GB2488874A

GB2488874A - Briquette based on a lignocellulosic compressed body impregnated with liquid fuel

Info

Publication number: GB2488874A
Application number: GB1203229.8A
Authority: GB
Inventors: Guillaume Foissac; Pierre Plion; Vincent Fichet; Fouzi Tabet
Original assignee: Electricite de France SA
Current assignee: Electricite de France SA
Priority date: 2011-03-09
Filing date: 2012-02-24
Publication date: 2012-09-12
Also published as: GB201203229D0; FR2972458A1; CN102676261A; BR102012005108A2; FR2972458B1; RU2012108893A; RU2507241C2; KR20120103478A

Abstract

The present invention relates to a briquette constituted- of a lignocellulosic compressed body comprising (a) from 60% to 90% by weight of grass stem debris and (b) from 10% to 40% by weight of a beaten lignocellulosic binder having a degree of beating of between 38 and 75Â°SR (degrees Schopper-Riegler), these percentages being expressed by dry weight relative to the dry weight of the sum of (a) and (b), and- of a fuel that is liquid at room temperature having a flash point between 30Â°C and 150Â°C, impregnating the lignocellulosic compressed body,said briquette having an essentially cylindrical shape 20 and comprising a star-shaped central chimney. It also relates to a process for manufacturing such a briquette and also to the use of such a briquette in torches or for heat production.

Description

Briquette based on a lignocellulosic compressed body impregnated with liquid fuel The present invention relates to a briquette based on a lignocellulosic compressed body impregnated with a liquid fuel, of plant or animal origin, and also to a process for manufacturing such a briquette and the use of such a briquette as fuel in portable or non-portable torches.

A fuel for torches, in particular for portable torches likely to be carried by children or by individuals in the middle of a crowd, must meet a large number of requirements, among which mention may be made of the following: -great compactness and lightness, -steady combustion with the same flame power throughout the duration of combustion, -ease of ignition, -low smoke generation, -low production of fly ash -high operational safety, especially owing to the absence of pressurized gaseous fuels.

Of course, as in many other fields, it would be

desirable to be able to provide a fuel which not only meets all of the above criteria but that additionally originates from renewable sources, that is to say non-fossil sources.

The applicant, after lengthy research, has succeeded in developing a fuel briquette that is both light and solid and that, owing to a novel combination of a solid lignocellulosic fuel and a liquid fuel and owing to a geometry that provides a plurality of ignition points sheltered inside a central chimney, combines all of the above advantages.

This briquette is essentially constituted of a compressed body of plant origin impregnated with a liquid fuel of plant or animal origin. The compressed body has a structure that is simultaneously rigid, light and dense enough to guarantee the mechanical strength of the briquette throughout its combustion, generating a very limited amount of ash, while making it possible to make sufficient spaces so that the propagation of the combustion takes place gradually and steadily.

One subject of the present invention is therefore a -of a lignocellulosic compressed body comprising (a) from 60% to 90% by weight of grass stem debris and (b) from 10% to 40% by weight of a beaten lignocellulosic binder having a degree of beating of between 38 and 75°SR (degrees Schopper-Riegler), preferably between 45 and 70°SR, these percentages being expressed by dry weight relative to the dry weight of the sum of (a) and (b), and -of a fuel that is liquid at room temperature having a flash point between 30°C and 150°C, impregnating the lignocellulosic compressed body, said briquette having an essentially cylindrical shape and comprising a central chimney with a star-shaped cross-section.

The briquette according to the invention is therefore constituted of two essential components: a compressed body of plant origin and a liquid fuel.

The compressed body comprises, for its part, at least two constituents: -a major constituent (a) formed by coarse grass stem debris, and -a minor constituent (b) formed by a highly beaten lignocelluiosic binder.

The constituent (a) may be obtained by dry milling or crushing of grass stems, also referred to hereinbelow as "straw", in a suitable mill or crusher. This is preferably a hammer mill. The fragments or particles constituting this first component (a) are relatively coarse and of uneven size. Most of them have a length of several millimetres, or even of several centimetres.

