COMBUSTOR MEANS OF A VAPOUR GENERATING AND VAPOUR SUPERHEATING UNIT AND A METHOD OF OPERATING SAME

Abstract: An arched furnace chamber (2) of a vapour generating and superheating unit is provided with ports (18, 18A) in the arch portions (14) and tertiary combustion air ports (20) in base portions of the walls (12). Pulverised fuel burners (22), directed to discharge downwardly toward a hopper bottom (24) are disposed, as groups, in ports (18) adjacent the side walls (4), with, in each port, the burners (22) flanked by secondary combustion air discharge nozzles (26). Secondary combustion air is ducted also to the centrally disposed ports (18A) for discharge through nozzles (26A). In operation, the burners (22) discharge pulverised fuel entrained in a sub-stoichiometric carrier air flow directed downwardly toward the hopper bottom (24) and biased toward the side walls (4) by the secondary combustion air flows from the centrally disposed nozzles (26A). The urging of the burning flow of pulverised fuel toward the water tube side walls (4) by the discharge through the nozzles (26A) of secondary combustion air at a temperature less than that of the combustion gases tends to limit the temperature attained in the burning flow of pulverised fuel, thereby limiting the production of oxides of nitrogen (NOx). Other configurations of the furnace chamber are envisaged.

Description: Combustor means of a vapour generating and vapour superheating unit and a method of operating same This invention relates to combustor means of a vapour generating and vapour superheating unit and, more particularly, to a vapour generating and vapour superheating unit having an upright, substantially rectangular cross-section, furnace chamber provided with at least one horizontal row of combustor means in one wall, or in two, opposed, walls. By the present invention, there is provided combustor means of a vapour generating and vapour superheating unit having an upright, substantially rectangular cross-section, furnace chamber provided with at least one horizontal row of combustor means in one wall, or in two, opposed, walls in which the or each horizontal row of combustor means includes a row of ports arranged as a centrally disposed group of ports and laterally disposed groups of ports disposed intermediate the side walls of the furnace chamber and the centrally disposed group with the ports of the centrally disposed group being provided solely with nozzle means for the supply of combustion air flows to the furnace chamber and the ports of the laterally disposed groups each being provided both with fuel nozzle means for the supply of fuel to the furnace chamber and with nozzle means for the supply of combustion air flows to the furnace chamber. The invention also includes a method of operating combustor means of a vapour generating and vapour superheating unit having an upright, substantially rectangular cross-section, furnace chamber provided with at least one horizontal row of combustor means in one wall, or in two, opposed, walls in which the or each horizontal row of combustor means includes a row of ports arranged as a centrally disposed group of ports and laterally disposed groups of ports disposed intermediate the side walls of the furnace chamber and the centrally disposed group and in which the whole of the fuel and associated primary combustion air flows to the furnace chamber is dischaged through the ports in the laterally disposed groups of ports and secondary combustion air flows to the furnace chamber are discharged through the ports in the centrally disposed group of ports and through the ports in the laterally disposed groups of ports. The invention will now be described, by way of example, with reference to the accompanying, partly diagrammatic drawing, of an arched furnace chamber portion 2 of a steam generating and superheating unit (not shown) having a form similar to that described in Japanese patent application published as JP-A2-1-200106. The chamber portion 2 is formed with water tube wall panels providing planar side walls 4 and stepped front and rear walls 6, 8 each including hopper bottom portions 10, upright main portions 12, arch portions 14 and upper portions 16. Ports 18, 18A and 20 are provided in the arch portions 14 and at the base of the upright main portions 12 by displacing the water tubes out of the plane of the associated panel. Pulverised fuel burners 22, directed to discharge downwardly toward a hopper bottom 24 are disposed, as groups, in ports 18 adjacent the side walls 4, with, in each port, the burners 22 flanked by secondary combustion air discharge nozzles 26. Secondary combustion air is ducted also to the centrally disposed ports 18A for discharge through nozzles 26A. Means (not shown) are provided to proportion, if required, the secondary combustion air flows discharged in a downward direction from nozzles 26A in the ports 18A in the arch portions 14 in relation to combustion air discharges through the ports 18 and 20 such as to bias the thermal input to the furnace chamber 2 toward the side walls 4. Tertiary combustion air flows discharged from