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Combined Heat and PowerOverviewDecentralised solutions for the generation of power, in the form of combined heat and power (CHP) stations, allow the heat which is given off during the generation of power to be used. This can give an overall efficiency of over 80%. In other words, 80% of the primary energy input to the system can be put to good use, some as electricity, the rest as heat. There is rarely an exact balance between the heat and electricity requirements from a plant. A distinction is, therefore, made between two types of operation: power-driven and heat-driven. In the case of power-driven CHPs, the prime consideration is the production of electricity when it is most profitable. In the case of heat-driven CHPs, the ecological considerations are at the forefront; electricity is only generated when all of the heat produced can be used. We consider systems based on the Organic Rankine Cycle (ORC) as the best option for smaller-scale electricity generation with biomass systems at the moment. In these systems, organic oils are heated to a high temperature. The evaporated oil drives a turbine connected to a generator, thus generating electricity. Some of the heat remaining after the generator stage is passed to low-pressure water that is continuously circulated through a heat exchanger. (Some is used for pre-heating the working fluid.) The water performs the necessary function of condensing the working fluid while it is being heated. In a heat-driven CHP system, the heated water can be put to good use, for example for space heating. Related Case Studies |
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