JPH0611101A - Structure of combustion chamber in boiler - Google Patents

Abstract

PURPOSE:To enable the manufacture of a boiler with large capacity, which has a combination of both stability of combustion on fire grates that can be easily used and rationality of suspended combustion in a boiler having therein the fire grates on which solid fuel such as biomass fuel and coal is burned. CONSTITUTION:In a boiler having therein fire grates 4a, 4b on which solid fuel such as biomass fuel and coal is burned, an intermediate partitioning wall 13 consisting of a group of water tubes is provided at the central part of combustion chambers 2, 2 and a group of nozzles 11 for supplying secondary air into the combustion chambers is disposed among the water tubes forming the intermediate partitioning wall.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to improvement of a combustion chamber of a boiler equipped with a grate for burning a biomass fuel such as bagasse, wood chips, and bark, or a solid fuel such as coal.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of diversifying energy sources and removing oil from the industrial world, utilization of biomass and coal as fuel for boilers has been actively promoted. For example, in a sugar factory, the power of the entire factory is covered by using the residue (called bagasse) after squeezing the sugar content from sugar cane as fuel for the boiler. Biomass such as wood chips, bark, and chaff is also widely used as a fuel for boilers, both for waste disposal by combustion and recovery of thermal energy. Thus, the use of solid fuels such as biomass and coal accelerates the removal of oil from the industrial world and makes a great contribution to solving energy problems.

The biomass fuel has a large amount of volatile matter and a small amount of fixed carbon (fixed carbon / volatile matter = 0.2 to 0.2).
0.3), low ash content (1-2%), irregular shape (particle size), no sulfur content, no air pollution, relatively high water content 30-
60%), bulky (apparent specific gravity 150-200k
g / m ³ ), etc. Moreover, the calorific value greatly varies depending on the water content, and is approximately 2000 to 300.
It is known that it is about 0 kcal / kg, and its combustion characteristics are better in ignitability and faster in combustion rate than bituminous coal that performs fire bed combustion.

By the way, a boiler that uses solid matter such as bagasse or coal as a fuel is generally equipped with any of a transfer type grate, a fixed type grate and a damping type grate at the bottom of a combustion chamber. 9 and 10 show an example of a combustion chamber portion of a boiler provided with a floor transfer type grate 18 at the bottom of the combustion chamber 17, and the grate 18 has a width dimension substantially the same as the width W of the combustion chamber 17. And has a length dimension substantially the same as the depth L of the combustion chamber 17. Further, as a drive system of the grate 18, a so-called reverse feeding system in which the combustion chamber 17 is driven from the inner part toward the front part is adopted, and combustion is completed at the front part of the combustion chamber 17. Is set to the drive speed.
Further, 70-80% of the air required for combustion is primary air, and the combustion chamber 17 from the lower part of the moving bed type grate 18
It is supplied to the inside of the combustion chamber 17, and the rest is supplied to the inside of the combustion chamber 17 as secondary air from the nozzle 20 arranged between the water pipes 19 on the front wall and the rear wall of the combustion chamber 17. In addition, 21 is a wind box for grate,
Reference numeral 22 is a secondary air wind box, and 23 is a fuel supply port.

In the boiler shown in FIGS. 9 and 10, when bagasse, coal, or the like is sprayed and burned, the fuel with large particles falls onto the grate 18 and undergoes grate combustion, and the fuel with small particles is also generated. The fuel undergoes so-called floating combustion in the combustion chamber 17. Thus, in the conventional boiler of this type, as described above, the grate 1
The area of 7 and the cross-sectional area of the combustion chamber 17 are designed to be substantially the same. However, basically, the grate 1
The area of 8 is based on the amount of fuel burned on the grate 18,
Further, the area and the volume of the combustion chamber 17 should be determined based on the amount of fuel that causes floating combustion. For example, in the case of bagasse fuel, 30 to 70% of the total sprayed weight is transferred to the grate 18. Since it is known that it will arrive, the required area of the grate 18 can be calculated from the numerical value. Further, the shape of the combustion chamber 17 should be selected as an ideal combustion chamber shape in consideration of the cross-sectional area determined by the rising speed of the combustion gas.

