GB2416542A - Pelletised carbonaceous fuel product - Google Patents

Abstract

A process for producing rigid fuel pellets from a particulate carbonaceous material and a silicate-based binder with one or more surfactants, and optionally water, comprising: admixing the material and binder; and agglomerating the mixture by tumbling, preferably using a rotary drum, to form rigid fuel pellets at ambient temperature. The agglomeration by tumbling allows pellets of a variable size distribution, which may be handled, stacked and transported without significant breakage, to be formed without moulding or heat treatment. Preferred binders comprise sodium or potassium silicate, with optional additional ingredients such as lime (as a sulphur-absorbing agent), inorganic binders, cements and waterproofing additives. Preferred particulate materials include coal dust, coal fines or peat. The pellets may be formed with hardened outer shell.

Description

24 1 6542 i 1 Fuel Product and Process 2....

3 The present invention relates to a fuel product and..

4 a process for making same. .

6 A continuing problem in many solid-based fuel 7 extraction processes is dealing with waste 'fine' 8 materials. As much as 10% of run-of-mine coal can 9 end up as fine (generally about <3mm) or ultra fine..

(generally about <0.lmm) coal dust. This fine coal 11 is often unsuitable for the end process and, even 12 where the size is not a problem, retains large 13 amounts of water (10%-30%) which can make it 14 "sticky", difficult and inefficient to handle transport and burn.

17 One solution has been to form briquettes. These are 18 formed by compressing the fines at very high 19 pressures to physically form a secondary fuel material. However, the high capital and operating 21 costs of briquetting plants have prevented their use 22 beyond some high cost countries In many places, 1 coal fines are currently simply 'dumped, near the 2 coal mine.

4 Another solution is to agglomerate carbonaceous fines using various processes, including pelletizing 6 and extruding. For this, various binder materials 7 have been suggested. In US 4219519, the major 8 material of the bonding agent is lime or an 9 associated calcium compound. US 3377146 lists various organic binders, and US 4357145 suggests 11 tall oil pitch. US 4025596 describes a method for 12 pelletizing finally divided mineral solids using a. . 13 latex, optionally with bentonite or starches. . . 14.

However, all of these processes involve the need for.

16 some sort of treatment of the pellets after their .,'.

17 formation, generally drying at an elevated...

18 temperature so as to provide the final form of the.

19 pellets. Thus, all of these processes require some form of heat treatment, usually in line with the use 21 of one or more organic binders. More importantly, 22 all these processes are over 20 years old, and none 23 are known to have been actually used, or used with 24 any success.

26 Another problem is the weight of moisture. High 27 moisture levels in coal make transportation and 28 combustion inefficient. Sub-bituminous coals, which 29 comprise a large and valuable part of the worlds coal reserves, contain chemically attached 31 moisture within the coal structure (up to 20%-30% 32 moisture). This Moisture severely limits the use 1 and value of sub-bituminous coals. For example, for 2 every 3 truckloads of coal that is transported, one 3 truckload of water must also be transported. That 4 moisture also takes (robs) energy from the flame (to turn the water into steam) as the coal is burnt.

6 Attempts to drive the moisture out by heating have 7 proved unsuccessful because the coal falls apart as 8 it dries and also becomes susceptible to spontaneous 9 combustion. As a result, very little sub-bituminous coal is traded internationally.

12 Another industry using the briquetting process is...

13 the peat industry. To form a suitably crushable; 14 material, the peat must be significantly dried, '.

often two or three times, as well as shredded and..

16 crushed, adding to the overall cost of forming the. ..

17 briquettes.

18 ' 19 It is an object of the present invention to provide. . a more efficient fuel product and process by 21 lowering costs of operations and capital 22 requirements.

24 Thus, according to one aspect of the present invention, there is provided a process for producing 26 rigid fuel pellets from a particulate carbon-based 27 material and a binder, comprising of the following 28 steps: admixing the material and binder, and 31 agglomerating the so-formed mixture by tumbling to 32 form the rigid pellets, 2 wherein the binder is silicate-based and includes 3 one or more surfactants, and the process is carried 4 out at ambient temperature.

6 The use of a silicate-based binder which includes 7 one or more surfactants allows the process of the 8 present invention to create rigid fuel pellets at 9 ambient temperature. Forming rigid fuel pellets at ambient temperature has not been achievable by any

11 prior art process.

13 The fuel pellets are 'rigid' in the sense that they.., 14 are handleable, and are able to be stored, stacked, and/or transported immediately, without requiring 16 any separate active curing step or steps. That is, 17 the pellets cure without any assistance or further 18 treatment, especially heat and/or pressure 19 treatment. The prior art processes required fuel pellets formed by tumbling of agglomeration to be 21 actively cured with heat and/or (forced air) 22 pressure before such fuel pellets were rigid and 23 handleable. Thus, the fuel pellets of the present 24 invention could be packaged and/or transported immediately after forming.

27 The tumbling action, such as in a rotary drum, 28 serves to agglomerate the particles and bind the 29 mixture into the pellets, usually with a variable size distribution. No mechanical compression force 31 is required, (with its attendant low production rate 32 and high cost), and the process of the present 1 invention can be carried out at ambient temperature.

