JP2015052418A - Drying method in drying process for manufacturing woody pellets using green wood and woody pellet manufacturing apparatus including drying process to which this drying method is applied - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable woody pellets to be manufactured and supplied in large amounts stably in applications including a material for co-combustion with coal in a thermal power plant using, as a raw material, green wood such as lumbers having a large water content fluctuation width.SOLUTION: To dry crushed green wood (crushed raw material) so as to have a preset water content by a hot air dryer, a water content A of the crushed raw material supplied to the hot air dryer and a supply amount B of the crushed raw material supplied to the dryer per unit time are consecutively measured, and the supply amount B is controlled so as to make a water supply amount (A×B) per unit time to be supplied to the dryer equal to a constant amount calculated so that the dried crushed raw material has a preset water content. Furthermore, a water content C and an unloading amount D of the dried crushed raw material are consecutively measured, and a temperature and/or a supply amount of hot air supplied to the dryer is controlled so that the water content C is equal to a preset water content.

Description

  The present invention relates to a drying method in a drying process for manufacturing wood pellets using raw wood, and a wood pellet manufacturing apparatus including a drying process to which this drying method is applied. It is characterized by being controlled to dry.

  Recently, plant biomass fuel has attracted attention as an alternative fuel in order to cope with rising prices of fossil fuels and environmental impacts. A typical example of the plant biomass fuel is a wood pellet obtained by forming wood sawdust into a pellet.

  Wood pellets are generally cut into a suitable size, removed foreign matter, pulverized with a pulverizer, dried and then extruded into a cylindrical pellet by a granulator. It is manufactured by.

  As raw materials for wood pellets, waste from wood processing plants such as wood mills, bark and sawdust and raw wood are used, which contributes to the recycling of resources and is expected to spread. Yes.

  Waste generated in wood processing plants such as wood mills has a low moisture content and is stable, so it is relatively easy to dry to a certain moisture content. Since the moisture content range is as large as about 30-60 wt%, depending on the size, period of time in the forest, and time of logging, it is difficult to stably dry a large amount of raw trees to a certain moisture content. It was.

  As for the amount of resources that can be used, it is difficult to collect a large amount of waste generated at wood processing plants such as wood chips, bark, and sawdust. It has become more difficult to secure raw materials. On the other hand, raw wood forest resources such as thinned wood are left unused in large quantities due to the collection and transportation costs carried out from the mountains.

  At the coal-fired power plant, there is a demonstration project ("forest residual wood biomass coal co-firing power generation demonstration project") in which wood pellets are mixed with coal and burned to generate electricity. It is necessary to stably supply a large amount of wood pellets using raw forest resources.

  As a conventional method for producing a wood pellet, Patent Document 1 discloses that a wood pellet molding line comprising a rotary kiln dryer, a granulator, a cooler, etc. is used to produce wood pellets from sawdust or wood chips. It is disclosed that the drying apparatus can be easily controlled by adjusting sawdust or wood chips to a predetermined moisture content in a storage drying yard before adding the powder or wood chips.

  Moreover, in patent document 2, when granulating wood waste using a pellet molding machine and manufacturing a porous wood pellet, as a wood waste, 30-50 weight% of sawdust and the long diameter obtained by grinding sawdust Is a mixture of 70 to 50% by weight of crushed sawdust with a diameter of 1 mm or less, and after adjusting the water content of the mixture to 20 to 35% by weight, the mixture is granulated and discharged to have a diameter of 1 to 7 mm and a length of It is disclosed to form cylindrical porous wood pellets in the range of 1 to 12 mm and then dry the wood pellets until the moisture content is 5 to 15% by weight.

  However, Patent Documents 1 and 2 do not disclose any technique for stably producing a large amount of wood pellets using raw wood having a large variation in moisture content as a raw material.

JP 2010-223440 A JP 2011-136312 A

  The problem of the present invention is that there is a large amount of available resources, but using raw wood with a large variation in moisture content as a raw material, it can be used in large quantities and stably for applications such as coal co-firing materials in thermal power plants. To manufacture and supply wood pellets.

