Note: Descriptions are shown in the official language in which they were submitted.
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DECONTAMINATION SYSTEMS AND METHODS OF USE THEREOF
Background of the Invention
The present invention relates to the destruction of contaminants entrained in
a
fluid stream, particularly to the destruction of non-biological particulate
matter or
15 biological contaminants such as spores, bacteria or viruses entrained in
this fluid stream,
particularly in a gas stream such as contaminated air. As used herein the term
"destroy"
broadly means killing or otherwise converting all or some of the contaminants
within the
fluid to a state which is less harmful to humans, animals or other organisms
or devices
present in environments requiring or benefited by a purified fluid. The
present invention
20 also is directed to destroying or altering chemical species which are
entrained in a fluid
stream, and particularly a contaminated air stream. As used herein the term
"alter"
broadly means any change in the chemical structure which results in the
chemical being
less harmful to humans, animals or other organisms or devices present in
environments
requiring or benefited by a purified fluid. In one aspect, the present
invention is directed
25 to destruction or altering of biological and/or chemical contaminants
(sometimes referred
to herein as "agents") as occurs by passage of the fluid stream through a
compressor, for
example a Roots-type or positive-displacement compressor, a centrifugal or
high pressure
fan centrifugal compressor, etc.. In a particularly contemplated embodiment of
the
present invention, some of the heat imparted to the fluid stream during
passage through
30 the compressor is recovered from the fluid stream outflow downstream of
the compressor
and fed back to add heat to the compressor, thereby reducing the energy
requirements for
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destruction of agents or chemical species through the compressor, as well as
optionally
producing a final fluid stream temperature more closely matching human and/or
machine-tolerable temperatures, ambient temperatures, or the like, if needed
for the
particular application.
In the world today pathogens, viruses, bacteria and chemical species in the
air
either naturally or deliberately placed there are becoming an increasing
health risk. Many
bacteria are developing resistance to antibiotics and fewer new antibiotics
are being
developed. Outbreaks of airborne infections have been reported in hospitals.
Clearly a
better way of dealing with this health threat is needed. Terrorists have used
bacteria and
chemical species in attacks. Anthrax contaminated a U.S. Capital office
building. The
defense today against these species is typically HEPA filters capable of
trapping particles
as small as 0.3 microns. However, HEPA filters must be changed frequently, and
used
HEPA filter materials in some cases must be treated as hazardous waste.
Furthermore,
the performance of HEPA filters is dependent on their installation, and on the
care taken
in their replacement. Thus, for example, poor installation can result in the
passage
through the filtering system of unfiltered air, defeating the purpose of the
filtration
system and, in a worst-case scenario, leading to human sickness or death from
contaminated air, e.g., air contaminated by biohazardous agents or chemical
agents.
As an alternative to HEPA filtration, biological and/or chemical agents may be
destroyed or altered rather than removed by filtration. In this regard,
studies have shown
some bacteria species can be destroyed at temperatures as low as 100 C. At
temperatures
approaching 250 C almost all pathogens, viruses and bacteria are destroyed. At
somewhat even higher temperatures, chemical species are destroyed or altered
by thermal
decomposition processes. Thus, sufficiently high temperatures may be used to
destroy
and/or alter biological and/or chemical agents.
While high temperatures may be used to destroy or alter such biological and/or
chemical agents as described above, the method or system by which such high
temperatures are generated is of utmost importance. Such heating methods and
systems
are useless unless they can demonstrate commercial viability. Thus, if the
heating method
or system has high power consumption and/or inordinately long processing times
(i.e.,
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time of exposure of the fluid stream to the high temperature), the
method/system would
simply not be commercially viable.
One possible method for high temperature destruction or altering of biological
and/or chemical agents in a fluid stream is by passage of a fluid stream
through, e.g., a
positive-displacement compressor such as a Roots-type compressor as is
described in
U.S. Patent No. 7,335,333, wherein it is disclosed how such passage through
the
compressor destroys bacteria, bacterial spores, and other biological agents in
the fluid
stream. As disclosed in the '333 patent, upwards of 99.9% of Bacillus glonigii
(Bg)
spores, an anthrax stimulant, where killed by compressive heating to about 200
C in a
single pass through a Roots-type positive displacement compressor.
