UK gas 'moratorium' generates opportunities25 March 1999
The UK government's de facto moratorium on gas-fired generation plant construction has renewed interest in a wide range of advanced coal gasification power plant projects.
None of the present projects assume that an IGCC (integrated gasification combined cycle) plant in the UK can be profitable based on coal combustion alone – it would need additional functions such as methanol production, peak topping, waste incineration or dual fuel sewage sludge/coal gasification, as at Schwarze Pumpe in Germany. As in Germany, most potential projects would not proceed without government or EU funding, the only possible exceptions being Global Energy's Fife Power and Fife Electric Ltd projects in Scotland and the South Wales project being developed by Progressive Energy Ltd.
The RJB/Texaco/National Power IGCC project at the RJB pit head site in Kellingley Colliery, West Yorkshire would use oxygen blown Texaco technology for 400 MWe output. The $450 million project will only proceed if government subsidises the project with funds up to £48 million/y (possibly from modified Non Fossil Fuel Obligation resources, which would be ironic).
The IGCC technology favoured is based on a the use of a quench gasifier with slurry feed, dispensing with the need for a radiant syngas cooler. It is thought that the extra efficiency can be picked up in other ways.
Kincardine ABGC project
Scottish Power plans to exploit the former power station site at Kincardine to develop a 100 MWe version of the Air Blown Gasification Cycle (ABGC), formerly known as the "British Coal topping cycle", originally developed by CRE and now pursued by Mitsui Babcock and Alstom. This exploits established "spouted bed" gasification technology.
The project planned on the site of the mothballed Kincardine power station has already received euro 5.5 million EU funding for the design phase and will apply for EU Framework 5 funding for construction which should cover 35 per cent of "novel components", possibly amounting to some $23 million out of the estimated $150 million construction cost. This will coincide with the detailed design phase commensurate with the 2 to 2.5 year construction phase from mid 2000 to end of 2002.
The original 12 t/day CRE pilot rig saw 6000 hours of testing. Currently, component development is being pursued at Mitsui Babcock in Renfrew and Alstom's development centres in the UK and France, most particularly in the Alstom Energy Centre at Whetstone, Leicester. The team are still working on two concurrent proposals for the demonstration plant at Kincardine:30 t/h plant driving a GE Frame 6B gas turbine to generate 40 MWe, giving 90 MWe in combined cycle; 40 t/h plant driving a new GE Frame 6FA gas turbine to generate 70 MWe, giving 150 MWe in combined cycle.
Further investors are being sought.
ABGC technology. The gasifier consists of a refractory lined cylindrical pressure vessel with a diameter determined by the gasifier output, eg, 3 m outside diameter for 150 MWe output.
The ABGC is a hybrid combined cycle power generation system. The process involves the partial gasification of coal in the gasifier to produce a low calorific value fuel gas and a char residue.
The fuel gas is cleaned in a cyclone initially, and then cooled in a raw gas cooler. After cooling to between 400 and 600 ºC, the gas is finally cleaned in a high efficiency ceramic candle filter. It is then burnt in gas turbine combustor cans and expanded through the turbine, generating electricity. The gas turbine flue gas passes through a waste heat boiler, where steam is raised for the steam cycle, before passing to atmosphere.
The char residue from the gasifier and the fine particulate matter collected in the cyclone and ceramic candle filter are cooled, depressurised and then transferred to an atmospheric pressure circulating fluidised bed combustion boiler, where they are burnt to raise further steam for the steam cycle.
Demonstration gasifier. The height of the Mitsui Babcock demonstration gasifier is about 20 m, which is sufficient to accommodate the bed and a transport disengagement zone, incorporated to minimise the elutriated solids loading.
Fluidising air and steam are divided into two streams prior to injection into the vessel. Some is injected at high velocity through the central spout tube, with the crushed coal and sulphur sorbent, into the bottom of the steep angled conical base. The high velocity spout jet promotes an upward movement of gas, inducing internal solids recirculation. This ensures that the devolatilising coal is rapidly mixed with non-sticky bed particles, thereby preventing agglomeration of the coal ash and swelling coal particles, and ensuring a more uniform bed temperature profile.
The remainder of the fluidising air and steam is added through nozzles set in the wall of the conical base section, promoting good particle mixing in this region. The fluidised bed operates at nominally 1m/s and at 900 to 1050 ºC, depending on the fuel properties and the solid/gas conversion required.
The plant will have a net power output of 91 MWe and an efficiency of 40 per cent (LHV basis).
The 6FA based ABGC should increase the power output to about 150 MWe and boost the efficiency by about 5 percentage points. The gasifier for the 6FA variant will be the same size as for the 6B, but operated at a higher pressure and a higher fluidising velocity to give a fuel gas energy flow of 220 MW and a coal throughput of 50 t/h.