  In order to solve the above problems, in the present invention, crushed raw wood (hereinafter referred to as “pulverized raw material”) is supplied to a hot air dryer, and the inside of the dryer is continuously supplied at a constant speed from the inlet to the outlet. The hot air is supplied into the dryer while being transported to dry the pulverized raw material, and the moisture content of the pulverized raw material after drying is controlled to be a predetermined constant value and dried. It is said.

  The term “raw tree” as used herein means a tree that has not been sufficiently dried, and representative examples thereof include standing trees immediately after being felled and remaining forest land such as thinned wood that is not carried out of the forest.

  As the control means, the moisture content A of the pulverized raw material supplied to the hot air dryer and the supply amount B per hour of the pulverized raw material supplied to the dryer are continuously measured and supplied to the dryer. Means for controlling the supply amount B so that the moisture supply amount per unit time (A × B) is a constant amount calculated so that the dried pulverized raw material has a preset moisture content (hereinafter referred to as “the supply amount B”). "First control means") is employed.

  Furthermore, the hot air supplied to the dryer is continuously measured by measuring the moisture content C of the pulverized raw material after drying, which is carried out from the outlet of the dryer, so that the moisture content C becomes a preset moisture content. A means for controlling the temperature and / or supply amount (hereinafter referred to as “second control means”) may be employed.

  Further, when the moisture content C and the carry-out amount D of the pulverized raw material after drying, which are carried out from the outlet of the dryer, are continuously measured, and the moisture content C is lower than a preset moisture content, it is insufficient. A means (hereinafter referred to as “third control means”) for automatically calculating and adding the moisture content is added based on the difference between the preset moisture content and the moisture content C and the carry-out amount D is employed. You can also.

It is a very important matter to control the moisture content of the pulverized raw material after drying to be a predetermined constant value for the following reason. The water content (wt%) in the present invention represents the water content on a wet basis (water weight divided by the sum of water and solid weight). That is, the water content (wt%) in the present invention is expressed by 100 × W _W / (W _S + W _W ) where W _W is the weight of moisture and W _S is the weight of the substance.

After drying, the pulverized raw material is kneaded at a temperature of 100 to 130 ° C. by frictional heat generated by kneading in a pellet molding machine, extruded from a circular through hole in a die, cut, and molded into cylindrical wood pellets. Is done.

  In order to use wood pellets as a coal co-firing material in thermal power plants, it retains its shape when stored and transported, and easily disintegrates when pulverized with coal in a coal mill for co-firing. Is needed. For this reason, it is necessary that the surface of the wood pellet is appropriately coated with lignin (a component contained in wood and acting as a binder).

  It is generally known that it is necessary to use a pulverized raw material having a water content of 5 to 20 wt% in order to solidify the pulverized raw material with a pellet molding machine and obtain a wood pellet whose surface is coated with lignin. (Wikipedia "wood pellet" http://en.wikipedia.org/wiki/%E6%9C%A8%E8%B3%AA%E3%83%9A%E3%83%AC%E3%83%83%E3 % 83% 88, R & D coordinator report “Wood pellet situation and pellet manufacturing method” http://www.joho-kochi.or.jp/johosi/0607/kenkyu.html)

  When the moisture content of the pulverized raw material after drying is too high, the frictional heat generated by kneading is taken away by the heat of vaporization of water and the kneading temperature does not rise to 100 ° C or higher, so the lignin does not come out on the surface of the wood pellets Insufficient coating. On the other hand, even when the moisture content is too low, the amount of water evaporation is small, so that the surface coating of the wood pellet with lignin is not sufficiently performed, and scoring occurs.

