"PELLET OF VEGETABLE ORIGIN"

TECHNICAL FIELD

The present invention relates to a pellet and a process for the preparation of a pellet.

BACKGROUND ART

Wood pellets are a fuel obtained from dried virgin sawdust which is then compressed in the form of small cylinders with a diameter of a few millimetres. Due to the pressing, the heating value of pellets (gross heating value approximately exceeding 3800 Kcal/kg) having equal volume, but not weight, is generally higher than wood.

Nevertheless, the wood pellets currently known have a relatively low heating value with respect to that of other fuels such as coal, for example (gross heating value approximately exceeding 7500 Kcal/Kg) , petrol (gross heating value approximately exceeding 10986 Kcal/Kg) and diesel (gross heating value approximately exceeding 10499 Kcal/Kg) .

Furthermore, wood as a raw material for the production of pellets may not always be available at low cost. This is a particularly important consideration in some geographical areas such as parts of Spain, Italy and Greece, for example.

Lastly, for some types of sawdust containing a low percentage of lignin, synthetic additives have to be used to keep the pellets constantly boundwhich would otherwise tend to disintegrate.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a pellet and a process for the preparation of a pellet which overcome, at least partly, the drawbacks of the known art and, at the same time, are easy and inexpensive to implement.

According to the present invention, a pellet and a process for the preparation of a pellet are provided as claimed in the following independent claims and, preferably, in any one of the claims depending directly or indirectly on the independent claims .

Unless explicitly specified to the contrary, in the present text, diameter of a particle means the diameter of a sphere equivalent to the particle. Equivalent sphere means the sphere having diameter equal to the maximum length of the particle .

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described below with reference to the accompanying drawings, which illustrate a non- limiting example of embodiment thereof, in which: figure 1 illustrates an enthalpic curve relative to a pellet produced in accordance with the present invention (the y axis shows the enthalpy variation - in mW - and the x axis shows the temperature - in ⁰ C ) ; and figure 2 illustrates an enthalpic curve relative to a mixture for preparation of the pellet of figure 1 (the y axis shows the enthalpy variation - in mW - and the x axis shows the temperature - in ⁰ C) .

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with a first aspect of the present invention, a process is provided for the preparation of a pellet. According to said process, a mixture of a first particulate of a first vegetable material and at least one second particulate of a second vegetable material different from the first vegetable material is extruded at a temperature ranging from approximately 7O ⁰ C to approximately HO ⁰ C. Advantageously, the extrusion is performed at a temperature ranging from approximately 75°C to approximately 9O ⁰ C, in particular at

approximately 80 ⁰ C.

Advantageously, immediately after extrusion, the pellet obtained by extrusion has a temperature ranging from approximately 55°C to approximately 65°C.

According to some embodiments, the extrusion is performed via holes with a diameter ranging from approximately 3 mm to approximately 10 mm.

The mixture has an oily vegetable component above approximately 4% in weight, advantageously below approximately 25% in weight, advantageously below approximately 20% in weight .

According to some preferred embodiments, the mixture has an oily component ranging from approximately 5% to approximately 15% in weight .

Unless explicitly specified to the contrary, in the present text the weight percentage of a component is expressed as a weight percentage of said component with respect to the overall weight, for example of the mixture or the pellet.

A sufficient quantity of the oily vegetable component allows good blend of the first and second material. Furthermore, it has been experimentally observed that with excessive percentages of the oily vegetable component, the pellet is inclined to crumble and moulds tend to form on its surface.

Advantageously, the oily component is combined with at least one of the first and second materials. In particular, the oily component consists of vegetable lipids.

According to some embodiments, the vegetable lipids can be: simple and/or complex lipids and/or derivatives and/or a

mixture thereof. Usually, the vegetable lipids contain a majority of unsaturated or polyunsaturated fatty acids, often in the form of triglycerides .

According to some embodiments, the mixture has a humidity (water) content ranging from approximately 10% to approximately 25% in weight, advantageously 15% to 20%.

According to some embodiments, the mixture has a vegetable starch component ranging from approximately 5% to approximately 20% in weight, advantageously approximately 7% to approximately 14% in weight.

Usually, the vegetable starch consists of approximately 20% in weight of amylose and approximately 80% in weight of amylopectin.

Advantageously, the mixture has a vegetable fibre component of below 80% in weight, advantageously below 70% in weight, advantageously above approximately 40%.

Usually the vegetable fibres consist of cellulose and hemicellulose .

According to some embodiments, the mixture comprises at least a third, advantageously at least a fourth, vegetable material different from the first and second vegetable material.

According to some embodiments, the vegetable materials are obtained, independently of one another, from a raw material chosen from the group consisting of: woody stalks and branches, grassy stalks (stems) and branches, leaves, fruit, seeds .

The term grassy stalks (or stems) indicates stalks that do not have secondary growth (in diameter) . The term woody stalks

indicates stalks that have secondary growth.

