JPS60238605A - Fluidized combustion - Google Patents

Abstract

PURPOSE:To reduce emission of NOx, etc. due to high-temperature combustion in free board part as well as raise the efficiency of combustion in bed portion by using an oxygen-enriched air of higher oxygen concentration than the usual air, obtained through an oxygen selectively permeable film, as a fluidizing gas. CONSTITUTION:Objects to be burned, such as wastes, etc., are charged into a furnace through a charging port 11. Since the combusting reaction of the wastes charged into the furnace by oxygen-enriched air supplied as a fluidizing gas in the bed portion 3 and an assisting fuel oil is quickly made, the wastes are mostly burned in the bed portion 3. In order words, the majority of the objects to be burned in the free board part of the conventional furnace can be burned in the bed portion. When spontaneously combustible wastes are burned, most of them is burned in the bed to prevent the occurrence of high temperature in the free board portion and the emission of thermal NOx.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fluidized combustion method, and more specifically, it is used in urban areas to treat various wastes such as sewage sludge, waste plastics, waste carbon, organic waste liquids, tar sand, The present invention relates to a fluidized combustion method for incinerating combustible materials such as solid fuels such as grade coal, coal, and petroleum coke, and liquid fuels such as asphalt, tar, and heavy oil in the presence of a fluidized medium.

(Prior art) In the conventional fluidized combustion method, fluidizing gas (ordinary air) is blown into the furnace from the lower part of the furnace through a distribution plate, and a bed of fluidized medium formed on the distribution plate and its The upper freeboard section incinerates combustible materials.

When burning natural waste using the conventional fluidized combustion method described above, nitrogen oxides (NOx) and hexavalent chromium (Cr6+
), a so-called two-stage combustion method is used in which the waste is thermally decomposed and partially combusted at an air ratio of 1.0 or less in the bed section, and then completely combusted in the freeboard section. However, in this case, the combustible content is 5 to 6
A portion of the fuel is burned in the bed, and the remaining 40 to 50% is burned in the freeboard, resulting in high temperatures in the freeboard, requiring upgrades to the refractories, and increasing the amount of NOx in the exhaust gas at the furnace outlet. There is a drawback.

In order to improve the above-mentioned drawbacks, a method of spraying water in the freeboard section has been proposed, but there is a problem in that the water spray causes localized low-temperature areas and complete combustion does not occur sufficiently within the freeboard section. . In addition, it is necessary to adjust the amount of water sprayed onto the free board according to fluctuations in the calorific value of the waste (), so there is a drawback that operation control is difficult.

On the other hand, in the case of incineration of non-natural waste (for example, high water content waste such as TL, sludge, etc.), the non-natural waste evaporates in the bed section. Since the process involves decomposition and then combustion in the freeboard section, the amount of heat necessary for evaporation must be provided in the bed section. For this reason, auxiliary fuel oil is required, but 70% of the auxiliary fuel is burned in the bed section and about 30% in the freeboard section. This auxiliary combustion oil is necessary to maintain the bed temperature, but it is desirable that 1.00% of it burns in the bed.
As the freeboard combustion rate increases, the amount of auxiliary fuel (1) increases, and uneconomical operation ends.

(Problems to be Solved by the Invention) In view of the above-mentioned problems of the prior art, the present invention has high combustion efficiency in the bed section and reduces high-temperature combustion in the freeboard section and the generation of nitrogen oxides etc. accompanying it. The object of the present invention is to provide a fluidized combustion method that can significantly reduce the amount of auxiliary fuel consumed.

(Means for Solving the Problems) The present invention provides a fluidized combustion method in which combustible materials are supplied to a bed section in the lower part of the furnace in the coexistence of a fluidized medium, and are combusted and atomized in the bed section and the freeboard section above the bed section. In this invention, the fluidized combustion method uses oxygen-enriched air whose oxygen concentration is higher than that of normal air using an oxygen selective permeation membrane as the fluidized gas for fluidizing the fluidized medium. Alumina or the like is used, but in the case of a single component, it is generally desirable to have a wide particle size distribution because it is easier to obtain a dilute fluidized bed.

Note that the fluid medium can be used by mixing two components, but in this case, the specific gravity, particle size,
The optimum mixing ratio is determined depending on the shape etc.

In addition, the fluidizing gas in the present invention is normal air (oxygen concentration 2
0.9%), the oxygen concentration is 21-40%, usually 2:
Oxygen-enriched air that has been increased to about 3-30% is used, but it is believed that this oxygen-enriched air can be obtained at low cost.
−＋Reru. Such oxygen-enriched air can be easily obtained by diluting high purity oxygen with normal air. However, when conventional oxygen sources are used, such as oxygen by slow cooling liquefaction method or acid 7 by adsorption separation with zeolite, so-called PSA method, there are problems in terms of cost, safety, operability, etc. For this reason, in recent years, many attempts have been made to concentrate and separate rjI/ element directly from air using organic polymer membranes. This method uses a so-called oxygen-selective permeable membrane in which oxygen and nitrogen, which are the compositions of air, pass through 71 L, and oxygen permeates more easily than nitrogen.
1 to create an appropriate pressure difference. Then air heart, 11,
permeates through this membrane. At this time, since oxygen permeates through the layers more easily, the air that has passed through the membrane becomes oxygen-enriched air with a higher oxygen concentration than the original normal air. Practical aspect 1. The oxygen-selective permeable membrane is modularized into a certain shape, one side of the membrane surface is exposed to air, and the other side is kept airtight. Connect. When the vacuum pump is operated, air is taken in from the membrane surface, enters the inside of the module, passes through the vacuum pump, and is discharged as oxygen-enriched air from the discharge port of the vacuum pump. Such a system is known, for example, from Japanese Patent Application Laid-open No. 58
-55310, No. 58-55311, etc.

