7 replies to this topic

[farid.k]

Hye all,

 

this might be a very basic question that plays in my mind. i just need somebody to make it clear cristal.

 

I have one project (to add one more compressor) 5000 nm3/h at pressure= 10 barg.

 

Currently they have already 3 nos centrifugal compressor. 2 run one standby. 2 electrical motor, 1 steam turbine driven compressor. Capacity for each existing centrifugal is 3400 nm3/h. that existing 3 contrifugal compressor sharing 2 air drier prior to instrument air header.

My plan for new compressor is, to buy one new bigger centrifugal compressor (5000 nm3/h) complete with air dryer.

 

The thing that is play in my mind are:

1. I plan to install new compressor + new air dryer parallel with existing compressor and tie in at existing instrument air and plant air header, since during peak, 3 compressor (2 small and one big new compressor) running in one time is possible. However, when I did the hydraulic calculation check at main header using hysys, during 3 compressor running in one time, the velocity inside the main header exceeding 30 m/s and I think the velocity is kind of big. Erosion might happen isn’t? Based on my standard, maximum velocity for air is 20m/2. I don’t think it is good idea to tie in at existing header since the header is under size. Yea, even they rarely run the compressor 3 nos in one time, but I have to size header to cater the biggest flowrate right? But if I increase the header size, I think it will cause the the cost increase abruptly. anyone have any idea on this? I don’t think we have any solution other than increase the header size.
2. Based on discussion with client, they plant to buy compressor 1^st as compressor is the long lead item. To be honest, I never do the sizing the compressor. But, I think, compressor is easier compared to the pump right? Because, I know the plant requirement is, to have pressure 10 barg, and the flowrate 5000 nm3/h. I think by issuing the process datasheet of the compressor, vendor should be able to size the compressor to me right?
3. I don’t know why turbine driven other than electrical motor. When I asked them operation really want to use steam why, they said that motor always trip. Then I asked why, they said due to surge. When I referred to the P&ID, I said none of them has any recycle line/control valve in order to protect from surge impact. The compressor has been assembled 1994. I trust that surge protection already considered by vendor during that time. I plan for new compressor, I will use motor+surge protection line. If I use turbine, it doesn’t mean surge will not happen isn’t?
4. any one can explain the basic on how to design compressor surge protection line? I think, it just same with minimum flow line for the pump isn’t? For the minimum flow line, just refer to the pump curve, by referring the pump curve, then we know what is the flow required and the setting pressure for the control valve to open. For compressor I think should be the same. Refering to the compressor curve, by looking at the minimum flow of the compressor, we can size the valve and determine the set pressure for the control valve to open. anyone agreed with the idea?
5. I think all the instrument item at the header stream need to be changed right? i.e. the flowtrasmitter.

thanks all for your time

[Zauberberg]

30 m/sec is excessive velocity in Instrument Air headers. Different standards have different values, but not matter which one you follow you end up way beyond the limits with this figure.

 

I'd suggest some reading of materials available online and after you are done with these please come back for further clarifications, if needed:

 

http://www.nfpa.com/...the-demands.pdf

http://www.klmtechgr...stems_Rev01.pdf

http://www.standard..../1132/p-100.pdf

https://www.scribd.c...-Process-Design

[breizh]

Farid.k

Consider the resource attached . You should also consider to consult big names of the compressors industry.

 

Good luck.

Breizh

[farid.k]

30 m/sec is excessive velocity in Instrument Air headers. Different standards have different values, but not matter which one you follow you end up way beyond the limits with this figure.

 

I'd suggest some reading of materials available online and after you are done with these please come back for further clarifications, if needed:

 

http://www.nfpa.com/...the-demands.pdf

http://www.klmtechgr...stems_Rev01.pdf

http://www.standard..../1132/p-100.pdf

https://www.scribd.c...-Process-Design

Dear all, thanks so much for endless support.

 

Can I ask regarding to the surge protection? Is there any other method for surge protection other than recycle line?

[Zauberberg]

Unit shutdown. Or to employ positive displacement machines.

[farid.k]

Unit shutdown. Or to employ positive displacement machines.

What do you mean for unit shut down? Is it by installing instrument transmitter like pt to trigger the shut down when it reached the set point?

For positive displacement, I don't have strong basis for that option as currently at site, they have 3 centrifugal compressor

[Zauberberg]

The transmitters would already be there to measure suction/discharge conditions and calculate proximity to surge. What is the surge protection for the existing machines?

 

As you already noticed yourself, this is a complex brownfield subject and there are no quick and easy solutions. I'm afraid nobody here can give you any definite recommendation because one would have to get into all the details of the existing facilities and of the revamp/upgrade targets, which is difficult to transmit via forum threads. What you need to do is to examine the entire system and find out what needs to be replaced/upgraded, if a new machine is installed. Then discuss with the unit supplier about configuration and modes of operation of the machine as well as equipment protection details. With the current level of known details, this is probably the best advice we can give you here.

[farid.k]

The transmitters would already be there to measure suction/discharge conditions and calculate proximity to surge. What is the surge protection for the existing machines?

As you already noticed yourself, this is a complex brownfield subject and there are no quick and easy solutions. I'm afraid nobody here can give you any definite recommendation because one would have to get into all the details of the existing facilities and of the revamp/upgrade targets, which is difficult to transmit via forum threads. What you need to do is to examine the entire system and find out what needs to be replaced/upgraded, if a new machine is installed. Then discuss with the unit supplier about configuration and modes of operation of the machine as well as equipment protection details. With the current level of known details, this is probably the best advice we can give you here.

I will dig for the existing basis design for the current installed compressor especially for the operating philosophy on how they controlled the compressor