JP2011219505A - Method for combusting chaff, method for gasifying chaff, method for converting chaff to fuel and chaff fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably combust chaff by preventing the aggregation of bed material particles in a fluidized bed in a fluidized bed furnace, a circulating fluidized bed furnace or the like.SOLUTION: In a method for combusting chaff which combusts chaff in a fluidized bed 42 in a fluidized bed furnace 4, at least one of limestone, slaked lime and dolomite is added to the chaff, as a hardly melting agent which raises the melting temperature of a melt formed from ash of the chaff, a mixture of the chaff and hardly melting agent is molded into pellets, and the pellets are combusted in the fluidized bed.

Description

  INDUSTRIAL APPLICABILITY The present invention relates to a rice husk combustion method, a rice husk gasification method, and a rice husk that are suitable for use as bioenergy by burning or gasifying the rice husk in a fluidized bed in which a fluid medium is flowed with an oxidizing gas. The present invention relates to a fuel conversion method and rice husk fuel.

  Attention has been focused on the effective use of biomass energy as a measure to prevent global warming. Among biomass energy, biomass energy derived from plants can effectively use carbon resources converted from carbon dioxide by photosynthesis in the process of plant growth. It has a so-called carbon neutral property.

  In general, organic resources derived from living organisms (plants) that are not fossil resources are called biomass, and biomass energy is obtained from this. Since biomass is an organic substance, carbon dioxide is emitted when it is burned. However, the carbon produced from this is derived from carbon dioxide that the biomass absorbed from the atmosphere by photosynthesis during the growth process. In other words, biomass is a resource that can be continuously regenerated because living organisms use solar energy to produce water and carbon dioxide. Therefore, even if biomass is used as a fuel, it can be considered that the amount of carbon dioxide in the atmosphere is not increased as a whole, and this property is called carbon neutral.

  Examples of agricultural biomass that can be used for such biomass energy include rice husk, rice straw, wheat straw, sugarcane straw, rice straw, and vegetation.

  In recent years, the role of biomass energy has been emphasized in relation to the global warming issue. As a technology for energy recovery and conversion from biomass, waste heat is recovered from combustion gas when biomass is burned to obtain steam to generate electricity, or biomass is pyrolyzed to produce gas fuel and burn this Development of power generation is under consideration.

  As a specific technique related to such biomass energy, a method of gasifying biomass particles such as wood fragments in a fluidized bed in which a particulate fluidized medium (hereinafter also referred to as fluidized medium particles) is fluidized with an oxidizing gas. However, it is disclosed in Patent Document 1, for example.

JP 2004-149556 A

  The use of rice and wheat husks as biomass for biomass energy is being studied. When such rice husk is burned in a fluidized bed furnace or a circulating fluidized bed furnace as described in Patent Document 1, there is a problem that the following phenomenon may occur.

  When the rice husk is burned in a fluidized bed in which fluidized medium particles are flowed, such as a fluidized bed furnace or a circulating fluidized bed furnace, the fluidized medium particles are fused, so the fluidized medium particles are agglomerated (agglomeration). As a result, the fluid state cannot be maintained.

  Even in the process of gasification by partially burning or thermally decomposing rice husks in a fluidized bed furnace or circulating fluidized bed furnace, if the furnace temperature exceeds 800 ° C, the fluidized medium particles are similarly fused and the fluidized state can be maintained. Disappear. In such a case, in order to maintain the fluid state, it is necessary to frequently perform the operation of exchanging the fluid medium particles by extracting a large amount of fluid medium particles and replenishing the new fluid medium particles. In other words, there is a problem that it cannot be operated, and a large amount of cost is required for the purchase of new fluid medium particles and the disposal of the extracted fluid medium particles.

  In particular, when inexpensive and general-purpose silica sand is used as the fluid medium particles, fusion occurs in a short time, which makes the operation more difficult, which is a particular problem.

  The present invention has been made in view of such circumstances, and in a fluidized bed such as a fluidized bed furnace or a circulating fluidized bed furnace, suppresses aggregation of fluidized medium particles and stably burns or gasifies the rice husk. It is an object of the present invention to provide a rice husk combustion method, rice husk gasification method, rice husk fuelization method, and rice husk fuel.

  The present invention relates to a method for burning rice husks in a fluidized bed, wherein at least one of limestone, slaked lime and dolomite and / or at least one of quick lime, magnesia and alumina is produced from rice husk ash. It is added as a fusogenic agent that raises the melting temperature of the melt to be melted, a pellet is formed by molding a mixture of the rice husk and the fusogenic agent, and the pellet is burned in the fluidized bed, thereby solving the above problem It is a thing.

