Improving Grid Power Balance Flexibility with Operation Optimization of the Cogeneration Units in Power Plant

Abstract

Presently exploring the peaking power capability potential of the existing cogeneration units has been regarded as one effective way to improve the grid power balance flexibility. Operation optimization technique of the high back-pressure cogeneration unit with its auxiliary turbine condenser and district heater is presented. Flexibility performance of the one example high back-pressure unit with auxiliary turbine condenser and district heater arrangement is studied and analyzed based on established models of 660MW cogeneration unit using Ebsilon software. The peaking power capability achieved and its economic influence on the unit is studied in detail for the different heating load conditions. Peaking electricity cost concept is introduced for comparing the opportunity cost incurred for realizing the peaking power capacity under each operation case. Three scenarios for five heating loads are analyzed. Taking Scenario I as the baseline condition, increasing the steam extraction flow for the auxiliary turbine in Scenario II can achieve moderate peaking power capacity of 12MW to 16MW, which is far less compared with capability achieved in Scenario III for heating load I. This peaking power capability is getting less with the increasing of the heating load as illustrated in various figures. The maximum peaking power capacity achieved is 63MW when the steam extraction flow to the district heater is 300t/h in Scenario III for heating load I, and this peaking power flexibility is further improved as the heating load gets higher. The peaking electricity cost is increased with the increasing steam extraction flow in various heating load conditions. It should be noted that the peaking electricity cost changing gradient is getting steeper with increasing of the steam extraction flow, which implies that careful consideration should be given to the high peaking electricity cost when significant peaking power capacity is expected for certain heating load.