JP5435973B2 - Fluidized incinerator - Google Patents

Description

The present invention relates to a large fluidized incinerator capable of incinerating sludge containing N while suppressing generation of N ₂ O, which is a warming gas.

Since sludge represented by sewage sludge contains a large amount of N derived from protein, various nitrogen oxides are generated by incineration and released into the atmosphere. Among these nitrogen oxides, N ₂ O (nitrous oxide) is a gas that exhibits a warming effect 310 times that of CO _2, and therefore its reduction is particularly strongly demanded.

Conventionally, fluid incinerators that do not easily generate dioxins have been widely used for sludge incineration, and incineration has generally been performed at about 800 ° C. But know that reduced until the incineration temperature to increase the N _{2 O} in the generation amount of about one third to 850 ° C., evaluation and effective way to call it N _{2 O} suppression to as "high temperature incineration method" Has been.

However, in order to increase the incineration temperature to 850 ° C., it is necessary to increase the amount of auxiliary fuel used to 1.4 to 1.6 times that of the prior art, which is not preferable from the viewpoint of energy saving. In addition, the recent situation in which the fuel cost is rising causes a problem that the running cost is significantly increased. As described above, the “high-temperature incineration method” is effective in suppressing N ₂ O, but a practical problem remains.

Such a problem of N ₂ O suppression also occurs in a fluidized bed combustion boiler using municipal waste as fuel. Therefore, in Patent Document 1, the generation ratio of N ₂ O and NO _X is suppressed by setting the air ratio of the fluidized bed to 0.9 to 1.0, and additional fuel and combustion air are supplied at the upper stage to perform high-temperature combustion. Thus, a multi-stage combustion method for a fluidized bed combustion boiler has been proposed in which N ₂ O is decomposed at a high temperature, and a sufficient amount of air is blown into the uppermost stage for complete combustion.

However, the multistage combustion method of Patent Document 1 requires a large amount of auxiliary fuel in order to form a high-temperature field in which additional fuel and combustion air are supplied to the upper stage of the fluidized bed and N ₂ O can be decomposed. Yes. However, since the multistage combustion method of Patent Document 1 relates to a boiler, the amount of heat of auxiliary fuel can be recovered, and the amount of auxiliary fuel used is not a significant problem. However, when this is applied as it is to a sludge incinerator, the amount of auxiliary fuel used becomes a problem, which is not satisfactory from the viewpoint of energy saving.

Moreover, in a large city sewage treatment plant, a large fluidized incinerator having a treatment capacity of 250 to 350 tons / day is used, and its diameter reaches 7 m or more. In such a large furnace, if air supply to the furnace is not appropriately performed, mixing and diffusion by the supply air in the furnace is not sufficiently performed, and it is not easy to sufficiently decompose N ₂ O. There was also.

Japanese Patent No. 3059995

The present invention solves the above-mentioned conventional problems, can suppress the amount of N ₂ O generated when incinerating sludge containing N to the same level as the “high temperature incineration method”, and uses auxiliary fuel. The purpose is to provide a fluidized incinerator that can significantly reduce the amount of N ₂ O even when it is a large-sized furnace having a furnace body inner diameter of 7 m or more, in which the amount can be significantly reduced as compared with the “high temperature incineration method”. It is what.

The fluidized sludge incinerator of the present invention made to solve the above problems is a large fluidized incinerator having a furnace body inner diameter of 7 m or more for fluidly incinerating sludge, and the lower portion of the furnace body has an air ratio. 1.1 or less is used as a pyrolysis zone where pyrolysis is performed by supplying slurging fluid while supplying air for flow with fuel, and only the secondary combustion air with an air ratio of 0.1 to 0.3 is supplied immediately above the zone. And forming a local high temperature field to decompose the N ₂ O into an upper combustion zone, and the uppermost portion of the furnace body to be a complete combustion zone for completely burning the unburned portion, and the secondary combustion zone in the upper combustion zone The supply position of the combustion air is divided into upper and lower stages, and the supply speed is set to a high speed of 70 m / s or more.