  The present invention is also a gasification method for rice husk in a fluidized bed, wherein the rice husk is provided with at least one of limestone, slaked lime and dolomite, and / or at least one of quick lime, magnesia and alumina. It is added as a fusogenic agent that raises the melting temperature of the melt produced from ash, and a pellet is formed by molding a mixture of the rice husk and the fusogenic agent, and the pellet is partially oxidized or pyrolyzed in the fluidized bed. Thus, the above-mentioned problem is solved in the same manner.

  The present invention also relates to a method for fuelizing rice husk that is combusted or gasified in a fluidized bed, wherein the rice husk includes at least one of limestone, slaked lime, and dolomite, and / or at least one of quick lime, magnesia, and alumina. Is added as a fusogenic agent that raises the melting temperature of the melt produced from the ash content of rice husk, a mixture of the rice husk and the fusogenic agent is molded to produce pellets, and the pellets are burned in the fluidized bed Alternatively, the above problem can be solved in the same manner by using a gas to be gasified.

  The present invention is also a rice husk fuel burned or gasified in a fluidized bed, wherein the rice husk contains at least one of limestone, slaked lime and dolomite, and / or at least one of quick lime, magnesia and alumina, Added as a fusogenic agent that raises the melting temperature of the melt generated from rice ash ash, molding a mixture of the chaff and fusogenic agent to produce pellets, and burning or gasifying the pellets in the fluidized bed The above-mentioned problem is solved in the same manner by using the fuel to be used.

  The present invention also provides a method for adding at least one of the limestone, slaked lime, and dolomite as a fusogenic agent in any of the rice husk combustion method, rice husk gasification method, rice husk fueling method, and rice husk fuel. Further, 2 to 20% by weight may be added to the rice husk weight.

  In the following, the contents and results of intensive studies by the present inventors in order to solve the above problems will be described in detail.

<Investigation of the cause of fluid media fusion aggregation>
The rice husk contains ash content of 10 wt% or more in the dry weight which becomes a residue when burned, and 70 wt% or more of the ash content is SiO ₂ . The present inventors have examined in detail the behavior of the particulate fluidized medium when such high SiO ₂ content biomass is burned in a fluidized bed furnace or a circulating fluidized bed furnace.

SiO ₂ contained in rice husk is also a main component of silica sand known as a general-purpose fluid medium, and itself does not cause fusion of fluid medium particles.

  Therefore, the present inventors have found that the following is a detailed study of the mechanism by which rice husks cause fusion to the fluid medium.

In the ash that is the combustion residue of rice husk, a slight amount of alkali metal (Na, K) of about 0.3 to 2 wt% is contained. Therefore, when the rice husk burns, SiO ₂ and the alkali metal are mixed in a high temperature field in the flame to form a melt having a melting point lower than that of SiO ₂ .

The melt produced from such ash content decreases the proportion of the melt state while producing precipitates in the process of cooling, but depending on the composition of the melt, the melt state May remain. In particular, when the SiO ₂ content in the ash is high, such as rice husk, it is easy to form a melt that leaves the melt even in a temperature atmosphere of about 800 ° C. Here, 800 ° C. is a temperature suitable for a fluidized bed (furnace) temperature capable of good combustion or gasification without leaving unburned matter.

  If the temperature in the furnace is sufficiently lower than 800 ° C., the melt produced from the ash content of the rice husk emitted from the flame immediately becomes solid and scatters as fly ash. However, if the temperature in the furnace is about 800 ° C. or higher, the melt produced from the ash content of the rice husks exists as a liquid, and therefore adheres to the fluid medium of the fluidized bed in the furnace. When the fluid medium particles are fused together as a binding substance, the fluid medium particles are aggregated. When the aggregated mass of the fluid medium particles becomes large, the fluid medium becomes non-flowable and good combustion can be continued. Disappear.

  If the rice husk is put into a fluidized bed in which the fluid medium is not flowing well, the rice husk cannot be evenly dispersed in the fluid medium, so that it burns in a partially collected state. As a result, the heat generating region is unevenly distributed in the furnace, and a hot spot that is a local high-temperature portion is formed. Therefore, generation of harmful gases such as NOx and fire resistance in the furnace Problems such as damage to objects and shortened service life occur.

In particular, when the fluid medium particles use silica sand whose main component is SiO ₂ , the composition of the silica sand is similar to a melt produced from rice husk ash (hereinafter also simply referred to as ash melt). Since the melt is more easily adhered to the fluid medium particles more easily, the above-mentioned problems are more likely to occur than when a fluid medium other than silica sand is used.

