AGGLOMERATION METHOD AND AGGLOMERATES ACCORDING TO THE METHOD

Abstract: Method for agglomerating fine-grained particulate material, in which the particle surfaces first are coated with a first water-insoluble binder in liquid phase, the particle surfaces having greater affinity to the first binder than possibly present water and/or other liquids. The fine-grained particulate material is mixed immediately before or within an agglomerating device with at least one other binder in solid phase, which together with the first binder forms a stable binding phase and are shaped to agglomerates. The second binder may have a surface coating with greater affinity to the first binder than other present liquids, said surface coating delaying the binding reaction. The invention also relates to an agglomerate produced according to the method.

Description: AGGLOMERATION METHOD AND AGGLOMERATES ACCORDING TO THE METHOD Thepresent invention relates to a method to produce agglomerates from fine-grained, particulate material, which at ambient tempera¬ ture or slightly increased temperature and possibly a certain amount of drying has sufficiently strong bounds to get the following properties:- Low dust release Good flowing characteristics No clogging or adhesion to solid surfaces In addition, the production costs for the agglomerates are low In order to obtain this, the invention is primarily characterized in that the particle surfaces are coated with a first water-insolubl binder in liquid phase, the particle surfaces having a natural or artifically produced greater affinity to the binder than possibly present other liquids, and after that are shaped to agglomerates in an agglomeration machine with at least one second binder in .solid phase, said second binder together with the first binder will make a binding phase between the particles, said second binder being added immediately before or within the agglomerating machine. The first binder alone creates no or insignificant binding forces between the particles, and therefore it is possible to store the fine-grained particulate material after addition of the first binder. However, the second binder should be added immediately before or in the agglomerating device. Suitably, the second binder together with the first binder should form a binding phase so slowly that the agglomerates will get time to be shaped before the binding phase obtains its full strength. In this way, the fine-grained particulate material can arrange itself in a densely packed arrangement. However, should the first and the second binder immediately form a firm binding phase, this would result in porous agglomerates. This time delay can be obtained by giving the solid binder particles a surface coating, which surface coating prevents or delays the binding reactio which may take place. Would there be one or more liquid phases presen in the particulate material in addition to the first binder, said surface coating on the second binder should have-a greater affinity to the first binder than to those other liquid phases which may be present. The fine-grained particulate material which may be subject to this agglomerating method is usually present together with water, for instance as a filter cake after a preceding wet treatment or as- ' a moist powder. A pre-requisite for the performance of the agglomera¬ tion method according to the invention is then that the first binder is water-insoluble. Such binders may suitably be .for instance mineral oil products, animal fats, vegetable fats or organic compounds produced from any of these products. These organic compounds as well as the animal or vegetable fats may suitably be summarized as mineral oil product-l ke substances. These mineral oil products and mineral oil product-l ke substances should not entirely consist of low volatile substances, which will remain unchanged in the binder phase after the agglomeration process. In that case these low volatil substances may evaporate and the final agglomerates will not retain their strength during storage. Various solid binders can be used depending upon the material charac- teristics of the first liquid binder. When using mineral oil products and mineral oil product-like substances as the first binder it has been found especially favourable to use metal oxides, " which with water form insoluble hydroxides. The oxides of the alkaline earth metals have been found to be especially favourable. In order to prevent the oxide or mixture of oxides in the second binder from premature reactions with water, they may be provided with a surface coating which prevents or delays the hydroxide forming reaction. This surface coating furthermore should have a greater affinity to the first binder than to other liquids which may occur with the fin grained particulate material. The oxide particles in the second bind will then get opportunity to combine with the first binder before an reaction takes place. Because that the surface coating on the second binder has great affinity to the first binder the- oxide particles in the second binder will completely or partly be surrounded by the fir binder. The the surface coating on the oxide particle is dissolved in the first binder, the oxide surfaces will be free to react with water and the oxide is then transformed to hydroxide, such that the hydroxide crystals are surrounded by the first binder under creation of a binding phase with a solid structure. Since the hydroxide forma tion in ' this way takes place with a time delay it is possible to accomplish the agglomeration before the binding phase * has got time to develop to such extent that it effects the ovabil ty of the mineral particles against each other, thus preventing the