JP2016089100A - Manufacturing method of wood chip for fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a wood chip for fuel for subjecting a wood chip to dehydration treatment in order to use the wood chip as a fuel that obtains a wood chip having a water content of 30-40%, which is suitable for being used as the fuel.SOLUTION: A method for manufacturing a wood chip for fuel includes: a step of determining a flat or slender wood chip which has a water content of 50% or more containing free water and has a thickness in a direction perpendicular to a fiber, as a target, and pressure-dehydrating a chip mat from the thickness direction by a press, in which the wood chips are arrayed and piled while regarding a major axis direction of the fiber of the wood chip as a parallel direction, with a press machine of which a pair of facing press surfaces have a fixed area are equal to each other. The pressing step includes: a) a first step of removing air existing in the chip mat; b) a second step of applying a compressive pressure of 15-25 MPa at the maximum in the thickness direction of the chip, and discharging the free water accumulated in lumen to the outside of the cell; and c) a third step of discharging the residual free water after having been held for 30 seconds or more in the second step, and setting the water content of the wood chip at 30-40%.SELECTED DRAWING: Figure 3

Description

  The present invention belongs to a technical field related to a method for manufacturing a wood chip for fuel that is dehydrated in order to use the wood chip as a fuel.

Recognizing the necessity of using renewable energy against the backdrop of global warming prevention, remnants of forest land with poor traits, left behind in forest land, and backboards, sawdust and bark discharged from wood processing plants The energy utilization of so-called unused wood resources such as residual materials has attracted attention. However, these wood resources generally have a high moisture content (hereinafter abbreviated as "water content") of 50 to 70%, which is not suitable as a fuel as it is, and lowers the moisture content to 40% or less suitable for fuel in advance. There is a need.
In the manufacture of wood materials such as lumber and plywood, mild drying techniques such as natural (sunlight) drying and heat drying have been put into practical use for a long time. Therefore, a processing technique capable of drying to a target moisture content in a short time at a lower cost is required. However, no such means has been found.

For example, as a method for producing wood pellets for fuel, Patent Document 1 discloses a technique in which wet wood powder generated during the processing of wood is compressed to squeeze (dehydrate) moisture, and at the same time, pellets are molded.
However, the outline of the method for producing wood pellets for fuel according to Patent Document 1 is that the ultrahigh pressure of 100 MPa or more is applied to the wood flour to squeeze the cells of the wood at once and dehydration is required, and the ultrahigh pressure is required. Therefore, the facility cost is large and the operation cost is increased.

JP2013-127047A

  According to the present invention, water having a moisture content of about 23% or more of water in wood is liquid free water existing in coarse gaps such as cell lumens, and this free water can be easily compressed by compressing wood. Focusing on the fact that it can be dehydrated, an attempt is made to provide a production method capable of obtaining wood chips with a low water content that can be used as fuel efficiently and with relatively simple equipment without requiring extremely high pressure. To do.

  In order to solve the above-described problems, the fuel wood chip manufacturing method according to the present invention employs means described in each of the claims.

The method for producing a wood chip for fuel according to claim 1 is intended for flat or elongated wood chips having a moisture content of 50% or more including free water and having a thickness in the direction perpendicular to the fiber, and has a pair of opposed constant areas. A step of pressure dehydrating with a press from the thickness direction of the chip mat deposited by arranging the fiber major axis direction of the wood chips parallel to the press surface by a press machine in which the pressed surfaces face each other at equal intervals. The pressure step comprises: a) a first step of lowering the press surface to remove air present in the chip mat; and b) applying a compression pressure of 15 to 25 MPa at the maximum in the thickness direction of the chip, A second step of discharging the free water accumulated in the lumen to the outside of the cell; and c) discharging the remaining free water while maintaining the maximum compression pressure in the second step for at least 30 seconds, and increasing the moisture content of the wood chip. 30-40% It consists of three steps.
According to a second aspect of the present invention, there is provided a method for producing a wood chip for fuel, wherein the wood chip according to the first aspect is a flat or elongated shape having a thickness in a direction perpendicular to the fiber, and the size passes through a sieve opening of 32 mm. The weight ratio of chips collected at 8 mm is 80% or more of the total chip weight, those passing through 8 mm and those passing through 63 mm and collected at 32 mm are less than 10%, and the length is 4 to 120 mm. It is characterized by that.

