In-line electromagnetic energy wave applicator

An in-line microwave applicator has an electromagnetic energy wave generating unit which transmits waves, particularly microwaves, dispersing from a longitudinal axis. The dispersing waves are interrupted by microwave diverters which cause the wave lengths to be transmitted through holes from the first chamber to a second surrounding chamber. The second surrounding chamber has interior walls which are reflective to the microwaves and may have a spiral rib to enhance reflectivity. Product for heating is passed through the second chamber to be irradiated by microwaves exiting the holes from the first chamber. The holes are generally elongate in shape and can be surrounded with microwave transparent material to prevent material from falling through. The microwave diverters can be protrusions extending from the holes into the inner chamber by increasing amounts as the distance from the microwave energy generating unit increases. Alternatively, cones placed at varying angles, a generally spiral shape member, or a series of disks can be used as microwave diverters. Product can be carried through the second chamber using a single or variable pitch helix or screw.

BACKGROUND OF THE INVENTION 
The present invention relates to apparatus and methodology for applying 
electromagnetic wave energy, particularly microwaves, to a product to be 
heated, such as contaminated and infectious waste products to be 
sterilized. 
Environmental concerns have motivated a search for waste incineration 
systems which efficiently incinerate waste materials while decreasing 
pollutant emissions. The need for such systems is particularly critical 
for disposal of contaminated and infectious wastes, such as hospital 
waste. Traditional incineration systems burn waste at relatively low 
temperatures and tend to emit unacceptably high levels of fly ash and 
other pollutants. 
The use of electromagnetic energy waves, in particular microwaves, to heat 
materials is well known. One heating apparatus using microwaves is 
disclosed in U.S. Pat. No. 4,565,670 to Miyazaki. Miyazaki discloses a 
stationary outer cylinder and a rotatable inner cylinder to form a passage 
in between the cylinders for the continuous heat treatment of a substance 
passing through the passage. Material passes from inlet pipe 1 through 
passage 14 to outlet pipe 2. As the material traverses the path it is 
exposed to microwaves through waveguides 3 located at the inlet end 
position, the outlet end position and an intermediate position on the 
circumferential wall of the outer cylinder 4. By applying microwave 
radiation from the periphery, Miyazaki requires the application microwaves 
at multiple locations. 
U.S. Pat. No. 4,608,261 to MacKenzie discloses a method and apparatus for 
producing a puffed foodstuff using a microwave generator 19 mounted within 
a microwave cavity 16 to apply microwave energy to raw material passing 
through a tubular conveyance section 17. Like Miyazaki, MacKenzie situates 
the microwave generator at a point above the material to be radiated. 
U.S. Pat. No. 4,330,946 to Courneya discloses a high efficiency material 
drying apparatus with microwave sources 30 located above a primary chamber 
40, where the heat is concentrated on the material moved along an auger 
pathway. Microwave sources or magnetrons 30 are offset to direct their 
energy to the location of the majority of material at any instant. Thus, 
Courneya also has the disadvantage of requiring a plurality of points 
applying microwaves to the material being heated. 
U.S. Pat. No. 4,087,921 discloses a microwave drying apparatus with 
microwave units 17 located on opposite sides of drum 11 which has 
longitudinally extending buffers 43 projecting radially inward from the 
inner surface of the drum. This causes a tumbling action of material 
passing through the drum to enhance the drying effect produced by the 
microwave units 17. Again a plurality of microwave application locations 
is required. 
All of the patent documents discussed above require the application of 
microwaves using one or more microwave sources located at various 
locations surrounding the material to be heated. As a result, each of the 
units is costly and inefficient. 
U.S. Pat. No. 4,193,448 to Jeambey discloses an apparatus for recovery of 
petroleum from petroleum impregnated media. The apparatus uses a microwave 
generator and a guide for directing microwaves to a dispersing chamber for 
heating the media. A plurality of holes is used for the flow of heated 
petroleum into the petroleum chamber. In operation, a hole is drilled in a 
petroleum impregnated media such as rock or shale and the apparatus is 
inserted into the hole. A drive motor is energized to rotate blades 50 of 
mixing device 48 causing microwaves to be dispersed from dispersing 
chamber 28 through the microwave transparent shell portion 46 into the 
surrounding media. The media is thus heated and the heated petroleum 
drains into the drilled hole. Shell 16 is moved up and down to facilitate 
recovery of oil into the chamber 32 through holes 64. Microwaves do not 
pass through the holes. 
