阅读说明：本技术 一种低NOx排放变截面循环流化床分级燃烧锅炉系统及方法 (Low-NOx-emission variable-section circulating fluidized bed staged combustion boiler system and method ) 是由 刘银河 张彦迪 杨欢 王博 于 2020-06-02 设计创作，主要内容包括：本发明公开了一种低NOx排放变截面循环流化床分级燃烧锅炉系统及方法,该系统包括：变截面积炉膛、流化床活化室和CO催化装置；变截面积炉膛上部烟气出口连接绝热旋风分离器,绝热旋风分离器下部返料机构与富燃料燃烧室之间增设流化床活化室,上部烟气排出后进入竖直烟道,与对流换热面换热之后进入补风燃烧室；补风燃烧室的下游布置CO催化氧化装置。本发明提出的变截面循环流化床锅炉系统,可实现煤的分级高效燃烧,同时降低了NOx原始排放,减轻大气污染；在一定程度上缓解尾部受热面的积灰结渣问题；对反料进行入炉前的活化,提高碳转化率；取消了SCR脱硝装置,节约了建设成本,同时避免了氨逃逸造成的催化剂失活、空预器堵塞等问题。(The invention discloses a low NOx emission variable cross-section circulating fluidized bed staged combustion boiler system and a method, wherein the system comprises: the device comprises a variable-section hearth, a fluidized bed activation chamber and a CO catalytic device; the flue gas outlet at the upper part of the hearth with the variable cross-sectional area is connected with a heat-insulating cyclone separator, a fluidized bed activation chamber is additionally arranged between a material returning mechanism at the lower part of the heat-insulating cyclone separator and the fuel-rich combustion chamber, and the flue gas at the upper part enters a vertical flue after being discharged, and enters an air supplementing combustion chamber after exchanging heat with a convection heat exchange surface; and a CO catalytic oxidation device is arranged at the downstream of the air supplementing combustion chamber. The variable cross-section circulating fluidized bed boiler system provided by the invention can realize the staged and efficient combustion of coal, simultaneously reduce the original emission of NOx and reduce the atmospheric pollution; the problem of ash deposition and slag bonding of the tail heating surface is relieved to a certain extent; the reaction materials are activated before being fed into the furnace, so that the carbon conversion rate is improved; an SCR denitration device is cancelled, the construction cost is saved, and the problems of catalyst inactivation, air preheater blockage and the like caused by ammonia escape are avoided.)

1. A low NOx emission variable cross-section circulating fluidized bed staged combustion boiler system is characterized by comprising a variable cross-section hearth, a fluidized bed activation chamber (11), a material returning mechanism (12), an adiabatic cyclone separator (14) and a CO catalytic oxidation device (18); wherein the content of the first and second substances,

the variable-section hearth comprises a fuel-rich combustion chamber (1) and a fast fluidized combustion chamber (7) which are communicated from bottom to top, the lower part of the fuel-rich combustion chamber (1) is provided with an air distribution plate (2), and the bottom of the fuel-rich combustion chamber is provided with a primary air inlet (4), a circulating flue gas inlet (3) and a slag discharge pipe (5); the sectional area of the upper end of the fuel-rich combustion chamber (1) is reduced, a fuel/desulfurizer inlet (9) is arranged at the position where the sectional area is reduced, and a flue gas outlet at the top of the fuel-rich combustion chamber (1) is communicated with the fast fluidized combustion chamber (7); a material returning port is arranged on the side wall of the lower part of the fuel-rich combustion chamber (1) and is connected with the fluidized bed activation chamber (11);

the fast fluidized combustion chamber (7) is provided with a flue gas inlet, a flue gas outlet and a plurality of secondary air inlets (8), and the flue gas inlet of the fast fluidized combustion chamber (7) is communicated with the flue gas outlet of the fuel-rich combustion chamber (1); the upper part of the fast fluidized combustion chamber (7) is connected with a heat-insulating cyclone separator (14) through a horizontal flue (13);

the heat-insulating cyclone separator (14) is communicated to the material returning mechanism (12) through a vertical pipe; a material outlet of the material returning mechanism (12) is connected with a material inlet of the fluidized bed activation chamber (11), and the fluidized bed activation chamber (12) is communicated with the fuel-rich combustion chamber (1); a plurality of activating agent inlets (10) are arranged at the lower part of the fluidized bed activation chamber (11);

