Cyril W Bishop Engineering Services Ltd. Pipefreezing examples.

 

Our competitors said that this freeze was not possible............   These three pictures show a freeze isolation at Teesside Power Station. The freeze is on a 20" vertical water/glycol line coming down from a 36" header to a heat exchanger.  The butterfly valve isolating the heat exchanger (just to the right of the scafolding in the first picture) needed to be replaced, without the flow in the header being stopped.  We used our heat-flux monitoring system to ensure that we had a complete ice-plug before attempting to drain down.  There is an article about this operation in the August 1998 issue of Plant and Works Engineering.  Click the pictures for a larger version.

 

	This picture shows the pipefreezing jacket quite clearly: it is built in two halves and bolted around the pipe.  Each half is a double-skinned welded aluminium construction, with foam insulation between the two skins.  Liquid nitrogen is fed into a fitting in the lower part of the jacket through a vacuum insulated hose attached to a pressurised vessel.  The nitrogen vapour produced in the jacket escapes through the collar at the top of the jacket.
	Monitoring pipe surface temperatures at the jacket extremities can give useful information about the extent to     which the ice plug has grown beyond the jacket.  Here, a hand-held digital thermometer is being used.    In spite of the foam insulation between the skins of the jacket, the extreme low temperature of the liquid nitrogen within the jacket causes considerable frosting on the outer surface.
	The new valve being lowered into position.  The freeze site is in the background.

 

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