Radiative Heating and/or Sterilization of Fluid by Infra-red and other Electromagnetic Energy Sources

Abstract

The present invention relates to a method and equipment intended to heat or sterilize liquid such as water, milk, broth, sauces, juices and similar foods and other fluids used in pharmaceutical and cosmetic applications. More specifically this describes a novel approach for continuously heating liquid food or liquid using an electro-magnetic (EM) radiation such as infra-red and other EM radiation sources. It achieves this by conveying radiation from a remote or local source and directing the radiation onto liquid dispersed into tiny droplets in a chamber. Infra-red and other EM radiations have a limitation in that the penetration depth of energy into the product/liquid is very short. Thus, product can be heated only in a thin layer near the periphery surface where the energy strikes. By dispersing liquid in drop droplets, the radiation effectively penetrates the whole body of fluid and consequently heats and destroys bacteria and some spores. The processed fluid then is commercially sterile or has much lower microbial load and hence it has a longer shelf life, under refrigeration.

Claims

1. A method of continuously heating or sterilizing fluid by electromagnetic radiation comprising: dispersing a fluid in a closed space into fine droplets so that the radiation can penetrate the droplets from all sides and thus penetrate the whole fluid mass and have multiple chances of impingement or incidence, dispersing a fluid in fine droplets that are large enough so that they move substantially under the influence of gravity, dispersing a fluid in fine droplets that are large enough with no fine mist formation, directing electro-magnetic radiative energy on to the dispersed droplets of fluid in an enclosed space, heating or sterilizing or treating the fluid as a result of droplet-radiation interaction, collecting processed fluid from the bottom of enclosed space and taking it away by some means such as a pump.

2. The method of claim 1, wherein infra-red electromagnetic radiation is used for processing fluid

3. The method of claim 1, wherein microwave electromagnetic radiation is used for processing fluid

4. The method of claim 1, wherein ultra-violet electromagnetic radiation is used for processing fluid

5. An apparatus or equipment for continuously heating or sterilizing fluid byinfra-red, microwave, ultraviolet and similar electromagnetic radiation comprising: a means for dispersing a fluid inside a closed space into fine droplets so that the radiation energy can penetrate the droplets from all sides and thus penetrate the whole fluid mass and have multiple chances of impingement or incidence a means for dispersing a fluid in fine droplets that are large enough so that they move substantially under the influence of gravity a means for dispersing a fluid in fine droplets that are large enough with no fine mist formation a mechanism for directing a focused beam of electro-magnetic radiative energy on to the dispersed droplets of fluid in an enclosed space a means of collecting processed fluid from the bottom of enclosed space and taking it away such as a pump an instrumentation and controls arrangement to control the temperatures at various points and flow rates

6. The apparatus of claim 5, where the disperser is in form of series of pipes with holes or perforations

7. The apparatus of claim 5, where the disperser is in form of series of pipes with narrow slits

8. The apparatus of claim 5, where the disperser is in form of trough with holes or perforations

9. The apparatus of claim 5, where the enclosure is rectangular or other shape

10. The apparatus of claim 5, where the mechanism for directing electro-magnetic radiative energy is through a waveguide designed for a radiation involved

11. The apparatus of claim 5, where electro-magnetic radiative energy is directed through a radiation source directly installed on the wall of the chamber through a large transparent window

12. The apparatus of claim 11, where electro-magnetic radiative energy is directed through a radiation source directly installed on the entire periphery of the chamber wall through transparent wall

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be more clearly understood with reference to the following detailed description when considered in conjunction with the drawings referenced here.

[0018] FIG. 1 shows schematically a cross section of the cylindrical heating chamber with conical bottom. It further shows the fluid entrance, exit and the droplet pattern inside the chamber.

[0019] FIG. 2 shows a schematic layout of a typical fluid processing system where the present invention can be used as an improved system.

