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(11) | EP 0 077 909 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | High consistency-aqueous slurry of powdered coal |
| (57) There is provided a high consistency-aqueous slurry of powdered coal capable of conveying
by a hydraulic pump and combusting as such comprising at least 60% by weight of powdered
coal, water and, as a viscosity lowering agent, a polyether compound or a derivative
thereof containing at least 10% by weight of oxyethylene units based on the polyoxyalkylene
chain thereof. |
BACKGROUND OF THE INVENTION
[0001] This invention relates to a high consistency aqueous slurry of powdered coal which may be conveyed by a hydraulic pump and is combustible as such.
[0002] 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.
DESCRIPTION OF THE INVENTION
[0003] According to the present invention, there is provided a high consistency aqueous slurry of powdered coal capable of conveying by a hydraulic pump and combusting as such.
[0004] The slurry contains, as a viscosity lowering agent an effective amount of a polyether compound selected from the group consisting of:
(a) an adduct of an active hydrogen compound with a lower alkylene oxide containing at least 10% by weight of oxyethylene unit based on the total oxyalkylene chain content;
(b) a cross-linked product of said compound a); and
(c) a reaction product of said compound a) or b) with an inorganic or organic acylating agent, a halogenating agent, an oxidizing agent or a monoisocyanate, said polyether compound having a molecular weight of at 1,000.
[0005] The viscosity lowering agents used herein may be prepared by first synthesizing the compound a) and then optionally converting the same into compounds b) or c).
[0006] 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.
[0007] 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 C3-C4 alkylene oxide, epichlorhydrine or ethylene carbonate under elevated pressures in the presence of an acid or alkaline catalyst. Where two or more different alkylene 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.
[0008] The active hydrogen compound used herein must have at least one hydrogen-containing, functional group such as hydroxyl, amino, imino, and carboxylic groups.
[0009] 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.
[0010] Aromatic hydroxyl compounds may also be used as a starting active hydrogen compound. 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-naphthohydrequinone; 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.
[0011] 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 alcohols, 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.
[0012] Examples of carboxylic acids include 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.
[0013] 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.
[0014] The average molecular weight of the resulting polyether may be easily estimated by determing the hydroxyl number thereof.
[0015] 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 an 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.
[0016] 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.
[0017] Cross-linked polyether compound b) may be prepared by reacting a polyether compound a) mentioned-above with a . cross-linking agent.
[0018] A variety of cross-linking agents may be employed for this purpose and include polyisocyanates such as hexamethylene diisocyanate, tolylene diisocyante, 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 fuctional derivatives (e.g. anhydride or halides) of these acids; polyaldehyde such as glyoxal and succinal- dehyde; peroxides (free radical generating catalysts) such as hydrogen peroxide, benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide and dicumyl peroxide; and formaldehyde in combination with acid catalysts.
[0019] When the above polyisocyanate or polyepoxide cross-linking agnets 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.
[0020] 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.
[0021] Cross-linking of polyethers with free radical-generating peroxide catalysts are known in 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.
[0022] When formaldehyde is used for 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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%. Exampels 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.
[0027] The floatation process may be carried out, as is well-known, by adding a very small amount of oil into a pluverized 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.
[0028] The above two processes may generally reduce the inorganic impurities by several tens percents of their original contents.
[0029] . The use of cleaned coal in the composition of this invention has an important advantage that the viscosity lowering agent used herein is more effective to cleaned coal than to 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.
[0030] 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 200 mesh screen.
[0031] The viscosity lowering agent used in the present invention may remarkably decrease the viscosity and impart 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 slurry of the present invention may 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.
[0032] 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.
[0033] Although the present invention is not bound to a particular theory, it is postulated that the viscosity 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 surroung coal particles, retaining coal particles as stable primary particles, increase in fluidity and decrease in viscosity.
[0034] 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.
[0035] The viscosity lowering agent used in the present invention may stabilize the aqueous slurry of powdered coal and prevent coal particles from sedimentating upon stationary standing for a long period of time, e.g. for one month.
[0036] Various methods for preparing the aqueous slurry and for mixing the viscosity lowering agent thereto may be employed. For example, coal blockes 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.
[0037] The invention is further illustrated by the following examples in which all parts and percents are by weight.
Example 1
[0038] 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 200 mesh screen. The viscosities and fluidities of the resultant slurries were determined at 25°C, respectively.
[0039] After standing for one month, the occurence of phase separation in each sample was visually observed.
[0040] 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.
[0041] 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 cps 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.
[0042] In contradistinction, control slurries in which no or conventional surfacts are added have a viscosity higher than 20,000 cps and exhibit almost no fluidity even at a coal consistency of 50%.
Example 2
[0043] The procedure of Example 1 was repeated except that cleaned powdered coal was used. Formulations and results obtained were shown in Table 3.
1. An aqueous slurry of powdered coal composition having a consistency of at least
60% by weight comprising powdered coal, water and an effective amount of, as a viscosity
lowering agent, a polyether compound selected from the group consisting of:
said polyether compound having a molecular weight of at least 1,000.
(a) an adduct of an active hydrogen compound with a lower alkylene oxide containing at least 10% by weight of oxyethylene units based on the total oxyalkylene chain content;
(b) a cross-linked product of said compound a); and
(c) a reaction product of said compound a) or b) with an inorganic or organic acylating agent, a halogenating agent, an oxidizing agent or a monoisocyanate;
said polyether compound having a molecular weight of at least 1,000.
2. The composition of Claim 1, wherein said active hydrogen compound has at least
one hydroxyl, amino, imino, or carboxylic group.
3. The composition of Claim 1, wherein said cross-linking agent is a polyisocyanate,
a polyepoxy compound, a polyaldehyde, a function derivative of polycarboxylic acid
or a free radical-generating peroxide catalyst.
4. The composition of Claim 1, wherein said reaction product with said acylating agent
is a sulfate or phosphate ester.
5. The composition of Claim 1, wherein said coal is cleaned coal.
6. The composition of Claim 5, wherein said consistency ranges from 70 to 80% by weight.
7. The composition of Claim 1, said amount of said polyether compound ranges from
0.01 to 5.0% by weight based on the slurry.
8. The composition of Claim 7, wherein said amount of said polyether compound ranges
from 0.03 to 2.0% by weight based on the slurry.