Feb. 19-21, 1962. Paper 3. New South Wales Universi ty Press L imi ted, Sydney.

38 Har twe l l , J. L. "Survey of Compounds w h i c h have been tested for Carcinogenic A c t i v i t y " (1951) U.S. Public Health Service Publ icat ion, second ed i t ion .

39 shub ik , P., and Har twe l l , J. L. "Survey of Compounds wh ich have been tested for Car­cinogenic A c t i v i t y " (1957) U.S. Public Health Service Publ icat ion, second ed i t ion , supple­ment 1.

40 Falk, H. L., Kot in, P., and Mi l ler , A. Int. J. A i r Pol l . (1960) 2, 2 0 1 .

41 Wynder , E. L, and Hof fman, D. Cancer (1959) 12, 1194.

42 Shear, M. J. , and Leiter, J. J. Nat. Cancer. Inst. (1941) 2, 254.

43 Hof fman, D., and Wynder , E. L. Symposium on the Analysis of Carcinogenic A i r Pol lutants (1962) p. 9 1 . Nat ional Cancer Inst i tute Mono ­gram No. 9.

—BHP, Koolyanobbing, WA—Wet scrubber type collection system.

Non-ferrous induction furnace fume control—Austral Bronze Co. Pty. Ltd.—Automatic fabric filter type collectors.

Complete dust control for the Glebe Island, Sydney, Grain Handling Terminal incorporating fabric type dust collectors—for the New South Wales Grain Elevators Board.

Fume control for Aluminium pot line reduction furnaces—Comalco Pty. Ltd., Tasmania — Mechanical multiple cell type collectors.

Stoker fired boiler flue grit control by multiple cell cyclone collectors for the Southern Electric Authority, Queensland, at Tennyson Power Station.

Fluoride emission control produced during superphosphate manufacture —Greenleaf Fertilizers Limited, Cockle Creek—Walsh Island Pro­jects—Controlled by Void Tower Scrubber units.

50 ton electric arc furnace fume control by Fabric filter type collec­tors — Commonwealth Steel Com­pany Limited plant, Waratah.

July Meeting of the

New South Wales

Branch The second meeting of the New

South Wales Branch was held at the Shell Theatrette, Carrington Street, Sydney, on July 5, 1967. Approxi­mately 35 members were present. A p a p e r entitled "Some Technical Aspects of a Modern Cement Plant with reference to the Berrima Works of Southern Portland Cement Ltd.", was presented by Mr. W. M. Gale, of Southern Portland Cement Ltd. (The paper is presented in this issue of the Journal). The meeting was followed by light refreshments.

The next meeting of the New South Wales Branch will take place at 8 p.m. in the Shell Theatrette, Carring­ton Street, on Wednesday, October 4, 1967, when a guest paper will be pre­sented by Mr. Ralph Goode of the Shell Company of Australia Ltd. Mr. Goode's paper is entitled "Oil fuels and clean air".

18 September, 1967—CLEAN AIR

Emissions from Large Municipal Incinerators and Control of Air Pollution By N. Y. Kirov, M.Sc. (Leeds), F.lnst.F., A .M . I . , Chem.E.,

Associate Professor and Head, Department of Fuel, University of N.S.W.

Abstract: Emissions and emission limits for refuse burning incinerator plant are discussed in relation to various Clean Air Acts. Methods of controlling these emissions and the type of equipment available for cleaning combustion gases from incinerators are outlined. USA and European practices in controlling air pollution from incinerators are critically com­pared, showing that in this regard European developments are well ahead of current American practice. The performance of various gas-cleaning equipment is examined and it is concluded that for large municipal incinerators only (i) fabric gas filters, (ii) wet gas scrubbers, and (iii) electrostatic precipitators are capable of achieving the high-collection efficiencies necessary for effective control within the requirements of the NSW Clean Air Act.

A MAJOR problem associated with the operation of incinerator plant

and more specifically of large municipal incinerators is that of con­trolling the gaseous and particulate emissions within the limits set by various Clean Air Acts.

Municipal incinerators are respon­sible for the generation of large amounts of fly ash and other un­desirable emissions which without adequate control would cause sub­stantial air pollution. The key to successful incinerator operation may thus be said to be the effective control of these emissions. Such control often requires well designed and expensive ancillary plant which in the early history of refuse incineration was either not available or its cost was considered economically prohibitive. Hence one tends to think that the incineration of refuse of necessity must be accompanied with obnoxious smells, dense smoke and intolerable emissions and air pollution.

This need not necessarily be so, however. There are various methods of trapping, collecting and removing these emissions with various degrees of effectiveness. As air pollution codes become more effectively imple­mented and with the growing tendency throughout the m o r e advanced countries in the world to lower the permissible limits on emissions of gaseous pollutants and particulate matter, it has become necessary to incorporate in the design of large incinerator plant some of the most sophisticated and advanced types of air pollution control equipment.

It is the aim of this paper to consider some of the more recent

] Publ ished by permission of the Organis-

! i nq Commi t tee of the First Austral ian i

j Refuse Disposal Conference.

Professor N. Y. Kirov.

developments and applications of such equipment to large incinerators and to discuss the extent to which they can meet the Clean Air Act require­ments in NSW.

Emissions and emission limits Emissions from refuse burning in­

cinerators fall into three main categories:—

(i) inorganic gases such as sulphur oxides, oxidizable sulphur compounds (H2S), carbon monoxide, carbon dioxide, nitrogen oxides, ammonia and chlorine-containing gases;

(ii) organic substances such as aldehydes, organic acids and esters, fats and fatty materials, phenols and polynuclear hydro-carbons. Some of these latter substances are known to be carcinogenic; and

(iii) particulate matter such as smoke, soot, fly-ash, grit, dirt and fairly large (c.1/16 in.) low density carbonaceous flakes probably result­ing from incomplete combustion of paper.