  The moisture content of the pulverized raw material after drying, which is required for appropriately coating the surface of the wood pellet with lignin, varies somewhat depending on the type of raw wood. For example, when cedar, beech and oak are mixed, about 8 to 9 wt%, when larch and red pine are mixed, about 9 to 12 wt%, and when cedar and cypress are mixed, 9 About 12.5 wt%. When actually operating, the raw wood raw material type and blending ratio will change, so the preferred moisture content of the pulverized raw material after drying according to the raw wood raw material type and blending ratio is determined in advance. A plurality of values are obtained by experiments or the like, and based on this, a “preliminary moisture content” that is a target value of the first to third control means is set.

  When cedar and cypress are mixed, about 12.5 wt% is generally most preferable, but if the range is generally 8 to 13 wt%, preferably 9 to 12.5 wt%, the surface is moderately lignin. Coated wood pellets suitable as a cofired material for coal in thermal power plants are obtained.

  The first control means of the present invention is a step of supplying a large amount of pulverized raw material having a large moisture content fluctuation range at a constant speed while supplying a hot air to the dryer and drying it. It is a control means that is not precise but quick response.

  Specifically, the moisture content A of the pulverized raw material supplied to the hot air dryer is measured continuously with a non-contact moisture meter on the weighing conveyor by a quantitative feeder and a weighing conveyor. Moisture supply per hour supplied to the dryer by continuously measuring the supply amount B of the pulverized raw material supplied per hour from the supply amount carried out from the metering feeder and the conveying speed of the weighing conveyor. The supply amount B is controlled so that the amount (A × B) is a constant amount calculated so that the dried pulverized raw material has a preset water content.

  The second control means of the present invention performs precise control after controlling the moisture content of the pulverized raw material after drying, although it is not precise by the first control means but is fast in response. is there.

Specifically, the moisture content of the crushed raw material after drying, which is carried out from the outlet of the dryer by a discharge conveyor and a weighing conveyor, is continuously measured with a non-contact moisture meter, and the moisture content is set in advance. The temperature and / or supply amount of hot air supplied to the rotary kiln is controlled so as to obtain a rate.

  The third control means of the present invention is a control means that is used supplementarily when the moisture content of the pulverized raw material after drying is lower than a preset moisture content in the first and second control means.

  Specifically, the moisture content C of the pulverized raw material after drying, which is carried out from the outlet of the dryer by a discharge conveyor and a weighing conveyor, is continuously measured with a non-contact moisture meter, and the carry-out amount D is Measured continuously from the supply amount carried out from the metering feeder and the conveying speed of the weighing conveyor, and if the moisture content C is lower than a predetermined value, the crushed raw material after drying is guided to the mixer and is insufficient The moisture content is automatically calculated based on the difference between the preset moisture content and the moisture content C and the carry-out amount D, and is added and mixed.

  In the present invention, even if a large amount of pulverized raw material having a large moisture content width is continuously dried at a constant speed by a hot air dryer by the first to third control means, the wood pellets It is possible to stably obtain a pulverized raw material after drying having a water content required for appropriately coating the surface with lignin.

  Furthermore, the dried pulverized raw material having a moisture content required for appropriately coating the surface of the wood pellets with lignin is formed into wood pellets by a pellet molding machine, thereby producing a coal-fired material for a thermal power plant. Suitable wood pellets with a suitable surface coated with lignin can be produced stably in large quantities.

It is a flowchart which shows an example of the process of manufacturing the wood pellet of this invention. It is a flowchart which shows the other example of the process of manufacturing the wood pellet of this invention. It is a schematic diagram which shows the drying method in the process of manufacturing the wood pellet of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.
FIG. 1 is a flowchart showing an example of a process for producing a wood pellet of the present invention.
The raw wood that has been carried in and received is carried into a cutting machine such as a wood cutting machine by a chain feeder or the like, cut, and then sorted by a vibration sieve machine and pulverized by a pulverizer. If the size of raw wood is reduced in multiple stages, such as a size of about 30 mm or less in the cutting process and a size of about 3 mm or less in the crushing process, the load on the machine such as a cutting machine or a crusher becomes smaller. There is a merit that failure or the like hardly occurs.

