Biofuel

Abstract

The invention relates to a biofuel, particularly an advanced solid biofuel, comprising waste coffee grounds.

Claims

1. A combustible biofuel composition comprising WCG.

2. A biofuel composition according to claim 1, wherein the composition is in the form of a pellet or briquette.

3. A biofuel composition according to claim 2, wherein the composition is a pellet for use in burning in a biomass boiler system.

4. A biofuel composition according to any preceding claim, wherein the composition comprises at least 75% WCG.

5. A biofuel composition according to any preceding claim, wherein the composition comprises a combustible fibrous filler.

6. A biofuel composition according to claim 5, wherein the filler is selected from sawdust, barley waste, hops waste, cocoa husk, sugar beet, straw, wood, nut husks, reeds, bread waste, maize, wheat chaff and barley chaff.

7. A biofuel composition according to claim 5 or 6, wherein the composition comprises less than 50% filler.

8. A biofuel composition according to any preceding claim, further comprising a binding agent.

9. A biofuel composition according to claim 8, wherein the binding agent is selected from a polysaccharide, glycerol, natural paraffin, plant oil, ligno-sulphonate and molasses.

10. A biofuel composition according to claim 8 or claim 9, wherein the composition comprises no more than 10% binding agent.

11. A feedstock for producing a biofuel composition according to any preceding claim.

12. A feedstock according to claim 11, comprising at least 70% WCG.

13. A method for producing a solid biofuel composition comprising WCG, the method comprising the steps of: a) providing a feedstock composition according to claim 11 or 12; and b) compressing that feedstock into pellets or briquettes.

14. A method according to claim 13, wherein the step of providing the feedstock comprises the step of drying the WCG.

15. A method according to claim 14, wherein the WCG are dried to a moisture content of between 6 and 20%.

16. A method according to any of claims 13 to 15, wherein the step of providing the feedstock comprises the step of mixing the WCG with at least one of a binder and a filler.

17. A method according to any of claims 13 to 16, wherein the step of compressing the feedstock into pellets comprises the step of pressing the feedstock through a pellet press.

18. A method according to claim 17, further comprising the step of cooling the pellets.

19. An apparatus for preparing a biofuel from WCG biomass, the apparatus comprising a means for drying WCG, a means for mixing WCG with one or more additives to produce a feedstock and a means for compressing the feedstock.

20. A biofuel composition or a feedstock composition for the production of a biofuel, the composition comprising at least 50% WCG, wherein at least 50% of the WCG are IWCG.

21. A composition according to claim 1, wherein the composition comprises at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, or about 100% IWCG.

22. A composition according to claim 20 or claim 21, further comprising a binding agent.

23. A composition according to any of claims 20 to 22, further comprising an oxidiser.

24. A composition according to any of claims 20 to 23, further comprising a combustible filler.

25. A composition according to any of claims 20 to 24, further comprising a processing agent.

26. A composition according to any of claims 2 to 10, wherein the composition comprises at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, or about 100% IWCG.

27. A biofuel composition according to any of claims 20 to 26, wherein the composition is a solid biofuel, optionally in the form of a pellet, briquette, puck or other compressed solid structure.

28. A biofuel composition according to any of claims 20 to 27, wherein the composition has a durability of at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98%.

29. A biofuel composition according to any of claims 20 to 28, wherein the composition has a net calorific value of between about 16 and 24 MJ/kg, or between about 17 and 23 MJ/kg, or between about 18 and 22 MJ/kg

30. A method for producing a biofuel composition according to any of claims 20 to 29, the method comprising the steps of: providing a feedstock composition according to any of claims 20 to 25; and compressing that feedstock into a solid biofuel.

31. A method according to claim 30, further comprising the step of decontaminating the feedstock to remove any unwanted contaminants.

32. A method according to claim 30 or 31, further comprising the step of pre-drying the feedstock.

33. A method according to any of claims 30 to 32, further comprising the step of drying the feedstock.

34. A method according to any of claims 30 to 33, further comprising the step of extracting coffee oil from the feedstock and optionally refining the extracted oil.

35. A method according to any of claims 30 to 34, wherein the step of providing the feedstock comprises the step of combining WCG with any one or more of a binder, a filler, a processing agent and an oxidiser.

