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Shell And Tube Heat Exchanger Design


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#1 varun555

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Posted 23 September 2020 - 12:55 AM

Hello,
 
I am working on checking the design for a shell and tube heat Exchanger. We have 4 shell and tube heat exchangers to cool the quench tank water from 160 deg f to 120 deg f using two water chiller connected to 1st & 2nd as well as 3rd & 4th heat exchanger. The temperature of cold water is 80 deg f. The pump flow rate for hot water is 375GPM & that for the cold water is 40GPM & 75 GPM respectively. The problem is that the water temp of the quench tank after coming out of the heat exchanger is 150 deg f. The area of the heat exchanger is correct as per the calculations. What measures I need to take to decrease the temperature of the quench tank. Do I need to increase the flow rate of the cold water and decrease the flow rate of the hot water or do I need to increase the quench tank area? Thank you.


#2 breizh

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Posted 23 September 2020 - 03:46 AM

Hi,

a) Any chance to work on the chillers ? 80 F is not very cold !

B) You can increase the flow rate of cold water @ 80F , the heat transfer coefficient will improve . Let you try 

c) Is the temp homogeneous at the outlet of each HX ? all behave the same with  T out # 150F  ?

 

Good luck

Breizh 



#3 Bobby Strain

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Posted 23 September 2020 - 09:24 AM

You must get a full data set and make an evaluation. And perform some calculations. Then get back to us.

 

Bobby



#4 latexman

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Posted 23 September 2020 - 09:48 AM

Heating - 375 gpm x 500 pph/gpm x 1 Btu/lb/F x (160-120 F) = 7,500,000 Btu/hr

 

Max. Cooling - (40+75 gpm) x 500 pph/gpm x 1 Btu/lb/F x (160-80 F) = 4,600,000 Btu/hr

 

Houston, we have a problem!


Edited by latexman, 23 September 2020 - 09:54 AM.


#5 breizh

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Posted 24 September 2020 - 09:51 PM

Hi,

Can you submit a sketch with all information available to review ?

We need to get flow rates, temperature in /out on cold and hot water for each HX , currently we have no clue about the temperature of cold water leaving the HX .

How can we perform  proper heat balances without having flow rates on each equipment ?  More less guess .

What is the Delta P on each HX ?  You may have equipment fouled !

What the HX arrangement ? serie and or // ? 

Can you submit your calculation sheets and or equipment data sheets ?

Is it a new problem or from the start up ?

 

 

We need your support to support you .

My view.

Breizh 


Edited by breizh, 25 September 2020 - 12:06 AM.


#6 varun555

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Posted 27 September 2020 - 11:34 PM

Hello,

 

Thank You for your response. Please find the attached Heat-Exchanger layout.

https://postimg.cc/V5DVtxWt

I don't have the exact temp of water coming out of each heat exchanger. I am going to install the temperature sensors this week to get the exact inlet and outlet temp of each heat exchanger. Currently, The temperature of hot water at inlet is 160 deg F and the temp at outlet is 140 deg F.


Edited by varun555, 27 September 2020 - 11:36 PM.


#7 breizh

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Posted 28 September 2020 - 01:02 AM

Hi ,

What a strange set up ! Difficult to isolate equipments without shuting down the plant. 

It seems to me that you have been "optimizing" the network over the years.  Am I right?

When was the last time you check and clean the heat exchangers ?  Do you have Pressure gauges installed to evaluate a possible fouling which is a very common issue with Cooling water and chilled water .

How can be true your statement about area without being able to perform any mass and heat balances?  weird to me . 

How do you measure the different flow rates , do you have meters installed on your network ? thanks to confirm .

Can you find a portable flowmeter to evaluate the flow rate in each branch and therefore confirm the balances after installing temperature sensors ? BTW you may find simple contact thermometers to install directly on the pipe ! 

Good luck.

let see comments from others .

Breizh 


Edited by breizh, 28 September 2020 - 05:58 PM.





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