[0006]

On the other hand, in recent years, drawing technology for sugar cane has progressed, and as a result, bagasse, which is a drawing slag, tends to contain more fine particles than coarse particles.
Therefore, in these boilers that use bagasse as a fuel, the amount of bagasse performing floating combustion is increasing more than that of grate combustion. In other words, in the design of the above-mentioned grate area, combustion chamber volume, and combustion chamber cross-sectional area, the grate area is made smaller and the combustion chamber, especially its cross-sectional area, is made larger, further promoting floating combustion in the combustion chamber. It is necessary to devise the method of supplying the secondary air.

In recent boiler equipment, the output of a single boiler is increasing in order to improve the economical efficiency and operability of the boiler equipment and facilitate maintenance. For example, in a twin-hulled water tube type natural circulation type medium- and low-pressure boiler, it is possible to increase the lateral width W of the combustion chamber as the amount of evaporation increases, and thereby to secure a necessary combustion chamber volume.
It has been established as a general design method. According to this method, the volume of the steam chamber in the attached steam drum and the heat transfer area for heat absorption are also increased in proportion to the lateral width W of the combustion chamber, thereby providing a well-balanced boiler design condition. Become. On the other hand, the depth dimension L of the combustion chamber is
Since it is mainly determined by the distance reached when fuel is sprayed,
There is not as much freedom as when determining the width W of the combustion chamber,
Depending on the type of fuel, a size of 6 to 7 meters is usually adopted depending on the boiler output. 11 to 1
3 shows a schematic shape of a transverse section of a combustion chamber of various boilers from a conventional small capacity to a large capacity, and an arrow shows a secondary air supply hole.

On the other hand, the most important secondary air supply for promoting the floating combustion is through the secondary air nozzles provided on the front and rear walls and side walls of the combustion chamber 17 as shown in FIGS. 11 to 13. Has been done. However, if the cross-section of the combustion chamber, especially the width W, is enlarged with an increase in the amount of evaporation, as shown in the range of the dotted line in FIG. 13, sufficient secondary air can be supplied in the central portion of the combustion chamber. There is a problem that some areas are not generated. In addition, in the conventional design,
Since the lateral width dimension W of the combustion chamber and the lateral width of the grate are designed to be substantially the same, the lateral width of the grate will also increase as the boiler output increases, and as a result,
There is a problem that the upper limit of the boiler output is limited by the manufacturing limit of the grate.

Thus, in a general transfer type grate,
Due to the economical manufacturing constraints of the drive part, the lateral width per grate is set to about 6 meters in the economical design range. Therefore, in a boiler equipped with a combustion chamber having a lateral width W exceeding this, as shown in FIGS. 14 and 15, the grate drive shaft is divided into left and right to be a mechanically independent mechanism. Speed reducer 25 installed at the shaft end of
A method of driving both grate 18a, 18b by a driving machine 24a, 24b via a, 25b has been put into practical use.
However, the method of FIGS. 14 and 15 is one in which two independent grate 18a and 18b are simply arranged side by side, and not only the equipment cost is high, but also the operation and maintenance of the grate. However, there is a drawback that it takes time. still,
The lengthwise dimension of the grate is considerably looser in terms of manufacturing restrictions than the widthwise dimension, and the length dimension L between chain wheels is L.
_A long length of _{1 up} to 8 meters has been put to practical use.

