WO2010010585A1

WO2010010585A1 - Drying plant

Info

Publication number: WO2010010585A1
Application number: PCT/IT2008/000501
Authority: WO
Inventors: Giovanni Cappello
Original assignee: AGT SRL
Current assignee: AGT SRL
Priority date: 2008-07-25
Filing date: 2008-07-25
Publication date: 2010-01-28
Anticipated expiration: 2011-01-25
Also published as: SMP201100005B; SMAP201100005A

Abstract

The invention regards a drier (1) for biomass comprising: an upper space (10) for containing the biomass; a lower chamber (11) for the diffusion of the hot air; a wall (102) for separating the space (10) from the chamber (11) supporting the biomass and allowing the passage of the hot air; a mixer (67) adapted to sweep a portion of the wall (102); and an extractor (15) placed below the wall (102) and adapted for extracting the biomass from the space (10).

Description

DESCRIPTION "Drying Plant"

[0001] Subject of the present invention is a drying plant or drier for biomasses, in particular a drier of small/mid-size dimensions fed with low temperature air for biomasses used in production processes of energy, heat or for food purposes .

[0002] The use of the biomasses in combustion or gasification processes directed for the production of heat or energy has been known for some time. Biomass is generally composed of wood chips, agricultural production waste, corn stubbles, wheat straw and rice straw, sorghum stubbles, sugar cane bagasse, common cane etc.

[0003] In a manner in se known, it is not always economically or technically possible to collect from fields or forests biomasses having the optimal moisture percentage for their subsequent storage or combustion or gasification use.

[0004] Similar problems, connected to the high moisture percentage, are also encountered in the collection, treatment and storage of the wood chips for the paper mills and of the cereals for food use. [0005] Different plant types have therefore been known for some time for the drying of the biomasses and/or cereals. Such plants generally exploit hot air flows which cross the biomass, removing the excess moisture. [0006] Various types of drying plants are known which are differentiated based on the drier structure, the hot air path with respect to the biomass and with respect to the drier, the temperature and the flow rate of the drying air etc .

[0007] The drying plants of known type can be grouped into three large categories. None of these, however, lacks drawbacks, above all regarding biomass of irregular size and hard to move such as wood chips, and cut-up sorghum.

[0008] The drying plants of the first category are characterised by large-size silos (up to several thousand cubic meters) . The moist material is loaded from the upper part of the silo and extracted from the lower part of the same. The hot air crosses the material in a counter-current manner, from the bottom towards the top, ensuring optimal heat exchange efficiency.

[0009] For the discharge of the material, screws are commonly used which are capable of making the biomass converge towards an outlet placed at the centre of the silo. The screws are rotatable along their own axis (for transporting the dry biomass) and rotatable on the bottom of the silos (for reaching all the dry biomass) . Such screws are thus extremely critical pieces from a mechanical standpoint, and thus are rather costly. In fact, in the motion of the screws through the biomass, extremely high stress conditions are generated therein. [0010] This first plant type thus requires large sizes for damping the great cost of the material discharge screw. This solution type has an ideal use in large plants which treat wood chips for paper mills and/or which treat biomass for energy production. [0011] These driers are also characterised by high residence times of the material (several hours) , in connection with the possibility of using low temperature hot air (less than 100⁰C) with high drying efficiencies.

[0012] The plants of the second category are characterised by the use of a perforated conveyor belt on which the biomass is extended. The hot air crosses the biomass extended on the moving belt, drying it. These plants are characterised by a low drying efficiency, since part of the hot air crosses already-dried zones of the biomass. This drawback can be prevented by optimising the flow of the hot air. In this manner, however, there is a considerable increase of the plant costs. [0013] These driers are characterised by low residence times (less than an hour) , use of hot air at medium temperature (between 100⁰C and 200⁰C) and medium-low drying efficiencies. Plants of this type usually are of medium size (between 100m³ and 200m³) and are used for flow rates up to 10m³/h.

