Flexibility Upgrading of LP Turbine Outage Scheme for Cogeneration Units and its Economic Cost Analysis

Abstract

With the increasing pressure of the strengthening the peak load regulating capability for the cogeneration units in North China, various flexibility upgrading schemes are suggested for the existing cogeneration units. Among these LP Turbine Outage Upgrading Scheme is one of the most attractive schemes. Model-based software is utilized for the performance simulation of the one 300MW subcritical cogeneration unit and its LP Turbine Upgrading Scheme. Based on the models simulation results, the unit peak load regulating capability and the economical cost effect under various heating load conditions is studied. It is shown from the calculation results that under same main steam inlet flow condition, the maximum heating steam supply capacity is increased by around 100t/h and the unit power output is decreased by 14-15MW from the adopted upgrading scheme, therefore LP Turbine Outage operation can significantly increased heating supply capacity of the cogeneration unit. Further analysis indicates that under same heating steam supply conditions, compared with the original cogeneration unit the unit minimum power output can be decreased by around 56MW using the upgrading scheme, and this peaking load capacity improvement stays nearly constant for a wide range of heating load conditions. However, under LP Turbine Outage operation mode the disadvantage of operating as a backpressure generation unit makes the unit impossible to adapt to external power demand fluctuations. In addition, in spite of the performance improvement on heat rate and coal consumption rate per kW.h under same heating steam supply condition, the total economic benefit of the cogeneration unit is less profitable in upgrading scheme operation than in original scheme, which implies some compensation mechanism has to be arranged. The minimum peak load regulating marginal cost for upgrading scheme is calculated for this purpose.