In near future, due to the growing share of variable renewable energy (VRE) in the electricity mix and the lack of large-scale electricity storage, coal power plants will have to gradually shift their role from base-load operation to providing fluctuating back-up power to meet unpredictable and short-noticed load variations, in order to improve the stability of the electrical grid. However, current coal power plants have been designed to operate at base-load and are not optimized for part-load operation, resulting in an intrinsic inadequacy when undergoing power output fluctuations. The founding idea of sCO2-Flex H2020 European funded project is to improve the flexibility of pulverized coal power plants by adopting a sCO~2~ Brayton power cycle instead of common steam Rankine cycles. Despite the large available literature about the design of sCO~2~ systems for different applications (solar, waste heat recovery, nuclear), there is still a little discussion about the part-load strategies that should be implemented in order to maximize system efficiency during real plant operation. This paper aims to provide more insight about the potential of sCO~2~ power plants for small modular coal power plants (25 MW~el~) highlighting the difficulties that must be faced during off-design operation in order to ensure high performance still guaranteeing a safe operation of the components. The selected cycle configuration (recompressed cycle with high temperature recuperator bypass) is implemented in a MATLAB+Refprop numerical tool specifically designed to optimize the plant design, to provide a preliminary sizing of each component and to evaluate and compare different off-design operating strategies. In particular, the off-design behavior and the operational constraints of each component will be implemented on the base of referenced numerical models, adopting reliable correlations and exploiting ad hoc codes for the performance evaluation. After cycle design and optimization in nominal condition the system performance during a reference year will be evaluated allowing to understand the efficiency penalization and the minimum load attainable with sCO~2~ power plants. Different operational strategies will be considered including minimum cycle pressure, maximum cycle temperature and inventory optimization. Results will be compared with the annual average performances of a subcritical steam Rankine cycle (as typical solution for small power output) that will be computed with Thermoflex software. The comparison will show the advantages in adopting sCO~2~ power cycle in terms of coal consumption, CO~2~ emission and minimum achievable load.


Part Load Strategy Definition and Annual Simulation for Small Size sCO2 Based Pulverized Coal Power Plant

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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