Although methods based on passage of a fluid stream through a positive
displacement compressor such as a Roots-type compressor as described in the
'333 patent
are desirable for the reasons set forth above, it would be advantageous to
further improve
the energy efficiency of these methods. For example, it would be particularly
advantageous to use some of the heat contained in the fluid stream at the
outflow end of
the positive-displacement compressor or downstream of the positive-
displacement
compressor to lower the energy costs of operating the compressor. For example,
recovery of some of the heat of the fluid in the outflow stream could be
redirected back
to the compressor (e.g., to heat the compressor body itself and/or the inlet
fluid to the
compressor, etc), thereby lowering the amount of additional heat required to
be generated
by the compressor to obtain the necessary kill/decontamination conditions in
the
compressor. Such methods would have an additional energy benefit of reducing
the
energy requirements for lowering the temperature of the output fluid stream to
a range
suitable for exposure to humans, machinery, or other end uses, as required. In
the
absence of removal of heat from the sterilized heated fluid outflow stream,
depending on
the application, this stream must be cooled prior to its introduction into
spaces occupied
by, e.g., humans, animals or other organisms or devices as discussed above. By
directly
removing some of the heat from this fluid output flow stream, energy input
that would
otherwise be required to cool this stream may thus be avoided.
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There therefore exists a need for improved, energy-efficient methods and
systems for destroying or altering biological and/or chemical agents in a
fluid stream.
Summary of the Invention
In one aspect, the present invention is directed to reducing the energy costs
of
destroying or altering targeted biological and/or chemical agents in a fluid
stream. The term
"targeted" is used herein to indicate certain applications may require
destruction of only one
or possibly several particular types of agents (e.g., mold spores) and the
operating
requirements of the system may therefore be set and optimized accordingly. In
one possible
embodiment, the present invention provides an energy-efficient method for
reducing or
substantially eliminating targeted biological and/or chemical agents within a
fluid stream,
comprising the steps of: a) introducing the fluid stream into a cold pass of
at least one
recuperator; b) optionally heating the fluid stream exiting the recuperator
using a heater; c)
introducing and compressing the fluid stream in a compressor, resulting in the
pressurization
and heating of the fluid stream to an elevated temperature; d) venting a
portion of the
compressed and heated fluid stream; e) bypassing a first portion of the
compressed and heated
fluid stream around a hot pass of the recuperator; 0 passing a second portion
of the
compressed and heated fluid stream through the hot pass of the recuperator;
and g)
recombining the first and second flow portions of the fluid stream, thereby
producing a
decontaminated fluid stream. The design and operation of recuperators are
discussed in
"Compact Heat Exchangers", 3rd Edition, W.M. Kayes and A.L. London, McGraw-
Hill,
1984.
In another aspect, the invention provides a system for purifying a gaseous
feed
fluid stream by reducing biological and/or chemical particulate contaminants
entrained within
a said gaseous feed fluid stream, comprising: a) at least one recuperator for
receiving from a
source said gaseous feed fluid stream with said biological and/or chemical
contaminants
entrained therein, said recuperator comprising a cold pass and a hot pass,
wherein said
contaminated gaseous feed fluid stream with said biological and/or chemical
contaminants
entrained therein is introduced into said cold pass; b) a compressor for
receiving said gaseous
feed fluid stream with said biological and/or chemical contaminants entrained
therein from
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said cold pass of said recuperator, said compressor operable to compress said
gaseous fluid
stream to an elevated pressure and thereby heat said gaseous fluid stream to
an elevated
temperature sufficient to destroy and/or alter said biological and/or chemical
contaminants
entrained within said gaseous feed fluid stream resulting in a compressed
purified gaseous
feed fluid stream; and c) passing at least a portion of said compressed
purified gaseous fluid
stream from said compressor through said hot pass of said recuperator while
maintaining said
elevated temperature as said compressed purified gaseous fluid stream enters
said hot pass and
thereby causing heat to be transferred from said compressed purified gaseous
feed fluid
stream to said gaseous feed fluid stream with said biological and/or chemical
contaminants
entrained therein passing through said cold pass.
