A METHOD OF HEAT TREATING PARTICULATE MATERIALS AND HEATER FOR USE IN PERFORMING THE METHOD

Abstract: In connection with heat treatments of particulate materials, primarily organic material such as grains and seeds, the particles of the material are caused to move in a floating or falling state in a treatment area (15). While floating in the treatment area, the particles are heat treated or thermally processed by emitting into the treatment area a heat flux which includes an increased proportion of radiant heat and thereby provides an intensive heating of the individual particles. A heater, in particular for use as heat source comprises at least one burner (16) which is mounted in a heater mantle (10) defining a flame chamber (12) and a heat discharge opening (14). The burner (16) is directed towards a mantle wall portion (18) which is located opposite to the heat discharge opening (14), and the inner surface of the mantle wall portion (18) consists of or is lined with a fireproof material which has the ability to glow and thereby provide heat radiation through the discharge opening (14).

Description: TITLE: A Method of Heat Treating Particulate Materials and Heater for Use in Performing the Method . The present invention relates to a method of heat treating or processing particulate materials, primarily but not exclusively, organic materials such as grains and seeds, the method comprising the step of causing the particles of the material to move in a float¬ ing or falling state in a treatment area. As used herein , the term "particulate materials" should be interpreted In a broader sense and should not be regarded as restrictive with respect to the shape, size and nature of the particles concerned. Thus, pulverulent materials or granulated materials can be treated in accordance with the invention as well as natural particulate materials such as grains or seeds. Conventionally, various pulverulent and particulate materials have been subjected to heat treatment, in particular drying , while maintained in a fluϊdϊzed state in a treatment area. The heating methods previously used in this connection have comprised either direct heating by directing one or more burner flames into or to- wards the treating area, or various forms of indirect heating e. g . by causing the hot combustion gases from burners to exteriorly sweep and thereby heat walls which define the treatment area. Generally such heating methods have operated efficiently In connection with usual drying of materials including organic materials . In particular traditionally constructed drum dryer plants have been successfully used for drying e. g . grain or comminuted green crops such as grass. German Patent No. 2,833,872 discloses an example of a known drum dryer plant for drying organic materials . Recently, however, still increasing interests have arisen with respect to particular heat treatments or thermal processings of par¬ ticulate organic materials, whereby specific effects or changes are provided to the interior structures of the particles . These special thermal processings are based on or require a very intensive and simultaneously uniform heat transfer to the individual particles . In other words, great amounts of heat should be transferred to the individual particles within a minimum period of time, and the heating methods previously used have shown to be quite insufficient for that purpose. One example of such special heat treatments is geiatϊπization of starchy materials such a grains. During this treatment or pro- cessϊng, a decomposition of starch takes place to more digestible forms which are easier to assimilate in the intestinal canal of single- stomach species of animals such as young pigs and fur-bearing animals. When heating e. g . a grain, there will be an evaportϊon of water from the surface of the grain , and this results in a diffusion of water from the interior of the grain towards the surface thereof. Regarding the rate of heat transmission to the interior of the grain, the decisive factor is mainly the heat transfer from air to the grain surface, whereas it is the diffusion rate which determines the rate of water evaporation . The water diffusion rate is substantially lower than the heat transmission rate, and this is the reason why the temperature can become very high in the interior of the grain at the same time as the water contents in the interior of the grain still is relatively high . Thus, with sufficiently high heating rates, the water contents would not have sufficient time to diffuse and evapo¬ rate and with sufficiently increased temperatures in the interior of the grain , the water vapour pressure can be sufficient to provide or cause burstings of cells in the grain . Other examples of such special thermal treatments are toasting of soya beans which is necessary in order to utilize the entire nu¬ tritional value of soya beans, and thermic protein protection or enzyme inhibition, whereby the normally extensive decomposition of proteins in the first stomach of ruminants can be reduced or delayed . On the above background, it is a general object of this invention to provide a method of heat treating particulate materials with an intensive and uniform transfer of heat to the individual particles . Another object of the invention is to provide a method of heat treating which is controllable or adjustable to practise more special thermal processings of organic materials as those mentioned above. These objects are accomplished by the method of this invention which is characterized by comprising the step of emitting through the treatment area a heat flux which includes an enhanced ratio of radiant heat and emanates from a heat source centrally arranged relative to the treatment area . Thus, the enhanced heat radiation Is very desirable and ad¬ vantageous in connection with several thermal processes, since a high proportion of radiant heat will be provided and ensures a fast heating of the particles to be treated. This is important because of the fact that the natural or Inherent contents of water frequently take part in the processes which are to be obtained by the treat¬ ment. Consequently, in order to optimize the effects or treatment results