C. W. Hamilton, Jr . , Division Chief, Chehicals Division . .

R. D. Rice, Research Consultant, Chemical Processing

united States Steel Corporation Research Laboratory

Monroeville, Pennsylvania

Abstract

This paper describes the commercial development,of the USS PHOSAM Process for the.recovery bf coke-oven ,by-product ammonia in the form of high-purity

anhydrous liquid ammonia. The process is gaining world-wide acceptance among coke producers, and applications outside the coke-plant field are anticipated.

. .

Introduction

The carbonization of coal produces ammonia, a gaseous compound of nitrogen and hydrogen, as one of the pyrolysis products. It is universally conceded that the ammonia must be rather thoroughly removed from the coke-oven gas before the gas can be utilized as fuel.

The traditional and predominant method of ammonia removal is to react the ammonia with sulfuric acid and to produce crystals of ammonium sulfate for sale. Sulfate contains about 25 percent ammonia, and thus it involves the purchase of 3 tons of sulfuric acid for every ton of ammonia recovered. And, of course, it involves the handling of 4 tons of solid product.

Ammonium sulfate production was profitable in the days before large-scale

production of synthetic ammonia, and before the large-scale production of by- product ammonium sulfate from caprolactam and other synthetic chemicals. It is

profitable again today in some locations owing to the world shortage of ferti- lizer nitrogen which has driven up the price of ammonia, urea, ammonium nitrate, and other forms including sulfate. But for two or three decades now, coke- plant operators have faced a very erratic market situation in which ammonium sulfate frequently could not be sold at any price, and seldom at a price which covered out-of-pocket expenses. In addition, the sulfate operation is inherently

messy - dusty, corrosive, and expensive in terms of capital plant, space requirements, and labor for operation and maintenance.

Therefore it is natural that coke-plant managers have sought viable alter- natives to sulfate. United States Steel Corporation, for example, carried out an exhaustive survey of the alternatives including ammonia destruction processes, the production of ammonium phosphate or phosphate/nitrate, and the production of anhydrous amm0nia.b~ some type of cyclic process. The latter category included the thermal and ultrasonic decomposition of ammonium sulfate on one hand, and the concept that was to become the USS PHOSAM Process on the other.

The concept was simple - phosphoric acid has 'three hydrogen atoms that can be replaced by ammonium ions in water solution, and,it.is a weaker acid than sulfuric. Therefore, there should exist a range of mole ratios, ammonia to phosphoric acid, over which the ammonia is bound tightly enough for good absorption but still loosely enough that it can be stripped back out under proper conditions. Thus a cyclic absorption process could be envisioned in. which a solution of ammonium phosphate would recycle between an absorption and a stripping zone, picking up and releasing ammonia which can be concentrated and purified in a subsequent step.

When the preliminary economic evaluation was favorable, United States Steel

Research proceeded with the development of the USS PHOSAM Process. The result

is a most attractive alternative to sulfate - a completely enclosed, dust- free, easy-to-operate, and economical process in which the product is liquid

anhydrous ammonia.

Anhydrous Ammonia

Pure ammonia, NH3, is a colorless gas, lighter than air, with a character- istic pungent odor.

Ammonia is readily liquefied by compression and cooling, and it is the

liquid form that is conveniently stored and transported. When a sample of anhydrous ammonia is let down to atmospheric pressure, it is self-refrigerated to-the normal boiling point (-33' C). Storage capacity appropriate for a coke

plant's production is provided by using uninsulated, pressure tanks designed for about 250 to 300 pounds per square inch (psig). Tank trucks and tank cars so designed are in extensive use in ammonia service in Canada and in t6e United States. The specifications for such trucks and cars are the same as those for liquefied petroleum gas (LPG), and many carriers transport propane in winter

and ammonia in the fertilizer season.

Ammonia is the predominant source of nitrogen in making fertilizers, for example ammonium nitrate, urea, ammonium phosphate, ammoniated superphosphate, and nitrogen solutions. ~mmonia is a major fertilizer in 'its own right, being plowed directly into the soil with simple tractor-towed rigs. Special high- purity grades of ammonia are also used in chemical synthesis, in refrigeration, and in steel plants. for the generation of reducing atmospheres. The latter

process involves. the dissociation of ammonia in a catalyst bed into nitrogen and hydrogen - exactly the reverse of the synthesis reaction:

~ N H ~ N + 3 ~ . (75 volume % hydrogen) 3 2 2

This produces a hydrogen-rich gas for use in stainless steel anneal.ing, aluminum coating of steel, and other metallurgical applications. To be suitable for this exacting application, ammonia must contain less than 100 parts per million (ppm) water and less than 3 ppm oils in order not totarnish the work nor degrade the catalyst. Similarly, stringent specifications are, imposed on ammonia to be used in refrigeration systems, and as chemical feedstock for the manufacture of nitric acid, acrylonit.rile, melamine, caprolactam, and other chemical intermediates. The USS PHOSAM process is capable of producing very- high-quality ammonia suitable for all these uses, as well as for fertilizer.