Next, an embodiment of an apparatus suitable for carrying out the method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a fluidized combustion furnace. 2, a fluidizing gas duct 9 that supplies fluidizing gas to the core air chamber 8, and a combustion gas duct 10 provided at the top of the freeboard section 4. . An inlet 1 for injecting materials to be combusted is provided in the upper part of the bed part, and an inlet 12 for auxiliary fuel oil is provided in the lower part of the bed part.

Materials to be burned (for example, waste) are introduced into the furnace through the waste input port 11 . The waste introduced into the furnace is mixed with fluidized gas in the bed section 3. 1st time, the combustion reaction between the f7'l1m enriched air and the auxiliary fuel oil supplied by the fuel tank takes place rapidly.
The situation appears as if most of the combustion of waste takes place in the bed section 3. By converting, most of the combustion that occurs in the freeboard section in conventional furnaces can be done in the entire bed section.

In order to further promote combustion in the upper bend, it is preferable to supply oxygen-enriched air to the oxygen-poor layer in the upper part of the bed section 3. Such enriched air is usually oxygen enriched air whose oxygen concentration is higher than that of the fluidizing air. Furthermore, when this blown air is supplied in the tangential direction of the furnace, the oxygen-poor layer at the top of the bed is agitated in the horizontal direction, further promoting combustion.

More specifically, when incinerating natural waste, most of it is burned in the bed, thereby preventing the freeboard from becoming too hot and generating thermal NOx. It is also possible to inject water into the bed, which allows the temperature inside the furnace to be easily controlled. Furthermore, since the heat capacity of the fluidized medium is very large, for example, about 200,000 Kcal/rd, it is not affected by fluctuations in waste materials, calorific value, etc. In addition, when the 1"llO:(, yr reduction measure operation is performed, the reduction of sNOXs(-r) can be further promoted by creating an 8-bag flow 4!I layer-deficient reducing atmosphere.

When incinerating non-natural waste, more than 90 liters of auxiliary fuel oil to maintain the bed temperature is burned in the bed, and more solubles in the waste are burned in the bed than before. Therefore, the amount of auxiliary fuel can be significantly reduced.

Figure 2 shows the application of the method of the present invention to the incineration of non-natural waste.
This is an example of a system in which oxygen-enriched air, whose oxygen concentration has been increased by passing through a separation membrane stored in an oxygen-enriching module 15, is sucked by a pump 17 through a pipe line 16. Further, the oxygen is mixed with normal air supplied from the pipe line 18 to adjust the oxygen concentration to a predetermined concentration, and then supplied to the fluidizing blower 20 via the pipe line 19. Thereafter, this enriched air exchanges heat with the high-temperature exhaust gas discharged from the combustion gas duct 10 of the combustion furnace 1 through 21 pipes in a heat exchanger 22, and then passes from a pipe 23 to the fluidizing gas duct 10 of the combustion furnace. 9 and is supplied to the air chamber 8.

24 is an air supply pipe to the oxygen enrichment module 15;
Air is supplied to the element enrichment module by an air fan 25 interposed in this air supply pipe.

18 is a discharge pipe for the remaining oxygen-depleted air. FIG. 3 shows an example of another system, in which oxygen-enriched air whose oxygen concentration has been increased by an oxygen-enriching module 5 is sucked by a vacuum pump 17 through a pipe 16, and then is provided in a pipe 19. A fluidizing gas flow path which is supplied to the air chamber 8 of the combustion furnace by a branch pipe 29 and a bed 7 of the combustion furnace. IS9''-7・: The auxiliary combustion gas supply pipe 30 and (C) supplied to the IS are separated.Then, oxygen-enriched air with a high oxygen concentration that has passed through the membrane module is supplied to the upper 1μ of the bed section. Oxygen-enriched air, which is mixed with normal air and whose oxygen concentration is adjusted to a predetermined concentration, is supplied to the air chamber of the combustion furnace.
The same parts as those in the figure are given the same numerals as -tfi, and their explanations will be omitted.

(Example) Sewage sludge with a water content of 80% was incinerated as waste using a combustion furnace with a fluidized bed inner diameter of 1200 W+ and a fluid medium of crushed sand No. 4 (average particle size 0.83 #) shown in FIG. The incineration conditions and results are shown in Table 1. For comparison, the results of the conventional method using ordinary air as the fluidizing gas are shown.

Table 1 (Effects of the invention) As is clear from the results in Table 1 above, the fluidized combustion method of the present invention lowers the temperature of the freeboard section and reduces the NOx concentration in the exhaust gas compared to the conventional method. This can be reduced by half, and when supplementary fuel oil is used, its consumption capacity can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a fluidized combustion furnace for carrying out the method of the present invention, and FIGS. 2 and 3 are system diagrams showing a system using the fluidized combustion furnace described above. 1... Fluidized combustion furnace 2... Dispersion plate 3... Bed section 4... Freeboard Department Patent Applicant Rira Co., Ltd. Agent Patent Attorney Ken Honda Figure 1 11゜Figure 2 Figure 3 figure

Claims (1)

[Claims] In a fluidized combustion method in which combustible materials are supplied to a bed section at the bottom of the furnace in the coexistence of a fluidized medium and then combusted in the bed section and a freeboard section above the bed section, oxygen is selected as the fluidizing gas for fluidizing the fluidized medium. A fluidized combustion method that uses oxygen-enriched air, which has a higher oxygen concentration than normal air, through a permeable membrane.