Can we pinch cooling water return valve in trim cooler? If not, why not?
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10/03/2010
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
I agree mostly with Mr. Pajaro. We monitored the cooling water outlet temp on pinched valves. I also agree with the comment on erosion of gate valves not fully open or fully closed. So, we had to replace some pinched C.W. valves every 15 years or so for that reason. Is it worth it to be able to optimize the cooling system?. I did it every summer for many years.
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08/03/2010
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Vishnu Ram A S, RIL, vishnu.selvaraj@ril.com
Pinching or any isolation of the exchanger can lead to:
1. Increase in velocity inside the tubes when you pinch the inlet valve, which leads to flow induced vibration and can damage the tube.
2. Decrease in velocity due to the outlet valve pinch, which leads to deposition of materials carried, deposition corrosion by the salt contents if any and blockages of the tubes. In worst cases the dissolved gasses evolve and obstructs the flow.
3. Usually the pinching of the inlet/outlet valves increases the velocity at the bottom of the seat of the valve and erodes the seat. Hence the valve does not hold tight shut off when we wanna isolate the exchanger/system.
I would like to conclude that the isolation valve is not for the throttling. And so if required, process hazard analysis to be carried out before doing such a kind of non-routine operation.
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08/03/2010
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keith bowers, B and B Consulting, kebowers47@gmail.com
It is almost NEVER a good idea to reduce or restrict the flow of cooling water through a heat exchanger.
While the cooling duty is reduced, this means the cooling water gets hotter !! leading to increased potential for deposits, scaling, and corrosion on the water side. Also deposits are more likely to develop in lower flow areas as the turbulence drops when the water rate is reduced.
It is FAR preferable to bypass a portion of the hot side fluid.
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08/03/2010
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Yes. There are typically many users on a circulating or once-through system. Pinching outlet valves on those users "hogging" water needed by users that need more water is a common way of balancing the system for overall improvement.
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08/03/2010
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Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com
You have to be very careful when you pinch the return valve, be sure water outlet temperature is below 120 - 125 F, also if water flowrate is too low, then water low velocity will increase fouling. If you pinch the valve please leave a visible mark, so when you do backwashing you can put the valve in the desire position quicker.
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