Abstrict A method, and systems for implementing such method, for purifying
and conditioning air of weaponized contaminants. The method includes
wetting a filter packing media with a salt-based liquid desiccant,
such as water with a high concentration of lithium chloride. Air
is passed through the wetted filter packing media and the contaminants
in are captured with the liquid desiccant while the liquid desiccant
dehumidifies the air. The captured contaminants are then deactivated
in the liquid desiccant, which may include heating the liquid desiccant.
The liquid desiccant is regenerated by applying heat to the liquid
desiccant and then removing moisture. The method includes repeating
the wetting with the regenerated liquid desiccant which provides
a regenerable filtering process that captures and deactivates contaminants
on an ongoing basis while also conditioning the air. The method
may include filtration effectiveness enhancement by electrostatic
or inertial means.
Claims 1. A method of purifying and conditioning a stream of air containing
contaminants, comprising: wetting a filter packing media with a
liquid desiccant comprising a concentration of a salt; directing
the stream of air to flow through the wetted filter packing media;
concurrently with the directing, capturing a fraction of the contaminants
in the stream of air in the liquid desiccant; concurrently with
the capturing, dehumidifying the stream of air with the liquid desiccant
in the filter packing media; deactivating at least a portion the
captured contaminants including heating at least a portion of the
liquid desiccant with the captured contaminants to a deactivation
temperature; regenerating the liquid desiccant including applying
a quantity of heat and removing moisture from the liquid desiccant;
and repeating the wetting with the regenerated liquid desiccant.
2. The method of claim 1 wherein the deactivating includes after
the capturing, collecting the liquid desiccant with the captured
contaminants, pumping the collected liquid desiccant to a capture
filter, and heating the filter to the deactivation temperature.
3. The method of claim 1 wherein the deactivating includes after
the capturing, collecting the liquid desiccant with the captured
contaminants and pumping the collected liquid desiccant through
an interchange heat exchanger wherein heat from the regenerated
liquid desiccant is transferred to the collected liquid desiccant.
4. The method of claim 3 wherein the deactivating further includes
pumping a portion of the collected liquid desiccant that has been
heated by the regenerated liquid desiccant to a slipstream heater
and applying heat to the portion of the collected liquid desiccant
to a regeneration deactivation temperature less than about 100.degree.
C.
5. The method of claim 1 further including ionizing the contaminants
in the stream of air and electrostatically precipitating the ionized
contaminants from the stream of air.
6. The method of claim 5 wherein the ionizing is performed prior
to the directing and the precipitating is performed after the directing.
7. The method of claim 1 further including creating turbulence
in the stream of air prior to the capturing to enhance inertial
filtering during the capturing.
8. The method of claim 7 wherein the turbulence creating is performed
concurrently with the directing.
9. The method of claim 1 further including treating the stream
of air prior to the directing, wherein the treating is selected
from the group of treatments consisting of fogging the stream of
air, applying additives to the contaminants, and condensing the
stream of air.
10. The method of claim 1 wherein the concentration is between
about 40 and 45 percent by weight.
11. The method of claim 1 wherein the salt is selected from the
group consisting of LiCl, CaCl.sub.2 and LiBr.
12. The method of claim 1 wherein the deactivation temperature
is in the range of 10 to 120.degree. C.
13. The method of claim 1 wherein the liquid desiccant further
includes metal ion additives.
14. The method of claim 1 wherein the captured contaminants include
anthrax spores.
15. The method of claim 1 wherein the captured contaminants are
contaminants selected from the group of contaminants consisting
of allergens, pathogens, anthrax spores, nerve agents, mustard gas,
phosgene, cyanogen chloride, chorine, salmonella bacteria, E. coli
bacteria, and small pox virus.
16. An apparatus for conditioning air and for capturing and deactivating
biological and chemical contaminants in the air, comprising: a filter
with a plurality of contact surfaces; an air intake in communication
with the filter gathering the air and directing the air to the filter;
a distribution manifold distributing a liquid desiccant with a concentration
of salt to the filter at a flow rate to wet the contact surfaces
with the liquid desiccant; a conditioner sump for collecting the
liquid desiccant that has passed through the filter and that has
captured at least a portion of the contaminants from the air; a
recirculation pump connected to the conditioner sump for pumping
the liquid desiccant with the captured contaminants to the distribution
manifold; and a regenerator linked to the conditioner sump for withdrawing
diluted portions of the liquid desiccant from the sump and for returning
the withdrawn liquid desiccant in a regenerated form, wherein the
regenerator includes a heater for applying heat to the liquid desiccant
and a regenerative filter for removing moisture from the heated
liquid desiccant.
17. The apparatus of claim 16 wherein the captured contaminants
include anthrax spores.
18. The apparatus of claim 16 wherein the captured contaminants
are contaminants selected from the group consisting of bioaersols,
respirable particles, vapors and gases, chemical agents, and biological
agents.
19. The apparatus of claim 16 further including a pair of capture
filters upstream of the distribution manifold, a valve for selectively
directing flow away from one of the capture filters, and a filter
heater contacting the capture filters for applying heat to the one
capture filter to raise the temperature of the liquid desiccant
in the one capture filter to a deactivation temperature selected
for deactivating the captured contaminants.
20. The apparatus of claim 16 further including an electronic
air filter with surfaces adapted for charging the contaminants and
collection surfaces electrically enhanced for attracting the charged
contaminants.
21. The apparatus of claim 20 wherein the filter comprises a wicking
filter or comprises structured packing.
22. The apparatus of claim 16 wherein the regenerator further
includes a slipstream heater in parallel to the regenerator heater
and a valve for directing a portion of the withdrawn liquid desiccant
to the slipstream heater, the slipstream heater heating to at least
partially deactivate the contaminants in the directed portion.
23. The apparatus of claim 16 the regenerator further including
a sump for collecting the regenerated form of the withdrawn liquid
desiccant, wherein during operation of the apparatus the flow rate
of liquid desiccant at the distribution manifold is in the range
of 10 and 20 gallons per minute, flow of the heated liquid desiccant
in the regenerator is in the range of 5 and 15 gallons per minute,
and interchange flow of the liquid desiccant between the conditioner
sump and the regenerator sump is less than 5 gallons per minute.
24 The apparatus of claim 23 wherein during operation of the apparatus
the temperature of the liquid desiccant in the distribution manifold
is in the range of about 10 to 30.degree. C., in the conditioner
sump is in the range of about 30 to 40.degree. C., downstream of
the regenerator heater is in the range of about 40 to 100.degree.
C., and in the regenerator sump is in the range of about 40 to 75.degree.
C.
25. The apparatus of claim 16 further including an inertial filtration
enhancement insert positioned in contact with the filter adapted
to create turbulent flow in the air in the filter adjacent sidewalls
of the insert and to direct the liquid desiccant to contact the
turbulently flowing air.
26. The apparatus of claim 16 further including a pretreatment
device positioned downstream of the air intake and configured to
pretreat the gathered air prior to directing the air to the filter
with a treatment selected from the group of treatments consisting
of fogging the gathered air, applying additives to the contaminants
in the gathered air, and condensing the gathered air.
27. A ventilation system for purifying and dehumidifying air having
one or more contaminants, comprising: a volume of liquid desiccant
comprising water and a concentration of a salt; a conditioner including:
an air intake for directing the air into the conditioner; a filter
media comprising corrosion-resistant packing arranged with a void
fraction creating a plurality of flow paths for the liquid desiccant
and the air defined by contact surfaces; a conditioner sump below
the filter media for collecting the liquid desiccant; and a recirculation
pump for pumping the liquid desiccant from the conditioner sump
to a distribution device above the filter media at a flow rate selected
to be large enough to substantially wet the contact surfaces with
the liquid desiccant, wherein the liquid desiccant captures a portion
of the contaminants from the air; and a regenerator in fluid communication
with the conditioner to receive a dilute portion of the liquid desiccant
from the conditioner sump and to return regenerated liquid desiccant
to the conditioner sump, wherein the regenerator includes a regenerator
heater for heating the diluted portion to a regeneration temperature
and a filter for removing moisture from the heated portion to generate
the regenerated liquid desiccant; wherein the captured contaminants
in the liquid desiccant are at least partially deactivated.
28. The system of claim 27 wherein the concentration of the salt
is less than about 60 percent by weight.
29. The system of claim 28 wherein the salt is a Halide salt.
30. The system of claim 27 wherein the flow rate is in the range
of about 10 to about 20 gallons per minute.
31. The system of claim 27 further including a capture filter
between the conditioner sump and the filter media and a filter heater
for heating the liquid desiccant within the capture filter to a
deactivation temperature.
32. The system of claim 31 wherein the deactivation temperature
is less than 100.degree. C. and the capture filter has a rating
of less than about 0.5 microns.
33. The system of claim 27 wherein the regenerator further includes
a slipstream heater in parallel to the regenerator heater for heating
at least a fraction of the diluted portion to a temperature greater
than the heated portion exiting the regenerative heater, whereby
at least a portion of the contaminants are deactivated.
34. The system of claim 27 wherein the conditioner includes a
charger upstream of the filter media for ionizing the contaminants
in the air and a set of collection surfaces electronically enhanced
to attract and collect the ionized contaminants.
35. The system of claim 27 further including a heat exchanger
positioned between the conditioner and the regenerator configured
to receive the regenerated liquid desiccant and the dilute portion
of the liquid desiccant and to enable heat to be transferred from
the regenerated liquid desiccant to the dilute portion.
36. The system of claim 27 wherein the at least partially deactivated
contaminants include weaponized chemical or biological agents.
37. The system of claim 36 wherein the agents are selected from
the group of agents consisting of anthrax spores, nerve agents,
mustard gas, phosgene, cyanogen chloride, chlorine, bacteria, and
viruses.
