JPH0235889B2 - - Google Patents

Abstract

1. A fluidised bed combustion chamber of variable heat output, delimited by a side wall (1) surrounding a central zone (6) and a fluidisation grid (2), in which the fluidised bed has a lower level (13) at the lowest output of the combustion chamber and an upper level (14) at the highest output of the combustion chamber, containing a tubular heat exchanger having tubes (7, 8) which extend in a vertical direction at least between the lower level (13) and the upper level (14) characterised in that injectors (12) for injecting air for confining the combustion zone are disposed above the upper level (14) in the vicinity of the side wall (1) and are directed towards the central zone (6) of the combustion chamber with an inclination relative to the vertical at an angle (a) of between 15 degrees and 75 degrees, the total flow rate of the confinement air injected by said injectors (12) being controllable at between 5% and 20% of the total flow rate of the air introduced into the combustion chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a solid fuel combustion furnace, for example for a fluidized bed boiler, which can be used for industrial purposes such as generation of steam, hot water, heated gas, etc.

[Conventional technology]

It is difficult to vary the heat output of known fluidized bed boilers while maintaining optimal operating conditions. The fuel flow rate and combustion air flow rate fed to the furnace can only be adjusted to vary by a ratio of approximately 1:2. Beyond this ratio, the operating conditions can no longer be satisfied. As the air flow rate increases, the resulting pressure drop across the grid has unacceptable effects.
When the air flow rate decreases, the distribution of fluidized air deteriorates, and the degree of internal fluidization deteriorates.

French Patent No. 8200815 describes a fluidized bed furnace with a special solution in which the quantity of fuel can be adjusted to a ratio greater than 2. This solution uses a specially designed fluidization grid with two independent gas injection circuits. The discharge orifice of one of the circuits, called the process gas circuit, is located at a higher level than the orifice of the fluidizing gas circuit. The adjustments that can be made with this solution are not always perfect. If the air velocity is high,
Although the fuel flow rate also increases, the generated heat cannot be removed sufficiently, so the temperature inside the bed becomes very high. Furthermore, a considerable amount of fuel is carried out of the floor without being combusted.

Furthermore, it is known to install heat exchanger pipes within a fluidized bed, but these pipes are generally placed horizontally in a zone near the top of the bed. This zone acts on and varies the velocity of the fluidizing gas, so that the heat exchanger pipes are more or less completely embedded in the bed. Therefore,
The heat exchange coefficient is much greater inside the bed than outside the bed.

[Problem of invention]

The problem of this invention is to maintain sufficient operating conditions and
In other words, another solution is provided in which the power output of a fluidized bed combustion furnace can be adjusted to a high ratio without causing an excessive increase in the temperature of the fluidized bed when the velocity of the combustion air is high, and without significant losses due to unburned materials. There is a particular thing.

[Solving issues]

The above problem is solved by the present invention, in which a fluidized bed combustion furnace consists of a side wall and a fluidized bed, both of which define a central area containing the fluidized bed, which corresponds to the lowest power of the furnace. and a high position corresponding to maximum power, the combustion furnace further comprising a heat exchanger comprising a number of pipes extending substantially perpendicularly between at least said low position and said high position. The solution is to have a large number of air inlets, which are arranged at a high position near the side walls and towards the central area of the furnace.

[Effect]

In one embodiment of the invention, primarily for large furnaces, the pipes or bundles of pipes are placed evenly spaced throughout the furnace.

In another embodiment of the invention, a pipe or a bundle of pipes is arranged near the side wall of the furnace. This approach is primarily relevant in relatively small cases, such as small boilers or small to medium boiler furnaces for relatively high ash fuels.

It is advantageous to install the secondary air injection higher than the highest height reached by the pipe bundle around the furnace. The secondary air jet is
These jets are directed at an angle of 15 DEG to 75 DEG to the central region of the furnace, and the total flow rate of these jets is set between 5% and 10% of the total flow rate of air introduced into the furnace.

