JP4883560B2 - Method for producing wood solid fuel - Google Patents

Description

The present invention mainly relates to this granular material in used as fuel for stoves and boilers timber in the raw material in the production method of the wood solid fuel obtained by molding into pellets.

  In recent years, environmental issues have been regarded as important, and with the recognition of the formation of a recycling-oriented society and the global challenges of carbon dioxide reduction, wood biomass energy with the characteristics of carbon neutral as a promising energy source to replace fossil fuels Has attracted attention. Among them, wood solid fuel, also called wood pellets, is widely used as a heat source for stoves and boilers because of its constant shape and high calorific value per unit volume.

This kind of solid wood fuel is roughly classified into three types: white pellets whose main part is wood, bark pellets whose main part is bark, and whole wood pellets mixed with bark part.
By the way, as a result of component analysis for the purpose of safety investigation for effective utilization of combustion ash of wood solid fuel, the inventors of the present application have found that in some wood solid fuel, It was found that hexavalent chromium exceeding the judgment standard value (1.5 mg / l) for specially controlled industrial waste based on the “Law” was released. Therefore, it was aimed at establishing the safety of solid wood fuel. We have developed a method for suppressing the dissolution of hexavalent chromium from combustion ash.

The following three factors can be considered as factors for adding chromium to the wood pellet combustion ash.
(I) Tree-derived (absorption from soil during growth)
(B) Derived from the manufacturing process (chromium contamination in metal due to wear of raw material crusher and pelletizer)
(C) Combustor-derived (mixed due to high-temperature corrosion and wear of stainless steel used in combustion parts, etc.)
Due to these factors, there is no problem as long as the chromium added to the ash is harmless and stable as metallic chromium or trivalent chromium, but in the combustion process, partly changes to harmful hexavalent chromium. .

  The inventors of the present application investigated the elution factor of hexavalent chromium and investigated the elution amount of hexavalent chromium and the ash composition. As a result, by adding a calcium compound to the raw material of the wood solid fuel, It was found that valence chromium elution can be greatly suppressed.

  Conventionally, as a technique for adding a calcium compound to a solid wood fuel, for example, there is a technique described in Patent Document 1 (Japanese Patent Laid-Open No. 61-228096). This is a technology for blending 0.2 to 3.2% by weight of calcium carbonate with respect to the entire fuel, but its purpose is to prevent the ash produced by combustion from solidifying and preventing the clinker from agglomerating. This is because the grate is prevented from being blocked and the combustion efficiency is not lowered.

Japanese Patent Laid-Open No. 61-228096

By the way, in the technique of adding the calcium compound, since the purpose is to prevent the ash produced by combustion from being melted and solidified to prevent the clinker from being agglomerated, the suppression of hexavalent chromium elution is not considered. However, there was a problem that the amount added was not within the proper range.
That is, if the added amount of the calcium compound is small, there is no effect, and if it is too much, calcium remains as ash, so that the amount of ash increases and the ash treatment is hindered.
The present invention has been made in view of the above points, and an object of the present invention is to make it possible to reliably suppress elution of hexavalent chromium by setting the amount of calcium compound added to an appropriate range.

As described above, the inventors of the present application investigated the hexavalent chromium elution amount and the ash composition in order to investigate the hexavalent chromium elution factor. As a result, although described later, the following tendency was confirmed.
(I) The calcium content in ash and the elution amount of hexavalent chromium tend to decrease exponentially (FIG. 1).
(Ii) The potassium content in ash and the elution amount of hexavalent chromium tend to increase exponentially (FIG. 2).
(Iii) For ash having a calcium / potassium ratio of 6 or more in ash, the elution amount of hexavalent chromium is surely below the reference value (FIG. 3).
Based on these tendencies, the results of the addition test of the calcium compound to the raw material of the solid wood fuel resulted in the addition of 1% by mass to 4% by mass of the calcium compound to the raw material of the solid wood fuel. It was confirmed that the elution amount of chromium decreased below the reference value.

