JP7770755B2 - Manufacturing method of powdered carbide - Google Patents

Description

The present invention relates to a method for producing a carbonized product by dry distilling a mixture of biomass such as rice husks and dewatered sludge to obtain a carbonized product, and to a carbonized product production facility used for this method.

Wastewater containing organic matter discharged from households and other facilities is generally treated in sewage treatment facilities.
This wastewater treatment generates organic sludge, and as the amount of wastewater treated increases, the amount of organic sludge generated also increases year by year, making its treatment and disposal a major problem.

When disposing of organic sludge, it contains approximately 99.9% water and cannot be disposed of as is. Therefore, various treatments are currently being carried out to reduce the volume, such as concentration and dehydration, or further incineration or melting.
One method proposed for reducing the volume of organic sludge is carbonization of the sludge by dry distillation. This carbonization process does not consume the carbon content of the sludge, as in incineration or melting, but rather involves pyrolysis (carbonization) of the sludge in an oxygen-free or low-oxygen environment, leaving the carbon content behind and producing a carbonized product with a new composition.

When carbonizing sludge through dry distillation, dehydrated sludge that has been dehydrated to a moisture content of approximately 80% using a dehydrator is used. However, if this sludge is dry distilled as is, problems with sludge adhesion may occur. Therefore, the sludge is first dried to reduce its moisture content, for example, to approximately 40%, and then the dried sludge is dry distilled. Carbonization equipment used for this type of process is disclosed, for example, in Patent Documents 1 and 2 below.

Figure 8 shows an example of a conventional carbonization treatment facility. 200 in the figure is a receiving hopper, into which dewatered sludge that has been dewatered to a moisture content of approximately 80% is first received. The dewatered sludge received here is sent to a dryer 204 by a sludge transfer pump (quantitative supply device) 202, where it is dried until it reaches a predetermined moisture content, for example, approximately 40%.

The dryer 204 is equipped with a rotary drum as a drying container, and sludge is supplied into the interior from one axial end of the rotary drum and moved axially along the interior while the rotary drum is rotated. During this movement, the sludge is dried by hot air, and the dried sludge is discharged from the other axial end. The dried sludge is then sent to the carbonization furnace 208 via the transport conveyor 206 and carbonized. Finally, carbonized material is discharged from the carbonization furnace 208 as a carbonization residue.
In FIG. 8, reference numeral 210 denotes a hot air generating furnace for generating hot air to be supplied to the dryer 204, in which supplied fuel is combusted under the supply of combustion air to generate hot air.

Such conventional carbonization treatment equipment requires a dryer 204 to dry the sludge and a hot air generating furnace 210 to generate the hot air used for drying, which increases the number of components required for the carbonization treatment equipment. Furthermore, the fuel consumed to generate the hot air increases treatment costs.

Incidentally, Patent Document 3 listed below discloses an invention for a "method for carbonizing organic water-containing waste," in which sewage sludge and rice husks are mixed and fed into a rotary kiln to produce a carbonized product. However, the carbonization method described in Patent Document 3 differs from the present invention in that it includes a step of drying the sewage sludge using a dryer, and in that it uses a mixture with a lower moisture content than the present invention and performs the dry distillation process.

Japanese Patent Application Publication No. 11-33599 Japanese Patent Application Publication No. 11-37644 JP 2011-68824 A

The present invention has been made against the background of the above circumstances, and aims to provide a carbonized material manufacturing method and carbonized material manufacturing equipment that can carbonize a mixture containing sludge with a simple configuration that does not require drying treatment using hot air.

Claim 1 relates to a method for producing a carbonized material , comprising: a mixing step of mixing biomass and dewatered sludge to obtain a mixture with an apparent moisture content of 30 to 70%; and a carbonization step of dry distilling the mixture, which is introduced into a retort of an externally heated rotary kiln-type carbonization furnace under oxygen-free or low-oxygen conditions, at 700 to 900°C to obtain a carbonized material .
A method for producing a carbonized product, characterized in that in the carbonization process, combustion of combustible gas generated from the mixture is used to heat the inside of the retort (excluding methods for producing a carbonized product in which a reforming reaction is performed on the combustible gas using a catalyst).

