Thermodynamic analysis of a micro turbine CHP system integrated with absorption-compression heat pump

Abstract

Micro gas turbine is a high-efficiency power generation device, which is easy to realize miniaturization. Included compressor, turbine and generator share only one shaft, thus reducing the required moving parts and the unit size. It is widely used in civilian use, industrial and agricultural sectors due to its low fuel consumption, noise and emissions. Meanwhile, steam is widely used in industrial processes such as iron and steel. Steam is generally generated by coal-fired boiler or heat recover steam generator. It is estimated that industrial boilers take up to 30% of the manufacturing industry energy consumption. Micro gas turbine combined with waste heat boiler is a common way to produce heat and electric power simultaneously. However, large amount of waste flue gas with a high temperature above 170°C is rejected to ambient, causing large energy waste and heat island effect. To solve this problem, a micro turbine CHP system integrated with absorption-compression heat pump (ACHP) is proposed. The waste flue gas of the Micro turbine CHP system is adopted as the heat resource, which could produce 0.5 MPa saturated steam in the proposed system. As a result, the energy and environmental performance of the proposed system can be improved significantly. The thermodynamic performances of the proposed system are mathematically investigated. The results show that the primary energy ratio and energy saving ratio of the new system reach 67.3% and 23.56%, respectively, which are 11.2% and 14.76% higher than those of a traditional micro turbine CHP system. An exergy analysis is carried out to determine the distribution of exergy destruction for further optimizing the system performance. The exergy analysis shows that the irreversible loss in the waste flue gas could be lowered by 78% in the proposed system, and the exergy efficiency is 1.79% higher than that of the reference system. Moreover, parametric analysis is conducted to study the effect of the reboiler outlet temperature, partial condenser outlet temperature, the rectifier inlet ammonia-water concentration and the generation pressure on the system performance. Meanwhile, the coefficient of the performance (COP) is selected to evaluate the performance of the system. The outlet temperature of reboiler and the rectifier inlet ammonia-water concentration have a great influence on the COP, while the effect of the generation pressure and the outlet temperature of the partial condenser is relatively small. The COP increase as the outlet temperature of reboiler rises, while there is a peak value (0.29) with the increase of the inlet ammonia-water concentration. The COP changes slowly as the outlet temperature of the partial condenser increases from 45°C to 75°C. The COP almost keeps constant before generation pressure reaches 0.6 MPa, and then decreases slightly afterwards.