Title of Invention


Abstract A method of humidifying gases to 100% relative humidity and a humidifier to carry out such a method are provided to humidify gases for fuel cells and for other applications. The humidification of gases is thermally controlled and thermal energy is managed to provide an efficient system. A pre-humidifier accommodates a wide range of flow rates of dry gas to initially humidify and pre-heat the gas, and a boiler provides steam to mix with the effluent from the pre-humidifier to humidify the gas to saturation. A thermal insulator between the boiler and bulk water and/or pre-humidifier enhances the steam generation from the boiler and prevents direct heating of water or gases by heat from the boiler. Above the boiler, bulk water, and pre-humidifier, a mixing chamber further functions as a condenser and water separator. The mixing chamber provides a space for mixing gases and steam and separates saturated gases from condensed water. By vapor condensation during the mixing, the gas can be humidified completely to its dew point at given temperature and pressure conditions.
The present invention relates generally to the field of continuous flow gas
humidification systems, and, more particularly, to a method and a system for
humidifying gas reactants for fuel cells or other gases. It also relates to the field of
temperature control and tracing of the humidified gas.
As described in U.S. Patent No. 6,338,472 to Shimazu etal., humidifiers, like
those of the field of the present invention, are typically used to humidify process
gases supplied to an anode or a cathode of a Solid Polymer Fuel Cell (SPFC). The
process gases comprise a fuel gas provided to the anode and an oxidizing gas
provided to the cathode. A solid polymer fuel cell generates electrical energy by
electrochemical reactions in which protons generated from a fuel supplied to the
anode transfer to the cathode through an electrolyte membrane and react with an
oxidizing gas supplied to the cathode to produce water. The humidifier of the present
invention, however, is not limited to fuel cells, but is generally applicable to the
humidification of gases.
Similarly, a Proton Exchange Membrane Fuel Cell (PEMFC), in contrast to
the SPFC device, generally consists of three main components: (1) a porous diffusion
catalytic anode, (2) a proton conductive membrane, and (3) a porous diffusion
catalytic cathode The PEMFC converts chemical energy to electrical energy with
catalytic electrochemical reactions of hydrogen and oxygen at the anode and cathode,
respectively. During the process, the conductivity of the proton exchange membrane
plays an important role in the performance of the PEMFC. The membrane
conductivity, however, depends on its water content. Usually, high water content
gives high conductivity. In fact, fuel and oxidant gases must be humidified to
maintain adequate water content in the membrane, therefore requiring a humidifier
and a method of humidifying reactant gases.
To operate a fuel cell normally, whether a SPFC or a PEMFC, the membrane
must be kept wet. To keep the membrane wet, the process gases are typically
humidified by one or more of a variety of techniques. For example, one commonly
used technique, referred to herein as a "bubbling-type" humidifier, involves bubbling
reactant gases up through a container of heated water so that water molecules are
taken up with the reactant gases. An energy source is provided to facilitate the water
evaporation into the gas bubbles or gas stream through the container.
In order to make gases highly humidified, the flow rate of gases should be low
enough, or the residence time in water should be long enough. Also, the distribution
of gases in the liquid water has a large influence on the final humidity of gases. A
bubbling-type humidifier should also avoid leaving water droplets to be carried out by
the gas stream, even when flow rate is relatively low because there is no typically gaswater
separation function in such a humidifier. This method of humidification has the
advantage of being very simple and inexpensive. However, typical bubbling-type
humidifiers cannot deliver 100% relative humidity to gases and only allow relatively
low gas flow rate for a certain cross area of humidifier. Another disadvantage of this
method is its uncertainty as to just how much humidity has been imparted to gases as
the gases leave the outlet of the humidifier. Many factors, including water
temperature, flow rate, gas distribution, inlet gas temperature and humidity, physical
structure and condition of the humidifier, affect humidity at outlet.
In bubbling-type humidifiers, it is difficult to control humidity unless using a
feedback signal developed from the measurement of actual humidity value at the
humidifier outlet. Even with such controls, the bubbling-type humidifier requires a
relatively large cross section area and water height to humidify the gas and the
response time for change of humidity is very long.
