RWE, owner of npower, is planning to invest heavily in the future of coal burning with proposals for 4000 MW of new clean coal plant at Tilbury and Blyth, in the UK
Npower, the UK generation subsidiary of energy giant RWE, has submitted preliminary proposals to the UK government to build the first new coal fired power station in the country for more than 20 years. The company has submitted its proposals, mainly in the form of a scoping document, to the Department of Trade and Industry for a £1 billion, 2×800 MW supercritical plant, and says that if consent is obtained the new facility will be operational by 2013. It will replace the company’s existing 1000 MW coal-fired plant at the site in Tilbury, in Essex.
It is anticipated that if consent is obtained site work would commence in 2009 with full commissioning by 2014. Decommissioning of Tilbury B would start that same year and be complete by mid-2015. Outline planning permission has been recommended by local authorities subject to some minor reservations about landscaping and building standards. The existing station would continue to operate whilst the new units are being constructed and commissioned.
Npower chose the Tilbury site, which is on the Thames estuary near the UK capital, because of its proximity to areas of high population and demand, and, clearly, because there is already an operating but now rather elderly coal fired plant on the premises. The company says it will be ‘reaching out’ to the local community and stakeholders as it develops the details of its plan.
Why build new coal plant?
By 2025 the UK will need to have brought on line around 25 GW of replacement capacity to maintain the existing figure of 80GW. 25 GW is the amount of plant that will have retired either by reason of age or by being opted out of the Large Combustion Plant Directive. The latter requires that opted-out plant be limited to a given number of total running hours after 1 January 2008 –
20 000 in Tilbury’s case – and to be shut down by 2015. Proposed new plant by RWE, the UK’s largest generator since it took over npower in 2002, would go a long way towards meeting that figure. Another of its proposed plants is a 3×800 MW facility at Blyth in Northumberland, apparently of a very similar, possibly identical basic design to Tilbury (see panel on page 41).
All increases in the coal burning proportion of the UK mix (currently 37% gas, 34% coal and 20% nuclear) contribute to giving the UK an opportunity to open up mothballed coal mines, closed in the 1970s and 80s when the industry was government owned. This shift towards a mix more appropriate to the UK’s own resources is given as a justification for new coal firing by RWE, but it is arguable whether that will have any force, given the UK preference for buying gas overseas. The impact of RWE’s enthusiastic endorsement of coal firing is also reduced a touch by its application for consent for a 2000 MW CCGT to be located at the former West Pennar plant in Pembrokeshire, Wales, and for a new 1500 MW CCGT plant at Staythorpe in Nottinghamshire, England. The latter was granted earlier this year.
Although the UK government is to date doing little in concrete terms to encourage the development of advanced coal firing technologies (compared especially to its support for renewables) it at least paying lip service to the importance of coal and is expected to launch later this year a competition for small funds towards the development of a CCS pilot.
There has been a power station on the Tilbury site for over fifty years. A 6×60 MW oil fired generating unit, originally intended to be coal fired but converted just before operation, first came on line there in 1956. The four coal fired 350 MW Tilbury B units, which include the three currently operating, were built in the sixties and came on line in 1967. Tilbury A was put in mothballs in 1981, eventually, in 1999, to be demolished altogether. B block however continued in operation and in the eighties was partially converted to dual coal/oil firing, but as gas became the new fuel of choice in the 1990s it moved to two shifting, only to come on line at continuous load again at the end of the nineties as relative fuel prices forced new changes. In fact the present plant, even with one unit not in use, has generated more electricity month by month in the last couple of years, having returned to fully coal firing mode, than at any other time in its history.
Tilbury B burns low sulphur coal as its primary fuel, to which is added a proportion of biomass to enable the plant to meet current emissions criteria. Coal comes in by waterborne craft to a quayside coaling station on the river. The river also supplies all the cooling water and cooling capacity needed by the plant.
In April 2006, RWE npower began a feasibility study to assess the potential for developing a clean coal power plant at the site, and to evaluate its carbon capture and storage possibilities. It had previously been looking at backfitting supercritical boilers into the existing plant but in the event elected to go for new build. However, npower has promised that before any firm proposals are developed a consultation programme will be conducted with stakeholders and the local community, the latter through a series of exhibitions. The new plant would be constructed on the existing site, with the facility continuing to operate while the new units are being constructed and commissioned.
It is expected that the existing station will be wound down by 2015. The new plant would have the capacity to reduce carbon emissions by 22% (on the basis of units generated) which would result in a CO2 reduction of almost two million tonnes per year compared to existing coal fired plant in the UK. RWE plans to reduce emissions at the plant through a combination of more efficient burning and use of carbon neutral biomass, such as sawdust and pine kernel, to replace up to 4% of the coal in the mix.
Npower submitted its environmental scoping document to the Department of Trade and Industry in March. ‘Scoping’ is an early stage of the environmental impact assessment, intended to determine what investigations are necessary to underpinning a sound judgement of that impact, and is a preliminary step preceding an application, under Section 36 of the Electricity Act, for consent to build the station.
