just want to know,TQwhen a steam boiler system for a plant having thermal deaerator, do we still need a flash vessel to separate the flash steam and return condensate?and if let say we install an economizer, the feedwater after the economizer will be pumped into boiler water tube by the feedwater pump, even though its temperature is around 150'C, it will not become steam because of the pressure, but when it reaches the water tube of the steam boiler, will it become steam?because the water tube have one sensor where it will detect the water level inside the tube,if steam formed and water level low, the boiler will have problems?help help helpTQ
Most steam systems pump the condensate to the deaerator where any non condensables such as air are removed. The condensate is then pumped by the boiler feed pumps to the boiler either through an economizer depending on the system design. The amount of boiler feedwater that is pumped to the boiler will depend on the water level in the boiler. As the steam demand varies more or less water will be added to maintain the correct level. The fire from the burner(s) will also vary to maintain the pressure in the boiler. It is the burner flame that produces the heat that vaporizes the water into steam. Most boilers have a steam drum at the top of the boiler that all of the tubes connect to. It here that the water level is maintained. In the case of fire tube boilers the level is a bit different but still controlled in a similar matter. See the two links below for infor on water tube and fire tube boilers. On very large industrial and power boilers the control of the boiler feedwater and the boiler level is maintained by an elaborate system of level sensors and flow sensors so that the boiler level can be maintained more accurately than with just a simple level control. The flow sensors can detect a change if steam load and begin to adjust the water level before there is an actual change in the level.
Deaerator and flash vessel have totally different functions.. the deaerator removes NCGs (O2 particularly) in the feedwater while the flash vessel recovers steam from high pressure blowdown or condensates. Normally the economizer is integral to the boiler and feedwater from the feedwater pump goes to the economizer tubes and then to the to the boiler drum. Depending on the size and capacity of the economizer, the water entering the boiler drum is ideally near saturated. The near saturated water goes down the downcomer tubes where it picks up heat from the flue gas (then to the water drum or mud drum if your boiler is of bi-drum type, or to the water headers if your boiler is of single drum type) and goes up through the riser tubes and then to the steam drum again. In the riser tubes, the fluid is a mixture of steam and water. The steam is separated from the water in the steam drum. There is no sensor in the boiler tubes. The drum water level is measured using a level lauge, switch and/or transmitter. The choice of level instuments type depends upon the sophistication of your boiler. The quantity is usually according to applicable codes (i.e. ASME Sec 1). The drum level output manipulates the feedwater control valve and regulates the flow of the feedwater. To avoid problems caused by low water level in the drum, a low water level cut-off is usually provided which shuts down the burner/combustion system when this cut-off is reached.
