Strategic And Optimization Analysis On Carbon Mitigation Technologies Of Thermal Power Plants

Global warming, induced by the excessive emission of CO₂, is one of the most severe challenges facing with human kind in the 21st century. The latest statistics reveal that China has surpassed the United States and became the largest CO₂ emitter all over the world. Considering that power industry especially thermal power industry contributes approximately 40% of the total CO₂ emissions of China, thus top priority should be given to the thermal power industry when it comes to CO₂ mitigation.As far as thermal power generation is concerned, three kinds of CO₂ mitigation methods are currently mature and available:increasing the energy utilization efficiency, carbon capture and storage and low-carbon fossil fuel substitution. Among them, increasing the energy utilization efficiency could cut down the CO₂ emissions directly, yet the potential of further improving the CO₂ mitigation level is rather limited; as a promising CO₂ mitigation approach, carbon capture and storage is considered to be unsuitable for large-scale application yet and still on the theoretical stage due to huge energy loss and high investment; low-carbon fossil fuel substitution presents excellent performances with respect to CO₂ mitigation and economic investment, but it raises the question:could China balance the supply and demand of natural gas in the future?To solve the huge energy loss caused by carbon capture and storage, an improved CO₂ separation and purification system was proposed. The proposed system is made up of two parts:the cryogenic separation subsystem and the distillation subsystem. For the cryogenic separation subsystem, the liquefaction temperature of CO₂ is increased by improving the initial pressure of the mixed gases, and multi-stage compression, refrigeration, and separation are adopted to ensure a high CO₂ separation ratio. Subsequently, the crude liquid CO₂ is distilled under high pressure and near ambient temperature conditions in the distillation subsystem. Simulation results show that:the proposed system exhibits excellent energy-saving performance since the CO₂ separation ratio reaches 90.4%, and the specific energy consumption for CO₂ capture is only 0.452 MJ/kgCO₂ with 99.9% CO₂ purity for the product; as for economic performance, the specific plant investment is only 0.470 M$/（kg·s-1） with the cost of CO₂ capture reducing to 14$/t CO₂, demonstrating the economic benefit of the proposed system.Meanwhile, to discuss the potential implication of low-carbon fossil fuel substitution approach towards the CO₂ mitigation of China’s power industry, by selecting 2020,2025 and 2030 as the projecting years, three different scenarios, including baseline, active and in-depth mitigation scenarios, were designed to carry out scenario analysis. Results indicate that:low-carbon fossil fuel substitution not only is beneficial to the energy structure optimization and diversification of China’s power industry, but also for its CO₂ mitigation. The largest CO₂ mitigation potential could reach approximately 419 million tons in 2030 under the most positive scenario, and the CO₂ avoidance cost of the proposed approach ranges from 10 to 104$/t CO₂, which is acceptable and could be further reduced. Besides, it can effectively cut down the traditional pollutant emissions of thermal power generation, such as SO2, NOx, and dust etc., which is helpful in promoting the environmental protection process of China’s thermal power industry.