an air supplementing combustion chamber (17) is arranged at the downstream of the flue gas outlet at the upper part of the heat insulation cyclone separator (14); the air supplementing combustion chamber (17) is provided with a flue gas inlet, a flue gas outlet and a plurality of high-temperature air inlets (16) which are arranged in a layered manner, and the flue gas inlet of the air supplementing combustion chamber (17) is communicated with the flue gas outlet of the heat insulation cyclone separator (14);

a CO catalytic oxidation device (18) is arranged at the downstream of a flue gas outlet of the air supply combustion chamber (17); the CO catalytic oxidation device (18) is provided with a flue gas inlet and a flue gas outlet, and the flue gas inlet of the CO catalytic oxidation device (18) is communicated with the flue gas outlet of the air supplementing combustion chamber (17).

2. The circulating fluidized bed staged combustion boiler system with the variable cross-section and the low NOx emission according to claim 1, wherein a flue gas outlet at the upper part of the heat-insulating cyclone separator (14) is communicated with a vertical flue which is arranged downwards, and a convection heating surface (15), an air supply combustion chamber (17), a CO catalytic oxidation device (18), an economizer (19), an air preheater (20) and a smoke exhaust port (21) are sequentially arranged in the vertical flue from top to bottom.

3. A low NOx emission variable cross-section circulating fluidized bed staged combustion boiler system according to claim 1, wherein the stoichiometric air/fuel ratio of the fluidized bed activation chamber (11) is less than 1, where the incoming coal particles are oxygen-lean to burn; the stoichiometric air-fuel ratio of the heat-insulating cyclone separator (14) is less than 1 and greater than that of the fuel-rich combustion chamber (1), and the stoichiometric air-fuel ratio of the CO catalytic oxidation device (18) is 1-1.05.

4. The low-NOx-emission variable-section circulating fluidized bed staged combustion boiler system according to claim 3, wherein a stoichiometric air-fuel ratio is maintained in the fuel-rich combustion chamber (1) at 0.7-0.8; the stoichiometric air-fuel ratio in the fast fluidized combustion chamber (7) is kept to be 0.9; the stoichiometric air-fuel ratio in the fluidized bed activation chamber (11) is maintained at 0.95.

5. A low NOx emission variable cross-section circulating fluidized bed staged combustion boiler system according to claim 1, characterized in that the central position of the air distribution plate (2) is provided with a slag discharge pipe (5); the inside of the fuel-rich combustion chamber (1) is paved with a guard combustion zone (6) to reduce the abrasion of the water wall of the area caused by the increase of the internal circulation times of the fuel.

6. A low NOx emission variable cross-section circulating fluidized bed staged combustion boiler system according to claim 1, characterized in that the high temperature air inlets (16) of the supplementary air combustion chamber (17) are arranged in layers above and below.

7. The boiler system of claim 1, wherein the CO catalyst in the CO catalytic oxidation unit (18) is CeO₂Aerogel supported CuO catalyst.

8. A fractional combustion method of a low-NOx-emission variable-cross-section circulating fluidized bed boiler, which is characterized in that the method is based on the low-NOx-emission variable-cross-section circulating fluidized bed boiler system of claim 2; the method comprises the following steps:

s1, enabling the fuel and the desulfurizer to enter an internal cavity of the fuel-rich combustion chamber, adopting a fluidized bed combustion mode, keeping the stoichiometric air-fuel ratio less than 1 in a high-temperature combustion gasification zone, and maintaining the reaction to be in an oxygen-poor fuel-rich combustion atmosphere;

s2, chamfering the upper part of the fuel-rich combustion chamber to reduce the sectional area of the hearth, wherein the particle size of the large-particle-size material is reduced after multiple internal circulations, and the large-particle-size material enters the fast fluidized combustion chamber along with the flue gas; introducing a proper amount of secondary air into the fast fluidized combustion chamber, and continuing combustion to ensure that the stoichiometric air-fuel ratio is less than 1 but greater than that of the fuel-rich combustion chamber; the flue gas after combustion enters a heat-insulating cyclone separator through a horizontal flue;

