WO2017134566A1

WO2017134566A1 - A process for the agglomeration of coal slurry including ultrafines

Info

Publication number: WO2017134566A1
Application number: PCT/IB2017/050527
Authority: WO
Inventors: Leon SWANEPOEL
Original assignee: Coal Tech Llc
Priority date: 2016-02-05
Filing date: 2017-02-01
Publication date: 2017-08-10

Abstract

The invention relates to a process for the production of an agglomerated coal product from a coal fines feedstock, the process comprising a step of mixing the feedstock with a binder comprising sodium silicate and a surfactant and optionally PVA and/or a waterproofing agent in a mechanical mixer to produce the agglomerated coal product and an agglomerated coal product produced by the process of the invention. The process may further comprise a step of drying or curing the agglomerated coal product.

Description

A PROCESS FOR THE AGGLOMERATION OF COAL SLURRY INCLUDING

ULTRAFINES

BACKGROUND OF THE INVENTION

This invention relates to a process for the production of an agglomerated coal product from a feedstock comprising coal fines, including coal fines slurries and fines derived from waste and discarded coal. This invention further relates to an agglomerated coal product produced by the process. In particular, the process results in the production of an agglomerated coal pellet or a briquette.

Generally, coal is mined out of the ground, by way of either an open cast mine or an underground mine. After extraction, the coal is separated from fines and other material including sand, dirt, stones, rocks and other non-coal material by means of a washing or screening process, sometimes utilizing water.

During this washing or screening process coal fines, which are small particles of coal material of less than or equal to 1 mm in diameter, are separated from the coal. Coal fines are distinguishable from larger coal particles such as "doves", "peas" and the like which have a diameter greater than 1 mm. The coal fines and other non-coal material, together with quantities of water from the washing process, are usually disposed of as waste material in large ponds of water called "slurry ponds". The larger coal particles are generally not committed to a slurry pond. There are numerous problems associated with coal fines. They are difficult to handle, store and transport. Slurry ponds or piles of coal fines are unsightly and not environmentally friendly. In particular, environmental damage may result from contamination of ground water if water runoff or seepage occurs from coal ponds or piles of coal-fines. Coal fines in the form of coal dust also contribute to air pollution. Furthermore, coal fines typically contain harmful and sometimes toxic substances, such as sulphur dioxide, hydrogen chloride, mercury, arsenic, cadmium etc. that may have serious health implications. Coal dust that has been subjected to thermal drying may also create an explosion hazard.

In order to solve the problems associated with coal fines, various processes for agglomeration of the coal fines into a solid product by pelletisation or briquetting have been developed.

However, there are a number of problems associated with these traditional processes including those set out below.

The traditional binders used in the coal fines agglomeration processes are generally very expensive. Furthermore, most traditional binders are petroleum based and therefore undergo chemical modification during combustion, resulting in changes to the chemical composition of the final agglomerated product, particularly changes in the calorific value of the final product as well as an increase in the volatiles content of the final product.

Additionally, the mechanical properties of pellets or briquettes produced using most traditional binders are inadequate for large-scale industrial purposes as the agglomerated products often need to be able to withstand bulk transportation and extensive mechanical handling without degradation into fine material or powder as a result of being too brittle.

Furthermore, agglomerated products produced by traditional methods typically have a very poor ability to withstand exposure to water, which is a particular problem in large industrial applications where product is often is exposed to the elements when being stored out in the open. The agglomerated product therefore disintegrates when exposed to rain water, becoming difficult to handle and often unusable.

Moreover, many traditional briquetting systems are costly and complex to operate and require the application of heat or pressure or both to produce the agglomerated product. Due to the high capital and operating costs associated with traditional agglomeration processes, most coal fine recovery and conversion processes remain uneconomical.

A particular problem in the case of agglomerated coal briquettes or pellets for combustion in a furnace, is that the binder used dissipates before the required temperature is reached for ignition of the carbon in the briquette or pellet, and therefore the briquette or pellet turns to dust, smothering the fire. Alternatively, the dust produced is extracted from the furnace through a dust extraction process before full ignition and full combustion of the carbon can take place.

Alternatively, a problem that sometimes occurs with briquettes or pellets during combustion in a furnace, is that the binder does not break down at the temperature at which the carbon combusts, thereby resulting in the formation of clinkers (a incombustible coal residue, fused into an irregular lump) in the furnace, causing choking or blocking of the furnace.