The method of manufacturing a wood chip for fuel according to the present invention comprises a pair of constant areas facing each other from a chip mat in which the fiber major axis direction of the wood chip is arranged in a direction parallel to the press surface. If the press surfaces are compressed and pressed by press machines that face each other at equal intervals, this compressive force is applied in the thickness direction of the chip, that is, in the diameter direction of the hollow spindle-shaped wood fiber, so that the cells can be crushed with a relatively small force. The free water present in the cell lumen can be effectively squeezed and dehydrated. In addition, the entire chip mat can be dehydrated with a single pressurization operation. In the pressurizing step, after the air existing in the chip mat is extracted in the first step, the second pressurizing step applies a compressive force up to 15 to 25 MPa in the thickness direction of the chip to apply cells. Is crushed in the direction of the diameter (perpendicular to the fiber), and the swell pressure of free water in the cell lumen acts on the wall holes distributed in the end wall, rupturing the cells and discharging the free water out of the cells. Further, in the third pressurizing step, the state in which the maximum pressure is maintained and the cell lumen is substantially consolidated is maintained for 30 seconds or more, and the remaining free water is discharged. In such a series of compression dehydration treatments, after passing through the final third step, the moisture content of the wood chips, which was initially 50% or more, is reduced to a range of 30% to 40% that can be sufficiently used as fuel. Can do. In order to realize this, it is possible to dehydrate wood chips very efficiently with the pressure of a normal press without requiring a special high pressure.
Wood chips are flat or slender with a thickness in the direction perpendicular to the fiber, and the dimensions are 8 mm when the weight ratio of chips passing through a sieve opening of 32 mm and collecting 8 mm is 80% or more of the total chip weight. Squeezing free water from the cell lumen due to cell rupture according to the second step, assuming that less than 10% of the sample passing through 63 mm and 32 mm passing through 63 mm and having a length of 4 to 120 mm are used. Out works effectively.

It is the photograph which shows the wood chip | tip for fuels which concerns on this invention, (A) shows a cutting chip | tip and (B) shows a crushing chip | tip. The schematic diagram which shows the longitudinal cross-section and compression force action direction of the wood cell structure concerning this invention. The graph which shows the relationship between the compressive stress and the chip mat thickness in the wood chip manufacturing method for fuel which concerns on this invention. The schematic diagram which shows the outline of the mat | matte thickness in each compression stage concerning this invention. The graph which shows the actual measurement example of the compressive stress and mat | matte thickness in various maximum compressive stress concerning this invention, (A) shows the case where 100 kg / cm <2> and (B) are 150 kg / cm <2>. In the same graph, (C) is 200 kg / cm 2 and (D) is 250 kg / cm 2. The graph which shows the relationship of the highest compressive stress which influences the chip | tip moisture content after a compression process. The graph which shows the relationship of the maximum stress retention time which influences the chip | tip moisture content after a compression process.

Hereinafter, the form for implementing the manufacturing method of the wood chip | tip for fuel of this invention is demonstrated.
As described above, a large amount of wood debris is discharged from a wood processing factory, and a large amount of forest land residue is discharged from a forest, and these effective uses are required. If these low-quality materials can be used for fuel, they can be one of useful applications. However, these woods are often unsuitable as fuel because they have a lot of raw wood and have a high moisture content.

Therefore, the present invention is intended for wood in a state close to these raw trees, and specifically, for wood having a moisture content of 50% or more, desirably 55% or more.
This moisture content is said to be higher for sapwood than for sapwood in coniferous trees, but for cedar and todomatsu, the sapwood is also as high as sapwood, and the target wood in the present invention is coniferous and hardwood This includes the heart and sapwood.
This is because the pressure dehydration step of the present invention, which will be described later, works effectively on those having a high water content.