38. A liquid desiccant dehumidification system for purifying air
of airborne contaminants including biological agents and chemical
agents and for deactivating the airborne contaminants, comprising:
means for filtering including providing a plurality of contact surfaces;
means for directing a volume of air including contaminants through
the filter means; means for distributing liquid desiccant to the
filter means to wet the contact surfaces, the liquid desiccant comprising
a concentration of salt and water, whereby the liquid desiccant
captures a portion of the contaminants in the air; means for collecting
the liquid desiccant with the captured contaminants; means for regenerating
the collected liquid desiccant; means for recirculating the regenerated
liquid desiccant to the distributing means; and means for maintaining
the liquid desiccant at a set of deactivation temperatures throughout
the system.
39. The system of claim 38 further including means for deactivating
the captured contaminants in the liquid desiccant including the
maintaining means.
40. The system of claim 39 wherein the deactivated captured contaminants
are contaminants selected from the group consisting of bioaeresols,
pathogens, respirable particles, vapors and gases, anthrax spores,
nerve agents, mustard gas, phosgene, cyanogen chloride, chlorine,
salmonella bacteria, E. coli bacteria, and small pox virus.
Description BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to the fields of
air purification and heating, ventilating, and air conditioning,
and more particularly, to systems and methods for filtering or removing
biological and chemical contaminants from air, such as an air stream
being conditioned for input to an inhabited building or selected
rooms in a building or protective shelters, and for deactivating
the filtered or captured contaminants.
[0004] 2. Relevant Background
[0005] Maintaining acceptable indoor air quality within commercial
and residential buildings is a serious and often difficult challenge
facing today's industrial society. Indoor air quality is generally
the condition of air in an enclosed space with respect to contaminants
or pollutants that have entered the air and that can cause health
problems for inhabitants of the enclosed space. Health authorities
are concerned with contaminants that are respirable particles, which
are typically 10 microns or less is size, and that are often drawn
into and distributed by the building ventilation system where people
breathe in the contaminants. The challenge facing designers of building
ventilation systems in to condition outside air to provide air with
an acceptable level of contaminants for the building and to maintain
an acceptable level of indoor quality for recirculated air.
[0006] To maintain indoor air quality, ventilation systems need
to be adapted to control a wide variety of contaminants. In typical
applications, the contaminants may include bioaersols including
allergens (e.g., pollens, fungi, mold spores, and the like) and
pathogens (e.g., bacteria and viruses), respirable particles such
as chemical pollutants, and vapors and gases (e.g., volatile organic
compounds, radon, and the like). In recent years, the use of chemical
and biological agents as weapons in war and by terrorists has given
rise to a need for ventilation systems designed to harden the building
against such attacks by attempting to prevent introduction of potentially
deadly contaminants into a building. Examples of these agents include
anthrax spores, nerve agents, mustard gas, phosgene, cyanogen chloride,
chlorine, bacteria such as salmonella and E. coli, and viruses such
as small pox. Designing a single ventilation system that effectively
controls this broad spectrum of potential airborne contaminants
has proven to be a very difficult task that has not yet been successfully
accomplished by broadly applicable means due to the diversity in
the physical and chemical characteristics of the contaminants. Many
of these contaminants, such as anthrax and other spore contaminants,
are notoriously resistant to deactivation by chemical, radiation,
and thermal techniques.
[0007] Conventional methods of controlling contaminants include
physical filtration (such as with a high efficiency particulate
air (HEPA) filter), electrical filtration (such as with an electrostatic
precipitator), thermocatalytic oxidation, photocatalytic oxidation,
carbon adsorption, or sequential combinations of these techniques.
While these methods can provide useful contaminant control, these
methods are often only effective against a single contaminant or
for select contaminants. Further, these existing methods often are
expensive to implement and maintain and typically require significant
modification and upgrades of conventional heating and ventilation
systems. For example, existing military systems utilize HEPA filters
for particulate contaminants in conjunction with carbon filters
that handle gaseous contaminants. These multiple filter systems
are large, heavy, and costly to produce, install, and maintain in
part because the systems demand high fan pressure and frequent replacement.
Unfortunately, most conventional heating and ventilation systems
are currently not built to handle the high airflow resistance of
HEPA filters and require major system modifications, such as installing
additional fans, modifying duct work, and, in some cases, installing
structural supports for the heavy equipment.
[0008] The existing systems fail to provide all of the desired
features of a filter system (such as the design criteria presented
by the United States Joint Forces Chemical/Biological Defense Command
for Collective Protection as detailed in the Collective Protection
Master Plan Summary, DOD Chemical & Biological Defense Program
AFRL/MLQ, 139 Barnes Drive, Suite 2 MS37 Tyndall AFB, Florida
USA 32403). These features include simultaneously controlling gases,
aerosols, and particulates including bacteria, viruses, and spores
with a single filter. Further, it is desirable that the filter provide
continuous agent destruction (i.e., be regenerable) such that the
filter's efficiency remains relatively constant (e.g., does not
decrease over its service life such as by the filter consuming one
or more essential decontaminating agents) and the filter does not
require frequent maintenance, manual cleaning, and/or replacement.
It is also important to minimize the need for maintenance when the
filtered contaminants may be dangerous or hazardous, and in this
regard, it is desirable that use of the filter does not result in
a filter that has captured numerous contaminants and has become
a concentrated disposal hazard.
[0009] Hence, there remains a need for an improved filter or filter
system for use in building or other ventilation systems to provide
protection against biological and/or chemical agents or contaminants,
such as the types of contaminants that may be released in a terrorist
attack. Further, it is desirable that such an improved filter or
filter system meets demands for low cost, reduced size, low maintenance,
and reduced energy demands. It is also desirable that the filter
system be "dual use" in that it serves a useful air quality
function in normal day-to-day operations as well as a protective
function in a biological or chemical attack. Specifically, it is
desirable that such a filter or filter system be compatible with
conventional building heating and ventilation systems while providing
filtration rates for contaminants that are comparable to those achieved
with many HEPA filters, such as in excess of 99 percent and even
in excess of 99.99 percent thereby avoiding the creation of a hazardous
waste disposal problem.
SUMMARY OF THE INVENTION
[0010] The present invention addresses the above problems in large
part due to the discovery that desiccant solutions, such as, but
not limited to, concentrated aqueous lithium chloride (LiCl), have
a strong deactivation effect against spores, such as Bacillus spores
(which include Bacillus anthracis or simply "anthrax").
The present invention builds on this discovery by providing ventilation
systems with liquid desiccant dehumidifier systems to effectively
capture airborne contaminants including anthrax and to kill or deactivate
the captured contaminants. Because it was further discovered that
there is a synergistic deactivation effect between the liquid desiccant
and its temperature (i.e., the application of heat), the ventilation
systems of the invention improve deactivation rates by applying
heat and/or controlling the temperature and by controlling flow
rates of the liquid desiccant. In one embodiment, additional heat
is provided by the addition of a heater used to heat liquid desiccant
and capture contaminants in a recirculation line of the conditioner
portion of the ventilation system and a slipstream heater for applying
additional heat (e.g., above that provided by the regenerative heater)
in the regenerative portion of the ventilation system.
[0011] By providing a high level of in-system deactivation, the
ventilation systems of the present invention significantly reduce
the risk of creating a concentrated health hazard, as was the case
with simple filtration systems. Additionally, the regenerator regenerates
the liquid desiccant such that the capture function of the system
is continuous and does not require frequent maintenance to clean
or replace filters. The deactivation and capture functions are also
concurrent with each function occurring on an ongoing basis whenever
the system is operating. Capture of contaminants within the conditioner
portion is enhanced according to the invention by the addition,
alone or in various combinations, of electrostatic precipitator
components, pretreatment devices, and inertial filtering enhancement
devices or inserts (such as devices to create turbulent flow). The
ventilation systems of the invention further continue to utilize
the liquid desiccant for conditioning or dehumidifying the intake
air stream such that the ventilation systems act as dual-purpose
devices to control the size and cost of the system. The present
invention can be utilized in many existing buildings without significant
modification of the building ventilation system, without remodeling
the roof or other structural supports, and without increased maintenance
and operating costs.
[0012] More particularly, a method is provided for purifying and
conditioning a stream of air that contains contaminants (such as
common particulates or weaponized biological or chemical agents).
The method includes wetting a filter media, packing media, or filter
packing media with a liquid desiccant comprising a concentration
of salt. The concentration is generally less than 60 percent by
weight and more typically between 40 and 45 percent with higher
concentrations being preferred (e.g., the concentration is not limiting
to the invention and may be varied significantly to practice the
invention), and the salt may be lithium chloride (LiCl), lithium
bromide (LiBr), calcium chloride (CaCl.sub.2), or other salts, e.g.,
any Halide salt. The method includes directing the stream of air
through the wetted filter packing media and concurrently, capturing
a large percentage of the contaminants in the air with the liquid
desiccant. Additionally, the liquid desiccant in the filter packing
media is acting to dehumidify the air. The method continues with
deactivating at least a portion of the captured contaminants, which
typically includes heating the liquid desiccant to achieve the synergistic
effects of the liquid desiccant salt and the heat acting on the
contaminants. The liquid desiccant is regenerated by applying a
quantity of heat to the liquid desiccant and then removing moisture
from the liquid desiccant. The method also includes repeating the
wetting with the regenerated liquid desiccant, thereby providing
a regenerable filtering process that captures and deactivates contaminants
on an ongoing basis while also conditioning the air. The method
may further include ionizing contaminants in the air and simultaneously
or sequentially electrostatically precipitating contaminants (such
as those not captured by the inertial filtration). The method may
also include pretreating the air, such as by fogging, applying additives
to the contaminants, and/or saturating the air and/or include enhancing
inertial filtration such as by creating a pressure drop at the air
intake or by creating turbulent flow in the air within the filter
packing media.
