Luyao Zhou

Analysis and Optimization of a Compressed Air Energy Storage—Combined Cycle System

Compressed air energy storage (CAES) is a commercial, utility-scale technology that provides long-duration energy storage with fast ramp rates and good part-load operation. It is a promising storage technology for balancing the large-scale penetration of renewable energies, such as wind and solar power, into electric grids. This study proposes a CAES-CC system, which is based on a conventional CAES combined with a steam turbine cycle by waste heat boiler. Simulation and thermodynamic analysis are carried out on the proposed CAES-CC system. The electricity and heating rates of the proposed CAES-CC system are lower than those of the conventional CAES by 0.127 kWh/kWh and 0.338 kWh/kWh, respectively, because the CAES-CC system recycles high-temperature turbine-exhausting air. The overall efficiency of the CAES-CC system is improved by approximately 10% compared with that of the conventional CAES. In the CAES-CC system, compressing intercooler heat can keep the steam turbine on hot standby, thus improving the flexibility of CAES-CC. This study brought about a new method for improving the efficiency of CAES and provided new thoughts for integrating CAES with other electricity-generating modes.

Optimum Design of a Double Reheat Steam System in an Ultra Supercritical Unit

Ultra supercritical power generation technology is entering a fast developmental stage. Thus, using the double reheat system is necessary to improve the thermal performance of ultra supercritical units. In this paper, steam system designs were optimized and exergy analysis research on ultra supercritical double reheat units is carried out. The double reheat steam system based on the traditional eight extractions regenerative system is presented. In addition, the regenerative system setting with an outside steam cooler and two additional extractions is put forward. The quantitative energy saving effect of main optimization measures after various systems are analyzed and compared is also given. The present study proved that the setting with outside steam coolers could obviously decrease the superheat degree of extractions for ultra supercritical double reheat units. Moreover, two additional extractions are helpful in optimizing the distribution of the increase in water enthalpy in the regenerative system. Both optimization measures are conducive in improving the unit efficiency and in decreasing the coal consumption rate. The current paper also presents case studies and exergy analysis based on the aforementioned cases. The results show that the coal consumption rate of the optimized double reheat unit is reduced by 2.36 g/kWh compared with the double reheat unit based on the traditional regenerative system with the same initial parameters. The total exergy loss of the regenerative system is reduced by approximately 10% for the setting with outside steam coolers. The total exergy loss of the regenerative system with ten extractions can be further reduced by nearly 18%. Therefore, setting with outside steam coolers and additional appropriate extractions are both conducive in improving the performance of ultra supercritical double reheat units. Thus, a remarkable energy saving effect is observed. The current paper provides a theoretical basis for performance evaluation and design optimization of ultra supercritical double reheat units.Copyright

A Novel Flue Gas Heat Recovery System Integrated With Air Preheating in a Utility Boiler

Exhaust gas temperature in coal-fired power plants can reach approximately 120 °C to 140 °C, with the thermal energy accounting for approximately 3% to 8% of the total input energy. Therefore, the heat recovery of exhaust flue gas can improve the thermal efficiency of coal-fired power plants. Currently, the waste heat of flue gas can be recovered by installing an extra heat exchanger, also called low-temperature economizer (LTE), at the end of the boiler flue to heat a part of the condensed water. Extra work can then be obtained by saving the extracted steam and using it to heat the condensed water. However, the temperature of exhaust flue gas is only about 130 °C, which causes the flue gas to heat only the condensed water in the #7 and #8 regenerative heaters. Thus, the energy savings are inconspicuous. This paper proposes a novel flue gas heat recovery system to dramatically increase the temperature of flue gas in the LTE by comprehensive optimization of the air preheater and the LTE. A low-temperature (LT) air preheater can be installed after the LTE in the novel system so that the flue gas can be divided into two parts to heat the air. Simultaneously, the LTE can be installed between the two air preheaters, causing the temperature of flue gas in the LTE to reach above 170 °C. Hence, the temperature of condensed water in the LTE can be increased significantly. In addition, the LTE can replace the high-pressure extracted steam from the turbine, resulting in better energy savings. We also conduct case studies based on a typical 1,000 MW supercritical power generation unit in China. The results indicate better performance of the novel system, with a decrease in exergy loss and improvement in heat transfer characteristics. The reduction in standard coal equivalent of the novel system can reach 3.31g/kWh, nearly 2.4 times that of the system that uses conventional waste heat recovery. Our achievements provide a promising waste heat recovery methods of the utility boiler flue gas.Copyright