As described above, when the capacity of the boiler is increased and the lateral width W of the combustion chamber reaches 13 meters, even if the method of driving the grate from the left and right by independent drive shafts is adopted, Many inconvenient parts occur in the mechanical structure, which makes the production of the grate extremely difficult. Further, even if the grate could be driven, there are problems that the facility cost of the grate will increase significantly and that operation and maintenance will be troublesome. The present invention was created in order to solve the above problems in a boiler equipped with a grate that uses bagasse or coal as a fuel, and improved the secondary air supply method and the moving direction of the grate. The present invention provides a structure of a boiler combustion chamber that makes it possible to realize a large-capacity grate type boiler with a steam generation amount exceeding 300 tons per hour, which has been conventionally impossible.

[0011]

In order to achieve the above object, the present invention provides a boiler equipped with a grate for burning biomass fuel such as bagasse, wood chips, and bark, or solid fuel such as coal. An intermediate partition wall composed of a water pipe group is provided in the central portion of the combustion chamber, and a nozzle group for supplying secondary air to the combustion chamber is arranged between the water pipes forming the intermediate partition wall. Adopt as a configuration.

More specifically, in the present invention, more specifically, the combustion chamber is divided into left and right by installing a partition wall in the center of the boiler combustion chamber, the lower part of which is inclined toward the front wall of the combustion chamber. At the same time, a transfer-type grate is provided at the bottom of each of the left and right combustion chambers. In addition, the partition wall connects adjacent water pipes of bare pipes at intervals of about 3000 mm with a metal object in order to provide lateral strength, and absorbs radiant heat in the combustion chamber without obstructing passage of combustion gas. It is a heat transfer tube installed, and boiler can water circulates inside. Further, in the lower part of the partition wall, a wall surface composed of water pipes inclined to the left and right is formed, and secondary air is supplied toward the inside of the furnace from secondary air nozzles arranged between the water pipe pitches. In addition, the grate provided below each of the left and right combustion chambers is driven by a separate driving device toward the front wall side of each of the left and right combustion chambers, and the grate is formed on the front wall side of each combustion chamber. The combustion of the above fuel is completed.

[0013]

The fuel is sprayed from the upper portions of the front walls of the left and right combustion chambers toward the partition wall in the center of the combustion chambers. The fuel components with relatively fine particles have a high temperature inside the combustion chamber, so that the water content is immediately evaporated, and the secondary air is supplied from the secondary air nozzles installed in the central partition wall or near the fuel supply port. Ignite, complete ignition and combustion in a floating state. On the other hand, in the fuel component having a relatively large particle diameter, part of the water content is evaporated by the combustion gas in the furnace during the spraying. However, since it has a large mass, it does not reach the floating state even when the combustion gas rises and falls onto the grate surface. The particles that have fallen onto the grate surface receive radiant heat from the combustion chamber to further evaporate water, and when they reach the ignition temperature, they are supplied with primary air from the lower part of the grate and start to burn. The transfer speed of each grate is adjusted so that the combustion of all the fuel deposited on the grate surface at the end of the grate is completed. As described above, both floating combustion and fire bed combustion are simultaneously performed in one combustion chamber depending on the size of the fuel particles, but in the combustion chamber of the present invention, the inclination of the lower part of the central partition wall is increased. Since the secondary air is evenly supplied from the secondary air nozzles installed on the surface in the lateral direction and the depth direction of the combustion chamber, the floating combustion in the combustion chamber is significantly promoted.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 and 2 are a schematic vertical sectional front view and a vertical sectional side view of a water tube boiler adopting a combustion chamber structure according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view taken along the line II of FIG. In the figure, 1 is a furnace wall, 2 is a combustion chamber, 2a is a front wall of each combustion chamber, 3 is a boiler main body, 4a and 4b are transfer type grate,
5 is a grate wind box, 6a and 6b are fuel inlets, 7 is an air preheater, 8 is a primary forced draft fan, 9 is a secondary forced draft fan, 1
0 is a secondary air wind box, 11 is an air injection nozzle, 12 is a combustion chamber side wall water pipe, 13 is a combustion chamber partition wall, and 14a, 14b.
Is a secondary air supply hole for fuel distribution, and 16a and 16b are driving machines. Bagasse is used as the fuel for this water tube boiler.

