JP2011190969A - System for waste disposal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system for waste disposal capable of reducing loads on the environment by suppressing the generation of nitrous oxide. <P>SOLUTION: The system includes: a pyrolysis furnace 3 for accepting organic waste to pyrolyze the organic waste under a reducing atmosphere at high temperature; a combustion furnace 4 for combusting the combustible pyrolysis gas generated in the pyrolysis furnace; one or more heat utilization equipment 2, 3, 5 for utilizing as a heat source the combustion exhaust gas generated in the combustion furnace; and reflux lines L7, L71, L72, L73 for refluxing a low temperature exhaust gas which resulted in low temperature since used in the heat utilization equipment, to any equipment disposed at the upper stream than the heat utilization equipment so as to be used in the upper stream equipment as a combustion air or dilution air therein. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a waste treatment system for treating organic waste.

  In a waste treatment system that treats organic waste such as dewatered sludge, pyrolysis gas (dry distillation gas) and pyrolysis residue (carbide) are obtained by thermally decomposing organic waste in a pyrolysis furnace in a low oxygen state. And combustible pyrolysis gas is combusted in a combustion furnace, and this combustion exhaust gas is used as a heat source for heat utilization equipment. The combustion exhaust gas is deprived of heat energy in the heat utilization device, the temperature drops, and is discharged as a low temperature combustion exhaust gas.

  For example, Patent Document 1 and Patent Document 2 describe an air preheater, a pyrolysis furnace, a waste heat boiler, a heat medium heater, a dryer, or the like as a heat utilization device that uses combustion exhaust gas in a waste treatment system. Yes.

Japanese Patent No. 4198426 JP 2007-270018 A

However, in the conventional waste treatment systems described in Patent Document 1 and Patent Document 2, when organic nitrogen is contained in the organic waste, nitrous oxide, which is a greenhouse gas, is generated. This nitrous oxide (N ₂ O) is a substance that increases the so-called environmental load that adversely affects the global environment, and its emission must be suppressed as much as possible.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a waste treatment system that can reduce the environmental load by suppressing the generation of nitrous oxide.

  A waste treatment system according to the present invention includes a pyrolysis furnace that receives organic waste and thermally decomposes the organic waste under a high-temperature reducing atmosphere, and combustible pyrolysis generated in the pyrolysis furnace. A combustion furnace for burning gas, one or a plurality of heat utilization devices that use combustion exhaust gas generated in the combustion furnace as a heat source, and a low-temperature exhaust gas after heat utilization that has been used by the heat utilization device to lower the temperature. A reflux line for refluxing from the heat utilization device to a device disposed upstream of the heat utilization device and used as combustion air or dilution air in the device disposed on the upstream side. And

  ADVANTAGE OF THE INVENTION According to this invention, the waste treatment system which can suppress generation | occurrence | production of nitrous oxide and can reduce environmental impact is provided.

1 is a configuration block diagram showing a waste treatment system according to a first embodiment of the present invention. Characteristic diagram showing the relationship between combustion temperature of N ₂ O concentration in the low-temperature combustion exhaust gas and the combustion furnace. The block diagram which shows the waste disposal system which concerns on the 2nd Embodiment of this invention. The block diagram which shows the waste disposal system which concerns on the 3rd Embodiment of this invention.

  (1) The waste treatment system of the present invention includes a pyrolysis furnace that receives organic waste and thermally decomposes the organic waste under a high-temperature reducing atmosphere, and a combustible material generated in the pyrolysis furnace. Combustion furnace that burns pyrolysis gas, one or more heat utilization devices that use combustion exhaust gas generated in the combustion furnace as a heat source, and a low temperature after heat utilization that is used by the heat utilization device to lower the temperature The exhaust gas is recirculated from the heat utilization device to a device arranged upstream of the heat utilization device, and has a reflux line for use as combustion air or dilution air in the device arranged upstream. And