Table I

Typical Analysis of PHOSMI Process Ammonia

Assay 99.99% NH 3

Color Colorless

Water 100 parts per million (ppm)

Oils 2 PPm

co2 3 PPm

H,S Non-de tectable

C 1 2 Ppm

A discussion of the world nitrogen market is beyond the scope of this

paper. However, the trade literature shows that world demands for nitrogen continue to increase while the raw materials for synthetic ammonia become scarce and costly. Thus, we have witnessed, just in the past year and a half, an increase in prices at the wholesale distribution level from about $40 to $150 per short ton. In Europe, where much of the ammonia production derives from petroleum, ammonia prices appear to be in the range of $200-$300 per metric ton (tonne) .

A'very large coke plant employing the PHOSAM process would produce about 30 tons ammonia per day. This is only a tiny fraction of the total market.

Thus one, or indeed many, coke producers could switch to anhydrous ammonia production without in any way affecting the market.

The same perspective shows that one should not market his small tonnage of

ammonia directly but in collaboration with a major producer or distributor already serving the market. For example, U. S. Steel's Agri-Chemicals Division

are a major producer and distributor and they are happy to have any additional -ammonia they can find. With the world shortage that has become apparent, long-

term and mutually attractive arrangements can be made with domestic producers to move one's anhydrous ammonia, produced by the PHOSAM process, into existing channels of distribution.

* . The USS PHOSAM Process

The PHOSAM process was developed by united States Steel Corporation's

Research organization from original conceptions in the late fifties, and is covered by patents issued in several countries.(l) The concept appeared more

promising technically and economically than the other alternatives to sulfate in U. S. Steel's survey, and was selected for development into a commercial process.

As a first step in evaluating and developing this process, an extensive laboratory investigation was conducted to determine the physical, chemical, and

thermodynamic properties of the aqueous ammonium phosphate system. Since the process depends on the relative ability of ammonium phosphate solutions to hold ammonia at the absorption tehperature and to release it at the stripping temper- ature, complete vapor-liquid equilibrium data were obtained. These proprietary data cover the entire range of temperature and composition of conceivable interest, and they, together with the associated heats of absorption and vapori- zation, have been correlated into the computer programs with which each PHOSAM plant is designed.

Additional lkboratory and literature research was done to obtain the

physical property data needed for the design and control of the process. These data include the complete solubility diagram, densities, viscosities and specific

heats of the ammonium phosphate system.

The vapor-liquid equilibrium data disclosed an unexpected fact - that the stripping equilibria are markedly improved at high pressures. Because of this,

a high operating pressure in the stripper greatly reduces the steam require- ments. This is in contrast to'other cyclic gas-absorption processes such as the vacuum-carbonate process for hydrogen sulfide recovery.

Following this phase of development, apilot plant was built and operated for about a year at U. S. Steel's Clairton Works to further investigate the process. .The pilot Olant provided. information and data on materials of construc-

tion, tray efficiencies, fouling, and other practical aspects of the process, and demonstrated. its operability. The successful development work ultimately led to the installation of the PHOSAM process as the first processing block in Clairton's new Keystone chemical facility. The Keystone facility is a completely new coke-oven-gas processing system downstream from the primary coolers. After compression and final cooling, the ammonia is removed by the PHOSAM process, and the gas goes directly into cryogenic processing. There, a series of opera- tions at low temperature remove hydrogen sulfide and light oils from the coke-

oven gas, and at still lower temperatures, remove the hydrocarbons and thus . .

enable production of a purified hydrogen stream. This stream is combined with nitrogen from an air separation plant and the mixture is fed to a large synthetic- ammonia plant. The PHOSAM plant' has an especially exacting and pivotal task, because the cryogenic processes in the Keystone facility.require a very low' ammonia content in the gas.

The Clairton PHOSAM plant (Figure 1) has been in successful operation since the beginning of 1968 and has been extended and modified so as to recover all the by-product ammonia from coke-oven gas and liquor& at the Clairton

, Works, including that gas which does not go through the Keystone cryogenic

plant. With a design capacity In excess of 350 million cubic feet of -coke-oven gas per day, the Clairton PHOSAM plant is the largest in the world.