36. A method according to any of claims 30 to 35, further comprising the step of conditioning the feedstock.

37. A method according to any of claims 30 to 36, wherein the step of compressing the feedstock comprises extruding, briquetting, pucking or pelleting the feedstock.

38. A method according to any of claims 30 to 37, further comprising the step of fuelling the dryer process using biofuel produced by the method of claims 30 to 37 or using biodiesel from the coffee oil extracted by the method of claim 34.

39. A method according to any of claims 30 to 38, comprising the step of recovering heat produced during the method.

40. An apparatus for preparing a biofuel from a feedstock comprising IWCG, the apparatus comprising a means for drying the IWCG and a means for compressing the feedstock.

41. An apparatus according to claim 40, wherein means for drying the IWCG is a dryer, such as a convection dryer, a conduction dryer, a radiant dryer, a dielectric dryer, a mechanical dryer and a means for natural drying.

42. An apparatus according to claim 40 or 41, further comprising a pre-drying means for pre-drying the IWCG, such as a centrifuge, a dewatering press or a drying floor.

43. An apparatus according to any of claims 40 to 42, further comprising a conditioning means, for conditioning the feedstock.

44. An apparatus according to any of claims 40 to 43, wherein the means for compressing the feedstock is a die having boreholes through which the feedstock is pressed or extruded, a pellet head, a cold press or a block press.

45. An apparatus according to any of claims 40 to 44, further comprising a heat recovery means, for recovering heat from other parts of the apparatus.

46. An apparatus according to any of claims 40 to 45, further comprising means for extracting coffee oil from IWCG.

47. An instant coffee factory comprising the apparatus according to any of claims 40 to 46.

Description

[0096] The invention will now be described in detail, by way of example only, with reference to the drawings.

[0097] FIG. 1 shows particle size distributions for different coffee types. The coffee grounds measured here are not WCG and have not yet been brewed.

[0098] FIG. 2 shows the effect of adding sawdust to the composition on durability.

[0099] FIGS. 3a and b show durability over the course of a production run.

[0100] FIGS. 4a and b show durability of the course of a production run for a composition comprising 20% sawdust, 5% lignobond (lignosulphonate) and 75% IWCG.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

[0101] A process for preparing a biofuel composition according to the invention.

[0102] The process comprises a series of steps to purify, dry, mix and compress the WCG. The WCG may or may not include IWCG.

[0103] The WCG are purified by removing any plastic and other rubbish by feeding the material into a trommel. The material is sieved through a rotating cylindrical screen to separate the coffee grounds from large contaminants. The undesired contaminants are collected and removed.

[0104] Coffee grounds exiting the trommel are sent to a rotary kiln drum dryer via a conveyor belt. The grounds are dried to the desired moisture content, whilst being mixed to ensure even drying.

[0105] The coffee grounds are then fed into a mixing screw, in which they are combined with other components to be included in the final composition.

[0106] When the solid biofuel is to be made in the form of pellets, the WCG mixture is transferred to a pellet press. It may be agitated before or during transfer to ensure it is evenly mixed and to help prevent any blockages or accumulation of material.

[0107] The pellet press consists of a die ring that runs around fixed rollers. The material is fed to the rollers sideways and pressed through the boreholes of the die from the inside to the outside. The conditioned material is fed into the pellet press and distributed evenly. It then forms a layer of material on top of the running surface of the die. The rollers overrun this layer and press the material that is in the channels of the die through the die forming a string of pellets. The long string of pellets that comes out of the die is cut into the desired length by a knife.

[0108] Pellets exiting the pellet press are at a temperature of about 80-120 C. and so are transferred to a cooler. Cooling enhances the mechanical durability of the pellet.

[0109] Following cooling, the pellets are sieved to screen out pellets that do not match the desired size.

[0110] Where the solid biofuel is to be in the form of a briquette or puck, the mixture is transferred from the mixing screw into a compressor, where it is compressed into briquettes or pucks. Again, the briquettes or pucks may be cooled.