  FIG. 2 is a flowchart showing another example of the process for producing the wood pellets of the present invention, in which a sawdust production process is adopted instead of the cutting process, the sorting process and the pulverization process of FIG. . In order to make the shape of the pulverized raw material uniform and to stabilize the quality of the wood pellets, it is preferable to make the raw wood finer in one step with a sawdust making machine. As shown in Utility Model Registration No. 2557582, the sawdust making machine cuts the raw wood being conveyed with a receiving blade and a plurality of rotating cutting blades to obtain a predetermined size of saw. The powder is produced.

The pulverized raw material obtained from such raw wood has a large fluctuation range of moisture content of about 30 to 60 wt%, and this is later described using a hot air dryer equipped with a control means, which will be described later. The moisture content of the pulverized raw material is the moisture content required for moderately coating the surface of the wood pellets with lignin, preferably in the range of 8 wt% to 13 wt%, more preferably 9 wt%
% To 12.5 wt% or less.

The dried pulverized raw material is kneaded by raising the temperature to 100 to 130 ° C. by frictional heat by kneading in a pellet molding machine, extruded from a circular through hole in a die, cut by its own weight, and cylindrical wood pellets To be granulated. In order to use it as a coal co-fired material in a thermal power plant, the wood pellets are appropriately coated with lignin on the surface, have a cylindrical shape with a diameter of about 8 mm and a length of about 15 mm, and a moisture content of 10 wt%. Hereinafter, the bulk specific gravity is preferably 0.6 t / m ³ or more.
The granulated wood pellets are cooled and temporarily stored, and then shipped to a thermal power plant.

FIG. 3 is a schematic view showing a drying method in a drying process for producing the wood pellets of the present invention.
In this drying method, the pulverized raw material supplied to the hot air dryer is dried while being continuously conveyed at a constant speed from the inlet to the outlet side in the dryer. As such a hot-air dryer (hereinafter referred to as “continuous hot-air dryer”) that dries the supplied pulverized raw material while continuously conveying the pulverized raw material from the inlet toward the outlet at a constant speed, the pulverized raw material is stirred. However, it is preferable to employ a rotary kiln because it can be uniformly dried and a large amount of pulverized raw material can be dried. A stirring blade is provided on the inner surface of the rotary kiln main body, and hot air is blown from the supply side of the pulverized raw material. The pulverized raw material supplied to the rotary kiln is stirred in the rotary kiln body by the rotation of the rotary kiln body and the stirring blade provided on the inner surface of the rotary kiln, and is contacted with hot air while being conveyed from the supply side to the outlet side at a constant speed. To be dried.

  In the continuous drying of the pulverized raw material by the continuous hot air dryer, as described above, the moisture content of the pulverized raw material after drying is a constant moisture content required to appropriately coat the wood pellet surface with lignin. Since it is very important to set the value, it is necessary to control by the first to third control means.

  The first control means of the present invention is a precise but fast responsive control means suitable for drying a large amount of pulverized raw material having a large fluctuation range of moisture content with a continuous hot air dryer. That is, the present invention has a large amount and a stable amount of wood pellets used as a coal co-fired material in a thermal power plant using raw wood with a large fluctuation range of water content as a raw material. Therefore, in order to prevent a large amount of wood pellets that do not conform to the standard from being manufactured, it is necessary to adopt a control means with quick response.

  This first control means is performed on the supply side of the continuous hot air dryer, and specifically, the moisture content A of the pulverized raw material supplied to the continuous hot air dryer by a quantitative supply machine and a weighing conveyor, Continuously measure with a non-contact moisture meter on the weighing conveyor, and supply the supply amount B per hour of the pulverized raw material supplied to the dryer to the supply amount set in the metering feeder and the conveyance of the weighing conveyor A constant amount measured from the speed and calculated so that the moisture supply amount per unit time (A × B) supplied to the dryer has a preset moisture content after drying. The supply amount B is controlled so that

  That is, the feature of the first control means is that “the amount of water per hour that is removed from the pulverized raw material by evaporation in the continuous hot air dryer” is regarded as a constant value, and the moisture carried into the continuous hot air dryer by the pulverized raw material. The amount is controlled to be a constant value.

