Process flow device with improved pressure measurement feature

[0002] Reference id hereby made to co-pending application Ser. No. 09/395,688, filed Sep. 13, 1999 and entitled “PROCESS FLOW PLATE WITH HIGH ACCURACY TEMPERATURE FEATURE”.

[0003] The invention relates to the process measurement and control industry. The measurement and control industry employs process variable transmitters to remotely monitor process variables associated with fluids such as slurries, liquids, vapors, gasses, chemicals, pulp, petroleum, pharmaceuticals, food and other food processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties.

[0004] FIG. 1 is an exploded view of a prior art process flow device 50 for measuring process variables, such as differential pressure and flow. As shown in FIG. 1, flow plate 52 is clamped between flanges 54, 56 in a flow path to produce a differential pressure across a constriction for measuring flow rate of fluids through a pipe 58. Differential pressure across the flow constriction is measured at pressure taps 60, 62. As illustrated in FIGS. 1-2, pressure taps 60, 62 are separate from flow plate 52 clamped between pipe flanges 54, 56 so that seams separate pressure taps 60, 62 from flow plate 52. Pipe 58 conveys process fluid at a high pressure. Such pressure is a combination of the differential pressure developed in response to the constriction and the static pressure within the pipe which can be 1000 psi or more. The high pressure can cause fluid and pressure to leak from seams between the flow plate 52 and pressure taps 60, 62. Vibration and other motion of the flow pipe can loosen the connection between the flow plate 52 and pressure taps 60, 62 contributing to fluid and pressure leakage at the seams.

[0005] Within device 50, flow rate is calculated based upon differential pressure across a flow constriction, pipe diameter and constriction profile. Pressure loss and leakage at seams changes the measured differential pressure across the flow constriction and the pressure loss or change is not attributable to flow rate. The non-attributable pressure loss at the seams degrades flow calculations. Additionally, device 50 requires significant field installation time due to the necessity of joining all the couplings together and performing leak checking upon the couplings. Moreover, whenever maintenance is required for device 50, significant disassembly/reassembly time is usually required which increases undesirable downtime. Thus, it is desirable to provide a process fluid flow measurement device with increased accuracy and reduced field installation time, downtime, and cost.

[0006] Embodiments of the invention relate to a flow plate having a seamless interface between first and second pressure taps and flow interrupter to reduce non-attributable pressure loss at seams between first and second pressure taps and the flow interrupter. Reduced non-attributable pressure loss improves measurement accuracy, while the seamless interface reduces field installation time.

[0007] FIG. 1 is an exploded perspective view of a prior art flow plate inserted between pipe flanges.

[0008] FIG. 2 is a cross-sectional view taken along line 2—2 of FIG. 1.

[0009] FIG. 3 is an environmental view of an embodiment of a process flow device of the present invention.

[0010] FIG. 4 is a schematic illustration of components of a process flow device of the present invention.

[0011] FIG. 5 is a cross-sectional view of an embodiment of a process flow device assembled in a flow pipe between flanges.

[0012] FIG. 6 is a detailed illustration of portion 6 of FIG. 5.

[0013] FIG. 7 is a cross-sectional view of an alternate embodiment of a process flow device assembled in a flow pipe between flanges.

[0014] FIG. 8 is a cross-sectional view of an alternate embodiment of a process flow device assembled between pipe flanges having a detachable edge portion.

[0015] FIG. 9 is a detailed illustration of portion 9 of FIG. 8.

[0016] FIG. 10 is a cross-sectional view of an alternate embodiment of a process flow device assembled between pipe flanges with exploded illustration of rings forming a conduit of the flow plate.

[0017] FIG. 11 is a perspective illustration of portion 11 of the flow plate of FIG. 10

[0018] FIG. 12 is a cross-sectional view of an embodiment of a process flow device assembled between pipe flanges with exploded illustration of an alternate embodiment of rings forming a conduit of the flow plate.

[0019] FIG. 13 is a perspective illustration of portion 13 of the flow plate of FIG. 12.

[0020] FIGS. 3-4 are environment illustrations of an embodiment of a process flow device 100 of the present invention including an instrument base 102, first and second different pressure passageways 104, 106 and a differential flow plate 108. The differential flow plate 108 includes a flow conduit 110 supporting a flow interrupter 112 and first and second pressure taps 114, 116 open to the flow conduit 110 (illustrated schematically in FIG. 4).