The present paper is concerned

essentially with the major problem, mainly the control of particulate matter emissions at levels below the maximum limits stipulated in the Regulations under the NSW Clean Air Act 1961-1965.

Quantitative emission criteria are usually formulated on the basis of grains of particulate matter per stan­dard cubic foot of dry flue gas corrected to some reference level of CO2—usually 12 per cent.; or on the basis of lb of particulate per 1,000 lb of wet gas corrected to 50 per cent, of excess air.

For NSW, the relevant regulation states:—

"(ii) Any boilers or incinerators emitting dust, fly-ash, soot or other solid particles—

The standard of concentration at the prescribed point, of dust, fly-ash, soot or other solid particles in each cubic foot of residual gas, ad­justed to a basis of 12 per cent, carbon dioxide shall be such that the total mass of such solid particles does not exceed 0.2 grains."

(Regulation 17 with effect on and from July 1, 1966.) Overseas, as a result of increasing

concern of the growing problem of air pollution, more attention is now being paid not only to the enforcement of quantitative emission standards but there is a tendency towards the fram­ing of more exacting and stringent regulations.

In this connection, for reasons dis­cussed later, USA practice lags well behind current European achieve­ments. However, the once accepted (ASME model air pollution control ordinance) limiting concentration of 0.85 lb of emissions per 1,000 lb of flue gas (i.e., approximately 0.45 grains/cu. ft) for incinerators con­suming over 100 tons of refuse per day, which more often than not is not

CLEAN AIR—September, 1967 19

complied with, is being gradually superseded by new local codes which call for much stricter maximum emission rates in urban areas, i.e., within the range of 0.15 to 0.30 grains/standard cubic foot. The following summary (Table 1) of some recent typical regulations in several US cities (Walker and Schmitz, 1966) illustrates this point:—

Table I

A Summary of Some Typical Emission Contro l Regulations Govern ing Large Refuse Incinerators

in the U.S.A.

Agency

Federal Guides, U.S. Public Health Service

Maximum Particulate Emission

0.2 gra ins/s tandard d ry cubic foo t adjusted to 12 per cent. C O 2 .

San Francisco Bay Area, 0.2 gra ins/s tandard dry Cal i fornia cubic f oo t adjusted to

6 per cent. CO2 on dry basis.

Detroit , Michigan

Cincinnati , Oh io

New York, N.Y.

0.3 lb . /1 ,000 lb. gas ad­justed to 50 per cent, excess air.

0.4 lb. gas adjusted to 12 per cent. CO 2 .

0.65 lb . /1 ,000 lb. dry gas adjusted to 50 per cent, excess air.

US Municipal incinerators have generally refractory-lined furnaces and ducts and are often operated with 200 to 300 per cent, or more of excess air in order to prevent the fly ash from slagging and to keep maximum tem­peratures at the furnace exit below 1,800 deg. Fahr. These combustion gases are then cooled, usually by the addition of air and water spray, to about 600 deg. Fahr. at which tem­peratures they can be handled by dust collectors and id fans.

The use of large volumes of dilution air makes the application of electro­static precipitators in such systems impracticable.

A survey of 169 US installations covering design practices for plants built since 1945 (Stephenson and Cafiero, 1966) clearly shows (see Fig. 1) a trend away from reliance on dry expansion chambers for satisfactory rly-ash removal. The popularity of wet systems is indicated by the fact that 71 wet plants were included in the total of 169, and of these 53 included wet baffles. Since 1963, the pro­portion of cyclones and scrubbers has grown considerably but the first electrostatic precipitator has only re­cently been installed.

A very different picture from that is presented by current European practice where a combination of water-walled furnaces for steam

generation and waste heat recovery makes it possible to operate at tem­peratures up to 1,800 deg. Fahr. and to control and restrict the excess com­bustion air to about 50 per cent, of the theoretical requirements; cooling of the gases to temperatures of 600 deg. Fahr. or less is readily achieved in heat exchangers and hence the volume of flue gas to be cleaned is considerably smaller, i.e., from half to a quarter of that produced in USA plants of the same capacity. Clean­ing to a higher efficiency of dust collection is thus economically justified and the usual practice is to use electro­static precipitators. European refuse-burning power-generating plant, there­fore, often claim to achieve emission standards in the range of 0.1 to 0.05 or less grains per standard cubic foot of dry gas corrected to 50 per cent, excess air.

In designing dust collecting equip­ment for municipal incinerators a loading of 3.5 lb dust per 1,000 lb of flue gas adjusted to 50 per cent, excess air is often assumed. For an average municipal refuse such load­ing corresponds to an entrainment of particulate matter equivalent to approximately 2 per cent, of the weight of refuse burnt.

Clean Air Act As mentioned earlier, the maxi­

mum permissible limit of particulate emissions from incinerators according to the regulations under the 1961-65 NSW Clean Air Act, is currently fixed at 0.2 grains/n. cub. ft corrected to 12 per cent. CO2. This value is approximately equivalent to 0.38 lb/1,000 lb of dry gas at 50 per cent, excess air. To meet this requirement therefore, cleaning equipment of at least 90 per cent, collection efficiency is required. In actual practice one would aim to attain a design perform­ance which is better than that just sufficient to comply with the maxi­mum permissible level of emissions, i.e., to reduce the emissions to 0.1 grain/standard cubic foot or better and this would require collection efficiency of over 95 per cent. In current E u r o p e a n practice, for example, specifications for cleaning plant for large municipal incinerators call for designs based on inlet dust loadings of up to 7 grains/standard cubic foot (in actual practice generally averaging about 31/2 to 4 grains/n. ft3) and guaranteed collection efficiencies within the range of 98 to 99.5 per cent, (see Table 2) .

