CN101721904A - Composite denitration method by biomass direct reburning and selective non-catalytic reduction - Google Patents

Abstract

The invention belongs to the technical field of low _NOx combustion and flue gas denitrification of pulverized coal furnaces. The technical scheme of the present invention is: pulverized coal enters the main combustion zone through the burner of the pulverized coal furnace to form flue gas containing _NOx , and mixes biomass particles with primary air and recirculated flue gas and sprays them into the reburning reduction zone, so that the main combustion Part of the NO _x formed in the zone reacts to generate N ₂ , which is sprayed into the overfired air from the upper part of the reburning reduction zone, and the mixed gas of circulating flue gas and compressed air is used as the atomizing medium of the mixed solution of amino reducing agent and additives, through the furnace and The nozzles in the horizontal flue atomize and spray the mixed solution of amino reducing agent and additives into the burnout area and the downstream horizontal flue, so that NO _x in the flue gas reacts to form N ₂ . The method improves the denitrification efficiency, improves the utilization rate of biomass and amino reducing agent, and reduces the generation and discharge of secondary pollutants.

Description

Biomass direct reburning and selective non-catalytic reduction composite denitrification method

technical field

The invention relates to biomass reburning denitrification and selective non-catalytic denitrification processes, and belongs to the technical field of low NOx combustion and flue gas denitrification of pulverized coal furnaces.

Background technique

Nitrogen oxides emitted by pulverized coal boilers are one of the main substances that cause air pollution. The denitrification efficiency of existing low NOx burner technology, air staged combustion technology, pulverized coal reburning technology and other low NOx combustion technologies is generally lower than 50%. . In reburning and denitrification technology, the reburning of ultra-fine pulverized coal has strict requirements on the coal type and preparation of ultra-fine pulverized coal. The operating cost of natural gas reburning is relatively high. The biomass reburning and denitrification technology depends on the scope and transportation of biomass fuel supply and affects its economy. sex and efficiency. Selective non-catalytic denitrification (SNCR) is restricted due to the narrow reaction temperature window and the emission of secondary pollutants such as ammonia escape. When the temperature is higher than 1100 ° C, the amino reducing agent is easily oxidized to generate NOx. When the temperature is lower than 900 ° C The reduction of the reaction rate between the amino reducing agent and NOx is likely to cause ammonia escape, so the space corresponding to the upper part of the furnace and the horizontal flue at 900 ° C to 1100 ° C is limited, and the mixing process of the amino reducing agent and flue gas takes a long time. This limits the efficiency of the SNCR denitrification reaction. Under the experimental conditions of good mixing and suitable temperature, the denitrification efficiency of SNCR reaches 80% to 90%, while the denitrification efficiency of SNCR technology engineering application is generally 30% to 50%. The invention patent with the authorized announcement number CN101244361A discloses "A Method for Promoting Selective Non-catalytic Reduction of Nitrogen Oxide", which proposes to use ultra-fine coal powder, natural gas or synthesis gas as SNCR additives to improve the denitrification efficiency of SNCR reaction at low temperature . The invention patent of authorized notification number CN101433799A discloses "Selective Non-catalytic Reduction Method of Biomass Gasification Gas Atomization and Boiler Used", which uses biomass gasification gas as an additive and mixes it with air as the physical and chemical medium of the amino reducing agent solution. The above two methods reduce the denitrification reaction temperature window to varying degrees, but it is difficult to guarantee the burnout of ultra-fine coal powder at the SNCR reaction temperature level, and the process of adding natural gas, syngas or biomass gasification gas is relatively complicated, and the above It is difficult to reduce the amount of ammonia escape to a lower level, generally between 5ppm and 15ppm.

Contents of the invention

The purpose of the present invention is to provide a composite denitrification method of direct reburning of biomass and selective non-catalytic reduction. Ammonia escape and other issues.

