Plant air control

[BZLAM21]

Hi,
How can we modulate the control of air plant if we would like to install a manager compressed air power plants ES4 (Atlas Copco)?
The current control is based on A low-low pressure switch (PSLL) on the instrument air receiver, set at 4 bar g, closes the air supply valve to the plant air header in order to give priority to the instrument air users.
A low-high pressure switch (PSLH) on the Instrument air header (Instrument air receiver outlet) will start the spare compressor upon low pressure and stop at high pressure.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1663853709/tips/air_system_sbszif.pdf[/url]

Best regards.

 

[1503-44]

The valve and PSH doesn't make sense. If you have 2 compressors, they should be sized to provide adequate feed for combined instruments and air use systems.

Just use 2 X PS
Use #1 as a PSL to start C1/run when P< PSL
Use #2 as a PSLL to start/run C2 when P< PSLL

If you still run out of air, you could use an on/off valve, which should simply close the user's valve at PSLL and open again at PSL, NO point in modulating anything that I can see, unless C2 is grosely undersized and you want to reach PSL as fast as possible.

I see no need for a PSH unless there is a reason to set the maximum discharge pressure lower than what both compressors can provide, ie if approaching a max system piping design pressure, or some other important limit. If everything downstream has a higher design pressure than both compressors running can reach, you do not need a PSH.

Why do you think you need a PSH and a valve?

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[horacio Torres]

The control loop is not design in the right way.. Any Process engineer with the mass flow of each system must design a control system of the air pressure


Horacio

https://www.linkedin.com/company/lagotuy/

 

[georgeverghese]

Looks like this ES4 control system relies on VSD to enable capacity control of the compressors, so do you already have VSD on your compressors ? Or does the ES4 system include the VSD for multiple compressors operating in parallel ?

 

[BZLAM21]

3 compressors are on service the last one standby ,we don't have a VSD on our compressors ,i want to add ES4 system including VSD for 4 compressors operating in parallel to optimize energy consumption and reduce costs.Are there any necessary modifications on the existing control loop or should I forget this idea.

 

[LittleInch]

We have no idea because it depends on how big your air storage is and what the variance in air demand is.

Your current system looks poor.

Are all these compressors the same capacity?

How do the compressors start and stop at the moment?

Turning compressors on and off regularly doesn't do them any good, but without knowing how your demand changes over time and what your compressor power is or what your perceived issue is a new controller may not be the answer.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Check your existing controls - you probably have 2-3 staggered pairs of settings for load and unload for the 3 compressors currently operating on fixed speed. If so, suspect there may not be much to gain from VSD operation through ES4. What is power consumption at fixed speed unload compared to VSD at load at min operating speed for these screw compressors?
In many large plants, savings in power consumption at utility air compressors doesnt figure much when compared to total plant demand - the big savings are elsewhere in the process plant.