JPS6122114A - Fluidized bed incinerator - Google Patents

Abstract

PURPOSE:To reduce the concentration of nitrogen oxides and permit a fluidized bed area to cope with a combustion load by a method wherein a blowing inlet, blowing the secondary air toward the fluidized bed in nearly virtically downward, is provided above the top side of the fluidized bed. CONSTITUTION:Combustion object (a) thrown from a throwing inlet 7 is dispersed into a fluidized bed 2. Combustion gas rises up through the fluidized bed. As the secondary air (b) is blown from the blowing nozzle 8 toward nearly virtical direction, turning flow is composed of descending flow at central portion along a furnace wall and ascending flow in the peripheral portion in a free board part 4, therefore, the combustion objects arrive at the fluidized bed effectively. Then, the temperature of the secondary air and gas are risen up by radiant heat during descending and gas and air collide against the gas ascending from the fluidized bed portion 2 near a throat portion 3 and unburnt portion is burnt effectively. Furthermore, they are premixed with the gas after combustion, concentration of oxygen becomes low and temperature rise of the flame portion is small, therefore, the generation of the nitrogen oxides is restrained. As the fluidized bed is heated effectively through a fluidized sand and radiant heat, a heat balance in the fluidized bed becomes good and the temperature of the fluidized bed is stabilized at high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a fluidized bed incinerator that uses a fluidized bed to incinerate combustion materials.

[Prior Art] In a fluidized bed combustion furnace, combustion air is mainly used as forced air that is supplied from a blow-off section on the surface of the fluidized bed to fluidize the fluidized sand that forms the fluidized bed. many. In that case, the pushing pressure can be approximately expressed by the following formula.

[Indentation pressure 1″, [Furnace pressure] + [Fluidized bed layer height]
× [Bulk density of fluidized bed] + [Pressure loss at blowout section] This indentation pressure usually exceeds 10'O'O' + nmAg, and in addition, duct pressure loss, air preheater, Kuntrol damper, etc. pressure loss is also expected. In the case of simple incineration treatment equipment, it was not uncommon for the blowing power of the forced air to reach around 30% of the total moving power.

In addition, 1. The flow of fluidized sand by forced air is due to the suspension of the fluidized sand based on the resistance to the blown air, and as the amount of forced air increases, the upward velocity of the air also increases, and the movement of the fluidized sand also increases rapidly. It gets intense. As a result, wear on the fluidized sand itself, the walls of the fluidized bed portion, the blowing portion of the bottom of the fluidized bed, etc. increases rapidly. Therefore, the area of the fluidized bed is determined by the forced air volume.

Therefore, in combustion furnaces of a size larger than 100, the entire amount of combustion air is not supplied as forced air by a forced air blower, but a part of it is supplied at another wind pressure of 100 to 30'.
By supplying secondary air to the 7-liquid board section of the furnace using a blower of approximately Om+nAg, it is intended to reduce the required power and hearth area. At that time, it is known that the combustion state in the freeboard section changes depending on how the secondary air is blown into the freeboard section, which greatly affects the concentration of nitrogen oxides in the exhaust gas and the temperature of the fluidized bed. ing.

When the combustion material contains a large amount of nitrogen or has a high calorific value, so-called low air ratio operation is usually performed. This is done by particularly increasing the ratio of secondary air and suppressing the amount of forced air, reducing the amount of air in the fluidized bed to less than 1.2 times the theoretical amount of air required for the combustible material. , the influence of the secondary air blowing method becomes even greater.

Looking at the effect of the secondary air blowing position, it was found that if the blowing position when blowing secondary air was too close to the fluidized bed section, the fluidized sand would suddenly stop and heat would be recovered from the freeboard section. , conversely, heat is taken away by the blown air,
Therefore, the heat balance in the fluidized bed section deteriorates. In a fluidized bed combustion furnace, the temperature of the fluidized bed is the combustion temperature in the fluidized bed section, and is an important factor that affects the combustion state. If it is too low, the combustion reaction rate will decrease and the heat balance will be affected. This worsens and the temperature of the fluidized bed decreases (1).
Eventually, combustion cannot be maintained. Therefore,
Although the temperature of the fluidized bed varies depending on the material to be combusted, it is necessary to maintain it at 500°C or higher, generally 600°C or higher.If the temperature drops below 600°C, this deterioration of the heat balance will cause the need for auxiliary combustion to maintain the fluidized bed temperature. It leads to the production of sex.