[0111] Analysis of the WCG Pellets

[0112] NO.sub.x Emissions

[0113] The inventors have recognised the need to limit the emissions of NO.sub.x produced when liquid, solid and gaseous biofuels are burned. In some countries, solid biofuels are required to meet standards on emissions in order to be sold and/or to receive government incentives and subsidies. Whilst it is generally understood that a biofuel that contains components with an increased level of nitrogen, such as WCG, is likely to produce higher NO.sub.x emissions than a biofuel with low nitrogen levels, the inventors have identified that the relationship between biofuel nitrogen content and NO.sub.x emissions is not linear. The mechanism of NO.sub.x emissions is poorly understood. The inventors have identified that NO.sub.x emissions are not solely dependent on biofuel nitrogen content and are affected by whether the nitrogen is volatilised or whether it remains in the char after burning.

[0114] WCG contain more nitrogen than some other forms of biomass, such as wood. However, the inventors have found that it is not simply a matter of combining WCG with a lower nitrogen biomass in order to reduce NO.sub.x emissions. NO.sub.x emissions may also be controlled by altering the oxygen available during combustion. The compositions prepared by the inventors meet the NO.sub.x requirements set out in the ISO standards for pellets for use in biomass boilers and for briquettes.

[0115] Mechanical Durability

[0116] Durability is important as the pellets and briquettes must remain intact during storage and transport. Durability is particularly important for the pellets as pellets with poor durability can be broken up during use in biomass boilers. The mechanical durability can also affect the emission release. If the durability is poor, then particulate matter emissions will be high because of the dust and fine emissions generated.

[0117] The inventors prepared WCG pellets and briquettes according to the invention and tested their durability.

[0118] The desired final durability of pellets for use in domestic applications is at least 85% and in industrial settings is at least 75%. The durability of the pellets was tested on pellets that had just been produced and that had not been sieved to remove less durable pellets. The inventors found that allowing the pellets to sit for at least 24 hours after production and sieving the pellets to remove loose material or poorly formed pellets increased the overall average durability by around 10%. Conditioning steps have also been found to improve overall durability. Based on this, the inventors considered durability of in excess of 70% for domestic use pellets produced on the main plant and 65% for pellets produced on the mini-pelleter, at this stage of testing, to be indicative of a pellet that would meet their final durability target. A durability in excess of 60% at this stage would be acceptable for industrial use pellets.

[0119] Ash

[0120] Upon complete thermochemical conversion (such as combustion in a biomass boiler) of WCG, an inorganic solid residue remains; this is referred to as ash. The ash content in biomass poses many problems in regards to its behaviour during combustion, in particular how it relates to slagging and fouling. Pure WCG have a very low ash content of 1.8%.

[0121] Ash fusion tests were carried out on ash from the pellets to measure the initial deformation temperature, the softening temperature, the hemisphere temperature and the flow temperature. These temperatures indicate the behavior of the ashes in the boiler. An indicative figure for the ash fusion temperatures of wood biofuels is that the initial deformation is in the region of 1200 C.

[0122] Calorific Value

[0123] One of the most important properties of biofuels in regard to their use in energy production is their energy content. There are various ways of expressing the energy content of biofuels, heating values such as the higher heating value (HHV) or gross calorific value and the lower heating value (LHV) or net calorific value (CV). HHV is defined as the amount of heat produced/released from the complete combustion (of a unit quantity or volume) of biofuel once the combustion products cool down and reach the same temperature as prior to combustion (this is usually 25 C.).

[0124] Combustion of most biofuels releases water, which is then evaporated in the combustion chamber. The process of evaporating the water requires energy and this is known as the latent heat of vapourisation. In most boilers/combustion chambers the water vapour released by combustion exits the system via the exhaust stream and is lost. There are advanced boilers that undergo a secondary condensation process, which condenses the water vapour and recovers the majority of the latent heat with it, which can be used to do work. HHV includes the latent heat of vapourisation and the difference between that and the LHV is equal to the amount of latent heat of vapourisation that can be recovered.

[0125] The CV of pure WCG is in the region of 22 MJ/kg, which is considerably higher than wood (wood chip has a CV in the region of 12.5 MJ/kg and wood pellets have a CV in the region of 17 MJ/kg. A mixture of 75% WCG, 20% sawdust and 5% binder gives a net CV of 18.72 MJ/kg which, despite the dilution of WCG with sawdust, is higher than wood pellets.

[0126] The calorific value of the biofuel is tested using standard techniques, generally using dry samples. Net CV is calorific value of a sample without it having been dried. Since the moisture content of samples varies, the Net CV is not comparable between samples. To allow a comparison, the Net CV is normalised for a moisture content of 10%. This is calculated using the Gross CV and hydrogen content, measured in a dry sample.