A further problem with briquettes or pellets of coal manufactured from coal fines according to traditional methods is that the coal fines agglomerated to make up such larger briquettes or pellets adsorb water onto their surface. Due to the enormous surface area of the coal fines making up such an agglomerated product, large amounts of moisture are adsorbed onto the product. This then makes the agglomerated coal product impossible to store since it adsorbs so much moisture that it is uneconomical to fire, using a large portion of its generated energy to evaporate the moisture.

It would therefore be useful if a process could be developed that would overcome the various abovementioned problems experienced in the past with the use of agglomerated coal products produced using traditional methods and binders.

SUMMARY OF THE INVENTION

According to a first embodiment of the invention, there is provided a process for the production of an agglomerated coal product from a feedstock comprising or consisting substantially of coal fines, the process comprising a step of mixing the coal fines feedstock with a binder comprising sodium silicate in a mechanical mixer.

The mixing step preferably further comprises addition of a surfactant to the mixer to form the coal agglomerate product. The sodium silicate may be added at an amount of from between about 1 .2% to about 3% of a sodium silicate solution (of about 55% w/v) or between about 0.5% to about 2% of sodium silicate powder (w/w), as a proportion by weight to the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

The surfactant may be a sodium surfactant or methylated spirits. Preferably, the surfactant is a sodium surfactant.

Typically, the surfactant is added to the mixer at an amount of about 0.3% to about 0.4% (w/w) of the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

Typically, prior to use in the process of the invention, the coal fines feedstock is tested and the calorific value (CV) is determined. Coal fines with a CV of less than 16 are discarded. The CV range for use with the method of the invention is from between about 17 to 26.

The mixing step may further comprise addition of a second binder comprising polyvinyl alcohol (PVA) to the coal fines feedstock, sodium silicate binder and surfactant.

The PVA may be partially or fully hydrolysed. For example, the partially hydrolysed PVA may have a degree of hydrolysis of 86 to 89 mol % or the fully hydrolysed PVA may have a degree of hydrolysis of 95 to 99.8 mol %. The PVA may have a molar mass of from about 80 000 to 200 000 g/mol more preferably between about 80 000 to 1 10 000 g/mol. The PVA may have a degree of polymerisation of between about 2000 and 4500 Pw, more preferably between about 2500 and about 3500 Pw. The PVA may further have a viscosity at 4% concentration in water at 20°C of between 16 and 50 mPa.s.

The PVA may be added at an amount of from between about 0.5% to about 3% of a PVA solution (of between about 2% to 15% w/v, preferably about 5% w/v) as a proportion by dry weight to the coal fines feedstock, sodium silicate binder and sodium surfactant mixture. Preferably the PVA is a 5% w/v PVA solution and is added at an amount of about 0.5% w/v as a proportion by dry weight of the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

The mixing step may further comprise addition of a waterproofing agent such as soft soap, bentonite, or acrylic resin or liquid to the coal fines feedstock, sodium silicate binder and sodium surfactant mixture or the coal fines feedstock, sodium silicate binder, sodium surfactant and PVA mixture in the mixer. In one preferred embodiment of the process, the waterproofing agent is acrylic liquid or resin. Typically, the acrylic liquid or resin is added in the ratio of 0.01 to 0.03 % proportion by dry weight of the coal fines feedstock, sodium silicate binder and sodium surfactant mixture or of the dry weight of the coal fines feedstock, sodium silicate binder, sodium surfactant mixture and PVA binder.

In a second alternative embodiment of the process, the waterproofing agent is soft soap. Preferably, the soft soap is the sodium salt of a fatty acid, for example, sodium stearate soap. More preferably, the soft soap comprises a water solution of the sodium salt of a fatty acid (e.g. sodium stearate soap) to which is added a hard fat (e.g. suet or tallow) and a solution of cresols in a soft soap solution (e.g. the disinfectant Lysol^®). The waterproofing agent may further comprise aluminium sulphate.

The soft soap mixture may be added at an amount of from between about 1 .5 to 3% dry weight as a proportion by weight to the coal fines feedstock mixture.

The mixing step may further optionally comprise addition of silicon oil, methylated spirits and/or lime.

The silicon oil may be added at an amount of from between about 1 .5 to 3% dry weight as a proportion by weight to the coal fines feedstock mixture.

The methylated spirits may be added at an amount of from between about 0.3 to 0.4% as a percentage of the weight of the coal fines feedstock mixture.

