Site situation
ESEC is combined cycle power plant which includes 2×1 power block, MHI 501 G steam cooling gas turbine, and one steam turbine, when the plant start up, it require a auxiliary boiler provide steam for steam cooling, in the air cooling power plant, auxiliary boiler is not necessary. This auxiliary boiler also can provide the steam for steam turbine glad steam, provides sealing to condenser vacuum set up.
When the plant finish start up, the HP steam turbine can provide steam for the gland sealing system, and HRSG IP drum can provided steam for CTG fooling and HP steam system all can provides the steam as back up to the cooling steam turbine, so Auxiliary is not necessary to keep operation, normal it is just stop for standby, it must keep it in hot standby if there is plant trip, the hot standby auxiliary boiler can provide steam to support STG gland steam and also can provide steam for the CTG warm sequence for next CTG start up.
Challenge.
M501Gs are steam cooled, so we have an auxiliary boiler to provide cooling steam during plant starts from zero. The mud drum is equipped with a heating coil that keeps everything hot for a quick start up. Drains are left cracked open when the boiler is offline to ensure the steam line to the main power block also remains hot. As a result, the water level slowly decreases in the boiler and operations was required to top up the level once per shift with the boiler feed water pump. With such a high frequency of pump start and stops, we were getting a high rate of failure on the pump, motor and mechanical seals.
Solution.
Design and installation of a 1” makeup line from our plant condensate system into a modified drain line downstream of the boiler level control valve.
Fig 1 new line for continuous make up to Aux.Boiler
Results.
Extra BFWP start/stops have been eliminated, leading to much less hard wear and tear. No repairs have been required since the makeup line was added. Total cost savings are $100,000 per year. Condensate is already chemically treated for boiler use, an added benefit of using condensate vs deaerator (demin) water.