  In the present invention, the low-temperature exhaust gas after use of heat is recirculated to the upstream arrangement device through the reflux line and used as combustion air or dilution air in the upstream arrangement device, so that combustion in a combustion furnace that is one of the upstream arrangement devices The temperature can be raised. When the combustion temperature of the combustion furnace rises, the amount of nitrous oxide produced in the combustion exhaust gas decreases. Even if the upper limit of the temperature of the combustion exhaust gas occurs due to problems such as the material of the heat utilization equipment, if the circulating low-temperature combustion exhaust gas is used as dilution air of the combustion exhaust gas, it is introduced into the heat utilization equipment even at the same temperature. The amount of combustion exhaust gas after dilution is increased, the amount of heat recovered by the heat utilization device is improved, and the thermal efficiency of the entire system can be increased. The combustion exhaust gas after use of heat is much hotter than the outside air, so it is suitable for use as combustion air or dilution air for upstream equipment, improving the heat utilization efficiency of the entire waste treatment system. Can greatly contribute to.

(2) In the above (1), it is preferable to suppress the generation of nitrous oxide by burning the combustion furnace in a temperature range of 900 ° C. or higher and 1000 ° C. or lower. The N ₂ O concentration in the combustion exhaust gas decreases as the combustion temperature of the combustion furnace increases, but becomes almost constant when the combustion temperature reaches 900 ° C. or higher. For example, when comparing the N ₂ O concentration in the flue gas when the combustion temperature is 870 ° C. with the N ₂ O concentration in the flue gas when the combustion temperature is 900 ° C., the temperature difference is 30 ° C. In the latter case, the N ₂ O concentration rapidly decreases to almost half of the former (about 50%) (FIG. 2). When the combustion temperature is further increased to 950 ° C. or higher, the N ₂ O concentration in the combustion exhaust gas hardly changes and becomes substantially constant (FIG. 2). For this reason, in this invention, it is made to burn more preferably so that the combustion temperature of a combustion furnace may be 950 degreeC or more.

  On the other hand, the design temperature of the combustion furnace is 1200 ° C., and the materials and structures constituting the combustion furnace are designed to withstand that temperature. However, for the purpose of extending the life of the combustion furnace, The actual combustion temperature when operated is up to about 1000 ° C. For this reason, in this invention, the upper limit of the combustion temperature of a combustion furnace shall be 1000 degreeC.

  (3) In the above (1) or (2), the moisture contained in the organic waste is disposed upstream of the pyrolysis furnace, and the organic waste is heated to evaporate the moisture from the organic waste. It is preferable to further have a dryer that reduces the amount of water.

  When organic waste is heated and dried using a dryer to reduce the moisture content of organic waste, there is an advantage that the thermal decomposition reaction of organic waste proceeds quickly and smoothly in the next pyrolysis furnace. . For example, when processing organic waste containing a large amount of moisture such as activated sludge, if this is sent directly to the pyrolysis furnace, it may overflow due to its large volume, increasing the load on the pyrolysis furnace. However, when the organic waste is preheated and dried with a dryer to reduce the volume, the load on the pyrolysis furnace is reduced.

  This dryer can be one of the upstream arrangement devices that use the retained heat of the low-temperature combustion exhaust gas after being heat-utilized by the heat-utilizing device. That is, the low-temperature combustion exhaust gas can be used in the dryer by supplying the low-temperature combustion exhaust gas after heat utilization from the heat utilization device arranged on the downstream side of the combustion furnace to the upstream dryer via the reflux line. It becomes possible. Incidentally, the temperature of the low-temperature combustion exhaust gas after use of heat discharged from the heat-utilizing device is 500 ° C. or less, and the process design temperature of the dryer is in the range of 100 to 300 ° C. In addition, various heat sources can be used for the dryer, and in addition to the above-described low-temperature combustion exhaust gas, known general-purpose heating devices such as a heat medium, an electric resistance heating device, and a combustion heating device can be used.

  (4) In the above (1) to (3), it is preferable that at least one of the plurality of heat utilization devices is a pyrolysis furnace.