[0021] As shown schematically in FIG. 4, instrument base 102 supports process instrumentation 120. In FIGS. 3-5 and 7, process instrumentation 120 includes a pressure sensor module 122 for isolating a differential pressure and transmitter 124 for transmitting process data to a computer or reading device 126 (FIG. 3). Transmitter 124, or any other any other appropriate readout device, can sense process variables and provide a related output over a process loop to a control room or computer 126, such that the process can be monitored and controlled. Computer 126 can be remote or locally integrated. The process loop can be a two-wire 4-20 mA process control loop. The loop may also have digital signals superimposed on the two-wire loop according to a process industry standard protocol such as the HART® (“Highway Addressable Remote Transducer”) digital protocol, as described in HART® Communication Foundation, Austin, Tex. 78759-6450. Local process control devices are connected to process control, for example, through a fieldbus interface and network system as described in “Fieldbus Technical Overview” Fisher-Rosemount Systems, Inc., Eden Prairie, Minn. Process transmitters 124 can also be configured to meet intrinsic safety requirements.

[0022] Instrument base 102 includes first and second differential pressure openings 130, 132 as shown in FIG. 4. Instrument base 102 supports process instrumentation 120 for fluid connection to differential pressure passageways 104, 106. FIG. 5 illustrates an embodiment of instrument base 102 that includes a manifold 134. Although not necessary for embodiments of the invention, manifold 134 provides calibration and maintenance convenience. Manifold 134 includes valve ports 136 to selectively obstruct or permit flow through the manifold during maintenance. Pressure passageways 104, 106 are in fluid communication with manifold channels. Although three valve ports are shown, any appropriate number of valve ports 136 can be used. In FIG. 7, instrument base 102 includes a base flange 138 illustrated diagrammatically having pressure channels 140, 142 extending through flange 138 and opened to pressure passageways 104, 106.

[0023] Pressure passageways 104, 106 fluidly couple pressure openings 130, 132 of the instrument base 102 to pressure taps 114, 116. In FIGS. 5 and 7, pressure passageways 104, 106 are formed by coaxial channels 146, 148 in a solid stem 150. Channels 146, 148 formed through stem 150 are straight for rodding the passageways for cleaning. In an alternative design, tubes can be used to form passageways 104, 106 and application is not limited to the solid stem 150 shown in FIGS. 5 and 7. Stem 150 can be bolted to instrument base 102 as illustrated in FIG. 3 or connected by other fasteners.

[0024] In FIG. 5, manifold 134 can be permanently connected to stem 150 to provide a permanent interface between stem 150 and manifold 134. A permanent interface reduces leakage at the interface of the stem 150 and manifold 134 due to assembly and disassembly.

[0025] Differential flow plate is coupleable between pipe sections 58-1, 58-2. In FIGS. 5 and 7, a sealing gasket 152 abuts a sealing surface of flow plate 108 and flanges 54, 56. Flow conduit 110 supports flow interrupter 112 to separate flow conduit into two sides. Flow conduit 110 is seamless between flow interrupter 110 and first and second pressure taps 114, 116 to provide a seamless interface 154 (as schematically illustrated in FIG. 4) in flow conduit 110 between flow interrupter 112 and first and second pressure taps 114, 116. Thus, the seams separating prior art flow plates from pressure taps as described in the Background of the Invention are eliminated. Elimination of the seams between the flow interrupter 110 and pressure taps 114, 116 limits non-attributable pressure loss at the seams which can degrade flow measurement. Additionally, such configuration reduces the likelihood of leak development and the associated undesirable fugitive emissions. Further, elimination of the seams reduces field installation time and cost because fewer seals need to be created and tested in the field.

[0026] In FIGS. 5 and 7, flow plate 108 is formed integrally with stem 150 to form a single assembly unit. The single assembly unit reduces connections between pressure taps 114, 116 and pressure openings 130, 132 to reduce non-attributable pressure loss.

[0027] Flow interrupter 112 can be an orifice plate 156 having a constricted flow orifice 158 as illustrated in FIG. 5. Although a conical edge concentric orifice plate 156 is shown in FIG. 5, other orifice plates can be used. Flow interrupter 112 can be a nozzle plate 160 having a constricted nozzle opening 162 as illustrated in FIG. 7. Detailed descriptions of various orifice plates and nozzle plates are described in Liptak, Beto, Instrument Engineer's Handbook: Process Measurement and Analysis, 3rd. Ed., Chilton Book Company (1995) and Miller, Richard, Flow Measurement Engineering Handbook, 3rd Ed., McGraw-Hill, Inc. (1996).

