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High Pressure Condensate Recovery To Low Pressure Deaerator

condensate recovery pressure control regulator safety high pressure condensate

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#1 hd_1982

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Posted 16 February 2024 - 12:51 AM

Gentlemen,
 
I am process engineer , designing a condensate recovery system for high pressure condensate of APH ( air pre heater.
 
Ambient air is heated till 260 C in air pre heater using high pressure superheater steam of 41 bar & 400 C & flow rate of 2000 Kg /Hr.
 
The condensate is already subcooled to 130 C while exiting air pre heater. 
 
This 40 bar high pressure subcooled condensate needs to be recycled to deaerator having operating pressure of 1.7 Bar.
 
There is Mechanical pilot operated Pressure control regulator is placed to control the pressure of the condensate.  Process diagram & parameters are shown in attached sketch.
 
I need help on below question.   
 
1) What should be Set pressure of this mechanical pressure regulator? 
   Considering Deaerator op pressure 1.7 Bar & Static elevation 18 mtr Back pressure on PVS is 3.5 Bar( 1.8 static head +1.7 Deaerator op    pressure). 
    Or it should be higher than 3.5?
 
  Alternatively, shall I consider only static elevation as back pressure on PCV, and go with 1.8 as set pressure.
 
2) The deaerator is having two PSVs having set pressure of 3.5 Bar.  Do I need to put additional PSV just after PCV ( mechanical regulator) to protect the system? If yes, then what should be its set pressure?  
 
3) Is this system shown in diagram safe? Or as a safe alternative, do I need to put condensate recovery system ( PPPU ) and isolate High pressure condensate with low pressure deaerator? 
However this would be last option as it involves cost & space requirement.
 
Thanks for your response in advance.
 
Dave  
 
 
 
 Attached File  HP condensate from air preheater to deaerator.jpg   133.03KB   1 downloads

Edited by hd_1982, 16 February 2024 - 12:57 AM.


#2 breizh

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Posted 16 February 2024 - 01:07 AM

Hi,

Perform a hydraulic calculation from the deaerator (backwards) to ensure that the driving force (outlet of the PCV) is sufficient enough to overcome the head loss and the static head.

Breizh



#3 shvet1

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Posted 16 February 2024 - 02:04 AM

https://armstrongint...ng/#opensystems

https://www.tlv.com/...recovery-piping

https://www.spiraxsa...ensate-recovery



#4 hd_1982

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Posted 16 February 2024 - 07:47 AM

Hi,

Perform a hydraulic calculation from the deaerator (backwards) to ensure that the driving force (outlet of the PCV) is sufficient enough to overcome the head loss and the static head.

Breizh

Hello Breizh,

Thanks for your response.

As a rough estimate,  'Back pressure' on the PSV will be

= Deaerator op pressure + Static head between PSV & Deaerator+ Friction loss in pipe & fittings

= 1.7+ 1.8+ 0.3

=  3.8 

 

Then My PCV set point will be 3.8 Bar.

Is that seems okay? Or do I need bit higher set pressure to 'inject' the steam in to Deaerator? 

 

reg

Dave



#5 breizh

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Posted 16 February 2024 - 11:02 AM

Hi,
head loss pipe and fittings is only 0.3 bar?

What is the point to have  a steam trap on a liquid line (condensate subcooled)?

Take a look at the link underneath:

https://www.spiraxsa...s?sc_lang=en-GB

 

BTW I don't understand what you want to achieve with this water spray above the liquid within the deaerator. 

 

To remove oxygen you need to bring steam bubbling into the liquid. Check Mollier diagram or other calculator , the steam region at 130 C is about 2.7-2.8 bars absolute.

Good luck

Breizh.



#6 Pilesar

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Posted 16 February 2024 - 01:59 PM

The deaerator pressure is not controlled by this PCV on the condensate line. What pressure do you think you can control with this valve? The steam flow to the air preheater is modulated to control the air temperature. There seem to be two steam traps already in series to discharge the condensate. I don't see any use for a pressure control valve on the condensate and would just remove it from the system. If you already have this valve, then use a very high pressure setpoint (max pressure for the downstream piping) for the controller so that the valve stays open all the time. The condensate flow will be controlled by the steam traps.


Edited by Pilesar, 16 February 2024 - 02:01 PM.


#7 shvet1

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Posted 18 February 2024 - 10:43 PM

Is that seems okay? 

 

 

That seems totally incorrect. Describe in details what problems you are solving what goals you are trying ti achieve.

Attached Files



#8 hd_1982

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Posted 20 February 2024 - 01:35 AM

 

Is that seems okay? 

 

 

That seems totally incorrect. Describe in details what problems you are solving what goals you are trying ti achieve.

 

Hi Shvet1 , 

 

The problem is to deliver high pressure subcooled condensate of air preheater directly to low pressure deaerator located at +18 mtr elevation, by using mechanical pressure control valve.

 

Shall PCV set pressure be  2.0 Bar, to cater static head & deliver condensate in to Deaerator? OR 

Shall PCV set pressure be 3.8 Bar , to match the total back pressure ( 18  mtr static head + 1.7 bar operating pressure of deaerator+ 0.3  bar Line losses) ? 



#9 hd_1982

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Posted 20 February 2024 - 01:44 AM

The deaerator pressure is not controlled by this PCV on the condensate line. What pressure do you think you can control with this valve? The steam flow to the air preheater is modulated to control the air temperature. There seem to be two steam traps already in series to discharge the condensate. I don't see any use for a pressure control valve on the condensate and would just remove it from the system. If you already have this valve, then use a very high pressure setpoint (max pressure for the downstream piping) for the controller so that the valve stays open all the time. The condensate flow will be controlled by the steam traps.

