METHOD AND SYSTEM FOR DRYING SOLID FUELS

Abstract: The system according to the invention comprises a receiving unit (1), from which the fuel is transferred to a drying unit (2), where the fuel is dried by solar-heated air, which is taken from solar collectors, which are arranged in the roof structure (13) and a portion of the wall structure (12) of a storage unit (3), to which the fuel is transferred after its drying. The drying preferrably is carried out on a drying table (8) having a surface, which for example may amount to one eightieth of the total surface of the solar collectors. The volumes air/ time unit produced in the solar collectors, thus, are great. This implies that the drying of the fuel is effected relatively quickly.

Description: - - Method and system for drying solid fuels This invention relates to a method and a system for drying and storing solid fuels, especially chips. Other fuels, which can be dried in the system, are bark, peat, dry refuse etc. The aforesaid fuels become ever more attractive, because oil increases in price and is available only with difficulty. A great disadvantage of said fuels, however, is their high moisture content, which implies high fuel consumption as well as poor boiler efficiency degree. Besides, considerable breakdowns can occur, especially in wintertime. A reduction of the moisture content in the fuel, therefore, yields substantial gains in the form of de¬ crease in fuel consumption, higher efficiency degree and safer operation. The reduced fuel consumption is favour¬ able from several aspects, a.o. due to less competition with industry on wood products, but also other advantages are obtained, for example from a handling, storage and transport point of view. The conλ'-entional technique closest related to the present invention is the drying of fuels outdoors, which is possible, however, only during two to three summer months, reduces the moisture content only to about 50 and, besides, is difficult to control. The present invention has the object to produce a system of the kind referred to in the introductory portion above, at which the fuel is dried in a-n automated and controlled way by utilizing solar energy. The object of the invention is achieved in that the method and system according to the invention have been given the characterizing features defined in the attached claims. An embodiment of the invention and of units com¬ prised therein is described in the following, with reference to the accompanying drawings, in which Fig- 1 is a.front view of a system according to the in¬ vention, Fig. 2 is a horizontal view of the system shown OMPI in Fig. 1 , Fig. 3 is an end view of the system according to Fig. 1 ,, Fig. 4 shows in a schematic manner en embodi¬ ment of a drying table comprised in the drying unit, ' Fig ___. 5 show τ s in a schematic manner an embodiment of a roof and wall structure of the storage unit,- and Figs. 6 and 7 are perspective views of alternative embodiments of the system according to the invention, certain portions of which are removed for reasons of clearness. The system shown in Figs. 1-3 comprises a receiving unit 1, a drying -unit 2 and a storage unit 5. The re.ceiving unit 1 comprises a bin 4, into which the material, preferably chips, to be dried is dumped, for example from a truck. A conveyor screw 5 transfers the material from the bin 4 to two silos 6. The conveyor screw means 5 is designed so that the material can be transferred optionally to either of said silos 6. The silos serve as buffers which, for example, can be filled before a holiday whereafter the system can be operated during the holiday, and they also serve for distributing the material according to type, moisture content, size etc. The contents in the silos 6 thereafter possibly can be mixed in desired proportions when being fed into the drying unit 2. From the silos 6 additional conveyor screw means 7 extend to the drying unit 2. In said drying unit 2 a drying table 8 is proλ'ided, on which the material is dried and thereafter trans¬ ferred to the storage unit 3. The structural design of the drying table 8 is described in greater detail in the following with refer¬ ence to Fig. 4. From the drying unit 2 the material is transferred via conveyors in the storage unit to the desired place therein. Said conveyors may have different design. At the embodiment shown the material is distri- buted by belt conveyors 9, 10 and ' travelling conveyors 11 to the desired place in the storage unit 2. By using travelling conveyors, the material can be spread in a O controlled manner to form uniform layers, whereby it is ensured that the material delivered from the storage unit has a substantially constant moisture content. The wall 12 of the storage unit 3 facing southward to the drying unit 2 and the roof structure 13 facing southward are designed as solar collectors. Air flowing through these channels is heated by the sun and there¬ after it is used for drying the fuel material. The design in detail of the wall 12 and the roof structure 13 in question is described below with reference to Fig. 5. The remaining walls of the storage unit are not insulated. The drying table 8 shown in Fig. 4 includes a re¬ ceiving bin 14, through which the material is supplied. Said receiving bin 14, which is provided ivith a control door 14a, opens on a feed means 15, which comprises a number of hydraulic cylinders 16, from which long piston rods 17 extend, on which drivers 18 are provided, which have the form of triangular members extending perpendi¬ cularly to the longitudinal, direction of the piston rods 17. The piston rods 17 with drivers 18 rest on a perforated table 19, which is supported on beams 20. The holes in said table 19 are not shown for reason of clearness. Below the table 19 a space 21 is formed,into which heated air from the solar collectors are introduced by means of a fan 22. From said space 21 the heated air is pressed through the b * ed 24 of material to be dried. At the throw-off end of the feed means 15 a conveyor screw means 25 is provided, which passes the dried ma¬ terial to the storage unit 3. The control of the drying process which depends on the moisture content, consistency etc. of the material supplied, can be effected in several different ways. One control possibility, for example, is the adjust¬ able door 14a, through which the thickness of the bed at the discharge from the bin 14 can be varied. OMPI Another possibility of controlling " the drying process is by varying the speed for the reciprocatory piston rods 17. In this connection can be imagined also that the height of the drivers 18 is varied. 5 A further possibility of controlling the drying pro¬ cess is by adjusting the air amount per time unit supplied for the drying process. It also can be imagined to vary the number and/or size of the holes in the table 19, though this will be 10 difficult to realize in practice. The aforesaid exemplified control possibilities imply that the drying always can be carried out at optimum. In Fig. 5 the structural design of wall 12 of the storage unit 3 facing toward the drying unit 2 and the 15 roof structure 13 of the storage unit are shown in a schematic manner. As mentioned above, the wall 12 and the roof structure 13 are designed as solar collectors and, therefore, oriented southward for obtaining the best possible solar collector effect. 20 At the embodiment the roof structure 13 is provided a surface layer 26 of light-permeable mate¬ rial. Inside of this surface layer 26 an air passage 27 is provided, in which an absorbator 29 provided with holes 28 is attached, λvhich is cooled by the air when 25 flowing according to the arrow τ s indicated. On the inside of said air passage 27 an insulation layer 29 is located. The wall 12, like the roof structure 15, has a sur¬ face layer 30 of light-permeable material. Inside of 30 this surface layer 50 an air passage 31 is provided, in which an absorbator 33 provided holes 32 is attached. The holes 32 decrease in size doλvnward in order to render possible air flow according to the arrows indicated. 35 Inside of the air passage 31 -an air tunnel 34 is formed, in which fans 55 are attached. The air tunnel 34 is defined to the storage space by an insulation OM layer 36. In operation, outdoor air enters through the openings 56 and 57, flows through the passages 27 and 51 according to the arrows, is heated and thereafter is sucked by the fans 55 into the air tunnel 34 in order to be passed to the drying unit 2. In Fig. 6 the system shown in Figs. 1-3 is shown in a perspective manner, where a -portion of the roof surface has been removed for showing the interior of the storage space 5. In Fig. 7 another embodiment of the invention is shown. As appears from Fig. 7, there is no wall facing southward, but only a roof half 57 facing southward is provided which is designed as solar collector. The transfer of the dried material from the drving unit 2 to the storage unit 3 is carried out by a conveyor screw means 38 whereafter the material is discharged on a belt conveyor 59, from which the material by means of a scraper is caused to fall down. By utilizing the angle of repose, a uniform spread of the material forming a stack is obtained. This ' type of system can be used only at plants of smaller size, because otherwise the height of the storage unit 5 will be too high. It is, thus, characteristic of systems according to the invention that the ratio between the total sur¬ face of the solar collectors and of the drying table is very great, in a normal case about 80:1. This implies that the process is a quick-drying process, because the total volume of heated air / time unit produced in the solar collectors is verv great. In a system, for example, the total surface of the solar -> collectors can be about 16 000 m " . hile the drving table - has a surface of about 200 m " . Systems of the aforesaid type are in operation about eight months a ear, preferably from March to October, which, however, varies according to geographic OMPI conditions . The system according to the invention, thus, implies that a larger storage building can be utilized combined as solar collector and as a seasonal storage for fuel. The invention, of course, is not restricted to the embodiment described above. It can be imagined, for example, to provide more than two silos for receiving material, so that more types and/or qualities of material can be mixed prior to the drying. The invention can also in other respects freely be λ'aried the scope of the attached claims. O

