JP2019099818A - Shaping fuel, method for producing the same, and method for baking limestone - Google Patents

Abstract

To provide a shaping fuel having high strength, environmentally friendly, and capable of reducing a pelletizing cost, and to provide a method for producing the same, and a method for baking limestone.SOLUTION: This invention relates to a shaping fuel, comprising a carbon material and a binder, wherein: the content ratio of carbon in the carbon material is 60 mass% or more based on a dried state; and in a state before reaction, the binder mainly comprises calcium oxide, has an average particle diameter of 15 μm or less, and has a powdering rate of 30% or less.SELECTED DRAWING: None

Description

  The present invention relates to a shaped fuel, a method for producing the same, and a method for firing limestone, and more particularly, to a shaped fuel using exhaust dust discharged by firing limestone, a method for producing the same, and a method for firing limestone.

  One of the ores that can be supplied in Japan is limestone, and in the past, limestone has been calcined (thermally decomposed) to produce quicklime. Limestone is produced by charging limestone with a fuel such as anthracite or coal coke into a calciner and continuously supplying the heat from the fuel to the limestone. Further, at the time of limestone firing, oxygen of air passing through the furnace is consumed, and a gas containing a large amount of carbon dioxide is discharged to the outside of the furnace. The gas contains not only gaseous components but also solids such as fine limestone, quicklime, unburned fuel, etc. generated in various processes, and these solids are simultaneously transported. If the gas is discharged from the chimney as it is, air pollution will occur, so solids are removed from the gas by the dust collection facility.

  Attempts have been made to use coal coke powder, which is less expensive than anthracite or coal coke, as a fuel used for calcining limestone. However, fuel needs to have a certain size and strength. For example, powdery fuel broken in the transportation process can not contribute to combustion due to the gas flow and is discharged to the outside of the furnace, and when it is compressed to limestone in the furnace and becomes powder, This is to fill the space and impede the gas flow. Therefore, development of a fuel in which a binder is blended with coal coke powder and granulated is being promoted.

  For example, Patent Document 1 discloses a particulate fuel for sintering, which comprises blending powdered coke with one or two types of quick lime and slaked lime (fresh lime), followed by granulation and curing. It describes and the slaked lime of about 0.5-3 mm is described. Patent Document 2 describes addition of a hydraulic binder such as cement and ground granulated blast furnace slag to finely divided coal and coke mixture to granulate and cure it to form granular fuel; It is stated that limestone or less (58.7% of particles having a particle size of 44 μm or less) may be mixed.

JP, 2006-290925, A Japanese Patent Application Laid-Open No. 62-220590

  However, under the conditions described in Patent Document 1, there is a problem that granulation is difficult, and in particular, strength can not be obtained for limestone firing. Moreover, since the granular fuel as described in Patent Document 2 uses coal itself, there is a problem that the cost becomes high.

  An object of the present invention is to provide a molded fuel which is high in strength and is environmentally friendly and capable of reducing granulation cost, a method for producing the same, and a method for calcining limestone.

  As a result of intensive investigations to achieve the above object, the present inventors have high strength by blending a specific binder with a carbon material having a carbon content of 60 mass or more on a dry basis. Furthermore, they have found that they can be environmentally friendly and reduce granulation costs, and have completed the present invention.

  That is, the present invention is a molded fuel containing a carbon source and a binder, wherein the carbon source has a carbon content of 60% by mass or more on a dry basis, and the binder is in a state before reaction. The present invention relates to a molded fuel characterized by containing calcium oxide as a main component and having an average particle diameter of 15 μm or less and a powdering ratio of 30% or less.

  In the present invention, there is also provided a mixing step of mixing a carbon raw material and discharge dust having an average particle diameter of 15 μm or less discharged when calcining limestone to obtain a mixture, and granulating the mixture to obtain a granulated product. The present invention relates to a method for producing a formed fuel, comprising the steps of: obtaining a granulated fuel; and curing the granulated product to obtain a molded fuel.

