6 replies to this topic

[Ghasem.Bashiri]

Dear Process Engineers.
I have a LP Steam Network. LP Steam Pressure is 3.5 Barg.
We have assigned 1 Bar Pressure drop for process steam users (one inlet valve in steam side, one flow meter, an exchanger, one condensate drum and one LV control valve). Then we route this LP Condensate to a piperack with 12 meter elevation for transfer to a condensate drum after 500 m distance.
However at outlet of LV valve we have 2% mass (50-60% volume percent) flashed condensate.
This flashed condensate may cause some problem for condensate transfer line which I dont know its limitation (maximum allowable vapor fraction for example). I need to know some engineering practice or recommendation for condensate (steam) recovery system.
I can install a condensate vessel with cooler after above mentioned LV but this good design need some cost.
Is there alternative solution?
Ghasem Bashiri (ghasem.bashiri@gmail.com)

[breizh]

Hi Ghasem ,
You may find some interesting information in the attached link :
http://www1.eere.ene...pubs_steam.html

Hope this helps.
Breizh

[saeed.s]

Hi
If condensate line have been selected truly , you dont have any problem and in all the condensate line exist flashed steam and it s usual .
If your plant has steam with lower pressuer than 3.5 barg for example 1.5 barg, you can install a flash drum on 3.5 barg condensate and connect the top outlet to llps header (1.5 barg) to recovery steam.
Otherwise you can install a condenser on top of condensate drum to condensate all the flashed steam .
I attached a simple scheme.

Attached Files

•  condensate.xlsx   11.03KB   446 downloads

[S.AHMAD]

Dear Ghasem

The problem is not on the pipeline but with the LV control valve. However, choose the valve type that can handle flashing and size the pipeline for two phase flow.

S.Ahmad

[Art Montemayor]

Ghasem

You have obtained some very good and useful recommendations from Breizh, behnam, and Ahmad.

What I can add is that 500 meters is a long trek to carry out a 2-phase flow that may be critical since it probably is needed to maintain critical process steam boilers on-stream. You are confronting a classical “trade off” situation: you either:

• design and operate the condensate line for 2-phase flow; or,
• design and operate the condensate line as sub-cooled condensate.

Depending on your specific local conditions and requirements, I would prefer to subcool the condensate and transport it back to the boilers as such. But you require either local process exchangers or aerial condensers to do that.

I would not worry about the level control valve that is expanding the saturated condensate. Good, appropriate trim and design will take care of any concerns there. The 500 meters of pipeline are another matter that you must calculate and operate successfully in the field. Calculating an accurate size for 2-phase flow is not easy. Operating a 2-phase line may also be a challenge if appropriate design and installation is not obtained. That is why I opt for subcooled transport whereever possible.

What you haven't furnished is basic data on what is available as potential heat sinks or process heat exchange that could furnish a source for subcooling the condensate. An aerial condenser is always an option and, outside of capital cost, should be a quick and viable option. But we don't know your local specific data or scope of work.

[Ghasem.Bashiri]

Dear All
Thank you for your kind reply.
Actually I want to modify some existing design (not installed design).
I have some Basic Design without local flash drum and cooler to send cold condensate to steam unit.
As I mentioned I have a pipe rack with 12 m elevation and 500 m as length.
Therefore with 3.5 Barg Condensate and in top of pipe rack I have 50-60% volume percent vapor and slug regime with HYSYS prediction.
I need to know is there any limiation for two phase flow condensate line to shift for local condensate design? Also and reply to above note I have not such low pressure such to route LPC vapor to it.
As side question and as I mentioned I have some exchanger as user of steam. with a control valve and Flow element at inlet of exchanger and a condensate drum and LV in outside of exchanger (fig 4.7 in http://www.driedger...._sh/CE4_SH.html). It was recommended to us for use 0.7 bar pressure drop for these valves to meet controllability of the system. But I think such high pressure drop is not required. But it is not possible to apply general rules for pressure drop of CV in these cases (e.g. Papers in HP). What is recommendation for this issue?

[Ghasem.Bashiri]

Dear All
Refer to my new point in previous reply, is there new issue that can complete this submit for other user and me.


If may be good to put your point to find final solution.

Ghasem Bashiri