METHOD AND APPARATUS FOR DRYING GRANULAR MATERIAL

Abstract: A method for drying and/or freezing granular and similar matter in a particle form, particularly organic materials. The granular material is subjected to a drying agent or refrigerant from below in a mainly vertical jet which helps to keep the granular material in motion. There is a drying chamber (11) in a circulation loop (10) with an organ (13) for the through flow of the drying agent and/or refrigerant. In the loop there is a heat pump unit (12) comprising a main condenser (19) for heating the drying agent and an auxiliary condenser (21) for the removal of the surplus heat, there is also a distribution valve (23) to distribute the refrigerant from an evaporator (15) to the two condensers, in accordance with the need to supply heat to the drying agent and/or refrigerant.

Description: Method and Apparatus for drying Granular Material Θ The invention concerns a method of the type indicated in the introduction to Claim of Patent 1 for the drying of granular materials and the equipment necessary to carry out the method. 5 Background: The drying of granular material for use in the foodstuffs industry, for example, places considerable demands upon the drying process. A method is required Θ which can give optimal product quality, where there is minimal deterioration in the product and no impairment of the product's appearance or physical, chemical and nutritional characteristics. The latter is particularly relevant for the drying of foodstuffs. 5 Known drying methods have mainly used warm air, where the heated air is released externally after use, meaning an inevitable energy loss. Another method which is used in the drying of fish, for example, is placing batches of fish or 0 whatever is to be dried in a drying room which is connected to a loop that circulates the dried air, this is sometimes combined with a heat pump. Freeze-drying in a vacuum is yet another method. However this is a very expensive process. 5 None of these methods are entirely satisfactory, either they result in a deterioration in quality, or they have high operating costs. Objective: The main purpose of the invention has been to find a method and suitable equipment to dry granular material where exact requirements were placed on the quality and the nonimpairment of the nutritional value, taste, chemical or physical characteristics. Moreover this should be achieved with low production costs, i.e., energy costs, equipment costs and operating costs. Drying should also be feasible as a continuous process . Principle: The basic principle of the invention is described in Claim of Patent 1. Claim of Patent 3 describes the equipment which could be used for this purpose, in accordance with the invention. Other advantageous features of the invention are described in the subsidiary claims of patent. The method hereby invented enables the drying conditions to be adjusted so that high quality can be maintained irrespective of the type of granular material, or the chemical and physical characteristics. The method can be used for drying marine fish food, roe-based feed, for example, and various foodstuffs such as shrimps, vegetables etc. Other applications are the drying of the raw materials for preserved food- stuffs, such as dishes sold in sachets and types of meat where the fat may become rancid. If the heat pump principle is used as envisaged in the invention, this will save considerable amounts of energy. In some cases this can lead to savings of 60-80% compared with drying units based on direct heating. Examp1e: The figure is a schematic illustration of a unit or plant for implementing the method which has been in¬ vented. The unit consists of a circulation loop 10 for a gaseous drying agent. There is a drying chamber 11 in the inlet part of the loop with a heat pump 12 ahead of this. The circulation loop 10, the parts surrounding and forming the drying chamber 11 and the main components of the heat pump 12 can be produced by existing techniques from material used in ducts, pipes and sheet metal cowlings. In the example, an enlarged part 10A of the drying chamber 11 is shown between the preceding and following parts of the pipe, 10B and IOC respectively. There is a perforated plate 13 in this enlarged part of the loop 10A, which will subsequently be termed the processing section. The processing section 10A is located in a vertical axis while the perforated plate 13 is horizontal. In addition, the supply inlet for granular materials 14 can be closed (not illustrated), described below. In an alternative design, the drying chamber can have a screw conveyor, or something similar leading inwards and an outlet channel for the processed product. This will enable a continual supply of granular material to the drying chamber 11, whilst the processed material is fed out. Here it could be advantageous to have sluices to retain the excess pressure required and prevent any loss of the drying agent . An alternative design could use a rotating perforated drum in the processing section 10A, this could either treat the granular material in batches or be based on continuous supply and outlet. This will be useful during continuous, extended drying, particularly when freezing is required. Comments: The following expands upon the details of the possible solutions, concentrating on original and specific features. The heat pump unit 12 has an evaporator 15 at its inlet end where a heated, moist drying agent, meets cold condensation plates, where the steam undergoes liquification. The condensation plates are cooled by a flowing refrigerant such as freon, which is admitted through a thermostatically-controlled valve 16 from a pressure tank 18. The valve 16 is controlled by a non- illustrated control circuit from a temperature sensor 17 in the outlet of the refrigerant from the condensa¬ tion plates in the evaporator 15. After the removal of the steam, the drying agent is led to a condenser 19 located downstream in the circulation loop 10. There is a motorized fan 20 positioned between evaporator and the condenser 19. The speed of the fan is controlled to ensure circulation of the drying agent. Apart from the main condenser 19, there is also an auxiliary condenser 21 outside the circulation loop 10. The refrigerant is sucked from the evaporator 15 by a compressor 22 which is powered by a motor (not illustrated), this increases the temperature of the refrigerant. The distribution of the refrigerant to the two condensers 19 and 21 is carried out by a powered valve 23 which is controlled by a regulator 24 with a temperature sensor 25 in the drying agent flowing towards the drying chamber 11. During stable operating conditions and equi¬ librium the energy which is absorbed by the evaporator 15 is returned to the condenser 19. If the heat loss from the circulation loop 10 is ignored, the heat loss in the system will be limited to the heat that has to be released from the auxiliary condenser 21, which quantitatively equates the amount of energy supplied to the compressor 22. The drying agent can be an inert gas, such as nitrogen. This avoids any fat oxidation of the product. In some cases it will also be possible to use air. The necessary temperature regulation will be achieved by varying the output from the main condenser 19. Surplus heat will be released in the auxiliary condenser 21. The valve 16 lowers the high-pressure refrigerant from the condensers 19 and 21 down to the pressure in the evaporator. The method and the equipment hereby invented has a variety of applications including the drying and preprocessing of feed for fish farming, such as roe- based feed, for example. As the drying conditions can be varied, the required physical characteristics can be obtained, such as the sinking velocity in water, product density and water solubility for proteins. A wide range of operational temperatures are available in the drying chamber 11, from over lOO ∞ C down to below zero. In the last case the granular material can already be frozen. As far as roe-based feed is concerned, freezing can either be done pre¬ viously or in the drying chamber 11. As the present invention permits frozen matter and raw material to be dried, the invention can dry a wider range of products than any other known drying methods or equipment. The drying chamber 11 can also have a funnel- shaped bottom towards an inlet arrangement.

