Using Fresh Air in Windbox Repowering of Existing Steam Power Plants

Repowering is increasing efficiency and output power of an existing steam power plants by integration them with gas turbine. Several approaches are proposed for repowering regards to condition of existing power plants. One of those approaches which provides opportunity for existing boiler reusing is windbox repowering. In this method, one or several gas turbines are installed near the existing steam unit and the exhaust of gas turbines is used as preheated combustion air for boiler. The main difficulty in integration of gas turbine and boiler is decreasing flame temperature in supplementary combustion of boiler due to low oxygen content of gas turbine exhaust compared with fresh air and its effect on heat transfer process especially in radiative sections. When advanced gas turbines are used in windbox repowering, the fresh air should be used for increasing oxygen due to low oxygen percent. In this study, the effect of using fresh air in wind box repowering will be investigated and two main arrangements, preheating and not preheating of fresh air will be compared. This study shows the advantages of using preheated air for mixing with gas turbine exhaust when advanced gas turbines are used for windbox repowering.