Feed Water System

Feed Water System at Power Plant

Water pumped back into the boiler is commonly known as a feed water system. The system that supplies feed water consists of several main equipment, namely:

1. Feed Water Pump ( Boiled Feed Pump ) 
2. Feed Water Tank ( Dearator )
3. Feed Water Heater ( High Pressure Heater and Low Pressure Heater )

The simple graphic in Feed Water System in Sub-critical Boiler is the following:

figure 1. feed water cycle

The steam leaving the turbine enters the condenser to be turned back into water. The water is pumped back into the boiler to be processed into superheated steam which is ready to turn the turbine. So here is the closed-loop system. Water and steam are treated continuously in a closed system to drive a steam turbine (steam turbine). Nevertheless there is still water or steam lost as a system loses in the process. So as long as the power plant operates it is always necessary to add new demineralized water continuously. 

Actually the number of low and high heater more than one, as an actual picture the PLTU block diagram is as follows:

figure 2. steam water cycle

DEAERATOR

Deaerator is one of the components in the installation of a Steam Power Plant. The function of this equipment:

1. reduce the oxygen content and uncondensable gas in the water before the water is put into the boiler system
2. increase the suction heat pump 
3. as a water storage tank to supply the water needs of the boiler
4. increase feed water temperature until saturated temperature.

The deaeration process is carried out by utilizing some of the steam coming out of the turbine to be used as a water heater that enters the deaerator. Water from the demineralization plant and condensate are sprayed to the deaerator through the nozzle, then to reduce the levels of gas and dissolved oxygen, low pressure steam is injected into the deaerator, as shown in the figure below. Gas and oxygen are then discharged into the air through the venting deaerator, whereas water that has reduced the level of dissolved oxygen enters the feed water tank.

figure 3. deaerator

FEED WATER HEATER

To increase the efficiency of a power plant, before pumping it into the boiler, the feedwater must be heated up to a certain temperature. The heating is carried out with a heater (heat exchanger), which takes place by conduction by utilizing hot steam taken (extracted) from the turbine. So besides being passed on to the condenser, there is a small amount of steam from the turbine that is taken to heat the feedwater heater.

The type of Feed Water Heater is shell and tube heat exchanger. Steam is going from upper to shell, whereas the Feed Water is going from lower to tube.

figure 4. feed water heater

FEED WATER PUMP

Feedwater is pumped by 3-4 feedwater pumps that work in parallel, usually one of the feedwater pumps is in standby condition. In some boilers, the feedwater pump is driven by a constant speed motor while one of the feedwater pumps uses a turbine driven pump that is mechanically driven by a steam turbine. Before the feedwater pump, there is a strainer or filter is installed to filter impurities in the feedwater. This strainer is equipped with a differential pressure transmitter with tapping points on the inlet and outlet strainer, so that it can indicate the amount of dirt on the strainer depending on how much pressure difference is on the inlet and outlet strainer.