The control of emissions and air pollution from any plant and more

specifically from large municipal in­cinerators should begin at the source (see Kirov, 1962) with (a) correct furnace design, followed by (b) careful operation and maintenance of the plant, and supplemented by (c) efficient and adequate gas cleaning within the Clean Air Act permissible limits.

These factors will now be briefly considered.

(a) Correct design of furnaces and combustion grates with appropriate proportioning, distribution and control of undergrate and overfire air would keep the carry-over of particulate emissions low and at the same time ensure adequate burning rates. It has been s h o w n experimentally, for example, that the dust burden is pro­portional to the square of the velocity through the grate, which means that doubling the air flow would result in four-fold increase in fly-ash emission. Hence the importance of providing adequate amounts of overfire air to promote turbulence and mixing of the gas and air in order to ensure com-pletness of combustion with a mini­mum of excess of air and a minimum of fly-ash carry over. Unfortunately, full use of effective overfire air control is often not made in the design of in­cinerator plant and one finds examples of well-engineered and designed in­cinerators completely lacking in pro­visions for admission of controlled secondary air. Moreover the use of large quantities of excess combustion air have been shown to lead to in­creased formation of nitrous oxides and conversion of SO2 to SO3, both of which are undesirable (see for example Stenburg et al., 1962).

The control of undesirable emissions at the source calls for a consideration of an upper limit on the combustion rates for a given grate design and also of the relative air flow through the grate and the fuel. It is not often realised by the user, for example, that some grates are intentionally designed so as to provide a comparatively high resistance and pressure drop in rela­tion to those offered by the fuel bed itself and that this in fact is a special design feature aimed at ensuring better and more uniform air distribution, efficient performance over a wide range of variable conditions and a reduction in the fly-ash carry over. There is much scope here for grate designers.

Adequate temperature control with a well chosen lower limit would ensure completeness of combustion and the elimination of unpleasant odours and harmful gaseous emissions.

20 September, 1967—CLEAN AIR

(b) Correct plant operation would ensure that such temperatures are maintained and that the introduction or infiltration of large quantities of excess combustion air are prevented. Large quantities of excess air not only cool the furnace below temperatures needed for efficient and complete combustion, but they also increase the gas velocities through the system and hence the dust burden. This in turn renders the efficient operation of gas cleaning equipment more difficult and the cost of such equipment to deal effectively with the greater dust burden and the increased gas volume would also be much greater, since the cost of cleaning gases is related both to flow rate and collection efficiency.

Again, the provision of metal casing round the furnaces and the careful maintenance of the brickwork settings would reduce excessive air infiltration, which could be a major factor in lowering the performance of the dust-collecting system.

(c) Efficient and adequate gas cleaning equipment is necessary to meet the stringent requirements of the Clean Air Act. These requirements would tend to become even more stringent as the volume of effluent discharged into the atmosphere in­creases with the growth of our cities and secondary industries.

Such equipment should be capable of operating well within the per­missible limits of the Act not only on the day of commissioning the plant

but within the life of the incinerator and over the expected range of load variations and fluctuations in refuse characteristics.

Equipment for cleaning combustion gases from incinerators

The control of air pollution from incinerators is essentially concerned with minimising the emissions of fly-ash and other particulate matter. Requirements may vary with in­dividual plants and maximum per­missible emissions but the type of equipment available and its suitability for use in large incinerators may be considered under five main groups:

(i) settling chambers, (ii) cyclone dust collectors,

(iii) gas scrubbers, (iv) fabric filters, and (v) electrostatic precipitators.

These will now be briefly con­sidered.

Settling chambers The simplest method of fly-ash

control is the gravity settling chamber which consists essentially of a large chamber between the furnace and stack. It allows gas velocities to be reduced and some of the suspended solids thus settle out. The application of settling chambers is limited to collection of the large particles, say, over 200 microns in size. The

chamber is often equipped with a wet bottom and an auxiliary settling tank.

Refinements of this method of dust collection may include provision for baffles to effect a sudden change in the direction of gas flow and the con­tinuous wetting of these baffles both of which help to improve ash reten­tion. The solids are allowed to settle out in a pond and the water is then recirculated.

Maintenance cost of and pressure drop across the settling chambers is low but this is offset by the relatively large floor area required and their low collection efficiency. The latter depends on the design of chamber and on the coarseness of the dust but is generally well below 50 per cent., and in the simplest type of gravity chamber may be as low as 10 to 20 per cent. This poor performance makes them completely inadequate to comply with modern air pollution control requirements. Nevertheless, such collectors are widely used in many large incinerator plants in Canada and the USA (see Fig 1).

Cyclone collectors In this type of collector the dust

laden gases enter tangentially a cylindrical chamber where a whirling (Vortex) motion is imparted by vanes, causing a downward spiral along the wall. The change in direc­tion and centrifugal force drives the suspended particulates to the outer

Table 2

DATA ON ELECTROSTATIC PRECIPITATORS INSTALLED ON LARGE MUNICIPAL INCINERATORS (after Bump, 1966)

Plant Locat ion

RWE E s s e n

Munich , Millkraftwerk

Frankfur t /Main

Dusseldorf

Mannheim

Birmingham, England

Par is

Osaka Ci ty , Japan

Edogawa, Tokyo

Type of Furnace

Babcock

Mart in

Von Roll

VKW

KSG

Heenan Froude, Ltd.