s3, enabling the solid material separated by the heat-insulation cyclone separator to enter a material returning mechanism through a vertical pipe; a fluidized bed activation chamber is additionally arranged between the material returning mechanism and the fuel-rich combustion chamber, and the deactivated materials are activated and upgraded;

s4, communicating flue gas at the upper part of the heat-insulating cyclone separator with a vertical flue, exchanging heat of the combusted flue gas through a convection heating surface, and then entering an air supplementing combustion chamber, wherein air is uniformly introduced into the air supplementing combustion chamber through high-temperature air inlets which are arranged in a layered manner;

and S5, enabling the flue gas after the air supply combustion chamber to enter a CO catalytic oxidation device after heat exchange through a convection heating surface, maintaining the stoichiometric air-fuel ratio in the CO catalytic oxidation device at 1-1.05, enabling CO which is not completely combusted in the flue gas to be completely oxidized, enabling the flue gas to flow through an economizer and an air preheater, reducing the temperature to the exhaust temperature, and then discharging the flue gas from an exhaust port.

Technical Field

The invention belongs to the field of boiler design, and particularly relates to a low-NOx-emission variable-section circulating fluidized bed staged combustion boiler system and a method.

Background

The Circulating Fluidized Bed (CFB) boiler has the advantages of low-temperature combustion, excellent burnout conditions, wide fuel adaptability and the like, and has the advantage of natural low NOx emission compared with a pulverized coal furnace. With the increasing requirements of people on environmental protection, the environmental protection advantages of the CFB boiler are not obvious due to the strict ultralow emission standard of a coal-fired unit, and various low NOx combustion measures and even selective non-catalytic reduction (SNCR) or Selective Catalytic Reduction (SCR) flue gas treatment equipment have to be adopted. The addition of the SNCR equipment or the SCR equipment can promote SO in the flue gas to a certain extent₂To SO₃The conversion and ammonia escaping from the flue gas form Ammonium Bisulfate (ABS), which causes the problems of catalyst deactivation, blockage corrosion of an air preheater and the like. At present, aiming at low NOx combustion modification of CFB boilers, the following methods are adopted: the secondary air nozzle is improved, and the oxygen content in the dense-phase area is reduced; the efficiency of the separator is improved; flue gas recirculation technology and the like are adopted. Engineering practices of ultra-low NOx emission and low NOx combustion technology reformation show that the original NOx emission can be reduced by adopting a low excess air coefficient in a hearth, but the reduction of the combustion efficiency and the emission of CO are easily caused, and even the safety problem of secondary combustion in subsequent equipment is caused.

CFB boilers are generally considered to have high combustion efficiency. The practice of burning lignite and other coal with high reaction activity abroad shows that the fly ash of the circulating fluidized bed has low carbon content. However, most circulating fluidized bed boilers in China mostly burn poor fuels such as lean coal and coal gangue, the carbon content of fly ash is obviously higher than the expected value, and the carbon content of some boiler fly ash is even as high as 30%. The high carbon content of fly ash has become an important factor which seriously restricts the continuous development of CFB boilers. At present, in order to reduce the carbon content of fly ash of CFB boilers, the following methods are mostly adopted: the penetrating power of secondary air is improved, and gas-solid mixing is enhanced; returning the fly ash at the dust remover to the hearth for recycling; activating, agglomerating and reburning fly ash water, and the like. The existing technology for reducing the carbon content of the fly ash takes the purpose of reducing the carbon content of the fly ash as much as possible in the original boiler as an eyepoint, is limited by abrasion of a heating surface at the tail part, energy consumption and the like, and is influenced by inactivation of fly ash particles, and even if the fly ash treated by the technology has a larger carbon content reduction space.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide a low-NOx-emission variable-section circulating fluidized bed staged combustion boiler system and a method. The circulating fluidized bed boiler system with low NOx original emission and low residual carbon content adopts the furnace with the variable cross-sectional area through the innovative design of the furnace structure, and forms a fuel-rich and oxygen-poor combustion atmosphere at the lower part of the furnace, thereby reducing the original emission of NOx, increasing the internal circulation times of large particles and improving the carbon conversion rate. The fluidized bed activation chamber is additionally arranged on the material returning system, and the low-activity carbon component separated by the heat-insulating cyclone separator is activated before entering the furnace, so that the carbon content of the fly ash can be further reduced.

