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At 4GW, Drax is the biggest coal-fired power station in Europe. More than double the size of any other power station in the UK, the six 660 MW units feed into the UK National Grid, supplying 7% of the UK’s electricity needs.
The plant, located near Selby in the north of England, has had an up-and-down history. It was constructed in 1974 and 1986. Damaged by fire in 1999, it nearly went into administration in 2003 during the UK power market slump. It was revived by a rise in wholesale electricity prices and floated on the stock market in December 2005.
It is the UK’s most modern coal-fired power station though and it hopes for another 20-years of operation. Although it has undergone upgrades to improve environmental performance, it is still criticised by the UK’s environmental lobby for its impact. Much progress has been made on reducing the release of sulphur, nitrogen oxides, metals, particulates and ash. Criticisms now centre on the huge volume of the carbon dioxide that is fuelling global climate change.
FGD AND BOFA REDUCE SULPHUR, NOx> EMISSIONS
Work is underway to reduce NOx> emissions. The Drax boilers have been retrofitted with low NOx> burners but the station still emits about 60,000 tonnes of NOx a year. It is also retrofitting Boosted Over Fire Air (BOFA) technology to reduce this to about 7,000 tonnes. The BOFA system is being supplied by Mitsui Babcock, and works by forcing air into the boiler. That means the coal burns at lower temperatures and that cuts the amount of NOx> produced. The ‘over-fire air’ injected into the boiler also mixes better with the flames, increasing the volume in which nitrogen oxide levels can be reduced.
The BOFA system should guarantee NOx> emissions levels of 450mg/Nm3, and will enable Drax to meet the 2008 requirements of the Large Combustion Plant Directive (LCPD). The directive proposes NOx> reductions from current limits of 650mg/Nm3 to 500mg/Nm3. The power station will then, however, need further large investments by 2016 to make it comply with further reductions in limits to 200mg/Nm3.
Drax also emits 450 tonnes of dust a year. The finer ash particles (pulverised fuel ash or PFA), left as residue when coal is burnt, are collected from the exhaust gases by electrostatic precipitators. Ash heavy enough to fall to the bottom of the boiler is collected as furnace bottom ash. The company sells around 40% of its ash, mainly to the construction industry, although leaving over 800,000 tonnes a year to be landfilled.
Continuous emission monitors for NOx>, SO2 and PM10 are installed off site. The direct effects of the site on local wildlife habitats and local Sites of Special Scientific Interest have been found to be low. Water consumption does have some environmental effects, though. Boiler feedwater for the plant comes from two on-site boreholes. Cooling water from the River Ouse feeds the indirect cooling system, cooling water dock and cooling towers. Around half the cooling water is returned to the River Ouse a few degrees warmer than the river, with drainage and discharges being monitored and treated to meet discharge consent limits.
IMPROVING EFFICIENCY REDUCES POLLUTION
Drax has recently begun burning up to 15% of a coal/petroleum-coke blend. Petroleum coke has higher heat content than coal, so less needs to be burnt for the same heat output. That should reduce CO2, NOx> and particulate emissions (which will also cut nickel and vanadium discharge). Interim results at the end of 2006 showed no noticeable impact on SO2, Polycylic Aromatic Hydrocarbons (PAHs) and water discharge quality. The 18-month trial, on one of the six Drax boilers, is being extended to all six units.
In February 2007, Drax announced a further £100 million upgrade. Billed as the largest steam turbine modernisation project in UK history, the turbine upgrade will only cut CO2 emissions by 5%, but that represents a saving of 1 million tonnes a year.
The turbine replacements will increase efficiency to near 40%, with Drax already promoted as the "largest, cleanest and most efficient coal-fired power station in the UK". Depressingly, however, that is not difficult. UK coal-fired power stations have efficiencies of 35-38% LVH. More recent plants in Europe and Asia, particularly China, use supercritical boiler-turbines to hit up to 46% LHV efficiency. Drax’s existing boilers could be replaced by supercritical units to increase efficiency by up to 20%, but would need huge investment and a 12-18 month outage and so is unlikely.
Drax claims that it is part of the transition towards a low carbon economy. This is, however, somewhat disingenuous. With no plans to invest in wind or other low-carbon sectors, the claim will only ever be convincing with some form of carbon sequestration, which still not proven on a large scale, and/or significant biomass burning.
