TWIN FLUIDISED BED PYROLYSER COMBUSTOR AS APPLIED TO A WATER TUBE BOILER

Ziel

To demonstrate on a commercial scale, the application of the twin bed pyrolyser combustor firing system to a water tube boiler. The technology (developed by British Coal under EEC Research Project nr. EED E2-322-UK) offers potential operational and environmental advantages over other forms of coal firing.
The project has demonstrated a number of difficulties in extrapolating this technology from a test rig situation to a commercial scale boiler plant. These problems relate to the problems of erosion prevention in shallow fluidised bed, in this case anti-erosion shelves were fitted to water walls. The anti-erosion shelves prevented adequate heat transfer from the bed to the furnace wall.
More work is required to determine heat transfer correlations to water walls where anti-erosions shelves are provided. Such a programme is proposed but outside of this project.
The gas transfer ports between pyrolyser chamber and the mixing chamber became chocked when operating in the pyrolyser mode. The deposits were pyrolytic carbon which steadily accumulated at a rate depending on the quantity of coal fired. The chocked transfer ports were simply cleared by reverting from the pyrolyser mode to normal excess air operation. The problem of choking in the pyrolyser mode could not simply be overcome on this boiler although numerous modifications were tried. A further programme, outside of this project, on a test rig is planned to investigate the problem further.
The boiler has a sophisticated control system which automatically starts the boiler from cold brings the bed upto operating temperature introduces coal. Once on line the boiler automatically transfers from excess air mode to pyrolyser/char bed mode and back again as appropriate. The automatic control system will on very low loads reduce the number of beds in operation and where appropriate slump them and later return them to service.
The NOx reduction was lower than expected and this was almost certainly due to extra air being used in the char bed due to the lack of heat trasnfer due to the anti erosions shelves of that bed.
The SO2 reduction achieved was very much as expected.
The boiler met its performance guarantees despite the problem detailed above.
The boiler consists of two adjacent shallow fluidised bed compartments whose gasses mix in a third chamber before passing through a convection bank and onto the economiser. When the boiler is operated in the pyrolyser combustor mode, one chamber acts as a pyrolyser whilst the second chamber acts as a char bed. The gas generated in the pyrolyser chamber passes via gas transfer ports to a mixing chamber where on meeting gases from the char chamber high temperatures of upto 1300 deg. C are generated. These high gas temperatures allow higher pressure and higher superheated steam boilers to be produced more compactly than in a normal shallow fluidised bed boiler. In addition staged combustion produces lower NOx emissions than would be expected from a normal shallow fluidised bed whilst the addition of limestone controls SO2 emissions.

Programm/Programme

ENG-ENDEMO C - Programme (EEC) of demonstration projects and industrial pilot projects (EEC) in the energy field, 1985-1989

Thema/Themen

8.1 - ATMOSPHERIC FLUIDIZED BED COMBUSTION

Aufforderung zur Vorschlagseinreichung

Data not available

Finanzierungsplan

DEM - Demonstration contracts

Koordinator

Senior Green

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