South West Water/Tecker

Portasilo were extremely professional, provided excellent support and did a great job of meeting all our specifications. The components were even delivered ahead of schedule, so they were ready for us on site when we needed them

Requirement

Specialist process engineering contractor, Tecker, was called in when South West Water needed to upgrade its existing powdered activated carbon (PAC) storage, handling and mixing system at Stithians water treatment works in Cornwall. The existing system offered insufficient capacity to meet the site’s future requirements and the mixing tanks were corroding. The PAC plant is used to control the taste, colour and odour associated with algae in potable water drawn from the reservoir. In addition, the plant needed a new lime storage and handling system to meet its future capacity requirements. Meanwhile, at Prewley water treatment plant in Devon, Tecker was asked to replace the mixing tanks for the existing lime handling system.

Solution

Ross Mitchell, Technical Support Engineer at South West Water, says: “All of these systems needed to be upgraded and reconfigured to meet our requirements. We’ve always received excellent service and the best-quality silo systems from Portasilo, so they were our first choice supplier. In fact, we have an agreement with Portasilo for the maintenance and upgrading of all our treatment plants. For the Stithians and Prewley projects we asked Tecker to work closely with Portasilo to deliver suitable solutions.” At Stithians, Portasilo manufactured a 3500mm diameter welded carbon steel PAC silo with a working capacity of 20Te at its York factory. The silo had to comply with ATEX 95 regulations due to the potentially explosive nature of PAC. A paint finish was applied in accordance with Water Industry Mechanical and Electrical
Specifications (WIMES).

The silo has twin wedge outlets that discharge into metering screw conveyors, which deliver precisely controlled quantities of PAC into two new slurry mixing tanks manufactured by Portasilo. A pneumatically actuated isolating valve is fitted at the point where the screws discharge into the mixing tanks to prevent the accumulation of damp PAC when the screws are not in use. The two slurry mixing tanks each have a working capacity of 2m2 and were designed to ensure thorough wetting and mixing of the PAC, using heavy-duty turbine-type mixers.

For the lime-handling system at Stithians, Portasilo manufactured a 4115mm-diameter silo with a working capacity of 30Te and supplied two metering screw conveyors to feed material into existing lime slurry mixing tanks. Access to the site at Stithians is very tight and there are height restrictions, which meant that the huge silo had to be supplied by Portasilo in four pieces, which were bolted together by Tecker engineers once on site. All silos and associated equipment arrived on site on the agreed date, with deliveries through the narrow Cornish streets managed and coordinated by Portasilo. The silos were installed onto load cells and fitted with a Portasilo protection system to guard against the risks of overfilling and pressurisation, in line with HSE guidelines.

Jason Rollinson, Project Manager for Tecker in Cornwall, says: “Everything was delivered on schedule and our team was able to assemble the large lime silo following detailed instructions provided by Portasilo. The Portasilo specialists were on hand at all times to provide advice and guidance. Portasilo were involved right from the consultation phase of the projects, ensuring the systems were designed in accordance with all South West Water’s specifications. South West Water were delighted with the installed systems and with the service from Portasilo.”

At Prewley, Portasilo provided two new specially designed mixing tanks and volumetric feeders, plus access platforms and stairways for the tanks. Simon Long, Project Manager for Tecker in Devon, says: “Access to the mixing tank building at Prewley was very tight, so we asked Portasilo to come up with a solution that would provide the capacity required by South West Water, while ensuring the tanks would fit into the building.”

The solution devised by Portasilo was to manufacture the tanks in two halves at its factory and deliver the pieces to site for assembly by the Tecker team.

Simon adds: “The result was a perfect example of precision engineering. The tank sections fitted through the door with millimetres to spare and we were able to assemble them easily once in the building.”

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