  It is possible to use low-temperature combustion exhaust gas in the pyrolysis furnace by supplying the low-temperature combustion exhaust gas after heat utilization to the upstream pyrolysis furnace via the reflux line from the heat utilization equipment arranged downstream of the combustion furnace. It becomes possible. Incidentally, the process design temperature of the pyrolysis furnace is in the range of 300 to 750 ° C.

  (5) In said (1)-(4), it is preferable to further have a dust collector between heat utilization apparatus and a combustion furnace (FIG. 3).

  The dust (solid content) generated in the combustion furnace adheres to the inner wall of the heat utilization equipment on the downstream side and lowers the heat utilization efficiency. Therefore, by separating and removing the dust from the combustion exhaust gas using a dust collector, Heat utilization efficiency can be improved. In the present invention, the dust collector is not limited to a specific type.

  (6) In the above (1) to (5), it is preferable to further include an auxiliary fuel supply device that supplies auxiliary fuel to the combustion furnace in order to make up for a shortage of heat in the heat utilization device (FIG. 4).

  The amount of heat of the combustion exhaust gas may be insufficient due to various causes such as incomplete combustion of the combustion furnace or abnormal operation of the pyrolysis furnace, and a necessary amount of heat may not be secured in the downstream heat utilization device. In such a case, the auxiliary fuel can be supplemented to the combustion furnace from the auxiliary fuel supply device to compensate for the shortage of heat.

  Hereinafter, various embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 1, the waste treatment system 1 of this embodiment includes a dryer 2, a pyrolysis furnace 3, a combustion device 4, and a heat utilization device 5. The inside of the processing system 1 is sucked and exhausted by one or a plurality of blowers (not shown) arranged on the downstream side. Further, the entire processing system 1 is centrally managed and controlled by a process computer (not shown).

  The dryer 2 is supplied with organic waste from an upstream waste input device (not shown) via the line L1, and the input organic waste is heated at a predetermined temperature (100 to 300 ° C.) to be organic. It removes water from toxic waste. Various heat sources can be used for the dryer 2. For example, a known general-purpose heating device such as a low-temperature combustion exhaust gas after being heat-utilized by the heat utilization device 5 on the downstream side, a heat medium, an electric resistance heating device, or a combustion heating device can be used. The waste supply line L1 includes, for example, a belt conveyor, a measuring instrument, a shooter, and a hopper.

  The pyrolysis furnace 3 is a rotary kiln type or screw feeder type horizontal installation apparatus having a hollow shaft chamber 31 that is rotationally driven and a heating jacket 32 that heats the hollow shaft chamber 31. The hollow shaft chamber 31 has a hollow cylindrical refractory material wall and a feed screw, and is rotatably supported by a rotation drive mechanism (not shown). The organic waste is supplied from the dryer 2 to the hollow portion of the hollow shaft chamber 31 via the waste supply line L2, and the organic waste is fed in the axial direction by rotating the feed screw in the forward direction. It is like that. The downstream end (exit end) of the hollow shaft chamber 31 is connected to the upper burner 43 of the combustion device 4 via a pyrolysis gas line L3. Further, a carbide discharge line L5 is provided at an appropriate position on the downstream side of the hollow shaft chamber 31, and the carbide, which is a residue after pyrolysis, is discharged from the hollow shaft chamber 31 through the carbide discharge line L5.

  The heating jacket 32 is a jacket container that surrounds at least a part of the hollow shaft chamber 31, and a heating medium supply pipe 33 and a heating medium discharge pipe 34 are connected to each other. High-temperature air (for example, 300 to 750 ° C. dry air) is supplied into the heating jacket 32 as a heating medium through a heating medium supply pipe 33 from a heating medium supply source (not shown), and the heating medium is heated after the waste is heated. The heat is discharged from the heating jacket 32 through the discharge pipe 34. Note that a circulation circuit may be formed by connecting the heat medium supply pipe 33 and the heat medium discharge pipe 34 through a return line, and the used heat medium may be repeatedly used in the pyrolysis furnace. A known general-purpose heating device such as an electric resistance heating device or a combustion heating device can be used as a heat source for the pyrolysis furnace 3, but the combustion exhaust gas discharged from the combustion furnace 4 in the next step is used from the viewpoint of economy. Most suitable to use. Further, a known general-purpose measuring instrument such as a thermocouple can be used as a temperature measuring device (not shown) as an auxiliary device.

