JPS5821162B2 - Fluid combustion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a fluidized combustion method, and in particular to a method for non-pollutingly burning various inferior combustibles that are considered unsuitable as fuel.

Conventionally, when fossil fuels, combustible materials containing fossil fuels, or similar materials are burned, the sulfur and nitrogen content in the combustibles, or the nitrogen content in the air, is converted to SOx or NOx, which is mixed into the exhaust gas. and was released into the atmosphere, causing air pollution.

For this reason, recently, the emission values of SOx and NOx have been legally regulated, and the situation has come such that combustion equipment cannot be operated without measures to remove and suppress SOx and NOx.

Measures to remove and suppress SOx and NOx include, for example, for SOx, a desulfurization method using the lime plaster method in the case of large-scale combustion equipment, and an absorption and removal method using caustic soda in the case of small-scale combustion equipment; , methods for suppressing NOx generation through combustion improvements such as burner improvements and exhaust gas recirculation, wet denitrification methods that add some kind of oxidizing agent to the combustion gas and absorb and remove NO after converting it into higher-order oxides;
A dry denitrification method in which Ox is reduced to N2 using a reducing agent has been developed and is being put into practical use.

However, these methods have drawbacks such as the need to install special dedicated equipment and the range of application (conditions) to which they can be applied is limited.

On the other hand, in recent years, various types of factory waste, such as waste with heavy oil adhering to it, heavy oil slurry, and other combustible materials that do not have co-constancy in shape or properties, or those that cannot maintain stable combustion in a normal combustion furnace, such as dust collection 2. Description of the Related Art There are increasing opportunities to burn and incinerate combustible materials, such as dust and other flame-retardant combustible materials, which are generally considered to be inferior combustible materials.

The present invention was made for the purpose of burning the above-mentioned fossil fuels, combustible materials containing them, their analogues, and defective combustible materials without causing pollution. This provides a fluidized combustion method that can easily reduce fuel consumption.

In general, in the fluidized combustion method, the mixing phenomenon of particles flowing in the fluidized bed is very good, so that the fuel is uniformly dispersed in the fluidized bed and is combusted at a relatively low temperature and a low excess air ratio.

Therefore, the generation of thermal NOx is extremely low, and ``NOx in the combustion gas is mostly due to the nitrogen content in the fuel, and the NOx is easily decomposed by the reducing gas in a reducing atmosphere and becomes N2, making it harmless. be done.

The reaction at this time is mainly shown in the following formulas (1) and (2), but also includes a reduction reaction using CmHn.

2CO+2NO-)N2+2C02(1)2H2+2N
O-+N2 +2H20 (2) However, when a combustion furnace is operated in a reducing atmosphere, complete combustion becomes difficult,
Inconveniences such as the generation of foul-smelling gas and a decrease in the carbon utilization rate occur.

Moreover, if lime is used as the fluidizing medium, SOx in the combustion gas can also be easily removed.

The reaction at this time is shown as follows. CaCO3-+
CaO+CO2(3)SO2+CaO+ 1/202
-+CaSO4 (4) That is, lime Ca C03 is decomposed by the combustion heat of the fluidized combustion furnace to produce CaO, which is converted into gypsum.

However, the CaO is extremely easily atomized in the fluidized combustion furnace, and most of it is discharged outside the furnace along with the exhaust gas.
An efficient dust collector is necessary to prevent secondary pollution, and the cost of purchasing and replenishing lime cannot be ignored.

The present invention is based on the above-mentioned facts and has developed a fluidized combustion method for completely burning (incinerating) the defective combustibles without causing any pollution.

That is, the present invention uses converter slag or electric furnace steel slag as the fluidized medium of the fluidized bed, provides a uniform and slightly oxidizing atmosphere throughout the fluidized bed, and has a temperature of 800 to 1100°C and an excess air ratio of 1.15 or less. It is characterized by combustion under the following conditions.

The fluidizing medium used in the present invention is converter slag or electric furnace slag (hereinafter abbreviated as slag) which is discharged from the steel manufacturing process and is generally of no use other than as a landfill material.

The slag has excellent characteristics as a fluidizing medium, such as being able to be crushed to an appropriate particle size, and having sufficiently fine grain hardness that there is little scattering.

Moreover, Ca contained in the slag acts as a desulfurization agent, and various metal oxides act as NOx decomposition catalysts in a partially reducing atmosphere that appears in a fluidized bed operated in a slightly oxidizing atmosphere. Furthermore, a large amount of iron forms FeO and Fe3O4 in the above partially reducing atmosphere and diffuses into the furnace.
When it becomes e2O3, it acts as a reducing agent for NOx.