In another conventional method, referred to herein as "steam injection or
steam mixing", water vapor steam is injected, usually in an excess amount, into a dry
gas stream to form a gas-vapor-water droplet mixture. The mixture then flows
through a heat exchanger to condense down to a set temperature by a chilling coolant.
Water droplets and extra water vapor in the mixture condense to a water stream,
which is further separated from the gas-vapor stream by a water separator and a water
drain. Because there is a condensation process, the set temperature is equal to the
Dew Point Temperature. In order to have a condensation procedure, extra water
vapor steam must be used. In this technology, a separate boiler, condenser, chiller,
water drain and their own individual control systems are usually needed. In order to
maintain good control of the dew point temperature, these types of humidifiers are
usually bulky, complicated, and expensive with very low energy efficiency.
Another known technique for humidifying reactant gases uses a "membranetype"
humidifier. One example of a membrane-type humidifier is shown and
described in U.S. Patent No. 5,996,976 to Murphy etal. In this technique, water is
pumped through a heating element and then directed to one side of a porous
membrane. The gases to be humidified are directed across the other side of the
membrane. Water molecules penetrate the membrane from the heated water side to
the reactant gas side where the water molecules evaporate into the gases and the gases
absorb heat from the water. The water may be circulated through a heating chamber
as described, or the water may be heated directly in an evaporation chamber. The
temperature of the gas-vapor mixture is lower than the temperature of the water
because evaporation occurs at the surface of the membrane. Because of this
phenomenon, the temperature and humidity of the gas-vapor mixture is rather difficult
to control Further, the difficulty of control increases as the rate of gas flow increases
because the amount of heat absorbed from the water is relatively high. Further, a
specialized membrane is required, increasing the overall cost of such a system.
Again, there is no mechanism to guarantee precise humidity control without further
condensation or employment of a humidity sensor.
U. S. Pat. No 5,262,250 to Watanabe and U. S. Pat. No. 5,952,119 to Wilson
teach a kind of self-humidification method for membrane electrode assemblies of fuel
cells. The former uses some narrow path or wicks within a membrane and the latter
sews hydrophilic thread through a backing layer to enhance the humidification of the
membrane. However effective such self-humidification may be in a laboratory
environment, it is difficult for commercial manufacturing in a large scale.
Yet another technique for the humidification of a gas involves the application
of ultrasonic energy to the gas and a water bath. A quantity of water is contained
within an enclosure and gas is introduced to the volume within the enclosure above
the surface of the water. An ultrasonic energy source within the enclosure extends
through the gas volume into the water bath. Application of ultrasonic energy
generates water vapor, which is taken up by the gas and the gas-vapor mixture is
withdrawn from the enclosure. This technique has the advantage of easily
controllable humidity of the gas-vapor mixture for "batch" processing of gas, but is
not suitable to generate and control the humidity of a continuous stream of gas.
Still another technique for humidification of a gas involves a variation of the
steam-injection-type humidifier, wherein water is injected onto a hot element, such as
a plate, to evaporate the water into an enclosure. Gas is pumped into the enclosure to
mix with the water vapor to develop a gas-vapor mixture. The amount of water that is
injected onto the heating element is calculated and controlled to meet certain humidity
requirements. Further, the temperature of the exit gas-vapor mixture is controlled by
controlling the temperature of the heating element.
However, this factor presents a drawback of this technique in that the heating
component must use a certain minimum power to reach a temperature sufficiently
high to flash the water to vapor instantly and this minimum temperature is usually
much higher than the preferred mixture temperature. Also, it is difficult to quickly
change the temperature of the heating element when the flow rate of gas or water
changes and it is difficult to precisely control the temperature of the gas-vapor
mixture, thus the mixture is likely to be overheated. Even if the mixture temperature
can be adequately controlled, the range of flow rate and the range of temperature is
unacceptably limited using this technique. This is because this technique requires the
simultaneous control of two parameters, i.e. the temperature of the gas-vapor mixture
and the temperature of the heating element, in one control loop by one means, i.e. the
power to the heating element. It is difficult, if not impossible, to simultaneously
control these parameters in a realistic control mechanism.
