JPH0359327B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] 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] ≒ [Furnace pressure] + [Fluidized bed layer height] ×
[Bulk density of fluidized bed] + [Pressure loss at blowout section] This pushing pressure usually exceeds 1000 mmAg, and in addition, the pressure loss of the duct, air preheater, control damper, etc. is also considered, so the blowing power of the forced air is:
In the case of simple incineration processing equipment, it was not uncommon for this to reach around 30% of the total power required.

In addition, the flow of fluidized sand by forced air is due to the suspension of the fluidized sand based on the resistance to the blown up air. 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 certain size or more, the entire amount of combustion air is not supplied as forced air by a forced air blower, but a part of it is supplied to the furnace with another blower with a wind pressure of about 100 to 300 mmAg. By supplying secondary air to the freeboard section,
The aim is 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. It is being

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 achieved by particularly increasing the ratio of secondary air and suppressing the amount of forced air, increasing the amount of air in the fluidized bed to 1.2 of the theoretical air amount required for combustibles.
In this case, the influence of the secondary air blowing method becomes even greater.

Looking at the effect of the blowing position of secondary air, it was found that if the blowing position when blowing secondary air was too close to the fluidized bed section, heat would be recovered from the freeboard section due to fluidized sand flying up. However, heat is taken away by the blown air, which deteriorates the heat balance in the fluidized bed. 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 continues to drop, eventually making it impossible to maintain combustion. Therefore, although the temperature of the fluidized bed varies depending on the combustion material, it is necessary to maintain it at 500°C or higher, generally 600°C or higher.If the temperature falls below 600°C, this deterioration of the heat balance will cause the temperature of the fluidized bed to be maintained. This results in the need for auxiliary combustion.

Note that if the temperature of the fluidized bed is too high, the strength of the fluidized sand decreases, leading to consumption, and depending on the type of combustible material, the fusion of the fluidized sand may occur. Although it varies depending on the salts contained, etc., it is generally necessary to avoid exceeding 800°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°C. It is.

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. The temperature of the gas decreases, which results in the opposite of promoting combustion.

In addition, when the combustion material contains a large amount of nitrogen, the fluidized bed combustion furnace operates at a low air ratio to promote the denitrification reaction, which is a reduction reaction, during the combustion reaction, reducing the concentration of nitrogen oxides in the exhaust gas. can be lowered. However, if secondary air is supplied immediately to the gas leaving the fluidized bed, the gas temperature may drop and the denitrification reaction may stop midway, or conversely, the flame temperature may rise too much and the secondary air There was also a risk that nitrogen oxides would be generated due to oxygen.

Furthermore, in low air ratio operation, a large amount of unburned matter is inevitably supplied to the freeboard section, so if combustion in the freeboard section is not carried out effectively, the unburned matter will be exhausted as is. This is also a problem in terms of pollution prevention, and in the case of equipment that uses heat exchangers or boilers to recover combustion heat, the energy that is emitted and unburned cannot be used, resulting in a decrease in efficiency. was unavoidable. Therefore, although it is said to be a low air ratio operation, in reality, it is necessary to supply an air amount equivalent to the theoretical air amount as forced air, which means that the fluidized bed incinerator's characteristic of high combustion speed cannot be fully utilized. 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 conventional systems, namely, the influence of the blowing position and direction of secondary air causes deterioration of the heat balance in the incinerator and inhibits combustion. secondary air may pass through unnecessarily, or the reduction in nitrogen oxide concentration may be prevented, or the amount of forced air for fluidized bed formation may be too large, causing the fluidized bed area to exceed the 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 provides a fluidized bed section 2 with a narrow gas passage area from below.
The incinerator 1 has a throat part 3 whose gas passage area gradually increases and a freeboard part 4 whose gas passage area is wide. In a fluidized bed incinerator equipped with a combustible material inlet 7 at the center of the furnace top wall 6 of the freeboard section 4 facing the fluidized bed, a secondary air blowing nozzle 8 is provided around the combustible material inlet 7. The air blowing section is installed facing vertically downward and is open to the top wall of the furnace, so that the freeboard section 4 is provided with a vertical recirculation flow in which the central part is a downward flow and the peripheral part of the furnace wall is an upward flow. This is a fluidized bed incinerator, characterized in that it is formed by air from a secondary air blowing nozzle and air from a secondary air blowing nozzle.