[0014] The plants of the third category are characterised by a rotating drum crossed by the hot air, in which the material is continuously moved and advanced by the drum movement. These plants are characterised by medium/low residence times (about 30 minutes) , by the need to use high temperature hot air (over 200⁰C) in order to not use overly large structural sizes and excessive manufacturing costs. In addition, if the speed of the air around the drum is sufficiently high, a driving effect is produced of the finest material, creating an excess dust problem at the exhaust and thus the need to introduce dust removal means . [0015] The object of the present invention is therefore that of providing a drier adapted to at least partially overcome the drawbacks marked with reference to the prior art .

[0016] In particular, one task of the present invention is that of providing a drier for biomasses of medium/small size (not more than 100m³) .

[0017] Still another task of the present invention is that of providing a drier capable of using low temperature hot air (less than 100⁰C) and with high efficiency. [0018] Further tasks of the present invention are those of providing a drier characterised by a low dust level of the exiting air; by a continuous functioning, even in the presence of extraneous bodies inside the supply biomass; by the possibility of functioning with hard-to-treat biomasses (wood chips and cut-up sorghum, for example) ; and by limited initial investments and operating costs. [0019] Such object and such tasks are achieved by means of a drier according to claim 1.

[0020] In order to better comprehend the invention and appreciate its advantages, several exemplifying and non- limiting embodiments thereof are described below, with reference to the attached drawings, wherein: - Figure 1 is a schematic view of the drier according to the invention in its entirety;

- Figure 2 is a view of the section obtained along the trace II-II of figure 1;

- Figure 3 is a top view of the drier; - Figure 4 is a view of the section obtained along the trace IV-IV of figure 3;

- Figure 5 is a view of the section obtained along the trace V-V of figure 1;

- Figure 6 is a view of the detail VI of figure 5; - Figure 7 is a view of the detail VII in figure 2; - Figure 8 is a perspective view of the detail of figure

7;

- Figure 9 is a perspective view similar to figure 5;

- Figure 10 is a perspective view of the detail of figure 6;

- Figure 11 is schematic view of a first plant comprising a drier according to the invention;

Figure 12 is a schematic view of a second plant comprising a drier according to the invention. [0021] In the following description, reference will often be made to the concepts "top" , "upper" and the like and respectively to the concepts "bottom" , "lower" and the like. Such concepts should be unequivocally intended with reference to the correctly assembled drier in functioning order, therefore subject to the force of gravity.

[0022] In the attached figures, a drier according to the invention is indicated in its entirety with the reference 1. [0023] The drier 1 according to the invention comprises:

- an upper space 10 adapted to contain the biomass;

- a lower chamber 11 for the diffusion of the hot air;

- a wall 102 for separating the upper space 10 from the lower chamber 11, the wall 102 being adapted to support the biomass and to permit the passage of the hot air; - a mixer 67 adapted to sweep at least a portion of the wall 102; and an extractor 15 placed below the wall 102, the extractor 15 being adapted for extracting the biomass from the space 10.

[0024] In accordance with several embodiments, for example that of the attached figure 1, the drier 1 has cylindrical shape with circular section and vertical axis. In other embodiments, the shape can be cylindrical with elliptical section or generally prismatic with polygonal section (for example square, pentagonal, hexagonal, heptagonal, octagonal, etc.). In further embodiments, the shape of the drier can be at least partially frustoconical and/or frusto-pyramidal .

[0025] The diameter of the drier 1 is preferably in the range of Im - 20m, preferably 3m - 8m. [0026] The upper space 10 is adapted to contain the biomass in a layer in the range of 0.1m - 10m. [0027] The lower chamber 11 has the function of dispensing and making uniform the hot air flow which is inserted in the drier 1. The air flow can be generated with different modes, described in detail below. In order to supply heat to the air flow, a suitable heating element can be used, or the heat can be recovered from other external sources. Such embodiment will be described in detail below.