Therefore, in order to solve the above-mentioned problems, the method for producing a solid fuel of the present invention uses a wood granule as a raw material, dries the granule, and forms the dried granule into a pellet. In the manufacturing method of the wooden solid fuel manufactured by
It is set as the structure which adds 1-4 mass% calcium compound with respect to the said dried granular material to the said granular material.

  If the addition of calcium is less than 1% by mass, the effect is uncertain, and if it exceeds 4% by mass, calcium remains in the combustion ash and the amount of ash increases, which impedes ash treatment. . Thereby, in the technique of adding this calcium compound, it is possible to reliably suppress elution of hexavalent chromium by setting the addition amount of the calcium compound within an appropriate range.

Moreover, in determining the addition amount of the calcium compound in the range of 1 to 4% by mass, it is desirable to reduce the addition amount as much as possible and to reduce the amount of combustion ash as much as possible. The determination of the amount of calcium compound by the elution amount of hexavalent chromium / calcium ratio was examined.
However, the elution amount of hexavalent chromium is difficult to estimate by semi-quantitative analysis such as fluorescent X-ray analysis of combustion ash, and the elution amount of hexavalent chromium must be performed by chemical analysis, so analysis work is extremely difficult. It has become complicated.
In addition, when determining the total chromium / calcium ratio, it is easy to determine the total chromium amount because it is relatively easy to measure. However, not all chromium is changed to hexavalent chromium by combustion, and the ratio is not limited. Since it varies depending on the combustion conditions, etc., it is difficult to estimate the amount of hexavalent chromium from the amount of total chromium. When the amount of calcium added is determined by the amount of total chromium, the amount of ash is substantial. There is a problem that it increases.

By the way, as shown in the above (ii) and (iii), the inventors of the present application are closely related to the potassium content in ash and the elution amount of hexavalent chromium. It was also confirmed that the ash having a potassium ratio of 6 or more had a hexavalent chromium elution amount that was surely below the standard value.
The fact that the potassium content in ash and the elution amount of hexavalent chromium are closely related to each other is that potassium in the form of potassium carbonate is usually contained in ash from which pellets are incinerated. When this potassium carbonate and chromium come in contact with each other at a high temperature, alkali melting occurs and it is considered that chromium is easily oxidized into hexavalent chromium in an atmosphere of high temperature oxygen.

  In general, the amount of potassium has an advantage that the combustion ash can be easily estimated by semi-quantitative analysis such as fluorescent X-ray analysis. Therefore, in the combustion ash obtained by burning the dried granule, The mass ratio of calcium is obtained, and the amount of calcium compound can be easily determined from this. That is, the amount of calcium compound can be easily determined by the calcium / potassium ratio.

Therefore, according to the present invention, the above-described calcium compound is added as necessary so that the mass ratio R of calcium to potassium in the combustion ash satisfies R ≧ Rs with the predetermined mass ratio Rs being Rs = 6.
Thereby, the calcium compound can be set and added with the required amount as small as possible, and the amount of combustion ash can be reduced as much as possible to reliably suppress the elution of hexavalent chromium.

In this case, the calcium compound is added so that the mass ratio R of calcium to potassium in the combustion ash is 7 ≧ R ≧ Rs, with the predetermined mass ratio Rs being Rs = 6.
As a result, the calcium compound can be added in an appropriate range with the addition amount as small as possible, and the amount of combustion ash can be reduced as much as possible to reliably suppress the elution of hexavalent chromium.

And if necessary, in determining the addition amount of the calcium compound, first, in the combustion ash obtained by burning the dried granule, the mass ratio Ra of calcium to potassium is obtained, and the mass ratio Ra is When the mass ratio is less than Rs, the difference E = Rs−Ra is obtained, and an amount of calcium compound corresponding to the difference E or more is added.
Thereby, the calcium compound can be set and added with the required amount as small as possible, and the amount of combustion ash can be reduced as much as possible to reliably suppress the elution of hexavalent chromium.