In 1969 U. S. Stee1,decided that the PHOSAM Process would be of economic value to other companies and should be made available for worldwide licensing. That decision, and a paper given in Pittsburgh in October 1969 marked the beginning of a sales and engineering effort by a U . S. Steel subsidiary, USS

Engineers and Consultants, Inc. This effort has resulted in a number of licenses throughout the world. Currently, five licensed plants, four in Japan and one in Canada, have been in operation for several years, another will start up soon in Brazil, and others are under construction in Japan, Canada, Taiwan, and the United States.

,

Interest in the PHOSAM Process, on the part of coke oven managers, is accelerating. Coke plant construction is underway again, and this, coupled

. with the dramatic increase in ammonia 'prices, has'set the stage for a much more

extensive utilization of this unique technology. Just a year or two ago, economic studies would show the PHOSAM process merely to be the least ,costly

- way to handle the ammonia problem in a new coke plant. Today it is likely to

show up as a profitable solution to the problem.

Process Variations

The PHOSAM Process will now be discussed in more detail, pointing out some of the variations that are possible and are being used.

Figure 2 shows the essential features of the USS PHOSAM Process, as applied to the direct recovery of ammonia from coke-oven gas. Coke-oven gas, from primary coolers, exhausters, and conventional gas-cleaning equipment, is passed through a two-stage spray-type absorber. Ammonia is scrubbed from the gas by countercurrent contact with ammonia-lean phosphate solution, which enters the top of the absorber. The gas leaves the absorber with 99 percent or more of its ammonia removed, and is suitable as such for further processing. The absorbing solution is stable and nonvolatile, and does not require periodic

replacement or purification. It is highly selective for ammonia, rejecting acidic gases such as hydrogen sulfide and organic compounds that are present in the feed gas.

Absorber pressure drop is low, normally 100 to 150 millimeters of water, and the operating pressure is that imposed by downstream equipment. Depending

on the temperature and humidity of the inlet gas, the gas may be heated slightly or cooled in passing through the absorber, where ammonia is absorbed and water is evaporated. Design techniques have been developed that permit satisfactory deslgns for most conditions of pressure, temperature, humidity, and ammonia content not only in coke-oven gas but also in gases or vapors of markedly different composition.

The ammonia-rich solution from the absorber is pumped through heat exchangers into the stripper, recovering heat enroute from the stripper bottoms and overhead vapor. In the stripper, the solution is countercurrently contacted with steam at elevated pressure, stripping out the absorbed ammonia and regenerating the lean solution. The lean solution is cooled and returned to the absorber. Automatic controls make it easy to operate the plant efficiently, despite

\ 1

variations in the feed gas, and to control the water content of the solution.

The overhead vapor from the stripper is condensed to form an aqueous

ammonia feed to the fractionator where anhydrous ammonia is produced by pressure fractionation, again by using direct steam. The overhead product is liquid anhydrous ammonia, of high purity, ready for shipment. An ingenious system of automatic controls for the fractionator assures the continuous production of specification ammonia product, despite variati0ns.h the feed rate and composi- tion, or temporary upsets in the system.

Both of the distillation operations are conducted under pressure for reasons of economy. The optimum pressures depend somewhat on the cooling-water temperature, but are generally in the range 180 to 200 pounds per square inch

gage. This means, in turn, .that 200 to 250 pound steam is required.

Although the basic scheme is simple, it will be recognized that an extensive body of "know-how" has been accumulated over the years of experience with the process in actual use. Each new plant design is in some way improved by the lessons learned in previous plants, and each license carries an obligation to feed back information and-ideas that may be useful to other licensees.

Stripper and fractionator towers in the PHOSAM Process are quite small in diameter, and, together with the associated heat exchangers and vessels can be accommodated in an area of about 30 x 70 feet. Figure 3 shows the PHOSAM plant at Ahagasaki Coke Company's large modern coke plant at Kakogawa, Japan. From left to right are electrostatic tar precipitators, the PHOSAM ammonia absorber, and the PHOSAM regeneration and fractionation area. The absorber shown is over 16 feet in diameter and about 65 feet In height. It has a coke-oven gas capacity of about 160 million standard cubic feet per day.

Larger absorbers are possible. However, it is more common to find two separate gas processing trains in the larger coke plants and to install one PHOSAM absorber in each train. These two absorbers are served by a single regeneration and fractionation area which may be remote from one or both ab- sorbers. This arrangement is commonly employed where there is a stepwise

expansion plan. The PHOSAM stripper and fractionator and certain of the heat exchangers are deslgned at the outset for the future capacity, but only one absorber is installed initially. The system is then operated at half load until the second phase of construction is carried out and the second absorber

is installed. Operation of PHOSAM plant at reduced rates, even as low as 20 percent of design capacity, is accomplished without difficulty.

