METHOD AND APPARATUS FOR HEATING ROCK MATERIAL

Abstract: The present invention relates to a method for heating rock material when concrete, asphalt mix and similar products are produced. According to the method, rock material is heated by the combined action of a heating unit (7) located above the conveyor and a heated heat-transmitting conveyor (6). Heat is transferred by the convection from the heated heat-transmitting conveyor (6) to the material that is being transported. Further, the invention relates to an apparatus for heating rock material. The apparatus comprises a heat-transmitting conveyor (6) which is heated, either merely by a heating unit (7) located above it, when the conveyor is not used for charging, or by a separate, additional heating device (9) or by a combination of the above mentioned alternatives.

Description: Method and apparatus for heating rock material The invention relates to a method for heating rock material, in which method rock material is conveyed by a conveyor, located between a feeding device and the production equipment, whereupon the rock material is heated by a heater arranged above it . Further, the present invention relates to an apparatus for heating rock material, which apparatus comprises a conveyor, located between the feeding device and the production equipment, and at least one heating unit arranged above the conveyor for heating the material that is conveyed by the conveyor. Rock material is used e.g. when concrete, asphalt mix and stone chips are produced. In the produc¬ tion process the rock material is heated to the tempera¬ ture required for production. Occasionally there is also a need for heating the rock material to dry it. A known solution is e.g. such that heat from an oil burner is used for heating and drying the rock material in a rotating drum. The heated rock material is conveyed to the production equipment for the actual product, where the rock material and the additive are mixed. When asphalt mix is produced the additive is bitumen. However, the solution in question produces emissions harmful both to people and the environment. Furthermore, the oil used in the apparatus has to be stored at the operation site, which is a risk factor. When the rock material is mixed and the fine particles dry, dusting constitutes another problem, which necessi¬ tates the use of expensive filtering equipment. More¬ over, the known equipment is sizeable, complicated and expensive . Furthermore, there are known solutions where asphalt material is heated by means of a heating appli- ance, arranged in connection with a conveyor, and where the asphalt is heated as it is conveyed forward by the conveyor. Finnish Patent Application 850 526 discloses a method and an apparatus for heating rock material, the apparatus comprising a conveyor on which radiators are placed that heat the rock material conveyed by the con¬ veyor. Furthermore U.S. Patents 4 256 414 and 4 Oil 023 and European Patent Applications 0 033 911 and 0 146 939 disclose apparatuses for heating and recycling used asphalt. In U.S. Patent 4 256 414 an apparatus is dis¬ closed that comprises a conveyor above which a heating device is provided. U.S. Patent 4 011 023 again disclo¬ ses an apparatus for lifting up weathered pavement material from the road, heating it and spreading it as new pavement material on the roadbed site, after an additive has been mixed into it. The apparatus comprises two conveyors, provided with heaters. The apparatus dis¬ closed in European Patent Application 0 033 911 com¬ prises two capacitive high-frequency heating units arranged above the conveyor. Further, European Patent Application 0 146 939 discloses an apparatus comprised of a conveyor screw for conveying crumbled asphalt and infrared heating devices provided above it. However, the drawback with the solutions mentioned above is that to be heated sufficiently the conveyor necessarily has to be made quite long or several conveyors must be employed, since enough heat cannot by using the methods in question, be transmitted to the material without impairing the quality of the material, when it is conve- yed only a short distance. If the surface temperature of the material is raised too high the material starts to fume or even burn. Moreover, the apparatus is large, complicated and expensive. It is an object of the present invention to provide a method for heating rock material that will make the processing of rock material effective and eco¬ nomical . Another object of the present invention is to provide a new type of apparatus for heating rock material, thereby avoiding the drawbacks of known solu¬ tions and making possible an effective processing of rock material . It is characteristic of the method of the pre¬ sent invention that the conveyor is heated, whereby the material will be heated both by a heating unit from above the conveyor and by heat transmitted by the heated conveyor. It is further characteristic of the apparatus of the present invention that the conveyor, located between the feeding device and the production equipment, is a heat-transmitting conveyor and that the