Claims: What I claim is: 1. A system for drying and storing solid fuels, especially chips, c h a r a c t e r i z e d in that it comprises a receiving unit (1), a drying unit (2) with a drying table (83 provided with holes and with means (16, 17, 18) for advancing a layer of the fuel along the drying table (8) , a storage unit (3) , means (7) for transferring the fuel from the receiving unit (1) to the drying unit (2), means (9, 10, 11) for transferring and spreading the dried fuel from the drying unit (2) to an optional place in the storage unit (3), that a portion of the walls (12) and the roof structure (13) of the storage unit (5) are designed as solar collectors in such a manner, that the total surface of the solar collectors is at least fourty times greater than the surface of the drying table (8) , and means (34, 55) are provided to pass the air heated in the solar collectors to the drying table (8) , and means (21, 22, 23) are to press the air through the holes in the drying table (8). 2. A system as defined in claim 1, c h a r a c t e r¬ i z e d in that the receiving unit includes a bin (14), into which the fuel is dumped, and one or more silos (6), to which the fuel is transferred by a conveyor screw means (5) . 5. A system as defined in claim 1 or 2, c h a r c¬ t e r i z e d in that the advancing means of the drying table (8) consists of a plurality of double-acting pres¬ sure medium cylinders arranged to the side of each other, and piston rods (17) extending from said cylinders (16), on which rods drivers (18) are attached. 4. A system as defined in claim 5, c h a r a c¬ t e r ! z e d in that the pressure medium cylinders (16) can be operated with variable speed. 5. A system as defined in any one or more of the claims 1-4, c h a r a c t e r i z e d in that the drying unit (2) includes a receiving bin (14) with adjustable discharge. ^^jTREA " OMPI 6. A system as defined in any one or more of the claims 1-5, c h a r a c t e r i z e d in that the means provided for pressing air through holes in the drying table (8) can operate w 7 ith varying speed. 7. A system as defined in any one or more of the claims 1-6, c h a r a c t e r i z e d in that the means for transferring and spreading the dried fuel from the drying unit (2) to the storage unit (3) consist of con¬ veyors (9, 10, 11) combined with scraper means. O

Inventors: MOSTROEM R
Applicants: MOSTROEM R
Application year: 1980
Main classification: F26B3
IPC codes: C10F5, F26B3