Heat Recarerr $t'slems Vol. I. No. 2. pp. 147 to 152 Perlgamon Press Ltd 1981. Printed in Great Britain

C O N F E R E N C E R E P O R T

PROFITABLE ENERGY SAVINGS IN THE TEXTILE INDUSTRY

12TH SHIRLEY INTERNATIONAL SEMINAR 16-18 SEPTEMBER 1980

THLS report, which is also by way of a review of the Conference Proceedings, data on the cost and availability of which are given at the end of the report, discusses some of the opportunities for waste "heat recovery within the textile industry. These opportunities were identified in 19 papers presented to delegates at the 12th Shirley International Seminar, held near Manchester, U.K., in September 1980.

The Shirley Institute, who organized the three-day conference and publish the proceed- ings, is an establishment, supported both by the textile industry and government, whose activities include detailed investigations of energy consumption and conservation measures in textile processes (as described in some of the papers).

Energy is particularly important to the textile industry when one studies the energy content of textiles when compared with other common manufactured products which are normally associated with 'energy intensive' industries. These are listed below.

GJ/t

Textiles 200-500 Bricks 2.6 Glass bottles 23 Cast iron 44 Diesel engine 86

Figures quoted in one paper [1] relating to the manufacture of a polyester/cotton shirt fabric identify the energy content of each process as follows, in terrors of gross energy requirement in GJ/t

GJ/t

Fibre production 100 Spinning 90 Weaving 80 Dyeing 75 Finishing 100

While areas of the textile industry are anything but energy-intensive--in 1979 energy costs representing only 3.3~ of total costs in 15 manufacturing units of J & P Coats Ltd--the total energy bill in such companies may be several million pounds, and conser- vation therefore has an important impact [2].

IMPROVEMENTS IN PROCESS PLANT

Much of the conference was devoted to an examination of the energy consumption of specific items of plant used in the textile production, dyeing and finishing processes. Marshal [3], in discussing jet dyeing processes, cites the energy consumed in raising the

147

148 Conference report

temperature of the dye liquor from ambient to 120-130°C for use, raising the tempera- ture to higher levels where creasing may have occurred, and raising temperatures from 80°C to dyeing temperature to shade dyeings of incorrect colour as major heat demands. Simple heat recovery using, for example, plate heat exchangers could lead to 459/o energy savings compared to the 'heating from cold' pattern. By starting the dyeing-at 50-60°C, improvements in productivity may also be achieved, where the batch dyeing machine may require one minute to raise its temperature by 2°C.

Marshall proposed a cascaded system of batch dyeing machines as the ultimate in energy conservation via heat recovery, and described the system thus

'So far emphasis has been placed on the important heat energy required to raise the dyeing to the required temperature. Once a dyeing vessel has been raised to 120°C and the dyeing cycle completed it should be possible in principle to transfer this heat directly to the next dye-batch so that the net heat used would amount only to the standing losses. Standard heat recovery methods cannot achieve this due to the tem- perature drop across heat exchangers. Even passing the exhaust dye liquor from one machine to the second directly through its heat exchanger would result in both machines finishing somewhat below 90°C (assuming initial temperatures of 120 and 60°C respectively). However, by a suitable design a series of machines, say 3 to 6, could be arranged in a unit with an integrated cascade system of heat transfer. A single multiple tube machine could also be designed in this way. Briefly the scheme would be that each of say 12 tubes would be at different points in its dyeing cycle, including heating and cooling. Each tube during its cooling cycle would be connected via its heat exchanger, or other heat transfer medium, to a corresponding tube in its heating cycle but at a lower temperature to give a 10-20°C temperature difference. Heat from the cooling dyebath would be transferred until the temperature difference became too low when reconnection to the next pair would automatically be made. The top temperature difference of 10-15°C would require additional heating either by direct steam or heat pump. Such a system would have other attractive features but no further details have been worked out. This would be highly efficient energy wise, but perhaps fuel costs must rise considerably yet before there is sufficient incentive to develop such a system.'