In order to achieve the purpose, the invention is realized by adopting the following technical scheme:

a low NOx emission variable cross-section circulating fluidized bed staged combustion boiler system comprises a variable cross-section hearth, a fluidized bed activation chamber, a material returning mechanism, a heat insulation cyclone separator and a CO catalytic oxidation device; wherein the content of the first and second substances,

the variable-section hearth comprises a fuel-rich combustion chamber and a fast fluidized combustion chamber which are communicated from bottom to top, the lower part of the fuel-rich combustion chamber is provided with an air distribution plate, and the bottom of the fuel-rich combustion chamber is provided with a primary air inlet, a circulating flue gas inlet and a slag discharge pipe; the sectional area of the upper end of the fuel-rich combustion chamber is reduced, a fuel/desulfurizer inlet is arranged at the position where the sectional area is reduced, and a flue gas outlet at the top of the fuel-rich combustion chamber is communicated with the rapid fluidized combustion chamber; a material returning port is arranged on the side wall of the lower part of the fuel-rich combustion chamber and is connected with the fluidized bed activation chamber;

the fast fluidized combustion chamber is provided with a flue gas inlet, a flue gas outlet and a plurality of secondary air inlets, and the flue gas inlet of the fast fluidized combustion chamber is communicated with the flue gas outlet of the fuel-rich combustion chamber; the upper part of the fast fluidized combustion chamber is connected with the heat-insulating cyclone separator through the horizontal flue;

the heat-insulating cyclone separator is communicated to the material returning mechanism through a vertical pipe; the material outlet of the material returning mechanism is connected with the material inlet of the fluidized bed activation chamber, and the fluidized bed activation chamber is communicated with the fuel-rich combustion chamber; a plurality of activating agent inlets are arranged at the lower part of the fluidized bed activation chamber;

an air supplementing combustion chamber is arranged at the lower stream of the flue gas outlet at the upper part of the heat insulation cyclone separator; the air supplementing combustion chamber is provided with a flue gas inlet, a flue gas outlet and a plurality of high-temperature air inlets which are arranged in a layered manner, and the flue gas inlet of the air supplementing combustion chamber is communicated with the flue gas outlet of the heat insulation cyclone separator;

a CO catalytic oxidation device is arranged at the downstream of a flue gas outlet of the air supplementing combustion chamber; the CO catalytic oxidation device is provided with a flue gas inlet and a flue gas outlet, and the flue gas inlet of the CO catalytic oxidation device is communicated with the flue gas outlet of the air supplementing combustion chamber.

The invention is further improved in that a flue gas outlet at the upper part of the heat-insulating cyclone separator is communicated with a vertical flue which is arranged downwards, and a convection heating surface, an air supply combustion chamber, a CO catalytic oxidation device, an economizer, an air preheater and a smoke outlet are sequentially arranged in the vertical flue from top to bottom.

In a further development of the invention, the stoichiometric air/fuel ratio of the fluidized bed activation chamber is less than 1, where the coal particles fed are burnt in an oxygen-poor manner; the stoichiometric air-fuel ratio of the heat-insulation cyclone separator is less than 1 and is greater than that of the fuel-rich combustion chamber, and the stoichiometric air-fuel ratio of the CO catalytic oxidation device is 1-1.05.

The invention has the further improvement that the stoichiometric air-fuel ratio is kept to be 0.7-0.8 in the fuel-rich combustion chamber; the stoichiometric air-fuel ratio in the fast fluidized combustion chamber is kept to be 0.9; the stoichiometric air-fuel ratio was maintained at 0.95 in the fluidized bed activation chamber.

The invention has the further improvement that a slag discharge pipe is arranged at the central position of the air distribution plate; the inside of the fuel-rich combustion chamber is paved with a guard combustion zone to reduce the abrasion of the water wall of the area caused by the increase of the internal circulation times of the fuel.

The invention is further improved in that a plurality of high-temperature air inlets of the air supplementing combustion chamber are arranged in a layered manner from top to bottom.

The invention is further improved in that CeO is adopted as a CO catalyst in the CO catalytic oxidation device₂Aerogel supported CuO catalyst.