Here, apparent moisture content is the ratio of the moisture weight of a mixture consisting of biomass and dewatered sludge to the total weight (the sum of the moisture weight of the mixture and the dry weight of the mixture). If the total weight of the mixture is T (g) and the moisture weight of the mixture is h (g), then the apparent moisture content p (wt%) can be expressed as p = h/T x 100.

Claim 2 is the same as claim 1, characterized in that the biomass is rice husks. Here, rice husks are the outer husk portion obtained from grains such as rice and wheat, which are generally known as rice husks and have both a grain grain and an outer husk. They may typically be rice husks produced during the threshing process of rice, wheat, etc.

The third aspect of the present invention is characterized in that, in the second aspect, the rice husks are pulverized so that the bulk density is 2 to 10 times that of the rice husks.
Here, bulk density refers to loose bulk density. Bulk density is measured by feeding rice husks into a container with an inner diameter of 2.3 cm (volume 100 ^cm3 ) from the top, scraping off the pile of rice husks with a spatula when the container is full, and measuring the weight of the total amount of rice husks in the container. Bulk density can be calculated using the following formula.
Bulk density (g/cm ³ )=weight of rice husks (g)/volume of container (cm ³ )
According to the above measurement, the bulk density of intact rice husks is approximately 0.1 g/cm ³ , and in the present invention, it is desirable to use rice husks whose bulk density after crushing is 0.2 to 1.0 g/cm ³ .

Claim 4 is a method according to any one of claims 1 to 3, characterized in that in the mixing step, the biomass such as rice husks and dewatered sludge are mixed using a biaxial paddle or biaxial rod mixer.

Claim 5 is a method according to any one of claims 1 to 3, characterized in that in the mixing step, the biomass, such as rice husks, and the dewatered sludge are mixed using a single-axis screw pump.

Claim 6 relates to a carbonized material manufacturing facility , which includes a mixer that mixes biomass and dewatered sludge to obtain a mixture, and a carbonization furnace that carbonizes the mixture by dry distillation at 700 to 900°C .
The carbonization furnace is an externally heated rotary kiln-type carbonization furnace comprising: a furnace body; a cylindrical retort disposed inside the furnace body; an external heating chamber disposed inside the furnace body and on the outer periphery of the retort; an outlet pipe disposed in the retort for allowing combustible gas generated from the mixture to escape from the inside of the retort to the external heating chamber; and an auxiliary burner disposed inside the furnace body for heating the inside of the external heating chamber, and is a carbonization production equipment characterized in that it does not have a dryer for drying the dewatered sludge (excluding carbonization production equipment having a catalytic reformer that performs a reforming reaction on the combustible gas).

As described above, the present invention produces carbonized material by using a mixture of biomass such as rice husks and sludge (dehydrated sludge) instead of pure sludge. Although rice husks after threshing are used as livestock bedding and the like, they are generally difficult to dispose of. However, according to the present invention, they can be used effectively without being discarded.
In the present invention, the apparent moisture content of the mixture is adjusted by mixing biomass such as rice husks with dewatered sludge, which eliminates the need for the dryers and hot air generators that have been used to adjust the moisture content of sludge, thereby simplifying the components of the carbonization treatment facility.In addition, since hot air for moisture adjustment is no longer necessary, the treatment cost (amount of fuel used) can be reduced.

The properties required of a carbide vary depending on its intended use. If a powdered carbide is required, an apparent moisture content of 30-40% is appropriate for the mixture, while if a granular carbide that is less likely to scatter is required, an apparent moisture content of 60-70% is appropriate. As the appropriate apparent moisture content differs depending on the properties required of the carbide, in this invention the apparent moisture content of the mixture can be appropriately determined within the range of 30-70%.

In the present invention, in addition to whole rice husks, crushed rice husks (rice husk flour) can be used. The use of crushed rice husks allows for more uniform mixing, thereby improving the quality of the resulting charcoal.
Furthermore, a mixture of intact rice husks with low bulk density and dewatered sludge has a low density and is prone to scattering into the exhaust gas path inside the carbonization furnace, which may result in a poor carbonized product yield. In contrast, a mixture of finely crushed rice husks and dewatered sludge can have a high density, is less likely to scatter inside the carbonization furnace, and can increase the carbonized product yield. To achieve this effect, it is desirable to use rice husks crushed to a bulk density of 2 to 10 times.