heat-trans¬ mitting conveyor is arranged to be heated so that the material in the apparatus is heated both by the heating unit located above it and by heat from the heated heat- transmitting conveyor. It is an essential idea of the invention that the conveyor is heated so that the rock material fed to the conveyor to be transported, is heated by the com¬ bined heating effect from heaters placed above the con- veyor and by heat from the heated conveyor. Furthermore, the essential idea in an embodiment of the invention is that the conveyor is run empty, without a load of rock material, with the heaters on, whereupon the conveyor is heated. After that rock material is fed to the con- veyor and heated while it is being transported. The essential idea in yet another embodiment of the inven¬ tion is that the conveyor is heated by a separate heater, meant to be used exclusively for heating the conveyor. Furthermore, it is an essential idea in another embodiment of the invention that the surface of the conveyor intended for transporting the rock material is furnished with projections penetrating into the material, whereby heat transmission from the conveyor to the material is enhanced. The advantage of the solution of the invention is that the heating effect of the apparatus considerably improves when heat is transmitted to the material both from the heater above the conveyor and from the conveyor itself, that is, essentially through the whole interface formed by the material. Thus the apparatus can be made smaller which renders it easier to handle under field conditions. Moreover, the heating method of the inven¬ tion is more gentle for the material to be heated, as the required heat does not have to be transmitted through one surface layer only. The invention will be explained in greater detail in the accompanying drawings, where Figure 1 is a schematic representation of an asphalt concrete mixing plant, where an apparatus ac- cording to the embodiment of the invention is utilized for heating rock material, and Figures 2 - 4 show a schematic, cut-away side view of some conveyor apparatus of the invention for heating rock material. Figure 1 is a schematic representation of an asphalt mixing plant, where the solution of the inven¬ tion is utilized for heating rock material. The embodi¬ ment in question comprises a device 1 for feeding rock material and a heating device 2 for conveying and simul- taneously heating rock material. Additionally the mixing plant comprises production equipment 3, which is charac¬ teristically a mixing device. The asphalt apparatus further comprises transport conveyor means 4 for convey¬ ing prepared asphalt material, produced by the produc- tion equipment 3 , to a storage section 5 and further to the site of application. In the apparatus illustrated in the figure, production will take place so that rock material or e.g. weathered asphalt material, lifted up from the roadbed site, is fed into the heating device 2 by the feeding device 1, which heating device 2 com¬ prises a conveyor and means for heating the material fed to be transported by the conveyor while it is conveyed to the production equipment 3. The heating device 2 heats the material to the temperature required for pro- duction. The rock material can also be dried by heating it by means of the heating device 2. Thus the heating device 2 is arranged between the feeding device 1 and the production equipment . The material heated by the the heating device 2 and conveyed to the production equipment 3 is mixed there with the other ingredients of the product, e.g. bitumen. The production process can be cyclic; i.e. the production equipment 3 is charged with material fed by the heating device 2 and with other materials, fed by other transport means, after which charging is interrupted and the production process started. The production equiment 3 is a mixing device that mixes the charged materials. When the production batch is ready, it is conveyed by the conveyor 4 to the storage section 5 to remain there until it is transfer- red to the site of application. After this the phases of the cycle described above are repeated. The whole apparatus illustrated above can be constructed to be highly mobile so that it can be moved to the vicinity of the site of application. It is further possible that the plant comprises several heating devices 2 and it is also possible to arrange weighing or handling appliances or intermediate storage between the feeding device 1 and the production equipment 3. Figures 2 - 4 show a cut-away side view of some heating devices 2 of the invention, presented in a sche- matical, simplified way. The heating device 2 shown in figure 2 comprises a heat-transmitting conveyor 6, pre¬ ferably a slat conveyor, but it can also be any other type of conveyor providing an equivalent function and forming a closed loop. Heating units 7, e.g. infrared units or similar radiant heaters, are arranged near the heat-transmitting conveyor 6, preferably above the heat- transmitting conveyor 6. Preferably liquid gas is used to provide heating energy, but other energy sources may also come into