JPH0252168B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a fluidized bed incineration method and a fluidized bed incinerator.

[Prior art]

In a fluidized bed incinerator, fluidized sand with a particle size in a narrow range of about 0.8 to 1.2 mm is suspended and fluidized using fluidized air blown in from the bottom or generated gas such as combustion gas or water vapor from the incinerated material. In addition, a fluidized bed section is formed that maintains a constant temperature range suitable for combustion reaction, for example, about 600 to 800°C. Maintaining this temperature is essential for incineration, so if the temperature tends to drop below that temperature, auxiliary combustion may be performed using a burner or mixing in the incinerated material.
To improve the heat balance in the fluidized bed section, the fluidized air is preheated using exhaust gas heat. In this case, the running cost of the fluidized bed incinerator can be said to be mainly the auxiliary combustion allowance and ventilation power (pushing fluidized air and drawing combustion exhaust gas).

By putting the incineration material into the fluidized bed in this way, dry ignition is carried out by the heat held by the fluidized sand, and dispersion and crushing are performed by the movement of the fluidized sand. The incineration material is combusted within the chamber, and a portion of the combustion heat is input to the fluidized bed section. Therefore, in a fluidized bed incinerator, fluidized air plays the dual role of floating fluidization of fluidized sand and combustion air. There is a close relationship between them.

Normally, the incineration load (the amount of heat generated) is assumed to be the rated value, the required combustion air flow rate is determined, and the hearth area is determined so that the rising gas velocity per unit area corresponds to the standard sand grain size. This rising gas velocity is often set to a velocity corresponding to an air volume that is approximately 2 to 3 times the minimum fluidization air volume GMF.

Here, regarding the heat balance of the fluidized bed section, the heat input can be listed as follows.

Of the calorific value of combustion materials, including incineration materials and combustion auxiliary materials, the heat input to the fluidized bed section.

The calorific value here is the lower calorific value, which is obtained by subtracting the latent heat of vaporization of entrained moisture and moisture generated by combustion from the absolute calorific value.

The combustion material, fluidized air, which is introduced into the fluidized bed section,
The sum of the sensible heat of sand or cooling water, etc., multiplied by the temperature and amount at the time of input, and the average specific heat at constant pressure.

Fluidized air is often preheated by indirect heat exchange with exhaust gas to improve the heat balance of the fluidized bed, but the temperature is usually lower than the fluidized bed temperature.

Fever is as follows.

The sum of the sensible heat of exhaust gas, ash, sand, etc. leaving the fluidized bed, multiplied by the temperature and volume of the fluidized bed and the average specific heat at constant pressure.

Latent heat of vaporization of cooling water.

This cooling water is used to prevent the temperature of the fluidized bed from becoming high due to the high calorific value of the combustible material.
It is not used if it is less than about 1500Kcal/Kg.

Heat dissipation loss.

Among the above, the main heat input is calorific value,
The main heat output is the sensible heat of the exhaust gas. The fluidized bed temperature is determined based on this balance.

[The problem that fever is trying to solve]

Therefore, even if the design is such that the heat balance is balanced during rated operation, if the amount of incinerated material to be processed is less than the rated value, that is, the amount of heat generated is less than the rated value, the heat dissipation loss will be ignored. If the amount of exhaust gas is not reduced by reducing the amount of fluidized air in proportion to the amount of heat generated, excess heat will be output and the temperature of the fluidized bed will drop.

However, as mentioned above, the amount of fluidized air is a constant value due to the flow of fluidized sand, that is, at most
It can only go up to about 90-70%.
Therefore, if you try to perform partial load operation with the throughput, that is, the amount of heat generated, reduced to less than that, it is necessary to compensate for the loss of heat carried away by the exhaust gas, and in order to compensate for this, the temperature of the fluidized bed section is increased to 600℃, etc. In order to improve the heat balance to maintain the temperature required for incineration operation, it is necessary to start auxiliary combustion or increase the amount of auxiliary combustion, and the ventilation power does not decrease, the amount of auxiliary combustion becomes high, and the amount of waste to be incinerated increases. The running cost per unit weight becomes extremely uneconomical.

Therefore, if you want to reduce the throughput to a range lower than 90% to 70%, it is necessary to adjust the operating time at the expense of starting up and stopping operations, or reduce the amount of equipment, maintenance, and operation. It is necessary to be prepared to use multiple furnaces, and the quantity and quality of the processed materials will greatly increase or decrease.
This has been a problem when applying fluidized bed technology to waste incinerators, where the amount of heat generated typically fluctuates significantly.

