Articles & Case Studies

Corrugated tube in tube units replace spiral heat exchangers

Posted: Tuesday 7th April 2009

The HRS Group is currently working with the Severn Trent Digester Team and GTS to replace old type spiral heat exchangers with HRS corrugated tube in tube units at various Severn Trent sites. The existing spiral heat exchangers have to be opened and cleaned on a daily basis whereas the HRS heat exchangers do not. This is because the corrugation of the unit when combined with careful velocity calculations ensure that all solids remain suspended inside the heat exchanger, rather than settling out.

At each site Severn Trent is retaining the existing pumps, and the sludge and hot water pipe work, both to and from the heat exchangers. This, combined with the fact that the replacement units had to be fitted into a very small foot print and the old units lifted out over the existing pipe work, make this a very challenging project.

The initial site to be supplied by HRS was at Claymills in Staffordshire where there are three digesters. Each digester is kept at the desired temperature of 36 degrees centigrade by a heat exchanger which adds 450 kW of heat to the sludge. The sludge is heated using hot water from the CHP plant.

The first heat exchanger was installed at the same time as the digester was refurbished and re-commissioned and was used by the installation team as a learning curve for the next two installations, where the heat exchangers had to be fitted onto a “live” system. This meant that the two digesters the heat exchangers were being connected to had to be kept within a certain temperature band. This was to ensure that the mesophillic digestion process was not disturbed by dropping the sludge temperature in the digester below a certain value.

After the first installation Dominic Williams, Severn Trent Digester Fleet Manager and his team worked closely with the installers GTS Maintenance and HRS to devise a phased plan for the next two installations. Severn Trent allowed for 48 hours to install each new exchanger, with shifts operating continuously. This had not been done before

In fact the second heat exchanger was successfully installed in 18 hours and the last and most difficult exchanger took just 12 before it was up and running.




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