Can the emergency shutdown procedure of a reciprocating compressor be carried out by using a self-acting unloader for unloading?
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I’d like to ask everyone for advice~~ I’ve seen many procedures for emergency shutdowns, where the process usually involves shutting down the system by cutting off power, then activating a bypass to enable circulation; simultaneously, the relief valve is opened to release pressure, after which the inlet and outlet valves are closed. However, given the high outlet pressures at stages 2 and 3, opening the bypass to equalize pressure may cause the safety valve at stage 1 to activate. Therefore, is it possible to have the unloader automatically discharge pressure to zero upon receiving an emergency shutdown signal, rather than using a bypass?
Unloaders are generally used at the start of operation; they have several settings, and there is no automatic mode
It is generally done through a bypass; if it is done via a unloader, it may cause overpressure at a certain stage
Since it is an emergency stop, the process bypass should still be used, following the three-back-one mechanism. Moreover, the unit was designed with accident conditions in mind; if, in an emergency, the three-back-one mechanism and the primary exhaust safety valve activate, it indicates that there is a problem with the unit’s design. We have encountered similar problems and negotiated with the manufacturer, who also admitted to the issues in their design.
Why does it cause overpressure? Is it because the intake valve was pushed open precisely during the compression process, causing high-pressure gas to flow back?
It really seems there’s a problem with the manufacturers’ design; we wanted them to calculate the equalizing pressure to determine whether overpressure might occur in the preceding stage, but they haven’t taken any action yet. In the normal shutdown procedures provided by the manufacturing plant, this also involves first closing the secondary and primary circuit valves, opening the suction valves at each stage, and then cutting off the power supply. Shouldn’t the circuit be turned off here as well? Although the steps seem reasonable, there seems to be nothing wrong with using a unloader to unload when one is available.
The return line can be operated from the control room, while the unloading control is operated at the machine.