question. The number of heating units 7 and their power is designed to meet the heat require¬ ments and suit the dimensions of the heating device 2. The heating device 2 is preferably fitted inside a cover, illustrated in figure 4. The heating device 2 illustrated in figure 2 is continuously working and it is cyclically charged from the feeding device 1 with material to be heated and transported. When the cycli¬ cally working production unit 3 is not charged with material by means of the heating device 2, the heating device 2 is run empty, without transported material, while the heating units 7 are working and heating the heat-transmitting conveyor 6. The heat-transmitting conveyor 6 stores heat in its structure. When the pro¬ duction equipment 3 has turned out the previous lot, it is emptied and recharging begun. Now feeding device 1 is charging material to the heat-transmitting conveyor 6, by which it is conveyed toward the production equip¬ ment 3, while the material is simultaneously heated by the heating units 7, arranged above the heat-transmit- ting conveyor 6. What is essential is that in accordance with the idea of the invention, the material is heated also by heat transmitted to it from the structure of the heated heat-transmitting conveyor 6. Figure 3 again shows an embodiment of the heat- ing device according to Figure 2,wherein the heat-trans- mitting conveyor 6 is arranged to be heated, in addition to the heating units 7 arranged above the conveyor, by separate, additional heaters 9, which can be con¬ structed like the heating units 7. The additional heat- ing units 9 can be arranged, as illustrated in the fig¬ ure, to heat the empty part of the heat-transmitting conveyor 6 below the conveyor part that returns empty. Thus it is possible to heat the heat-transmitting con¬ veyor 6 continuously, also when it is used for charging the production equipment 3. So this solution can be applied, not only in cyclical operation, but also in situations where continuous recharging is required. Further Figure 4 shows an embodiment of the heating device of Figure 2, where the additional heaters 9 are arranged inside the closed loop formed by the heat-transmitting conveyor 6, in the space between that part of the conveyor that is conveying the material and the part that is returning empty. Preferably the addi¬ tional heaters 9 heat the empty part of the heat-trans- mitting conveyor 6 from the inner side of the conveyor part that returns empty, i.e. the side that is not meant to lie against the material to be conveyed, as illus¬ trated in the figure. The additional heaters 9 are pre¬ ferably positioned so that the heating effect is directed downwards, which prevents material possibly dropping from the heat-transmitting conveyor 6 from entering the additional heater 9 and catching fire there. It is also shown in the figure that protrusions 10 are provided on the surface of the heat-transmitting conveyor 6 that lies against the material, to improve heat transmission from the heat-transmitting conveyor 6 to the material. The protrusions 10 can be either fixed or replaceable elements protruding from the sur¬ face of the heat-transmitting conveyor 6. Preferably the protrusion 10 is of a laminar construction so that its heat-emitting surface is large. The protrusion 10 can also comprise e.g. a lattice and form a kind of grate. Further, if the conveyor is arranged to slope enough vertically, a mixing of the material can be achieved with these protrusions 10. Due to the additional heaters 9, the apparatus in Figure 4 can be used both for cycli¬ cal and continuous charging. Additionally, a cover 8 is shown in the figure, which can be insulated to minimize energy consumption and be provided with devices for removing gases, formed during the heating process, from inside the cover 8. The gases are sucked out by a fan 11 and led to the feeding device 1 through a duct 12. The air heated in the heating device 2 is thus being utilized for preheating the material and simultaneously air impurities like dust and harmful gases are bound to the charged material. A filtering apparatus can be arranged in the duct 12 for removing impurities. Although the invention has been described in the foregoing with reference to examples in accordance with the accompanying drawings, it is obvious that the invention is not restricted merely to them, but can be modified in many ways within the scope of the inventive idea disclosed in the claims. Thus the invention is also suitable for heating a ready mixture like rock material and bitumen, for example. In the same way, it can also be used for heating and handling materials other than rock materials. The invention to which the application relates can be implemented in conveying and simulta¬ neously heating plastic, glass and similar materials. Further, the invention can be implemented in processing and drying waste liquor from the paper industry. It is also possible that the apparatus comprises the addi¬ tional heaters arranged both as shown in Figure 3 and in Figure 4, which will make the heating of the heat- transmitting conveyor very effective.

