Gas turbine exhaust gas heat recovery at South Baghdad (Iraq) power plant

Abstract

Gas turbine exhaust is usually relatively clean, especially the exhaust from natural gas turbines. The use of such gases to improve the overall thermal efficiency of a steam power plant has the advantage of reducing the cost of cleaning the equipment and reducing the maintenance costs of the heat recovery equipment used in the application. In this paper, two proposals for recovering the waste energy of the exhaust gases from a gas turbine unit, fuelled by natural gas at south Baghdad Power Plant (Iraq) are discussed. The proposals cover improvements to the thermal efficiency of a steam power plant installed near the gas turbine unit. The first proposal is to use the exhaust gases to preheat the feed water at four feed water heaters, in order to increase the power output. This arises because of the savings in the amount of steam extracted at a different level used for preheating the feed water line. The second proposal is to use the thermal energy in the exhaust gases to reheat the extracted stream, at five points at a high thermal potential, to increase the thermal gain at the preheating feed water line. This avoids the complexity associated with rejection of the extracted steam. The first roposal shows that a 1.22–14.9% saving in fuel consumption is achievable and the overall thermal efficiency of the steam power plant becomes 29–34% (at different gas turbine plant loads). The second proposal shows that a 2.3–7.35% saving in fuel consumption can be attained and the corresponding thermal efficiency will be 30.3–32%.