  Moreover, it is set as the structure which uses 1 type (s) or 2 or more types among calcium carbonate, calcium hydroxide, and calcium sulfate as said calcium compound as needed. It can be used relatively inexpensively.

According to the method for producing a woody solid fuel of the present invention, it is possible to reliably suppress the elution of hexavalent chromium in the combustion ash by setting the addition amount of the calcium compound in an appropriate range. Further, if the calcium compound is added so that the mass ratio R of calcium to potassium is R ≧ Rs with the predetermined mass ratio Rs being Rs = 6, the calcium compound is set with the required amount as small as possible. The amount of combustion ash can be reduced as much as possible, and the elution of hexavalent chromium can be reliably suppressed.
As a result, the elution of hexavalent chromium in the solid wood fuel ash can be suppressed, the anxiety about the wood pellet fuel can be eliminated, and the use of wood biomass energy can be expanded.

Hereinafter, with reference to the accompanying drawings, with the production method of the wood solid fuel according to an embodiment of the present invention will be described in detail. The types of solid wood fuel are roughly classified into three types: white pellets in which the wood part is the main raw material, bark pellets in which the bark part is the main raw material, and whole wood pellets mixed in the xylem bark part.

  As shown in FIG. 1, the method for manufacturing a wood solid fuel according to the embodiment of the present invention uses wood particles as a raw material. As the timber, various timbers are used. For example, bark and sawdust discharged from a lumber mill / chip factory, and wood processing by-products such as planer scrap and sawdust discharged from a laminated lumber factory / precut factory are used.

When the raw material is sawdust, large wood is pulverized by a known pulverizer and processed into powder.
Then, with a known dryer, the moisture content (dry basis) is about 15% to 45% depending on the conditions of the tree species / pellet molding machine.

  Next, as shown in FIG. 1, the dried granular material is formed into a pellet shape while being heated to, for example, 250 ° C. by a known pellet forming machine.

In the case of this shaping | molding, as shown in FIG. 1, 1-4 mass% calcium compound is previously added and mixed with the granular material with respect to the dried granular material. As the calcium compound, one or more of calcium carbonate, calcium hydroxide, and calcium sulfate are used.
The calcium compound is added so that the mass ratio R of calcium to potassium in the combustion ash satisfies R ≧ Rs, where Rs = 6. In this case, the calcium compound is added so that the mass ratio R of calcium to potassium is 7 ≧ R ≧ Rs, with the predetermined mass ratio Rs being Rs = 6.

  In determining the addition amount of the calcium compound, first, in the combustion ash obtained by burning the dried granular material, the mass ratio Ra of calcium to potassium is obtained, and the mass ratio Ra is a predetermined mass. When the ratio is less than Rs, the difference E = Rs−Ra is obtained, and an amount of calcium compound corresponding to the difference E or more is added.

Specifically, for example, when the calcium compound is calcium carbonate, the analysis result of the content (mass%) in the combustion ash before addition is 40% calcium and 20% potassium, and the granular material as the raw material The amount of addition when the ash content is 0.5% will be described.
The mass ratio of potassium to calcium in this granule is Ra = 2, and the amount of calcium carbonate required to add the difference E = Rs−Ra = 6-2 = 4 to make Rs = 6 is It becomes as follows.
The ash mass generated from 1 kg of the granular material having an ash content of 0.5% is 5 g, the calcium mass in the ash is 2 g, and the potassium mass is 1 g. In order to set E = 4, the calcium mass is insufficient 4 g. Since the molecular weight of calcium carbonate is 100.09 and the atomic weight of calcium is 40.08, the mass of calcium carbonate corresponding to 4 g of calcium is 10 g. In this case, calcium carbonate is added to 1 kg of the weight of the granule. Add 10 g, ie 1% by weight.

In woody solid fuel produced by such a production method, when the burned as fuel for stoves and boilers, but the combustion ash generated by the addition of calcium compound, elution of hexavalent chromium is suppressed. In this case, the calcium compound is added so that the mass ratio R of calcium to potassium in the combustion ash is 7 ≧ R ≧ Rs with the predetermined mass ratio Rs being Rs = 6. Can be added in an appropriate range as small as possible, and the elution of hexavalent chromium can be reliably suppressed by reducing the amount of combustion ash as much as possible.

