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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of regenerative gas or air
drying systems and more particularly to such regenerative gas or air
drying systems which employ a desiccant contained in a chamber to adsorb
moisture of the wet gas inserted into the chamber to dry the gas and in
which dry purge gas is subsequently inserted into the chamber to
regenerate saturated desiccant which had absorbed the moisture in drying
the previously inserted wet gas.
2. Description of the Related Art Including Information Disclosed Under 37
C.F.R. .sctn.1.97-1.99
Drying devices which receive a wet gas under pressure such as air
containing a high level of moisture are well known. These gas drying
devices are commonly used in many industrial applications such as spray
painting, pneumatic control systems and air operated equipment. It is also
known in such devices to utilize a desiccant such as activated alumina,
carbons, silica gels or molecular sieves located in a chamber to adsorb
and remove the moisture from the inlet inserting the wet air under
pressure to one end of the chamber. Such air drying devices frequently use
a portion of the dried air also called a purge gas from one desiccant
chamber that is drying air to regenerate the desiccant in another chamber
that has already removed moisture from the wet air earlier. The portion of
dried air or purge gas is often diverted to a heater to elevate the
temperature of the purge gas. Thereafter, the heated purge gas is moved to
the other desiccant chamber to dry out and regenerate the saturated
desiccant located therein.
These known regenerative gas drying devices typically use a dual chamber
system in which wet gas is received through an inlet at the top of one of
the chambers. As the wet gas migrates through the chamber, moisture is
adsorbed by the desiccant thereby drying the gas. The majority of the
dried gas is carried to a gas outlet thereby leaving the gas drying
system. However, a small portion of the gas called purge gas is diverted
to a transport pipe which carries the dry gas to a heater.
The purge gas is heated and transported to the other chamber which is
operating to regenerate or dry out the previously adsorbed desiccant. The
heated purge gas dries the saturated desiccant in the other chamber during
the regeneration cycle. The high moisture air resulting from the drying of
the saturated desiccant is removed from the other chamber at an opposite
end from the end which receives the purge gas.
Once the desiccant in the first chamber drying the wet gas is sufficiently
saturated during the air drying cycle and the desiccant in the other
chamber is dried out during the regeneration cycle, the cycles are
reversed by flipping diverter valves interposed between the two pressure
chambers. The dry and heated purge gas received from the other chamber
drying wet air is, in turn, used to dry and regenerate the saturated
desiccant in the first chamber. These drying systems are cycled back and
forth in this manner to continuously dry out the wet gases and regenerate
desiccant.
Disadvantageously, many problems arise in employing such known gas drying
systems. A significantly large percentage of the dried air must be used
for purge in order to regenerate the saturated desiccant. This results in
an inefficient use of the dried air since a high percentage of it must be
used as purge to dry saturated desiccant instead of being used right away
or collected, contained and sold for industrial purposes. Furthermore, the
high percentage of the diverted dry air must be heated by heaters which
utilize large quantities of energy and operate at very high temperatures.
The high temperatures can precipitate fire hazards particularly when such
heaters are in close proximity to oil lubricated compressors used in
conjunction with these systems to pressurize the desiccant chambers.
Attempts have been made to dry material in a cylindrical receptacle by
subjecting the material to electromagnetic waves. In U.S. Pat. No.
4,339,648 to Jean issued Jul. 13, 1982, an antenna extends the entire
length of a single receptacle to provide radiation energy from top to
bottom of the receptacle. Jean also shows a coiled antenna which extends
along a helix inside the receptacle. Jean, however, is not used in a dual
chamber regenerative gas drying system in which dry purge gas is inserted
at one end of one chamber regenerating desiccant. Disadvantageously, the
antenna of Jean extends the entire length of the chamber which
inefficiently wastes radiant energy on areas which are relatively dry in
regenerative gas drying systems and which do not necessarily need such
radiant energy. Since the apparatus of Jean is not employed in a
regenerative gas drying system, it does not concentrate the distribution
of energy on areas within the chamber which require the most heat to
regenerate saturated desiccant contained therein.
Attempts have further been made to transmit microwave energy into
pressurized tanks in regenerative gas drying systems to heat gases
adsorbed by desiccant materials contained therein. In U.S. Pat. No.
