FR2551184A1 - METHOD FOR INJECTING A PULVERULENT MATERIAL IN A BOILER FIREPLACE, AND DEVICE FOR CARRYING OUT SAID METHOD - Google Patents

Abstract

1. A method of injecting a powder material into the hearth of a solid fossil fuel boiler, wherein the powder material is put into suspension in a gas, and is then inserted (1) into the hearth, the method being characterized in that the powder material is put into suspension in a small flow rate of gas which is injected into the hearth at low speed, and in that an auxiliary flow of hot air or hot gas is inserted (4) into the hearth around the suspension gas or slightly below it at a rate of at least 1 kg per kg of material in suspension in said gas, and at a speed on inlet into the hearth lying between 30 meters per second (m/s) and 70 m/s.

Description

-1 Process for injecting a powdery material into a firebox

  The present invention relates to a method of injecting a powder material into a fossil fuel fired boiler furnace, wherein the powder material is suspended in a gas, then introduced into the home It also extends to a

  device for implementing this method.

  A paper by AL Plumley, O D. Whiddon, FW Shutko and J Jonakin, presented at the American Power Conference, Chicago, 1967, has been proposed to suspend dolomite in air in Jecté. the upper row of burners of a pulverized coal furnace furnace, in order to reduce the quantities of sulfurous and sulfuric anhydrides formed in the furnace, by reaction with them resulting in the formation of magnesium sulphate, and consequently reducing However, if the sulfur trioxide appeared to be completely eliminated in the fumes, the percentage of elimination of the anhydride

sulfurous was weak.

  Other publications, notably that of K Hein and A Schiffers, Brennst-Warm-Kraft, 31, 1979 No. 10, pp. 389-391, have proposed

  Mixing additives such as slaked lime, calcium carbonate or quicklime with lignite prior to milling and powdering into a boiler furnace to reduce emissions of sulfur dioxide and sulfuric acid at the chimney of the boiler.

  The object of the present invention is to provide a method of injecting a powder material into a boiler furnace which ensures a better contact between the grains of pulverulent material and the combustion gases, and consequently improves the efficiency of the injection of pulverulent material, and in particular the percentage reduction of sulfur dioxide and sulfuric anhydride contents in the fumes at the outlet of the boiler in the case where the pulverulent material is an oxide or a salt of an alkaline earth or alkaline metal capable of It is also intended to allow the injection of large quantities of pulverulent material and to ensure a good dispersion of it in the hearth without disturbing it.

  noticeably the operation of the boiler.

  The process according to the invention is characterized in that the pulverulent material is suspended in a low gas flow, which is introduced into the furnace at low speed, and in that in the hearth around the gas suspending or a little below it a much higher flow of hot air or

  auxiliary hot gas at higher speed.

  It also preferably meets at least one of the following characteristics. The suspending gas of the powder material is cold air. The gas loaded with pulverulent material is injected

points on the edge of the hearth.

  The velocity of the suspending gas at its outlet in the furnace is low and lower than that of the hot air or auxiliary hot gas. The flow of hot air or hot gas introduced into the fireplace

  around or a little below the suspending gas is at least 1 kg per kg of pulverulent material.

  The velocity of hot air or auxiliary hot gas introduced into the firebox around or a little below the suspending gas

  is included at its outlet in the home between 30 and 70 m / s.

  The hot air introduced into the hearth around or slightly below the suspending gas is taken from the furnace feed.

combustion air.

  The powder-laden gas is injected into the firebox at a level where the maximum flue gas temperature is between 1000

and 1500 C.

  The injection points in the hearth are chosen so that the residence time of the powder material in the hearth between its injection level and the level where the flue gas temperature is reduced to 8000 C

  is sufficient for the powder material to react chemically.

  The invention further extends to a pulverulent material injection device in a fossil fuel fired boiler furnace, characterized in that it comprises at least one injection nozzle in the furnace of pulverulent material. suspension in a low gas flow, and at least one injection nozzle with a higher flow of hot air or hot gas around or a little below the injection nozzle 5 of the carrier gas of the powder material at a higher rate than this carrier gas. The invention applies to boilers with solid fossil fuel, coal or lignite, whether they are introduced into the boiler in the pulverized state, in the granular state, on a grid or possibly using spotlights. , or are suspended therein

fluid bed.

  The powdery material may be an alkaline earth or alkaline oxide, or an alkaline earth or alkaline metal salt, for example quicklime, limestone, magnesia or dolomite, its effect then being react on sulfur dioxide and sulfuric anhydride

  formed during the combustion of the solid fuel by forming a solid sulphate, and thereby reducing the content of the fumes in these anhydrides But it may also be a material intended to modify the fusibility of the ashes, or more generally to influence the chemical reactions occurring in the focus.