Crushed coal and limestone are pneumatically conveyed from lockhoppers to the central air jet, where they mix with the fluidising air and steam and are carried high into the bed. Initially the coal dries in the steam/air stream, and then rapidly devolatilises as it is heated by recirculating solids and by radiation from the bed.
Some of the evolved volatiles and char in the spout burn in the air stream to give a peak bed temperature around the point where the jet breaks down into bubbles. This combustion is necessary to generate the heat to drive the endothermic gasification reactions in the upper part of the bed.
The coal pyrolyses in the spout and lower bed and this produces carbon monoxide, methane, and hydrogen. Carbon is gasified by carbon dioxide and steam in the bulk bed. Together, the products of pyrolysis and gasification form the calorific value of the fuel gas.
Gasification air is extracted from the gas turbine compressor in advanced power plant applications, such as the ABGC and further pressurised in a boost compressor. The steam used is partially de-superheated, medium pressure steam, extracted from the steam turbine.
The gasifier has a high flexibility in terms of fuel feedstock and can be fired with locally available renewables such as biomass and sewage sludge. It has been tested successfully using a wide range of feedstocks, from a selection of UK run-of-mine and internationally-traded bituminous coal to lignites, including co-gasification of biomass and coal.
Based on reports of the Clean Coal Power Generation Technology Task Force of the Foresight Energy Panel, the ABGC has market potential to secure 8 per cent of the IGCC market, amounting to some $3 billion over the next 15 years. This estimate is based on the suitability of the ABGC for high ash coals common in areas of rapidly expanding power generation markets such as India and China.
This project has the great simplicity of an air blown system without integrated air separation units, and easier process dynamics. It should be free from the kind of teething problems encountered at Puertollano, Buggenum, and some of the US demonstration plants.
South Wales GCC project
Progressive Energy Ltd, an independent company spun off from BNFL Magnox Generation, has been actively developing a 350-400 MW oxygen blown unintegrated gasification combined cycle power plant in South Wales.
The site will use the same existing South Wales grid infrastructure as Pembroke power station, for which Orimulsion combustion without FGD has been banned. Progressive Energy has been working with local coal companies capable of providing the fuel for the station. Progressive has been aiming to produce a simple design with excellent environmental performance. A conceptual design has been produced, but the gasifier has not yet been selected.
The group is considering a range of entrained flow gasifiers but only quench gasifiers, with no waste heat recovery boiler, are being considered. The target overall efficiency of 42 to 44 per cent matches the 43 per cent of Buggenum without recourse to a boiler.
The designers do not want the air separation unit to be fed from the gas turbine compressor. They say that, "integration is a mistake, this was the main trouble during the early operation of the Buggenum and Puertollano demonstration plants as well as difficult fuel feed."
Present work is concentrated on finding economic suppliers and financing. The project aims to compete on a commercial basis.
Fife clean energy
Global Energy of the USA and other investors, have committed substantial funds to further exploitation of the classic BGL (British Gas/Lurgi) slagging gasifier technology at Westfield, Fife, Scotland. Global Energy holds the first BGL (British Gas/Lurgi) technology licence in the world and was a founder member of the Washington DC based Gasification Technologies Council.
The plan at Fife is to integrate IGCC technology with Global Energy's AFT (advanced fuel technology) which produces fuel briquettes from waste and coal/petroleum coke. The technology, known as AFT-IGCC, as well as generating power, provides a route for the elimination of waste materials including sewage sludge, municipal solid waste and refuse derived fuel.
AFT involves briquetting the waste materials with coal (or petroleum coke) to produce fuel briquettes, which are then gasified to produce syngas. This gas runs a combined cycle plant.
Fife Energy Ltd (part of Global Energy) took over the former Westfield Development Centre site from British Gas including the two BGL slagging gasifiers used for the original development work The aim is establish the site, now called Fife Environmental Energy Park, as a centre for clean coal and renewable-fuel power generation technology, with current projects including:Fife Power 120 MW AFT-IGCC plant; Fife Electric 400 MW AFT-IGCC plant; Global Environmental (an affiliate of Global Energy) 15 MW AFT-IGCC plant.
Fife Power 120 MW project. This project is being addressed in a phased way and is based on a General Electric Frame 6FA gas turbine, which arrived on site in January 1998 and entered commercial operation in November 1998 in the natural gas fired, open cycle mode, exporting around 75 MWe. El Paso Energy has acquired a 50 per cent share in the initial power island phase, while Global Energy retains ownership of the other 50 per cent. Bank of Scotland is also providing finance.
