CN100491822C - Denitrification method using biomass direct combustion and re-combustion and flue gas recirculation process - Google Patents

Abstract

The present invention belongs to a denitration method by utilizing biomass direct combustion and secondary combustion and flue gas recirculating process and its equipment, and relates to a coal powder boiler low NOx combustion process and its equipment. The invented method includes the following steps: making coal powder be passed through the combustor of coal powder boiler and fed into main combustion zone to make combustion and form the flue gas containing NOx; utilizing the mixture of once air and recirculating tail portion flue gas to spray biomass particles into secondary combustion reduction zone and make NOx formed in the main combustion zone be reacted and formed into N2; at the same time make the biomass coke ad NOx produce isophase reduction reaction to form Nz; spraying burning air from upper portion of secondary combustion reduction zone to make non-burnt combustible material be burnt up.

Description

Denitrification method using biomass direct combustion and re-combustion and flue gas recirculation process

technical field

The invention relates to a low NOx combustion technology for a pulverized coal boiler, in particular to a combustion method utilizing biomass direct combustion and then combustion for denitrification.

Background technique

Pulverized coal combustion is an important source of nitrogen oxide emissions. The denitrification efficiency of existing low-excess air ratio, air-staged combustion technology, and dense-lean combustion technology and other low-NOx combustion technologies is generally lower than 50%, so they cannot meet the increasingly stringent environmental protection requirements. Require. Reburning technology, also known as fuel classification or in-furnace reduction (IFNR) technology, is one of the most effective measures among many in-furnace methods to reduce NOx emissions. The denitrification efficiency of reburning technology can reach more than 60%. At present, most of the existing reburning and denitrification projects at home and abroad use natural gas as the reburning fuel, and some use fine coal powder as the reburning fuel. my country's natural gas resources are mainly distributed in the west, and the reserves are limited. The use of natural gas as reburning fuel has high operating costs. Fine pulverized coal reburning and denitrification technology has strict requirements on the coal type and particle size of reburning pulverized coal.

The patent application document with the publication number CN415891A discloses a combustion method and device for reburning denitrification with biomass pyrolysis gas, which uses biomass pyrolysis gas as the reburning fuel, and adds an A gasifier for pyrolysis gasification and a transmission device for pyrolysis gas. Due to the technical risk of the existing biomass gasification technology, and the calorific value of the produced biomass pyrolysis gas is relatively low, and it only contains a small amount of CH ₄ , and CH ₄ is the most effective denitrification component , so the effect of using biomass pyrolysis gas for destocking is not ideal, and part of the energy of biomass is lost in the process of biomass gasification, so that the energy of biomass cannot be fully utilized. The gasifier and pyrolysis gas transmission device added to the device in this patent application complicate the structure of the system and increase the cost of the system.

Contents of the invention

The method for denitrification using biomass direct combustion and reburning and flue gas recirculation process provided by the present invention is realized based on the following device, which includes a pulverized coal boiler, which also includes a biomass feeding device, and the biomass The connecting device between the feeding device and the pulverized coal boiler and the recirculation induced draft fan, the outlet of the biomass feeding device is connected with the primary air inlet pipe, and one end of the primary air inlet pipe is connected with the reburning fuel nozzle, The air inlet of the recirculation induced draft fan is connected with the tail flue of the pulverized coal boiler, the air outlet of the recirculation induced draft fan is connected with the primary air inlet pipe, and the inlet of the recirculation induced draft fan is connected with the air preheater and the dust collector The tail flue is communicated with, or communicated with the tail flue section before the air preheater, and the steps of the method are:

A. Pulverized coal enters the main combustion zone at the bottom of the pulverized coal boiler furnace through the burner of the pulverized coal boiler to burn to form flue gas containing NOx;

B. Use the mixture of primary air to mix and recirculate the tail flue gas to spray biomass particles into the middle of the furnace to form a reburning reduction zone;

C. Biomass particles precipitate active groups such as hydrocarbon groups and amino groups under the condition of low stoichiometric ratio in the reburning reduction zone, and react with NOx formed in the main combustion zone of the pulverized coal boiler to form N ₂ . At the same time, biomass coke and NOx are in the reburning reduction A heterogeneous reduction reaction occurs in the main combustion zone, reducing the NOx produced in the main combustion zone to N ₂ ;

D. Inject the burn-out air from the burn-out air nozzle on the upper part of the reburning reduction zone of the pulverized coal boiler furnace to form a burn-off zone, so that the incompletely burned combustibles can be completely burned.

Wherein the excess air ratio in the main combustion zone described in step A is 0.8-1.0.

The proportion of the tail gas in the mixture of the primary air 30 mixed with the recycled tail gas in step B is 0%-100%.

Wherein the excess air ratio in the reburning reduction zone described in step C is 0.8-0.9.

