A Coupled Computational Modeling Approach for Fireside Heat Flux Optimization within Coal-fired Supercritical CO2 Power Cycles

Supercritical CO2 (sCO2) power cycles have the potential to deliver high efficiency, low-cost, water-free operation for coal-fired power generation. To achieve these high efficiency levels, design temperatures of the working fluid (both furnace inlet and turbine inlet) and the secondary/combustion air are typically higher than for steam-based power cycles. Therefore, to avoid exceeding tube temperature limitations, it is critical that peak local heat fluxes be minimized while maintaining efficient overall heat distribution. The primary heat exchanger in these cycles is a major risk item, as the heat transfer properties of CO2 are substantially different from those of water and steam. In addition, the primary heat exchanger is a crucial factor determining the overall cost and performance of the power plant, and thus high fidelity modeling of the heat transfer surface design can substantially improve the overall plant techno-economic design and optimization process. The small business will utilize its expertise in the modeling of coal combustion in boilers and collaborate with a company that pioneers in the development, utilization and commercialization of indirect-fired sCO-based heat recovery equipment, to develop optimized fired heater (firing system and primary heat exchanger) design concepts. The approach will utilize computational fluid dynamics (CFD) based tools for multi-phase reacting flows coupled with advanced models of the heat transfer fluid cycle to optimize cycle efficiency and performance. The proposed effort will leverage recently developed capabilities and expertise for the modeling (including real gas and transport properties) of high-pressure sCO2 conditions encountered in indirectly heated power cycles. In the phase I effort, the small business will work with the equipment developer to establish the appropriate boundary conditions for the modeling effort based on previous work to develop commercial designs for related applications. Existing data will be used to verify the suitability of the modeling approach. Modeling efforts will then be used to iteratively evaluate promising design features and operational conditions to determine optimal design concepts and corresponding operational conditions based on material limitations and system efficiency. Based on model results and prior experience, a Phase II test program will be developed to provide data validation for the heat transfer and corrosion modeling. Code modifications associated with describing the combustion environment and the thermodynamic properties of the sCO2 working fluid in indirect sCO2 power cycles will be used by the small business and other equipment developers to develop and optimize combustion system and heat exchanger designs. The software tools that can accurately simulate the physical processes occurring on the fire side and CO2 side of indirect SCO2 systems will provide a means for economical investigations of design limitations, equipment requirements, and proper materials selection to bring indirect sCO2technologies to market.