Mart in

Taguma Boiler Mfs

Taguma Boiler Mfs

Refuse C a p a c i t y t o n s / d a y

1440

1200

600

960

800

-

1600

600

600

No . of F u r n a c e s /

Prec ip i ta to rs

4 / 4

2 /2

2 /2

4 / 2

2 / 2

1/1

4 / 8

4 / 2

3 / 3

Year of Commiss ion­ing of plant

1964

1964

1965

1965

1965

1966

1965

?

1966

Gas volume s . c . f . m .

3 ,816 ,000

651,000

350,000

350,000

320,000

60,000

2 ,221 ,000

408,000

738,000

Design inlet dust loading, g r a i n s / s . c . f .

2 . 6 - 4 . 4

6.9

2 . 6 - 6 . 9

2 .2

6 .5

3 .5

1 . 7 - 7 . 8 +

n . a .

n . a .

Inlet temperature

°F

356

338

6 .7

500

400

482

518

662

662

Guaranteed col lect ion

efficiency of precipitator

%

9 8 . 5 (99.4 actual)

99 .53 (99.8 actual)

98

99

99.35

9 8 . 3

99 (99.4 actual)

99 .33

96 .67

CLEAN AIR—September, 1967 21

wall from which they drop into a hopper, and the cleaned gas rises and leaves axially in the opposite direc­tion.

For a cyclone, with a tube diameter D, the centrifugal force F and, hence the separating action, is given by the formula:—

flooded plate scrubbers. These latter increase the effectiveness of the spray and enable maximum mixing and contact to be achieved between the gas and water.

Gas scrubbers may treat gases at any temperature; they require a com­paratively small space for installation and are relatively low priced; they cover a range of efficiencies from 60 to 80 per cent, for the simple spray type which have found wide applica­tions in American incinerator practice, to the more efficient (c.97 per cent.) venturi-type designs, which however are not economically attractive for in­cinerator applications. Wet scrubbers suffer from a number of disadvan­tages:

(a) Removal of the fine dust particles requires very fine water sprays at high pressures. For example, p r e s s u r e drop requirements for venturi-type collectors may be as high as 40 in.w.g.;

(b) Corrosion due to acidity in the scrubber is not an uncommon problem and corrosion-resistant materials may have to be used:

(c) To operate economically they require plenty of low cost water and an additional installation to deal with the slurry; and

(d) The saturated exhaust gases and the low exit temperatures tend to leave long white plumes, particularly in cold weather, and to disperse at low levels.

Fabric filters Fabric filters usually incorporate a

number of cloth bags acting as filters of the dust-laden gases. The ac­cumulated dust on the cloth is dis­lodged by cyclic blowing or rapping and collected on hoppers positioned below the unit. They are particularly suitable for the removal of fine dust. When made of finely-spun glass fibres and treated with silicones which act as a lubricant between the fibres, they can be used at temperatures of up to about 550 deg. Fahr.

This is a promising but as yet little-used type of collector in in­cinerator practice, although it has been used successfully in many chemical engineering and combustion applica­tions, e.g., cement plants, foundry cupolas, and is presently under en­gineering evaluation for power genera­tion (one such example is the filter house at Alamitos Generating Station, Southern California Edison Com­pany).

Fabric filters have a very high collection efficiency (>99 per cent.), and require moderate pressure drop

(3 to 5 in.). Their relative space re­quirements and initial running and maintenance costs are high, and moisture-laden gases tend to form sticky sooty deposits on the filter cloth. Since bag replacement costs are high, when dealing with combustion gases, close control of the upper temperature limit of the inlet gases is essential. On the other hand, with moist gases, when the gas temperatures approach or drop below dew point, there is the risk of clogging and rendering the bag filters unserviceable. For this reason gas temperatures should not be allowed to fall below a minimum tem­perature of about 300-350 deg. Fahr.

The gravel bed filter can also be considered within this group. It works in continuous operation at tempera­tures up to 650 deg. Fahr. and has high dust collecting efficiencies, low operating costs and a low pressure drop. It uses filter beds consisting of one or more layers of abrasion resist­ing material such as gravel. The captured dust is removed from the filter bed by a vibrating system which shakes the spring-supported filter bed containers. Successful operation of such filters depends on an efficient method for separating the collected dust from the filter bed material without the necessity of removing it from the filter bed container. An example of this type, of which many units have been installed in industrial works during the past 10 years, is the Lurgi-MB-Filter. This may have use­ful applications on the smaller-type of incinerators.

Electrostatic precipitators Electrostatic precipitators have be­

come an inseparable part of modern power generation plants in spite of their high capital and installation costs.

Efficient separation depends on the principle of passing the gas stream between a pair of electrodes: a dis­charge electrode at a high negative potential (consisting of wires of relatively small diameter) and an electrically earthed collecting electrode (consisting of plate or tube collecting surfaces). At a sufficiently high potential difference a corona dis-c h a r g e surrounds the discharge electrode. This is a visible manifesta­tion of the ionisation of the gas be­tween the two electrodes. The nega­tively-charged gas ions formed move toward the collecting electrode and on colliding with the dust particles in the stream transfer their charge to them. These charged particles then migrate towards the collecting electrode and

22 September, 1967—CLEAN AIR

where M = mass of the particle and V = the gas velocity It is thus clearly seen, that the

separating action will be greater as the tube diameter is reduced; also, for a given set of conditions, the larger the particle, the greater will be the force, which explains why the efficiency of separation tends to decrease with a reduction in the particle size of the dust.

