KR20130008664A - Method for heat treating biomass used for combustion with high thermal efficiency and method for preparing combustable pellet using the biomass - Google Patents

Abstract

PURPOSE: A biomass heat-treating method for combustion for increasing a thermal efficiency and a pellet manufacture method for combustion using the heat-treated biomass are provided to maximize a combustion efficiency due to moisture absorbed by the pallet during storage as physical-chemical characteristics of the pallet changes to hydrophobicity when a raw material for the pallet is heat-treated. CONSTITUTION: A biomass heat-treating method for combustion for increasing a thermal efficiency comprises steps of: supplying a lignocelluloses-based biomass to a heat-treating apparatus, increasing a temperature of the biomass in the heat-treating apparatus to from 60 deg. C to 500 deg. C to remove moisture by sequentially drying the biomass, removing a volatile organic compound, and hydrophobitizing by heat-treating the biomass. In the heat-treating apparatus, an exhaust gas is ejected to a biomass supply unit. The ejected exhaust gas is heated to have a temperature of 300 deg. C to 500 deg. C and supplied to a biomass outlet unit of the heat-treating apparatus after passing through a heat exchanger. [Reference numerals] (AA) Drying exhaust gas and cleaning; (BB) Gas heating device; (CC) Heat exchanger; (DD) Drying; (EE) Evaporating volatile materials; (FF) Pyrolysis; (GG) Lignocelluloses biomass; (HH) Pyrolysis device; (II) Pyrolized biomass; (JJ) Pulverizer; (KK) Pellet manufacturing device; (LL) High-temperature gas of 300-500°C; (MM) Processed gas; (NN) Gas refining device using a filter and activated charcoal

Description

TECHNICAL AND HEAT TREATING BIOMASS USED FOR COMBUSTION WITH HIGH THERMAL EFFICIENCY AND METHOD FOR PREPARING COMBUSTABLE PELLET USING THE BIOMASS}

The present invention relates to a heat treatment method of biomass for improving thermal efficiency of combustion biomass and a method for producing combustion pellets using heat treated biomass, and more specifically, pyrolysis by heat treatment of natural materials such as wood. The present invention provides a combustion biomass and a method for producing the pellets having improved calorific value.

Conventionally, as a pellet using biomass of natural materials, wood raw materials, such as sawdust, have been pelletized and used, and these are used for combustion, such as a boiler. Pellet using such wood is known as a clean fuel with a low content of nitrogen, sulfur and ash. However, in general, the calorific value of such wood pellets is approximately 4200-500 kW / kg, which is relatively lower in thermal efficiency than coal or petroleum fuels. In addition, thermally unstable to form a concentrated tar (tar) in the gasifier (gasifier) such as a boiler to induce pipe blockage, thereby causing problems such as obstruct the fluid flow. Furthermore, these wood pellets have a high water content of about 10% even after drying, and there is a limit to using them as raw materials for combustion.

Despite these shortcomings, the cost of biomass pellets is only about 50% of the calorific value compared to fossil fuels, and due to the recent surge in the price of fossil fuels, interest is increasing rapidly.

On the other hand, since Korea's self-sufficiency rate of wood is only about 10%, there is a significant limitation in the supply and demand of raw materials for combustion pellets based on wood. Therefore, it is necessary to diversify the resources of the combustion pellets. In addition, it is necessary to meet the market demand by improving the combustion efficiency of the pellets obtained from these.

As a fuel using conventional wood, raw wood is pelleted without additional treatment, or carbonized wood at a temperature of about 900 ° C. to produce charcoal, and then used or pelletized as it is. However, when pelletizing without a separate treatment, there is a problem of low thermal efficiency due to moisture contained in the wood, and when pelletized after making charcoal, a lot of ash is generated and a high temperature of 900 ° C is required during manufacturing. Energy consumption is large, and the obtained pellets are easy to absorb moisture, which is not preferable.

