Abstract
A method for preventing flow reversal due to an upstream pressure drop in a natural gas supply line. The method, using a unique system configuration, includes setting a threshold low pressure for the upstream gas flow, continually sensing the upstream pressure, activating a trigger valve when the upstream pressure falls below the threshold low pressure, and closing a control valve in response to the trigger valve to prevent reversal of flow in the gas supply line.
Claims
1. A method for preventing flow reversal in a natural gas supply line due to an upstream pressure drop, the method comprising: throttling a gas pressure through the natural gas supply line, using a worker regulator positioned downstream of a monitor control valve, to maintain a downstream delivery side gas flow pressure; setting a threshold low pressure (X) for gas flow upstream of the monitor control valve; continually sensing an actual gas flow pressure, P.sub.1, at a point upstream of the monitor control valve; continually sensing an actual gas flow pressure, P.sub.2, at a point downstream of the monitor control valve, wherein the threshold low pressure (X) is set to be greater than the actual gas flow pressure (P.sub.2); and closing the monitor control valve when the actual flow pressure upstream of the monitor control valve, P.sub.1, falls below the threshold low pressure (X) to prevent reversal of flow in the gas supply line.
2. The method of claim 1, further comprising re-opening the closed monitor control valve when the actual flow pressure upstream of the monitor control valve, P.sub.1, exceeds the threshold low pressure (X).
3. The method of claim 1, wherein the monitor control valve is a rotary control valve.
4. The method of claim 1, wherein the monitor control valve is a linear control valve.
5. The method of claim 1, further comprising throttling gas flow with the monitor control valve when actual gas flow pressure at a point downstream of the monitor control valve, P.sub.2, exceeds a predetermined pressure value.
6. The method of claim 5, wherein the threshold low pressure (X) is greater than 220 psig.
7. A gas supply line control system comprising: a worker regulator for maintaining a downstream pressure in a gas supply line at a target pressure; a monitor control valve upstream of the worker regulator and having an inlet, an outlet, and a mechanism for moving within a range between and including a fully open position and a fully closed position to control gas flow in the gas supply line, wherein gas flows from upstream to the inlet, to downstream through the outlet; a first pressure sensor for determining a flow pressure upstream of the monitor control valve inlet; and a trigger valve responsive to the sensor; wherein the trigger valve triggers the monitor control valve mechanism to fully close to prevent reverse gas flow when the upstream flow pressure falls below a first predetermined value.
8. The gas supply line control system of claim 7, further comprising a second pressure sensor for determining a flow pressure downstream of the monitor control valve outlet.
9. The gas supply line control system of claim 8, wherein the monitor control valve throttles the gas flow when the second pressure sensor detects a downstream pressure exceeding a second predetermined value.
10. The gas supply line control system of claim 9, wherein the second predetermined value is 160 psig.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings, embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated.
[0016] FIG. 1 is a schematic showing a prior art approach which splices a check valve into a gas line upstream of flow control regulators to prevent reverse flow in the event of a line rupture;
[0017] FIG. 2 is a schematic showing normal operation of a standard prior art gas line regulation system with a worker regulator and an upstream monitor regulator-worker control valve in control;
[0018] FIG. 3 is a schematic showing operation of a standard prior art gas line regulation system with a worker regulator and an upstream monitor regulator after failure of a worker regulator and activation of the monitor regulator;
[0019] FIG. 4 is a schematic showing operation of a standard prior art gas line regulation system with a worker regulator and an upstream monitor regulator after a gas line rupture upstream;
[0020] FIG. 5 is a schematic showing normal operation of a standard prior art gas line regulation system with a worker regulator and an upstream monitor regulator having an upstream check valve-worker valve in control;
[0021] FIG. 6 is a schematic of the system of FIG. 5 showing operation after failure of the worker regulator-monitor valve in control;
[0022] FIG. 7 is a schematic of the system of FIG. 5 showing operation after a pipeline rupture upstream-check valve engaged to prevent flow reversal;
[0023] FIG. 8 is an operational schematic showing normal operation of an embodiment of the disclosed gas line regulation system-worker valve in control;
[0024] FIG. 9 illustrates an embodiment of the disclosed control system during normal operation with a worker regulator controlling flow and a monitor control valve in a full-open position;
[0025] FIG. 10 illustrates the system of FIG. 9 showing operational changes after failure of the worker regulator with overpressure prevention logic of the monitor control valve throttling flow; and
[0026] FIG. 11 illustrates the system of FIG. 9 showing operational changes after a pipeline rupture upstream with backflow prevention logic of the monitor control valve in a full-closed position.