  In addition, the present invention has a fuel production process for obtaining a molded fuel containing a carbon raw material and exhaust dust discharged when calcining limestone, and a sintering process for sintering limestone using the molded fuel. The present invention relates to a method for calcining limestone characterized by

  According to the present invention, it is possible to provide a molded fuel which has high strength and can be environmentally friendly and can reduce granulation cost, a method for producing the same, and a method for calcining limestone.

1. Molded Fuel A molded fuel according to the present invention comprises a carbon material having a carbon content of 60% by mass or more on a dry basis, and a binder having an average particle diameter of 15 μm or less mainly containing calcium oxide in a state before reaction. And a binder). As used herein, "dry basis" is based on a shaped fuel having a moisture content of less than 1%.

  In the formed fuel according to the present invention, as a carbon raw material having a carbon content of 60% by mass or more on a dry basis, powdery combustion products such as coal coke powder, powder of anthracite coal, powder of steam coal, soot and coke dust Can be mentioned. Coal coke powder alone can be used as a carbon source. Coal coke powder may be used as a mixed carbon raw material in combination with about 0 to 30% of fine slag or about 0 to 25% of PC carbon. The mixed carbon raw material can also contain about 0 to 10% of PC carbon together with about 0 to 15% of fine slag. In addition, carbon means fixed carbon.

The carbon material (hereinafter also referred to as a flammable material) contains 60% by mass or more of carbon on a dry basis, but the carbon content is preferably 70% by mass or more, and from the viewpoint of securing the calorific value of the formed fuel, 80% by mass or more More preferable. The carbon raw material may contain moisture, sulfur, ash and the like in addition to carbon. The carbon content on a dry basis can be determined using the water content mass, water content, and carbon content of the carbon raw material.
The carbon raw material preferably has a particle diameter of 10 mm or less at 95% by mass or more, and more preferably a particle diameter of 8 mm or less at 95% by mass or more. 15 mm or less is preferable and, as for the average particle diameter of a carbon raw material, 10 mm or less is more preferable. The average particle size of the carbon raw material can be determined by hand sieving using a test sieve and laser diffraction method.

  An example of the binder having calcium oxide as a main component and an average particle diameter of 15 μm or less before the reaction includes an exhaust dust discharged when calcining limestone. The “pre-reaction state” refers to a state in which calcium oxide before reacting with water and carbon dioxide gas is the main component, and can be confirmed by component analysis. Moreover, "having as a main component" means that 40 to 65 mass% of the whole is occupied. The average particle size of the binder is 15 μm or less, preferably 10 μm or less. The average particle size of the binder can be determined by laser diffraction.

  Exhaust dust discharged when calcining limestone is dust containing solids such as fine limestone, quicklime, unburned fuel, etc. generated in various steps of calcining limestone, and carbon dioxide and solid content from calciner When the gas containing this is discharged, it is obtained by removing solid content from the gas with a dust collection facility composed of a cyclone separator, a bag filter and the like. In the present invention, in order to obtain an exhaust dust having an average particle size of 15 μm or less, the exhaust dust removed by a bag filter is used.

It is preferable that content of CaO as a main component is 40-65 mass% of discharge dust. The impurity component in the exhaust dust is 10 to 30% by mass of SiO ₂ , 0.5 to 5% by mass of Fe ₂ O ₃ , 1 to 10% by mass of Al ₂ O ₃ , 5% by mass or less of MgO, 5% by mass It is preferable that it is following P, 5 mass% or less S, 5 mass% or less Na, 5 mass% or less K.

  The pulverization rate of the formed fuel according to the present invention is 30% or less, preferably 20% or less, and more preferably 10% or less. In the present specification, the powdering rate is defined as the powdering rate measured by the method described in the examples described later. If the pulverization rate is more than 30%, the powdery fuel may collapse in the transportation process, and the pulverized fuel in powder form is not preferable because it travels to the gas flow and does not contribute to combustion and is discharged out of the furnace.