  As in claim 2, it is preferable to set the air ratio of the pyrolysis zone to 0.7 to 1.1, the temperature to 550 to 750 ° C, and the temperature of the upper combustion zone to 850 to 920 ° C. As in claim 3, it is preferable that the total air ratio of primary air supplied as fluidized air and secondary combustion air supplied to the stratified combustion zone be 1.0 to 1.3. Further, as in claim 4, it is preferable that the air ratio of the air supplied to the complete combustion zone is 0.1 to 0.3 and the overall air ratio is 1.5 or less.

Further, as in claim 5, the lower supply height of the secondary combustion air is preferably set to 600 to 1000 mm from the upper surface of the static sand layer, and the secondary combustion in the upper and lower stages as in claim 7. By supplying the working air, it is preferable to form an on-layer combustion zone having a temperature equal to or higher than the decomposition temperature of N ₂ O and lower than the generation temperature of thermal NO _x therebetween.

According to the present invention, sludge is put into a fluidized furnace and pyrolyzed while flowing in a pyrolysis zone in which air for flow having an air ratio of 1.1 or less is supplied together with fuel. In this pyrolysis zone, the air ratio is 1.1 or less and the amount of oxygen is small, so that the oxidation of N hardly proceeds, and the generation of N ₂ O and NO _x is suppressed. Nevertheless, the sludge is vigorously stirred by the fluid medium in the temperature field of 550 to 750 ° C., and the combustible component in the sludge is sufficiently pyrolyzed.

Further, in the present invention, combustion air having an air ratio of 0.1 to 0.3 is blown into the pyrolysis gas at a position immediately above it, divided into two upper and lower stages, and a local high temperature of 850 to 920 ° C. over a predetermined height therebetween. A field is formed and N ₂ O in the pyrolysis gas is decomposed, but only air is blown into a portion having a low oxygen concentration to locally burn the pyrolysis gas, so no auxiliary fuel is required in the upper combustion zone . N ₂ O is produced mainly directly above the sand layer. In the present invention, a high-temperature field is formed in this N ₂ O production region, so that the N ₂ O is formed immediately above the sand layer (from the sand layer to 1/3 of the furnace height). Secondary combustion air is supplied. Further, by introducing secondary combustion air directly above the sand layer, heat dissipation is hindered, and a local high temperature field is more easily formed.

In the present invention, the secondary combustion air having an air ratio of 0.1 to 0.3 is divided into upper and lower two stages, the nozzle diameter is reduced, and the supply speed is set to a high speed of 70 m / s or more. Even in a large furnace having an inner diameter of 7 m or more, secondary combustion air is supplied to the entire cross section of the furnace. Therefore, even in a large fluidized incinerator having a processing capacity of 250 to 350 tons / day, mixing and diffusion by the supply air in the furnace are sufficiently performed, and N ₂ O can be sufficiently decomposed.

  As described above, according to the present invention, the amount of pyrolysis gas discharged from the pyrolysis zone is smaller than the combustion exhaust gas in normal combustion, and the amount of heat required for heating is only air, or the high-temperature field is localized. In addition, since the temperature of the fluidized bed is low, the amount of auxiliary fuel used can be greatly reduced as compared with the “high temperature incineration method”. Further, since air is blown at the uppermost part to completely burn the unburned matter, no harmful components are contained in the exhaust gas.

  The pyrolysis zone is operated at an air ratio of 1.1 or less, but as the air ratio is lowered, there is a problem that the temperature of the sand layer becomes gradually difficult to maintain. Therefore, it is difficult to lower the air ratio below 0.8. However, if the supply height of the lower stage of the secondary combustion air is 600 to 1000 mm from the upper surface of the stationary sand layer as in claim 5, a local high temperature field can be formed at a position immediately above the fluidized sand layer. It becomes easy to maintain the temperature of the sand layer, and the air ratio in the pyrolysis zone can be lowered to about 0.7. Along with this, the overall air ratio of the fluidized furnace can be lowered. However, if the air ratio in the pyrolysis zone is too low, the flow is poor and toxic gases such as cyan and carbon monoxide may be generated, so about 0.7 is the lower limit.