<Adjusting the melting point of the melt of rice husk ash>
The melting point of the rice husk ash as described above can be increased by adjusting the composition of the melt in order to suppress the occurrence of fusion and aggregation between the fluid medium particles. Focused on. That is, if the melting point of the melt can be adjusted to be higher than 800 ° C. suitable for the temperature in the fluidized bed or circulating fluidized bed furnace (fluidized bed temperature), the ash emitted from the flame when the rice husk burns Since the molten product is a solidified solid at 800 ° C. in the furnace, it will be scattered as fly ash and theoretically cannot exist in the molten liquid state. It is possible to prevent (suppress) the fusion of each other.

  Therefore, the present inventors have intensively studied a substance to be added to rice husks, which is suitable for increasing the melting point of the melt and reducing the ratio of the melt state in the 800 ° C. temperature atmosphere. It has been discovered. This finding will be described in detail below.

1) Combustion method of rice husk according to claim 1 At least one of limestone, slaked lime, and dolomite is added to the rice husk as a fusogenic agent and molded to form pellets, which are burned in a fluidized bed.

By adding at least one of limestone: CaCO ₃ , slaked lime: Ca (OH) ₂ and dolomite: (CaCO ₃ ) _m (MgCO ₃ ) _n to the rice husk, the ash melt produced by burning the rice husk These components dissolve and raise the melting point of the melt, and the melt is solidified in an atmosphere at a temperature of 800 ° C. to form a solid, or the ratio of the melt state is reduced to fuse the fluid medium particles. This can be suppressed.

As the fusogenic agent, in addition to limestone, slaked lime and dolomite, if it contains a substance having an action of increasing the melting point of the melt when mixed with SiO ₂ , the same effect can be obtained by adding it. Without limitation, for example, an inorganic substance (fusogenic agent) containing at least one of quick lime: CaO, magnesia: MgO, and alumina: Al ₂ O ₃ may be used.

  The above-mentioned additive (at least one of quick lime, magnesia, and alumina) is added to the rice husk as a fusogenic agent, formed into pellets, and combusted or gasified in a fluidized bed. Fusion and aggregation can be suppressed, and the fluidized bed can be stably flowed. When the rice husk and the above-mentioned additive are separately supplied to the fluidized bed and burned, the additive may not be sufficiently mixed with the ash melt of the rice husk. Can be reliably mixed with the additive.

2) In the rice husk combustion method of 1) above, at least one of limestone, slaked lime and dolomite is added in an amount of 2 to 20% by weight based on the rice husk weight, that is, 2 to 20 of the latter is added to the rice husk 100 in units of weight. It is preferable.

  If it is less than 2% by weight, the effect of increasing the melting point of the melt is not sufficient, and even if added in an amount of more than 20% by weight, there is no difference in the effect of increasing the melting point of the melt. It is not preferable because the amount is increased excessively.

Since the SiO ₂ content in the rice husk varies depending on the rice husk actually used, and the composition of limestone, slaked lime, and dolomite also varies depending on what is actually used. More preferably, the components contained therein are analyzed, and the added amount is determined. It is desirable to decide. The amount of each component can be measured by ICP method, fluorescent X-ray analysis method or the like, but is not limited thereto.

When adding an inorganic substance containing at least one of quick lime, magnesia, and alumina, 20 to 20 of at least one of quick lime, magnesia, and alumina with respect to the SiO ₂ weight contained in the mixture of rice husk and the added inorganic substance. It is preferable to add 60% by weight.

  If the amount is less than 20% by weight, the effect of increasing the melting point of the melt is not sufficient, and even if added in an amount of more than 60% by weight, there is no difference in the effect of increasing the melting point of the melt. It is not preferable because the amount is increased excessively.

  The explanation of 1) and 2) related to the combustion method of rice husk according to claim 1 described in detail above includes the gasification method of rice husk according to claim 3, the method of fuelizing rice husk according to claim 5, and claim 7. Since the same is true for the rice husk fuel according to the above, detailed description is omitted.

  According to the present invention, at least one of limestone, slaked lime, and dolomite and / or at least one of quicklime, magnesia, and alumina is added to the rice husk, which is a high silica-containing biomass, and pelletized. Therefore, even if it is put into a fluidized bed furnace or a circulating fluidized bed furnace and burned or gasified in the fluidized medium forming the fluidized bed, the fluidized medium particles can be prevented from fusing and agglomerating, and the operation can be continued stably. It becomes possible.