The addition of a heat recovery steam generator (HRSG) and steam turbine/generator is due to start shortly, to convert the plant to combined cycle operation and increasing the output to 120 MWe. This will be followed by the construction of a Fuel Island to accept dried sewage sludge (with a moisture content of 10 per cent) and coal, and will produce AFT fuel briquettes with a nominal sludge:coal ratio of 2:1. The larger of the existing BGL gasifiers will be refurbished and will be operated using these fuel briquettes as a feedstock to produce syngas.
The gas turbine is configured for dual fuel firing (syngas and natural gas), and once the fuel island and gas island are ready, the gas turbine will be operated on a mixture of syngas and natural gas in the ratio 50:50 on a heat basis (74:26 on a volume basis). There is a range over which this ratio can be altered, providing operational flexibility.
Fife Electric Limited 400 MW project. This project is based on a General Electric Frame 9FA gas turbine with associated heat recovery steam generator and steam turbine. The EU procurement procedure has been carried out for the selection of EPC contractors, and an application has been submitted for the necessary UK Electricity Act Section 36 consent to export 400 MW. A public inquiry has been called by the Secretary of State for Scotland, due to start in April 1999.
As with the Fife Power Project, the Fife Electric Limited 400 MW project comprises the same three units: fuel island, gas island and power island.
The fuel island will accept MSW and coal. The MSW will be converted into RDF by extracting the white goods and recovering the ferrous and non-ferrous metal and glass for recycling. The fuel briquettes in this case will comprise RDF to coal nominally in a ratio of 1:1, although higher ratios are envisaged. These briquettes will then be the feedstock for up to three BGL gasifiers. As with the Fife Power project, the Fife Electric gas turbine will have dual fuel firing capability and will be operated with a syngas to natural gas ratio of 55:45 on a heat basis (79:21 on a volume basis). Again there is a range over which this ratio can be altered, providing operational flexibility.
Global Environmental 15 MWe project. This project is based on a technology called Slagging Gasifier Injection, and involves the elimination of industrial waste materials by injection into a slagging gasifier via the tuyeres. It has been successful in gaining acceptance under the Scottish Renewables Obligation scheme to export 15 MWe.
The 15 MWe waste gasification plant is being operated with an element of government funding through the Scottish renewables programme.
Celtic Power is an enterprising form of sponsored MBO which bought up the best assets of the British Coal's open cast mining operations in Wales. It has negotiated an option with the demolition company taken on by National Power to raze the old, ill fated Uskmouth generating station. The plan was to refurbish the old plant with a PFBC gasifier and gas turbine system.
An ABB 336 MW PFBC gasification system of the kind used at Vartan in Sweden, Tidd in the USA, and sites in Spain and Japan would be the basis of the project. Thermal efficiency of the upgraded plant would be less than 34 per cent, but the cost of the refurbishment would only be around $30 - $45 million.
Celtic Power and Eastern have also been investigating the prospects of installing a higher efficiency 360 MWe PFBC plant at the Dowlais Colliery open cast pit on a purely commercial basis. This project may be a fall back in case the 336 MW project is blown out.
Canatxx Energy Ventures (CEV) has also been looking at the Anglesey location for a 1 GW IGCC project, but it has an alternative site near Fleetwood in Lancashire for the J W Grimes project. The aim was to have 2 GW of generating plant up and running by 2000, either 1 GW on each site or 2 GW on one of them, using the first field service units of the new GE 9H steam cooled gas turbines. Since CEV was allegedly looking to store pressurized natural gas in underground salt cavities on the Wyre estuary, close to the Fleetwood site, this might have made this location a more economic choice, but the government moratorium has put an end to all that.
Scottish Hydro Power's Keadby 2 project, an enterprising GTCC scheme to increase output from 760 to 1200 MWe, may become an IGCC project now that the de facto moratorium has effectively ditched the new GTCC project.
The main aim is to gain the utility's fair share of any available government or EU subsidies. The site near to Scunthorpe could use imported coal delivered through Immingham or indigenous coal water-transported from the Nottingham and Yorkshire coal fields.
Government prevarication seems to threaten prospects of successful development of clean coal combustion in the United Kingdom, much as it did with nuclear technology in former years. In spite of this, it now seems probable that at least two, and probably three, coal gasification demonstration plants using a range of different technologies will be constructed in the United Kingdom to operate within the first couple of years of the new millennium.
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| one-of-the-advantages-of-gasification-combined-cycle-projects-is-their-capability-to-utilize-a-range-of-feedstocks-and-produce-a-variety-of-co-products-through-co-production-of-an-alternative-parallel-product-to-electricity-gcc-plant-can-be-swung-from-the-alternative-product-to-electricity-during-periods-of-peak-demands-jacobs-engineering-proposes-a-novel-form-of-fuel-arbitrage-trading-peak-demand-electricity-generation-against-methanol-and-ammonia-production-using-three-optional-feedstocks-as-fuel-priTablesTable 1 Design features for Kincardine ABGC demonstration plant
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