In particular, the grass stem debris is advantageously more than 60% by weight, preferably more than 75% by weight and in particular more than 90% by weight constituted of fragments having a size such that their larger dimension is between 3 and 20 mm, preferably between 5 and 15 mm. This does not of course exclude the presence of finer, or even very fine particles or even the presence of much larger fragments or fibres.

In the compressed body of the present invention, these coarse fragments of straw are joined together by the lingoceilulosic fibres of the "binder" or wlignocellulosic binder".

Lignocellulose is a mixture of three types of natural, water-insoluble polymers, namely cellulose, hemi-cellulose and lignin, present in variable proportions depending on the origin of the lignoceliulose.

Lignocellulose has a fibrillar structure.

The lignocellulosic binder used in the present invention is obtained by beating lignocellulosic materials. Beating is the mechanical treatment of a lignocellulosic material in the presence of water with a view to obtaining the hydration, fibrillation or cutting of the fibres composing it. Beating has always been used for manufacturing paper pulp.

The method oommonly used for evaluating the beating rate, or degree of beating, of a lignooellulosic material is the Schopper-Riegler test (standard ISO 52 67/1) . It measures the drainability of a material that has undergone a beating operation. The more a material has been beaten, the more the fibres oomposing it are individualized, hydrated and short, and the more the material will retain water. A highly beaten material consequently has a low drainability and a high Schopper-Riegler degree of beating.

The lignocellulosic binder used in the present invention must have a Schopper-Riegler number of at least 38°SR, preferably of at least 42°SR and ideally of at least 45°SR.

The lignocellulosic binder used in the present invention may be obtained in principle from any lignified plant material, the lignocellulosic materials that can be used encompassing of course, but not only, the grass stems used for the component (a) . Besides these grass stems, use may be made, for example, of wood debris, hemp or else recycled paper.

A beating process that makes it possible to obtain the lignocellulosic binder (b) is described in detail in patent EP 0 877 646. At the end of this process, the beaten lignocellulosic binder (b) is in the form of a pulp having a water content between approximately 40% and 70%, in other words its solid content is between 30% and 60% by weight, preferably between 35% and 55% by weight.

The grass straw debris forming the component (a) may be in principle debris from any grasses having lignified stems. Mention may be made, as examples of such grasses, of sugarcane, cereals such as maize, rice, wheat, barley, oat, rye, or millet, bamboo and miscanthus.

One plant that is particularly preferred for the present invention is Miscanthus giganteus, a hybrid species obtained by crossing Miscanthus sinensis and Miscanthus sacchariflorus. Specifically, this plant is distinguished by its high productivity, its high lignocellulose content, and its low environmental impact, resulting in particular from the low water requirement of this plant and from the absence of depletion of the soils in which it grows, generally rendering the provision of fertilizer unnecessary.

Miscanthus giganteus may be used as a source of the grass stem debris of component (a) or as a source of lignocellulosic binder (b) or for both at once.

In one particularly preferred embodiment, the component (a) and the lignocellulosic binder (b) are obtained partly, and preferably completely, from one and the same plant, preferably stems of Miscanthus giganteus.

Before being mixed with one another, the components (a) and (b), or at least one of them, is first put into suspension in water. The amount of water added is preferably between 40% and 90%, preferably between 50% and 80%, relative to the total dry weight of components (a) and (b) In one preferred embodiment, from 40% to 80% by weight of water is added to component (a) before mixing it with component (b) In one preferred embodiment, the compressed body contains, in addition to the components (a) and (b) of plant origin, an alkali metal mineral component (c), the essential role of which is to strengthen the binding power of component (b) . This is for example calcium oxide (CaO), also referred to as quicklime, sodium hydroxide, potassium hydroxide or sodium oarbonate. Caloium oxide is partioularly preferred.

