JP7656905B2 - Manufacturing method for wood-based water-repellent pellets - Google Patents

Description

The present invention relates to a method for producing wood pellets made from wood, in particular water-repellent pellets that have water-repellent, hydrophobic and deodorizing properties.

Wood pellets are manufactured primarily for the purpose of being used as fuel. In general, they are solid fuels made by grinding dried wood into fine powder and compressing it into pellets measuring 6-8 mm in diameter and 10-25 mm in length. They are easier to handle than fuels made from other biomass resources and are suitable for long-distance transportation. They can also be stored for long periods of time because they are heat-treated and have a low moisture content.

In recent years, in order to prevent global warming and to curb and reduce carbon dioxide emissions into the atmosphere worldwide, various research and development efforts have been conducted on fuels that use biomass resources as renewable energy sources. Among these biomass fuels, wood fuels made from thinning materials, which are industrial waste that were previously simply incinerated, have attracted attention as an alternative fuel to fossil fuels such as petroleum and coal, and there are high expectations for improvements to increase the calorific value per unit weight.

As alternative fossil fuels, the following have attracted particular attention: white pellets (made from wood excluding bark), bark pellets (made from bark only; see, for example, Patent Documents 1 and 2), and whole wood pellets. These wood pellets are made by compressing and forming into granules crushed bark, sawdust, and scraps generated during thinning and lumber processing. They are formed into pellets by melting and solidifying the lignin, a component of wood, with heat (see, for example, Patent Document 3).

However, compared to fossil fuels, these wood pellets have the following problems:
(1) The amount of heat generated by combustion per unit weight is low.
(2) The manufacturing process is complicated, resulting in high costs.
(3) When it comes into contact with water, it expands and loses its shape, making it difficult to store it outdoors like coal.

Therefore, for example, a method has been proposed in which sawdust for wood pellets and sawdust for powdered charcoal, i.e., charcoal, are mixed to improve the calorific value (see Patent Document 4). Other methods have been proposed, such as coating with vegetable oils such as palm oil, or fatty acids or esters derived from beef tallow or lard to improve water resistance (see Patent Document 5).

JP 2006-266546 A JP 2008-297532 A JP 2007-40542 A JP 2008-303305 A JP 2008-7711 A

However, because wood pellets absorb moisture and lose their shape, turning into powder, they need to be stored in a warehouse with a roof and walls, and are therefore outclassed by fuels that can be stored outdoors, such as coal. As a fuel, wood pellets are mainly used in pellet stoves and other general household applications, and a small amount is sold commercially as bedding for pet toilets.

As mentioned above, wood pellets are also suitable as litter box bedding for pet animals. In particular, in recent years, an increasing number of dogs and cats are being kept indoors in elderly care facilities and households for the purpose of providing biotherapy (healing), and there is a demand for materials that can be used to cover litter trays to treat their waste, and that have functions such as preventing waste from scattering, high water repellency and hydrophobicity, and deodorizing properties, as well as being safe and inexpensive. For this reason, there is a demand for wood pellets to have improved functions such as high water repellency and hydrophobicity.

