Calculation of net positive suction head at the inlet of the ethylene pump
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When calculating the effective net positive suction head at the inlet of an ethylene pump, should the vapor pressure at the top of the pressure tank and the vapor pressure at the pump inlet be taken as the same value? If they are, the effective net positive suction head of the pump can reach 4–5 meters, which is sufficient for ordinary centrifugal pumps; no special sac-type pumps are needed. In reality, however, the effective net positive suction head when the pump specifications are submitted is only around 0.5 meters. Should the increase in vapor pressure due to the rise in temperature at the pump inlet be taken into account in the calculations, and if so, by how many degrees? Thank you
The pressure at the pump inlet is the same as that for transporting normal liquids: it equals the tank pressure plus the pressure due to the liquid column height, minus the resistance in the pipeline from the tank to the pump inlet. The transport pipeline must be insulated, and any increase in inlet temperature must be taken into account (since vapor pressure is closely related to temperature). The exact degree of supercooling required should be determined based on actual conditions; it is advisable to supercool the ethylene in the tank. Generally, to prevent cavitation in the pump, it is necessary to increase the pressure in the storage tank, install the pump on the ground, and use as thick an inlet pipe as possible to reduce inlet resistance.
Hehe, in my humble opinion, there’s no need to worry about increased pressure; liquids require consideration, while gases can be assumed to remain unchanged
The pressure at the pump inlet, just like for normal liquids, is the tank pressure plus the pressure due to the liquid column height, minus the resistance in the pipeline from the tank to the pump inlet. Generally, to prevent cavitation in the pump, it is necessary to increase the pressure in the storage tank (or raise the tank) and install the pump on the ground in an inverted flow configuration. If the net positive suction head is insufficient, the following measures can be taken: 1. Increase the diameter of the pump inlet pipe, 2. Minimize the use of fittings and bends as much as possible, 3. Install pressure buffers
The steam pressure at the top of the pressure storage tank and the steam pressure at the pump inlet should be set to the same value. When performing calculations, the resistance in the pipeline leading to the pump inlet must be taken into account; an appropriate margin should also be considered for the increase in steam pressure due to rising temperatures. The height difference between the tank and the pump should be more than 2 meters greater than the net positive suction head
For liquefied gases, I personally believe that the saturated vapor pressure must be taken into account within the inlet pressure range; of course, the liquid level is also a key factor. Therefore, if the saturated vapor pressures at the top and bottom of the tank are the same, the calculations will be identical as well.