Wherein the excess air ratio in the burnout zone described in step D is 1.15-1.2.

In the above method, the calorific value of coal in the furnace of the pulverized coal boiler accounts for 80-90%, and the calorific value of biomass accounts for 10-20%.

In step B of the present invention, the biomass is sprayed into the reburning reduction zone together with the mixture of primary air and recirculated tail flue gas, which not only helps to form the conditions of low stoichiometric ratio required for reburning, but also can strengthen the biomass Jet rigidity and mixed conditions in the reburn reduction zone.

Compared with the prior art, the present invention has the following advantages:

Using tail recirculation flue gas as the transport medium of biomass reburning fuel is conducive to the formation of low stoichiometric ratio conditions required in the reburning reduction zone. Requirements for biomass types and physical parameters are conducive to the reduction reaction of CHi, NHi and other active groups with NOx formed in the main combustion zone.

The invention directly uses the crushed biomass particles as the reburning fuel, conforms to the national high-efficiency comprehensive development and utilization policy of biomass energy, combines the rational utilization of biomass with reburning technology, and reduces the technical risk and cost of the biomass conversion process , effectively reducing the emission of nitrogen oxides under the condition of basically not affecting the original combustion conditions of pulverized coal boilers.

The invention is suitable for newly-built boilers and the transformation of boilers in operation.

Description of drawings

Fig. 1 is a schematic structural diagram of a device for denitrification using biomass direct combustion and reburning and flue gas recirculation processes according to the present invention.

Detailed ways

Specific implementation mode 1: The method for denitrification using biomass direct combustion and re-combustion and flue gas recirculation process in this embodiment, the specific steps are:

A. The pulverized coal enters the main combustion zone X at the bottom of the furnace of the pulverized coal boiler through the burner 21 of the pulverized coal boiler and burns to form flue gas containing NOx;

B. Use the mixture of primary air 30 to mix and recirculate the tail flue gas to spray biomass particles into the middle of the furnace to form a reburning reduction zone Y;

C. Biomass particles precipitate active groups such as hydrocarbon groups and amino groups under the condition of low stoichiometric ratio in the reburning reduction zone Y, and react with NOx formed in the main combustion zone X of the pulverized coal boiler to form N ₂ , and at the same time, biomass coke and NOx are in A heterogeneous reduction reaction occurs in the reburning reduction zone Y, and the NOx produced in the main combustion zone X is reduced to N ₂ ;

D. Inject the overburning air 31 from the overburning air nozzle 23 on the upper part of the reburning reduction zone Y of the pulverized coal boiler furnace to form the overburning zone Z, so that the incompletely combusted combustibles can be completely burned.

The excess air ratio of the main combustion zone X described in step A is 0.8-1.0.

The proportion of the tail gas in the mixture of the primary air 30 mixed with the recycled tail gas in step B is 0%-100%.

The excess air ratio in the reburning reduction zone Y in step C is 0.8-0.9.

The excess air ratio of the burnout zone Z in step D is 1.15-1.2.

In the above method, the calorific value of coal in the furnace of the pulverized coal boiler accounts for 80-90%, and the calorific value of biomass accounts for 10-20%.

In the step B, the biomass particles are sprayed into the reburning reduction zone Y by using the mixture of the primary air 30 mixed with the recirculated tail flue gas, which is not only conducive to the formation of the low stoichiometric ratio conditions required for reburning, but also can strengthen the Biomass jet rigidity and reburn reduction zone Y mixing conditions.

The device for denitrification using biomass direct combustion and reburning and flue gas recirculation process for this method is composed of biomass feeding device 1, pulverized coal boiler 2 and the connection between them and recirculation induced draft fan 3. The outlet of the material feeding device 1 is connected with the primary air inlet pipe 4, one end of the primary air inlet pipe 4 is connected with the reburning fuel nozzle 22, the air inlet of the recirculation induced draft fan 3 is connected with the tail flue of the pulverized coal boiler 2 27 communicates, and the air outlet of the recirculation induced draft fan 3 communicates with the primary air inlet duct 4.

