Sensitivity and Techno-Economic Analysis of Leading Oxy-Combustion Power Cycles with Full Carbon Capture: NetPower and Supercritical CES
18 Pages Posted: 4 Apr 2019 Last revised: 27 Oct 2020
Date Written: May 3, 2019
The increasing concern on climate change has led to global efforts to reduce carbon dioxide (CO2) in the environment. It appears that by far the largest contribution to the greenhouse effect stems from emissions of carbon dioxide CO2. A large part of the CO2 emission are produced by the combustion of fossil fuels in conventional power plants and industrial processes. However, the Carbon Capture and Sequestration (CCS) technologies have been developed to minimise the CO2 emission to the atmosphere. Three main capture technologies (pre-combustion, post-combustion and oxy-fuel combustion) have been mainly developed for solid fuels (e.g., coal, biomass) combustion systems. However, there are many gas-fired power plants and industrial process burning natural gas as a cleaner fuel. Natural gas has the lowest CO2 emissions per unit of energy of all fossil fuels at about 14 kg C/GJ, compared to oil with about 20 kg C/GJ and coal with about 25 kg C/GJ. Although gas-fired plants emit less CO2 but still to achieve the environmental goals of the Paris Agreement it is essential to develop CCS technologies for the growing gas-fired systems. Among the available technologies, turbine-based oxy-combustion cycles (Oxyturbine cycles) are one of the most suitable carbon capture technologies for the gas-fired power plants. In this technology, natural gas is burned with pure oxygen, and temperature moderation is done by Flue Gas Recirculation (FGR) so that the exhaust gas includes mainly CO2 and water vapour ready for sequestration and storage. Recent developments in oxy-combustion technology have reduced the cost of capture and made it competitive with post- combustion technology.
Several oxyturbine cycles have been introduced by means of thermodynamic analysis. However, only NetPower and Supercritical CES cycles have recently proceeded to the demonstration phase. The NetPower cycle recirculates only carbon dioxide as the working fluid, and the Supercritical CES cycle uses water as its working fluid. The Supercritical CES cycle that has best efficiency among other type of CES cycles includes high, medium and low-pressure turbines (HP, MP, and LP) and the exhaust gas from the high-pressure turbine is reheated and expanded in an MP and LP. Pure oxygen is produced in an Air Separation Unit (ASU) and directly inject into the combustion chamber. The NetPower cycle includes a single turbine with high inlet pressure and a main multi-stream heat exchanger. Pure oxygen is produced in the ASU and mixed with the recycled carbon dioxide, before being introducing to the combustion chamber. Both cycles include recycling loops and carbon dioxide purification sections. These novel cycles reduce the cost for power generation with complete CO2 capture and sequestration with nearly zero emission.
In this paper, The NetPower and Supercritical CES Cycles are investigated by means of process simulation and the technologies and utilised facilities compared using sensitivity analysis. Both cycles are simulated with Aspen Plus software with the same initial conditions, and the simulation results are compared with IEA 2015 report for validation. The sensitivity of both cycles are analysed with respect to the Turbine Inlet Temperature (TIT), Combustion Outlet Pressure (COP) and Heat Exchanger Approach Temperature (HET). The efficiencies are extracted for both the NetPower and CES cycles, and partial load behaviour of the cycles are investigated. The initial results show that the NetPower cycle is more sensitive to the Turbine Inlet Temperature (TIT) variations in comparison with S-CES cycle. The results of this paper provide a platform for a comprehensive techno-economical and sensitivity analysis of the NetPower and Supercritical CES Cycles as the leading Oxy-combustion power cycles with full carbon capture.
Keywords: Oxycombustion: process modelling, GHGT-14
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