Currently, the materials used as litter box bedding for pets can be broadly classified into the following types, each of which has its own characteristics, advantages and disadvantages.
(1) A type made from raw materials such as zeolite, silica gel, and sand, processed into granules and permeated with deodorant and fragrances.
Advantages: It absorbs water from human waste, reducing the amount of urine that reaches the absorbent sheet placed at the bottom of the toilet, and reducing the consumption of absorbent sheets. In addition, it has a strong deodorizing effect, so there is no problem with installing it indoors as long as its effect lasts.
Disadvantages: Removing the areas where human waste has adhered or been absorbed and replenishing the removed areas with bedding material becomes a daily routine. If this cleaning task is neglected, the odor will fill the room as the deodorizing effect will be exceeded. Also, the area around the toilet tray will become an unsanitary environment. Furthermore, it must be disposed of as non-combustible garbage for general waste processing, and the treated material is heavy because it has absorbed moisture when it is brought to the garbage collection site for disposal, which means a considerable labor burden for elderly people who are carrying it. Also, costs are high because the raw materials are expensive and the manufacturing process is complicated.
(2) A type made from natural coniferous wood that has been crushed and processed into pellets and impregnated with water repellents, antibacterial agents, and fragrances.
Advantages: Since it does not absorb urine, which is a liquid, you only need to remove feces (solid matter). It can be used until the deodorizing effect weakens, and it only needs to be replaced about once a month. It can be disposed of as combustible waste. When it comes to disposal, the treated material is lightweight because it has not absorbed moisture, so the burden of transportation is reduced when it is brought to the garbage collection site.
Disadvantages: The manufacturing process is complicated and expensive. In addition, the use of chemically synthesized water repellents raises concerns about the safety of the product to animals and humans.
(3) White pellets and whole wood pellets, which are usually sold commercially as fuel.
Advantages: It absorbs water from human waste, reducing the amount of urine that reaches the absorbent sheet placed at the bottom of the toilet, and therefore reducing the consumption of absorbent sheets. It can be disposed of with burnable garbage. It is inexpensive.
Disadvantages: Removing the areas where human waste has adhered or been absorbed and replacing the removed areas with bedding material becomes a daily routine. If this cleaning work is neglected, the odor will fill the room as the deodorizing effect will be exceeded. Also, the area around the toilet tray will become an unsanitary environment. Furthermore, when the waste is brought to the garbage collection site for disposal, it is heavy because it has absorbed moisture, and this can be a considerable burden for elderly people who are carrying it.
(4) A type made by mixing crushed pulp with sand, processing it into pellets, and permeating it with deodorizing agents and natural fragrances.
Advantages: It absorbs water from human waste, reducing the amount of urine that reaches the absorbent sheet placed at the bottom of the toilet, and therefore reducing the consumption of absorbent sheets. It also has a strong deodorizing effect.
Disadvantages: Removing the areas where human waste has adhered or been absorbed and replenishing the removed areas with bedding material becomes a daily routine. Furthermore, it must be disposed of as non-combustible garbage for general waste processing, and when it is brought to the garbage collection site for disposal, the treated material absorbs moisture and is heavy, which is a considerable labor burden for elderly people who carry it. In addition, the raw materials are expensive and the manufacturing process is complicated, so costs are high. Furthermore, as a chemically synthesized water repellent is used, there are concerns about its safety for animals and people.

As described above, the pet litter boxes currently on the market each have their own advantages and disadvantages, but it would be desirable to develop a product that combines the advantages of each product, that is, a litter box that is water-resistant, water-repellent, and deodorizing, and that can be manufactured economically without using synthetic chemical water-repellents. At the same time, it would be desirable to develop a product that combines the water-resistant and water-repellent properties with a high calorific value (burning calories) per unit weight, in addition to being able to be used as fuel, which is the original purpose of wood pellets.

In order to solve the above problems, the inventor developed technology to easily and efficiently produce wood pellets that suppress moisture absorption without using chemically synthesized water repellents, and at the same time developed a method to easily and efficiently produce high combustion calories per unit weight without impregnating wood pellets with high combustion calorie ingredients.

The inventor also focused on the properties of roasted coffee beans, for example, that they burn very strongly when ignited and that they do not absorb moisture unless they are ground and soaked in hot water, and as a result of extensive research, he came up with the present invention.

In view of the problems with the conventional technology described above, the present invention aims to provide a simple and low-cost method for producing water-repellent wood pellets that not only increase the amount of heat generated by combustion per unit weight, but are also useful as litter box bedding for pet animals.

The first feature of the method for producing water-repellent wood pellets of the present invention is that the pellets are produced by roasting a wood raw material. The second feature of the method is that the method includes a step of preheating the wood raw material in pellet form, a step of roasting the preheated wood raw material, a step of immersing the roasted wood raw material in hot water to instantaneously cool it, and a step of naturally cooling the instantaneously cooled wood raw material. The wood raw material is preferably at least one material selected from bark, scraps, thinnings, pruning materials, sawdust, construction waste, waste packaging materials, waste pallets, rice husks, and bamboo.

The present invention has the following excellent effects.
(1) Since it does not absorb moisture, it retains its shape well and does not crumble into mud. Therefore, when used as a bedding material for pet toilets, the only daily cleaning required to dispose of the excrement (sewage) is to remove the feces (solid matter), and there is no need to replenish the bedding material that has been removed.
(2) Because the product does not absorb moisture, there is no need to have a warehouse with a roof and walls in which to store the product; outdoor storage is possible, which makes storage at the factory and loading at the time of shipment simple and easy.
(3) It can be produced by a simple method, and the cost required for production equipment can be reduced, making it economical.
(4) It is made of wood, has a semi-carbonized porous interior, and has a high absorption effect for specific odors, so it can suppress the odor of human waste. Therefore, it is safe for animals and humans without the use of synthetic chemical deodorants.
(5) When the product is disposed of after use, since it does not contain moisture, it is lightweight and reduces the effort required by those, especially elderly people and women, to transport it to a garbage collection site.
(6) Product prices can be set low, reducing the purchasing burden on low-income and elderly households.
(7) Because it has high water resistance, water repellency, and high burning calories, it can be used not only as an alternative fuel to coal, but also as a bedding material for pet toilets, which will help expand the sales market.

