JP2000213726A - Method and device for dioxin reduction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently burn and decompose a dioxin reduction obstructing substance, and reduce the discharge of dioxin by promoting the decomposition of dioxin, by thermally keeping the whole body in a combustion cylinder within a specified temperature range extending to a specified zone, by the heat energy owned by an incineration gas. SOLUTION: This dioxin reducing device 4 is constituted of a combustion cylinder 5 comprising an internal cylinder 6 and an external cylinder 7, a combustion device 11 which is provided on the upper end section of the internal cylinder 6, and a heat- keeping body 21 which is provided at the lower end of the internal cylinder 6. A flame 15 is formed by a produced gas 3 comprising a fuel and combustion air, and the combustion is continued. The temperature of the flame coming out from a nozzle 12 becomes one thousand and several hundreds degree, but an introduction hole for the produced gas 3 is provided on the internal cylinder 6, and the produced gas 3 flows in as secondary air, and the temperature of a combustion gas 19 at the lower section of the internal cylinder 6 becomes 850-950 deg.C. A gas residing time in the internal cylinder 6 until the produced gas is introduced to the heat-keeping body 21 is short, but the gas temperature high, and the reduction of dioxin occurs in this period as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a dioxin reduction method and apparatus.

[0002]

2. Description of the Related Art The gas discharged from a general waste incinerator or an industrial waste incinerator contains a very toxic dioxin. Under generally known dioxin thermal decomposition conditions, decomposition starts at around 700 ° C., and the higher the temperature, the shorter the decomposition time. For example, at 850 ° C., it is decomposed in about 2 seconds. In order to reduce this dioxin by thermal decomposition, attempts have been made to maintain the high temperature state by increasing the temperature with combustion gas.

[0003]

The data described above are data obtained when only dioxin is contained in a very clean gas, for example, nitrogen gas. In the gas discharged from an actual incinerator, dioxin is contained. Besides fly ash, H
Various substances such as Cl and a precursor for producing dioxin are contained, and they hinder the reduction of dioxin in a complicated manner. Therefore, the dioxin itself cannot be reduced unless the dioxin reduction inhibitor is also reduced.

[0004] The present invention has been made in view of the above points, and it is an object of the present invention to provide a method and apparatus for reducing the emission of dioxin by efficiently burning and decomposing a dioxin reduction inhibitor.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to efficiently combust and decompose dioxin-reducing substances. Therefore, it is necessary to secure a sufficient decomposition time in a compact space and not only to decompose by a gas phase reaction but also to decompose. For ash and the like, dioxin is reduced to a value close to the limit by using thermal decomposition by a solid surface reaction. The reason for reducing dioxin to a value close to the limit here is to avoid re-generation of dioxin after the temperature of the gas is reduced or after the gas is released to the atmosphere.

The present invention specifically provides the following method and apparatus.

The present invention relates to a dioxin reduction method for decomposing dioxin by heating a dioxin-containing product gas discharged from an incinerator. Provided is a dioxin reduction method in which the whole is kept at 850 to 950 ° C. to promote the decomposition of dioxin.

[0008] The present invention relates to a dioxin reduction device for decomposing dioxin by heating a dioxin-containing product gas discharged from an incinerator, wherein a combustion means for introducing the product gas and heating the product gas with a combustion gas. The present invention provides a dioxin reduction device configured to include a combustion cylinder including: and a heat holding member formed of a heat-resistant material and arranged to mix the combustion gas downstream of the combustion cylinder.

In the present invention, a ceramic material is further used as a heat-resistant material, and the heat retaining member is an aggregate of a hollow pipe, a solid pipe, a hollow rectangular rod, a solid rectangular rod, a perforated plate, an L-shaped rod, and the like. Provided is a dioxin reduction device in which a group of heat retainers are arranged at right angles to a combustion cylinder.

[0010] The present invention further provides a dioxin reducing device in which the produced gas contains a combustible component, and the produced gas itself is burned, and a part of the produced gas becomes a combustion gas.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, as a first embodiment, a method and an apparatus for reducing dioxin in a product gas generated from a combustion furnace of a type that directly burns waste will be described. In the figure, a generated gas 3 from a combustion furnace 1 containing a large amount of dioxins is introduced into a dioxin reduction device 4 via a pipe 2. The generated gas 3 contains 1
It has an oxygen concentration of 0-15%.

The dioxin reducing device 4 includes a combustion cylinder 5 composed of an inner cylinder 6 and an outer cylinder 7, a combustion device (combustor) 11 provided at an upper end of the inner cylinder 6, and a heat generator provided at a lower end of the inner cylinder 6. It is composed of a holder 21.

The combustion device 11 comprises a nozzle 12, a fuel injection device 13, and an air introduction pipe 14. The fuel burns the air contained in the pipe 2 and the air introduced from the air introduction pipe 14 as combustion air, and a flame 15 To form Nozzle 12
Gas 19 flowing out of the inner cylinder 6 flows into the heat holding body 21
Leads to. The inner cylinder 6 is cooled by the generated gas 3 flowing through the generated gas path 8 formed between the outer cylinder 7 and the inner cylinder 6.
When the fuel is a liquid fuel, the liquid fuel is atomized by air. When the combustion air required for combustion can be provided by the air in the generated gas, the introduction of air from the air introduction pipe 14 is not required.