The furnace wall 1 is a finned water pipe or a bare water pipe type water cooling wall, and a large number of water pipes 1 are provided on the inner wall surface thereof.
2 are arranged in the vertical direction at a constant pitch. Further, the combustion chamber 2 is formed by surrounding an upper space of the transfer bed type grate 4 with a furnace wall 1 or a partition wall 13 which will be described later, in which the fuel undergoes floating combustion.

At the center of the combustion chamber 2, there is arranged a partition wall 13 in which bare water pipes having the structure shown in FIG. 4 are connected to each other. That is, in FIG. 4, 13 is a combustion chamber partition wall,
Reference numeral 13a is a water pipe, and 13b is a metal piece for connecting the water pipes together. As is clear from FIG. 4, the partition walls 13 are arranged at a pitch of about 1.5 times the diameter of the water pipes, and therefore the combustion gas. There is no obstacle to the passage of.

As shown in FIG. 2, the lower portion of the combustion chamber partition wall 13 is inclined toward the left and right combustion chamber front walls 2a, 2a, and the inclination angle α of this inclined portion is scattered. The angle of repose is equal to or greater than the angle of repose of the fuel. That is,
The inclination angle α is set to an angle such that the fuel dropped on the inclined wall surface slides down along the wall surface.
Specifically, the angle α is set to 50 ° to 80 ° with respect to the horizontal plane. Further, a secondary air wind box 10 is arranged on the inclined wall surface portion, and the secondary air wind box 10 is connected to the nozzle 11
Secondary air is being supplied to.

The nozzles 11 are arranged between the water pipes 13a in the inclined portion of the partition wall 13 at regular intervals as shown in FIG. 5, and are directly connected to the secondary air box 10. There is. That is, the nozzle 11 sprays secondary air to evenly disperse the large-mass fuel particles and ash that have fallen to the inclined portion of the partition wall 13 onto the transfer-type grate 4a, 4b, and at the same time, burn the combustion. Secondary air is supplied to the floating fuel particles and volatile components in the chamber 2 to promote floating combustion.

Referring to FIGS. 1 and 2, the air required for combustion is supplied from the forced draft fan 8 to the air preheater 7 and the air passage 15.
And is supplied to the grate wind box 5 and the secondary air wind box 10, respectively. That is, a part of the combustion air is supplied from the grate wind box 5 to the transfer-type grate 4a, 4b to be used as primary air, and the rest is further pressurized by the secondary forced draft fan 9, After being supplied to the air box 10 for the next air, the nozzle 1
1 is ejected into the combustion chamber 2 and is used as secondary air. The fuel (bagasse) supplied from the fuel inlets 6a and 6b is blown into the combustion chamber 2 by the secondary air nozzles 14a and 14b arranged in the vicinity of the fuel inlet 6, and part of the fuel is a transfer bed lattice. It is sprayed on 4a and 4b. Then, here, the primary air supplied from the grate wind box 5 to the transfer floor grate 4a, 4b burns the grate to become ash, which is dropped and discharged from the transfer floor grate 4a, 4b. In addition, the remaining fuel performs floating combustion in the combustion chamber 2 by the secondary air ejected from the nozzle 11 into the combustion chamber 2. At this time, a part of the fuel scattered in the combustion chamber 2 falls to the inclined surface portion of the partition wall 13 and slides down on the inclined surface, and the transfer bed grate 4
Attempts to deposit non-uniformly on a and 4b, but the nozzle 11
Is blown off by the secondary air jetted into the combustion chamber 2 from the above, and the large particles are re-dispersed evenly on the transfer bed grate 4a, 4b. Also, fine particles will be resuspended.

