JPH0151960B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for carbonizing sludge, etc., which completely prevents gas leakage and reduces the generation of dust.

Conventionally, a multistage carbonization apparatus is often used as an apparatus for drying and incinerating highly water-containing combustible materials such as dehydrated sludge. As shown in FIG. 1, this apparatus is comprised of a multistage carbonization furnace 1, a reburning furnace 2, a hot air generating furnace 3, etc., which have the same structure as a normal multistage incinerator. The multi-stage carbonization furnace 1 has a rigid cylindrical outer shell 1a made of a steel plate, and the inner side of the outer shell is lined with a refractory material 1b. Furthermore, it is divided into multiple stages by a firebrick hearth 1c. A vertical rotating shaft 1d is provided at the center of the multistage carbonization furnace 1, and a metal arm 1e is attached to this rotating shaft 1d. The material to be treated, such as dehydrated sludge, is inputted into the input port 1f at the top of the multistage carbonization furnace 1, and the hot air generating furnace 3 is input through the hot air inlet 1g at the bottom of the multistage carbonization furnace
Blow in hot air for heating generated by The object to be treated is dried while being stirred by the arm 1e,
Every other step is dropped from the center and periphery of the partition step to the lower step and gradually moves downward. The lower stage of this multi-stage carbonization furnace 1 is a carbonization zone, and a smaller amount of air than in a general incinerator is blown into this area from the air inlet 1h. The dried material to be treated is carbonized in a carbonization zone, and the carbonized product is taken out to the outside.
The flammable gas generated in the carbonization zone is used together with the hot air to dry the material to be treated in the upper drying zone.
The exhaust gas is led out from the exhaust gas outlet 1i and introduced into the reburning furnace 2. In order to completely burn the combustible gas in the exhaust gas, air A and fuel B are blown into the reburning furnace 2 as necessary. Moreover, air A and fuel B for generating hot air are introduced into the hot air generating furnace 3. By the way, since the above-mentioned multistage carbonization furnace 1 is intended for ordinary processing objects,
There are problems when processing special objects. For example, in experimental facilities that administer alpha-emitting radioactive substances to large numbers of animals and study their effects,
Large amounts of feces, urine, uneaten feed, etc. contaminated with radioactive materials will be generated. Since the waste water that has been washed cannot be discharged as it is, the organic matter contained therein is treated with microorganisms, and then treated with activated carbon adsorption and the like before being discharged. High-moisture sludge (for example, animal excrement, feed, surplus sludge, etc. with a water content of about 98%) generated from such wastewater treatment facilities is perishable and in large quantities, so it cannot be stored as is. If it is dried to a moisture content of 10% or less, it will not spoil easily, but it is extremely difficult to store it for a long time because it cannot be reduced in volume significantly and will rot if it absorbs moisture. In order to bring this sludge into a stable state with a large volume reduction ratio, it is best to incinerate it. However, when incinerating such sludge, the above-mentioned apparatus has the following problems.

(1) There is little consideration given to the airtightness of the equipment. For example, the shaft seal is not strictly sealed, such as using a sand seal. For this reason, it is inappropriate to dispose of waste containing radioactive materials, especially alpha nuclides, which must also avoid dispersing small amounts of dust into the outside air.

(2) Since the lifespan of the refractory materials and refractory bricks inside the furnace is short, inspections and repairs are frequent, and when processing objects containing radioactive materials, etc., it is necessary to prevent the scattering of dust inside the furnace. A large amount of cost and effort is required in addition to protective measures for repair workers.

(3) Because the lining of the furnace is made of refractory material and the multi-tiered hearth is made of refractory bricks, it is difficult to miniaturize the furnace, and the amount of radioactive materials that can be processed is lower than that of ordinary sludge incinerators. It is difficult to apply this method to carbonization incinerators for materials to be treated.