[0013] According to another aspect of the invention, an apparatus
is provided for conditioning air and for capturing and deactivating
biological and chemical contaminants in the air. The apparatus includes
a filter with a plurality of contact surfaces and an air intake
for gathering or drawing in the air and then directing the air into
the filter. A distribution manifold is provided for distributing
a liquid desiccant over the filter at a flow rate sufficiently large
to wet a large portion of the contact surfaces. The liquid desiccant
has a concentration of salt (such as LiCl, LiBr, CaCl.sub.2 and
the like at a concentration between 20 to 60 percent or greater
by weight) and is typically provided at an elevated temperature
to enhance deactivation of the contaminants (such as anthrax). The
apparatus further includes a conditioner sump for collecting the
liquid desiccant that has passed through the filter and captured
the contaminants. A recirculation pump is provided to pump liquid
desiccant from the conditioner sump back to the distribution manifold.
The apparatus includes a regenerator that pumps diluted liquid desiccant
from the condenser sump and returning regenerated liquid desiccant.
During operation, the regenerator removes water absorbed by the
liquid desiccant solution in the conditioner unit. The regenerator
includes a heater for applying heat to the diluted liquid desiccant
and a contact media for removing moisture from the heated liquid
desiccant.
[0014] In one embodiment, a pair of capture filters are positioned
upstream of the distribution manifold and a valve is provided for
selectively directing flow away from one of the capture filters.
A filter heater is included in the apparatus for applying heat to
at least the one filter to which flow has been temporarily blocked.
Typically, the temperature is raised by the filter heater to a temperature
(such as a deactivation temperature) that is high enough to deactivate
the contaminants within the liquid desiccant in the filter during
the time the flow is blocked. The apparatus may include an electronic
air filter for charging incoming contaminants and for removing via
electric attraction a portion of the charged contaminants. A pretreatment
device may also be provided to treat the incoming air to enhance
capture, such as by fogging, by condensing, or by introducing additives.
In some embodiments, an inertial filtering enhancement device is
positioned within the filter so as to contact the filtering packing
media, to create turbulence in the air within the filter adjacent
the device, and to direct liquid desiccant flow to contact the turbulent
air, thereby enhancing contaminant capture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic illustrating air and liquid desiccant
flow in a dual-purpose purifying and conditioning ventilation system
according to the present invention;
[0016] FIG. 2 is a schematic similar to FIG. 1 illustrating a second
embodiment of a purifying and conditioning ventilation system according
to the present invention adapted with a filter heater in a conditioner
and an additional heater in a regenerator to provide improved deactivation
or kill of captured contaminants;
[0017] FIG. 3 is a schematic similar to FIGS. 1 and 2 illustrating
a third embodiment of a purifying and conditioning ventilation system
according to the present invention further adapted with an electrostatic
precipitator for further enhancing capture of contaminants within
the conditioner of the ventilation system;
[0018] FIG. 4 is a schematic similar to FIGS. 1-3 illustrating
a fourth embodiment of a purifying and conditioning ventilation
system according to the present invention that is still further
adapted with a pretreatment device for enhancing contaminant capture
within the conditioner and a filtration enhancement insert for creating
turbulent flow within the filter packing media for enhancing contaminant
capture within filter packing media in the conditioner;
[0019] FIG. 5 is a partial exploded view of one embodiment of the
filtration enhancement insert shown in FIG. 4;
[0020] FIGS. 6-8 are top and side views of the filtration enhancement
insert and its components providing additional design features of
this embodiment of the insert;
[0021] FIG. 9 is side-view schematic of an alternative embodiment
of a purifying and conditioning ventilation system according to
the invention utilizing a liquid desiccant system with a wicking
conditioner and a wicking regenerator and with enhanced capture
components to effectively capture and deactivate contaminants with
liquid desiccant (while not shown the embodiment of FIG. 9 may be
modified to include the modifications of FIGS. 2-4);
[0022] FIGS. 10-13 illustrate graphically the results of testing
using liquid desiccant with varying salt (i.e., LiCl) concentrations
for capturing and deactivating anthrax surrogates, i.e., Bacillus
cereus and Bacillus subtilus, within a ventilation system, such
as those shown in FIGS. 1-4 and FIG. 9 under various concentrations
and liquid desiccant temperatures; and
[0023] FIG. 14 is flow chart providing exemplary steps for the
process of using a ventilation system with a liquid desiccant system
as a regenerable filter for capturing and deactivating contaminants
in an air stream.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The present invention is directed toward ventilation systems
that serve the dual-purposes of conditioning or dehumidifying air
and, more significantly, systems that purify the air of a wide range
of airborne contaminants with the use of a regenerable liquid desiccant.
In this regard, the inventors evaluated the capabilities of modified
liquid desiccant dehumidification systems to directly capture and
deactivate aerosolized and gaseous contaminants. For example, deactivation
rates for Bacillus spores of the type used in aerosol form as weapons
were found, when exposing the spores to salt solutions of the type
used in desiccant humidifiers, to be in excess of 99.99 percent
for the anthrax surrogates Bacillus cereus and Bacillus subtilus,
and these results, which are surprising as these spores are notoriously
resistant to deactivation by chemical, radiation, and thermal techniques,
are discussed in detail with reference to FIGS. 10-13.
[0025] The following description begins with a description of a
relatively basic ventilation system that can be used to capture
and kill or deactivate airborne contaminants with reference to FIG.
1. The description then continues, with reference to FIGS. 2-8
by describing a number of embodiments in which additional components
have been added to the base system of FIG. 1 to increase the deactivation
and/or the capture effectiveness of the system. An alternative ventilation
system that utilizes lower desiccant flow rates is then described
with reference to FIG. 9. Following the description of these exemplary
systems, FIGS. 10-13 are discussed to explain the tested effectiveness
of liquid desiccant in the ventilation systems of the invention
in capturing and deactivating particular contaminants (i.e., anthrax
surrogate spores). Finally, the general process of using liquid
desiccant as a regenerable filter for contaminants is described
with reference to FIG. 14. The ventilation systems of the invention
are described stressing the use of concentrated LiCl liquid desiccant
for effectively capturing and killing spores, such as anthrax, but
it will be understood that the systems are useful with numerous
liquid desiccants having a concentration of salt (such as, but not
limited to lithium bromide solution, calcium chloride, and the like)
and ranges of additive concentrations for capturing and deactivating
a wide range and variety of contaminants. Because liquid desiccant
systems are designed to effectively pull moisture vapor from air,
the liquid desiccant systems and components of the invention have
mass transfer features useful in capturing contaminants, such as
gaseous weapons including phosgene, chlorine, nerve agents, and
the like, while the filter packing media and capture enhancement
components act alone and in combination to provide collection efficiencies
comparable with HEPA filtration rates, e.g., in excess of 99.99
percent.
[0026] FIG. 1 shows a conditioning and purifying ventilation system
10 according to the present invention configured to use liquid desiccant
as a regenerable filter for capturing and deactivating contaminants.
The system 10 is modeled generally upon a conventional liquid desiccant
dehumidification system (such as an industrial packed tower scrubber
or air washer design) and includes a conditioner 12 and a regenerator
70. As with conventional systems, the system 10 provides the function
of conditioning the air 14 and outputting dehumidified air 16 to
an interior space via air discharge 30. To this end, concentrated
or dry liquid desiccant is recirculated through the conditioner
12 and sprayed countercurrent to the flow of the intake air 14 to
remove moisture from the air 14. To regenerate the system 12 diluted
or wet liquid desiccant is recirculated through the regenerator
70 where heat is applied and the desiccant is sprayed over outside
air 72 to release absorbed water or moisture which is discharged
in scavenger air 73 to reconcentrate the liquid desiccant for reuse
in the conditioner 12. Interchange flow carries diluted desiccant
from the conditioner 12 to the regenerator 70 and concentrated desiccant
back from the regenerator 70 to the conditioner 12 to maintain steady,
regenerable operations.
[0027] Potentially contaminated air or contaminated air 14 is drawn
into the conditioner via air intake 18 which may include a fan
and ductwork. The system 10 may be utilized as part of a building
ventilation system for hardening or securing the building and as
such the intake air 14 may be the only intake air for the building
with a positive pressure being created in the building (as is well
known in the ventilation arts and not described in detail here)
such that air is not drawn into the building at other locations.
The source of the air 14 may also be recirculated air from interior
sources with the system 10 being used to quickly purify an interior
space, such as one that is determined to be a critical space that
needs to be protected against attack or in which pure air is deemed
more critical. Of course, more than one system 10 may be utilized
in a building to provide purified and conditioned air to one or
more spaces (or one or more conditioners 12 and/or regenerators
70 may be combined in a system 10), and these alterations are considered
within the bounds of the described invention.
[0028] As illustrated, the contaminated air 14 is passed from the
air intake 18 into a conditioner tower 20 and flows 50 upward through
a filter packing media 24. The filter packing media 24 may take
a number of forms useful for providing a desirable liquid-to-air
contact area for effective mass (e.g., water vapor) exchange leading
to contaminant capture. For example, the filter packing media 24
may be a plastic or ceramic media (or other material resistant to
corrosion when exposed to the liquid desiccant and air) useful in
air washer and scrubber applications such as structured packing
(e.g., Pall rings, Berl saddles, Intalox saddles or snowflakes,
and the like) with an appropriate support grid or structure. The
liquid desiccant 40 is sprayed by distribution manifold 26 (which
may include openings and/or nozzles) over the filter packing media
24 at a flow rate, F.sub.1 selected in part to be large enough
to at least wet the media 24 surfaces to improve contaminant capture
in the system 10.
[0029] After flowing through the media 24 the liquid desiccant
44 with captured contaminants is collected by the conditioner sump
22. The liquid desiccant is recirculated via return line 32 and
pump 38 to the manifold 26. The liquid desiccant is passed through
capture filter(s) 34 which filters captured contaminants over a
selected size. For example, in one embodiment, a 0.5-micron filter
is utilized for capture filter 34 to filter out spores and other
particles that are 0.5 microns or larger in size (such as anthrax
spores). Note, as will be explained fully, it is not necessary that
all contaminants be filtered out of the liquid desiccant by the
filter 34 because the system 10 is configured to provide kill or
deactivation throughout the system 10 (i.e., by the combination
of the chemistry of the liquid desiccant and the temperature of
the desiccant at various locations within the system 10). A desiccant
cooling heat exchanger 39 is provided to remove heat (i.e., control
the temperature of the liquid desiccant in the conditioner 12) from
the liquid desiccant prior to spraying it over the filter packing
media 24. Although not shown, the heat from the liquid desiccant
is typically removed in the heat exchanger 39 by the exchange of
heat with a fluid at a lower temperature, such as chilled water
or cooling tower water.
