JPH05223209A - Fluidized layer burning apparatus and burning method therefor - Google Patents

Abstract

PURPOSE:To reduce NOx to be discharged from a fluidized layer burning apparatus. CONSTITUTION:The air introduced from an air inlet 1 to a window box 2 is diffused into a fluidizing chamber 4 through an air dispersing plate 3 to fluidize particles of fuel coal, limestone, etc., filled in the chamber 4, and a fluidized layer is burned. Generated burned waste gas is raised in a free board 7 and guided from a burned exhaust gas outlet 8 out of a burning furnace through a gas passage 10 formed of flow contracting members 9 mounted in the board. Vortexes of the gas are formed in the passage among the members 9. An area having a high concentration of unburned carbon particles contained in scattered particles in the passage 10 is formed by an effect for collecting the scattered particles by the members 9. An area in which the gas containing the scattered unburned solid carbon particles floated in high concentration is agitated to be mixed is formed in the board, and NOx reducing reaction of the carbon is expedited to reduce NOx concentration in the exhaust gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidized bed combustion apparatus and a combustion method therefor, and more particularly to a low-N method for denitrifying nitrogen oxides in combustion exhaust gas in a combustion furnace when burning fuel such as coal.
TECHNICAL FIELD The present invention relates to a fluidized bed combustion apparatus that enables Ox combustion and a combustion method thereof.

[0002]

2. Description of the Related Art In a conventional fluidized bed combustor using coal or the like as a fuel, as a method for reducing NOx generated by combustion, a method for performing denitration in a separate denitration facility installed at the rear of the combustor and combustion There is a method of denitration in the furnace. In the method of performing denitration in a combustion furnace, conventionally known methods include (1) multi-stage fluidized bed, (2) injection of denitration agent, (3) denitration using solid carbon, etc. Has been.

As the method (1), a two-stage fluidized bed is installed in the furnace, primary air is placed below the lower dispersion plate, secondary air is placed below the upper dispersion plate, and tertiary air is placed above the upper fluidized bed. A method is known in which the gas is introduced and the lower stage is burned in a reducing atmosphere suitable for denitration, and the upper stage is burnt in an oxidizing atmosphere suitable for desulfurization and combustion efficiency improvement (see JP-A-58-40411). As the method (2), ammonia is used as a denitration agent, and in order to avoid the generation of NOx due to the oxidation of ammonia under high temperature and oxidizing atmosphere in the fluidized bed, ammonia is sprayed together with secondary air in the freeboard section. A method is known (see JP-A-62-169917, etc.).

As the method (3), there is known a method of performing denitration by using carbon in char produced in the combustion process from coal as a fuel. In this method, the solid carbon itself is N
A reaction of reducing O and a reduction reaction of NO with CO catalyzed by char are used. As a known technique, there is known a method of activating char using an internal circulation type fluidized bed and increasing the residence time of char in the bed to accelerate the denitration reaction (Japanese Patent Laid-Open No. 2-282601).
No.

Further, a plurality of particle separators are provided at intervals in a freeboard portion of a fluidized bed combustion apparatus, and the particle separators are formed by arranging a plurality of long members in an inverted triangular shape, which has not been conventionally used. There is also known one in which fine fuel particles discharged outside the furnace as they are burned are supplemented and completely burned in the furnace (see JP-A-62-142906).

[0006]

In the above-mentioned conventional technique, the following points are raised as technical problems. 1
As a point, there is a problem of progress of corrosion of the metal material in the reducing atmosphere. In particular, when a reducing atmosphere is created in the fluidized bed, there is a great fear that the heat exchanger and the like will be corroded by sulfur.

Second, there is a problem of ammonia leakage. When ammonia, which is a harmful substance, is used as a denitration agent, it is necessary to prevent unreacted ammonia from leaking out of the combustion facility after being used in the denitration reaction. It is necessary to install a facility for ammonia recovery or strictly control the amount of injected ammonia.

Third, there is a problem of inhibition of denitration by limestone which is a desulfurizing agent. 80 for limestone (CaCO ₃ )
In the fluidized bed at a high temperature of 0 to 900 ° C., a decarboxylation reaction occurs and it exists as CaO. This CaO serves as a catalyst to promote the oxidation reaction of the nitrogen compound released from the coal and NOx.
It is known to increase the generation amount of (for example, GJVo
gel, Annual Report of ANL / ES-CEN 1007, 1974). Therefore, there is a limit to increase the denitration efficiency in a fluidized bed in which a large amount of desulfurizing agent is present.

