Abstract:
Apparatus to convert LNG to gas, comprising a vaporizer having passages to pass the cool or cold LNG in heat transfer relation with warming gas flowing downwardly to discharge in multiple directions, and flow control means to control discharge of the gas flow in selected direction or directions, as a function of wind direction.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to efficient vaporization of cryogenic fluids, and more particularly to control of flow of ambient air acting to transfer heat to the cryogenic fluid, with control of air discharge as a function of incident wind direction.  
         [0002]     Ambient air vaporizers have been used to convert cryogenic liquids into warm gas for over fifty years. To move the ambient air across the heat transfer surfaces, many rely on the natural draft effect. The cryogenic fluids being warmed (vaporized) are passed adjacent vertical heat transfer surfaces while being heated; and the ambient air descends at the other sides of such surfaces. The change in the density of the air as it cools induces a draft (the opposite of a chimney). The velocity of the induced draft is a function of the change in density. At the outlet (bottom) of the vaporizer, the cooled air typically turns to flow horizontally. For a single operating unit, this will cause discharge of the air in a 360° horizontal fan. In large vaporizer arrays, such as large industrial gas users (steel mills) or LNG re-gasification terminals, the exits may be confined to a single directional axis. As long as sufficient height is provided underneath the vaporizer, as by the vaporizer unit legs, this works well. However, in the event of adverse winds, the static pressure generated by the wind is sufficient to slow or even stop the induced draft, thus curtailing the desired vaporization. With high enough winds, the flow may even reverse, disturbing the temperature profile of adjacent vaporizers.  
       SUMMARY OF THE INVENTION  
       [0003]     It is a major object of the invention to provide an efficient solution to the above problem and difficulties. Basically, the improved apparatus comprises:  
         [0004]     a) a vaporizer having passages to pass the cool or cold LNG in heat transfer relation with warming gas flowing downwardly to discharge in multiple directions, such as opposite directions,  
         [0005]     b) and air flow control means to control discharge of the gas flow, such as air flow, in selected directions, as a function of wind direction.  
         [0006]     Typically, a space is provided beneath the vaporizer to receive downward gas flow, for lateral discharge in such selected directions. Also, the flow control means typically includes shutters located at different gas flow discharge locations, and drives to selectively operate the shutters.  
         [0007]     It is another object of the invention to provide for vaporization of LNG (liquefied natural gas) in the improved apparatus.  
         [0008]     Another object is to provide laterally extending walls, at the lower exteriors of the vaporizers, to block downward flow of ambient air, exteriorly of the vaporizers, into the lateral discharge of gas from the space below the vaporizer.  
         [0009]     A further object is to provide an efficient method of vaporization, using ambient air, the method including the steps:  
         [0010]     a) providing and operating a vaporizer having passages to pass the cool or cold LNG in heat transfer relation with warming gas flowing downwardly to discharge in multiple directions,  
         [0011]     b) and providing and operating air flow control means to control discharge of the gas flow in selected directions, as a function of wind direction.  
         [0012]     These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which:  
     
    
     DRAWING DESCRIPTION  
       [0013]      FIG. 1  is an elevation showing vaporizers, flow spaces below the vaporizers, and flow control shutters at ends of such spaces, in positions for no wind operation;  
         [0014]      FIG. 2  is a view like  FIG. 1 , but showing the shutters in positions for a wind condition; and  
         [0015]      FIG. 3  is a plan view showing multiple vaporizers as operating during wind conditions indicated at a), b), c) and d). 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  shows two vaporizers,  10  and  11 , extending upright, with access space  12  therebetween. That space is closed off, by horizontal wall  13 , extending between the vaporizers. Each vaporizer includes upright tubing  14  to pass cryogenic fluid, such as LNG upwardly between tubing inlets at  14   a  at or near the bottom of the tubes, and tubing outlets  14   b  at or near the upper ends of the tube. Appropriate manifolds are typically provided to supply cryogenic fluid to the inlets, and to remove gas product from the outlets.  
         [0017]     Spaces  15  between the tubes pass warming gas such as ambient air downwardly, with natural downward draft, from the regions  16  above the vaporizers, to space  17  below the vaporizers. Appropriate legs, indicated at  18 , may be used to support the vaporizers directly above spaces  17 . Arrows at  19  and  20  show directions of warming gas or air flow from spaces  17 . Arrows  19  indicate air flow to the nearest exterior region  21 , from space  17   a  directly below vaporizer  10 ; and arrows  20  indicate air flow to the nearest exterior region  22 , from space  17   b  directly below vaporizer  11 . Those flow direction conditions prevail during vaporizer operation under exterior windless or near windless conditions. Lateral walls  23  and  24  at the lowermost sides of the vaporizers block any downward exterior air flow (indicated at  25  and  26 ) interference with the horizontally escaping air flow at  19  and  20 ; and also provide for turning of the downward flows  25  and  26  at  25   a  and  26   a  so as to assist in inducing flows  19  and  20 .  
         [0018]     In  FIG. 2 a  wind condition prevails, in direction indicated by arrows  30 . Flow control means is provided to control discharge of the gas flow in spaces  17  selected directions, as a function of wind direction.  
         [0019]     Such flow control means may advantageously take the form of shutters shown in a bank at  41  to control flow  19 , and in a bank at  42  to control flow  20 . One or more shutters may be provided at each bank. The shutters may be rotatable about horizontal axes as shown, to extend at opposite sides of such axes, as shown for balance. Drives may be provided to rotate the shutters between or toward open and closed positions, in response to detected prevailing wind direction. The drives and detectors are indicated schematically at  43  and  44 .  
         [0020]     In an example of operation, the exits at the bottoms of the vaporizers are oriented on an EAST/WEST axis and equipped with movable shutters. With no wind, or NORTH/SOUTH winds, the shutters remain open as in  FIG. 1 . In the event of an easterly wind above a threshold (normally 5 to 10 knots), the EAST shutters in bank  42  are closed, forcing all of the cold ambient air discharging from the array out the western portal, i.e. toward  22 , as shown in  FIG. 2 . In the event of westerly winds, the WEST shutters in bank  41  are closed, and shutters in bank  42  remain open. This keeps all vaporizers functioning in a downward natural draft, without substantial interference by wind. The shutters can be self-powered, or power actuated, or latched/released actuated. The shutters can take many forms. Horizontal slat types are illustrated, but they also can be vertical, swing or roll-up doors, or anything that will block air flow.  
         [0021]      FIG. 2  shows wind flow impingement at  45  on closed shutters in bank  42 ; warming air flowing downwardly and angularly at  46  and  46   a  and in spaces  17   a  and  17   b,  toward and through open shutters in bank  41 . Flows at  46  and  46   a  are not disturbed by the incident wind  45 .  
         [0022]      FIG. 3  shows at  3 ( a ) and in plan view, banks  10   a  and  11   a  of vaporizers  10  and  11 . Walls  49  and  49   a  separate the banks of vaporizers. Vaporizer cells are indicated at  60 .  
         [0023]      FIG. 3 ( b ) shows ambient warming air flow discharged at  62  and  63 , for no or low incident wind conditions, shutters in banks  41  and  42  being open.  
         [0024]      FIG. 3 ( c ) shows warming air flow discharged at  64  and  65 , for low EAST wind incidence conditions (flow at  65  reduced, and flow  64  increased).  
         [0025]      FIG. 3 ( d ) shows warming air flow discharged at  67 , for high EAST wind  66  incidence conditions (flow at  67  increased and shutters  41  open, and discharge flow at exit  68  blocked, and shutters  42  closed. Incident wind  66  is directed at  69 , so as not to enter spaces  17   a  and  17   b.