Cement, Energy and Environment

The ABB Power Plant based on Organic Rankine Cycle (ORC) technology (further referred to as "ABB ORC power plant") is designed to make use of exactly this low and medium temperature waste heat. It excellently converts /A. low temperature waste heat from cement plants into electricity. ORC Plant The ABB ORC power plant Heat extraction Heat Heat Electric feed in and control conversion dissipation Basic working principle Fig.2: Functional principle ABB ORC Power Plant The core piece of the power plant is a steam turbine. Due to low waste heat temperature, the temperature of the steam is low as well. Therefore, water vapour cannot be used efficiently, both in terms of energy and of costs. Here, organic fluids are used. Organic media evaporate at relatively low temperatures and condense against ambient air at a pressure over 1 bar, thus no vacuum has to be produced in the condenser. Between the evaporation and condensation pressure/ temperature levels the organic fluid delivers a considerable amount of energy when it is expanded in the turbine. The ORC power plant consists of the following main systems: • • • • Heat extraction Heat conversion Heat dissipation Electric feed in and control. Heat extraction In cement plants, the waste heat is normally discharged from two sources; from the clinker cooler air (AQC) and after the preheater tower. The air from the cooler can be cooled as much as possible to extract the maximum amount of heat, so a conversion system with low operating temperatures is advantageous. The waste gas after the preheater is used in the subsequent process steps: the waste heat is used in the raw mill to dry and preheat the raw mix and in the coal mill to eventually dry the coal. Therefore, the temperature must not be reduced below typically 200 -250 ·c; this limits the extractable amount of heat. Consequently, one heat exchanger is used per waste heat source. The extracted heat is conveyed to the intermediate cycle and finally transported to the evaporator: the interface to the organic fluid cycle. ~:J Pressurised water is used in the intermediate cycle. Because no evaporation occurs, the surfaces of the heat exchangers are comparatively small. 6'000 - net available electric power " cumulated aMUal electridty production - ~ 10 15 zo zs 30 35 40 i 3: The nfllir{ailable elect~ ~.,~ 35' 30'~ mJ zo·J 115'000 i 10'000 e a. ?: S'OOO ~ ~ • 0 Heat conversion In the conversion cycle, the waste heat is used to preheat, evaporate and superheat the organic fluid under high pressure. The superheated fluid then gets expanded in the turbine and the mechanical work is converted into electrical energy in the generator. 29