U.S. Pat. No. 4,410,553 to McGinty discloses a method and apparatus for 
cooking particular foodstuffs. The apparatus uses an elongated source of 
radiant heat, preferably a single resistance electric heater element which 
emits infrared radiation. Alternatively, multiple bar resistance electric 
heater elements having an associated concave reflector could be used. 
McGinty also discloses the use of a helix which can rotate to advance 
foodstuffs or can be fixed inside a retaining means and rotate therewith. 
The helix is further disclosed to have a variable pitch with the smallest 
pitch being in the area where the cooking is conducted for the longest 
length of time. Neither Jeambey nor McGinty discloses the use of reflected 
microwaves to provide heating of a material passing from an inlet to an 
outlet. In addition, none of the references discloses an efficient means 
for using a single source of microwave radiation to heat a product. Thus, 
the current art fails to disclose an in-line microwave applicator which 
can apply microwaves to material to be heated in an efficient manner. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a less costly 
and more efficient system for applying electromagnetic energy to material 
to be heated. 
It is still another object of the invention to provide substantially 
uniform heating of material without hot spots to extremely high 
temperatures, where necessary. 
It is another object of the invention to provide an efficient in-line 
microwave applicator which requires only a single source of microwave 
energy to heat a product to high levels, for example, to sterilize 
infectious wastes. 
It is another object of the invention to eliminate the need for multiple 
radiation sources around a periphery of material to be heated. 
It is a further object of the invention to improve heating efficiency by 
making use of direct and reflected energy in heating product. 
It is a further object of the invention to divert microwave energy from a 
single microwave energy source to heat a product moving along an axis 
parallel to a longitudinal axis of the microwave source. 
It is a further object of the invention to divert such microwaves through 
holes in the walls of a first chamber into which the microwaves are 
applied while the product to be heated is passed through a second chamber 
surrounding the first chamber. 
It is a further object of the invention to divert the microwaves in the 
first chamber to the holes using protrusions extending from the holes, 
with the protrusions progressively increasing in size as the microwaves 
travel farther from the source of microwave generation. 
It is still another object of the invention to divert microwaves through 
the holes using either diverting discs or a spiral shaped member which 
interrupts the microwaves travelling in the first chamber. 
It is still another object of the invention to configure an outer chamber 
surrounding an inner chamber having holes through which the microwaves 
pass to accommodate products of various thickness and moisture contents. 
It is still another object of the invention to cover the holes of the first 
chamber with one or more sleeves of substantially microwave transparent 
material, such as TEFLON, to prevent waste product from being communicated 
into the first chamber. 
It is still another object of the invention to provide a conveying means 
for non-liquid products to be heated in the outer chamber. 
It is still another object of the invention to configure the conveying 
means to accommodate products of various thicknesses and moisture content. 
It is still another object of the invention to provide a helical or screw 
type conveying means having a straight shaft and full pitch for products 
which have a consistent moisture mix to permit maximum loading of the unit 
with the variation of sterilization controlled only by the speed of the 
helix rotation. 
It is another object of the invention to provide a straight shaft with 
variable pitch for use with products with higher moisture content by 
restricting the in-feed flow area and the length of the wave exposure to 
the depth of material. 
It is still a further object of the invention that the variation of the 
pitch along the length of the helix slow the product flow and increase the 
holding time in the core to increase the efficiency of microwave exposure. 
It is another object of the invention to provide a compression shaft 
sterilizer in the outer chamber in which the exposure to the microwave 
pattern is maximized on a discharge end by decreasing the product bed 
depth. 
It is a still further object of the invention to vary the pitch on the 
compressive microwave sterilizer shaft to slow or speed up the transfer of 
material through the system resulting in an increase or decrease in 
microwave exposure. 
It is another object of the invention to provide a decompression shaft 
sterilizer for use with extremely high moisture products which controls 
the in-feed depth of the product at the inlet while broadening the product 
bed depth at the outlet. 
