A CFD Simulation of Coal Syngas Oxy-Combustion in a High-Pressure Supercritical CO2 Environment

Abstract

The Allam Cycle is an oxy-fuel supercritical CO2 power cycle that generates low-cost electricity from fossil fuels while producing near-zero air emissions. The turbine exhaust (sCO2) is then available for partial injection into underground storage while remainder is reused in the power cycle. Novel combustors required by this and other sCO2 cycles are critical to their commercialization. A conceptual design was developed for a coal syngas-fueled oxy-fuel combustor that meets the conditions of the Allam Cycle. The design of this combustor utilizes a 300MWe coal syngas-fired Allam Cycle thermodynamic analyses and ASPEN process models as inputs to the combustor. The primary inputs for design of the combustor included the fuel mixture compositions and respective flow rates for the constituent gases, pressures, and operating temperatures which were scaled to a 5MWth test article. The combustor was sized to accommodate the required pressures, heat release rate, flow rates, and residence times to produce well mixed turbine inlet flows with complete combustion. A preliminary design for a 5MWth test scale combustor was then developed, and a numerical study using Computational Fluid Dynamics (CFD) simulations was carried out to demonstrate the feasibility of that combustor. Steady-state RANS simulations were used to qualitatively examine the preliminary design of the 5MWth combustor and predict the fluid mechanics, heat transfer, and combustion. The purpose of the analysis was to verify the following criteria: 1) good mixing of the fuel and oxidizer in the primary zone, 2) uniform exhaust gas temperature and 3) efficient combustion with complete CO burnout. Additionally, the analysis investigated wall temperature and the impact of varying the fuel composition on combustion performance. The CFD model results were in good agreement with the equilibrium one-dimensional (1D) Aspen model results. The CFD predictions of the current conceptual design verified the identified key criteria for the combustor and demonstrated its feasibility.