The more efficient cyclone collec­tors are of the multiclone type which consists of many individual cyclone tubes of small diameter set in a common casing, all operating in parallel.

The inlet gases have to be cooled to temperatures below 650 deg. Fahr. but maintenance and initial cost are relatively low and the pressure drop moderate (H to Ik in.w.g. but may be as high as 7 in.w.g. in the high efficiency multiclone type). Collection efficiencies may be in the range of 50 to 85 per cent., but since the centri­fugal force increases in proportion to the mass of the particle, the perform­ance of cyclone collectors is largely dependent on particle size. The equip­ment is therefore most efficient when dealing with the larger particles of dust and does not lend itself to collection of the fine particles, say, below 20 microns which may comprise as much as a half of the suspended solids in incinerator gases. Moreover, with moist gases clogging troubles in the cyclones may be experienced.

It is thus doubtful that cyclones alone can achieve a level of perform­ance to enable them to meet even the most lax solids emissions codes. However, they are sometimes used for collection of the larger fly-ash and charred paper particles in conjunction with electrostatic precipitators, either before, or, as is Japanese current practice, after the precipitator.

Gas scrubbers These are generally wet collectors

using water as the scrubbing liquid. They vary from a simple curtain of water sprays in a settling chamber to specially-designed scrubbing plant, such as the high duty Venturi or the

are deposited thereon. In some designs, and this is particularly impor­tant in the case of incinerator gases, the collecting electrodes are shaped to retain the dust so collected and to prevent its re-entrainment in the gas flow. The particles adhere lightly to the electrode and are dislodged either in a dry form from the collecting electrodes by rapping or are flushed with water for removal. Operating problems may arise in the handling of this precipitated dust if the ash removal system is not properly en­gineered.

Electrostatic precipitators have low running and maintenance costs and have low draft losses (usually <1/2 in.w.g.) but the gases have to be cooled to temperatures below 600 deg. Fahr. and the gas velocities through the precipitator must be uniform and reduced to only several (1 1/2 to 4) ft/sec. to allow sufficient time for the

charged particles to migrate to the collecting plate electrodes. Hence the comparative space requirement is high. However very high collection efficiencies in the range of 95 to nearly 100 per cent., are obtainable even when the dust is in the sub-micron range.

Electrostatic precipitators are being more and more widely used with modern incinerators and have almost become an integral part in incinerator design in Japanese and West-European practice. This is particularly true when the incinerator is used for the genera­tion of steam and in conjunction with the use of auxiliary fuels and when the amount of excess combustion air is effectively controlled.

Developments and improvements in design now ensure that fly-ash particles with widely variable electrical properties and light, charred paper flakes are effectively precipitated

without subsequent re-entrainment in the gas stream. In the case of particles of high electrical resistivity, the addition of moisture to the gases by evaporation spray cooling would be an advantage, but care is required if corrosion problems are to be avoided.

The design and performance of an electrostatic precipitator depends on a number of factors, most important of which are:—

(i) Physical and chemical proper­ties of the dust and associated gases and moisture content (e.g., alkali or acid mineral matter, carbon, ability to agglomerate, nature of particle surface, presence of SO 3 , etc.);

(ii) Electrical resistivity of the particles to be collected;

(iii) Particle size distribution and concentration at operating conditions (grains/cubic foot);

x Based on tes t data by Stairmand (1956)

+ Estimates of Fowler and Doig (1966) for equipment handling 60,000 c . f . m . of gas at 68oF and with a standard dust loading of 5 g ra ins / cub . f t . Instal led cost including cost of auxiliary plant.

* Based upon 8,000 hr per year operati on and includes 10'/. amortization costs plus maintenance, power and (where applicable) water c o s t s .

Note: These est imates do not take into account additional coists for equipment necessary to reduce the gas temperature to the required inlet conditions

CLEAN AIR—September, 1967 23

(iv) Gas volume and operating temperatures and range of variations expected;

(v) Available pressure drop. The collection performance of an

electrostatic precipitator is expressed by the following formula:—

for control of particulate matter emissions from large municipal in­cinerators, there are at present three possible alternative systems which offer practical control capable of a c h i e v i n g the high collection efficiencies required, namely (i) fabric bag filtration, (ii) wet gas scrubbing and (iii) electrostatic precipitation. Of these, electrostatic precipation although one of the most expensive methods in initial capital cost, is perhaps the most effective and most promising one as well as the most economic in total operating costs (see Tables 3 and 4) . Present-day air-pollution control regulations cannot be met by the use of settling chambers

or mechanical cyclone collectors no matter how efficiently these may be designed.

The problem of cleaning incinerator exhaust gases in the USA is still largely unsolved for reasons given in the paper. In Europe, on the other hand, the widespread use of electro­static precipitators occasionally pre­ceded or followed by mechanical separators has helped to reduce par­ticulate matter emissions often well below the most stringent legal code requirements. The use of tall exhaust stacks, often in excess of 300 ft, helps to dissipate the undesirable noxious gases and aldehydes.

These measures are proving not

TABLE 4

CAPITAL AND OPERATING COSTS OF EQUIPMENT TO CONTROL EMISSIONS FROM MUNICI PAL INCINERATORS (Based on estimate! for U.S.A. by Fife and Boyes, 1966, assuming a dust loading of 3. 5 lb of dust per 1000 lb of flue gas

(corrected to SDK excess air), and a plant burning 500 tons/day of refuse In two 250 ton/day refractory-lined furnaces).