Next, experimental examples will be described.
[Experimental Example 1]
Four types of wood solid fuel, white pellets made from wood parts and whole wood pellets mixed with wood bark, are prepared for two tree species and burned to obtain combustion ash. The calcium content of each combustion ash And the elution amount of hexavalent chromium were investigated.
The results are shown in FIG. From this result, it was found that the calcium content in the combustion ash and the hexavalent chromium elution amount tended to decrease exponentially.

[Experiment 2]
For each combustion ash used in the above experimental example, the correlation between the potassium content and the hexavalent chromium elution amount was examined.
The results are shown in FIG. From this result, it was found that the potassium content in the combustion ash and the hexavalent chromium elution amount tended to increase exponentially.

[Experiment 3]
For each combustion ash used in the above experimental example, the correlation between the calcium / potassium ratio and the hexavalent chromium elution amount was examined.
The results are shown in FIG. From this result, it was found that the ash having a calcium / potassium ratio of 6 or more in the combustion ash has a hexavalent chromium elution amount lower than the reference value (1.5 mg / l).

  From this experimental result, it was found that the elution amount of hexavalent chromium was reduced below the reference value by adding 1% by mass to 4% by mass of the calcium compound to the raw material of the solid wood fuel. Moreover, since excessive addition of a calcium compound leads to an increase in ash content and an increase in pellet manufacturing cost, it is necessary to grasp the minimum necessary addition amount. As a guideline for the optimum addition amount, a calcium / potassium ratio of 6 or more was found to be a guide.

Next, examples will be described. In this example, a granular material obtained by pulverizing larch with the highest elution amount of hexavalent chromium was added to calcium carbonate and formed into a pellet. A wood solid fuel containing 1% by mass of calcium carbonate (Example 1). ), 2 mass% added wood solid fuel (Example 2), and 4 mass% added wood solid fuel (Example 3).
And the elution amount of hexavalent chromium was investigated about the combustion ash after combustion for the wood solid fuel which does not add calcium carbonate as a comparative example.
The results are shown in FIG. It was found that the elution amount of hexavalent chromium was reduced to about 1/1000 by the addition of the calcium compound.

It is a figure which shows the manufacturing method of the wood solid fuel which concerns on embodiment of this invention. It is a graph which concerns on the experiment example of this invention, and shows the correlation with a calcium content rate and hexavalent chromium elution amount about combustion ash. It is a graph which concerns on the experiment example of this invention, and shows the correlation with potassium content rate and hexavalent chromium elution amount about combustion ash. It is a graph which shows the correlation with calcium / potassium ratio and hexavalent chromium elution amount about combustion ash regarding the experiment example of this invention. It is a table | surface figure which shows the result of the elution suppression of hexavalent chromium about the Example of this invention with the data of a comparative example.

Claims (3)

In a method for producing a solid fuel of wood, which uses a powder of wood as a raw material, dries the powder, and forms the dried powder into a pellet.
While adding 1 to 4% by mass of calcium compound to the dried granules ,
A method for producing a solid wood fuel, wherein the calcium compound is added so that the mass ratio R of calcium to potassium in the combustion ash satisfies 7 ≧ R ≧ Rs, where Rs = 6 . In determining the addition amount of the calcium compound, first, in the combustion ash obtained by burning the dried granular material, the mass ratio Ra of calcium to potassium is obtained, and the mass ratio Ra is less than the predetermined mass ratio Rs. when, it calculates the difference E = Rs-Ra, the production method of the wood solid fuel according to claim 1, characterized by adding an amount of calcium compound corresponding to more than the difference E. The method for producing a woody solid fuel according to claim 1 or 2, wherein one or more of calcium carbonate, calcium hydroxide, and calcium sulfate is used as the calcium compound.

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