EXAMPLES

Example 1

[0127] Durability

[0128] Pellets containing 95% WCG and 5% glycerol were produced and tested for durability. Initial tests with a small-scale pelleting machine produced pellets with mechanical durability of 90% using 5% glycerol and 95% WCG.

Example 2

[0129] Durability

[0130] Pellets produced from feedstock mixtures containing WCG, sawdust and lignosulphonate and WCG, sawdust and glycerol were tested. The results were as follows:

TABLE-US-00001 TABLE 1 90% WCG, 85% WCG, 80% WCG, 75% WCG, 75% WCG, 85% WCG, 5% 10% 15% 20% 25% 10% sawdust, 100% sawdust, 5% sawdust, 5% sawdust, 5% sawdust, 5% sawdust, 0% [RW2] 5% glycerol WCG lignosulphonate lignosulphonate lignosulphonate lignosulphonate lignosulphonate Ash % 1.9 1.8 2.4 2.3 2.3 2.1 1.8 NCV 18.634 21.918 19.223 19.214 18.572 18.718 16.611 (MJ/kg) Nitrogen 2.03 2.21 2.24 1.83 1.67 1.53 1.21 content Sulphur 0.12 0.14 0.31 0.31 0.33 0.29 0.19 content

[0131] The results show that the use of glycerol in place of lignosulphonate lowers the sulphur content from 0.31% to 0.12%. The initial deformation (ash melting temperature) of the 5% glycerol, 10% sawdust, 85% WCG mixture was 1270 C., which is lower than pure WCG but greater than the minimum of 1200 C. required for use in biomass boilers.

Example 3

[0132] Tests Completed with Retail Coffee.

TABLE-US-00002 TABLE 2 Lignobond (50% Glycerol None lignosulphonate) (Univar) (control) PERCENTAGES Coffee 75% 75% 75% Sawdust 22% 23% 25% Binding Agent 3% 2% 0% WEIGHTS (kg) Coffee 37.5 37.5 37.5 Sawdust 11.0 11.5 12.5 Binding Agent 1.5 1.0 0.0 Durability 84.6 77.8 71.6 Moisture Content 10.7 10.9 11.5 Length 14.5 13.3 14.6

Example 4

[0133] Compositions Produced in Accordance with the Invention, Using Different Coffees and Sawdust as the Filler.

TABLE-US-00003 TABLE 3 Ref Retail coffee (%) Instant coffee (%) Sawdust (%) 1 100 0 0 2 0 100 0 3 75 0 25 4 0 75 25 5 50 50 0

Example 5

[0134] Compositions Produced in Accordance with the Invention, Using Lignobond (Lignosulphonate) as the Binder and Sawdust as the Filler.

TABLE-US-00004 TABLE 4 Binder - Ref Coffee source Coffee (%) Sawdust (%) lignobond (%) 1 Retail 75 23 2 2 Retail 75 22 3 3 Instant 75 23 2 4 Instant 75 22 3 Binder - Ref Coffee source Coffee (%) Sawdust (%) glycerol (%) 5 Retail 75 23 2 6 Retail 75 22 3 7 Instant 75 23 2 8 Instant 75 22 3

Example 6

[0135] Lab Analysis of Wet IWCG Vs Wet RWCG.

[0136] Moisture content and Net CV are measured on the sample as received. All other measurements are made after the sample has dried.

TABLE-US-00005 TABLE 5 Parameter 100% IWCG wet 100% Retail wet Moisture 66.3 55.1 Ash 0.8 1.5 Net CV (as received) 6.683 8.697 Normalised Net CV (10% m/c) 21.907 19.871 Nitrogen 1.97 2.25 Sulphur 0.13 0.11 Chlorine 0.03 0.02 Arsenic 0.1 0.1 Cadmium 0.01 0.03 Chromium 2.18 0.75 Copper 40.03 30.71 Lead 0.71 0.6 Mercury 0.01 0.01 Nickel 2.67 1.39 Zinc 20.54 13.66

Example 7

[0137] Effect of Increasing Filler.

[0138] Example biofuels according to the invention were prepared. The biofuels contained IWCG, a filler, specifically sawdust, and approximately 5% lignobond (lignosulphonate) as a binding agent. The durability of the biofuels was tested, the results are shown in the table below and in the graph in FIG. 2. Durability could have been further increased by conditioning the biofuel feedstock during preparation.