formation of a dense packing in the agglomerate. It has been found when using binder combinations including a first binder consisting of mineral oil products or mineral oil product-lik substances together with a second binder consisting of oxides with insoluble hydroxides, preferably oxides of the alcaline earth metals, the strongest bounds are achieved when the binders are present in about the same weight proportions, preferably with no greater dis- proportion than 1:3 in either direction. Depending upon the specific gravity of the first and the second binder and other reasons such as process technical or metallurgical reasons other weight proportions are conce-ivable. When other binder compositions comprizing other type of solid and liquid binder components are used, other proportions between the binders included in the binding phase are possible. This is entirely depending upon what kind of bounds which are used to keep the agglomerates together. The invention also includes agglomerates produced according to the method described above. The invention has been found especially suitable for agglomeration of pulverized coal. The first binder is then suitably a mineral oil product or a mineral oil product-like substance, and the second binder oxides of one or more of the alkali earth metals, preferably quicklime. The pulverized coal is usually moist but may also be completely dry, in which case the necessary water for the reaction with the oxides is introduced immediately before and/or in the agglomeration machine. When the pulverized coal is present in the moist condition the mineral oil product or the mineral oil product-like substance is introduced in a nixing device, and the first binder will then form a coating on the coal particles because ' of its greater affinity to coal in comparison to water. The pulverized coal may occur either as a moist powder or as a water suspension. In the latter case all coal will be coated with the bind and no free binder will occur in the water because the mineral oil products and mineral oil product-like substances are water-insoluble Excess water may then be separated from the binder-coated coal particles in customary way by means of a filter. Because the coal particles have got a hydrofobic coating consisting of the binder, an improved dewatering of the coal could be expected compared to what otherwise would be the case. The pulverized coal with its surface coating from the first binder may then be stored in storage bins at least for a shorter time period without any hazard that any major reactions will take place. The pulverized coal coated with the first binder and the second binder, in this case preferably comprizing oxides of the alkaline earth metals, are then mixed immediately before or in the agglomera¬ tion machine such that the second binder is evenly distributed, in the pulverized coal. The agglomeration machine may be any known agglomerating device, such as bricketting machine, extrution machine, balling drum, balling disc, pug mill or micropelletizing drum. The use of agglomeration machines with a circulating load has the dis¬ advantage that strong bounds may have been created in the recirculat undersized balls, hence causing weak bounds to the material which is deposited on the outside, and "shelling" will take place. It ha been found especially feasible to use a pug (pin) mill or a micropelletizing drum such as described in the Swedish patent 390 38 The mixing of a second binder will then be accomplished by means of the pins or blades of the pug mill or the mixing blades in the micro pelletizing drum, thus making a special mixing device for the binder unnecessary. Because the second binder, i.e. oxides of the alkaline earth metals, have a hydrofobic surface coating the binder particles will preferentially associate themselves with the oil-coated coal particle surfaces. The hydrofobic surface coating prevents the oxides from reacting with water before the oxides reach contact with the oi coated coal surfaces. The oxides will completely or partly be sur¬ rounded by the oil, i.e. the first binder, whereuppn the hydrofobic surface coating slowly is dissolved ' in the oil and the oxide surface will get opportunity to react with water. The hydroxide crystals formed will completely or partly be surrounded by the mineral oil product or the mineral oil product-like substance, thus creating a strong binding phase, which will bind the coal particles together. Since the oxide particles initially have a hydrofobic surface coatin which prevents reactions with water, the full strength of the bindin face will arise with a time delay. In this way the coal particles wil be free. to move relatively to each other such that they can rearrang themselves in a dense packing during the agglomeration process. " The finished agglomerates will then soon reach their full strength. A further increase in strength can be achieved by a later drying treatment. Other binder compositions may be a first binder comprizing a liquid metal and a second binder comprizing a metal powder, which forms an alloy with the liquid metal. Examples of such metal based binder combinations are mercury and powder of one or more metals, which together with mercury forms amalgam. Other metals may also be used as a first binder, in which case the agglomeration process must be performed at such a temperature that these other metals are in the liquid state. The fine-grained particulate material, which is bound together into agglomerates may be any chemical compound or element * which will not alloy or react with any of the binders. The invention is not limited to the described e body eπts but can be modified within the scope of the following claims.