[Example] The present invention will be described below based on an example 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 the air for forming the fluidized bed pushed in from below, and the suspended fluidized sand above the bottom surface 5 forms the fluidized bed section 2. The throat part 3 is an intermediate area between the freeboard part 4 and the fluidized bed part 2, and the fluidized sand is not in a stable floating state, but the fluidized sand rising from the fluidized bed part and the fluidized sand falling from the freeboard part 4 are violently mixed. This is an area where fluid sand is densely distributed. The freeboard section 4 is an area where the fluidized sand that has risen from the fluidized bed section 2 through the throat section 3 is thin. Top wall 6 of the furnace top of the freeboard section 4
A combustion material inlet 7 is provided in a portion corresponding to the vertically upper portion of the central portion of the fluidized bed, and a secondary air blowing nozzle 8 is installed around the inlet 7 facing vertically downward. Furthermore, a combustion exhaust gas nozzle 9 is provided in a protrusion formed at a corner of the top wall 6. From the bottom of the freeboard part 4, there is a combustion material inlet 7 and a blowing nozzle 8.
The inner wall of the furnace up to the top wall 6 excluding the exhaust gas nozzle 9 is configured as a so-called boiler wall 10 by installing water pipes and the like.

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

In the fluidized bed section 2, fluidized bed air is blown from the bottom 5, so that the fluidized sand is in a suspended state. The combustible material introduced from the combustible material inlet 7 falls into the center of the fluidized bed. There, the combustible material is heated by the fluidized sand and the gas in the fluidized bed, generating steam due to evaporation of water and gas due to combustion or thermal decomposition. dispersed into 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. Then, a blowing nozzle 8 is installed at the center of the top wall 6 so as to assist the above-mentioned downward flow.
Since the secondary air is blown almost vertically downward, a vertical circulation is formed in the freeboard section 4, with a downward flow in the center and an upward flow in the peripheral part along the furnace wall. Therefore, the combustible material inputted from the input port 7 efficiently reaches the fluidized bed.

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 can be 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 throat portion 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 when the rate of combustion of the combustible material in the fluidized bed, that is, the combustion rate, is low and the amount of unburned matter discharged to the freeboard portion is large, the heat balance is good. Moreover, if the combustion rate in the fluidized bed 2 decreases, the flame in the freeboard section 4 will be further strengthened to compensate for it, and the amount of heating by the flame will increase, so the temperature of the fluidized bed will be high. and stable.

According to this embodiment, since the flame position can be lowered, combustion in the freeboard portion can be almost completed at that lower portion, and therefore, the amount of freeboard portion 4 is smaller than the amount of unburned material. The volume 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. It is possible to obtain a combustion furnace.

In this embodiment, the flame is formed in the lower part of the freeboard section 4, and the combustion can be almost completed there. There is little risk of adverse effects on 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 the moving bed section 1.
1 and a fluidized bed section 12, and by providing a deflector 13 overhanging from the furnace wall, a swirling flow is generated even within the fluidized bed section 2.

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,
The fluidized sand is kept in a state of heteronomous movement. On the other hand, in the fluidized bed section 12, the amount of air blown from the bottom 5 is increased,
The fluidized sand moves violently, jumps out from the throat part 3, and is held in a state where it flies up to the freeboard part 4.

