Study on the integrated system of LNG oxy-fuel power plant and the application of supercritical CO2

Abstract

With the increasing acceleration of urbanization, the amount of urban sewage is raising dramatically. Supercritical CO2 extraction is a promising method for wastewater treatment, and how to obtain supercritical CO2 with low cost has become a hot issue. In this work, the liquefied natural gas (LNG) oxy-fuel combustion power system integrated with supercritical CO2 wastewater treatment process was proposed to realize near-zero CO2 emissions and sewage disposal. The captured CO2 was partly transformed to supercritical CO2 and further applied to wastewater treatment process, which significantly reduced the cost of sewage treatment. The parametric analyses of gas turbine discharge pressure and the amount of treated sewage on the system efficiency were carried out. The results showed that the optimal gas turbine discharge pressure was 0.1 MPa, and the corresponding gross power generation efficiency was 0.69. The amount of treated sewage directly affected the system efficiency. The upper limit amount of treated sewage was 32 t/h with the supercritical CO2 flow rate of 5000 kmol/h when the captured CO2 was not utilized in the wastewater treatment. When the sewage amount to be processed exceeded this value, the liquid CO2 stored in the tank was utilized. As the treated sewage flow rate increased, the corresponding power generation efficiency loss showed an increment. When the mass flow rate of treated sewage was 32 t/h, the net power generation efficiency was 0.47 under the optimized conditions, and the corresponding exergy efficiency was 0.38. The near-zero carbon emissions and low cost wastewater treatment were achieved in the proposed system.