The present inventors need to diversify the resources of the combustion pellets, and together with this, there is an urgent need for the development of a technology for improving the calorific value of fuels made of such natural materials, and the present invention is thermally decomposed by heat treatment of cellulose-based biomass. It is intended to improve the calorific value by modifying to have hydrophobicity.

Furthermore, the present invention provides a method for producing combustion pellets using the modified biomass.

The present invention comprises the steps of supplying the lignocellulosic biomass to the heat treatment apparatus and the temperature applied to the biomass in the heat treatment apparatus from 60 ℃ to 500 ℃ by sequentially drying from the biomass to remove moisture, A method of heat treating a biomass comprising volatilizing off a volatile organic compound and pyrolyzing to hydrophobize is provided.

At this time, the exhaust gas from the heat treatment apparatus is discharged to the biomass supply unit side, and the exhaust gas is heated to 300 to 500 ° C. and supplied to the biomass discharge unit side of the heat treatment apparatus by heating through the heat exchanger to reduce energy consumption for heat treatment. Can be reduced.

It provides a method for producing biomass pellets for combustion comprising the step of pulverizing the heat-treated biomass obtained by the method as described above.

According to the present invention, since the physical and chemical properties are converted into hydrophobic properties by modifying the raw material for pellets by heat treatment, it is possible to maximize the combustion efficiency due to moisture absorption of the pellets during storage.

In addition, in the reforming treatment of the biomass, the heat generated during the heat treatment may be circulated to supply the heat source required for the heat treatment, thereby reducing energy use during the heat treatment.

Furthermore, according to the present invention, biomass of various natural resources including wood can be utilized to manufacture pellets for combustion, thereby increasing domestic raw material self-sufficiency.

1 is a pyrolysis process chart of lignocellulosic biomass.
2 is a schematic diagram showing a pyrolysis process of lignocellulosic biomass in a vacuum heat treatment apparatus.
3 is a view schematically showing a structure and a process flow of a pyrolysis apparatus according to the present invention.

The present invention relates to a method for obtaining combustion pellets having excellent thermal efficiency by removing water and volatile organic compounds by thermally decomposing biomass, which is a raw material used to prepare combustion pellets having excellent thermal efficiency.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

1 is a view showing a pyrolysis process diagram of lignocellulosic biomass, FIG. 2 is a schematic diagram showing in detail the pyrolysis process of lignocellulosic biomass inside a vacuum pyrolysis apparatus during the pyrolysis process, and FIG. 3. Is a view schematically showing a structure and a process flow of a pyrolysis apparatus according to the present invention.

The present invention is to maximize the utilization of resources by providing a variety of natural materials as a raw material for combustion in addition to wood generally used as a raw material for combustion. The biomass that can be used in the present invention is not particularly limited as long as it is a lignocellulosic material. Specifically, agricultural by-products, including but not limited to wood, which are typically used for the production of combustion pellets, include, for example, rice straw, palm bark, palm fibers, coconut, stalks and roots, sorghum, soybeans, Red pepper leaves and fallen leaves.

Cellulose-based biomass such as wood is a clean fuel having a low content of nitrogen, sulfur and ash. However, it is thermally unstable to form concentrated tar in a gasifier, causing problems such as clogged pipes and resulting fluid flow obstruction. In particular, such a biomass has a high water content of about 10% even after drying, and has a low energy density of about 18 MJ / kg (= 4,300 kW / kg).

The present inventors have recognized this problem, and have studied and found that in order to solve the problem, it is required to lower the ratio of O / C constituting wood, and the most effective method for this is pyrolysis treatment. In the method of the present invention, the lignocellulosic biomass is pulverized to a predetermined size, and then supplied to a pyrolysis device through a feeder such as a screw and pyrolyzed to obtain a biomass having improved thermal efficiency by water removal and hydrophobization treatment. .