[0028] In accordance with one embodiment, the wall 102 comprises, at least in some of its parts, grates, nets or perforated plates. By appropriately sizing the openings of the wall 102, this accomplishes the double function of supporting the biomass inside the space 10 and allowing the uniform distribution of the hot air flow in the biomass itself. [0029] In accordance with one embodiment, the drier 1 according to the invention is designed for treating biomass with a minimum size of 3mm x 3mm x 3mm and a maximum size of 100mm x 100mm x 100mm. The openings of the wall 102 are therefore sized on the minimum design size. Small biomass percentages outside the abovementioned standards do not compromise the functioning of the system.

[0030] In accordance with the represented embodiment, the wall 102 at the same time constitutes the bottom of the space 10 and the cover of the chamber 11.

[0031] In accordance with one embodiment of the invention, the drier 1 comprises an opening 14 in the upper part, for example in the cover 101. This opening 14 is adapted to receive the moist biomass entering in the drier l. In accordance with several embodiments, the drier 1 also comprises, in its top part, a stack 13. [0032] The extractor 15 is positioned below the level of the wall 102 which separates the space 10 from the chamber 11. The extractor 15 can comprise a screw 151, a Redler, a conveyor belt, or other linear transport means adapted for the purpose.

[0033] The extractor 15 of the biomass is positioned in a suitable, at least partially open channel 152, for example in the upper part, and thus communicating with the space 10 containing the biomass. The dimensions of the extractor 15 and related channel 152 are therefore sized on the maximum design size of the biomass. [0034] From this configuration, one has a counter- current drier, i.e. a very efficient drier. In fact the moist biomass enters into the top part of the drier 1 and exits from the bottom part thereof. On the other hand, the hot air enters from the bottom of the drier and exists from the top of the same, for example through the stack 13. [0035] In accordance with the embodiment of the drier 1 of figures 1-3 and 5, the air flow is generated by a fan 12 arranged so as to blow the air in the chamber 11. In accordance with other embodiments, the air flow could be generated in a different manner. For example, a fan and/or an ejector could be arranged on the stack 13 so as to suction the air from the space 10. Or the air flow could be simultaneously generated by a fan which blows in the chamber 11 and by a fan/ejector which suctions from the stack 13. [0036] With particular reference to figures 2 and 5 - 10, the mixer 67 adapted to sweep the wall 102 will now be described below in detail .

[0037] The mixer 67 comprises a ring gear 16 on which one or more furrowing elements 17 are mounted. The mixer 67 is preferably arranged on the bottom of the space 10. The ring gear 16 has a diameter substantially equal to that of the wall 102, and is therefore arranged in the peripheral zone of the wall 102. The furrowing elements 17 can for example be chains, cables, cords or rigid rods.

[0038] In accordance with the embodiment of figure 7, one end of the chain 17 is fixed to the inside of the ring gear 16 and the other end is fixed to a pinion 18. The pinion 18 and the ring gear 16 are rotatable around a common axis. In such a manner, the chain 17 is generically arranged along a radius of the ring gear 16.

[0039] In accordance with other possible embodiments, both ends of the furrowing element 17 are connected, at different points, inside the ring gear 16, without passing from a central pinion 18. In this configuration, the furrowing element 17 can be arranged along a cord, or in the absence of central bulk, along a diameter of the ring gear 16.

[0040] As seen in figure 4, the ring gear 16 is substantially parallel to the wall 102 and arranged immediately above it. In this manner, the chains 17 (or other furrowing elements) sweep the surface of the wall 102, being moved just a few centimetres from it. [0041] As seen in figures 4 - 6 and 10, the ring gear 16 is moved by a motor 40 by means of a gear wheel 20.

The continuous movement of the ring gear 16 and consequently of the chain 17 constantly mixes the biomass in the bottom zone of the space 10 where it is drier.

[0042] The continuous mixing of the biomass has various positive effects. First of all, it ensures the movement of the biomass itself towards the channel 152 of the extractor 15, which is fed by dropping. Then, it constantly breaks the bridges which can be formed in the biomass, bridges which could block the drop of the biomass itself into the channel 152 of the extractor 15.

