Modelling gasification in Combined Heat & Power plants The Institute for Chemical Processing of Coal in Poland undertook research into fuelling Combined Heat and Power plants with sewage sludge, culminating in the creation of a relevant computer model. Industrial Technologies © PhotoDisc Combined Heat and Power (CHP) plants recover and use heat normally lost to the environment in conventional power plants. Due to this increased efficiency, CHP plants are also often referred to as total energy or cogeneration plants. CHP plants can also utilise sewage sludge as fuel, making them even more environmentally attractive. In order to advance the implementation of such technology in Europe, the EESD Programme funded the CHP SEWAGE GASFN project. One of its participants, the Polish Institute for Chemical Processing of Coal, examined the potential of different fuel mixes. Bench scale tests led to the development of a computer model for gasification optimisation in for a circulating fluidised bed reactor. The fuel mixes tested included raw and dried sewage sludge as well as sewage sludge mixed with coal. Various mixtures were tested over a range of temperatures. Data on the chemical composition of the gas as well as on the amounts of pyrolysis by-products was collected and analysed. Temperature was a key parameter, and a lower threshold of 700 degrees Celsius was identified for efficient combustion of both wet and dry sewage sludge. The computer model built by the Institute for Chemical Processing of Coal incorporated the experimental results as well as the necessary particle physics. It was then applied to determine the optimal fuel mix and combustion conditions. The best fuel mix turned out to be coal combined with no more than 25% dried (thermally or mechanically) sewage sludge. Furthermore, modelling of Poland's sewage sludge data indicated that CHP power plants employing such fuel are economically viable.