[0030] The purified air 52 is then passed through a mist eliminator
28 which is included to eliminate mist in the air 52 to control
passing the liquid desiccant (such as LiCl), which can be highly
corrosive to nearly all metals, to the HVAC ductwork and building
structural materials via the discharged air 16. The use of a mist
eliminator 28 further reduces the risk that contaminants captured
in the liquid desiccant 40 would be emitted in the air 16. The de-misted
air 54 then passes through the air discharge 30 as purified and
conditioned air 16 to an interior space, directly or via additional
HVAC ductwork and components. Another benefit of using liquid desiccant
in the tower 20 (and in the system 900 of FIG. 9) is that it improves
any potential contaminant sorption efforts downstream because of
the reduction in competitive sorption with water vapor.
[0031] The regenerator 70 is included in the system 10 to regenerate
the liquid desiccant 40 passed over the filter packing media 24
in the conditioner 12. In this regard, the conditioner sump 22 is
linked via discharge lines 62 and 64 and return lines 66 68 with
the regenerator 70 and, more particularly the regenerator sump 78.
In the illustrated embodiment of system 10 an interchange heat
exchanger 60 is provided between the discharge and return flows
of the liquid desiccant to preheat desiccant going to the regenerator
70 and to pre-cool desiccant going to the conditioner 12 thereby
increasing energy efficiency of the system 10. The regenerator sump
78 is connected to a pump 79 that provides a flow rate, F.sub.2
in the regenerator 70 and forces the diluted liquid desiccant through
a regenerator heater 81 that supplies thermal energy to the liquid
desiccant to increase its temperature to a regeneration temperature,
T.sub.2 and regenerate the liquid desiccant.
[0032] The liquid desiccant 83 is sprayed via distribution manifold
76 over a filter packing media 80 (typically, but not necessarily,
similar in configuration and material as the filter packing media
24) to wet the media 80. From the air intake 74 the air 90 is directed
up through a tower 76 of the regenerator 70 through the filter packing
media 80 to remove moisture from the heated desiccant 83 on the
surfaces of the media 80. The moisture-laden air 92 is then passed
through a mist eliminator 84 that (as with the conditioner 12) is
provided to control release of liquid desiccant to control corrosion
in downstream components and ductwork. The de-misted air 94 then
passes through the air discharge 86 to be released as scavenger
air 73. Regenerated liquid desiccant 85 is collected in the regenerator
sump 78 and returned to the conditioner sump 22 via the return lines
66 and 68 and on the return loop is cooled in the interchange heat
exchanger 60 by releasing heat to the dilute liquid desiccant carried
in lines 62 64. Flow 66 is typically provided by pump 79 (e.g.,
as a slipstream off the outlet (not shown)). Similarly, flow 62
is typically provided by pump 38 (e.g., as a slipstream off pump
38 before the heat exchanger 39). Outside air 72 is shown being
drawn into the regenerator 70 but some embodiments may utilize previously
purified interior space air. The outside air 72 may be contaminated
as is air 14 and the system 10 is configured to effectively deactivate
or kill contaminants captured in the regenerated liquid desiccant
90 by controlling temperatures at various locations within the system
10 and controlling flow rates of liquid desiccant to match deactivation
or kill times for the particular liquid desiccant being used and
anticipated contaminants.
[0033] Although specific capture and kill results are discussed
in detail with reference to FIGS. 10-13 it is useful now to note
that the system 10 is effective at concurrently capturing and deactivating
a wide range of airborne contaminants. The effectiveness of the
system 10 is achieved by the synergistic effects on the contaminants
of the use of a liquid desiccant with a high salt concentration
(such as concentrations of LiCl, LiBr, CaCl.sub.2 or any Halide
salt) and the addition of heat. The heat generally is added by controlling
the temperature of the liquid desiccant at various locations in
the system 10 which is achieved through the provision of heater
81 and interchange heat exchanger 60 and the control of flow rates
with pumps 38 and 79. The flow rates of course are also selected
to fully wet the filter packing media 24 80 and to support the
air flow rates through the conditioner 12 and regenerator 70. For
example, the set of flow rates that is useful for a typical 2000
cubic feet per minute (CFM) conditioner may not necessarily be appropriate
for another conditioner operating at a different air flow rate,
but generally, a higher air flow rate would lead to a higher liquid
desiccant flow rate to keep the media 24 wetted.
[0034] With these design stipulations in mind, the following is
a set of operational parameters that are useful for a system 10
that is utilizing LiCl solution as the regenerable liquid desiccant
and that is operating with approximately 2000 CFM air flow through
the conditioner tower 20. The LiCl liquid desiccant 40 being sprayed
over the filter packing media 24 can range in concentration and
is preferably as high as practical to enhance deactivation of captured
contaminants while controlling crystallization of the Halide salt
being used. In one embodiment, the concentration of LiCl in liquid
desiccant 40 is maintained in the range of about 0 to about 45 percent
by weight, and in another embodiment the concentration of LiCl is
maintained in the range of about 40 to about 45 percent by weight.
The temperatures of the liquid desiccant at various points in the
system 10 are: (a) T.sub.1 in the range of about 10 to 30.degree.
C.; (b) T.sub.2 in the range of about 40 to 100.degree. C.; (c)
T.sub.CS in the range of about 30 to 40.degree. C.; and (d) T.sub.RS
in the range of about 40 to 75.degree. C. The flow rates of the
liquid desiccant in the system 10 are: (a) F.sub.1 in the range
of about 10 to 20 gallons per minute (GPM) and more preferably about
15 GPM; (b) F.sub.2 in the range of about 5 to 15 GPM and more preferably
about 11 GPM; and (c) F.sub.3 in the range of 0.5 to 8 GPM and more
preferably in the range of about 1 to 4 GPM.
[0035] While the system 10 of FIG. 1 is useful for purifying and
conditioning intake air 14 modifications can be made to further
enhance the deactivation of contaminants or the capture of the contaminants.
FIG. 2 illustrates such an improved system 100 in which modifications
to the system 10 have been made to improve the deactivation efficiency
by better controlling the temperatures of the liquid desiccant and
by allowing additional quantities of heat to be applied to the liquid
desiccant to quicken the deactivation of the captured contaminants.
The system 100 is configured to take advantage of the direct relation
between kill rates and temperature of the liquid desiccant.
[0036] Since the conditioner recirculation flow, F.sub.1 is much
larger than the interchange flow, F.sub.3 the system 100 is adapted
to minimize the risk that active contaminants that are captured
in the liquid desiccant 44 would be reintroduced to the tower 20
(even though emission via the mist eliminator 28 and air discharge
30 are unlikely). In one embodiment (not shown), the conditioner
sump 22 is adapted to encourage larger contaminants or particles
to settle in the sump 22 where the settled contaminants are exposed
to permanent residence time in the salt solution of the liquid desiccant.
Such a design of the sump 22 would likely deactivate contaminants
but such deactivation may take a relatively long period of time
(such as hours or days).
[0037] In contrast, as shown, the conditioner 112 includes a pair
of capture or desiccant filters 134 and 135 with a valve 133 controlling
the flow of liquid desiccant via line 32 to the two filters 134
135. The control valve 133 is preferably operated to direct flow
to one filter 134 or 135 which would filter the entire desiccant
recirculation flow, F.sub.1 at any particular time. The filters
134 135 are preferably sized to be useful in filtering particles
in the size range anticipated for weaponized contaminants, such
as 0.5 micron or smaller filters. A filter heater 136 is provided
for heating concurrently or separately the filters 134 135 to elevate
the temperature of the liquid desiccant and contaminants captured
in the desiccant and by the filter to a temperature selected for
its usefulness for more rapidly deactivating the contaminants (such
as a temperature equal to or greater than T.sub.1 and up to 100.degree.
C. or more but less than a destabilization temperature for the liquid
desiccant). In one embodiment, the filter heater 136 is operated
to heat the liquid desiccant and captured contaminants to a temperature
in the range of about 60 to about 120.degree. C. The flow would
be alternated between the filters 134 135 by the control valve
133 periodically depending on the temperature selected for the capture
filters 134 135 but preferably at least with a period that is adequately
long (based on the liquid desiccant, the elevated filter temperature,
and the anticipated contaminants) to ensure deactivation of the
contaminants within the filter 134 or 135 that is being blocked
from flow, such as periods of 2 to 6 hours or some other useful
time period depending on the temperatures used and the contaminants
being deactivated. The desiccant cooling heat exchanger 39 is operated
(such as at higher cooling water flow rates) to remove excess or
unwanted heat from the liquid desiccant added by the filter heater
136 to maintain a desired desiccant solution temperature, T.sub.1.
[0038] To enhance deactivation within the regenerator 170 a slipstream
heater 184 with a control valve 182 is provided parallel to the
regenerator heater 81. The slipstream heater 184 is sized to put
a small portion of the recirculation desiccant flow, F.sub.2 through
a similar time and temperature profile as is achieved in the filters
134 135. Flow through the primary regenerator heater 81 is modulated
by control valve 182 such that the total regeneration energy added
by both heaters 81 184 is appropriate to maintain the system 100
in steady operation, i.e., providing desired regeneration of the
liquid desiccant returned via lines 66 68 and maintaining desired
desiccant temperatures in the system 100.