  The combustion furnace 4 is a combustion apparatus having a combustion injection type burner at one end. A pyrolysis gas line L3 and a combustion air line (not shown) are respectively connected to the burner, and combustible pyrolysis gas and combustion air are injected and mixed at a predetermined ratio and burned. . At the other end of the combustion furnace 4, an exhaust port 41 communicating with the combustion exhaust gas line L4 is provided. The combustion exhaust gas line L4 is branched into two lines L41 and L42, one branch line L41 is connected to the heat medium supply pipe 33 of the pyrolysis furnace 3, and the other branch line L42 is connected to the inlet of the heat utilization device 5. ing. That is, a part of the combustion exhaust gas discharged from the combustion furnace 4 is supplied to the heating jacket 32 of the upstream pyrolysis furnace 3 through the lines L4 and L41, and the other part is passed through the lines L4 and L42. Then, it is supplied to the heat utilization device 5 on the downstream side.

  In this embodiment, the combustion exhaust gas line is divided into two and the combustion exhaust gas is distributed to the thermal cracking furnace 3 and the heat utilization device 5, but the combustion exhaust gas line is further branched into three and the pyrolysis furnace. 3 and the heat utilization device 5 as well as the dryer 2 can distribute the combustion exhaust gas. Or you may make it connect a combustion exhaust gas line in an order from an apparatus with high process temperature, without branching a combustion exhaust gas line.

  The heat utilization device 5 has an inlet connected to the flue gas line L42 and an outlet connected to an exhaust line L5 that discharges the low-temperature flue gas. For example, a waste heat boiler or the like can be used as the heat utilization device 5. In the main body of the heat utilization device 5, an internal flow path through which a heat medium that exchanges heat with the combustion exhaust gas flows is formed. The internal flow path of the heat utilization device 5 can have various forms such as a counter flow path, a parallel flow path, or a serpentine flow path.

  The discharge line L5 from the heat utilization device 5 is branched into two lines L6 and L7. One branch line L6 is further connected to another downstream heat utilization device (not shown) or opened to the atmosphere via a detoxifying device (not shown).

  The other branch line L7 branches into two reflux lines L71 and L72 for refluxing the low-temperature combustion exhaust gas to the combustion furnace 4 and the heat utilization device 5, respectively. The first recirculation line L71 merges with the combustion air on the inlet side of the combustion furnace 4 or communicates with the burner injection port of the combustion furnace 4. The second recirculation line L72 merges with the combustion exhaust gas line L42 on the inlet side of the heat utilization device 5, or proceeds in parallel with the combustion exhaust gas line L42 and merges with the line L42 in the internal flow path of the heat utilization device 5. ing.

  The operation of this embodiment will be described.

  The organic waste is introduced into the dryer 2 from the waste input device (not shown) via the line L1, and the input organic waste is heated to a temperature of 100 to 300 ° C. to become an organic waste. The contained moisture is evaporated to obtain a dry organic waste having a moisture content of several percent or less. This dry organic waste is supplied to the hollow shaft chamber 31 of the pyrolysis furnace 3 through the line L2, and heated to a temperature of 300 ° C. or higher by the pyrolysis furnace 3, so that the organic components in the waste are pyrolyzed. Thereby, the organic waste is decomposed into carbide (solid content) and combustible pyrolysis gas (gas content). Of these, the solid carbide is discharged and collected through a discharge line L8 into a collection container (not shown). On the other hand, the combustible pyrolysis gas is supplied to the burner of the combustion furnace 4 through the line L3, mixed with the combustion air, and burned. The combustion air is supplied as compressed air from a compressor (not shown), but may be a mixed gas in which the low-temperature combustion exhaust gas from the heat utilization device 5 is mixed.