4,312,640 to Verrando issued Jan. 26, 1982, and U.S. Pat. No. 4,312,641 to
Verrando issued Jan. 26, 1982, microwave energy is passed through
microwave pressure windows and into tanks carrying sorbent or desiccant
material. The microwaves are used to release and remove a polar gas
adsorbed by sorbent or desiccant material in the tanks. The microwave
energy is prevented from being sent into the tanks in response to the
desorbtion of the moisture from the sorbent material. Purge gas is still
moved through the desorbing desiccant until the moisture level of the
chamber is adequately lowered.
In U.S. Pat. No. 4,322,394 to Mesey et. al. issued Mar. 30, 1982, microwave
energy is used to dielectrically heat saturated solids of noncarbon
adsorbents for the removal of adsorbed materials. The microwaves heat the
adsorbents internally to bring the adsorbents to a temperature for
desorbing some of the adsorbate in the absence of any activating or purge
gas.
Disadvantageously, in these systems the distribution of the microwave
energy within the pressurized tanks is limited. Furthermore, there is
continued inefficient use of purge gas to aid in the drying cycle for
regenerating desiccant contained therein. The microwave energy in such
devices which is sent through pressure windows adjacent the tank enhances
the ability of removal of the adsorbed material proximate to the pressure
windows. However, since these known air drying systems do not sufficiently
disperse the microwaves through concentrated areas of high saturation in
the tank, the material adsorbed by the desiccant located away from the
pressure windows does not get sufficiently energized by the microwaves to
efficiently adsorb the adsorbate material. Thus, desorbtion of wet gas is
achieved only at locations proximate to the pressurized windows while
desiccant further away from the pressure windows does not receive
effective and beneficial microwave energy for desorbtion. Additionally,
such systems do not use microwave energy to ultimately heat dry gas which
is inserted into the regenerating tank as purge.
SUMMARY OF THE INVENTION
Accordingly, it is the principal object of the present invention to provide
a regenerative gas drying system which overcomes the problems of known gas
drying systems by efficiently utilizing microwave energy and purge gas
during a regeneration cycle to desorb moisture absorbed by desiccant in a
chamber.
Another object of the present invention is to provide a conduit disposed
within the desiccant of the regenerating chamber in which the conduit
carries the drier gas directed from the adsorbing chamber to the
regenerating chamber and provide a microwave antenna in communication with
microwaves generated by a microwave generator coupled with the antenna in
which at least a portion of the antenna is positioned within desiccant
contained in the regenerating chamber which will cause desorbing of
moisture carried by the desiccant in the regenerating chamber and heating
of the dry gas carried by the conduit.
Another object of the present invention includes providing a method for
positioning a conduit within the desiccant of the regenerating chamber in
which the conduit carries the drier gas directed from the adsorbing
chamber to the regenerating chamber and positioning a microwave antenna in
communication with microwaves generated by a microwave generator coupled
with the antenna in which at least a portion of the antenna is positioned
within desiccant contained in the regenerating chamber which causes the
desorbing of moisture carried by the desiccant in the regenerating chamber
and heating of the drier gas carried by the conduit.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing objects and advantageous features of the invention will be
explained in greater detail and others will be made apparent from the
detailed description of the preferred embodiments of the present invention
which are given reference to the several figures of the drawing, in which:
FIG. 1 is a schematic view of the regenerative gas drying system of the
present invention;
FIG. 2 is a schematic view of the regenerating chamber of the present
invention;
FIG. 3A is a cross sectional view along line III--III of FIG. 2;
FIG. 3B is a cross sectional view along line III--III of FIG. 2 of another
embodiment;
FIG. 3C is a cross sectional view along line III--III of FIG. 2 of another
embodiment; and
FIG. 4 is a cross sectional view along line IV--IV of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, regenerative gas drying device 30 is shown in which
wet gas 31 (illustrated by solid arrows) enters through wet gas inlet 32
and is introduced through channel 34 and screen 35 into adsorbing or gas
drying chamber 36 containing desiccant material 38. The desiccant 38
contained in chamber 36 adsorbs moisture from the wet gas 31 in order to
dry the wet gas. The drier or dried gas 40 (illustrated by hollow arrows)
exits the chamber 36 through screen 42 and is carried to dry gas outlet 44
at which dry gas 40 leaves the regenerative gas drying system 30. These
regenerative gas drying systems 30 are commonly used to dry wet air,
however, other gases can be similarly or analogously treated with use of
these types of devices. In addition, the chambers that hold the desiccant
often have gas under pressure introduced into the chamber in either the
adsorption procedure and the regeneration procedure or both, however, the
present invention would also be contemplated to work not only with
chambers utilizing gas under pressure but also in ambient or
nonpressurized environments.
