13 replies to this topic

[bosun]

Hello,

I have a shell and tube heat exchanger that heats amine acid gas with IP saturated steam. I am trying to find ways increase duty of this heat exchanger.

There is a balance line that connects from condensate drum overhead to steam inlet line, not to the channel head. With this design how can I control level of condensate in heat exchanger therby controlling heat exchanged area.

I have attached detailed drawing of the process.

Attached Files

•  heat exchanger.xlsx   13.88KB   648 downloads

[fallah]

bosun,

With such configuration of balance line the level in the condensate drum (or piping pot) might not represent the level in the channel head due to possibility of pressure difference between mentioned points. Hence the balance line should be connected from top of drum to below the pass partition baffle of channel head.

Fallah

[bosun]

Then with the design I have would the level of condensate in the drum be higher or lower than the level of condensate in the heat exchanger?
The drum is located about 3 m below the heat exchanger.

[fallah]

bosun,

Appears this configuration cannot do the job. Please upload a simple sketch showing the levels of equipment respect to each other if you want to get further advise.

Anyway as a general guideline the top T.L of the condensate drum should be usually located at 300-400 mm above top of exchanger's tube bundle.

Fallah

[Art Montemayor]

bosun:

Fallah is correct. Your sketch is badly drawn. One can't tell which side the steam is on. I am going to guess that you meant to have the steam in the shell side.

The enclosed revision of your workbook will show you what I mean by you having a bad sketch. I show a vertical exchanger because that is the surest and best way to control the condensate flooding and control the down-turn of capacity.

Attached Files

•  Acid Gas Heater with variable Area.xlsx   22.65KB   656 downloads

[Bobby Strain]

If you want maximum use of the exchanger, connect the TC to the condensate flow valve out of the level tank. Just use the tank LC to prevent steam blowby. This assures that the level is where it needs to be, drained exchanger included. And no need for a control valve on the steam supply. Simple. Temperature control with dramatic flow change is a bit sluggish, but you can't have everything. Unless you over-instrument and leave the steam control valve in place as a high temperature override.

Bobby

[S.AHMAD]

1. You need to determine the position of the liquid level by hydraulic balance since the pressure on the HE shell side is the same as the drum pressure.
2. If the liquid level is at the downcomer/outlet of the HE then you need a new bigger exchanger.
3. However, if the liquid level is in the HE, you can increase the surface area either by increasing the downcomer/HE outlet piping or by increasing the elevation of the HE or both such that the liquid level is at the downcomer.
4. Hope the obove suggestion makes sense to you
5. The best option is to revamp/redesign as per drawing by Art.

Edited by S.AHMAD, 29 October 2012 - 10:03 PM.

[Atttyub194]

Dear all

Good day

This may be possible , however , there are certain questions which need to be answered and few documents need to be reviewed

• Do you have heat exchanger data sheet, if yes please upload it
• Where condensate is routed
• Is it possible to use steam trap instead of Control valve
• What type of control valve is in use. Please upload data sheet
• Is there any bypass available across control valve
• Is amine degradable
• Can steam pressure be increased slightly

Best regards

[gerpo123]

I have the same problem bosun describe above.

 

What I want is to redesign the whole Heat exchanger I want to change the control from steam control to a condensate control. The heat exchanger works at two capacities low (output steam control valve 2 %) and high ( output control valve 75 %).

 

Most of the time the heat exchanger works at low capacity (steam control valve 2%).

 

Therefore I want to change the construction. I want to put the regulation organ in the condensate line. So by drowning the heat exchanger I regulate the capacity.

 

Have some of you some experience with this?

 

Gerpo123

 

[Bobby Strain]

I don't know why you want to change a control system that is working OK. The operation is a bit unusual, but to cover this range of operation you are better off leaving the control as it is. The condensate probably floods the bundle anyway to maintain sufficient pressure for the condensate to flow through the trap and into the header. If you switch to controlling the condensate, the level is likely to increase to the point that you will experience hammering in the exchanger. I am assuming that this is a horizontal exchanger with baffling on the shell side.

 

Bobby

[Pilesar]

Consider adding a smaller parallel control valve for use during normal operation if your problem is only one of control. If a split range steam control would satisfy your needs, it should be a simpler, cheaper option to implement.

[gerpo123]

thanks for answers.

 

THe Heat exchanger is a vertical plate heat exchanger.

 

Bobby thank you for your answer. the system isn't working OK, its a brand new heat exchanger only 2 years and is  already leaking  . it will cost us around 75000 euro to get a new heat exchanger with a redesign. The problem is that at some point because the heat exchanger in under vacuum the condensate don't got to the header. so i have water hammering.

 

Pilesar: thats a solution i have heard before. have you some experience with that in your Work

 

quostion: Is it Ok to use one HEAT EXCHANGER for two situations.

Edited by gerpo123, 08 April 2013 - 02:11 PM.

[Bobby Strain]

Yea, I can understand your problem now. You must have a big trap and it is unstable at the low flow. So I must agree with you that you should control condensate from the exchanger. And maybe with a large and small valve. So, why are you using a vertical plate in a service like this? But you should not have hammering in the plate exchanger even at low duty. Good luck.

 

Bobby

[Pilesar]

gerpo123, you did not mention the hammering before. In normal mode, your need for heat is small and the pressure in the steam chest is reduced to the point where you cannot get the condensate out due to backpressure. The condensate builds in the exchanger until it can overcome the condensate system backpressure then it goes through the trap all in a hurry. The result is very unstable control. One way to fix this is to redesign the contol system so that the condensate outlet valve is the manipulated variable. This may not be the best choice depending on your heat exchanger and piping configuration -- the system may not easily allow converting to variable area heat exchange without undue expense. Another option is to make sure your condensate can get out of the exchanger at all times. You can do this by removing backpressure (exiting to the ground instead of to the condensate header) but the better solution may be to install a condensate pump. Look up "pressure powered pumps" on the spiraxsarco website for examples of pumps that operate without motors and very reliably. After you take care of the condensate problem, then you can consider adding a parallel steam control valve if you need it for control.