It is still another object of the invention that the decompression area 
slow the product speed and allow more exposure and time for exposure to 
the microwaves, thus improving the efficiency of sterilization. 
In accomplishing these and other objects, there has been provided, in 
accordance with one aspect of the present invention, a microwave 
applicator having an inner and outer chamber. The inner chamber receives 
microwaves which disperse from a longitudinal axis from a single source 
and are diverted out of the first chamber by diverters. The diverters 
interrupt the microwave flow and direct it through holes in the walls of 
the first chamber into the second chamber. In the second chamber, product 
travelling from the inlet to the outlet is radiated with the microwave 
radiation diverted through the holes. Microwaves which are not absorbed by 
the product are reflected by the interior wall of the outer chamber and 
the exterior wall of the inner chamber which are reflective to microwaves. 
The interior wall of the outer chamber may also have a spiral shape to 
increase its microwave reflectivity characteristics. Liquid material can 
pass through the outer chamber without any additional assistance. Solids 
or solid-line materials can be moved through the outer chamber using a 
screw type or helix configuration unit. The pitch of the helix can be 
varied, preferably in segments, to accommodate the moisture content of the 
materials. The variation of the pitch along the length can slow the 
product down to increase the holding time in the core and, hence, increase 
the efficiency of the microwave exposure. In addition, the shaft of the 
conveyor can be varied from a straight shaft, which permits maximum 
loading of the unit with the variation of the heating controlled only by 
the speed of the helix, to a compressive unit in which the product bed 
depth is decreased at the discharge end for use with highly infectious low 
moisture content materials. 
A decompressive microwave heating unit can be used for extremely high 
moisture products which cannot be pumped, or slurred and then pumped, 
through the sterilizer unit. In the decompressive microwave heating unit, 
the product bed depth at the outlet is allowed to increase while the 
in-feed depth of the product at the inlet is controlled to avoid 
overloading the microwave distribution in the feed. As a result of the 
decompression, the product speed slows and more of the material is exposed 
to microwaves for a longer time period to effect better heating or 
sterilization. 
According to another aspect of the present invention, a method for heating 
material has been provided that comprises the steps of applying 
electromagnetic radiation from a single source into a first chamber; 
diverting at least a portion of the electromagnetic radiation from the 
first chamber into a second chamber provided around said first chamber; 
and then transporting material through the second chamber such that the 
material is heated by absorption of electromagnetic radiation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
An in-line electromagnetic energy applicator according to the present 
invention has an electromagnetic energy generation unit for transmitting 
energy waves along a longitudinal axis. The energy waves, preferably of 
microwave wavelength, are transmitted into a first chamber with a 
plurality of openings in its walls. A second chamber surrounds the first 
chamber at some distance. The first chamber has at least one 
electromagnetic energy diverter which intersects waves in the first 
chamber as they disperse from a longitudinal axis or are reflected off 
reflective material on the inner walls of the first chamber. This causes 
the electromagnetic energy to be diverted through the openings into the 
second chamber. The second chamber has a product inlet and outlet and may 
also be equipped with a conveyor for moving product from the inlet to the 
outlet. Electromagnetic energy entering through the holes is absorbed by 
the product in the second chamber as it passes from the inlet to the 
outlet resulting in heating of the product. The inner walls of the second 
chamber and the outer walls of the first chamber are made reflective to 
divert energy not absorbed by the product back toward the product to 
improve heating efficiency. Absorption of the electromagnetic energy by 
the product both directly as the waves pass through the holes and 
indirectly as the waves are reflected within the second chamber allows 
highly efficient heating of the product. In addition, heating of the 
product to very high temperatures for sterilization of highly contaminated 
wastes is possible due to efficiencies achieved from the use of direct and 
reflected energy. 
FIG. 1 shows one configuration of a heating unit using an in-line 
applicator. The heating unit shown generally at 1 has an electromagnetic 
energy wave applicator 3 which has an electromagnetic energy wave 
generation unit 5. Electromagnetic waves 7 are transmitted through 
transition section 9 to inner chamber 11. Inner chamber 11 has a 
surrounding wall 13 with a plurality of holes 15 Walls 13 are surrounded 
by a second set of walls 17 which, with walls 13 form a second or outer 
chamber 19. 
