Abstract

Analysed is the modification of the thermodynamic cycle with the negative CO2 power plant concept by its combination with the organic Rankine cycle. The analysed power plant operates on a gas produced from the gasification of sewage sludge. The negative emission term comes from the aggregated CO2 balance resulting from the capture of the CO2, while the sewage sludge is one of the inevitable environmental sources of CO2 to be avoided. In short, the principle of this power plant is to produce electrical power by converting sewage sludge fuel as the substrate to CO2 as a product, which is an intricate process in-between, with many opportunities for waste heat recovery. There are four main sources of waste heat in such a system. One is the drying process of the producer gas, which must be properly cooled from the high temperature after gasification to the temperature at which no moisture is present in the gas. In the wet combustion chamber, the syngas is oxy-combusted under high temperatures with water injection to control the combustion temperature. This mixture is then expanded in the gas turbine. The mixture leaving the turbine is a major source of heat supply for the ORC. The second heat source is a mixture of steam and gas – a major supply of heat source for ORC. Next, the mixture is undergoing separation process in a cyclone separator and then the CO2 (with a small content of moisture) is directed to carbon capture unit. The CO2 is then compressed in a system that requires intercooling. Due to the wide range of temperatures of the listed waste heat sources, the double ORC combination is investigated. The combined ORC cycle is connected by a cascade heat exchanger. The ORC fluid parameters are selected computationally to match the temperature distribution lines. The power plant processes are simulated in the steady-state process simulator using the most accurate equations of state from the literature. Optimum operating conditions of the ORC integrated power plant are obtained through optimization techniques.

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Authors (3)