RU2613327C2 - Method and device for refining pellets - Google Patents

Abstract

FIELD: packaging industry.

SUBSTANCE: invention describes a method of refining pellets, pressed from biomass, including following steps: providing of pellets, pressed from biomass and performing heat treatment of pellets while heating to temperature between 210 °C and 390 °C for 1–30 minutes. Invention also describes a device, used to refine pellets pressed from biomass.

EFFECT: pellets processed using said method are water-repellent and therefore can be stored in open air.

15 cl, 5 dwg

Description

The invention relates to a method for refining briquettes. This method is used in the case of briquettes pressed from biomass. The invention also relates to a device suitable for implementing this method.

The practice of pressing biomass to produce briquettes is widespread. Briquettes can be used, for example, as fuel - in particular in the form of co-burning at power plants - to generate thermal or electric energy. However, briquettes obtained from biomass tend to lose their shape under the influence of moisture and rot quickly. Therefore, you cannot store such briquettes outdoors. This is unfavorable for use in power plants, as they usually store fuel outdoors.

The invention is based on the goal of proposing a method and device with which it is possible to improve the safety of briquettes. Based on the prior art set forth at the beginning, this goal has been achieved by the features of the independent claims. Preferred embodiments are described in the dependent claims.

According to the method, the briquettes are subjected to heat treatment. In this operation, the briquettes are heated to a temperature in the range from 210 ° C to 390 ° C. Heat treatment takes place from 1 minute to 30 minutes.

First, some terms will be explained. Briquettes pressed from biomass are briquettes, the source material for which is mainly biomass. This does not exclude other materials, such as, for example, waste added to the starting material. The proportion of such other materials should be less than 30%. After the pressing operation, the briquettes have a higher density than the starting material. The term "biomass" includes, for example, all grassy and wood renewable materials and mixtures thereof. Briquettes can consist entirely of biomass.

The biomass from which the briquettes are pressed can be, for example, wood, the moisture content of which is usually from 30% to 60% from the initial state. Another example of biomass is straw with a moisture content of 15% to 20% in its original state. In general, the initial moisture content in the biomass may therefore be from 15% to 60%.

Before receiving the briquettes, said starting material must be dried based on the type of biomass. Usually up to 6% -12% moisture in the case of wood and up to 10% -20% in the case of straw. Another part of the moisture leaves the material upon receipt of the briquettes, and therefore the moisture content of the briquettes pressed from biomass is lower. In the case of briquettes made from straw, the moisture content can be, for example, 8% and 9% in the case of briquettes made from bamboo, 11% in the case of briquettes made from steppe grasses.

Generally speaking, the moisture content of the briquettes can be, for example, from 6% to 12% before processing according to the invention. The moisture content in each case is indicated as a percentage by weight. This makes it clear that the biomass briquettes that are the subject of the invention are significantly different from coal briquettes, which are described, for example, in US Pat. No. 4,412,840, FR 1187244 and GB 1010452. Coal briquettes have nothing to do with the present invention.

The heat treatment according to the invention takes place in a temperature range which is higher than the temperature at which the briquettes are dried and which is lower than the temperature at which the briquettes are burned. In the temperature range according to the invention, processes that are not known in detail are activated in briquettes. These processes probably include the pyrolytic decomposition of inorganic compounds and the release of various volatile components. Tests have shown that as a result of processing according to the invention, briquettes are obtained which have strong water-repellent properties. Therefore, briquettes are refined in such a way that they can be stored in the open air even for a relatively long time. Tests have shown that in addition to this, the energy content in briquettes (in MJ / kg) increases.

If the briquettes are exposed to heat, a temperature gradient can be set in them, since a certain time may elapse before the heat penetrates into the center of the briquettes. The temperature specification according to the invention relates to the surface of briquettes.

The fact that changes in the temperature range lying between drying and burning can occur in biomass does not constitute a new discovery as such. For example, it is known that biomass, crushed into small pieces (chips) and subjected to heat treatment in the corresponding temperature range, will undergo a significant change in its internal structure. The corresponding process is also called drying.

