Comparative study on off-design characteristics of CHP based on GTCC under alternative operating strategy for gas turbine

As the rising proportion of natural gas in China energy structure, gas-steam combined cycle based CHP (combined heating and power) systems are expected to have wider applications. To study the performance of CHP systems under two different operating strategies, i.e., IGV (inlet guide vanes) strategy and TIT (turbine inlet temperature) strategy, a stage-stacking method was used for axial-flow compressor characteristics, a stage-by-stage model including blade cooling was adopted for the turbine, and analytical method was employed to solve HRSG (heat recovery steam generator) part-load performance. The model was validated by the field data from an existing MPCP1-M701F3 gas-steam combined cycle power unit. Maximum and minimum steam extraction lines for heating supply were obtained. The selection of operating point between the two lines to meet the same heating demand was discussed from the views of economic benefit and energy utilization efficiency. The results show that, compared to TIT strategy, CHP system with IGV strategy shows advantages in PES (primary energy saving) and total energy utilization efficiency whereas disadvantages in heat to power ratio under part-load conditions. Otherwise, for the same operating range of TIT, CHP system with IGV strategy can reach broader performance at the same steam extraction ratio.