Part load operating strategies for gas turbines in district heating applications

Abstract

Centralized heating and cooling systems (i.e. district heating and cooling networks) are becoming increasingly widespread in many countries. At the same time, environmental concerns related to climate change are forcing many countries to consider increased implementing co-generation of heat and power. Gas turbines are well suited to combined heat and power (CHP) applications in district heating systems. Gas turbines can produce electricity at relatively high efficiency, and the hot exhaust gases can be used either directly to provide heat to the district heating network or to generate steam to drive a conventional steam turbine in a combined cycle system. However, the heat load of a district heating network varies considerably over the course of the year, and the gas turbine CHP system must therefore often operate in off-design conditions, particularly at part load. When evaluating the overall performance of a gas turbine CHP system, it is important to account for all operating conditions encountered in the course of a typical heating season. This study examines the performance of gas turbine CHP systems for different operating conditions encountered when they are providing heat to a district heating system. Special emphasis is placed on evaluating part load performance and discussing different operating strategies for part load operation of the CHP plant. The different strategies discussed are compared in terms of fuel usage and overall economy.