Next, an embodiment of the present invention will be described with reference to the accompanying drawings.
1 is a flowchart showing a manufacturing process of wood-based water-repellent pellets according to the present invention. FIG. 1 is an explanatory diagram showing a schematic configuration of an example of a manufacturing apparatus for producing water-repellent wood pellets according to the present invention.

The manufacturing method of wood-based water-repellent pellets according to the present invention will be explained with reference to Figure 1. As the wood raw material, white pellets 1 (manufactured by Tsuno Pellet, product name: Dragon Pellet) made only from commercially available wood were used. Ordinary wood pellets are formed into granules by lignin decomposition caused by compression and temperature rise during the manufacturing process, but by adding a roasting process, the pellet raw material is overdried to exhibit a water-repellent effect, and high-temperature heating increases the synthesis of water-repellent components on the pellet surface and inside and further decomposition of lignin components, increasing the adhesion, and it is expected that water repellency, hydrophobicity, and underwater shape retention will be significantly improved. The target was to ensure underwater shape retention for more than 6 hours as an indicator of this.

First, 200 g of white pellets 1 in a plastic airtight container 2 were weighed out using a tabletop weighing scale 3, and the pellets were preheated by heating them for 1 minute at 600 W in a microwave oven 5 to raise the temperature of the white pellets 1 to nearly 75°C (step S1). This was to reproduce the temperature of the pellets when they are discharged from a disk rotation compression extrusion type disk pelleter in the process of manufacturing normal pellet fuel, which is 70°C to 100°C. An aluminum pot 6 for heating was heated using a gas stove 7, and the heat was adjusted so that the temperature of the bottom of the pot was measured with a non-contact thermometer and was in the range of 250°C to 310°C. To measure the moisture content of the white pellets 1 before processing, they were crushed using a tabletop grinder and pre-weighed using a near-infrared moisture meter 4.

When the white pellets 1 preheated in step S1 are placed in the heated aluminum pot 6 and heated while stirring (step S3), the moisture contained in the white pellets 1 evaporates first. The temperature of the bottom of the pot drops to about 200°C, but the heat of the gas stove 7 is adjusted so that the temperature range is 250°C to 280°C, while checking the state of bubbles of evaporating moisture. When the pellets are first placed in, steam from evaporation is generated vigorously, but after about 5 minutes the temperature of the raw material exceeds 150°C and volatile gas begins to be generated. The color of the raw material gradually becomes brown, and when the temperature of the raw material reaches 270°C, gas generation becomes intense, so the heating of the gas stove 7 is stopped and the drying and roasting process is completed (step S4).

Immediately after the roasting process (step S4), the roasted white pellets 1, which are overdried and in a high temperature state, are transferred to a stainless steel colander 8, and the weight and moisture content are measured using a weighing scale 3 and a moisture meter 4 (step S5). In order to prevent spontaneous combustion due to contact with air, the transferred colander 8 is instantly lowered into another aluminum cooling pot 9 containing boiling water in advance so that the roasted white pellets 1 are completely submerged, and then the pellets are immersed for a few seconds until the product temperature drops to 160°C or less, and then pulled out (step S6). The roasted white pellets 1 are removed from the boiling water and naturally dried by the residual heat, while the moisture adhering to the surface dries and cools (step S7). In this way, the water-repellent pellets 10, the product of the present invention, are obtained.

The obtained water-repellent pellets 10 were transferred to a paper cup and their weight was measured using a tabletop measuring device. The initial weight of 200 g was reduced to 153 g after the roasting process. This weight reduction was due to the evaporation of water and the removal of volatile substances. In order to measure the moisture content of the obtained water-repellent pellets 7, they were crushed using a tabletop grinder and measured using a near-infrared moisture meter. The moisture content of the white pellets 1 before the process was 7.4%, and after the roasting process it dropped to 0.2%. When cooled with hot water, the moisture content increased to 6.4%, but the weight was 156 g, indicating that there was almost no absorption of moisture. After that, about 10 water-repellent pellets 10 were placed in a paper cup of water and an underwater shape retention test was performed. As a result, even after soaking for about 10 days, the water only slightly discolored, and no change was observed in the pellet shape.