  It is described hereinafter, by way of example and with reference to the figures of the accompanying drawing, a device for injecting quicklime in a

  pulverized coal boiler fireplace.

  FIG. 1 shows in vertical section a lime-laden cold air injection nozzle surrounded by an annular injection nozzle.

hot air.

  FIG. 2 schematically represents in vertical section the

  injection levels of lime-laden cold air, warm air holding slurry of lime and combustion air in the furnace hearth.

  FIG. 3 represents in horizontal section a provision

  cold air injection nozzles loaded with lime into the boiler.

  In FIG. 1, the lime-laden cold air in a metering device (not shown) arrives through the nozzle 1 which opens into the wall 2 of the firebox 3. This air could be replaced by hot air or

by recycled fumes.

  The nozzle 1 is surrounded by the annular nozzle 4 of hot air, at a temperature of 250 to 320 C, taken from the combustion air circuit, the flow rate of which is adjustable by the flap 5 The annular air duct The hot air surrounding the vein of lime-laden cold air ensures a distribution of lime throughout the straight section of the hearth, and in particular prevents the grains of lime from moving towards the bottom of the hearth along its wall. In FIG. 2, the level 11 of the lime injectors in the cold air corresponds to a maximum flue gas temperature of 1350 C. The height H separating this level from that of the superheaters 6, where the maximum flue gas temperature is about 800 ° C., is such that the residence time of the lime particles in the boiler between these two levels is about 2 seconds, which allows them to react to a large extent with sulfur dioxide and sulfuric anhydride, without however being brought to a temperature too high which would cause their fusion

  superficial and a decrease in their reactivity.

  The warm air holding lime enters the pipe at level 15, a little below the level of lime injection.

  Finally the pulverized coal burners are arranged at levels 12, 13

  and 14, noticeably below the lime and hot air injectors.

  Figure 3 shows the arrangement of lime injectors 11A, 11B, 11C, 11D in horizontal cross section, in the corners of the focus. Other arrangements would however be possible The injectors could be arranged on two opposite sides of the hearth (for example face

  front and rear) in the case of a firebox.

Claims (8)

  1 / A method of injecting a powdery material into a fossil fuel fired boiler furnace, in which the pulverulent material is suspended in a gas and then introduced into the furnace, characterized in that the suspension is carried out in a low gas flow, which is introduced (1) into the firebox at low speed, and that is introduced (4) into the hearth around the gas suspension or a little below this one a much higher flow   hot air or auxiliary hot gas at higher speed.   2 / A method according to claim 1, characterized in that the gas   in suspension of the powder material is cold air.   3 / A method according to claims 1 or 2, characterized in that one injects the charged gas of powder material at several points on the   around the hearth (11 A, 11 B, 11 C, 11 D, Figure 3).   4 / A method according to one of claims 1 to 3, characterized in that the   The velocity of the suspending gas at its outlet in the furnace is low and lower than that of the hot air or auxiliary hot gas.   / Method according to one of claims 1 to 4, characterized in that the flow of hot air or hot gas introduced into the hearth around or slightly below the suspending gas is at least 1 kg per kg of   suspended material in the latter gas.   6 / A method according to one of claims 1 to 5, characterized in that the speed of the hot air or hot gas introduced into the hearth around or slightly below the suspension gas is included in its   outlet in the home between 30 and 70 m / s.   7 / A method according to one of claims 1 to 6, characterized in that the hot air introduced into the hearth around or a little below the suspending gas is taken from the furnace feed air from combustion.   8 / Method according to one of claims 1 to 7, characterized in that the   The powder-laden gas is injected into the firebox at a level where the maximum flue gas temperature is between 1000 and 1500 ° C.   9 / A method according to one of claims 1 to 8, characterized in that the injection points in the focus are chosen so that the residence time of the powder material in the home between its injection level 2551 1? 6.   and the level where the flue gas temperature is reduced to 8000 C is   sufficient for the powder material to react chemically.   A device for injecting a powder material into a furnace (3) of a fossil fuel-fired boiler, characterized in that it comprises a nozzle (1) for injecting into the furnace of pulverulent material suspended in a low flow rate of gas, and at least one nozzle (4) for injecting hot air or hot gas around or slightly below the nozzle for injecting the carrier gas of the powder material, in a more   higher than that of this carrier gas.