2 By being able to carry out the process at ambient 3 temperature, no additional equipment is required for 4 any active second stage treatment, or to provide an elevated temperature. This naturally eliminates the 6 need for a power source, e.g. fuel to be burnt, to 7 create the elevated temperature, which action is 8 usually a significant economic requirement of an 9 industrial process.

11 The binder of the present invention allows the fuel 12 pellets of the present invention to be formed and to....

13 cure in a scold fusion' process. That is, the 14 pellets can be formed and cure without the need for any external heat input. ..

16 e 17 In addition, the present invention is particularly 18 advantageous by being able to be a 'single stage' ..

19 process, avoiding the need for any pre-mixing or treatment of the constituents involved, and the 21 requirement for any post-forming treatment. From a 22 capital and economic perspective, a single stage 23 process reduces the requirements needed to set up a 24 plant adapted to provide the process of the present invention, and lowers the costs of operation by 26 having a single stage process which is run at 27 ambient temperature.

29 The present invention is also advantageous in using inorganic binders, as opposed to the generally

31 organic materials used as binders in prior art

32 processes. The use of inorganic binders reduces the 1 complexity of the process, and again reduces the 2 need for any pre-treatment or mixing of binder 3 materials. The use of an inorganic silicate-based 4 binder has two further advantages. Firstly, such binders do not impact on the burn quality of the 6 carbonaceous material (as they do not burn), in 7 contrast with organic materials such as starches, 8 (which do burn, and which therefore effect the burn 9 quality and thus heat content value of the formed material). Such binders are also clear of any 11 environmental implications (as they do not burn), 12 again in contrast with organic binders. ....

13. ..

14 Once the rigid fuel pellets are formed, they cure to provide the final form of the fuel pellets. In view..

16 of the present invention, such curing can occur at. . . 17 ambient temperature, and can also occur without any a.

18 active and/or separate curing step, especially a . 19 heat treatment step as used in the prior art. The.. . rigid fuel pellets will cure over time without any 21 external influence. Thus, they could be allowed to 22 stand, for example, for some time, such as 1-10 23 days, at a suitable position or location, whilst 24 curing occurs after the tumbling. Like concrete, curing may continue for some time, for example over 26 several days, but the invention provides rigid 27 pellets with sufficient solidity after tumbling, 28 that they are ready to be stored, stacked, 29 transported eta as they cure.

31 The concept of curing as used herein includes any 32 drying required of the formed pellets in addition to 1 the chemical process occurring at at least the 2 surface of the pellets as they are being formed, 3 preferably to provide a hardened shell. As such, it 4 is not intended that the present invention provides any separate drying step or action, ( being in 6 relation to one or more liquid materials or 7 substances, such as water, evaporating from the 8 pellets as they are formed and cured). Any such 9 post pellet-forming drying action is regarded as secondary or minor compared to the act of forming 11 and curing the pellets.

12....

13 Preferably, the process provides pellets having a.

14 hardened outer portion, skin, casing or shell. More preferably, the interior of the pellets is dry, and...

16 wholly or substantially has a small, preferably. . . 17 micro, aerated or porous form. That is, the action - ..

18 of the surfactant to draw the silicate binder to the .. ..

19 surface of the pellets as they are being formed : creates air pockets and bubbles in the interior, the 21 benefit of which is discussed hereinafter.

23 In one embodiment of the present invention, water is 24 part of the material and binder mixture, either by being part of the material, part of the binder, 26 added separately, or a combination of any of these.

28 The amount of water needed or desired for the 29 process of the present invention may depend upon the nature of the particulate material and the binder.

1 For example, listed below are various types of mined 2 coal, and their generally found moisture content 3 (m/c) as the coal is mined, their heat content (h/c) 4 and their carbon content.

m/c h/c (mj/kg) Carbon Bituminous <20% 24-35 45-86% Coal Anthracite <15% 26-33 86-98% coal Lignite 10-20 25-35% Coal Sub bituminous <30% 20- 21 35-45% ..

coal... .

- .e 7 The heat content of coal can be directly linked to A. a 8 the moisture content. Therefore, the heat content .. : 9 of high grade anthracite with a moisture content of 15% will have a heat content of 26-33mj/kg on a 11 moist mineral-matter free basis. At the other end 12 of the scale, lignite, the lowest rank of coal, will 13 have a moisture content of up to 45%, with a heat 14 content of only 10-20 mj/kg on a moist, mineral matter free basis.

17 In most power stations using coal, the coal is 18 generally ground into a fine powder to be sprayed 19 into the combustion furnaces. However, the power for crushing coal having a moisture content of, for 21 example, 25% is relatively high. Thus, at some 1 power stations, there is currently million tonnes 2 a year of 'unusable coal' product in stockpiles, as 3 it is too wet, i.e. its moisture content is too 4 high, for efficient burning. As mentioned above, freshly mined bituminous coal can have a moisture 6 content of up to 20%, lower ranking coal can have a 7 moisture content of up to 30%, with lignite going up 8 to 45%. To drive off this level of moisture (by 9 turning it into steam) prior to any combustion of the actual coal requires so much energy to start 11 with, that this coal is simply not used, as it is 12 not efficient. Grinding such coal to be more....

13 burnable, is also inefficient as the moisture-rich.

14 coal generally clogs up the grinder.

