JPH07166180A - Reforming method of low-grade coal - Google Patents

Abstract

(57) [Summary] [Purpose] Increases the calorific value of low-grade coal such as peat, lignite, and subbituminous coal, reduces the risk of spontaneous combustion, and has a high economic value suitable for transportation and storage. Provided is a reforming method for producing coal. [Structure] The dry coal after the water content of the low-grade coal is removed is heat-treated at a reforming temperature of 200 to 400 ° C. using a gas containing hydrogen and carbon monoxide (reducing gas). The dry coal has a water content of 20% by weight or less, and the reducing gas is hydrogen 10
-40% by volume, carbon monoxide 5-30% by volume, H
It is preferable that the ₂ / CO capacity ratio is 0.3 to 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the reforming of low-grade coal, and more particularly, it increases the calorific value of low-grade coal such as peat, lignite and subbituminous coal and reduces the risk of spontaneous combustion. , A reforming method for producing coal of high economic value suitable for transportation and storage.

[0002]

2. Description of the Related Art Low-grade coal such as peat, lignite, and subbituminous coal generally has a high water content, a low calorific value, and is contained in the coal when the water content is lost due to natural drying or the like. Since it has a relatively large amount of oxygen, it has a drawback that it is easy to ignite spontaneously. This hinders the expansion of consumption areas and storage stability due to long-distance transportation, and low-grade coal is effectively used only in a very limited area, that is, a location relatively close to the production area.

Under these circumstances, various proposals have been made for the purpose of dehydrating these low-grade coals, preventing spontaneous ignition, or improving the calorific value.

For example, as a dehydration method, (a) a method of drying low-grade coal at a relatively low temperature of 80 to 150 ° C. (Japanese Patent Laid-Open No. Sho 6-66)
3-32839), as a method for preventing spontaneous combustion,
(B) A method of coating the surface of coal with tar (Japanese Patent Laid-Open No. 61-23889), and as a method of further improving the calorific value, (c) a high temperature gas (combustion exhaust gas) or a gas containing steam in the high temperature gas (JP-A-62-50393), and (d) a method of reforming with copper acetate as a catalyst in a hydrogen gas atmosphere (CHEME).
CA'88, p246-250, 28-31 Aug.
1988).

[0005]

The low-temperature dehydration method (a) described above has an effect of improving heat generation by removing water, but is not effective in preventing spontaneous ignition.

[0006] The coating method (b) can obtain the same amount of heat as the low-temperature dehydration method, and since the surface of the coal is coated with tar to reduce the oxidation rate of the coal at room temperature, it is spontaneously ignitable. Can be improved, but it is still difficult to say enough.

In the high temperature reforming method using the combustion exhaust gas of (c), since the treatment is carried out at a high temperature, the oxygen-containing groups are thermally decomposed and most of them disappear, so that the calorific value is improved as compared with the coating method. Moreover, since the oxygen content in the coal decreases and the coal itself becomes inactive, spontaneous combustion is prevented, but this is also not a sufficient improvement.

On the other hand, in the hydrogen gas reforming method (d), the effect of increasing the calorific value is great and the spontaneous ignition is also improved, but since expensive hydrogen gas and a catalyst are used, it is economical. It is a disadvantage.

As described above, the conventional techniques still have problems of spontaneous combustion and economic problems, and it is necessary to take measures to solve these problems.

The present invention has been made under these circumstances, in which the water content of the low-grade coal is removed and the selective deoxidation is performed to improve the calorific value and to improve the spontaneous combustion. It is an object of the present invention to provide a reforming method for improving coal and obtaining economically valuable coal.

[0011]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the inventors of the present invention have found that if heat treatment is performed under a specific atmosphere and a specific temperature condition, low-grade coal is obtained. The inventors have found that it is possible to obtain economically valuable coal by improving the amount of heat generation and improving spontaneous combustion, and have completed the invention.

That is, the present invention is characterized in that the dry coal after removing the water content of the low-grade coal is heat-treated at a reforming temperature of 200 to 400 ° C. using a gas containing hydrogen and carbon monoxide. To do.

The low-grade coal of the present invention is coal having a relatively low carbon content, and is classified according to the classification of coal.
Means peat, lignite, lignite, subbituminous coal.