Combustion biomass pellet production method of the present invention by supplying the lignocellulosic-containing biomass to the heat treatment device to continuously dry the biomass, remove the volatile organic compounds from the dried biomass, and thermally decomposes the biomass Hydrophobizing the biomass. Furthermore, the heat treatment apparatus is controlled to increase in the range of 60 to 500 ° C.

The lignocellulosic biomass used as a raw material for pellet production in the present invention generally includes cellulose, hemicellulose, and lignin, and each of the components included in the lignocellulosic biomass raw materials in the vacuum pyrolysis apparatus is different for heat. Show behavior First, since cellulose has a crystal structure and an amorphous structure at the same time, the cellulose is dried at about 200 ° C., and in the range of 200-300 ° C., depolymerization and recondensation of cellulose partially occurs and at the same time volatile organic The compound is removed. On the other hand, hemicellulose is very reactive unlike the cellulose because it is composed of an amorphous region, it is easily dried even at a temperature below 150 ℃, depolymerization and condensation process at 150-200 ℃, limited level in the range of 200-250 ℃ As a result, the removal and carbonization of volatile organic compounds occurs, and the complete removal of volatile organic compounds occurs with complete carbonization above 250 ° C. In addition, lignin has a glass transition and softening phenomenon simultaneously at a temperature of 150 ° C. or lower, depolymerization and recondensation occur in a range of 150-240 ° C., and volatile organic compounds are removed together with carbonization at higher temperatures.

In addition, the cellulose-based biomass is a natural polymer and contains a large amount of oxygen and hydrogen. For example, timber imported as raw materials typically has a water content of 20-35% by weight. When the wood having such a water content is pelletized without a separate treatment as in the prior art and used as a combustion source, the calorific value is about 3,700 mW / kg, which is lower than that of fossil fuel. This is because the oxygen or hydrogen contained in the biomass easily hydrogen bonds with the moisture in the atmosphere, so the thermal efficiency loss is relatively large compared to carbon.

Accordingly, such oxygen and hydrogen are preferably removed as much as possible, and thus the present invention first includes drying the biomass raw material. 1 and 2, the lignocellulosic biomass is pulverized to a predetermined size and then supplied to a pyrolysis device through a supply device such as a screw. The pyrolysis device has a drying unit. Oxygen and hydrogen contained in the cellulose-based biomass are removed in the drying unit. Drying the biomass may be performed at a temperature in the range of 60 to 200 ℃.

The biomass dried in the drying unit includes removing volatile organic compounds such as acetic acid, furan, methane, carbon dioxide, and carbon monoxide. Water vapor and volatile organic compounds contain significant amounts of oxygen that can easily react with water and must be removed in the early stages of pyrolysis. Such removal of the volatile organic compounds is carried out at a temperature in the range of 200 to 300 ℃. At this time, the remaining moisture is removed together with the removal of the volatile organic compound without being removed in the drying process.

Furthermore, the process of the present invention includes the step of pyrolysis. The thermal decomposition means thermal decomposition of the biomass in the absence of oxygen, and combustion and gasification always occur during the complete or partial oxidation of the biomass. During pyrolysis, all organic compounds such as methane are released together with hydrogen, water vapor and the like, and a product with a large amount of carbon remaining is produced. In the case of wood, pyrolysis starts at 200-300 ° C. Among the components constituting lignocellulosic, cellulose is usually degraded at 305-375 ° C, hemicellulose is degraded at 225-325 ° C, and lignin is gradually degraded in the temperature range of 250-500 ° C.

Thus, the heat treatment apparatus used in the method of the present invention is controlled to increase in the range from 60 to 500 ° C. in the direction from the biomass supply to the discharge. The temperature range may be heated by heating the temperature in the heat treatment apparatus at a predetermined rate, and may be configured to increase the temperature along the traveling direction in the apparatus in which the biomass proceeds continuously. The configuration of such a device will be readily understood by those skilled in the art.