When it is used, this component (c) is preferably present in a proportion of from 2% to 15% by weight, in particular in a proportion of from 3% to 8% by weight, relative to the total dry weight of (a) and (b) . The calcium oxide may be added either to one of the two components (a) and (b) before mixing, or else to the aqueous mixture of components (a) and (b) before the moulding step. It is preferably added to component (b) The aqueous suspension of components (a) and (b), and optionally (c), is then moulded at high temperature and under pressure according to a process described in greater detail below.

The compressed body obtained, having a lost a large part of its water content, is then impregnated with a fuel that is liquid at room temperature. The impregnation of the compressed body does not require complete pre-drying. At the time of the impregnation, this compressed body may have a water content of between 5% and 20% by weight.

The fuel must not be too volatile, which is the case for liquids that have a flashpoint above 30°C.

The flash point of the liquid fuel is preferably between 40°C and 120°C, in particular between 50°C and 70°C.

The liquid fuel may be a plant oil such as microalgae oil, Pongamia pinnata oil (or Karanja oil), linseed oil, jatropha oil, palm oil, sunflower oil, rapeseed oil, almond oil, peanut oil, coconut oil, maize oil, olive oil or castor oil, an animal oil such as whale oil, sperm whale oil, cod liver oil, beef suet or tallow, lard or pork fat, an alkyl ester of such a plant or animal oil, or a mixture of these compounds.

In one preferred embodiment, the liquid fuel is an alkyl ester, preferably a methyl ester, of a plant oil, and in particular an ester of coconut oil.

The lignocellulosic compressed body resulting from the hot-pressing step preferably has a density between 0.20 and 0.85 g/cm3, in particular between 0.30 and 0.70 g/cm3.

This compressed body may be impregnated with the liquid fuel by various known methods, such as dip-coating, vacuum dip-coating or spraying. Depending on the impregnation method used, a fuel penetration and/or drainage phase may prove necessary in order to eliminate the excess liquid and to ensure a homogeneous distribution of the liquid fuel in the volume of the compressed body.

It is possible to adjust the amount of fuel introduced into the compressed body by varying, for example, the immersion time of the compressed body in the fuel bath and/or the temperature of the immersion bath, the fuel penetrating into the heart of the compressed body even more easily when its viscosity is low. It is also possible to make the fuel penetrate into the compressed body under pressure.

The applicant has observed that the compressed body was generally able to absorb up to its own weight in fuel.

In certain cases, it may however be advantageous not to saturate the compressed body with liquid fuel and to remain well below complete impregnation. The applicant has obtained good results in terms of combustion performances for a weight ratio of the liquid fuel to the lignocellulosic ccmpressed body of between 3/10 and 10/10, preferably between 5/10 and 9/10 and in particular between 6/10 and 9/10.

Another subject of the present invention is a process for manufacturing a briquette as described in the present application. This process comprises the following successive steps: (1) mixing an aqueous suspension of a lignocellulosic binder (b) with grass stem debris (a), in proportions such that the ratio, by dry weight, of the lignocellulosic binder (b) to the grass stem debris (a) is between 10/90 and 40/60, (2) moulding the mixture obtained in a suitable mould (female part)/countermould (male part) assembly at a temperature between 40°C and 120°C, under a pressure between 3 and 12 bar, applied for a duration of 5 to 120 seconds, (3) demoulding the compressed body obtained, and (4) impregnating the demoulded compressed body with a fuel, which is liquid at room temperature, having a flash point between 30°C and 150°C.

Step (1) of mixing the two components (a) and (b) is preferably carried out in a sigma blade mixer until a homogeneous suspension is obtained where the straw fragments are uniformly coated with binder. Obtaining a homogeneous composition generally takes 5 to 30 minutes.

This composition may of course also contain the alkali metal mineral component (optional component (c)) added before or after mixing components (a) and (b) The composition ready for moulding is fibrous and pulpy. It requires a manual or automatic filling of the mould via a funnel or via a vacuum filling system.

The mould is constituted of a male part and a female part. The female part, placed on the bottom, is a hollow cylinder, at the centre of which is positioned a solid section having a star-shaped cross-section. The male part has a shape complementary with the female part, in other words it comprises a solid cylinder, hollowed out at its centre following the star-shaped section corresponding to the female shape. Figure 2 is a photograph showing the shape complementarity between the male part on the left and the female part on the right.