  The shaped fuel according to the present invention is particularly preferably used for calcining limestone, and the particle size is preferably in the range of 10 to 100 mm, more preferably in the range of 20 to 70 mm. In the present specification, the particle diameter of the formed fuel refers to the length of the shortest line segment among the line segments passing through the center of the formed fuel and connecting any two points on the surface of the formed fuel. When the particle size is smaller than 10 mm, when calcining limestone or the like, the gaps in the filled limestone may be clogged to inhibit the gas flow. If the particle size is larger than 100 mm, the production is difficult, and when packed with limestone, it tends to be broken and clogged in gaps of limestone.

The crushing strength of the formed fuel according to the present invention is preferably 1500 N or more, more preferably 2000 N or more, and still more preferably 3000 N or more at a load at which the formed fuel crushes. As the crushing stress, preferably 2.0 N / mm ² or more, more preferably ^{2.7N / mm 2, 4.0N / mm} 2 or more is more preferable. In the present specification, the crush strength and crush stress are defined as crush strength and crush stress measured by the method described in the examples described later. If the crushing load is less than 1500 N, the strength may decrease at the time of firing, and the shape of the formed fuel may not be maintained in the combustion furnace. If the formed fuel is compressed into limestone in the furnace to become powder, it fills up the space between the limestone, which is not preferable because it obstructs the gas flow.

2. Method for Producing Molded Fuel The molded fuel according to the present invention can be obtained by the method for producing a molded fuel according to the present invention described below. The method for producing a shaped fuel according to the present invention comprises mixing a carbon raw material and an exhaust dust having an average particle diameter of 15 μm or less discharged when calcining limestone to obtain a mixture; granulating the mixture And a granulating step of obtaining a granulated product, and a curing step of curing the granulated product to obtain a shaped fuel.

(Mixing process)
The mixing step is a step of mixing the carbon raw material and the discharge dust having an average particle diameter of 15 μm or less, which is discharged when the limestone is calcined, to obtain a mixture.
The carbon source preferably has a carbon content of 60% by mass or more on a dry basis. In the case of using a plurality of carbon raw materials having different carbon contents on a dry basis, the carbon content of the entire carbon raw material may be blended so as to be 60% by mass.

When mixing carbon source and exhaust dust, 80% to 90% by mass of such carbon source (combustible) on a dry basis, and an average particle diameter of 15 μm or less discharged when calcining limestone as a binder Dust can be used at 10 to 20% by mass on a dry basis. The proportion of the carbon source is preferably 70 to 90% by mass. It is achieved by adjusting the amount of water to be added so that the total amount of water is 10 to 30% in consideration of the moisture brought in from the combustibles and the discharged dust, and uniformly mixing.
For mixing, for example, a device such as a mill (fret mill) or mix miller can be used. The shorter the time to granulation after mixing, the better the properties of the formed fuel are obtained. Specifically, the shorter the time from mixing to granulation, the higher the strength of the resulting shaped fuel.

The combustibles used here are granular or powdery, and they may be a mixture of two or more types of combustibles, and the total amount of the mixture may contain 60% by mass or more of carbon on a dry basis. In general, combustibles containing 60% by mass or more of carbon on a dry basis are poor in viscosity components, and are difficult to be granulated as they are. By adding the discharge dust discharged when calcining limestone as an inder, it is between the carbon in the combustibles and the impurity component (the above SiO ₂ , Al ₂ O ₃ etc.) and the Ca component in the discharge dust. The reaction takes place. It is believed that calcium compounds (such as calcium aluminate, calcium silicate, etc.) are formed and that the product affects the properties of the formed fuel.