At present it is envisaged that the steam raising plant will consist of once through water wall designs operating at pressure in excess of 221.2 bar, the supercritical point at which the steam/water distinction disappears. There are no supercritical units operating in t he UK at present (since Drakelow closed down) but units operating in Europe, the USA and elsewhere tend to have with an operating efficiency between 42 and 46%. The Tilbury units are expected to achieve 45%, which compares favourably with the 35% being achieved by the plant they will replace.
Tilbury B currently operates under UK Integrated Pollution Control legislation, but has applied for a permit to operate under the Integrated Pollution and Prevention Control (IPPC) regime, which embodies an approach similar to IPC but takes in a wider range of environmental impacts with a view to integrated permitting. Its objectives must be met through the application of BAT – Best Available Technology.
To fulfil its existing air quality management plan the Tilbury site collects air data from two local monitoring sites. This data will be part of the basis for an assessment of air quality effects associated with the new plant, using ADMS, a predictive computer based model for atmospheric dispersion.
It is currently proposed that exhaust emissions from the two 800 MW units would be via two new stacks, one for each unit. Initial modelling indicates that they should be between 165 and 225 m in height, depending on final target levels. The existing stacks at Tilbury reach 170 m.
Atmospheric emissions would be compliant with the new plant standards stipulated by the Large Combustion Plant Directive as follows:
•NOx < 200 mg/Nm3 @ 6% O2
•SOx < 200 mg/Nm3 @ 6% O2
•Particulates emissions < 30 mg/Nm3 @ 6% O2
The assessment of emissions would also consider atmospheric deposition, in particular of acid gases, in order to determine the impact on sensitive natural habitats.
A primary consideration in these times is the so called ‘carbon footprint’ which in respect of coal generation points to clean coal technology and CCS readiness. Using the 45% figure quoted above, and assuming 100% coal burn and 85% load factor, CO2 production from each 800 MW unit would be 4.5 Mte per annum. This compares to approximately 5.8 Mte pa at 35% efficiency, an improvement of 22% on the basis of unit production.
Assuming a heat input from biomass (eg palm nut kernels, PKE), of 10% then CO2 emissions reduce further to around 4.0 Mte, equivalent to a further 460 kte of coal equivalent.
RWE backs up its assertions about being CCS ready in practical terms with plans (see below) for the construction of its own r1bn 450 MW ‘CO2 free’ plant in Germany, announced last year. It expects to have a viable CCS plant by 2014 and is investigating on- and offshore possibilities for CO2 storage. Its own feasibility study into Tilbury, started in April last year, was predicated on carbon capture based around amine scrubbing and oxyfuel combustion.
RWE originally considered retrofitting the existing Tilbury plant with carbon capture technology but concluded that it makes more sense to build new units that emit considerably less carbon dioxide (CO2) per unit of output.
Andy Duff, npower’s CEO, insists that the company remains interested in carbon capture and sequestration. “At this time,” he said, “there are still many financial, legal, regulatory, and technical hurdles to clear on CO2 transportation and storage technology. However, [CO2 emissions are] too important to ignore, and we are committed to further research and development as we assess our next steps in this area.”
The new plant will therefore be CCS ready. In the words of Mr Duff “Coal is a vital component of the UK’s future generation mix, but the environmental impact must be addressed. A ‘supercritical’ coal plant on its own would result in a significant net reduction in CO2 levels, but we have also chosen to make the power station ready for carbon capture and storage technology.”
It is anticipated that a capability of up to 10% biomass co-firing (as measured by heat output) will be considered as part of the Tilbury design, but subject to the outcome of the UK government’s review of the Renewables Obligation currently being undertaken. Carbon neutral biomass fuels that could be used to fire supercritical boiler plant include sawdust, wood pellets, PKE, olive, and wheat straw.
Although there are no plans at present for CHP operation, UK DTI guidance notes insist that wherever possible the waste heat from power stations is to be used beneficially, and that therefore developers are expected to explore fully the opportunities for using CHP, including its application to community heating. RWE will be following this guidance.
RWE intends to build in Germany the world’s first large-scale power plant with integrated coal gasification, CO2 separation and CO2 storage, most likely underground onshore. The new plant, with an expected gross output of around 450 MW, could come on stream in 2014 if planning and implementation proceed smoothly.
Total investment costs for the entire plant and the transport and storage of CO2 is estimated at approximately h1 billion. Apart from successful technical feasibility, this integrated project requires the necessary political framework conditions and authorisations as well as approval by the responsible Supervisory Boards within the RWE Group.
First concrete planning steps have already been initiated. The use of hard coal and the gasification of lignite are to be explored and tested in parallel. The results of the research will determine RWE’s decision in the second half of 2007 as to the primary energy source. Tentative indications are that it will be lignite, a non-subsidised domestic energy source.
RWE will also be breaking new ground by opening up an onshore CO2 depository, although the underlying work has yet to be done even on developing the criteria for evaluating the suitability of a candidate depository in geological terms.
Photomontage showing the proposed new units at Tilbury Tilbury A , as it was in 1956 Schematic of the 2×800 MW supercritical boiler arrangement proposed for Tilbury UK generation capacity development The present generating station Tilbury B