Reciprocating compressor control
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How are the reciprocating compressors in hydrogen production plants controlled? Does the control valve on the return line regulate the inlet pressure or the outlet pressure? Should high selection or low selection be used?
The regulating valve on the return line of the reciprocating compressor controls the inlet pressure. Low selection is used. There are also those controlled by a stepless gas flow regulation system.
In our facility, the return valves for manual control are selected based on either the inlet pressure of the new hydrogen generator or the inlet pressure of the circulation machine (i.e., the pressure in the reaction system). If it is necessary to control the pressure in the hydrogen pipeline network, the control is set using the inlet pressure of the new hydrogen generator; if it is necessary to control the pressure of the reaction system, then the control is set using the inlet pressure of the circulation machine. Generally, a high selection is used (that is, a signal requiring a large valve opening), with the aim of preventing the reaction system from overpressuring. However, nowadays hydrocoms (i.e., variable volume control systems) are generally used; the return valves are usually kept fully closed, and the hydrocom is used to adjust the opening time of the inlet valve, resulting in significant energy savings.
If the low setting is chosen, then the pressure opening signal at the compressor outlet will likely be low, which in effect means that the outlet pressure is being controlled. Instead of controlling the inlet pressure.
There is a dedicated pressure control valve at the inlet of the hydrogen production raw material compressor; the two-to-one feedback mechanism of the compressor is primarily used to control the outlet pressure
The so-called low-selection mechanism involves comparing the difference between the inlet pressure and the set value, as well as the difference between the outlet pressure and the set value; the option with the lower difference is chosen. In this way, low-selection allows for control of both the inlet pressure and the outlet pressure! The discussions upstairs have confused me!
What was said upstairs is correct; many designs are established in this way. So, if a high-priority selection is made, both the entrance and the exit can be controlled.