One proposed solution to this control problem involves the use of a condenser
in the stream for the gas-vapor mixture. In principle, the humidification is carried out
in two steps and two devices. The first step involves steam injection as previously
described to generate an over-heated, over-humidified gas-vapor mixture. The second
step involves passing the mixture through the condenser to condense the gas-vapor
mixture at its dew point. A chiller is required to carry away the heat released from the
condensation to maintain the condenser at the dew point. Thus, additional energy is
needed to generate the over-heated and over-humidified mixture in the first step, and
even more energy is required to drive the chiller to dissipate the additional heat from
the cooling and condensation of the mixture. This means that this technique is very
energy inefficient, and it is also bulky, complicated, and expensive to build and use.
Another humidification method for PEMFC is taught in U. S. Pat. No.
6,383,671 to Andrews. This method uses a heater to vaporize liquid water and then
lets the steam directly mix with dry gases. Effective humidification may obtained for
the reactant gases under certain conditions. However, one of problems with this
apparatus is that the reactant gases are not pre-heated; that is, the temperature and
humidity of gases are far from saturation status of dew point. When vapor mixes with
these cool gases, condensation occurs This phenomenon makes the precise control of
humidity difficult because the gases and steam vapor are not mixed evenly. In order
to mix the gases and vapor well, the practical size of this humidifier must be quite
Thus, there remains a need for a system and a method of humidifying gases
that is energy efficient, simple, and easy to control, and more importantly, provides
precisely a desired amount of humidification of a continuous gas stream. The present
invention is directed to such a solution.
The present invention addresses these and other drawbacks in the art by
providing a continuous flow of gas through two stages. The first stage provides prehumidification
of reactant gases with a bubbling action, while the second stage
provides generating vapor steam in a steam generator and mixing the pre-humidified
gases with the vapor steam in a mixing chamber. No permeable membrane is used,
and only a single parameter (temperature) is used for precise control of the
humidification of the gas at the dew point. That is, the temperature at the outlet is
used as the sole parameter to control the operation of the heating element in the steam
Gas is introduced into an enclosure or vessel under pressure. The gas then
bubbles up through a bubbling evaporator. Above the water bubbling evaporator, the
gas-vapor-water droplets mixture mixes with injected water vapor steam to form
saturated gas-vapor-water droplets mixture. The saturated gas-vapor-water droplets
mixture then flows through a moisture separation region having "Y"-shaped cross
section Water droplets fall by gravity and inertia to bulk water while saturated gas
flows up and exits from the humidifier.
It is therefore an object of the invention to provide a gas humidifier that is
simple and easy to control to precisely produce saturated gas at the dew point. It is a
further object of the invention to provide a method of humidifying gas with such a
humidifier. It is yet another object of the invention to provide a gas humidifier that
produces saturated gas at the dew point over a wide range of temperatures using a
single measured parameter (temperature) within the enclosure without dew point
"calibration" It is another object of the invention to provide simple, economic, and
effective means to further heat and trace the gas temperature after humidification.
In order to realize these and other features and advantages of the invention,
enhanced thermal insulation is provided between the steam generating boiler and bulk
water within the vessel and/or the pre-humidifier. The thermal insulation prevents
direct heating of bulk water or pre-humidified gas by heat from the boiler. Thus,
thermal energy from a heating element with the steam generating boiler is contained
with the boiler to only generate vapor. Heat is therefore passed to the gases only
through gas-vapor mixing and/or vapor condensing.
Although the boiler is thermally isolated from other functions of the gas
humidifier, openings at the bottom of the boiler are provided so that bulk water from
the vessel flows back into boiler. This arrangement eliminates the necessity of a
separate water supply and recycling system and further provides water leveling for the
pre-humidifier, the condenser/water separator and the boiler. On the other hand,
because water flows from the bulk water in the vessel into the bottom of the boiler,
the water path does not cause convection of heat from the boiler to the pre-humidifier
or the bulk water.