Nozzle 1 provided on the partition wall 13 in the middle of the combustion chamber
As shown in FIG. 6, the secondary air ejected from No. 1 has its ejection position in the vicinity of the central portion of the combustion chamber 2, that is, at a position capable of covering about 1/2 of the total cross-sectional area of the combustion chamber. Secondary air is evenly supplied to the central portion, and in combination with the secondary air supply from the fuel supply unit, it is in sufficient contact with floating fuel particles and volatile components in the combustion chamber 2. As a result, the floating combustion is further promoted, and the floating combustion particles and the volatile components are completely burned, so that the amount of dust in the exhaust gas component is reduced and the generation of unburned CO can be suppressed.

Further, in the present invention, the lower side of the intermediate partition wall 13 is inclined to reduce the cross-sectional area of the lower portion of the combustion chamber 2 and to reduce the area of the transfer bed grate 4a, 4b. As a result, the thickness of the fuel layer and the ash layer on the transfer grate 4a, 4b is increased, and the blow-through phenomenon is prevented. This improves the combustion efficiency, protects the transfer bed grate 4a, 4b from the radiant heat from the combustion chamber 2, and prevents the transfer bed grate 4a, 4b from burning. Further, since the area of the transfer grate 4a, 4b is reduced, the cooling effect of the transfer grate 4a, 4b by the primary air can be enhanced,
Burning of the transfer grate 4a, 4b can be prevented more effectively.

Further, in the present invention, as shown in FIG. 6, both grate 4a and 4b are driven in the direction of moving the combustion products from the central partition wall 13 side toward the front wall side of both combustion chambers. . That is, in the conventional boiler as shown in FIG. 15, the width of the fire bed of one grate installed in the left or right combustion chamber is dominated by the lateral width W of the combustion chamber. However, in the present invention, as shown in FIG. 7, the fire bed width of the grate can be made substantially the same as the depth dimension L of the combustion chamber 2, and the floating combustion is promoted by the nozzle 11 provided in the partition wall 13. By adopting a secondary air supply function for this, the length of the grate can be significantly shortened compared to the conventional one.

Further, when the depth dimension L of the combustion chamber 2 is large and the design inconvenience of the grate 4a, 4b occurs, FIG.
The grate 4a, 4b is divided into front and rear as shown in
1, 4a2, 4b1 and 4b2, and individual driving machines 16a
By driving with 1, 16a2, 16b1, 16b2, it becomes possible to make a grate for a larger capacity boiler, and the production of a large capacity boiler equipped with a grate, which was previously impossible due to manufacturing restrictions. Is possible. In other words, it is possible to manufacture a characteristic large-capacity boiler that has both the safety of grate combustion and the rationality of floating combustion.

As described above, in the structure of the boiler combustion chamber according to the present invention, the radiant heat transfer surface by the partition wall is arranged in the middle portion of the combustion chamber, so the radiant heat transfer amount by the flame in the combustion chamber. Can be increased. Also, by inclining the lower side of the water cooling wall, which is a component of the partition wall, toward the fire bed located in the lower part of the combustion chamber, the cross-sectional area of the combustion chamber is gradually reduced, and the water pipe of the inclined part of the partition wall is Since a group of nozzles for ejecting secondary air to the combustion chamber is arranged between them, the area of the grate can be reduced and the fuel particles and ash falling on the inclined part of the furnace wall are evenly distributed on the grate. Can be sprayed. As a result, the thickness of the fuel layer and ash layer on the grate is increased to prevent blow-through phenomenon, which improves combustion efficiency, protects the grate from radiant heat from the combustion chamber, and prevents burnout of the grate. To be prevented.
However, since the area of the grate can be reduced, the effect of cooling the grate by the primary air can be enhanced, and the burnout of the transfer bed grate can be further prevented. Further, the secondary air ejection hole in the lower part of the intermediate partition wall is provided near the center of the combustion chamber,
Since the secondary air completely covers the range of about 1/2 of the cross-sectional area of the combustion chamber, the floating combustion is significantly promoted, and the complete combustion of the floating fuel particles and volatile components in the combustion chamber is possible. As a result, the amount of soot and dust in the components of the exhaust gas is reduced and CO
Can be suppressed. In addition, in the present invention, since the transfer direction of both grate is the direction from the central partition wall side to the front wall side of both combustion chambers, the drive shaft should have substantially the same length as the depth L of the combustion chambers. In addition to being able to make a selection within a mechanical strength and economical range, it is possible to realize a stoker-fired boiler with an evaporation amount of 300 tons or more per hour, which has been impossible in the past. As described above, the present invention enables the realization of a large-capacity boiler that combines the safety and ease of use of a boiler equipped with a grate, the rationality of floating combustion, and the like, and exhibits excellent practical utility. It is a thing.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a boiler equipment including a boiler combustion chamber according to the present invention.