(4) Since hot air is blown into the multistage furnace as a heating heat source, the amount of exhaust gas increases and the gas flow rate increases, reducing the amount of dust in the exhaust gas (usually 5.6 to 19.0g/
(about Nm ³ ). Therefore, it is unsuitable for processing objects containing radioactive substances, for which radioactive substances in exhaust gas are strictly regulated.

(5) The surfaces of refractory materials and refractory bricks are porous and fine cracks are generated by heating, so substances to be treated accumulate in these areas and are difficult to remove. (Removal of contamination by radioactive substances is called decontamination.) The present invention was made in view of the above circumstances, and is mainly based on a metal multi-stage furnace and a cyclone-type afterburning furnace, and the amount of exhaust gas is small and the exhaust gas is The purpose of the present invention is to provide a method and apparatus for drying and incinerating sludge, etc., which can reduce the amount of dust contained in the sludge as much as possible.

An embodiment of the present invention will be described in detail below with reference to the drawings. 2 to 4 show examples in which the present invention is applied to the treatment of sludge containing radioactive materials, and FIG. 2 is a schematic diagram of the apparatus. High moisture sludge D containing radioactive substances is mixed with an appropriate amount of flammable dehydration aid E (e.g. wood flour, dried sludge, etc.),
The water is dehydrated by a dehydrator 11. If, for example, a high compression vacuum suction type dehydrator is used as the dehydrator 11, the high moisture sludge is dehydrated to about 50 to 60% water content and temporarily stored in the dehydrated cake hopper 12 as a dehydrated cake F. Note that H is a liquid. This stored dehydrated cake F is fed into the upper part of a metal multi-stage furnace 21 by a feeder (not shown). At this time, the hopper and feeder are designed to maintain the airtightness of the multistage furnace 21 so that the dehydrated cake F can be charged therein. The charged dehydrated cake F passes through a drying zone and a carbonization zone while sequentially moving from the top to the bottom of the metal multi-stage furnace 21. Further, in the combustion zone, the ash is combusted by a limited amount of air A introduced from the lower part of the multi-stage furnace 21, and the ash G is taken out from the lower part and stored safely in a sealed state. Further, the combustion gas discharged from the upper part of the multistage furnace 21, the carbonized product gas, and the steam generated from the dehydrated cake are sent to a cyclone-type reburning furnace 31. The exhaust gas containing the flammable carbonized gas introduced into the reburning furnace 31 is completely combusted by the introduced air A while a considerable portion of the dust is removed. The air A introduced is
In order to reduce the heat load on the multistage furnace 21 and the reburning furnace 31, they can be heated in advance with a heater or the like. The completely combusted gas then enters the exhaust gas treatment device 13, where the contained dust is removed and the gas temperature is lowered. This exhaust gas treatment device 13 is a wet or dry type device generally used in incineration of radioactive waste. Most of the dust is removed by this exhaust gas treatment device 13, and the cooled exhaust gas is passed through a high-performance air filter 14 that collects fine particles.
After being passed through the air, the air is discharged from the stack 16 into the atmosphere by the blower 15.

Of the above devices, the metallic multi-stage furnace 21 has an important function of drying and carbonizing the processed material containing radioactive materials and then incinerating it, and the cyclone-type reburning furnace 31 is made of metal and is small in size. It has the function of completely burning the carbonized gas generated in the multi-stage furnace 21 and collecting dust.