DETAILED DESCRIPTION

[0020] The invention is schematically described with the help of a sketch as shown in FIG. 1. The liquid to be processed is brought to the top of a thin walled vertical cylinder 1 and is fed from top 11 through a disperser 2 and thus a liquid spray of fine particle is created inside the chamber. The cylinder has a conical bottom for removal of heated product which is done by a pump 3. The heating/processing space can be rectangular or other shape that provides space for droplets to travel downwards while heating. The outer wall would preferably be covered with insulation 8 to minimize heat losses from chamber while the jacket 9 through which a medium is circulated at controlled temperature. The temperature of medium in upper jacket is maintained at a level such that inner walls are at or slightly above the temperature of liquid inside the chamber while temperature of medium in lower jacket is maintained at the temperature the outgoing liquid. The temperature of inner wall of the cylinder is maintained to avoid any condensation on the wall. Absence of liquid on inner wall will prevent formation of any drops or liquid film on the inner walls. Droplets or liquid film formed on the wall would absorb the radiation and heat up. These stagnant or slowly moving drops and film will be over exposed to radiative heat and overheated, resulting in possible burns at the wall and more extensive chemical changes in these elements. This will ultimately result in some portion of fluid receiving more energy while some receiving less energy. The current invention avoids this situation by making all fluid droplets going to the bottom only and preventing condensation at inner vertical walls. The jacket over the lower cone helps to avoid over-heating and maintaining temperature of outgoing liquid. Liquid level is maintained at the lower end of conical, thus containing EM radiation inside the chamber space.

[0021] Infrared (IR) energy is generated by a heater 5 and a reflector 6 assembly at some distance away from the cylinder. The generated IR energy is conveyed to the chamber wall by a wave guide 4. The inner surface of the wave guide preferably has a mirror finish so as to have a high reflectivity. The inner surface may also have some special coating for increasing reflectivity. The waveguide is insulated for minimizing heat losses. The IR energy is conveyed into chamber space by connecting the other end of wave guide to a high point on vertical wall through a flat window 7 which is transparent to IR or EM radiation. The connection of waveguide may be made at a slight angle downwards to facilitate reflection of energy through the inner walls of cylinder.

[0022] For EM radiation other than IR, suitable modification must be made in the design and dimensions of the waveguide 4 based on wavelength of specific EM radiation. Similarly, the flat window 7 must transparent to the EM radiation employed.

[0023] The liquid is fed from top 11 through a disperser 2 which typically is a spiral shaped piping with multiple perforations downwards or a trough with multiple perforations. In place of perforations narrow slits facing downwards would also serve the purpose. These perforations may or may not have removable inserts. The intention here is that liquid leaving the disperser creates a multiple of small droplets falling down through the cylinder space under the influence of gravity with a minimum axial velocities and negligible radial velocities. Under these conditions droplets travel down in the direction of the conical section at the bottom and no droplets go to the side walls as shown by flow pattern shape 10. The disperser design is such that almost entire enclosed space is occupied by the spray.

[0024] The minimum diameter of droplets is estimated at 1.5 mm for water like fluids but is largely governed by flow rates, pressure drops and properties such as viscosity and surface tension. The minimum particle diameter is thus determined experimentally for any specific fluid. During atomization, very small droplets are formed and these move under influence of two forces, namely gravity force acting downwards while drag force opposing the downward motion. The particle then travels downward with a terminal settling velocity according to Stokes law. The main idea here is that the droplets are just large enough so that the gravitation force is significantly higher than the drag force. For example, for a droplet of 1.5 mm diameter, gravitation forces are about 6 times larger than the drag forces after first second of downward travel. With large droplets as in this invention, the droplets sizes are comparable to one coming from a shower head, where droplets are largely influenced by gravity and fall downwards. The relatively large diameter is also critical because the bacterial kill in droplet is taking place only by interaction with IR/EM radiation energy since no other forces such as internal pressure or shear forces exist in significant level inside the droplet exiting the disperser. Further, the particles do not travel to the side wall of vertical section of the cylinder.

