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System and method of delivering liquefied gases for vaporization

IP.com Disclosure Number: IPCOM000028133D
Publication Date: 2004-Apr-27
Document File: 25 page(s) / 87K

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SYSTEM AND METHOD OF DELIVERING LIQUEFIED

GASES FOR VAPORIZATION

Background:

The present embodiment relates to a system and method to deliver and vaporize liquefied gases.  In particular, the embodiment provides a system and method to deliver and vaporize liquefied gases at a controlled rate for one or more users.

In many applications, gases are stored in liquid form under their vapor pressure.  Upon the demand for gas in its utilization, gas is withdrawn from the upper region of the liquefied gas vessel.  The liquefied gas must absorb heat energy to sustain the gas withdrawal.  The heat energy needed for the liquid vaporization varies from gas to gas as listed in table 1.  For example, to vaporize 1 kilogram of ammonium (NH3) liquid at 20 oC needs 1163 kjoule energy, and to vaporize the same amount of sulfur hexafluride (SF6) at 20 oC needs only 67 kjoule.

In some cases, the liquefied gases must be transferred from a source vessel to another vessel or a device for vaporization.  Depending on the application, the distance between the source vessel and the vaporization device could be as far as 100 meters or further.  A pump is usually used for transferring the liquefied gas to another location.  However, the pump may be failed in function due to either its moving part problem, or a broken sealing problem, or others.  If a gear pump is used to handle the liquefied gases, special attention should also paid to eliminate the gas bubbles in the liquid because the gas bubbles may damage the pump.

Before the liquefied gas is used at a user station, it must be vaporized.  Many approaches have been proposed to supply heat to liquefied gases for vaporization.

In U.S. Patent No. 6,363,728, a heating device is installed outside of gas vessel to heat the liquefied gas to produce vapor.  With a pressure sensor and a PLC control device, gas pressure and vaporization can be automatically controlled and the gas supplying pressure can be maintained to some satisfactory level.  Gas is supplied to users from the vapor section inside vessel.  In the operation, however, one may find that the heating device may not provide the heat to the liquid effectively.  The necessary heat exchanger surface area will change as the liquid level changes inside the vessel.  When the liquid level becomes low, the contact area between liquid and the wall of vessel is too small for liquid to receive sufficient heat energy for vaporization.  Also, the heating device is rather expensive.

In another method as stated in U.S. Patent No. 6,474,077, the liquefied gas cylinder is heated with a heating device set to the outside surface of the vessel.  The heat exchange surface area decreases as the liquid level becomes lower, and therefore, the amount of liquid to be vaporized will not be stable and the cylinder pressure will not be stable.  Since there is a time lag for controlling the heating device, the liquid and also the gas may be too easily overheated to a temperatur...