fluid pipe temperature, insulated and not

[djoko]

hi..
I have a CO2 stripping tower in my ammonia plant.there is a quench water pipe taken from the middle of the tower (at about 60 m from the ground) that will be pumped and cooled by PHE and then back to the top of the tower.
The temperature of the quench water out of tower is about 102 C(it's not so exact because there is no temperature measurement, it taken from design). There is an opinion to remove the insulation (cause it will be cooled) so the quench water temperature inlet to the pump is decrease.I'm not so sure that the temperature decrease is big enough, but I should calculate it.
In my mind, the heat of the fluid will be absorbed by pipe and blows by wind (natural convection) but I can't calculate what the temperature of the fluid inlet the pump is.
Can somebody give me some procedure/advice how to calculate it??

thanks

 

[TD2K]

Treat the pipe as a heat exchanger.

You know the area from the pipe size and length.

You know the flow of water through the inside of the pipe so you can calculate the heat transfer coefficient.

You have to make some assumptions (or do several cases) on air temperature and wind speed to calculate the outside heat transfer cofficient.

The determine the overall heat transfer coefficient, calculate the heat from the pipe and the subsequent dT for the dT.

For the first calculation of Q, assume the dT from the water is small (eg, you assume T at both ends is 102C) so you can come up with a dTlogmean. Then you can calculate the amount of heat transferred and the new outlet temperature and then recalculate Q. Continue until Tout no longer changes. I suspect the dT will be quite small so it's not something you will have to do 10 iterations.

If you want something quicker, assume the piping temperature is the water temperature and assume an overall Uo to the air is between 2 and 5 BTU/hr/ft2/F.

 

[pmover]

in addition to tdk comments, you should investigate whether the insulation is needed for personnel protection. if so, then proposal is a mute point.

without knowing pipe dimensional and process fluid properties, determining actual heat loss can not be done.

curious question, why is their consideration for removing insulation? is their a problem with pump operation?
-pmover

 

[djoko]

TD2K..
thanks for your advice.I'll begin my calculation..

pmover..
I read from PID, the insulation is needed for heat recovery, not for personal protection. The vertical pipe is about 2 m from stairs up to the tower. There is no problem with the pump. Actually, the main problem is the high CO2 temperature product (design is 36C but the fact now is 45 C). The main cause is the PHE has over duty so the quench water entered the tower is high. The PHE will be cleaned on the shut down this year. But there is an opinion to remove the insulation because the quench water will be cooled. We hope by this action, the water temperature inlet the pump (and then to PHE) is decrease cause of natural convection by air. If my calculation result that the temperature decrease is small, I think it is not necessary to remove the insulation...

 

[TD2K]

Pmover brings up a good point for the personnel protection insulation.

If the original intent was for heat conservation, the PP requirement is automatically met. If you are now removing the insulation the PP requirement would have to be considered. Typically, you look at places were personnel could be under normal operations and where they could reach. Around a pump would be such a place, up the side of a column away from platforms would not be. Some companies use 7' or so 'reach' to define what areas would need PP.