(Granulation process)
The granulation step is a step of granulating the mixture obtained in the mixing step to obtain a granulated product.
In the granulation step, as a granulation method, a compression granulation method for producing a pillow type briquette or an almond type briquette with a briquette machine (roll type compression granulator) having a pair of forming rolls, a pan pelletizer (pan type granulation Rolling granulation method etc. which are formed into a spherical shape by

As granulation conditions, it is preferable to granulate to a size of about ^{20 to} 70 mm at a pressure of 30 to 100 N / mm ² . In addition, by adjusting the water content in the granulated material immediately after granulation to 10 to 25%, in the next curing step, the impurity component (the above-mentioned SiO ₂ , Al ₂ O ₃ etc.) and the Ca component in the discharged dust Reaction can be efficiently advanced. The water content in the granulated material is more preferably 15 to 20%.

(Care process)
The curing step is a step of curing the granulated product obtained in the granulation step to obtain a shaped fuel. Through the curing step, the granulated material becomes a strong molded fuel.
As curing conditions, curing is carried out under conditions of temperature 0 to 100 ° C. and humidity 60 to 100% until reaching a predetermined strength (for example, 1500 N). As an example, if it is under the atmosphere (temperature: 10 to 30 ° C., humidity: 60 to 100%), almost predetermined strength can be obtained by curing for 24 hours. The higher the temperature and humidity, the shorter the curing time.

3. A method of calcining limestone according to the present invention comprises the steps of: producing a shaped fuel containing a carbon raw material and exhaust dust discharged when calcining the limestone; and using the shaped fuel to produce limestone. And a firing step of firing.

(Fuel production process)
In the fuel production process, a shaped fuel is obtained that contains a carbon source and exhaust dust discharged when calcining limestone. The carbon source preferably has a carbon content of 60% by mass or more on a dry basis. The discharged dust preferably has an average particle size of 15 μm or less.
The molded fuel obtained in the fuel manufacturing process is the same as the molded fuel according to the present invention described above, and the description will be omitted.

(Firing process)
The firing step is a step of firing limestone using the molded fuel obtained in the fuel production step. The firing furnace is not particularly limited, and examples thereof include vertical furnaces such as Meltz furnace, Beckenbach furnace, co-fired furnace, shaft kiln, and top furnace, and horizontal furnaces such as rotary kiln. Among them, the vertical firing furnace is preferable, and the Beckenbach furnace is particularly preferable. The firing conditions may be the firing conditions of the respective firing furnaces. For example, in the Beckenbach furnace, in the Beckenbach furnace with a maximum production capacity of 200 to 400 t / day, the maximum temperature is 1000 ° C., and the residence time is 24 hours Methods etc. However, it is not limited to this condition.
In addition, by using the exhaust dust discharged in the firing process and passing through the fuel production process again, it is possible to circulate the firing process and the fuel production process to enable recycling, thus achieving both environmental considerations and cost reduction. It is possible to

  Hereinafter, the present invention will be specifically described based on examples, but these do not limit the object of the present invention, and the present invention is not limited to these examples.

First, the measurement method, the carbon raw material, and the binder used in the present example are shown.
[Fall strength (powdering rate)]
The formed fuel was dropped 5 times repeatedly from the height of 1 m onto the ground (smooth concrete floor). The crushed material of 8 mm or less generated by the impact of falling was sieved to measure the mass, and the falling strength was evaluated using the ratio to the total amount as the powdering rate.
[Crushing strength]
The cylindrically produced molded fuel was placed in an electric furnace and heated to 400 ° C. at a heating rate of 5 ° C./min. After 30 minutes while maintaining the temperature at 400 ° C., a load was applied in the axial direction of the cylinder to perform uniaxial compression, thereby measuring a crushing strength which is a load resistance. The load resistance was divided by the cross-sectional area of the compression surface (end face of the cylinder) to calculate the crush stress.

[Carbon raw material]
As a carbon material, use is made of coal coke powder, fine slag (FS) which is a fine powder portion of the residue generated from a coal gasification furnace, and PC carbon obtained by collecting unburned components generated from an oil coke combustion boiler with an electrostatic precipitator It was. The composition of each carbon source is shown in Table 1 below. In addition, the average particle diameter of coal coke powder, fine slag, and PC carbon is respectively 2000 micrometers, 108 micrometers, and 112 micrometers.