Hi Pilesar,

 

Thanks for response.

 

I had a talk with Forbes marshall team on this  & they suggested that Pressure upstream & downstream of steam trap will be equal .. i.e. 40 Bar here in this case !!

 

To protect the downstream equipment ( deaerator)  form over pressurization , I need to reduce the condensate pressure from 40 Bar to lower , so that it can travel till deaerator by overcoming back pressure caused due to static elevation of 18 mtr , plus deaerator operating pressure of 1.7 bat & , line losses ( approx 1.3 mtr.)

 

Now the challenge is - to select PCV set pressure.

 

Shall PCV set pressure be  2.0 Bar, to cater static head & deliver condensate in to Deaerator? OR 

Shall PCV set pressure be 3.8 Bar , to match the total back pressure ( 18  mtr static head + 1.7 bar operating pressure of deaerator+ 0.3  bar Line losses) ? 



#10 shvet1

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Posted 20 February 2024 - 05:38 AM

 

 

Is that seems okay? 

 

 

That seems totally incorrect. Describe in details what problems you are solving what goals you are trying ti achieve.

 

Hi Shvet1 , 

 

The problem is to deliver high pressure subcooled condensate of air preheater directly to low pressure deaerator located at +18 mtr elevation, by using mechanical pressure control valve.

 

Shall PCV set pressure be  2.0 Bar, to cater static head & deliver condensate in to Deaerator? OR 

Shall PCV set pressure be 3.8 Bar , to match the total back pressure ( 18  mtr static head + 1.7 bar operating pressure of deaerator+ 0.3  bar Line losses) ? 

 

 

PCV shall not exist in this scheme.

Why do you believe the condensate is subcooled?

Consider studying training materials at links I have posted above.



#11 hd_1982

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Posted 20 February 2024 - 07:30 AM

 

 

 

Is that seems okay? 

 

 

That seems totally incorrect. Describe in details what problems you are solving what goals you are trying ti achieve.

 

Hi Shvet1 , 

 

The problem is to deliver high pressure subcooled condensate of air preheater directly to low pressure deaerator located at +18 mtr elevation, by using mechanical pressure control valve.

 

Shall PCV set pressure be  2.0 Bar, to cater static head & deliver condensate in to Deaerator? OR 

Shall PCV set pressure be 3.8 Bar , to match the total back pressure ( 18  mtr static head + 1.7 bar operating pressure of deaerator+ 0.3  bar Line losses) ? 

 

 

PCV shall not exist in this scheme.

Why do you believe the condensate is subcooled?

Consider studying training materials at links I have posted above.

 

Hi,

I subcooled condensate is defined from Air pre heater data of HTRI. The Air pre heater contains 3 modules inside  which passes the steam counter currently into Air pre heater.

 

Desuperheater module ( steam temp 400 C goes to 256)  

Condensate module ( Steam turns into Condensate by removal of latent heat temp remains 256 C)

Sub cooler ( Where condensate temperature reduces from saturation temp 256 up to  130 C).

 

Steam Pressure drop across the Air pre heater is 1 Bar. Hence subcooled condensate is considered as 40 Bar.

 

regards



#12 shvet1

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Posted 20 February 2024 - 07:36 AM

HTRI has calculated subcooling based on particular inlet/oulet conditions you have assumed and inputted in HTRI's interface. What process means are you going to implement to provide&control those?


Edited by shvet1, 20 February 2024 - 07:38 AM.


#13 hd_1982

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Posted 20 February 2024 - 11:07 PM

HTRI has calculated subcooling based on particular inlet/oulet conditions you have assumed and inputted in HTRI's interface. What process means are you going to implement to provide&control those?

 

Hi shvet1,

 

Pl refer attached process design data across air pre heater, which states in subcooler module of the air pre heater the condensate temperature will reach to 130 C. 

 

For ensuring the liquid condensate, a steam trap is provided in between condensate module & subcooling module of the APH.

 

 

Note: I could not send snapshot because of forum disallows it. 



#14 shvet1

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Posted 20 February 2024 - 11:12 PM

What does 'PI' stand for?

Steam trap ensures total liquid passes through, that's all, this device does not control degree of subcooling. Repeated - what process means do you implement to ensure condensate is subcooled to values you had assumed and inputted to HTRI?


Edited by shvet1, 20 February 2024 - 11:58 PM.


#15 hd_1982

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Posted 21 February 2024 - 03:47 AM

What does 'PI' stand for?

Steam trap ensures total liquid passes through, that's all, this device does not control degree of subcooling. Repeated - what process means do you implement to ensure condensate is subcooled to values you had assumed and inputted to HTRI?

Pl stands for 'Please' :) .

To answer your question -No process means can assure subcooling , except heat transfer between cold in coming air &  hot saturated condensate entering sub cooler module of APH  @ 256 C .

But let us assume that it is subcooled liquid @ 130 C, then what should be the set pressure of Pressure control valve?  2.0 Bar or 3.8 Bar?



#16 shvet1

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Posted 21 February 2024 - 05:52 AM

No process means can assure subcooling , except heat transfer between cold in coming air &  hot saturated condensate entering sub cooler module  

Heat transfer is not a process mean. Personnel is unable to control&correct such.

 

what should be the set pressure of Pressure control valve?  2.0 Bar or 3.8 Bar?

Incorrect as 

PCV shall not exist in this scheme.


Edited by shvet1, 21 February 2024 - 05:52 AM.





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