Some misconceptions about high-pressure feed pumps and compressors
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High-pressure pumps do not take variable frequency into consideration; the pump is switched on normally, and the minimum flow rate requirement is not taken into account. There are two check valves at the outlet of the high-pressure pump, with an outlet gate valve following them. It is well understood why the outlet valve needs to be closed when starting the pump – the outlet valve is opened after the pump starts and pressure builds up. However, the feed material first passes through the check valves before reaching the gate valve. For a pump that is in operation, the outlet is at the operating pressure, while the outlet gate valve of the standby pump is fully open (full opening prevents overflow). If the standby pump is started directly, before its pressure reaches the operating level, the check valves will not be able to hold back the flow, which means it functions like a gate valve – only faster in opening. Could it be that the motor will experience overflow at the moment when the check valves open quickly? If it doesn’t exceed the limit, can we open the outlet of the standby pump fully and switch to it? ? ? ? ? ?
Check valves cannot replace gate valves; their function is merely to prevent reverse flow； The functions of a gate valve also include sealing, shutting off, and regulating flow ； It is generally required to open the outlet valve gradually when starting a pump, as there is often air in the outlet pipeline at that time and the pressure is relatively low. If the outlet valve is opened fully and suddenly, it may cause the pump to overload, leading to an excessively high current that results in a power shutdown. When switching to the backup pump, after it starts up, it should operate at a low flow rate for a while to allow monitoring of the performance of the pump’s mechanical seal, bearings, motor, etc., thereby laying the foundation for subsequent operation at a higher flow rate; therefore, the pump’s outlet valve is also used to control the flow rate ； Starting the pump and immediately opening the outlet valve fully, or even not closing the outlet valve at all when starting or switching the pump, is reckless behavior.
It is acceptable for a centrifugal pump to experience pressure buildup for a short period of time after it is started; moreover, when switching between high-pressure pumps, it is usual to first operate them at the minimum flow rate to prevent pressure buildup in the high-pressure pump. If the outlet valve is opened fully right when starting the pump, the current cannot handle it. Reciprocating machines suffer from pressure buildup at the outlet, and generally, unloaders are used with such machines; when the machine is started, the outlet valve is opened fully, and since the air valve does not function, no pressure buildup occurs.
In the end, the outlet wasn’t fully open, and the minimum flow setting wasn’t activated either; when the outlet was gradually opened, it was set to 2.5 turns only, as opening it further would cause the current to exceed the limit. I remembered that with my previous hydrogen compressor, starting it was straightforward – the inlet and outlet were fully open, the check valves didn’t leak, and the pressures on both sides were equal. The motor was started, load was applied, and that’s it. But now, it’s impossible to start it in the same way; the motor stops after running for a short while. It’s necessary to leave the outlet slightly open, waiting until the motor runs smoothly before fully opening the outlet and applying more load.
In your area, doesn’t the pressure compressor cause any fluctuations when switching to mixed hydrogen? With such a switching method, does the bed temperature not rise too high?
The hydrogen mixture level fluctuates, but the bed temperature is fine
There are fluctuations, but just for that brief moment, the bed temperature cannot get out of control
During normal switching of large-scale units, disturbance-free switching is used, with Pump A being switched out for Pump B. After completing the mechanical, electrical, and instrumentation inspections for pump B’s cranking, the last electric valve at the final outlet of pump B remains. The minimum flow rate setting is generally between 80 and 100; adjust this value according to the manufacturer’s recommendations during testing before starting the pump. The low outlet flow interlock can be applied to temporarily disable, allowing the flow to be controlled manually. The electric valve at outlet B is opened to 25%, while that at outlet A is closed at 25%. The minimum flow rate condition triggers both valves: A is opened to 25% and B is closed at 25%. This process is repeated several times to ensure a smooth operation, with the ultimate state being full closure of outlet A and full opening of outlet B. The A minimum flow line is fully open. The B minimum flow line is fully closed. Once Star B is operating normally without any issues, A will prepare to stop~~~~ Practice a few more times; with proper coordination, overcurrent won’t occur~~~~