CONTINUOUS METHOD AND APPARATUS FOR HEAT TREATMENT OF MASS

Abstract: The method relates to a continuous method for heat treatment of mass. In the method, mass is supplied to a rotatable chamber (4) where it is stirred, thereby subjecting it to hot gas that is in the chamber (4). The treated mass is then dried and cooled in a drying section (11). The mass is heated by using a burner (9), the combustion gases of which are conveyed via a gas pipe (14) supplied through the chamber (4) into the drying section (11). The gas in the chamber (4) is indirectly heated through the walls of the gas pipe (14). In the drying section (11) the combustion gases are supplied to the mass to be treated. The invention further relates to a continuous apparatus for heat treatment of mass. The apparatus comprises a processing vessel (3) rotatable about its longitudinal axis, the vessel comprising a chamber (4) and a drying section (11). At one end of the chamber (4) there is a burner (9), the combustion gases of which are conveyed via a gas pipe (14). The gas pipe (14) is supplied through the chamber (4) and connected to the drying section (11).

Description: CONTINUOUS METHOD AND APPARATUS FOR HEAT TREATMENT OF MASS The invention relates to a continuous method for heat treatment of mass, whereby the mass to be treated is supplied for the heat treatment to a chamber rotatable about its longitudinal axis, the chamber being incompletely filled with the mass in such a way that it contains mass and gas, the gas in the chamber being heated and mixed with the mass in the chamber. The invention further relates to a continuous apparatus for heat treatment of mass, the apparatus comprising a heatable chamber rotatable about its longitudinal axis for the heat treatment of mass; means for heating gas that the chamber contains; and also means for mixing the mass to be treated with the hot gas in the chamber, the hot gas being arranged to heat the mass to be treated. Various kinds of mass, such as feed, are produced today by heat treating a basic mass in an autoclave, for example. The treatment usually aims at heating the mass to a particular temperature to provide a desired change in its properties. Further, the mass can be softened and its cellular structure can be appropriately changed with the heat treatment. When feed or other nutrient mass is concerned, the aim is usually to cook and sterilize the mass to make it more suitable as animal feed or human food. A treated nutrient mass is free from bacteria and both humans and animals can better use the nutrients of cooked food. Today the process is usually carried out on a batch basis, i.e. a large load of the basic mass is supplied into an autoclave and heated. Due to batch drive, charging and discharging times are long and the production is not efficient. In addition, the autoclave does not provide a sufficiently smooth process because in order to provide the desired temperature also in the centre of the mass supplied into the autoclave, the mass must occasionally be overheated by about 10°C above the temperature required by the actual treatment. In the autoclave, heat is transferred from the outer portions of the mass load to its inner portions by conduction. When heat is applied through the layer of mass to the inner portions of the mass, the outer portion of the mass must be over-heated. Over-heating is disadvantageous because it changes mass properties and destroys them, and it requires a lot of extra energy. On the other hand, if the heating time is extended to allow an even temperature to be provided also in the inner portions of the mass layer, the processing time becomes unreasonably long in view of the efficiency of the manufacturing process. The long processing time can also harm the chemical structure, nutrients and the properties of the mass. In addition to the autoclave, also different heating apparatuses arranged in connection with conveyors, heating chambers, and oil heating carried out in a coaxial piping system are known to a person skilled in the art. These solutions also have the shortcoming that during heat treatment, heat is always transferred by conduction either from the conveyors moving the mass or from any other structure bordering the mass. Heat is transferred into the inner portions of a layer of mass by conduction through the mass layer, therefore the mass must be occasionally over-heated. On the whole, heating is not even. WO Patent Application 85/02248 discloses an apparatus in which mass is heated by applying a heat flux. A burner is used to heat a wall structure which is thus made to glow. The heat radiation thus generated is used to heat the mass to be treated. The mass is stirred in the heat flux, the particles in the mass thus receiving a granule-specific heat treatment. In the solution according to the publication, the combustion gases of the burner are sucked away before they come into contact with the mass to be treated. A shortcoming of the described apparatus is its poor energy economy, for example. An object of the present invention is to provide a continuous method for the treatment of mass, the method enabling a more efficient and cost- effective heat treatment of mass than before. Another object of the invention is to provide an apparatus allowing the shortcomings in prior art to be avoided. The method of the invention is characterized in that after the chamber is arranged a drying section into which the mass is supplied after the heat treatment; that the mass is heated by using a burner, the combustion gases of which are conveyed via a gas pipe supplied through the chamber, the gases indirectly heating the gas in the chamber through the walls of the gas pipe; and that the combustion gases coming from the gas