KR910006132B1 - Process for preparing coal-water dispersion - Google Patents

Abstract

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Description

Process for preparing coal-water dispersion

The present invention relates to a liquid fuel composed of coal powder dispersed in a liquid having a very good shelf life and suitable for transportation and energy generation. More specifically, the present invention relates to a dispersion comprising a liquid consisting of some water, powdered coal and additives, with a coal content of at least 55% by weight.

Dispersion of coal produces relatively less pollution and is easier to handle than solid liquids and can eliminate some of the risks incurred during storage and transportation. Such dispersions are also desirable from an economic point of view.

The use of coal dispersions is due to the planned use of coal as a primary energy source on a large scale, as well as the use of small plants that need to generate electricity and heat. In this respect handling of solid coal is difficult for a variety of reasons and therefore the general method of converting coal into liquid form has been considered beneficial. Chemical conversion of coal to liquid products, the so-called liquefaction, is still not able to compete with oil, and this method was considered to contribute to the global supply of energy other than oil before the 2000s. Chemical conversion, so-called gasification, to convert coal to gaseous products is a more promising method of using coal. However, this method still has a great deal of technical difficulties, although it has spent a lot of resources on technology development.

Physical conversion is another method of converting coal into liquid form and therefore the present invention relates to this method. There is a wealth of experience in dispersing coal in liquids, which can consist only of water or mixed with some organic fuel such as heating oil, methanol and the like.

The present invention basically relates to the dispersion of coal powders in water.

One problem with making coal-water fuels is that the surface structure of the coal will be adjusted when impurities, sometimes chemically additives, are removed, which may add more difficulty to the dispersion of coal particles in the next process.

When the present invention is applied to stabilize a thermodynamically unstable coal-water dispersion, sedimentation and aggregation rates will reduce the formation of a barrier that reacts to particle attraction. This repulsive effect is obtained by three main principles: electrostatic and steric stabilization and stabilization by hydration.

This stabilization regulates the energy of the particles and / or forms a high barrier for their mutual access.

Based on these principles it is possible to stabilize high content of coal particles in aqueous solution by adding small amounts of organic additives.

In attempts to create new colloidal systems, it is necessary to give the system properties such as minimizing the attraction between particles and developing repulsive barriers to condensation and the resulting settling. Some form of steric stabilization by hydrophilic polymers provides effective conditions for long term stabilization of coal-water dispersions.

Processes for the preparation of coal-water fuels often include some form of purification step to remove organic components. Basically, coal is crushed into one or more mills resulting in a polydispersed particle size distribution. All particles are smaller than about 300 μm and about 35% of the total amount is smaller than 40 μm.

The production of coal-water fuels according to the invention is the main process, enriching coal by flocculation and separating and filling coal and impurities by hydrophobization selectively. Then other forms of reagent are usually used, which usually consist of a mixture of blowing agents, such as fatty alcohols. Other reagents suitable for coal flotation include mixtures of oils and traces of alkylsulfosuccinates that are insoluble in water, such as Zwitter ionic surfactants and blowing agents.

After the flocculation process the coal is mechanically dewatered, for example by a rotary vacuum filter. The use of surfactants in dewatering coal has been studied at the laboratory scale as well as at the laboratory scale. Two major types of surfactants have been found to increase the rate of dehydration.

1) Surfactant to control the interfacial tension of water

2) hydrophobic substances

Of the surfactants, the first major form of anionic surfactants has proven to be the most suitable. Alkylarylsulfonates and alkylsulfosuccinates are examples of surfactants that can be used.

The final process in the production of coal-water fuel is the addition of dispersants, which may also be stabilizers. Among the dispersants for coal powders in water or oil are already known, for example anionic polynaphthalene sulfonates, polycarboxylic acids and non-ionic ethylene oxide derivatives.

It is already known that the total amount of dispersant per weight percent of total dispersion is completely determined by the physical properties of the dispersion. Without coal, dispersants are one of the most expensive items in the manufacture of dispersions.

It has also been found that different coals require different types of dispersants and that the present invention can provide a method for preparing effective dispersions for coal particles by varying the charge but with different base charges.

Particularly effective dispersants are formed around the hydrophobic-aromatic moiety and include one or more hydrophilic ethylene oxide chains.

The charge on the molecule may be an anion, a cation or preferably a zwitter ion. The charge on the molecule depends on the charge of the coal itself.

Preferred zwitterionic ionic alkylarylethoxylates of this type of zwitterionic compound are, for example, nonylphen methoxymethyl taurate sodium.

The compound is prepared by the simplest method by reacting a halide obtained by reacting a terminal hydroxide group of nonylphenolethoxylate and a sulfonyl chloride with natriummethyl tauride.

The overall formula of the compound is as follows.

