HEATING DEVICE FOR HEATING A CONTINUOUSLY, FLUIDIZED MATERIAL FLOW WITH INFRARED RADIATION AND PREHEATED AIR

Abstract: In an apparatus for continuous heat treatment, a mechanically fluidized stream of material consisting preferably of a granular or highly viscous material is heated in a rotating chamber in co-current with heat energy originating from a burner (1), in which solid, liquid or gaseous fuel is burned. A portion of the energy liberated by the combustion heats the internal part of a thin-walled chamber (5), the external part of which at the material inlet (10) transfers energy to said stream of material in the form of radiant heat. The remaining portion of the energy liberated by the combustion, bound in the exhaust gases from the combustion process, are subjected to heat exchange in a primary convective heat exchanger (7) and one or more secondary heat exchangers (8) in counter-current with a gaseous process medium, preferably atmospheric air, said process medium transferring further energy to said stream of material in the form of convective energy.

Description: HEATING DEVICE FOR HEATING A CONTINUOUSLY, FLUIDIZED MATERIAL FLOW WITH INFRARED RADIATION AND PREHEATED AIR, TECHNICAL FIELD The invention relates to an apparatus for continuous intensive heat-treatment of a stream of material consisting of granular or highly viscous substances. BACKGROUND ART Heat treatment of granular or highly viscous substances, such as grain, other vegetable seed crops, nuts, spices, flavourings, meat, bone pieces as well as porridge-like and pasty substances and the like is well-known technology. The purpose of a heat-treatment of e.g. the above-mentioned materials may be dehydration (drying), germ reduction, sterilizing as well as developing e.g. positive effects with regard to digestibility, or other expedient chemical, bio-chemical and/or physical changes etc., and further, combinations of the above examples. It is known technology (cf. e.g. patent applications Nos. 5276/83 and 6408/88) that the above heat treatment takes place in a rotating chamber, into which the material has been brought in a mechanically fluidized state. Further it is known technology that the supply of energy advantageously can take place in co-current with the stream of material by means of a combination of intense radiant heat from a flame body and/or a heated surface, as well as convective heat transmission from the exhaust gases and heated air. The advantages of the above-mentioned technology are inter alia to be found in a very flexible process adaptation covering the interval from gentle drying to intense heat-treatment of the material by heating to a high temperature (130-170°C) in a short period of time (on the average 30-360 seconds), a small surplus of air and hence good energy economy, as well as the possibility of heat-treating materials of widely differing consistency, extending from free-running, grainy particles (also of fine grain) to paste-like or porridge-like substances. The known technology is, however, limited by the fact that the exhaust gases from the combustion process make contact with the product being treated in a state, where they are more or less diluted with air. Frequently, it is not desirable to establish contact between the products being treated and the exhaust gases in a more of less diluted state. In all combustion processes, a series of chemical compounds (N0 X , CO, PAH etc.) are formed, said compounds in certain cases, often in connection with biological products, e.g. foodstuffs, forming toxic compounds. DISCLOSURE OF THE INVENTION The apparatus according to the invention overcomes these drawbacks, as the effect of radiant heat liberated by the combustion process is utilized to the full for intense heat transmission, at the same time as the exhaust gases do not make contact with the products being treated. Trials with the apparatus according to claims 1-4 have surprisingly shown that the chimney loss (volume x heat content x ΔT) corresponds to approximately 15% of the energy supplied in the fuel, whilst in the conventional system with contact between flue gas and product and without heat exchange there is a chimney loss of approximately 20% of the fuel energy. BRIEF DESCRIPTION OF THE DRAWING Now, the apparatus according to the invention will be described in more detail below: Figure 1 shows the heating unit according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENT In a burner 1, solid, liquid or gaseous fuel is burned with surplus of air, so that the combustion zone 2 (the flame) has an average temperature in the interval 400°C to 1200°C, preferably 600-1000°C. The combustion takes place in a burner tube 3 being insulated internally with a refractory material, so that the heat transmission from the inner wall of the burner tube to its outer wall is minimized. Thus, the energy liberated by the combustion will mainly be carried to the mouth of the burner tube and out into the inner part 4 of a thin-walled chamber 5. As shown, the chamber 5 may be shaped like a cylinder with a bottom shaped like a part-spherical surface, and may consist of a highly refractory material (metal or ceramics). The chamber 5 will be heated in the interval 400°C to 1200°C, preferably 600-1000°C, and emit heat radiation from the external part of the chamber. After a stay in the inner part 4 of the chamber 5 the exhaust gases will pass in an interspace 6 between the outside of the burner tube and the chamber 5, e.g. the cylindrical part, referred to below as the primary convective heat exchanger 7. By means of the above-mentioned passage, the exhaust gases may be assured a turbulent flow by means of guide plates of the like, so that the contact with the primary convective heat exchanger is maximized. The exhaust gases leave the primary convective heat exchanger 7 by means of suction, and may be further cooled down in one or more external secondary convective heat exchangers 8. After cooling and after having been exhausted by means of the fan 16, the exhaust gases leave the system at 17. The gaseous process -medium, e.g. atmospheric air, is taken in at 19 by means of the fan 18, and is heated in one or more convective heat exchangers 8, before e.g. the air passes between the refractory primary convective heat exchanger 7 and the manifold 21, and is made to flow into the process chamber 11. By the above-mentioned passage, e.g. the air can be assured a turbulent flow by means of guide plates or the like, so that the contact with the primary convective heat exchanger is maximized. The material to be processed according to the invention is taken in at the inlet chute or skid 10 in the rotating chamber 11. By means of vanes, scoops or the like and using known principles, the material is held in a mechanically fluidized state, and is moved from the inlet chute or skid 10 to the ejecting box 12. In the inlet end of the rotating chamber 11, the material is subjected to intense heat, partly in the form of radiant heat emitted by the chamber 5, partly in the form of convective energy transmission from the heated gaseous process medium. The intensity of the action of heat upon the material diminishes concurrently with the movement of the material from the inlet end, at the inlet chute or skid 10, towards the outlet end at the ejecting box 12. The transmission of heat from the chamber 5 to the stream of material diminishes concurrently with the units of the material, e.g. the particles, casting their shadows upon each other, and the temperature of e.g. the particles rises. The transmission of heat from the heated gaseous process medium to the stream of material diminishes concurrently with the process medium being cooled and the temperature of e.g. the particles rises. After a predetermined interval of influence by heat, the material and the process medium are separated according to known principles in the ejecting box 12, and the material is taken out through the air-tight lock chamber 13. The cooled process medium is made to flow through the tube 14 to the cyclone 15, in which any powdery constituents are separated out according to known principles, after which it is further cooled, possibly together with the exhaust gases, in a secondary heat exchanger 8. Any condensate formed by the further cooling of the process medium and possibly the exhaust gases is drained at 20.

