Patent Description:
The present disclosure relates generally to flow meter assemblies and, in particular, to flow meter assemblies with two-phase flow detection for use in cryogenic fluid dispensing systems. Examples of flow meter assemblies with two-phase flow for use in cryogenic fluid dispensing system are disclosed in <CIT> where the dispensing line is equipped with a valve having at least a pressure sensor and a temperature sensor to determine iteratively the mass flow rate of fluid under different two-phase flow conditions.

Cryogenic fluids, that is, fluids having a boiling point generally below - <NUM> at atmospheric pressure, are used in a variety of applications, such as mobile and industrial applications. Dispensing of the cryogenic fluids, such as liquefied natural gas (LNG), nitrogen, argon, oxygen, hydrogen, helium, can be a complicated process that requires extensive monitoring.

One important consideration in dispensing of cryogenic liquid is the accuracy of the amount dispensed. For accurate flow measurement of liquids, it is important to ensure that the product remains in the liquid state while flowing through the meter. Gas, which has a much lower density than liquid, can cause significant metering errors due to displacement of liquid, which results in over registering. Two-phase flow (gas & liquid) normally occurs when the supply tank is running out of liquid or the line pressure falls below the saturation pressure of the product.

There are several different approaches to the two-phase flow problem currently being used. For example, current dispensing systems may utilize a phase separator upstream of the flow meter in conjunction with a differential valve. However, phase separators are large and heavy. Two-phase flow may also be detected using optical sensors for measurement of the vapor content in the liquid. Optical sensors are expensive and require calibration. Both solutions cause unneeded complication and expense to a cryogenic fluid dispensing system.

The example embodiments disclosed herein provide an advantageous flow meter assembly for cryogenic liquid dispensing systems that overcome disadvantages of the prior art flow meter assemblies. The disclosed flow meter assembly is able to better manage and detect two-phase flow and prevent inaccurate dispensing.

In one aspect, a flow meter assembly for a dispensing line comprises a differential pressure transmitter, a pressure transmitter, a temperature transmitter, and a controller in communication with each transmitter. The controller is configured to compare a discharge pressure from the pressure transmitter to a saturation pressure determined using a temperature from the temperature transmitter to determine if there is subcooling or two-phase flow of a fluid flowing through the dispensing line and to meter fluid flowing through the dispensing line if there is subcooling or no two-phase flow.

In a further aspect, a cryogenic fluid dispensing system includes a tank defining an area that holds cryogenic liquid, a dispensing line in liquid communication with the tank and configured to direct cryogenic liquid from the tank to a use device and a dispensing valve associated with the dispensing line.

In still a further aspect, a method of monitoring flow in a cryogenic fluid dispensing system includes the steps of storing cryogenic fluid in a tank, directing cryogenic fluid so that it flows through a dispensing line to a use device, monitoring a temperature and a discharge pressure of the cryogenic fluid flowing in the dispensing line, determining a saturation pressure of the cryogenic fluid flowing in the dispensing line using the monitored temperature, comparing the discharge pressure to the saturation pressure, metering the cryogenic fluid flowing in the dispensing line as long as the discharge pressure is a predetermined level above the saturation pressure and terminating metering of the cryogenic fluid flowing in the dispensing line when the discharge pressure is less than the predetermined level above the saturation pressure.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and provided for the purposes of explanation only and are not restrictive of the subject matter claimed. Further features and objects of the present disclosure will become more fully apparent in the following description of the preferred embodiments and from the appended claims.

In describing the preferred example embodiments, references are made to the accompanying drawing figures wherein like parts have like reference numerals, and wherein:.

It should be understood that the drawings are not to scale. While some mechanical details of example dispensing systems and of alternative configurations have not been included, such details are considered well within the comprehension of those of skill in the art in light of the present disclosure. It also should be understood that the present disclosure is not limited to the example embodiments shown.

Cryogenic fluids, due to unique storage conditions, are extremely susceptible to temperature fluctuations when a cryogenic fluid is flowing through a storage or dispensing system. It is, therefore, useful to monitor and adjust for changes in temperature and pressure when metering while dispensing to a use device. The disclosed embodiments include flow meter assemblies, systems, and processes designed to monitor metering and check for two-phase flow. While the embodiments are described as cryogenic fluid dispensing systems, the technology of the disclosure may be applied to alternative types of dispensing systems containing alternative types of fluids.

As described below, when dispensing of the cryogenic fluid is demanded in an embodiment of the system disclosed, the cryogenic fluid may be pumped through a pump, or otherwise driven, into the dispensing line to the use device. The cryogenic fluid passes through the flow meter assembly before being distributed through a product line to a use device. During the dispensing, the flow meter assembly is used to measure properties of the fluid flowing through the dispensing line. If the properties of the fluid indicate two-phase flow or a possibility of two-phase flow, the flow meter assembly can prevent further dispensing.

