Patent Application
20160200997
The present application relates to a solid fuel composition, and in particular, to a solid fuel composition useful for manufacturing artificial firelogs and fire-starters. The solid fuel composition comprises cellulosic materials treated with torrefaction and a binder.
Manufactured solid fuels in the form of firelogs have been used as an alternative to natural wood fires for decades. They offer users greater convenience in a number of ways. Since they are manufactured to have a higher energy density and flame output than natural wood, there is less material for the user to carry to their fireplace, and less need for the user to constantly stoke the fire. Similarly, there is less mess associated with manufactured firelogs than is the case with natural wood. Finally, manufactured firelogs generate less particulate emissions, sparks and ash than natural wood fires. Manufactured solid fuels in the form of fire-starters have also been used, in combination with natural wood, to facilitate the starting of the fire.
Firelogs are typically comprised of cellulosic materials, a volatile binder (wax, oil, fat, fatty acid, pitch, etc.) and may include a coking agent. Sometimes other additives are included to either modify the colour of the flame or to enhance the sound of the fire. In wood-based logs (a common type of firelog), wood typically accounts for 30-45% of the weight of the log and the volatile binder accounts for 55-65% of the weight of the log. In addition to serving as a binder, waxes, fats, fatty acids, pitches or other oil products are used as an ingredient in the production of fire logs for two reasons.
U.S. Pat. No. 4,326,854 and U.S. Pat. No. 8,007,550 disclose alternative binders to improve performance and/or reduce costs of processed solid fuels. Both teach the use of fatty acids and pitches to improve the properties of the binders and of the aggregate mixture.
U.S. Pat. Nos. 6,113,662, 5,910,454, and 8,123,824 disclose that the substitution of cellulosic materials with higher energy densities and higher volatiles/fixed carbon ratios, such as coffee grounds, in place of wood (or in addition to wood), enable the manufacture of an attractive firelog with less volatile binder. The ability to manufacture an attractive firelog with less volatile binder is desirous for several reasons. Volatile binders have numerous other, higher value uses and are typically more costly than cellulosic materials. Also, consumers often perceive an offensive odour and sooty black smoke when using firelogs where there is too much volatile binder relative to the combustion capacity of the heating appliance.
The prior art does not realize the benefits of distinction between different types of volatiles. For instance, all of the above prior art teach the benefits of utilizing high volatile (oil or fat containing) cellulosic materials, but do not realize the negative effects of certain low quality volatiles on combustion performance—such as acetic acid—and trapped gases—such as CO2 and CO.
As noted above, prior art has focussed on the substitution of cellulosic or volatile binder materials so as to optimize product performance and/or cost. The present application offers an alternative approach to solid fuel design optimization. It involves a composition that includes cellulosic material treated with torrefaction—either in place of, or in addition to, non-torrefied cellulosic materials, so as to generate a more cost-effective manufactured solid fuel product.
Torrefaction involves the heat treatment of cellulosic materials in a low oxygen environment, so as to burn off low quality volatiles and transform otherwise low energy generating biomass into a more energy-dense material. While the benefits of torrefaction for the development of an environmentally friendly alternative fuel have been previously recognized, the potential to adopt torrefaction technology in a composition for a manufactured solid fuel product, that meets a need for both flame output and energy output has not been realized.
There is a need for a low cost manufactured firelog having a good flame output and/or more heat output.
Objects of the present application include providing a more cost-effective—in terms of both heat and flame output—manufactured solid fuel product. Use of this technology will provide a use for low-value wood and other low-value cellulosic materials, thereby reducing environmental waste and generating alternative, environmentally friendly renewable resources. Furthermore, by providing a use for low-value wood and other low-value cellulosic materials that can be harvested in a wide range of localities, an opportunity for wealth and job creation will likely result at the local level.
In one aspect, there is provided a low cost processed solid burnable fuel composition comprising a torrefied cellulosic material and a binder. In accordance with a further aspect of the application, the low cost processed solid burnable fuel composition comprises torrefied cellulosic material from 15% to 75% of the composition. In accordance with another aspect of the application, the low cost processed solid burnable fuel composition comprises binder from 25% to 50% of the composition.