In the mixing step of the present invention, the biomass such as rice husks and the dewatered sludge can be mixed using a twin-shaft paddle type or twin-shaft rod type mixer.
A twin-shaft paddle or twin-shaft rod mixer is suitable for obtaining a mixture using rice husks with a low bulk density, such as intact rice husks. Furthermore, a mixture produced using a twin-shaft paddle or twin-shaft rod mixer is discharged in a finer, more dispersed state (loose state) than a mixture produced using a single-shaft screw pump (described later) if the apparent moisture content is the same, and is therefore suitable for obtaining finer-grained carbonized material.

In the mixing step of the present invention, it is also possible to mix the biomass such as rice husks with the dewatered sludge using a single screw pump.
When a single-screw pump is used, biomass such as rice husks and dewatered sludge are mixed in a compacted state, making it suitable for forming a dense mixture with few voids. Furthermore, the mixture produced using a single-screw pump is discharged in larger chunks than when the aforementioned twin-screw paddle or twin-screw rod mixers are used, making it suitable for obtaining carbonized material with large particle sizes. Furthermore, when a single-screw pump is used, by directly connecting the single-screw pump and the carbonization furnace with piping, it is possible to omit a conveying device such as a conveyor, thereby simplifying the configuration of the carbonization treatment equipment.

According to the present invention, it is possible to provide a carbonization method and carbonization equipment that can carbonize a mixture containing sludge using a simple configuration that does not require drying treatment using hot air.

1 is a diagram showing the configuration of a carbonization treatment facility using a carbonization treatment method according to one embodiment of the present invention. FIG. 2 is a diagram showing a main part of the mixer in FIG. 1 . FIG. 2 is a diagram showing the internal configuration of the carbonization furnace in FIG. 1. FIG. 2 is a diagram showing the configuration of a carbonization furnace input device in FIG. 1. FIG. 10 is a diagram showing the configuration of a carbonization treatment facility using a carbonization treatment method according to another embodiment of the present invention. FIG. 6 is a diagram showing a main part of the mixer in FIG. 5 . FIG. 10 is a diagram showing the configuration of a carbonization treatment facility using a carbonization treatment method according to still another embodiment of the present invention. FIG. 1 is a diagram showing the overall configuration of a conventional carbonization treatment facility.

Next, an embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 shows the configuration of a carbonization treatment facility 1 that uses a carbonization treatment method according to one embodiment of the present invention. The carbonization treatment facility 1 includes a first receiving hopper 10, a second receiving hopper 16, a mixer 14, and a carbonization furnace 40, and produces carbonized material using organic sludge generated during wastewater treatment. Note that the following embodiment uses rice husks as an example, but the present invention can also be applied to biomass other than rice husks.

The first receiving hopper 10 is a dewatered sludge storage tank that receives dewatered sludge that has been dewatered to a moisture content of approximately 70-85% (usually approximately 80%). The dewatered sludge received in this first receiving hopper 10 is then sent to the mixer 14 by the constant volume feeder 12.

On the other hand, the second receiving hopper 16 is a rice husk storage tank, and rice husks are received in this second receiving hopper 16. The moisture content of rice husks is about 10%.
A rotary valve 17 is connected to the downward discharge outlet 16 a of the second receiving hopper 16 , and the rice husks received in the second receiving hopper 16 are sent to the mixer 14 via the rotary valve 17 .
In this example, dewatered sludge and rice husks are respectively supplied to the mixer 14 in a fixed amount so that a mixture with an apparent moisture content of 40% is obtained in the mixer 14. More specifically, they are supplied to the storage tank 20 of the mixer 14.

The mixer 14 is a twin-shaft paddle mixer, and the mixing step of the present invention is carried out using this mixer 14. The mixer 14 includes a paddle mixer section 21 and a storage tank 20 attached to an inlet 21a of the paddle mixer section 21. The paddle mixer section 21 has a pair of rotating shafts 22, 24 (see FIG. 2) provided inside a casing, and approximately flat mixing blades 26, 28 are fixedly mounted radially on each of the rotating shafts.
In the paddle mixer section 21, the rotary shafts 22, 24 rotate in opposite directions, and the dewatered sludge and rice husks supplied from the storage tank 20 to the paddle mixer section 21 are mixed by being kneaded at the overlapping portions of the mixing blades 26, 28.