pipe are supplied to the drying section at the other end of the pipe, thus allowing the combustion gases to come into contact with the mass in the drying section. Further, an apparatus of the invention is characterized in that one end of the chamber is provided with a burner; that a gas pipe is supplied through the chamber, the combustion gases of the burner being conveyed via the pipe in such a way that they indirectly heat the gas in the chamber through the wall of the gas pipe; that the other end of the chamber is provided with a drying section into which the mass is arranged to be supplied after the heat treatment; and that the gas pipe is interconnected with the drying section to allow the combustion gases to come into contact with the mass in the drying section. An essential idea of the invention is that the heat treatment takes place in a chamber rotatable about its longitudinal axis and containing mass and heated gas. The mass is heated by using a burner, the combustion gases of which are conveyed via a gas pipe supplied through the chamber, the gases thus indirectly heating the gas in the chamber. The heat in the combustion gases is conducted by the walls of the gas pipe. On an extension of the chamber is a drying section into which the mass is supplied after the heat treatment. One end of the gas pipe is connected to the drying section, the combustion gases of the burner being supplied, as they are, to the drying section to allow them to come into direct contact with the mass to be treated. When the mass is mixed with the heated gas, the heat of the gas space is directly transferred into the particles of the mass to be treated, therefore conduction through a layer of mass is not needed. The hot and humid gaseous atmosphere inside the chamber heats the mass and, when necessary, a further processes the mass by providing a granule- or drop-specific sterilization of the mass, for example. An essential idea in a preferred embodiment of the invention is that the chamber contains a pressure higher than normal air pressure. An essential idea in another preferred embodiment is that when the chamber is rotated about its longitudinal axis, the rotating motion causes scoop-like members arranged in the inner parts of the chamber to lift mass upward from the bottom of the chamber. As the rotation continues, the mass flows from the scoop as a thin flow through the hot gas space in the chamber, comes into contact with the hot gas and receives a granule-specific heat treatment. To enhance the stirring and to provide the gas space, the degree of fullness of the chamber is kept low. An advantage of the invention is that the use of temperature and energy is as optimal as possible. It allows heat energy generated with the burner to be better utilized than before because in the process combustion gases are supplied into the mass that is to be heat treated. Good energy economy lowers the price of the end product. A further advantage is that the structure of the treated mass can, when necessary, be kept unchanged better than before, i.e. its outer appearance and internal structure change less than before. This is because heat is now transferred in the heating part directly to each mass particle, i.e. each drop or granule of mass receives almost an individual heat treatment. In addition, the mass, or any portion of it, does not need to be over-heated at any point, therefore the properties of the mass do not degrade and the treated mass is homogenous and better in quality. For example, the nutrients of a food mass are better preserved and proteins do not coagulate unintentionally or change their structure in a way that would impair the ability of animals or humans to utilize the food mass. In addition, the temperature of the treatment and its duration can be better controlled and adjusted to be precisely correct. The invention will be described in greater detail with reference to the accompanying drawings, in which Figure 1 is a schematic, partly sectional side view of an apparatus of the invention; Figure 2 is a schematic side view of the apparatus of Figure 1 and its peripheral equipment; and Figure 3 is a schematic view of a process diagram of a method of the invention. Figure 1 is a simplified view of the apparatus of the invention. The mass to be treated is supplied from a feeding tank 1 by means of a feeder 2 into a conduit leading to a chamber 4 in a rotatable processing vessel 3. In the chamber the mass is heated and further processed preferably under a pressure higher than normal air pressure. The chamber 4 need not necessarily be pressurized, the treatment can also be carried out in normal pressure. However, using a pressurized chamber speeds up heat treatment. The input of the mass can be enhanced by blowing air into the mass flow by means of a compressor 5 and/or by supplying steam into the mass flow from an steam conduit 7 by means of a steam ejector 6. If the mass is not moist enough, hot water can be supplied into the mass flow, when necessary, from an hot water conduit 8 to moisten the mass. Both the steam generation and the heating of the water are arranged at a burner 9. Water injected in the above described manner into the mass flow to be supplied moistens the mass evenly, thus reducing the amount of water needed. Consequently, the process also consumes less energy because the mass does not contain extra water to be heated. The amount of water needed depends on the material and it can be easily determined by means of test runs so that on the basis of them the mass is moistened only to the extent needed. The mixture of steam, water and mass is then conveyed via an input conduit 10 to the front part of the chamber 4. Since the processing vessel 3 is rotatable, the input