16 It is a particular advantage that the present. . . 17 invention can use any type of 'wet' or 'dry' 18 particulate carbon-based material, although any wet 19 material preferably has a maximum water content of a.: 10-15%. Such a moisture level can be achieved by 21 grinding, which has a drying effect, (although the 22 power required therefor is a lot lower than the 23 power required for grinding coal to a ponderous form 24 ready for immediate burning as described above).

Such material is generally still regarded in the art 26 as being wet', especially in relation to e.g. the 27 briquetting process, which requires its material to 28 be absolutely dry.

In some circumstances, it is preferred to have a dry 31 particulate material. In other circumstances, the 32 material may be derived from a wet fuel source, such 1 as peat and coal tailings dams, and any reduction in 2 the amount of drying needed (compared with for 3 example the briquetting process) reduces the overall 4 energy input required to form the fuel product.

6 The process of the present invention is directly 7 usable with moisture-rich coal fines and similar 8 products, as any water content of the binder can be 9 reduced in line with the level of moisture in the coal without affecting the process. Once the 11 pellets have been formed, their hardened shell 12 wholly or substantially stops or significantly, 13 reduces water ingress, especially if waterproofing.

14 additives are used. Once fully cured, the pellets can have a moisture content of at least half that of...

16 the particulate starting material, and possibly less. ...

17 than 5%, and thus be sufficiently dry for immediate 18 and easy grinding to form a suitable fuel product 19 for a power station. .: 21 A reduction in moisture also provides a direct 22 increase in the heat content value of the product 23 which it is burned, hence increasing its efficiency 24 and economic value. This economic benefit extends to transportation of such a product, in comparison 26 with cost of transporting 'wet' or moisture-rich 27 material as described hereinabove. Indeed, the 28 present invention provides a process whereby with 29 consideration of the type and amount of binder(s) used, and the process parameters, a fuel material 31 can be provided which has a desired or pre 32 determined burn value or the like, which, in 1 particular, could suit the local economic conditions 2 for the fuel source. Different locations and 3 countries mine different types and grades of coal, 4 and they therefore use such coals in different ways in order to try and maximise their economic value.

6 The present invention provides a particular 7 advantageous process to benefit what is currently 8 regarded as a waste material from current industrial 9 processes.

I 11 Thus, the present invention also provides 12 significant moisture reduction in a fuel product, ..

13 converting an inefficient fuel product into an. . .

14 efficient fuel product. -:.

16 In a preferred embodiment of the present invention, . 17 the amount of water for the process is adjusted in - 18 the binder component prior to its admixing with the..

19 particulate material. The calculation of this .

binder to water adjustment is dependent on the 21 moisture content of the particulate material.

23 According to another embodiment of the present 24 invention, the particulate material is generally of a maximum size or grade of 3mm or lower. Coal 26 'dust' or 'fines' can often be of a sub-micron size.

27 Peat is a fuel material which is generally 28 dried/shredded/dried/crushed prior to briquetting.

29 Some shredding of the peat material may still be required to provide a particulate material suitable 31 for the present invention, but to a much lesser 32 extent than that required for briquetting.

2 More preferably, the particulate material has a 3 range of sizes or grades; preferably biased towards 4 fine or finer particle sizes.

6 Carbon-based particulate material suitable for the 7 present invention can be accepted wet or dry, and 8 could be provided by any type of maceral fuel, 9 including peat and lignite through to sub-bituminous coals, anthracite fines, petroleum coke fines and 11 the like, as well as sewerage wastes, biomass, 12 animal wastes and other hydrocarbon materials that..

13 could be considered a fuel source. The particulate: .

14 material may also be a combination of two or more starting materials or 'ingredients', not necessarily. . 16 premixed, and such as those hereinbefore mentioned, 17 so as to provide 'hybrid' fuel pellets. 19 Suitable materials also include low grade or processed fuels, as well as hitherto 'waste' 21 products, whose clean combustion would help lower 22 overall pollution levels.

24 The present invention is not affected by high ash content or sulphur content in the particulate 26 material.

28 Any suitable silicate-based binder can be used for 29 the present invention, which binder may be a homogeneous or heterogeneous material, such as 31 cements and raw silicates like calcium, sodium or 32 potassium.

2 The process may include the addition of one or more 3 further ingredients into the mix, either separately 4 or integrally with the binder. Such further ingredients include lime, inorganic binders, 6 cements, and waterproofing additives. A cementitious 7 material can assist in the green-strength of the 8 pellets, and possibly in forming the hardened outer 9 surface or shell for the pellets as described hereinafter 12 Lime or cement helps to inhibit sulphur emission I 13 upon burning of the so-formed pellets. It is a: . 14 particular advantage of the present invention that the use of lime or other types of calcium hydroxide. . 16 (which are known to be sulphur-absorbing agents) are 17 admixed with the particulate carbon-based material. . . 18 The increased mixing of such sulphur-absorbing. :.

19 agents with sulphur-containing carbon-based materials reduces the need for current sulphur 21 absorbing apparatus such as scrubbers and the like 22 at the end of fuel-burning process. Indeed, it is 23 considered that the present invention can achieve a 24 reduction of sulphur emission (usually in the form of sulphur dioxide) by 70-90%, or possibly more.

26 Again, this is a significant reduction in current 27 power station requirements, and therefore costs.

29 In most coal-burning power stations, the coal is generally ground into a fine material and then 31 injected into the fuel burner to provide the power.