Brief Description of the Drawings
FIG. 1 provides a schematic illustration of one embodiment of the
decontamination system of the present invention wherein the treated feed fluid
may be at a
temperature above the ambient system inlet temperature;
FIG. 2 provides a schematic illustration of one embodiment of the
decontamination system of the present invention where compression, heat
exchange and
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expansion stages are used to cool the decontaminated fluid stream obtained
from a
recuperator; and
FIGS. 3 and 4 provide schematic illustrations of two embodiments of the
decontamination system of the present invention that use stages of
compression,
expansion and heat exchange, when the treated fluid steam is required to be
delivered
above, below, or at the ambient system inlet temperature
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Detailed Description of the Invention
The term "contaminant" or "contamination" or "agent" as used herein refers to
undesirable particulate matter (living or not), biological agents such as a
viruses, fungi,
molds, spores, bacteria, etc., or unwanted or dangerous chemical species
entrained within
a fluid flow.
"Fluid" as used herein refers to the fluid passing through the system of
components of the present invention, including but not limited to the systems
of the
present invention shown in the accompanying figures. "Fluid" includes liquids
and
gases, and preferentially refers to gases such as air contaminated by
biological and/or
chemical agents. However the present invention is also directed to liquids,
including, for
example, water from a municipal or other water supply that is contaminated by
biological
and/or chemical agents.
FIG. 1 shows one embodiment of the present invention. In FIG. 1, feed fluid 10
first flows through a cold pass 30 of recuperator 40. As described further
below, once the
system is operational and begins providing an output flow, during passage
through cold
pass 30, the feed fluid temperature is increased by transfer of heat from the
heated fluid
flow 110' passing through the hot pass 110 of recuperator 40. In this
embodiment, feed
fluid 10 enters cold pass 30 at the pressure of the source from which it is
taken, for
example, sources such as an open or enclosed and/or environmentally-
conditioned space,
a piping or duct system, or a pressure vessel. Thus, once heated fluid flow
110' begins
passing through hot pass 110, feed fluid 10 begins increasing in temperature
as it flows
through cold pass 30 of recuperator 40. In the preferred embodiment,
recuperator 40 is a
counter-flow recuperator.
After passage through cold pass 30 of recuperator 40, feed fluid 10 may be
further
heated by passing through optional heater 50, which may be powered by any
appropriate
source such as electricity or fuel combustion, for example. Although all the
drawings
provided herein show heater 50 as a standard component of the system of the
present
invention, it may be dispensed with in some contemplated embodiments of the
invention.
In general, however, the presence of heater 50 is preferred, as it allows for
the fluid
stream flowing through the system to be heated more quickly to a sufficiently
high
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temperature, preferably about 200 C to about 300 C, to achieve destruction
and/or
alteration of some or substantially all targeted biologic and/or chemical
agents in the
fluid stream.
Thus, for example, heater 50 can be operated as the system starts up, enabling
treatment temperature to be reached in less time than the system without
heater 50.
Additionally, heater 50 may be operated continuously or intermittently during
steady
state operation of the system in order to achieve other advantageous effects.
Feed fluid 10 next passes from heater 50 to a compressor 60 which can be
driven
by electrical motor 70 or any other appropriate power source. Compressor 60
may be any
suitable compressor for the particular application such as a centrifugal or
high fan
centrifugal compressor, or a Roots-type compressor, such as the positive-
displacement or
Roots-type compressors operated as described in the previously mentioned U.S.
Patent
No. 7,335,333.