The heat treatment is preferably carried out under the oxygen-free state, that is, under atmospheric pressure of an inert atmosphere or lower than the lignocellulosic raw material for combustion pellets.

It is preferable from the viewpoint of moisture drying and removal of volatile organic compounds that the biomass stays in the pyrolysis apparatus for 15 to 90 minutes at a rate of temperature increase of 5 to 50 ° C./min. Further, among these, the pyrolysis time of the lignocellulosic biomass in the pyrolysis device is preferably performed for 3 to 30 minutes at a temperature of 200 to 500 ° C. When the temperature is less than the above range, thermal decomposition is not sufficient, so that hydrophobization of the biomass is not sufficient, which is easy to absorb moisture during storage or distribution, which may cause thermal efficiency deterioration. Further, at the pyrolysis temperature of the biomass, some carbonization of cellulose, hemicellulose, or lignin occurs, but if the pyrolysis is over too long for a long time, oxidation occurs over an acceptable range and excessive carbonization of the biomass occurs. Bar is not desirable. Therefore, it is preferable to satisfy the thermal decomposition conditions.

This heat treatment removes the water and volatile organic compounds contained in the biomass of lignocellulosic raw materials, and partially decomposes the cellulose, hemicellulose, and lignin into black solids. The resulting pyrolyzed biomass removes much of the water and volatile organic compounds, which account for about 20% of the weight of the biomass before it is introduced into the heat treatment apparatus, and furthermore, the hydroxyl group (-OH) contained in cellulose or hemicellulose is pyrolyzed. The biomass obtained is hydrophobic because it is destroyed in the process.

Furthermore, the lignocellulosic biomass undergoes a chemical change process with a slight loss of mass, whereby it is converted into a nonpolar, unsaturated structure. The lignocellulosic raw materials modified by the present invention have a calorific value about twice that of the calorific value compared to pellets using wood which has not undergone a general heat treatment.

Therefore, to obtain the same calorific value using general wood pellets requires more than twice the amount of logistics costs and storage space as compared to the case of using the pyrolyzed pellets according to the present invention. Therefore, the pellet of the present invention will be more effective in terms of logistics costs such as transportation and storage. This results in a significantly improved calorific value than ordinary pellets, which reduces the storage space required for pellets to produce the same calorific value, even when transporting the same amount or even less. There is an even more favorable aspect in terms of logistics costs since equal or greater calorific value can be obtained.

On the other hand, it is possible to recycle the gas, such as water and volatile organic compounds removed in the heat treatment apparatus of the present invention can be supplied to the energy source used in the pyrolysis apparatus of the present invention. Before supplying to an energy source, a drying process for removing water molecules contained in the gases generated by the heat treatment apparatus and a washing process for removing fine particles, hydrocarbons, and other dissolved substances contained in the gas are performed. The washed gas can be concentrated and heated to a temperature of 300-500 ° C. and then passed through a heat exchanger to be used as an energy source for the pyrolysis device.

By re-injecting the hot gases obtained by such a step into the heat treatment apparatus of the present invention, the lignocellulosic material may be dried to remove moisture, volatile organic compounds, and thermal decomposition. For this reason, since the heat energy entering the heat treatment apparatus can be used by recycling the gas generated from the pyrolysis apparatus except for the initial operation, it is possible to reduce the use of energy required to heat the biomass.

The heat-treated biomass obtained after the heat treatment as described above is pulverized into fine particles using a pulverizer such as a pulverizer, and then sent to a pellet forming apparatus to produce lignocellulosic pellets having high energy efficiency. The pellet manufacturing method may be used as long as it is a method generally used in the technical field to which the present invention belongs, and the method is obvious in the technical field of the present invention, and thus will not be described in detail herein.

However, since the biomass that is heat-treated is in a high temperature state, it may be manufactured into pellets or briquettes without additional treatment such as using an adhesive when pulverized as it is.

