Our customer, a dyeing and finishing textile company in Oldham, required a heat recovery system to provide hot water for dyeing. Our solution was simple and the reduction in boiler steam use resulted in a 15 month return on investment.
Situation: A characteristic of most textile dyeing and finishing plants is clouds of steam hovering around. Our client was no exception.
Fashion dictates and the plethora of different colourways usually gives rise to short run batch processes with the dye-house manager ending up having multiple dumpings of hot liquor followed by cold rinse wash offs, usually into a communal drain system. This effluent will be contaminated with lints and dye at no specific temperature. By law it cannot be discharged untreated and above 40ºc. The batch process, communal drain and effluent pit system is usually enough to satisfy these requirements but does not lend itself to a simple heat recovery option. Some dyeing processes have to start from cold whereas others can accept preheated hot water, in either case process steam is used as the heating medium either by direct contact or using calorifiers, but in both cases via a steam boiler. The production flexibility required by the dye-house manager usually results in an oversized boiler operating in an uneconomic high/low firing mode with the chimney flue gases widely fluctuating in volume and temperature, however, they are a valuable source of waste heat and can be used to provide preheated hot water for dyeing.
Solution: Our client already had a stainless steel break tank which took water in at a steady rate via a coil in the effluent pit. This ensured the effluent was cooled and the capacity of the tank allowed the operators to fill a dye vat very quickly with warm water. The system then comprised circulating water to and from the storage tank via a heat recovery heat exchanger connected to the base of the chimney. A small centrifugal fan drew boiler flue gases from the base of the chimney, passed them over a stainless steel finned tube heat exchanger and returned them back to the stack. The fan was on/off and controlled by a water flow switch, a water outlet thermostat and an interlock with the boiler control panel, thus making the whole system fully automatic irrespective of water or gas flows or temperatures.
Result: The reduction in boiler steam use resulted in a 15month simple return on investment for our client.