Biomass direct reburning and selective non-catalytic reduction compound denitrification method, pulverized coal enters the main combustion zone at the bottom of the pulverized coal furnace through the burner of the pulverized coal furnace to form flue gas containing NO _x , and the mixture of primary air and recycled tail flue gas will Biomass particles are sprayed into the middle of the furnace to form a reburning reduction zone, and part of the NO _x produced in the main combustion zone is reduced to N ₂ ; the burnout zone is formed by injecting overburning air from the upper part of the reburning reduction zone, which is characterized in that: the use of circulating flue gas Mixed gas with compressed air is used as the atomization medium of the mixed solution of amino reducing agent and additive, and the mixed solution of amino reducing agent and additive is atomized and sprayed into the burnout area and the downstream horizontal flue through the nozzle, so that NO _x in the flue gas reacts to form N ₂ .

In the technical solution of the present invention, the excess air ratio in the main combustion zone is 0.8-1.0, the excess air ratio in the reburning reduction zone is 0.8-0.9, and the excess air ratio in the burnout zone is 1.15-1.2. The calorific value of coal input in the main combustion zone accounts for 80% to 90% of the total input heat of boiler fuel, and the calorific value of biomass input in the reburning zone accounts for 10% to 20%. The temperature of the biomass injection into the reburning reduction zone is 1100°C-1400°C, and the temperature of the overburning air injection inlet is 1100°C-1200°C. The mixed solution of amino reducing agent and additive is atomized and sprayed into the burnout zone and the downstream horizontal flue through multiple nozzle devices. The temperature range of the burnout zone and the downstream horizontal flue is 800°C to 1100°C. The molar ratio of NH _i in the reducing agent to NO _x in the flue gas indicates that the molar ratio is 1.0-2.0. The additive is a mixture of sodium salt and ethanol with a molar ratio of 1, and the molar ratio of the injected sodium salt, ethanol and NO _x in the flue gas is 1/20-1/3. Sodium salt is one of sodium carbonate, sodium formate and sodium acetate.

The combined denitrification method of biomass direct reburning and selective non-catalytic reduction has the following advantages:

The mixed gas of recirculated flue gas and air is used as the atomizing medium of the mixed solution of amino reducing agent and additives, which is beneficial to avoid the reduction of denitrification efficiency due to the high oxygen concentration in the selective non-catalytic reduction reaction area, and at the same time, it can enhance the rigidity of the atomizing jet. Strengthen the mixing of amino reducing agents, additives and flue gas to ensure the reduction reaction between amino reducing agents and NO _x and reduce the possibility of ammonia escape; alkaline substances in biomass ash and added sodium salts can widen the temperature window of SNCR and promote Reaction of amino reducing agent with NO _x , and can inhibit ammonia slip, generation and emission of CO and N ₂ O secondary pollutants. As an additive, ethanol can widen the temperature window of SNCR towards low temperature; solve the defects of low denitrification efficiency of reburning denitrification and selective non-catalytic reduction technologies, and the denitrification efficiency can reach more than 80%. The sodium salt and ethanol additives used are cheap and easy to obtain, and are easily dissolved in the amino reducing agent solution, and the addition method is simple and convenient for implementation.

Description of drawings

Fig. 1 is the schematic flow chart of biomass direct reburning and selective non-catalytic reduction composite denitrification method of the present invention;

Among them, 1 is the mixed solution of amino reducing agent and additives, 2 is compressed air, 3 is pressurized recirculation flue gas, 4 is gas mixing device, 5 is atomizing medium, 6 is the main burner, 7 is primary air mixed coal powder, 8 is the reburning burner, 9 is the primary air and recirculated flue gas mixed biomass fuel, 10 is the overburning air nozzle, 11 is the overburning air, 12 is the main combustion area, 13 is the reburning reduction area, and 14 is the combustion air 15 is an atomizing nozzle, 16 is a front panel superheater, 17 is a rear panel superheater, 18 is a reheater, 19 is a low-temperature superheater, and 20 is a horizontal flue.

Figure 2 is a simulation curve of the influence of sodium carbonate and ethanol on the selective non-catalytic denitrification of ammonia.

Figure 3 is a simulation curve of the influence of sodium carbonate and ethanol on the selective non-catalytic denitrification of urea.

Fig. 4 is a curve showing the influence of different additions of sodium carbonate and ethanol on the formation of CO in the selective non-catalytic denitrification process of ammonia and urea.

Fig. 5 is a curve showing the effect of sodium carbonate on N ₂ O generation in the selective non-catalytic denitrification of urea.