FIGS. 3a and 3b are longitudinal and cross-sectional views of a metal multi-stage furnace 21, in which 21a is a cylindrical furnace body made of heat-resistant steel (for example, centrifugal cast copper equivalent to Incoloy 800). A heater 21b, for example, an electric heater, is attached to the outer periphery of the furnace body 21a to indirectly heat the inside of the furnace. This heater 21b is the furnace main body 2
1a is divided into several parts in the vertical direction, and each heater is equipped with a temperature detector and a temperature regulator (not shown) that can detect the temperature in the corresponding furnace and maintain it at a desired temperature. A heat insulating material 21c is attached to the outside of this heater 21b. Insulation material 21c
A steel exterior plate 21d for protecting the exterior surface is attached to the outside of the housing. Further, the lower portion of the furnace body 21a is exposed from the lower surface of the exterior plate 21d, and an annular convex portion 21f is provided on the outer periphery of this exposed portion 21e. The multistage furnace 21 has the convex portion 21f mounted on a furnace body support member 22e fixed to a lower beam 22d attached to a base 22, and is supported by upper beams 22b connecting the pillars 22a and the pillars 22a. Supported. Further, an air inlet 21p is attached to the lower part of the furnace body 21a, and an ash outlet 21g is provided at the lower end. The upper end of the furnace body 21a protrudes above the heat insulating material 21c to form an upper open end 21h, and the upper edge of the expansion joint 21i is airtightly attached to the outer periphery of the upper open end 21h. The lower edge of the steel exterior plate 21
d It is airtightly attached to the top surface. A steel exterior plate 21d' to which a refractory heat insulating material 21q is attached inside is provided to cover the protruding upper opening end 21h and the expansion joint 21i, and forms a lid 21j of the furnace body 21a. This lid body 21j is vertically divided into an upper lid body 21j' and a lower lid body 21j'', and the upper lid body 21j' and the lower lid body 21j'' are each formed by an exterior plate 21d'. It is attached removably and airtightly using bolts, nuts, etc. via the flange. The outer plate 21d' of the lower cover 21j'' is airtightly attached to the upper surface of the outer plate 21d of the furnace body 21a.The cover 21j is provided with an inlet 21m for the material to be treated and an exhaust gas outlet 21n. Further, inside the furnace body 21a, there is provided a metal rotating shaft 23 that vertically passes through the center of the furnace body 21a. ) through the furnace body support member 22e.
The lower bearing 23a is rotatably and airtightly attached to the lower bearing 23a supported by the lower bearing 23a. Further, a gear 23b is attached to the lower end of the rotating shaft 23 for transmitting rotational driving force to the rotating shaft 23 via an electric motor and a transmission (not shown). A lower expansion joint 23c is airtightly attached between the lower bearing 23a and the bottom surface of the furnace body 21a. The upper end of the rotating shaft 23 is rotatably supported by an upper bearing 23d that passes through the lid 21j and is attached to the upper surface of the exterior plate 21d' of the lid 21j via a support member 22c. An upper expansion joint 23e is provided between the upper bearing 23d and the upper surface of the exterior plate 21d of the lid 21j. Note that the expansion joints 21i, 23
For example, an all-metal bellows type expansion joint can be used for c and 23e, which connects the furnace body 21a and the rotating shaft 2.
The elongation due to heating in No. 3 can be absorbed without impairing the airtightness of the furnace. Furthermore, upper bearing 23d
is commonly used as a bearing for a rotating shaft, and has a structure that allows it to be easily extracted from the rotating shaft 23. This upper bearing 23d has a known sealing gas mechanism (not shown), which uses an inert gas or air, etc. at a pressure slightly higher than the internal pressure of the multistage furnace 21 as a sealing gas, between the upper bearing 23d and the rotating shaft 23.
The gas inside the multi-stage furnace 21 is prevented from leaking to the outside by flowing through the gap between the two. Also, the furnace body 2
The interior of 1a is partitioned into multiple stages by partition stages 24. Further, a stirring member 25 for stirring the objects to be processed on each feed stage 24 is attached to the rotating shaft 23 passing through the center of the central opening of the partition plate 24. Arms 25a, 25a are attached to this stirring member at symmetrical positions with respect to the rotating shaft 23, and a blade 5b is provided at the lower part of the arms 25a, 25a for scraping the material to be processed on the partition stage 24 toward the center. ...is installed. Further, a lower edge of a guide member 25c in the shape of a canopy is attached to the upper part of the arms 25a, 25a, and the lower edge of the guide member 25c is attached to the outer circumference of the partition step 24 so that the workpiece dropped from the central opening of the upper partition step slides onto the outer periphery of the partition step 24. The top of the member 25c is attached to the rotating shaft 23. Note that 21m is an inlet for introducing the material to be treated into the inside of the furnace body 21a, and 21n is an exhaust gas outlet for leading out the exhaust gas generated by incinerating the material to be treated to the outside of the furnace body 21a. This exhaust gas outlet 21n can also be attached to the middle part (lower part of the drying zone) of the furnace body 21a.