The type of vegetable material can be selected according to the heating value required, the content of the various components, availability and cost (which can be affected by the period of the agricultural year and/or the geographical area) .

Advantageously, the vegetable materials are obtained, independently of one another, from a raw material chosen from the group consisting of: wood, straw, grass, leaves, grassy stalks, sunflower, maize, colza, grapes, olives, sorghum.

According to some advantageous embodiments, the vegetable materials are obtained, independently of one another, from a raw material chosen from the group consisting of: wood, straw, grass, maize cob, maize seed, main body (stalk) of sunflower, sunflower inflorescence, sunflower seed, main body of sorghum, sorghum seed, main body of colza, colza seed, sunflower cake (i.e. remains of sunflower seeds after pressing), grape pomace (i.e. remains of grapes after pressing), grape seeds, olive pomace (i.e. remains of olives after pressing) .

According to some embodiments, the first vegetable material is obtained from a raw material chosen from the group consisting of: woody stalks and branches, grassy stalks (stems) and branches, leaves. Advantageously, the first vegetable material is obtained from raw material chosen from the group consisting of: wood, straw, grass, maize cob, main body (stalk) of sunflower, sunflower inflorescence, main body of sorghum, main body of colza, sunflower cake.

Advantageously, the mixture comprises at least 20% in weight of wood (advantageously at least 25%), advantageously no more than 70%.

Advantageously, the second material is obtained from a raw material chosen from the group consisting of: sunflower seeds, maize seeds, colza seeds, sorghum seeds, grape seeds, olive pomace, sunflower cake.

According to some embodiments, the third (and possibly the fourth) material is obtained from a raw material chosen from the group consisting of: sunflower seeds, maize seeds, colza seeds, sorghum seeds, grape seeds, olive pomace, sunflower cake .

Advantageously, the mixture comprises at least 15% in weight of sunflower seeds (advantageously at least 25%) , advantageously no more than 50%.

Advantageously, one or more of the materials are dried and ground (for example sawdust can be obtained from the wood) before extrusion so as to obtain the first and/or the second particulate.

According to some embodiments, the particulates consist of particles with mean diameter ranging from approximately 0.01 to approximately 30 mm, advantageously approximately 0.1 to approximately 10 mm. The particles can be seeds.

According to a further embodiment of the present invention, a pellet is provided comprising a combination of a first vegetable material and at least one second vegetable material different from the first material. The pellet has an oily vegetable component above approximately 4% in weight, advantageously below 25% in weight, advantageously below 20% in weight.

According to some preferred embodiments, the pellet has an oily component ranging from approximately 5% in weight to

approximately 15% in weight.

In particular, the oily component consists of vegetable lipids, which can be: simple lipids, complex lipids or derivatives or a mixture thereof. Usually, the vegetable lipids contain a majority of unsaturated or polyunsaturated fatty acids, often in the form of triglycerides.

According to some embodiments, the pellets have a diameter of 3 mm to 10 mm.

Advantageously, the pellet has a humidity component (water) below or equal to approximately 15% in weight, advantageously approximately 8% to approximately 14%.

According to some embodiments, the pellet has a vegetable starch component ranging from approximately 5% to approximately 20% in weight, advantageously approximately 7% to approximately 14% in weight.

Usually, the vegetable starch consists of approximately 20% in weight of amylose and approximately 80% in weight of amylopectin .

Advantageously, the pellet has a vegetable fibre component of below 80% in weight, advantageously below 70% in weight, advantageously above approximately 40% in weight.

Usually, the vegetable fibres consist of cellulose and hemicellulose .

According to some advantageous embodiments, the pellet comprises at least a third (and, advantageously, at least a fourth) of vegetable material .

Advantageously, the vegetable materials are defined in

accordance with the above in relation to the procedure for preparation.

According to some embodiments, the pellet is (or can be) obtained by means of a method in accordance with the above.

By means of experimental tests, the pellet as defined above has surprisingly shown various advantages, including: relatively high heating value (in particular compared to wood pellets) ; relatively low tendency to disintegrate (in particular compared to wood pellets) ; combustion with relatively long duration and relatively uniform profile (heat emitted/time) ; - relatively low ignition temperature.

Experimentally (by means of enthalpic analysis), it was also possible to verify that the pellet surprisingly has structural characteristics which differ significantly from the simple mixture of particulates (the blend appears to be particularly intimate). This structural difference is presumably responsible for the particularly surprising combustion characteristics (long duration, uniform profile, low ignition temperature) .

A further advantage of the above with respect to the state of the art lies in the fact that, for the production of pellets, it is not necessary to separate the various plant components (for example the stalk from the seed) and/or perform extraction of the oil. It is also possible to use waste materials such as olive pomace and sunflower cake, for example .

Further characteristics of the present invention will become clear from the following description of some merely illustrative and non-limiting examples.