Detailed ways

The present invention is described below in conjunction with accompanying drawing:

Fig. 1 is technological process of the present invention, and concrete steps are:

A. The primary air mixed with pulverized coal 7 enters the main combustion zone 12 at the bottom of the furnace through the main burner 6 to form flue gas containing _NOx .

B. The biomass fuel 9 mixed with primary air and recirculated flue gas enters the furnace through the reburning burner 8 to form a reburning reduction zone 13 . Under the condition of low stoichiometric ratio in the reburning reduction zone 13 _, the biomass particles precipitate gas-phase hydrocarbon groups, amino groups and other active groups, and react with the NO _x formed in the main combustion zone 12 to form N ₂ . Heterogeneous reduction reaction occurs in zone 13 to reduce NO _x produced in main combustion zone 12 into N ₂ .

C. Inject the overburning air 11 from the overburning air nozzle 10 on the upper part of the reburning reduction zone 13 to form a burnout zone 14 to completely burn the incompletely burned combustibles.

D. Compressed air 2 and pressurized recirculated flue gas 3 enter the gas mixing device 4 to form an atomizing medium 5 . The atomizing medium 5 flows through a plurality of atomizing nozzles 15 to atomize and spray the mixed solution 1 of the amino reducing agent and the additive into the burnout zone 14 and the horizontal flue 20 . The atomizing nozzle 15 is arranged in the burnout zone 14 and the area between the front panel superheater 16 , the rear panel superheater 17 , the reheater 18 and the low temperature superheater 19 .

The excess air ratio in the main combustion zone in step A is 0.8-2.0, and the pulverized coal accounts for 80%-90% of the total fuel input heat of the furnace.

The ratio of the recirculation flue gas in the mixed biomass fuel 9 of the primary air and the recirculation flue gas to the mixed gas in step B is 30%-100%. The reburning ratio, that is, the biomass fuel accounts for 10% to 20% of the total fuel input heat of the furnace. The excess air ratio in the reburning reduction zone 13 is 0.8-0.9. The mixture of primary air and recirculated flue gas injects biomass into the reburning reduction zone 13, which is beneficial to ensure the low stoichiometric ratio conditions required for reburning and strengthen the rigidity of the biomass fuel jet and the mixing with flue gas.

The excess air ratio in the burnout zone 14 described in step C is 1.15-1.2.

In step D, the atomizing nozzles 15 arranged in the burnout zone 14 and the horizontal flue 20 correspond to the flue gas temperature range of 800° C. to 1100° C. in the furnace. The total amount of amino reducing agent solution injected is represented by the molar ratio of NH _i produced by the reducing agent to _NOx in the flue gas of the burnout zone 14 before the reducing agent is injected, and the molar ratio of NH _i to _NOx in the flue gas is 1.0- 2.0. The amino reducing agent solution is one of ammonia water, urea solution and ammonium bicarbonate solution. The additive is a mixture of sodium salt and ethanol with a molar ratio of 1, and the molar ratio of the injected sodium salt and ethanol to _NOx in the flue gas is 1/20-1/3. Sodium salt is one of sodium carbonate, sodium formate and sodium acetate. The proportion of recirculated flue gas in the atomizing medium 5 to the atomizing medium is 30%-100%, which is beneficial to ensure the rigidity of the atomizing jet of the mixed solution 1 of the amino reducing agent and the additive and the mixing of the flue gas.

Figure 2 is the influence curve of sodium carbonate and ethanol on selective non-catalytic denitrification of ammonia. The experimental conditions are: the initial _NOx concentration of flue gas is 600ppm, the oxygen concentration is 3%, the molar ratio of ammonia nitrogen is 1.5, and the molar ratio of sodium carbonate, ethanol and _NOx is 1/3. Sodium carbonate and ethanol can widen the temperature window from 50°C to 100°C toward the low temperature, and 20°C toward the high temperature, and sodium carbonate can increase the denitrification efficiency at each reaction temperature.

