JPH0142993B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a coal/solvent paste suitable for a pre-treatment or a pre-liquefaction process for coal liquefaction, specifically, a method for producing coal such as lignite, sub-bituminous coal, bituminous coal, etc. In order to effectively utilize especially inexpensive lignite, coal such as lignite (hereinafter abbreviated as lignite) is subjected to non-evaporative dehydration treatment, and then the dehydrated lignite and circulating solvent from the liquefaction process are fed to a wet mill to reduce the particle size. Coal (lignite), which is made to improve economic efficiency and yield in the liquefaction process by causing mild thermal decomposition to reduce carboxyl groups during preparation.
The present invention relates to a method for producing a solvent paste.

[Conventional technology]

BACKGROUND ART Conventionally, techniques for effectively utilizing coal containing a large amount of water by liquefying it are already generally known. In particular, effective use of inexpensive lignite to improve the yield of liquefied oil will reduce the cost of lignite liquefied oil and become an effective way to use resources.

[Problem to be solved by the invention]

Lignite contains a large amount of oxygen in the form of functional groups such as carboxyl groups (-COOH groups), hydroxyl groups (-OH groups), and carbonyl groups (-CO groups). It contains a large amount of water, and some lignite coals can have a water content of about 60% by weight. For this reason, when lignite is directly hydrogenated and liquefied, carboxyl groups, etc. are separated by heat, hydrogen, etc. during the liquefaction process, and carbon dioxide and water vapor are generated, which greatly increases the amount of hydrogen consumed under hydrogenation. However, this method has disadvantages in that it is not economical, the yield of submerged oil is reduced because the liquefaction reaction product contains a large amount of carbon dioxide and water vapor, and the cost of processing these by-products is high.

Furthermore, when lignite is non-evaporatively dehydrated to reduce the moisture content from 60 to 70% by weight to around 20% by weight, the porosity of dehydrated lignite increases to 50%.
At the stage of mixing this dehydrated lignite with a circulating solvent, which is a liquefaction solvent, to prepare a slurry, the viscosity becomes extremely large, making it difficult to improve the lignite/solvent ratio, and it is difficult to prepare the slurry. When adding catalyst in stages, the viscosity of the catalyst increases due to its large porosity, which may cause problems with the boost pump needed to obtain the high pressure required for submerged reactions, impairing continuous operation. There was an inconvenience. FIG. 1 is a curve diagram showing the results of a test conducted by the present inventors, and shows the relationship between the amount of powder added and the viscosity of the slurry when preparing a slurry using powder and a solvent. The solid line indicates high porosity (60-70
%) and heavy oil, the dashed line indicates the case where the slurry was prepared using fine powder with a low porosity (10% or less) such as coal and heavy oil. There is. In FIG. 1, it can be seen that when the amount of powder added is, for example, 40% by weight, the high porosity slurry has a viscosity approximately three times that of the low porosity slurry.

The present invention was developed in view of the above points, and in the slurry preparation stage, a slight thermal decomposition reaction of the coal/solvent system is caused, the coal particles are completely dissolved, a paste is prepared, and the residual moisture and carbon dioxide content are removed. By removing these substances, it is possible to process coal, which tends to be in the form of a slurry with high porosity and high viscosity, even at a low solvent ratio, and to improve the liquefied oil yield in the liquefaction process. The purpose is to provide a manufacturing method.

[Means and actions for solving the problem]

In order to achieve the above object, the present invention
The manufacturing method of solvent-based is that in the coal liquefaction process, which uses coal containing a large amount of water as a raw material, the coal is heated under high pressure with steam or high-temperature water to perform non-evaporative dehydration, and then the dehydrated coal and the liquefaction process are heated. The circulating solvent from
A coal/solvent paste with a viscosity that can be supplied to a liquefaction reactor is prepared by performing mild thermal decomposition at ~450°C for a reaction time of 0.2 to 2 hours, and residual moisture and carbonates are removed. be.