The present invention solves these conventional problems,
The object of the present invention is to provide a fluidized bed incineration method and a fluidized bed incinerator that can reduce ventilation power and consumption of combustion aids even in the case of partial load.

[Means for solving problems]

In order to achieve the above-mentioned object, the inventors conducted repeated research and developed the present invention by focusing on reducing the fluidizing air volume by reducing the particle size of fluidized sand.

The present invention provides an incineration method using a fluidized bed, which is characterized in that, in incineration using a fluidized bed, the particle size of fluidized sand is made smaller in accordance with the reduction in the amount of heat generated, and the incineration is performed while reducing the fluidization air volume. and its fluidized bed incinerator.

[Effect]

At rated load, the fluidizing air volume is normally about three times the minimum fluidizing air volume GMF. When the load, that is, the amount of heat generated, decreases, for example, by about 2/3, the fluidization air volume also decreases by 2/3 in proportion to this.
(i.e., 2 x GMF), the fluid state can still be maintained, so it is possible to continue incineration while keeping the air ratio almost constant. At this time, the heat input decreases, but the heat output also decreases accordingly. Since the combustion temperature decreases (as the exhaust gas air volume decreases, the heat carried away with the exhaust gas also decreases), combustion occurs without a drop in combustion temperature.

Furthermore, if the load, that is, the amount of heat generated, decreases, the particle size of the fluidized sand is reduced accordingly (for example, by replacing it with fluidized sand whose particle size distribution is closer to the smaller diameter), and the minimum fluidization air volume GMF is lowered. The practical lower limit of 2×GMF is also lowered. This prevents an increase in the air ratio, reduces the exhaust gas flow rate, reduces heat output in proportion to the decrease in heat input, and therefore reduces or eliminates the consumption of auxiliary combustion materials and also reduces the ventilation power.

In this way, by changing the fluidized sand to finer sand that corresponds to the amount of combustion air at partial load, it is possible to operate at the same appropriate air ratio as at rated operation even if the throughput is reduced to about 1/3. .

In this way, the method of the present invention is applied to the following cases where the amount of heat generated is reduced due to partial load.

(1) When incinerating waste, the calorific value varies greatly depending on the season, being low in summer and high in winter.
Since the incinerator's rating is adjusted to the winter conditions when the calorific value is high, it will be at partial load in the summer when the calorific value is low. Since this variation in calorific value can be predicted in advance, the fluidized sand is replaced at an appropriate time before the onset of summer, replacing it with sand whose particle size distribution is closer to the small diameter side, thereby reducing the amount of fluidizing air.

(2) When the type of incinerated material (lower calorific value is predicted) is changed every certain period.

(3) If there is a change in combustion temperature during operation, and this is due to a change in calorific value.

etc. In either case, fluid sand is replaced depending on the situation, either all at once or gradually over several days.

Figure 2 shows fluidized sand grain size Dp and minimum fluidization air volume GMF
It is a graph showing the relationship between the temperature and the fluidized bed temperature.
Regarding the particle size Dp and GMF, it can be considered that the particle size Dp is approximately proportional to the square root of GMF.

Note that the air ratio is the theoretical amount of combustion air required for incineration Lo [Nm ³ /h] (the amount of combustion air that completely burns the incinerated material and the oxygen concentration in the combustion exhaust gas is 0%). Actual combustion air amount L [Nm ³ /
h] and can be expressed by the following formula.

m=L/Lo 〔Example〕 Embodiments of the present invention will be described using the drawings.

Figure 1 shows the lower calorific value with some auxiliary combustion.
This is an example of a sludge incinerator with a capacity of around 500Kcal/Kg.

The incinerator 1 is composed of a freeboard part 2 and a fluidized bed part 3 formed by sand in a fluidized state, and an air blowing part 5 is provided on almost the entire surface of the bottom surface 4 of the fluidized bed part 3.
The structure is such that fluidized air is blown into the fluidized bed section 3 from there through a pressure equalization chamber 6. The fluidized bed section 3 is equipped with a variable feeder 8 and a dispersion feeder 9 for charging sludge 7, which is the incineration product, and a burner 11 for combustion of auxiliary fuel oil 10, and a sand supply tank on the wall of the freeboard section 2. 12 and a sand inlet nozzle 14 equipped with a sand supply valve 13, and a sand discharge nozzle 16 equipped with a sand discharge valve 15 at the lowest position of the fluidized bed section 3.

17 is a pressure gauge, 18 is burner air, 19 is flowing air, and 20 is exhaust gas.