It was mentioned earlier that U. S. Steel's Clairton Works' PHOSAM plant was expanded to recover all the by-product ammonia, including that from gas '

that does not go through the Keystone cryogenic plant. This was accomplished by making some minor internal modifications of a spray-type saturator in Clairton's Number 1 by-product plant, so as to provide countercurrent contact, and running rich and lean solution lines to the PHOSAM plant some 1200 feet away. The stripping'- and fractionating capacity. had been provided initially, with the intention to expand the cryogenic plant to process all the gas. This may yet be done, but meanwhile the conversion, which has been in operation sinde ~e'bruary 1972, has provided Clairton with a major cost reduction over the past three years, by eliminating the high-cost ammonium, sulfate operatio?.

. ,

It should be noted that the placement of the PHOSAM absorber just downstream from exhausters and tar precipitators 1s conventional, but not the only possible location. The absorption of ammonia is carried out at relatively high tempera- tures of 4 0 " to G O 0 C, always above the napthalene dew point established in the primary coolers. Therefore, there is no need for naphthalene scrubbers, H2S scrubbers, nor secondary coolers ahead of the PHOSAM ammonia absorber. When ammonia liquor stills are operated, the vapor from the still is added to the absorber feed gas.

Another alternative to sulfate is the destruction of ammovia by burning in anincinerator. A number of coke plants, especially in Europe and Japan, have installed indirect ammonia removal systems like the one shown in Figure 4. The 'coke-oven gas, which must first be.passed through a naphthalene scrubber (not shown), is scrubbed with water in countercurrent multl-stage ammonia absorbers. Ammonia 1s absorbed, together with perhaps a third of the H2S and other acid gases, and the avonla-rich water is passed to a free ammonia still or stripping tower in which the absorbed ammonia and other gases are stripped out and the

vapor is passed to the incinerator. The sulfur dioxide emission in the flue

gas from the incinerator is a serious problem, and has led to the prohibition of this process in some countries, notably West Germany. A considerable reduc- tion in the amount of H2S burned can be achieved by a two-stage distillation of the ammonia-rich solution. Using an additional tower called a deacidifier, which is not shown in the illustration, much of the H2S can be distilled out of the solution, with only a part of the ammonia, and fed to the desulfurization system. However, this -separation is incomplete atbest, and it complicates an already complicated flowsheet.

In contrast, the Basic PHOSAM Process (Figure 5) can be applied to ammonia destruction with considerable advantage, resulting from the high absorptive capacity of the ammonium phosphate solution and its high degree of selectivity. Compared to water-washing, the ~asic PHOSAM process has much smaller flow rates and smaller heat duties, and therefore, smaller equipment and space requirements. The Basic plant is very much simplified by the omission of heat exchangers, tanks and pumps associated with the fractionator. It produces ammonia-water

vapor for incineration that is essentially free of H2S and therefore the flue

gas will be free of S02. The Basic PHOSAM Process, therefore, offers significant advantages and should be considered in the smaller coke plants where the recovery of abonia in a saleable form is perhaps.not justified.

. . .. . .

We believe, however, that under present and forseeable market conditions, the recovery of ammonia in some form salable, at least, for fertilizer use is almost always justifiable.

Figure 6 shows a USS PHOSAM plant set up for the recovery of saleable aqua ammonia solution - not the crude concentrated ammonia liquor usually identified with coke plants but a relatively pure grade containing, for example, 28- 30 percent ammonia and about 0.5 percent of total impurities by weight. The equipment requirements and cost of this type of plant are very much closer to the Basic plant than to the typical PHOSAM plant designed to make 99.99 percent pure anhydrous ammonia, and should prove attractive to the coke plant handling,

say, less than 30,000 cubic meters per hour of coke-oven gas and less than 10 tons per day of ammonia. Also, it is applicable where the available steam pressure is too low for a normal fractionator design, and refrigeration or other special means would be required to make anhydrous ammonia. ,

We turn now to another type of conversion that is being made, particularly in Japan and Europe. A number of companies that have installed the so-called indirect process to remove ammonia by water-washing and destroy it by burning,

are reconsidering that decision. In Japan, the compelling reason is a nationwide concern about nitrogen oxides or NOx pollution, some of which is traceable to ammonia combustion units. But everywhere, the plain economic fact that ammonia has increased in value five-fold in the past year cannot be overlooked. Put another way, we feel that the destruction of significant quantities of fixed nitrogen can no longer be justified in view of world shortages of food and

fertilizer.