Claims: Claim of Patent: 1. A method for drying and/or freezing granular and similar matter in a particle form, particularly organic materials, such as foodstuffs, feed, and raw materials for pharmaceutical purposes, possibly combined with a process such as heat treatment or freezing where the granular material is fed into an area which is permeated by a gaseous drying agent or refrigerant, c h a r a c t e r i z e d by the granular material being subjected to a drying agent and/or refrigerant from below in a mainly vertical jet which helps to keep the granular material in motion, since the drying agent is led using known technology in a closed circuit connected to a heat pump. 2. A method in accordance with Claim of Patent 1, c h a r a c t e r i z e d by the use of an inert gas, such as nitrogen or a mixture of inert gas and air as the drying agent and/or refrigerant. 3. Equipment for implementing the method in accordance with Claim of Patent 1, with a heat pump unit (12) for the condensation of moisture from a drying agent and/or refrigerant and the heating of the dried drying agent, which is circulated in a closed loop, c h a r a c t e r i z e d by the circulation loop (10) having a drying chamber (11) where the drying agent and/or refrigerant rises in a mainly vertical axis of flow from the heat pump unit, and with a zone and/or organ (13) to ensure the flow of the drying agent and/or refrigerant, which can keep the granular material or similar in motion whilst the drying agent and/or refrigerant flows through. 4. Equipment in accordance with Claim of Patent 3, c h a r a c t e r i z e d by the organ for the through flow of the drying agent and/or refrigerant being a perforated plate (13). 5. Equipment in accordance with Claim of Patent 4, c h a r a c t e r i z e d by the plate being a rotatable drum, which is preferably designed to permit continual supply and outlet of granular material or similar, particularly for the purpose of freezing. 6. Equipment in accordance with Claim of Patent 3, c h a r a c t e r i z e d by the drying chamber having a funnel- shaped bottom towards an inlet aperture for the drying agent and/or refrigerant. 7. Equipment in accordance with one of Claims of Patent 4-6, c h a r a c t e r i z e d by a heat pump unit comprising a main condenser (19) for heating the drying agent and an auxiliary condenser (21) for the removal of the surplus heat, and that there is a distribution valve (23) to distribute the refrigerant to the two condensers, in accordance with the need to supply heat to the drying agent.

Inventors: MAGNUSSEN OLA M, SONG XIAOMEI, STROEMMEN INGVALD, MAGNUSSEN, OLA, M., SONG, XIAOMEI, STROEMMEN, INGVALD
Applicants: STIFTELSEN IND OG TEK FORSK, STIFTELSEN FOR INDUSTRIELL OG TEKNISK FORSKNING VE
Application year: 1989
Main classification: F26B3
IPC codes: A23B4, A23K1, A23L3, A23N12, A61J3, F25B6, F26B3, F26B21, F26B23