Booster Pump's Size

A booster pump and a boiler feed pump need not be the same size, for the flow/pressure characteristics of the two pumps may well differ.

Discuss the requirements with a couple of pump suppliers by telephone.

Find someone who has knowledge of pumps and ask them.

Or, as PWSlack said ask the pump companies.

Dear Mr. mohnish powermech,

First of all what is the need for booster pump, when Boiler Pump capacity and Pressure can be suitably decided.

But the answer for your quiery is YES. The Capacity should be equal or slightly more in the capacity but certainly NOT LESS.

DHAYANANDHAN.S

If the same flow is going through both pumps one after the other, then what is the point of having two pumps (rhetorical question - NNTR)? One could size correctly and select one pump to do the job.

Dear Mr. Pwslack,

That is why I raised, "WHY BOOSTER PUMP IS REQUIRED......."

Original Pump Pressure is lower than required, it may need the Booster Pump. But better to avoid.

DHAYANANDHAN.S

It depends on why you want/need the booster.

Assuming that you need the booster to increase the suction pressure at the BWF Pump due to a lack of NPSH Available needed to meet the NPSH Required by the Boiler Water Feed pump then the capacity of the booster MUST be equal to or greater than the BWF pump or you will limit the capacity of your BWF pump to that of your booster or possibly suffer some severe cavitation at the higher capacity. Since BWF pumps are often pressed to higher through-puts at times of emergencies then that is definitely not a good time to suffer severe cavitation issues. If the capacity is reduced then the booster will simply back up its curve and increase the suction pressure to the BWF pump thereby increasing the NPSHA. But if the capacity needed to be provided by the booster isn't sufficient then the inlet pressure to the BWF pump may not be sufficient to prevent cavitation and cause severe damage to the BWF pump or loss of water to boiler.

Dear Mr.Spinco

I take a quote from your posting

"the booster to increase the suction pressure at the BWF Pump due to a lack of NPSH Available needed to meet the NPSH Required by the Boiler Water Feed pump then the capacity of the booster MUST be equal to or greater than the BWF pump or you will limit the capacity of your BWF pump"

My Comment is:

If NPSH AVAILABLE IS LESS THAN REQUIRED WE SHOULD NOT START THE BOILER, or else, we should reduce the Feed Water Temp. and hence CAPACITY OF THE BOILER /EFFICIENCY will REDUCE, - resulting in increase of fuel cost.

DHAYANANDHAN.S

Can't say that I agree with your philosophy. Most plants require the operation of a deaerator prior to the BWF pump to remove entrained oxygen. Most deaerators raise the water temperature to within a few degrees of the steam used for deaeration. The temperature of BFW is generally kept high to prevent thermal shock to the boilers. Cooling the water prior to the pump to reduce the vapor pressure and therefore increase the NPSHA would be counterproductive to the overall plant efficiency and would then mean you need a BFW heater after the pump to reheat the water to prevent thermal shock. Granted there is generally always some use of an exchanger to preheat the BFW after the BFW pump but cooling prior to the pump and then reheating after is counterproductive. Increasing the elevation of the deaerator to provide additional suction pressure is very desirable but if not possible a booster pump may prove more feasible to insure that the NPSHA is sufficient to meet the NPSH Required by the BFW pump.

Spinco has pretty much covered it all and the reasons for a booster pump. The only thing that I would add is that you can have different arrangements for the boosters and BFW pumps eg

Boosters 3 x 50% and BFW 3 x 33%

As spinco said you must have excess capacity available in the Boosters so that they are NEVER the limiting flow, and that under ANY circumstances they provide the required head so that the flow conditions exceed the NPSHr for the BFW pumps