Thermal efficiency of the humidifier is also improved by enhanced thermal
insulation applied to the mixer/condenser wall to prevent heat transfer to the gas
stream at 100% relative humidity along the path to the outlet of the humidifier. This
feature ensures the gas stream remains at 100% relative humidity. The thermal
insulation of the boiler and the mixer/condenser eliminates the need to pass the
humidified gas through an additional humidification stage.
As previously described, the outlet of the mixing chamber and condenser
defines a "Y11 shape in cross section. The bulk water level within the vessel is
maintained lower than this outlet. This keeps the gas-vapor mixture from flowing
through the bulk water and causing bubbling, which would limit the maximum flow
rate of gas through the humidifier. This arrangement increases maximum flow rate
for the same cross sectional area by more than 10 times without this feature.
From the mixing chamber, the gas vapor mixture makes a number of distinct
changes in direction before reaching the outlet of the vapor. This circuitous route for
the gas vapor mixture causes water droplets to fall back into the bulk water, while
maintaining saturated gas out the outlet of the humidifier. This also means that it is
not necessary to use the bulk water or a separate water separator and drain for water
A temperature sensor for (dew point) temperature measurement and control is
mounted in an outlet chamber of the humidifier, and not in the bulk water. This
measurement point reflects the gas-vapor mixture temperature more accurately than in
The mixing chamber also serves as a condenser. Thus, it is not necessary to
use bulk water for condensation. Relatively cold, pre-humidified gas cools down the
water steam while mixing with it. This cooling process condenses some of the steam
in the mixture Condensed water and the heat it carries with it will be used for prehumidification
and steam generation. This condensation recycles water and heat for
natural, automatic heat and water balancing.
In a presently preferred embodiment of the invention, the same coolant (such
as, for example, city water or chill water) is used for temperature regulation in the
humidifier, the gas heater, the gas line and the humidity sensor assembly. This
feature simplifies the control system and makes temperature control smooth and
stable. When city water is used, it eliminates a complicated, separate cooling,
heating, and circulating systems for each of those functions.
These and other features and advantages of this invention will be readily
apparent to those skilled in the art from a review of the following detailed description
along with accompany drawing figures.
Figure 1 is an elevation view of a dew point humidifier of the invention.
Figure 2 is a presently preferred embodiment of a dew point humidifier of the
Figure 3 is a schematic diagram of a dew point humidifier including
temperature controlling aspects of the invention.
Figure 1 show the core structure of a humidifier 10 and a method humidifying
gas, in accordance with the present invention. The humidifier 10 principally
comprises a vessel 12, preferably cylindrical in aspect, with a top 14 and a bottom 16.
An inlet line 18 introduces dry gas into the vessel 12, and an outlet 20 directs
humidified gas from the vessel. Dry gas is shown entering the vessel by an arrow 22
and humidified gas is shown exiting the vessel by an arrow 24.
The dry gas 22, which is at a lower temperature than set dew point
temperature, is initially humidified by flowing through pre-humidifier 26. The dry
gas 22 bubbles up through the pre-humidifier 26 forming bubbles 28, which rise up
through the pre-humidifier, thereby picking up some moisture and being warmed to a
higher temperature by the water in the pre-humidifier column. The pre-humidifier 26
defines an elongated container, such as a tube, with openings 30, preferably along the
bottom of the tube inside the vessel. The openings 30 provide a water path to a boiler
32, which is also preferably an elongated container, such as a tube, adjacent to the
pre-humidifier 26 The openings 30 further provide a water flow path to a reservoir
34 of bulk demineralized water retained with the vessel. A water inlet 38 provides
makeup water to make up for water released from the vessel in humidified gas, as
controlled by a control valve 39.
The pre-humidifier 26 defines an open top outlet 40, preferably above a water
level 42 of the bulk demineralized water. The gas bubbles 28 rise up through the prehumidifier,
and when gas flow rate is very slow, the pre-humidifier functions in the
manner of a conventional bubbling humidifier. However, when gas flow rate is high,
a large volume of gas mixes with small amount of water and this action develops a
foam-like mixture, the mixture includes a humidified gas. The foam-like mixture
rises out of the outlet 40 of the pre-humidifier, carrying a substantial quantity of
water, and into a mixing chamber 44. The mixing chamber 44 is defined by a
cylindrical thermal insulator 46 having a cylindrical, vertically oriented side member
48 and a horizontally oriented top 50. The side member need not be cylindrical, but
may take other shapes, so long as it defines an open bottom container with a bottom
edge 49 above the water level and below the tops of the pre-humidifier and the boiler.
