EP0077909B1

EP0077909B1 - High consistency-aqueous slurry of powdered coal

Info

Publication number: EP0077909B1
Application number: EP19820108435
Authority: EP
Inventors: Akihiro Naka; Shuichi Honjo; Tominobu Mayuzumi; Yasuharu Tanakamaru; Yoshihisa Nishida
Original assignee: Dai Ichi Kogyo Seiyaku Co Ltd
Current assignee: DKS Co Ltd
Priority date: 1981-09-14
Filing date: 1982-09-13
Publication date: 1986-04-09
Also published as: ES8308918A1; EP0077909A3; EP0077909A2; CA1180555A; ES515682A0; DE3270436D1; EP0077909B2; AU8833182A; AU553292B2

Description

Background of the Invention

This invention relates to a high consistency (coal solids content) aqueous slurry of powdered coal which may be conveyed by a hydraulic pump and is combustible as such.
It is well-known that one of major disadvantages of coal compared with petroleum as an energy source is the difficulty of transportation and storage. Powdered coal cannot be conveyed pneumatically because of the danger of spontaneous explosition. It has been proposed to transport powdered coal as an aqueous slurry by pumping. However, as the consistency of powdered coal increases, the slurry will become too viscous and lose its fluidity completely so that its transportation by a hydraulic pump becomes impossible. Transportation at lower consistencies is not attractive not only for economical reasons but also for the incapability of combusting as such.
Polyalkylene oxide nonionic surfactants are already described in EP-A-57 576 which is prior art according to article 54 (3) EPC. Those surfactants disclosed therein are glycol ethers of alkylated phenols of the formula I
poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) of the formula II:
and, block polymers of ethylene oxide and another alkylene oxide derived from alkylene diamines of the formula III:
The starting active hydrogen compounds of nonionic surfactants of formulae I, II and III are alkylated phenols having only one active hydrogen atom, propylene glycol having only two hydrogen atoms and alkylenediamines having only two nitrogen atoms.
Therefore, this prior art does not teach the use of the polyalkylene oxides as described hereinafter.

Description of the Invention

According to the present invention, there is provided a fluid aqueous coal slurry having at least 60% by weight coal solids content and consisting essentially of a mixture of water and powdered coal rendered fluid by the presence therein, as a viscosity lowering agent, of an amount effective to render the slurry fluid of a polyalkylene oxide having a molecular weight of at least 1000 and an oxyethylene unit content of at least 10% by weight, based on the total oxyalkylene unit content, which is characterized in that the polyalkylene oxide is a polyether adduct of a lower alkylene oxide and an active hydrogen compound selected from the group consisting of

(a) polyhydroxyl compounds having at least three active hydrogen atoms;
(b) polyamines having 5 or more active hydrogen atoms;
(c) condensates of a phenolic compound with an aliphatic aldehyde;
(d) polyalkyleneimines and derivatives thereof having 7 to 200 nitrogen atoms;
(e) carboxylic acids; and
(f) compounds having two or more different active hydrogen-containing functional groups.

According to a further embodiment the fluid aqueous coal slurry is characterized in that the polyalkylene oxide is (a) the reaction product of a cross-linking agent with a polyether adduct of an alkylene oxide and an active hydrogen compound, or (b) the reaction product of (a) or of said adduct with an inorganic or organic acylating agent, a halogenating agent, an oxidizing agent or a monoisocyanate.
The polyether compounds may be prepared by first synthesizing the compound a) and then optionally converting the same into compounds b) or c).

a) The compound a) typically has the formula:
wherein Z is the residue of an active hydrogen compound, RO is a C₃ or C₄ oxyalkylene unit, n and m each represents a recurring number, and x is the number of oxyalkylene chain bonded to the residue Z.