[Roasting experiment results]
As a result of the above experiments, the following facts became clear.
(1) White pellets are dried and roasted until the raw material temperature reaches 270°C while generating volatile gases. Wood pellets do not change shape even when immersed in water for more than a week, and have excellent water repellency and hydrophobicity, so there is no need to use a separate water repellent.
(2) The calorific value (combustion calories) has increased from 4,200 kcal/kg to 5,170 kcal/kg. This is the result of removing the moisture contained in the raw material, as well as the increased carbon content due to the removal of non-combustible substances through the generation of volatile gases. This allows for a reduction in the amount of space required for fuel storage to obtain the same amount of combustion heat.
(3) Because it has excellent water-repellent and hydrophobic properties, it can be stored outdoors, eliminating the need for huge warehouses to pack it into tonbags (flexi-con bags) and store it indoors. Furthermore, it can be stored outdoors, similar to the current storage conditions for coal.
(4) The product itself had almost no unpleasant odor, and it was confirmed that the carbonized components had an odor-eliminating effect.
(5) It was found that even if the hot raw materials are instantly immersed in boiling water to cool them down in order to prevent spontaneous combustion immediately after roasting, the high heat of the raw materials and the excessive dryness inside the materials prevent moisture from penetrating into the interior, and the moisture content of the product does not increase. In other words, it was found that "water immersion cooling of wood pellets" is possible and that sufficient shape retention in water can be ensured.

[Equipment for practical use]
As shown in Fig. 2, wood pellets are usually processed using a disk pelleter 10 with a disk rotation compression extrusion system. After processing, the pellets reach a high temperature of 70°C or more due to frictional heat. If the pellets are stored in the product bunker 12 in this state, the evaporated water will condense, which will have the adverse effect of causing mold to grow inside the product bunker 12. Therefore, the pellets are cooled in a counter cooler 11 before being transported to the product bunker 12 for storage.

In the present invention, by adding a continuous roaster or continuous oven (including superheated steam type) 13 and a continuous hot water instantaneous immersion cooler 14 to the above-mentioned existing equipment configuration, it is possible to obtain water-repellent pellets with water-repellent, hydrophobic and deodorizing properties.

In addition, even if there is no space to install a continuous roaster or continuous oven (including superheated steam type) or a vibration separator 15 in the equipment configuration of the existing equipment, and wood pellets are produced and temporarily stored in a product bunker 12 (storage hopper), they can be discharged and transported from the bottom of the product bunker 12 (storage hopper) using a discharge and pellet transport conveyor, and water-repellent pellets with water repellency and hydrophobicity can be obtained by adding a continuous roaster or continuous oven (including superheated steam type), a continuous hot water instant immersion cooler 14, and a counter cooler 11. In addition, water-repellent pellets with water repellency, hydrophobicity, and deodorizing properties can be obtained by configuring new equipment and factories for processing waterproof pellets.

When roasting a small amount of wood pellets, it is possible to prepare a manual roaster or oven (including superheated steam type) or a water cooler of a size appropriate to the amount of raw material to be processed and process it in batches. The wood raw material is not limited to the above examples, and may be at least one selected from bark, scraps, thinned wood, pruning wood, sawdust, construction waste, waste packaging material, waste pallets, rice husks, and bamboo, as long as it does not deviate from the gist of the claims.

1. White pellets (wood raw material)
2. Plastic airtight container 3. Weighing scale 4. Moisture meter 5. Microwave oven 6. Aluminum pot for heating 7. Gas stove 8. Stainless steel colander 9. Aluminum pot for cooling 10. Water-repellent pellets 11. Countertop cooler 12. Product bunker 13. Continuous roaster (continuous oven)
14 Continuous hot water instantaneous immersion cooling machine 15 Vibration separator

Claims (3)

A step of preheating the pelletized wood raw material;
A step of roasting the preheated wood raw material;
A process of instantly cooling the hot wood raw material, which has generated volatile gases during the roasting process, by immersing it in boiling water for a few seconds ;
A method for producing water-repellent wood pellets, comprising the step of naturally cooling the flash-cooled wood raw material. The method for producing water-repellent wood pellets according to claim 1, characterized in that the hot water is in a boiling state. The method for producing water-repellent wood pellets according to claim 1 or 2, characterized in that the natural cooling step involves evaporating moisture adhering to the surface of the wood raw material using residual heat to cool it.

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