This paper presents the approach of thermoeconomic analysis of centralized cold generation in trigeneration system integrated with steam-powered absorption chillers (ACs). The analysis was conducted for real back-pressure combined heat and power (CHP) unit BC-50 and single-effect absorption refrigerators using water and lithium bromide as the working fluids. It has been assumed that the heating medium supplied to the chiller generator is technological steam from the existing steam bleeding. The calculations take into account changes of energy demand for heating and cooling for each month of the year. Mathematical simulation models of cogeneration and trigeneration systems have been developed with the commercial program for power plant simulation EBSILON Professional. System effects of heat and electricity cogeneration and cogeneration with additional cold production have been calculated compared to separate production of heat, electricity, and cold (replaced heating plant and power unit). The effect of trigeneration has been assessed quantitatively by the coefficient of the increasing cogeneration effects, which has been calculated as a ratio of chemical energy savings of fuels to the demand for heat by the consumers in the cases of trigeneration and cogeneration. This paper includes also analysis of economic effectiveness of a trigeneration system with ACs for cold agent production. The results of economic calculations show that an acceptable payback period of approximately 13 yr for a CHP and absorption system may be achieved. Discounted payback (DPB) is equal to the half of assumed operating time of the system. Sensitivity analysis shows that the most important impact on profitability is the selling price of cold and the purchase of fuel—hard coal.
At present, power systems based on gas turbines are mainly used for electricity and heat generation. Gas turbines are used in industrial and institutional applications due to high-temperature exhaust, which can be used for heating, drying, or process steam production. The combined cycle gas turbine plants are a mature technology with high reliability and offering rapid response to changing demand for electricity and heat. The combination of a gas turbine with a heat recovery system and a heat accumulator makes the combined heat and power (CHP) plant a flexible unit. The paper presents the optimization tool for the planning process of electricity and heat production in the gas-fired CHP plant with a heat accumulator. The detailed mathematical model of the analyzed cogeneration plant was developed with the EBSILON®Professional and verified based on the results from on-site tests and warranty measurements. The implemented optimization algorithm is used to maximize the profits of the CHP plant operation. The presented solution is based on an evolutionary algorithm. The optimization algorithm is applied to the production determination for the day-ahead planning horizon, with 1-h time step. The obtained results show that the developed optimization model is a reliable and efficient tool for production planning in a CHP plant with gas turbines. The comparative exergy analysis for different technologies of heat recovery from gas turbine exhaust gases was performed to evaluate the quality of the energy conversion process in the CHP plant.
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