Patent Publication Number: US-8978396-B2

Title: Vent ice prevention method

Description:
BACKGROUND 
     Ice buildup on cold compressor seal gas discharge vents is a problem in some cryogenic plants. The function of vent lines can be defeated by the formation of ice (from condensed moisture) in the vent line. This can also be a safety issue, if a large piece of ice should fall from an elevated vent stack. A need exists in the industry for a simple and economical solution to this icing problem. 
     SUMMARY 
     An improved vent ice prevention method including introducing a cold vent stream into a first conduit, wherein at least a portion of the first conduit is concentric with a second conduit, thereby producing an annular region, introducing a hot vent stream into a third conduit, wherein the third conduit is in fluid connection with the annular region, thereby preventing the first conduit from forming condensation or ice. The cold vent stream is a cold compressor seal vent stream. The hot vent stream is a warm compressor seal vent stream. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates one embodiment of the present invention. 
         FIG. 2  illustrates another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     As used herein, the term “cold compressor” means a device for raising the pressure of a vapor in which both the inlet and discharge streams are below the freezing point of water. 
     As used herein, the term “warm compressor” means a device for raising the pressure of a vapor in which both the inlet and discharge streams are above the freezing point of water. 
     By inserting the cold compressor discharge pipe inside a larger pipe, that is discharging the warm compressor seal gas, the warm gas prevents the ice formation. In the interest of clarity, element numbers are consistent between both figures. Turning now to  FIG. 1 , a cold vent stream  101  and a hot vent stream  105  are provided. Cold vent stream  101  a may be the seal vent stream from a cold compressor  114 . Cold vent stream  101  may be air or nitrogen. Hot vent stream  105  may be the seal vent stream from a warm compressor  115 . Hot vent stream  105  may be air, nitrogen, instrument air, or any other available warm dry vapor stream. 
     Cold vent stream  101  may be directed through a first conduit  102 . At least part of first conduit  102  may be heat traced  104 , thermally insulated  103 , or both. At least part of first conduit  102  is concentric with a second conduit  107 , thereby producing an annular region  112 . Hot vent stream  105  may be directed through a third conduit  106 , which intersects with second conduit  107 . This allows hot vent stream  108  to flow through annular region  112  and thereby warming at least part of the exterior of first conduit  102  to a temperature above which icing will not occur. Cold vent stream  104  then combines with warm vent stream  108  to produce combined warm vent stream  109 , which may be expelled into the atmosphere. 
     As the temperature difference between the cold vent stream  101  and the hot vent stream  105  increases, the hot vent stream  105  blankets first conduit  102  and acts as an insulator, preventing condensate to form. This prevents condensate and ice to form in the first place, thus making the de-icing of the second conduit  107  a less critical mechanism. 
     Combined warm vent stream  109  may have a mean temperature greater than 32 F. The exit of the first conduit  102  may be recessed from the exit of the second conduit  107 . The exit of the first conduit  102  may be recessed from the exit of the second conduit  107  by at least twice the outside diameter of the second conduit  107 . The exit of the first conduit  102  may be recessed from the exit of the second conduit  107  by at least 5 inches. The exit of the first conduit  102  may be flush with the exit of the second conduit  107 .