and also in order to avoid destruction of the product or particles, It is important that heat is transferred to the interior of the particles at a rate which is sufficient to prevent that the water contents would have the possibility to evaporate to an excessive extent. Any heat flux emmanating from traditional heat sources will include at least some radiant heat. However, in connection with the invention , the ratio or proportion of radiant heat in the heat flux used should at least be appreciably enhanced or increased over the ratio or proportion which normally is present in the heat flux from conventional heat sources such as oil or gas burners . I n accordance with a preferred embodiment of the method of the invention, the particles are tumbled in a rotary drum which receives the heat flux axially through one end thereof. In this manner, the particles are moved at least temporarily and repeatedly along a, generally descending, predominant direction of motion which is transverse to the principal , generally axial , direction of the heat flux. By repeatedly moving the particles in cross-flow with the heat flux in this manner, it is possible to obtain that each particle eventually will have received a uniform heat radiation over the entire surface. The present invention also relates to a heater apparatus, in particular for use as heat source in practising the method of the invention . The heater apparatus comprises at least one fuel or gas burner device arranged in a mantle which defines a flame chamber and a heat discharge opening . I n conventional heaters of this type which are used e. g . in connection with usual drying of grain , the burner device is located in a rear wall of the mantle and is directed towards an oppositely located heat discharge opening. In such heaters, the ratio or proportion of radiant heat has been esta- blished to be In the order of 20%. The heater of the invention is characterized by the burner device being directed towards a mantle wall portion which is located opposite to said the discharge opening, at least the inner surface of the mantle wall portion consisting of or being lined with a material having the ability of glowing . By appropriately choosing the glow material for the mantle wall portion it has been established that the ratio or proportion of radiant heat can be increased to about 40% of the discharged energy. However, the contents of radiant heat can be further increased by increasing the heater temperature e.g . by preheating the combustion air by exchange of heat with the com¬ bustion products. The heater of the invention could be considered as a "spot¬ light" which emits a beam of heat radiation through the heat discharge opening . Such a beam of radiant heat may be useful for other heating purposes but is particularly useful for emission into a particle treatment area in accordance with the method of this invention . The treatment area may be defined by suitable chamber- -defϊnϊngs walls or structures, but preferably, the heater of the invention is combined with a rotary drum with the heat discharge opening of the heater communication with or debouching into one end of the drum . In a particular embodiment, the heat discharge opening commu¬ nicates with the interior of the rotary drum via an intermediate annular connecting mantle which includes means for feeding parti¬ culate material into the interior of the rotary drum. With this em¬ bodiment, it is possible to continuously perform heat treatments of particles in accordance with the method of the invention , including drying of such particles . Further aspects and advantageous features of the present invention will become apparent from the following description of particular embodiments in conjunction with drawings in which OMPI Figure 1 is a schematic sectional view showing an embodiment of the heater of the invention , and Figure 2 Is a schematic sectional view showing a further embo¬ diment of the heater of the invention combined with a rotary drum for continuous heat treatment of particulate material in accordance with the invention . Referring now to the drawings, Figure 1 thereof illustrates a sectional view through an embodiment of the heater of the invent¬ ion . A mantle 10 defines a flame chamber 12 and a heat discharge opening 14. In the wall of the heater mantle there are mounted one or more burners 16 directed towards a mantle wall or wall portion 18 which is located opposite to the heat discharge opening 14. The inner side of the mantle wall 18, which will be heated by the burners 16, is made of or lined with a fireproof material which .will be caused to glow by the heat from the burners 16. Preferably, the entire mantle 10 is made of the fireproof material . Accordingly, and as indicated in Figure 1 , the heater will discharge heat through the opening 14 and the discharged heat includes an increased pro¬ portion of radiant heat due to the glowing fireproof material . The mantle wall 18 operates in other words as a source of radiant heat which discharges a relatively steady or uniform heat flux through the opening 14. The mantle 10 may be shaped in par¬ ticular manners, e.g . tapering, in order to control or direct the discharged radiation . Similarly, the inner surface of the mantle wall 18 may also be shaped in particular manners, e. g . as a parabolic surface. Figure 1 also includes schematic indications of conduit systems whereby combustion air for the burners 16 can be preheated by exchange of heat with the combustion products or exhaust gases from the flame chamber 12. A preheating of the combustion air will result in a higher heater temperature and thereby provide a further increase of the heat radiation . Regarding the fireproof material it is advantageous to make use of a material which , in addition to having the ability to glow, also is an effective heat Insulator. Moreover, the material should suitab¬ ly have a low heat capacity and provide a good heat transfer be¬ tween the material and combustion gases from the burners 16. Specific types of known ceramic fibrous materials are very suitable. Comparative tests made with a heater in accordance with the Invention and a corresponding heater in which the burners were