The moving bed section 11 is formed in 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. Then, the combustion material that has fallen into the moving layer section 11 is transported to the throat section 3.
They are quickly covered with fluidized sand that has fallen from the bed or flowed in from the upper part of the fluidized bed, and are dragged into the descending moving bed and 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 that slopes inward in an overhanging manner, so that the gas containing air blown in from below is given strong directionality and flows through the fluidized bed. 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 flow of combustion gas 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. , thus the absolute amount of heat recovery can be increased. 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 exceeds 800°C, water has traditionally been injected directly into the bed in order to suppress the temperature, but this conventional method reduces the amount of heat recovered. 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, even if the furnace does not have a boiler wall and the freeboard part is slanted and is connected directly to the gas cooling room or boiler, the central downward flow and throat The situation around the part is essentially the same as in the first and second embodiments, and the present invention can be effectively applied. Further, particularly in the case of the fluidized bed having a narrow width of 1 to 2 m in the second embodiment, it is not necessarily necessary to supply the combustion material from the top of the furnace, but it may be supplied from the center of the side wall of the furnace.

[Effects of the Invention] The present invention provides a secondary air blowing nozzle that is installed around the combustion material inlet so as to face vertically downward and open to the top wall of the furnace. The air from the air blowing section and the air from the secondary air blowing nozzle form a vertical circular flow in which the air flows downward and the area around the furnace wall rises, thereby forming a flame in the low part of the freeboard section. There, combustion can be almost completed, and even if heat is actively taken out to the outside in the freeboard section, there will be no adverse effect on the combustion or the temperature of the fluidized bed.Furthermore, since the burned high-temperature gas flows along the wall surface, the surrounding wall of the furnace The amount of heat transferred through the boiler walls of the boiler is increased, and the effective use of heat recovery during waste combustion is greatly increased, i.e., the secondary air is sufficiently preheated and heated before it reaches the fluidized bed from the inlet. It later collides with gas containing unburned content and immediately forms a flame near the throat, so combustion can be accelerated without cooling the burning gas and worsening the heat balance. It becomes possible to reduce the amount of air and the area of the fluidized bed, making it possible to obtain a compact combustion furnace.

For example, the lower heating value of the combustion material is 3000Kcal/Kg
If there is, the amount of air blown from the bottom of the fluidized bed can be reduced to about half the theoretical air amount without residual heat, and the area of the fluidized bed can therefore be reduced to about half, so combustion can be achieved without increasing the freeboard volume. No problems arise. Moreover, if the boiler wall is used, it is possible to recover a large amount of heat with a small heat transfer area, and the heat transmission coefficient can be raised to an average of 80 Kcal/m ² hours Celsius.

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 drawings]

FIG. 1 and FIG. 2 illustrate the first embodiment of the present invention, respectively.
and FIG. 7 is a vertical side view of the second embodiment. DESCRIPTION OF SYMBOLS 1... Combustion furnace, 2... Fluidized bed part, 3... Throat part, 4... Freeboard part, 5... Bottom surface, 6...
...Top wall, 7...Combustible material inlet, 8...Blowing nozzle, 9...Exhaust gas nozzle, 10...Boiler conversion wall,
11...Moving bed section, 12...Fluidized bed section, 13...
deflector.

Claims (1)

[Claims] 1. An incinerator 1 having a fluidized bed part 2 with a narrow gas passing area, a throat part 3 with a gradually expanding gas passing area, and a freeboard part 4 with a wide gas passing area sequentially from the bottom, the fluidized bed part In a fluidized bed incinerator, the bottom surface 5 of 2 is used as an air blowing part for forming a fluidized bed, and a combustible material inlet 7 is provided at the center of the furnace top wall 6 of the freeboard section 4 facing the fluidized bed. A secondary air blowing nozzle 8 is installed around the port 7 so as to face vertically downward and open to the top wall of the furnace, so that the freeboard part 4 has a downward flow in the center and a flow in the peripheral part of the furnace wall. 1. A fluidized bed incinerator characterized in that a vertical recirculation flow, which is an upward flow, is formed by air from the air blowing section and air from a secondary air blowing nozzle.