The mixing chamber wall is thermally insulated so that a 100% relative humidity gasvapor
mixture flows up through an annulus 62 between the mixing chamber and the
inside surface of the vessel 12 will not be heated up.
At this point, it should be noted that the pre-humidifier functions in a
substantially different manner than a conventional bubbling humidifier. In a bubbling
humidifier, only water vapor with no water droplets should get out from the water
retained within the bubbling humidifier. The flow rate through a bubbling humidifier
is hence very limited. However, the pre-humidifier of the present invention can pass a
gas stream of very high flow rate, in fact more than ten times higher than that of a
conventional bubbling humidifier with same cross section.
Returning to Figure 1, positioned within the boiler 32 is a heater element 52
Preferably, the heater element is a resistive element, although other heating means
may be used within the spirit of the invention. The heater element terminates a top
end 54, which is positioned below the water level 42. The heater element generates
water vapor steam in the boiler , which is enclosed within a thermal-insulated wall 56.
Water vapor steam rises from the boiler and out an open top 58 into the mixing
chamber 44. Just as with the pre-humidifier, the boiler 32 includes openings 31 along
the inside surface of the bottom 16 for the flow of bulk water from the vessel into the
bottom of the boiler Bulk water also flows into the bottom of the pre-humidifier
through the openings 31.
Water vapor steam is released from the boiler 32 into the mixing chamber 44,
which also serves as a condenser to condense steam into droplets which fall back into
the bulk water. The steam released from the open top or outlet of the boiler flows
naturally and freely, without obstruction. The boiling temperature within the boiler is
typically much higher than the set dew point temperature in the present invention.
However, pre-humidified gas exiting the pre-humidifier 26 is typically cooler than the
dew point temperature. Thus, pre-hurnidified gas from the pre-humidifier, which is
cooler than the dew point, mixes with steam from boiler, which is typically hotter than
the dew point
Under normal operating conditions, water steam mixes with the prehumidified
gas and heats it. In doing so, the water steam releases thermal energy,
thereby cooling down to the point that it condenses in the mixing chamber and
condenser. As long as there is a condensing process, the mixture in the mixing
chamber by definition is saturated. The mixing procedure generates 100% relative
humidity gas-vapor mixture in the mixing chamber at a predetermined dew point
temperature or higher The mixing procedure also generates condensed water droplets
60 at a temperature around the dew point temperature. The water droplets carry heat
from condensation process to the pre-humidifier.
The mixture of water droplets, water steam, and pre-humidified gas flows
down between the outside of the tube forming the pre-humidifier and the side member
48 of the mixing chamber 44. A water separator or moisture separation region 61 is
defined at the bottom edge of the side member 48. In cross section, the water
separator 61 resembles a "Y" shape. In that way, the moisture separation region has a
downward gas-water mixture path, an upward gas path, and a water collector below
the bottom edge. As the steam/gas mixture flows downward out the bottom of the
mixing chamber, gravity and inertia force the condensed water droplets to continue
down to flow into the bulk water. Saturated steam, however, flows down under the
bottom edge of the side member 48, continuing to flow in the annulus 62 between the
outside surface of the side member 48 and the inside surface of the vessel. This flow
action effectively separates the heavier water droplets from the saturated steam. It
also retains the energy contained in the water droplets and this energy is returned to
the bulk water. The gas, now saturated with water, flows up through the annulus 62
and into an exit chamber 64, above the top surface of the horizontally oriented top 50.
The saturated gas then exits the vessel at the gas outlet 20.