[binder]
Among the exhaust gases discharged from calcining limestone at 1000 ° C for 24 hours using a Beckenbach furnace, bag filter (BF) dust collected on a bag filter after passing through a cyclone separator, collected on a cyclone separator Used cyclone dust, limestone dust collected by transportation system of raw material limestone. The composition of the compound contained in each dust is shown in Table 2 below. The average particle sizes of BF dust, cyclone dust and limestone dust are 6 μm, 150 μm and 55 μm, respectively.

(Example 1) Coal coke powder and bag filter (BF) dust 5 g of BF dust having a particle diameter of 20 μm or less and 2% moisture was added to 22 g of coal coke powder containing particle size 8 mm or less, moisture 7%, and fixed carbon 87%. . Further, 3 g of water was added, and the mixture was shaken in the bag for 1 minute to perform hand mixing. The mixture was placed in a 30 mm diameter metal frame and granulated at a pressure of 100 N / mm ² . The granulated product was left to stand at room temperature for 24 hours, and curing was carried out to obtain a cylindrical shaped fuel with a diameter of 30 mm and a height of 28 mm according to Example 1.

(Example 2) Coal coke powder and fine slag (FS): 15% substitution rate and bag filter (BF) dust particle diameter 8 mm or less, moisture 7%, coal carbon powder containing 87% fixed carbon particle diameter 0. 6 g of fine slag containing 7 mm or less, 50% moisture, and 68% fixed carbon was added, and the mixture was shaken until uniform in the bag. Next, 5 g of BF dust having a particle diameter of 20 μm or less and 2% of water was added to 24 g of a mixed carbon raw material of coal coke powder and fine slag, 2 g of water was further added, and the mixture was shaken for 1 minute in a bag. The mixture was placed in a 30 mm diameter metal frame and granulated at a pressure of 50 N / mm ² . The granulated product was left to stand at room temperature for 24 hours, and curing was carried out to obtain a cylindrical shaped fuel with a diameter of 30 mm and a height of 28 mm according to Example 2.

(Example 3) Coal coke powder and fine slag (FS): substitution rate 25% and bag filter (BF) dust particle diameter 8 mm or less, moisture 7%, coal carbon powder 16% containing fixed carbon 87% particle diameter 0. 10 g of fine slag containing 7 mm or less, 50% moisture, and 68% fixed carbon was added, and the mixture was shaken until uniform in the bag. Next, 5 g of BF dust having a particle diameter of 20 μm or less and 2% of water content was added to 26 g of a mixed carbon raw material of coal coke powder and fine slag, 1 g of water was further added, and the mixture was shaken for 1 minute in a bag. The mixture was placed in a 30 mm diameter metal frame and granulated at a pressure of 50 N / mm ² . The granulated product was left to stand at room temperature for 24 hours, and curing was performed to obtain a cylindrical shaped fuel with a diameter of 30 mm and a height of 28 mm according to Example 3.

(Example 4) Coal coke powder and PC carbon (PC): 20% substitution rate and bag filter (BF) dust particle diameter 8 mm or less, water content 7% coal coke powder containing 87% fixed carbon particle diameter 0. 4 g of PC carbon containing 5 mm or less, 1% moisture, and 92% fixed carbon was added, and the mixture was shaken until uniform in the bag. Next, 5 g of BF dust having a particle diameter of 20 μm or less and 2% of water was added to 21 g of a mixed carbon raw material of coal coke powder and PC carbon, 5 g of water was further added, and the mixture was shaken for 1 minute in a bag. The mixture was placed in a 30 mm diameter metal frame and granulated at a pressure of 38 N / mm ² . The granulated product was left at room temperature for 72 hours, and curing was performed to obtain a cylindrical shaped fuel with a diameter of 30 mm and a height of 28 mm according to Example 4.

  The mass, the water content, and the carbon content of the carbon raw materials used for the molded fuels of Examples 1 to 4 are summarized in Table 3 below.