Note that if the temperature of the fluidized bed is too high, the strength of the fluidized sand will decrease and it will be wasted, and depending on the type of combustible material, the fluidized sand will be fused. Although it varies depending on the temperature, it is 900℃, generally 800℃
It is necessary to avoid exceeding .degree. C., and the temperature of fluidized sand, for example in municipal waste incinerators, generally needs to be maintained in the range of 600 to 800.degree.

Contrary to the above, if secondary air is blown in from a position too high above the freeboard section in a nearly horizontal direction, it will be discharged from the furnace as exhaust gas before being sufficiently utilized as combustion air.

Additionally, if secondary air is blown directly into the flame from the wall near the flame formed in the freeboard area, combustion will occur due to direct mixing with the secondary air, unless the secondary air is preheated to a high temperature. This lowers the temperature of the gas, which is the opposite of promoting combustion.

In addition, when the tI & baked goods contain a large amount of nitrogen, the fluidized bed combustion furnace operates at a low air ratio to advance the denitrification reaction, which is a reduction reaction, during the combustion reaction and reduce the concentration of nitrogen oxides in the exhaust gas. can be done. But long 1
If secondary air is supplied immediately to the gas that has passed through the fluidized bed, the temperature of the gas will drop and the denitrification reaction will stop midway.
On the other hand, if the flame temperature rose too much, there was a risk that nitrogen oxides would be produced by the oxygen in the secondary air.

Furthermore, in low air ratio operation, a large amount of unburned fuel is inevitably supplied to the freeboard section, so the 717-
If combustion is not carried out effectively in the board section, the unburned material will be discharged as is, which is a problem in terms of pollution prevention.Additionally, the heat of combustion must be recovered using heat exchangers, boilers, etc. In the case of equipment, energy could not be used for the amount of unburned energy that was emitted, and a decline in efficiency was unavoidable. Therefore, in reality, the air volume equivalent to the theoretical air volume has to be supplied as forced air, making it difficult to take full advantage of the high combustion speed of the fluidized bed incinerator. However, the disadvantage was that the area of the fluidized bed was large.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems in the conventional ones, namely, the heat balance inside the incinerator deteriorates due to the influence of the blowing position and direction of the secondary air, resulting in combustion. secondary air may be blocked, the secondary air may pass through the turnips, or the reduction in nitrogen oxide concentration may be prevented, or the amount of forced air for fluidized bed formation may be excessive and the fluidized bed area may become subject to combustion load. The purpose of the present invention is to provide fluidized bed incineration that solves problems such as excessive waste.

[Means for solving the problems] The present invention, as a means for solving the above problems,
The present invention provides a fluidized bed incinerator characterized in that it is equipped with a secondary air blower I above the fluidized bed for blowing secondary air almost vertically downward toward the fluidized bed.

[Example] The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 shows a first embodiment of a simple type fluidized bed combustion furnace with a freeboard section with boiler walls.

The combustion furnace 1 can be roughly divided into three parts, from the bottom: a fluidized bed part 2 with a narrow gas passing area, a throat part 3 with a gradually increasing gas passing area, and a freeboard part 4 with a wide gas passing area. The bottom surface 5 of the fluidized bed section 2 serves as a blowout section for air for forming a fluidized bed pushed in from below, and the suspended fluidized sand above the bottom surface forms the fluidized bed section 2. Throat part 3 is 7'
In the intermediate area between the J-board section 4 and the fluidized bed section 2, the fluidized sand is not in a stable floating state, and the fluidized sand rising from the fluidized bed section and the fluidized sand falling from the 7-board section 4 are heavily intersected. However, this is an area where fluid sand is densely present. The 7 reel board section 4 is an area where the fluidized sand that has risen from the fluidized bed section 2 through the throat section 3 is diluted. A combustible material charging lower is provided on the top wall 6 at the top of the furnace of the freeboard section 4, which corresponds to the vertically upper part of the central part of the fluidized bed. is set up. Further, a combustion exhaust gas nozzle 9 is provided in a protrusion formed at a corner of the top wall 6. The inner wall of the furnace from the lower part of the freeboard section 4 to the top wall 6 excluding the combustion material input lower, the blowing nozzle 8 and the exhaust gas nozzle 9 is configured as a so-called boiler wall 10 by installing wood pipes or the like.

Next, the operation of the first embodiment will be explained.

