Calculations for centrifugal pumps and pipeline pressure ranges

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This post was last edited by zw1902 on 2019-5-29 09:17. Hello, friends from Sichuan! I’m in trouble and would like to ask all the friends from Sichuan to help take a look. Thank you! As shown in the diagram, I have recently been working on a small project to repurpose existing equipment for a calcium chloride brine system operating at -35°C (there is no available reference material at all). The heat exchanger section of this project was designed with the assistance of a design institute, while the rest was designed by us. The design institute suggested not using the approach shown in the diagram, recommending instead the use of a head tank. However, since sodium dichromate is added to the calcium chloride solution, I am inclined to avoid using a head tank. But here’s the problem ； Without using a high-level tank, the head calculated for the pump is incorrect – it comes out to only 10 meters, when it should actually be 55 meters. That 10 meters value must be wrong, as the height of the heat exchanger above the ground level is 15.6 meters; including the base of the heat exchanger, the height is at least 16 meters. After some consideration, I think the issue lies in the points I selected during the calculation. So the questions are as follows: 1. Should the pressure and liquid level at the pump outlet be based on the screw pump or the heat exchanger? 2 For the pump inlet equipment, should pressure and level measurement be done using a heat exchanger or the inlet main pipe? Could it even detect the liquid level in the fluid reservoir located in front of the fluid pump? Previously, when calculating the pump inlet and outlet pressures as well as the liquid level values, the heat exchanger was used as the reference, which resulted in incorrect calculations ； 4 Additionally, the calculated value of net positive suction head available, NPSHa, is equal to the net positive suction head available at cavitation onset, Sc, plus the selected value of NPSHa’. Does this selected value have to be 6? When the calculated value of the net positive suction head is higher than the value obtained by using the total head, where is the mistake? First, I’d like to thank all the folks from Sichuan. Furthermore, a safety valve is installed at the outlet of the heat exchanger. Since heat exchange takes place between a calcium chloride solution at 6 bar and silicon tetrachloride at 15 bar, the setting pressure for the safety valve is set at 13 bar. The pressure at which the pump shuts down is around 15 bar. The design team stated that pipes with a strength of 300 LB are necessary for this application, but shouldn’t 300 LB correspond to pressures above 2 Mpa? Moreover, it is said that when using stainless steel, pipes with a rating of 300LB are required when the pressure exceeds 1.2 Mpa. I really can’t understand how the shutdown pressure of a pump affects the selection of the pressure rating for the pipes in the entire system, including those in the heat exchanger Thank you!