Objective To evolve the equipment necessary to enable a boiler plant to combust low calorific value (L.C.V.) low H2 B.F. gas efficiently. This took place at Port Talbot Works (British Steel Corporation) on the low pressure (11 bar gauge) service boilers.One of the blast furnace sub-burners was set-up in the BSC (Welsh Laboratory) Aerodynamics Laboratory for cold testing. Smoke-laden air was passed through the sub-burner at minimum flow conditions (where any insert would be expected to have its least effect). The gas and air flowrate at minimum fire is 25 l/s, so this flowrate was used for smoke-laden air. A 30 deg.C insert shape was adopted as a 'core-buster' for each of the sub-burners, designed with four wings: the wing span of each is 5 MM less than the nominal bore of the venturi.Six core busters were produced by casting from aluminium and when inserted into the sub-burners which had demonstrated the worst stability problems, considerable improvement was effected, the flame stabilising behind the plane of the cone. It was also decided at this stage to produce the remaining 300 core-busters (plus spares) from refractory material.Ten trials at blast furnace gas rates of 5.87 and 8.01 m3/s were carried out, after the boilers were optimised, as follows:- Combustion air was reduced until ppm CO in stack began to rise and the blast furnace gas spade valves were individually operated until blast furnace pressures equalised. Total airflow was then trimmed using the main butterfly and excess air reduced by air louvres and fine trimming of the blast furnace gas was applied by slightly increasing the flow to each burner until ppm take-off point was reached in the stack in each case. Finally the main furnace gas flow was trimmed to give a stack ppm CO reading of +/- 250. All flames became stable and the refractory fronts of the burners came to a dull red heat. Combustion chamber pressures, air and blast furnace gas supply pressures were all completely stable, in sharp contrast to the instability which existed previously. The lower mass flow and temperature of the stack gases with the improved conditions relative to the initial situation results in a fuel saving of +/- 9%.The project has shown marked improvements in both flame stability and stack losses, the latter by +/- 6%.The level of blast furnace contamination at Port Talbot is such that accretion of residues in the burners occurs at a rate necessitating a major cleaning after 4000 hours operation. This accretion does not take place without the inserts, hence it is a penalty which must be balanced against benefits which accrue from using inserts.No serious problems should exist in efficiently combusting blast furnace gas of 2.6 MJ/m3 (STP) calorific value and %H2 < 1% in a boiler plant, providing the following conditions are met:- good housekeeping;- reasonably clean blast furnace gas;- air and blast furnace gas pressures for each large burner are equalised;- air to blast furnace gas mixing is enhanced by using a conical bluff body placed in each sub-burner;- the large burners are sub-divided (the extent to which the sub-burners of this project can be enlarged without combustion burners has not been investigated).The project began on 1st December 1984 with the commencement of the first phase which was the monitoring of the boiler plant in its initial level of performance. This phase was completed by 31st March 1985.The second phase comprised a literature survey on flame stability of low calorific value gas burners and selection of the optimum technique. This was followed by laboratory modelling work (in Welsh Laboratory - Aerodynamic Laboratory) using cold isothermal, smoketracer techniques on an appropriately sized perspex model. Finishing date was expected to be 31st May 1985.The third phase which began on 1st June 1985 consisted of the construction or modification of he low C.V. burners and the commissioning thereof. This phase finished on 31st August 1985.The fourth phase is the evaluation and monitoring of the performance of the new or modified burners. This phase began on 1st September 1985 and will be concluded by 31st August 1986.This period covered a period of even furtherdecline in the blast furnace gas calorific value. Reporting was included in this phase.Port Talbot Works experienced a steady fall in both calorific value and hydrogen content of blast furnace gas, as operation improved and tuyere oil injection was discontinued on the blast furnaces. It became evident in 1984 that the blast furnace gas, at 2.6 MJ/m3 (STP) with < 1%H2 content was a source of considerable combustion problems in the Service Boiler Plant, where it is combusted without enrichment.The major difficulty encountered was that of flame instability (lift-off) with explosive re-ignition, even occasionally to the point of flame extinguishing with consequent boiler shut-down and explosion risk. Prior to start of this project, these problems had been partially overcome by increasing excess air levels to improve air/blast furnace gas turbulance and the intimacy of mixing. The penalty for this mode of operation is a fall in overall boiler efficiency due to increased stack losses, and reduced steam output.Both boilers have three blast furnace gas burners: each burner has 50 sub-burners in a matrix, each of which is an air venturi with axial blast furnace gas injector. The nominal capacity of each burner is 20,000 m3 (STO/h) of blast furnace gas of 3.55 MJ/m3 (STP) calorific value, a hydrogen content of 3-4% and a blast furnace gas feed pressure of 375 mm WG.Conditions prevailing during 1984 and after are that the blast furnace gas rate is required to be maximised with respect to design conditions, despite a fall in calorific value to 2.6 MJ/m3 (STP), a fall in %H2 to below 1% and a blast furnace gas feed pressure of 450 mm WG.Analysis of the combustion of the lean blast furnace gas highlighted the basic instability which existed, even at excess air levels of 100% over stoichiometric, problems which became exacerbated when attempts to reduce excess air to 10% above stoichiometric were made. Programme(s) ENG-ENALT 2C - Programme (EEC) of demonstration projects relating to the exploitation of alternative energy sources and to energy saving and the substitution of hydrocarbons, 1983-1985 Topic(s) 3.2 - INDUSTRY Call for proposal Data not available Funding Scheme DEM - Demonstration contracts Coordinator British Steel plc EU contribution No data Address Moorgate S60 3AR Rotherham United Kingdom See on map Total cost No data