TABLE-US-00006 TABLE 6 % Sawdust 5% 10% 15% 20% Durability 63.7% 75.5% 82.9% 89.0%

Example 8

[0139] Durability Distribution Over a Production Run.

[0140] The durability distribution of a production run of biofuel comprising approximately 5% lignobond (lignosulphonate) and about 20% sawdust. Samples were taken at 30-second intervals and tested.

[0141] Again, the production run did not involve conditioning of the feedstock before compression. Conditioning the feedstock would allow for further improvements in durability. The results are shown in the table below and in FIG. 3.

TABLE-US-00007 TABLE 7 Durability (%) Test Time Test 1 Test 2 0 85.4% 91.9% 30 89.6% 93.0% 60 91.6% 92.7% 90 90.6% 91.8% 120 88.7% 89.7% 150 87.8% 89.2% 180 88.0% 87.9% 210 88.0% 87.8% 240 86.8% 87.0% 270 86.5% 87.5% 300 87.4% 86.5% 330 88.4% 86.0% 360 89.0% 89.0% 390 86.2% 87.8% 420 87.5% 86.8% 450 87.5% 87.6% 480 85.4% 86.7% 510 83.5% 83.6% 540 85.6% 64.0% 570 83.2% 83.9% 600 82.2% 83.9% 630 81.8% 81.0% 660 80.5% 78.9% 690 78.2% 79.3%

Example 9

[0142] Production of Various Compositions.

[0143] Examples of compositions that may be produced in accordance with the invention are as follows.

TABLE-US-00008 TABLE 8 % coffee % filler % binder A. Addition of filler 95 5 0 90 10 0 85 15 0 80 20 0 75 25 0 70 30 0 65 35 0 60 40 0 B. Glycerol binder with filler <100 0 0-10 <90 10 0-10 <80 20 0-10 C. Glycerol binder 99 0 1 97 0 3 95 0 5 93 0 7 91 0 9 D. Glycerol binder + filler 87 10 3 85 10 5 77 20 3 75 20 5 E. Lignobond (lignosulphonate)binder 99 0 1 97 0 3 95 0 5 93 0 7 91 0 9 F. Lignobond (lignosulphonate)binder + filler 87 10 3 85 10 5 77 20 3 75 20 5

Example 10

[0144] Further compositions according to the invention were prepared and tested for durability. The experiments were carried out on a pilot scale mini-pelletiser and the full scale plant. The results are detailed in tables 9 to 12 and FIGS. 4 to 8.

[0145] Mini-Pelletiser

[0146] A set mass of WCG was dispensed into a flexi-container and was mixed by hand with a set amount of binder. This mixture was passed through the prewarmed pelletiser to further homogenise and add heat to the mixture. The remaining binder material was added to the mixture and this feedstock was passed through the pelleter. Samples collected mid-stream whilst discharging from the pelletiser.

[0147] Full Scale Pelletiser

[0148] 400 kg of WCG was measured into a hopper and an appropriate amount of sawdust was added to obtain the desired composition. For example, 21 kg of sawdust was added to make up the batch with 95% WCG and 5% sawdust. The WCG and sawdust were then conveyed via a mixing auger screw up to a live bin above the pellet head. The mixture was left in the live bin for 10 minutes to allow the components to mix thoroughly. The mixture was then passed through the preconditioner into the pellet press at a fixed feed rate. Lignobond was added to the mixture at a fixed rate through a nozzle at the feed end of the preconditioner. Samples were taken midway through the run at the outlet of the cooler.

[0149] Results

[0150] A. WCGs/Filler Ratio

[0151] Table 9 shows the variation of pellet durability with WCG/Filler ratio. This demonstrates that, surprisingly, good pellet durability can be obtained across a range of coffee:filler ratios.