Fourth, there is a problem of complication of combustion furnace structure and control. The fluidized bed combustor has an advantage that the structure of the combustion furnace is simple, which is an advantage. On the other hand, the technique of specializing the arrangement and shape of the fluidized bed has problems such as a complicated combustion furnace structure, complicated maintenance, and an increase in size of the combustion furnace. Further, the specialization of the fluidized bed shape and the plurality of air inflow locations lead to the complicated operation control of the combustion device.

Further, in a fluidized bed combustor in which a plurality of particle separators are provided at intervals in a freeboard portion of the fluidized bed combustor so that fine fuel particles are captured and completely combusted in a furnace, Because of its structure, the solid carbon component is not actively stirred and mixed with the exhaust gas in the high-concentration solid carbon region formed in the freeboard portion, and therefore the solid carbon is not expected to accelerate the denitration reaction. However, it is not always satisfactory from the viewpoint of low NOx combustion.

An object of the present invention is to solve the above-mentioned problems, and more specifically, a denitration region suitable for carrying out a NOx reduction reaction is formed in a freeboard section in a fluidized bed combustion furnace. The present invention provides a fluidized bed combustion apparatus capable of low NOx combustion and a combustion method thereof.

[0012]

In order to solve the above-mentioned problems, the present invention forms a region in the freeboard portion where the concentration of solid carbon is high and promotes the reduction of NOx by the solid carbon in the region. It is configured as follows. That is, according to the present invention, a combustion furnace having an air supply port on the lower side and a combustion exhaust gas discharge port on the upper side, an air dispersion plate provided in the lower part of the combustion furnace, and formed on the air dispersion plate. In a fluidized bed combustor comprising a fluidized bed made of a fluidized medium and a freeboard portion above the fluidized bed, and performing combustion in the fluidized bed, in the freeboard portion, solid carbon is contained in another region in the freeboard portion. Disclosed is a fluidized bed combustor in which a region having a higher concentration than that of the above is constituted, and in which the high concentration solid carbon is agitated and mixed with combustion exhaust gas rising from the surface of the fluidized bed.

By providing a single or a plurality of contraction members for forming a turbulent flow of the combustion exhaust gas, thereby forming a part having a reduced cross-sectional area in the freeboard part,
Alternatively, the gas supply means is further provided with a gas supply means for carrying air-borne particles containing solid carbon, and the gas supply means is connected to a plurality of gas supply openings opened on the wall surface of the freeboard portion, and the solid carbon is supplied from the gas supply opening. , Forming a partial area in the freeboard where turbulence such as swirling or swirling flow occurs, and also capturing scattered particles containing unburned carbon blown up by combustion exhaust gas or particles containing solid carbon. An area in which the solid carbon is present at a higher concentration than other areas in the freeboard portion is formed by a method such as addition.

A state in which the contraction member is constituted by a rod-shaped member having a substantially Y-shaped cross section, and one of them is inverted with respect to the other so that the Y-shaped leg portions face each other at a predetermined position in the freeboard portion. It is a particularly preferable embodiment that a plurality of staggered arrangements are provided to form a gas passage between the flow-contracting members, and the solid carbon and the exhaust gas are stirred and mixed in the gas passage. ..

[0015]

In the combustion apparatus and the combustion method of the present invention, the above-mentioned means forms a region where solid carbon is present at a higher concentration than in the freeboard portion of the conventional fluidized bed combustor, and within this region. The turbulent flow of the combustion exhaust gas is caused to increase the residence time of the combustion exhaust gas in the region from 7 to 10
A denitration area that doubles in size is formed. In this denitration region, regarding the reduction reaction of NOx by solid carbon, (1)
Increasing amount of solid carbon as a reactant, (2) solid carbon and N
The effect of increasing the contact time of Ox is obtained, and the efficiency of denitration by reducing NOx is improved.