32 The addition of a sulphur-absorbing agent into the 1 pellet-forming process, along with grinding of the 2 pellets for subsequent use in a fuel-burning plant, 3 therefore provides two particular advantages.

4 Firstly, the ability of the process of the present invention to provide wholly or substantially dry, 6 pellets reduces the energy input required to effect 7 the grinding of the pellets prior to their burning, 8 as described above, and secondly, grinding of the 9 pellets increases the mixing of the sulphur absorbing agent(s) with the carbon-based material, 11 thus increasing the efficiency of the sulphur 12 absorption, and so reducing the sulphur-emission.

13: . 14 There is increasing legislation around the world to reduce sulphur emissions, especially from coal- . . 16 burning power plants. The present invention helps 17 achieve such reduction without requiring additional 18 or other physical and/or chemical sulphur absorption. :.

19 apparatus or processes such as scrubbers and the like, (which also require regular regeneration to 21 work effectively, which is another energy intense 22 process).

24 Thus, the process of the present invention can further include the step of grinding, crushing or 26 otherwise particularizing the pellets, preferably in 27 a form ready to use in a fuel-burning power plant.

29 One or more other mineral additives such as zeolites or vermiculite could also be used as a further 31 ingredient to help bind any metallic contaminants in 1 the ash of the pellets, and so prevent any soluble 2 metals being released from the ash.

4 The particulate material and binder, and any other separate reagents or ingredients to be added, can be 6 admixed using any known process or arrangement, 7 including simple mixing. Because the next part of 8 the process is a tumbling action, absolute 9 homogenous mixing of the reagents or ingredients prior to the tumbling is not essential, as the I 11 tumbling action will generally further the mixing 12 action if necessary or desired. In some .

13 circumstances, the admixing may at least partly. ..

14 occur during the tumbling action, such that the actions of the invention may not be wholly. . 16 distinct. 17

18 In one embodiment of the present invention, the. :.

19 binder is coated on to the particulate material.

One method of coating is to spray the binder on to 21 the material. ( 22

23 In another embodiment of the present invention, the 24 particulate material is moving prior to and/or during mixing with the binder, and/or the material 26 is in a dispersed arrangement. One particular 27 suitable form of this is a falling curtain of 28 particulate material, such as at conveyor transfers, 29 inside pelletising drums or pans, and from stockpile load outs, etc. 1 In another embodiment of the present invention, the 2 particulate material and binder are directly and/or 3 immediately undergo tumbling after their contact 4 with each other.

6 The tumbling action serves to agglomerate the 7 particulate material and binder mixture to form 8 particles of greater and greater size, generally 9 having a spherical or ovoid shape. The size of the so-formed pellets can be adjusted based on the 11 process conditions for tumbling, such as rotation 12 speed, moisture content, impact force and residence..

13 time. The pellets could also be screened and/or . 14 recycled during or after pelletising to produce a desired, e.g. narrower, size distribution. . . - 17 One suitable apparatus for providing tumbling action. , 18 is a rotary drum. Rotary drums are well known in,.

19 the art. Their output can be dependent upon the length, diameter, speed of rotation and angle of 21 mounting of the drum, and the output can vary from 1 22 single figure tonnes per hour, to hundreds of tonnes 23 per hour per drum.

The general sizes and dimensions of agglomerator 26 drums, such as pan, rotary and conical drums, are 27 known in the art, as are their process variations to 28 provide variation in the products formed. See for 29 example UK Patent No 787993.

31 Rotary drums have low capital and low operating 32 costs, especially in comparison with briquetting 1 plants. They can even be provided in mobile form, 2 such that the process of the present invention can 3 be provided where desired or necessary, e.g. moved 4 and located to where a particulate material is currently stored or 'dumped', rather than requiring 6 significant movement (and therefore cost) for 7 transporting the material to a fixed processing 8 site.

The agglomeration action may be carried out in one 11 or more stages, which stages could be connected, 12 such as the tumbling conditions changing in the same 13 drum, or the material being fed directly into. .

14 another agglomerator. Or, such actions could be separate. In one arrangement for multi-stage 16 agglomeration, the tumbling conditions are variable ' 17 or varied for each stage. The conditions may be. . 18 altered either in a continuous manner or action, or. ..

19 discretely.

21 Where the process of the present invention involves 22 tumbling the mixture in a rotary drum, one or more 23 rotary drums may be used for the agglomeration, 24 preferably in series.

26 The surfactant(s) serve to draw the silicate-based 27 binder towards the surface of the forming pellets, 28 such that as they are created and start to cure, 29 the pellets will form and then continue to have a harder outer portion, skin, shell or surface, 31 compared to their interior. Thus the pellets have a 32 variable density towards the core; the density being 1 greater at the surface. Indeed, the 'shell' layer 2 or portion will generally have a high density in 3 comparison with the lower density of the interior'.

More preferably, the pellets have sufficient 6 hardness once formed to allow handling, stacking 7 and/or transportation without any significant 8 breakage.

The curing of the pellets may start during or be 11 part of the agglomeration action.

13 The method of the present invention may include one I. . 14 or more sizing steps. That is, to grade the size of the so-formed pellets to that desired or necessary. '.

16 This could include extracting those pellets which .^ 17 are damaged or undersized, which pellet material....

18 could be recycled back into the process of the.