Preheating in the conventional coal liquefaction process involves preheating the supplied pulverized coal (70 to 80°C in this case) using the heat of the circulating solvent itself. In addition, when sending high moisture lignite etc. to the liquefaction process, the necessary
The slurry is heated in a heating furnace to provide heat of 430 to 500℃, but since dehydrated lignite contains about 20% water by weight, a separate preheating furnace is used to prevent the partial pressure of water vapor from rising in the heating furnace. It is necessary to remove the moisture by means such as evaporation flashing.

Usually, the preheating furnace is for the above purpose,
This preheating furnace can reach temperatures above 100°C, which is necessary for moisture evaporation.
It is usually carried out in a temperature range of up to about 150°C. However, even if high-moisture lignite is dehydrated without evaporation and then finely pulverized as it is, the size of the porosity does not change, and the above-mentioned normal operation cannot produce a high-concentration slurry, resulting in a decrease in liquefaction yield. Moreover, at the above operating temperature, it is impossible to completely drive out the heteroatoms that form the moisture contained in lignite.

In the case of the present invention, while pulverizing and mixing bulk non-evaporative dehydrated lignite and circulating solvent in a ball mill, slight thermal decomposition is caused over time at a temperature lower than the liquefaction reaction temperature and higher than the conventional preheating temperature. The water in the lignite is evaporated and separated in the form of heteroatoms, creating a water-free coal/solvent paste (close to swollen coal), which is then led to the next heating furnace and liquefied. It is heated to a predetermined temperature and sent to a hydrogenation reaction tower.

Therefore, preheating in conventional liquefaction is for removing moisture, and the heat load on the heating furnace in the next step is large, but in the case of the method of the present invention, a heat load is applied to the light pyrolysis furnace, and the heating furnace This reduces the heat load on the As mentioned above, heteroatoms such as carboxyl groups, hydroxyl groups, and carbonyl groups, which are the cause of residual moisture in lignite, are difficult to remove by conventional evaporation and flashing methods. This is an important method for improving the liquefaction yield because it can be completely removed for the first time.

In this specification, the term "mild" is used because pyrolysis at 450 to 500°C usually involves the production of liquid through thermal decomposition, as well as the generation of gas and heavy components.
The expression "mild" is used to mean that the reaction with the solvent takes time (because it is at normal pressure) at a thermal decomposition temperature that does not generate gas or heavy components, and the meaning of preheating is Rather, it can be described as the first stage of normal pressure low temperature liquefaction in a two-stage liquefaction process.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows an example of the manufacturing process of the present invention. Lignite (raw coal) containing a large amount of moisture is first coarsely crushed in a crusher, then heated under high pressure with steam or high-temperature water for non-evaporative dehydration treatment, and then dehydrated lignite and water under normal pressure. separated. As mentioned above, lignite contains oxygen in the form of functional groups such as carboxyl, hydroxyl, and carbonyl groups, and due to the presence of these hydrophilic functional groups, it contains a large amount of water in the capillaries, so water evaporates. When the temperature is raised in a non-evaporating atmosphere, such as a saturated steam atmosphere, functional groups such as carboxyl groups decompose to generate a decomposed gas mainly composed of carbon dioxide, and moisture is released in liquid form. Therefore, dehydration can be performed without providing latent heat of vaporization, and heat recovery of the mixture (hot water) of dehydrated water and condensed water of the steam used to heat the raw material lignite is also possible. Since the oxygen content in the brown coal is reduced, there are advantages such as being able to reduce the amount of hydrogen added in the liquefaction process. The dehydrated lignite is supplied to a wet mill such as a ball mill along with the circulating solvent from the liquefaction process, and the particle size is adjusted to suit the liquefaction process. Mild thermal decomposition is carried out under conditions, preferably 350 to 430°C, reaction time 0.2 to 2 hours, preferably 0.5 to 1.5 hours,
That is, wet pulverization and thermal decomposition are performed to prepare a coal/solvent paste having a viscosity that can be supplied to a liquefaction reactor. In addition, during wet grinding and thermal decomposition, carbon dioxide and water vapor that cannot be removed by non-evaporative dehydration are released by thermal decomposition, releasing heteroatoms in the brown coal, and improving the grade of the brown coal. Hydrogen is then added to the lignite/solvent paste, which is further preheated to liquefy in the reactor, the reaction product is fractionated, and a portion of the distillate oil and/or a portion of the reaction product is transferred to the circulating solvent. Use as.
In this case, the heat value of the distillate oil and/or the reaction product can be effectively utilized, so there is an advantage that it is extremely thermoeconomical.

