Abstrict A method and apparatus for regenerating aqueous desiccants used
in liquid desiccant air conditioners is disclosed. The method and
apparatus utilizes a desiccant boiler and a desiccant evaporator/steam
condenser in combination with heat exchangers. The evaporator/condenser
receives steam produced by the boiler to provide a reuse of heat
for regeneration. The boiler and the evaporator/condenser each can
provide substantially complete regeneration of a portion of the
liquid desiccant.
Claims What is claimed is:
1. A process for regenerating a liquid desiccant, said process
comprising the steps of:
regenerating a diluted liquid desiccant first portion in an evaporator/condenser
unit to form a regenerated liquid desiccant first portion;
regenerating a diluted liquid desiccant second portion in a desiccant
boiler unit to form a regenerated liquid desiccant second portion,
said desiccant boiler unit vaporizing moisture in said diluted liquid
desiccant second portion;
transferring said vaporized moisture to a condenser portion of
said evaporator/condenser unit to provide heat thereto;
distributing said diluted liquid desiccant first portion into a
chamber of said evaporator/condenser unit;
heating said chamber with said condenser portion;
passing a gas through said chamber;
transferring sensible heat from said regenerated liquid desiccant
second portion from said desiccant boiler to said diluted liquid
desiccant in a second heat exchange unit;
transferring sensible heat from said regenerated liquid desiccant
second portion from said second heat exchange unit and said regenerated
liquid desiccant first portion to said diluted liquid desiccant
first and second portions in a first heat exchange unit;
transferring sensible heat for a vapor/condensate material from
said condenser portion to said dilute liquid desiccant first and
second portions, and
transferring heat from said chamber with said gas prior to passing
said gas through said chamber.
2. The process of claim 1 further comprising the steps of:
applying diluted liquid desiccant to said first heat exchange unit
from an air conditioner to form said diluted liquid desiccant first
and second portions; and
applying said regenerated liquid desiccant from said first heat
exchange unit to said air conditioner.
3. Apparatus for regenerating a liquid desiccant from an air conditioning
system, said apparatus comprising:
a first heat exchange unit having a diluted liquid desiccant and
a regenerated liquid desiccant transmitted therethrough, said first
heat exchanger unit adapted to transfer sensible heat from said
regenerated liquid desiccant to said diluted liquid desiccant;
an evaporator/generator unit regenerating a firs portion of said
diluted liquid desiccant form said first heat exchange unit to form
a regenerated liquid desiccant first portion, said regenerated liquid
desiccant first portion being applied to said first heat exchange
unit;
a second heat exchange unit having a second portion of said diluted
liquid desiccant and a second portion of a regenerated liquid desiccant
transmitted therethrough, said second heat exchange unit adapted
to transfer sensible heat from said regenerated liquid desiccant
second portion to said diluted liquid desiccant second portion;
and
a desiccant boiler regenerating said diluted liquid desiccant second
portion from said second heat exchange unit to form said second
regenerated liquid desiccant portion, said desiccant boiler vaporizing
moisture in said diluted liquid desiccant second portion, said vaporized
moisture being transferred to said evaporation/condenser unit for
transfer of heat thereto; wherein said vaporized moisture is applied
to a condenser portion of said evaporator/condenser unit, and wherein
a vapor/condensate output from said condenser portion is applied
to said first heat exchange unit, said first heat exchange unit
adapted to transfer sensible heat from said vapor/condensate output
to said diluted liquid desiccant first and second portions.
4. The apparatus of claim 3 wherein said evaporator/condenser unit
includes:
a chamber region, said condenser portion extending into said chamber;
distribution apparatus for distributing said diluted liquid desiccant
first portion into said chamber; and
gas apparatus for moving a gas through said chamber.
5. The apparatus of claim 3 wherein said diluted liquid desiccant
first and second portions are provided by an air conditioner; and
wherein said regenerated liquid desiccant first and second portions
are transferred to said air conditioner.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to improved regeneration of liquid
desiccants of the type found in air conditioners which utilize liquid
desiccants for dehumidifying air.
