JP6728516B2 - Exothermic particles and heating element - Google Patents

Description

TECHNICAL FIELD The present invention relates to heat-generating fine particles composed of an incineration residue of vegetable biomass and a heating element using the heat-generating fine particles.

Conventionally, an electric heater using a nichrome wire, an infrared lamp, a burner using a flammable gas or flammable oil, etc. have been used as a heat source of a heating device. Each of these heat sources has advantages and disadvantages. For example, a burner is capable of rapid heating, but it increases carbon monoxide and carbon dioxide to pollute the air, and also has a fire, which is problematic in terms of environmental hygiene and safety. It was a thing.

A heating device using microwaves is known as a heating device using a heat source other than the above. For example, Patent Document 1 includes a heating element made of carbon powder as a main material and sintered into a honeycomb shape, an electromagnetic microwave generating means for irradiating the heating element with an electromagnetic microwave, and an air blower. A microwave heating device is disclosed.

JP, 6-231880, A

However, the heating element used in the heating device of Patent Document 1 is mainly composed of carbon powder, and when the carbon powder is oxidized, an oxide film is formed, and there is a concern that durability may be reduced.

Generally, the heating element is required to be capable of heating up to a high temperature in a short time, excellent in energy efficiency, and excellent in durability.

The present invention has been made in view of such a situation. That is, an object of the present invention is to provide a heat-generating fine particle capable of high-temperature heating and rapid heating, capable of being sustained for a long time, and capable of being repeatedly heated, and a heating element using the heat-generating fine particle. ..

The present inventors have made extensive studies on how to effectively use a large amount of plant biomass produced every year. When plant biomass such as rice husk is self-burned at high temperature for a long time, almost all organic combustibles are incinerated, leaving a residue. We focused on how to effectively use this residue.

The main component of plant biomass incineration residue is silicon dioxide. In addition, as a component other than silicon dioxide, it contains a trace amount of carbon element, metal element, and the like. The present inventors have found that when microwaves are applied to the incineration residue of plant biomass, surprisingly, it rapidly generates heat up to several hundreds of degrees Celsius. Further, it was found that the heat generation phenomenon occurs repeatedly every time microwave irradiation is repeated. The present invention has been made based on these findings. That is, the present invention has the following configurations.

(1) Exothermic fine particles composed of incineration residue of vegetable biomass, containing silicon dioxide as a main component, and containing carbon element, wherein the content of carbon element is 28% by mass or less, and microwave irradiation is performed. Exothermic fine particles characterized by being heated by.

(2) The heat-generating fine particles as described in (1) above, which contains a metal element.

(3) The heat-generating fine particles as described in (1) or (2) above, wherein the content of silicon dioxide is 60 to 96 mass %.

(4) A heating element using the heat-generating fine particles according to any one of (1) to (3) above.

The exothermic fine particles of the present invention and the heating element using the exothermic fine particles can be heated at high temperature and rapidly, can be sustained for a long time, and can be repeatedly heated.

Hereinafter, the present invention will be specifically described. The embodiments shown below are examples, and the present invention is not construed as being limited to these embodiments.

The heat-generating fine particles of the present embodiment consist of incineration residue of vegetable biomass, contain silicon dioxide as a main component, and contain carbon element. The contents of the heat-generating fine particles will be described below.

(Vegetable biomass)
The plant biomass of this embodiment contains silicon. Specific examples thereof include rice husk, rice straw, straw, wood, bark, bamboo, bagasse, coconut shell and the like. Among these, rice husks are preferable from the viewpoints of handling and availability. Below, an explanation will be given by taking rice husk, which is a typical plant biomass, as an example.

About 70 to 90% by mass of rice husk is an organic component mainly composed of cellulose, and the remaining about 10 to 30% by mass is an inorganic component. The inorganic component is mainly silicon dioxide (silica), and contains a trace amount of mineral components. Since silicon dioxide has the possibility of being developed for various uses, it was attempted to burn rice husks in air to almost completely remove organic combustible substances.