Claims: CLAIMS 1. An apparatus for continuous heat treatment of a stream of material being mechanically fluidized in a rotating chamber and preferably consisting of a granular or highly viscous material, in co-current with heat energy originating from a burner (1), in which solid, liquid or gaseous fuel is burned, c h a - r a c t e r i z e d in that a portion of the energy liberated by the combustion heats the internal part of a thin-walled chamber (5), whereby the external part of said thin-walled chamber at the material inlet (10) transmits energy to said stream of material in the form of radiant heat, and that the remaining portion of the energy liberated by the combustion, bound in the exhaust gases from the combustion process, is heat-exchanged in a primary convective heat exchanger. (7) and one or more secondary convective heat exchangers (8) in counter-current with a gaseous process medium, preferably atmospheric air, said process medium transferring further energy to said stream of material in the form of convective energy. 2. Apparatus according to claim 1, c h a r a c¬ t e r i z e d in that the thin-walled chamber (5) and the primary convective heat exchanger (7) are constructed as bottom and cylinder in a co-terminus unit. 3. Apparatus according to claim 1 and 2, c h a ¬ r a c t e r i z e d in that the cylinder-shaped, primary convective heat exchanger (7) on its outside and inside is provided with guide plates so as to ensure a turbulent flow of process medium and exhaust gases. 4. Apparatus according to claim 1, c h a r a c ¬ t e r i z e d in that the gaseous medium after exiting the ejecting box (12) is made to flow through the conduit (14) together with the exhaust gases to one and more secondary convective heat exchangers and are heat-exchanged in counter-current with the gaseous process medium, before the latter is made to flow to the primary convective heat exchanger. 5. Apparatus according to claim 1, c h a r a c¬ t e r i z e d in that the static gas pressure in the gaseous process medium is always higher than the gas pressure in the exhaust gases.

Inventors: CHRISTENSEN LARS, KAU MIKAEL, CHRISTENSEN, LARS, KAU, MIKAEL
Applicants: CIMBRIA UNIGRAIN LTD, CIMBRIA UNIGRAIN LTD. A/S
Application year: 1990
Main classification: A23L3
IPC codes: F26B3, F26B11, F26B23