The feedstock comprising coal fines may include coal fine slurries, fines derived from waste and discarded coal. The feedstock may be the product of upstream processing including crushing, grinding, sieving, and other upstream processing methods for obtaining coal fines known to those skilled in the art.

In particular, the coal fines have a particle diameter of 1 mm and less.

More particularly, the process may comprise the steps of:

(i) adding the coal fines feedstock into a mechanical mixer;

(ii) adding the sodium silicate binder and the surfactant to the coal fines material of (i); and (iii) mixing the components of steps (i) and (ii) in the mixer thereby to form the agglomerated coal product.

Optionally, where the agglomerated coal product is likely to be subjected to moisture during transport or storage, the waterproofing agent may be added to the mechanical mixer during or after step (iii), thereby to coat the agglomerated coal product.

Alternatively, the process may comprise the steps of:

(i) adding the coal fines feedstock into a mechanical mixer;

(ii) adding the sodium silicate binder and the surfactant to the coal fines material of (i) in the mixer to form a feedstock mixture;

(iii) adding the second binder comprising PVA to the feedstock mixture of (ii);

(iv) optionally adding any one or more of: the silicon oil, the methylated spirits or the lime (i.e. calcium hydroxide) to the product of step (iii) in the mixer; and

(v) mixing the components of steps (i) to (iv) thereby to form the agglomerated coal product.

Optionally, where the agglomerated coal product is likely to be subjected to moisture during transport or storage, the waterproofing agent may be added to the mechanical mixer during or after step (v), thereby to coat the agglomerated coal product.

The process may comprise a step of adjusting the moisture content of the feedstock comprising coal fines prior to addition of the binder to a total moisture content of between about 22% and 26% for the production of coal agglomeration products in the form of pellets, and to a total moisture content of between about 15% to 18% for the production of coal agglomeration products in the form of briquettes.

The process may additionally comprise a step of shaping the agglomerated coal product by any means known to those skilled in the art such as, but not limited to tumbling, extruding, rolling, pressing, cutting, pelletizing, briquetting and the like.

The step of shaping the agglomerated coal product may either be performed substantially simultaneously with the mixing step in the mechanical mixer, or may be performed subsequent to the mixing step in a product shaping apparatus. Where shaping occurs subsequent to the mixing step, the waterproofing agent may be added either to the mixer after adding the binder during the mixing step or to the shaper during the shaping step. The process may further comprise a step of drying or curing the agglomerated coal product in order to ensure that the agglomerated product has the required green strength and water resistance. Preferably, the agglomerated coal product is dried or cured to have a total moisture content of from about 3% to about 9% water, for example 3%, 4%, 5%, 6%, 7%, 8% or 9%, depending on the market into which the product is being supplied.

In particular, the curing process may comprise the steps of:

(i) feeding the agglomerated coal product formed during the mixing or shaping step above through a drier comprising a heat source, an agglomerated coal product feed, an agglomerated coal product outlet and a conveyer connecting the feed and product outlet;

(ii) conveying the agglomerated coal product from the product feed through the drier to the product outlet of the drier, thereby to dry the agglomerated coal product;

(iii) collecting the dried agglomerated coal product from the product outlet of the drier.

The drier is preferably an air suspension drier with a vibrating bed.

The heat source may be gas combusted from dried coal fines having less than about 2% moisture. The combustion is preferably performed with a pulverised fuel (PF) burner.

According to a further aspect of the invention there is provided an agglomerated coal product formed by the process of the invention.

The agglomerated coal product may be a pellet or a briquette.

According to a further aspect of the invention there is provided a method of operating a furnace comprising the use of the agglomerated coal product formed by the process of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by way of the following illustrations which are not to be construed as limiting in any way the scope of the invention.

Figure 1 : shows a schematic block diagram of a first embodiment of the coal agglomeration process according to the invention, with optional steps shown in dashed lines;

Figure 2: shows a schematic block diagram of a second embodiment of the coal agglomeration process according to the invention, with optional steps shown in dashed lines;

Figure 3: shows a flow process diagram of one example of an agglomeration plant for performing the process of the first embodiment of the invention;

Figure 4: shows a flow process diagram of a second example of an agglomeration plant for performing the process of the second embodiment of the invention; and

Figure 5: shows a flow diagram of the agglomeration process of the third embodiment of the invention, including the process of curing or drying of the agglomerated coal product of the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a process for the production of an agglomerated coal product from a feedstock comprising coal fines, including coal fine slurries and fines derived from waste and discarded coal. This invention further comprises a process of curing the agglomerated coal product. This invention further relates to an agglomerated coal product produced by the process.

