Study on Energy Efficiency Loss of Supercritical Thermal Power Units Under Different Primary Frequency Regulation Operation Strategies

Thermal power units are the most important primary frequency regulation (PFR) resource for the power system with a high proportion of renewable energy. In order to provide higher PFR capacity during the dynamic process, thermal power units need to reserve more valve opening margin or set higher main-steam pressure under steady-state. However, higher PFR capacity leads to lower energy efficiency, which leads to a lack of sufficient quantity results. This study investigates the energy efficiency loss under different PFR operation strategies for a supercritical thermal power unit. New steady-state valve control strategies are designed to improve the PFR capacity based on the dynamic model during the PFR process. A coupled steady-state valve–turbine model is solved to quantify how different reserved control valve openings affect throttling loss, effective enthalpy drop, required steam flow, fuel demand, and heat rate. The control valve route has been modeled in detail, while the boiler side is treated as a fixed upstream boundary. Energy efficiency loss is obtained under different strategies by taking a 300 MW supercritical thermal power unit as a case. Results show that the steady valve opening from 0.95 to 0.70 lowers the valve-downstream pressure from 16.124 to 15.659 MPa, raise the required steam flow increases from 273.319 to 274.131 kg/s. Under the same 300.102 MW load condition, increasing the reserved control valve opening margin from 10% to 30%, i.e., a 20% absolute increase, reduces the steady-state operating efficiency by approximately 0.26%, with fuel flow and specific fuel consumption increasing by 0.059 kg/s and 0.714 g/kWh, respectively.