Finally, the formation of preferential channels for the passage of the hot air is prevented, thus avoiding the loss of efficiency of the drying process.

[0043] The particular conformation described above for the mixer 67 allows reducing the forces which are generated in the furrowing elements 17 to a minimum. [0044] The conventional configuration of the furrowing elements (for example the rotatable screws of the prior art) requires affronting extremely high stress conditions in order to oppose the load exerted by the mass within which the furrowing element must proceed.

[0045] In the mixer 67 according to the invention, on the other hand, the presence of the ring gear 16 arranged on the outer circumference of the swept area, allows considerably lightening the furrowing elements. Finally, these are elements sized for essentially working via traction and can thus be much lighter than elements of equal length sized for opposing bending loads. For this reason, chains, cords or cables can be employed, while the possible rigid rods are intended for simple connecting rod function.

[0046] In accordance with one embodiment of the invention, the ring gear 16 is held in position by guide elements 19 arranged along its circumference. Such guide elements 19 allow a secure positioning of the ring gear 16, independent of its connection to a central pin. Such guide elements can comprise rollers 19, as is well illustrated in the attached figures 5 and 8-10. Otherwise, in other embodiments, the guide elements can be gear wheels, sliding blocks or other similar solutions .

[0047] In accordance with one embodiment, the position of the guide elements 19 is adjustable, mainly along the radial direction of the ring gear 16. [0048] In accordance with the embodiment of the attached figures, the ring gear 16 does not comprise a conventional cylindrical toothing with involute profile. Due to the large diameter of the ring gear 16 and the relatively non- stringent tolerances, a toothing has been advantageously chosen constituted by a series of pins 161 or rollers positioned along the circumference of the ring and spaced by the pitch defined by the gear wheel 20 moved by the motor 40. Such solution allows considerably limiting the manufacturing costs of the ring gear 16. [0049] In accordance with several embodiments, the drier 1 comprises a secondary extractor 30, similar to the extractor 15. The secondary extractor 30 is placed in the bottom zone of the chamber 11 and has the function of automatically extracting the dust and the biomass of smaller size than the minimum design size which could possibly fall from the wall 102 into the chamber 11.

[0050] In accordance with several non-illustrated embodiments, the drier 1 can be uncovered. In accordance with other embodiments, for example those of figures 1, 3 and 4, the drier 1 is closed by a cover 101. Such cover 101 accomplishes two functions: it prevents the entrance of meteoric water on the biomass, and at the same time it avoids the dispersion of dust in the environment. [0051] In accordance with several embodiments, the drier 1 comprises a treatment device of the air exiting through the stack 13. As a function of the current laws, it may in fact be necessary to remove the dust and/or possible polluting substances. [0052] The drier 1 according to the invention allows the treatment of biomasses, grains and the like, whether intended for the paper industry, for the production of energy or for the food sector .

[0053] With reference to figures 11 and 12, two biomass gasification plants will be described below which employ a drier 1 according to the invention.

[0054] The plant, in its minimum form of figure 11, comprises a drier 1 as described above and a gasifier. The moist biomass is inserted in the drier where the excess moisture is removed. The dry biomass exiting from the drier is fed to the gasifier. Inside the gasifier the biomass is transformed into fuel gas, which is in turn made available .

[0055] Upon exiting from the gasifier, the gas generally has a temperature in the range of about 600⁰C to about 700⁰C. In view of the subsequent uses, it must be cooled, thus making available a certain amount of heat. Such heat can be usefully employed for the functioning of the drier, in particular it can be supplied to the air flow entering into the chamber 11 of the drier. This plant configuration therefore allows exploiting a clear synergy between the drier and the gasifier .

[0056] The plant, in the embodiment of figure 12, comprises a drier 1 as described above, a gasifier and an internal combustion engine. The moist biomass is inserted into the drier, where the excess moisture is removed. The dry biomass exiting from the drier is supplied to the gasifier. Inside the gasifier, the biomass is transformed into fuel gas, which is then in turn supplied to the internal combustion engine. Inside the engine, the fuel gas is transformed into mechanical power which is in turn made available .