Traditional processes and binders used for agglomeration of coal fines are plagued with problems. The applicant has therefore developed an innovative and versatile new process for agglomeration of coal fines feedstocks. Typically, coal fines that may be used in the process of the present invention include coal fine slurries, fines derived from waste, the immediate discard from DMS (Dense Media Separation) plants (commonly referred to as Wash Plants), and other discarded coal. Coal fines are defined to have a particle size of less than 1 mm diameter.

In the context of this application, the term "agglomeration" means the binding of coal fines together to form a mechanically stable transportable product.

At the core of the invention, the applicant has surprisingly discovered that a simple process for agglomeration of coal fines feedstocks of various types and compositions is possible by addition of a sodium silicate binder and a surfactant to coal fines feedstock and agglomeration by mixing in a mechanical mixer. The product formed has similar characteristics to that of base coal, including the calorific value and green strength, but is resistant to moisture adsorption and has superior mechanical and handling characteristics. The agglomerated product is therefore able to be transported and handled without the adversely affecting the integrity of the product substantially.

Furthermore, the applicant has developed a process for curing the agglomerated coal product, thereby to ensure that the agglomerated product has the required green strength, water resistance and the optimal moisture content maintained during storage such that the agglomerated product provides a commercially feasible feedstock for combustion. Typically, the agglomerated coal product is dried or cured to have a total moisture content of from about 3% to about 9% water, for example 3%, 4%, 5%, 6%, 7%, 8% or 9%.

The coal fines feedstock is typically provided at from 2% up to 18% or 19% water content. The process may comprise a step of adjusting the moisture content of the coal fines feedstock to a total moisture content of between about 22% and 26% for the production of coal agglomeration products in the form of pellets and to a total moisture content of between about 15% to 18% for briquettes.

Sodium silicate is a common name for a class of compounds with the formula Na2(SiQ₂)_nQ. One example of such a compound is sodium metasilicate, Na₂SiG₃, also known as waterglass or liquid glass which is available in aqueous solution and in solid form. Another example that may be used is anhydrous sodium silicate containing a chain polymeric anion composed of corner shared {Si0₄} tetrahedral, and not a discrete SiOs^2" ion. In addition to the anhydrous form, there are sodium silicate hydrates with the formula Na₂Si03^«nH₂0 (where n = 5, 6, 8, 9) which contain the discrete, approximately tetrahedral anion Si02(OH)₂ ^2~ with water of hydration.

In industry, the various grades of sodium silicate are characterized by their 8i02: a20 weight ratio, which can vary between 2:1 and 3.75:1 . Grades with this ratio below 2.85:1 are termed 'alkaline'. Those with a higher Si0₂:Na₂0 ratio are described as 'neutral'. Either form may be used. The sodium silicate may be a liquid phase or solid phase sodium silicate. Further non-!imiting examples that may be used include sodium orthosilicate, Na₄Si0₄, sodium pyrosilicate, Na₆Si₂G7, and others known to those skilled in the art.

Surfactants are well known compounds that are able to lower surface or interfacial tension between two liquids or between a liquid and a solid. These may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. Non-limiting examples of surfactants that may be used include linear alkylbenzenesulfonates, lignin sulfonates, fatty alcohol ethoxylates and alkylphenol ethoxylates and others known to those skilled in the art.

Mixing may comprise the steps of mixing and shaping the agglomeration product substantially simultaneously, or the mixing may comprise subsequent shaping of the agglomeration product in a product shaping apparatus after mixing in a mixer. The mixer and/or shaper may be an agglomerating machine, a briquetting machine, a pelletiser, including a drum pelletiser or any other suitable mechanical mixer known to those skilled in the art. Typically, the agglomerated product has a diameter of between 6 and 15mm.

The agglomeration process may be performed successfully with the addition of the sodium silicate alone to the feedstock, but a preferred embodiment of the invention as illustrated in Figure 1 , comprises providing to a mechanical mixer (10) a coal fines feedstock (12), a sodium silicate binder (14) and a surfactant (16). The components are then mixed until an agglomerated product (18) is formed. It is possible to shape the agglomerated product in the mechanical mixer. However, alternatively, the agglomerated product is shaped subsequent to the mixing step in the mechanical mixer (10) in a product shaping apparatus (20).