[0039] In some applications, the capture effectiveness of the systems
10 and 100 can be improved by the addition of one or more components
in the conditioner portion to treat contaminants in the intake air
14 and/or to create desired flow characteristics in the conditioner
tower 20. One technique of improving the capture function of the
systems 10 and 100 is to implement an electrostatic subsystem or
electronic air filter within the tower 20 that uses the precipitation
principle to collect airborne particles. Generally, the systems
10 and 100 can be modified to include one or more of the known types
of electronic air filters such as ionizing-plate filters, charged-media
non-ionizing units, and charged-media ionizing (the operation of
each is well-known in the air cleaning industry and is, therefore,
not explained in detail here). The task of implementing one of these
electronic air filters is complicated by the fact that salt solutions
severely corrode most metals. Using the filter packing media 24
itself is an option (not shown) that may be utilized such as by
implementing a charged-media non-ionizing filter or a charged-media
ionizing filter. The packing in media 24 may be formed of titanium
(but this is an expensive solution) or electronically conductive
plastics or polymer coatings like polyaniline, polyacetylene, polythiophene,
fluorophenylthiophene, polypyrrole, and electro-luminescent polymers
may be used.
[0040] As shown in FIG. 3 the corrosion issues are addressed in
the system 200 by implementing an ionizing-type electronic air filter
in conditioner 212 having two parts (although in some embodiments
a single stage electrostatic precipitator (ESP) may be installed
downstream of the filter packing media 24 and preferably downstream
from the mist eliminator 28). A charger 220 is provided in the conditioner
212 between the air intake 18 and the tower 20 (although charging
could be performed within the media 24). The incoming air 14 passes
through a series of high-potential ionized wires (or plates) in
the charger 220 that generate positive ions that adhere to the contaminants
carried in the air 222. The air with charged contaminants 222 then
passes through the filter packing media 24 where some enhancement
of capture can be expected due to the greater attraction of the
ionized contaminants with the liquid desiccant 40 on the media 24
surfaces. More importantly, though, an electrostatic precipitator
230 is provided. downstream of the mist eliminator 28 and the filtered
air 224 is passed through the precipitator 230. The precipitator
230 may take a number of forms and configurations but generally,
the charged contaminants are passed through an electric field in
the precipitator 230 that attracts the charged contaminants to attracting
plates (or grids and the like). The plates typically are arranged
to offer little resistance to air flow and are typically evenly
distributed in the precipitator 230. The plates may be coated with
water to act as an adhesive for the charged contaminants, and the
plates are periodically cleaned by use of water or other liquid
sprayed on the plates of the precipitator 230 which drains into
the sump 22 (flushing may be performed manually during maintenance
periods or with the use of an automated flushing device (not shown)
mounted on the tower 20).
[0041] Another technique for improving capture according to the
invention is to treat the incoming air 14 and/or to create turbulent
airflow within the tower 20 to increase inertial filtration effectiveness.
As shown in FIG. 4 the ventilation system 300 provides improved
capture by providing a conditioner 312 that includes a pretreatment
device 320 between the air intake 18 and the tower 20 (and also
upstream of the charger 220 but this is not required). The pretreatment
device 320 may provide a number of treatments such as fogging to
enhance the performance of the electrostatic precipitator 230. Alternatively
(or additionally), the pretreatment device 320 may include components
for applying additives to contaminants in the air 14 to alter contaminant
particle surface properties for improved collection in the filter
packing media 24 (especially, when the media is electrostatically
enhanced). The additives may include chloride salts of magnesium
or aluminum, lithium or sodium salts of anions such as sulfate,
phosphate, or pyrophosphate, or other useful additives. The pretreatment
device 320 may further act as a condenser to increase the effective
aerodynamic diameter of the contaminant particles to increase effectiveness
of the liquid desiccant capture in the filter packing media 24 (e.g.,
larger diameter particles are more readily captured by the liquid
desiccant).
[0042] One way to improve the inertial filtration achieved within
the filter packing media 24 is to select a desirable packing void
fraction. Generally, the tighter the packing in media 24 the greater
the pressure drop and air turbulence within the media 24 which augments
inertial deposition in the liquid desiccant on the wetted surfaces
of the media 24. Of course, the amount of pressure drop is preferably
balanced with the pressure drop or fan capacity of the conditioner
312 to limit the need for modifying the downstream HVAC system receiving
the purified air 16. Another option for improving the level of inertial
filtration is to provide the filtration enhancement insert 330 within
the structured packing or filter packing media 24 to produce turbulence
in proximity to the wetted surfaces of the media 24 adjacent the
sides of the insert 330.
[0043] FIGS. 5-8 illustrate one useful embodiment of such insert
700. FIG. 7 illustrates a top view (i.e., looking downward within
the tower 20) of the assembled insert 700. The insert 700 includes
a plug 500 that is mounted onto a mounting plate 710 which in turn
can be mounted to the support structure (not shown) for the filter
packing media 24. The mounting plate 710 can be solid to block air
flow 222 upward into the media forcing the air 222 to flow through
the plug 500 and out of the side plate 518 and filter 520 to create
turbulent flow. The liquid desiccant flow 40 is forced to flow over
the cap 530 into the media 24 adjacent the side plate 518 and filter
520 i.e., into the turbulent air 222 and then to flow out of drain
pipes 712 714 that extend outward below the plate 710 toward the
sump 22 and below the liquid surface of the sump 22. The drain pipes
712 714 include an upper mounting plate 810 and pipe 820.
[0044] The plug 500 includes cap 530 which provides a downwardly
sloped surface for directing liquid desiccant 40 in the media 24
and which preferably extends outward from the side plate 518 and
filter 520 when the plug 500 is assembled. The plug 500 further
includes mounting rings 510 514 (such as for positioning on opposing
sides of plate 710 to mount the plug 500 to plate 710), perforated
side plate 518 filter 520 and sealing flange 524. The plug 500
is mounted in tower 20 such that all or substantially all of the
air 222 goes through the perforated side plate 518 and through filter
520 which produces turbulence in the air in the adjacent media
24 without the side plate 518 becoming wetted with the liquid desiccant
40. The side plate 518 is shielded from desiccant flow by the overhang
or extension of the cap 530 and by the adjacent filter 520 (such
as a layer of plastic mesh). Maintaining dry perforations in the
side plate 518 is important because droplets or mist would likely
be generated to an unacceptable extent if desiccant was allowed
to pass over the perforations or holes in the plate 518 and then
shattered or impacted by the air coming out of the holes at a high
velocity. The plug 500 may extend upward within the media for a
fraction of the media 24 (as shown for insert 330 of FIG. 4) or
extend upward out of the packing of filter packing media 24 such
that the cap is partially or fully above the upper level of the
media 24.
[0045] The use of liquid desiccant for capturing and deactivating
airborne contaminants is not limited to the packed tower configurations
such as those described with reference to FIGS. 1-8. FIG. 9 illustrates
a ventilation system 900 that utilizes liquid desiccant as a regenerable
filter for airborne contaminants and that is modeled upon a parallel
plate or wicking filter conditioner and/or regenerator. The general
operation and configuration of such parallel plate liquid desiccant
dehumidifiers are known in the arts (e.g., as such systems are configured
according to the invention to capture and deactivate contaminants).
For more explanation on operating parameters and useful components
and configurations for such systems, see U.S. Pat. No. 5351497
issued to Lowenstein, which is hereby incorporated in its entirety
by reference.
[0046] The system 900 includes a wicking filter, wicking surface,
or filter contact surface 920 in its conditioner portion to contain
the liquid desiccant which is pumped to the filter contact surface
920 via line 984 by pump 980 at a given flow rate, F.sub.4 and
temperature, T.sub.4. The filter contact surface 920 typically includes
a number of parallel, elongate plate surfaces that provide the mass
exchange area between the air 902 and the liquid desiccant that
is distributed at the top of the filter contact surface 920 and
then captured in the conditioner sump 924. Potentially contaminated
air 902 is forced to flow through or across the plates of the filter
contact surface 920 where contaminants are captured in the liquid
desiccant. The flow rates of the air 902 and the desiccant, F.sub.4
are typically kept relatively low to avoid high flooding rates in
the conditioner and to avoid generating desiccant droplets that
could be aerosolized and discharged in the purified air 932 thereby
eliminating the need for a mist eliminator (although a mist eliminator
928 may be included to provide an even higher level of assurance
of contaminant capture). In some embodiments, the plates of the
filter contact surface 920 are internally cooled or heated with
water or other fluids to eliminate the need for external conditioner
filter heaters and regenerator heaters or heat exchangers.
[0047] The regenerator portion of the system 900 is configured
similarly with a wicking filter or filter contact surface 964 across
which outside air 960 is passed to remove moisture from the liquid
desiccant provided at a flow rate, F.sub.5 and at a temperature,
T.sub.5 in discharged scavenger air 970. A regenerator sump 968
captures the regenerated liquid desiccant which is pumped via lines
974 and 976 to the pump 980 for return to the conditioner of system
900. The system 900 generally also includes discharge lines 940
946 950 958 interchange heat exchanger 944 discharge or circulation
pump 948 and preheater 956. The preheater 956 is operated in some
embodiments to increase the kill rate of the system 900. The preheater
956 is sized to bring the entire interchange flow, F.sub.5 up to
a desired elevated temperature (i.e., greater than T.sub.1 and up
to 100.degree. C. or more, such as in the range of 60 to 120.degree.
C.). Any steam generated in such a preheater 956 may be fed into
the regenerator internal heating channels of the plates of wicking
filter 964 for a second stage of regeneration, with steam flow and
heating being modulated or controlled to maintain the system 900
in a relatively steady operational state.
[0048] The system 900 is configured to have much lower flow rates
than the systems of FIGS. 1-4 which generally leads to effective
kill rates without the need for additional heaters (i.e., the time
which captured contaminants are exposed to the temperatures is increased
and high temperatures are not as important). Generally, the flow
values in system 900 are about 5 percent of those found in the systems
of FIGS. 1-4 while temperatures are similar. For example, in one
embodiment of the system 900 desiccant flow rate, F.sub.4 is in
the range of about 0.5 to 1 GPM; desiccant flow rate, F.sub.5 is
in the range of about 0.25 to 0.75 GPM; liquid desiccant temperature,
T.sub.4 is in the range of about 10 to 30.degree. C.; liquid desiccant
temperature, T.sub.5 is in the range of about 40 to 100.degree.