Note that the gas and vapor mixture makes six distinct changes of direction
from the mixing chamber to the outlet 20. It moves (1) horizontally outward, then
(2) downward, then (3) horizontally outwardly again, then (4) vertically upward, then
(5) horizontally inward, and finally (6) vertically upward out the outlet. This
circuitous route eliminates the water droplets from the gas and vapor mixture,
ensuring a saturated gas at the outlet.
The water level 42 is lower than the outlet of mixing chamber 44. This
structure prevents the gas-vapor mixture from flowing through water. Water level is
maintained by a water level sensor and a water pump (not shown). If the gas-vapor
mixture were to flow through water, the turbulent action could potentially create a
foaming action, thereby carrying water droplets up to the outlet of the humidifier,
severely limiting the maximum gas flow rate. Thus, placing the outlet of the mixing
chamber above the bulk water level increases the maximum flow rate of gas through
the humidifier by a factor often, over a bubbling-type humidifier of the same cross
sectional area
A temperature sensor 70 is mounted on the top of the vessel, penetrating into
the outlet chamber 64. In this way, the precise temperature of the saturated gas is
measured by the sensor 70 The sensor 70 provides a temperature measurement to a
temperature controller 72, which controls the cycling of the heater element 52 in the
boiler. This function controls the temperature of gas-vapor mixture at the gas outlet
20 to be at the desired dew point temperature by adjusting the thermal energy
provided by the boiler 32. Because the gas-vapor mixture is at 100% relative
humidity, the temperature at the outlet 20 is at true dew point temperature. Dew point
temperature is hence accurately controlled by controlling this gas outlet temperature.
To further assist in temperature regulation, a jacket 80 may be mounted on the outer
surface of the vessel to circulate chilled or ambient temperature water, fed from a chill
water inlet 79 and emptying into a chill water outlet 81. This feature of the invention
is described in greater detail in respect of Figure 3.
As previously described, water and heat from condensation in the mixing
chamber go back to the bulk water 34 to be used for pre-humidification and steam
generation. The pre-humidification process not only functions to partially humidify
dry gas, it also uses, or recycles, this water and heat from condensation. Prehumidification
keeps the temperature of the bulk water at a lower temperature than
the selected dew point temperature. Lower water temperature guarantees prehumidified
gas at a lower temperature than dew point temperature. The mixing of gas
at lower temperature with vapor steam at higher temperature will bring the vapor
temperature down and cause condensation, guarantying 100% relative humidity for
the humidified gas. This pre-humidification procedure, which consumes water and
heat, keeps water and heat balanced, thereby conserving demineralized water and
heat. This feature substantially enhances the efficiency of the invention and
simplifies temperature humidity control.
An alternative embodiment of the present invention is shown in Figure 2. In
this embodiment, a boiler 90 is mounted as a separate component outside of a
humidifier vessel 92. The vessel encloses a pre-humidifier 94, constructed as
previously described in respect of Figure 1. Dry gas enters at a gas inlet 96 and
humidified gas exits the vessel at a gas outlet 98. A water path 100 from the prehumidifier
94 or bulk water within the vessel is provided so that water can be supplied
to the boiler naturally from the vessel, thereby maintaining a water level 102 in the
vessel 92, the pre-humidifier 94, and the boiler 90. The water path 100 eliminates the
need for a separate water level sensor and a water supply and recycling device. With
this water path, the boiler may be considered to be integrated with humidifier for
purposes of water level control, gas humidification, and temperature control Water
in the vessel and in the boiler are thus maintained at a level 105, and both may be
drained through a drain 107. A heater element 104 develops vapor steam, which is
introduced into the vessel through a steam injection line 106. The steam injection line
penetrates into a mixing chamber 108 which is constructed and functions as
previously described. The mixing chamber also serves as a condenser, and
condensation from the mixing chamber is returned to the bulk water as before. The
humidifier also may include a chill water jacket 110, fed from a chill water inlet 109
and emptying into a chill water outlet 111, as previously described.
Figure 3 illustrates another presently preferred embodiment of a humidifier of
this invention. This embodiment provides a simple, efficient integration of the
various components for humidification, gas heating, temperature tracing, and
humidity sensing together, using the same coolant.
