RESUMO
A hybrid scheme integrating the current waste heat recovery system (WHRS) for a silicon arc furnace with plasma gasification for medical waste is proposed. Combustible syngas converted from medical waste is used to drive the gas turbine for power generation, and waste heat is recovered from the raw syngas and exhaust gas from the gas turbine for auxiliary heating of steam and feed water in the WHRS. Meanwhile, the plasma gasifier can also achieve a harmless disposal of the hazardous fine silica particles generated in polysilicon production. The performance of the proposed design is investigated by energy, exergy, and economic analysis. The results indicate that after the integration, medical waste gave rise to 4.17 MW net power at an efficiency of up to 33.99%. Meanwhile, 4320 t of the silica powder can be disposed conveniently by the plasma gasifier every year, as well as 23,040 t of medical waste. The proposed design of upgrading the current WHRS to the hybrid system requires an initial investment of 18,843.65 K$ and has a short dynamic payback period of 3.94 years. Therefore, the hybrid scheme is feasible and promising for commercial application.
RESUMO
Sulfuric acid condensation has long been considered as the major cause of the corrosion issues at the cold-end of coal-fired boilers. However, in a flue gas cooler, where flue gas is cooled to around 90 °C for heat recovery, the influence of chlorides might be underestimated. In this article, some elbows of the heat transfer tubes in the flue gas cooler of a coal-fired power plant were found to be badly corroded, after a 5-year operation. The corroded elbows, coupled with the corrosion products and deposits on the tube wall, were sampled and analyzed by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, X-ray fluorescence spectroscopy, and ion chromatography. The results indicated that chlorides, unexpectedly, formed in flue gas before the dew point for hydrochloric acid was met. The corrosion layer on the steel surface was mainly composed of Fe2O3, Fe3O4, and FeO(OH), while showing an oxidation gradient in depth. The sulfates in the corrosion products were rather limited. Instead, Cl- from the deposits gradually accumulated deep inside the corrosion layer, resulting in a considerable generation of Cl-containing compounds. The enrichment of Cl induced cracking and spalling of the corrosion products, and greatly accelerated the failure of the tube wall.
RESUMO
A novel compressed air energy storage (CAES) system has been developed, which is innovatively integrated with a coal-fired power plant based on its feedwater heating system. In the hybrid design, the compression heat of the CAES system is transferred to the feedwater of the coal power plant, and the compressed air before the expanders is heated by the feedwater taken from the coal power plant. Furthermore, the exhaust air of the expanders is employed to warm partial feedwater of the coal power plant. Via the suggested integration, the thermal energy storage equipment for a regular CAES system can be eliminated and the performance of the CAES system can be improved. Based on a 350 MW supercritical coal power plant, the proposed concept was thermodynamically evaluated, and the results indicate that the round-trip efficiency and exergy efficiency of the new CAES system can reach 64.08% and 70.01%, respectively. Besides, a sensitivity analysis was conducted to examine the effects of ambient temperature, air storage pressure, expander inlet temperature, and coal power load on the performance of the CAES system. The above work proves that the novel design is efficient under various conditions, providing important insights into the development of CAES technology.