FIG. 2 is a schematic cross-sectional view taken along the line E-I of FIG.

FIG. 3 is a schematic cross-sectional view taken along line E-I of FIG.

FIG. 4 is a perspective view showing a part of an intermediate partition wall.

FIG. 5 is an explanatory view showing a mounting state of the nozzle 11.

FIG. 6 is an explanatory diagram showing an injection state of secondary combustion air from a nozzle 11.

FIG. 7 is an explanatory diagram showing a relationship between a width dimension of the grate and a depth dimension L of the combustion chamber.

FIG. 8 is an explanatory diagram of another example showing the relationship between the width dimension of the grate and the depth dimension L of the combustion chamber.

FIG. 9 is a schematic explanatory view of a boiler combustion chamber including a conventional grate and using a biomass fuel.

FIG. 10 is a schematic cross-sectional view taken along the line BB of FIG. 9.

FIG. 11 shows a plan view of a combustion chamber of a conventional small capacity boiler.

FIG. 12 shows a plan view of a combustion chamber of a conventional medium capacity boiler.

FIG. 13 shows a planar shape of a combustion chamber of a conventional large capacity boiler.

FIG. 14 is a schematic vertical sectional view of a combustion chamber of a large-capacity boiler in which a plurality of conventional grate is juxtaposed.

FIG. 15 is a schematic cross-sectional view taken along line BB of FIG.

[Explanation of symbols]

Reference numeral 1 is a furnace wall, 2 is a combustion chamber, 2a is a front wall of each combustion chamber, 3 is a boiler body, 4a and 4b are transfer type grate, 5 is a grate wind box, 6a and 6b are fuel inlets, 7 is an air preheater, 8 is a primary forced draft fan, 9 is a secondary forced draft fan, 10 is a secondary air box, 11 is an air blowing nozzle, 12 is a combustion chamber side wall water pipe, and 13 is a combustion chamber partition wall. , 14 is a secondary air supply hole for fuel distribution, 15 is an air passage, 16 is a grate drive, and 17 is a speed reducer.

Claims (4)

[Claims] 1. A boiler equipped with a grate for burning a biomass fuel such as bagasse, wood chips, bark or the like, or a solid fuel such as coal or the like, wherein an intermediate partition wall composed of a water pipe group is provided in a central portion of the combustion chamber, A structure of a boiler combustion chamber, characterized in that a group of nozzles for supplying secondary air to the respective combustion chambers on both sides is arranged between water pipes forming the intermediate partition wall. 2. Below each combustion chamber on both sides of the intermediate partition,
The structure of the boiler combustion chamber according to claim 1, further comprising: a grate for moving the combustion products from the side of the intermediate partition wall toward the front wall of each combustion chamber. 3. The method according to claim 1, wherein the intermediate partition wall is configured so as not to substantially prevent the flow of combustion gas, and the lower portion of the intermediate partition wall is inclined toward the front wall side of each combustion chamber. Item 2. The structure of the boiler combustion chamber according to Item 2. 4. The structure of the boiler combustion chamber according to claim 1, wherein the fuel is supplied from the front wall side of each combustion chamber toward the intermediate partition wall side.