Articles & Case Studies

Utility group reaps benefits of Siemens control technology at sewage processing plant with improved efficiency and lower costs

Posted: Tuesday 28th June 2011

Most of them will never know it, but the Mersey Valley Processing Centre (MVPC) makes a vital contribution to the quality of life of millions of people across the North West of England.

MVPC at Shell Green, Warrington, is the sewage processing centre for a huge swathe of the region stretching from Liverpool to parts of Greater Manchester, handling and incinerating up to 87,000 tonnes of biosolid waste each year that is fed to it by the Mersey Valley Sludge Pipeline (MVSP).

United Utilities, MVPCís operator, has now completed a major upgrade to key elements of the plant, including the installation of a new, more efficient sludge processing and incineration stream. At the heart of the upgrade was the deployment of a Siemens Simatic PCS7 distributed control system (DCS) to give United Utilities real-time visibility and operational control across the plant and its sludge supply network.

The water company began planning the upgrade project more than five years ago in a bid to improve plant efficiency while simultaneously reducing operational expenditure.

The adoption of the PCS7 DCS as a common control platform, in conjunction with Siemens S7-400 controller technology at key stages of the process, has already delivered significant benefits to United Utilities. When fully realised, the upgrade is expected to lead to a reduction of up to 50% in operational expenditure per cubic metre of raw waste.

The ability to move from reactive to preventive maintenance is one example of how the deployment of PCS7 in conjunction with condition monitoring technology has improved operations at Shell Green. The upgraded plant uses centrifuges rather than older, less efficient plate presses to dewater the sludge to a specified dry solids content before incinerating or otherwise disposing of it. The Siemens DCS has allowed Shell Greenís operators to set specific alarms that trigger in response to increased vibration levels, a sign that the centrifugeís bearings are suffering from excessive wear. This allows planned maintenance to take place with minimal operational disruption to one of the plantís core processes.

Similar condition monitoring across Shell Greenís operations has seen a dramatic fall in the level of reactive maintenance needed. In 2007, 90% of the plantís maintenance costs were reactive. That will fall to 20% by the middle of 2012, according to United Utilitiesí own estimates.

A major benefit offered by the PCS7 system is real-time monitoring, measurement and control at every stage of the complex sludge treatment process. Implementation of the Siemens DCS at Shell Green brought the processing plant under the same control system as the MVSP, where PCS7 deployment had already taken place at an earlier stage of the upgrade process.

With plant and pipeline both under the same control umbrella, United Utilities is already making full use of the new operational benefits available thanks to advanced networking technology that constantly supplies performance data from across the operation.

For example, under the old control regime the process was compromised by the quality of the sludge arriving at the plant. In some cases the sludge arrived at the wrong consistency for efficient dewatering, often as a result of being stored for too long at local pumping stations and turning septic. This could result in the sludge sent for incineration being too wet to combust without the addition of natural gas to the process, at considerable extra cost.

The PCS7 control system ensures that sludge arriving at the new, centrifuge-based dewatering process is the correct consistency to produce a dry, solid cake that is autothermic Ė meaning that it can be combusted without the need for gas or other additives.

If sludge of poor consistency is arriving at Shell Green, the new DCS allows United Utilitiesí control team to pinpoint the source, even if it is back down the pipeline at a local pumping station, and take appropriate action.

The transformation of operational visibility made possible by the upgrade is exemplified by the dashboard interface available to operators, which shows the real-time cost of treatment of sludge passing through the plant against planned targets.

With plant and pipeline both on a common control platform, United Utilities is equipped to provide its customers with an efficient, reliable service for decades to come.

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