Chips, however, cannot be directly comparable in terms of their properties to briquettes, because, among other things, the density of the chips is much lower than the density of briquettes. In the case of briquettes, one cannot expect that a structural change will propagate to the center of the briquettes. This would be unfavorable for the safety of briquettes, if only the surface of the briquettes acquired a water-repellent structure, and the components in the center of the briquettes remained essentially unchanged.

Heat can be supplied to the briquettes by means of an air stream with a suitable controlled temperature. The advantage here is that the volatile components exiting the briquettes are directly drawn into this air stream.

The power of the air stream is preferably such that the briquettes are driven by a stream of air. This contributes to the penetration of heat into the briquettes. In addition, through constant impacts, volatile components can more easily exit briquettes.

For particularly intense heat transfer and thorough mixing, the air flow can be adjusted so that the briquettes rise up by the air flow and then deviate sideways with the air flow. Then the briquettes fall down from the deflected air stream. An inclined surface can be located here on which the briquettes slide back to the starting point. Tests have shown that briquettes can withstand even this powerful movement and strong blows without collapsing. This stability of the briquettes is the result of the fact that the biomass from which the briquettes are pressed contains components that have significant adhesion forces. These components include components that dissolve by heat treatment according to the invention. In this regard, it is preferable for the method according to the invention to perform briquetting before heat treatment.

It is possible that the processing of briquettes is performed continuously, for example, briquettes are continuously transported further during heat treatment. This can occur, for example, by means of a device in which the drum rotates around a substantially horizontal axis. Briquettes are introduced into the drum at one end, and they move in the drum to the opposite end, where they exit the drum. The circumference of the drum may be provided with inwardly directed vanes, which transport the briquettes forward when the drum rotates. In addition to or as an alternative to the blades, a screw for conveying briquettes may also be provided.

For heat treatment, an air stream of suitable controlled temperature can be supplied through the drum, and this air stream preferably also moves from one end surface to the opposite end surface. The air flow can move through the drum in the same direction as the briquettes, or in the opposite direction. The air stream can also be used to heat the drum itself. For example, the air flow may first be directed through the drum on the outside and then directed through the drum. For this purpose, the drum may be surrounded by a casing. Such a device can be used to implement the method according to the invention.

If the treatment is carried out in batches, it will be easier to separate the chamber in which the treatment takes place from the environment. This is desirable since materials exiting the briquettes will in some circumstances be flammable and may pose a safety risk if they enter the environment.

In the case of batch processing, the amount of air for processing briquettes can be easily controlled. This variable can be used to control the process. The volume of air flow is preferably from 6 m ³ to 20 m ³ per kilogram of briquettes. This characteristic refers to the total amount of air that is supplied to the briquettes during heat treatment.

There are other possibilities for transferring heat to briquettes. For example, briquettes can be brought into contact with a warm object or can be placed on a warm surface. In comparison, a very intense heat transfer to the briquettes occurs when an air stream is used. Heat transfer is preferably carried out in such a way that a treatment time of 3 minutes to 16 minutes is sufficient.

In general, the structure of briquettes changes the faster the higher the temperature. However, at very high temperatures, the risk also increases that the change in the structure will occur non-uniformly, and rather that unwanted combustion will occur on the surface, while in the center the structure will not change at all. Good results both with respect to the duration of the heat treatment and the uniform structure of the briquettes were obtained in the temperature range from 250 ° C to 300 ° C. In addition, the advantage can be reactions in briquettes, if the heat treatment is carried out in an atmosphere with a low oxygen content. The oxygen content may, for example, be less than 10%, preferably less than 6%, relative to the volume.

In tests, it turned out to be preferable if the briquettes have a diameter of from 4 mm to 20 mm. Before implementing the method according to the invention, the briquettes preferably have a moisture content of from 5% to 15% by weight.

After the end of the heat treatment of the briquettes, a certain amount of heat is stored in them. It is possible that due to this amount of heat inside the briquettes, reactions continue, even if no heat is supplied from outside. This is undesirable since the thermal power of the briquettes can be degraded as a result. Therefore, it is preferable if the briquettes are sharply cooled after heat treatment. For rapid cooling, you can use, for example, water, the temperature of which, preferably, does not exceed room temperature.