Claims: Claims 1. A method for heating rock material, in which method rock material is conveyed by a conveyor, located between a feeding device (1) and production equipment (3) , wherein the rock material is heated by a heater ar¬ ranged above it, c h a r a c t e r i z e d in that the conveyor is heated, whereby the material will be heated both from above the conveyor and by heat from the heated conveyor. 2. A method according to claim 1, c h a r a c¬ t e r i z e d in that the rock material is heated by means of a heating unit (7) and the conveyor used in a cyclical manner so that the conveyor, as it is running empty, is first heated by the heating unit (7) , and when the conveyor has been heated enough, material is fed to the conveyor by the feeding device (1) to be heated by the combined action of the heat from the heating unit (7) and heat transmitted by the conveyor as the material is conveyed to the production equipment (3) by the con¬ veyor. 3. A method according to preceding claim 1 or 2, c h a r a c t e r i z e d in that the conveyor is heated by an additional heating device (9) separate from the heating unit (7) . 4. An apparatus for heating rock material, which apparatus comprises a conveyor located between a feeding device (1) and production equipment (3) and at least one heating unit (7) , arranged above the conveyor for heating the material transported by the conveyor, c h a r a c t e r i z e d in that the conveyor located between the feeding device (1) and the production equip¬ ment (3) is a heat-transmitting conveyor (6) and that the heat-transmitting conveyor (6) is arranged to be heated in such a way that the heating of the material in the apparatus is accomplished both by the heating unit (7) located above it and by heat from the heated heat-transmitting conveyor (6) . 5. An apparatus according to claim 4, c h a r- a c t e r i z e d in that an additional heating device (9) is arranged to heat the heat-transmitting conveyor (6) . 6. An apparatus according to claim 5, c h a r¬ a c t e r i z e d in that the additional heating device (9) is arranged to heat that part of the heat- transmitting conveyor (6) underneath the heat-trans¬ mitting conveyor (6) that is free from material. 7. An apparatus according to claim 5, c h a r - a c t e r i z e d in that the additional heating device (9) is arranged inside the closed loop formed by the hea -transmitting conveyor (6) . 8. An apparatus according to any one of the preceding claims 4 - 7, c h a r a c t e r i z e d in that the heat-transmitting conveyor (6) is charged cyc- lically and that the heat-transmitting conveyor (6) is arranged to be heated by means of the additional heating device (9) and/or by the heating unit (7) while it is empty. 9. An apparatus according to any one of claims 4 - 8, c h a r a c t e r i z e d in that that surface of the heat-transmitting conveyor (6) , which lies against the material is provided with protrusions (10) that improve heat transmission from the heat-transmit¬ ting conveyor (6) to the material. 10. An apparatus according to any one of claims 4 - 9, c h a r a c t e r i z e d in that the heating device (2) comprises an insulated cover (8) , a duct (12) leading from the cover (8) to the feeding device (1) , and a fan (11) for conducting gases and heat produced in the heating device (2) to the material in the feeding device (1) .

Inventors: HEIKKINEN HANNU, KARILAINEN MATTI, HEIKKINEN, HANNU, KARILAINEN, MATTI
Applicants: AMOMATIC OY, HEIKKINEN HANNU, KARILAINEN MATTI, HEIKKINEN, HANNU, KARILAINEN, MATTI
Application year: 1996
Main classification: E01C19
IPC codes: E01C19, F26B3