[0057] In addition to the heat provided by the gas, this plant type is capable of similarly exploiting also the heat deriving from the cooling of the cooling of the engine, as well as that contained in the exhaust gas. This plant configuration therefore allows exploiting a clear synergy between the drier, the gasifier and the internal combustion engine.

Claims

1. Drier (1) comprising:

- an upper space (10) adapted for containing the biomass;

- a lower chamber (11) for the diffusion of hot air; - a wall (102) for separating the upper space (10) from the lower chamber (11) , the wall (102) being adapted to support the biomass and to allow the passage of the hot air ;

- a mixer (67) adapted to sweep at least one portion of the wall (102) ; and

- an extractor (15) placed below the wall (102) , the extractor (15) being adapted for extracting the biomass from the space (10) .

2. Drier (1) in accordance with claim 1 moreover comprising, in the top part, an opening (14) adapted for receiving the entering moist biomass.

3. Drier (1) in accordance with any one preceding claim, wherein the extractor (15) is positioned in a suitable channel (152) which is at least partially open and communicating with the space (10) .

4. Drier (1) in accordance with any one preceding claim, characterised by a counter-current drying, i.e. wherein the moist biomass enters in the top part of the drier (1) and the dry biomass exits from the bottom part of the same, while the hot air enters from the bottom part of the drier and exits from the top part of the same.

5. Drier (1) in accordance with any one preceding claim, wherein the mixer (67) comprises a ring gear (16) on which one or more furrowing elements are mounted (17) .

6. Drier (1) in accordance with the preceding claim, wherein the ring gear (16) is arranged in the peripheral zone of the wall (102) .

7. Drier (1) in accordance with claim 5 or 6, wherein the furrowing elements (17) are elements sized for working essentially via traction and comprise chains, cables, cords or rigid rods.

8. Drier (1) in accordance with any one preceding claim from 5 to 7, wherein one end of the furrowing element (17) is fixed to the inside of the ring gear (16) and the other end is fixed to a pinion (18) , the ring gear (16) and the pinion (18) being rotatable around a common axis.

9. Drier (1) in accordance with any one preceding claim, wherein the ring gear (16) is substantially parallel to the wall (102) and arranged directly above it, such that the furrowing elements (17) sweep the surface of the wall (102) , being moved just a few centimetres from it.

10. Drier (l) in accordance with any one preceding claim, wherein the ring gear (16) is held in position by guide elements (19) arranged along its circumference, said guide elements (19) allowing a secure positioning of the ring gear (16) , independent of its connection to a central pin.

11. Drier (1) in accordance with any one preceding claim, wherein the ring gear (16) is moved by a motor (40) by means of a gear wheel (20) .

12. Drier (1) in accordance with the preceding claim, wherein the ring gear (16) comprises a toothing constituted by a series of pins (161) or rollers positioned along the circumference and spaced by the pitch defined by the gear wheel (20) moved by the motor (40) .

13. Drier (1) in accordance with any one preceding claim, moreover comprising a secondary extractor (30) placed in the bottom zone of the chamber (11) with the function of extracting the dust and the biomass of smaller size than the minimum design size which fell from the wall (102) into the chamber (11) .

14. Drier (1) in accordance with any one preceding claim, moreover comprising a fan (12) arranged so as to blow air into the chamber (11) .

15. Plant comprising a drier (1) in accordance with any one preceding claim, and a gasifier; wherein the heat contained in the gas produced by the gasifier is supplied to the air flow entering into the chamber (11) of the dryer (1) .

16. Plant comprising a drier (1) in accordance with any^¬ one claim from 1 to 13, a gasifier and an internal combustion engine; wherein the heat contained in the gas produced in the gasifier, the heat deriving from the cooling of the engine and the heat contained in the exhaust gas of the engine are supplied to the air flow entering into the chamber (11) of the drier (1) .