The vessel 12, pre-humidifier 26, boiler 32, the mixing chamber 44, and other
various components are constructed as previously described in respect of Figure 1. In
this embodiment, however, chill water is provided at an inlet 120 flows into the jacket
(see also Figure 1) for temperature regulation and fast dew point decreasing. Instead
of chill water, regular city tap water may be used for circulating chill water because it
never comes in contact with the gas and vapor of the humidifier. The chill water
flows upward through the jacket 80, until it reaches a chill water outlet 122 at the top
of the vessel. At this point, the chill water has been heated to about dew point
temperature, having received thermal energy from the outside surface of the vessel.
The cooling effect of chill water makes the temperature control of boiler easier and
The heated circulating chill water then goes from the humidifier into a gas
heater jacket 124, which surrounds and encloses a substantially horizontal gas heater
126. The gas heater 126 includes a heater element 128 positioned therein. The
circulating chill water further heated in the gas heater jacket 124. The chill water then
passes into a connecting line 130 and into a water jacket 132 for a humidity sensor
134. It then flows into a gas outlet jacket 136. The gas outlet jacket 136 discharges
into a chill water discharge line 138, through a back pressure controller 140 and out a
chill water outlet 142
The gas heater 126 heats up the gas-vapor mixture from the outlet 20 of the
humidifier to approximately the set gas temperature. Because the circulating chill
water is preheated in the jacket 80 to temperature close to dew point, it does not need
to be preheated before meeting 100% humidified gas in the gas heater to prevent
condensation The water in the gas heater jacket 124 makes temperature control
smooth and stable It enables fast temperature change, both up and down, without
significant overshoot
The circulating chill water, which is further heated in gas heater jacket 124, is
used for temperature tracing along a gas line or conduit 144. Thus, the gas line or
conduit defines a jacketed tubing for gas transportation and gas temperature tracing
along the gas line Gas temperature in the gas line 144 may measured at a gas outlet
148 from the gas line 144 with a gas temperature sensor 146. The sensor 146
provides a temperature signal to a heater temperature controller 150 to control the
cycling of the heater element 128. The use of the heated circulating chill water
enables the temperature to be maintained at desired temperature at the outlet 148 from
the gas line 144 and to be maintained at temperature close to this temperature along
the gas line This heated water enables uniform temperature control and smooth
temperature transaction without significant overshoot.
The circulating chill water at the end of line can also be used for temperature
control of humidity sensor jacket 132. It is important to have the temperature of
humidity sensor to be kept close to gas temperature. Without this heated water, it is
complicated and expensive to use a heater unit for the humidity sensor assembly, such
as heat tape, to accomplish this function. Instead of using separate temperature
control loops for gas heating, temperature tracing, and humidity sensor jacket heating,
which will need separate temperature control systems, this method needs no extra
heaters and controllers but only one heating loop for these functions. It eliminates
extra systems, which include heating, cooling, circulating and control units.
Typically, a humidity sensor requires the condition of limited flow rate,
usually less than 0.2 slpm (standard flow, standard liters per minute). Under
conditions of high flow rate, a sampling mechanism is usually applied to a humidity
sensing unit, which makes it complicated and expensive. The present invention,
however, makes the humidity sensor 134 work properly for a high flow rate gas
stream. A check valve 152 is installed in the main gas line and in parallel with a
humidity sensor assembly 154. The check valve keeps pressure drop across the
humidity sensor assembly lower than a preset value and hence controls the flow rate
through the humidity sensor assembly lower than the pre-set value. When the flow
rate of humidified gas through the line 144 is lower than this preset value, all gas
flows through the humidity sensor assembly.
Operation of the Gas Humidifier
The thermodynamic operation of the humidifier starts with dry gas at or lower
than ambient temperature and results in saturated gas at the dew point temperature at
the outlet of the humidifier. In a first step, the gas travels through the pre-humidifier,
an un-insulated pipe, absorbing heat from the bulk water and cooling the bulk water
by the same amount of energy. In a second step, gas from the pre-humidifier mixes
with steam from the boiler and forms a saturated gas-vapor-water droplets mixture
and condenses. In a third step, the mixture flows through the "Y"-shaped water
separator, where a saturated gas-vapor mixture flows up to the outlet. Water droplets
carry heat from condensation down to the bulk water, thereby providing heat-water
recycling and heat-water balancing.
