DG type boiler feed water pump is the main equipment when the boiler is in operation. It can mainly be used for boiler water supply and water supply operations, so as to meet the normal water demand of the boiler. Then when the DG type boiler feed water pump is selected, its flow rate is The head is very noteworthy, so how to determine and calculate it?
1. Determining the flow and head of DG type boiler feed water pump
(1) Calculation of boiler feed water pump flow rate:
Q=k(Q1+Q2)
Where: Q-the flow rate of the boiler feed water pump, m3/h;
Q1—Total water supply at the maximum steam load of the supplied boiler, m3/h
Q2-other water consumption, such as continuous blowdown, regular blowdown and desuperheater, m3/h;
k—spare coefficient 1.1～1.2
(2) Calculation of the lift of the boiler feed water pump:
H=H1+H2+H3+H4
Where: H-boiler feed water pump head, m
H1—The opening pressure of the safety valve of the boiler under the designed pressure, MPa;
H2—The resistance of the economizer and water supply piping system, MPa;
H3—The difference between the highest and lowest water level of the water supply system, MPa;
H4—other
(3) Boiler feed water pumps should be set up for standby. When the largest feed water pump stops running, the remaining total flow should be able to meet 110% of the required feed water volume of all operating boilers at the rated evaporation capacity; when the boiler room is equipped with a reduction When the temperature device or heat accumulator is used, the total flow of the boiler feed water pump should be included in its water consumption.
(4) For one or more boilers with the same steam pressure, two or more feedwater pumps can be selected for parallel operation. If the main pipe is used for water supply, two pumps can be selected, one for use and one for backup, and then variable frequency water supply.
2. DG type boiler feed water pump flow and lift calculation engineering example
The two 25t/h saturated steam boilers of our company are selected according to the above method when selecting the feed water pump.
2.1 Feed water pump flow
(1) Maximum steam load: Q1=26.1t/h (calculated according to the production process);
(2) Regular blowdown and continuous blowdown are taken at 13% of the boiler steam flow rate, i.e. Q2=3.39t/h;
(3) Spare coefficient: k=1.2;
(4) Calculate the feed water pump flow: Q=k(Q1+Q2) =1.2×(26+26×13%)=35.26t/h
Check the water pump samples, only 25t/h and 46t/h are close to 35t/h, so 46t/h is chosen.
2.2 Boiler feed pump head
(1) The opening pressure of the safety valve of the boiler under the designed working pressure:
H1=1.6×1.06 =1.7MPa
(2) Economizer and water supply pipeline resistance:
H2=0.21MPa
(3) The difference between the highest and lowest water level of the water supply system:
H3=0.08MPa
(4) Other:
H4=0
(5) Calculate the head of the boiler feed pump:
H=H1+H2+H3+H4 =173+21.2+8.8+0=203m
Check the feed water pump sample, the pump head is determined to be 200m, because the selected flow rate is 46t/h, which is larger than the actual 35t/h, and the head can be supplemented by the flow rate, so it is determined that the flow rate is 200m to meet the conditions.
Determine the model of the boiler feedwater pump. According to the feedwater pump flow rate of 46t/h, the head is 200m, check the boiler feedwater pump sample, and determine the model: DG46-50×4, two sets are used and one is prepared.
