JPH0248036B2 - - Google Patents

Description

Claim 1 Consisting of water, pulverized coal and additives, the pulverized coal content is 60 to 80% by weight, lecithin and other zwitterionic surfactants are adsorbed on the surface of the pulverized coal as additives, and A pulverized carbon aqueous dispersion system characterized in that a zwitterionic surfactant and a polymer cooperate, and at least one of the polymers is a copolymer of polyethylene oxide and polypropylene oxide in which the amount of polypropylene oxide is larger.

2. The finely divided carbon aqueous dispersion system according to claim 1, wherein the copolymer has a molecular weight of 5,000 to 50,000.

3. The pulverized carbon aqueous dispersion according to claim 2, wherein said copolymer contains at least 70% by weight of polyethylene oxide and has a molecular weight of 8,000 to 15,000.

4. The finely divided carbon aqueous dispersion system according to claim 1, wherein one of the polymers is polysaccharide.

5. The finely divided carbon aqueous dispersion system according to claim 4, wherein the polysaccharide is xanthan gum or guar gum.

6. The pulverized carbon aqueous dispersion system according to claim 1, wherein the total amount of additives is less than 2% by weight.

Description The present invention relates to a coal-water dispersion system that is highly suitable for storage and for transportation and energy production. More particularly, the invention relates to a dispersion comprising water, pulverized coal and additives, with a coal content of 60-80% by weight.

Coal dispersions are considerably less polluting and easier to handle than solid coal, while eliminating the risks associated with transportation and storage. Moreover, such a dispersion system is preferable from an economic point of view.

The reason for using coal-dispersed systems is that the use of coal is expected to increase on a large scale as a basic energy source and in small factories to produce electricity and heat.
In this context, solid coal is difficult to handle for several reasons, and therefore conversion of coal to a liquid state is generally considered the preferred method. The so-called liquefaction process, which involves chemically converting coal into liquid products, has not yet been able to compete with oil, and it is thought that this method could only play a supporting role in global energy supplies before the year 2000. ing. The so-called vaporization process, which chemically converts coal into gaseous products, appears to be the preferred method of utilizing coal. However, this method still has considerable technical difficulties, even though a considerable amount of money has been invested in its technological development.

Another method of converting coal into a liquid state is physical conversion, and the present invention relates to this method. It is done by dispersing the coal in a liquid consisting of heating oil, some type of organic fuel such as methanol, etc., or water.

The problem in aqueous dispersions of pulverized coal lies primarily in making the dispersion stable at low viscosities. Coal particles must not settle during storage or transportation of the coal dispersion. Additionally, the coal dispersion should have rheological properties to be suitable for combustion using conventional techniques, optionally with slight modifications, and should have high pumpability.

Among the earlier proposals for stabilizing coal-water dispersions were the Soviet publication Khim, Pereab. Topl. 1975,
30(2), pp. 19-29, and Chemical
There is a proposal summarized in Abstracts 87:55532b.
In this case, salts of polycarboxylic acids, polyphosphates, and others are used as stabilizers. The optimum mixture viscosity is about 5P at a coal content of 57-63%, so this dispersion is not satisfactory for the demand. Furthermore, the stability of the precipitate is insufficient.

Swedish Application No. 7805632-2 describes a coal-water dispersion in which the stabilizing effect against precipitation is achieved with customary polyelectrolytes, especially polyphosphates (according to the same principles as described in the above-mentioned Soviet publication). system is disclosed. In this case too, stability against precipitation is insufficient.

US Pat. No. 4,242,098 describes a coal-water dispersion in which stabilization is achieved with the addition of several water-soluble polymers (polyethylene oxide, polyacrylamide, etc.). This dispersion is an improvement over the previously described dispersion.

The theory of stability of dispersion systems has recently been considerably refined. The theory evolved to include more dense systems, but especially new types of interactions were tested. Besides the traditionally known effects, such as electrostatic stabilization by surfactants and polyelectrolytes and steric stabilization by polymers, there is a further central effect, the so-called hydration force. This hydration power has recently been verified and explained theoretically. This hydration force, optionally together with other types of interactions, forms the main basis of the present invention to provide long-term stable coal-water dispersions of the type described above. This coal-water dispersion is well suited to be directly combusted using available technology, optionally with slight modifications. According to the invention, this dispersion has the characteristics of claim 1.

This dispersion has rheological properties that allow it to be pumped and transported in pipelines with greatly reduced frictional forces, and, inter alia, has considerably improved stability against agglomeration and sedimentation.