Figure 7 shows in simple block diagram the installation of a PHOSAM Process plant in place of the incinerator in an. existing indirect system. This can be

done very easily and without any interruption of the coke-plant operation. It

is rather a novel idea that a reversible absorption process can be eff.iciently performed at temperatures in excess of 100° C when one considers that the normal PHOSAM abso-rber operates on coke-oven gas at 40-60" C. It is neverthe- .less, entirely feasible to do so, and the exact calculation of such a "hot

absorption" process is within the range of the fundamental equilibrium data and the computer programs developed for the PHOSAM technology.'

We would not recommend an indirect water-wash system coupled with a hot PHOSAM absorber for a grass-roots installation because it involves the very considerable capital cost and operating costs of the indirect system in addition to the costs of the PHOSAM plant. But where the indirect system already exists and one contemplates ammonia recovery by the PHOSAM Process this option should

be considered along with the option of replacing the ammonia absorber in the coke-oven gas train.

PHOSAM with Desulfurization

The PHOSAM absorbent picks up ammonia selectively and rejects hydrogen sulfide and the other acid gases. heref fore, it makes no dffference whether the coke-oven gas is desulfurized upstream or downstream, or not at all.

Certain of the desulfurization processes are carried out on the gas upstream from the ammonia removal system, and they employ the natural ammonia from the

coke-oven gas in'water solution as a chemical absorbent for the H2S. These processes are quite old and well established, particularly in German technology. They utilize H2S scrubbers followed by ammonia scrubbers. The H2S scrubbers are supplied with an ammonia-water solution, and the NH3 scrubbers with softened water. The circulating solution, rich in H ~ s and NH3, is distilled in a deacidi- fier column to regenerate the H2S-lean ammonia solution for return to the H2S

absorber, and the surplu? solution is further distilled in a free ammonia still. The overall result of this process is to remove both H2S and NH3,

which appear in a single vapor stream.

Figure 8 shows a combination of the USS PHOSAM Process with the wet desul- furization by ammonia solutions. In this combination there is a primary PHOSAM absorber in the coke-oven gas line after the H2S absorber, and a small, secondary absorber treating the vapor stream from the deacidifier column. The rich solutions from both absorbers are processed together in a conventional PHOSAM stripper and fractionator to produce pure anhydrous ammonia. The use of the PHOSAM Process in this way, not only recovers the ammonia values, but also reduces the volume of waste water to be treated and leads to savings in the

conversion of the H2S stream to sulfuric acid or to elemental sulfur. Two U. S. plants, now under construction, will employ this combination of PHOSAM

with desulfurization. However, it should be noted that the PHOSAM Process may be applied equally well without prior desulfurization.

We have described some of the adaptations of the USS PHOSAM Process tech- nology that are being designed and used in by-product coke plants around the world. We feel the boundaries have not yet been fixed - for example the design of shop-assembled, skid-mounted and standardized PHOSAM units for small plants is'an intriguing idea on which we are just beginning work. -

PHOSAM costs

USS Engineers and Consultants, Inc., license the PHOSAM Process directly to the ultimate user and provide the.licensee and his engineering contractor with a specific and detailed process engineering design package. The civil engineering, procurement and erection' of the plant are provided by the contrac- tor, and therefore we do not usually learn the capital cost'of PHOSAM plants. However, comparisons that have been made by others have shown repeatedly that USS PHOSAM Process plants are considerably cheaper to build 'than ammonium sulfate plants and are at least cost-competitive with ammonia burning plants.

Operating labor requirements for PHOSAM are substantially lower than for the equivalent sized ammonium sulfate plant because of the basic simplicity of the process, and the fact that no solids need be handled. Regardless of the size of the plant the total labor requirement for operation and analytical control amounts to less than two men per shift. Maintenance costs will also be lower than for the equivalent ammonium sulfate plant.

chemicals and utilities costs may be estimated from Table 11.

Table I1

Consumption per pound Anhydrous NH3 Produced

H PO (makeup, as 100%) 3 4

0.0075 lb

NaOH (as 100%) 0.01 1b 2

Steam, 18 kg/cm (250 psig) 10-11 lb

Cooling water circulation 150-250 lb

~lectricity 0.10 kilowatt hour .

When one considers operating costs and product values, ainmonia destruction

schemes can no longer be justified even if they incorporate waste heat recovery from the burning of ammonia. A recently published study concluded that ammonia destruction is unfavorable in comparison with sulfate at prices above $32 per short ton and with anhydrous ammonia above $36 per short ton.(2) Of course, these price levels' have been passed and it seems likely that ammonia will at least remain above $100 per ton in the foreseeable future.