The block diagram which shows the outline | summary of the process of one Embodiment of this invention. Schematic diagram showing the outline of the device used in one embodiment

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

<Method of burning rice husk>
About the method for burning rice husks according to one embodiment of the present invention, an outline of steps until the rice husks are burned is shown in a block diagram in FIG. 1 together with devices used in the respective steps.

  The rice husk is introduced into the mixer 1 and mixed after at least one fusogenic agent of limestone, slaked lime and dolomite is added. The obtained mixture is introduced into the granulation molding machine 2 and molded into rice husk pellets of a predetermined size, and then supplied and charged into the fluidized bed furnace 4 by the feeder 3. The rice husks produced from the mixture charged as pellets are burned in a fluidized bed and used as bioenergy.

  Hereinafter, the present embodiment will be described more specifically.

<Manufacture of rice husk pellets>
-The additive to be mixed with the rice husk is preferably in a powder form so that it can be sufficiently mixed with the rice husk and can be easily molded into a pellet. The surface area / weight ratio (surface area per unit weight) is preferably large, and in order to be well dispersed and obtain an effect in a small amount, the diameter is 0.3 mm or less, more desirably 0.1 mm or less. It is good to use as a powder.

  The rice husk is well mixed with the powdered additive added by the mixer 1 and is put into the granulation molding machine 2 of a disk die type or a ring die type. These types of granulation molding machines, which mix the material (mixture) while crushing in the equipment, and then mold it into a pellet by pushing it into a hole in a thick metal plate. It is excellent in the effect of dispersing things well.

  The granulation molding machine is not limited to a disk die type or a ring die type, and it is also effective to ground and knead the mixture once before feeding the mixture into the granulation molding machine.

  In addition, a binder such as starch may be further added to the mixture in order to improve moldability during granulation molding.

  -As for the size of the pellet, the smaller the pellet diameter, the more the rice husk is ground and the added additive powder is well dispersed. The pellet preferably has a diameter (φ) of about 5 to 30 mm and a length (t) / diameter ratio of about 1 to 2, but is not limited thereto.

  -By forming rice husks into pellets, the bulk density increases, so that the rice husks can be transported more easily and transport efficiency can be improved. The pellets (made as described above) are put into a fluidized bed furnace or a circulating fluidized bed furnace or the like by a feeder 3 such as a screw feeder, and combustion or gasification is performed.

  Hereinafter, the embodiment will be specifically described by way of examples.

[Example]
In a fluidized bed furnace 4 schematically shown in FIG. 2 together with the pellet feeder 3, pellets formed by adding additives to rice husks were put into a combustion experiment.

  The pellet feeder 3 is rotated by a hopper 31 for storing charged pellets (not shown) and a motor 32 and feeds pellets introduced from the lower end of the hopper 31 to the upper end portion of the fluidized bed furnace 4. And a screw conveyor 33.

  The fluidized bed furnace 4 includes a cylindrical part 41 constituting a furnace body, a breathable dispersion plate 43 constituting a bottom part of the fluidized bed 42 inside the cylindrical part 41, and the fluidized bed 42 for heating the fluidized bed 42. And an electric heater 44 disposed on the outer periphery of the cylindrical portion 41.

  In the fluidized bed furnace 4, air (oxidizing gas) adjusted by a flow meter 46 from an air cylinder 45 continuous at the lower end is introduced from below the dispersion plate 43 to flow the fluidized medium particles. Thereby, the fluidized bed 42 is formed.

  In the experiment, a fluidized bed furnace 4 in which the cylindrical portion 41 is formed of a stainless steel pipe having an inner diameter of 50 mm is used, and 200 g of silica sand is put as a fluidized medium on a dispersion plate 43 installed in the stainless steel pipe 41. Then, air was supplied from below the dispersion plate 43 and fluidized to form a fluidized bed 42. Heating was performed from the outside of the stainless steel tube 41 with the electric heater 44, and the internal temperature (fluidized bed temperature) was maintained at 800 ° C.

  Rice husk pellets were continuously charged into the fluidized bed 42 to burn or gasify, and the flow state of silica sand was observed. The relationship between the input amount of pellets and the amount of supplied air in which the air ratio, which is the ratio of the actual amount of air supplied to the theoretical amount of air required for the combustion of the pellets, is greater than 1, is a combustion state, and the air ratio is In a relationship smaller than 1, the pellet is partially oxidized and thermally decomposed to be in a gasified state.

The rice husk used here had an ash content of 11 wt%, and the SiO ₂ content in the ash content was 75 wt%.

