Refurbishment programme calls for new blowers

Severn Trent Water has chosen to install energy efficient ZS oil-free rotary screw blowers from Atlas Copco at six of its water treatment plants in the UK. This forms part of a major infrastructure refurbishment programme, including upgrades to its Rapid Gravity Filters (RGF) that require low pressure air for sand descouring duties.

The latest phase of the project has seen ZS blowers installed at the Little Eaton Water Treatment Works in Derby, which supplies safe, clean drinking water to the city’s North-West area. Over time, it became clear that the site’s RGF process required an overhaul in order to improve efficiency, which meant the replacement of its existing blower installation.

Taking up less land than other treatment processes, a combination of Rapid Gravity Filters and disinfection has become the most widely used method of purifying a drinking water supply. The process involves water pretreatment in flocculation tanks to bulk up impurities and particle size. Following this, the untreated water is passed through several layers of coarse grained sand and anthracite to trap all particulates. The saturated filters are then backwashed several times a day to clean the media with a combination of treated water and low pressure air to de-scour the sand filters. Such a continuous process requires a dependable, uninterrupted supply of oil-free compressed air at 0.5 bar, and relies on the efficiency of low pressure blowers to maintain the required flow rate and pressure.

As one of the main contractors for the upgrade project, civil engineering company MWH Treatment took on responsibility for the Little Eaton refurbishment programme, and turned to authorised Atlas Copco distributor Cooper Freer to specify, deliver and install two ZS 75+VEA-C-600 low pressure blowers, together with all associated stainless steel pipework, in order to replace the existing blowers. The new blowers were positioned on a high level external site adjacent to the RGF galleries.

The ZS blower units comprise a complete, fully integrated package. The rotary screw blowers are commonly available with integrated VSD control. However, the new blowers at Little Eaton were supplied as variable speed units linked to the plant’s own inverter control system.

Commenting on the successful installation progress, MWH project manager Kelvin Smith said: “Atlas Copco’s distributor, Cooper Freer were very pro-active at the design phase in accommodating quite a few changes at an early point in the progress of this project.”

Stephen James, Severn Trent Water’s project manager for the upgrade at Little Eaton, stressed the importance of the ZS blowers: “Not only do the blowers enable a smoother flow in the filter descouring process, they also provide the peace of mind in providing 100% oil-free air to reduce the risk of contamination to the drinking water supply.”

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