Further, as in claim 6, by supplying the secondary combustion air to the upper and lower two stages, if an upper combustion zone between the decomposition temperature of N ₂ O and less than the generation temperature of thermal NO _x is formed therebetween, The production of N ₂ O is more reliably suppressed.

It is a longitudinal cross-sectional view which shows embodiment of this invention. It is a longitudinal cross-sectional view which shows the modification of this invention. It is a horizontal sectional view showing a modification of the present invention. It is a schematic diagram of the furnace temperature.

Preferred embodiments of the present invention are shown below.
FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, in which 1 is a furnace body of a fluidized incinerator, 2 is a sludge inlet formed on the side wall of the furnace body 1, and sludge is discharged from this inlet 2. Directly charged into the furnace body 1. Sludge is sewage dewatered sludge. The object of the present invention is a large fluidized incinerator having a furnace body inner diameter of 7 m or more, and the maximum diameter is about 10 m. The interior of the furnace body 1 is divided into three zones in the height direction. In order from the bottom of the furnace body 1, there are a pyrolysis zone 3, an upper combustion zone 4 and a complete combustion zone 5.

  The pyrolysis zone 3 is a zone formed at the lowermost portion of the furnace body 1 and includes a flow air supply pipe 6 and a fuel supply pipe 7. From the air supply pipe 6 for flow, the air for flow which is primary air is supplied, and sludge is made to flow with a well-known fluid medium. Auxiliary fuel is supplied from the fuel supply pipe 7 and is combusted by flowing air to maintain the temperature of the thermal decomposition zone 3 at 550 to 750 ° C. The introduced sludge is heated while being vigorously stirred by the flowing air. As the auxiliary fuel, a gas fuel such as city gas or propane gas or a liquid fuel such as heavy fuel oil A is used.

In the present invention, the supply amount of primary air (flowing air) from the flowing air supply pipe 6 is based on the theoretical air amount necessary for burning auxiliary fuel and sludge, and the air ratio is 1.1 or less. Preferably, it is set to be 0.7 to 1.1. For this reason, although sludge is thermally decomposed, since the air ratio is low and the amount of oxygen is insufficient, the amount of N ₂ O generated can be suppressed as compared with the case where normal fluid combustion is performed. As will be described below, in the present invention, a local high temperature field is formed immediately above the pyrolysis zone 3, so that it is easy to maintain the temperature of the sand layer by the radiant heat, and the air ratio of the pyrolysis zone is reduced to about 0.7. Can be lowered. If the air ratio is less than 0.7, the amount of heat generated by partial combustion in the fluidized bed will be less than the amount of heat output from sludge moisture evaporative heat, heat of thermal decomposition, heat release, etc., making it difficult to maintain the temperature of the fluidized bed. In addition, since there is a possibility that toxic gases such as cyan and carbon monoxide are generated, it is preferable to set the ratio to 0.7 or more and 1.1 or less.

An upper combustion zone 4 is formed immediately above the pyrolysis zone 3. The upper-layer combustion zone 4 is a zone for supplying only secondary combustion air in an amount such that the air ratio is 0.1 to 0.3 from the combustion air supply pipes 8 and 9. The pyrolysis gas rising from the pyrolysis zone 3 is combusted in contact with the secondary combustion air to form a local high temperature field having a temperature of 850 to 920 ° C. Therefore, N ₂ O contained in the pyrolysis gas is decomposed and reduced in this local high temperature field.

If the total air ratio of the primary air from the flow air supply pipe 6 and the air supplied from the combustion air supply pipe 8 is less than 1.1, a local high temperature field of 850 to 920 ° C. cannot be formed. If it exceeds 1.3, the amount of surplus air not involved in combustion increases, and it is necessary to supply auxiliary fuel to form a local high temperature field of 850 to 920 ° C. Therefore, the total of primary air and secondary combustion air The air ratio needs to be 1.1 to 1.3. As described above, in the present invention, only a small amount of air is blown into the reducing atmosphere to form a local high-temperature field, and N ₂ O is decomposed. This is a feature that exceeds the amount necessary for maintaining the temperature of the thermal decomposition zone. There is an advantage that it is not necessary to use auxiliary fuel.