FIG. 3 shows an example of a wet mill device, that is, a wet grinding/pyrolysis device. Reference numeral 1 denotes a heating furnace, and a cylindrical wet ball mill 2 is disposed within this heating furnace 1. A supply screw 3 is connected to one end of the wet ball mill 2, and an intermediate tank 4 is connected to the other end of the wet ball mill 2. The coarsely pulverized dehydrated coal input from the dehydrated coal input port 5 and the circulating solvent introduced from the solvent inlet 6 are mixed by the supply screw 3 and supplied into the wet ball mill 2, where they are crushed and mixed, and are It is heated to a certain temperature and is thermally decomposed. In other words, residual moisture contained in lignite and carbon dioxide caused by carboxyl groups are removed. The lignite/solvent paste prepared in the wet mill device flows into the intermediate tank 4 and is temporarily stored therein, and is then sent to a preheater and a reactor (not shown) by a high-pressure pump 7 to be liquefied. The gas generated in the wet crushing/pyrolysis process is extracted from the upper part of the intermediate tank 4 and introduced into the condenser 8, and the oil component of the liquid condensed in the condenser 8 is returned to the intermediate tank 4.
Moisture is extracted from the system through a moisture extraction pipe 9, and at the same time, acidic gases such as carbon dioxide and hydrogen sulfide are extracted from the system through an acidic gas extraction pipe 10. 11
1 is a circulation pump connected to the intermediate tank, 12 is a burner of the heating furnace, and 13 is an exhaust port of the heating furnace.

In the present invention, a wet ball mill is used because
A wet ball mill has a structure suitable for producing mild thermal decomposition while preparing lignite to the particle size required for the liquefaction process, provides a grinding and appropriate mixing effect, and can be processed continuously. When using the method of the present invention as a pre-liquefaction treatment, compared to the conventional method of liquefying while maintaining homogeneous mixing of the three components of solid-liquid and gas phases, only the paste and gas phases are treated, which is particularly sensitive to solids. There is no need to use .

〔Effect of the invention〕

As explained above, the method of the present invention removes residual moisture and heteroatoms such as carboxyl groups contained in lignite in the wet grinding/pyrolysis process before the main liquefaction process. It has effects such as being able to improve the liquefied oil yield in the liquefaction process and reducing hydrogen consumption.

[Brief explanation of drawings]

FIG. 1 is a curve diagram showing the relationship between the amount of powder added and the slurry viscosity when preparing a slurry using powder and a solvent, where the solid line indicates a high porosity slurry and the broken line indicates a low porosity slurry. FIG. 2 is a manufacturing process diagram showing an example of the method of the present invention, and FIG. 3 is an explanatory diagram showing an example of a wet crushing/pyrolysis apparatus. 1... Heating furnace, 2... Wet ball mill, 3... Supply screw, 4... Intermediate tank, 5... Dehydrated coal inlet,
6...Solvent inlet, 7...High pressure pump, 8...Condenser, 9...Moisture extraction pipe, 10...Acidic gas extraction pipe, 1
1...Circulation pump, 12...Burner, 13...Exhaust port.

Claims (1)

[Claims] 1. In a coal liquefaction process that uses coal containing a large amount of water as a raw material, after heating the coal under high pressure with steam or high-temperature water to perform non-evaporative dehydration,
The dehydrated coal and the circulating solvent from the liquefaction process are fed to a wet mill, and the particle size is adjusted to suit the liquefaction process, while under normal pressure, at a temperature of 250 to 450°C, and for a reaction time of 0.2 to 400°C.
A coal/solvent paste characterized by performing mild thermal decomposition under conditions of 2 hours to prepare a coal/solvent paste having a viscosity that can be supplied to a submerged reactor, and removing residual moisture and carbonates contained therein. manufacturing method.