Briquettes obtained by the method according to the invention can be used for what is called co-burning in power plants. Briquettes are therefore burned together with the main fuel, for example coal, at a power plant. For this purpose, briquettes must be crushed so that, for example, 95% of the particles by weight have a size of less than 2 mm. It is proved that the method according to the invention gives particles having significantly increased fragility. Therefore, briquettes can be ground at a significantly lower energy consumption than classic briquettes. In addition, for grinding, you can use mills, usually used in power plants, which is impossible in the case of classic briquettes made from untreated biomass. For the same reason, briquettes obtained according to the invention are better suited for co-burning than classic briquettes. In addition, the energy content of the briquettes is increased by processing according to the invention.

The invention also relates to a device for refining briquettes. The device includes a processing chamber with a support floor, a first side wall and a second side wall. The supporting floor is provided with a number of holes. The first side wall and the second side wall are adjacent to the support floor on opposite sides. The second side wall has a groove that leads to the support floor. A channel is provided for the air flow that leads under the support floor. The air stream can be heated and removed from under the floor through the openings with a heating device and a drive device. The deflecting surface is located above the support floor, so that the air flow and briquettes captured by the air flow deviate in the direction of movement from the first side wall in the direction of the second side wall. According to the invention, the partition is located between the first side wall and the second side wall, so that the briquettes move upward between the first side wall and the partition.

In this device, the batch to be processed is placed on the support floor, and the air flow is discharged through openings in the support floor, and the power of the air flow is such that it moves the briquettes up. During this process, the briquettes move substantially parallel to the first side wall of the processing chamber. The air flow is deflected by the deflecting surface so that it moves with the briquettes in the direction of the second side wall. Briquettes fall from the air stream, hit the trench of the second side wall and move back along the trench in the direction of the support floor.

The invention has recognized that an advantage for the movement of air and briquettes will be if the region in which the upward movement is separated from the region in which the briquettes move downward. Therefore, a partition is proposed between the first side wall and the second side wall, this partition being arranged so that the briquettes mainly move upward between the partition and the first side wall. In the invention, in particular, it is recognized that the briquettes are only slightly damaged in collisions with the partition. Therefore, the briquettes are strong enough than allows the use of partitions.

Briquettes can cross the plane of the partition above and below the partition. For this purpose, the partition is preferably made in such a way that in each case there is some distance between the support floor and the lower end of the partition and between the upper end of the partition and the upper end of the deflecting surface. In contrast, the baffle may extend across a width substantially of the entire processing chamber. In one preferred embodiment, the partition is substantially parallel to the first side wall.

In order to be able to adjust the flow conditions in the processing chamber, the distance between the partition and the first side wall can be adjustable. If the partition is located above the support floor, then the air flow preferably passes so that the briquettes mainly move upward between the partition and the first side wall. Therefore, the support floor can be designed so that the holes near the first side wall are larger than next to the second side wall. Then a powerful stream of air rises exactly in the area where the briquettes should move up.

The support floor may be inclined. The advantage of this is that the briquettes exit the device by gravity when the hole near the lower end of the support floor is open. Therefore, the device can be easily drained. The trough on the second side wall is preferably located near the upper end of the inclined support floor. This trough may have a greater inclination than the support floor.

In some circumstances, the device can also be used to implement the method without a partition. In one preferred embodiment, the support floor is inclined.

Below the invention will be described by the example of preferred embodiments with reference to the accompanying drawings, in which:

FIG. 1 is a first embodiment of a device for implementing the method according to the invention.

FIG. 2 is a detail of FIG. 1 enlarged view.

FIG. 3 is a second embodiment of a device for implementing the method according to the invention.

FIG. 4 - a device according to the invention.

FIG. 5 - results of comparative tests.

The device shown in FIG. 1 includes a processing chamber 14, which is intended for heat treatment of briquettes. As shown in an enlarged view in FIG. 2, the lower end of the treatment chamber 14 includes an inclined support floor 15, which is provided with a number of holes 16. A distribution space 17, into which an air flow through the supply line 18 can be supplied, is formed under the support floor 15. An air flow can propagate in the distribution space 17 and pass from below through holes 16 in the support floor 15.