2. Description of the Related Art
The use of hydroscopic liquids, such as lithium chloride (LiCl),
lithium bromide (LiBr) or calcium chloride (CaCl.sub.2) solutions,
to dehumidify air are well known. However, use of these devices
has been limited owing to problems associated with regenerating
(i.e., removing water from) the liquid desiccant. Regeneration generally
requires contacting the liquid desiccant with hot gas which absorbs
the excess moisture or heating the liquid desiccant to drive off
excess moisture. The heated air regenerators are costly to operate
especially where waste heat is not available. Utilization of boiler-type
regenerators is found to be expensive, requiring specialty corrosion-resistant
metals. If pressurized boilers are employed to provide higher efficiency
operation, costly components are needed and safety issues become
more complex.
U.S. Pat. No. 4939906 entitled Multi-Stage Boiler/Regenerator
For Liquid Desiccant Dehumidifiers, issued on July 10 1990 and
invented by Mark W. Spatz and John J. Tandler, describe a liquid
desiccant rejuvenation system which uses both a desiccant boiler
and an evaporator/condenser. The evaporator/condenser unit, coupled
in series with the desiccant boiler serves as a preconditioning
unit for the desiccant boiler unit. Some energy reuse is disclosed,
however, all of the desiccant to be regenerated must be introduced
into the desiccant boiler unit.
A need has therefore been felt for apparatus and an associated
method which can provide regeneration of hydroscopic liquids while
reducing the liquid heat exchange needs for the process and reducing
the requirements for specialized materials in fabricating the apparatus.
FEATURES OF THE INVENTION
It is an object of the present invention to provide an improved
method and apparatus for regeneration of liquid desiccants.
It is a feature of the present invention to provide an improved
method and apparatus for the regeneration of liquid desiccants reduces
the requirements for heat exchange units.
It is yet another feature of the present invention to provide a
method and apparatus for the regeneration of liquid desiccants which
reduces the requirements for non-corrosive materials.
SUMMARY OF THE INVENTION
The present invention overcomes the above mentioned problems by
providing a novel desiccant boiler and a combined desiccant evaporator/steam
condenser to produce an effective and economic liquid desiccant
regeneration system for air conditioners. The term "air conditioner"
as used herein refers to a liquid desiccant using apparatus which
dehumidifies air and may also provide cooling.
Regeneration of the liquid desiccant from an air conditioner is
accomplished by heating the liquid desiccant in a first liquid-to-liquid
heat exchanger, and a portion of the liquid desiccant in an evaporator/condenser,
and another portion of the liquid desiccant in a second liquid-to-liquid
heat exchanger and in a boiler. This heat is provided from concentrated
liquid desiccant flowing back to the air conditioner, from condensing
steam in the evaporator/condenser provided from the boiler, and
from energy furnished to the boiler by, for example, combustion
products of a natural gas-fueled burner or electrical heaters. The
regeneratable liquid desiccant from the air conditioner flows through
the first liquid-to-liquid heat exchanger with part of this liquid
desiccant flow directed to the evaporator/condenser which provides
for complete regeneration of the liquid desiccant while a second
but diminished second liquid desiccant flow passes through a second
liquid-to-liquid heat exchanger and is regenerated within the boiler.
The regenerated desiccant liquid is cooled as it returns to the
air conditioner through the first and second liquid-to-liquid heat
exchangers.
As complete regeneration of the desiccant liquid occurs both in
the boiler and in the evaporator/condenser using steam from the
boiler, energy is reused. In a preferred embodiment, the steam condensate
is collected from the evaporator/condenser and then flowed through
the first liquid-to-liquid heat exchanger wherein it is cooled and
the sensible energy transferred to the heating liquid desiccant
flow.
