CEE Oct-Dec 2002

The plant has 3 conventiona l cement mills of 130-tph capacity (OPC basis). The plant's tota l power consumption is 100 kWh/ tonne of cement. The preheater gas is used for drying of raw material , while the cl inker coo ler exhaust gas at 275° C is used for cogeneration. Before installat ion of the cogeneration system, the cooler exhaust air flow used to be cleaned in a hot ESP before venting to the atmosphere. Over 70 per cent ofthe heat picked up by the cooling air, having a heat content of 60MW equivalent, is supplied to the kiln. The remai ning cool ing ai r with exhaust gas volume of 150000 m 3 / h (STP) at 275°C temperature has a heat output of 14MW equivalent. A heat-transfer oil (pentane) is brought into contact with the heating surfaces of the waste heat boiler to recover the heat flow. This cools the cooler exhaust ai r wh ich passes counter-current to the heat– transfer oil mass flow, from 275°C to 125° C and the heat-transfer oil with an input temperature of 85°C is heated to about 230 11 C. The absorbed heat is supplied to the coge ne ration plant by a recircu lating pump. A three-way valve upst ream th e ORC plant controls the heat flow supplied to the pentane evaporator or diverts it to the heat transfer oil bypass. The ORC plant consi sts of the pentane evaporator and preheater . the turbines, the ge nerator and th e motive medium. The fiowshect of the ORC plant is shown in Figure I. While Figure 2 depicts the principle of the process , Figure 3 gives a view of the waste heat boi Icr. The max imum achievable nominal output of 1500 kW of the ' . . Glinl1ar Pooler Waste heat boiler · ORC Plant . AI( conthmtor Wasla ha~t !>Ourr.e Heat recove~ Power generatic;>~ Aocoolluy .· -·--~-- ... --- ~ . Figure 2 Generation ofpower.from low temperature waste heat by ORC process ORC plant tS achieved for a recoverable heat capacity of9.6 MW. The net power generati ng capacity ofabout 1214 kW is realised, i.e. it meets about 12 per cent of the total power requirement of the plant. The total cap it al cost of the installation was 7.88 million DM, out of whi ch 3.99 million DM was accounted for by the ORC plant with pentane cooling circuit and the rest by the waste heat boiler, heat transfer plant. c iv il Figure 3 Waste heat boiler with connection to hot electrostatic precipitator const ruction, electricals, design, erection and commissioning, etc. The plant executi ves estimated the present va lue of th e total cogeneration system at£ 3.3 million (equivalent to$ 3.5 million). For further detai Is of the system and its function ing one may refer 26 to th e article .. f-irst wa ste heat power generating plant using the organic rankine cycle process" by Eng. Eduard Baatz and Gerhard ll e id t pub li shed in the ZKG Inte rnational, No. 8/2000 (I 2 pages). • - • .I.. ' I