Articles & Case Studies


Posted: Monday 21st September 2009

When South West Water required bespoke silo systems at two water treatment works, it immediately contacted the UK’s leading bulk storage and handling specialist, Portasilo.

At Stithians water treatment works in Cornwall, Portasilo was tasked with upgrading an existing powdered activation carbon (PAC) storage, handling and mixing system.

Portasilo was also briefed to provide assistance in replacing mixing tanks for the existing lime handling system at Prewley water treatment plant in Devon. In both instances Portasilo worked in conjunction with Tecker, the appointed specialist process engineering contractor.

Ross Mitchell, South West Water’s Technical Support Engineer, said: “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.”

With the current system offering insufficient capacity and the mixing tanks corroding, Portasilo undertook a detailed inspection of the Stithians plant which is used to control the taste, colour and odour associated with algae in potable water. Portasilo was tasked with providing a new lime storage and handling system to meet future capacity requirements on site.

The tailor-made system manufactured by Portasilo, which had to comply with ATEX 95 regulations due to the potentially explosive nature of PAC, included a 3500mm diameter welded carbon steel PAC silo with a capacity of 20Te. In addition, Portasilo applied a paint finish in accordance with Water Industry Mechanical and Electrical Specifications (WIMES).

Delivering controlled quantities of PAC into two slurry mixing tanks manufactured by Portasilo, the system installed contained twin wedge outlets that discharge into metering screw conveyors.

Crucially, Portasilo ensured against the accumulation of damp PAC when the screws are not in use by fitting a pneumatically actuated isolating valve at the point where the screws discharge into the mixing tanks.

In order to ensure thorough wetting and mixing of the PAC, Portasilo designed two slurry mixing tanks each with a working capacity of 2m3 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 tanks.

Tasked with delivering the silo to a challenging location with limited accessibility to the site at Stithians, Portasilo supplied the system in four pieces which could be bolted together by Tecker engineers once in situ. Nevertheless, Portasilo ensured all silos and associated equipment arrived on the agreed date to the exact specification required.

Jason Rollinson, Project Manager for Tecker in Cornwall, said: “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.”

Portasilo undertook all work in accordance with HSE guidelines to guard against the risks of overfilling and pressurisation with the silos installed onto load cells and fitted with a protection system.

At Prewley, Portasilo were also tasked with working in a restrictive area to provide two new bespoke mixing tanks and volumetric feeders, plus access platforms and stairways for the tanks. Portasilo devised a solution to manufacture the tanks in two halves at its factory and deliver the pieces to site for assembly by the Tecker team.

Simon Long, Project Manager for Tecker in Devon, said: “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 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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