In this mixer 14, the rotating shafts 22 and 24 rotate at unequal speeds. Therefore, there is a difference in peripheral speed between the mixing blades 26 and 28, and this difference in peripheral speed allows the dewatered sludge and rice husks to be mixed together with high efficiency.

The mixing blades 26, 28 are mounted at an angle relative to the rotating shafts 22, 24, respectively. The dewatered sludge and rice husks supplied to the paddle mixer section 21 are mixed and sent axially by the feeding action of the mixing blades 26, 28. A mixture of dewatered sludge and rice husks with a predetermined apparent moisture content (40% apparent moisture content in this example) is then discharged from the discharge outlet 21b located at the axial end. The discharged mixture is transported to the carbonization furnace 40 by the transport conveyor 38.

In some cases, the mixing blades 26, 28 of the mixer 14 in this example can be replaced with rods to create a twin-rod mixer.

The carbonization furnace 40 is an externally heated rotary kiln type carbonization furnace that dehydrates and pyrolyzes the material to be treated in an oxygen-free or low-oxygen atmosphere with an oxygen concentration of 10% or less, and the carbonization process in the present invention is carried out using this carbonization furnace 40.
As shown in Figure 3, the carbonization furnace 40 has a cylindrical retort 44 as a dry distillation container inside the furnace body 42, and a mixture as the material to be treated, with a moisture content adjusted to 40%, is placed inside the retort 44 on the left end side in the figure.
The charged mixture is first heated by heating the atmosphere inside the external heating chamber 48 using the auxiliary burner 46 installed inside the furnace body 42. Then, the combustible gas contained in the mixture escapes into the atmosphere inside the external heating chamber 48 through the blow-out pipe 45 installed in the retort 44, and this combustible gas ignites, and thereafter the mixture inside the retort 44 is heated by the combustion of this combustible gas. At this stage, the combustion of the auxiliary burner 46 is stopped.

The furnace body 42 surrounding the external heating chamber 48 is formed with an air inlet 43 for introducing combustion air into the external heating chamber 48. In this example, a control unit (not shown) adjusts the amount of combustion air introduced into the external heating chamber 48 through the air inlet 43, thereby controlling the temperature of the external heating chamber 48 to match a preset target temperature.

The mixture inside the retort 44 moves from the left end of the figure to the right as the retort 44 rotates (the retort 44 has a slight gradient), and the water is efficiently evaporated in the upstream part of the retort 44. After moving to the downstream part of the retort 44, it is carbonized at 700-900°C, which is close to the atmosphere in the external heating chamber 48. Finally, the carbonized product (carbonized product) as the carbonization residue is discharged from the outlet 52 at the right end of the retort 44 in the figure, i.e., the carbonization furnace 40.

An exhaust gas treatment chamber 50 separated from the external heat chamber 48 is provided inside the furnace body 42, and exhaust gas from the external heat chamber 48 is led into this chamber. An exhaust gas treatment chamber burner 47 is provided in the exhaust gas treatment chamber 50, and unburned gas in the exhaust gas led into the exhaust gas treatment chamber 50 is subjected to secondary combustion in this exhaust gas treatment chamber burner 47.
The exhaust gas in the exhaust gas treatment chamber 50 is then discharged from an exhaust port 51. An exhaust gas passage extends from the exhaust gas treatment chamber 50 through the exhaust port 51, and the exhaust gas from the carbonization furnace 40 is passed through the exhaust gas passage by a carbonization furnace exhaust gas fan, passes through a carbonization furnace exhaust gas heat exchanger, and is discharged to the outside from a chimney, as shown in Figure 8, for example.