A low NOx discharges the sectional area circulating fluidized bed boiler staged combustion method, this method is based on the above-mentioned a low NOx discharges the sectional area circulating fluidized bed boiler system; the method comprises the following steps:

s1, enabling the fuel and the desulfurizer to enter an internal cavity of the fuel-rich combustion chamber, adopting a fluidized bed combustion mode, keeping the stoichiometric air-fuel ratio less than 1 in a high-temperature combustion gasification zone, and maintaining the reaction to be in an oxygen-poor fuel-rich combustion atmosphere;

s2, chamfering the upper part of the fuel-rich combustion chamber to reduce the sectional area of the hearth, wherein the particle size of the large-particle-size material is reduced after multiple internal circulations, and the large-particle-size material enters the fast fluidized combustion chamber along with the flue gas; introducing a proper amount of secondary air into the fast fluidized combustion chamber, and continuing combustion to ensure that the stoichiometric air-fuel ratio is less than 1 but greater than that of the fuel-rich combustion chamber; the flue gas after combustion enters a heat-insulating cyclone separator through a horizontal flue;

s3, enabling the solid material separated by the heat-insulation cyclone separator to enter a material returning mechanism through a vertical pipe; a fluidized bed activation chamber is additionally arranged between the material returning mechanism and the fuel-rich combustion chamber, and the deactivated materials are activated and upgraded;

s4, communicating flue gas at the upper part of the heat-insulating cyclone separator with a vertical flue, exchanging heat of the combusted flue gas through a convection heating surface, and then entering an air supplementing combustion chamber, wherein air is uniformly introduced into the air supplementing combustion chamber through high-temperature air inlets which are arranged in a layered manner;

and S5, enabling the flue gas after the air supply combustion chamber to enter a CO catalytic oxidation device after heat exchange through a convection heating surface, maintaining the stoichiometric air-fuel ratio in the CO catalytic oxidation device at 1-1.05, enabling CO which is not completely combusted in the flue gas to be completely oxidized, enabling the flue gas to flow through an economizer and an air preheater, reducing the temperature to the exhaust temperature, and then discharging the flue gas from an exhaust port.

Compared with the prior art, the invention has at least the following beneficial technical effects:

the invention relates to a low-NOx-emission variable-section circulating fluidized bed staged combustion boiler system, which is characterized in that coal is sequentially subjected to staged combustion and CO catalytic oxidation in a variable-section hearth (the lower part is a fuel-rich combustion chamber, and the upper part is a fast fluidized combustion chamber) and an air supply combustion chamber, low-activity carbon residue particles separated by a heat insulation cyclone separator are activated and lifted in an activation chamber of a fluidized bed, and then the activated and lifted low-activity carbon residue particles are fed into the hearth for combustion, so that the boiler can realize low original NOx emission, high alkali metal retention rate and high carbon conversion rate when high-alkali coal such as eastern Junggar coal is combusted. The variable cross-section fluidized bed boiler system provided by the invention is combusted at high temperature in a fuel-rich reducing atmosphere, and NOx is hardly generated in a downstream fluidized bed activation chamber and an air supply combustion chamber, so that the system does not need to be additionally provided with an SCR/SNCR denitration device, and the problems of catalyst inactivation, blockage corrosion of an air preheater and the like caused by ammonium bisulfate formed by ammonia escape can be avoided. The fluidized bed activation chamber is used for introducing high-temperature gas to activate and upgrade the inactivated carbon residue, so that the reaction activity of the activated carbon residue is improved, and the carbon conversion rate is further improved. The stoichiometric air-fuel ratio in the fuel-rich combustion chamber is less than 1, the fuel is combusted under the condition of fuel-rich low temperature, the original emission of fuel type NOx and thermal type NOx is greatly reduced, part of incompletely combusted residual carbon is continuously combusted in the fast fluidized combustion chamber and the air supply combustion chamber along with the flue gas, and CO in the flue gas is completely oxidized through the CO catalytic oxidation device, so that the effective utilization of energy is improved, and the environmental pollution is reduced. The reducing atmosphere of the fuel-rich combustion chamber inhibits the release of alkali metal, and can relieve the problem of ash deposition and slag bonding on the tail heating surface.

