Patent Publication Number: US-6988717-B2

Title: Method and system for near saturation humidification of a gas flow

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to the field of gas supply for a point of use. More particularity, the present invention concerns the generation and supply of gas of high humidity. 
   2. Description of the Related Art 
   Highly humidified, or near saturation, flow gases of variety are often required at a point of use such as a reaction chamber of a semiconductor wafer processing equipment. Some example gases are air, Nitrogen, Oxygen or an inert gas such as Argon. Typically, the required relative humidity is 90% and above. Such a high relative humidity of the flow gas, being near the point of condensation, is difficult to reach and maintain near a constant state. Many current humidification methods require large humidity contact surfaces and/or humidity contact time to reach near saturation. Some current example methods are:
         1) Bubbling the flow gas through a liquid medium to gain humidity. The liquid medium can be water or a water containing solution.   2) Pressure techniques through a small orifice to spray and atomize the water into the flow gas.   3) Membranes with capillaries under pressure for separation of water into a mist for humidification of the flow gas.
 
Therefore, a compact, effective and fast acting method for near saturation humidification and control of a gas flow is desired.
       

   SUMMARY OF THE INVENTION 
   The present invention provides a method and system of near saturation humidification of a gas flow by mixing a steam and a gas flow to reach a humidity level that is near the point of saturation. The mixing is done by injecting the steam into the gas flow or vice versa. 
   The injecting steam is generated with a heating device and with a controlled generation rate from a steam-generating liquid contained in a steam-generating vessel located in physical proximity to the point of use of the humidified gas flow. 
   The controlled generation rate is achieved with a feedback loop to controllably heat the steam-generating liquid while measuring the steam temperature with a thermocouple so as to maintain the temperature around a set point. 
   The humidification delivery rate is adjustably controllable by adjusting the above temperature set point and/or by adjusting the supply pressure of the gas flow. 
   A manifold device is connected to the steam-generating vessel for supplying the gas flow, supplying the steam-generating liquid, injecting steam into the gas flow and delivering the humidified gas flow to its point of use. 
   The undesirable components, other than the steam and the flow gas, are removed from the humidified gas flow with an in-line filter after its point of generation. Condensation from the humidified gas flow before its point of use is removed with a drain pipe in combination with a drain valve triggered by a condensation level sensor. 
   To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other objects, features and attendant advantages of the present invention will become fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawing, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
       FIG. 1  illustrates an embodiment of the present invention method of near saturation humidification of a gas flow; and 
       FIG. 2  illustrates a refinement of the embodiment of the present invention method of near saturation humidification of a gas flow. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will become obvious to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, materials, components and circuitry have not been described in detail to avoid unnecessary obscuring aspects of the present invention. The detailed description is presented largely in terms of simplified schematics. These descriptions and representations are the means used by those experienced or skilled in the art to concisely and most effectively convey the substance of their work to others skilled in the art. 
   Reference herein to “one embodiment” or an “embodiment” means that a particular feature, structure, or characteristics described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of process flow representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations of the invention. 
   The present invention of near saturation humidification of a gas flow proposes to generate and mix a steam with a gas flow to reach a humidity level that is near the point of saturation. The mixing of the steam and the gas flow can be accomplished by injecting the generated steam into the gas flow or vice versa. 
     FIG. 1  illustrates a system embodiment of the present invention. A steam-generating vessel  1  holds water  1   a  used to generate a steam  1   b  when heated with an attached heating device  2 . The steam-generating vessel  1  can be made of a housing canister. The heating device  2  can be designed as a replaceable heater cartridge for easy service replacement. Steam generation rate can be controlled, around a desired value, by a thermocouple  3  attached to the housing of the steam-generating vessel  1  for measuring the temperature of the generated steam  1   b . The thermocouple  3  and the heating device  2  then form a feedback loop to controllably heat the water  1   a  while measuring the temperature of the generated steam  1   b  so as to maintain the steam temperature around a desired set point. An embodiment of simple control scheme is to use the set point of the thermocouple  3  to turn the heating device  2  off or on although more complex and accurate schemes known in the art such as proportional controls, etc. can be used as well. Notice that, for generality, the thermocouple  3  can alternatively be any one of a variety of temperature measuring devices. 
   A manifold device, including manifold sections  20   a ,  20   b ,  20   c ,  20   d ,  20   e ,  20   f  and  20   g , is provided for connection to the steam-generating vessel  1  for supplying a flow gas  9  through a gas in-take port  18 , for supplying water  1   a  through a feed line  8  via a liquid in-take port  6 , for injecting thus mixing the steam  1   b  with the flow gas  9  and for delivering, via a humidified gas exit port  7 , the humidified gas flow to its point of use through a port of use  10 . Thus, the mixing of water  1   a  with flow gas  9  takes place both inside the steam-generating vessel  1  and within the manifold sections  20   e ,  20   f  and  20   g . By now, for those skilled in the art, the humidification system of the present invention can also be characterized as injecting the flow gas  9  into the steam  1   b  causing the desired mixing action. Because the steam-generating vessel  1  can be made very compact in size, the injecting steam  1   b  can be located in physical proximity to the port of use  10  of the humidified gas flow thus realizing numerous advantages like reduction of heat loss, gas pressure loss and condensation. As a remark, the flow gas  9  can be made of air, Nitrogen or an inert gas. The water level within the steam-generating vessel  1  can be adequately maintained by a liquid level sensor  4 , as part of the manifold device, that senses the water level within the steam-generating vessel  1  and turns a feed valve  5  along the feed line  8  off and on as appropriate. 
   The humidification delivery rate of the humidified gas flow from the port of use  10  can be controlled around an adjustable value by at least one or combination of the following:
         a. adjusting the temperature set point of the steam  1   b.      b. adjusting the supply pressure of the flow gas  9 .       

   To remove condensation from the humidified gas flow before its port of use  10 , a condensation removing device  16  is provided. The condensation removing device  16  includes a drain pipe  11  attached to the manifold device, in this case at manifold sections  20   f  and  20   g , to receive its condensation between a point of steam generation and the port of use  10 , a condensation level sensor  13  located with the drain pipe  11  for sensing the cumulated condensation level and a drain valve  12 . Thus, when the cumulated condensation reaches a pre-determined level as sensed by the condensation level sensor  13 , the condensation level sensor  13  would trigger and open the drain valve  12  to drain the condensation around its lowest point. Of course, the drain pipe  11  can be alternatively implemented as a collection vessel. Hence, the illustrated system embodiment of the present invention can reliably deliver a humidified gas flow with an adjustable flow rate while maintaining a relative humidity of 90% and above. 
     FIG. 2  illustrates a refinement of the embodiment of the present invention method of near saturation humidification of a gas flow. An extraneous material removing device is provided for removing components, other than the desired steam and the desired flow gas, from the humidified gas flow after its point of generation. Examples of such extraneous material are large water droplets or simply impurity particles. In this embodiment, the extraneous material removing device is an in-line filter  14 , located within the manifold section  20   f , for passing the steam  1   b  and the flow gas  9  while blocking other extraneous materials from the humidified gas flow and allowing them to flow back to the water  1   a.    
   As described with numerous exemplary embodiments, a method and system of near saturation humidification of a gas flow includes mixing a steam and a gas flow to reach a humidity level that is near the point of saturation. However, for those skilled in this field, these exemplary embodiments can be easily adapted and modified to suit additional applications without departing from the spirit and scope of this invention. Thus, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements based upon the same operating principle. The scope of the claims, therefore, should be accorded the broadest interpretations so as to encompass all such modifications and similar arrangements.