The first control means will be specifically described with an example. A pulverized raw material having a moisture content of 50 wt% is supplied at a supply rate of 2500 g / s, and the pulverized raw material after drying having a moisture content of 12.5 wt% is supplied. In the continuous hot air dryer operated so as to obtain a water content of the ground raw material supplied is 5
In the case of a change from 0 wt% to 45 wt%, the supply amount is changed from 2500 g / s to 2,780 g / s (50 × 2,500 / 45), and the moisture content of the powder raw material after drying after the change The rate is maintained at a value of about 12.5 wt% in the calculation.

  “In a continuous hot air dryer, the amount of moisture per hour removed by evaporation from the pulverized raw material” is affected by the supply amount, moisture content, etc. of the pulverized raw material. In one control means, this is regarded as a constant value, and on the supply side of the continuous hot air dryer, control that is not precise but has high responsiveness is performed.

  The second control means of the present invention is performed on the outlet side of the continuous hot air dryer, and after the first control means performs the control with a fast response but not the precision, the response is slow but the precise control. Is carried out by measuring the moisture content of the pulverized raw material after drying.

Specifically, the moisture content C of the pulverized raw material after drying, which is carried out from the outlet of the continuous hot air dryer by a discharge conveyor and a weighing conveyor, is continuously measured with a non-contact moisture meter. The temperature and / or supply amount of hot air supplied to the continuous hot air dryer is controlled so as to have a preset moisture content.
As described above, the second control means supplements the first control means and performs precise control on the outlet side of the continuous hot air dryer, although the response is slow.

  The third control means of the present invention is a control means that is used supplementarily when the moisture content of the pulverized raw material after drying is lower than a preset moisture content in the first and second control means. In particular, it is used to supplementarily adjust the moisture content of the pulverized raw material after drying until the effects of the first control means and the second control means appear.

  Specifically, the moisture content C of the pulverized raw material after drying, which is discharged from the outlet of the continuous hot air dryer by a discharge conveyor and a weighing conveyor, is continuously measured with a non-contact moisture meter, and the discharge amount D is , Continuously measured from the supply amount set in the metering feeder and the conveying speed of the weighing conveyor, and when the moisture content C is lower than a predetermined value, the pulverized raw material after drying is guided to the mixer, The deficient moisture content is automatically calculated based on the difference between the preset moisture content and the moisture content C and the carry-out amount D, and is added and mixed.

Hereinafter, the drying method of the present invention will be described more specifically.
A raw cedar tree is cut to an average size of 30 mm by a wood cutting machine, sorted by a vibration sieve, and then pulverized to an average size of about 3 mm by a pulverizer to obtain a pulverized raw material.
This pulverized raw material is supplied to a rotary kiln (diameter: 2.89 m, length 17.0 m, hot air temperature: 450 ° C., hot air volume: 1800 m ³ / min) equipped with first and second control means, and dried. The raw material for the later grinding is obtained.

  Table 1 shows the moisture content (inlet moisture) and drying of the pulverized raw material to be dried when the pulverized raw material having the above shape is supplied to the rotary kiln having the first control means and the second control means for drying. The water content (exit moisture) of the pulverized raw material is shown.

  As shown here, the water content of the pulverized raw material is from 42.6 wt% in the super dry period (September 27, 10:00) to 53.0 wt in the super wet period (October 19, 13:00). %, The moisture content of the pulverized raw material after drying is stably controlled in the range of 10.7 to 12.5 wt%.

Wood pellets that are suitable as a co-fired material for coal in thermal power plants, with the surface being appropriately coated with lignin from the pulverized raw material after drying in this moisture content range, and with little collapse of the pellets due to storage and transportation Is obtained.

