Key operating points for piston-type high-pressure liquid nitrogen pumps
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Our facility is equipped with two piston-type liquid nitrogen pumps, with a maximum operating pressure of 8 Mpa; after vaporization by a water-bath vaporizer, the output flow rate is 400 cubic meters. The inlet and outlet pipes are vacuum jacketed tubes, while the pump body and the outlet buffer tank lack insulation; as a result, vaporization occurs frequently during the initial phase of operation. Even keeping the return valve on the pump body at a certain opening degree or fully open during normal operation does not help to prevent this issue. Occasionally, it was found that keeping the return pipe of the pump body open allowed liquid nitrogen and gas to be discharged from the outlet, which in turn ensured that the pump could maintain proper pressure and flow rates. To meet the demand for high-pressure nitrogen from downstream processes, this method is being used temporarily. However, discharging low-temperature liquid is neither economical nor safe; therefore, I am seeking advice from everyone here – is there any solution?
Personally, I think the following attempts could be made~~ First, an insulating section could be added to the outlet pipe as a trial~~ Additionally, on-site discharge can help avoid vaporization issues; could it be that the back pressure of your return gas is quite high? Is it possible to use a lower back pressure?~~
In cases like this, it is necessary to check factors such as the insulation at the inlet, the inlet pressure, the distance of the inlet pipeline from the pump, the liquid level in the storage tank, as well as the inclination of the inlet and return pipelines – all of these can affect whether cavitation occurs during the pump’s operation I sometimes encounter this issue here as well: the pump is too far away from the tank. If it operates together with the plunger pump, the results will be much better!
The return gas goes to the liquid nitrogen storage tank; there is a back pressure of 10~~15 Kp, and it’s not possible to change this for now
It’s not possible to check this for now; it can only be done during future parking for maintenance or technical upgrades.
Is your return pipe connected to the return pipe at the piston pump outlet on the same pipeline?
Yes, but the outlet check valve did not open at the beginning of operation; all water was sent out through the outlet. It only opened a little after the pressure in the pipeline system exceeded 7.5 MPa, in order to prevent the outlet pressure from rising too high.
Pre-cooled; the pre-cooling method involves keeping the inlet and return valves fully open, while the outlet discharge valve is slightly open.
Is liquid coming out of the return line drain when the pump is cold?