C.; condition sump 924 temperature is in the range of about 30 to
40.degree. C.; and regenerator sump 968 sump is in the range of
about 40 to 75.degree. C.
[0049] As with the packed tower configurations of FIGS. 1-4 the
system 900 preferably includes one or more components to enhance
capture of contaminants that may be used individually or in various
combinations. As shown, the system 900 includes a pretreatment device
906 a charger 910 and an inertial filtration enhancement component
914 on the upstream side of the wicking filter 920 and a precipitator
930 downstream of the wicking filter 920. As with the systems of
FIGS. 1-4 the charger 910 and precipitator 930 act in conjunction
to ionize contaminants in air 902 and to attract and then capture
charged contaminants. Note, the parallel plate configuration of
the wicking filter 920 is more similar to conventional electronic
air filter designs, which lends the media of the filter 920 to being
used as a single stage ESP (or the liquid desiccant itself can act
as the collection surface when the contaminants are ionized). In
such embodiments of the system 900 the plates of the wicking filter
920 can be made of conductive plastic or the plates may be coated
with conductive, corrosion-resistant materials or flocking (or even
the adhesive for the flocking) that forms the wicking surface on
the plates may be conductive. Alternatively, the plates, the flocking,
and/or the adhesive can be modified with carbon black or other conductor
to make the plate surfaces suitable for electrostatic enhancement.
[0050] The pretreatment device 906 again can provide fogging, act
to saturate the air 902 and/or apply additives to contaminants
in the air 902 to enhance capture by the liquid desiccant and/or
the precipitator 930. Because wicking filter 920 creates little
turbulence in the air and has a low pressure drop, an inertial filtration
enhancement component 914 can be included upstream of the filter
920 or within the filter 920 to induce turbulence in the air 902
flowing into the filter 920 at the wetted surfaces to increase inertial
filtration in the filter 920. Although not shown in FIG. 9 it will
be understood that typically fluid loops or water loops or piping
are provided to allow fluid such as water to flow within the flat
plates of wicking filters or filter contact surfaces 920 and 964.
One embodiment of system 900 includes a cold-water loop (with heat
exchanger) running through the flat plates of the conditioner filter
contact surfaces 920 and a hot-water loop running through the flat
plates of the regenerator filter contact surfaces 964. As with the
systems of FIGS. 1-4 these embodiments may include a conditioner
cooler or heat exchanger (such as heat exchanger 39) and a regenerator
heater or heaters (such as heaters 81 184). In this regard, it
will be clear to those in the art that the system 900 can readily
be adapted as was the system 100 of FIG. 1 to include additional
enhancements, including a capture filter(s) with or without a filter
heater, additional heaters in the conditioner and/or regenerator
portions, and similar pretreatment and/or ESP configurations.
[0051] While not shown, a sensor, such as an anthrax detector,
a weapon-grade gas or aerosol detector, and the like, can be provided
at the inlet to the conditioners of the systems in FIGS. 1-4 and
9 to detect various contaminants. For example, it may be useful
to determine when weaponized contaminants are introduced into the
systems and to operate in a different mode. For example, the systems
may operate mainly for dehumidification when no attack or contaminants
are sensed by the sensor, but when an attack is sensed a controller
may initiate a "defense" operation mode. In the defense
mode, additional heat may be added to more rapidly deactivate captured
contaminants. Additionally, in this mode, the number of recirculations
utilized by the system (or interior air and, in some cases, of liquid
desiccant) may be increased to more rapidly capture contaminants
by insuring that interior air is fully pumped through the liquid
desiccant system which may require more rapid air change in the
interior spaces and lead to more rapid deactivation of captured
contaminants.
[0052] FIGS. 10-13 illustrate the results of testing performed
to determine the combined effect of a liquid desiccant used to kill
spores that are surrogates for anthrax spores. In FIG. 10 the graph
1000 illustrates the effect of increased temperatures of LiCl liquid
desiccant on Bacillus cereus spore viability. Lines 1010 1020
and 1030 are provided to represent liquid desiccant with 40 percent
by weight concentrations of LiCl at increasing temperatures (as
are utilized in systems of FIGS. 1-4 and 9) of 30.degree. C., 45.degree.
C., and 60.degree. C., respectively. As can be seen, the test represented
by graph 1000 illustrates the relationship of temperature on deactivation
time of the Bacillus cereus spores. As the temperature of the liquid
desiccant approaches 60.degree. C. the viability decreases significantly
within the first few hours. Hence, liquid desiccants at higher temperatures
are much more effective at reducing viability of the spores (as
measured by decreased number of viable spores per milliliter). In
contrast, lower temperature liquid desiccant (such as 30.degree.
C. liquid desiccant) requires longer deactivation times to deactivate
the spores.
[0053] FIG. 11 provides another graph 1100 representing another
test for the anthrax surrogate Bacillus cereus at varying liquid
desiccant concentrations. The test represented by graph 1100 illustrates
that at the same temperature (i.e., 60.degree. C.) increasing the
concentration of salt (i.e., LiCl) in the liquid desiccant significantly
reduces the deactivation time required to deactivate the Bacillus
cereus spores. The test was performed using Bacillus cereus spores
in LiCl liquid desiccant maintained at 60.degree. C. but of varying
concentrations. The varying concentrations (as measured by weight)
are represented by lines 1110 1120 1130 1140 and 1150 and were
20 percent LiCl, 25 percent LiCl, 30 percent LiCl, 35 percent LiCl,
and 40 percent LiCl, respectively. As shown, increasing the concentration
of LiCl from 20 to 25 percent by weight significantly enhances the
deactivation effectiveness (as measured by reduction in percentage
of viable spores/deactivation time) and, similarly, increasing the
concentration of LiCl from 25 to 30 percent provides another significant
improvement in deactivation effectiveness. Further increases in
concentration do not provide as significant of improvements (at
least with the accuracy of the graph 1100) but do result in improvements.
The test illustrated in FIG. 11 is useful for indicating the desirability
of utilizing the highest concentration of LiCl in a liquid desiccant
at a given temperature that is practical within a given ventilation
system. For the tests shown in FIGS. 10 and 11 there is no significant
reduction in the number of colony forming units (CFUs) under identical
conditions in deionized water (as was observed and shown for the
experiments of FIGS. 12 and 13).
[0054] FIG. 12 provides a graph 1200 that compares the activity
of Bacillus subtilus spores in deionized water (i.e., "control")
and in liquid desiccant having approximately 40 percent LiCl concentration
by weight. The test measured the colony forming units (CFU) per
milliliter in two samples over a period of time. The control sample
is illustrated by line 1210 and contained deionized water maintained
at 60.degree. C. for 32 hours into which a fixed amount of Bacillus
subtilis spores were added. As shown, the effect of temperature
alone over time did not result in a significant reduction in the
activity of the spores. In contrast, the second sample shown by
line 1220 shows a marked reduction in spore activity within the
first several hours. This sample contained liquid desiccant having
a concentration of LiCl of about 40 percent by weight that was maintained
at 60.degree. C. for a period of 32 hours. The test represented
by graph 1200 illustrates that heat alone is not effective for deactivating
surrogate spores of anthrax, but the combined effect of LiCl and
heat does act to deactivate the spores.
[0055] FIG. 13 illustrates a graph 1300 representing the results
of a test similar to the one illustrated in FIG. 12 further showing
the results of increasing the concentration levels of LiCl. In the
test, each sample was maintained at approximately 60.degree. C.
for about 72 hours and the activity was measured by determining
the CFUs existing per milliliter of sample. As shown, the deionized
water and 20 percent concentration of LiCl, represented by lines
1310 1320 provided almost identical results, i.e., only a small
amount of deactivation that occurred very gradually over the testing
or deactivation time period. In contrast, the samples having 30
and 40 percent concentrations of LiCl represented by lines 1330
1340 produced results indicating that increased concentrations of
LiCl in liquid desiccant when combined with heat result in rapid
and significant deactivation of the Bacillus subtilis spores. As
with the test of FIG. 11 this test indicates the desirability of
utilizing a higher concentration of salt, such as LiCl, in the liquid
desiccant used in the systems of FIGS. 1-4 and 9 to achieve more
rapid and higher levels of deactivation of spore contaminants.
[0056] While FIGS. 1-9 illustrate particular systems for purifying
and conditioning potentially contaminated air, an important aspect
of the invention is the use of liquid desiccant as a regenerable
filter for capturing and deactivating a range of potentially harmful
airborne contaminants independent of the particular system configuration.
In this regard, FIG. 14 illustrates an exemplary process of using
desiccant to filter air, to kill or deactivate captured contaminants,
and to condition the air. In FIG. 14 exemplary steps of a purifying
and conditioning process 1400 are illustrated that can be used in
a variety of ventilation systems (including systems shown in FIGS.
1-4 and 9 and other arrangements not specifically described herein).
The process starts at 1404 typically with the design and installation
(or modification) of a ventilation system with one or more liquid
desiccant dehumidification systems adapted for use as a regenerable
filter for airborne contaminants.
[0057] At 1410 the process 1400 continues with taking in potentially
contaminated air from outside an enclosed space (such as the exterior
of a building or vehicle) and/or from the enclosed space itself
(i.e., recirculated air that is directed to the liquid desiccant
system for purification and further conditioning). At optional step
1416 the intake air may be treated to enhance later capture of
the contaminants within the air stream such as by fogging, by introducing
additives to the air stream that effect the size or physical or
chemical characteristics of the contaminant particles, and/or by
condensing. For example, fogging may be performed at 1416 to enhance
later precipitation of particles using an electronic air filter.