Where the agglomerated product is likely to be exposed to moisture during storage or transport, a waterproofing agent (22) is further added to the agglomerated product (18) in the mechanical mixer (10) or in a product shaping apparatus (20), thereby to coat the agglomerated product (18), waterproofing it so that it maintains structural integrity during moist conditions, such as in high humidity or during exposure to rain. The agglomerated product (18) is typically shaped into a pellet or briquette, depending on the desired requirements of the user.

The waterproofing agent may be any one of the acrylic resins that are derived from acrylic acid, methacrylic acid and related compounds, including polymethyl acrylate, polymethyl methacrylate.

Alternatively, the waterproofing agent may be any one or more of a group of organic compounds that are salts of fatty acids, usually stearic acid (with 18 carbon atoms) or palmitic acid (with 16 carbon atoms). The source may be any vegetable oil or animal fat. Soaps are emulsifying agents commonly used for cleaning; they have long been made from lye and fat. Aluminum, calcium, magnesium, lead, or other metals may be used in place of sodium or potassium for soaps used in industry as paint driers, ointments, and lubricating greases and in waterproofing. Fillers are added to many soaps to increase lathering, cleansing, and water-softening properties; the sodium salt of rosin is commonly used in yellow laundry soap to increase lathering. Soap substitutes include saponin-containing plants such as soapwort and shagbark and the modern soapless detergents (usually sulfonated alcohols), which may be used in hard water and even in saltwater without forming curds.

This alternative possible water proofing agent for the invention is made up of a water solution of the sodium salt of a fatty acid to which is added a hard fat such as suet or tallow, and a soft soap solution of a disinfectant, for example such as the disinfectant Lysol®, which consists of a solution of cresols in a soft soap solution.

It is preferred that sodium stearate soap be employed in making up the preparation of the invention. The preferred formula consists of a 5% solution of the sodium stearate soap, in water, to which is added 2% of melted suet. In order to incorporate the suet in the solution, the latter is heated to about 50 °C and the melted suet is then stirred in. There is then added to the soap and suet mixture, the Lysol® or a similar soft soap solution of cresols, in the proportion of approximately one tablespoon fluid oz. of the Lysol® to each two gallons of solution.

An alternative preferred embodiment of the invention includes the addition of a second binder, polyvinyl alcohol (PVA) to the process resulting in a product with greater elasticity than the product produced in the previously stated embodiment of the invention. The steps as set out in Figure 2 include sequentially providing to a mechanical mixer (100) a coal fines feedstock (120), a sodium silicate binder (140) and a surfactant (160) to form a feedstock mixture. A PVA binder (180) is then added to the feedstock mixture and the components are mixed until the agglomerated product (200) is formed.

It is possible to shape the agglomerated product in the mechanical mixer (100). However, alternatively, the agglomerated product is shaped subsequent to the mixing step in the mechanical mixer (100) in a product shaping apparatus (220).

Furthermore, where the agglomerated product is likely to be exposed to moisture during storage or transport this process may comprise the optional additional step of adding a waterproofing agent (240) to the agglomerated product (200) in the mechanical mixer (100) or the product shaping apparatus (220) to form a waterproof agglomerated product. The agglomerated product (220) is formed preferably into a pellet or briquette.

Furthermore, if desired, the following additional components may be added to the agglomerated product (220) in the mechanical mixer (100): any one or more of: a silicon oil, methylated spirits or lime.

Non-limiting examples of silicon oil known to those skilled in the art include hexamethyldisiloxane, polydimethylsiloxane, cyclosiloxanes simethicone.

Methylated spirits comprise ethanol and one or more additives such as, but not limited to, methanol, isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and denatonium and any would be suitable for use in the process of the invention.

According to a third embodiment of the invention, the agglomerated product is dried or cured. Typically, the curing process comprises the steps of:

(i) feeding the agglomerated product formed during the mixing or shaping step through a drier (24) (260), preferably an air suspension drier, comprising a heat source, an agglomerated product feed, an agglomerated product outlet and a conveyer, preferably a vibrating fluidised bed conveyer, connecting the feed and product outlet;

(ii) conveying the agglomerated product from the product feed through the drier (24) (260) to the product outlet of the drier, thereby to dry the agglomerated product (26) (280); and

(iii) collecting the dried agglomerated product (26) (280) from the product outlet of the drier.

The heat source is typically gas combusted from dried coal fines having less than about 2% moisture, although other heat sources known to those skilled in the art such as liquid petroleum gas or LPG, bunker oil, diesel or electricity generated through diesel may be used, although these are less commercially feasible. The combustion is preferably performed with a pulverised fuel (PF) burner.