The composition to be moulded is introduced into the female part, in the space defined between the inner wall of the cylinder and the section. Once the female part has been filled, the male shape is gradually inserted into the female shape by the thermopress.

The whole of the mould (male and female parts) is brought to the moulding temperature by the thermopress.

This temperature, preferably between 60°C and 100°C, in particular between 65°C and 95°C, and also the pressure generated make it possible to bring about the activation of the binding power of component (b) within the composition. At the end of the hot-pressing operation, the pistons raise the male shape thus releasing, in a twofold movement, the briquette formed.

The briquette is left for around 1 to 30 minutes in the open air in order to allow a large portion of the water to evaporate.

After this drying step, the compressed body may be directly impregnated with the liquid fuel.

The geometry of the solid cylinder of the female part of course directly determines that of the central chimney. According to one preferred embodiment, the latter has a star shape comprising at least 3 arms, preferably from 4 to 20 arms and in particular from 5 to 10 arms. The term "star-shaped" also encompasses the variants where the points and/or hollows of the arms of -10 -the star are rounded. A rounded shape of the points of the star has proved particularly advantageous for reasons of ease of demoulding, limiting the detaohment of fibres when the briquette is raised up along the female part.

The hollows between the arms of the star are preferably not rounded. Indeed, these hollows form, after demoulding, the points of elements that project from the wall towards the centre of the chimney of the briquette. These points constitute a plurality of ignition points and it is easily understood that the ignition of the briguettes is even easier when the points of the projecting elements are sharp and pointed.

The advantage of the star shape of the central chimney is threefold. Firstly, as already explained above, the points of the elements that project towards the inside of the central chimney of the briquette allow a very easy ignition. The second advantage, which ensues directly from the first, lies in the fact that the combustion surface is located inside the briquette and is thus in a sheltered position, protected by the briquette itself. Finally, the star shape enables a combustion surface that is pretty much constant throughout the combustion since the gradual reduction of the combustion surface due to the consumption of the projections is compensated for by the gradual increase in the diameter of the internal chimney as the combustion progresses. This change is illustrated in figure 1, which is a schematic representation of a cross-section of a briquette according to the invention. The various lines 1, 2, 3 and 4 show the combustion surface at successive stages of combustion.

The size of the briquettes may be chosen freely as a function of the envisaged applications. The height of the briquettes may be, for example, between 5 cm and -11 -cm, and its external diameter between 3 cm and cm. For use as a solid fuel for portable torches, the height of the briquettes is generally between 8 cm and 20 cm with an external diameter between 4 cm and 10 cm.

The ratio of the height of the cylindrical briguette to the external diameter thereof is preferably between 0.5 and 5, preferably between 1 and 4, in particular between 1.5 and 3.

Figure 3(a) shows a compressed body before impregnation and Figure 3(b) a batch of impregnated briguettes according to the present invention where the height/external diameter ratio is approximately egual to 2.

The impregnation of the compressed body by the liquid fuel preferably takes place by complete immersion of the compressed body in the liquid fuel, for a time between 2 and 60 seconds, preferably between 10 and 40 seconds. This immersion is generally followed by a drainage step. A drainage time of 15 seconds to 5 minutes is generally sufficient to eliminate all of the excess liquid fuel.

For use as fuel for torches, the briguettes are inserted in a rigid sheath that is resistant to high temperatures. This sheath facilitates the handling and transport of the briquettes and protects them against mechanical stresses liable to deteriorate them. The sheath also prevents, during the combustion, the combustion surface from extending to the outer cylindrical wall of the briquette.

The briquettes are advantageously packaged in leaktight bags or containers in order to prevent the volatilization of the liquid fuel or the transfer -12 -thereof to surfaces that come into contact with the impregnated briquette.

Finally, another subject of the invention is the use of such a briquette as a fuel in torches, as a firelighter or for heat production, preferably for cooking or reheating food.