located centrally in a rear wall (corresponding to wall 18) of the mantle have shown that the heater of the invention supplies as much as 40% of the discharged energy as radiant heat, whereas the known heater only supplied 22% of the energy as heat radiation . Accordingly, the particular design of the heater of the invention provides a substantial increase as to the ratio of radiant heat In the discharged heat flux. A heater as that shown in Figure 1 is very suitable for vari¬ ous heating purposes e.g . within the ceramic Industry. In parti¬ cular, if the entire mantle 10 is made of fibrous material , possibly enclosed by an outer wail of steel plates, the heater will have a very low weight. Moreover, the combustion will be of high quality due to the very hot walls and the high degree of turbulence in the flame chamber 12. As mentioned above, the mantle 10 or the inner surfaces thereof can be shaped in particular manners. In addition , the mantle can be generally box-shaped with a rectangular opening 14. However, the overall configuration of the mantle 10 is preferably cylindrical with a circular heat discharge opening or outlet 14. As indicated in Figure 1 , the heater of the invention is parti¬ cularly useful for emitting a heat flux with increased contents of radiant heat into a treatment area 15 for heat treating or thermally processing materials in accordance with the method of the invention. Various chamber-defining designs are possible to provide the treat¬ ment area 15. The decisive feature is that provisions should be made to maintain or move individualized particles in a generally floating or falling state while the particles are being heat treated in the area 15. The chamber or structures which defines the treatment area 15 can be adapted for treating the material in charges or for continuous through-flow of material . Reference is now made to Figure 2, which schematically ilfu- strates an embodiment of the heater of the invention combined with a rotary drum 26. The heater shown includes a recuperative burner 20 including means for preheating the combustion air. The heater discharge opening 14 communicates with a stationary connection mantle 22 which is provided with means for feeding particulate materials as indicated at 24. The connecting mantle 22 opens into one end of the rotary drum 26 and the respective inner diameters of the heater mantle 10, the stationary connecting mantle 22 and the drum 26 are preferably substantially equal to each other. However, in order to protect possible transport vanes 28 on the Inner surface of the drum 26, the annular connecting mantle 22 may include a radiation shield member 23 projecting from and extending circumfe- rentlally of the inner surface of the connecting mantle 22. With an appropriately inclined orientation of the axis of rota¬ tion of the drum 26 and possibly by means of the vanes 28, the material will be moved to the opposite end of the drum 26, wherein the material is discharged to an outlet possibly shaped as a lockage -chamber. During the transportation through the drum 26, the parti¬ culate material is tumbled and to a wide extent maintained in a freely flowing state in the interior of the rotating drum 26. In this floating state, the particles are subjected to the heat radiation from the heat discharge opening 14, and an effective and uniform heat treatment of the particles can be performed in this manner. During the transportation through the drum 26, the individual particles will most probably be impinged by the heat radiation several times and under different angles or lines of incidence. Although particular embodiments of the invention and modifica- tlons thereof have been described above for illustrative purposes, it will be understood that further modifications and structural changes may be made without departing from the spirit and scope of this invention .

Claims: CLAIMS : 1 . A method of heat treating particulate materials, primarily organic materials such as grains and seeds, the method comprising the step of causing the particles of said material to move in a float- ing or falling state in a treatment area, and the method being CHARACTERIZED by further comprising the step of emitting into said treatment area a heat flux which includes an enhanced ratio of radiant heat and emanates from a heat source centrally arranged relative to said treatment area. 2. A method as defined in claim 1 , CHARACTERI ZED by moving said particles, at least temporarily, along a general or predominant direction of motion which is transverse to a principal direction of said heat flux. 3. A heater, in particular for use as said heat source in prac- tising the method of claim 1 or 2, the heater comprising at least one fuel or gas burner device (16) arranged in a mantle (10) which defines a flame chamber (12) and a heat discharge opening (14), and the heater being CHARACTERIZED by said burner device (16) being directed towards a mantle wall portion (18) which is located opposite to said heat discharge opening (14) , the inner surface of at least said mantle wall portion (18) consisting of or being lined with a material having the ability of glowing . 4. A heater as defined in claim 3, CHARACTERI ZED in that said heat discharge opening (14) communicates with one end of a rotary drum (26) . 5. A heater as defined in claim 4, CHARACTERIZED in that said heat discharge opening (14) Is circular and has a diameter which Is substantially equal to the inner diameter of said rotary drum (26) . 6. A heater as defined In claim 4 or 5, CHARACTER I ZED in that said discharge opening (14) communicates with the interior of said rotary drum (26) via an intermediate, annular connecting mantle (22) including means (24) for feeding particulate material Into the Interior of said rotary drum (26) . 7. A heater as defined in claim 6, CHARACTERIZED in that said annular connecting mantle (22) includes an annular radiation shield member which projects from and extends circumferential ly of an interior surface of said connecting mantle.

Inventors: KAU MIKAEL, SCHMIDT FLEMMING, KAU, MIKAEL, SCHMIDT, FLEMMING
Applicants: DANTOASTER APS
Application year: 1984
Main classification: F26B3
IPC codes: F23C7, F26B3, F26B11