Figures 3 and 4 provide examples of a typical agglomeration product production plant, excluding the optional curing or drying step above. In particular, Figure 3 shows the design of an agglomeration plant for producing an agglomeration product according to the first embodiment of the invention.

The exemplary plant of Figure 3 includes: (i) A hopper (A) to feed the coal fines into the plant;

(ii) A feeder (B) which controls the feed rate of the coal fines entering the plant;

(iii) A conveyor (C);

(iv) A moisture adjustment means (D; K) for adjusting the moisture of the coal fines as required;

(v) A mixer (E), adapted to add the sodium silicate binder and surfactant mixture;

(vi) A tank containing the sodium silicate binder and surfactant mixture (F);

(vii) A tank containing the waterproofing agent (G) for addition either into (E) or (H);

(viii) A product shaping apparatus (H) for shaping the agglomeration products, typically into pellets or briquettes;

(ix) An exit conveyor (I) for conveying the shaped agglomeration products; and

(x) A moisture sensor (J) adapted to measure the moisture of the coal fines feedstock.

Figure 4 shows the design of an agglomeration plant for producing an agglomeration product according to the second embodiment of the invention.

The exemplary plant of Figure 4 includes:

(i) A hopper (A) to feed the coal fines into the plant;

(iii) A conveyor (C);

(vi) A tank containing the sodium silicate binder and surfactant mixture (F);

(ix) An exit conveyor (I) for conveying the shaped agglomeration products; and

(x) A moisture sensor (J) adapted to measure the moisture of the coal fines feedstock

(xi) A tank containing the PVA binder additive (L).

Figure 5 shows a flow diagram of the complete process for producing the agglomerated coal product according to a third embodiment of the invention, wherein the process includes a drying or curing plant for drying or curing the agglomeration product.

1 . Pre-treatment Process The coal fines feedstock material (500), due to the fact that it comes mainly from dumps, can contain other unwanted content such as rock, stones and other waste material. Additionally, some of the coal fines feedstock may be compressed into large lumps which can be difficult to process back into fine material.

This feedstock material (500) is therefore first fed into a trommel (520). A trommel (520) is a rotating cylindrical sieve or screen used for washing and sorting pieces of ore or coal. Trommels are well known in the art and are typically fitted with lifters or chains that break up the agglomerated coal lumps by mechanical force. The trommel screen comprises fine square apertures, allowing the coal fines feedstock material of the desired dimension to fall through the apertures for collection, whereas the unwanted rock is discarded out of the end of the trommel. The feed rate into the trommel is controlled by a small vibrating feeder, fed by a feed hopper. The sieved coal fines product is then fed into a coal fines product feed bin (520).

2. Granulation process

From the coal fines feed bin (520) the sieved coal fines are fed over a vibrating feeder (540) onto a dedicated weigh belt (560), the mass per second is both logged and fed into a programmable logic controller (PLC) (not shown) which in turn controls the rate that the vibrating feeder (540) feeds the sieved coal fines to the plant at a fixed rate compatible to the design and required level of curing required.

The sieved coal fines being fed to the plant have a constant moisture content which is periodically checked by means of a moisture meter. With the constant flow of sieved coal fines the amount of moisture in the coal fines is kept at the required level for the granulation process to take place, thereby allowing an agglomerated coal pellet to form.

Water in a quantity sufficient to bring the feed material up to about 18% moisture is added to a first pug mill (580) (a type of through-flow mixer) to generate a homogenous coal fines product. The homogenous coal fines product is then fed into a second pug mill (600) where a binder mixed with water is added to bring the material up to a moisture content of between 24% and 26%.

On exiting the second pug mill (600) the coal fines product will already have started to form small agglomerated pellets which drop into a granulator (620), which is a rotating drum, where the pellets increase in size. After a sufficient period of time in the granulator to achieve the desired pellet size, a waterproofing agent is sprayed onto the exterior of the pellet before it is discharged from the granulator and then conveyed upwards on a chevron belt (640).

Next the agglomerated pellet passes through a trommel screen (660) comprising screen apertures that reject material smaller than 5 mm, which will then be recycled to the start of the process. The trommel screen (660) has a hood and is fitted with a fan which blasts air across the product to absorb any excess external moisture without using heat and ensures that there are no loose particles on the agglomerated pellets. The agglomerated pellets exit the trommel screen (660) and then pass into the drier (680) to start the curing process.