According to the International Coal Classification System, volatile matter (anhydrous ashless standard, weight%) and total calorific value (ashless standard, kcal /
The coal is classified according to two parameters (kg, 30 ° C. 96% relative humidity). The low-grade coal according to the present invention is classified as Class 5 to Class 9 of this International Coal Classification System,
For example, lignite (grade 8) has a volatile content of 33% by weight or more,
The total calorific value is 6100 to 7200 kcal / kg.
Here, the volatile content is a value measured by a predetermined test method, in other words, a gas and a tar content generated by decomposing when coal is heated.

Low-grade coal generally has a high water content, for example, some lignite coal contains about 60% by weight of water.

The water content of the low-grade coal in the present invention means the moisture physically attached to the coal. In addition, the water content described below means that the sample has a water content of 11
It refers to the weight loss when heated and dried at 0 ° C. for 2 hours, as a percentage of the weight of the sample before heating.

[0017]

[Equation 1]

Generally, in the process of gasification and liquefaction of bituminous coal, it is not necessary to consider the drying of the raw coal, but when handling low-grade coal having a high water content, the raw coal is usually used. This requires a drying process.

That is, when reforming low-grade coal,
It is preferable to remove as much water as possible before the reforming step within a range that does not hinder the reforming reaction. what if,
If reforming is performed without sufficient dehydration in the drying process,
This is because a large amount of wastewater containing phenols generated by the heat treatment may be generated, which is disadvantageous in terms of wastewater treatment.

As for the degree of drying at this time, there is no particular problem as long as the water content of the dry coal is about 20% by weight or less. The lower limit of the water content is not particularly limited, but is preferably 0% by weight in the present invention.

In the reforming method of the present invention, first, the above-mentioned low-grade coal having a high water content and a low carbon content is used as a raw material, and this is used in air, preferably in an inert gas such as nitrogen gas,
Heat drying is performed under a temperature condition of 85 to 120 ° C. until the water content becomes 20% by weight or less. The drying time at this time is determined in consideration of the type of coal, the water content, the heating temperature, and the like.

Next, the coal dried as described above is
Heat treatment is performed at a predetermined temperature in a reducing gas atmosphere using the hydrogen and carbon monoxide-containing gas (hereinafter referred to as reducing gas).

In the present invention, the above predetermined temperature, that is, the reforming temperature of coal is the temperature at which the oxygen-containing groups decompose.
The temperature is 0 to 400 ° C., preferably 350 to 380 ° C. Two
When the temperature is lower than 00 ° C, the thermal decomposition reaction does not occur so much, and therefore, the oxygen content is not lowered, so that it does not contribute to the improvement of the spontaneous ignition property. On the contrary, when the temperature exceeds 400 ° C, the thermal decomposition reaction becomes excessive. This is because the carbon content will decrease and the carbon content will also decrease, which will exceed the category of coal reforming and lead to the gasification of coal.

According to the present invention, the heat treatment with the reducing gas is performed in this manner to improve the heat generation amount of the low-grade coal,
Moreover, the present invention aims to suppress the risk of spontaneous combustion more than the conventional reformed coal.

In the present invention, as the reducing gas, a gas having a composition of 10 to 40% by volume of hydrogen, 5 to 30% by volume of carbon monoxide, and a H ₂ / CO volume ratio of 0.3 to 8 is used. it can. Preferably, hydrogen is 20 to 30% by volume, carbon monoxide is 10 to 20% by volume, and H ₂ / CO volume ratio is 1.
~ 3.

If the hydrogen content in the reducing gas is less than 10% by volume, the substantial amount of the gas directly involved in the reforming reaction will decrease, which is not preferable. A gas purification facility for increasing the hydrogen concentration is required in the process of producing the reducing gas, which may be economically disadvantageous. Further, if the carbon monoxide content is less than 5% by volume, the substantial amount of gas is reduced for the same reason as above, which is not preferable, and if it exceeds 30% by volume, a hydrogen amount commensurate with this is preferable. _Two
If you try to secure with the / CO ratio (for example 2.3), H
_Since it is almost 100% by volume only with ₂ and CO, C which is usually contained in the produced gas in the reducing gas production process.
It becomes necessary to remove O ₂ , N _{2 and the} like, and a new separation facility for this is installed, which is not preferable in practice.
Furthermore, when the H ₂ / CO ratio (capacity ratio) becomes extremely large or small, it approaches the case of using pure H ₂ or pure CO, respectively, which may be disadvantageous in terms of process economics. Conceivable. Therefore, in the present invention,
0.3-8, preferably 1-5, more preferably 1-3
And

The composition of this reducing gas is close to that of the partial oxidation method of fossil fuels, which is produced by a process using natural gas, petroleum naphtha and the like, which are technically advantageous. In the present invention, the method for producing the reducing gas is not particularly limited, and a gas obtained by a steam reforming method, a partial oxidation method or the like using coal, petroleum naphtha, LPG, natural gas or the like as a raw material can also be used. Considering the economical efficiency of the process, the optimum one may be selected from the processes, and the reducing gas obtained by this process may be used.