(Incineration residue)
In order to burn a large amount of rice husks continuously, a continuous combustion furnace was manufactured. When rice husks are continuously charged with air into a continuous combustion furnace, an external ignition source is required at the start of combustion, but after ignition, self-combustion starts continuous and steady combustion in air. did. The combustion temperature was in the range of 1000 to 1900° C. by appropriately adjusting the introduction speeds of rice husks and air. The average burning time was in the range of 5 to 15 hours.

The obtained incineration residue was fine particles containing silicon dioxide as a main component and containing carbon element, metal element and the like. Here, having silicon dioxide as a main component means that the content of silicon dioxide with respect to the fine particles exceeds 50 mass %. Although the content of silicon dioxide varies depending on the production area, variety, etc. of rice, which is a raw material for rice husks, it is substantially in the range of 60 to 96 mass %. Hereinafter, the fine particles of the incineration residue of the rice husk will be referred to as silica-based fine particles.

The present inventors conducted an experiment in which 10 g of silica-based fine particles were placed in a pottery container, a pottery lid was put on, and a microwave (2.45 GHz) of a 700 W microwave oven was irradiated for 1 minute. It was found that the system fine particles rapidly generate heat up to about 900°C. Further, it was found that the exothermic phenomenon repeatedly appears every time irradiation with microwaves is repeated. It was also found that the heat generation phenomenon is maintained by continuing irradiation with microwaves.

(Exothermic particles)
The obtained silica-based fine particles are heat-generating fine particles that generate heat when irradiated with microwaves. The silica-based fine particles can be rapidly heated to a high temperature of 300° C. or higher in a short time within 10 minutes by microwave irradiation. It can be maintained for several hours and can be repeatedly heated. Therefore, the silica-based fine particles are useful as heat-generating fine particles.

It is presumed that the silica-based fine particles show such a peculiar exothermic phenomenon because a small amount of components such as carbon element and metal element contained in the silica-based fine particles cause induction heating, dielectric heating, etc. due to microwave irradiation. .. It is also presumed that the carbon element and the metal element are present in the structure containing silicon dioxide as the main component in an appropriately finely dispersed state. Further, it is presumed that a part of the carbon element is combined with the silicon element to form silicon carbide.

It is preferable that the heat-generating fine particles of the present embodiment contain silicon dioxide as a main component, and the content of silicon dioxide is 60 to 96 mass %. Further, the content of silicon dioxide is more preferably 60 to 85% by mass, and further preferably 70 to 85% by mass from the viewpoint of heat generation performance.

The heat-generating fine particles need to contain a carbon element. 28 mass% or less is preferable, as for content of the carbon element in an exothermic fine particle, 3-28 mass% is more preferable, 5-25 mass% is further more preferable, 5-20 mass% is especially preferable.

The heat-generating fine particles preferably contain a metal element. The total content of the metal elements in the heat-generating fine particles is preferably 10% by mass or less, more preferably 1 to 7% by mass, further preferably 2 to 7% by mass, and particularly preferably 3 to 7% by mass. Here, the content of the metal element is a numerical value calculated as the total content of the metal oxides when the metal elements contained in the heat-generating fine particles are replaced with stable oxides. Examples of the metal element include potassium, magnesium, calcium, iron, aluminum, sodium, manganese, zinc, chromium, titanium and nickel. The existence form of these metals in the heat-generating fine particles may be a simple metal, an alloy, a metal oxide, or a composite oxide.

The heat-generating fine particles have an average particle size of about 10 to 300 μm. The shape of the heat-generating fine particles is not particularly limited. Further, silicon dioxide may be amorphous or crystalline and is not limited.

(Heating element)
In order to utilize the heat-generating fine particles as a heat-generating body utilizing its characteristics, it is preferable that the heat-generating fine particles have a form excellent in handleability. Specifically, a sintered body composed of heat-generating fine particles and ceramic particles or a molded body in which heat-generating fine particles are wrapped with ceramics can be formed.

The ceramic particles in the sintered body composed of the heat-generating fine particles and the ceramic particles are melted during sintering to bond the heat-generating fine particles together. The heat-generating fine particles and the ceramic particles are mixed and bonded to each other, so that the sintered body can have a stable form. Specific examples of the ceramic particles include soda lime glass, borosilicate glass, lead glass, and quartz glass. The type of ceramic particles, the average particle size, and the mixing ratio of the heat-generating fine particles and the ceramic particles can be appropriately adjusted as necessary.