At least the particle size of the fluidized sand supplied to the incinerator 1 is such that the particle size is 1.5 times or more the GMF under operating conditions. It should be noted that particles with a fine particle size are discharged out of the furnace along with the exhaust gas by pneumatic transportation, so they are useless even if they are thrown in. Therefore, particles with a particle size close to the optimum particle size calculated from GMF etc. are desirable.

Here, during rated operation, in the incinerator 1 where the particle size is 1 mm and the hearth area, that is, the horizontal cross-sectional area of the fluidized bed section 3 is set to three times the GMF, the air volume can be reduced to about twice the GMF. It is. That is, it is possible to reduce the processing amount, that is, the amount of heat generated, to 2/3 of the rated value without changing the air ratio. At this time, the amount of auxiliary combustion is
The amount used per unit weight of the incinerated material only needs to be increased to the extent that it corresponds to the heat dissipation loss, which does not change in absolute amount, and the absolute amount of ventilation power can also be reduced slightly in accordance with the reduction in air volume.

If you try to reduce the processing amount any further, the amount of fluidized air cannot be reduced, so the processing amount will decrease, and the temperature of the fluidized bed section 3 will not be maintained unless you compensate for the decrease in the calorific value of the incinerated material by using auxiliary combustion. , the amount of auxiliary combustion is extremely large, making it uneconomical.

Therefore, once the sand is extracted from the sand discharge nozzle 16, new sand with an appropriate particle size distribution (grain size is closer to the smaller side) corresponding to the partial load is supplied from the sand input nozzle 14 to replace the sand. do.

For example, in this example, if you want to reduce the processing amount, that is, the amount of heat generated, by 1/3, use sand with a GMF of 1/2 of the rated value, about 0.7 mm, so that the air volume is 1/3 and the GMF is twice the GMF. This can be done in terms of particle size. That is, point A in Figure 2
This becomes possible by setting the point B as point B.

This makes it possible to keep the air ratio constant, that is, to reduce the throughput and flowing air to 1/3 of the rated value at the same ratio as at the rated time, and the consumption of auxiliary combustion materials per unit of incinerated material is relatively low. This is enough to compensate for the increased heat dissipation loss, and the absolute amount of ventilation power is reduced to 60% of the rated power by controlling the suction damper according to the reduction in air volume.
The rotation speed can be controlled to about 40% of the rated value.

Therefore, partial load operation up to 1/3 of the rated load is possible without significantly impairing economic efficiency.

The above example deals with low calorific value incineration materials that require auxiliary combustion. The same applies to things. Even in such cases, if the ventilation volume is not reduced, auxiliary combustion will be required in most cases when operating at a large partial load, but with this example, it is possible to do without auxiliary combustion or with a small amount of auxiliary combustion. Also, the effect of reducing the ventilation power can be achieved in the same manner as in the above-mentioned embodiment.

Next, another embodiment shown in FIG. 3 will be described. This is because the lower calorific value with some auxiliary combustion is
This is an example of a swirling flow fluidized bed incinerator for sludge of around 500Kcal/Kg.

The incinerator 1 is composed of a freeboard section 2 and a fluidized bed section 3 formed of sand in a fluidized state, and the horizontal cross section of the fluidized bed section 3 is smaller than the freeboard section 2 at least at the furnace outlet. Furthermore, the bottom surface 4 of the fluidized bed section 3 has a gentle slope, and an air blowing section 5 is provided over almost the entire surface. Room 23
There is a pressure equalizing chamber 6 consisting of a pressure equalizing chamber 6, and flowing air can be distributed and supplied to each chamber through an air volume adjusting damper 24. A sand discharge nozzle 16 with a sand discharge valve 15 is provided at the lowest position of the fluidized bed section 3, and a sand supply tank 12 and a sand input nozzle 14 with a sand supply valve 13 are provided in the freeboard section 2.

The incinerated sludge can be supplied in a variable quantity by a variable feeder 8, and is directly extruded into the fluidized bed section 3.

The flowing air is supplied to the first
A flow rate of air is blown into the chamber 21 to create a slow flowing state, which is approximately twice the GMF on average, and an air volume that is blown into the third chamber 23 on the opposite side is blown into a strong flowing state, for example, about 6 times the GMF. The second chamber 22 located in the middle is blown with an air volume that is between the two.

As a result of this, the overall flow becomes a downward flow in the first chamber 21 and an upward flow in the third chamber 23, and the fluidized sand forms a swirling flow in the fluidized bed as shown in Fig. 3, and the stirring and mixing in the fluidized bed becomes smooth. The situation is such that it will be carried out.