Passage of feed fluid 10 through compressor 60 results in elevation of the
feed
fluid temperature to treatment conditions. The heated fluid is preferably
discharged from
compressor 60 as indicated by line 62 into a residence chamber 80 which allows
the
heated fluid stream to remain at treatment temperature for a period of time
sufficient to
allow a substantially complete destruction and/or alteration of undesirable
biologics
and/or chemical species. Although residence chamber 80 is preferred, in other
aspects of
the present invention it may be dispensed with altogether, or it may be
replaced or
supplemented with other devices such as, for example, a catalytic converter
vessel
containing a catalyst that promotes destruction and/or alteration of targeted
biological
and/or chemical species more quickly and/or at a lower temperature. Even in
the absence
of a residence chamber, it is of course understood that as the fluid flows
through conduit
from compressor 60 through and out recuperator 40, the flow is, in effect, in
dwell time,
i.e., time at elevated temperature prior to release from the system into the
surrounding
space.
When residence chamber 80 is employed in the method of the present invention,
the residence time of the fluid to be treated in residence chamber 80 is
determined as that
amount of time required to destroy and/or alter the desired amount of targeted
agents.
The volume of fluid being treated as well as the types of agents being
targeted for
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destruction and/or alteration are of course factors that will help determine
the required
dwell time. For example, the minimum residence time in chamber 80 may be
determined
and optimized by testing whether or not substantially all harmful agents in
the fluid
contained in residence chamber 80 have been destroyed and/or altered. Such
determination may be made by, for example, withdrawing a fluid sample from
residence
chamber 80, e.g., by use of an outlet port (not shown) of residence chamber
80, and
measuring biological and/or chemical contaminant levels in the sample.
Alternatively or
in addition to sampling, biological and/or chemical sensors may be placed
within
residence chamber 80 such that the levels of these materials may be
continuously or
periodically tested during residence of the fluid within residence chamber 80.
Such
sensors are described in, for example, the previously mentioned U.S. Patent
No.7,335,333, and are also commercially available for various types of
biological and/or
chemical agents.
Following passage through residence chamber 80, FIG 1 shows the fluid flow as
divided into: 1) a first flow portion 100 that bypasses recuperator 40; 2) a
second flow
portion that passes through the hot pass 110 of recuperator 40 and is
recombined with
first portion 100; and 3) optionally, a third flow portion 90 that may be
vented from the
system. Although this arrangement is preferred because it allows for enhanced
control of
the temperature of the leaving stream 150 downstream of recuperator 40, other
contemplated embodiments include only recuperator 40 (i.e., without dividing
and/or
recombining of the fluid stream from compressor 60 or optional chamber 80), as
well as
recuperator 40 in combination with either (but not necessarily both) of the
other two fluid
flow streams, i.e., first portion 100 or third portion 90. It is understood
that fluid flows
through the system are provided via appropriate conduit. Additionally,
variations in fluid
flow volume and/or rate through these first, second, and/or third portions may
be
obtained by introducing into the fluid flow control conduit of the system of
the present
invention appropriate fluid control devices, i.e., petcocks, valves, etc., to
redirect fluid
flow through one or more of these three portions as appropriate. Although such
fluid
flow devices are not shown in the drawings, they are well-known to the skilled
artisan.
As discussed above, fluid flow may be directed through the three portions
shown
in FIG 1 in order to selectively vary the temperature of leaving stream 150,
as well as to
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obtain other desirable properties for the system of the present invention.
Thus, for
example, an increase of third flow portion 90 can increase the effectiveness
of
recuperator 40 by removing energy from the system and thereby even further
lowering
the temperature of the flow leaving hot pass 110 of recuperator 40. First flow
portion
100, which bypasses hot pass 110 of recuperator 40, can serve to allow the
temperature
of the treated fluid to be increased when heating is required in the
decontaminated
stream. Finally, the third flow portion 110' that passes through hot pass 110
of
recuperator 40 is used to decrease the temperature of leaving stream 150 by
transfer of
heat to cold pass 30 and stream 10 flowing therethrough.
Specifically, with regard to venting from the system of the third flow portion
90,
such venting provides a lower mass flow in hot pass 110 than in cold pass 30
of
recuperator 40, thereby increasing recuperator effectiveness and lowering
leaving air
temperature of stream 150. The vented mass flow may be selected to be that
amount of
flow volume required to remove the heat of compression imparted by the
compressor 60
that is not otherwise lost through heat leaks from the system components and
piping. The
amount of venting may be varied according to the amount of cooling of the
output flow
150 as desired or required.