Furthermore, the variable cross-section hearth provided by the invention has large lower part and small upper part, and the sectional area of the lower part is larger, so that the variable cross-section hearth is a fuel-rich combustion chamber, the internal circulation times of fuel with large particle size are increased, the retention time in a fuel furnace is prolonged, and the carbon conversion rate is further improved; the upper part is a fast fluidized combustion chamber, the penetration capacity of secondary air is improved by adjusting a proper secondary air inlet and air speed, secondary sufficient combustion of the fuel with small particle size escaping from the fuel-rich combustion chamber is realized, and the carbon conversion rate is further improved.

Further, a fluidized bed activation chamber is arranged, and high-temperature O is introduced₂/CO₂/H₂And O, etching groove marks on the surface of the inactivated carbon residue to open the originally blocked holes of the carbon residue particles, increase the number of active point positions, promote the reaction activity of the carbon residue particles, promote the carbon residue particles to be further converted in a fuel-rich combustion chamber, and reduce the loss of incomplete combustion heat.

Go toStep by step, the lower part of the fuel-rich combustion chamber is provided with a circulating flue gas inlet, the temperature of a flue gas adjusting bed layer is introduced, the generation of NOx caused by local high temperature is avoided, and the CO can be realized₂And (4) enriching.

Furthermore, high-temperature gas inlets of the air supply combustion chamber are arranged in a layered mode, and a proper amount of high-temperature gas is introduced, so that the uniformity is improved.

Further, CeO is adopted as a CO catalyst in the CO catalytic oxidation device₂The aerogel supported CuO catalyst is low in price and remarkable in cost economy. The CuO catalyst has an active temperature of about 600 ℃, and can well oxidize CO in incompletely combusted flue gas.

Furthermore, the stoichiometric air-fuel ratio of the whole boiler system is lower, the heat loss of the boiler exhaust smoke can be reduced, and the thermal efficiency of the boiler is improved.

In conclusion, the fuel has wide application range and is suitable for low-quality fuels such as high-alkali coal, high-ash coal, coal gangue and the like. The boiler system provided by the invention is also suitable for other variable cross-section circulating fluidized bed boilers obtained by the method.

Drawings

FIG. 1 is a schematic diagram of a low NOx raw emission, low carbon residue circulating fluidized bed boiler system of the present invention.

FIG. 2 is a schematic structural diagram of a variable cross-section furnace.

FIG. 3 is a schematic structural view of a variable cross-section circulating fluidized bed boiler.

Description of reference numerals:

1. a fuel-rich combustor; 2. a wind distribution plate; 3. a circulating flue gas inlet; 4. a primary tuyere; 5. a slag discharge pipe; 6. a sanitary burning zone; 7. a fast fluidized combustion chamber; 8. a secondary air inlet; 9. a fuel/desulfurizer inlet; 10. an activator inlet; 11. a fluidized bed activation chamber; 12. a material returning mechanism; 13. a horizontal flue; 14. an adiabatic cyclone separator; 15. a convection heating surface; 16. a high temperature gas inlet; 17. a supplementary air combustion chamber; 18. a CO catalytic oxidation unit; 19. a coal economizer; 20. an air preheater; 21. and a smoke outlet.

Detailed Description

The invention is described in detail below with reference to the drawings and the specific embodiments.

As shown in figure 1, the variable cross-section circulating fluidized bed staged combustion boiler system with low NOx emission of the invention comprises a fuel-rich combustion chamber 1, a fast fluidized combustion chamber 7, a fluidized bed activation chamber 11, a CO catalytic oxidation device 18 and other equipment of a boiler body.

As shown in FIG. 2, the variable cross-section hearth is divided into an upper part and a lower part, the sectional area of the lower part hearth is larger, and the lower part hearth is a fuel-rich combustion chamber 1; the sectional area of the upper hearth is smaller, and the upper hearth is a fast fluidized combustion chamber 7. The boiler body further comprises a heat-insulating cyclone separator 14, a material returning mechanism 12, a convection heating surface 15, an air supplementing combustion chamber 17, an economizer 19, an air preheater 20 and a smoke outlet 21. The fluidized bed activation chamber 11 is arranged between the material returning mechanism 12 and the fuel-rich combustor 1. The CO catalytic oxidation device 18 is arranged before the economizer 19.