A flame 15 is formed by the fuel and the product gas 3 serving as combustion air, and the combustion is continued. Although the temperature of the flame exiting the nozzle 12 becomes a thousand and several hundred degrees, since the inner cylinder 6 is provided with an introduction hole for the generated gas 3, the generated gas 3 flows in as secondary air and is generated in the lower part of the inner cylinder 6. The temperature of the combustion gas 19 becomes 850-950 ° C. Although the gas residence time in the inner cylinder 6 before being introduced into the heat holding body 21 is short, dioxin is reduced during this time because the gas temperature is high.

The heat holding body 21 includes a heat holding pipe group 22 made of a heat-resistant material and a support casing 2 for supporting the same.
3 These heat holding pipe groups 22 are provided downstream of the inner cylinder 6.

One embodiment of the structure of the heat retaining pipe group 22 will be described with reference to FIGS. FIG. 2 shows the heat holding body 2
1 shows an upper surface of the entrance, and FIG. 3 shows a cross section taken along line AA of FIG. In these drawings, among various heat-resistant materials, silicon carbide as a ceramic material was used here. Hollow pipes, which are also advantageous for thermal distortion, are arranged at right angles to the gas flow, and are provided in a plurality of stages parallel to the flow direction. Each stage is configured in a staggered arrangement. Thus, the heat holding pipe group 22 is configured. A part of the combustion gas 19 reaching the inlet of the heat retainer collides with the surface of the ceramic pipe of the first stage and collides with the surface of the ceramic pipe of the next stage while changing the flow direction. By repeating this, the combustion gas moves in the radial direction. Therefore, the combustion gas is well mixed, and the gas temperature becomes uniform in the radial direction of the inner cylinder 6. If the gas temperature becomes uniform, dioxin contained in the low gas temperature will eventually decompose due to the rise in gas temperature,
Will decrease. In addition, the gas flow path becomes longer, so that a longer residence time can be ensured even for a short distance, and a sufficient decomposition time can be ensured. Since fly ash is a solid, it is difficult to carry out the reaction in a gas phase in a short time, but if the fly ash is kept on the surface of a glowing solid, the reaction will proceed very much. Fly ash in the combustion gas 19 comes into contact with the glowing ceramic at a considerable frequency by passing through a plurality of ceramic groups, and the dioxin in the fly ash is decomposed.

The combustion gas 19 that has reached the upstream of the heat holding pipe group 22 supplies heat to the heat holding body while passing through the heat holding body. Therefore, this group of heat retainers is constantly heated to a high temperature. Dioxin, fly ash,
The combustion gas 19 containing HCl and the precursor comes into contact with the surface of the heat holding body heated to a high temperature, decomposes dioxin in the process while changing the flow direction in a complicated manner, and flows downstream as the combustion gas 31. As a result, dioxins contained in the combustion gas 31 are significantly reduced.

In FIG. 1, the combustion tube 5 is connected at its lower end to a flue 30. The stack 30 is provided with a temperature reducer 32. The cooler 32 includes a main body 33 and a water injector 34.
And water is injected from a water injector 34 to form a spray 35.

Combustion gas 31 obtained by decomposing dioxins
Further flows in the flue 30 maintained at the dioxin decomposition temperature to become combustion gas 36 and combustion gas 37. Cooler 3
In the state of the combustion gas 36 immediately before 2, the dioxin is hardly detected. From this state, the temperature of the combustion gas is reduced by the temperature reducer 32 to such an extent that there is no problem even if the combustion gas is released into the atmosphere. The combustion gas 38 which has dropped in temperature and contains no dioxins is discharged 40 into the atmosphere through a chimney 39.

Referring to FIG. 4, a case of an incinerator of the type in which waste is gasified and taken out will be described as a second embodiment. The same components as those of the first embodiment are denoted by the same reference numerals, and description thereof will not be repeated. The gasified gas component is hydrogen,
This gas contains combustible components such as carbon monoxide and methane, and this gas itself can be used as fuel. Of course, this fuel gas also contains dioxins. This is supplied from the fuel input device 13 to the combustion device 11 as fuel. In this case, a blower 41 for supplying combustion air is provided, introduced through a pipe 42, and burned at a predetermined combustion temperature. Once the flame 15 is formed, the subsequent dioxin decomposition mechanism follows the same course as described in the first embodiment.

As described above, according to these embodiments: A heat storage structure made of a material with excellent heat resistance in the middle of the combustion reaction path in a combustion device that completely combusts gas containing dioxins discharged from the incinerator and reduces dioxins released into the atmosphere. Is provided.

2. The heat storage structure made of a material having excellent heat resistance in the middle of the combustion reaction path is configured such that the gas flowing into the heat storage structure repeatedly changes the flow direction therein and actively mixes the gases with each other.