3. Curing process

The pellet drier (680) comprises a heat source (700), and a vibrating bed combined with an air suspension fluid bed that maintains the agglomerated pellets in suspension with hot air as they pass across the bed. The hot air is produced by combustion of coal fines. The dried agglomerated pellets exit the drier (680) and are then conveyed to a stockpile of cured products (720).

The agglomerated pellets exiting the drier (680) retain their dimensions of between 6mm and 15mm and have sufficient green strength to meet the handling, storage and transportation requirements, not absorb moisture, and have a final moisture content of about 4 to 5%.

4. The Heat Source

The cost of gas (liquid petroleum gas or LPG), bunker oil, diesel or electricity is uneconomical when consumed in the drying of coal fines. However, the applicant has determined that hot gas from combusted coal fines, being a slurry discard product, having a moisture content of less than 2% are the most cost effective source of heat.

Claims

1 . A process for the production of an agglomerated coal product from a coal fines feedstock, the process comprising a step of mixing the feedstock with a binder comprising sodium silicate and a surfactant in a mechanical mixer to produce the agglomerated coal product.

2. The process according to claim 1 , wherein the sodium silicate is added at an amount of from between about 1 .2% to about 3% of a sodium silicate solution (of about 55% w/v) or between about 0.5% to about 2% of sodium silicate powder (w/w), as a proportion by weight to the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

3. The process according to either claim 1 or claim 2, wherein the surfactant is a sodium surfactant or methylated spirits.

4. The process according to either claim 1 or claim 2, wherein the surfactant is a sodium surfactant.

5. The process according to any one of claims 1 to 4, wherein the surfactant is added to the mixer at an amount of about 0.3% to about 0.4% (w/w) of the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

6. The process according to any one of claims 1 to 5, wherein the coal fines feedstock comprises a calorific value (CV) of from between about 17 to 26.

7. The process according to any one of claims 1 to 6, wherein the total moisture content of the coal fines feedstock is between about 22% and 26% where the coal agglomeration product is in the form of pellets.

8. The process according to any one of claims 1 to 6, wherein the total moisture content of the coal fines feedstock is between about 15% to 18% where the coal agglomeration product is in the form of briquettes.

9. The process according to any one of claims 1 to 6, wherein the mixing step further comprises addition of a second binder comprising polyvinyl alcohol (PVA) to the coal fines feedstock, sodium silicate binder and surfactant.

10. The process according to claim 9, wherein the PVA is partially or fully hydrolysed.

1 1 . The process according to claim 10, wherein the PVA is partially hydrolysed and has a degree of hydrolysis of about 86 to 89 mol %.

12. The process according to claim 10, wherein the PVA is fully hydrolysed PVA and has a degree of hydrolysis of about 95 to 99.8 mol %.

13. The process according to claim 9, wherein the PVA has a molar mass of from about 80 000 to 200 000 g/mol.

14. The process according to claim 9, wherein the PVA has a molar mass of from about 80 000 to 1 10 000 g/mol.

15. The process according to claim 9, wherein the PVA has a degree of polymerisation of between about 2000 and 4500 Pw.

16. The process according to claim 9, wherein the PVA has a degree of polymerisation of between about 2500 and about 3500 Pw.

17. The process according to claim 9, wherein the PVA has a viscosity at 4% concentration in water at 20°C of between 16 and 50 mPa.s.

18. The process according to any one of claims 9 to 17, wherein the PVA is added at an amount of from between about 0.5% to about 3% w/v of a PVA solution (of between about 2% to 15% w/v) as a proportion by dry weight to the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

19. The process according to claim 18, wherein the PVA solution is about 5% w/v as a proportion by weight to the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

20. The process according to claim 18, wherein the PVA is a 5% w/v PVA solution and is added at an amount of about 0.5% w/v as a proportion by dry weight of the coal fines feedstock, sodium silicate binder and sodium surfactant mixture.

21 . The process according to any one of claims 1 to 20, wherein the mixing step further comprises addition of a waterproofing agent.

22. The process according to claim 21 , wherein the waterproofing agent is selected from soft soap, bentonite, acrylic resin or acrylic liquid.

23. The process according to either claim 21 or claim 22, wherein the waterproofing agent is acrylic liquid or resin.

24. The process according to claim 23, wherein the acrylic liquid or resin is added in the ratio of 0.01 to 0.03 % proportion by dry weight of the coal fines feedstock, sodium silicate binder and sodium surfactant mixture or of the weight of the coal fines feedstock, sodium silicate binder, sodium surfactant mixture and PVA binder.