The invention can be used with any type of fluidized bed grid, provided that slanted or vertical pipes can be installed in the fluidized bed. In particular, the invention can be used in a specially designed fluidization grid having two independent circuits and a double height blowing orifice as described in the aforementioned French Patent No. 8200815.

〔Example〕

Although an example of a combustion furnace is described, it is not intended to be limiting or to exclude any equivalent variations.

The examples described herein are of relatively complex constructions chosen to demonstrate that the invention is compatible with various known means for improving furnaces.

The illustrated furnace has side walls 1 surrounding a square fluidized bed grid 2. The fluidized bed grid 2 is of the type with independent blowing circuits 3, 4, since only solid fuel combustion furnaces are considered, both circuits are supplied with air.

The first circuit 3 is located on the top surface of the fluidized bed grid 2,
It ends at an upwardly opening orifice 3A. The second circuit 4 terminates at an orifice 4A opening horizontally at the top of a vertical tube 4B which extends upward from the top surface of the grid 2 between the orifices 3A of the first circuit 3. A detailed description of this fluidized bed grid can be found in the aforementioned French Patent No. 8200815.
It is disclosed in the publication No. The details of this method are included herein for reference.

However, other types, i.e. orifice 3
It should be understood that a single air blowing circuit fluidized bed grid with A can be used.

The side walls 1 and the fluidized bed grid 2 together define a space 5 having a central area 6. According to this invention,
Pipes 7 and 8 are installed vertically within this space 5. These pipes are arranged in two parallel rows so that the central region 6 is empty, and are arranged in steps near the side wall 1. In the attached drawings, only the pipes 7 and 8 that are close to the vertical cross section are shown, and pipes that are far away are omitted for the sake of simplicity. Pipes 7 constitute the first bundle of heat exchangers, and pipes 8 constitute the second bundle.
At the lower end, these pipes are connected to an inlet collector 9 for the heat exchange liquid, and at the upper end to an outlet collector 10 for that liquid.

The air pipe 11 is located on a horizontal plane, and the air injection part 1
2, but is arranged around the furnace, and the side wall 1
Pipes 7, 8 arrive near the exhaust collector 10
It is located above the height of The air inlets 12 are uniformly distributed along the air line 11 and are oriented in the direction of the central region of the furnace and make an angle a with the vertical direction. The air injection portions 12 may be individually attached to the side wall, and air may be supplied individually. As another variant, the air line 11 may be placed outside the side wall and connected to each injection port 12 via the side wall. In any case, the injectors 12 are spaced toward the central area of the furnace and are balanced with a total flow rate of secondary air corresponding to 5-20% of the total air flow rate introduced into the furnace. .

The angle of inclination a of the air injection part 12 does not have a precise critical value; this angle can be selected from 15° to 75° with respect to the vertical direction, the main value being about 60°.

According to one embodiment of the invention, the orientation of the air injection part 12 can be adjusted so that the inclination angle a can be changed depending on the output of the fluidized bed. If desired, means may be provided to automatically adjust this angle and increase it as the height of the fluidized bed increases.

Depending on the total flow rate of air passing through the fluidization grid 2, the fluidized bed has a low position 13, shown in solid lines, and a high position 14, shown in dash-dotted lines. The low position 13 is
This corresponds to the lowest heat output of the furnace, and the high position 14 corresponds to the highest heat output of the furnace.

The pipes 7, 8 of the heat exchanger are generally connected to the fluidized bed grid 2.
It extends vertically from the top to the top of the elevated position 14 of the fluidized bed. In the last mentioned operating state, ie at maximum power of the furnace, the pipes 7, 8 are completely submerged in the fluidized bed, so that they operate at their maximum heat removal capacity.

To obtain the above results, it is not necessary to arrange the pipes 7, 8 strictly vertically. These pipes are
It may be inclined with respect to the vertical direction. Furthermore, it does not necessarily have to be straight. However, it is important that the pipes 7, 8 run continuously in the vertical direction, at least from the low point 13 of the fluidized bed, and mainly from the fluidized bed grid 2 to the high point 14 of the fluidized bed.