19 present invention. When coal is mined, cleaned and transported, considerable quantities of fine coal 21 (particles less than 5mm) are generated. The 22 present invention can form this fine coal into 23 approximately 50mm lumps with very low moisture, 24 without any change to the chemical properties of the coal. The pellets can then be handled, transported 26 and used as normal lump coal.

28 Following any initial curing, the formed pellets are 29 rested for some time, possibly a number of days such as 3-7 days, to provide or allow for curing to 31 finish. Like other curing products, the pellets 1 continue to cure to gain strength over time, such as 2 a further number of days or weeks.

4 In another aspect, the present invention provides a process for producing rigid fuel pellets at ambient 6 temperature from a particulate carbon-based material 7 and a silicate-based binder which includes one or 8 more surfactants, the process comprising the steps 9 of: admixing the material and binder, and 11 agglomerating the so-formed mixture by tumbling to 12 form the rigid fuel pellets. '.. ë

13: . 14 According to another aspect of the present d invention, there is provided a rigid fuel pellet 16 product formable at ambient temperature by 17 agglomeration of a particulate carbon-based material I. 18 and a silicate-based binder including one or more.. '.

19 surfactants.

21 According to another aspect of the present 22 invention, there is provided a fuel pellet product 23 whenever formed by a process as herein described.

The fuel pellet product of the present invention is 26 a material which is easily storable. It is also 27 easily transportable due to its variable diameter 28 distribution. This enhances stacking concentration, 29 which also reduces abrasion and consequential breakage of the pellets.

1 The product of the present invention is ready for 2 use as a fuel in many situations, e.g. domestically 3 such as in a home fire, industrially, such as in a 4 power plant, etc. 6 The product is formed from currently 'waste' 7 materials, thereby increasing the efficiency of 8 current solid-fuel extraction and production.

The product preferably allows a very high percentage 11 of combustion (possibly 100% combustion), so as to 12 leave little or no combustible fuel in the ash. ; . 14 Embodiments of the present invention will now be described by way of example only, and with reference 16 to the accompanying drawings in which: 9 17 , 18 Figure 1 is a flow diagram of a process according to. . 19 one embodiment of the present invention in the context of the material handling and production 21 stages in an industrial plant; 23 Figure 2 is a front view of tumbling action of 24 agglomerating pellets according to the present invention; and 27 Figure 3 is a view of a number of pellets according 28 to another embodiment of the present invention.

Fine coal recovery systems are now a common part of 31 modern coal process operations, but there has been a 32 requirement for a cost effective high tonnage 1 solution for utilising the wet coal fines generated 2 by the various beneficiation (benefaction) 3 processes.

High capital and operating costs of briquetting 6 plants have prevented numerous operations from 7 maximising their coal reserves. Briquetting is a 8 process where some type of material is compressed 9 under high pressure. Compression of the material causes the temperature to rise, which makes the raw 11 material liberate various adhesives.

13 There are low-priced hydraulic briquetting presses. . 14 which are designed to operate for only a number of.. . hours a day. Bigger mechanical presses are used for 16 large-scale installations making hundreds of 17 kilograms per hour, but these require approximately I.. 18 200kWh energy input (for drying and processing) per....

19 tonne of briquetting material. The cost of this is prohibitive in countries where the cost of coal is 21 already low, such that coal fines are currently 22 simply dumped on nearby ground in many countries 23 around the world.

Similarly, the current method of forming peat 26 briquettes requires initial drying of the dug peat 27 to about 55% moisture, shredding, further drying to 28 a lower moisture content, followed by crushing, 29 followed by high pressure briquetting. Each mechanical step requires significant energy input.

1 Other waste materials include petroleum coke, a by 2 product from cracking oil, which is sold off at a 3 low cost.

The process of the present invention allows for use 6 of all these materials in a cost-efficient process, 7 to provide a beneficial fuel product.

9 Figure 1 shows a flow diagram for the process of the present invention in the context of an industrial 11 plant.

13 Preparation The raw fuel feed is prepared for agglomeration.

16 Depending on its raw state, it may - be beneficial 17 to carry out some grinding, screening or drying.

18 The finer the raw feed is, the more effective the 19 process. Preferably, (but not limiting), the moisture content of the feed is 10-15% (by weight) 21 at most.

23 Depending on the moisture content and chemical 24 characteristics of the raw fuel feed, the liquid feed is adjusted to suit. This will involve 26 balancing the quantity of water relative to the 27 binder and surfactants used.

29 The above parameters can be established during pre testing of the process and apparatus. For coal 31 fines agglomeration, it has been found that between 32 20-25% of liquid binder (to weight of raw feed) is 1 generally desired for efficient agglomeration.

2 Generally, the wetter the raw feed, the less water 3 is required to be added at this stage.

Agglomeration 7 The fuel feed is carried along and any dry reagents 8 are added to the feed. It then falls from the end of 9 a conveyor belt. The liquid binder is sprayed onto the falling curtain of fines, which together fall 11 into a rotating drum, generally 1-5m (such as 3m) in 12 diameter. As the mixture tumbles while being 13 sprayed with the binder and water mixture, it forms 14 small pellets which agglomerate and grow, forming rigid pellets of desired shape and size as shown in ë 16 Figure 2. -

18 The drum can be lined with loosely fitting heavy..

- ..