Outer chamber 19 also has product inlet 21 on the side nearest the 
electromagnetic energy wave generator and an outlet 23 on an opposite end. 
In order to divert microwaves 7 from inner chamber 11 to outer chamber 19, 
a plurality of diverters 25 are located along an interior portion of walls 
13 of inner chamber. As shown in FIG. 1, the diverters are formed as a 
series of inverted reducing cones 25 facing the microwave length. The 
angle of the cones 25 increases relative to angle of the wavelength 
compared to the directional flow of microwaves from the electromagnetic 
energy wave generation unit 5. This is done to concentrate the deflection 
of the microwaves through the holes into the product to be heated in the 
outer chamber. It also causes the wavelength to hit the interior wall of 
the outer chamber at different angles, which results in more radical 
bounce to create a crisscross microwave pattern for better exposure of the 
product. A small cone 27 at the end of the inner chamber deflects any 
wavelengths that have not been affected by the preceding microwave 
diverters. 
As the microwaves in the inner chamber are interrupted and diverted by cone 
diverters 25 and 27, they are transmitted through holes 15 into outer 
chamber 19. Product passing from inlet 21 to outlet 23 through outer 
chamber 19 is radiated by the microwaves passing through the holes. 
Microwaves which are not absorbed by the product are reflected off the 
inner surface of the outer chamber to be absorbed by the product on a 
reflected path. Microwaves which are not absorbed at this stage are again 
reflected off the outside walls 15 of inner chamber 13. As a result, 
material passing through the outer chamber is efficiently radiated and 
heated. In order to prevent product in the outer chamber 19 from falling 
into the inner chamber 13, the holes can be sealed with an external sleeve 
16 made from material which is substantially transparent to microwaves. 
One such material is TELFON. Alternatively, the entire outer wall 15 of 
inner chamber 13 can be surrounded by the sleeve. For example, the inner 
tube applicator assembly can be inserted directly into the cavity inside 
the sleeve. In addition, a screw type conveyor which is inside the outer 
chamber, as discussed below, can incorporate the sleeve into which the 
applicator is inserted. 
The length of the outer chamber is longer than the length of the inner 
chamber. As is further discussed below, this allows further application of 
microwaves to product in the distal section 29 of the heating unit 
furthest from the electromagnetic energy wave generating unit 5. 
FIG. 2 shows a top view of the microwave applicator which is formed by 
microwave energy generating unit 5, transition coupling 7 and inner 
chamber 11. The electromagnetic waves typically have wave lengths of 
between 0.3 cm and 30 cm, corresponding to frequencies of 1 GHz to 100 
GHz. For sterilizing infectious wastes, the generator could be constructed 
to generate 80,000 Watts of usable output energy. However, other amounts 
of power could be used for other applications. 
As shown in FIG. 2, a portion of inner chamber 11 has holes 15 which are 
formed in lines substantially parallel to each other with adjacent lines 
of holes being offset. FIG. 3 further illustrates the orientation of the 
holes 15 and their shape. In a preferred embodiment, each hole 15 has a 
substantially continuous or curved end 31 and a substantially 
discontinuous or squared end 33. The curved ends of the holes are on the 
side closest to the electromagnetic energy wave generating unit 5. As 
shown in FIGS. 8 and 10, protrusions 53 can be extended from holes 15 into 
the interior portion of the inner chamber to form microwave diverters. 
Protrusions 53 are used instead of cones 25 in applications which require 
very even heating of the material in the chamber with a minimum of hot 
spots. Cones 25 and 27 are best used as energy diverters when the material 
to be heated has a high moisture level and can tolerate hot and cold 
spots. High moisture content may result from the material itself or may be 
the result of pre-treatments, such as steam heating of the material to 
pass through the applicator. 
The extension of the protrusions 53 into the inner chamber 11 becomes 
increasingly larger as the distance from electromagnetic energy wave 
generating unit 5 increases. The protrusions 53 can be individual pieces 
connected to the inner chamber walls. Preferably, however, the protrusions 
53 are formed by punching the holes into the walls of the inner chamber 
and using the punched lip to form the protrusion. Each punched hole in the 
line would have an increased size protrusion or lip 53 protruding into the 
flow of the wavelength, so as to direct the wavelength out of the slot at 
each contact with the punched lip. The wavelength is then directed into 
the product in the outer chamber, and, if not absorbed, hits the side wall 
of the outer chamber and then bounces back toward the product. With 
multiple waves, this procedure sets up a crossing of wavelengths bouncing 
against the chamber wall and the applicator metal, thus increasing the 
exposure to the material to be sterilized. 