The furnace of the existing pulverized coal boiler 2 is divided into a main combustion zone X, a reburning reduction zone Y and a burnout zone Z. In this embodiment, cheap and easy-to-obtain biomass is used as a raw material for reburning after simple crushing and processing, and the mixture of recirculated tail flue gas and primary air 30 is used as the transport medium of biomass, which can not only enhance the rigidity of the jet flow of the reburning nozzle 22, Strengthening the mixing conditions in the reburning reduction zone Y is also conducive to the reduction reaction of CHi, NHi and other active groups with the main combustion zone X to form NOx. The biomass injected into the reburning reduction zone Y is incompletely combusted under the condition of low excess air coefficient, forming a stable reducing atmosphere in the reburning reduction zone Y. At the same time, the alkali metal oxides such as potassium and sodium in the biomass have great effect on the NOx reduction reaction. Good catalytic effect. After the flue gas containing NOx formed in the main combustion zone X in the pulverized coal boiler 2 enters the reburning reduction zone Y, the NOx in the flue gas reacts in the same phase with the volatile matter precipitated from the biomass injected into the reburning nozzle 22, and reacts with the precipitated volatile matter Biomass coke undergoes a heterogeneous reaction to form a gas containing N2. After the gas enters the burnout area Z, because the overburning air 31 is injected into this area through the overburning air nozzle 23, the unburned combustible substances in the flue gas from the reburning reduction area Y are further burned in this area, and the hot The flue gas passes through the superheater 24, the economizer 25, and the air preheater 26 for heat exchange, and finally is purified by the dust collector 28, and is discharged through the chimney under the action of the exhaust fan. The inlet of the recirculation induced draft fan 3 may communicate with the tail flue between the air preheater 26 and the dust collector 28 , or communicate with the tail flue 27 section before the air preheater 26 . Since part of the conveying medium of the biomass particles supplements part of the tail flue gas, the present invention realizes the dual functions of biomass reburning denitrification and flue gas recirculation denitrification.

Specific embodiment 2: The difference between the denitrification device using biomass direct combustion and reburning and flue gas recirculation process in this embodiment and the specific embodiment 1 is that the feeding device 1 is composed of a feeding bin 11 and an auger 12, The auger 12 is fixed on the bottom of the feeding bin 11, and the outlet of the auger 12 communicates with the primary air inlet duct 4.

Specific embodiment three: The difference between the denitrification device using biomass direct combustion and reburning and flue gas recirculation process in this embodiment and specific embodiment one is that it also includes a biomass crushing device 5 and a buried scraper hoist 6. The outlet of the biomass crushing device 5 is connected with the inlet of the biomass feeding device 1 through a buried scraper elevator 6 . After the biomass is crushed by the biomass crushing device 5 , it is transported to the biomass feeding device 1 by the buried scraper elevator 6 .

Claims (5)

1. A method for denitrification using biomass direct combustion and reburning and flue gas recirculation, which is realized based on the following devices, which include a pulverized coal boiler (2) and a biomass feeding device (1) , and the connecting device between the biomass feeding device (1) and the pulverized coal boiler (2) and the recirculation induced draft fan (3), the outlet of the biomass feeding device (1) and the primary air The air inlet pipe (4) is connected, one end of the primary air inlet pipe (4) is connected with the reburning fuel nozzle (22), and the air inlet of the recirculation induced draft fan (3) is connected with the tail flue (27) of the pulverized coal boiler (2). ) is connected, the air outlet of the recirculation induced draft fan (3) is connected with the primary air inlet duct (4), and the inlet of the recirculation induced draft fan (3) is connected with the air preheater (26) and the dust collector (28). The tail flue between is communicated, perhaps communicates with the tail flue (27) section before the air preheater (26), it is characterized in that the concrete steps of described method are: A, pulverized coal enters the main combustion zone (X) at the bottom of the furnace of the pulverized coal boiler through the burner (21) of the pulverized coal boiler to burn to form flue gas containing NOx; B. Use the mixture of the primary air (30) to mix and recirculate the tail flue gas to spray the biomass particles into the middle of the furnace to form a reburning reduction zone (Y); C. Biomass particles precipitate hydrocarbon and amino active groups under the condition of low stoichiometric ratio in the reburning reduction zone (Y), and react with NOx formed in the main combustion zone (X) of the pulverized coal boiler to form N ₂ , while the biomass coke A heterogeneous reduction reaction occurs with NOx in the reburning reduction zone (Y), and the NOx produced in the main combustion zone (X) is reduced to N ₂ ; D. Inject the overburning air (31) from the burnout air nozzle (23) on the upper part of the reburning reduction zone (Y) of the pulverized coal boiler furnace to form a burnout zone (Z) to completely burn the incompletely combustible combustibles. 2. The method for denitrification using biomass direct combustion and reburning and flue gas recirculation process according to claim 1, characterized in that the excess air ratio in the main combustion zone (X) in the step A is 0.8 to 1.0 . 3. The method for denitrification using biomass direct combustion reburning and flue gas recirculation process according to claim 1, characterized in that the excess air coefficient in the reburning reduction zone (Y) in the step C is 0.8-0.9 . 4. The method for denitrification using biomass direct combustion and reburning and flue gas recirculation process according to claim 1, characterized in that the excess air ratio in the burnout zone (Z) in the step D is 1.15 to 1.2 . 5. The method for denitrification using biomass direct combustion and reburning and flue gas recirculation process according to claim 1, characterized in that the calorific value of coal in the furnace of pulverized coal boiler accounts for 80-90%, and the calorific value of biomass accounts for 10%. ~20%.

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