19 duty rubber sheet to avoid material sticking to the. .

sides of the drum. The drum is set at an incline 21 (e.g. 1-3%) to aid progression of the pellets 22 therealong, and to control the residence time in the 23 drum. The completed pellets exit at the opposite 24 end of the drum onto another conveyor.

26 Pellets can be varied in size with only operational 27 drum adjustments (speed of rotation, moisture 28 content and longitudinal drum angle which directly 29 affects residence time in the drum). Expensive mould changes, such as in present briquetting 31 operations, are not required to vary the product 32 dimensions.

2 Some forming and even some curing may take place in 3 another rotating drum, similar to but having a 4 larger diameter than the agglomerating drum. It may also be of greater diameter and longer than the 6 agglomeration drum. Here the pellets progress 7 slowly through the drum, allowing sufficient time 8 for the pellets to initially cure or receive surface 9 treatment, and thereby allow immediate handling and stacking. The residence time within this drum is 11 dependent on the fuel characteristics, and its use !\ 12 can be determined in pre-production tests. 13 '

14 Selected surface treatment additives can be added at. . . this stage to increase the surface area of the 16 pellet skin, to prevent sticking, and/or to prevent 17 leaking fluid into bags, etc. ..

18 '..

19 Should the green strength of the pellets be poor, . certain additional binders or cementitious chemicals 21 can be added to rapidly speed-up the curing 22 process, and thereby give quicker and stronger

I

23 initial green strength to aid handling, or 24 handleability, etc. Broken and undersized pellets can be removed using for instance a slotted section 26 of drum or a vibrating screen at the drum exit. The 27 damaged and undersized pellets can then be returned 28 to the agglomerating drum for reprocessing.

Final Sizing (if required) 1 At this stage the pellets can be further graded to 2 the desired cross section if necessary. Any damaged 3 and undersized pellets can then be returned to the 4 agglomerating drum for reprocessing.

6 The pellet sizing could even be designed to be made 7 dependent upon proposed use. The pellet size can be 8 adjusted by means of changes to process conditions, 9 equipment configuration, and even reagent dosage.

11 The pellets can then be stockpiled for curing.

12 During this time, generally between 3-7 days for 13 coal fine pellets, and depending on ambient. . 14 temperature, the pellets reach such strength as to. . . allow full handling. No heating or force draught 16 drying is required. An example of formed pellets is.

17 shown in Figure 3. . 18 .

19 The spherical shape of the pellets will allow air to.

move freely through the stockpile to assist the 21 curing process and prevent heat build up and the 22 risk of spontaneous combustion. At this stage, the 23 pellet surface is also tightly sealed, preventing 24 air ingress into the pellets, and so also slowing the effect or chance of any spontaneous combustion.

26 If spontaneous combustion is still a problem, 27 preventative reagents can be added during 28 agglomeration.

Transportation and Packing 1 Tumble and growth agglomeration can result in a wide 2 variation in the final pellet size - as in natural 3 lump coal. This has the advantage of lowering the 4 bulking factor of the pelletised product, resulting in lower transportation costs.

7 The formed product could then be bagged or stacked 8 and allowed to continue to cure at ambient 9 temperatures, curing time being dependent upon local humidity. Generally, the higher the moisture content 11 of the feed, the longer the pellets will require to 12 be cured at ambient temperatures and humidity. 13 .

14 Process rates can be selected, but production rates a of between 10100 tonnes per hour of coal material 16 per drum would be a general rate. The production:.

17 rate can be scaled up using multiple process units, 18 or scaled down with smaller equipment.

19. .

Production costs are dependent upon the production .

21 rate, particle size distribution of the feed, and 22 characteristics of the particulate materials.

23 However, energy input per tonne of product has been 24 measured at approximately 0.5 to 2kWh, at least a hundred times less than the energy input needed for 26 briquetting.

28 In particular, the process of the present invention 29 can be modified to treat very high ash and/or very high sulphur coals, as the pellets remain stable 31 throughout the combustion process, allowing even for 32 low rank coals to burn efficiently.

2 The present process is also suitable for fuel 3 products that need to lower ash and sulphur to be 4 sellable. The present process allows fine grinding to release contaminants by gravity or flotation 6 methods, generating a much higher quality fuel 7 source. The process also provides the manner of re 8 forming the fine pure concentrate into a usable 9 stable and valuable product form.

11 Sulphur emissions, even from very poor quality coal, 12 can be wholly or substantially eliminated by simple 13 adjustment of pelletising additives, significantly 14 reducing or even possibly eliminating any sulphur . . dioxide pollution leading to acid rain. The process 16 of pelletising also simultaneously reduces fly ash 17 by the inherent cementation, silicification and .

18 stabilization of the residual ash instigated by the..

19 reagents used. Additionally, higher product.

combustion temperatures are easier to generate due 21 to high gas transfer rates, not only between the 22 pellets, but also between particles within the 23 pellets, providing more rapid and/or more 24 controllable combustion than normal fuels.

26 A further advantage of the present invention is the 27 very complete combustion of the contained fuel in 28 the pellets due to the high gas transfer rates and 29 the maintenance of the integral structure of the pellets until combustion is complete. The retaining 31 hardened shell, skin, etc. allows for significant 32 heat increase or build-up inside the pellet, causing 1 very high levels of combustion, resulting in the 2 completion of any pre-designed chemical reactions in 3 the interior content of the pellet. As the content 4 is dry and porous form, generally of a fine, nature still, and is now pre-heated, rapid and so complete 6 combustion of the content occurs. The pellets 7 maintain their form even at white heat, and show 8 very stable combustion characteristics.