conduit 10 is also rotatable. The degree of fullness of the apparatus is continuously kept low, between 10 to 20%, for example, to provide a more advantageous mixing and heat transfer, and to provide space for the hot gas in the chamber. In addition to the chamber 4, the processing vessel 3 comprises a drying section 11 on an extension of the vessel. The processing vessel 3 is rotatable about its longitudinal axis advantageously on rolls 12 by an actuator 13 illustrated in Figure 2. The actuator is advantageously an electric motor but, when necessary, it can be a hydraulic motor or a combustion engine, the speed of rotation of which can be steplessly regulated to influence the treatment of the mass. A gas pipe 14 provided with the burner 9 at one end of the pipe is supplied through the chamber 4, the other end of the pipe being connected to the drying section 11. The burner 9 uses solid, liquid or gaseous fuel. The gas pipe 14 heats up when the hot combustion gases from the burner are conveyed via the pipe. The gas pipe 14 then warms the chamber 4, thus heating the gas space above the mass and providing the chamber with a hot and humid gaseous atmosphere well suited for cooking. The outer circumference of the gas pipe 14 is provided with suitably attached flow control plates 15 enhancing the transfer of heat. The inner circumference of the chamber 4 is also provided with flow control plates 15 arranged alternately in the gas pipe 14 and in the chamber 4, thus dividing the chamber 4 into smaller spaces in the direction of flow of the mass. The chamber 4 is further provided with specific scoops 16, or the like, aimed at lifting the mixture of mass upward, as a result of the rotating motion of the. chamber, from the bottom of the vessel so as to spread the mass and to move the mass forward from the space defined by the flow control plates 15 to a next space in the direction of travel of the mass. A thin veil of mass thus flows down from the scoops 16 through the hot gas and steam space in the chamber 4, improving the transfer of heat into the mass. The scoops 16 are attached to the inner wall of the chamber and to the flow control plates 15, and they are advantageously formed into at least a somewhat cup-like form to enhance the lifting of the mass. The scoops are advantageously further formed into a shape allowing them to guide the mass forward in co-operation with the flow control plates 15, in a controlled manner, in the direction of travel of the mass. The scoops 16 can also be adjustable, thereby allowing the mixing of the mass with the gas to be varied according to need. The dimensions and the speed of rotation of the chamber 4 and the number of the flow control plates 15 and scoops 16 are determined in such a way that desired process properties are provided and a sufficient stirring of the mass is achieved. The relatively low degree of fullness of the chamber and the stirring of the mass caused by the rotating motion ensure that the mass does not form an accumulated layer that remains rotating in the lower part of the chamber, in which case the transfer of heat would be essentially poorer. The stirring also prevents harmful clodding of the mass. The rotation having caused the mass to move to the rear end of the chamber 4, i.e. to the end where the drying section 17 is, the heat treated mass is lifted with mass control plates 17 onto an adjustable discharger 18. The discharger 18, can be operated, for example, by a motor coupled to the discharger or by providing the discharger with rotating force by means of a gear rack. With the discharger 18, the mass flow to be supplied from the chamber 4 to the drying section 11 can be regulated. Figure 2 is a side view of the apparatus shown in Figure 1 , illustrating also at least some of the peripheral equipment of the apparatus. When entering the drying section 11 , the mass treated with heat in the chamber 4 is hot and moist. In the drying section 11 the mass is dried and cooled before it is supplied to a cyclone 19 located at the rear end of the drying section. From the cyclone it can be further supplied to packing and other end-processing by applying a feeder 20. The drying section 11 shown in the Figure is a part of the processing vessel 3, separate from the chamber 4 and rotatable with the support of rolls 12, or the like. It can naturally also be connected to the chamber 4, in which case they rotate together. When a separate chamber is used, such as the one shown in the Figure, the rotating speed of the drying section 11 can be separately regulated, independently of the chamber 4, by means of a specific rotation motor 21. The drying section 11 is usually not pressurized. As can be seen from Figure 1 , the drying section 11 comprises flow control plates 15 and scoops 16, similar to those in the chamber 4, which lift and move the mass to be treated, similarly as in the chamber 4, as a result of the rotating motion further to the rear end of the drying section 11. Stirring makes drying and cooling also efficient, causing as few unintentional changes as possible in the structure of the mass. The drying section 11 uses air for the drying and cooling, the air being taken via an air conduit 22 from outside the process and divided in two. Some of the air is supplied to a blower 23 to be blown into the drying section 11 and some is supplied to the conduit 24 from where the air is further divided, some of it being supplied to a conduit 25 to be conveyed directly to the blower of the burner 9, and some to a blower 26 from which it is blown to the burner 9 via a conduit 27. The power of the burner 9 can be regulated by adjusting the blow power of the burner's blower, by changing the blow power of the blower 26 or by choking the