4 replies to this topic

[Kaodan]

Dear all,

We have to design a condenser which is fed with :

- 15.15T/h of steam at T=136.3°C and P=3.13 barA, and

- 17.85T/h of liquid water at T=154°C and P=11 barA.

At the exit the mass flow rate will be 33T/h of condensates at T=110°C and P=10 barA.

Regarding thermodynamic, the problem is clear and I find that after mixing of steam and liquid water at the entry, we obtain a mix of 13,6 T/h of steam and 19,4 T/h of liquid water at P=11 barA and T=184°C (phase change temperature at P=11 barA).

My question is : what is opinion regarding feeding of steam at the entry? Don't you think steam could reflux because of the pressure gradient which is opposite to the steam flow direction?

Do you have experience in this kind of application? and what solution do you preconize to do this mixing (separate mixing zone in the condenser,...)?

Thanks in advance for your help.

Edited by Kaodan, 29 September 2009 - 07:32 AM.

[joerd]

Something is fundamentally wrong here, and I think you recognized it.
Steam does not flow against a pressure gradient. So, if it is available at 3.13 bara, you cannot feed it to a condenser operating at 10 bara. There will be no flow. Your condenser pressure has to be below 3.13 bara for your system to operate.

[Kaodan]

Thank you for your reply Joerd,

Your comment matches exactly what I want to point out.

However, I forgot to tell about dynamic pressure which contribute to the steam flow. With a DN400 steam nozzle I calculate a 1/2rhoV² of 3.8 barA. Then Ptotal = 3.13+3.8~7 barA which remain less than static pressure in the condenser. Consequently, feedind the condenser with steam is impossible in these conditions.

Am I right?

Something is fundamentally wrong here, and I think you recognized it.
Steam does not flow against a pressure gradient. So, if it is available at 3.13 bara, you cannot feed it to a condenser operating at 10 bara. There will be no flow. Your condenser pressure has to be below 3.13 bara for your system to operate.

[Technocrat]

Dear Kaodan,

Please confirm the type of condenser: direct contact or shell and tube type.

Regards.

[Chem01]

Kaodan,
You are entering water at 11 bar and taking condensate out at 10 bar (before any pump) with 3.1 bar steam which is looking impractical. Your condenser is a direct contact type and clearly it is not completely filled with water.
Rather the vapor space of the condenser is filled with steam at 3.1 bar and after condensation, condensate will come out at a pressure 3.1 bar + water head inside condenser.

How you bring the mixing temperature to 184 is not clear to me.
Regards,