COAL-WATER DISPERSION

Abstract: Dispersion containing water, pulverized coal and additives, which is stable for storage, pumpable and combustible by conventional technique applied for liquid fuels. The coal content amounts to at least 55 % by weight. The dispersion contains as an additive a ionic surfactant polymer with at least one hydrophobic part with great affinity to the coal surface and at least one hydrophilic part based on ethylene oxide with the mole weight exceeding 1,000. The charge of the polymer is preferably zwitterionic or cationic.

Description: COAL-WATER DISPERSION The present invention relates to a liquid fuel comprising pulverized coal dispersed in a liquid, which has a very long storage life and is suitable for transport and energy production. More particularly, the invention relates to a dispersion comprising a liquid which at least partially consists of water, pulverized coal and additives, the coal content being at least 60 % by weight. A dispersion of coal is considerably less pollut¬ ing and can be more easily handled than solid coal and also eliminates some risks involved in transport and storage. Such a dispersion is also preferred from an economical point of view. The reason for using coal dispersions is the planned increased use of coal as a basic energy source in large as well as small plants for producing electricity and heat. The handling of solid coal in this connection is difficult for several reasons and, therefore, the transformation of the coal to liquid form generally is considered an interesting method. Chemical conversion of coal to a liquid product, so- -called liquefaction, still cannot compete with oil and it is considered that this method can contribute to the global energy provision only marginally before the year 2000. Chemical conversion of the coal to a gaseous product, so-called gasification, seems to be a more prosperous method of utilizing coal . However, also this method still involves considerable technical difficulties although large resources have been spent on technical development. Physical conversion is another method of transform¬ ing the coal into liquid form, and the invention relates to this method. It is practised by dispersion in a - " BUREAIT OMPI liquid which may consist of water only or water in combination with some organic fuel such as heating oi 1 , ethanol , etc. The present invention principally relates to a dispersion of pulverized coal in water. One of the problems in producing a coal-water fuel is that the surface structure of the coal is modified in removing impurities, often by means of chemical additives, and that the dispersion of the coal particles in a later processing stage will be more difficult as a consequence thereof. When coal-water dispersions which by definition are thermodynamically instable, are being stabilized the sedimentation and aggregation rates are reduced, in applying the invention, by creating a barrier which counteracts the particle attraction. This repulsive effect can be achieved by three main principles: electrostatic stabilization, sterical stabilization, and stabilization by means of h dration forces. The stabilization changes the energy of the particles and/ or creates a high barrier preventing particle attrac¬ tion. On the basis of these principles it is possible to stabilize high contents of coal particles in a water solution by -the addition of small amounts of organic additives. In order to create new colloidal systems it is necessary to impart to the system such properties that the attraction forces between the particles are minimized and a repulsive barrier against flocculation and subsequent sedimentation is developed. Some form of sterical stabilization by means of hydrophilic polymers provides favourable conditions for a long-term stabil¬ ization of coal-water dispersions. The process of manufacturing a coal-water fuel often includes removal of inorganic constituents in one way or the other. Initially, the. coal is ground in one or more mills to a polydisperse particle size distribution. All particles are smaller than about 300 microns and about 35 % of the total amount are smaller than 40 microns. When manufacturing a coal-water fuel according to the present invention, a main process step included • therein is a flotation enrichment of the coal, which by selective hydrophobization and charging separates coal and contaminants. For this purpose, different types of reagents are used which generally comprise mixtures of aliphatic alcohols together with a frothing agent. Other reagents which are suitable in the flota¬ tion of coal are mixtures of zwitterionic surfactants and oils insoluble in water together with a frothing agent and trace amounts of al kylsul pho-succinates . After the flotation process the coal is dewatered mechanically, e.g. by means of a rotating vacuum filter. The use of surface-active substances in dewatering coal has been studied in laboratories as well as pilot scale. It has been found that there are two types of surfactants improving the degree of dewatering: 1/ Surfactants changing the surface tension of the water. 2/ Substances having hydrophobi zing properties. Among surfactants of the first main type anionic surfactants have shown to be the most suitable. Examples of surfactants which can be used are alkylaryl-sulpho- nates and al kylsul pho-succi nates . In the final processing stage in manufacturing the coal-water fuel a dispersion agent and possibly a stabilizer are added. Among dispersion agents already known for pulverized coal in water or oil are e.g. anionic polynaphtalen sulphonates, polycarboxyl ic IfϋREAl OMPI acids and non-ionic ethylene oxide derivatives. It is previously known that the total amount of dispersion agent calculated as a weight percentage of the total dispersion, is completely decisive for the physical properties of the dispersion. Apart from the coal, the dispersion agent is one of the significant items of expenditure in the manufacture of the dispersion. It has also been found that different types of coal require different types of dispersion agents and therefore the present invention provides a method of effecting dispersion of coal particles with the same type of basic compound but with different charges. Particularly active dispersion agents are built-up around a hydrophobic aromatic part and one or more hydrophilic ethylene oxide chains. The molecular charge can be anionic, cationic or preferably zwitterionic.. The charge of the molecule is varied with the surface charge of the coal itself. Among the zwitterionic compounds of ttiis type it is suitable to choose a zwitterionic alkylaryl ethoxylate e.g. sodium nonyl phenetoxy methyl tauride. The compound is most easily produced by a reaction between the terminal hydroxide group of the nonyl phenol ethoxylate and sulphonyl chloride, the resultant halid-e being allowed to react vfith sodium methyl tauride The sum formula of the compound is V< y Ar - 0(C 2 H 4 0) n C a H b N(CH 3 )C c H d S0 3 Na Other zwitterionic compounds which constitute excellent dispersion media for certain coals are ethoxylated quartenary nitrogen sulphates . This type of compound is sold commercially by GAF under the designa¬ tion PC-37. Cationic compounds which can be used according to the invention are based primarily on pyridine and quinoline. An aromatic ring structure with hydrophobic properties is common to them all. Pyridine reacts with ethers to form compounds of the type alkoxymethyl pyridine. These cationic dispersion agents, moreover, are characterized in that they contain at least 50 ethylene oxide units. Among the anionic dispersion agents which are applied to a less extent due to the higher price thereof there may be mentioned salts of alkylaryl ethoxylate. Anionic compounds of this type are most appropriate for hydrophilic coals. All dispersion agents according to the invention have mole weights over 1,500 and are soluble in water. The invention will be described by means of an illustrative example. 1/ A non-mi celle-forming and therefore relatively sparingly soluble zwitterionic surfactant such as lecithin or alkyl betaine, is emulsified in water to form a liquid crystalline phase. The emulsion (0.03 % by weight of the coal) is supplied to the grinding step of the fuel preparation process. In a mixing step immedi- ately before the flotation step, a preparation consisting of lecithin, hexadecane and methyl- isobutyl ketone is added in the ratio 1/5/2. The total additive amount and the composition can be varied for different coal qualities (0.01 - 0.05 % by weight of the coal). After the flotation process, a small amount of alkylsulpho-succinate (10 - 50 g/ton coal) is added to improve the dewatering degree in the filter. The filter cake contains between 15 and 22 % moisture. 2/ About 90 grammes of the moist purified coal filter cake from the process (22.2 %) is homogenized and mixed with 0.25 grammes dispersion agent dissolved in water and comprising an ammonium salt of nonyl phenoxy polyethylene oxyethanol with a mole weight of about 5,000. By varying the concentration of the aqueous solution with regard to the dispersion medium the resultant coal content of the mixture is adjusted to 70 % . The dispersion obtained in this manner has excellent properties for transport and direct combustion as a liquid - fuel. In order to achieve storage stability, stability against coalescense and sedimentation a gelation agent can be added to the dispersion. The gelation can be reversible as well as irreversible. Reversible gelation can be attained with small amounts of polysaccharide, xantan gum, guar-gum, alginate or a modified starch in combination with a metal ion, e.g. aluminium or boron. The reversible gelation process can be controlled by changing the temperature or the pH. Irreversible gelation of the coal-water dispersion can be effected e.g. by means of different clays, bentonite, Chinese clay, etc. The fuel product obtained has now a clearly pseudoplastic rheology. The coal-water fuel has been found to be a very good oil" substitute for heat as well as steam production. The fuel is purified from a lot of inorganic contaminents and is preferred from an environmental and handling point of view to conventional coal technology. jUREΛϋ OMPI