Therefore, in this example, in order to reduce the load without changing the sand grain size compared to the rated load, the air flow rate in the first chamber 21 remains the same, and the second chamber 22 and the third chamber 2
3 can reduce the overall fluidized air blowing volume to the point where the volume of air in the third chamber 23 is reduced to about three times the GMF. Assuming that the air volume is distributed equally between rooms 1 to 3, the following calculation: 1/3 x 1 + 1/3 x 1/2 + 1/3 x 1/2 = 2/3, the air volume will be reduced to about 2/3. Therefore, partial load operation at 2/3 of the rated capacity is possible with the same air ratio.

In order to reduce the amount of incineration to less than this, it is necessary to change the sand grain size, just as in the example shown in Fig. 1.

Incidentally, a sand circulation facility as shown in FIG. 4 may be provided to facilitate the exchange of sand grain sizes. Classifier 2 is here
The sieve 26 in No. 5 is replaceable, and several sieve openings are arranged. 27 is circulating sand, 28 is discharged sand, 2
9 is supplementary sand.

The sand is circulated before the air volume is reduced, and coarse sand that cannot be fluidized when the air volume is reduced is passed through a sieve using an appropriate sieve and removed as discharged sand. Preliminary removal is done by replenishing with replenishment sand of appropriate particle size. In this way, the sand grain size distribution can be changed through a process similar to sand exchange without having to stop the furnace especially for sand exchange.

It should be noted that the valves shown in FIGS. 1, 3, and 4 may be used without any problems even if other means such as a screw or a double damper are used.

Contrary to the above example, if you increase the load while increasing the air volume from a partial load state, there is no need to worry about sand not being able to be fluidized and accumulating on the bottom of the fluidized bed. Since the minimum sand grain size discharged outside the furnace becomes larger and the amount of sand decreases, it is only necessary to fill the amount with sand of an appropriate grain size into the furnace as supplementary sand.

However, if it is preferable to throw it away with the ash, you can pull out the sand, or conversely, in the example shown in Figure 4, you can use the fine sand from under the sieve as discharged sand and store it separately. It is.

〔Effect of the invention〕

According to the present invention, by simply changing the sand grain size, it has become possible to operate the fluidized bed in a good fluidized state with the air flow rate required for combustion even under partial load. As a result, the amount of incineration will increase in the future,
Even if we build a large furnace that takes into account the amount of incinerated material that changes depending on the season or various circumstances,
Even when the amount of material to be incinerated is small, it is now possible to avoid operations that are uneconomical in terms of running costs such as ventilation power and combustion aid consumption. Therefore, it is possible to eliminate problems such as the need for a storage tank to adjust the operating time, startup/stop operations during operation, and bad odors that occur during storage.

Therefore, it would be highly effective to make the fluidized bed technology for incineration even broader and more economical.

[Brief explanation of drawings]

Figure 1 is a flow diagram of an embodiment of the present invention, Figure 2 is a graph showing the relationship between the minimum fluidizing air volume GMF, fluidized bed temperature, and fluidized sand particle size, and Figures 3 and 4 are another example of the present invention. FIG. 1... Incinerator, 2... Freeboard section, 3...
Fluidized bed section, 4... bottom surface, 5... air blowing section, 6...
...Pressure equalization chamber, 7...Sludge, 8...Variable feeder, 9
... Dispersion feeder, 10 ... Auxiliary fuel oil, 11 ... Burner, 12 ... Sand supply tank, 13 ... Sand supply valve, 14
... Sand input nozzle, 15 ... Sand discharge valve, 16 ...
Sand discharge nozzle, 17... Pressure gauge, 18... Burner air, 19... Fluid air, 20... Exhaust gas, 2
1...1st room, 22...2nd room, 23...3rd room
chamber, 24...air volume adjustment damper, 25...classifier,
26...Sieve, 27...Recirculation sand, 28...Discharge sand, 29...Replenishment sand.

Claims (1)

[Scope of Claims] 1. A fluidized bed characterized in that in incineration using a fluidized bed, the particle size of the fluidized sand is made smaller in accordance with the reduction in the amount of heat generated, and the incineration is carried out by reducing the volume of fluidized air. Incineration method. 2 A fluidized sand discharge section is provided at the lowest part of the fluidized bed section,
A classification mechanism that includes a fluid sand input section that opens in the freeboard section, classifies the fluid sand discharged from the discharge section, and supplies fluid sand that has been classified into a particle size distribution different from that of the discharged fluid sand to the input section. A fluidized bed incinerator characterized by comprising: