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Air Extraction from Compressor Discharge
Cooling of extracted air from compressor discharge.

At the power plant where I work, we are looking at extracting the compressor discharge air for plant instrument and service air use.

@MIKEVI, I notice you use this system already in your plant as you stated in the topic "Extraction of Air from the Gas turbine" dated July 2013. I would like to know

1.How the temperature of the compressor discharge was reduced and what type of coolant was used in details.

2.If anyone has been able to ascertain the power generation dip(if any) from the design.

Thanks in Anticipation
Derickson4oxygen@yahoo.com

2 out of 2 members thought this post was helpful...

Dear Obiloko4,

the machine we are extracting CDP from was originally built as a dual fuel unit. During unit installation all liquid fuel components were removed since the site had no plans to ever run liquid fuel. One component not removed was the purge air cooler, which is basically a large water to air cooler using water from the plant closed loop cooling system. This cooler was repurposed to cool the CDP air being sent to the instrument air system.

The loss in unit output calculation was something I was never part of so I can't comment on that. The system has been in operation since 2010 with no problems.

Thank you very much Mikevi

I still have few concerns which I think it will be very kind for you to clarify me on.

1. What is the temperature after cooling?

2. What is the pressure at the discharge and is there a significant pressure drop?

3.Our instrument pressure is at 6.5-7.5bar while CDP is 8.5bar Max. How do I keep the pressure from dropping in the cooler.

4. What control systems where installed.

Derickson4oxygen@yahoo.com it will be appreciated if you can also mail me.

2 out of 2 members thought this post was helpful...

Dear Obiloko4,

you asked:

1. What is the temperature after cooling? The temperature of the air after cooling is typically the same temperature as the cooling water being supplied to the cooler. It is typically less than 100 degf.

2. What is the pressure at the discharge and is there a significant pressure drop? We are extracting air from a 1" pipe tap at the combustion wrapper that was previously used for a drain. Pressure varies depending on the mwatt output of the machine. At full load pressure is around 175 psig. It falls to around 115 psig at 50% load. For this reason we always have instrument air compressors in standby to start if demand on the instrument air system is more than can be supplied from the gas turbine extraction system.

3.Our instrument pressure is at 6.5-7.5bar while CDP is
8.5bar Max. How do I keep the pressure from dropping in the
cooler. I am not sure I understand this question. We use a Dresser/Mooney regulator to regulate pressure in the instrument air system. It is set to try and maintain instrument air pressure at approximately 120 psig. There are check valves to prevent instrument air pressure from backfeeding into the gas turbine at times when gas turbine extraction air pressure is low, like during starting and shutdown.

4. What control systems where installed. The turbine control system is a GE MKVI.

I made an error in my description of the cooler. It is not a "purge air cooler" but rather the atomizing air cooler.

I will try to contact you offline, but please understand I like to keep as much of the information here on Control.com so all can have access.

1. put heat exchanger after the extraction.

2. put a control valve which will control the output header pressure at 6.5kg/cm2 (avg).

3. install an air drier unit to get dry air for instrument air supply.

4. keep an s/b motor operated compressor in auto start mode.

5. try to keep your extraction air flow not more than 10% or total GT air flow. (thumb rule at 20MW air flow is 2 lac m3/hr), so if your machine is operating at 10MW do not extract more than 10,000m3/hr.

6. you power reduction will come effective as your turbine will face base load before the full load MW. abruptly. Thumb rule for 7000 m3/hr air extraction gas turbine will face base load at 1 MW less than its without air extraction base load.

Questions to Barindra75

Dear Barindra75, would you please give more details about points 5 & 6 below? and How much air could be extracted from axial compressor?

>5. try to keep your extraction air flow not more than 10% or
>total GT air flow. (thumb rule at 20MW air flow is 2 lac
>m3/hr), so if your machine is operating at 10MW do not
>extract more than 10,000m3/hr.

>6. you power reduction will come effective as your turbine
>will face base load before the full load MW. abruptly. Thumb
>rule for 7000 m3/hr air extraction gas turbine will face
>base load at 1 MW less than its without air extraction base
>load.

We have 3 (three) 10MW turbogenarators and I'm asked to extract, as much as possible, air from wrappers but I don't know what's the maximum allowable ??

Thanks in Advance for your help

Regards
Karim

By Ramses GC on 9 April, 2019 - 4:44 am

Greetings,

At the company where I work we have a 501G SIEMENS, and we are interested in implementing the system that is spoken in this forum.

My question is, in your plants the extraction air pipe of what diameter is it? like you have an operating range that goes between 8 - 9 bar.

Dear Sir;

Kindly, i need your help to extract air instrument from gas turbine MS5001.

I would like to know

1- Which stage in compressor, i can extract this air?

2- How much temperature in outlet?

3- How the temperature of the compressor discharge was reduced and what type of coolant was used in details?

4- Which safety instrument can i put it in this line of air instrument?

maatallah.djafer@gmail.com
Many thanks