In the present invention, the shape of the wood chip is a flat or slender chip having a thickness in the direction perpendicular to the fiber regardless of the manufacturing method. For example, a cutting chip or a crushing chip as shown in FIG. 1 is used. The fiber mainly refers to a temporary canal and a wood fiber found in conifers and broad-leaved trees, and any of them may be used as long as it has the above shape. This is because an effective dehydrating action can be obtained by pressing in the thickness direction of the flat or elongated wood chip in relation to the press described later.
Specifically, the shape of the wood chip is, for example, passing through a sieve opening of 32 mm, and the weight ratio of chips accumulated in 8 mm is 80% or more of the total chip weight, passing 8 mm and 63 mm. Those that pass and accumulate at 32 mm are each less than 10% and have a length of 4 to 120 mm.

The press used in the present invention refers to a press in which a pair of opposed press surfaces having a certain area face each other at equal intervals. For example, it has two (a pair) press surfaces on the upper and lower sides or the right and left sides, and the opposed press surfaces do not face each other linearly like a roller, but are opposed as surfaces having a certain area. The press surface is mainly a flat surface, but is not limited to this, and may be a curved surface, a part of a spherical surface, a folded surface, etc. provided that the opposing surfaces face each other at equal intervals. To do. This is because, as will be described later, when a wood chip is sandwiched between a pair of press surfaces, the entire chip is pressed with as even pressure as possible and in a direction perpendicular to the fiber major axis direction.

  Then, the chip mat is formed by arranging the fiber major axis direction of the wood chip in a direction parallel to the press surface. Here, the direction parallel to the press surface is a flat or slender wood chip, and it may be assumed that linear parallelism may be slightly uneven due to the inclination of the chip or the entanglement of the fibers. I mean. In short, this means a relationship in which the compressive force is applied in the direction perpendicular to the fiber as much as possible with respect to the long axis of the chip (see FIG. 2).

Next, a pressure dehydration step is performed on the chip mat by pressurizing and depressurizing with a press from the thickness direction. The pressure dehydration step includes the following first to third steps. Although it constitutes, in carrying out this process, the present invention pays attention to the structure of a cell provided with wood-bound water and free water.
In other words, the moisture in the wood is liquid water that is contained in the cell wall and retained by physical and chemical bonding forces such as hydrogen bonds and the wood substance, and liquid that is retained in the coarse voids such as the cell lumens by capillary force. There is free water. Of these, since it is only free water that can be easily dehydrated by pressurization, in the present invention, the object to be pressure dehydrated is free water. This free water can move between adjacent cell lumens through small holes called wall holes (pits). In particular, many wall holes are distributed in the end wall adjacent in the fiber long axis direction, facilitating the flow in the fiber long axis direction. On the other hand, the wall hole is weak in strength, and also serves as a starting point for cell rupture against the sudden expansion of free water caused by pressurization. That is, the present invention focuses on the cell structure related to cell arrangement and free water extraction in the wood chip (see FIG. 2).

  First, in the pressure dehydration step, as shown in FIG. 3, there is a region where no stress is generated even when the mat is subjected to compressive deformation in the initial stage of pressurization. This is the first step, and air present in the chip gap is released by pressing the chip mat, and as a result, the density of the chip mat is increased. This first step continues from the start of pressurization until the thickness of the chip mat is reduced to about 60% of the initial thickness (see FIGS. 3 and 4). In this case, the compression deformation speed can be made relatively fast, and can be set to, for example, 5 mm / s to 200 mm / s.