If the process includes utilizing electronically enhanced filtering,
step 1420 is performed to ionize or chare the contaminants in the
intake (and optionally pretreated) air. At 1424 it may be useful
to include in the process a step for generating turbulence or otherwise
disturbing (such as creating a pressure drop) the flow of the contaminated
air to take advantage of inertial filtering. Step 1424 may be performed
in numerous ways (including forcing air to flow through a pressure
drop device or an insert for redirecting air (and liquid desiccant
flow) in a manner that causes turbulence in the air at a point where
the air is contacting liquid desiccant (such as the insert shown
in FIGS. 5-8). Step 1424 may also be performed by forcing the air
through a filter or filter packing media that is relatively tightly
packed producing irregular flow paths and a large contact surface
area between the air and the filter or packing media.
[0058] At 1430 the pretreated, "enhanced" air is directed
through a filter packing media with a selected void space to provide
a desired contact area. Concurrently with step 1430 step 1436 is
performed to provide liquid desiccant at selected temperatures and
flow rates to the filter packing media. The temperature of the desiccant
is preferably selected to provide cooling/dehumidification. The
flow rate is selected to provide effective wetting of all or substantial
portions of the filter packing media (e.g., in most cases not all
of the exterior packing surfaces are wetted) such that contact surfaces
are covered with liquid desiccant. At 1440 contaminants are captured
or filtered from the air and concurrently the air is dehumidified.
The liquid desiccant passing through the filter packing media performs
both of these processes by removing moisture from the air and concurrently
filtering a substantial amount of the contaminants from the air
as the air contacts the surfaces of the filter packing media and
contacts flowing liquid desiccant. Such capture of contaminants
is, in some cases, enhanced by the pretreatment of the air at 1416
by the creation of a turbulent or otherwise enhanced flow at 1424
and by the ionizing of the contaminants at 1420 which increases
attraction of the contaminants by the desiccant.
[0059] At 1444 mist is removed from the filtered air, such as
by passing the filtered air through a mist eliminator or other device.
At 1450 if the contaminants have been ionized, the charged particles
(that were not captured by the liquid desiccant) are precipitated
out of the air such as by attraction to portions of an electrostatic
precipitator (ESP), to portions of the filter packing media, and/or
to the liquid desiccant itself. Alternatively, steps 1420 and 1450
can be combined by employing a single stage ESP. The process 1400
may further include a step of cleaning the electrically-attracted
contaminants from the collection surfaces. At 1460 the purified
and conditioned air is discharged to an interior space or to another
ventilation system.
[0060] At 1470 the process 1400 continues with the deactivation
of captured contaminants in the liquid desiccant. Note, the deactivation
of step 1470 typically is an ongoing process that occurs concurrently
with capturing of contaminants and is performed so the process 1400
does not require manual removal of a component having a concentration
of hazardous contaminants. The deactivation of captured contaminants
is an important feature of the invention that has been discussed
in detail with reference to FIGS. 1-13 and that is further discussed
below with particular reference to deactivating biological agents
and chemical agents with liquid desiccant and heat. The process
1400 then includes the step 1480 of regenerating the liquid desiccant
(such as with a regenerator portion of a liquid desiccant dehumidifying
system such as that shown in FIGS. 1-4 and 9) to allow the liquid
desiccant to be reused in steps 1436 1440 and 1470 (i.e., to avoid
frequent maintenance of a filter as was the case when using HEPA
or other conventional filter devices).
[0061] With a general understanding of the use of liquid desiccant
as a regenerable filter and of useful ventilation system arrangements,
it may now be helpful to provide separate discussions of how and
why liquid desiccant has proven effective for biological agents
and for chemical agents. In general operations of systems according
to the invention, the liquid desiccant solution ranges in salt concentration
from 0 percent to as high as practical (such as in generally in
the range of about 20 to 45 percent for most Halide salts and about
40 to 45 percent for LiCl, in particular, by weight). In some embodiments,
there are lower concentrations of other additives (such as molybdate
ion) that provide anticorrosion or other functions in the ventilation
system and the balance of the liquid desiccant used is water. The
vapor pressure of water is reduced by the high salt concentration,
which provides the desiccant or conditioning function. In thermodynamic
terms, the salt decreases the activity of water with pure water
having an activity of 1 at 0.degree. C. and water activity of LiCl
solutions at 40.degree. C. is about 0.5 for a 25 percent concentration
and about 0.1 for a 45 percent concentration. Most bacteria will
not grow below a water activity of about 0.9 (see, for example,
http://web.utk.edu/.about.golden/Courses/FST- 521/notes/aw.htm).
Bacterial spores have an estimated water activity of about 0.7 (see,
for example, Marquis, R. E., et. al., J. Bact. Symp. Suppl., 76
(1994) pp. 40S-48S).
[0062] The reduced water content of Bacillus spores (such as anthrax
spores) is believed to be one of its protective mechanisms. The
reduced water content contributes to the heat stability and is a
contributor to the fact that dry heat is less effective than wet
heat (saturated steam) in deactivating spores. More particularly,
higher temperatures or longer deactivation times are typically required
to kill spores under dry heat conditions (see, Brown, K. L., J.
Bact. Symp. Suppl., 76 (1994) pp. 67S-80S). Another feature of Bacillus
spores that is believed to have a protective function is the high
concentration of calcium. Spores are about 9 percent by weight calcium
dipicolinate whereas cells contain none. Other forms of calcium
also contribute to the calcium content of spores, such as Bacillus
spores (see, Marquis, R. E., et. al., J. Bact. Symp. Suppl., 76
(1994) pp. 40S-48S and Setlow, P., J. Bact. Symp. Suppl., 76 (1994)
pp. 49S-60S). The protection of the spore content is not due to
a spore wall that is impermeable because, in fact, there is free
movement of water and ions in and out of the spore so that the contents
are in communication with the spore's environment.
[0063] During experimentation and design of the systems of FIGS.
1-4 and 9 it was found that the synergistic effect of salts, such
as LiCl, and heat was unexpectedly useful for deactivating or killing
spores. Prior to these efforts of the inventors, it might have been
expected that the lower water activity of the liquid desiccant solution
would result in further desiccation of the spores to make the water
content in spores captured in liquid desiccant even lower than in
normal spores. Since lowered water content is generally considered
one of the protective mechanisms, the additional desiccation would
have been expected to impart greater thermal resistance. As experimentation
(such as that shown in FIGS. 10-13) has shown, the spores captured
in liquid desiccant are not more thermally resistant, and the increase
in deactivation effectiveness may be provided by the interaction
of the salt, such as LiCl, in the liquid desiccant with the spore
or spore content. Regardless of the specific cause of the increased
Bacillus spore deactivation, the use of liquid desiccant and systems
provides a decided advantage over applying only wet heat or dry
heat at lower temperatures (i.e., such as less than 100.degree.
C. which is much lower than the higher temperatures often utilized
to deactivate spores, such as those utilized in the food and medical
industries of greater than 200.degree. C.). Other kinds of microbial
agents (such as viruses, vegetative forms of bacteria, fungal and
yeast cells and spores, protozoa, and the like) are generally accepted
to be easier to deactivate than Bacillus spores, and thus, it can
reasonably be concluded that the deactivation functions described
for the systems and methods of the invention associated with liquid
desiccant would also be effective for deactivating these other microbial
agents.
[0064] A number of modifications can be made to the systems of
FIGS. 1-4 and 9 and method of FIG. 14 to improve the capture and/or
deactivation of microbial agents. The following modifications or
additional features are considered to be covered by the present
invention. Altering the chemistry of the liquid desiccant is expected
to enhance the killing of microbes including increasing the acidity,
increasing the lithium ion activity, and adding metal ions that
are detrimental to microbes, e.g., bacteria, fungi, viruses, protozoa,
and spores. More particularly, in some embodiments, Lewis acids
are added, such as aluminum (+3), zinc (+2) ion, iron (such as +2
or +3) ions, or others selected from the main, transition, or lanthanide
groups in the Periodic Table, to provide specific beneficial effects
on microbe deactivation. Changing the lithium ion activity may be
particularly important if the synergistic effect of LiCl and heat
is due to the replacement of calcium by lithium ions in the spore
driven by a chemical equilibrium effect. The goal of the inventive
process and systems implementing the process need not be physical
destruction of the spores but instead it may be sufficient to render
the spore systems that trigger germination of the spore inactive.
It is also possible to destroy spores by creating conditions in
the liquid desiccant systems that initiate the irreversible chain
of events that lead to germination of the spore while it is in the
desiccant medium, which would remove the protection features of
the spore and result in death of the germinating cell.
[0065] Chemistry altering agents can include, but are not limited
to, positively charged metal ions such as those of magnesium, aluminum,
boron, the first row transition metals, and the lanthanides. The
oxidation state of the metal ions can be any state that is possible
for a particular metal and stable in the desiccant medium. The metal
ions may be added to the liquid desiccant as chloride salts in order
to minimize the effect on the desiccant medium. Negatively charged
ions such as sulfate, phosphate, pyrophosphate, or others can also
have an effect on the surface properties of microbes. Certain organic
compounds that exist as salts or are in polar form that renders
them soluble in the desiccant may also be useful as an additive
to the liquid desiccant to enhance contaminant deactivation.
[0066] The nature of the microbes themselves, either in their natural
state or altered (e.g., weaponized) state to make them more lethal
or more easily disseminated, may be exploited according to the invention
to increase the capture in the ventilation system and purification
processes, to concentrate the microbes at certain locations in the
system to focus lethal treatments, and/or to facilitate removal
of viable or deactivated forms during maintenance. These modifications
of the illustrated systems include incorporation of surfaces designed
to selectively bind the microbial agents using hydrophobic forces
or other characteristics of the microbes. These surfaces can be
in the form of specially textured surfaces, hydrophobic surfaces
such as polymers (e.g., polypropylene and the like), and/or a filter
placed in a recirculation line.