Hole size is a function of energy required for the heating application, 
such as sterilization. For instance, if an electromagnetic energy 
wave-generating unit is used with a large power capability on the order of 
100,000M Watts, and the material to be sterilized has a solid-to-liquid 
ratio between 12% and 15% and if a conveyor moves the material through the 
outer tube at 250 lbs/hr, then the holes are sized to be 3/4 inch by 11/4 
inch. For applications in which the flow rate or the solid-to liquid-ratio 
is different, the required size of each hole changes proportionally, 
according to a linear relationship. For example, an applicator with a 
50,000M Watt power source and hole sizes whose area is 50% that above for 
the 100,000M Watt power source would accommodate loads of 125 lbs/hr. 
As another example of the linear relationship assume that an applicator has 
a length required for a 100,000M Watt power source. The applicator 
typically can accommodate turn down of 60% power without producing either 
hot spots or areas of low heat transfer in the material to be heated. 
Operating such an applicator at less than 60% of the power, for example, 
to accommodate lower temperatures, results in cold spots (low heat 
transfer areas) generally located in the material to be heated near the 
middle of the applicator. This is because a large portion of the energy 
escapes in the first section of the applicator nearest the power source. 
As a result a wavelength bouncing pattern is not established and much of 
the heating effect achieved from bouncing electromagnetic waves is lost. 
Some waves are reflected off the end opposite the power source, so that 
the least heating tends to be in the middle of the applicator. By reducing 
the power capability to 60% or 60,000 MW and similarly reducing the size 
of the applicator and its elements by the same percentage to 60% of the 
size used with a 100,000M Watt source, a wavelength bouncing pattern can 
again be established. Thus, the length of the inner and outer chambers and 
the size of the holes and protrusions are arranged to be 60% of the size 
required for the 100,000MW power source. It should be noted that the 
distance from the inner chamber 11 to the walls 17 of the outer chamber 19 
is not changed to accommodate the same wavelength. This is to insure 
reflective bounce for better heating. Since effective operation can be 
maintained to a turndown of power to 60% of the source capability, such a 
configuration would operate at power levels between 36,000M Watts and 
60,000M Watts. 
In heating applications requiring especially even heating, better 
distribution of the microwaves can be obtained by arranging the 
protrusions according to a spiral pattern. The spiral pattern is arranged 
to be clockwise or counter clockwise to correspond to the spiral pattern 
of screw type product conveyors which move the material to be heated 
through the outer chamber as discussed below. Such a spiral pattern of 
protrusions can be established by offsetting the centerlines in a 
horizontal plane of each row of holes by five to ten degrees from the 
centerline of the adjacent row as illustrated in FIG. 12. Eventually, the 
centerline of a row matches the centerline of a first row. The spiral 
pattern of protrusions along with the increasing size of each protrusion 
as the distance from the electromagnetic wave generator increases work 
together with the spiral screw shaped conveyors to establish greater 
distribution of electromagnetic energy to the product passing through the 
outer chamber. 
In applicators employing cones rather than protrusions, hole size is 
reduced as described above. The size of the center cone 27 decreases in 
the same proportion as described above. It should be noted that the cone 
type applicator can be employed in a screw type chamber discussed below. 
FIG. 11 illustrates another possible microwave diverter. In the microwave 
diverter arrangement shown in FIG. 11, a plurality of disks 37 is used to 
interrupt the wave lengths and divert the microwaves out of holes 15. FIG. 
12 shows a spiral or screw type diverter pattern of the lips or 
protrusions in which waves traveling through inner chamber 11 are 
interrupted by the protruding portions arranged in the screw pattern and 
are then diverted out holes 15 to the second chamber. It should be noted 
that the size of the screw protrusions can be varied from one end of the 
applicator unit to the other and that the spiral or screw type pattern 
follows the right or left hand screw pattern of the screw type conveyor in 
the outer chamber. 