Claims: AMENDED CLAIMS (received by the International Bureau on 21 June 1982 (21.06.82)) 1. Method for producing agglomerates from fine grained particulate material, c h a r a c t e r i z e d in that the particle surfaces are coated with a first water-insoluble binder in liquid phase, the particle surfaces having a natural or artificially produced greater affinity to the binder than possibly present other liquids, and after that are shaped to agglomerates in an agglomeration machine with at least one second binder in solid phase, said second binder together with the first binder will make a binding phase between the particles, said second binder being added immediately before or within the agglomerating machine. 2. Method according to claim 1, c h a.r a c t e r. z e d in that the full strength of the binding phase will arise with a time delay. 3. Method according to any of preceding claims, c h a r a c t e r i z in that the first binder is a mineral oil product or a mineral oil produkt-like substance. 4. Method according to any of preceding claims, c h a r a c t e r i z in that the second binder is one or more oxides, which reacts with wate to form insoluble hydroxides. 5. Method according to claim 4, c h a r a c t e r i z e d in that th oxide or oxides-have a surface coating with greater affinity to the firs binder than other liquids present, said surface coating preventing or delaying the hydroxide forming reaction. 6. Method according to any of preceding claims, c h a r a c t e r i z in that the second binder in the binding phase formed is completely or partly surrounded by the first binder. 7. (amended) Method according to claims 5 and 5, c h a r a c t e r i z e d in that the surface coating of the second binder is dissolved in the first binder thus permitting the surface of the second binder to react with water and said second binder together with water forming insoluble hydroxides surrounded by the first binder. ___ 8. (new) Method according to claim 7, c h a r a c t e r i z e d in that the necessary water for the hydroxide formation originally is present in the fine grained particulate material. - 9. (new) Method according to claim 7, c h a r a c t e r ! * z e d in that the necessary water for hydroxide formation is added immediately before and/or in the agglomeration machine. 10. (original claim 8.) Method according to any of preceding claims, c h a r a c t e r ! z in that the first and second binders are added in approximately equal weight proportions. 11. (original claim 9.) Agglomerates of fine grained particulate material, produced by firs coating the particle surfaces with a first water-insoluble binder in liquid phase, the particle surfaces having a natural or artificially achieved greater affinity to the binder than -to possibly present other liquids, and in a second step the- particulate material is shaped to agglomerates in an agglomerating apparatus with at least one second binder in solid phase, said second binder together with the first binder forming a binding phase between the particles, and at least the second binder is introduced immediately before or within the agglomerating apparatus. 12. (original claim 10. - amended) Agglomerates according to claim 11 produced according to the method of one or more of claims 1 - 10, c h a r a c t e r ! " z e d in that the fine grained particulate material is coal, the first binder a mineral oil or mineral oil-like material and the second binder is oxides of the alcal c earth metals, preferably quick lime, with a hydrofobic surface coating, said surface coating is dissvoled in the first binder, thus permitting the surface of the second binder to react with water and the second binder together with water forming insoluble hydroxides surrounded by the first binder.

Inventors: FALK THOMAS SVEN ADOLF
Applicants: FALK THOMAS SVEN ADOLF, SALA INTERNATIONAL AB
Application year: 1982
Main classification: B01J2
IPC codes: B01J2