Wednesday, 2 July 2014

John Guthrie, Energy Efficiency Manager, ABB writes: Most people have got the energy saving message of variable-speed drives (VSDs). However many users adopt drives not for their energy efficiency benefits but for other advantages they can bring, advantages that can be equally lucrative.

Take Alkane Energy for instance. The company is one of the UK’s fastest growing independent power generators, operating mid-sized 'gas to power' electricity plants based on methane pumped from mines. Alkane has 81 MW of installed generating capacity and an electricity grid capacity of 100 MW.

A sound business then, yet Alkane had a problem.
Many of Alkane Energy’s pumps run direct-on-line and operate at full capacity all the time. As methane is pumped from deeper in the mine, the pumps need to work even harder. This causes extreme wear on pumps, which tend to fail after only a few months.

With a failed pump costing around £10,000 to repair, plus lost generation revenue and the cost to remove the failed pump, Alkane Energy was looking for a solution.

Could variable-speed drives stop pump failure?
The company already had experience of VSDs, which it used to control vacuum pumps on new sites – it wanted to know if this solution would work on existing sites.

ABB authorised value provider, Inverter Drive Systems, was asked to investigate a retrofit, with a trial carried out at the Old Mill Lane site in Nottinghamshire.

Here’s how it worked
The existing set up used soft starts to slowly start the pumps. When the pump is at full speed, the soft start is bypassed with a contactor. The pressure was then controlled with a by-pass valve.

The 75 kW ABB industrial drive does away with this valve and modulates the pump to keep the pressure constant. This ensures the pumps are not over stressed, allowing them to last longer. It also saves the previously wasted by-pass energy.

And did it work?
The VSD solution gives fine control of the gas pumping, compared to the coarse control of the soft starts. As well as the money saved from cutting the number of pump repairs and the lost production, the VSDs save around 12 kW in energy that Alkane Energy can sell to the grid. And the company now also knows that the older sites can be successfully retrofitted with VSDs.

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