In the embodiment of this invention, the collector 10 is omitted,
A cooling pipe 15 with pipes 7 and 8 running along the wall of a radiation/convection chamber 16 above the fluidization chamber in a known manner.
can be directly connected to.

The illustrated example shows that the present invention
It has been shown that it is compatible with using a heat exchanger known per se with horizontal pipes 17 arranged close to. As is known per se,
In addition to a fixed fuel supply (not shown), a circuit 18 for recirculating inert material, such as ash, can be installed.

〔Effect of the invention〕

During operation, as the power, i.e. the flow rate of fuel and the flow rate of combustion air increases, the height of the fluidized bed grid 2 increases and at the same time a turbulent flow area is created, so that the pipes 7, 8 simultaneously increase the efficiency. enhance At the same time, the air jet leaving the air injection section 12 improves the combustion at the fluidized bed below the air piping, and the air jet leaving the air injection section 12 better retains solid particles inside the furnace. , reducing the proportion of incompletely burned solid particles that exit the furnace faster.

In this way, there is a simultaneous restriction of the combustion area and an increase in the furnace area, in which the combustion of the particles is sufficient to exchange heat with a heat exchange coefficient close to that observed in a dense fluidized bed.

In practice, by combining the measures according to the invention, it is possible to maintain the temperature of the furnace between 850 and 950 °C, and for example to increase the velocity of the gas through the fluidized bed between 1 m/s and 4 m/s.
It was observed that the output changed by a ratio of 1 to 4.

[Brief explanation of drawings]

The attached figure is a longitudinal cross-sectional view of a combustion furnace according to the present invention, which is a steam boiler. Reference symbols in the figure: 1...Side wall, 2...Fluidized bed grid, 6
...Central region, 7, 8...Pipe, 12...Air injection part, 13...Low position, 14...High position.

Claims (1)

[Claims] 1. The fluidized bed is located at a low position 13 corresponding to the lowest output of the furnace.
and a high position 14 corresponding to the maximum power of the furnace, and is equipped with a pipe-shaped heat exchanger, with a central region 6 partitioned by surrounding side walls 1 and a fluidization grid 2. , the pipes 7, 8 of the heat exchanger run vertically at least between the low point 13 and the high point 14, while the air inlet 12 is located near the side wall 1 and above the high point 14, and is located in the center of the furnace. A combustion furnace characterized in that it is arranged toward area 6. 2. Combustion furnace according to claim 1, characterized in that the air injection part 12 is inclined by an angle a between 15° and 75° with respect to the vertical direction. 3. The combustion furnace according to claim 2, wherein the air injection part 12 is arranged at an inclination angle a of about 60 degrees. 4. The combustion furnace according to claim 2, wherein the inclination angle a of the air injection part 12 is adjustable. 5. The combustion furnace according to claim 2, characterized in that the pipes 7, 8 of the heat exchanger extend from near the upper surface of the fluidization grid 2 to a high position 14 of the fluidized bed. 6. Claims 1 to 5, characterized in that the pipes 7, 8 of the heat exchanger run vertically between the lower inlet collector 9 and the upper discharge collector 10 for the heat exchange liquid. The combustion furnace according to any one of the above. 7. A radiation/convection chamber 16 having a cooling pipe 15 installed in the upper part thereof is disposed, and the pipes 7 and 8 of the heat exchanger are connected to the cooling pipe 15 of the radiation/convection chamber 16. A combustion furnace according to scope 1. 8. The combustion furnace according to claim 1, characterized in that the pipes 7, 8 of the heat exchanger are distributed throughout the furnace. 9. Claim 1, characterized in that the pipes 7, 8 of the heat exchanger are arranged near the side wall 1.
Combustion furnace as described in section. 10. A combustion furnace according to claim 1, characterized in that the air injection section 12 has a total flow rate between 5% and 20% of the total flow rate of air introduced into the furnace.