This system might, it is claimed, lead to energy savings of the order of 80%. The recycling of waste water would be particularly attractive in textile plant, particu.

larly finishing works, if a method of water purification could be found which was both economic and effective. The IBK Recycling System meets both these criteria, claimed Koeppl in his paper [41. The system accepts waste water which has previously been treated for the removal of coarse solids. The water then is introduced into a deaerator via a condenser and distiUate-heated preheater. In the deaerator the water is raised to 104°C (under pressure) using steam, and is then passed through a distillate cooler and con- denser for further preheating, before the final preheating takes place using a heat transfer oil-water heat exchanger, as shown in Fig. 1. The evaporators and separators, which in the four-stage plant are arranged in series, boil off the water, the first evaporator being heated via heat transfer oil while subsequent stages use multiple effect techniques--the vapour from the previous stage is used to heat the next stage. The energy from the final evaporation stage is used in finishing machines as steam.

The concentrate resulting from stage 4 is reduced to minimum water content in a thin film evaporator, and it is suggested by the manufacturers, may be incinerated, producing more energy. Distillates from each evaporator are depressurized, producing steam. The steam is used to heat the thin film evaporator and preheat waste water.

Such a system, which bears a close resemblance to the Wanson 'Stillpac' unit available in the U.K. and Europe, requires high grade energy for operation. The Wanson system may be heated using waste heat from processes at a sufficiently high temperature, and there appears to be no reason why the IBK system may not be operated under similar conditions.

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150 Conference report

REVIEW PAPER

A review of waste heat recovery techniques appropriate to the textile industry was presented by Reay [5-]. The paper covered gas-gas heat recovery, as applied to dryers and stenters, liquid-liquid heat exchangers, in particular the plate unit, and heat pumps. In addition a number of gas-liquid heat exchangers were described. One liquid-liquid example was as follows:

'The conventional plate heat exchanger is finding wide application in dye-effluent heat recovery and other processes involving discharging from textile plant. In one appli- cation effluent from holding vessels downstream of dye pans is discharged at 60°C into a plate heat exchanger which it leaves at 38°C. Incoming water is raised from 10 to 49°C, recovering approximately 500 kW. This is sufficient to supply nearly 50~ of the energy needed to heat the incoming water and reduces dramatically the requirements for steam heating in the holding tank. This APV heat exchanger saves a company well in excess of £10000 per year.'

Heat pumps are seen as having considerable potential in textile finishing, and two systems were described:

'The heat pump is of particular interest in the industrial liquid effluent context, because, unlike many gaseous effluents at relatively high temperatures, the low grade heat cannot always be re-used by applying conventional heat exchangers. While in the context of the textile industry the application of a heat pump to the high temperature effluent from an individual machine seems unlikely to be economical in comparison with the results that can be achieved by conventional heat exchanger (plate liquid- liquid heat exchangers described above, for example). It is likely to be much more attractive to use heat pumps in heat recovery from low grade mixed effluents in textile plant. It should also be pointed out that a role can be found for both a plate heat exchanger and a heat pump in the same system, where this can effectively increase the COP by reducing heat source-sink temperature differences. (It should be noted that the COP of a given unit is a direct function of the temperature difference between the heat source and the heat sink.)

The Westinghouse Templifier heat pump is typical of the industrial electric drive liquid-liquid heat pumps on the market. Based partly on experience gained with large refrigeration plant, the Westinghouse system comprises a range of standard heat pumps using centrifugal compressors capable of generating useful heat at tempera- tures of up to 100°C, covering heating capacities up to 3 MW or higher. Liquid effluents in the temperature range 27-77°C would be used as a heat source for this particular heat pump.

A typical Templifier application using a heat source at 35°C and deliver hot water at 65°C would have a coefficient of performance of 4.4.'

Gas engine drives were also stated by Reay as being of interest. (These are to be described in detail in forthcoming papers in the journal.)

CASE HISTORIES

The most persuasive method for presenting the case for energy conservation in general, and in this context waste heat recovery in particular, is to present 'case histories' where installations have been shown to save money, and to save money at a very attractive rate. The most important papers presented at the conference were possibly the 5 case histor- ies [2, 6-9].