Application to Other Industries

The PHOSAM technology is applicable beyond the field of coal carbonization, for example, in the fields of coal gasification and liquefaction, oil shale

and tar sands processing, and oil refining. All of these processes concerned with the conversion of fossil fuels give rise to waste waters and gases con-

taining ammonia, carbon dioxide, hydrogen sulfide, etc.

The application.of the PHOSAM technology to this system is unique in that it permits the ammonia and acid gases contained in the water to be separated and the ammonia,recovered as a high purity.product.

A typical installation of this process, called PHOSAM-W, would be for one of the Lurgi type coal gasification plants planned for the western United States. Each of these plants will produce 250 million cubic feet a day of high-Btu pipeline gas. The contaminated water from one of these plants is treated by solvent extraction for phenol removal, then processed to remove ammonia and acid gases (C02, H2S, etc.). When using the PHOSAM-W process, the water, about 2000 GPM is stripped with steam in a multi-stage stripper. The hot vapors from the water stripper (mostly water, ammonia, C02, and H2S) are contacted with lean PHOSAM solution in a multi-stage absorber located directly above the stripper in the same column shell. Thus, in one tower, 2000 gpm of water is stripped of its ammonia and acid gases, and the ammonia is removed ..

from the vapor by absorption into PHOSAM solution. The ammonia is recovered as anhydrous ammonia by conventional PHOSAM process stripping and fractionation. A water stream suitable for reuse leaves the bottom of the water stripper and after partial condensation, the ammonia-free vapors are sent to a sulfur recovery unit.

This technology has been demonstrated in commercial operation for over two years on an ammonia-containing water stream in U. S. Steel's Clairton Works. The extension of proven coke plant technology such as PHOSAM to other industrial applications exemplifies the technicaladvancements being made by the steel industry.

Conclusions

The USS PHOSAM Process deserves consi,deration by coke plant managers who are mindful to the economic crunch and alert to the new market situation in

.. fertilizers .

Wherever coke-plant expansion requires' new investment in by-product facilities, or where major rehabilitation of an existing ammonia-removal facility is needed,.PHOSAM will prove to be the most attractive of the alter- natives available.

The conversion of existing plants in which the ammonia is destroyed by burning, or recovered as ammonium sulfate or low-grade liquor, to the recovery of high-quality anhydrous ammonia should also be considered. At current and projected ammonia prices it is quite possible that the replacement of'those facilities by a USS PHOSAM Process Plant can be justified by a satisfactory return on investment.

Wastewater streams containing large,'amounts of ammonia and acid gases can now be treated for recovery of anhydrous ammonia using the PHOSAM-W process.

USS Engineers and C o n s u l t a n t s , I n c . , i n v i t e i n q u i r i e s d i r e c t l y , o r th rough

q u a l i f i e d e n g i n e e r i n g c o n t r a c t o r s on t h e PHOSAM P r o c e s s and o t h e r o f Uni ted S t a t e s S t e e l C o r p o r a t i o n ' s p r o c e s s e s and c a p a b i l i t i e s .

Refe rences

1. P a t e n t s a s s i g n e d t o U. S. S t e e l Corpora t ion : G r e a t B r i t a i n 958,054; 1 ,018,003

Uni ted S t a t e s 3,024,090; 3,054,726; 3,186,795

Canada 711,665 Germany 1,153,733; 1 ,195,283

2. L a u f h u e t t e , D . , "~ydrogen.~ulfide/~mmonia Removal from Coke-Oven Gas," Ironmaking Proceed ings , The M e t a l l u r g i c a l S o c i e t y o f A.I.M.E., Vol. 33,

A t l a n t i c C i t y 1974, pp. 142-154.

>

F i g . 1. O r i g i n a l PHOSAM P l a n t a t C l a i r t o n , P .ennsylvania , Works o f

U. S. S t e e l c o r p o r a t i o n .

F ig . 2 . USSPHOSAM P r o c e s s , S i m p l i f i e d Flowsheet f o r D i r e c t Recovery o f

Ammonia from coke-oven g a s and ammonia - s t i l l vapors .

Fig. 3. ~magasaki.Coke Company, Ltd., PHOSAM plant at Kakogawa, Japan. From left, tar precipitators, ammonia absorbers, solution regeneration and ammonia fractionation columns.

Fig. 4. ~mmonia ~estruction by the Water-Wash Process. ~ypical arrange- .merit of ammonia absorbers, stripping still, and incinerator. Naphthalene scrubber and possible deacidifier not shown.

Fig. 5. Ammonia Destruction with the Basic PHOSAM Process. Advantages in compactness and avoidance of sulfur dioxide emissions, com- pared to water-wash process.