The operation of the heating element in the boiler is controlled by the
temperature of the gas-vapor mixture at the outlet of the humidifier as determined by
a temperature sensor in order to maintain the dew point and maintain thermal balance
within the apparatus. Using the structure of the present invention, a separate
condenser and chiller is therefore eliminated, and the heat from the condensing gasvapor
mixture is released directly into the bulk water, thus conserving the energy that
is lost in prior art systems using a separate condenser and chiller.
Thus, the heat balance of the apparatus is given by the following equation.
Total heat needed to generate 100% = Total heat from steam generator - heat
humidified gas at the dew point from loss to environment - heat to chill
inlet gas and water water
This means that by controlling one simple parameter, the power of the heating
element, the temperature of the gas-vapor mixture at the outlet of the humidifier is
assured of being at the desired dew point. The precise humidification of the gas
stream is assured for a continuous gas stream, regardless of the flow rate of the gas.
In known humidification systems, the level of humidification of the gas stream varies
with the flow rate and other parameters of the system before entering a separate
condenser, and this drawback in the art is eliminated by the present invention.
In another preferred embodiment, the temperature of the humidified gas is
further controlled by the operation of the gas stream heater, which is cycled by a
control signal based on the temperature of the gas at the gas outlet. Chill water is
circulated through the apparatus to provide stable operation of the humidification
The principles, preferred embodiment, and mode of operation of the present
invention have been described in the foregoing specification. This invention is not to
be construed as limited to the particular forms disclosed, since these are regarded as
illustrative rather than restrictive. The invention should not be limited to water as
coolant either. Moreover, variations and changes may be made by those skilled in the
art without departing from the spirit of the invention.

1 claim:
1. A gas conditioning system comprising:
a. a gas stream humidifier adapted to develop a humidified gas;
b a gas heater line to receive humidified gas from the humidifier, the gas heater line
having a gas heating element therein;
c. a first chill water jacket around the humidifier, the chill water jacket having a first
chill water inlet and a first chill water outlet; and
d. a second chill water jacket around the gas heater line adjacent the gas heating
element, the second chill water jacket having a second chill water inlet in fluid
communication with the first chill water outlet, the second chill water jacket
further having a second chill water outlet.
The system of claim 1, further comprising a check valve within the gas heater line.
3 The system of claim 2, further comprising a humidity sensor in the gas heater line in
parallel with the check valve.
4 The system of claim 3, further comprising a third chill water jacket around the humidity
sensor and having a third chill water inlet in fluid communication with the second chill water
outlet, the third chill water jacket having a third chill water outlet.
5 The system of claim 4, further comprising a fourth chill water jacket around the gas
heater line a spaced apart distance from the gas heater element, the fourth chill water jacket
having a fourth chill water inlet in fluid communication with the third chill water outlet, the
fourth chill water jacket further having a fourth chill water outlet
6 The system of claim 1, wherein the gas heater line comprises jacketed tubing for gas
transportation and gas temperature tracing along the gas heater line.
7 The system of claim 3, wherein the humidity sensor provides a control signal to maintain
temperature within the gas heater line such that humidified gas within the gas heater line remains
close to the dew point temperature.










5204-DELNP-2005-Description (Complete)(18-12-2007).pdf

5204-delnp-2005-description (complete).pdf














Patent Number 226600
Indian Patent Application Number 5204/DELNP/2005
PG Journal Number 01/2009
Publication Date 02-Jan-2009
Grant Date 19-Dec-2008
Date of Filing 11-Nov-2005
Name of Patentee Chaojiong Zhang
# Inventor's Name Inventor's Address
PCT International Classification Number H01M 8/00
PCT International Application Number PCT/US2004/010188
PCT International Filing date 2004-04-02
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/428,582 2003-05-02 U.S.A.