  Part of the combustion exhaust gas passes through lines L4 and L41 from the exhaust port 41 of the combustion furnace, is introduced into the heating jacket 32 of the pyrolysis furnace from the heat medium supply pipe 33, and the organic in the rotating hollow shaft chamber 31 is rotated. It becomes a heat source for thermal decomposition of radioactive waste. Another part of the combustion exhaust gas passes through lines L4 and L42 from the exhaust port 41 of the combustion furnace, is supplied to the internal flow path of the heat utilization device 5, and is heat-exchanged with the heat medium.

  The combustion exhaust gas after heat utilization in the heat utilization device 5 is recovered by the heat utilization device 5 to fall to a temperature of 500 ° C. or lower, and is used as the low temperature combustion exhaust gas via the discharge line L5. Discharged from. A part of the low-temperature combustion exhaust gas flows from the branch portion in the order of the reflux line 7 → the first reflux line L71 → the combustion furnace 4 and is injected from the burner of the combustion furnace. Further, another part of the low-temperature combustion exhaust gas flows from the branch portion in the order of the reflux line 7 → second reflux line L72 → line L42 → heat utilization device 5 and mixes with the combustion exhaust gas to mix inside the heat utilization device 5. It is supplied again to the flow path. In addition, as an apparatus which can become the heat utilization apparatus of this embodiment, the air preheater (not shown), the thermal decomposition furnace 3, the waste heat boiler (not shown), or the dryer 2 can be mention | raise | lifted.

  The effect of this embodiment will be described.

  According to this embodiment, since the temperature of the low-temperature combustion exhaust gas after being heat-utilized by the heat-utilizing device is higher than at least the outside air, by using a part thereof as combustion air in the burner of the combustion furnace 4, The combustion temperature of the combustion furnace 4 can be maintained with a smaller flow rate than when outside air is used. For this reason, the amount of low-temperature combustion exhaust gas is reduced, the amount of heat that is wasted can be greatly reduced, and the thermal efficiency can be improved.

  Even if the upper limit of the temperature of the combustion exhaust gas arises due to problems such as the material of the heat utilization device 5, if the circulating low-temperature combustion exhaust gas is used as the dilution air of the combustion exhaust gas, it is introduced into the heat utilization device 5 even at the same temperature. The amount of combustion exhaust gas after dilution is increased, the amount of heat recovered by the heat utilization device 5 is improved, and the thermal efficiency of the entire system can be increased.

When combustible gas obtained by pyrolyzing organic waste is combusted, nitrous oxide (N ₂ O), which is a greenhouse gas, is emitted depending on the type of waste and the state of combustion. FIG. 2 shows the result of examining the relationship between the temperature (° C.) of the combustion exhaust gas in the combustion furnace and the N ₂ O concentration (volume ppm) of the combustion exhaust gas.

As is apparent from FIG. 2, the N ₂ O concentration decreases as the combustion temperature of the combustion furnace increases, becomes almost constant at a combustion temperature of 900 ° C. or higher, and changes almost at a temperature range of 950 ° C. or higher. No longer. In order to reduce the N ₂ O concentration, a high combustion temperature is required. However, in this embodiment, the low-temperature combustion exhaust gas is hotter than the outside air, so it is used as combustion air for combustion furnaces or as dilution air for combustion exhaust gas. There is an advantage that high temperature can be maintained with a smaller flow rate and thermal efficiency can be improved.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. In addition, description of the part which this embodiment overlaps with said embodiment is abbreviate | omitted.

  The waste treatment system 1 </ b> A of the present embodiment further includes a dust collector 10 on a line L <b> 42 that connects the combustion furnace 4 and the heat utilization device 5. For example, the dust collector 10 is a cyclone in which combustion exhaust gas is introduced into the upper portion, the introduced gas is lowered as a swirl flow, and solids (such as soot containing incombustible dust) in the combustion exhaust gas are centrifuged from the gas component.

