Inverters and motors help reduce power station emissions

16 December 2014

E.ON has guaranteed the future viability of its Ratcliffe-on-Soar coal-fired power station by installing a new selective catalytic reduction (SCR) emission control facility to reduce emissions. Driving the SCR process, which uses ammonia to neutralise nitrogen oxide (NOx) in exhaust gases, are eight WEG 4300kW MGF710 motors, equipped with variable speed drives (VSDs).

The Ratcliffe site has a generation capacity of 2,000 MW from four 500 MW units. The site covers 700 acres and has been producing electricity for over 40 years. The move to cleaner running is required to comply with the UK Government’s Large Combustion Plant Directive (LCPD) regulations, intended to reduce emissions from UK coal and oil-fired power stations. 

Meeting the first stage of reducing emissions at Ratcliffe required a Flue Gas Desulphurisation (FGD) plant that removes sulphur dioxide before it is released into the atmosphere. This process, which is powered by two 750kW WEG MGF pump motors, is based on a chemical reaction between warm exhaust gases from the coal-fired boiler and atomised limestone slurry. This removes 92% of the sulphur dioxide from the flue gas and converts the limestone into calcium sulphite. 

The second stage of compliance requires all plants to reduce NOx emissions from below 500mg/m3 to below 200mg/m3 by 2016. The SCR equipment injects ammonia into the exhaust stream which reacts with the gas and converts the NOx into nitrogen and water. The process is used widely in both Germany and Japan, reducing the NOx emissions by 80-90% in the process.

The project to install the SCR system between the boiler house and existing extraction system required the use of Europe’s largest mobile crane and cost approximately £200 million. Considering the high level of investment and the continuous nature of the process, reliability and efficiency were vital when specifying the main fan drive motors. Since the FGD plant has already been driven by WEG machines, the company was asked again to offer a solution with its fan motors for the new SCR process.

Commenting on the project, Chris Bennett, senior electrical engineer at Ratcliffe Power Station, said: “Any power we consume on-site has to be generated and represents a significant cost to the site, although we produce up to 2000MW from our four main turbines, that equates to 20,000 tonnes of coal per week and any efficiency we gain from the operational plant is passed on to our overall site efficiency, which is a key performance indicator and something we take very seriously.”

WEG is also providing availability and reliability guarantees with the motors.

“Unplanned downtime is also something we try to avoid wherever possible as we have power demands to meet and costs to control. The reliability of the WEG machines has been proven on other areas of the plant and also on other large applications around the UK and the rest of the world; that, plus availability, good technical support in the UK and competitive pricing meant we were confident about approving WEG as a supplier on this project,” said Bennett.

WEG MGF HV and MV motors
WEG motors offer a solution for multi-megawatt applications as they are suited to use in arduous operating conditions. The motors are designed to be compact and robust, using precision fabricated housings and high purity copper windings. The windings are sealed using a specialist Vacuum Pressure Impregnation (VPI) system and a specially formulated epoxy based resin which is said to offer high quality insulation and stator protection.

Operating temperature is crucial to both the efficiency and the longevity of electric motors - high electrical efficiency relates directly to better thermal efficiency. The WEG units also employ a combination of internal cooling circuits and high efficiency cooling fans to ensure that an optimum temperature is maintained within the motor, even under full load.

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