Further, the reburning furnace 31 has the following configuration. That is, as shown in FIG. 4, a cylindrical furnace body 31a made of heat-resistant steel with a cone-shaped lower part is provided. An exhaust gas inlet 31c is provided tangentially to the furnace body 31a, an air inlet 31d is attached to the side of the cone, and an ash outlet 31e is attached to the lower end of the cone. Further, a heater 31f is attached to the outer peripheral surface of the cylindrical portion of the furnace body 31a. This heater 31f and the furnace body 31a to which the heater 31f is not attached are covered,
and each of the above-mentioned outlet/outlet ports 31b, 31c, 31d,
A heat insulating material 31g is attached so that 31e opens to the outside. Further, the inner upper surface of the furnace body 31a is provided with an appropriate gap between it and the cylindrical portion of the furnace body 31a, is concentric with the cylindrical portion, and has a lower end near the lower end of the cylindrical portion. A combustion tube 31h made of a heat-resistant material is provided so that a gas outlet 31b is located within the extension of the inner surface of the combustion tube 31h.

Next, the operation of the apparatus according to the present invention configured as described above will be explained.

High-moisture sludge containing radioactive materials (hereinafter referred to as sludge) is processed into dehydrator 1 after adding a coagulation aid if necessary and then mixing with a combustible dewatering aid such as wood flour.
Dehydrate according to step 1. Dehydrator 11 reduces moisture to 50% or more
Sludge that has been dehydrated to about 60% is dehydrated cake hopper 12.
From there, the feeder feeds the multistage furnace 21 through the input port 21m while maintaining airtightness. The introduced sludge is scraped up to the center by the slow rotation of the stirring member 25, dropped to the lower stage from the central opening of the partition stage 24, and is moved to the outer periphery of the upper surface of the partition stage 24 by the shade-shaped guide member 25c. be dropped. Additionally, stirring member 25
The rotation speed of is determined by the required retention time of sludge in the furnace. In this way, the sludge is transferred to the multi-stage furnace 2.
1, it gradually moves from the top to the bottom, dries, carbonizes, and passes through the combustion zone. During this time, the sludge is heated to heater 2.
It is dried and carbonized by indirect heating from the outside by 1b and high-temperature combustion gas generated in the combustion zone at the bottom of the multistage furnace 21, which will be described later. In this case, since the amount of external heating can be controlled to maintain each part in the multistage furnace 21 at a required temperature, complete drying and carbonization can be performed at a relatively low temperature (about 600° C.). The carbonization residue, whose combustible content has been greatly reduced by carbonization, further falls into the lower combustion zone, where it is combusted by air blown in a limited amount from the lower part of the multistage furnace 21, or is dropped to the lower stage while being combusted. Since the fuel is burned in several stages, the combustion is further promoted. The amount of combustion gas generated during this combustion is smaller than that in the case of direct combustion without carbonization, because the combustible content in the carbonization residue is greatly reduced by carbonization. Ash is in multi-stage furnace 2
The ash is taken out from the ash outlet 21g at the bottom of 1. Depending on the water content of the sludge, the multi-stage furnace 21 and the afterburning furnace 3 may be used.
1, the temperature of the exhaust gas may drop and the moisture in the exhaust gas and the carbonized gas may condense.In this case, an exhaust gas outlet 21n is provided in the middle part of the multistage furnace 21 (below the drying zone). The heating amount of the upper part of the heater 21b, which is attached separately to the outer periphery of the furnace body 21a, is increased to increase the exhaust gas temperature and prevent condensation.