[Example 1]
5 wt% dolomite powder was mixed with respect to the rice husk weight, and molded into pellets of φ5 mm × t5 mm with a ring die type granulation molding machine.

  When this was put into a fluidized bed furnace and burned, no abnormal flow occurred and stable combustion could be continued.

[Example 2]
2 wt% of slaked lime powder was mixed with respect to the rice husk weight, and molded into a pellet of φ5 mm × t5 mm with a ring die type granulator.

  When this was put into a fluidized bed furnace and burned, no abnormal flow occurred and stable combustion could be continued.

  In Examples 1 and 2, gasification was performed by increasing the input amount of pellets, but no flow abnormality occurred.

[Comparative Example 1]
Only rice husks were molded into pellets of φ5 mm × t5 mm with a ring die granulator.

  When this was put into a fluidized bed furnace, when the accumulated amount of pellets became 1.8 to 2.2 times the weight of silica sand, a flow abnormality occurred and the operation could not be continued. In other words, a lot of silica sand agglomerated in the fluidized bed was formed, and the flow of the silica sand was hindered, so the loaded pellets piled up on the silica sand layer and burned without flowing. A spot (partial abnormally high temperature part) was formed.

[Comparative Example 2]
1 wt% slaked lime powder was mixed with rice husk and molded into a pellet of φ5 mm × 5 mm with a ring die type granulator.

  When this was put into a fluidized bed furnace, when the accumulated amount of pellets became 5 to 5.5 times the weight of silica sand, a flow abnormality occurred and the operation could not be continued. The same phenomenon as in Comparative Example 1 occurred.

Although only the rice husks have been described in the above embodiment, the present invention can be applied effectively to biomass such as rice straw, wheat straw, and diatom containing SiO ₂ at a high concentration in the ash.

DESCRIPTION OF SYMBOLS 1 ... Mixer 2 ... Granulation molding machine 3 ... Feeder 4 ... Fluidized bed furnace 41 ... Cylindrical part (stainless steel pipe)
42 ... Fluidized bed 43 ... Dispersion plate 44 ... Electric heater

Claims (8)

A method for burning rice husks in a fluidized bed,
At least one of limestone, slaked lime and dolomite and / or at least one of quick lime, magnesia and alumina is added to the rice husk as a fusogenic agent for increasing the melting temperature of the melt formed from the ash content of rice husk. A method for burning rice husks, comprising forming a pellet by molding a mixture of the rice husk and a fusogenic agent, and burning the pellet in the fluidized bed.   The method for burning rice husks according to claim 1, wherein when adding at least one of the limestone, slaked lime and dolomite as a fusogenic agent, 2-20% by weight is added to the rice husk weight. A method for gasifying rice husks in a fluidized bed,
At least one of limestone, slaked lime and dolomite and / or at least one of quick lime, magnesia and alumina is added to the rice husk as a fusogenic agent for increasing the melting temperature of the melt formed from the ash content of rice husk. A method for gasifying a rice husk, comprising forming a pellet by molding a mixture of the rice husk and a fusogenic agent, and gasifying the pellet by partial oxidation or thermal decomposition in the fluidized bed.   The method for gasifying a rice husk according to claim 3, wherein when at least one of the limestone, slaked lime, and dolomite is added as a fusogenic agent, 2 to 20 wt% is added to the rice husk weight. A method for fueling rice husks that are combusted or gasified in a fluidized bed,
At least one of limestone, slaked lime and dolomite and / or at least one of quick lime, magnesia and alumina is added to the rice husk as a fusogenic agent for increasing the melting temperature of the melt formed from the ash content of rice husk. A method for converting a rice husk into a fuel, comprising forming a pellet by molding a mixture of the rice husk and a fusogenic agent, and using the pellet as a fuel for burning or gasifying in the fluidized bed.   The method for fuelizing rice husks according to claim 5, wherein when at least one of the limestone, slaked lime and dolomite is added as a fusogenic agent, 2-20% by weight is added to the rice husk weight. A rice husk fuel that is burned or gasified in a fluidized bed,
At least one of limestone, slaked lime and dolomite and / or at least one of quick lime, magnesia and alumina is added to the rice husk as a fusogenic agent for increasing the melting temperature of the melt formed from the ash content of rice husk. A rice husk fuel characterized by forming a pellet by molding a mixture of the rice husk and a fusogenic agent and burning or gasifying the pellet in the fluidized bed.   8. The rice husk fuel according to claim 7, wherein when at least one of the limestone, slaked lime, and dolomite is added as a fusogenic agent, 2 to 20 wt% is added to the rice husk weight.

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