FIG. 8 shows the NOx concentration distribution in the height direction in the freeboard section in the fluidized bed combustion apparatus of the present invention and the conventional fluidized bed combustion apparatus. The base of the fluidized bed surface (height 0
m) and the range up to the top of the furnace (height 4.6 m) is shown. In the fluidized bed combustor of the present invention, the solid carbon concentration in the portion 1 to 1.5 m from the surface of the fluidized bed is 1.5 times as high as the average in the freeboard portion of the conventional fluidized bed combustor. A denitration area is formed. In the conventional combustor, the decrease of NOx concentration draws almost an exponential function curve, whereas in the combustor in which the denitration region is formed,
Only in the denitration region, the NOx concentration is greatly reduced. The outlet NOx concentration was 71.2 ppm in the combustor of the present invention, which was about 25% lower than 95 ppm in the conventional combustor, and this NOx concentration reduction was almost entirely in the denitration region. There is.

As shown in the above results, the combustion apparatus and the combustion method of the present invention can obtain the same effect as the NOx concentration reduction by increasing the denitration agent (ammonia) injection amount or increasing the fluidized bed height. And, the combustor is upsized,
The NOx concentration at the combustion furnace outlet can be reduced without complicating the structure of the fluidized bed and increasing the injection amount of the denitration agent.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Figure 1
Is an example of a boiler using a fluidized bed combustor to which the present invention is applied. An air dispersion plate 3 is installed at the bottom of the furnace body 6, and a wind box 2 is formed below the air dispersion plate. An air inlet 1 is opened in the wind box 2, and the air supplied from the air inlet 1 is supplied into the furnace through an air dispersion plate 3. A flow chamber 4 is provided above the air dispersion plate 3, and a heat exchanger 5 is arranged inside the flow chamber 4. The fuel coal particles and particles such as the desulfurizing agent filled in the fluid chamber 4 form a fluidized bed by the gas supplied through the air dispersion plate 3, and burn the coal particles.

In the freeboard portion 7, a plurality of contracting members 9 to be described later are arranged so as to cross the freeboard portion 7,
A gas passage 10 through which combustion exhaust gas discharged from the fluidized bed passes is formed between the contracting members 9. An exhaust gas outlet 8 for discharging combustion exhaust gas to the outside of the furnace is opened in the upper part of the furnace body 6. FIG. 2 shows an example of the contracting member and the combustion exhaust gas passage, and is an enlarged view of the contracting member 9 and the combustion exhaust gas passage 10 in FIG. This contraction member 9
Has a substantially Y-shaped cross section, and is staggered in a state in which one of them is inverted with respect to the other so that the Y-shaped leg portions 91, 91 face each other at a predetermined position in the freeboard portion 7. A plurality of gas passages 10 are arranged in the shape of a gas flow path, and the gas passages 10 are formed between the flow contracting members.

That is, the leg portions 91, 9 of the contraction member 9
Each of the protrusions including 1 has a function as a protrusion for narrowing the width of the gas passage, that is, a function of forming a contracted flow portion, and the combustion exhaust gas 14 passing through the gas passage 10 is formed by each protrusion of the contracted flow member 9. A vortex is formed in the space. In this vortex, the scattered particles 15 flowing with the combustion exhaust gas 14 are held in the space for a certain period of time, and are agitated and mixed with the combustion exhaust gas. Further, in the space where the vortex is formed, the contracting member 9 becomes an obstacle and the scattered particles 15 are easily trapped. As a result, the concentration of solid carbon contained in the scattered particles floating in the space is reduced. It is higher than the concentration in the freeboard section when not installed. As a result, in the swirl region formed in the contraction member 9 installation portion, the denitration reaction by the solid carbon in the freeboard portion 7 is promoted.

The contraction member may have a structure having three functions of forming a reduction reaction space, generating a turbulent flow such as a vortex inside the space, and concentrating solid carbon in the space, and many other shapes. There can be things. FIG. 3 shows another embodiment of the contraction member 9, which has a different shape on the upstream side (that is, the lower stage).
The member 9a1 located on the lower side and the member 9a2 located on the downstream side (that is, the upper stage) form a contracting member 9a. The member 9a1 is a member having a substantially T-shaped cross section with widened leg portions 91a, and the member 9a2 is a member having the same shape as the contracting member 9 in the embodiment shown in FIG.