The above polyether compound may be prepared in per se known manner by reacting a starting active hydrogen compound with ethylene oxide and optionally with a C_3-C₄ alkylene oxide, epichlorhydrin or ethylene carbonate under elevated pressures in the presence of an acid or alkaline catalyst. Where two or more different alkyene oxides are combined, the resulting copolymer may be either a block or random copolymer. However, the copolymer must contain at least 10% by weight of oxyethylene unit based on the total oxyalkylene chain content. The molar ratio of alkylene oxide to the starting active hydrogen compound is adjusted such that the resulting adduct has a molecular weight of at least 1,000, preferably from 1,000 to 600,000.
The active hydrogen compound used herein must have at least one hydrogen-containing, functional group such as hydroxyl, amino, imino, and carboxylic groups.
Examples of hydroxyl group-containing compounds include water; monohydric alcohols such as ethanol, butanol, octanol, cyclohexanol and benzyl alcohol; dihydric alcohols such as ethylene glycohol, polyethylene glycol, propylene glycol, polypropylene glycol, butanediol, pentanediol and hexanediol; trihydric alcohols such as glycerine, butanetriol, hexanetriol, trimethylolpropane and triethanolamine; tetrahydric alcohols such as diglycerine and pentaerythritol; those having five or more hydroxyl groups such as xylitol, sorbitol, glucose, sucrose, partially saponified products of vinyl acetate polymers or copolymers, cellulose and starch; and the like.
Aromatic hydroxyl compounds may also be used as a starting active hydrogen compounds. Examples thereof include monophenols such as phenol, cresol, xylenol, butylphenol, nonylphenol, aminophenol and hydroxybenzoic acid; polyphenols such as catechol, resorcine and pyrogallol; mono- and polynaphthols such as naphtol, methylnaphthol, butylnaphthol, octylnaphthol, naphthoresorcine and a-naphthohydroquinone; bisphenols such as bisphenol A and bisphenol S; condensates of these aromatic hydroxyl compounds with an aliphatic aldehyde such as formaldehyde, acetaldehyde or glyoxal; and the like.
Examples of amino or imino group-containing compounds include secondary amines such as dimethylamine and N-methyllaurylamine; primary amines such as methylamine, ethylamine, propylamine, butylamine, allylamine, amylamine, octylamine, dodecylamine, laurylamine, tetradecylamine, pentadecylamine, octadecylamine, tallow alkylamine, coconut alkylamine, aniline, p-toluidine, m-toluidine, nitroaniline, benzylamine, chloraniline, p-dodecylbenzylamine and cyclohexylamine; amines having three active hydrogen atoms such as ammonia and tallow propylenediamine; amines having four active hydrogen atoms such as urea, ethylenediamine, tetramethylenediamine, hexamethylenediamine, phenylenediamine, benzidine, dicyandiamide and cyclohexyldiamine; amines having five or more active hydrogen atoms such as diethylenetriamine, triethylenetetramine and tetraethylenepentamine; polyalkyleneimines such as polyethyleneimine, polypropyleneimine, addition products of alkyleneimine such as ethyleneimine or propyleneimine with alochols, phenols, amines or carboxylic acids; condensates of said polyalkyleneimines with aldehydes, ketones, alkyl halides, isocyanates, thioisocyanates, active double bond-containing compounds, epoxy compounds, epihalohydrines, cyanamides, guanidines, urea, carboxylic acids, their acid anhydrides and acid halides; and the like. The polyalkyleneimines and their derivatives preferably have 7 to 200, more preferably 9 to 200 nitrogen atoms per mole.
Examples of carboxylic acids includes monocarboxylic acids such as acetic acid and lauric acid; dicarboxylic acids such as oxalic acid, fumaric acid and maleic acid; tri- or higher carboxylic acids such as trimesic acid, butanetetracarboxylic acid, and pyromellitic acid; and the like.
Compounds having two or more different active hydrogen-containing functional groups such as lactic acid, glycolic acid, glycine, N-monoalkylglycine, malic acid, tartaric. acid, monoethanolamine, diethanolamine and aminoethylethanolamine may also be used as a starting active hydrogen compound.
The average molecular weight of the resulting polyether may be easily estimated by determining the hydroxyl number thereof.
The polyether compounds of the above class a) have at least one free hydroxyl group at the terminal of oxyalkylene chain. This hydroxyl group may be entirely or partially reacted with an appropriate acylating agent to obtain the corresponding inorganic or organic ester. Examples of inorganic acylating agents include sulfuric acid, chlorosufonic acid, sulfamic acid and sodium bisulfite for sulfate esters, and phosphorus pentoxide, metaphosphoric acid and thiophosphates for phosphate esters. These esters may take the form of a free acid or salt with a metal such as sodium, potassium, calcium and magnesium, or other cations such as ammonia, organic amines and quaternary ammonium ions.