flow in the conduit 27. To the air conduit 22 is connected a filter 28 and the air heater 29, the heater recovering the heat that is in the hot process gases sucked from the rear end of the drying section 11. The air supplied to the burner 9 is thus pre-heated. The air heated by the burner 9 is supplied to the gas pipe 14, one end of which is connected to the drying section 11 where the heat is used for drying the mass. In the drying section the burner's combustion gases and the air mass heated with the burner are supplied, as they are, into the mass that is to be dried. Further, air pre-heated with the air heater 29 is supplied to the blower 23 and blown into the drying section 11 through holes at the front part of the drying section 11 and together with the hot gas supplied from the gas pipe 14, a more efficient drying is provided. At a distance from the front part of the drying section 11 there are holes 30, illustrated in Figure 1 , through which unheated air is supplied into the drying section 11 for cooling, which takes place at the rear end of the drying section 11. Both the pre-heated drying air supplied to the front part of the drying section 11 and the cooling air supplied to the rear end of the drying section 11 can be supplied to a bacteria filter 31 , thus ensuring that impurities in the air taken from outside the process cannot spoil the mass to be treated. The gases to be conveyed to the gas pipe 14 do not necessarily need to be supplied to the bacteria filter because the gases to be conveyed in the gas pipe 14 are heated in the burner 9, which destroys bacteria. The process gases, the drying air and the cooling air are sucked out at the rear end of the drying section 11 by means of a suction unit 32. With the gases, humidity is discharged at the same time. The removing gases are supplied to the air heater 29 which, as already stated, recovers the heat that is in the gases. Similarly, the water used at the front part of the process for moistening the mass and for generating steam is pre-heated with a water heater 33 that also uses the heat energy that is in the gases to be sucked. Figure 3 further illustrates a strongly simplified process diagram of the method of the invention. A moistened or already suitably moist raw material mass is supplied from the feeding tank 1 to the chamber 4 where the heat treatment of the mass takes place, i.e. heating 34 and further processing 35. The treated mass is then supplied to the drying section 11 to dry up 36 the extra moisture the mass contains and to cool 37 the mass. The heat treatment having been completed, the mass is supplied to the cyclone 19 for end- processing. Hot gases are sucked out at the rear end of the drying section 11 by the suction unit 32 and conveyed through the pre-heater 29 and the water heater 33 which are used for pre-heating the water needed in the process and the air taken from outside the process. At the burner 9 the water needed for moistening the mass is heated 38 and the steam needed is generated 39. In addition, the burner 9 is also used for generating 40 heating air for the apparatus. In addition to various nutrient masses, an example of organic masses that can be treated with the method and apparatus of the invention is fibre-like mass, such as wood fibre mass, which can, after a suitable heat treatment, be used as a raw material in paper manufacture, as thermal insulation or as food mass, for example. The heat treatment can be used for softening the fibre cells before further processing, or for changing the chemical structure of fibres as desired. One alternative for treating a fibre-like mass with heat is to supply a suitably moistened mass into a chamber of the invention where it is heated by applying a predetermined heat at a particular over- pressure. The mass then enters the drying section, or other space, where the mass softened by the heat and moisture expands as it moves from a higher pressure to a lower pressure, thereby advantageously changing its structure with view of further processing. This allows the. cell structure of fibres to be broken, for example. The apparatus of the invention is therefore also suitable for the above described process known as expanding. An example of inorganic mass that can be treated is iron sulphate. Powdery iron sulphate is moistened and supplied to the chamber for heat treatment. In the chamber the iron sulphate is heated to a predetermined temperature, whereby crystal water is released and the sulphate is liquified. Over-pressure applied to the chamber enhances the process. The liquid generated in the chamber is supplied to the drying section where it granulates. The pressure in the drying drum is lower than the pressure in the chamber. The drawings and the related description are only meant to illustrate the basic idea of the invention. The details of the invention can vary within the scope of the claims. As already mentioned, it is not necessary to provide an over-pressure in the chamber. Depending on the circumstances, the heating and the further processing can also take place under a normal pressure. When over-pressure is used, the moisture content of the mass can be changed by regulating the pressure. A high pressure used in a pressure chamber allows only a small amount of moisture to be evaporated from the mass into the gas space and, correspondingly, when a small pressure is used, a larger amount of moisture is evaporated. Consequently, the moisture content of the mass that is to be moved into the drying section and the amount of drying needed by the mass can be influenced by regulating the pressure. The processing vessel can naturally be provided with suitable insulation, thereby further improving the energy economy of the apparatus.

