4 replies to this topic

[lokesh_09]

Dear all,

We have Shutdown valve located downstream of the compressor which is also called fast acting valve. This shut down valve will act faster than the normal recycle valve (pressure control valve)when the suction pressure decreases.
But i dont have any idea how the shut down valve will fuction as control valve for this case.
Could anyone please explain me the working principle of fast acting valve(shut down valve)

Thanks in Advance.

Regards,
Lokesh

Attached Files

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Edited by lokesh_09, 06 November 2009 - 05:56 AM.

[Art Montemayor]

Lokesh:

I have never seen this type of proposed control on a centrifugal. That doesn’t mean it is bad or it won’t or shouldn’t work. You have not supplied any degree of specific, basic data with the exception of the sketch – and thank God for the sketch, because it helps to better understand what you have failed to tell us.

Basically, I can’t recommend anyone to connect the discharge of a compressor with the suction side in the manner you show us in the sketch. You are saying that a quick-opening valve is used to route hot, discharge gas into the suction side of the compressor to avoid a low suction pressure – without any control on what level of pressure (or temperature) the suction side will reach. I not only cannot support that type of so-called controls, but I seriously doubt if any compressor supplier will allow it on their machines.

You must have a very narrow and delicate suction pressure limitation on your machine in order to force a complete, hot discharge gas to enter the suction – without any modulation. That is not what I would do if I knew what your constraints are. But since you haven’t given us any constraints and basic data, I can’t recommend any other solution to what you presumably are trying to accomplish.

The suction pressure of a centrifugal compressor can be controlled and held constant and steady by a variety of methods. It all depends on the scope of your project, your process, your type of machine, and other factors.

[djack77494]

I have seen this configuration in the past for a centrifugal machine. The fast acting valve is for "Hot Recycle" and may be used where some combination of the physical layout and/or machine characteristics make such a step necessary. The way this system should operate is that as a surge condition is approached, the Hot Recycle valve is activated to very rapidly "dump" the discharge pressure to move away from a surge condition. Simultaneously the slower responding "normal" or Cold Recycle valve opens. After a very short period of time, the cold recycle valve is sufficiently opened to control the situation and keep the machine out of surge. The Hot Recycle valve is then closed. Obviously being on hot recycle for any significant period of time could lead to overheating the machine, but this system should not let that happen.

[lokesh_09]

I have seen this configuration in the past for a centrifugal machine. The fast acting valve is for "Hot Recycle" and may be used where some combination of the physical layout and/or machine characteristics make such a step necessary. The way this system should operate is that as a surge condition is approached, the Hot Recycle valve is activated to very rapidly "dump" the discharge pressure to move away from a surge condition. Simultaneously the slower responding "normal" or Cold Recycle valve opens. After a very short period of time, the cold recycle valve is sufficiently opened to control the situation and keep the machine out of surge. The Hot Recycle valve is then closed. Obviously being on hot recycle for any significant period of time could lead to overheating the machine, but this system should not let that happen.

Jack,

Thanks for your response. But i my concern is How to route the hot discharge gas(eg.80 C or above) to compressor suction it normally operats 40C.
Can i have any literature or standards(like API 617) specifying this type of arrangement.

Regards,
Lokesh

Edited by lokesh_09, 11 November 2009 - 01:39 AM.

[djack77494]

Can i have any literature or standards(like API 617) specifying this type of arrangement.

I am not aware of any standard that deals with this topic. Your best source of information should be the compressor manufacturer. They are knowledgable and they want their compressors to perform well. Good combination.

I've tried to indicate that you should not be overly concerned with routing hot recycle gas back to the compressor suction scrubber (which is the path I would recommend). This is a special "event" and it occurs for a very short period of time. I'd venture to say that the thermal inertia of your system will keep temperatures reasonably under control. Your compressor is not going to fly apart within milliseconds of "seeing" higher than normal gas temperatures.