Similarly, the hydroxyl group of compound a) may be modified by per se known reaction to obtain the corresponding ester with inorganic or organic acid, halide such as chloride or bromide, aldehyde, carboxylic acid and urethane.
b) Cross-linked polyether compounds b) may be prepared by reacting a polyether compound a) mentioned-above with a cross-linking agent.
A variety of cross-linking agents may be employed for this purpose including polyisocyanates such as hexamethylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate and 4,4'-diphenylmethane diisocyanate; polyepoxy compounds such as diglycidyl bisphenol A, diglycidyl ethylene glycol and diglycidyl tetraoxyethylene glycol; polycarboxylic acids and their functional derivatives (e.g. anhydrides and halides) such as oxalic acid, malonic acid, phthalic acid, maleic acid, glutaric acid, adipic acid, azelaic acid, sebatic acid, dodecanedioic acid, dimer acid, hemimellitic acid, trimellitic acid, butanetetracarboxylic acid, pyromellitic acid, ethylenediamine tetraacetic acid, polymers and copolymers of acrylic acid, polymers and copolymers of methacrylic acid, polymers and copolymers of maleic anhydride. partially saponified polymers and copolymers of acrylates or methacrylates; and functional derivatives (e.g. anhydride or halides) of these acids; polyaldehydes such as glyoxal and succinaldehyde; peroxides (free radical generating catalysts) such as hydrogen peroxide, benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide and dicumyl peroxide; and formaldehyde in combinatioon with acid catalysts.
When the above polyisocyanate or polyepoxide cross-linking agents are used, they may be added in 0.05 to 5, preferably 0.1 to 3 equivalents per equivalent of terminal hydroxyl group present in the polyoxyalkylene chain of the polyether compound a). The reaction may be carried out by heating the reaction components at a temperature of 40 to 150°C, preferably 50 to 120°C optionally in the presence of a conventional acid or alkali catalyst.
Polycarboxylic acids or their derivatives may be used in 0.05 to 5, preferably 0.1 to 3 equivalents per equivalent of said hydroxyl group. The reaction may be carried out at a temperature of 60 to 250°C, preferably 80 to 220°C optionally in the presence of a conventional esterifying catalyst. When acid halides are used, the reaction temperature may be lowered to -10'to 150°C, preferably 0 to 120°C with blowing an inert gas into the reaction mixture or in the presence of an acid acceptor.
The cross-linking of polyethers with free radical-generating peroxide catalysts is known from e.g. Journal of Applied Polymer Science, Vol. 7, 461-468 (1963). Using this technique, polyethers a) may be reacted with 0.05 to 10% by weight, preferably 0.1 to 5% by weight of a peroxide catalyst at a temperature of 50 to 250°C, preferably 70 to 180°C optionally in an inert solvent.
When formaldehyde is used for the cross-linking reaction, 0.1 to 10 equivalents, preferably 0.5 to 5 equivalents of formaldehyde are reacted with one equivalent of polyethers a) in the presence of 0.005 to 0.05 equivalents of a conventional acid catalyst by heating at a temperature of 60 to 100°C for 1 to 3 hours and then continuing the reaction at a temperature of 100 to 180°C.
When the resulting cross-linked polyethers b) still have remaining hydroxyl group or groups, they may be converted into their derivatives c) by modifying the residual hydroxyl group by per se known reactions. Said derivatives include esters with inorganic or organic acids, halides such as chlorides and bromides, corresponding aldehydes or carboxylic acids, and urethanes with monoisocyanates.
Various types of coal may be used for preparing the aqueous slurry of powdered coal of the present invention and include anthracite, bituminous coal, subbituminous coal, lignite and cleaned coal of these types.
The term "cleaned coal" as used herein refers to those products obtained from mined coal by removing or decreasing its inorganic impurity contents such as ash and sulfur. Several processes are known for cleaning coal in this manner such as the heavy media separation process, the oil agglomeration process, the floatation process and other processes. Any process may be applied for preparing cleaned coal used in the present invention.