TABLE-US-00009 TABLE 9 Moisture Moisture Moisture Run Retail Filler Binder Content: Content: Content: WCG/Filler Number WCG (Sawdust) (Lignobond) Total Sawdust WCG Pellets Ratio Durability Equipment 1 35% 60% 5.00% 100% 0.58 86.0% Mini- Pelletiser 2 45% 50% 5.00% 100% 0.90 74.0% Mini- Pelletiser 3 50% 45% 5.00% 100% 1.11 68.0% Mini- Pelletiser 4 58% 39% 2.91% 100% 10.75% 8.30% 10.50% 1.50 82.8% Plant 5 68% 29% 2.91% 100% 10.75% 8.19% 11.00% 2.33 86.5% Plant 6 73% 24% 2.91% 100% 10.75% 8.10% 10.10% 3.00 87.8% Plant 7 78% 19% 2.91% 100% 10.75% 8.10% 8.70% 4.00 73.7% Plant 8 92% 5% 2.91% 100% 10.75% 8.10% 8.90% 18.98 74.1% Plant 9 97% 0% 2.91% 100% 8.50% 9.70% 100.000 82.2% Plant

[0152] B. Retail WCGs Instant WCGs Ratio

[0153] The table below shows the blend of Urban WCGs and Instant WCGs. In these experiments the total proportion of coffee grounds in the mixture was set at 75%.

TABLE-US-00010 TABLE 10 Moisture Moisture Instant Filler Binder Content: Content: Retail WCG WCG (Sawdust) (Lignobond) Total Sawdust Pellets Durability Equipment 75% 0% 20% 5% 100% 10.75% 8.70% 73.7% Plant 50% 25% 20% 5% 100% 10.75% 10.00% 83.6% Plant 25% 50% 20% 5% 100% 10.75% 9.70% 70.8% Plant 0% 75% 20% 5% 100% 10.75% 8.70% 63.2% Plant

[0154] C. Binder Level

[0155] In these experiments the amount of binder used in the pellet composition was investigated. The results are tabulated below. These results suggest that filler has more impact on the pellet durability than binder.

TABLE-US-00011 TABLE 11 Moisture Moisture Moisture Retail Filler Binder Content: Content: Content: Filler/Binder WCG (Sawdust) (Lignobond) Total Sawdust WCG Pellets Ratio Durability Equipment 77.7% 19.42% 2.91% 100% 10.8% 8.1% 8.7% 4.00 73.7% Plant 75.0% 20.0% 5.0% 100% 10.8% 8.7% 4.80 73.7% Plant 75.0% 17.0% 8.0% 100% 8.5% 2.13 60.0% Plant

[0156] D. Alternate Filler

[0157] Pellets were prepared using milled bean husk as an alternative filler, instead of sawdust. The pellets with the milled bean husk had a durability of 55.5%. Although the pellets with the milled bean husk did not achieve the durability target of >75%, it is believed that this could be attained. The results are shown in Table 11.

TABLE-US-00012 TABLE 12 Filler 2 Binder Moisture WCG/ Retail Filler (Bean (Ligno- Content: Filler Dura- Equip- WCG (Sawdust) Husk) bond) Total Pellets Ratio bility ment Sawdust .sup.78% 19% 0% 2.91% 100% 8.70% 4.00 73.70% Plant Milled 76.2% 0% 19% 4.8% 100% 11.60% 4.00 55.50% Plant Bean Husk (~0.5 mm)

[0158] E. Alternate Binder

[0159] Pellets were prepared using various types of glycerol binder. The durability was tested as before. The results are shown in Table 12.

TABLE-US-00013 TABLE 13 Durability % Glycerol 1 2 3 4 5 6 Univar 90.4% 85.5% 83.1% 70.4% 78.2% 58.8% (technical) Verbio-Rape 91.8% 89.0% 88.0% 78.0% 62.9% (technical) Olleco 90.7% 80.8% 86.5% 68.9% 75.7% 65.3% (crude) Ample 90.4% 89.5% 83.6% 85.3% 72.8% 78.7% (crude) Average 90.8% 86.2% 85.3% 75.7% 72.4% 67.6% WCG (%) 53.0% 56.0% 59.0% 79.0% 82.0% 85.0% Sawdust (%) 42.0% 40.0% 38.0% 16.0% 14.0% 12.0% Glcerol (%) 5.0% 4.0% 3.0% 5.0% 4.0% 3.0%

[0160] High durability values from experiment 1 are probably attributed more to the higher sawdust content than the action of any particular glycerol binder. This is further evidenced as when the sawdust concentration decreases the durability also decreases. When sawdust concentration reaches a typical value (c15-25%) durability is somewhat reduced but values between 70% and 85% is still achievable.