  Tables 2 and 3 show that after starting the rotary kiln equipped with the first and second control means and idling for 17 minutes, the supply of the pulverized raw material having the water content of about 47% is started. The elapsed time (minutes) from the start of supply of the pulverized raw material and the moisture content (wt%) of the pulverized raw material after drying are shown.

  As shown here, the moisture content of the crushed raw material after drying decreases to an allowable upper limit of 13 wt% in 4 to 5 minutes from the start of supply, and is an optimal value from 9 to 30 minutes from the start of supply. It can be seen that it is stably controlled in the range of 12.5 wt%.

  Although the former is not precise, the control with fast responsiveness is performed by the first control means, and the latter responsiveness is slow but precise control is performed by the second control means.

In this way, when the moisture content of the pulverized raw material is changed by the first control means, the supply amount is immediately changed, and the moisture content of the pulverized raw material after drying carried out of the rotary kiln is within a preferable range at an early stage. Since it can be controlled in the range of ˜13%, the surface is appropriately coated with lignin, which is required as a co-fired material of coal, without producing a large amount of wood pellets that do not meet the standard, storage, It is possible to obtain wood pellets that are less likely to collapse even during transportation at an early stage.

  Furthermore, since the moisture content of the pulverized raw material after drying can be stably controlled to the optimum value of 9 to 12.5 wt% by the second control means, the surface required as a co-fired material for coal, Is optimally coated with lignin, and it is possible to stably obtain wood pellets that hardly collapse even when stored and transported.

  In addition, the 3rd control means of this invention is utilized in order to adjust the moisture content of the grind | pulverized raw material after drying until the effect of a 1st control means and a 2nd control means appears. For example, in Table 2 and Table 3, when the moisture content of the pulverized raw material after drying is temporarily reduced to 7.4 wt% after an elapsed time of 21 minutes, the moisture content of the powder raw material after drying is It can be supplementarily adjusted to a range of 10 to 12.5 wt% which is an optimum value.

Claims (7)

A drying method for drying a crushed raw tree with hot air, which is used in a process of producing a wood pellet using a raw tree such as thinned wood,
The crushed raw wood is supplied to a hot air dryer, and while the inside of the dryer is continuously conveyed at a constant speed from the inlet to the outlet, hot air is supplied into the dryer to pulverize the raw wood. As it dries
The moisture content A of the crushed raw wood supplied to the dryer and the supply amount B per hour of the crushed raw wood supplied to the dryer are continuously measured and supplied to the dryer. The supply amount B is controlled so that the water supply amount per hour (A × B) is a constant amount calculated so that the crushed raw wood after drying has a preset moisture content. Drying method.   Further, the moisture content C of the crushed raw wood after drying, which is carried out from the outlet of the dryer, is continuously measured and supplied to the dryer so that the moisture content C becomes a preset moisture content. The drying method according to claim 1, wherein the temperature and / or supply amount of hot air to be controlled is controlled.   Furthermore, when the amount D of the pulverized raw wood that has been dried and carried out from the outlet of the dryer is continuously measured and the moisture content C is lower than a preset moisture content, the amount is insufficient. 3. The drying method according to claim 1, wherein the moisture content is automatically calculated and added based on the difference between the preset moisture content and the moisture content C and the carry-out amount D. 4.   The drying method according to any one of claims 1 to 3, wherein a preset moisture content of the crushed raw wood after drying is in a range of 8 wt% to 13 wt%.   The drying method according to claim 4, wherein a preset moisture content of the crushed raw wood after drying is in a range of 9 wt% to 12.5 wt%.   An apparatus for producing wood pellets from forest land residue such as thinned wood, comprising a cutting process, a sorting process, a grinding process, a drying process, a granulation process, a cooling process, etc. A wood pellet manufacturing apparatus comprising a drying step to which the drying method according to any one of 1 to 5 is applied.   A device for producing wood pellets from forest land residue such as thinned wood, comprising a sawdust production process, a drying process, a granulation process, a cooling process, etc. A wood pellet manufacturing apparatus comprising a drying process to which the drying method according to any one of the above is applied.

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