In the present invention, as shown in FIG. 1, the supply position of the secondary combustion air is divided into two upper and lower stages, and the supply speed of the secondary combustion air from the combustion air supply pipes 8 and 9 is set to 70 m / s. As described above, the speed is 100 m or less. By ensuring such a supply speed, the secondary combustion air can be supplied substantially uniformly to the entire cross section of the furnace even in a large furnace having an inner diameter of 7 to 8 m. When the supply speed is lower than this, in a large fluidized incinerator having a furnace inner diameter of 7 m or more, it becomes difficult to sufficiently mix and diffuse air in the furnace, and N ₂ O can be sufficiently decomposed. There is a risk of disappearing. Further, if the pressure is 100 m / s or more, the pressure loss in the pipe increases, so the blower power for supplying air must be increased.

  As shown in FIG. 2, only the lower combustion air supply pipe 8 may be inclined obliquely downward to increase the efficiency of mixing and stirring with the pyrolysis gas rising from the pyrolysis zone 3. Further, as shown in FIG. 3, the upper and lower combustion air supply pipes 8 and 9 are arranged in the tangential direction of the furnace body 1 and the directions thereof are opposite to each other, or the upper combustion air supply pipe 9 is attached in the direction of attachment. May be the center direction of the furnace body 1.

Thus, by dividing the supply position of the secondary combustion air into two upper and lower stages, an upper combustion zone 4 having a predetermined height is formed between them. If the secondary combustion air is blown in one stage, a temperature peak due to local excessive temperature rise is formed at the blowing position as shown in the graph of FIG. Its the temperature can of course exceed 850 to 900 ° C. is a decomposition temperature of _{N 2} O, exceed 920 ° C. is a generation temperature of the thermal NO _{x, N 2} O is thermal NO _x is generated be decomposed There is a risk of doing. On the other hand, if the supply position of the secondary combustion air is divided into two upper and lower stages as in the present invention, local overheating is suppressed, and the temperature is higher than the decomposition temperature of N ₂ O and lower than the generation temperature of thermal NO _x. Thus, it is possible to decompose N ₂ O without generating thermal NO _x .

  The interval between the upper and lower combustion air supply pipes 8 and 9 is preferably about 200 to 600 mm. This is because if it is closer than this, the meaning of the above-described two-stage division becomes thin, and conversely, if it is too far away, it becomes difficult to form a stable upper combustion zone. The height of the lower combustion air supply pipe 8 is preferably set to 600 to 1000 mm from the upper surface of the stationary sand layer (the sand layer in the flow stop state). If it is such a position, it will be located in the vicinity of the upper surface of the fluidized bed during operation, and there is an effect that it is possible to prevent the temperature of the sand layer from being lowered by the radiant heat from the hot upper layer combustion zone 4.

The uppermost part of the furnace body 1 is a complete combustion zone 5 in which unburned components are completely burned. A tertiary air supply pipe 10 is disposed in the complete combustion zone 5 to supply air. The supply amount is such that the air ratio is 0.1 to 0.3. The temperature of the complete combustion zone 5 is 800 to 850 ° C., and N ₂ O that was not decomposed in the upper combustion zone 4 is further decomposed, and CO is oxidized to CO ₂ and discharged outside the furnace. Exhaust gas treatment is performed.

The total amount of air supplied from the flow air supply pipe 6, the secondary combustion air supply pipes 8 and 9, and the tertiary air supply pipe 10 is 1.5 or less, preferably 1 Set to be 3 or less. As a result of reducing the air ratio and supplying the auxiliary fuel only from the fuel supply pipe 7 of the pyrolysis zone 3, the generation of N ₂ O is achieved while the amount of auxiliary fuel used is almost the same as the conventional incineration level. The amount could be reduced significantly (in the example, 1/4) compared to the conventional method. In addition, although the suppression effect of N ₂ O according to the present invention is the same as or higher than that of the “high temperature incineration method”, the amount of auxiliary fuel used is 1.4 to 1.6 times the conventional level in the “high temperature incineration method”. . As described above, according to the present invention, the amount of N ₂ O generated can be suppressed to a level equal to or lower than that of the “high temperature incineration method”, and the amount of auxiliary fuel used can be significantly reduced compared to the “high temperature incineration method”. It becomes possible to make it.