FIG. 4 shows still another embodiment of the contraction member, in which the contraction member 9b is composed of a lower member 9b1 and an upper member 9b2 having different shapes as shown in FIG. ing. The member 9b1 is the lower member 9 in the embodiment of FIG.
The member 9b2 has the same shape as that of a1, and the member 9b2 has a substantially T-shaped cross section, but its upper side 92b is horizontal and its upper surface is inclined downward.

In the contracting members shown in FIGS. 3 and 4, as in the case of FIG. 1, a space for reduction reaction is formed by the member located above and the lower member, and a vortex or the like is generated in the space. It will be readily understood that solid carbon is enriched as turbulent flow occurs. Especially in the case shown in FIG.
Although the volume of the reduction reaction space is reduced, it is possible to prevent ash and the like from depositing on the upper part of the member, which allows continuous operation for a longer time.

FIG. 5 shows another embodiment of the fluidized bed combustor of the present invention. In this combustor, an opening 12 for ejecting gas to the freeboard portion 7 in the furnace is formed on the wall surface of the freeboard portion 7, and the airflow carrier pipe 11 is connected to the opening 12. As shown in FIG. 6, the openings 12 are arranged at two corners located diagonally in the cross section of the furnace body 6. Therefore, a swirl flow is generated in the freeboard portion 7 by the gas ejected from the airflow carrier pipe 11, and
The combustion exhaust gas generated by the combustion in the flow chamber 4 similarly forms a swirling flow. Due to this swirling flow, in this area,
Similar to the swirl in the embodiment shown in FIGS. 1 to 4, the floating solid carbon concentration is increased and the combustion exhaust gas residence time is increased. As a result, a sufficient denitration effect can be achieved.

In this embodiment, the air flow carrier pipe 1
The number, position and opening direction of the openings 12 connected to 1 are not limited to those shown in the figure, and the point is that they may be arranged in a state suitable for generating a swirling flow in the freeboard. is there. For example, it may be arranged with an angle in the horizontal direction, and it is also effective to have the angle in the vertical direction with the angle in the horizontal direction so as to be downward in the furnace.
Furthermore, it is also possible to dispose them in a state in which the positions are vertically shifted to some extent.

One mode of operating the fluidized bed combustor of the embodiment shown in FIGS. 5 and 6 will be described with reference to FIG. In this operation mode, air or another gas is introduced as the transport gas 16 into the air flow carrier pipe 11 and is jetted into the furnace through the opening 12. At the same time, the combustion exhaust gas 14 generated by the combustion in the fluidized bed passes through the freeboard portion and the exhaust gas outlet and is discharged to the outside of the furnace. This exhaust gas contains scattered particles having a relatively small particle size. Therefore, the scattered particles are collected by the cyclone 13, and the collected scattered particles are mixed with the gas flowing through the airflow carrier pipe 11 and ejected into the furnace together with the gas.

By adopting such a combustion method, it is possible to prevent the temperature from dropping when the gas is jetted into the furnace. Therefore, it is possible to improve the concentration of suspended solid carbon in the swirling flow formed in the furnace. The denitration effect can be increased, and at the same time, improvement in combustion efficiency can be expected. The above description is merely a description of some embodiments of the present invention, and there are many other modifications. For example, as described above, the structure of the contraction member is not limited as long as it has a three-action structure of forming a reduction reaction space, generating turbulent flow such as vortex inside the space, and concentrating solid carbon in the space. Obviously, the objects of the invention can be achieved, and there can be many forms other than those shown. Further, in the operation of the fluidized bed combustor of the form shown in FIG. 5, it is not always essential to mix the scattered particles collected by the cyclone 13 into the gas flowing through the air flow carrier pipe 11, and it is not necessary to mix gas such as air. It may be simply flowed in, or solid carbon may be supplied into the gas from outside the machine and flowed into the freeboard.

It is also possible to arrange the contracting means shown in FIG. 1 and the swirling flow generating means for feeding gas shown in FIG. 5 in the freeboard at the same time, and to use these means simultaneously to perform combustion. It is possible.