The oil agglomeration process, for example, may be carried out by adding an amount of oil to an aqueous slurry of pulverized coal particles or suspending oil-coated pulverized coal particles in water, and then stirring the slurry. Organic components in the coal are wetted selectively with oil to agglomerate into a mass, while inorganic impurities thereof remain in the aqueous phase. Separation of aqueous phase from the mixture gives cleaned coal having a greatly reduced inorganic impurity content. The process is generally carried out at a coal concentration from 10 to 65%. Examples of oils which may be used in the oil agglomeration process include petroleum crude oil and liquid fractions thereof such as kerosine, light oil, bunker A, bunker B, bunker C and the like. Other mineral oils such as residue from ethylene-cracking, shale oil, lubricant oil and cleaning oil as well as benzene, toluene, xylene and various animal and vegetable oils may be used. Heavy oils such as bunker C or tar residue oil are preferable for economical reason. The amount of oil needed for giving a satisfactory result is generally less than 20% by weight based on the weight of coal.
The floatation process may be carried out, as is well-known, by adding a very small amount of oil into a pulverized coal-water slurry and then vigorously stirring the slurry to form froth. Organic components of coal selectively adhere to oil films of the froth while inorganic impurities remain in the aqueous phase. Examples of oils which may be employed in the floatation process include terpene oil, tar, bunker A, bunker C, light oil and kerosine.
The above two processes generally reduce the inorganic impurities by several tens of percent of their original contents.
The use of cleaned coal in the composition of this invention has the important advantage that the viscosity lowering agent used herein is more effective with cleaned coal than with uncleaned coal thereby allowing the preparation of slurries having several points higher consistencies than when uncleaned coal is employed. Additionally, damages to boilers and loads to desulfuring and ash disposal equipments are greatly decreased.
It is preferable that the particle size of powdered coal used herein complies with the requirements by various users such as power plants and is such that at least 70% of the particles can pass through a standard screen having 74 x 74 pm square eyes according to JIS.
The viscosity lowering agent used in the present invention remarkably decreases the viscosity of and imparts fluidity to aqueous slurries of powdered coal which are otherwise too viscous to be conveyed by pumping. Normally, simple aqueous slurries of powdered coal will lose fluidity completely at a consistency of 50% or higher. The aqueous slurries of the present invention have a consistency higher than 60%, preferably 70% by weight while retaining sufficient fluidity to be conveyed by pumping. When cleaned coal is used, the consistency may be further increased by 3 to 10 points.
The amount of viscosity lowering agent needed for achieving satisfactory results lies generally from 0.01 to 5.0%, preferably from 0.03% to 2.0% by weight based on the entire composition.
Although the present invention is not bound to a particular theory, it is postulated that the visocosity lowering agent used in the present invention is strongly adsorbed by coal particles on their surfaces because of their unique structure and then hydrated with surrounding water molecules. This results in the formation of lubricant configuration of water molecules surrounding coal particles, while retaining coal particles as stable primary particles, thereby increasing in fluidity and decreasing in viscosity.
It is also postulated that cleaned coal can be fluidized more effectively with the viscosity lowering agent because of its increased organic nature due to the removal of hydrophilic, fine ash components.
The viscosity lowering agent used in the present invention stabilizes the aqueous slurry of powdered coal and prevents coal particles from sedimentating upon stationary standing for a long period of time, e.g. for one month.
Various methods for preparing the aqueous slurry and for mixing the viscosity lowering agent thereto may be employed. For example, coal blocks may be disintegrated in the dry process and the powdered coal may be mixed with water containing the viscosity lowering agent. Alternatively, coal may be disintegrated in a mill by the wet process in the presence of water and the viscosity lowering agent.
The invention is further illustrated by the following examples in which all parts and percents are by weight.

