Pipes and tubular conduits – With flow regulators and/or baffles – Flow facilitating
Reexamination Certificate
1999-09-07
2001-02-13
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
With flow regulators and/or baffles
Flow facilitating
C138S044000, C366S340000, C073S861520
Reexamination Certificate
active
06186179
ABSTRACT:
The present invention relates to flow measurement, and particularly to flow measurement systems employing non-mechanical or non-invasive measurement apparatus, such as systems using ultrasonic signals.
A large number of ultrasonic flow meters operate by propagating an ultrasonic signal through the medium, and determining its flow rate from the propagation time of the signal. By suitable choice of signal paths, the flow in the axial direction, the swirl or even the cross-flow may be measured. Such a system can be quite adaptable, and may launch signals into the fluid from transducers which conveniently clamp to the outside of a conduit, without requiring separate mounting holes or other machining of the pipe or vessel. Moreover, ultrasonic measurement units may come pre-equipped with a microprocessor which enables the unit to conveniently set a number of dimensions (such as spacing between transducers), fluid properties (such as composition or molecular weight) and correction constants (such as pipe material and wall thickness) so that they are easily set up to provide accurate measurements for the system to which they are attached under a range of flow and temperature conditions. Such systems may also perform signal conditioning, range gating, and other specialized signal processing, such as Doppler analysis of received signals, to implement different flow measurement protocols.
However, while ultrasonic measuring systems can be quite versatile, they are predicated to some extent on knowing in advance a number of the properties or parameters of the fluid, and on the flow being moderately well behaved. For example, the measurements of a known fluid are often taken in a straight segment of conduit and a fully settled flow profile is assumed. Commonly, a meter or measurement system is assigned a meter factor which is a function, among other things, of the actual fluid flow profile in a given conduit. Since in practice flow is substantially disturbed by junctions along the flow path, measurements are typically taken at a position located far away from the nearest T or elbow, and in a relatively long uninterrupted segment of pipe where flow profile may be assumed to be stationary.
Often it is not possible to locate a suitable segment in an existing flow path, and when a system of this type is designed knowing that a measurement must be taken, it is not uncommon to install flow conditioners to smooth the irregular distribution introduced by a T or elbow, so as to produce a more laminar, or more symmetric flow profile along the length of conduit where measurements are to be taken. However, such flow conditioning devices must be installed in-line, requiring special fitting of pipe segments or internal elements, and this is a relatively cumbersome and expensive procedure. Perhaps the simplest of these hardware approaches to flow conditioning is to install an obstructing device directly in the flow path to impede certain forms of irregular flow and produce a substantially uniform or stationary altered flow that is more readily subject to measurement.
Devices for producing a fully developed or smooth steady state flow under otherwise turbulent or irregular flow profile conditions often include a plurality of axially extending vanes for conditioning the flow by impeding swirl, or a plate with a pattern of apertures to uniformize the flow profile. Examples of such flow conditioners are described in U.S. Pat. No. 5,762,10; U.S. Pat. No. 5,529,093, and elsewhere. When used, for example, in the measurement of natural gas flowing at high speeds and at a very high pressure, such plates may be used to produce a steady state velocity profile and turbulence structure while substantially eliminating swirl of the fluid flowing in the conduit. In other applications, several such plates may be stacked or spaced in sequence one after the other along a flow path to more effectively remove the undesired irregularities introduced by structures along the upstream flow. In such a case, for example, the plate furthest upstream may have holes of different size configured to correct the overall velocity profile toward a condition of greater symmetry, while successive downstream plates may have a more regular pattern of apertures which are intended to counteract swirl without substantially further impeding flow, or to correct a profile imbalance, at least for a short distance where the sendind and receiving transducers are located, without introducing swirl.
In general any such flow conditioning plates must be designed to not erode or create debris in the conduit or downstream, and also will in general be designed, perhaps with extensive trial and error, to function for the particular conduit size, type of fluid, and velocity/pressure ranges involved. Of course, once such a flow conditioning plate is designed, the meter placed downstream may still require further on-site calibration and setting up to operate on the standardized set of conditions produced by the flow plate. Thus the installation of an ultrasonic flow measurement system remains a specialized task.
Accordingly it would be desirable to provide a flow conditioner applicable to a wide range of field installations.
It would further be desirable to provide a flow conditioner in the form of an aperture plate which simplifies meter installation and calibration protocols.
It would also be desirable to design a flow conditioner which creates, rather than corrects, a set of irregular field conditions, and which allows a meter to be set up, tested, or calibrated for these conditions in the factory so that it will accurately meter the flow of an actual plant.
SUMMARY OF THE INVENTION
This is achieved in accordance with the basic aspect of the present invention by providing a flow conditioning plate for interposition in a flow line which has a pattern of apertures effective to introduce a flow irregularity. In different embodiments the irregularity corresponds to the profile and/or swirl introduced by an elbow, T or other junction, or to that introduced by a set of two or more junctions in a standard conduit. The irregularity persists for a well defined distance along the flow path, allowing an ultrasonic meter to be placed downstream and produce measurements under the defined flow irregularity. The meter calibrated in this fashion is then used directly on an actual process flow line having the corresponding actual elbow, T or other junction or junctions upstream of its conduit. By using a flow conditioning plate to create a standard disturbance rather than to smooth the flow the meter may be calibrated in the factory and subsequently sent to the field to be fitted downstream of a junction without further intervention in or conditioning of the flow line for setting up or calibrating the meter.
In addition the simulation studies which are extensively required for the development of a new meter application are greatly simplified, since it is not necessary to install one or more junctions in the piping of an experimental test conduit or flow system. Instead a relatively thin simulator plate, or succession of such plates, are simply clamped between flanges in a straight test section to produce the required flow conditions, and the meter is tested or calibrated while a defined volume of fluid is passed through the test conduit to determine the necessary meter constants of calibration data.
REFERENCES:
patent: 3582048 (1971-06-01), Sarem
patent: 4786185 (1988-11-01), Knief
patent: 5215375 (1993-06-01), Ditzler et al.
patent: 5341848 (1994-08-01), Laws
patent: 5495872 (1996-03-01), Gallagher et al.
patent: 5529093 (1996-06-01), Gallagher et al.
patent: 5762107 (1998-06-01), Laws
patent: 6042263 (2000-03-01), Mentzer et al.
Brinson Patrick
Nutter & McClennen & Fish LLP
Panametrics, Inc.
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