  When dust from solid incombustible material is mixed in the combustion exhaust gas, this solid incombustible material cannot be combusted in the combustion furnace and is mixed as soot in the combustion exhaust gas. If it adheres to the road or the inner wall, the thermal conductivity is lowered, so that the thermal efficiency may be lowered. However, according to the system of the present embodiment, soot and dust are separated and removed from the combustion exhaust gas by the dust collector, it is possible to prevent a decrease in the thermal conductivity of the heat utilization device and to reduce the release of air pollutants to the atmosphere.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIG. In addition, description of the part which this embodiment overlaps with said embodiment is abbreviate | omitted.

  The waste treatment system 1B of the present embodiment further includes an auxiliary fuel supply device 11 that injects auxiliary fuel into the pyrolysis gas line L3. The auxiliary fuel supply device 11 has an injection line L9 connected to the pyrolysis gas line L3, injects auxiliary fuel into the pyrolysis gas flowing through the pyrolysis gas line L3, and burns from the burner of the combustion furnace 4 It is to be injected.

  Although combustible pyrolysis gas is used as a heat source for maintaining the temperature of the combustion furnace 4, when the amount of heat recovered by the heat utilization device 5 is increased due to demand on the heat utilization side, the amount of heat of the pyrolysis gas is If it is constant, the temperature of the low-temperature combustion exhaust gas is lowered, and problems such as condensation may occur. In order to increase the amount of heat recovered by the heat utilization device 5 while maintaining the temperature of the low-temperature combustion exhaust gas, the amount of heat of the pyrolysis gas may be increased. In this case, the organic waste that is the raw material of the pyrolysis gas is treated. It is necessary to increase the amount, and there is a limit due to restrictions on the pyrolysis furnace specifications.

  Therefore, in this embodiment, when the heat source of the heat utilization device is insufficient, the shortage of the heat source can be solved by injecting auxiliary fuel such as methane gas as fuel of the combustion furnace 4 from the auxiliary fuel supply device 11. . In addition, according to the present embodiment, there is an advantage that the auxiliary fuel from the auxiliary fuel supply device 11 can be used as a fuel at the time of starting and stopping without introducing organic waste.

1, 1A, 1B ... waste treatment system,
2 ... dryer, 3 ... pyrolysis furnace, 4 ... combustion furnace,
5 ... Heat utilization equipment,
10 ... Dust collector,
11 ... auxiliary fuel supply device,
L3 ... pyrolysis gas line, L4, L41, L42 ... combustion exhaust gas line,
L6 ... Low-temperature combustion exhaust gas line,
L7, L71, L72, L73 ... recirculation line (line for recirculating low-temperature combustion exhaust gas after use of heat),
L8 ... Carbide discharge line.

Claims (6)

A pyrolysis furnace for receiving organic waste and thermally decomposing the organic waste under a high-temperature reducing atmosphere;
A combustion furnace for burning the combustible pyrolysis gas generated in the pyrolysis furnace;
One or a plurality of heat utilization devices that utilize the flue gas generated in the combustion furnace as a heat source;
The low-temperature exhaust gas after use of heat, which has been used by the heat-use equipment and whose temperature has dropped, is circulated from the heat-use equipment to the equipment arranged upstream of the heat-use equipment, and the equipment arranged on the upstream side A reflux line for use as combustion air or dilution air in
A waste treatment system comprising: The waste treatment system according to claim 1, wherein generation of nitrous oxide is suppressed by burning the combustion furnace in a temperature range of 900 ° C or higher and 1000 ° C or lower. It further has a dryer which is disposed upstream of the pyrolysis furnace and reduces the water content of the organic waste by heating the organic waste and evaporating water from the organic waste. The waste disposal system according to any one of claims 1 and 2. The waste treatment system according to any one of claims 1 to 3, wherein at least one of the plurality of heat utilization devices is the pyrolysis furnace. The waste disposal system according to any one of claims 1 to 4, further comprising a dust collector between the heat utilization device and the combustion furnace. The waste treatment system according to any one of claims 2 to 5, further comprising an auxiliary fuel supply device that supplies auxiliary fuel to the combustion furnace in order to make up for a shortage of heat in the heat utilization device.

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