Example 1

Using various viscosity lowering agents listed in Table 1, aqueous slurries as shown in Table 2 were prepared from powdered coal pulverized to 80% passing through a screen having 74 x 74 µm square eyes according to JIS. The viscosities and fluidities of the resultant slurries were determined at 25°C, respectively.
After standing for one month, the occurrence of phase separation in each sample was visually observed.
Alternatively, the slurries were poured into a cylinder up to 18 cm level and allowed to stand for one month. Thereafter, the consistencies at upper layer (up to 1 cm below the top level) and lower layer (up to 1 cm above the bottom) respectively were determined.
The results obtained were shown in Table 2. As shown in Table 2, the aqueous slurries of the present invention have a viscosity ranging from 800 to 2 800 mPas and retain a sufficient fluidity for pumping transportation at a powdered coal consistency ranging from 72 to 77%. It is also noted from Table 2 that the slurries of the present invention are stable upon storage and no or little sedimentation of coal particles occurs upon standing for at least one month.
In contradistinction, control slurries in which no or conventional surfactants are added have a viscosity higher than 20 000 mPas and exhibit almost no fluidity even at a coal consistency of 50%.

Example 2

The procedure of Example 1 was repeated except that cleaned powdered coal was used. Formulations and results obtained were shown in Table 3.
The slurries have a viscosity ranging from 1000 to 2800 mPas and retain a sufficient fluidity for pumping transportation at a coal consistency ranging from 76 to 80%, while control samples exhibit a viscosity higher than 20 000 mPas and no fluidity even at a coal consistency of 50%.
In tables I and 11 compounds nos. 1-3, 5, 7, 4346, 56, 69-70, 74 and 91-93 are outside the scope of the invention. However, these compounds are listed for comparison purposes.

Claims

1. A fluid aqueous coal slurry having at least 60% by weight coal solids content and consisting essentially of a mixture of water and powdered coal rendered fluid by the presence therein, as a viscosity lowering agent, of an amount effective to render the slurry fluid of a polyalkyleneoxide having a molecular weight of at least 1000 and an "oxyethylene unit content of at least 10% by weight, based on the total oxyalkylene unit content, characterized in that, the polyalkyleneoxide is a polyether adduct of an lower alkylene oxide and an active hydrogen compound selected from the group consisting of

(a) polyhydroxyl compounds having at least three active hydrogen atoms;

(b) polyamines having 5 or more active hydrogen atoms;

(c) condensates of a phenolic compound with an aliphatic aldehyde;

(d) polyalkyleneimines and derivatives thereof having 7 to 200 nitrogen atoms;

(e) carboxylic acids; and

(f) compounds having two or more different active hydrogen-containing functional groups.

2. The slurry of claim 1, wherein said starting active hydrogen compound is glycerine, butanetriol, hexanetriol, trimethylolpropane, triethanolamine, diglycerin, pentaerythritol, xylitol, sorbitol, glucose, sucrose, partially saponified poly(vinyl acetate), cellulose or starch.

3. The slurry of claim 1, wherein said active hydrogen compound is diethylenetriamine, triethylenetetraamine or tetraethylenepentamine.

4. The slurry of claim 1, wherein said active hydrogen compound is a condensate of phenol, cresol, xylenol, butylphenol, nonylphenol, aminophenol, hydroxybenzoic acid, catechol, resorcine, pyrogallol, naphthol, methylnaphthol, butylnaphthol, octylnaphthol, naphthoresorcine, a-naphthohydroquinone or a bisphenol with formaldehyde, acetaldehyde or glyoxal.