In the present invention, the combustion temperature is set to 800 to 1100°C because at temperatures below 800°C, odor components in combustible materials cannot be completely combusted and decomposed, and incomplete combustion occurs in waste reburned materials with a high degree of carbonization. CO gas generation) rate is increased to 1100
This is because at temperatures above 800°C to 110°C, combustion generated ash fuses and destabilizes the fluid state.
This is because NOx decomposition proceeds most effectively in the temperature range of 0°C.

Further, in the present invention, the excess air ratio is set to 1.15 or less because if the excess air ratio is higher than this, the frequency of generation of the above-mentioned partial reduction atmosphere will be drastically reduced, and the NOx decomposition effect will be significantly reduced. , preferably 1.1 or less.

Hereinafter, embodiments of the present invention will be described in detail using FIG. 1 attached.

In the figure, 1 is a fluidized combustion furnace shell, 2 is a fluidized bed, 3 is a wind box,
4 is an air distribution plate, 5 is a combustible material supply port, 6 is a slag input port,
7 is a combustion residue and slag extraction outlet for combustible materials, 8 is a thermometer,
9 is a heat transfer means installed as necessary; 10 is a blower;
11 is a damper, 12 is an oxygen concentration meter, and 13 is a dust collector.

In the present invention, the combustion temperature is controlled within the above temperature range by detecting it with a thermometer 8, adjusting the amount of combustible material supplied, and removing combustion heat with the heat transfer means 9 as necessary. Also, the amount of slag supplied is adjusted depending on the characteristics of the combustible material.

Furthermore, in the present invention, the oxygen concentration in the combustion gas is measured using an oxygen concentration meter 1.
2, and the amount of air sent from the blower 10 to the wind box 3 is adjusted by the damper 11 to maintain a slightly oxidizing atmosphere inside the furnace.

The combustion gas is discharged into the atmosphere after removing accompanying slag and combustion residue in the dust collector 13.

Next, examples of the present invention will be given.

Example 1 A test fluidized bed with a diameter of 30 cm was filled with converter slag particles (average particle size: 750 μm) having the following composition and a static height of about 60 cm, and coke fine powder with an average particle size of imm was heated at a fluidized bed temperature of 900 to 98 μm.
The combustion was carried out at 0° C. and a gas superficial velocity of 2.4 m/sec.

Fluidized bed preparation involves inserting a water-cooled pipe into the fluidized bed, and adjusting the degree of insertion (
The heat transfer area of the water-cooled tube immersed in the fluidized bed changes depending on the degree of insertion.

In addition, the amount of air was adjusted to vary the excess air ratio, and changes in NOx concentration in the combustion exhaust gas were measured.

The results are shown in graph 1 of FIG.

The graph shows that the NOx concentration decreases rapidly when the excess air ratio is 1.15 or less.

In addition, SOx in combustion exhaust gas with an excess air ratio of 1.15 or less
The concentration was approximately 70 ppm.

Furthermore, when electric furnace steel slag was used instead of the converter slag, the same results as above were obtained.

Comparative Example 1 Combustion was carried out under the same conditions as in Example 1, except that limestone with an average particle size of 800 μm was used as the fluidizing medium, and changes in NOx concentration in the combustion exhaust gas were measured.

The results are shown in graph 2 of FIG.

Comparing Graph 2 with Graph 1, it will be seen that even if the excess air ratio is made low, it is impossible to discharge low concentration NOx as in Example 1.

In addition, SOx in combustion exhaust gas with an excess air ratio of 1.15 or less
The concentration was approximately 50 ppm.

Example 2 Coal particles having an average particle diameter of 1.2 mm were combusted under the same conditions as in Example 1 except that the combustion temperature was 800 to 860° C. and the excess air ratio was 1.1.

In the combustion exhaust gas, the SOX concentration was 55 ppm on average, and the NOx concentration was 60 ppm on average.

Comparative Example 2 Combustion was carried out under the same conditions as in Example 2 except that limestone was used as the fluidizing medium.

In the combustion exhaust gas, the SOx concentration was 45 ppm on average, and the NOx concentration was 130 ppm on average.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, and Fig. 2 is a chart showing changes in the amount of NOx generated depending on the excess air ratio. This is based on a comparative example using limestone.

Claims (1)

[Claims] 1 In the fluidized combustion method, which reburns in a fluidized combustion furnace,
Converter slag or electric furnace steel slag particles are used as the fluidized medium of the fluidized bed, and a uniform and slightly oxidizing atmosphere is maintained throughout the entire area within the fluidized bed, at a temperature of 800 to 1100°C and an air excess ratio of 1.
A fluidized combustion method characterized by combustion at a temperature of 15 or less.