The heat treatment apparatus used for heat treatment of the biomass of the present invention is not particularly limited, but may have a cylindrical or polygonal structure, and the material may be made of mild steel having excellent thermal conductivity.

The heat treatment apparatus may include a screw to continuously heat the biomass. While mixing and uniformly supplying and transporting the biomass, which is a combustion raw material, by the screw at a constant speed, the temperature inside the heat treatment apparatus is gradually increased according to the moving direction, thereby drying step by step, removing volatilization and pyrolysis of volatile organic compounds. Can make it happen. At this time, the left and right sides of the pyrolysis apparatus are connected to the biomass input unit and the biomass discharge unit by a closed tube, and the length, the inner diameter and the biomass input speed of the pyrolysis apparatus can be adjusted according to the capacity of the cylinder. It is not limited.

In addition, the heat treatment apparatus may be charged with a predetermined temperature for a predetermined time after charging the biomass into the heat treatment apparatus without a screw, to perform drying, volatilization removal of volatile organic compounds and pyrolysis.

Hereinafter, the present invention will be described more specifically with reference to examples. However, it should be noted that the present invention is not limited only to the following examples.

Example

Example  One

Water content (%), calorific value (㎉ / ㎏), ash content (%), pellet strength, fine dust generation, hygroscopic properties and degree of biological degradation (decay) for oak wood, wood pellets, palm bark and rice straw It is shown in Table 1 after measurement or observation.

As shown in FIG. 1 illustrating a pyrolysis process of biomass, as a lignocellulosic biomass, wood, palm bark and rice straw each having a predetermined size are supplied to a silo, and 50 kg of the biomass is 10 m long and 10 mm in diameter through a screw. It was supplied to a cylindrical heat treatment apparatus of 750 mm mild steel. Heat was applied to the heat treatment apparatus to raise the internal temperature to 180 ° C., and then maintained for 15 minutes to dry. Then, the internal temperature of the heat treatment apparatus was raised to 250 ° C. and maintained for 20 minutes. Next, after gradually raising to 400 ° C., the heat treatment was completed by maintaining for 15 minutes to obtain a black biomass.

The obtained heat treated biomass was discharged from the cylinder, and then fed to a grinder to grind the biomass. The temperature of the pulverized biomass was about 120 ° C., and pellets were prepared through a pellet manufacturing apparatus at such a high temperature. No separate binder was used.

The strength of the pellets was determined by whether the pellets passed through the pellet forming machine were visually evaluated in the form of a cigarette filter, and was determined as the state of generating fine dust in the pellet production space. The criterion of biological deterioration was determined by contamination by microorganisms during storage.

Water content (%), calorific value (㎉ / ㎏), ash content (%), pellet strength, fine dust generation, hygroscopic properties and biological deterioration (corrosion) of heat-treated wood and pellets from each biomass. It is shown in Table 1 after measuring or observing.

Biomass before heat treatment Pyrolyzed biomass wood wood
Pellet Palm shell Straw wood Wood pellets Palm bark pellets Straw
Pellet Moisture content (%) 20-35 10 9.43 8.01 2-5 1-5 4.3 4.2 Calorific value
(Kg / kg) 2,200-
3,703 3,810-
4,700 5,012 3,670 4,750-
4,890 4,820-
5,420 6,280 4,515 Ashes (%) 0.4 0.3 1.87 11.9 0.3 0.2 0.9 9.53 Carbon content (%) 46.94 45.81 46.51 41.2 64.37 66.5 60.87 57.2 Pellet strength - Good - - - Very good Very good Good fine dust part
Occur part
Occur part
Occur part
Occur much
Occur Rarely Rarely Rarely Hygroscopic property plethora plethora Limited plethora Hydrophobic Hydrophobic Hydrophobic Hydrophobic Biological
Deterioration Occur Occur Limited
Occur Occur Not occurring Not occurring Not occurring Not occurring

The lignocellulosic biomass that passed through the pyrolysis device exhibited the characteristics shown in Table 1. The moisture content of wood imported as raw materials is 20-35%, which has a very high water content compared to other lignocellulosic biomass. Therefore, when used as a combustion source, the calorific value is very low, less than about 3,700 kcal. . On the other hand, in the case of wood pellets, the moisture content is about 10%, which is very low compared to the moisture content of the raw material, and because it is manufactured in a densified form, it was confirmed that the calorific value is significantly improved compared to the raw material at the level of 3,800-4,700 kcal.