SUCCESSFUL WILLOW PROCESSING TRIALS
Drax has been studying biomass fuels for co-firing, a relatively low cost and efficient renewable technology for directly replacing coal burning. Possible crops include short rotation coppice willow, forestry, miscanthus and rape grown within 50 miles of the power station. Other possible solid biomass fuels include olive cake and pellets, milled palm nuts and sawdust or wood pellets.
Willow processing has been studied in two phases. Phase one identified the issues associated with processing the wet wood, including the transport and handling of processed fuel. The six-month trial used wood-derived biomass fuel, including SRC from 1,100 hectares of willow plantation. The willow was ground and supplied by the company Renewable Fuels which, like the wood growers themselves is a local company, another advantage of biomass. In this phase, wood particles delivered by lorries were fed into a coal mill via an existing conveyor, and so to the furnace.
The wood chip has to be ground to a particle size of less than 5mm to make it suitable for standard pulverised fuel boilers and the mills can get clogged at biomass levels over 5% or so by weight. Phase two, starting in September 2005, integrated the grinder itself into the power plant. Screw feeders take the biomass into an air stream and so to a mill outlet pipe. The biomass is then directly injected into the coal burners, bypassing the coal pulverising mills. The biomass has a separate stream, through separate burners or injectors. That is better than through-the-mill operation, because the biomass then does not affect milling and coal classification.
BIOMASS BURNING CUT BACK
Despite the great initial publicity, Drax has cut back biofuel use in 2006. For the first quarter of 2006, the station was achieving biomass throughputs of about 2.5% by heat, but that has now been reduced to much less than 1%. The power station is citing cost as the reason for the decrease, with biomass generally being at least three times more expensive than coal once all factors, including transport and processing, are considered.
Despite a promise of another £67m to enable it to burn more biomass in the future, Drax has received severe criticism recently because the increase in greenhouse gas emissions came at the same time as a profit increase of nearly 150%, with a windfall to investors of nearly £500m in dividends.
Even if Drax does increase biomass firing, there are still serious unresolved issues. Meeting the Government’s 10% target will need 1.5m tonnes of biofuel by 2010. That has been calculated to need around 750,000 hectares of short-rotation willow. This would be very hard to achieve, although ecologically it is the most desirable outcome since coppiced willow is a traditional British crop and encourages biodiversity.
Less than this – although still 400,000 hectares – could be needed for elephant grass, rape seed or other crops. That is much more than the 20,000 hectares planned by Renewable Fuels Ltd by 2011, and would bring many of the problems associated with crop monoculture.
REDUCING POLLUTION WITH CARBON CREDITS
Without increasing its renewables contribution, the only other way Drax can continue to operate is to buy carbon credits. The power station uses the EU-wide greenhouse gases Emissions Trading Scheme to offset its CO2 emissions. So, for every tonne of carbon dioxide produced, Drax must surrender one EU carbon allowance, with the allowances being traded across Europe.
There have, however, been complaints that the large number of credits given out in phase one of the scheme led to a surplus, so the price for credits collapsed without cutting emissions noticeably. This will hopefully change in phase two but environmentalists are not hopeful.
Emissions trading is proving to be a cost-ineffective way of reducing emissions. Much of the money goes in pushing pieces of paper around, and employing expensive consultants to check that the right pieces of paper have been pushed. A lot of so-called ‘free money’ seems to be going to oil companies, but with no real pressure being placed on them to reduce emissions. There have also been allegations that much of the money now spent on Kyoto credits (also accepted by the EU scheme) is actually fraudulent, either on projects that don’t reduce emissions or actually increase them.
Critics say that, although increased taxes concentrate the mind, the bureaucracy surrounding even proper emissions trading makes it at best just a distraction. The technical measures that reduce energy consumption and increase fuel efficiency are well known, according to protestors, who say that the real need is for legislation and investment to implement those specific measures.
DEMONSTRATORS JOINED BY GIANT OSTRICH
Drax now effectively converts around 10m tonnes of coal per year into 24,000 GWh/year of electricity plus over 20m tonnes of carbon dioxide. Coal generates far more CO2 per unit of electricity than any other fuel, and Drax was responsible for many of the emissions that went to label the UK as ‘the dirty man of Europe’ in the 1990s.
Drax has, therefore, been a focus of protest within the UK, with protesters claiming it is obsolete and should be closed down and replaced with cleaner forms of power. In 2006, for example, more than 600 people converged on a nearby field for ten days to protest against pollution and global climate change. The company at the time claimed that closure would cause major disruption to UK power supplies, but presumably no more disruption than if Drax had been closed in 2003 when it nearly went into receivership.