The reducing gas may contain a considerable amount of an inert gas such as nitrogen or helium, specifically 30 to 85% by volume, preferably 50 to 70% by volume.

[0029]

[Function] Coal often contains a large amount of oxygen-containing functional groups, and bituminous coal having a large carbon content contains a large amount of phenolic hydroxyl groups (-OH groups) as oxygen-containing functional groups and carboxyl groups ( -COOH group) and carbonyl group (> C =
Very few O groups are present. On the other hand, in the above low-grade coal having a low carbon content, the phenolic hydroxyl group (-
OH group) is the main, but carboxyl group (-C
It is known that OOH groups) and carbonyl groups (> C = O groups) are present in a considerable amount.

Generally, when coal is heated, a thermal decomposition reaction starts at a certain temperature. The temperature at which pyrolysis starts varies depending on the type of coal, but is said to be about 180 ° C. or higher for low-grade coal having a low carbon content. Oxygen-containing functional groups in coal decompose to produce H ₂ O, CO, CO _{2, and the} like.

Then, as the thermal decomposition temperature is increased,
The C—C bond in the coal also undergoes cleavage, and a large amount of coal structure having a small molecular weight is generated. Further, a phenol component which is not produced in the thermal decomposition reaction at a relatively low temperature is also produced in the high temperature thermal decomposition.

That is, the coal is 180
When heated above ℃, oxygen-containing groups such as phenol groups and carboxyl groups undergo thermal decomposition. This reduces the amount of oxygen in the coal and improves the amount of heat generated. Further, when the reforming temperature is 300 ° C. or higher, by using the reducing gas, it is possible to remove the oxygen-containing groups that are difficult to remove only by low-temperature pyrolysis, so that the calorific value can be further increased and the coal can be increased. Becomes hydrophobic, the hygroscopicity decreases, and the coal surface can be inactivated, so that the spontaneous combustion can be decreased.

By reforming in this way, the oxygen content in coal is reduced. Due to this decrease, the concentrations of carbon, hydrogen, etc. relatively increase, and the amount of heat generation improves. Generally, the calorific value of coal is measured by a pump calorimeter or the like, but as a simple measuring method, the calorific value can also be calculated from the elemental analysis value in coal by the calculation shown in Formula 2.

[0034]

[Equation 2]

Further, the self-ignitability of coal is improved by reforming as described above. By the way, when a large amount of coal is stored in open piles, or when piles of hard coal produced by coal preparation in a coal mine are piled up, there is often a phenomenon of self-ignition and continued combustion. This is called spontaneous combustion of coal. Regarding the cause of ignition, the oxygen and moisture present in the air cause the coal to gradually proceed with the oxidation reaction, and the reaction heat generated by this reaction gradually accumulates under the environment, which causes the temperature rise. It has been confirmed by many experiences and experimental facts that the oxidation reaction is accelerated, the temperature is further increased, and the ignition temperature is finally reached. In this case, it is said that the oxidation of pyrite in coal plays a major role. That is, a reaction as shown in Chemical formula 1 occurs and heat is generated.

[0036]

[Chemical 1]

From the above, it is impossible to measure the true pyrophoricity of coal unless it is evaluated by a field test or the like. However, there are the following methods as a method for easily measuring this spontaneous ignition property.

When the temperature of the solid fuel is raised in the air,
It is observed that the oxidation reaction suddenly intensifies from a certain temperature. In the case of solid fuel, this temperature is defined as the ignition temperature.
In Willer's method, the sample is placed in a reaction tube, heated in a sand bath while passing air, and the temperature at which the temperature of the sample rises rapidly is taken as the ignition temperature (the lowest temperature that can be ignited is the ignition temperature or spontaneous ignition). It is defined as the temperature or the ignition point). According to the method of Willer, for example, the ignition temperatures of brown coal (air dried product) and bituminous coal are 250 to 4 respectively.
It is said to be 50 ° C and 325 to 400 ° C. There is also a method using a thermogravimetric / differential thermal analyzer (TG / DTA).

