Shetland Islands Waste to Energy Facility Gets Upgraded Controls

25 February 2011 Being the most northerly town in the UK Lerwick in the Shetland Islands has come to rely on the district heating supplied by its waste to energy incineration facility, however fears that the ageing facility could be heading for obsolescence led to a control system overhaul. The Lerwick's Waste to Energy (WtE) facility incinerates some 22,000 tonnes of waste collected from Shetland, Orkney and the Highlands each year, providing heat for the town's District Heating System (DHS), which pumps hot water around the clock to 1100 homes and other buildings in the Shetland Islands' capital. Both the WtE and DHS systems rely on a Distributed Control System (DCS) to manage the entire process, from regulating the WtE facility's 1100 degrees C furnace, to ensuring that pressure and temperature levels are correct as the water is pumped around Lerwick. However, concerned that the system was fast becoming obsolete and would be unable to support ambitious plans for expansion, in early 2010 the operators began the hunt for a replacement DCS. William Spence, the manager in charge of the facility for Shetland Islands Council, said the tight regulation of emissions needed in a waste incineration plant is just one of several key areas where the DCS simply has to deliver. "It is critical. If anything is going wrong with the control system then it probably means that the plant's emissions are not within the permitted range," explained Spence. After a tender process Shetland selected Digital Applications International (DAI) to build a control and reporting solution based on the Siemens SIMATIC PCS 7 platform, for which DAI is an approved integrator. Neville Martin, District Heating Manager for operator Shetland Heat Energy and Power (SHEaP), admitted that migrating to a new supplier was a nervous prospect. More immediately, a project beginning in March 2010 had to be completed before winter and the peak demand for heat, without disrupting the service while replacement was underway. According to the operators of the plant, both DAI and Siemens helped to ensure that migration to the Snew platform was smooth and timely. Thanks to the flexibility of the system, the DAI project team says that it was able to build several features into its changeover strategy, helping to keep the risk of operational disruption to a minimum. For example, because the technology is designed around open networking and communications standards it was possible to retain the existing I/O modules - reducing project time, costs and changeover risk. "DAI did a great job," declared Martin. "They really went to town on understanding our system and its needs, and then coming up with their own solutions to make things work better than they did before." The Benefits Three months after migration, the WtE and DHS were both able to report tangible benefits from the new system. At the ERP, Spence particularly noted improvements to furnace regulation and a consequent reduction in maintenance time, which also cuts the use of oil as a back-up fuel. The plant's operators have found the new system a pleasure to work with. "It's very operator-friendly, which was one of the things we were concerned about before installation," said Spence. As for Martin and his DHS colleagues: "We are very happy. There is no doubt that it works a lot more smoothly," said Martin, adding that a range of individual operations had seen benefits. "Probably the biggest single improvement is that it is regulating itself better to avoid unnecessary alarms." Simon Ellam, Business Manager, Process Automation, for Siemens Industry Automation said: "We understand that legacy migration can seem like a leap of faith. The key to successful migration is the ability to move to a new platform with as little impact as possible on the day-to-day running of the facility." Ellam added that the success of the Shetland migration exposed the limitations of the old approach based around proprietary standards for each manufacturer. "That was done to tie the customer in. But customers don't want to be tied in. They want open technology which allows the flexibility of operation and mainte