Claims: CLAIMS 1. Dispersion containing water, additives and pulverized coal, the surface of which has been modified by absorption of zwitterionic or other hydrophobi zing substances, the coal content being at least 55 % by weight of the dispersion, c h a r a c t e r i z e d in that at least one of the additives included in the dispersion is a ionic surfactant polymer containing at least one hydrophobic group with affinity to the coal surface and at least one water-soluble group based on ethylene oxide with the mole weight exceeding 1,000. 2. Dispersion as claimed in claim 1 , c h a r a c t e r i z e d in that the hydrophobic part is built-up on one or more aromatic groups. 3. Dispersion as claimed in claim 1, c h a r a c t e r i z e d in that the additive has zwitterionic charge. 4. Dispersion as claimed in claims 1 and 3, c h a r a c t e r i z e d in that the additive contains zwitterionic groups of imidazolene derivatives, betaine derivatives, zwitterionic amino acid derivatives, or lecithin derivatives. 5. Dispersion as claimed in claims 1, 3, and 4, c h a r a c t e r i z e d in that the additive is a zwitterionic salt of an ethoxylated quartenary nitrogen compound or a zwitterionic alkylaryl ethoxylate. 6. Dispersion as claimed in claims 1 and 2, c h a r a c t e r i z e d in that the additive has a cationic N charge. 7. Dispersion as claimed in claims 1, 2, and 6, c h a r a c t e r i z e d in that the additive is an ethoxylated cyclic al kylammoni um compound. 8. Dispersion as claimed in claims 1, 2, 6, and 7, c h a r a c t e r i z e d in that the additive is based on an unsaturated heterocyclic compound including at OMPI least one of the groups pyridine, quinoline, iso- quinoline, benzindazole, benzthiazole, benztriazole, pyrrolidine, imidazole, or derivatives of these groups.. 9. Dispersion as claimed in claims 1, 2, 6, and 7, c h a r a c t e r i z e d in that the additive is based on a saturated nitrogen compound including at least one of the groups piperidine, morpholine or derivatives thereof. 10. Dispersion as claimed in claims 1 and 2, c a r a c t e r i z e d in that the additive has an anionic charge. 11. Dispersion as claimed in claims 1, 2, and 10, c h a r a c t e i z e d in that the additive is a salt of an alkylaryl oxyethylene oxyalcohol. 12. Dispersion as claimed in claims 1, 2, 10, and 11, c h a r a c t e r z e d in that the additive is an ammonium salt of an alkyl phenoxy polyethylene oxyethanol . 13. Dispersion as claimed in claims 1 to 12, c h a r a c t e r i z e d in that the total amount of additive does not exceed 2 % of the total weight of the dispersion. 14. Dispersion as claimed in claims 1 to 13, c h a r a c t e r z e d in that the total amount of additive does not exceed 0.8 % of the total weight of the dispersion.

Inventors: STIGSSON LARS LENNART, STIGSSON, LARS, LENNART
Applicants: FLUIDCARBON INTERNATIONAL AB
Application year: 1983
Main classification: C10L1
IPC codes: C10L1