A first embodiment of a flow meter assembly configured in accordance with the disclosure is indicated in general at <NUM> in <FIG> and shown schematically as part of a cryogenic liquid dispensing system (<FIG>). The flow meter assembly is placed along a dispensing line <NUM> of a cryogenic liquid dispensing system (<FIG>) for metering and measuring the properties of a fluid travelling in the direction of the arrow <NUM> of <FIG>. The flow meter assembly includes a temperature transmitter <NUM>, a pressure transmitter <NUM> and a differential pressure transmitter <NUM>. The transmitters are in communication with a controller <NUM> (<FIG>). The pressure transmitters are placed downstream from the temperature transmitter <NUM> in <FIG>, but may be otherwise oriented along the length of the dispensing line <NUM>.

The temperature transmitter <NUM> includes a temperature sensor <NUM>, placed within the dispensing line <NUM> to measure the temperature of the fluid passing through the dispensing line <NUM>. The temperature transmitter and sensor may be any known in the art for attaching to a pipe and reading the temperature of the fluid within the pipe.

The pressure transmitter <NUM> and differential pressure transmitter <NUM> are placed in combination along the dispensing line. The differential pressure transmitter <NUM> includes an orifice <NUM>, placed within the dispensing line pipe <NUM>. Although an orifice is utilized in the disclosed embodiment, any restrictive element may be placed inside the pipe coordinating with the differential pressure transmitter <NUM>. An inlet portion <NUM> of the dispensing line <NUM> is located upstream from the orifice <NUM> or other restrictive element. An outlet portion <NUM> of the dispensing line <NUM> is located downstream from the orifice <NUM> or other restrictive element. The differential pressure transmitter <NUM> includes an inlet pressure sensor or tap <NUM> and an outlet pressure sensor or tap <NUM>. The pressure transmitter <NUM> also includes a pressure sensor or tap <NUM> connected to the inlet pressure sensor or tap <NUM> of the differential pressure transmitter <NUM>.

The flow meter assembly <NUM> constantly measures temperature and discharge pressure of the liquid using the temperature transmitter <NUM> and the pressure transmitter <NUM>. The differential pressure transmitter <NUM> monitors flow rate of the fluid through the flow meter assembly. Alternatively, a turbine flow meter or other type of flow meter may be substituted for the differential pressure transmitter, and the orifice <NUM> or other restrictive element, in the cryogenic fluid dispensing system for monitoring flow rate of the fluid through the flow meter assembly.

A first embodiment of a cryogenic fluid dispensing system including the flow meter assembly <NUM> configured in accordance with the disclosure is indicated in general at <NUM> in <FIG>. The cryogenic liquid dispensing system <NUM> includes a tank, indicated in general at <NUM>, defining an area that holds cryogenic liquid <NUM>. The cryogenic liquid <NUM> can be at least one of nitrogen, helium, neon, argon, krypton, , hydrogen, liquefied natural gas and oxygen, although other types of fluids are within the scope of this disclosure. Other non-cryogenic liquids, including, but not limited to, carbon dioxide and nitrous oxide, are also within the scope of this disclosure. The tank <NUM> preferably includes a double-wall construction including inner vessel <NUM> and outer jacket <NUM> with insulation therebetween. The tank <NUM> also includes a refilling port (not shown).

The tank of the cryogenic fluid dispensing system can be configured horizontally or vertically. In one embodiment there is a separate fill pipe and a separate withdrawal pipe, but the two pipes may optionally be combined. There may be other paths out of the inner vessel to fill and remove the liquid as well. The fill and withdrawal pipes may be any suitable conduit for conveying or allowing the flow of fluid therethrough.

A dispensing conduit or line <NUM> is in liquid communication with the tank at a first end <NUM> and a use device (when connected) at the second end <NUM>. The second end <NUM> may include a connector compatible with a use device or system and a valve to control dispensing. The dispensing line <NUM> may be connected to a pump <NUM> within cryogenic liquid <NUM> of tank <NUM>. When the pump <NUM> is activated, liquid <NUM> is pumped through dispensing line <NUM>. Alternatively, the pump <NUM> may be positioned in a sump that receives liquid from the tank <NUM>, along the dispensing line <NUM> or omitted from the cryogenic liquid dispensing system <NUM> with the dispensing line <NUM> connecting to the bottom portion of the tank <NUM> so that gravity drives fluid flow from the tank.

The dispensing line <NUM> includes at least one dispensing valve <NUM>. The dispensing valve <NUM> may be located downstream from the flow meter assembly, as illustrated.