In a further aspect, there is provided a high flame output per dollar of input cost fuel composition which contains torrefied cellulosic material from 5% to 45% by weight of the composition. In yet another further aspect of the application that provides a high flame output per dollar of input cost, the fuel composition contains a volatile binder from 50% to 65% by weight of the composition.
In yet another aspect, there is provided a high energy output, which contains torrefied cellulosic material from 5% to 45% by weight of the composition. In yet another further aspect of the application that provides a high energy output, the fuel composition contains a volatile binder from 55% to 65% by weight of the composition.
For a better understanding of the present application, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawing, where:
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
As used in the specification and claims, the singular forms “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.
The term “comprising” as used herein will be understood to mean that the list following is non-exhaustive and may or may not include any other additional suitable items, for example one or more further feature(s), component(s) and/or ingredient(s) as appropriate.
Terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.
As noted above, prior art has focussed on the substitution of cellulosic or volatile binder materials so as to optimize product performance and/or cost. The present application offers an alternative approach to solid fuel design optimization. It involves a composition that includes torrefied cellulosic material—either in place of, or in addition to, cellulosic materials, so as to generate a more cost-effective manufactured solid fuel product.
The present application discloses solid fuel compositions comprised of torrefied cellulosic material along with a binder. Use of torrefied of cellulosic material (such as wood, leaves, grass, agriproducts), enables optimization of the composition in terms of the flame and/or heat output as well as the cost of manufactured solid fuel products such as firelogs and fire-starters. In addition, use of torrefied cellulosic material provides a number of advantages in the manufacture of solid fuel products, including reduced storage costs and grinding costs. In addition to enabling the manufacture of a more cost-effective solid fuel, use of torrefied cellulosic material offers environmental advantages, by providing a use for low-value wood that has few alternative uses.
Torrefaction involves the heat treatment of cellulosic materials in a low oxygen environment, so as to burn off low quality volatiles and transform otherwise low energy generating biomass into a more energy-dense material. While the benefits of torrefaction for the development of an environmentally friendly alternative fuel have been previously recognized, the potential to adopt torrefaction technology in a composition for a manufactured solid fuel product, that meets a need for both flame output and energy output has not been realized.
As disclosed herein, the advantages associated with torrefaction of cellulosic material is achieved at different temperature ranges. These temperature ranges may be realized through use of a variety of torrefaction processes and/or a variety of reactor designs including rotary drum reactor, screw conveyor reactor, multiple hearth furnace, fluidized bed reactor, microwave reactor, compact moving bed, and oscillating belt conveyor. Further there are a number of innovative technologies in development such as torrefaction with thermal fluids and direct fired rotary kilns. All of these reactors have key process parameters that are used to control the torrefaction process to achieve specific degrees of torrefaction. Key process parameters other than temperature, as exemplified in the present application, include residence time, material particle size, flow rate and any other controlled process parameters specific to any one torrefaction process and/or torrefaction reactor.
As one example, samples of the torrefied material for use in obtaining solid fuel compositions of the present application were obtained from a direct fired rotary kiln reactor. As noted above, the parameter used to control the degree of torrefaction was temperature. In these examples the residence time was approximately 30 minutes. However, a skilled worker would readily realize these process parameters are easily modified to suit the desired level of torrefaction of cellulosic material. In the present application varying degrees of torrefaction of cellulosic material is represented by the recited temperature ranges disclosed in the tables and FIGURE below. Generally, a low temperature range indicates a low degree of torrefaction and a high temperature range results in a cellulosic material with a higher degree of torrefied material.
Considerations with respect to using torrefied cellulosic materials are much more complex than simply the energy content of the cellulosic materials. Torrefaction changes both the chemical make-up and mechanical properties of cellulosic materials. As is described below, there are many degrees of torrefaction and the impacts on the chemical makeup and mechanical properties are not simple linear functions of the torrefaction levels. While prior art focuses on using alternate binders and cellulosic materials to control the performance or cost, the present application discloses the advantages of using torrefied cellulosic materials and the opportunities to control performance and/or cost by using cellulosic materials torrefied to different levels, either alone or in combination with non-torrefied cellulosic materials.
