Waste to energy plant controls migration is hot solution 01 February 2011

Lerwick's energy recovery plant, which generates heat for the town's district heating system, has now been running successfully with its new control system throughout the winter months.

The flagship plant – which incinerates 22,000 tonnes of waste per year from Shetland, Orkney and the Highlands, pumps hot water to 1,100 dwellings in the Shetland Islands' capital – recently swapped from ageing ABB controls to a system based on Siemens Simatic PCS 7 DCS (distributed control system).

System integrator Digital Applications International (DAI) ran the project, and the system now manages everything from the energy recovery plant's 1,100oC furnace to pumps and valves controlling pressure and temperature throughout the district heating system.

Neville Martin, district heating manager for operator Shetland Heat Energy and Power (SHEaP), concedes that migrating to a new supplier was a slightly worrying prospect – even though the Siemens solution came in at a lower cost. "We were wary. In some ways staying with ABB seemed the easy option," he says.

And the project was critical. On the one hand, it had to be completed before winter, without disrupting the service while replacement was underway. On the other, tight emissions regulation on waste incineration plants meant the DCS system had to deliver reliably.

As William Spence, energy recovery plant manager for Shetland Islands Council, puts it: "If anything is going wrong with the control system then it probably means the plant's emissions are not within the permitted range."

Martin says that DAI did a great job, due in large part to the flexibility of Siemens technology, which enabled a smooth migration to Simatic PCS 7. He cites, for example, Siemens open communications, which meant it was possible to retain existing ABB I/O modules, so reducing project time, costs and changeover risk.

The new system also provided for an emergency fallback option of retaining ABB's controllers, though this did not prove necessary.

With the benefit of a few months' plant operation, Spence observes that, for example, furnace regulation has improved, resulting in reduced maintenance – and hence also reduced oil, which is available as a back-up fuel.

As for the district heating system, Martin comments: "There is no doubt that it works a lot more smoothly." And he adds: "Probably the biggest single improvement is that it is regulating itself better to avoid unnecessary alarms."

Brian Tinham

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