The smoke outlet at the upper part of the fuel-rich combustion chamber 1 is narrowed, and the internal circulation times of large particles are increased; the upper part of the rich fuel combustion chamber 1 is communicated with a fast fluidized combustion chamber 7; the heat-insulating cyclone separator 14 is connected with the fast fluidized combustion chamber 7 through a horizontal flue 13; solid particles separated by the heat-insulating cyclone separator 14 enter the material returning mechanism 12 from the lower part and return to the fuel-rich combustion chamber 1 through the fluidized bed activation chamber 11, a plurality of activator inlets 10 are arranged at the bottom of the fluidized bed activation chamber 11, so that residual coke particles entering the activation chamber form a fluidized state, the activators and the residual coke are fully mixed, traces are etched on the surfaces of the deactivated residual coke particles, the blocked aperture is opened, the active point position is increased, and the reaction activity is further improved; the flue gas outlet at the upper part of the heat insulation cyclone separator 14 is connected with a second vertical flue, and the second vertical flue is sequentially provided with a convection heating surface 15, an air supply combustion chamber 17, a CO catalytic oxidation device 18, an economizer 19, an air preheater 20 and a smoke outlet 21 from top to bottom.

The fuel-rich combustion chamber 1 is in an adiabatic oxygen-poor combustion atmosphere and comprises an air distribution plate 2, a circulating flue gas inlet 3, a primary air inlet 4, a slag discharge pipe 5, a combustion control zone 6 and a fuel/desulfurizer inlet 9. The side walls of the fuel-rich combustion chamber 1 are covered with refractory material to form refractory bands 6, which help the ignition of the fuel and reduce the wear on the water walls due to the increase of the number of internal cycles. 4 primary air ports and 4 circulating flue gas inlets are symmetrically arranged at the lower part of the fuel-rich combustion chamber 1, and a stable airflow field is formed in the furnace through the air distribution plate 2. The fuel and the desulfurizer enter the rich fuel combustion chamber 1 through the fuel/desulfurizer inlet 9, and reach stable fluidization under the action of the airflow in the furnace, thereby realizing rich fuel combustion. The rich fuel combustion chamber 1 adopts a bottom deslagging mode, partial blast caps are removed and a deslagging pipe 5 is arranged in the central area of the air distribution plate 2, so that large slag in the rich fuel combustion chamber is removed, and the particle storage quantity in a bed is maintained to be fluidized.

In the fuel-rich combustion chamber 1, coal particles are blown up by primary air to form a stable fluidized combustion process, the stoichiometric air-fuel ratio in the region is kept to be less than 1 and about 0.7-0.8, the reaction is kept in an oxygen-poor combustion atmosphere, the combustion temperature is about 900 ℃, the selective directional conversion of fuel nitrogen is realized, and the generation amount of thermal NOx and fuel NOx is reduced. Because the stoichiometric air-fuel ratio is low, the combustion of coal particles is insufficient, and part of CO is formed, and the content is about 10%. In addition, the small particle size fuel, which is partially incompletely combusted, travels upward with the flue gas and enters the fast fluidized combustion chamber 7. The pulverized coal in the fuel-rich combustor 1 is burned in a reducing atmosphere, and NOx is hardly generated.

The fast fluidized combustion chamber 7 is arranged at the upper part of the fuel-rich combustion chamber 1, the sectional area is smaller than that of the fuel-rich combustion chamber, and a 45-degree chamfer is formed at the joint part so as to increase the internal circulation frequency of large-particle materials in the fuel-rich combustion chamber 1. 4 secondary air inlets 8 for conveying high-temperature gas are arranged at the position of the fast fluidized combustion chamber 7 close to the lower part, and the high-temperature gas and the flue gas are mixed and then continuously combusted. Where the stoichiometric air-fuel ratio is less than 1, about 0.9, and the unburned small particle size fuel is combusted, further increasing the carbon conversion. The combustion temperature is slightly lower than that of the fuel-rich combustion chamber 1, the temperature is lower than the ash melting temperature of most of the fuel (especially high-alkali coal), the problems of contamination, slag bonding and the like on the surface of the heating surface can be avoided, and the design and the arrangement of the heating surface are facilitated.