System

1. Baffled Spray Chamber

2. Spray Chamber/Cyclone Collector

3. Water-cooled Furnace /Cyclone Collector

4. Wet Scrubbers

5. Spray Chamber/Electrostatic Precipitator

6. Water Cooled Furnace /Electrostatic Collector

7. Spray Chamber/Bag Filter

8. Water Cooled Furnace /Bag Filter

Average Cons t ruc t ion

C o s t U . S . do l la rs

18S .200

2 7 0 , 3 6 0

9 1 . 8 0 0

4 0 0 , 9 0 0

5 0 1 . 7 7 0

2 1 0 , 3 0 0

7 1 2 , 1 9 0

2 4 3 , 0 0 0

U . S . Dol la rs per ton of

Refuse Burned

0 .77

1.23

0 . 3 8

2 . 1 0

1.21

0 .39

2 . 0 0

0 . 6 5

S t a c k Out le t l b / 1 0 0 0 l b .

Flue G a s of

at 50% E x c e s s Air

1.75

0 . 7 7

0 . 7 7

0 . 1 4

0 . 1 7 5

0 . 1 7 5

0 . 0 3 S

0 . 0 3 5

Stack Out le t g r / c u b . f t . a t

12%C0 2

(approx.)

0 .92

0 .40

0 .40

0 .07*

0 . 0 9 *

0 . 0 9 *

0 .02*

0 . 0 2 *

* Assuming a market for the steam generated In a water-cooled furnace

* Complying with the requirements of the N.S.W. Clean Air Act

only successful in solving the air pollution problem but are also economically successful. The use of waste heat boilers and/or water-cooled furnace walls have made it possible to control furnace temperatures and to achieve combustion with the mini­mum of excess air (about 50 per cent.), thus reducing considerably the volume of gas requiring cleaning. This has also helped to reduce the amount and sizes of particulate matter en­trained in the furnace exhausts and to alleviate the formation of nitrous oxides.

The cost of efficient refuse disposal and air pollution control is high and some may say that we cannot afford it; the cost of polluting our land, our water supplies and the air we breathe, however, is many times greater and with the present rate of population growth and industrialisation of our cities, is one which we cannot afford to neglect for very long.

References Bump, R. L, 1966. Proceedings of 1966 Nat ional

Incinerator Conference, A m . Soc. Mech. Engrs., N.Y. pp. , 161-166.

Fife, J. A. , and Boyer, R. H., 1966. Proceedings of 1966 Nat ional Incinerator Conference, A m . Soc. Mech. Engrs., N.Y., pp . 89-96.

Fowler, R. T., and Doig , I. D., 1966. Proceedings of Clean Ai r Conference, 1965, Paper No. 8 Sydney, N.S.W.

Kirov, N. Y., 1962. Proceedings of Clean A i r Conference, Paper No. 22, Sydney, N.S.W.

Stenburg, R. L, Hangebrauck, R. P., Lehmden, D. J. , and Rose, A. H., 1962. Jour. A i r Pol lu­t ion Control Asscn., Vo l . 12, No . 2, pp . 83-89.

Stephenson, J. W., and Cafiero, A. S., 1966. Pro­ceedings of 1966 National Incinerator Con­ference, A m . Soc. Mech. Engrs., N.Y., pp . 1-38.

Walker, A. B., and Schmitz, F. W. , 1966. Ib id . , pp . 64-73.

W. HOWARD COCK, Dip.App.Chem.A.R.A.C.I.

Consulting Chemist Specialising in Air Pollution and Occupational Health Problems, Isokinetic Stack Sampling, Dust and Fume Collector Efficiency Tests, Particle Size Analyses, Atmospheric Sampling and Testing, Dust and Toxic Vapours in Air Determina­

tions, etc.

151 NORTHERN ROAD, HEIDELBERG WEST,

VICTORIA 3081. Phone: 45 4506

APPROXIMATELY 330 delegates A registered for the Conference, representing a wide cross section of interested segments of the community from all States in Australia (exclud­ing the Northern Territory); and about 100 requests for the Conference Papers have been received by the Organising Committee, many of these originating from overseas.

The Conference was opened by the Hon. P. H. Morton, MLA, NSW Minister for Local Government and Highways. In his opening remarks, the Minister referred to the problems facing Local Government authorities in large cities in general and in the County of Cumberland in particular, in disposing of the half-million or so tons of garbage collected annually, and referred to the practicability of various disposal methods such as landfill, incineration and composting. Mr. Morton also stated that in NSW, refuse disposal has been the concern of local councils, and should, in his view, remain so. In considering the various problems associated with refuse disposal, the associated aspects of air pollution by incinerators, the disposal of liquid trade wastes and improvement in the current methods of household garbage collection should not be overlooked.

The Vice Chancellor of the Uni­versity of New South Wales, Professor Sir Philip Baxter, in thanking the Minister for opening the Conference, said that present day archaeologists should be thankful for the lack of refuse disposal methods of past civilisations, who had buried the re­mains of their communities under mounds of their own garbage. Refuse disposal was therefore an old as well as a modern problem, which a con­ference of this type should help to alleviate.

The Conference was divided into five general Sessions. The first four were under the Chairmanship of a

CLEAN AIR—September, 1967 25

representative of each of the four sponsoring organisations, while the fifth, a Forum Discussion, was chaired by Professor R. T. Fowler of the School of Chemical Engineering, Uni­versity of New South Wales.

A brief review of the proceedings is as follows.

SESSION No. 1 Chairman: Associate Professor N.