As the one drying or adsorbing chamber 36 dries out wet gas 31,
regenerating chamber 46 of drying system 30 removes moisture adsorbed by
desiccant 38 contained in the regenerating chamber 46. Desiccant 38 of
regenerating chamber 46 was saturated with moisture when wet air was
previously passed through regenerating chamber 46 in an earlier gas drying
cycle. In regenerative gas drying systems 30 both chambers 36 and 46 cycle
back and forth while drying gas in the former the latter is drying
desiccant and once the former chamber is saturated the cycle reverses and
the former chamber is now a regenerating chamber drying out the desiccant
while the latter is drying wet gas. This cycling back and forth assists in
providing a more continuous production of dry gas.
Disposed within each chamber 36 and 46 is an antenna member 48 which is in
communication with microwaves 50, during a desiccant regenerating cycle,
which are generated by microwave generator 52. Waveguide 54 is oriented
with respect to microwave generator 52 to receive the microwaves so
generated from generator 52 and carry them to a portion of the antenna
member 48A disposed within the waveguide. The microwaves are carried along
the length of the antenna 48 which has a portion 48A extending outside of
the chamber 46 and disposed within waveguide 54. Antenna 48 extends
through chamber 46 having portion 48B mounted or disposed outside of
desiccant 38 and another portion 48C within the chamber immersed within
the desiccant. The microwave energy is conducted by antenna 48 and travels
along its length into the chamber 46 carrying the desiccant 38. The
microwave energy carried into chamber 46 is adsorbed by the moisture held
by the desiccant 38 which heats the moisture adsorbed by the desiccant and
thereby release the moisture from the desiccant 38 to remove the moisture
adsorbed by the desiccant 38 within the chamber. Thus in the interest of
maintaining a relative continuous dry air flow through dry gas outlet 44,
as mentioned above, one chamber 36 is drying wet gas 31 while the other
regenerating chamber 46 is in the process of drying and regenerating
desiccant 38 utilizing microwave energy as well as with heated drier or
purge gas 40 as will be discussed more fully below. This process will be
reversed once the desiccant 38 in chamber 36 becomes saturated.
Preferably microwave antenna 48 is a solid, rod shaped, elongated aluminum
member. The aluminum antenna rod 48 has an outside surface which is
substantially smooth to prevent arcing of the high frequency microwaves
which are conducted by the aluminum antenna rod. However, it is
contemplated that other shapes and configurations of antenna members may
be used, as well as, various commonly known materials may be used in
constructing the antenna member of the present invention.
Regenerative gas drying system 30 of this invention utilizes microwave
antenna 48 as described above in conjunction with conduit 55 which is
disposed in desiccant 38 of regenerating chamber 46 in which conduit 55
carries drier or dry gas 40, directed from adsorbing chamber 36 to
regenerating chamber 46.
Drier gas 40, as seen in FIG. 1, exits the bottom portion of adsorbing
chamber 36 at screen 42 and moves along exiting conduit 45 where a vast
majority of the drier gas 40 exits dry gas outlet 44 for a desired use
while a small percentage of drier gas 40 is diverted into a transport pipe
56. Transport pipe 56 moves drier gas 40 in a direction toward the upper
area of chambers 36 and 46. Since chamber 46 in FIGS. 1 and 2 is being
used to regenerate desiccant 38, shut off valve 59 is closed, preventing
drier gas 40 from entering adsorbing chamber 36 while it is operating to
dry wet gas 31, and shut off valve 61 is open permitting drier gas 40 to
enter regenerating chamber 46 while contained in conduit 55.
