Abstract
Oxy-fuel combustion is one of the most promising methods for CO2 capture and storage (CCS) but the operating costs—mainly due to the need for oxygen production—usually lead to an obvious decrease in power generation efficiency. An “oxy-enrich combustion” process was proposed in this study to improve the efficiency of the oxy-fuel combustion process. The oxidizer for oxy-enrich combustion was composed of pure oxygen, air and recycled flue gas. Thus, the CO2 concentration in the flue gas decreased to 30–40%. The PSA (pressure swing adsorption), which has been widely used for CO2 removal from the shifting gases of ammonia synthesis in China, was applied to capture CO2 during oxy-enrich combustion. The technological economics of oxy-enrich combustion with PSA was calculated and compared to that of oxy-fuel combustion. The results indicated that, compared with oxy-fuel combustion: (1) the oxy-enrich combustion has fewer capital and operating costs for the ASU (air separation unit) and the recycle fan; (2) there were fewer changes in the components of the flue gas in a furnace for oxy-enrich combustion between dry and wet flue gas circulation; and (3) as the volume ratio of air and oxygen was 2 or 3, the economics of oxy-enrich combustion with PSA were more advantageous.
Highlights
Traditional energy resources account for approximately half of all the electric power currently generated in the world [1,2,3]
For oxy-enrich combustion, the volumes of pure oxygen and recycled flue gas decreased with an increase in the volume ratio of air and oxygen
Under oxy-enrich conditions, coal was burnt in a mixture of air, recycled flue gas and pure oxygen, where air was used to support combustion and to replace part of the recycled flue gas to adjust the temperature in the furnace
Summary
Traditional energy resources (coal, gas, oil, etc.) account for approximately half of all the electric power currently generated in the world [1,2,3]. Compared with air combustion, extra energy is required (e.g., ASU (air separation unit) etc.) for oxy-fuel combustion, which can lead to a decrease in generating efficiency from 38.5% (Supercritical pulverized coal plant) to 30.6% (Supercritical oxy-fuel plant) [8]. PSA technology for CO2 removal from the shifting gases of ammonia synthesis has been commercialized in China, where the CO2 concentration is approximately 30–40% This technology has been verified successfully in modern industry. According to the “oxy-enrich combustion” mode suggested in this study, the CO2 concentration in flue gas is approximately 30–40% and the flue gas volume is less than half that of air combustion; it provides the possibility for the use of PSA technology in modern power plants, even in a 600 MW or more coal-fired boiler. Using a 600 MW pulverized coal boiler as an example, a techno-economic analysis for oxy-enrich combustion plus PSA was conducted to provide a reference for the practical application of this technology
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