The UK government’s Large Combustion Plant Directive gave power stations a stark choice – invest in reducing their emissions or opt out, limit their operating hours to 20,000 between 2008 and 2015 and then close down completely.
The Ratcliffe site has a generation capacity of 2,000 MW from four 500 MW units, enough to meet the needs of approximately 1.5 million homes.
At the Ratcliffe-on-Soar coal-fired power station which has run for 40 years, operator E.ON decided to ensure it continued to operate, providing a generation capacity of 2,000 MW from four 500 MW units, enough to meet the needs of approximately 1.5 million homes.
Key to this was the installation of a new selective catalytic reduction (SCR) emission control facility at a cost of £200 m. Driving the SCR process, which uses ammonia to neutralise nitrogen oxide (NOx) in exhaust gases, are eight highly efficient WEG 4300kW MGF710 motors equipped with state-of-the-art variable speed drives (VSDs).
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, which are far more neutral by-products from an environmental point of view. 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. Considering the high level of investment and the continuous nature of the process, reliability and efficiency were of vital importance when specifying the main fan drive motors. Since the FGD plant has already been driven by WEG machines the company was in prime position to supply the fan motors for the new SCR process.
Driven by a WEG VSD with a full speed range from 30% to 100%, each fan motor is used to create movement in the flue gas to force it through the SCR process.
“Ratcliffe Power Station is recognised as one of the most efficient coal-fired power stations in the UK and with the WEG motors delivering a confirmed 97.6% at peak efficiency they can only add to this reputation,” said Mick Daulman, contracts and proposals manager at WEG.
Driven by a WEG VSD with a full speed range from 30% to 100%, each fan motor is used to create movement in the flue gas to force it through the SCR process, before being passed through the FGD plant.
“Any power we consume on-site has to be generated and represents a significant cost, 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,” said Chris Bennett, senior electrical engineer at Ratcliffe Power Station.
“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.”
WEG MGF HV and MV motors
WEG’s HV and MV motors are used on power stations, printing presses, oil and gas platforms, refineries, minerals processing sites and other heavy industrial applications around the world. They are designed to offer flexibility in terms of dimensions, poles, voltages power output, lubrication, control and cooling in arduous conditions.
WEG is a major global player in the power distribution, automation and control sector. The company employs 28,000 people worldwide with global sales of more than US $3 bn, representing a wide range of product groups. These include the latest generation of transformers, LV control gear, generators, gear motors, inverter drive systems, soft starters, LV/MV and HV motors, ATEX- compliant explosion proof motors, smoke extraction motors and full turnkey systems.