The heating unit 1, shown in FIG. 1, works well for liquid product which is 
easily pumped in and removed. Solids and semi-solids require a conveyor 
means to traverse the outer chamber 19. FIG. 4 shows a single pitch 
helical or screw type conveyor 39 used in the outer chamber 19. As 
discussed below, for some applications one or more pitches are used. Screw 
type conveyors can be constructed of microwave transparent material, such 
as TEFLON, to avoid affecting the microwave paths in the outer chamber. 
Extending from the end of first chamber 11 to the end of second chamber 19 
in the area 29 of the second chamber is straight shaft 41. The straight 
shaft full pitch unit allows sufficient heating of products with a 
substantially consistent moisture mix. The straight shaft permits maximum 
loading of the unit so that the variations in heating are controlled only 
by the speed at which helical coil 39 is turned. 
FIG. 5 illustrates a compression shaft heating unit with a full pitch 
helical coil for conveying the materials. In the compressive shaft, the 
product bed depth at the discharge end is forced to be narrower than the 
product bed depth at the in-feed end. This is because of the increasing 
thickness of shaft 43 in the outer chamber 19. As FIG. 5 shows, the 
distance between the walls of inner chamber 11 and outer chamber 19 is 
greatest at the in-feed end nearest the electromagnetic energy wave 
generation unit 5 and narrowest at the end of the outer tube furthest from 
the electromagnetic energy wave generation unit 5. As a result, the bed 
depth of the product is greater at the in-feed end than at the discharge 
end. This type of unit would be used for materials with low moisture 
content and which may be very infectious. The compression end maximizes 
the exposure to the wave pattern on the discharge end by decreasing the 
product bed depth. In addition, this configuration allows for a large 
volumetric feed and maximizes the in-feed rate. 
FIG. 6 illustrates a decompression shaft microwave heating unit. In this 
unit, the distance between the walls of the shaft and the walls of the 
outer tube is smallest at the infeed end nearest the electromagnetic 
energy wave generation unit 5 and largest at the discharge end on the 
opposite side of the outer chamber 19. This controls the in-feed depth of 
the product at the inlet, so as not to overload the microwave distribution 
in the feed. As the product traverses the length of the outer tube, the 
decompression slows the product speed and allows more of the material to 
be exposed for a greater time period to the microwaves. This provides 
better heating and would therefore be best used for extremely high 
moisture content products which cannot be pumped or which could not be 
slurred and then pumped through a liquid unit such as that shown in FIG. 
1. 
FIG. 7 illustrates a variable pitch helical conveyor. One example is shown 
in FIG. 7, in which the helical conveyor 39 has a full pitch section 47, a 
3/4 pitch section 49 and a 1/2 pitch section 51. These sections or 
segments in the pitch of the conveyor allow for variations in the product 
flow through the outer chamber. As shown in FIG. 7, in the half pitch 
section 51 the number of turns is twice that of the full pitch section 47. 
As product moves from the half pitch segment toward the full pitch segment 
of the helical conveyor coil, it slows down and the holding time in the 
second chamber during which the product is irradiated with electromagnetic 
energy waves is increased. As a result, the heating and sterilization 
efficiency of the product is improved. In some cases, this may also allow 
operating at lower power levels. 
FIG. 8 illustrates a straight shaft sterilizer with a variable pitch helix 
or screw. As FIGS. 4, 5 and 6 also illustrate, any of these configurations 
can be used with a variable pitch screw to achieve the effects discussed 
above. Thus, it will be known to those of ordinary skill that the full 
pitch versions shown in FIGS. 4, 5 and 6 are by way of illustration and 
not by limitation. 
FIG. 9 further illustrates the use of cones in the inner chamber to divert 
microwaves into the outer chamber. FIG. 9 also shows outer chamber 19 
having interior walls with a substantially spiral shape. This spiral rib 
along the interior walls of chamber 19 causes a deflection in the 
directional flow of microwaves, thus increasing the exposure pattern. As a 
result the efficiency of microwave energy transfer to the product within 
the outer chamber is increased and more effective heating is accomplished. 
While specific embodiments of the invention have been described and 
illustrated, it will be clear that variations in the details of the 
embodiments specifically illustrated and described may be made without 
departing from the true spirit and scope of the invention as defined in 
the appended claims.