Exhaust gas consisting of water vapor generated in the drying zone of the multistage furnace 21, carbonization product gas generated in the carbonization zone containing combustible gas, and combustion gas generated in the combustion zone exits from the exhaust gas outlet 21n and is introduced into the young combustion furnace 31. Ru. Since the exhaust gas inlet 31c is attached to the furnace body 31a in a tangential direction, the dust falls downward due to the cyclone action, and the introduced exhaust gas becomes a swirling flow that flows through the furnace body 31a and the furnace body 31a, which are heated by the heater 31f. The combustible gas is fully preheated by passing between the combustion tubes 31h, is introduced into the lower part of the combustion tube, is mixed with air supplied from the air inlet 31d, and is combusted in the combustion tube 31h, so that the combustible gas is completely combusted. The gas is sent to the next process through the gas discharge port 31b.

As described above, the carbonization incinerator according to the present invention has the following advantages. First of all, the multi-stage furnace (1) has a furnace body made of metal, so by using expansion joints that can cover the parts of the furnace body where gas tends to leak and absorb the elongation of the furnace body due to heat, Airtightness can be easily achieved. (2) Since the furnace body is made of metal and the amount of indirect heating can be controlled, the furnace body can be easily maintained at a relatively low required temperature, increasing the durability of the furnace, ensuring a long life and sufficient dry carbonization. It can be done. (3) Since the refractory insulation material is used only in the upper part of the furnace where the ambient temperature is low, the chance of damage to the refractory insulation material is extremely low. Therefore, there is less repair work for multi-stage furnaces. (4) Since the furnace body is made of metal and has a smooth surface, dust containing radioactive substances only adheres to the surface, making decontamination much easier than with fireproof insulation materials. (5) Since the furnace body is made of metal and has an indirect heating section, and a heat insulating material is provided on the outside, a small furnace can be easily manufactured. (6)
Since indirect heating using an external heater is used as a heating method, there is no need for hot air for heating or a burner for fuel oil or the like. Furthermore, the amount of air required to combust the carbonized residue whose combustible content has been greatly reduced by the carbonization of sludge and the amount of combustion gas generated by combustion are reduced. Therefore, the gas velocity rising through the furnace is low and less dust is entrained. Furthermore, the capacity of the treatment device, filter, etc. in the exhaust gas treatment system may be small.

In addition, the reburning furnace of this example is made of heat-resistant steel and is of a cyclone type with a concentric combustion tube inside, so (1) the introduced exhaust gas swirls between the furnace body and the combustion tube and dust is dropped. At the same time, air is mixed with indirect heating from the furnace body and sufficiently preheated from both sides of the combustion tube and enters the combustion tube, so that the combustible carbonized gas contained therein is completely combusted. (2) Furthermore, since the furnace body does not come into direct contact with the flames, but rather with the relatively low temperature gas introduced from the carbonization incinerator, there is no deterioration due to heat effects even after long-term use, increasing durability. Therefore, only the combustion tube that is inspected and repaired most frequently needs to be replaced. (3) When the combustion gas containing the flammable gas generated by carbonization and the water vapor generated by drying is extracted from the top of the multistage furnace, the material to be processed is exposed to the high temperature combustion gas at the material inlet and dried. However, clogging often occurs (this phenomenon occurs particularly when the materials to be processed are introduced in batches), and when the temperature at the top of the multi-stage furnace is lowered, the above-mentioned problems occur between the multi-stage furnace and the reburning furnace. Although there is a risk that the combustion gas may condense, a gas outlet is installed approximately in the middle of the multi-stage furnace in the height direction, and the combustion gas containing the combustible gas generated by carbonization and the water vapor generated from drying is transferred to the upper part of the multi-stage furnace. If the combustion gas is led out only from the gas outlet and then introduced into the reburning furnace and combusted, the above problems are solved.
The temperature at the top of the multi-stage furnace has been lowered, allowing the material to be processed to be smoothly fed into the multi-stage furnace without clogging, and the problem of the bearing part of the rotating shaft being difficult to seal due to its high temperature has been improved. Also, the combustion gas does not condense between the multistage furnace and the reburning furnace.