Further, the exothermic fine particles are covered with and protected so that the components such as carbon element and metal element contained in the exothermic fine particles are not directly exposed to the outside by forming a sintered body made of ceramic particles. be able to. As a result, when the heat-generating fine particles are repeatedly heated and cooled by irradiation with microwaves, it is possible to prevent the carbon element and the metal element in the heat-generating fine particles from being oxidized and deteriorated by oxygen, and durability is improved. Can be improved.

A known method can be used as a method for producing a sintered body composed of heat-generating fine particles and ceramic particles. That is, after mixing the heat-generating fine particles and the ceramic particles, the mixture is put into a mold, the inside of the mold is heated to a temperature equal to or higher than the melting point of the ceramic particles, and the mixture is cooled. Let it be a unity. The shape of the sintered body can be freely designed.

In addition, the molded body in which the heat-generating fine particles are wrapped with ceramics can be handled without directly touching the heat-generating fine particles or installed in another device by holding the aggregate of heat-generating fine particles in the ceramic container. It becomes easy to fix. Further, by confining the heat-generating fine particles in the ceramic container, it is possible to suppress the heat-generating fine particles from directly contacting the atmosphere. As a result, it is possible to prevent the carbon element and the metal element in the heat-generating fine particles from being oxidized and deteriorated by oxygen when the heat generation and cooling are repeated by the irradiation of microwaves, and the durability can be improved. ..

The method for producing a ceramic molded body is not particularly limited, such as a ceramic integrally molded product, a combination of ceramic plates, a sintered body of ceramic particles, and a combination thereof. The type and shape of the ceramics forming the molded body are not particularly limited, and can be freely designed by appropriately selecting an appropriate type and shape as necessary.

(Microwave generation means)
Microwave generators such as magnetrons, klystrons, gyrotrons, and traveling wave tubes are used as microwave generation means for irradiating the heat-generating fine particles and the heating element with microwaves. Among these, magnetron is common. The frequency of microwaves is in the range of 0.3 to 30 GHz, but microwaves having a frequency of 2.45 GHz are usually used. By changing the oscillation output (W) of the microwave oscillator, the heat generation energy fluctuates, and the heat generation temperature of the heating element can be controlled.

The heat-generating fine particles and the heat-generating body of this embodiment are rapidly heated to a high temperature by being irradiated with microwaves. The surface temperature of the heating element incorporating the heat-generating fine particles can be adjusted within a wide range from several tens of degrees Celsius to about 1000° C. by changing the microwave oscillation output and the irradiation time.

The heating element using the heat-generating fine particles of the present embodiment can be used for various purposes such as heating, drying, temperature control, and reaction. Further, the heating element using the heat-generating fine particles of the present embodiment, to be used in various industrial applications in various technical fields such as food, chemistry, rubber, wood, castings, ceramics, paper, printing, painting, textiles, medical treatment, etc. You can

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

The continuous combustion furnace used for producing the exothermic fine particles of Examples and Comparative Examples has the following constitution.
It is a combustion furnace that continuously produces incineration residue by self-burning plant biomass in air under atmospheric pressure. A storage tank for storing plant biomass, a transport pipe for transporting the plant biomass by air, a blower for sending air into the transport pipe, and a combustion furnace for self-burning the plant biomass. An accumulation tank for accumulating the incineration residue, a dust collector for accumulating the incineration residue present in the exhaust gas after combustion, and an exhaust device for exhausting the exhaust gas after combustion. The temperature in the combustion furnace can be adjusted by changing the amount of plant biomass input per hour or the mixing ratio of plant biomass and air. The temperature in the combustion furnace can be measured by a thermocouple.