In the fluidized bed section 2, fluidized bed air is blown into the bottom 5, so that the fluidized sand is in a suspended state. The combustible material introduced from the combustible material input lower falls into the center of the fluidized bed. There, the combustible material is heated by the fluidized sand and gas in the fluidized bed, generating water vapor due to evaporation of water and gas due to combustion or thermal decomposition, and the combustible material itself is dispersed within the fluidized bed by collision with the gas and fluidized sand. do. In addition, the gas rising in the fluidized bed is deflected to the side by the combustion materials and the gases generated from the combustion materials, creating an upward flow along the furnace wall. A downward flow is formed. Since secondary air is blown almost vertically downward from the blowing nozzle 8 into the center of the top wall 6 to assist the above-mentioned downward flow, the freeboard section 4 has a downward flow from the center to the furnace wall. A swirling flow is formed in which the peripheral portion along the direction is an upward flow. Therefore, the combustible material charged from the charging lower reaches the fluidized bed efficiently.

In addition, the blown secondary air mixes with gas that has almost completed combustion, receives radiant heat during its descent, and is sufficiently heated, and then the air that rises from the fluidized bed section 2 near the throat section 3 Since it collides with gas containing a large amount of combustible material, a flame is formed immediately after the collision, and the unburnt material is effectively combusted. Furthermore, since it is premixed with the gas after combustion, the oxygen concentration is relatively low, and the temperature rise in the flame section is relatively small, which has the effect of suppressing the formation of nitrogen oxides in the flame section. Further, the position of the flame is near the throw 1 part 3, and the fluidized bed is efficiently heated through the moving fluidized sand, and the fluidized bed below is directly heated by the radiant heat. Therefore, even if the rate of combustion of the material to be read in the fluidized bed, that is, the combustion rate, is low and there is a large amount of unburned material discharged to the 71-board part, the heat balance is good. However, if the combustion rate in the fluidized bed 2 decreases, the flame in the 7 re-board section 4 (3) will be further strengthened to compensate for it, and the amount of heating by the flame will increase. The temperature of the floor becomes high and stable.

According to this embodiment, since the flame position can be lowered, combustion in the freeboard part can be almost completed at that lower part, and therefore, compared to the amount of unburned matter,
The volume of the re-board section 4 can be reduced. As a result, if the combustion amount is the same, the air for the fluidized bed that is blown in from below, that is, the air ratio is lowered, the fluidized bed area is reduced, and the freeboard volume is the same or smaller than the conventional one. You can start a combustion furnace.

In this embodiment, the fire and flame can be formed in the lower part of the free board part 4 and the combustion can be almost completed there, so even if the heat is actively taken out to the outside in the free board part 4, Less risk of adverse effects on combustion or fluidized bed temperature. Furthermore, as the burned high-temperature gas flows along the wall surface, a secondary effect occurs in that the amount of heat transferred through the boiler wall 10 increases. Therefore, the combustion furnace of this embodiment is extremely advantageous when burning waste and recovering and effectively utilizing the heat.

FIG. 2 shows a second embodiment of the present invention in which the structure of the portion from the throat section 3 to the upper freeboard section 4 is the same as that of the first embodiment, but the fluidized bed section 2 below the throat section 3 has a special structure. An example is shown.

In the second embodiment, the fluidized bed section 2 is composed of three parts: a moving bed section 11 and a fluidized bed section 12. It is designed to generate a swirling flow.

In the moving bed section 11, the amount of air blown from the bottom surface 5 is set to the minimum necessary for floating the fluidized sand, and the fluidized sand is maintained in a heteronomous moving state. On the other hand, in the fluidized bed section 12, the amount of air blown from the bottom surface 5 is increased, and the fluidized sand is kept in a state where it moves violently, comes out from the throat section 3, and floats up to the 7 reel board section 4.

The moving bed section 11 is formed at the center of the fluidized bed where the combustion material falls, and the fluidized bed sections 12 are provided with deflectors 13 on both sides thereof. The combustible materials that have fallen into the moving bed section 11 are quickly covered with fluidized sand that has fallen from the throat section 3 or that has flowed in from the upper part of the fluidized bed, and is swept into the descending moving bed. , it will be buried in the fluidized bed section 2.

On the other hand, on the fluidized bed section 12 side at the bottom, the fluidized sand is flying up violently, so the fluidized sand on the moving bed section 11 side is dragged by the movement on the fluidized bed section 12 side, and performs a swirling motion as shown in the figure. Along with this, the feed combustion material is also dispersed and diffused throughout the fluidized bed.

