Condensate return system

[lotus7312]

If there are two reactors heated up by steam. The steam header pressure is same, say 6 bar. But the two reactors need different steam pressure due to the different process(say reactor 1 needs 5bar which reactor 2 needs 1bar). Therefore, the inlet steam pressure is regulated by cracking the isolation valves in the steam line. Can I send condensate from these two reactors back to boiler if I connect the two condensate return line from these two reactors together? If not, is there any way to solve this problem?

 

[TD2K]

Using isolation valves to control the steam pressure in the reactors is going to very likely result in wire drawing these valves and you won't be able to get tight-shutoff later when you need it. I would suggest using a bypass valve arrangement with a globe valve for throttling and a gate or other tight-shutoff valve for isolating the bypass line.

Anyway, that wasn't your question. Whether you can combine the two condensate streams depends on the pressure you need to get the condensate back to the boiler. If it's less than the 1 bar steam pressure in the low pressure reactor, you can use a steam trap (or condensate pot and control valve) on each reactor and combine both condensate streams together to return to the boiler.

If the return line pressure is higher than 1 bar, then you'll need to either dump the condensate from that reactor to sewer or some other location, pump it back or use a self powered condensate trap to get it into the condensate return header.

 

[lotus7312]

TD2K,
Thank you for your reply.
I still have one question regarding to this issue.
Say the pressure I need to get the condensate back to the boiler is less than 1 bar. The condesate discharge line of 5 bar reactor is in the downstream of the other one. If the condensate discharge pressure from 5 bar reactor is 2bar while the pressure from the other reactor is 0.5bar. Is it true that this condensate(0.5bar)can't get back to the header because its downstream condesate has higher pressure? If it is true, the heating of the 1bar reactor will then be interrupted.
Best regards

 

[TD2K]

How are you getting/estimating the 2 bar and 0.5 bar condensate pressures downstream of the reactors?

Rx 1 Rx 2 Boilers
l l
l l
l l
l-----------------l--------------------------------

Sorry for the lousy picture. Let's say the condensate arrives at the boilers at 0 bar. The pressure in the condensate header where the second reactor connects to it is the pressure required to flow the condensate to the boiler OR putting it another way, the pressure drop through the piping plus the final delivery pressure at the boilers.

The pressure where the first 1 bar reactor connects into the condensate header is the pressure where the second reactor connects plus the pressure drop in the line between the first and second reactor.

This also sets the dP available for the steam traps. At the second reactor it is (5 bar minus tie-in pressure) and at the first reactor it is (1 bar minus tie-in pressure at Rx 2 plus the additional dP to Rx 1).

 

[saxon]

lotus7312, This question may be off base, but why are you trying to control steam flow to two reactors manually through block valves? As TD2K mentioned, wire drawing will occur, wrecking the valves. Not too mention, loss of reactor process control. You're never going to be able to control those valves fast enough manually to maintain your process variables. My suggestion would be to install either PCV's or TCV's in the supply side depending on how you need to set up the control, trap out on the discharge side and dump both into a common condesate return header that is running at equal or lower pressure.

It is a fundamental law of fluid flow that all flow occurs from regions of higher energy (e.g. higher press)to regions of lower energy (e.g. lower press.). This should answer your second question.

Hope this helps.
saxon

 

[lotus7312]

TD2K and Saxon,
Thank you for your answer.It is really helpful.
The reason I asked this question is that I am trying to improve our energy recovery system. I am think to send all the condensate from different reactors(more than 20reactors) back to our boiler by just rearraging the pipeline.But I am not sure whether I can do that since there are so many reactors with different operation(i.e. different steam pressure). Right now I am looking for the following issues:
1. Specific operation required for each reactor
2. Calculate head needed to send the condensate back to the boiler for each reactor. Here I have problems. There is no flow meter/pressure guage in a single line. I don't have the exact flow rate of condensate. I don't have the discharge pressure of the condensate.

Can you give me some advices that what I should to consider to proceed the project?
Thanks a lot