The second step begins with the generation of compressive stress. A compressive force acts directly on the chip itself, and the cells start to compressively deform in the diameter direction. When the thickness of the mat is reduced to a little over 30% of the initial thickness = When the compressive stress reaches about 1 MPa, which corresponds to the lateral compressive fracture strength of wood, the cells are crushed and the free water present in the lumen is also When pressure is applied, cells are ruptured by the pressure, and free water begins to be squeezed. Furthermore, when compressive deformation is applied, the consolidation of the chip and cells is further promoted, the stress increases rapidly, and the ejection of free water is also accelerated accordingly. In the second step, pressing is stopped when the maximum compression stress of 15 to 25 MPa is reached. The mat thickness at that time is extremely thin, about 10% of the initial thickness (see FIGS. 3 and 4).
The third step is a period from the time when the pressing of the mat is stopped in the second step until the maximum stress is maintained for a certain time and the pressure is released. In this state, the chip cells are almost consolidated, and an effect of promoting discharge of free water remaining in the mat is expected. The holding time of the maximum stress is in principle until the discharge of the squeezed water ends. However, since a considerable amount of time is required for the water discharge to stop completely, the stress holding time is from the stop of pressing until the time when the drainage speed decreases.
Table 1 shows the results obtained through the above steps using the maximum pressing stress and holding time as independent variables. The shape of the wood chips used in the tests in Table 1 is that the size of the chips that pass through a sieve opening of 32 mm, the weight ratio of the chips that accumulate in 8 mm is 80% or more of the total chip weight, those that pass 8 mm, and 63 mm Those that pass and accumulate at 32 mm are each less than 10% and 4 to 120 mm in length.

That is, as shown in FIGS. 3 and 4, when compressive pressure is applied in the thickness direction of the chip mat, the thickness of the chip mat becomes lower and stress is generated. When the pressurization is continued, dehydration is started at a certain point, and as described above, the outflow of the zir and a large amount of water is observed around the chip mat. When the set maximum stress is reached, the pressurization is stopped, the maximum stress is maintained for a certain period of time, the pressure is released, and a series of compression and dehydration processes are completed.
FIGS. 5A, 5B, 6C, and 6D show the measured compressive stress and mat thickness when the maximum set stress is set to 100 kg / cm ² (10 MPa) to 250 kg / cm ² (25 MPa). The time curve is shown. The mat thickness ratio at each time point of stress generation, dehydration start and maximum stress in FIG. 4 is determined based on the actual measurement results. In this test, the deformation speed is different from that shown in FIG. 3 because a press tester having a constant deformation speed is used.
Furthermore, from the relationship between the maximum set stress and the moisture content (see Fig. 7 and Table 1), the moisture content of chips before compression dehydration shows a high rate of 60-70%, but the moisture content after treatment is set to the maximum. As the stress increases, it is reduced from about 40% to about 35%. Especially when the maximum stress is 15MPa or more, it is confirmed that even a high moisture content chip exceeding 60% can be reduced to the target of 40% or less. It was done.
On the other hand, adoption of the maximum pressure exceeding 25 MPa is effective for manufacturing chips with a lower moisture content, but increasing the set pressure inevitably increases the size of the press machine. It was decided that the decision should be made in view of the risks caused by rising running costs.

The reason why this excellent dehydrating effect is induced is assumed as follows.
First, as described above, the water in the wood includes bound water and free water, and the free water can move between adjacent cell lumens through a wall hole (pit). As shown in FIG. 2, many wall holes are distributed particularly in the end wall adjacent to the fiber long axis direction to facilitate the flow in the fiber long axis direction. On the other hand, the wall hole is weak in strength, and also serves as a starting point for cell rupture against the sudden expansion of free water caused by pressurization. Therefore, when the fiber major axis direction of the wood chip is arranged in a direction parallel to the press surface and pressurized in the perpendicular direction, the cells are crushed in the diametrical direction, and free water is also pressed, which eventually causes a weakness in strength. The destruction of a wall hole and cell rupture is caused. Such cell destruction occurs at a pressure as low as about 10 kg / cm ² (1 MPa), and it is considered that the increase in pressure gradually leads to tissue destruction at a high strength level. By the way, it is added that the quality of the fuel chip is not related to the tissue destruction unlike the wood for material.

  In particular, in the second step, it is important that the squeezed free water can flow out from the deposited chip to the outside. Therefore, it is preferable to relatively slow the mat pressing speed in order to secure the flow path. The lowering speed is at least slower than that of the first pressurizing step, and is preferably about 1 to 10 mm / s, for example.

