LNG冷能用于O_2/H_2O富氧燃烧碳捕获系统的模拟研究

目前的天然气发电系统以富氧燃烧(O_2/CO_2循环燃烧)为主,其空分制氧以及碳捕获能耗过高,导致发电效率明显降低;较之于前者,O_2/H_2O燃烧系统作为新一代的Oxy-combustion燃烧方式系统,污染物排放量更低,但其燃烧过程仍需采用空分制氧,CO_2的压缩耗能依然较高。为此,构建了一套将LNG冷能用于O_2/H_2O富氧燃烧的碳捕获系统,并建立了该系统的数学模型以计算其热效率、效率,在此基础上开展与同样利用LNG冷能进行碳捕获的COOLCEP系统的对比分析。结果表明:(1)该系统采用高压燃烧方式,以水作为燃烧循环工质,同时对LNG采用梯级利用方式,降低了空分制氧和碳捕获系统的能耗,提高了系统的发电效率,同时以低成本完成了碳捕获;(2)该系统的热效率和效率随燃气轮机进口温度升高不断提高,在循环水量和燃烧压力分别为13.5 kmol/s和1.6 MPa、燃气轮机进口温度达到1 328.1℃时,热效率达到最大值,系统热效率、效率分别为57.9%和42.7%;(3)较之于COOLCEP系统,O_2/H_2O燃烧系统能耗明显降低,系统热效率、效率分别提高了6.3%、5.4%。

Simulation study on the carbon capture system applying LNG cold energy to O2/H2O oxy-fuel combustion

At present, oxy-fuel combustion (O2/CO2 circulating combustion) is dominant in natural gas generating systems, but it consumes much energy for air separation oxygen generation and carbon capture, leading to a severe reduction of generating efficiency. The O2/H2O combustion system, as the new generation of oxy-combustion system, is superior to the oxy-fuel combustion, and its pollutant emission is lower, but during its combustion, air separation oxygen generation is still needed, so CO2 compression energy consumption is still higher. In this paper, a set of carbon capture system applying LNG cold energy to O2/H2O combustion was developed, and its mathematical model was established to calculate thermal efficiency and exergy efficiency. And then, it was compared with COOLCEP system. The combustion process of this system is operated under high pressure with H2O as the circulation medium, and LNG is utilized in a cascading pattern, so the energy consumption of air separation oxygen generation and carbon capture system is reduced, the generating efficiency of the system is increased and carbon capture is conducted at low cost. The thermal efficiency and exergy efficiency of this system increase continuously as the inlet temperature of gas turbine rises. When the flow rate of circulating water is 13.5 kmol/s, the combustion pressure is 1.6 MPa, and the inlet temperature of gas turbine reaches 1 328.1 ℃, the thermal efficiency and exergy efficiency is 57.9% (maximum) and 42.7%, respectively. Compared with COOLCEP system which also makes use of LNG cold energy for carbon capture, O2/H2O combustion system is much lower in energy consumption and its thermal efficiency and exergy efficiency are 6.3% and 5.4% higher, respectively.