A horizontal flue 13 communicated with a heat-insulating cyclone separator 14 is arranged at the upper part of the variable cross-section hearth, solid particles in the flue gas are separated to a material returning mechanism 12 through the heat-insulating cyclone separator 14, and the part of the solid particles pass throughThe fuel-rich combustor 1 and the fast-fluidized combustor 7, which have highly reactive components and react to completion, the remaining portion is mainly low in reactive components or deactivates residual carbon. Therefore, a fluidized bed activation chamber is additionally arranged between the fuel-rich combustion chamber 1 and the material returning mechanism 12, and high-temperature O is introduced through a high-temperature gas inlet 16₂/CO₂/H₂And O, etching groove marks on the surface of the inactivated carbon residue to open the originally blocked holes of the carbon residue particles, increasing the number of active point positions, improving the combustion reaction activity of the carbon residue particles, further improving the carbon conversion rate and reducing the carbon content of the fly ash.

The flue gas separated by the heat-insulating cyclone separator 14 enters an air-supplementing combustion chamber 17 after heat exchange through a convection heating surface 15, high-temperature gas is introduced into the air-supplementing combustion chamber 17 through a high-temperature gas inlet 16 which is arranged in a layered manner, the fly ash carbon residue with micro particle size which is not separated by the heat-insulating cyclone separator is reburned, and meanwhile, CO in part of the flue gas is eliminated. The flue gas enters a CO catalytic oxidation device after flowing downwards through a convection heating surface, the stoichiometric air-fuel ratio at the CO catalytic oxidation device is kept between 1 and 1.05 by adjusting the amount of high-temperature gas introduced at the air supplementing combustion chamber 17, and CO which is not completely combusted in the flue gas is completely oxidized in the CO catalytic oxidation device 18. Then, the flue gas passes through the economizer 19, the air preheater 20, and the like, and is sufficiently heat-exchanged with the economizer, and the flue gas is discharged from the exhaust port 21 after the temperature of the flue gas is lowered to the exhaust temperature.

The boiler system described above is equally applicable to a variable cross-section circulating fluidized bed boiler as shown in fig. 3.

The invention provides a low-NOx-emission variable-section circulating fluidized bed staged combustion method, which is based on any one of the low-NOx-emission variable-section circulating fluidized bed staged combustion boiler systems and comprises the following steps of:

s1, enabling the fuel and the desulfurizer to enter an inner cavity of the rich fuel combustor 1 to generate oxygen-poor fluidized combustion, keeping the stoichiometric air-fuel ratio less than 1 in the high-temperature combustion gasification zone, and maintaining the reaction to be an oxygen-poor rich fuel combustion atmosphere;

s2, chamfering the upper part of the fuel-rich combustion chamber 1 to reduce the sectional area of the hearth, wherein the particle size of the large-particle-size material is reduced after multiple internal circulations, and the large-particle-size material enters the fast fluidized combustion chamber 7 along with the flue gas; introducing a proper amount of secondary air into the fast fluidized combustion chamber 7, and continuously maintaining combustion to ensure that the stoichiometric air-fuel ratio is less than 1 but greater than the fuel-rich combustion chamber 1; the flue gas after burning enters a heat insulation cyclone separator 14 through a horizontal flue 13;

s3, the solid material separated by the heat insulation cyclone separator 14 enters the material returning mechanism 12 through the vertical pipe; a fluidized bed activation chamber 11 is additionally arranged between the material returning mechanism 12 and the fuel-rich combustion chamber 1, and the deactivated materials are activated and upgraded before being returned to the furnace;

s4, enabling flue gas on the upper part of the heat-insulation cyclone separator 14 to be communicated with a vertical flue, enabling the combusted flue gas to enter an air supplementing combustion chamber 17 after heat exchange is carried out on the combusted flue gas through a convection heating surface 15, and uniformly introducing air into the air supplementing combustion chamber 17 through high-temperature air inlets which are arranged in a layered mode;

and S5, exchanging heat of the flue gas after the air supply combustion chamber 17 through the sparsely arranged convection heating surface, then entering the CO catalytic oxidation device 18, maintaining the stoichiometric air-fuel ratio in the CO catalytic oxidation device 18 at 1-1.05, completely oxidizing the CO which is not completely combusted in the flue gas, then enabling the flue gas to flow through the economizer 19 and the air preheater 20, and discharging the flue gas from the smoke outlet 21 after the temperature is reduced to the smoke discharge temperature.