Cole of Courtaulds Ltd [6] discussed examples of heat recovery from a tenter dryer and from dyehouse effluent. The tenter dryer, which handles heavy woollen fabric, was fitted with an air-air heat exchanger to enable it to be operated over a longer period on a given quantity of steam. Exhaust air is cooled from 85 to 50°C, preheating supply air by 17°C to 61°CI (The high air ambient is due to preheating by radiation on top of the tenter

Conference report 151

Hot exhaust gases Cold air intake

Heat pipe heat exchanger F, Iler ~ 1 [

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Fig. 2. Schematic diagram of heat recovery system applied to a stenter.

prior to the air entering the heat exchanger.) An improvement of 17% in dryer output was achieved.

A system in hand for recovering heat from 50000 gallons per hour of effluent at 27°C and preheating water from 5 to 22°C, originating from a bore-hole, will lead to fuel oil savings of £170000 per annum, or a payback period of 4--5 months.

The case history presented by Sykes of Tootal Ltd related to the use of intermediate storage of recovered hot water--a system common to many effluent heat recovery plant [7]. It was pointed out that intermediate storage involved relatively high capital costs in providing a well-insulated storage facility, and for this and other reasons it was recommended that the storage facility should be as small as possible and that only recovered heat should be stored, no supplementary heating taking place in the storage facility.

Among the systems described by Collis [8] was a heat pipe heat exchanger on a stenter. Shown schematically in Fig. 2, the heat exchanger is mounted on a 4 bay stenter which is fired indirectly with 8 oil burners, with full modulating controls. The installation cost £13000, and subsequent experiments to determine optimum running conditions has led to oil savings of 32%, giving a simple payback of less than one year.

The paper by Lubert of Marks and Spencer Ltd, the major retailers, was the only one to deal with the textile industry as seen by the purchaser of its products [9]. A most successful energy saving exercise has been conducted by this company, the energy costs of which in the 1979/80 financial year were £6.3 million, and the role of heat recovery is not insignificant. The recovery of heat from refrigerator condensers for domestic water heating has led to savings of 76% in energy use in this area in a 6 month trial, and is being extended to a further 12 sites. Payback is anticipated to be less than 3 years.

A most provocative contribution was made by Robinson of Shell U.K. Ltd [10]. In a paper entitled: 'Why is energy conservation so slow in exploitation', he discussed barriers to implementation, but, of considerable interest to readers of this Journal, identified an 'energy conservation industry: worth £600 million.

To learn more, the conference proceedings, which are highly recommended to those with an interest in textiles and/or energy conservation, are available from

The Shirley Institute Didsbury Manchester M20 8RX U.K.

152 Conference report

The cost is £16.00 for U.K. buyers and £20.00 to overseas purchasers. Ask for Shirley Institute Publication S.40.

REFERENCES

1. J. G. Roberts, Energy audits, Prec. 12th Shirley International Seminar, pp. 219-239. The Shirley Institute, Manchester (1980).

2. J. M. Barclay, Energy conservation at J & P Coats Ltd, Ibid. pp. 175-181 (1980). 3. W. J. Marshall, Energy saving aspects of jet dyeing, Ibid. pp. 75-99 (1980). 4. F. Koeppl, Waste water purification and recycling in textile finishing processes, Ibid. pp. 139-154 (t980}. 5. D. A. Reay, Waste heat recovery, Ibid. pp. 119-138 (1980). 6. E. H. Cole, Case histories at Counaulds Limited, Ibid. pp. 155-159 (1980). 7. N. Sykes, Case study to evaluate the requirements and value of hot water storage (Tootal Ltd.), Ibid. pp.

161-165 (1980). 8. P. Collis, Energy saving case histories (Carrington Viyella Ltd.), Ibid. pp. 167-179 (1980). 9. B. Lubert, Energy conservation--the essential strategies---(Marks & Spencer Ltd.), lbid. pp. t83-189 (1980).

10. S. J. Q. Robinson, Why is energy conservation so slow in exploitation, Ibid. pp. 191-206 (1980).