[0029]

As described in detail above, according to the present invention, solid carbon is present at a high concentration in the freeboard portion in the fluidized bed combustor combustion furnace, and the turbulence of the flow of combustion exhaust gas is formed. It is possible to promote the denitration reaction in the combustion furnace by forming a region to be controlled. As a result, the cost required for exhaust gas denitration can be reduced. At this time, there is no need to increase the size of the fluidized bed combustion furnace and complicate the structure for denitration in the fluidized bed combustion furnace. Further, when used in combination with the method of adding the denitration agent into the combustion furnace, it is possible to improve the denitration efficiency without increasing the addition amount, so that it is possible to prevent the ammonia as the denitration agent from leaking out of the combustion furnace. it can.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a combustor of the present invention.

FIG. 2 is an enlarged cross-sectional view of a contracting member of the combustor shown in FIG.

FIG. 3 is a cross-sectional view showing another embodiment of the contraction member.

FIG. 4 is a cross-sectional view showing still another embodiment of the contracting member.

FIG. 5 is a vertical cross-sectional view showing another embodiment of the combustor of the present invention.

6 is a cross-sectional view of the combustor shown in FIG.

FIG. 7 is a diagram showing a method of operating the combustor shown in FIGS. 5 and 6.

FIG. 8 is a comparison of NOx distribution in a conventional fluidized bed combustion apparatus and in the freeboard section of the present invention.

[Explanation of symbols]

1: Air inlet, 2: Wind box, 3: Air dispersion plate, 4: Flow chamber, 5: Heat exchanger, 6: Furnace body, 7: Freeboard part, 8: Combustion exhaust gas outlet, 9: Flow reducing member 10:
Gas passage, 11: air flow carrier pipe, 12: air flow carrier pipe outlet,
13: cyclone, 14: combustion exhaust gas, 15: scattered particles, 16: transport gas, 17: air

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahide Nomura 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Works, Ltd., Hitachi Research Laboratory (72) Inventor Atsushi Morihara 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Nitate Works Co., Ltd. Hitachi Research Laboratory (72) Inventor Kazuki Ouchi 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd.

Claims (6)

[Claims] 1. A combustion furnace having an air supply port on the lower side and a combustion exhaust gas discharge port on the upper side, an air dispersion plate provided in the lower part of the combustion furnace, and formed on the air dispersion plate. In a fluidized bed combustor comprising a fluidized bed made of a fluidized medium and a freeboard portion above the fluidized bed, wherein solid carbon is contained in the freeboard portion more than other regions in the freeboard portion. Also has a region with a high concentration, and in this region, the high concentration of solid carbon is agitated and mixed with the combustion exhaust gas rising from the surface of the fluidized bed. 2. The fluidized bed combustion apparatus according to claim 1, wherein a single or a plurality of contraction members for forming a turbulent flow of combustion exhaust gas are provided in the region. .. 3. The contracting member is a rod-shaped member having a substantially Y-shaped cross section, and one of them is inverted with respect to the other so that the Y-shaped leg portions face each other at a predetermined position in the freeboard portion. In the state, a plurality of staggered arrangements are provided to form the gas passages 10 between the contraction members,
The fluidized bed combustion apparatus according to claim 2. 4. A gas supply means for carrying particles containing solid carbon in an air stream is further provided, and the gas supply means is connected to a plurality of gas supply openings opened on the wall surface of the freeboard part of the combustion furnace, and from the gas supply opening. 4. The fluidized bed combustion apparatus according to claim 1, wherein the region is formed by supplying the solid carbon according to claim 4. 5. A dust collector for treating gas discharged from the fluidized bed combustor is further provided, and scattered particles containing unburned solid carbon separated by the dust collector are supplied to the gas supply means. The fluidized bed combustion apparatus according to claim 4, wherein the fluidized bed combustion apparatus is configured. 6. A fluidized bed having an air dispersion plate in a lower portion of a combustion furnace, and performing combustion in a fluidized bed in which a fluidized medium is fluidized on the air dispersion plate by a gas supplied from the air dispersion plate. A method of combustion in a combustion device, in which a region where solid carbon is present at a high concentration is created in a specific region within the freeboard section, and in this region solid carbon and combustion exhaust gas rising from the fluidized bed surface are agitated and mixed for combustion. A combustion method for a fluidized bed combustion device, characterized in that NOx generated by combustion in the fluidized bed is reduced by performing the above.