[0025] Further, as in the case of spray nozzles or other such devices generally known as atomizers, the atomized particles exhibit a wide range of size distribution. The particles range from a couple of hundreds of microns to a few microns. The intention of atomization, for example in spray drying equipment, is to create a large surface of liquid through which evaporation of liquid takes place almost instantaneously once the liquid comes out of such atomizers. As a result, very fine liquid particles are formed and they travel with a velocity close to terminal settling velocity and a large portion of it also travel to the side walls. It creates a situation where the entire space in the chamber is filled with fine liquid particles that travel to wall and form a film there. Instead of using such fine spraying devices, the present invention employs a disperser which ensures that the liquid particles are large and hence the force of gravity is significantly higher than drag forces, making the particles travel straight downwards largely under the influence of gravity. The disperser is designed to disperse the fluid rather than form a mist as in the case of atomizers.

[0026] One important feature that results from the fact that the droplets move largely under gravity is that the invention results in a very narrow residence time distribution for the fluid. This is because, all particles have nearly the same velocities as they all move substantially under gravity as gravity force on droplet is significantly higher than the drag force. This situation is also very different than the flow in pipe wherein all particles move with different velocities and hence have a wide residence time distribution. Even in the previous art, where the flow is moving in annular space, the residence time is wide because of channeling effect.

[0027] Further, the air inside chamber will become saturated with solvent (water or any other liquid) at the operating temperature and if the side walls are at a temperature lower than inside temperature, there will be a possibility of some solvent or fluid condensing on the inner wall. Since the temperature of inner walls are maintained at slightly higher temperature, such condensation is avoided. Further, since there is no mist formation and droplets do not go to walls.

[0028] As the droplets are falling downwards, IR is incident upon them virtually from all sides, IR gets absorbed by droplet and the liquid temperature increases. Since, the inner walls of cylinder has high reflectivity, radiation not absorbed by droplet is reflected by the wall and it is incident on the droplet again. Thus, there are multiple interactions between droplet and IR radiation by the time droplet reaches bottom. Further, there are numerous air interstices between two neighboring droplets which gives numerous chances for the radiation to reach most droplets. Thus, the whole body of liquid gets access to the radiation effectively penetrating the whole moving body of liquid.

[0029] Another advantage of this invention is the way radiation is directed to the liquid droplets. The directly mounted energy source above the product surface as in solids heating requires a large surface. For the arrangement in the present invention, direct mounting of energy source is not necessary and the wave guide also actually focuses the radiation and hence it can be applied only from a relatively small window on the cylinder wall. The radiation is normally reflected and focused because of the shape of wave guide, but it can be optically carried out too. On the other hand, energy source can be mounted directly on the wall through a transparent window if so desired.

[0030] FIG. 2 illustrates one way of using this invention in a pasteurization system for milk or other similar products. Here raw product is allowed in a balance tank 1 from which it is pumped through a heating regenerator 3 and the IR heater 5 (current invention) as described in FIG. 1 and through hold tube 6. From this point, it cools down through regenerator 3 and then final cooling is done in heat exchanger 7 before going to filler or cold storage tank. In certain cases, it may be necessary to hold the milk at a certain temperature and time so as to activate dormant bacterial spores by an additional hold section 4. In this arrangement, the final heating section of a regular pasteurization system such as High Temperature Short Time (HTST) or Higher Heat Shorter Time (HHST) is replaced by the current invention heater, thus, the overall efficiency of the system remains high. Further, the critical control point (CCP) in this arrangement is the hold temperature at hold tube 6, just like conventional HTST system.

[0031] The advantage can be further extended by this invention in that Extended Shelf Life (ESL) like quality can be achieved at lower temperature than those used in conventional UHT units where temperature as high as 285290 F. are used. This is possible because spores can be destroyed by application of high energy of IR and other EM radiation. For example, if milk is heated to a final heating temperature of 195 F. through IR heating by the present invention and held for 30 seconds, the chemical degradation will be only 20% (C* or 3%Thiamin destruction basis) of what would occur at 285 F. holding for 4 seconds which are routinely employed for ESL milk. Thus, this invention has a great potential for increasing shelf life of milk with better nutritional and flavor quality than conventional ESL milk using UHT/aseptic temperature and hold profile.

[0032] While the invention has been shown and described with preference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the claims here.