Pipe freezing keeps Enron's heat on
15 Jan 2000
A seized butterfly valve in a 20in line from a water/glycol plate heat exchanger threatened to bring the gas turbine generating sets at Enron's Teesside power station to a grinding halt - and with them part of the adjacent ICI site at Wilton which takes low pressure steam from the power station.
The valve isolates the exchanger when maintenance work needs to be carried out on it. The only alternative would be to stop the coolant flow and shut down the entire plant until the maintenance work can be finished.
On discovering the seized valve, Enron called in Cyril W Bishop Engineering Services to isolate the exchanger by pipe freezing. Their task involved forming the ice plug in a four-hour time window and guaranteeing the integrity of the ice plug/freeze seal during the valve replacement programme.
According to maintenance supervisor Martin Small, `positive isolation was vital without any glycol draining out of the system during the process. We also needed proof during the actual freeze that optimal conditions were being achieved. Cyril W Bishop was the only company prepared to guarantee all of this.'
The freeze was achieved using liquid nitrogen and Bishop's newly designed pipe-freeze jacket which incorporates reheating facilities. The growth of the plug was confirmed by a heat flux monitoring system. This indicates to the operators any problems that may be arising during the freezing process due to temperature or flow changes. Moreover, it enables the thermal stability of the plug to be constantly checked, giving early warning of any changes.
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