In the third pressurizing step, the maximum pressure state is maintained (see FIGS. 3 and 5). This is because, at the end of the second pressurization step, most of the free water present in the cell lumen will be discharged, but there is still a possibility that the free water may remain at a certain rate, Is to encourage
As shown in FIG. 8, the holding time at this time is 150 kg / cm 2 (15 MPa) to 250 kg / cm 2 (25 MPa). It can be seen that 20 seconds is insufficient and at least 30 seconds or more is necessary. However, even after 30 seconds or more, the water content after dehydration hardly decreased, so 30 seconds was judged appropriate.
Thus, the moisture content of the wood chips can be 40% or less, and the moisture content suitable for use as fuel can be achieved.
On the other hand, the minimum water content achieved by dehydration was 30%. The chip fuel moisture content of 30-40% is sufficient for quality and practical use.

  Before and after the first pressurization process to the third pressurization process, a pre-process in which the press surface descends to the deposit and a post-process in which the press surface is lifted after depressurization are added. The pressure dehydration process is performed again, and the compression dehydration process for a predetermined amount of wood chips is completed by repeating these steps (see FIG. 3).

Summing up the above, the present invention has a flat or slender chip shape with a thickness in the direction perpendicular to the fiber for wood having a moisture content of 50% or more, and the fiber long axis direction of the chip is arranged in parallel to the press surface. Since the deposited chip mat is compressed and pressed by a surface press from a right angle direction, it effectively works in the direction of discharging free water existing in the cell lumen to the outside of the cell. In addition, a relatively large amount of chips can be dehydrated by a single pressurizing operation.
In the pressurization step, in the first step, the air existing in the gaps between the accumulated flat chips can be discharged, and the density can be increased to a close state.
After the intimate state, the process reaches a second step in which stress is generated inside, and dehydration starts from a very small value of compressive stress of about 1 MPa, and dehydration is progressed by consolidation until the maximum set stress of 15 to 25 MPa is reached. Will continue. This is due to the action of stress that shrinks the diameter of the hollow spindle-shaped cells that make up the chip, causing cell destruction due to turgor pressure generated in the free water present in the cell lumen. It will be squeezed out.
The third step aims to maintain the maximum pressure for a certain period of time (30 seconds or more) and to promote the discharge of remaining free water.
By these, the wood chip containing water having a water content of 50% or more is dehydrated to 30 to 40% or less, and the wood chip can be reduced to a water content suitable for use as fuel.
In realizing this, the wood chip can be efficiently and economically dehydrated by the pressure of a normal press without requiring a special high pressure or a large-scale apparatus.

Claims (2)

With a press machine with a moisture content of 50% or more including free water and a flat or elongated wood chip having a thickness in the direction perpendicular to the fiber as a target, a pair of opposed press surfaces having a constant area face each other at equal intervals,
Comprising the step of pressure dehydrating with a press from the thickness direction of the chip mat deposited by arranging the fiber major axis direction of the wood chips in a direction parallel to the press surface;
The pressurizing step
a) a first step of lowering the pressing surface and removing air existing in the chip mat;
b) a second step of applying a compression pressure of up to 15 to 25 MPa in the thickness direction of the chip to discharge free water accumulated in the cell lumen to the outside of the cell;
c) comprising the third step of maintaining the maximum compression pressure in the second step for at least 30 seconds or more and discharging the remaining free water and setting the moisture content of the wood chips to 30 to 40%.
A method for producing a wood chip for fuel. The shape of the wood chip according to claim 1 is a flat or slender shape having a thickness in the direction perpendicular to the fiber, and the size passes through a sieve opening of 32 mm, and the weight ratio of chips collected at 8 mm is 80% of the total chip weight. The method for producing a wood chip for fuel according to the above, wherein what passes through 8 mm and what passes through 63 mm and accumulates at 32 mm are each less than 10% and have a length of 4 to 120 mm.