nozzles 28, which may be adjustable in discharge direction, in the ports 20 in the base of the upright main wall portions 12 are proportioned to inject a sufficiency of air as to complete the combustion process of the pulverised fuel discharged into the furnace chamber 2 from the burners 22. It will be appreciated that the ports 18, 18A and 20 may be arranged in pluralities of groups and/or rows to facilitate control of combustion gas flow patterns or other parameters within the furnace chamber and that a small proportion of fuel may be discharged through the centrally disposed ports. In operation, the burners 22 are arranged to discharge pulverised fuel entrained in a sub-stoichiometric carrier air flow which, following ignition, burns in elongated paths directed downwardly toward the hopper bottom 24 and are biased toward the side walls 4 by secondary combustion air flows discharged from the centrally disposed nozzles 26A in the arch portions 14. Both the urging of the burning flow of pulverised fuel toward the water tube side walls 4 by the discharge through the centrally disposed nozzles 26A and the parallel discharges through the nozzles 26 of secondary combustion air at a temperature less than that of the combustion gases tend to limit the temperature attained in the burning flow of pulverised f el, thereby limiting the production of oxides of nitrogen (N0 χ ) as a result of thermal reactions in the carrier air. In addition, since the combustion of the pulverised fuel is largely completed in the downwardly directed path under sub-stoichiometric, or reducing, conditions prior to mixing the products of combustion with the secondary and tertiary combustion air flows respectively discharged from the nozzles 26 and 26A and from the nozzles 28, the formation of N0 χ as a result of reactions arising in conjunction with volatile nitrogenous compounds in the pulverised fuel is limited. In one arrangement, eighteen, equi-distantly spaced, ports are positioned in each arch portion 14 with a centrally disposed group of six ports 18A discharging secondary combustion air flows through nozzles 26A and two groups of six ports 18 laterally disposed to either side of the centrally disposed group discharging pulverised fuel, such as anthracite, entrained in primary combustion air flows through nozzles 22 together with secondary combustion air flows through the nozzles 26, all of the flows being directed downwardly toward the hopper bottom 24. Eighteen, equi-distantly spaced, ports 20 are positioned at the bases of the front and rear walls 12 for the discharge of tertiary combustion air flows though the nozzles 28 in each port 20. The flows of pulverised fuel entrained in primary combustion air are substantially equally divided between the twenty four nozzles 22 and the flows of secondary combustion air are substantially equally divided between all thirty six ports 18, 18A. The primary combustion air flows are approximately 13% of the total air flow, the secondary combustion air flows are in the range of approximately 48% to 54% of the total air flow and the tertiary combustion air flows are in the range of approximately 39% to 33% of the total air flow. The total air flow is such as to achieve an overall furnace chamber stoichiometry of 1.2. Optimum reductions in NO χ emission of around 40% compared with an arrangement in which discharges of pulverised fuel and primary combustion air flows are evenly distributed across the arch portions 14 is achieved with secondary combustion air flows of approximately 48% of the total air flow. It will be appreciated that the invention has application in other arrangements of furnace chambers involving firing through one wall or through an opposed pair of walls. In another embodiment of the invention, not shown, burners are positioned in ports in horizontal rows in vertically extending front and rear wall portions of a furnace chamber. The burners are positioned in ports adjacent side walls of the furnace chamber whilst centrally disposed ports are utilised for the supply of additional combustion air. Further combustion air may be supplied through a further horizontal row or further horizontal rows of ports. In operation, the burners are arranged to discharge pulverised fuel entrained in a sub-stoichiometric carrier air flow which, following ignition, burns in elongated paths biased toward the side walls by combustion air flows discharged through centrally disposed ports, thereby tending to avoid the creation of high temperature combustion gas flows centrally of the furnace chamber and thereby tending to avoid the formation of NO χ . It will further be appreciated that the invention is applicable to other forms of burner, such as cylindrical burners, to other burner configurations, such as a front wall fired furnace chamber having tertiary combustion air supplied at an upper level of the furnace chamber, and to other fuels, as well as to an arrangement in which the side walls are protected by means of air flows interposed between the side walls and the flows of fuel and combustion air discharged from the laterally disposed groups of ports.

