Pumps – Condition responsive control of pump drive motor – With condition responsive control of pump fluid valve
Reexamination Certificate
2001-01-31
2002-10-29
Rivell, John (Department: 3753)
Pumps
Condition responsive control of pump drive motor
With condition responsive control of pump fluid valve
C417S279000, C137S002000, C137S487500, C073S861040, C073S861355
Reexamination Certificate
active
06471487
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to fluid delivery systems, and more particularly, to a simplified fluid delivery system that substantially prevents the measurement of a multiphase fluid flow during the delivery of a fluid product from a source to a destination.
2. Statement of the Problem
Fluid delivery systems are designed to deliver various types of fluid products from a source to a destination. Some examples of these products include petroleum products, such as liquid petroleum gas, gasoline, kerosene, oil and other similar products. Other examples of these products, include agricultural chemicals, corn syrups, milk and corn sugars. The source is often a truck, railroad car, or sea going vessel, with the destination being a storage vessel located at a processing plant or dock. Similarly, the opposite is also true where the source is the storage vessel and the destination is a truck, railroad car, or sea going vessel.
Fluid delivery systems typically include, a pump connected to the source, which provides the required pressure to move the fluid through the system from the source to the destination. A strainer connected to the pump is used in some, but not all applications, to provide filtration from the intrusion of grit and other foreign matter that can damage downstream components such as the meter. The meter is typically a positive displacement or turbine volumetric measuring device that measures a volume of the fluid as the fluid is delivered from the source to the destination.
It is a problem in fluid delivery systems to prevent the measurement of entrained air or vapor in the fluid during delivery. For example, as the source of the fluid is emptied, pressure from the pump can break the surface tension of the remaining fluid in the source causing a multiphase flow of air and fluid to be pumped through the delivery system. When this occurs, the volumetric meter cannot differentiate between a pure fluid flow and the multiphase fluid flow comprising both the air and fluid.
One solution to this problem is to use an air eliminator to separate and remove undesired air or vapor from the fluid prior to delivery to the meter. An air eliminator removes entrained air by decreasing the velocity of the fluid to a relatively calm state by permitting the fluid to accumulate in a chamber in the air eliminator. The substantial decrease in velocity causes trapped air bubbles or vapor to rise out of the fluid and collect in the upper portion of the chamber where it is vented. The air eliminator also prevents damage to the meter by preventing large amounts of air from passing through the meter. Large amounts of air passing through the meter can cause over-speeding of the measuring unit or excessive wear that eventually results in meter failure.
Unfortunately, several problems exist in present delivery systems due to the necessity of an air eliminator. A first problem with the air eliminator is the overall size required for some applications. For example, the rate of separation for high viscosity products, such as oil based petroleum products, results in the need for a large air eliminator. Similarly, high viscosity products require a longer retention time for separation that results in slower fluid delivery and a less efficient delivery system.
A second problem with air eliminators is that products such as fuel oil, diesel oil, and kerosene, often foam up as they pass through the delivery system causing air to discharge in the form of vapor. The vapor from these products is hazardous and cannot be discharged directly into the atmosphere, thus requiring a separate storage tank to accommodate vented vapors.
A third but related problem with air eliminators is the cost added to the delivery system by the inclusion of the air eliminator and in some cases a storage tank for vented vapor. For example, in delivery systems designed for heavy oils, the required tank size is so large that it is often more economical to prevent the entrance of entrained air rather than remove it during delivery. In this case, however, various additional and expensive precautions must be taken that significantly add to the transportation and storage cost for these products.
It is known in the art to use mass flowmeters to measure mass flow and other information for materials flowing through a conduit. Some types of mass flowmeters, especially Coriolis flowmeters, are capable of being operated in a manner that performs a direct measurement of density to provide volumetric information through the quotient of mass over density. See, e.g., U.S. Pat. No. 4,872,351 to Ruesch assigned to Micro Motion for a net oil computer that uses a Coriolis flowmeter to measure the density of an unknown multiphase fluid. U.S. Pat. No. 5,687,100 to Buttler et al. teaches a Coriolis effect densitometer that corrects the density readings for mass flow rate effects in a mass flowmeter operating as a vibrating tube densitometer.
Coriolis flowmeters directly measure the rate of mass flow through a conduit.
As disclosed in U.S. Pat. Nos. 4,491,025 (issued to J. E. Smith et al. on Jan. 1, 1985, hereinafter referred to as the U.S. Pat. No. 4,491,025) and U.S. Pat. No. Re. 31,450 (issued to J. E. Smith on Feb. 11, 1982, hereinafter referred to as U.S. Pat. No. Re. 31,450, these flowmeters have one or more flowtubes of straight or curved configuration. Each flowtube configuration in a Coriolis mass flowmeter includes a set of natural vibration modes, which could be of a simple bending, torsional or coupled type. Fluid flows into the flowmeter from the adjacent pipeline on the inlet side, is directed through the flowtube or tubes, and exits the flowmeter through the outlet side of the flowmeter. The natural vibration modes of the vibrating fluid filled system are defined in part by the combined mass of the flowtubes and the fluid within the flowtubes. Each flow conduit is driven to oscillate at resonance in one of these natural modes.
When there is no flow through the flowmeter, all points along the flowtube oscillate with identical phase. As fluid begins to flow, Coriolis accelerations cause each point along the flowtube to have a different phase. The phase on the inlet side of the flowtube lags the driver, while the phase on the outlet side leads the driver. Sensors can be placed on the flowtube to produce sinusoidal signals representative of the motion of the flowtube. The phase difference between two sensor signals is proportional to the mass flow rate of fluid through the flowtube. A complicating factor in this measurement is that the density of typical process fluids varies. Changes in density cause the frequencies of the natural modes to vary. Since the flowmeter's control system maintains resonance, the oscillation frequency varies in response. Mass flow rate in this situation is proportional to the ratio of phase difference and oscillation frequency.
The Coriolis flowmeter is intended for use in environments where multiphase flow exists. Multiphase flow is defined as flow including at least two states of matter: solid, liquid or gas. The flowmeter is especially useful in multiphase systems including gas and liquid or gas and solids. These environments are especially common in the petroleum industry where a petroleum product is delivered from a source to a destination. Unfortunately, Coriolis flowmeters have not been used in petroleum delivery systems, in part, because they measure mass, as opposed to volume, and the sales of petroleum take place in volume. Furthermore, while these meters can functionally detect multiphase flow they cannot remove a gas or solid from the flow, and therefore, an air eliminator would still be required.
SOLUTION
The present invention overcomes the problems outlined above and advances the art by providing a fluid delivery system that includes a Coriolis mass flowmeter to eliminate the need for an air eliminator and/or a strainer. In a first embodiment of the present invention, the fluid delivery system comprises a Coriolis mass flowmeter, a pump, and a reci
Jones Steven M.
Keilty Michael J.
Faegre & Benson LLP
Krishnamurthy Ramesh
Micro Motion Inc.
Rivell John
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