Operational efficiency delivered on Mersey network

Control and management of wastewater in the newly upgraded Mersey Valley Sludge Pipeline has delivered on cost and efficiency for United Utilities, says Mark Chung of Siemens Industry Automation

Reducing operational expenditure and increasing operational efficiencies lay at the heart of a major United Utilities (UU) project to upgrade a 40km wastewater biosolids pipeline and pumping station network.

And to help it improve its control and management of the volumes of waste being transported through its pipe network to a central processing centre, UU called on its framework partner, Siemens.

The utility sought to underpin a business need to augment capacity so it can safely and effectively transport and treat the increasing volumes of raw waste expected in the future. Collaboration with Siemens Industry Automation has seen the implementation of a new automated PCS7 distributed control system (DCS) across the length of the pipeline.

Providing a DCS to monitor the whole catchment, together with various plant and process improvements, will achieve a 40-50% reduction in operational expenditure per m3 of raw waste treated, and increase processing capacity. The single-process control platform provides accurate ‘real-time’ pipeline performance data analysis and reporting, reduced unplanned maintenance occurrences, enhanced self-diagnostics and improved visibility of the entire pipeline network.

It also forms the foundation for further planned process enhancements to the daily operation of handling and treating biosolids from a regional population of over 3.5M people.

At the centre of the upgrade project is the Mersey Valley Sludge Pipeline, a 40km network that handles raw wastewater across the north-west region, from Liverpool to Oldham.

The sewage pipeline feeds into the central Mersey Valley Processing Centre (MVPC) at Shell Green in Warrington, and it was a need to better understand and manage the control and treatment of the wastewater to the centre that underpinned UU’s desire to seek a new process-control solution. By doing this, the company believed it could address overall operational expenditure levels.

Shell Green handles up to 87,000t of biosolids per annum, with the treated waste either ending up as material exported for agricultural purposes or incinerated to produce a sludge cake for use in landfill.

With the processing centre receiving waste from several separate feeder sites along the length of the pipeline, the quality (% dry solids) and age of the biosolids being transported and treated was of primary concern, as it has a considerable effect on the costs of pumping and treatment.

Homogenous consistency of the feed stock or raw materials sent to Shell Green is important, as it directly influences the efficiency of the processing centre’s operations. United Utilities’ management at the centre thus needed a better understanding of the consistency of the raw material it was about to receive, so it could improve its management of the sources of the biosolids waste.

If raw materials are either too thick (compact) or too thin (watery), treatment processes such as dewatering can incur significant additional costs. If the feedstock for incineration is too wet, for example, it will require more energy to reach its optimum auto-thermic state. In such cases, higher gas consumption results in extra expenditure for UU.

To help bring the processing centre under greater control, Siemens generated a PCS7 DCS for the pipeline and pumping-station network. This provides a single and consistent DCS platform along the length of the pipeline linked to the centre, so that greater efficiencies can be achieved through control, monitoring and accurate reporting.

Previously, the processing centre had to deal with the varied feedstock it was sent – often without warning. The new control platform allows operational personnel to identify the consistency of the raw materials at a much earlier stage along the pipeline, and then to use real-time data and analysis to decide the optimum way to treat it.

The DCS system now enables management to remotely monitor the performance of each of the distributed donor sites that feed into the pipeline. With closer control, more accurate decisions can be made concerning the materials being sent along the pipeline before it reaches the MVPC.

In essence it provides the information to get it right first time.

Two other critical features of the DCS system have also supported UU in its objective to improve its operational expenditure (OPEX) commitments. Firstly, a DSL wide-area network with VPN technology was implemented.

This means that improved connectivity is built into the DCS platform, whereas previously UU had relied upon leased lines. This ensures that the operational management has accurate and timely information at its disposal when making decisions. Likewise, access via Profibus technology to the performance of the remote sites has vastly improved the ability for self diagnostics, which has had a real impact on what were costly maintenance commitments.

Traditional high-maintenance spend is being turned on its head as a programme of predictive maintenance has been put in place courtesy of the visible diagnostic sequence steps available via the DCS platform. Indeed, UU expects most (80%) of its maintenance commitments across the pipeline to switch to a planned/proactive nature by 2012, as opposed to just 10% in 2009.

Predictive maintenance brings with it cost savings, improved critical-equipment reliability and better overall plant availability, as previously undetected issues are dealt with on a proactive basis before they can interfere with day-to-day operational performance.

It is clear that the DCS platform is now delivering real and quantifiable benefits for UU. At the start, the project faced a number of challenges: the need to reduce OPEX at the processing centre; trusting a new and different technology, as the DCS solution is vastly different to the traditional SCADA platform; the need to integrate the various elements of the control platform without affecting the day-to-day operation of the pipeline and processing centre; and the proposed use of VPN technology as a reliable source of data transfer especially for reporting needs.

The challenges have been met and the DCS solution supports the project’s central objectives, which were to improve OPEX performance and the overall ability to handle increased volumes of raw waste over both the short and long term. Better process control and enhanced reporting provides better knowledge and operational flexibility, which in turn supports operational performance improvements.

As a result of the pipeline upgrade, UU has redesigned its processes, which have led directly to measurable reductions – for example, in its overall energy use, and in the levels of chemical procurement needed as part of the treatment process at Shell Green.

It now boasts a single, more reliable hardware solution that should provide 15-25 years of fully supported performance capability. It has also given the company a solid foundation for additional project enhancements, so that it can continue meeting the needs of the many millions of people served by the Mersey Valley Pipeline.

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