Objective
To demonstrate the technical and economic feasibility of using gas reburn technology to reduce the emissions of NOx from large, coal, front wall-fired power station boilers and to ensure that the partners in the project gain commercial advantage in gas reburn technology with a view to promoting its commercial exploitation in the international energy market.
Gas reburn is a technique for reducing NOx emissions which has been proven on pilot plants and small scale combustion processes but has not yet been applied to a coal, front wall-fired boiler in Europe. The application requires the innovative use of 'state of the art' theoretical and experimental models to a practical situation.
Gas reburn is a means of achieving NOx reductions and is not an energy saving process in the conventional sense. It is expected that with 19% gas reburn, reductions in NOx emissions of at least 45% from the levels achieved with low NOx burners or reductions of 70% from the levels without low NOx burners.
The results indicated that, whilst air staging produced significant reductions in NOx, it also produced a substantial increase in carbon-in-ash levels. With the introduction of reburn at 10% gas, NOx levels were seen to reduced along with a marked reduction in carbon-in-ash. This trend continued as the percentage of gas was increased with the optimum NOx and carbon-in-ash being produced at 20% gas. The carbon-in-ash produced when operating at 20% gas is typical of other Longannet Units.
A reduction in NOx of up to 50% was achieved with this technology.
The commercial performance of the boiler was not compromised by the installation.
These results have validated the design tools used in the process design.
Gas reburn will initially be applied to one of the four 1550 MWth front wall, dry bottom, pulverised fuel fired boilers at Longannet Power Station which is owned and operated by Scottish Power plc. The Longannet Project aims to extend the gas reburn technique to the greater than 500 MWe plus range of boilers for the first time.
A feasibility study, completed in July 1993, assessed the technical and economic merits of gas reburn compared to the alternative technology of selective non-catalytic reduction (SNCR) and concluded that the design and operational characteristics of the Longannet boilers strongly favoured gas reburn.
The process design was undertaken by the partners in the project (British Gas, ESB, ENEL, Ansaldo Energia, EdF and Mitsui Babcock Energy). The process design involved the extensive use of in-house experimental and theoretical (mathematical) models to determine the process flow parameters; to optimise the position of the gas reburn nozzles and overfire air portsand the injection velocities of the natural gas, recycled flue gas and overfire air; and to determine the impact of reburning on the operational characteristics of the boiler.
The application of gas reburn required the provision and installation of additional fans (gas recirculation and overfire air) and associated ductwork. In addition, the requirement for gas injectors and overfire air ports has necessitated additional openings being formed in the furnace walls. This work was carried out during the planned outage of Unit 2 extending from April to October 1996.
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DEM - Demonstration contractsCoordinator
G44 4BE Glasgow
United Kingdom