Increasing peak load gas turbine fuel efficiency by utilizing its waste heat in the preheater chain of a district heating power plant

There has been an increased interest in utilizing gas turbine facilities with batteries due to continued increase in intermittent energy source production. Gas turbine-battery combination is able to cover the different categories of frequency containment reserve. One issue with operating gas turbines in the frequency reserve is their low efficiency, amounting to ∼30% for small engines. Thus, 70% of the heat will be wasted. To increase energy efficiency while also providing additional power to the grid, a proposed setup is to include a heat recovery unit in the preheater chain of existing steam power plants. This proposed setup gave additional power from 3.87 MW up to 16.70 MW depending on the gas turbine size with the steam turbine accounting for 2.8 and 4.2 MW, respectively. The efficiency also improved for the steam cycle as well as the gas turbine. Assessed individually, the former had an efficiency increase of around 3.1–4.4%-points while the latter gave an average increase of around 12.8%-points. Grouping both cycles gave a total cycle efficiency from 37.2% to 38.4%-points, an improvement from the base gas turbine, which had efficiencies from 30% to 35% and base steam cycle, which had an efficiency of 35.2%-points. Adding a condensing tail allowed 3.61–4.32 MW of extra power depending on HRU configuration. It was shown that it is possible to reheat the steam in the turbine crossover in the HRU, increasing exergy efficiency and the power gained.