A sludge incineration experiment was performed while changing the conditions using an experimental fluid furnace simulating a large fluid incinerator having an inner diameter of 7 m or more. The input amount of sludge was 80 kg / h, and A heavy oil was used as auxiliary fuel. Experiments are conventional incineration, high temperature incineration with increased incineration temperature, the method shown in FIG. 1 of the present invention, and the method shown in FIG. 1 of the present invention. There are four types of methods (comparative examples). For each incineration method, the amount of auxiliary fuel used (indicated by the calorific value of auxiliary fuel per kg of sludge), freeboard maximum temperature, furnace outlet temperature, concentration of exhaust gas components including N ₂ O, total air ratio, primary air The ratio was measured and shown in Table 1.

As is clear from the above data, according to the present invention, the amount of N ₂ O generated during sludge incineration is significantly reduced compared to high-temperature incineration while maintaining the amount of auxiliary fuel used at or below the level of conventional incineration methods. There are advantages that can be done.

Next, the concentration of exhaust gas components containing N ₂ O was measured by changing the number of secondary air blowing stages and the flow velocity as shown in Table 2. The total air ratio was a constant value of 1.3, and the primary air ratio was a constant value of 1.0.

As is apparent from the above data, the CO combustion concentration, N ₂ O concentration, and NO _X concentration are lowered by setting the supply position of the secondary combustion air to the upper and lower stages and the supply speed to 70 m / s or more. be able to. In particular the CO concentration due to the fact that the supply position of the secondary combustion air and the upper and lower stages, reduction of the NO _X concentration is remarkable, also decrease in CO concentration due to the faster feed rate is evident.

Next, the supply position of the secondary combustion air was set in two upper and lower stages, and the influence of the distance between them on the CO concentration, N ₂ O concentration, and NO _X concentration was evaluated. The results are shown in Table 3. The secondary air flow rate was constant at 70 m / s.

  As is clear from the above data, it was confirmed that the most excellent effect was obtained when the supply position of the secondary combustion air was set at the upper and lower stages and the distance between them was 200 to 600 mm.

DESCRIPTION OF SYMBOLS 1 Furnace 2 Sludge inlet 3 Pyrolysis zone 4 Upper combustion zone 5 Complete combustion zone 6 Air supply pipe for flow 7 Fuel supply pipe 8 Air supply pipe for combustion (lower stage)
9 Combustion air supply pipe (lower)
10 Tertiary air supply pipe

Claims (6)

A large fluidized incinerator with an inner diameter of 7m or more that fluidizes and incinerates sludge. The lower part of the furnace body is heated while supplying sludge by supplying air for fuel with an air ratio of 1.1 or less together with fuel. An overlying combustion zone that decomposes N ₂ O by forming a local high temperature field by supplying only secondary combustion air with an air ratio of 0.1 to 0.3 as a thermal decomposition zone that decomposes The uppermost part of the furnace body is a complete combustion zone for completely burning the unburned portion, and the supply position of the secondary combustion air in the upper combustion zone is divided into two upper and lower stages, and the supply speed is 70 m / A fluid incinerator characterized by a high speed of s or more.   The fluidized incinerator according to claim 1, wherein the air ratio of the pyrolysis zone is 0.7 to 1.1, the temperature is 550 to 750 ° C, and the temperature of the upper combustion zone is 850 to 920 ° C.   The fluidized incinerator according to claim 1, wherein a total air ratio of primary air supplied as fluidized air and secondary combustion air supplied to the upper combustion zone is set to 1.0 to 1.3. .   2. The fluidized incinerator according to claim 1, wherein an air ratio of air supplied to the complete combustion zone is 0.1 to 0.3, and an overall air ratio is 1.5 or less.   The fluidized incinerator according to claim 1, wherein the supply height of the lower stage of the secondary combustion air is 600 to 1000 mm from the upper surface of the stationary sand layer. The upper combustion stage is supplied to the upper and lower two stages to form an upper combustion zone between the decomposition temperature of N ₂ O and lower than the generation temperature of thermal NO _x therebetween. Fluid incinerator.

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