In particular, the process of the present invention 11 can involve no forced drying of the pellets because 12 the action of any surfactant(s) used is maximized in 13 ambient temperatures. Moreover, where water is ' 2.

14 used, the surfactant causes the binder-containing A. . moisture to rapidly migrate to the surface of the 16 pellet by capillary action, giving the egg shell' 17 effect of a hardened surface and softer interior, .' 18 due to the final heavy surface concentration of the....

19 binder. This results in a significantly enhanced..

skin strength, giving a very robust and low moisture 21 content pellet (approximately 5%), which also 22 resists moisture absorption from the air.

24 One further application of the present process is lowering the feed moisture of pulverised coal fuels 26 in power and heat stations, where the coal fines or 27 coal tailings are pelletised and allowed to 28 thoroughly cure and dry before being pulverised and 29 burnt in the furnace. The general moisture content found in current coal fines dumps is usually in the 31 range 12-35%, making them very difficult to use or 32 blend with other feeds.

2 As can be recognized from the above, the process of 3 the present invention, overcomes or solves a number 4 of financial and operational problems.

6 Once the t egg shell, effect has been fully developed 7 after curing, the pellet will retain its strength 8 even during white heat combustion. This allows high 9 temperature reactions to take place inside the pellet resulting in much higher levels of combustion 11 of the fuel, giving effective oxidation and 12 sequestration of any contained sulphur, and 13 negligible unburnt carbon levels in the residue ash. .....

14 The shell effect allows the pellet to retain its . structure during combustion, resulting in less 16 particulate emissions in the flue gas.

18 The egg shell pelletisation could also be used on. . 19 sulphide concentrates and iron ores to allow the. ..

manufacture of pre-fluxed furnace feeds which can 21 lead to sulphur emission free' smelter technology.

22 This could be used in existing operations cost 23 effectively with high industrial tonnage output.

The present invention provides significant benefits 26 compared with present technologies, including: 28 <3mm coal/lignite fines can be pelletised dry or 29 direct from a filtration plant.

Tonnage throughput can be from 10 tones per hour 31 (community size) up to 100 tonnes per hour per 32 pelletising line.

1 High level of automation can be used during 2 pelletising for accurate control and reagent 3 usage.

4 Pellets just air dry while chemically 'curing'.

Pellets can be handled by bulk handling equipment 6 when cured or alternatively bagged when 'green'.

7 Pellet size can be customised from 5mm to 150mm 8 if required depending upon coal characteristics 9 and process parameters.

Special heavy duty reagents can be added for high 11 strength, for rapid cure, for high temperature 12 strength, and for enhanced water resistance. .. .

13 Pyrite removal can be reduced or eliminated due 2.. . 14 to various binder combinations to eliminate SO2 due to gas transfer to form CaSO4 inside the .

16 pellet. I 17 Due to excellent combustion characteristics, high 18 ash coal fines will ignite and burn with high. . .

19 efficiency.

Long lasting combustion, with high percentage 21 carbon combustion.

22 <20mm coal can be crushed and pelletised with 23 fines for high value pellets.

24 Contaminated coal or waste products such as sawdust, rice husks, sewage, animal wastes, 26 petroleum coke or waste oil can be included into 27 the pellets.

28 Residual ash has negligible un-burnt fuel (e.g. 29 coal) residue and is excellent for other industrial uses.

1 Residual ash can also be pelletised with similar 2 binder reagents for concrete feedstock, aggregate 3 blending and high porosity landfill.

4 Lignite and peat can be treated with identical technology or can be blended with other fuel 6 sources to create hybrid pellet fuels with pre 7 designed characteristics such as smokeless 8 burning.

The present invention is usable with all types of 11 coal fines, which will have a varying amount of 12 moisture and sulphur content. Generally, pellets....

13 ranging from 5-50 mm diameter are formed, which 14 sized pellets are easily handable, storable, .

transportable and then burnable, and, if required, ...

16 in an optimal form and size for grinding prior to. . . 17 burning. ....

19 The present invention provides a simple but . efficient process for using waste carbon-based 21 materials, and forming a useable fuel product, which 22 is easily transportable and efficiently combustible.

23 Rotating drum or pan agglomerators are relatively 24 low cost to build, and are capable of very high tonnage throughputs. Customised products can be 26 produced and the present invention enhances the 27 economics of ash and sulphur removal in coal upgrade 28 plants.

Low technology applications in countries where there 31 is little investment for efficient coal process 32 plants can also easily utilise the present 1 invention, therefore allowing the provision of high 2 efficiency, environmentally friendly and cost 3 effective process plants to be manufactured and 4 operated. In such places, any materials not immediately useable are currently treated as waste 6 and simply stockpiled in bigger and bigger piles, 7 increasing the environmental hazard thereof. ë c a. . :. ë he c -.

A ë

Claims (1)

1 Claims 3 1. A process for producing rigid fuel pellets from 4 a

particulate carbon-based material and a binder, comprising of the following steps: 7 admixing the material and binder, and 8 agglomerating the so-formed mixture by tumbling 9 to form the pellets, I 11 wherein the binder is silicate-based and 12 includes one or more surfactants able to form 13 rigid fuel pellets as the process is carried out ' 14 at ambient temperature. . 2

16 2. A process as claimed in claim 1 carried out as,. . 17 a single stage process.