This invention further includes means for heating the drier gas 40 carried
in the conduit 55 which is disposed in desiccant 38 of regenerating
chamber 46. This heating means includes the microwave energy transmitted
from antenna 48 into desiccant 38 in which the energy is adsorbed by the
moisture carried by desiccant 38. The moisture is heated by the microwave
energy and in turn heats the surrounding desiccant 38 and conduit 55. As
conduit 55 becomes heated the heat energy is in turn conducted to drier
gas 40 carried by conduit 55. Thus, the temperature of drier gas 40 rises
and is elevated over the temperature drier gas 40 was as it exited
adsorbing chamber 36. This heated drier gas 40 carried in conduit 55 is
removed from chamber 46 by an additional conduit 63 which is connected to
conduit 55 which returns the now removed heated drier gas 40 to
regenerating chamber 46 through additional conduit 63 being connected to
purge gas inlet 58. As a result, purge or drier gas 40 now heated can be
used to dry the saturated desiccant 38 contained in regenerating chamber
46.
As shown in FIG. 2, it is preferable for microwave antenna 48 to be
inserted at one end of the regenerating chamber 46, which in this drawing
is top portion 65 and in which the heated drier gas 40 returns to
regenerating chamber 46 at another end or bottom portion 67 of
regenerating chamber 46 opposite the top end at which microwave antenna 48
is inserted. As will be mentioned below, a higher moisture content of the
desiccant is located in the upper region of chamber 46 and the microwave
energy can be greatly used at that location while on the other hand the
lower regions of desiccant 38 will contain less moisture of which will be
desorbed by drier gas 40.
Conduit 55 is made of a conductive material such that the conduit carrying
drier gas 40 acts as a secondary antenna to microwave antenna 48 in
regenerating chamber 46. As a secondary antenna, microwave energy can be
further distributed throughout desiccant 38. Additionally, by being
conductive, conduit 55 readily conducts heat received from the surrounding
heated moisture carried by desiccant 38 to drier gas 40 thereby elevating
drier gas 40 as discussed above. With the temperature elevated in drier
gas 40 it will work more effectively in drying desiccant 38 in chamber 46.
There are many commonly known conductive materials which would be suitable
such as aluminum that will perform well in conducting and transmitting
microwaves as well as conducting heat.
Thus, the present invention provides a very efficient regenerative device
in which microwave energy is transmitted into saturated desiccant and
conduit 55 which carries drier gas 40 from adsorbing chamber 36 through
desiccant 38 which is being exposed to microwave energy. Conduit 55 in
turn retransmits the microwave energy for better dispersement of the
energy throughout the saturated desiccant and conducts heat energy, to
drier gas 40 contained in conduit 55, which is received from surrounding
desiccant 38 carrying moisture that is being energized by the microwave
energy. As a result, drier gas 40 becomes heated just prior to releasing
it into regenerating chamber 46 to assist in drying desiccant 38 and
moving moisture being desorbed from desiccant 38 to outlet 62 of chamber
46.
As shown in FIGS. 1-4, conduit 55 carrying drier gas 40 is made of hollow
tubing which is shaped or configured into a helical coil shape. The
helical coil shape of the hollow tubing has a plurality of adjacent turns
69. Adjacent turns 69 are spaced apart from each other. This spread out
helical coil provides an efficient distribution of conduit 55 being
disposed within desiccant 38. Other shapes or configurations that provide
even distribution of conduit 55 are contemplated.
In this particular configuration of conduit 55, adjacent turns 69 of the
hollow tubing define an opening 71 in which microwave antenna 48 is
positioned. This positioning of microwave antenna 48 within opening 71 of
conduit 55 permits microwaves to radiate outwardly from antenna 48 and be
retransmitted by conduit 55. It is further desired for efficient
distribution to place microwave antenna 48 along central longitudinal axis
73 of opening 71 defined by adjacent turns 69, as shown in FIG. 4.
In other embodiments, as shown in FIGS. 3B and 3C, of the present invention
a plurality of other microwave antennas 75 are placed within opening 71
substantially equally spaced apart and oriented in a substantially
parallel direction to each other and to microwave antenna 48 positioned
along central longitudinal axis 73 of opening 71.
