RU2088848C1 - Method and system for burning solid pulverized fuel - Google Patents

Abstract

FIELD: power engineering; pulverized fuel combustion. SUBSTANCE: basic component in solid pulverized fuel combustion process is dust fluidizing unit 1 affording subsequent transfer of fuel over process channel with minimal content of air-carrier in it. Fluidized stream of fuel 4 goes to dust heating unit 5 wherein it comes in contact with high-temperature gaseous coolant 6. Then heated gas-dust mixture 10 arrives at gasification unit 11. Upon gasification, modified fuel 12 is passed to burner 13 to be burned together with hot air 14. EFFECT: improved efficiency of fuel combustion. 3 cl, 2 dwg

Description

 The invention relates to a furnace technique and can be used in coal dust combustion systems.

Known methods of burning solid pulverized fuel, including the operation of heat treatment (preheating) of coal dust by the combustion products of auxiliary fuel up to 600 800 ^o C followed by mixing it with hot air at the outlet of the burner into the combustion chamber.

 This operation is an effective means of converting bound fuel nitrogen to molecular nitrogen and, accordingly, reducing nitrogen oxide emissions while improving the most important technical and economic indicators of the boiler, such as expanding the range of its stable operation, reducing mechanical underburning, increasing the stability of the work with instability of fuel quality.

 Methods of burning solid pulverized fuel with its preliminary heat treatment (Preparation and burning of fuel in the furnaces of powerful steam boilers: Cb. Articles / proceedings of VTI, M. 1989).

 One of them is a method of burning solid crushed fuel (ed. St. USSR N 1198315, F 23 C 11/00 1984), providing for the heat treatment of fuel and burning it together with air in a fluidized bed.

 The main condition for the efficiency of gasification of solid pulverized fuel (coal dust) in reducing emissions of nitrogen oxides during the heat treatment is the absence or minimum oxygen content in the heat treatment zone.

 This provides two ways: either by transporting fuel to the heat treatment zone with flue gases taken from the furnace or behind the boiler, or using air as a conveying medium, while part of the air is removed from the mixture of fuel, air and flue gases in the heating zone to limit oxygen concentration in this zone.

 The prototype of the invention and the basic option for comparison is the Federal Republic of Germany patent N 3537388. A method and apparatus for reducing the formation of nitrogen oxides during the combustion of pulverized fuels.

In this method, air is used as a transporting medium for pulverulent solid fuel, while air is removed from the heating zone until the oxygen concentration in it is limited to 8%
The disadvantage of this method is the complexity of its implementation.

A simpler and more reliable method of burning pulverized solid fuel with a reduced yield of nitrogen oxides is proposed, comprising preheating the dust with combustion products of auxiliary fuel to 600-800 ^o C and subsequent burning of a high concentration fuel-air mixture with a ratio of conveying air and pulverized solid fuel by weight 1 : (30-50), characterized in that the pulverized solid fuel (coal dust) in the heat treatment zone is served in a fluidized state.

 A schematically proposed pulverized solid fuel combustion technology is shown in FIG. one.

 The starting element is a pulverized solid fuel fluidization unit 1, to which dust 2 and compressed air 3 are supplied. Using the fluidization unit, the fuel is subsequently moved along the process path with a minimum content of carrier air.

 The fluidized stream of fuel 4 enters the dust heating unit 5, where it is contacted with a gas high-temperature coolant 6, which is formed in block 7 by burning a mixture of auxiliary fuel 8 and the required amount of air 9.

 From the dust heating unit 5, the heated dust-gas mixture 10 enters the gasification unit 11. After the gasification process is completed, the modified fuel 12 (semi-coke dust and gaseous gasification products mixed with the gas coolant) enters the burner 13 for combustion mixed with hot 14.

 The fuel-air mixture 15 ignites at the cut of the burner, and the combustion process develops in the combustion chamber 16 of the boiler.

 The proposed method of burning pulverized solid fuel in comparison with the prototype (basic version) provides an oxygen concentration in the heat treatment zone from 0-1.5% in the initial section of the zone to 0 in the output section (excess air in the auxiliary burner to obtain a coolant α 1.0) . Thus, the main part of the gasification process develops when the oxygen content in the gas mixture in contact with gasified dust is almost close to zero.

 Compared with the prototype, which involves the introduction of pulverized solid fuel into the heating and gasification zone in the form of a dust suspension, its transition to a fluidized state makes it possible to simplify the design of the dust heat treatment unit, since the nodes necessary for the separation of the dust from the system, which carry out the process of separating the gaseous medium from the zone, are excluded heat treatment of excess air.