19 3. A process as claimed in Claim 1 or Claim 2 . . wherein the process is carried out without 21 requiring a separate active curing step or 22 steps. 23,

24 4. A process as claimed in any one of the Claims 1 to 3 wherein the soformed rigid pellets cure 26 after tumbling at ambient temperature.

28 5. A process as claimed in any one of the preceding 29 claims wherein the pellets form a hardened shell.

1 6. A process as claimed in any one of the preceding 2 claims adapted to provide pellets of a variable 3 size distribution.

7. A process as claimed in any one of the preceding 6 claims wherein the particulate material and/or 7 binder mixture includes water.

9 8. A process as claimed in Claim 8 wherein the binder includes water prior to admixture with 11 the particulate material.

13 9. A process as claimed in any one of the preceding. . 14 claims wherein the particulate material is . . generally of a maximum size or grade of about 16 3mm or lower. : 18 10. A process as claimed in any one of the. . 19 preceding claims wherein the particulate.

material is coal dust or coal fines.

22 11. A process as claimed in any one of Claims 1 to 23 10 wherein the particulate material is partly, 24 substantially or wholly peat.

26 12.A process as claimed in Claim 11 wherein the 27 peat is in combination with coal fines.

29 13.A process as claimed in any one of the preceding claims wherein the particulate material is a 31 combination of two or more starting materials.

2 14.A process as claimed in any one of the preceding 3 claims wherein the binder is partly, wholly or 4 substantially sodium silicate or potassium silicate.

7 15.A process as claimed in any one of the preceding 8 claims wherein the process includes the addition 9 of one or more further ingredients.

11 16.A process as claimed in Claim 15 wherein the or 12 each further ingredient is selected from the .

13 group comprising: lime, inorganic binders, .

14 cements and waterproofing additives. . . : - 16 17.A process as claimed in any one of the preceding 17 claims wherein the particulate material and 18 binder are at least partly mixed with agitation. ..

18.A process as claimed in any one of the preceding 21 claims wherein the binder is sprayed on to the 22 particulate material.

24 l9.A process as claimed in any one of the preceding claims wherein the particulate material is moving 26 prior to and/or during mixture with the binder.

1 20. A process as claimed in any one of the 2 preceding claims wherein the pellets have a 3 spherical or ovoid shape.

21. A process as claimed in any one of the 6 preceding claims wherein the pellets are screened 7 after tumbling.

9 22. A process as claimed in any one of the preceding claims wherein the tumbling is carried 11 out in a rotary drum.

13 23. A process as claimed in any one of the.... . 14 preceding claims wherein the process does not ..

require any pre-treatment of the particulate 16 carbon-based material.

18 24. A process as claimed in any one of the. . 19 preceding claims for reducing moisture in the. ..

carbon-based material, preferably to less than 5%, 21 compared with the weight of the moisture in i 22 particulate carbon- based starting material.

24 25. A process as claimed in any one of the preceding claims wherein the mixing of the 26 particulate material and binder occurs by the 27 tumbling.

29 26. A process as claimed in any one of the preceding claims further comprising the step of 31 grinding the formed pellets.

1 27. A rigid fuel pellet product formable at 2 ambient temperature by agglomeration of a 3 particulate carbon-based material and a silicate 4 based binder including one or more surfactants.

6 28. A fuel pellet product whenever formed by a 7 process as claimed in any one of Claim 1 to 27.

9 29. A fuel pellet product as claimed in claim 27 or claim 28 ready for combustion.

12 30. A fuel pellet as claimed in any one of Claims 13 27 to 29 wherein the pellet product includes one. . 14 or more sulphur-absorbing agents. .. . 16 31. A fuel pellet as claimed in any one of Claims.

17 26 to 30 in a ground form, preferably ready for . 18 fuel-burning. ....

19. : 32. A fuel pellet as claimed in any one of Claims 21 27 to 31 having a hardened shell.

23 33. A fuel pellet as claims in any one or Claims 27 24 to 32 having a variable density towards its core.

27 34. A fuel pellet as claimed in any one of Claims 28 27 to 33 having a dry interior.

35. A fuel pellet as claimed in any one of Claims 31 27 to 34 having sufficient rigidity after 1 tumbling to allow handling, stacking and/or 2 transportation without any significant breakage.

4 36. A fuel pellet as claimed in any one of Claims 27 to 35 being wholly or substantially 6 combustible, so as to leave little or no 7 combustible fuel in the ash.

9 37. A fuel pellet as claimed in any one of Claims 27 to 36 being formed from a coal dust or coal 11 fines.

13 38. A fuel pellet as claimed in any one of Claims. . 14 27 to 37 having substantially no sulphur. . emission during combustion, preferably 70-90% or 16 more reduction in sulphur emission. ..

17 .,...

18 39. A fuel pellet as claimed in any one of Claims.. , 19 27 to 38 wherein the moisture in the pellet is ' substantially less than the moisture in the .

21 starting particulate material.

23 40. A fuel pellet as claimed in any one of Claims 24 27 to 39 wherein the pellet has a moisture content of < 5%.