Fig. 6. PHOSAM Process, simplified for production of 3 0 % aqua amnonia solution.

Fig. 7. . Conversion from Ammonia Destruction to Anhydrous Ammonia Recovery

by the PHOSAM Process. "Hot" absorber.

Fig. 8. Combination of PHOSAM Ammonia Recovery with Wet Desulfurization

by Ammonia Solutions.

aavid M. O'Hara Di.vl.sion Forernan - By Products

?%.e S tee l Company of Canada, Limited Yarn?'.lton., Ontario

Mr. ~am5. l ton 's yaper on t h e US5 PIIOS-Qt Process i.s of p s s t f c u l a r h t e r e s t t o us a t Ste lco a s we have had a PH0S.A-M p l a n t , i n whi ch we prod1,lce anhydroi.1 s amonfa , i.n operat?..on i n our 27 P r ~ d u c t F v i s i o n since J a n ~ a r y IS., 1-973. ' I n ,nsneral ve have been y i t , e sat i s f i ed wit!? t.be n ~ e r a t f o n of t h e p lan t and t h e q-lalZ.ty of t h e product has been exce l l en t .

A typl.cal ana.!..ysj.s o f t.he product which we product i.s:

99.99:i IF, / Colorless

05.1 I..? ?.p.m.

(=@, . - p a c e H2S !!on Detectable

!~!e have not, , however, be?n 8I.I.e t o arhi pve more t,han ?F .4$ removal. of ammoni a f r o 9 t h e Coke Cven Gas s t r ean .

The l.nstrrmentat.lon.s i n t h e p lant ha.? been p a r t . i c l ~ l e r l y ~ o o d and t ,here i s no nrohbem w5t.h t h e ?].ant, when operat ing on control , however 5t. i s our experience t b ~ t it i s v i r t u a l l y impossible t.o oporate t h e p lan t manl~ally and ~ o o d instrument, ma.Znt.enance i s an ahsol.l.ite necessi ty. , ' kre Tarry an operator f u l l t.j.me i n t h e .plant. and besides; h l s di.1.t i e s of rnonitor?'.ng t h e operati-on be ris a l s o r e q i ~ i r e d t.o un!.oad raw mater ia ls a.nd t o load out. t h e prorli.ict . In a.ddit,ion t o t h e op?r,ator t h e ~ 1 z r . t rclq~?.ires a ch~zrntcal l.eh assi.st,ant an average of f i v e hours ner day f o r samplins and a n a l y t i c a l work.

The average consumption of phosphoric ac id f o r t h e pas t twelve months has been 0.212 lbs . per pound of anhydrous ammonia produced. This i s higher than Mr. Hamilton's reported requ5.rement of 0.0075 l b . This i s explainable by solut jon losses which have occurred a t times when i t has been necessa r j t o shijt down f o r maintenance on various p j eces of equipment,. With improvements, t h e frequency of these shut-downs i s dimj.nishin2 and our consumption of phosphoric ac id i s expected t o improve.

Some of t h e maintenance shut-downs have been du? t o corroslon problems, parti.c?rlarly in t h e s t r ipp ing .s t i l l and i n t h e f rac t . ionater . Also the re j.s a problem of t a r accumu.lation and p1uggi.n:: i n t h e l ean and r?.ch solut ion heat exchanger.

Other than t h i s , t h e ~ a i n operat ing problems s r e i n malfnnrt.ion of instrumentati.on. These problems invar iably shut t h e p lant down and can resl l l t i n solut ion l o s s .

M t e r a shut down, t h e p lant i.s able t o produce excellent prodvct v i t h i n t h r e e hours of start-up.

Mr. Hamilton has descriSed some j.nterest#i.n~ va.riat 5 ons on t h e appl icz t ion of t h e bas ic PHOW process and hi-s comments have been qvit,e tho).l;ht, provck5n~. One questi.on T would E k e t o ask him hgwever 5s a v e T p-ac+,iczl one, and that . r e l a t e s t o t h e problem of t a r carryover and pllzt$r;: of t h e system. 1% j.s my understanding t h a t t h i s i s a problem experience? a t othpr p lan t s t.han our obm and I wonder i f t h e r e has been a successful qethod d~velo-ed of reaovjng t a r from t h e solllti.nn t o t h e dezree t.hat y l .ug~in2 ! . r i l l not occQr j.n t3.n 56.t e x c h a n ~ e r o r tFe stri .pping st 5 . 1 1 .

Answer t o D i s c u s s e r

NEW DEVELOPMENTS I N THE USS PHOSAM PROCESS

C . W . Hamil ton, J r .