In the conventional reforming method, an inert gas containing oxygen, a gas containing steam in a high temperature gas, or 100% steam is used as the atmospheric gas during the heat treatment. Free hydrogen and carbon monoxide are not present. Therefore, the decarboxylation reaction and the dephenol reaction proceed only by thermal decomposition. Therefore, although selective deoxidation is unlikely to occur and the calorific value is improved, the spontaneous ignition property has not been sufficiently improved.

On the other hand, in the reforming method of the present invention, not only the water content of the coal can be sufficiently removed but also oxygen in the coal can be removed as H ₂ O, CO _2, etc.
The amount of heat generation can be improved. Further, as compared with the above-mentioned conventional reforming method, the hydrophilic oxygen-containing group can be removed and the coal can be further inactivated, so that the spontaneous combustion can be significantly reduced. .

[0041]

【Example】

Measurement method of calorific value: Calculated from the elemental analysis value in coal by the calculation shown in Formula 2. At this time, the numerical value is based on the true calorific value.

Self-ignitability evaluation method: Using a commercially available thermogravimetric / differential thermal analyzer (TG / DTA), the ignition point was measured by the following procedure. That is, about 10 mg of a sample was filled in a sample container for a thermobalance, and while flowing air (research grade) at a flow rate of 200 mL / min, 110
The temperature was raised from 0 ° C. at a heating rate of 2 ° C./min, and the final temperature reached was 500 ° C.

An example of the TG / DTA curve obtained at this time is shown in FIG. FIG. 1 shows the results of measurement using the dry coal used in Comparative Example 1 described below as a sample. In the figure, a peak is seen near 333 ° C. in the differential thermal analysis curve, which is due to burning of the sample. It is shown that. Figure 2
1 shows an enlarged view of the peak rising portion of FIG. Figure 2
In, the broken line A shows the tangent line before the start of combustion, and the broken line B shows the tangent line after the start of combustion. The intersection of the broken line A and the broken line B is C. The temperature at this intersection C was used as an index of spontaneous combustion and was defined as the ignition point.

Example 1 500 g of a raw material brown coal containing 20 wt% of water was mixed with a particle size of 1
The powder was pulverized to a size of not more than mm and dried in an ordinary atmosphere at 110 ° C. for 2 hours until the water content became 0 wt%. Table 1 shows the properties of the obtained dry carbon.

[0045]

[Table 1]

2 g of this dry charcoal was placed in a glass reactor having an inner diameter of 30 mmφ, and the glass reactor was placed with an inner diameter of 50 mm.
It is installed in the central part of a quartz glass tube of φ and 750 mm in length, and a reducing gas having the composition shown in Table 2 is completely supplied from the lower side of the glass reactor by the reducing gas to the glass reactor and the quartz glass tube. 15 minutes until replacement, flow rate 200 mL
/ Min.

[0047]

[Table 2]

After the completion of the substitution, the temperature was raised from room temperature to 300 ° C. at a temperature rising rate of 15 ° C./min at a flow rate of 200 mL / min. After reaching the reforming temperature of 300 ° C., the temperature was maintained for 10 minutes and then cooled to room temperature. The cooling time required about 60 minutes.

The weight of the obtained reformed carbon was immediately measured together with the above glass reactor. After measuring the weight loss due to heating in this manner, elemental analysis was performed using a part of the reformed carbon as a representative sample, and the calorific value was calculated by the formula (2).

Next, the reformed coal was attached to a TG / DTA apparatus, the combustion start temperature was measured, and the inflection point at which the weight reduction started was taken as the ignition point. The results at this time are shown in Table 4 as Example 1. Table 4 also shows the measurement results of the dry coal before the reforming treatment.

Example 2 Example 1 was repeated except that the reforming temperature was 325 ° C. The results at this time are shown in Table 4 as Example 2.

Example 3 Example 1 was repeated except that the reforming temperature was 350 ° C. The results at this time are shown in Table 4 as Example 3.

Example 4 Example 4 was repeated except that the reforming temperature was 375.degree. The results at this time are shown in Table 5 as Example 4.

Example 5 Example 5 was repeated except that the reforming temperature was 400 ° C. The results at this time are shown in Table 5 as Example 5.

