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What are the different kinds of pumps used at power plants?
Many different kinds of pumps are used in power plants to fulfill a wide range of applications. Boiler feed pumps are crucial for the operation of power plants. These pumps are typically multistage and deliver feedwater to boilers. An example of a multistage boiler feed pump can be seen in Image 1. Feedwater is then turned into steam, which is what turns the turbines generating power at the power plants.
Image 1. Multistage boiler feed pumpImage 1. Multistage boiler feed pump
To assist in the pumping of feedwater, boiler feed booster pumps are also present upstream of the feed pumps. The booster pumps increase the suction pressure of feedwater fulfilling the NPSH requirement of the main boiler feed pump.
Condensate pumps collect saturated water from the condenser hot well and pumps it either to a deaerating heater or back into the boiler feed pump. Condensate pumps operate at extremely low suction pressures. For this reason these pumps are often located at the lowest level of any pump in the power plant and installed in a suction can that is below ground level. The velocity of the flow entering the condensate pipe is kept to a minimum to limit frictional losses in the piping to keep the elevation difference as the only contribution to NPSH available (NPSHa).
Condenser circulating pumps deliver cool water from freshwater sources near the power plant and pump it through the condenser to condense exhaust steam from the turbine. These pumps can be either located in dry pits or wet pits.
If they are in wet pits, then they are a vertical design.
Boiler circulating pumps pump water through a boiler helping to increase the effectiveness of the boiler. The water is at the same temperature and pressure as the boiler and the pump operates at a low total head requirement only needing to overcome the friction in the tubes of the boiler. However, these pumps operate at very high temperatures and suction pressures and are welded into the boiler itself.
Heater drain pumps are necessary in power plants to pump condensate from closed heaters back into the feedwater system. Similar to condensate pumps they have very little NPSHa.
For more information on the application of pumps in power plants, refer to the HI Guideline Power Plant Pumps&#;Guidelines for Application and Operation and the Rotodynamic Pump Certificate training modules at www.pumps.org.
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Steam Forum
We are installing two electric driven feed water pumps. The original configuration was one electric and one turbine driven.The NBIC Part 1 states: Each boiler shall have a feed supply which will permit it to be fed at any time while under pressure. A power boiler having more than 500 square feet of water heating surface shall have at least 2 means of feeding.The question is does one of the pumps need to be on emergency power per code to be considered a separate source of power? Or does it mean each pump is fed by separate breakers?
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If it were a shipboard case, I may say that the Regulations state that any boiler, whether main or auxiliary, must have two separate feed lines, this including pumps, pipings and check and stop valves only the connection to the boiler, after the last valves fitted, may be a common fitting.As for the pumps, it is stated that one of the pumps MAY be connected to some source such as a main propulsion diesel engine, I assume this might be in accordance to a steam-driven feed pump, and the other MUST be driven by an independent source, an electric motor. As the Rules state may in the case of a diesel-engine-driven pump, I believe the option of two electric motor pumps is acceptable. In such case, I understand the electric connections should be absolutely independent.The problem I imagine might arise is that following a black-out, both FWP would be out of action, unless there is some quick emergency system available. Soon others will further comment, I believe.Claudio Molanes
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You will need to check with local code. We here in Maine have 2 separate FW pumps both full capacity supplied by separate power supplies. We have 6- Volt busses that supply our mill. Each pump is off a separate power supply. However if we go blackand we have we have no pumps to supply any water. Our insurance co. and state boiler inspector know this. Another thing is we operate CFB boilers that have a large amount of bed material which stops transferring heat when the fans go down Thus the boiler stop producing steam. But they still boil mostly dry when power failures happen.If it were my plant I would not recommend operating this way. A steam driven pump is cheap assurance.Thanks Doug
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The NBIC purpose is to prevent damage to boilers and ensure safety.It does not care about continuous production.As is implied in Dougs answer, the full reference you refer to makes a difference to boilers which are fired with a fuel which stops heat input to the boiler on tripping, such that no damage to the boiler will take place on loss of feedwater if the boiler is fitted with a low level trip. For such boilers the code allows only one pump to be used in conjunction with a trip.For boilers with a fuel that continues to heat the boiler after it is tripped and would thus damage the boiler, the code requires two boiler feed pumps. They must be installed in such a way that they are not subject to a single event causing loss of both pumps.No specific method is mentioned so both can be electric if not subject to a single event.Obviously Oil gas and Pulverised fuel boilers fall into the first category.
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I agree with Doug , a steam driven feed pump is the best insurance . In times gone by steam ships always had a turbo feed , and large utility plants followed the same philosophy. Today we see large steam boiler coal fired with all electric feed pumps !!
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Doug actually said cheap assurance and you have upped the ante to best insurance.I am not sure what you are insuring against as the feedwater can be lost by many process faults or human errors such as loss of Dea level feedwater valve shutting HP heater shutting etc and a steam pump does not help. The only real insurance against boiler damage is to trip when the drum level cannot be maintained for any reason.If you think it will somehow keep the boiler running without electricity you are also out of luck on your fans.Power plants do not use steam pumps for reliability simply because they are not effective.In the very old days which you must be referring to, Power plants still had natural draft capability and a steam pump was useful to allow a black restart.Steam pumps are used in some modern power plants to increase efficiency by using bled steam from the turbine and in these cases electric dives are added for starting and conting operation after turbine trip , ie theinsurance is the electric drive.Ships at sea have a totally different set of priorities as the best insurance for the boiler is probably the worst insurance for the ship and no expense is to high if the boiler is operable and can be made to operate.Boiling nearly dry in the case of a water tube boliler is not damaging, but I would think there should be some procedure for Doug to follow such as not allowing steam to escape below safety valve pressure and using an economiser recirc to help keep cool
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