A s I u n d e r s t a n d i t , t h e r e a r e t h r e e b a s i c q u e s t i o n s t o be answered. F i r s t , ammonia removal e f f i c i e n c y . A s Dave s t a t e d , he h a s n o t ach ieved more t h a n 98.4 p e r c e n t removal of ammonia. The d e s i g n of t h e S t e l c o p l a n t was s l i g h t l y less t h a n t h e 98.4 p e r c e n t and t h e a c t u a l r e s i d u a l ammonia remain ing i n t h e g a s i s less t h a n t h e d e s i g n l e v e l s . Designs g r e a t e r t h a n 9 9 p e r c e n t have been made.

The second q u e s t i o n r e g a r d e d phosphor ic a c i d consumption. I n your e a r l i e r o p e r a t i o n a l p e r i o d s , I b e l i e v e your a c i d con- sumption was w e l l w i t h i n t h e 0 . 0 0 7 5 pounds p e r pound of ammonia expec ted . A s you p o i n t e d o u t , t h e h i g h e r consumption now b e i n g

. s e e n i s r e l a t e d t o u p - s e t s caused by t h e t h i r d i t em-ment ioned - t a r f o u l i n g .

I t h i n k it would b e i n o r d e r t o review t h e h i s t o r y o f t a r problem t o answer what can b e done a b o u t it. Our f i r s t PHOSAM p l a n t was b u i l t a t C l a i r t o n and o p e r a t e d on g a s b e i n g s e n t t o o u r c r y o g e n i c p r o c e s s i n g system. T h i s g a s was v e r y c l e a n and t h e r e w e r e never any f o u l i n g problems a s s o c i a t e d w i t h t h i s o p e r a t i o n . PHOSAM was n e x t ex tended t o remove ammonia from a s e p a r a t e d i r t y ( t a r c o n t a i n i n g ) g a s s t r e a m a t C l a i r t o n and a new PHOSAM p l a n t

was b u i l t f o r M i t s u b i s h i Chemical ( M C I ) i n Japan . I n t h e C l a i r t o n e x t e n s i o n , w e i n s t a l l e d a f r o t h f l o t a t i o n d e v i c e c a l l e d a "Depura- t o r " t o remove t a r from t h e PHOSAM s o l u t i o n b e f o r e t h e s o l u t i o n was p r o c e s s e d i n t h e r e g e n e r a t i o n sys tem. The MCI p l a n t d i d n o t i n c l u d e t a r removal equipment . The C l a i r t o n sys tem was s u c c e s s f u l l y o p e r a t e d ; however, t h e MCI p l a n t e x p e r i e n c e d t a r f o u l i n g a f t e r two months o p e r a t i o n . From t h i s e x p e r i e n c e it was concluded t h a t i n a s t a n d a r d COG t r e a t m e n t sys tem, a t a r removal s t e p s h o u l d b e i n c l u d e d . W e have recommended t h e f r o t h f l o t a t i o n sys tem f o r t a r removal and a l l p l a n t s e x c e p t M C I ' s a r e equipped w i t h t h e f l o t a - t i o n equipment , MCI i s u s i n g a sand f i l t e r of t h e i r own d e s i g n . Based on c u r r e n t o b s e r v a t i o n i n a l l of t h e J a p a n e s e p l a n t s , t h e f l o t a t i o n sys tems a r e working w e l l and a r e performing b e t t e r t h a n t h e sand f i l t e r . I t shou ld b e s t r e s s e d t h a t t h e c lean-up s t e p ( f l o t a t i o n u n i t ) i n PHOSAM i s d e s i g n e d t o remove s m a l l amounts of l i g h t t a r t h a t a r e e n t r a i n e d p a s t a good se t of p r e c i p i t a t o r s . Large q u a n t i t i e s of e n t r a i n e d t a r w i l l b e d i f f i c u l t t o remove.

I b e l i e v e t h a t t h e h e a v i e r t a r load ing a t t h e second absorber a t ~ t e l c o i s more than normal and more than t h e e x i s t i n g f l o t a t i o n system i s removing. A s a s o l u t i o n t o t h e problem, I t h i n k we should review t h e gas c l ean ing system o p e r a t i o n and a l s o t r y a d d i t i o n a l a d d i t i v e s t o improve t h e f r o t h f l o t a t i o n sys tem's e f f i c i e n c y . - A s you know, we w i l l a s s i s t you i n any way we can. When U. S . S t e e l b u i l d s i t s nex t PHOSAM f o r our own p l a n t , we w i l l use t h e " f r o t h f l o t a t i o n system" f o r t r a c e t a r removal.