Cooling water temperature for a Distillation unit
Cooling water temperature for a Distillation unit
(OP)
We were wanting to do a temperature test on our cooling towers. We wanted to increase the variable speed fans to 100% and see how far the temperature could decrease.
Problem:
Here we have several distillation columns and all use water cooled condensers. The distillation department would not let us decrease the cooling water temperatures. He stated it would upset the process. All of the condensers condense the vapor 100% now with cooling water at 25C. If we lowered the temperature to 20C, what would this hurt?
Thanks in Advance
Problem:
Here we have several distillation columns and all use water cooled condensers. The distillation department would not let us decrease the cooling water temperatures. He stated it would upset the process. All of the condensers condense the vapor 100% now with cooling water at 25C. If we lowered the temperature to 20C, what would this hurt?
Thanks in Advance





RE: Cooling water temperature for a Distillation unit
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RE: Cooling water temperature for a Distillation unit
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RE: Cooling water temperature for a Distillation unit
Some condenser types (such as horizontal shellside) would not show much additional subcooling, due to the fact that condensed liquid falls off the tube before it can be cooled substantially. A vertical tubeside condenser may show additional subcooling.
Of course this all depends on the process, esp. how sensitive the columns are, but I'm guessing that you could pull off a test while running. I sincerely doubt that cooling water temperatures do not fluctuate substantially through the year, so your distillation guy should be able to handle it. Ramp your fans to 100% slowly and there shouldn't be a problem.
RE: Cooling water temperature for a Distillation unit
This is what I call trading temperature for flow at constant duty (Q=dT*F): Consider an existing CW operating range from 40 to 30degC. Operating with a CW supply of 25degC could potentially reduce the CW circulation pump horsepower by 1/3. Although you will have to increase the fan horsepower to get the airflow higher, the fans operate at inches of water head vs the pump dP which could be as much as 100psid. Even after all the efficiencies (at pumps, HX's, cooling tower, etc) are considered, the economics will likely increase in favor of the coldest water temperature that you can maintain. If the CW flows are balanced manually, then some field rebalancing would be required, but the electrical savings could make it very worthwhile.
best wishes,
sshep