Figure 3 is a simulation curve of the influence of sodium carbonate and ethanol on the selective non-catalytic denitrification of urea. The experimental conditions are: the initial _NOx concentration of flue gas is 600ppm, the oxygen concentration is 3%, the molar ratio of ammonia nitrogen is 1.5, and the molar ratio of sodium carbonate, ethanol and _NOx is 1/3. Sodium carbonate and ethanol can widen the temperature window to about 50°C toward the low temperature, and sodium carbonate can increase the denitrification efficiency in the temperature window.

Fig. 4 is a curve showing the influence of different additions of sodium carbonate and ethanol on the formation of CO in the selective non-catalytic denitrification process of ammonia and urea. The experimental conditions are: the initial _NOx concentration of flue gas is 600ppm, the oxygen concentration is 3%, the ammonia nitrogen molar ratio is 1.5, and the reaction temperature is 1223K. With the increase of sodium carbonate addition, the CO emission decreased, while with the increase of ethanol addition, the CO emission increased.

Fig. 5 is a curve showing the effect of sodium carbonate on N ₂ O generation in the selective non-catalytic denitrification of urea. The experimental conditions are: the initial _NOx concentration of flue gas is 500ppm, the oxygen concentration is 3.9%, the amino reducing agent is urea, the molar ratio of ammonia to nitrogen is 1.5, the additive is sodium carbonate, and the molar ratio of sodium carbonate to _NOx is 6%. Both experiments and simulations show that sodium carbonate can significantly reduce the amount of N ₂ O produced.

By adjusting the biomass reburning ratio, the molar ratio of NH _i to _NOx in flue gas, and the molar ratio of additive to _NOx in flue gas, the denitrification efficiency of the method can reach 80%-92%. Ammonia slip is reduced to below 5ppm, and there is no obvious generation and emission of CO and N ₂ O.

Claims (7)

1. directly combustion and SNCR composite denitration method again of living beings, coal dust enters the formation of coal-powder boiler burner hearth bottom primary zone by the coal-powder boiler burner and contains NO _xFlue gas, the mixing biomass particle of the tail flue gas of wind and recirculation spray into the burner hearth middle part, form and fire the reducing zone again, the part NO that the primary zone is produced _xBe reduced into N ₂Spray into after-flame wind formation burning-out zone from firing top, reducing zone again, it is characterized in that, adopt circulating flue gas and fuel-air mixture compression as atomizing medium, with sodium salt and alcohol mixture as additive, by nozzle amino reductive and the atomizing of additive mixed solution are sprayed in after-flame zone and the downstream horizontal flue, make NO in the flue gas _xReaction forms N ₂

2. living beings according to claim 1 are combustion and SNCR composite denitration method more directly, it is characterized in that the primary zone excess air coefficient is 0.8～1.0, fires reducing zone excess air coefficient 0.8～0.9 again; Burning-out zone excess air coefficient 1.15～1.2.

3. according to claim 1 and the directly combustion and SNCR composite denitration method again of 2 described living beings, it is characterized in that coal-powder boiler burner hearth primary zone drops into the caloric value of coal and account for boiler oil and always import 80%～90% of heat, the caloric value that living beings are dropped in the reburning zone accounts for 10%～20%.

4. according to the directly combustion and SNCR composite denitration method again of claim 1,2 and 3 described living beings, it is characterized in that living beings spray into that to fire the reducing zone temperature again be 1100 ℃～1400 ℃, 1100 ℃～1200 ℃ of after-flame wind entrance temperature.

5. living beings according to claim 1 are combustion and SNCR composite denitration method more directly, it is characterized in that amino reductive and additive mixed solution spray into burning-out zone and downstream horizontal flue through the atomizing of a plurality of positions, 800 ℃～1100 ℃ of the temperature ranges of burning-out zone and downstream horizontal flue, the straying quatity of amino reductive is with NH in the reducing agent _iWith NO in the flue gas _xMol ratio represent that its ratio is 1.0～2.0.

6. according to claim 1 and the directly combustion and SNCR composite denitration method again of 5 described living beings, it is characterized in that additive is that sodium salt and ethanol mol ratio are 1 mixture, NO in the sodium salt that sprays into, ethanol and the flue gas _xMol ratio be 1/20～1/3.

7. according to claim 1 and the directly combustion and SNCR composite denitration method again of 6 described living beings, it is characterized in that: sodium salt is a kind of of sodium carbonate, sodium formate and sodium acetate.

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