When a coal-water dispersion, which is naturally thermodynamically unstable, is stabilized, the rate of precipitation and agglomeration is reduced by the creation of a barrier that acts against particle attraction. This repulsion is achieved by three main principles: electrostatic stability, steric stabilization, and hydration stabilization. Stabilization alters the energy of the particles and/or creates a barrier that prevents attraction of the particles. Based on these principles, it is possible to stabilize high content coal particles in aqueous solution by adding small amounts of organic additives.

In order to create new colloidal systems, it is necessary to impart properties to the system that minimize the attractive forces between particles and develop a barrier against agglomeration and subsequent precipitation. Some form of steric stabilization by hydrophilic polymers provides favorable conditions for long-term stability of coal-water dispersions.

Studies of lamellar liquid crystal phases in ionic surfactant systems have shown that these phases can swell and take up large amounts of water. This is explained by repulsion in the water layer between adjacent layers of surfactant and may also be related to electrostatic double layer forces. For zwitterionic materials such as the phospholipid lecithin, the swelling is less pronounced but very pronounced. This shows that significant repulsion exists even in the absence of pure charge. This repulsive force, or so-called hydration force, changes approximately exponentially with distance, with a deviation of 2 to 3 Å. This force is of a general nature, does not change depending on the length of the alkyl chain or the physical state of the alkyl chain (liquid or solid), and it is
It is also present when a surfactant is included in the system. Hydration forces were also verified by directly measuring the forces acting between surfaces several angstroms apart from each other. A theoretical model of hydration forces has recently been devised, which makes it possible to link hydration forces to the presence of so-called mirror charge at interfaces where the effective dielectric constant is changing. Such mirror charge by zwitterionic groups is common in micro and macro heterogeneous systems. This is utilized in the present invention to impart desired properties to suspensions of low dielectric materials. Zwitterionic surfactants such as lecithin can then be adsorbed onto the surface of the solid particles. Then, a strong repulsive force exists between the particles at a short distance.
This principle is therefore particularly useful for dense dispersions.

The invention will be explained in more detail with reference to the following examples.

Example 1 A non-micelle-forming zwitterionic surfactant such as lecithin or alkyl betaine (which is therefore relatively poorly soluble in water) is first dissolved in an organic solvent. The solvent may consist, for example, of octanol, hexadecane or methanol and may be recovered in a suitable manner or may contain a small amount of dispersant.

2 Add the prepared surfactant to the dispersion of pulverized coal and water. The appropriate size of coal powder has a wide particle size distribution (polydisperse coal powder)1
~200μm. Particle size and particle size distribution can be selected depending on the desired stability. The smaller the particle size, the greater the stability, but it is expensive to grind coal to ultra-micrometer particle sizes. Particle concentration can vary over a wide range. Considering economic and technical aspects, the particle concentration should be optimized accordingly. Coal-water dispersions with a dry matter content of 65 to 75% by weight are particularly useful as they have good rheological properties (eg for transport in pipelines). In order to achieve the maximum coal content (70-80% by weight) the particle size distribution must be particularly taken into account. In the normal case, this can be done based on simple geometrical calculations that ensure the least free space when packing particles of different sizes.

After the adsorption step, to provide some form of steric barrier and to reduce friction between the particles,
Two or more hydrophilic anions and nonionic polymers are added to the dispersion. It can be chosen, for example, among polyethers, polysaccharides, polyalcohols, polyacrylates. Particularly suitable according to the invention are polyethylene oxide, copolymers of the polyethylene oxide-polypropylene oxide type, carboxymethyl cellulose, and xanthan gum. In terms of weight percent based on total weight, the polymer concentration can be from 0.1 to 5%, but economically, about 0.5% is optimal.

Certain alkali or alkaline earth metal salts may be added to the dispersion to make it more attractive as a non-polluting alternative to oil. Preferably the salt is calcium hydroxide or dolomite powder. Salt neutralizes acidic gas components generated by fuel oxidation and is used in particle separators (particle separators).
percipitator).

Auxiliary agents may be added to the dispersion to form a monolayer at the interface to prevent water from evaporating from the dispersion. Such auxiliaries include cetyl alcohol and hexadecanol.

The present invention has substantial advantages over prior art techniques for stabilizing coal particles in aqueous solutions. Due to the excellent precipitation stability combined with rheological properties favorable for pumping, the resulting dispersions can be used in a suitable manner in conduits or pipelines, for example for use in the chemical industry or for direct energy production. Well suited for transport.

Combustion tests in boilers designed for heavy oil showed that the dispersion system is very suitable for replacing all or part of heavy oil.