Y. Kirov, Department of Fuel Tech­nology, University of New South Wales.

Paper 1. "Refuse Disposal—A Growing World Problem", by Assoc. Professor N. Y. Kirov, University of New South Wales, and Mr. H. K. Toner, Waverley Municipal Council.

Mr. Toner, in introducing this paper, reviewed the world-wide problem facing Municipal authorities in the collection and disposal of refuse, and indicated that the paper serves as an introduction to the various papers presented at this symposium.

It was pointed out that the need for basic data and systematic surveys and research into methods and costs of refuse collection, transportation and disposal is shown to be one of the prerequisites for efficient future planning. Several examples of regional schemes were considered and it was emphasised that there has been a tendency throughout the world for local authorities to com­bine in joint refuse disposal schemes.

Trends in handling, transportation and available r e f u s e disposal methods, including some special problems of disposal of "difficult" wastes were then briefly discussed, and Mr. Toner concluded with some economic considerations and costs relating to municipal refuse disposal.

Paper 2. "Refuse Disposal, the Sydney Problem" was presented by Alderman V. H. Parkinson, Mayor of Mosman Municipal Council and representing the Local Government

The First Australian Refuse

Disposal Conference By K. S. Basden, Ph.D.

This Conference, which was announced in an earlier issue of this Journal, was held at the University of New South Wales on August 22 and 23, 1967. The Conference was sponsored by four organisations which are interested in various technical and administrative aspects of the refuse disposal problem, namely: (i) the Department of Fuel Technology, Uni­versity of New South Wales; (ii) the Local Government Association of NSW; (iii) the Clean Air Society of Australia and New Zealand; and (iv) the Institute of Fuel, Australian Membership.

Association of NSW. Alderman Parkinson mentioned that the City of Sydney and its outlying areas was serviced for refuse disposal by 35 Municipal and 4 Shire Councils, and referred to the problems faced by these authorities.

Alderman Parkinson concluded his remarks by suggesting that the dis­posal problem in Sydney can only be executed efficiently by the joint action of the various Councils. If they should fail to respond to the challenge, they would be inviting the State Government to step in and establish a special authority to take over the operations. During the last few months, a major proportion of the 39 Councils had each contributed $200 to finance a special investiga­tion of the problems associated with the disposal of refuse.

Paper 3. "The Physical and Chemical Characteristics of Municipal Refuse", by Dr. K. S. Basden and Associate Professor N. Y. Kirov, University of New South Wales.

This paper was introduced by Dr. K. S. Basden, who pointed out that a knowledge of the composition and characteristics of refuse is desirable as it is a prerequisite for planning for its efficient disposal by methods such as sanitary landfill, composting or incineration.

As no comprehensive surveys had been undertaken in Australia, this paper consisted essentially of a collation of information from over­seas surveys made during the past six or seven years, as obtained either from actual visits and discussions in the localities concerned, or from relatively obscure and inaccessible technical publications. The paper discussed the definition of various terms such as "refuse", "garbage", "rubbish", and the desirability and difficulties of conducting local refuse surveys. Also provided in the paper was a number of tables which summarise existing data on refuse composition, its a n a l y s i s and calorific value, seasonal variations and projected trends, etc., for a number of cities throughout the world.

SESSION No. 2 Chairman: Alderman H. G. Coates,

MLA, President, Local Government Association of NSW.

Paper 4. "The Handling and Collection of Municipal Refuse". Mr. H. K. Toner, Waverley Municipal Council.

Mr. Toner mentioned that the collection and disposal of refuse is a problem causing concern to all.

26

Current emphasis in this community is on disposal, which however, cannot be divorced from a well planned collection and handling system.

Some collection systems and plants used overseas were then described and illustrated by slides. Modern refuse-collection vehicles of the side-loaded, rear-loaded and revolving drum type used to compact the waste material were discussed, and this was followed by some comments concern­ing bulk handling of refuse, its re­moval from high density flats, disposal by sack collection and the bulk transfer of refuse by road vehicles. It is believed that the application of these modern developments to local conditions may well have an effect in assisting in the improvement of current practices in Australia.

Paper 5. "Refuse Disposal by Sanitary Landfill and Composting as practised in Australia". Mr. D. M. Watkins, Canterbury Municipal Council.

The successful disposal of refuse by sanitary landfill methods was dis­cussed by Mr. Watkins in introducing his paper, and particular emphasis was made to the precautions to be taken to safeguard the health and convenience of the community. These precautions related to the choice and preparation of site, the landfilling operations and the c o n t r o l of nuisances such as flies, rodents and fires. The details given were based on experience in connection with an ambitious and interesting reclamation project being undertaken by Canter­bury Municipal Council at a site situated in a mangrove swamp on the upper reaches of Salt Pan Creek. Mr. Watkins also described the development and operation of a large composting plant which was erected by Canterbury Council for the treat­ment of refuse by bacteriological means. Mr. Watkins illustrated his introduction to the paper with a colour film of Canterbury Council's refuse disposal practices.

Paper 6. "Treatment and Dis­posal of Liquid Trade Wastes". Dr. T. L. Judell and Dr. D. T. Laccy, Water & Trade Wastes Consultants Pty. Ltd.

In introducing this paper, Dr. Judell stated that the pollution of streams and coastal waters is a matter of increasing public concern, and that control of the pollution of streams and coastal waters has become one of the principal problems facing modern civilisation. Industrial waste is one of the important causes of water pollution.

Dr. Judell indicated that the treat­ment and disposal of trade wastes cover a wide field of operations, and significant economic benefits may be derived from the recovery of by­products. Although the recovery equipment is usually more expensive than disposal equipment, the recovery of chemicals and water occurring in trade wastes may be found to be profitable in many cases. Dr. Judell illustrated his introduction with a number of slides.

