Problems with compressor startup
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When starting a reciprocating compressor, does the output from all cylinders flow back first, before starting at a low load? When starting a screw compressor, does each stage of the compressor also start at a low load, just like in the case of reciprocating compressors? How does a centrifugal compressor achieve start-up at a low load?
When starting the compressor, (1) check whether the pressure and temperature of the lubricating oil are normal. (2) Start the cranker to rotate the shaft for 5–10 minutes, then remove the cranker (use manual rotation). (3) Check whether the outlet flow of the compressor is unobstructed, and open the secondary valve. (4) Send a start-up signal to the instrument, initiate the operation of the main motor, and slowly open the primary inlet valve under normal conditions. (5) Based on the secondary outlet pressure, open the outlet valve while closing the secondary valve.
Guides with IGV vanes are started at the minimum angle
Whether it is centrifugal or reciprocating, keep the outlet and inlet valves fully open, as well as the inlet and outlet valves; for regulation under load, set it to 0 load before starting
Screw compressors are not classified by the number of stages; there are only single-screw and twin-screw types. The startup of any equipment is carried out at low load; for positive displacement compressors, the outlets of each stage are usually left open for reflux, while for centrifugal compressors, the inlet valve is set at 5%–10% and reflux is used at the outlet.
The inlet valve is fully closed, the return valve is fully open; startup is performed at 0 load. The guide vanes, including those at the inlet, have a mechanical opening angle, and closing them fully is sufficient
For the 6M compressor unit, during startup, the inlet valves – one-time use, two-time use, and five-time use – are all opened fully, while the outlet valve is kept closed. The vent valve is also closed (it is opened only when necessary, such as during maintenance). After startup, the pressure is raised to the desired level using the five-time use valve; once that is achieved, the outlet valve is opened. The two-time use and one-time use valves are then adjusted based on the amount of gas being vented, serving as means for load regulation. The inlet pressure (flow rate) of the reciprocating machine is too low, causing the upstream tank to deflate
How can starting with full import and export enabled result in 0 load?
When starting a screw air compressor, it is usually done in a unloaded state first, after which the inlet valve is opened fully to start the loading process; however, some brands allow an opening degree of 15% (as with volume control valves in certain units from CompAir and Ingersoll Rand)； In centrifugal air compressors, the inlet valve (IGV) is usually kept fully closed; there is a gap in the IGV valve plate to prevent vacuum formation at the first stage. The blowoff valve (BOV) is kept fully open. Then, depending on the pressure in the main pipeline and the air demand, the load is increased gradually (that is, the IGV is gradually opened while the BOV is gradually closed until it is fully closed).
You also need to learn on your own* the principle of compressor load regulation.