 To implement the considered method of burning pulverized solid fuel with a reduced yield of nitrogen oxides, a system is proposed which is a burner with an integrated dust heating and gasification unit.

 A solid pulverized fuel combustion system comprises a device for feeding and burning a fuel-air mixture to produce a heat carrier gas, a device for supplying a pulverized fuel, a device for mixing, heating and gasifying fuel particles and a channel for supplying heat-treated dust together with gasification products and a heat carrier gas in firebox.

 This system differs from the prototype (system according to the FRG patent N 3537388) in that it is equipped with a device for aeration (fluidization) of the dust stream at the entrance to the heat treatment zone.

 In addition, in it, the device for burning auxiliary fuel-air mixture is made in the form of an isolated annular cavity located concentrically to the dust supply pipe forming the inner annular wall of the combustion chamber and connected to the working channel, narrowed by a conical pipe.

 In FIG. 2 shows a longitudinal section through a system that includes a burner body 1 with an adjacent hot air supply pipe 2, a central working channel 3, an auxiliary fuel combustion chamber 4 connected thereto with an air blade swirl 5 and an air supply pipe 6 for supplying the air necessary for combustion auxiliary fuel (gas), auxiliary burner 7 with a gas supply pipe 8. The burner housing 1 is adjacent to the furnace 9.

 The auxiliary burner 7 is installed concentrically with the pipe 10 located along the axis of the burner body 1.

 For aeration of the dust stream and giving it the properties of a fluidized medium, an aeration device 11 is provided, for example, of the jet type, to which the nozzle 12 for supplying the dust-air mixture adjoins and into which aeration air is supplied through the nozzle 13.

 The combustion chamber 4 is connected with the Central working channel 3 of the burner narrowed conical pipe 14.

 During the operation of the system, the mixture of auxiliary fuel (gas) coming from the nozzle 8 and the air coming from the nozzle 6 (in the ratio corresponding to the stoichiometric composition of the mixture, i.e., a 1.0) burns out mainly within the chamber 4. In the afterburning of the mixture in the central working channel 3, air from the fluidized central pulverized coal stream entering the burner through the pipe 10 takes part.

 In the main section of the central working channel 3, where coal dust is gasified, the oxygen content is close to zero.

 As a result of high-speed heating of coal particles by the combustion products of auxiliary fuel, thermal decomposition of nitrogen-containing compounds is carried out with the formation of molecular nitrogen. At the same time, the process of pyrolysis of coal.

The length of the central working channel 3 is selected from the conditions for ensuring the heating and completion of the conversion of nitrogen compounds of fuel to the furnace: the speed in the working channel 3 is maintained at 20-25 m / s, which eliminates the deposition of dust in it and the separation of semi-coke dust from the torch in the furnace . The temperature at the outlet of the channel 600-800 ^o C.

 Thus, the proposed solid pulverized fuel combustion system differs from the prototype (basic version) by the presence of a central nozzle 10 with an integrated aeration device 11 for introducing a fluidized dust stream, with an auxiliary fuel combustion chamber 4 concentrically located and isolated from this stream.

 The implementation of the burner with the spatial separation of the channel for introducing fluidized dust into the heating zone, the bias chamber and the combustion of auxiliary fuel and the corresponding amount of air, and the bias chamber of the gas coolant with coal dust makes it possible to practically exclude oxygen from the gasification zone of pulverized coal particles, which contributes to the most complete conversion of the bound nitrogen of the fuel into molecular nitrogen.

Claims (3)

 1. A method of burning a pulverized solid crowd with a reduced yield of nitrogen oxides, comprising pre-heating the dust with combustion products of auxiliary fuel and subsequent burning of the high-concentration crowd-air mixture, characterized in that the pulverized solid crowd is fed to the heat treatment zone in a fluidized state.  2. A system for burning pulverized solid fuel with a reduced yield of nitrogen oxides, comprising a device for supplying pulverized fuel, a device for supplying and burning a fuel-air mixture to produce a heat carrier gas, a device for mixing, heating and gasifying fuel particles and a channel for supplying heat-treated dust together with gasification products and heat carrier gas into the furnace, characterized in that at the entrance to the heat treatment zone it is equipped with a device for dust aeration.  3. The system according to claim 2, characterized in that the device for burning the air-fuel mixture is made in the form of an isolated annular cavity located concentrically to the dust supply pipe forming the inner annular wall of the combustion chamber and connected to the working channel by a tapered conical pipe.

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