As explained above, when treating sludge containing radioactive materials, by incorporating such a multi-stage furnace and reburning furnace, repair costs can be reduced, and the capacity of the exhaust gas treatment equipment can be increased by reducing the amount of exhaust gas and dust. The benefits in terms of safety, operating costs, repair costs, equipment costs, etc. are extremely large.

In the examples, the treatment target was sludge containing radioactive materials, but it can also be applied not only to sludge but also to combustible materials such as used activated carbon, shredded paper and cloth, and animal carcasses. Needless to say.

[Brief explanation of drawings]

Fig. 1 is a schematic flow diagram of a conventional carbonization incinerator, Fig. 2 is a schematic configuration diagram showing the entire processing equipment using the device of the present invention, and Fig. 3 a and b are an example of an implementation of a metal multi-stage incinerator. For example, Figure 3a is a vertical cross-sectional view;
b is a cross-sectional view, and FIG. 4 is a longitudinal cross-sectional view of a cyclone-type reburning furnace. 21...Multi-stage furnace, 21a...Furnace body, 21b...
...Heater, 21d...Exterior plate, 21d'...Exterior plate of lid body, 21g...Ash removal outlet, 21h...Top opening end, 21i...Expansion joint, 21j...Lid body, 2
1j′...Upper lid body, 21j''...Lower lid body, 21m
...Inlet, 21n...Exhaust gas outlet, 21p...
...Air inlet, 21q...Fireproof insulation material, 23...
Rotating shaft, 23a...Lower bearing, 23c...Lower expansion joint, 23d...Upper bearing, 23e...Upper expansion joint, 24...Partition stage, 25...Stirring member, 2
5a...Arm, 25b...Blade, 25c...
...Guide member, 31... Reburning furnace, A... Air, F
...Dehydrated cake, G...ash.

Claims (1)

[Claims] 1. A workpiece is introduced into a sealable cylindrical metal multi-stage furnace that is divided vertically into a plurality of furnaces and indirectly heated by electric heaters that control the temperature in each furnace. The ash is then moved downward and passed through a drying zone, a carbonization zone and a combustion zone, where it is combusted with a limited amount of air.The combustion ash is taken out from the bottom of the furnace and the generated combustion gas is directly heated. The drying and carbonization are performed while controlling each part of the furnace to the required temperature to prevent fluctuations in the carbonization zone using a plurality of divided electric heaters that serve as heat sources and heat sources for the indirect heating. A carbonization incineration method characterized by introducing combustion gas containing generated combustible gas and water vapor generated by drying into a reburning furnace and burning it. 2. The carbonization incineration method according to claim 1, wherein the combustion gas containing the combustible gas generated by carbonization and the water vapor generated by drying is extracted only from the middle part in the height direction of the multistage furnace. 3. A cylindrical metal furnace body with an open top,
an electric heater that is divided into a plurality of parts in the vertical direction on the outer periphery of the furnace body as an indirect heating part and controls the temperature in the corresponding furnace; a heat insulating material provided on the outer side of the electric heater; and a heat insulating material provided on the outer side of the heat insulating material. a lid body having a furnace exterior plate provided on the side, a lid exterior plate that covers the upper end opening of the furnace body without contacting the upper end opening and is airtightly attached to the furnace exterior plate; A rotating shaft with an attached arm that sequentially scrapes the objects to be processed to the lower stage, an incineration ash take-out port and an air inlet provided at the bottom of the furnace body, and an inlet for the objects to be processed provided in the lid body. and a gas outlet provided in the lid or the furnace body. 4. The carbonization incinerator according to claim 3, wherein the gas outlet port is attached to a substantially middle portion in the height direction of the multistage furnace.