The processed solid burnable fuel compositions in accordance with the present application involve the use of torrefied cellulosic material to achieve a number of advantages relative to existing compositions used by industry. Torrefied cellulosic materials have more energy per unit weight than non-torrefied cellulosic materials, making them an ideal substitute for wood.
In addition, the use of torrefied cellulosic materials presents an opportunity to use “low-value” cellulosic materials that would otherwise go to waste. Such low-value cellulosic material includes but is not limited to green wood, diseased wood, scrap wood products, contaminated wood and other wood products with undesirable properties. Given that most torrefaction processes involve the use of machinery that is commonly available in farming communities across North America, the demand for torrefied low-value cellulosic products offers the additional advantage of providing a potential financial benefit to generators of low-value cellulosic waste and farmers with the appropriate machinery, thereby contributing to wealth and jobs at the local level.
The embodiments are disclosed in detail in below, each one enabling the targeting of a specific consumer preference. The first embodiment addresses consumer preference for low cost manufactured solid fuel products that provide a reasonable flame and heat output, but are significantly less costly than other solid fuel products on the market, or other products possible with the use of non-torrefied cellulosic material.
Additional aspects of the application provide compositions that allow the manufacture of manufactured solid fuel products with a high flame-output per input cost and/or a high energy output (both in absolute terms and on a per input cost basis). This lower cost fuel composition comprises a torrefied cellulosic material and a binder, and in some cases may include a non-torrefied cellulosic material and/or a coking agent that affords greater flame per dollar cost or greater heat output per dollar cost.
Table 1 presents a summary of the findings on impacts of different heating temperatures and torrefaction levels on the constituents of cellulosic materials (based on research primarily from Prins et. al. (2006), Dhungana (2011), Bergman (2005) and Basu (2010)), the relevance of the findings when torrefied product is used as a fuel, and the impact on the quality and cost of firelogs and fire-starters manufactured with cellulosic material which is treated with torrefaction. The testing results disclosed in this Example as set out in each row of Table 1 are described as follows.
Torrefaction involves the heating of cellulosic materials in a low oxygen environment. Torrefaction normally involves heating at temperatures between 200° C. and 300° C. However, in a torrefaction process where the reactor is pressurized, at temperatures below 200° C.—indeed for temperatures between 100° C. and 200° C., benefits associated with torrefaction occur, as H2O and other trapped gases (CO2, CO) are released. Torrefaction at this temperature enables the release of smoke-causing volatiles with small heating values, such as acetic acid and furfurals. The result is that the torrefied material has a higher energy density and will produce less smoke than non-torrefied cellulosic material. The implication, if the torrefied material is used as a substitute for non-torrefied cellulosic material in the manufacture of a firelog or fire-starter, is that the resulting firelog or fire-starter would have a higher BTU/lb, a cleaner burn and faster ignition.
During torrefaction and temperatures of between 140° C. and 250° C., the hemicellulose begins to depolymerise, and some devolatilization and depolymerisation of the lignin and cellulose occurs. The amorphous nature of hemicellulose in combination with lignin act as a flexible binder to hold the microfibrils together. The combination of these components provide the micro and macro level structural integrity to wood. The decomposition of the hemicellulose and limited lignin decomposition makes the wood more brittle. This means that it is easier to grind torrefied cellulosic material, thereby decreasing the grinding costs associated with preparing the material for use in a firelog. The increased brittleness means that a processed solid fuel mixture would have less elasticity and therefore require less force during the extrusion of a firelog or similar processed solid fuel product. Similarly, because the torrefied cellulosic material is more brittle and less elastic, less volatile binder is necessary to achieve the optimal mixture viscosity for efficient extrusion.
Between 250° C. to 300° C., severe devolatilization of the depolymerised hemicellulose combined with limited devolatilization of lignins, results in a relatively higher ratio of lignin in the remaining volatiles. Firelog manufacturers typically use expensive hard waxes or less expensive waxes that are soft at room temperature (i.e. calcium lignin sulfonate) together with lignins to harden the mixture. Because torrefied cellulosic materials have a higher ratio of lignin in the remaining volatiles, less additives are required for torrefied cellulosic material fuels in order to achieve hardness at room temperature.