Comparative Example 1 Example 1 was repeated except that the composition of the gas introduced from the lower side of the glass reactor was changed to the combustion gas shown in Table 3.
The results when the reforming temperature was 300 ° C. are shown in Table 6 as Comparative Example 1.

[0056]

[Table 3]

Comparative Example 2 The same procedure as in Comparative Example 1 was carried out except that the reforming temperature was 325 ° C. The results at this time are also shown in Table 6 as Comparative Example 2.

Comparative Example 3 The same procedure as in Comparative Example 1 was carried out except that the reforming temperature was 350 ° C. The result at this time is also shown in Table 6 as Comparative Example 3.

Comparative Example 4 The procedure of Comparative Example 1 was repeated except that the reforming temperature was 375.degree. The results at this time are shown in Table 6 as Comparative Example 4.

Comparative Example 5 The same procedure as in Comparative Example 1 was carried out except that the reforming temperature was 400 ° C. The results at this time are shown in Table 6 as Comparative Example 5.

Further, the above Examples 1 to 5 and Comparative Example 1
The ignition points of the reformed coals obtained in ~ 5 are summarized in Fig. 3. It should be noted that in FIG. 3, the treatment temperature is used to indicate the maximum value of the reforming temperature because a continuous temperature raising method is adopted when reforming coal, and is substantially referred to as the reforming temperature. it can.

[0062]

[Table 4]

[0063]

[Table 5]

[0064]

[Table 6]

As is clear from Tables 4 to 5, the calorific value is
In contrast to the dry coal of 5791 kcal / kg, in the present invention, at the reforming temperature of 300 ° C., 6252 kcal / kg.
It can be seen that there is an increase of about 8%, and an improvement of about 8% is seen. When the reforming temperature is raised to 400 ° C., it is increased to 6761 kcal / kg, which is an improvement of about 17%.

The pyrophoric property has a reforming temperature of 300 ° C.
Has an ignition point of 334.4 ° C and a reforming temperature of 375 ° C.
Up to 344.8 ° C and the reforming temperature is 400
When the temperature reaches ℃, it decreases to 335.5 ℃. That is, it is understood that the reforming temperature is preferably around 370 ° C. from the viewpoint of improving spontaneous combustion.

As shown in the comparative example, the ignition point is
Even when the reforming temperature is 375 ° C., it is 336.4 ° C., and even when the reforming temperature is raised to 400 ° C., it is only 339.7 ° C., and improvement in spontaneous combustion is not so much improved.

As a result, the effect of improving spontaneous combustion is shown in FIG.
According to the present invention (Example) shown in Fig. 3, at a reforming temperature of about 370 ° C, the ignition point is about 13 ° C compared to the ignition point of dry coal of 332.0 ° C.
It has a high ignition point, which is about 8 ° C. higher than that of the comparative example (combustion gas reforming method), indicating that the ignition point is considerably improved. This temperature difference becomes a considerable advantage if environmental conditions leading to spontaneous combustion (for example, temperature rise due to heat storage of coal) are taken into consideration. Therefore, according to the present invention, it is understood that a large reforming effect can be obtained as compared with the conventional drying method and combustion gas reforming method.

[0069]

As described above in detail, according to the method of the present invention, it is possible to increase the calorific value of low-grade coal as a raw material, suppress the risk of spontaneous ignition, and transport the coal. -It is possible to obtain coal with high economic value suitable for storage.

[Brief description of drawings]

FIG. 1 is a graph showing an example of a thermogravimetric / differential thermal analysis (TG / DTA) curve.

FIG. 2 is a graph showing an enlarged view of a peak rising portion of FIG.

FIG. 3 is a graph showing the ignition points of the reformed coals obtained in Examples 1-5 and Comparative Examples 1-5.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Yoshizawa 1134-2 Gongendo, Satte City, Saitama Cosmo Research Institute Co., Ltd. Research and Development Center (72) Inventor Hiroshi Echigoya 1-1-1, Shibaura, Minato-ku, Tokyo 1 Cosmo Oil Co., Ltd. (72) Inventor Hiroshi Ishikawa 1-1-1 Shibaura, Minato-ku, Tokyo Cosmo Oil Co., Ltd.

Claims (2)

[Claims] 1. A low-grade coal characterized by heat-treating dried carbon after removing water from the low-grade coal at a reforming temperature of 200 to 400 ° C. using a gas containing hydrogen and carbon monoxide. Reforming method. 2. The method for reforming low-grade coal according to claim 1, wherein the dry coal has a water content of 20% by weight or less.