Venting can be provided at any location between compressor 60 (if present,
then
dwell chamber 80), and the outlet of recuperator 40. If the inlet to the
compressor 60 is
above ambient pressure, venting can also be accomplished at the inlet to
compressor 60,
further improving system efficiency by not compressing the vent flow in
compressor 60.
Of course it is understood that venting of any flow prior to entry of the flow
into
compressor 60 will be vented outside the area intended to be decontaminated by
the
inventive system. As stated above, bypassing fluid flow 100 around recuperator
hot pass
110 can be used to increase the output flow 150 temperature. Venting and/or
bypass of
fluid flows as described herein can thus be used to selectively and precisely
control the
final temperature of the treated feed gas stream.
The embodiment of the invention in FIG. 1 provides decontaminated fluid at a
temperature above that of initial feed fluid 10. The feed fluid 10, if it is
air or a gas
mixture that humans can breathe in conditioned spaces occupied by humans, can
consist
only of air taken from the conditioned space, or it can include a portion of
gas taken from
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a source outside the conditioned space such as outside air or from an other
source of
breathable gases. Targeted chemical species in other gas flows can be changed
especially
from dangerous or undesirable species to desirable or benign species at
different and
possibly higher and lower treatment and/or input and output flow temperatures.
Since fluid stream 10 is heated by recuperator and/or heater 50 before input
into
compressor 60, one possible embodiment of the present invention provides for
compressor 60 to be operated at pressure ratios below 2.0, and preferably of
pressure
ratios between 1.0 and 1.2, and still more preferably pressure ratios between
1.02 and
1.08. Pressure ratio is defmed herein as the compressor stage outlet pressure
divided by
the compressor stage inlet pressure or Po/Pi.
As discussed above, any compressor type can be employed as the compressor 60.
Preferred are compressor types that do not have a built-in volume ratio, such
as a Roots-
type compressor or a centrifugal compressor that match and adjust to
variations in
discharge/outlet pressure without throttling. Scroll compressors may be
advantageous in
low-flow systems. At very low pressure ratios, compressor 60 can be a high
pressure fan
operating alone or with a continuously or intermittently operating heater 50.
FIG. 2 depicts an embodiment of the invention in which an air cycle cooling
process is added to the numbered elements of the embodiment schematically
depicted in
FIG 1. Specifically referring to the numbered elements of FIG. 2, fluid stream
120 is
compressed in a secondary compressor 20, cooled through heat exchanger 130,
and
expanded through expander 140. Any expander type can be employed as expander
140,
for example, an axial, radial, positive displacement, Roots-type, turbine or
scroll
expander. Preferred are expander types that provide the maximum efficiency for
the
pressure ratio and flow of a particular application. The power produced in
expander 140
may be used to drive compressor 20 as indicated by drive shaft "S". The
pressure of
stream 120 entering compressor 20 may be as much as twice the pressure of
stream 150
leaving expander 140.
Other cooling systems known to the skilled artisan can be used in place of the
air
cooling cycle represented by FIG. 2.
FIG. 3 illustrates yet another embodiment of the invention that may be
particularly advantageous when the temperature of the treated fluid flow 150
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be above or below the temperature of inlet fluid feed stream 10, and minimum
power is
desired to operate the system. In this embodiment, the power from expander 140
is used
to drive the compressor 10 via a drive shall "S", and the temperature of the
treated fluid
stream may also be controlled. The numbered elements of FIG. 3 correspond to
those of
FIGS. 1 and 2 for common elements, and these common elements and their
function will
not again be described in detail. Replacement or substitution of elements in
this
embodiment may be made as previously stated for FIG 1, unless otherwise noted,
with
the same substitutions applying to the embodiments of FIG. 2 and FIG. 4 as
well, unless
otherwise noted.