Claims

-13 -CLAIMS-of a lignocellulosic compressed body comprising (a) from 60% to 90% by weight of grass stem debris and (b) from 10% to 40% by weight of a beaten lignocellulosic binder having a degree of beating of between 38 and 75°SR (degrees Schopper-Riegler), preferably between 45 and ° SR, these percentages being expressed by dry weight relative to the dry weight of the sum of (a) and (b), and -of a fuel that is liquid at room temperature having a flash point between 30°C and 150°C, impregnating the lignocellulosic compressed body, said briquette having an essentially cylindrical shape and comprising a central chimney with a star-shaped cross-section.
2. Briquette according to Claim 1, wherein the grass stem debris is more than 60% by weight, preferably more than 75% by weight, and in particular more than 90% by weight, constituted of fragments having a size such that their larger dimension is between 3 and 20 mm, preferably between 5 and 15 mm.
3. Briquette according to Claim 1 or 2, wherein the grass stems are stems of Miscanthus giganteus.
4. Briquette according to any one of the preceding claims, wherein the compressed body additionally comprises from 2% to 15% by weight, preferably from 3% to 8% by weight, relative to the dry weight of (a) and (b), of at least one alkali metal mineral component (component (c)), preferably calcium oxide.

-14 -
5. Briquette according to any one of the preceding claims, wherein the central chimney has a star-shaped cross-section, the star comprising at least 3 arms, preferably 4 to 20 arms and in particular 5 to 10 arms.
6. Briquette according to any one of the preceding claims, wherein the liquid fuel has a flash point between 40°C and 120°C, preferably between 50°C and 70°C.
7. Briquette according to any one of the preceding claims, wherein the liquid fuel is an oil of plant or animal origin, an alkyl ester of an oil of plant or animal origin, or a mixture thereof.
8. Briquette according to any one of the preceding claims, wherein the liquid fuel is a coconut oil alkyl ester.
9. Briquette according to any one of the preceding claims, wherein the grass stem debris (a) is debris of cereal or miscanthus stems, preferably debris of Miscanthus giganteus stems.
10. Briquette according to any one of the preceding claims, wherein the density of the compressed body alone is between 0.20 and 0.85 g/cm3.
11. Briquette according to any one of the preceding claims, wherein the weight ratio of the liquid fuel to the compressed body is between 3/10 and 10/10, preferably between 5/10 and 9/10, and in particular between 6/10 and 9/10.
12. Briquette according to any one of the preceding claims, wherein the ratio of the height of the cylindrical briquette to the diameter thereof is between 0.5 and 5, preferably between 1 and 4, in particular between 1.5 and 3.

-15 -
13. Process for manufacturing briquettes according to any one of the preceding claims, comprising the following successive steps: (1) mixing an aqueous suspension of a lignocellulosic binder (b) with grass stem debris (a), in proportions such that the ratio, by dry weight, of the lignocellulosic binder (b) to the grass stem debris (a) is between 10/90 and 40/60, (2) moulding the mixture obtained in a suitable mould/countermould assembly at a temperature between 40°C and 120°C, under a pressure between 3 and 12 bar, applied for a duration of 5 to 120 seconds, (3) demoulding the compressed body obtained, and (4) impregnating the demoulded compressed body with a fuel, which is liquid at room temperature, having a flash point between 30°C and 150°C.
14. Process according to Claim 13, wherein the impregnation of the compressed body by the liquid fuel is carried out by complete immersion of the compressed body in the liquid fuel, for a duration of between 2 and 60 seconds, this immersion being followed by a drainage step.
15. Use of a briquette according to any one of Claims 1 to 12, as a fuel in torches, as a firelighter or for heat production, preferably for cooking or reheating food.
16. A briquette substantially as described herein with reference to the accompany drawings.
17. A process for manufacturing briquettes substantially as described herein with reference to the accompanying drawings.-16 -
18. Use of a briquette substantially as described herein with reference to the accompanying drawings.