[0028] FIGS. 8-9 illustrate a flow interrupter 112 having a base portion 164 and a removable edge portion 166 including constricted flow passage 168. Base portion 164 is integral with flow plate 108 and the edge portion 166 is removably coupleable (as illustrated) to the base portion 164. When edge portion 166 wears, a new edge portion 166 is installed for continued use of the flow plate 108, which extends the useful operating life of the flow plate 108. In the embodiment illustrated in FIGS. 8-9, edge portion 166 is externally threaded 170 to mate with internal threads 170 on the base portion 164. A mechanism to lock and seal plate 108 (not shown) is desirable to prevent the insert from dropping and/or falling out. Although a cooperating thread arrangement is shown for removably connecting base portion 164 and edge portion 166, alternate coupling methods can be used employing, for example, screws, bolts, etc.

[0029] Differential pressure taps 114, 116 are in fluid communication with flow conduit 110. The first pressure tap 114 is opened to the flow conduit 110 on a first side of the flow interrupter 112 and is in communication with the first differential pressure opening 130 through the first differential pressure passageway 104 as schematically illustrated in FIG. 4. The second pressure tap 116 is opened to the flow conduit 110 on an opposite side of the flow interrupter 112 and in communication with the second differential pressure opening 132 through the second differential passageway 106.

[0030] In FIGS. 5, 6, 7 and 8, pressure taps 114, 116 are formed of a hole in flow conduit 110 on opposed sides of the flow interrupter 112. In FIGS. 10-13, pressure taps 114, 116 include annular pressure channels 174, 176 extending about a perimeter of flow conduit 110 and in fluid communication with flow conduit 110, on opposed sides of flow interrupter 112, and differential pressure passageways 104, 106 to provide an average pressure measurement upstream and downstream of the flow interrupter 112.

[0031] In FIGS. 10-11, an annular openings 178, 180 extend about the perimeter of conduit 110 on opposed sides of flow interrupter 112. Openings 178, 180 fluidly couple flow conduit 110 to annular pressure channels 174, 176, respectively. In FIGS. 12 and 13, a plurality of openings 182 are spaced about the perimeter of conduit 110 on opposed sides of the flow interrupter 112. Openings 182 fluidly couple flow conduit 110 and annular pressure channels 174, 176 for pressure measurement. Openings 182 can be any suitable shape including holes, slots, and semicircles.

[0032] In FIGS. 5-7, flow plate 108 is formed of a unitary construction. In FIGS. 10-13, flow plate 108 is constructed of an outer block 184 and inner rings 186, 188. Outer block 184 includes flow interrupter 112 extending into a central opening of outer block 184. Rings 186, 188 are sized for insertion into central opening of outer block 184 on opposed sides of flow interrupter 112 to form conduit wall 110. The inner diameter of rings 186, 188 can vary for sizing the flow plate 108 for various pipe inside diameters. In one embodiment, rings 186, 188 are welded to outer block 184 to provide a relatively fluid-tight connection for conduit walls 110, although other connections can be used.

[0033] In FIGS. 10-11, edges of the rings 186-1, 188-1 are spaced from flow interrupter 112 to form the annular openings 178, 180 extending about the perimeter of the flow conduit 110 to fluidly couple conduit 110 to pressure channels 174, 176. In FIGS. 12 and 13, rings 186-2, 188-2 include openings 182 extending about the perimeter of rings 186-2, 188-2 to fluidly couple conduit 110 and annular pressure channels 174, 176.

[0034] Flow plate 108 is inserted into flowpath for process measurement and control. Flow through pipe 54 creates a differential pressure across flow interrupter 112. Differential pressure across flow interrupter 112 is conveyed by first and second pressure taps 114, 116 on opposed sides of the flow interrupter 112 to process instrumentation 120 to measure differential pressure across first and second pressure taps 114, 116 and transmit measurement data to a computer 126. Flow conduit 110 of flow plate 108 supporting flow interrupter 112 is seamless and includes pressure taps 114, 116 to provide a seamless interface between pressure taps 114, 116 and flow interrupter 112 for pressure measurement as previously described.

[0035] Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.