Referring to FIG. 3, fluid feed stream 10 is compressed in compressor 20 and
heated by passage through cold pass 30 of recuperator 40, and the resulting
heated
compressed stream is passed through optional heater 50, and then fed to
compressor 60,
which is driven by a drive shall "S" and power source 70.. The compressed
fluid stream
at elevated temperature passes from compressor 60 into optional residence
chamber 80,
allowing the fluid stream to remain for some period of time at elevated
temperature. As
stated above, this residence chamber 80 may alternately comprise a catalytic
converter
containing a catalyst that promotes destruction of pathogens or chemical
species more
quickly or at a lower temperature.
The fluid stream from residence chamber 80 can be divided into up to at least
three flow portions: an optional bypass flow portion 100 that bypasses hot
pass 110 of
recuperator 40, a hot pass flow portion that passes through the hot pass 110
of recuperator
40 and, optionally, a vented flow portion 90 that may be vented from the
system.
The hot pass flow portion110' is cooled by passing through hot pass 110 of
recuperator 40 due to heat transfer to cold pass 30. Upon leaving recuperator
40, hot pass
flow portion 110' is recombined with bypass flow portion 100 and passes
through a heat
exchanger 130 where heat may be rejected to the surroundings. The further
cooled fluid
leaving heat exchanger 130 is directed through and expanded by an expander 140
which
further reduces the fluid stream 150 to the desired pressure and temperature.
In the case
where the feed fluid stream 10 is air, the treated and output air stream may
be reduced to
a temperature at which it may pass into a conditioned space and, if desired,
closely match
the heating or cooling load of the conditioned space. In the embodiment shown
in FIG.
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3, the power produced by expander 140 can be used to drive secondary
compressor 20 as
indicated by drive shaft "S".
FIG. 4 depicts a further embodiment of the invention that uses all the
components
of FIG. 3; however, the compressors are connected to different power sources.
In this
embodiment, as with that illustrated by FIG. 3, expansion power is used to
drive the
compressor, and the temperature of a fluid stream after destroying or altering
of
biological and/or chemical species may be further controlled
The component numbering of the embodiment of FIG. 4 corresponds to the
component numbering of the embodiment of FIGS. 1-3 for common elements, and
these
common elements and their function will not again be described in detail. In
the
embodiment depicted in FIG. 4, the power produced by expander 140 is used to
drive
compressor 60, and the power source 70 is used to drive compressor 20 via
drive shafts
To illustrate the invention and the advantages available thereby, a computer
simulation of the embodiment of the present invention depicted schematically
in FIG. 2
was performed. In this simulation, the fluid feed stream was air, compressors
20 and 60
were assumed to have an efficiency of 70%, and the expander 140 was assumed to
have
an efficiency of 70%. The recuperator 40 used was a counter-flow device with
an
effectiveness of 95%. 0% of the feed gas flow was vented, and none of the flow
bypassed recuperator hot pass 110.
The results of the example and comparative example are shown in TABLE 1,
where column A refers to the invention, and column B refers to simple heating
of the
fluid feed stream to treatment temperature with a compressor operating at a
pressure ratio
high enough to reach the required treatment temperature. As can be seen from
the
results presented in TABLE 1, the example of the invention operates with a
power input
to the compressor of only 5% of that required by a system using a compressor
alone to
reach treatment temperature.
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TABLE 1
A
Invention Comparison
Embodiment of FIG. 2 Compressive heating
Inlet Temperature, C 21 21
Treatment Temperature, C 250 250
System Exit Temperature, C 21 250
Compression Ratio
Compressor 60 1.033
Compressive Heating Compressor 2.55
Machine Efficiencies
Compressor 60 0.7
Compressor 20 0.7
Turbine 140 0.7
Heat Exchanger Effectiveness Ratio
Recuperator 40 0.95
Rejection Heat Exchanger 130 0.7
Compressive Heating, kJ/kg 129.6
Compressor Power, kJ/kg 6.48
Relative Power Input to Compressor 5% 100%
Although the invention has been described in detail with reference to
certain embodiments, those skilled in the art will recognize that there are
other
embodiments of the invention within the scope of the claims.
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