Claims: CLAIMS 1. A continuous method for heat treatment of mass, whereby the mass to be treated is supplied for the heat treatment to a chamber (4) rotatable about its longitudinal axis, the chamber (4) being incompletely filled with the mass in such a way that it contains mass and gas, the gas in the chamber (4) being heated and mixed with the mass in the chamber (4), characterized in that after the chamber (4) is arranged a drying section (11) into which the mass is supplied after the heat treatment; that the mass is heated by using a burner (9), the combustion gases of which are conveyed via a gas pipe (14) supplied through the chamber (4), the gases indirectly heating the gas in the chamber through the walls of the gas pipe; and that the combustion gases coming from the gas pipe are supplied to the drying section at the other end of the pipe, thus allowing the combustion gases to come into contact with the mass in the drying section. 2. A method according to claim 1, characterized in that the heat treatment is carried out by applying an air pressure higher than normal air pressure. 3. A method according to claim 1 or 2, characterized in that scoops (16) are arranged on the inner circumference of the chamber (4), the scoops lifting, as a result of the rotation of the chamber (4), the mass to be treated with heat upwards from the bottom of the chamber (4), a thin veil of mass then flowing from the scoops (16) back to the lower part of the chamber (4) through a hot layer of gas in the chamber (4). 4. A method according to claim 3, characterized in that the mass is supplied to the processing apparatus in such a way that its degree of fullness is from 10 to 20%. 5. A continuous apparatus for heat treatment of mass, the apparatus comprising a heatable chamber (4) rotatable about its longitudinal axis for the heat treatment of mass; means for heating gas that the chamber contains; and also means for mixing the mass to be treated with the hot gas in the chamber, the hot gas being arranged to heat the mass to be treated, characterized in that one end of the chamber (4) is provided with a burner (9); that a gas pipe (14) is supplied through the chamber, the combustion gases of the burner being conveyed via the pipe in such a way that they indirectly heat the gas in the chamber (4) through the wall of the gas pipe; that the other end of the chamber (4) is provided with a drying section (11) into which the mass is arranged to be supplied after the heat treatment; and that the gas pipe (14) is interconnected with the drying section (11) to allow the combustion gases to come into contact with the mass in the drying section. 6. An apparatus according to claim 5, characterized in that it comprises means for pressurizing the chamber (4). 7. An apparatus according to claim 5 or 6, characterized in that the chamber (4) and the drying section (11) are interconnected and arranged to rotate together. 8. An apparatus according to any one of claims 5 to 7, characterized in that scoops (16) are arranged on the inner circumference of the chamber (4), the scoops being arranged to stir the mass to be heat treated as a result of the rotating of the chamber (4). 9. An apparatus according to any one of claims 5 to 8, characterized in that the chamber (4) is divided into smaller spaces in the direction of flow of the mass to be treated by using flow control plates (15) and that the scoops (16) are arranged to move the mass, one space at a time, from the front end of the chamber (4) towards its rear end. 10. An apparatus according to any one of claims 5 to 9, characterized in that the drying section is divided into smaller spaces in the direction of flow of the mass to be treated by using flow control plates (15) and that the scoops (16) are arranged to move the mass, one space at a time, from the front end of the drying section towards its rear end. 11. An apparatus according to any one of preceding claims 5 to 10, characterized in that the apparatus comprises means for recovering the heat that is in the gases sucked from the rear end of the drying section (11) and to use them for pre-heating water and air needed in the process.

Inventors: TILKANEN JUHA, TILKANEN, JUHA
Applicants: AMOMATIC OY, BIOKASVU OY, TILKANEN JUHA, TILKANEN, JUHA
Application year: 1999
Main classification: F26B23
IPC codes: A23K3, A23L3, A23N17, F26B11