However, when pyrolyzing wood, the calorific value is 4,700-4,900 kcal / kg, which is a significant improvement over wood pellets. Furthermore, in the case of pellets manufactured using such pyrolyzed wood, the calorific value is 4,800-5,400 kcal / kg. Increasingly, it was confirmed that the pyrolysis treatment contributed significantly to the calorific value of the lignocellulosic pellets.

This same trend was observed in palm bark and rice straw. In the case of the palm shell, the pyrolysis according to the present invention increased the calorific value from 5,000kcal / kg to 6,280kcal / kg, and thus it was confirmed that the palm shell had a value close to the calorific value of 6,978 kcal / kg. Furthermore, in the case of rice straw, it could be confirmed that it has an improved calorific value than before pyrolysis. However, ash content was somewhat higher than wood or palm bark.

From the above results, it can be seen that the water content of the pyrolyzed lignocellulosic biomass is significantly lower than before pyrolysis. The moisture content of palm bark and rice straw before pyrolysis was about 8-9.5%, especially about 20% when it was brought into raw materials. If the initial moisture content is excessive, it is a very big obstacle to obtaining the optimum combustion efficiency, and it causes a biological deterioration factor in the storage of raw materials. However, when the pyrolysis treatment (torrefaction) according to the present invention changes the hydrophobic cellulose hemicellulose and lignin components of the lignocellulosic biomass, the water content of the fuel is drastically lowered to 5% or less, thereby the bio Biological deterioration can be prevented with an increase in the calorific value of the mass raw material. In addition, due to the low water content of the pellets there is a side advantage that can also reduce the cost of pellet transport.

Example  2

In Example 1, except that the heat supply was cut off after heat was applied during the initial heat treatment of wood, the wood was thermally decomposed by supplying wood to the heat treatment apparatus in the same manner as in Example 1.

At this time, by collecting the hot gas (H ₂ O, CO ₂ , H _2, etc.) discharged by the heat treatment of the biomass in the heat treatment apparatus, drying and washing the collected, condensed neutral gas through a condenser, It was heated to a temperature of about 450 ° C. through the summer chamber, which was circulated to the heat treatment apparatus. The circulated gas was supplied to the side of the biomass outlet of the heat treatment apparatus. The supplied hot gas was moved in a direction opposite to the direction of biomass movement in the heat treatment apparatus and discharged through the upper end of the biomass inlet side. At this time, the temperature of the gas at the gas outlet side was measured, and it was confirmed that the temperature was about 180 ° C.

As described above, the same items as in Example 1 were observed to determine whether or not the thermal decomposition of the wood obtained by using the exhaust gas without supplying additional heat as described above. there was.

Claims (3)

Supplying lignocellulosic biomass to the heat treatment apparatus
Increasing the temperature applied to the biomass in the heat treatment apparatus from 60 ° C. to 500 ° C. to sequentially dry the biomass to remove water, and to volatilize and remove volatile organic compounds, and pyrolyze to hydrophobize. Method of heat treating biomass.
The method of claim 1, wherein the exhaust gas from the heat treatment apparatus is discharged to the biomass supply unit side, and the exhaust gas is heated to 300 to 500 ° C and supplied to the biomass discharge unit side of the heat treatment apparatus through a heat exchanger. Method of heat treating the biomass.
Method for producing biomass pellets for combustion, comprising the step of pulverizing the heat-treated biomass obtained in claim 1 or 2.

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