At torrefaction temperatures of 200° C. to 300° C., OH groups are destroyed. As a result, the hygroscopic property of cellulosic materials is partially lost, meaning that the torrefied cellulosic material will adsorb less water and other liquids, than its non-torrefied counterpart. Since torrefied cellulosic materials adsorb less moisture (in the air, from rain, etc.), there are lower storage costs for torrefied cellulosic materials than non-cellulosic material.
In summary, the properties of using torrefied cellulosic materials are many and varied depending upon the treatment conditions. Extrapolations based on these scientific findings and experimentation, as disclosed in the present application describe how best to leverage the characteristics afforded by the use of torrefied cellulosic materials. Results from a series of experiments with torrefied cellulosic material, wherein the cellulosic material is wood and non-torrefied cellulosic material are presented below. However, the benefits of torrefaction have been shown to apply to a wide range of cellulosic materials, such as switchgrass, coffee husks, bagasse, municipal waste and other agricultural by-products. Those skilled in the art will appreciate that a variety of types of cellulosic materials may be used as ingredients in firelogs and fire-starters. The benefits of using torrefied materials as described in the present application, pertain to the wide range of cellulosic materials typically considered for inclusion in solid fuel products.
One of the key advantages of using torrefied cellulosic material in place of untreated cellulosic material, is the higher energy density. The advantages offered by torrefied fuels are further amplified when costs are taken into account. For example, in the case of wood, wood sawdust is typically more expensive per pound than torrefied wood, as torrefied wood uses green wood which is unprocessed and has few (if any) alternative uses. Using the price and energy value assumptions provided in Table 2, it is estimated that a firelog made with 50% wax and 50% torrefied fuel has 9% more energy per unit weight than one made with 50% wax and 50% wood. However, given the lower cost for torrefied wood, the torrefied fuel mixture provides 11% more heat energy per unit cost than the wood mixture.
There are also advantages to combining torrefied components with non-torrefied components. When the desired firelog is one with a high flame output but low heat output, the use of untreated wood together with torrefied wood can offer several advantages, because the non-torrefied component will have higher volatile/fixed carbon ratios and therefore generate more flame per unit energy. Finally, while higher moisture contents (more common in non-torrefied components) result in lower BTU/lb, moisture within a processed solid fuel can provide the added advantage of increasing the surface area as the moisture evaporates and therefore contributing to higher flame output per BTU.
In order to investigate the optimal proportions of wood/torrefied wood, a variety of mixtures were created, using various combinations of wax, molasses, wood sawdust, and green wood torrefied at different temperatures as depicted in Table 3 and Table 4. For these examples, mixtures were compressed into 10 gram samples with a diameter of 0.875 inches, which were then burned and assessed for flame output (See Table 3, table 4 and
For illustration purposes, Table 3 includes some results of fuel composition burn tests made with wood torrefied at 240° C. and where the wax content was held at 50%. It is apparent from these results that inch-seconds of flame output and inch-seconds of flame output per unit cost of mixture are maximized when an approximately equal combination of wood and torrefied wood are used together. However, the heat energy per unit cost is maximized when more torrefied wood is used.
While Table 3 only shows a higher inch-second/$ values when torrefied wood comprises 25-30% of the mixture, the actual cost-savings benefit of using torrefied wood is even greater. This is because the samples above all assume a fixed amount of wax and no use of a coking agent. However, for any level of cellulosic material, a mixture using non-torrefied cellulosic material would require more binder and/or more coking agent than a mixture using only torrefied cellulosic material, in order to have the mixture hold together while burning and to be able to extrude the mixture.
For compositions using non-torrefied materials, higher wax contents are required to both hold the mixture together while burning and to enable the extrusion of the mixture.
Additional wax is also needed in the non-torrefied mix to facilitate extrusion. The current industry standard extrusion method for premium processed solid fuels employs a low shear, high speed extruder. These extruders cannot process mixtures with an excessively high viscosity. Because the hemicellulose has been partially devolatilized in torrefied cellulosic materials, the material is more brittle than non-torrefied cellulosic materials, and requires less binder for proper extrusion. Cellulosic material that has not been torrefied is more elastic in nature and therefore exerts greater resistance during the extrusion process, requiring more wax, fatty acids or other volatile binders.
