Patent Specification 1575413

Inventors:

 Michael James Cannon

  Eric John Clayfield

 Olive Pinnington

 Peter Sant

Method for agglomeration of coal fines

   We, Shell Internationale Research Maatschappij B.V., a company organized under the laws of the Nether­lands, of 30, Carel van Bylandtlaan. The  Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the  following statement: –

   The invention relates to a process for the agglomeration of coal fines from an aqueous slurry thereof with simultaneous ash removed in case ash it present.

   In coal mining techniques wet fines with small diameters (e.g., of less than 1.5 mm) are generated, which mostly become avail­able as aqueous slurries. The fines com­prise particles which are rich in coal and particles which are rich in inorganic material (also called ash). Techniques have been developed to separate at least part of the ash from the coal with simultaneous preparation of coal agglomerates with a low ash content, which coal agglomerates are suitable to be used as fuel or as fuel-components. The said techniques may also be used for the agglomeration of coal fines from slurries thereof which do not contain ash. In order to prepare coal agglomerates an oil fraction is added as a binder to the slurry fines, by which binder the coal particles are preferably wet and agglo­merated by sticking together.   Ash particles are not or only to a slight extent wetted by the oil fraction and accordingly are not agglomerated to any substantial extent.

   An unattractive large entry input is needed in the prior art processes to obtain the oil fraction in the slurry of fines in droplets of sufficiently small size and a relatively large amount of the binder is needed in order to agglomerate the greater part or all of the coal particles present in the  slurry of fines.

   A method has now been found in which agglomeration of coal fines can be achieved with only small amounts of an oil fraction and a low energy input.

   According to the invention there is provided a process for the agglomeration of coal fines from an aqueous slurry thereof with simultaneous ash-removal in case ash is present which comprises addition to the said slurry of an aqueous emulsion of a hydrocarbon    oil    fraction,    agitating   the mixture,   removing   agglomerates   formed, and  repeating at least once said addition and  following treatments   with   the  slurry remaining after the removal of the agglomerates.

   The oil fraction may consist of a tar or shale or rock oil fraction, but in most cases it will consist of a mineral oil fraction.

   In general the mineral oil fraction present in the aqueous emulsion thereof will con­sist  of higher boiling components, prefer­ably no material being present with a boiling point below 200°C. Very suitable are crude oils, bituminou fractions, deasphalted  residual  fractions,   lubricating oils and gas oils.

   The amount of water present in the aqueous emulsion of an ail fraction may vary between wide limits. In general amounts between 30 and 70% by weight, in particular between 40 and 60% by weight of water of the total emulsion are very suitable.

   It is preferred that the aqueous emulsion of the oil fraction comprises a surface-active agent, because such an agent strongly reduces the energy input needed to emulsify the oil fraction and enables the formation of small oil droplets, which is of advantage in the agglomeration process of the coal fines. Moreover by conditioning the sur­face of the coal particles the surface-active agent enables a reduction in the amount of oil needed.

   The surface-active agent may consist of a cationic, a non-ionic or preferably an anionic detergent such as a fatty acid soap. Very suitable are alkali metal sulphates or  sulphonates of aliphatic or alkyl aromatic compounds uch as sodium alkyl-benzene sulphonates, sodium  primary alkyl sulphates (e.g., sodium dodecyl sulphate)   and   sodium secondary alkyl sulphates.

   The amount of surface-active agent may vary between wide limits, in general the amount of this agent will be between 0.01 and  5% by weight in particular between 0.1 and 2% by weight, of the aqueous emulsion and between 20 and 200 p.p.m. by weight, in particular between 40 and 150 p.p.m. by weight of the total solids (coal fines and ash) present in the feed.

   The aqueous emulsion of the oil fraction is to be added to the aqueous slurry of the fines in at least two steps, in each of which agglomerates are formed, because it has been found that the yield obtained as agglomerated coal is lower in case the same amount of aqueous emulsion of the oil fraction is added in one step.

   In general the addition of the aqueous emulsion of the oil fraction in two steps is

 optimal, addition of the said aqueous emulsion to the slurry remaining after the second step not giving an attractive higher yield of agglomerated coal taking into account the extra  equipment  and  energy input needed for such a third step.

   The total amount of oil (as aqueous emulsion) to be added to the fines may vary between wide limits; it is an advantage of the present method that the amounts are

between 1 and 10% by weight, preferably between 2 and 6% by weight of the total solids present in the feed.

   The amount of oil added in the first step in general will be between 10 and 80% by weight in particular between 30 and 50% by weight of the amount of oil (as aqueous emulsion)   to   be   added   in  total   to   the aqueous slurry of fines.

   The mixture obtained after the addition of the aqueous emulsion of an oil to the aqueous slurry of fines is to be agitated, which can be achieved by any suitable method, e.g., by stirring. The time of agitation necessary for agglomeration of the

 coal   particles   may   depend   on    several factors such as type of coal and stirring rate.   In general agitation times between 1 and 10 minutes are very suitable.

   The    agglomerates    formed,    which    in general will have diameters between 0.5 and 5 cm, can be removed by any suitable means e.g., centrifugation. It is preferred to remove the agglomerates with the aid of a vibrating sieve; the agglomerates remain on the sieve and the remaining slurry which comprises non-aggregated coal; fines and ash passes through it.

   It has been found to be of advantage to wash the agglomerates on the sieve with water in order to remove ash which has adhered to the agglomerates in particular     in case the original aqueous slurry of fines had a high solids content.

   Preferably the addition of the aqueous emulsion of oil to the slurry of fines, agitation and removal of agglomerates formed is carried out continuously, as will be exemplified in the process scheme to be discussed later on.

   The    aqueous    slurry    which    becomes available after removal of the agglomerates formed is treated in a second step with an amount of the aqueous emulsion of the oil, agitated and the agglomerates formed are removed in a way similar to that described above.

   The agglomerates obtained in each step can be used separately or if desired, they may be combined.   They can easily be de-watered to a water content below 10% w e.g., by centrifuging.    They can be used as fuel or fuel components and are very suitable as components of fluid fuels pre­pared by incorporating them into a mineral oil e.g., as described in the British patent specification No. 1 548 402.

   A nonlimitative schematic embodiment of the invention is illustrated with re­ference to figure 1 of the drawing accom­panying the provisional specification.