C _x H _y Ar-O (C ₂ H ₄ O) _n C _a H _b N (CH ₃ ) C _c H _d SO ₃ N _a

Another zwitterionic compound that can be used as a good dispersant for a particular coal is the quaternized quaternary nitrogen sulphate. Compounds of this type are available from GAF under the trade name PC-37.

Cationic compounds which can be used according to the invention are mainly based on pyridine and guinoline. They usually have aromatic ring structures with hydrophobic properties. Reaction of the pyridine with ether gives a compound of the alkoxymethylpyridine type. Further characterizing these cationic dispersants is that they contain at least 50 ethylene oxide units.

Among the anionic dispersants, due to their high cost, they are applied to a small extent, but mention may be made of salts of alkylarylethoxylates. Anionic compounds of this type are the most useful for hydrophilic coal.

All dispersants according to the invention have a molar weight of at least 1500 and are soluble in water.

Examples are given for the purpose of illustrating the invention and do not limit the invention.

EXAMPLE

1) A liquid crystal phase is formed by emulsifying a zwitterionic surfactant such as lecithin or alkylbetaine that does not form a micelle and is relatively insoluble. The emulsion (0.03% by weight of coal) is introduced into the grinding stage of the fuel manufacturing process. In the mixing step just before the flotation step, a formulation consisting of lecithin, hexadecane and methylisobutylketone is added at a ratio of 1/5/2. The amount and composition of the whole can vary depending on the quality of the various coals (0.01-0.05% by weight of coal)

After the suspension step a small amount of alkylsulfosuccinate (10-50 g / 1000 kg coal) is added to improve the dehydration rate in the filter. The filter cake contains 15 to 22% humidity.

2) Approximately 90 g of the extracted coal filter cake (22.2%) from the process is homogenized and mixed well with 0.25 g of a dispersant consisting of ammonium salt of nonylphenoxypolyethyleneoxy ethanol dissolved in water and having a molar weight of about 5000.

The resulting coal content of the mixture is adjusted to 70% by variation of the concentration of the dispersion in aqueous solution. The dispersion thus obtained exhibits excellent properties for transport and direct combustion as a liquid fuel.

Zwitterionic or cationic dispersants are used in a similar manner when coal-water fuels are made from hydrophobic coal.

Gelling agents can be added to the dispersion to achieve stability during storage, lumping and stability to settling. Gelation can be irreversible as well as reversible. Reversible gelling can be performed by controlled starch in combination with small amounts of polysaccharides, xanthine gum, cured gum, alginic acid salts or metal ions such as, for example, aluminum or boron. The irreversible gelling process can be adjusted by changing the temperature or pH.

The irreversible gelation of coal-water dispersions can be carried out, for example, with various clays, bentonites, Sino-clays and the like. The fuel product obtained in this way obviously exhibits pseudoplastic rheological properties.

Coal-water fuels are very good oil substitutes for steam generation as well as heat generation. The fuel is refined from many inorganic compounds and is preferred over conventional coal utilization techniques for environmental issues and handling.

Claims (14)

The coal content is characterized by adding to the dispersion an ionic surfactant polymer containing at least one hydrophobic group having affinity to the coal surface and at least one water soluble group based on ethylene oxide having a molar weight of more than 1000. A method for producing a dispersion consisting of powdered coal and water whose surface is controlled by adsorption of zwitter ions or other hydrophobic materials. The method of claim 1 wherein the hydrophobic moiety is formed on one or more directional groups. The method of claim 1 wherein the additive has a charge of zwitter ions. The method of claim 1 wherein the additive comprises a zwitterion group of an amide azoline derivative, a betaine derivative, an amino acid derivative or a lecithin derivative. The method according to claim 4, wherein the entry agent is a zwitter ionic salt or zwitter ionic alkylaryl ethoxylate of an ethoxylated quaternary nitrogen compound. 3. The method of claim 1 or 2, wherein the additive has a cationic charge. 7. The method of claim 6, wherein the additive is an ethoxylated cyclic alkylammonium compound. 8. The unsaturated heterocyclic compound according to claim 7, wherein the additive is added to at least one pyridine, quinoline, isoquinoline, benzidazole, benzthiazole, benztriazole, pyrrolidine, imidazole group or a derivative of these groups. The method as above, characterized in that it is based. 8. The method of claim 7, wherein the additive is based on a saturated nitrogen compound containing at least one piperidine, morpholine group or derivatives thereof. 3. The method of claim 1 or 2, wherein the additive has an anionic charge. The method of claim 10 wherein the additive is a salt of alkylaryloxy ethyleneoxy alcohol. 12. The method of claim 11, wherein the additive is an ammonium salt of alkylphenoxy polyethyleneoxyethanol. The method of claim 1 wherein the total amount of additives does not exceed 2% of the total weight of the dispersion. The method of claim 1 wherein the total amount of additives does not exceed 0.8% of the total weight of the dispersion.