While the use of more wax in mixtures utilizing non-torrefied cellulosic materials results in easier extrusion and reduced expansion upon burning, this additional wax results in higher costs relative to torrefied wood mixtures as well as an excessively high combustion rate. Furthermore, using higher binder contents can result in un-combusted binder ‘dripping’ from the mixture during combustion—a serious safety issue. These problems associated with high wax contents are typically addressed by adding coking agents (which are more costly and offer lower energy output than cellulosic materials).
Hence, in order to retain the shape required while burning, coking agents are typically added to processed solid fuel mixtures made from (non-torrefied) cellulosic materials and wax. Coking agents may be any coking agent typically used in solid fuels, including but not limited to, a starch, molasses, a sugar, black liquor, or other coking agents or combinations thereof. The coking additives are typically more costly than cellulosic materials. Hence, for any given level of cellulosic material, the non-torrefied version will require more coking agent than the torrefied one, and thus the cost-benefit of using torrefied wood is amplified further relative to that shown in Table 3 above.
However, the findings in Table 1 and Table 3 also suggest that some volatiles are eliminated during torrefaction while prior art has shown that volatiles have a higher flame output to energy ratio than is the case for fixed carbon. However, as mentioned previously, the prior art does not realize the benefits of distinction between different types of volatiles. Hence, the optimal torrefaction levels for generation of an ingredient in a manufactured solid fuel product where flame output is a desirable characteristic have not previously been investigated. Consequently, a variety of mixtures were created, using various combinations of wax, molasses, wood sawdust, and green wood torrefied to different levels. The mixtures were used to create 10 gram samples (as described above) which were then burned and assessed for flame output. The results of the test are presented in Table 4. As is illustrated in Table 4, the flame output, measured in terms of inch-seconds, per unit cost of mixture, is substantially higher for wood torrefied at 190° C. (5,918), wood torrefied at 240° C. (6,007) and wood Torrefied at 251° C. (5,879) than non-torrefied wood (5,383).
The types and extent of advantages that can be realized through the use of torrefied cellulosic materials vary according to the torrefaction level. The greater the torrefaction level, the greater the densification of the energy in the cellulosic materials. Hence, as illustrated in Table 4 below, the highest torrefaction temperature results in the highest heat energy per unit cost advantage relative to wood (19%). However, as explained above, the higher the torrefaction level, the lower the volatiles/fixed carbon ratio. While these volatiles contribute less energy per unit weight than the fixed carbon, they do contribute to a higher flame output. As the following Table 4 illustrates, the mixture that is based on wood that was torrefied at 240° C. generates an estimated 12% higher inch-second flame output per unit cost of mixture relative to wood.
In summary, the use of torrefied cellulosic material allows the manufacturer to achieve greater performance-cost efficiencies than the use of untreated cellulosic materials. Specifically, using the results herein, the use of torrefied cellulosic materials can be used to generate a mixture that offers 12% higher inch-second flame output per unit cost of mixture relative to non-torrefied wood or a 19% higher energy per unit cost relative to non-torrefied wood. These cost efficiencies are in excess of the cost savings that would be achievable due to: a) the lower storage costs as a result of the hydrophobicity of the wood and b) the lower grinding energy costs due to the more brittle nature of the torrefied cellulosic materials. Many different embodiments of the fuel composition disclosed herein can be produced according to consumer preferences.
In one embodiment, where cost is the key consideration, maximizing the use of torrefied products minimizes the need for high cost wax inputs. In one embodiment there is provided a fuel composition comprising a torrefied cellulosic material and a binder wherein the torrefied cellulosic material is from about 15% to about 75% of the composition and the binder is from about 25% to about 50% of the composition. At wax/binder levels in the lower end of this range, a coking agent would not be required. However, in order to generate a mixture that is easily extrudable, a liquid coking agent, or any other liquid, including water, is provided, where the liquid accounts for up to about 5% of the weight of the total mixture. Non-torrefied cellulosic material may be included up to 35% by weight. This is the embodiment that would benefit best from maximum torrefaction (one example is between 250° C. and 300° C.). This level of torrefaction results in the elimination of more volatiles, and a more energy dense product, more decomposition of the hemicellulose to enable easy grinding and greater hydrophobicity to minimize storage costs, but more loss of volatiles that contribute to a high flame output per unit weight of mixture, then would be the case with either other embodiments.