The fan 19 and the burner 20 are located further in the supply line 18. Fresh air is supplied through the inlet 21 and is heated by the burner 20 to a temperature of approximately 300 ° C. The air flow is accelerated by the fan 19 in the direction of the distribution space 17. The air flow passes through the holes 16 in the support floor 15 into the processing chamber 14 and first moves there essentially vertically upward. At the upper end of the processing chamber 14, an air stream hits a deflecting surface 22, as a result of which it swings laterally to the left. The air flow is again deflected on the opposite wall and therefore moves upward and discharged into the environment through the exhaust channel 23. The wall, on which the air flow deviates upward, is defined as a groove 24, which, passing to the left, leads to the support floor 15.

In addition, the device includes a storage tank 25, which is connected to the upper end of the processing chamber 14 through the gateway 26. The lower end of the processing chamber 14 is provided with a gateway 27, through which material lying on the supporting floor 15 can be removed from the processing chamber fourteen.

Storage tank 25 is filled with briquettes pressed from biomass as a source material. The starting material may be, for example, grass or wood renewable raw materials or mixtures of such materials. In addition, briquettes may contain a certain proportion of non-renewable materials in an amount up to 30%, such as, for example, waste. Briquettes may have a diameter of, for example, 6 mm and a length of several centimeters.

A batch of briquettes is passed into the processing chamber 14 through the gateway 26. In the processing chamber 14, the briquettes fall down and accumulate on the supporting floor 15. The burner 20 and the fan 19 heat the air flow to a temperature of approximately 300 ° C and direct this air flow to the distribution chamber 17 and then through the supporting floor 15.

The power of the air flow is such that it raises the briquettes from the support floor 15 and moves them up. The air flow together with the briquettes is deflected laterally on the deflecting surface 22. The briquettes fall from the air flow under the influence of gravity and fall on the groove 24, along which the briquettes pass back to the supporting floor 15. Therefore, the briquettes follow a contour in which they repeatedly rise upstream air and then move back along the gutter 24 to the support floor.

This heat treatment is carried out for approximately 8 minutes and leads to the release of volatile materials from the briquettes and to the splitting of various compounds with a long chain. Due to this, the briquettes become hydrophobic and acquire a fragile internal structure. During heat treatment, a certain amount of air, in total about 8 m ³ per kilogram of briquettes, is conducted through the processing chamber 14.

After the end of the heat treatment, the gateway 27 opens and the briquettes exit the processing chamber 14 through the gateway 27. Immediately after exiting it, the briquettes are treated with water, which has approximately room temperature, and therefore the briquettes are rapidly cooled, and the reactions taking place in the briquettes abruptly stop .

According to FIG. 4, the device may include a partition 31 located in the processing chamber 14. The partition 31 extends parallel to the first side wall 32 of the processing chamber 14, this side wall adjacent to the lower end of the inclined support floor 15. There is a gap above and below the partition 31, so that briquettes can cross the plane of the partition wall 31. In another dimension, the partition wall 31 extends over the entire width of the processing chamber 14. The partition wall 31 is movably suspended in the processing chamber 14, and therefore the distance between the first side wall 32 and the over the rod 31 can be adjusted to obtain optimal flow conditions in the processing chamber 14. The holes 16 in the support floor 15 are designed so that a very powerful upward air flow is created in the region between the partition wall 31 and the first wall 32, while the air flow carries with it briquettes. In the area between the partition 31 and the opposite side wall 32, on which the groove 24 is made, the upward flow of air is weakened. The air flow here serves mainly to give the briquettes movement in the direction of the first side wall 32, so that the briquettes can be captured there by a powerful stream of air.

In the embodiment of FIG. 3, a return line 28, which leads back through the separator 29 to the burner 20, is connected to the output channel 23 of the processing chamber 14. In the separator 29, the solid components are separated from the air stream and accumulate on the floor of the separator 29. These solid components can be removed at regular intervals by means of a gear wheel 30.

A stream of air that is free of solid components but still containing gaseous components from the briquettes is directed back to burner 20. These gaseous components partially burn out and can serve as fuel for burner 20. A closed loop, ideally controlled without fresh air, is ideally achieved. and without supplying new fuel. The oxygen content in the air stream is optionally reduced, and this may be an advantage for reactions in briquettes.