4, a carbonization furnace charger 54 is provided at the front end of the carbonization furnace 40 of this example. The carbonization furnace charger 54 includes a screw conveyor 60, and a storage tank 56 is attached to an inlet 60a of the screw conveyor 60.
A rotating shaft 57 is rotatably supported inside the storage tank 56, and a plurality of scraping pieces 58 that rotate integrally with the rotating shaft 57 are provided at different axial positions of the rotating shaft 57. The rotating shaft 57 and scraping pieces 58 are connected to the drive mechanism of the screw conveyor 60 so as to rotate in conjunction with the screw conveyor 60.

The screw conveyor 60 comprises a screw shaft 61, screw blades 62 that protrude spirally from the screw shaft 61, and a drive motor 63 that rotates the screw shaft 61. The discharge end of the screw conveyor 60 is inserted into the retort 44 of the carbonization furnace 40.

In this example, the mixture introduced into the storage tank 56 falls toward the screw conveyor 60 below due to the rotational movement of the scraping pieces 58 inside the storage tank 56. The falling mixture is contained in the groove between the screw blades 62 of the screw conveyor 60, and is pushed forward as the screw shaft 61 rotates, and is introduced into the retort 44.

According to the carbonization method of this embodiment, the apparent moisture content of the mixture is adjusted by mixing the rice husks with the dewatered sludge, eliminating the need for the dryers and hot air furnaces conventionally used to adjust the moisture content of the sludge, thereby simplifying the components of the carbonization treatment facility 1. Furthermore, since hot air is no longer required to dry the mixture before the carbonization treatment, processing costs (fuel consumption) can be reduced.

In addition, in this embodiment, a twin-shaft paddle mixer 14 is used in the mixing process in which rice husks and dewatered sludge are mixed to obtain a mixture. Therefore, if the apparent moisture content is the same, the resulting mixture is discharged in a finer, more fragmented state (loose state) than when a single-shaft screw pump (described below) is used, making it suitable for obtaining finer-grained carbonized material.

In this embodiment, in addition to whole rice husks, crushed rice husks (rice husk powder) can be used. By using crushed rice husks, more uniform mixing with sludge can be achieved, and the quality of the generated carbonized material can be improved.
Furthermore, a mixture of intact rice husks with low bulk density and dewatered sludge has a low density and is likely to scatter into the exhaust gas path inside the carbonization furnace 40, which may result in a decrease in the yield of carbonized material. In contrast, a mixture of finely crushed rice husks and dewatered sludge can have a high density and is less likely to scatter inside the carbonization furnace 40, thereby increasing the yield of carbonized material. To achieve this effect, it is desirable to use rice husks that have been crushed to a bulk density of 2 to 10 times the original size. Crushing of rice husks can be carried out using a mortar and pestle, a hammer mill, or the like.

Figure 5 shows another embodiment (second embodiment) of the present invention. This example differs from the first embodiment in that a single-shaft screw pump is used in the mixing process to mix the rice husks and dewatered sludge. The other configurations are the same as those of the first embodiment.

A mixer 64 in a carbonization treatment facility 1B shown in FIG. 5 includes a uniaxial screw pump 68 and a storage tank 66 attached to an inlet 68a of the uniaxial screw pump 68.
As shown in Figure 6, the uniaxial screw pump 68 includes a stator 70 and a rotor 72 housed inside a cylindrical casing 69. The stator 70 is twisted at a constant twist angle and has an oval cross-sectional through-hole extending in the axial direction. The rotor 72 is rod-shaped with a circular cross-section and is disposed along the through-hole of the stator 70. A spiral cavity 74 is formed between the stator 70 and the rotor 72, continuing in the axial direction.

The rotor 72 is connected to the drive motor 76 via a joint member (not shown). When the drive motor 76 rotates, the rotor 72 rotates within the through-hole with an oval cross-section, causing the contents contained within the cavity 74 to gradually move in the axial direction.

The discharge port 68b of the uniaxial screw pump 68 is connected to the carbonization furnace 40 (more specifically, the storage tank 56 of the carbonization furnace input device 54) via piping 77, as shown in Figure 5.

In this example, the rice husks and dewatered sludge that flow into the cavity 74 through the inlet 68a are mixed in a compressed state by the rotating rotor 72, so that a mixture with fewer voids and higher density can be continuously formed compared to the twin-shaft paddle mixer used in the first embodiment above.
As described above, according to the carbonization method of this embodiment, a high-density mixture is supplied to the carbonization furnace 40, so that it is possible to prevent the mixture from scattering into the exhaust gas path inside the carbonization furnace 40, which would result in a decrease in the yield of char. This effect is particularly effective when using rice husks that have been pulverized to increase the bulk density by 2 to 10 times.