Many consumers of firelogs are often using them primarily for aesthetic purposes and may prefer a higher flame relative to the cost and/or the heat output. In this embodiment there is provided a fuel composition comprising torrefied cellulosic material from about 5% to about 45% by weight of the composition and binder from about 50% to about 65% by weight of the composition. In this case, one embodiment would be a firelog with more volatiles, either through the use of a less torrefied product, or through the combined use of torrefied and non-torrefied products along with a significant amount of volatile binder. The preferred constituent makeup would be about 50% to about 65% wax, about 5% to about 45% torrefied cellulosic material, about 1% to about 10% coking agent and the balance (as little as about 5% and as much as about 45%) non-torrefied cellulosic material. In this embodiment, the wood should ideally be torrefied at temperatures between about 190° C. and about 250° C. This level of torrefaction results in the elimination of the lower quality volatiles to give a more energy dense product, partial decomposition of the hemicellulose to enable easy grinding and some hydrophobicity to minimize storage costs, but minimizes the loss of the volatiles that contribute to a high flame output per unit weight, in the present case pound, of mixture. Such embodiments can provide a high flame output per unit cost.
In yet another embodiment, where the consumer is desirous of a firelog that generates more heat, a higher proportion of torrefied product would be more desirable. In one embodiment there is provided a fuel composition comprising about 5% to about 45% torrefied cellulosic material and about 55% to about 65% binder. In this case, the preferred constituent makeup would be—about 55% to about 65% binder, about 5 to about 45% torrefied cellulosic material, about 1% to about 10% coking agent and the balance, if any, up to about 25% non-torrefied cellulosic material. In this embodiment, the wood should ideally be torrefied at temperatures between 200° C. and 300° C. This level of torrefaction results in the elimination of more volatiles, thereby providing a more energy dense product, more decomposition of the hemicellulose to enable easy grinding and greater hydrophobicity to minimize storage costs, but more loss of volatiles that contribute to a high flame output per lb of mixture, then would be the case with the previous embodiment.
Table 5 provides examples of the various potential constituent components of the solid fuel based compositions and the associated outcomes and advantages of each composition. In column 8, compositions that have a cost per pound that is in the bottom 35 percentile are shaded. In columns 9 through 12, compositions that are in the top 35 percentile within each measured parameter depicted in each column are shaded.
While specific embodiments are described above using current cost estimates, it is important to note that alternative permutations can be used and still leverage the benefits of using torrefied cellulosic materials. This would be particularly true if the cost of torrefied cellulosic material varied by torrefaction level. For example, if higher levels of torrefaction become more expensive relative to lower levels of torrefaction, it can be more advantageous to use wood that has been torrefied at lower temperatures to achieve the lowest cost product. Alternatively, if higher levels of torrefaction become less expensive relative to lower levels of torrefaction, it can be more advantageous to use wood torrefied at higher temperatures to achieve the best flame output per unit cost or the best energy output per unit cost. Similarly, reductions in the relative cost of torrefied wood relative to wax, would make a substitution between the torrefied wood and the wax binder more advantageous. Similarly, the advantages associated with torrefying cellulosic material at different temperatures can be achieved by varying other process parameters such as but not limited to residence time, material particle size, flow rate and any other parameters specific to any one torrefaction process and/or torrefaction reactor that different temperatures ranges exemplified in the present application achieve.
All publications, patents and patent applications mentioned in this Specification are indicative of the level of skill of those skilled in the art to which this invention pertains and are herein incorporated by reference to the same extent as if each individual publication, patent, or patent applications was specifically and individually indicated to be incorporated by reference.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2014/050775 | 8/15/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61866841 | Aug 2013 | US |