Using a continuous combustion furnace, the rice husks were burned at a burning temperature of about 1800° C. and a burning time of about 10 hours to burn out almost all the organic combustibles to obtain an incinerated residue of the rice husks. As rice husks, rice husks from Saitama Prefecture were used. The amount of the obtained incineration residue was about 20% by mass with respect to the rice husk as a raw material. The incineration residue was a black powder. When the incineration residue was analyzed, it was 77 mass% silicon dioxide and 8.5 mass% carbon element. In addition, the total content of the metal element when replaced with the metal oxide was 6.2 mass %. As the metal element, potassium, magnesium, calcium, iron, aluminum, sodium, manganese, zinc, etc. were contained. A wavelength dispersive X-ray fluorescence analyzer was used as an analyzer for metal elements.

An incineration residue of rice husks was obtained in the same manner as in Example 1 except that the burning temperature was set to about 1000°C. The amount of the obtained incineration residue was about 21% by mass based on the rice husk as a raw material. The incineration residue was a black powder. When the incineration residue was analyzed, it was 63 mass% silicon dioxide and 27 mass% carbon element. In addition, the total content of the metal element when replaced with the metal oxide was 4.2 mass %.

(Comparative Example 1)
An incineration residue of rice husks was obtained in the same manner as in Example 1 except that the burning time was changed to 15 hours. The amount of the obtained incineration residue was about 20% by mass with respect to the rice husk as a raw material. The incineration residue was a white powder. When the incineration residue was analyzed, it was 93 mass% silicon dioxide and 0 mass% carbon element. In addition, the total content of the metal element when replaced with the metal oxide was 3.1% by mass.

(Comparative example 2)
Rice husk incineration residue was obtained in the same manner as in Example 1 except that the burning temperature was set to about 1000° C. and the burning time was set to 15 hours. The amount of the obtained incineration residue was about 21% by mass based on the rice husk as a raw material. The incineration residue was a white powder. When the incineration residue was analyzed, it was 93 mass% silicon dioxide and 0 mass% carbon element. Further, the metal element was 3.3 mass% as the total content when replaced with the metal oxide.

(Comparative example 3)
A burning residue of rice husks was obtained in the same manner as in Example 1 except that the burning temperature was set to about 800° C., the burning time was set to 20 minutes, and the batch type burning was performed in the air. The amount of the obtained incineration residue was about 21% by mass based on the rice husk as a raw material. The incineration residue was a black powder. When the incineration residue was analyzed, it was 63 mass% of silicon dioxide and 30 mass% of carbon element. In addition, the total content of the metal element when replaced with the metal oxide was 6.3% by mass.

Approximately 10 g of each obtained incineration residue (silica-based fine particles) was enclosed in a spherical sintered body having a diameter of 15 cm made of soda-lime glass fine particles, which was further enclosed in a spherical ceramic container having a thickness of 2 mm. To be a heating element.

A microwave of 2.45 GHz was irradiated for about 25 minutes using a 700 W magnetron. The surface temperature of the heating element of Example 1 after irradiation was about 400°C. Similarly, the surface temperature of the heating element of Example 2 was about 360°C. The heating element of Comparative Example 1 hardly raised the temperature. The heating element of Comparative Example 2 hardly heated. The surface temperature of the heating element of Comparative Example 3 was about 250°C. Each temperature was measured using a thermocouple.

Next, using the heating element of Example 1, microwave irradiation was continued for about 5 hours, and after the irradiation was stopped, the heating element was allowed to stand for about 2 hours until the surface temperature of the heating element dropped to about 30° C., Then, the operation of continuing irradiation for about 5 hours was repeated for about 8 days. As a result, the behavior that the surface temperature of the heating element was heated to about 400° C. each time the irradiation was performed, the temperature was maintained during the irradiation, and the surface temperature decreased when the irradiation was stopped was repeatedly shown. ..

Claims (3)

Consisting of incineration residue of plant biomass,
A heat-generating fine particle containing silicon dioxide as a main component and containing a carbon element and a metal element ,
The content of carbon element is 3 to 28 % by mass,
The content of the metal element is 1 to 7% by mass,
Exothermic fine particles that generate heat when irradiated with microwaves. The heat-generating fine particles according to claim 1 , wherein the content of silicon dioxide is 60 to 96 mass %. A heating element comprising the heat-generating fine particles according to claim 1 or 2 .