# Boiler Feed Pump Selection and Calculation

Boiler feed pump selection1. The seal of the drive shaft should be mechanically sealed as much as possible, especially the steam boiler room feed pump. Although the packing seal is simple to repair, the failure rate and maintenance rate are high and the workload is large. Therefore, mechanical seals should be used and the service life should be greater than 8000h. 2. The pump motor is the power source for the pump to operate. If the motor fails, the pump cannot run. Therefore, the structure and...
How to Calculate Capacity and Head?

Calculation of steam boiler feed water pump

1. Calculation formula of boiler feed pump flow rate in steam boiler room:

2. Calculation formula for the head of boiler feed pump in steam boiler room
hs=hs,1+△hs,2+△hs,3+hs,4 (2)
hs(m): total head of boiler feed pump
hs,1(m): the opening head of the safety valve of the steam boiler under the actual use pressure
△hs,2(m): head loss of economizer and water supply pipe
△hs,3(m): Maximum and minimum water level difference of the water supply system

3. The steam boiler room should adopt multiple boiler centralized water supply systems. The performance and quantity of the feed water pump should meet the requirements of parallel operation and annual load regulation. The number of feed pumps should not be less than two. When any one of the feed pumps is stopped, the flow of the other feed pumps should be sufficient to meet the required water supply of all steam boilers at the rated evaporation. When the steam boiler room is equipped with a desuperheating device or a heat accumulator, the design flow rate of the feed water pump should be included in the water consumption of the desuperheating device or the regenerator.

4. One or more steam boilers with the same steam pressure can choose two or more feed pumps to run in parallel. If the main pipe water supply is used, two feed pumps (1 use, 1 backup) can be used, and the frequency conversion water supply is adopted, which not only reduces the power consumption, but also stabilizes the water supply pressure. Although the cost is high, through the frequency conversion energy-saving measures, the investment cost can be recovered in general for 3 to 4 years.

5. The steam feed pump is used as the accident backup pump, and the flow rate should be 20% to 40% of the required water supply for all operating boilers at the rated evaporation. Only when the boiler house and the feed water pump with the first-level electric load stop operation will not cause the boiler to be dehydrated, the steam feed pump may not be provided. The non-power station steam boiler room of the general industrial enterprise does not have such conditions, so it must be set.

Calculation of circulating pump in hot water boiler room
1. Calculation formula of circulating pump flow rate in steam boiler room:

2. Calculation formula for the head of hot water boiler room circulating pump
hw=△hw,1+△hw,2+△hw,3+△hw,4+△h (4)
hw(m): head of hot water boiler room circulating pump
△hw,1(m): heat exchanger and its pipe head loss
△hw,2(m): return water main pipe head loss
△hw,3(m): the most unfavorable user head loss

3. The circulating pump of the hot water boiler room is generally not less than two, one of which is reserved. The circulating pump is generally installed on the inlet side of the hot water boiler, but when using a normal pressure hot water boiler for heating, the circulating pump should be installed on the outlet side of the atmospheric hot water boiler.

Pump Selection & Project Case

Boiler feed pump selection
1. The seal of the drive shaft should be mechanically sealed as much as possible, especially the steam boiler room feed pump. Although the packing seal is simple to repair, the failure rate and maintenance rate are high and the workload is large. Therefore, mechanical seals should be used and the service life should be greater than 8000h.

2. The pump motor is the power source for the pump to operate. If the motor fails, the pump cannot run. Therefore, the structure and insulation level of the motor should meet the requirements of the installation and use environment to ensure the safe operation of the motor.

3. If variable frequency water supply is used, the pump head selected should be slightly higher than the design value. Since the pump is running for 3 to 5 years, the head will drop 20 to 30 m with the impeller wear and the gap expansion. Therefore, the selected pump head should be 30% higher than the design value to ensure that the pump can still supply water after many years. And the energy saving effect of the frequency converter is good, thereby prolonging the service life of the water pump.

4. When the feed water temperature is normal temperature, it may not be specified when selecting. If the feed water temperature is greater than 100 ° C, the feed water temperature should be emphasized when selecting the pump. This is because the high temperature pump and the cryopump are different in material, structure and anti-cavitation function.

5. When the highest position of the water pump inlet is lower than the water level of the water tank (or pool), no special instructions are required when selecting. When the pump inlet is at the highest position above the tank (or pool) level, a strong self-priming pump should be selected.

Project case
1. Project Overview
A natural gas liquefaction plant boiler room has a natural gas steam boiler and a natural gas hot water boiler. The steam pressure for the process steam and the preparation of sanitary hot water in the plant is 0.5 MPa, the steam volume for the process is 0.89 t/h, and the steam volume for the preparation of sanitary hot water is 0.65 t/h.

2. Steam boiler room feed pump selection
The maximum steam load is 1.54t/h. The regular discharge volume and continuous discharge amount are taken as 5% of the boiler steam flow, which is 0.1t/h. The reserve factor is taken as 1.2. Calculated by equation (1), the flow rate of the feed pump is 1.968t/h. Check the pump sample and select the flow rate as 2t/h.

The opening pressure head of the safety valve of the steam boiler under the actual use pressure hs, 1=52m, the head loss of the water supply pipe △hs, 2=2m, the highest and lowest water level difference of the water supply system △hs, 3=3m, additional head △ Hs, 4 = 5 m. Calculated from equation (2), the head of the steam boiler feed pump is hs=62m. Check the pump sample and select a lift of 72m.

In addition to the selection and calculation of the steam boiler boiler feed water pump, hot water boiler room circulating pump, you have to visit manufacturer for further inspection.

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