Briquettes refined in this way are hydrophobic and therefore can be stored outdoors for a relatively long period of time. This, as well as a high degree of brittleness of the material, which makes it easy to grind the briquettes, makes the briquettes well suited for use in the form of co-burning in power plants. In addition, the energy content in the briquettes increases as a result of processing according to the invention.

The success of the method according to the invention was confirmed in a series of tests. For example, ordinary wood briquettes with a diameter of 6 mm with certified DinPlus quality and with a moisture content of 9% were placed in the above device. These briquettes were processed in a device at a temperature of from 240 ° C to 320 ° C for 3 to 21 minutes. The briquettes treated in this way showed an improvement in the characteristics of the burning force, for example, (approximately) from 18.5 MJ / kg to 21 MJ / kg. Even after storage in water for 3 days, the briquettes were stable. Briquettes had a high uniformity of brownishness even in briquettes, which makes it possible to conclude that the processing intensity is very uniform.

Other tests were performed with other wood briquettes (diameter 8 mm, quality EN14961-2-B), briquettes made from bamboo (9% moisture), briquettes made from straw (8% moisture), and briquettes made from steppe grasses (11% moisture). All trials demonstrated a characteristic increase in burning power after treatment. In FIG. 5 shows a comparison in each case of the burning power in MJ / kg, the light bar showing the burning power in the initial state of the briquettes, and the dark bar showing the burning power after implementing the method according to the invention. The left lanes are for straw, the second lanes are for steppe grasses, the third lanes are for wood and the right lanes are for bamboo.

Claims (25)

1. The method of refining briquettes pressed from biomass, comprising the following steps: a) the provision of briquettes pressed from biomass, b) heat treatment of briquettes with the following parameters: i) the briquettes are heated to a temperature between 210 ° C and 390 ° C; ii) the heat treatment takes place from 1 minute to 30 minutes. 2. The method according to p. 1, characterized in that the briquettes are heated by a controlled stream of air of suitable temperature. 3. The method according to p. 2, characterized in that the power of the air flow is such that the briquettes are driven by an air stream. 4. The method according to p. 1, characterized in that the briquettes are processed in batches. 5. The method according to p. 4, characterized in that the heat treatment occurs when the air flow from 6 m ³ to 20 m ³ per kilogram of briquettes. 6. The method according to one of paragraphs. 1-5, characterized in that the heat treatment is performed in an atmosphere with a low oxygen content. 7. The method according to one of paragraphs. 1-5, characterized in that the heat treatment takes place over a period of time from 3 minutes to 16 minutes. 8. The method according to one of paragraphs. 1-5, characterized in that the briquettes are heated to a temperature of from 250 ° C to 300 ° C. 9. The method according to one of paragraphs. 1-5, characterized in that the briquettes provided in stage A., have a diameter of from 4 mm to 20 mm 10. The method according to one of paragraphs. 1-5, characterized in that the briquettes provided in stage A., have a moisture content of from 5% by weight to 15% by weight. 11. The method according to one of paragraphs. 1-5, characterized in that the briquettes are rapidly cooled after heat treatment. 12. A device for refining briquettes pressed from biomass, according to the method in accordance with any one of paragraphs. 1-11, and the device has the following features: a) a processing chamber (14) that has a supporting floor (15) for briquettes and a first side wall (32) and a second side wall (33), the supporting floor (15) having a number of holes (16), and the first the side wall (32) and the second side wall (33) are adjacent to the support floor (15) on opposite sides, and the second side wall (33) has a groove (24) that leads to the support floor (15); b) a channel for air flow, said channel leading under the support floor (15); c) a heating device (20) and a drive device (19) for air flow to conduct a heated air flow from below through openings (16) in the support floor (15); d) a deflecting surface (22) located above the support floor (15), so that the air flow and briquettes trapped in the air flow deviate in the direction of movement from the first side wall (32) in the direction of the second side wall (33), characterized in that e) a partition (31) is located between the first side wall (32) and the second side wall (33) so that the briquettes move upward between the first side wall (32) and the partition (31). 13. The device according to p. 12, characterized in that the distance between the partition (31) and the first side wall (32) is adjustable. 14. The device according to p. 12, characterized in that the holes (16) next to the first side wall (32) are larger than the holes next to the second side wall (33). 15. The device according to one of paragraphs. 12-14, characterized in that the support floor (15) is inclined.

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