[0067] In order to enhance the capture of particulates, aerosols,
and chemical vapors and also to increase the rate of deactivation
of chemical and biological agents, the liquid desiccant can be modified
by the addition of other substances, such as a wide range of metal
ions that can be added while not degrading the desiccant function.
The additives can be selected to affect the surface properties of
bioaerosols (such as in a pretreatment device) to increase the dispersion
in the liquid desiccant filter packing media. If contaminants are
homogenously dispersed throughout the total hold-up volume of a
desiccant tower (or wicked filter containing device) the probability
of reemission in droplets that are carried out in the air stream
exiting the conditioner is very low by virtue of the ratio of total
volume of particles to the hold-up volume. In the case where spores
or other aerosols are not absorbed into the liquid desiccant but
are carried on the surface of the liquid or contained in the liquid
as agglomerates, these spores can be adsorbed on the surface of
structures included in the conditioner such as filter plates, screens,
or porous media to which the spores or aerosols selectively adhere.
In this case, the captured agents can be deactivated in place by
the liquid desiccant and/or its additives or removed with the media
during maintenance for treatment outside the system. The additives
can be selected to enhance deactivation of biological and chemical
agents by interfering with critical functions in the microbial structure
(for example, with the site that triggers germination of spores).
The additives may also be selected for their ability to interfere
with the mechanisms that impart thermal stability to spores. Additionally,
the additives can be selected for their ability to act to catalyze
chemical reactions of chemical agents that result in reduction in
toxicity (for example, by catalyzing the rate of hydrolysis, i.e.,
reaction with water, of reactive bonds in the chemical agent).
[0068] Turning more specifically to the capture and deactivation
of chemical agents, the characteristics of the system and processes
of the invention that improve capture of water vapor, small particles,
and aerosols also cause the liquid desiccant systems and processes
to be effective in removal of chemical agents, such as nerve agents
or blister agents. Nerve agents are organophosphorus compounds similar
to many pesticides and are typically dispersed as aerosols. Blister
agents are organosulfur compounds with reactive carbon-chlorine
bonds that also have low vapor pressures and are dispersed as aerosols.
There is also concern about the potential use of hazardous industrial
chemicals by terrorists, which includes a very wide range of substances
some of which will be amenable to capture and neutralization by
liquid desiccant systems of the invention. The capture and deactivation
features described for chemical warfare agents are applicable to
many other forms of hazardous chemicals or contaminants.
[0069] Destruction of stockpiles of chemical agents by hydrolysis
(i.e., reaction with water), oxidation, or a combination of both
has been described (see, for example, Yang, Y. C., Acc. Chem. Res.,
32 (1999) pp. 109-115 and Yang, Y. C., et al., Chem. Rev., 92 (1999)
pp. 1729-1743). Nerve agents have phosphorus bonds to sulfur, nitrogen,
oxygen, or fluorine that can be replaced by hydroxyl groups by reaction
with water under acidic or basic conditions (e.g., hydrolysis).
The reaction can also be catalyzed by Lewis acids or basic catalysts.
The sulfur mustard agents have reactive carbon-chlorine bonds that
can also be hydrolyzed and the sulfur site can be oxidized. Mixtures
formulated to clean contaminated surfaces or conditions designed
for the destruction of chemical agents are described in the above-referenced
review articles.
[0070] The liquid desiccant systems and processes of the invention
are based on very concentrated solutions of salts (such as LiCl)
in water, and this presents a different approach to the capture
of hazardous gases or aerosols and to the deactivation of the captured
contaminants in the liquid desiccant. Capture by and absorption
of the chemical agents into the liquid desiccant medium is a precursor
to the deactivation of the agents. The modifications of the liquid
desiccant medium that enhance its chemical reactivity described
above with relation to biological agents can also increase the capture
efficiency and solubility of the chemical agents in the liquid desiccant.
[0071] In some embodiments of the invention, the hydrolysis reactions
are catalyzed by the high concentration of lithium ion or by added
metal ions (such as those discussed previously). Ions of metals,
for example but not limited to aluminum, boron, iron, copper, and
lanthanide metals, can have a strong catalytic effect on hydrolysis
reactions. These ions can be added to the liquid desiccant as chloride
salts. Catalysis by substances dissolved in the liquid desiccant
where the chemical reactions are occurring can be termed "homogeneous
catalysis." Hydrolysis reactions are also sometimes catalyzed
in the processes and systems of the invention by acidic or basic
surfaces. This is termed "heterogeneous catalysis" since
the catalyst is a solid in contact with the liquid phase. Representative
heterogeneous catalysts include metal oxides such as alumina or
titania, zeolites, and activated carbon. These kinds of materials
are characterized by high surface area, are acidic or basic in nature,
and provide enhanced interaction of surfaces of the system with
the compounds or contaminants considered targets for deactivation.
The heterogeneous catalyst is normally supported (e.g., bound to)
a non-reactive structure such as a honeycomb or textured surface
or to packing materials (such as in the filter packing media or
wicking filter of the systems in FIGS. 1-4 and 9) such as saddles,
extruded shapes, polymer packing materials, and the like. These
filter or packing media increase the efficiency of contact between
the liquid and solid phases (e.g., between the liquid desiccant
and the contaminants).
[0072] The chemical reaction rates increase with increasing temperatures
of the liquid desiccant. It is therefore advantageous in the case
of heterogeneous catalysts to deploy the catalytic structures in
parts of the systems of the invention where the temperature is greatest,
such as near the heaters and heat exchangers that heat the fluid
for regeneration and/or in the heated capture filters. The homogeneous
catalysts are dispersed throughout the system and locations of the
liquid medium so that reaction takes place at rates that vary with
the temperature of the liquid desiccant in different parts of the
described systems. Heterogeneous and homogeneous catalysts have
certain advantages for use in the ventilation systems of the invention.
Heterogeneous catalysts are localized, they do not modify the bulk
liquid medium, and the nature of the heterogeneous catalyst does
not present a materials compatibility problem. Homogeneous catalysts
being dispersed throughout the liquid medium can function everywhere
in the system (at varying rates) and eliminate mass transfer limitations
on deactivation rates. The choice of metal ions, for example, may
be limited in the systems by potential for corrosive reactions with
some surfaces that the liquid desiccant contacts, e.g., metal heat
exchanger surfaces. However, most of the liquid desiccant portion
of the described ventilation systems, with exception of portions
of the heaters and/or heat exchangers, is preferably constructed
of polymeric materials that are resistant to corrosion. Deactivation
of chemical agents results in the formation of some chemical residues
in the system that are harmless or that only present a low level
of chemical hazard, which may require that there be some maintenance
procedures over the life of a system constructed and operated according
to the invention to remove any significant collection or deposit
of such residue.
[0073] Although the invention has been described and illustrated
with a certain degree of particularity, it is understood that the
present disclosure has been made only by way of example, and that
numerous changes in the combination and arrangement of parts can
be resorted to by those skilled in the art without departing from
the spirit and scope of the invention, as hereinafter claimed. For
example, the specific materials described above can be varied significantly
to practice the invention as will be readily appreciated by those
skilled in the art. The systems shown in FIGS. 1-4 and 9 may be
utilized within or as part of a wide variety of HVAC configurations
to provide the dual purposes of conditioning and purification (i.e.,
capture and deactivation of contaminants) of air (or, more accurately,
any gas) stream. For example, the air intakes of these systems may
be configured to purify the indoor or recirculated air of a building.
More specifically, the systems and methods of the invention may
be used to condition and purify air in spaces that are more prone
to contaminants or to an attack (i.e., high risk spaces). For these
high risk spaces (e.g., mailrooms, lobbies, and the like), the systems
may be operated for multiple air passes to more quickly and effectively
remove contaminants that may be in the air or such a multiple-pass
operating mode may be instigated in response to a sensor detecting
the presence of a contaminant within the high risk space.
[0074] Further, the teachings of the systems of FIGS. 1-4 and 9
and the method of Claim 1 can readily be applied to applications
that do not require heat to be added to obtain acceptable deactivation
of certain contaminants, and these non-heated embodiments are believed
to be within the breadth of the above disclosure and following claims.
For example, a non-heated application may utilize ventilation air
enthalpy exchange, which typically utilizes CaCl.sub.2 in the liquid
desiccant because of its lower cost. In this embodiment, the liquid
desiccant is regenerated by exposure to building exhaust air. Accelerated
deactivation or kill may not occur in this embodiment due to the
lower temperatures, but inactivation does occur over longer periods
of time (such as days or weeks) due to the permanent residence time
for the contaminant in the liquid desiccant.
[0075] A non-heated system would have a configuration similar to
that shown in FIGS. 1-4 and 9 except the system would most likely
not include an interchange heat exchanger 60 or a desiccant cooling
heat exchanger 39. The primary difference would be found in the
airflows and in the liquid desiccant temperatures. Outside air would
be taken into the conditioner portion (as is typically seen in FIGS.
1-4 and 9) but building exhaust air would be taken into the regenerator
portion instead of outside air. The liquid desiccant temperatures
would vary with outdoor conditions such as a summer range of 15
to 30.degree. C. and a winter range of -5 to 15.degree. C. The conditioner
would pre-cool/dehumidify in the summer (and pre-heat/humidify in
the winter) the outdoor air while removing contaminants. The liquid
desiccant would then be pumped from the conditioner sump to the
top of the regenerator media for regeneration via contact with the
building exhaust air. In a parallel plate geometry such as in the
system 900 of FIG. 9 a closed-loop water line would be used to
circulate water between the regenerator and the conditioner plates.
[0076] The foregoing discussion is intended to illustrate concepts
by way of example with emphasis upon the preferred embodiments and
instrumentalities. Accordingly, the disclosed embodiments and instrumentalities
are not exhaustive of all options or mannerisms for practicing the
disclosed principles hereof. The inventors hereby state their intention
to rely upon the Doctrine of Equivalents in protecting the full
scope and spirit of the invention. |