3. The temperature distribution deviation of the gas flowing out of the heat storage structure is smaller than the temperature distribution deviation of the gas flowing into the heat storage structure made of a material with excellent heat resistance in the combustion reaction path. A heat storage structure is provided.

Embodiments of the structure can be modified in various ways.

1. A hollow pipe, a solid pipe, a hollow rectangular rod, or a solid rectangular rod may be provided in several stages so as to be perpendicular to the flow direction.

2. Several perforated plates may be installed so as to be perpendicular to the flow direction.

3. The L-shaped bar may be provided in several stages so as to be convex in the flow direction (in a U-shape) and perpendicular to the flow direction.

By doing so, 1. Since the inflowing gas repeatedly changes the flow direction therein, a long residence time can be ensured even in a short distance in the axial direction, and the decomposition of dioxins, that is, dioxins and dioxin reduction inhibitors proceeds.

2. Since the gas phase reaction and the solid surface reaction occur simultaneously, dioxins in the ash are also easily decomposed.

3. Even after the combustion device is stopped, the decomposition reaction of dioxins due to heat storage proceeds.

In the above-described embodiment, the dioxin reducing device 4 is arranged outside the incinerator 1 outside the incinerator.
It is possible to integrate this device with the incinerator 1 in an integrated arrangement.

FIG. 5 shows the effect of the heat retaining member 21 on the decomposition of dioxin. The Y axis is the dioxin concentration ng-
TEQ / Nm ³ is shown, and the X-axis shows the arrangement position of the element of each embodiment. In the comparison between the case where the heat holding pipe group 22 is provided and the case where the heat holding pipe group 22 is not provided, in the case where the heat holding pipe group 22 is not provided, at the heat holding body outlet (FIG. 1), between 1 × E10 ⁻¹ and 1 × E10 ⁻² . In contrast, when the heat retention pipe group 22 is installed, 1 × E10 ⁻³ and 1 × E10
The value is between 10 ^-4 .

The figure shows the difference in the decomposition performance of dioxins between the case where the heat retainer is provided and the case where the heat retainer is not provided. In the case where the heat retainer is used, the concentration is reduced by two orders of magnitude at the smoke outlet. .

[0035]

The inflowing gas supplies heat to the heat holding body, so that the entire inside of the combustion cylinder is uniformly and heat-maintained at a high temperature, and the dioxins contained in the generated gas can be moved in a short distance in the axial direction. However, the decomposition of dioxins can be promptly promoted due to the high temperature retention.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a top view of an entrance of a heat holding body which is a part of the structure used in FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an overall configuration diagram showing a schematic configuration of another embodiment.

FIG. 5 is an explanatory diagram illustrating an effect of a heat retaining body on dioxin decomposition.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Combustion furnace, 2 ... Piping, 3 ... Product gas, 4 ... Dioxin reduction device, 5 ... Combustion cylinder, 6 ... Inner cylinder, 7 ... Outer cylinder, 11 ...
Combustion device, 12 nozzle, 13 fuel injection device, 14
Air introduction pipe, 15 flame, 19 combustion gas, 21 heat holding body, 22 heat holding pipe group, 23 support casing,
32: temperature reducer, 33: body, 34: water injector, 35: spray, 41: blower.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Teruhumi Kawasaki 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power and Electricity Development Division (72) Inventor, etc. Ishimaru et al. Hitachi City, Ibaraki Prefecture 3-1-1, Machi F-term in Hitachi Plant of Hitachi, Ltd. (Reference) 3K070 DA05 DA09 DA37 DA55 DA56 DA73 3K078 AA01 AA08 BA03 BA26 EA01 EA02 EA07 4D002 AA21 AC04 BA05 BA12 BA13 CA01 DA35 DA66 DA70 GA01 GA02 GA03 GB02 GB03 HA03 HA08

Claims (4)

[Claims] 1. A dioxin reduction method for decomposing dioxin by heating a product gas containing dioxin discharged from an incinerator, wherein the heat energy of the incineration gas causes the entire inside of the combustion cylinder to cover a predetermined area. A method for reducing dioxin, comprising decomposing dioxin by maintaining heat at 850 to 950 ° C. 2. A dioxin reducing apparatus for decomposing dioxin by heating a dioxin-containing product gas discharged from an incinerator, comprising a combustion means for introducing the product gas and heating the product gas with a combustion gas. A dioxin reduction device, comprising: a combustion cylinder; and a heat retaining member formed of a heat-resistant material and arranged to mix a combustion gas downstream of the combustion cylinder. 3. An assembly according to claim 2, wherein a ceramic material is used as the heat-resistant material, and the heat retaining body is formed of a hollow pipe, a solid pipe, a hollow rectangular rod, a solid rectangular rod, a perforated plate, an L-shaped rod, or the like. A dioxin reduction device, wherein a group of heat retaining bodies as bodies are arranged at right angles to a combustion cylinder. 4. The dioxin reduction device according to claim 2, wherein the product gas contains a combustible component, and the product gas itself is burned and a part thereof becomes a combustion gas.