5. The slurry of claim 1, wherein said active hydrogen compound is polyethyleneimine; polypropyleneimine; an addition product of ethyleneimine or propyleneimine with an alcohol, phenol, amine or carboxylic acid; or a condensate of polyethyleneimine or polypropyleneimine with an aldehyde, ketone, alkyl halide, isocyanate, thioisocyanate, active double bond-containing compound, epoxy compound, epihalohydrin, cyanamide, guanidine, urea or a carboxylic acid or anhydride or acid halide thereof; all containing 7 to 200 nitrogen atoms.

6. The slurry of claim 1, wherein said active hydrogen compound is acetic acid, lauric acid, oxalic acid, fumaric acid, maleic acid, trimesic acid, butanetetracarboxylic acid, or pyromellitic acid.

7. The slurry of claim 1, wherein said active hydrogen compound is lactic acid, glycolic acid, glycine, N-mono-alkyl glycine, malic acid, tartaric acid, monoethanolamine, diethanolamine, or aminoethanolamine.

8. The slurry of claim 1, wherein said coal is cleaned coal.

9. The slurry of claim 8, wherein said slurry has a coal solids content of from 70 to 80% by weight.

10. The slurry of claim 1, wherein said polyether adduct is present in an amount from 0.03 to 2.0% by weight of the slurry.

11. The slurry of claim 10, wherein the coal is cleaned coal, the coal solids content is 76 to 80%, the viscosity lowering agent content of said slurry is about 0.1 to 0.3% by weight and the slurry has a viscosity ranging from 1000 to 2800 mPas.

12. The slurry of claim 10, wherein the coal is uncleaned coal, the coal solids content is 72 to 77%, the viscosity lowering agent content of said slurry is about 0.1 to 0.3% by weight and the slurry has a viscosity ranging from 800 to 2800 mPas.

13. A fluid aqueous coal slurry having at least 60% by weight coal solids content and consisting essentially of a mixture of water and powdered coal rendered fluid by the presence therein, as a viscosity lowering agent, of an amount effective to render the slurry fluid of a polyalkylene-oxide having a molecular weight of at least 1000 and an oxyethylene unit content of at least 10% by weight, based on the total oxyalkylene unit content, characterized in that the polyalkyleneoxide is (a) the reaction product of a cross-linking agent with a polyether adduct of an alkylene oxide and an active hydrogen compound, or (b) the reaction product of (a) or of said adduct with an inorganic or organic acylating agent, a halogenating agent, an oxidizing agent or a monoisocyanate.

14. The slurry of claim 13, wherein said active hydrogen-containing compound has at least one hydroxyl, amino, imino or carboxylic group.

15. The slurry of claim 14, wherein said polyether is (a) and said cros-linking agent is a polyisocyanate, a polyepoxy compound, a polyaldehyde, a functional derivative of polycarboxylic acid or a free radical-generating peroxide catalyst.

16. The slurry of claim 13, wherein said polyether is the reaction product of said adduct or of (a) with a sulfate or phosphate ester.

17. The slurry of claim 13, wherein said coal is cleaned coal.

18. The slurry of claim 17, wherein said powdered coal is present in an amount from 70 to 80% by weight of the slurry.

_.19. The slurry of claim 13, wherein said reaction product is present in an amount from 0.03 to 2.0% by weight of the slurry.

20. The slurry of claim 13, wherein the coal is cleaned coal, the coal solids content is 76 to 80%, the viscosity lowering agent content of said slurry is about 0.1 to 0.3% by weight and the slurry has a viscosity ranging from 1000 to 2800 mPas.

21. The slurry of claim 13, wherein the coal is uncleaned coal, the coal solids content is 72 to 77%, the viscosity lowering agent content of said slurry is about 0.1 to 0.3% by weight and the slurry has a viscosity ranging from 800 to 2800 mPas.