Claims: Claims 1. Combustor means of a vapour generating and vapour superheating unit having an upright, substantially rectangular cross-section, furnace chamber (2) provided with at least one horizontal row of combustor means in one wall (12) , or in two, opposed, walls, characterised in that the or each horizontal row of combustor means includes a row of ports (18, 18A) arranged as a centrally disposed group of ports (18A) and laterally disposed groups of ports (18) disposed intermediate the side walls of the furnace chamber and the centrally disposed group with the ports (18A) of the centrally disposed group being provided solely with nozzle means (26A) for the supply of combustion air flows to the furnace chamber and the ports (18) of the laterally disposed groups each being provided both with fuel nozzle means (22) for the supply of fuel to the furnace chamber and with nozzle means (26) for the supply of combustion air flows to the furnace chamber (2) . 2. Combustor means as claimed in Claim 1, characterised in that in the or each wall (12) of the furnace chamber (2) provided with combustor means there is additionally provided a horizontally extending row of ports (20) for the discharge of tertiary combustion air to the furnace chamber (2) . 3. Combustor means as claimed in Claim 1 or Claim 2, characterised in that the ports (18, 18A, 20) are equidistantly spaced in the or each horizontally extending row. 4. Combustor means as claimed in any preceding Claim, characterised in that fuel supply to the furnace chamber is arranged to be divided substantially equally between the fuel nozzle means (22) of the ports (18) of the laterally disposed groups. 5. Combustor means as claimed in any preceding Claim, characterised in that flows of primary combustion air associated with the fuel supply to the furnace chamber (2) are arranged to be divided substantially equally between the fuel nozzle means (22) of the ports (18) of the laterally disposed groups. 6. Combustor means as claimed in any preceding Claim, characterised in that flows of secondary combustion air to the furnace chamber (2) are arranged to be divided substantially equally between the nozzle means (26A) of the ports (18A) of the centrally disposed group of ports and the nozzle means (26) of the laterally disposed groups of ports (18) . 7. A method of operating combustor means of a vapour generating and vapour superheating unit having an upright, substantially rectangular cross-section, furnace chamber (2) provided with at least one horizontal row of combustor means in one wall (12) , or in two, opposed, walls, characterised in that the or each horizontal row of combustor means includes a row of ports (18A) arranged as a centrally disposed group of ports and laterally disposed groups of ports (18) disposed intermediate the side walls of the furnace chamber and the centrally disposed group in which the whole of the fuel and associated primary combustion air flows to the furnace chamber (2) is discharged through the ports in the laterally disposed groups of ports (18) and secondary combustion air flows to the furnace chamber are discharged through the ports (18A) in the centrally disposed group of ports and through the ports (18) in the laterally disposed groups of ports. 8. A method of operating combustor means as claimed in Claim 7, characterised in that tertiary air flows to the furnace chamber are discharged through a horizontally extending row of ports (20) positioned adjacent a base portion of the or each wall provided with combustor means. 9. A method of operating combustor means as claimed in Claim 7 or Claim 8, characterised in that the flows of fuel and associated primary combustion air are divided substantially equally between the ports (22) of the laterally disposed groups of ports. 10. A method of operating combustor means as claimed in Claim 7, Claim 8 or Claim 9, characterised in that the flows of secondary combustion air to the furnace chamber are divided substantially equally between each of the ports (18, 18A) in the horizontally extending row.

Inventors: DOWNER BARRY MICHAEL, PANESAR RAGHBIR, DOWNER, BARRY, MICHAEL, PANESAR, RAGHBIR
Applicants: MITSUI BABCOCK ENERGY LIMITED
Application year: 1997
Main classification: F22B21
IPC codes: F22B21, F22B31, F23C5