Steam Generation

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Low-pressure feedwater heaters use steam from the turbine to heat and pressurize water drawn from the hotwell condenser. A deaerator removes excess oxygen from the water before it flows through the high-pressure feedwater heaters and the boiler economizer. From there, water goes into the steam drum where steam is separated and drawn off to the superheater. The remaining water passes through the downcomer and into the bottom of the boiler tubes. Water returning from the tubes passes back into the steam drum where more steam is drawn off and the remaining water sent back through the boiler. The boiler is essentially a large convection oven with tube bundles for steam generation. It draws water in the bottom and sends it through tubes directly above the burners before going to the steam drum.

Feedwater heaters must be carefully monitored for pressure, temperature and level. Each successive heater has higher temperatures and pressures, so instrumentation must be selected for each specific heater’s needs. The economizer is a group of boiler tubes set at the end of the heat path. It absorbs some of the unspent heat from boiler gases to pre-heat water moving to the steam drum. The line feeding from it to the steam drum must be monitored for pressure, temperature and flow.

The steam drum is a long cylinder with baffles to separate water and steam. After separation steam is drawn into the superheater. Water levels, pressure and temperature in the drum and its inlet/outlet lines must be monitored. Pressure instruments on the drum require either a pigtail siphon or diaphragm seal to protect from heat.