25. The process according to either claim 21 or claim 22, wherein the waterproofing agent is soft soap.

26. The process according to claim 25, wherein the soft soap is the sodium salt of a fatty acid including sodium stearate soap.

27. The process according to either claim 25 or claim 26, wherein the soft soap comprises a water solution of the sodium salt of a fatty acid to which is added a hard fat selected from suet or tallow and a solution of cresols in a soft soap solution.

28. The process according to any one of claims 25 to 27, wherein the soft soap further comprises aluminium sulphate.

29. The process according to any one of claims 25 to 28, wherein the soft soap mixture is added at an amount of from between about 1 .5 to 3% dry weight as a proportion by weight to the coal fines feedstock mixture.

30. The process according to any one of claims 1 to 29, wherein the mixing step further optionally comprises addition of silicon oil, methylated spirits and/or lime.

31 . The process according to claim 30, wherein the silicon oil is added at an amount of from between about 1 .5 to 3% dry weight as a proportion by weight to the coal fines feedstock mixture.

32. The process according to either claim 30 or claim 31 , wherein the methylated spirits is added at an amount of from between about 0.3 to 0.4% as a percentage of the weight of the coal fines feedstock mixture.

33. The process according to any one of claims 1 to 32, wherein the coal fines feedstock includes coal fine slurries, fines derived from waste and discarded coal and wherein the coal fines have a participle diameter of 1 mm and less.

34. The process according to any one of claims 1 to 33, which comprises the steps of:

(i) adding the coal fines feedstock into a mechanical mixer;

(ii) adding the sodium silicate binder and the surfactant to the coal fines of (i); and

(iii) mixing the components of steps (i) and (ii) in the mixer thereby to form the agglomerated coal product; and

(iv) where the agglomerated coal product is likely to be subjected to moisture during transport or storage, optionally further comprising a step of adding a waterproofing agent to the mechanical mixer during step (iii), thereby to coat the agglomerated coal product.

35. The process according to any one of claims 1 to 33, which comprises the steps of:

(i) adding the coal fines feedstock into a mechanical mixer;

(iii) adding a second binder comprising PVA to the feedstock mixture of (ii);

(iv) optionally adding any one or more of: silicon oil, methylated spirits or lime (i.e. calcium hydroxide) to the product of step (iii) in the mixer;

(v) mixing the components of steps (i) to (iv) thereby to form the agglomerated coal product; and

(vi) where the agglomerated coal product is likely to be subjected to moisture during transport or storage, optionally further comprising a step of adding a waterproofing agent to the mechanical mixer during step (v), thereby to coat the agglomerated coal product.

36. The process according to any one of claims 1 to 35, comprising a step of shaping the agglomerated coal product by any means known to those skilled in the art such as, but not limited to tumbling, extruding, rolling, pressing, cutting, pelletizing, briquetting and the like and wherein the step of shaping the agglomerated coal product is either performed substantially simultaneously with the mixing step in the mechanical mixer, or subsequent to the mixing step in a product shaping apparatus.

37. The process according to claim 36, where the shaping occurs subsequent to the mixing step, wherein a waterproofing agent is added either to the mixer during the mixing step or to the shaper during the shaping step.

38. The process according to any one of claims 1 to 37, which comprises an additional step of drying or curing the agglomerated coal product to have a total moisture content, after drying or curing, of from about 3% to about 9% water.

39. The process according to claim 38, wherein the drying or curing process comprises the steps of:

(i) feeding the agglomerated coal product formed during the process according to any one of claims 1 to 37 through a drier comprising a heat source, an agglomerated coal product feed, an agglomerated coal product outlet and a conveyer connecting the agglomerated coal product feed and agglomerated coal product outlet;

(ii) conveying the agglomerated coal product from the agglomerated coal product feed through the drier to the agglomerated coal product outlet of the drier, thereby to dry the agglomerated coal product; and

(iii) collecting the dried agglomerated coal product from the agglomerated coal product outlet of the drier.

40. The process according to claim 39, wherein the drier is an air suspension drier with a vibrating bed.

41 . An agglomerated coal product formed by the process of any one of claims 1 to 40.

42. The agglomerated coal product according to claim 41 which is a pellet or a briquette.

43. A method of operating a furnace comprising the use of the agglomerated coal product according to either claim 41 or 42.