These and other features of the present invention will be understood
upon reading of the following description along with the drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic view of a liquid desiccant regeneration system
according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
1. Detailed Description of the FIGURE
Referring to FIG. 1 the regenerator will be described with reference
to its operation. Major elements are a first heat exchanger 20
a second heat exchanger 30 a boiler 40 and an evaporator/condenser
50. Liquid desiccant from an air conditioner is brought via pipe
11 to heat exchanger 20 which may be any suitable form of liquid-to-liquid
heat exchanger, wherein the liquid desiccant is increased in temperature
from 32.degree. C. to 82.degree. C., for example. The liquid desiccant
moves by pipe 21 to tee 22 where more than half of the liquid desiccant
is caused to flow via pipe 23 by control pump 24 to heat exchanger
30 which may be any suitable liquid-to-liquid heat exchanger. While
in heat exchanger 30 the liquid desiccant increases in temperature
to over 138.degree. C., for example, and is routed by pipe 31 to
boiler 40. The desiccant may be controlled to boil at a set temperature
of 149.degree. C. for example when utilizing lithium bromide, with
energy furnished by heater 41. Energy supply to heater 41 may be
combustion products of a natural gas or wood for instance, or the
energy supply may be from resistance or radiant electric heaters.
The liquid desiccant leaving boiler by pipe 42 and at the approximate
temperature of the boiling liquid enters heat exchanger 30 where
it exchanges sensible energy with the liquid desiccant moving to
boiler 40 and may exit into pipe 32 at 88.degree. C., for example.
The liquid desiccant then passes through heat exchanger 20 losing
heat to the liquid desiccant stream arriving from the air conditioner
and exits heat exchanger 20 at 35.degree. C. for instance returning
to an air conditioner via pipe 12.
After passing through a liquid/vapor separator zone 43 of boiler
40 steam moves through pipe 44 to evaporator/condenser 50 where
the steam enters condenser 51. In a preferred embodiment, condenser
51 is a spiral tube although other types of condensers may be utilized.
The heated liquid desiccant arriving to evaporator/condenser 50
via pipe 21 may be sprayed on condenser 51 causing heat transfer
utilizing a spray means consisting of a spray nozzle 52 connected
to pump 53 which draws liquid from basin 54. Evaporation of water
from the liquid desiccant is affected by increasing the temperature
of an air stream passing approximate to condenser 51 and further
contacting liquid desiccant droplets 55 developed through spray
nozzle 52. For example, heating of an ambient air stream of 35.degree.
C. 40% relative humidity to 88.degree. C. will lower its relative
humidity to 3%. In simplest operation, ambient air enters duct 56
by air movement caused by fan 57 and following its rise in temperature
and gain in absolute humidity in the evaporator/condenser 50 the
air exits to the atmosphere via duct 58. In a more complex and energy
saving configuration, air supplied to evaporator/condenser 50 is
preheated by first entering duct 59 to heat exchanger 60 which
may be any suitable air-to-air heat exchanger. Heated air exiting
evaporator/condenser 50 is routed to heat exchanger 60 by means
of duct 61 therein exchanging its heat with incoming ambient air
before discharging via duct 62. The regenerated liquid desiccant
exits evaporator/condenser 50 via pipe 25 which joins the desiccant
stream in pipe 32 by means of tee 26 and flows through heat exchanger
30 surrendering its heat. Condensate from condenser 51 may be drawn
off as hot water by means of pipe 27 or may be routed to heat exchanger
20 via pipe 28 giving its heat to the liquid desiccant stream from
the air conditioner that entered heat exchanger 20 by means of pipe
11. The cooled water exits heat exchanger 20 through pipe 13 and
may be returned to an air conditioner of air humidification or may
be used for any other suitable purpose.
2. Description of the Preferred Embodiment
The present invention provides that a evaporator/condenser and
a desiccant boiler operate in parallel to regenerate the liquid
desiccant. The heat from the desiccant boiler is reused in the evaporator/condenser
unit and the heat from both the desiccant boiler and the evaporator/condenser
unit are reused to heat the incoming diluted desiccant. The parallel
operation of the desiccant boiler and the evaporator and condenser
is important because the size of the liquid heat exchange units
can be reduced. The evaporator/condenser unit, operating at a relatively
high temperature, permits the air, heated as a result of the liquid
desiccant regeneration, to be reused to heat the incoming air.
The foregoing description is included to illustrate the operation
of the preferred embodiment and is not meant to limit the scope
of the invention. The scope of the invention is to be limited only
by the following claims. From the foregoing description, many variations
will be apparent to those skilled in the art that would yet be encompassed
by the spirit and scope of the present invention. |