In addition, in this example, the discharge port 68b of the single-axis screw pump 68 is directly connected to the carbonization furnace 40 via piping 77, so the mixture can be supplied to the carbonization furnace 40 without using a separate transport device such as the conveyor 38 in the first embodiment, further simplifying the configuration of the carbonization treatment equipment.

Figure 7 shows yet another embodiment (third embodiment) of the present invention. This example differs from the second embodiment in that a second twin-shaft paddle mixer 80 is provided between the mixer 64 using a single-shaft screw pump 68 and the carbonization furnace 40. The configuration of the second mixer 80 is the same as the twin-shaft paddle mixer 14 in the first embodiment.

In this example, the discharge port 68b of the uniaxial screw pump 68 is connected to the storage tank 20 of the second mixer 80 by a pipe 82, and the mixture mixed by the uniaxial screw pump 68 is transported to the second mixer 80 via the pipe 82. In addition, a transport conveyor 38 is provided between the second mixer 80 and the carbonization furnace 40, and is configured to transport the mixture discharged from the second mixer 80 to the carbonization furnace 40.

In this example, a more uniformly mixed mixture can be obtained by using two types of mixers 64, 80. In addition, the mixture can be finely granulated by the second twin-shaft paddle mixer 80 installed downstream and supplied to the carbonization furnace 40.

<Other modified examples and application examples>
In the present invention, it is also possible to mix biomass other than rice husks with dewatered sludge to obtain a mixture with a predetermined moisture content. Here, biomass refers to organic resources derived from living organisms, and specific examples include: (1) inedible parts of agricultural crops such as rice straw, banana stalks, coffee grounds, coconut shells/husks, coconut husks, corn cobs, sugarcane pomace, cassava stems, and other food residues; (2) resource crops such as sugarcane, corn, and cassava; and (3) wood chips/pellets, thinned wood, and waste wood obtained from wood.

These biomass materials have various properties. Therefore, biomass can be cut or crushed as needed to ensure uniform mixing with the dewatered sludge and to obtain carbonized material of the desired particle size. The length of the biomass used is preferably 30 mm or less, and more preferably 20 mm or less.
The moisture content of the biomass used is preferably 30% or less, and more preferably 20% or less.

When using biomass other than rice husks, it can be mixed with dewatered sludge using the twin-shaft paddle or twin-shaft rod mixer exemplified in the above embodiment, and/or a mixer equipped with a single-shaft screw pump.

The above detailed description of an embodiment of the present invention is provided by way of example only. The present invention can be implemented in various modified forms without departing from the spirit of the invention.

1, 1B, 1C carbonization treatment equipment 14, 64, 80 mixer 40 carbonization furnace

Claims (5)

a mixing step of mixing biomass and dewatered sludge to obtain a mixture having an apparent moisture content of 30 to 70% (excluding 60 to 70%) ;
a carbonization step of carbonizing the mixture introduced into a retort of an externally heated rotary kiln-type carbonization furnace at 700 to 900°C under oxygen-free or low-oxygen conditions to obtain a powdery carbonized product;
A method for producing a powdered charcoal, characterized in that in the carbonization process, combustion of combustible gas generated from the mixture is used to heat the inside of the retort (excluding methods for producing charcoal by carrying out a reforming reaction of the combustible gas using a catalyst). 2. The method for producing a powdery charcoal according to claim 1, wherein the biomass is rice husk. The method for producing powdered carbide according to claim 2, characterized in that the rice husks are pulverized so that their bulk density is 2 to 10 times that of the original. The method for producing powdery carbonized material described in any one of claims 1 to 3, characterized in that in the mixing step, the biomass such as rice husks and dewatered sludge are mixed using a biaxial paddle type or a biaxial rod type mixer. The method for producing powdery carbonized material according to any one of claims 1 to 3, characterized in that in the mixing step, the biomass such as rice husks and the dewatered sludge are mixed using a single-axis screw pump.