Fluent material handling – with receiver or receiver coacting mea – With material treatment – Heating or cooling
Reexamination Certificate
2003-03-17
2004-11-02
Douglas, Steven O. (Department: 3751)
Fluent material handling, with receiver or receiver coacting mea
With material treatment
Heating or cooling
C222S146200, C222S146500
Reexamination Certificate
active
06810924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and filling station for introducing a compressed gas stream into one or more vessels with a controlled filling temperature. More particularly, the present invention relates to such a method and filling station in which a vapor phase stream composed of a vapor phase of a cryogen stored within a cryogenic, liquid storage tank is compressed to form the compressed gas stream that is introduced into the vessel(s). Even more particularly, the present invention relates to such a method and filling station in which a liquid phase of the cryogen is heated to maintain the vapor phase at a constant density and a filling temperature of the compressed gas stream is controlled by selective addition of heat thereto.
BACKGROUND OF THE INVENTION
In filling various vessels with compressed gases within set time intervals, the temperature of the compressed gas within the vessel will tend to rise due to the inability of the vessel to dissipate the heat produced from the enthalpy of the incoming compressed gas. Such vessels can be compressed gas cylinders that are used to store industrial gases and vehicle fuel tanks in which a fuel in the form of compressed natural gas or hydrogen is to be stored.
In all such filling applications, it is important to control the temperature of the compressed gas within the vessel being filled. An important reason for such temperature control is to ensure that the vessel is filled to capacity. For instance, if the temperature within the vessel being filled is allowed to rise, the pressure of the compressed gas within the vessel will eventually drop to a pressure in equilibrium with ambient temperature (the settle pressure) as heat dissipates from the vessel. Thus, the pressure reached within the vessel during filling will not guarantee that the vessel will be filled to the desired capacity. As a result, either the vessel has to be topped off after having been initially filled, or the filling pressure has to be raised substantially in excess of the settled pressure, or the filling has to be accomplished at a rate slow enough so that near ambient temperature conditions are maintained within the vessel during vessel filling.
As may be appreciated, such a filling procedure is time consuming and therefore not very desirable in industrial filling applications. It is particularly undesirable in vehicle fuel tank filling applications in that consumers have an expectation of filling times with respect to alternative fuels, such as compressed natural gas and hydrogen, that are comparable to those experienced with conventional petroleum based fuels. Preferably, a vehicle fuel tank should be able to be completely filled from an empty condition with compressed natural gas or hydrogen in between about three and about five minutes.
When very short filling times are contemplated, such as time periods that have been discussed above, another problem surfaces. The time period is so short that the heat generated during filling can exceed the upper structural limiting temperature of the tank being filled. Additionally, when the compressed gas such as hydrogen is to be stored as a liquid, the resultant filling temperature can be below the lower structural limiting temperatures of the fuel tank. At such temperatures, failure occurs due to materials becoming brittle. These problems can be particularly exacerbated in fuel tanks that are designed to store hydrogen. In order for the vehicle to have sufficient range, hydrogen gas must be stored at anywhere from between about 5,000 psi and about 10,000 psi. A fuel tank designed to hold such pressure, if conventionally fabricated, would be quite heavy. Therefore, such fuel tanks are and will be fabricated from lighter materials such as carbon fiber and resin. The tank mass to gas ratio in carbon fiber reinforced tanks is much lower than the ratio for conventional tanks. Consequently, these lighter tanks are more prone to encounter high temperatures during filling.
The problem of filling pressure vessels to a desired pressure with reasonable time periods has been dealt with in at least one patent, namely, U.S. Pat. No. 5,934,081. In such patent, in order to ensure that compressed gas cylinders are completely filled, without being topped off, the filling temperature of the compressed gas is controlled. In this patent, the gas is stored within a cryogenic liquid storage tank. A liquid stream, composed of the liquid phase, is pumped and then vaporized within a vaporizer. Pressure within the tank is maintained by a pressurized stream of pumped liquid that is vaporized and fed to a head space of the liquid storage tank and into the vapor phase. Another stream of liquid, pressurized by the pump, is left unvaporized and introduced into the vaporized stream from the vaporizer to cool the compressed gas being introduced into the cylinders by direct heat exchange.
The problem with the foregoing patent is that the liquid storage tank must be located above the pump in order to allow gravity feeding to the pump. In order to allow for the underground storage of liquid, in U.S. Pat. No. 5,787,940, which concerns the use of liquefied natural gas as a fuel source, an underground storage tank is disclosed that also has an associated sump and a submerged pump to pump a stream of liquefied natural gas above ground to a liquefied natural gas fueled vehicle. The advantage of the sump is to allow for pump maintenance through the sump. In any case, the pumped liquid has to be vaporized and therefore, such a system is rather complex and difficult to control.
The problem of filling vehicle fuel tanks with hydrogen has been recognized in U.S. Pat. No. 6,432,283. In this patent, a hydrogen fueled replenishment system is disclosed in which hydrogen is generated onsite by an electrolytic cell. The hydrogen is compressed to a filling pressure and in order to compensate for the resultant temperature rise, the fill rate is adjusted to accomplish delivery to the vehicle within a minimum of time to meet the filling requirements of the vehicle. In another system disclosed in U.S. Pat. No. 5,628,349 that involves the dispensing of a pressurized gas, for instance, ompressed natural gas from a pressurized gas source, the temperature within the receiving tank is monitored and is used by a computer to adjust the fill pressure to compensate for the temperature and pressure rise occurring within the compressed gas during the filling of the tank. The problem with both of these systems is that they would have limited utility with respect to lightweight, carbon fiber fuel tanks for use in hydrogen fueled vehicles due to the higher pressures involved and the relatively short fill time periods.
As can be appreciated from the above discussion, an advantageous filling station would utilize an underground storage tank in which the compressed gas to be dispensed were stored as a liquid and gas was compressed from the vapor phase. The problem with such operation is that as gas is taken from the vapor phase, the pressure decreases within the storage tank. This results in inefficient compressor operation. In U.S. Pat. No. 5,520,000 a system is disclosed that is designed to deliver a gas, such as hydrogen for a hydrogen fuel tank at a temperature of 6,000 psia in a manner that maximizes the compressor output. This is accomplished by using a gas liquid mixer before the compressor or compressor stages in which gas and liquid are mixed in a packing contained within a miniature column to control the temperature of the gas entering the compressor and thereby maximize the output rate of the compressor. The temperature of the gas that is introduced into a storage bank is controlled by either heating or cooling the gas in a subsequent heat exchanger.
U.S. Pat. No. 5,243,821 discloses a method of delivering a high pressure gas in which a piston-type pump/compressor is adapted to pump liquid, vaporized liquid or a two-phase mixture of vapor and liquid while maintaining the inlet fluid under cryogenic conditions. The gas/liquid composition of the
Douglas Steven O.
Praxair Technology Inc.
Rosenblum David M.
LandOfFree
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