With regard to conduit 55 being disposed within desiccant 38 stored in
chamber 46, desiccant 38 forms a pair of ends 77 and 79, which corresponds
to top end and bottom end 77,79 respectively, of the desiccant 38 in
regenerating chamber 46. As can be seen in FIGS. 1 and 2 conduit 55 in the
shape of a helical coil is positioned closer to one of the pair of
desiccant ends 77, 79 than the other. In this embodiment it is preferable
to position conduit 55 closer to top end 77 of the desiccant 38 than the
other or bottom end 79. In this embodiment the top end 77 of desiccant 38
in chamber 46 has typically higher moisture content than bottom end 79,
since in the drying of the air cycle, as seen in adsorbing chamber 36, wet
gas 31 comes into the chamber from the top end 79 of desiccant 38. This
moisture content will contribute to generating a higher level of heat with
the exposure of microwave energy to the moisture which can in turn be
conducted through conduit 55 to heat drier gas 40. Also, with the higher
moisture content at the top portion of desiccant 38 in chamber 46 more
distribution of microwave energy will be facilitated by conduit 55.
The present invention provides a method for drying desiccant 38 in
regenerative gas drying system 30 having adsorbing chamber 36 and
regenerating chamber 46 with both chambers containing desiccant 38 in
which adsorbing chamber 36 receives wet gas 31 for adsorption of moisture
by desiccant 38 contained therein to create a drier gas 40 and in which a
portion of drier gas 40 exiting adsorbing chamber 36 is directed and
carried to regenerating chamber 46 to dry desiccant 38 contained within
regenerating chamber 46, which includes the step of positioning conduit 55
within desiccant 38 of regenerating chamber 46 in which conduit 55 carries
drier gas 40 directed from adsorbing chamber 36 to regenerating chamber
46. The method further includes the step of positioning microwave antenna
48 in communication with microwaves generated by microwave generator 54
coupled with antenna 48 in which at least a portion of antenna 48 is
positioned within desiccant 38 contained in regenerating chamber 46.
The method further includes regenerating chamber 46 having an upper and
lower portions 65 and 67, respectively, in which the step of positioning
microwave antenna 48 includes inserting antenna 48 through upper portion
65 of chamber 46 and downwardly into chamber 46 and into desiccant 38.
As can been seen in FIG. 2, the step of positioning microwave antenna 48
includes regenerative chamber 46 being filled with desiccant from bottom
portion 67 of chamber 46 to a point below the top portion 65 of chamber 46
and placing antenna 48 to extend to a point in desiccant 38 above bottom
portion 67 of chamber 46. It is desirable, as mentioned above to position
antenna 48 along longitudinal axis of chamber 46.
As discussed earlier conduit 55 is formed of a conductive material such as
aluminum and the like which will readily conduct heat and transmit
microwave energy. The step of positioning conduit 55 within desiccant 38
includes placing conduit 55 in a spaced apart relationship to microwave
antenna 48.
Also previously mentioned, conduit 55 is in the configuration of a helical
coil in which adjacent turns 69 in the helical coil are spaced apart from
one another, as shown in FIG. 2. Turns 69 of the helical coil define an
opening in which the step of positioning conduit 55 preferably includes
placing microwave antenna 48 within opening 71 defined by the helical
coil.
The method also includes the step of carrying drier gas 40 through conduit
55 disposed in desiccant 38 and elevating the temperature of drier gas 40
higher than the temperature of drier gas 40 exiting adsorbing chamber 36,
as described above in detail. As well as, carrying drier gas 40 of the
elevated temperature to lower portion 67 of the regenerative chamber 46
through another conduit 63 and releasing drier gas 40 from another conduit
63 directly into regenerative chamber 46.
This method further includes the step of removing dry gas 40 which has been
released directly into regenerative chamber 46 after it has adsorbed
moisture formerly carried by desiccant 38 regenerative chamber 46, through
outlet 62.
Advantageously, purge gas 40 is heated in an efficient and safe manner as
it passes through conduit 55 and at the same time conduit 55 further
distributes microwave energy throughout regenerating chamber 46.
While a detailed description of the preferred embodiments of the invention
have been given, it should be appreciated that many variations can be made
thereto without departing from the scope of the invention set forth in the
appended claims.
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