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.
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.
It is a major object of the invention to provide an efficient solution to the above problem and difficulties. Basically, the improved apparatus comprises:
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,
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.
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.
It is another object of the invention to provide for vaporization of LNG (liquefied natural gas) in the improved apparatus.
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.
A further object is to provide an efficient method of vaporization, using ambient air, the method including the steps:
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,
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.
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:
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 17a directly below vaporizer 10; and arrows 20 indicate air flow to the nearest exterior region 22, from space 17b 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 25a and 26a so as to assist in inducing flows 19 and 20.
In
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.
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