Sage-Tips

What methods are used to control the capacity of a centrifugal compressor?

A centrifugal compressor’s flow and pressure are typically controlled by a combination of an inlet control device and unloading valve (UV). The inlet can be throttled on a dynamic compressor to continuously reduce the capacity of the compressor.

How do you unload a centrifugal compressor?

Loading and Unloading – during low flow demand, it may be necessary to unload or stop the flow of the compressor. This is done by closing the inlet valve completely and opening a bypass valve after the final compression stage. While the impellers are still rotating at full speed, no air compression occurs.

How does the pressure rise in a centrifugal compressor where is it used?

Centrifugal compressors; also known as turbo-compressors belong to the roto-dynamic type of compressors. In these compressors the required pressure rise takes place due to the continuous conversion of angular momentum imparted to the refrigerant vapour by a high-speed impeller into static pressure.

What is performance control in compressor?

Performance control adjusts the compressor loading via the motor’s variable frequency drive (VFD), the turbine’s governor, inlet guide vanes (IGV), or suction throttling valve to meet process demands for compression, as measured by: Suction pressure.

How do you control compressor discharge pressure?

The method comprising the steps of running a discharge pressure control routine, comprising the steps of: calculating the difference between the actual discharge pressure and a predetermined setpoint discharge pressure; computing the required change in valve position to achieve the setpoint discharge pressure, the …

How do you control compressor capacity?

Adding and subtracting fixed clearance is one of the most common methods used to control the capacity of a reciprocating compressor. When fixed clearance is added to the compression chamber of a compressor cylinder the VE is reduced thus reducing capacity. This is an efficient method of capacity control.

What are two methods of unloading a centrifugal compressor?

Centrifugal compressors to avoid surge when they are equipped with is simple turndown or throttled inlet modulation, with or without inlet guide valves. Centrifugal compressors are available with dual-control unloading that incorporates turndown and load/no load to avoid blow off.

What is turndown of a centrifugal compressor?

Turndown is the percentage below full load flow the compressor can run without experiencing surge. For example, 15\% turndown means the unit can run at 85\% flow or higher, as equipped without hitting surge.

What is pressure coefficient in centrifugal compressor?

Centrifugal compressors are usually designed in the flow coefficient range = 0.01 to 0.16. Figure 1 shows the typical application area of various compressor impellers and the typical areas where most industrial radial impellers are designed.

How do you control a compressor surge?

6 Ways to to Avoid Centrifugal Compressor Surge

1. Larger Anti-surge Valve (ASV) Size with a Quick Opening Valve.
2. Suction and Discharge Pipe Re-Routing.
3. Re-Positioning Anti-surge Tap off- Point.
4. Slowing Compressor Speed during Coast down.
5. Discharge Side Gas Flaring.
6. Hot Gas Recycle Valve Installation.

What is compressor discharge pressure?

Discharge pressure (also called high side pressure or head pressure) is the pressure generated on the output side of a gas compressor in a refrigeration or air conditioning system. An extremely high discharge pressure coupled with an extremely low suction pressure is an indicator of a refrigerant restriction.