SESSION No. 3 Chairman: Mr. W. T. Cooper,

Chairman, The Institute of Fuel— Australian Membership.

Paper 7. "Domestic and Industrial Incinerators and the Clean Air Act". Mr. R. P. Murphy, NSW Department of Public Health.

Mr. Murphy gave an account of investigations into the performance of, and the emissions which occur from, various types of incinerators operated in multi-storey dwellings, retail stores and industrial premises which burn general refuse and wood waste. The results of a number of tests listed in the paper were described and some important relevant aspects of the Clean Air Act were discussed.

Mr. Murphy suggested that the design of many incinerators must be improved, and appropriate d u s t collecting equipment needs to be in­stalled if on-site incinerators are to comply with the levels of emissions prescribed by the NSW Clean Air Act.

Paper 8. "Problems Encountered in the Incineration of some Difficult Trade Wastes". Dr. J. R. Harry and Mr. J. McLeod, NSW Department of Public Health.

Dr. Harry stated that past ex­perience has shown that the incinera­tion of laminated papers and scrap copper cable causes objectionable air pollution problems when conducted in standard incinerators or by open burning. A description was given of two incinerators specifically designed to cope with these problems and their performance was evaluated.

Paper 9. "Disposal of Municipal Refuse by Incineration". Associate Professor N. Y. Kirov, Department of Fuel Technology, University of New South Wales.

In introducing his paper, Professor Kirov referred to the problem of hygienic refuse disposal, which is of major and growing c o n c e r n to Municipal authorities, and which is a direct consequence of population g r o w t h and technical advances

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EARLY MORNING SMOG OVER SYDNEY DURING JULY, 1967

The photograph was taken at 8.30 a.m. on one of the Clean Air Society's charter flights.

characterising our present day in­dustrialised civilisation. Professor Kirov stated that for a number of reasons, as set out in his paper, the incineration of municipal refuse by modern high temperature techniques has become the preferred method of refuse disposal in most of the large cities of the world. This is a develop­ment which has taken place only dur­ing the past 15 years.

The objectives of high temperature incineration were described followed by considerations of refuse as a fuel and of the basic requirements for its efficient combustion. Professor Kirov then described the advances and principal design features of modern incinerator plant and of the various firing systems which have led to the successful development in municipal refuse incineration practice through­out the world. The introduction was illustrated by an excellent film depict­ing a particular type of modern in­cinerator plant and its operation in a number of the world's major cities.

Paper 10. "Incinerator Instru­mentation Systems". Dr. K. S. Basden, Department of Fuel Tech­nology, University of New South Wales.

Dr. Basden stated in the intro­duction to this paper that the subject was only a subsidiary one, and was incorporated in the Conference pro­gramme to complete the description of modern high temperature incinera­tor plants as described by Professor Kirov in the previous paper and illustrated so strikingly in the films shown earlier that morning and on the previous day.

As delegates would have observed, the modern high temperature in­cinerators are complex installations, and the films and slides associated with the present and previous papers had shown the elaborate control rooms with sophisticated instrumenta­tion and control panels. The purpose of the present paper was to outline briefly the nature and function of the most essential instrumentation and control systems for incineration plants of this type.

SESSION No. 4 Chairman: Mr. K. N. Berrie, Vice-

Chairman, The Clean Air Society of Australia and New Zealand.

Paper 11. "Emissions from Large Municipal Incinerators and Control of Air Pollution11. Associate Pro­fessor N. Y. Kirov, The University of New South Wales.

Professor Kirov described the

various emission limits for refuse incinerators in relation to a number of Clean Air Acts, and outlined the methods which are available for con­trolling these emissions and for the cleaning of the combustion gases.

The performance of various types of gas cleaning equipment was examined and it was concluded that for large municipal incinerators that fabric filters, wet gas scrubbers and electrostatic precipitators are capable of achieving the high collection efficiencies necessary for control within the requirements of the NSW Clean Air Act.

Paper 12. "The Performance of a Catalytic Afterburner in the destruc­tion of an Industrial Odour". Dr. G. J. Cleary, Mr. J. F. Pottinger and Mr. L, M. Ferrari, NSW Department of Public Health.

This paper, introduced by Mr. Pottinger, described four industrial situations in which afterburners were used in the destruction of industrial odours. Catalytic afterburners were employed to treat the exhaust products from coffee and chicory roasters and from an oven drying phenol formaldehyde bonded plastic sheeting, and thermal afterburners were used to treat the exhaust products from a small coffee roaster and from a foundry core oven. The units were described separately and their per­

formances in the destruction of the odours concerned were evaluated.

SESSION No. 5 Chairman: Professor R. T. Fowler,

School of Chemical Engineering, Uni­versity of New South Wales.

FORUM DISCUSSION The panel consisted of Associate

Professor N. Y. Kirov, Mr. S. Lipson (representing the Sydney Division of the Australian Planning Institute), Mr. R. P. Murphy, Alderman V. H. Parkinson, Mr. H. K. Toner and Mr. D. M. Watkins.

This session consisted of a general and very interesting discussion in which a number of delegates from the floor contributed. A range of topics, covering the whole field of the Con­ference and introducing points of view not raised during the earlier discussion sessions (which followed each one or two papers) was traversed.

In closing the Conference, Pro­fessor Fowler thanked the Organising Committee and all others who had contributed to its success, and invited delegates who had any suggestions for a possible Second Refuse Disposal Conference, which could be held in two or three years' time, to send these to members of the Organising Com­mittee or to the Hon. Organising Secretary.

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