Therefore, even when the fluidized bed area is larger than in the first embodiment, a good combustion state can be obtained without using a special method to supply the combustion material.

At the upper end of the furnace wall of the fluidized bed section 2, a deflector 13 is provided which is inclined inward in an overhanging manner.
The gas containing air blown in from below ejects from the fluidized bed part while being given strong directionality, and after passing through the throat part 3, it advances so as to collide with the opposite wall or side wall, and after the collision, the first As in the case of the embodiment, the kinetic energy is dispersed and becomes an upward flow along the inner surface of the furnace wall. Since the upward flow ejected from the fluidized bed section is strengthened by the deflector 13, the swirling flow in the freeboard section 4 is even stronger than in the first embodiment.

In addition, since the ascending gas flow is strong and intersects left and right, it mixes well with the central downward flow, resulting in a flame with a high burning rate and a large volume. The heat receiving efficiency is also high, and the effect is stronger than that of the first embodiment.

In the first and second embodiments, the boiler wall 10 is heated not only by the combustion gas flow rising near the furnace wall but also by radiant heat from the flame. Therefore, a high heat transmission coefficient can be obtained due to the flame having a large volume. In addition, since heat exchange occurs directly in the furnace, cooling of the gas by excessive secondary air blowing, etc., which suppresses the furnace top temperature and prevents water spray and dust from melting and adhering to the flue, is avoided. ,
Therefore, it is desirable to increase the absolute amount of heat recovery. In this way, even if the heat transfer area is small, a large amount of heat can be recovered.

When the temperature of the fluidized bed reaches 800° C. or higher, it has conventionally been done to directly inject water into the fluidized bed in order to suppress the temperature, but such conventional methods reduce the amount of heat recovery. On the other hand, if the combustion rate is lowered by reducing the amount of air blown into the fluidized bed, in the case of the combustion furnace of this embodiment, it is possible to reliably burn the unburned matter in the freeboard part, and This is advantageous because the effectiveness of the flame can be increased without reducing the amount of heat recovery.

Note that the combustion furnaces of the first and second embodiments may have a horizontal cross section that is rectangular or circular.

In addition, the ceiling wall does not necessarily have to be horizontal; for example, if the furnace is not a boiler wall, but the freeboard part is slanted, and it is connected directly to the gas cooling room or boiler, the central downward flow and throat The situation around the area is essentially the first and second
The present invention is effectively applied. Moreover, especially in the case of the narrow fluidized bed with a width of 1 to 2 m in the second embodiment, it is not necessarily necessary to feed the combustion material from the top of the furnace, but it may be fed from the center of the side wall of the furnace.

[Effects of the Invention] As configured as described above, the present invention allows the secondary air to be sufficiently preheated and heated before it reaches the fluidized bed from the inlet, and then collides with gas containing unburned components and immediately throats the secondary air. Since the flame is formed near the combustion chamber, combustion can be promoted without cooling the combustion gas and worsening the heat balance, and the amount of air for the fluidized bed can be reduced to reduce the area of the fluidized bed. This makes it possible to obtain a compact combustion furnace.

For example, the lower calorific value of the combustion material is 3000 Kca/kg.
If there is, the amount of air blown from the bottom of the fluidized bed can be about half of the theoretical air amount without residual heat, and therefore the area of the fluidized bed can be reduced to about half, and therefore combustion can be achieved without increasing the volume of the freeboard section. There is no problem. Moreover, if the boiler wall is used, large heat recovery is possible with a small heat transfer area, and the heat transmission coefficient is 80Kcaρ/m on average at 2 hours °C.
The end is to raise the level to a certain level.

According to the present invention, the performance of a fluidized bed combustion furnace has been greatly improved, and the improvement is particularly remarkable in a furnace that incinerates waste and recovers and utilizes the combustion heat.

[Brief explanation of the drawing]

1 and 2 are longitudinal sectional side views of a first and second embodiment of the invention, respectively. 1-m-combustion furnace, 2--fluidized bed section, 3--throat section, 4--117 Lee board section, 5--bottom surface, 6--
Top wall, 71--combustible material inlet, 9-11 exhaust gas nozzle, 10--boiler wall, 11-11 moving bed section, 12-11 fluidized bed section, 13- 11 deflector.

Claims (1)

[Claims] 1. A fluidized bed incinerator characterized by having a secondary air inlet above the fluidized bed that blows secondary air almost vertically downward toward the fluidized bed.