The valve <NUM> or valves of the dispensing line may be automated to function to start and stop the flow of liquid when desired.

The flow meter assembly <NUM>, including temperature transmitter <NUM>, pressure transmitter <NUM> and differential pressure transmitter <NUM>, is placed along dispensing line <NUM>.

The controller <NUM> can be a microcontroller or any other computer device. The controller <NUM> is in communication, as shown by dashed lines <NUM>, <NUM>, and <NUM>, with each transmitter. The controller can also be in communication with dispensing valve <NUM> and pump <NUM>, indicated by dashed lines <NUM> and <NUM>. Controller can be wired or wirelessly connected to each transmitter, pump <NUM> and dispensing valve <NUM>.

The controller <NUM> may store specific product data, including saturation pressure at different temperatures, in a look-up table. Alternatively, or in addition, the controller <NUM> may be programmed with polynomials for use in calculating saturation pressure, given a fluid temperature. As an example, for Nitrogen between <NUM>°K and <NUM>°K, the equation is: <MAT>.

As another example, for Propane between <NUM>°K and <NUM>°K, the equation is: <MAT>.

Using these tables and/or equations, the controller <NUM> can determine the saturation pressure of the fluid flowing in line <NUM> using the temperature detected by temperature transmitter <NUM>. The controller <NUM> also monitors the discharge pressure using pressure transmitter <NUM> to check that the discharge pressure is greater than the determined saturation pressure by applying a suitable safety margin, such as <NUM> bar, and thereby ensuring sufficient subcool of the liquid stream in line <NUM>.

If the discharge pressure drops and/or the temperature rises so that the minimum subcool requirement is no longer met, the controller <NUM> will either stop totalizing or terminate the delivery by stopping pump <NUM> and/or closing dispensing valve <NUM> downstream of the flow meter assembly <NUM>. The flow meter assembly <NUM> therefore ensures that while it is metering, the liquid in the meter does not contain any vapor. In an alternative embodiment, the dispensing valve <NUM> may be a three-way valve including a setting whereby fluid, after flowing through the flow meter assembly <NUM>, may be directed back to the tank <NUM> as pump <NUM> continues to run when the minimum subcool requirement is no longer met.

The controller <NUM> may also perform density compensation during metering by using temperature or temperature and pressure data from transmitters <NUM> and <NUM>. The controller <NUM> may be provided with a density look-up table and/or equations for use in calculating fluid density given the temperature or temperature and pressure of the fluid in line <NUM> from temperature transmitter <NUM> and pressure transmitter <NUM>. If temperature and pressure are used, the system takes into account compressibility and provides enhanced system accuracy while utilizing the same pressure transmitter as the meter. The controller <NUM> takes the flow rate recorded by the differential pressure transmitter <NUM> and, using the determined fluid density, can accurately totalize the amount of liquid dispensed.

The dispensing system <NUM> may also include a conditioning system to adjust the temperature of the cryogenic fluid before dispensing. The conditioning system may include a conditioning heat exchanger for cooling or heating cryogenic liquid as it is dispensed. The conditioning system may be on the dispensing line <NUM> before or after the flow meter assembly <NUM>. In one embodiment, the flow meter assembly <NUM> is upstream from the conditioning system and the transmitter readings are utilized to assess whether the fluid is at the correct temperature and pressure for distribution or needs to pass through the conditioning system.

<FIG> and <FIG> each illustrate a graph of inputs and calculated data used by the controller <NUM> to monitor and prevent two-phase flow during metering. The saturation pressure is calculated based on the type of liquid (propane and nitrogen are used in the charted examples) and temperature. The minimum discharge pressure, about <NUM> bar above the saturation pressure (as an example only), ensures that the fluid will not have two-phase flow, as long as the pressure is maintained above that curve. Any pressure below the calculated saturation pressure could trigger a two-phase flow. As described above, the density is also utilized by the controller to provide density compensation during metering.

Claim 1:
A flow meter assembly (<NUM>) for a dispensing line comprising:
a differential pressure transmitter (<NUM>);
a pressure transmitter (<NUM>);
a temperature transmitter (<NUM>); and
a controller (<NUM>) in communication with the differential pressure transmitter (<NUM>); the pressure transmitter (<NUM>) and the temperature transmitter (<NUM>);
wherein the controller (<NUM>) is configured to compare a discharge pressure from the pressure transmitter (<NUM>) to a saturation pressure determined using a temperature from the temperature transmitter to determine if there is two-phase flow or subcooling of a fluid flowing through the dispensing line
and to meter fluid flowing through the dispensing line if there is subcooling or no two-phase flow.