The BF dust used in Examples 1 to 4 has a water content of 5 g, a dry weight of 4.9 g, a water content of 2%, and a water content of 0.1 g.
Table 4 below summarizes the dry basis mass ratio of each of the molded fuels.

Comparative Example 1 Coal Coke Powder and Cyclone Dust 6 g of cyclone dust having a particle diameter of 200 μm or less and 1% water was added to 24 g of coal coke powder containing particle size 8 mm or less, moisture 12%, and fixed carbon 87%. Hand mixing was done for a minute. The mixture was placed in a 30 mm diameter metal frame and granulated at a pressure of 100 N / mm ² . The granulated product was left to stand at room temperature for 24 hours, and curing was performed to obtain a shaped fuel having a diameter of 30 mm and a height of 28 mm according to Comparative Example 1.

(Comparative example 2)
A molded fuel according to Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that the number of days for aging was changed to 72 h.

Comparative Example 3 Coal Coke Powder and Limestone Dust 6 g of limestone dust having a particle diameter of 100 μm or less and 1% water is added to 24 g of coal coke powder containing particle diameter 8 mm or less, moisture 12%, fixed carbon 87%. Hand mixing was done for a minute. The mixture was placed in a 30 mm diameter metal frame and granulated at a pressure of 100 N / mm ² . The granulated product was left to stand at room temperature for 24 hours, and curing was performed to obtain a shaped fuel having a diameter of 30 mm and a height of 28 mm according to Comparative Example 3.

(Comparative example 4)
A molded fuel according to Comparative Example 4 was obtained in the same manner as in Comparative Example 3 except that the number of days for aging was changed to 72 h.

Comparative Example 5 Coal Coke Powder 30 g of coal coke powder containing a particle diameter of 8 mm or less, moisture 12%, and fixed carbon 87% was placed in a metal frame with a diameter of 30 mm, and granulated at a pressure of 100 N / mm ² . The granulated product was left to stand at room temperature for 24 hours, and curing was performed to obtain a shaped fuel having a diameter of 30 mm and a height of 28 mm according to Comparative Example 5.

(Comparative Example 6) Coal coke powder and starch 0.9 g of starch was added to 30 g of coal coke powder containing a particle diameter of 8 mm or less, moisture 12%, and fixed carbon 87%, and hand mixing was performed for 1 minute in a bag. The mixture was placed in a 30 mm diameter metal frame and granulated at a pressure of 100 N / mm ² . The granulated product was left to stand at room temperature for 24 hours, and curing was performed to obtain a shaped fuel having a diameter of 30 mm and a height of 28 mm according to Comparative Example 6.

  The drop strength (powdering ratio), crushing strength and crushing stress of the molded fuels of Examples 1 to 4 and Comparative Examples 1 to 6 are summarized in Table 5 below.

  From Table 5, it can be seen that the shaped fuels according to Examples 1 to 4 using BS dust (average particle diameter 6 μm) as a binder have a low pulverization ratio and high crushing strength and crushing stress as compared with Comparative Examples.

Claims (6)

A shaped fuel containing a carbon source and a binder,
The carbon raw material has a carbon content of 60% by mass or more on a dry basis,
The binder is mainly composed of calcium oxide and has an average particle diameter of 15 μm or less in a state before the reaction,
A shaped fuel having a powderization rate of 30% or less.   The formed fuel according to claim 1, wherein the binder is an exhaust dust discharged when calcining limestone.   The molded fuel according to claim 1 or 2, wherein the particle size is 10 to 100 mm and the crushing strength is 1,500 N or more.   The shaped fuel according to any one of claims 1 to 3, which is for limestone firing. A mixing step of mixing a carbon raw material and discharge dust having an average particle diameter of 15 μm or less discharged when calcining limestone to obtain a mixture;
Granulating the mixture to obtain a granulated product;
And curing the granulated material to obtain a shaped fuel. A fuel production process for obtaining a shaped fuel containing a carbon source and exhaust dust discharged when calcining limestone;
And a calcining step of calcining limestone using the formed fuel.