Air-assisted unloading and air-free unloading of reciprocating compressor unloaders
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Sea friends, I’d like to discuss with you the differences between the two unloading methods for reciprocating compressors: \"loading with air and unloading without air\" versus \"loading without air and unloading with air\". We have several reciprocating compressors with different applications, and the unloading methods suggested by the manufacturers are either unloaded without air or with air; in other words, instrument air or nitrogen is used only during unloading to push open the suction valve in order to achieve unloading. There are several questions I would like to discuss with you regarding this: 1. Since the normal operating condition is at 100% flow rate, and operations at 50% flow rate occur less frequently, for a control method that involves wind loading, the unloader is usually supplied with pressurized instrument air most of the time. Does this require higher standards for the material used in the unloader, which in turn leads to a higher price? 2. Considering safety factors, once the entire plant has to be shut down urgently due to problems with the nitrogen supply or the instrument air system, the compressor loses its unloading capability; isn’t shutdown operations dangerous in such a situation? I wonder if the above two viewpoints are reasonable? Previously, some users on Haichuan mentioned that medium and low-pressure compressors usually use wind-free loading and wind-assisted unloading, while another unloading method offers higher safety levels; were these two factors taken into consideration? Are there any other considerations? I also hope that all fellow sailors will contribute their ideas and discuss this together!
From a safety perspective, \"loading in still wind and unloading in windy conditions\" is more appropriate. If considering the scenario of an emergency shutdown due to problems with the nitrogen source or instrument air system, an emergency air supply should be available, and some organizations already handle it this way.
Why is this type of unloading method actually safer? How is an emergency gas source provided? Is it an external gas source similar to nitrogen cylinders? Thank you for the answer~
For the compressor itself, \"loading with air and unloading without air\" is more intrinsically safe. However, in practice, \"loading without wind and unloading with wind\" is the common approach, which prevents instability in the instrument air or nitrogen supply from affecting the proper operation of the reciprocating machine. Considering the advantages and disadvantages of both, choose the latter in most cases.
Most are unloading in windy conditions and loading in calm conditions
The compressor unloading and backflow should also be possible
Personal opinion: If there are no special requirements, \"loading in still air, unloading in windy conditions\" is a more suitable approach. Normally, reciprocating compressors are equipped with circuits on which manual valves or control valves are installed to enable the compressor to be unloaded; it is not necessary to use a unloader. “With loading under wind conditions and unloading in calm weather, if there is a failure in the air supply or in the solenoid valve, the compressor will lose pressure, which will affect the entire manufacturing process. As far as I know, compressor manufacturers use the same types of unloading devices for both the \"loading with air, unloading without air\" and \"loading without air, unloading with air\" unloading methods; the only difference lies in the control system.
It’s the same as whether the control valve operates on air open or air closed principle. Most compressors have air unloading and air loading, so a disruption in the air supply does not cause shutdown. But for example, in the new hydrogen generators of hydrogenation units, when the air supply is interrupted, to ensure the safety of the unit, operation must be stopped; hence it is an unload without air