Example 1

Particulates (particles of wood with mean diameter less than 1 mm; particles of olive pomace with mean diameter less than 5 mm; particles of maize with mean diameter less than 0.1 mm; sunflower seeds) of the vegetable materials indicated were mixed together to obtain the following mixtures:

MIXTURE 1

Wood 30% in weight Olive pomace 57% in weight

Sunflower 3% in weight

Maize (seed and cob) 10% in weight

MIXTURE 2

Wood 50% in weight Sunflower 25% in weight

Maize (seed and cob) 25% in weight

MIXTURE 3

Wood 25% in weight

Sunflower 25% in weight Maize (seed and cob) 50% in weight

MIXTURE 4

Wood 40% in weight

Sunflower 20% in weight

Sunflower flour 40% in weight (mean diameter less than 1 mm)

MIXTURE 5

Wood 60% in weight

Sunflower 40% in weight

MIXTURE 6 Wood 35% in weight

Olive pomace 25% in weight

Sunflower 20% in weight

Maize (seed and cob) 20% in weight

MIXTURE 7 Wood 65% in weight

Sunflower 20% in weight

Maize (seed) 15% in weight MIXTURE 8

Wood 20% in weight

Olive pomace 60% in weight Maize (seed) 20% in weight MIXTURE 9

Olive pomace 50% in weight

Maize (seed and cob) 50% in weight MIXTURE 10 Straw 50% in weight

Maize (seed and cob) 50% in weight

Each of the above mixtures was pelletized using a pelletizer, model Tanchini ^{^} 640, which had extrusion holes with diameter 3 mm (mixtures 9 and 10) , 6 mm (mixtures 4, 6-8) and 7 mm

(mixtures 2, 3 and 5) and operated at a working temperature of approximately 80°. The pellets coming out of the pelletizer were at a temperature of approximately 60°.

Example 2

The different pellets (5 Kg) were tested, separately, in the same boiler, adjusting the boiler thermostat so that the pellets were fed to the boiler at intervals. Feeding began when an external temperature of 100 ⁰ C was detected (at the combustion fume outlet) and stopped when an external temperature of 150 ⁰ C was detected (at the combustion fume outlet) .

The following results were observed: 5 Kg of beech wood pellets (reference) :

^■ overall boiler operating time (TEC) 108 minutes

■ efficiency 46 g/min

5 Kg of pellets obtained from mixture 2 :

■ TEC 150 minutes ^■ efficiency 34 g/min

5 Kg of pellets obtained from mixture 3:

^■ TEC 131 minutes

^■ efficiency 38 g/min

5 Kg of pellets obtained from mixture 5: " TEC 150 minutes

" efficiency 27 g/min

The composite pellets according to the mixtures in example 1 surprisingly showed a higher efficiency than the known wood pellets.

Example 3

Different pellets were tested separately and the following results were observed: Wood pellets (reference) : gross heating value approximately 4000-4500 Kcal/Kg (the heating value varies considerably according to the type of wood and type of production) .

Pellets obtained from mixture 1: gross heating value exceeding 5010 Kcal/Kg; ignition temperature approximately 400 ⁰ C.

The pellets obtained from the mixtures as defined above showed surprisingly better characteristics than the raw materials taken individually. Moreover, the pellets are easy to handle (in particular compared to the olive pomace which is powdery), have relatively low ignition temperatures (for example compared to maize, which has an ignition temperature above 700 ⁰ C), have relatively uniform combustion with relatively long duration (in particular compared to the olive pomace and maize which tend to burn very rapidly) and have a relatively low ash content [see example 5 below - in particular compared to olive pomace (6% in weight) and sunflower (3.5% in weight) ] .

Example 4

An enthalpic analysis was performed on the mixture 1 of particulates (figure 2, relative to 9.06 mg of particulate) and on - a pellet obtained from the mixture 1 (figure 1, relative to 9.12 mg of pellets). As can be easily seen, the two materials show a markedly and surprisingly different behaviour. In particular, starting from the left, the concavity of figure 2 defines a normalised integral of -701 Jg ^"1 ; the concavity of figure 1 defines a normalised integral of -179 Jg ^"1 ; the peak on the right of figure 2 defines a normalised integral of 9.07 Jg ^"1 ; the peak on the right of figure 1 defines a normalised integral of 32.70 Jg ^"1 .

Such a different behaviour is presumably due to a significant structural difference which could at least partially explain the surprising characteristics highlighted in example 2.

Example 5

The pellets obtained from mixture 1 were analysed and showed the following characteristics: Net heating value 4570 Kcal/Kg

Gross heating value 5010 Kcal/Kg

Humidity 11.22 % in weight

Density - 1-1.4 Kg/dm ³

Ash 1.73 % in weight Nitrogen 0.23 N % S/S

(Gazzetta Ufficiale Italiana no. 132 dated 25/05/92)

Sulphur <0.01 % S/S

(EPA 610C 2000 + EPA 3050B 1996) Chlorine <0.1 % S/S

(EPA 610C 2000 + EPA 3050B 1996)