DETAILED DESCRIPTION OF THE INVENTION
[0027] While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail at least one preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to any of the specific embodiments illustrated.
[0028] A schematic of the prior art use of a check valve 24 to prevent flow reversal in a gas line 100 is illustrated in FIGS. 1 and 5-7. The addition of the check valve 24 is a time-consuming and costly undertaking requiring annual maintenance. The issue of flow reversal is more readily addressed by the present invention, which adds upstream pressure sensing and valve control to an existing control valve system.
[0029] Referring to FIG. 8, operational parameters of the disclosed system are shown. The schematic of FIG. 8 is simplified for a general understanding of operation, as some actual components may be combined. The illustrated embodiment is directed to a control system 10 for a natural gas supply line 100. The particular illustrated supply line 100 has a preferred upstream pressure (P1) in the range of 230 to 500 psig, while the downstream preferred pressure (P2) is 160 psig. Obviously, other set points for P1 and P2 pressures would be similarly addressed by the disclosed system 10. Generally speaking, the control system 10 comprises a worker regulator valve 20, a monitor control valve 26, and a pressure controller (or valve pilot controller (VPC)) 30 with pressure sensing capabilities both upstream (P1) and downstream (P2). The monitor control valve 26 has an inlet side (upstream), an outlet side (downstream), and is controlled by trigger valve 28 via the pressure controller 30. In the illustrated embodiment of FIGS. 9-11, the trigger valve 28 is also coupled to an upstream pressure sensor 31. Operationally, the monitor control valve 26 has a full-open default position, which can be (1) unchanged by the trigger valve 28, (2) throttled via loading pressure from the trigger valve 28 in response to the controller 30 sensing increased P2, and (3) closed via loading pressure from the trigger valve 28 in response to pressure sensor 31 sensing decreasing P1 (below minimum setpoint).
[0030] For example, with respect to FIGS. 9-11, the control system 10 maintains the set pressures, P1 and P2, by continuously monitoring both pressures. The upstream (supply side) pressure setpoints (e.g., 230 min. and 500 max.) are set at sensor 31, which continually reads pressure on the upstream supply side of the monitor control valve 26. Pressure controller 30 monitors P2 via line 15, as shown-worker valve/regulator 20 also receives pressure feedback via line 17 of FIG. 8. As P2 drops below a minimum setpoint, worker valve/regulator 20 is actuated to open to allow P2 to increase. Conversely, as P2 rises, worker valve/regulator 20 throttles flow to bring P2 back to 160 psig. When P1 is within the setpoint limits and P2 is at 160 psig, normal operation of the worker valve 20 occurs and the monitor valve 26 is at full-open position.
[0031] As can be seen in FIG. 9, the system 10 is in normal operation. The worker regulator 20 is used to reduce delivery side pressure of the preferred normal upstream pressure (P1) from 230-500 psig to a preferred normal downstream delivery pressure (P2) of 160 psig. The monitor control valve 26 is in a full-open position (default), allowing the worker valve 20 to control flow pressure.
[0032] Referring now to FIG. 10, the schematic illustrates control failure of the worker valve/regulator 20. The failure of the worker valve 20 allows excess pressure in the downstream flow (i.e., delivery side) to reach a level greater than the preferred normal 160 psig. If allowed to continue, this scenario with reach what is called an over-pressure condition. This can be dangerous to residences and businesses which may not be equipped to regulate such high gas pressures. To prevent further climbing of the downstream (P2) pressure, the VPC pressure controller 30 senses the downstream pressure increase and transmits this pressure to the monitor trigger valve 28. The upstream pressure sensor 31 also transmits the upstream pressure P1 to the 3-way trigger valve 28, which then acts on the monitor valve 26 as a result of the climbing P2, to throttle flow. This continues to bring P2 back to the targeted 160 psig.
[0033] A final scenario is illustrated by the embodiment of FIG. 11. Here the schematic presents a situation where an upstream event (e.g., a line rupture) 102 has caused a drop in upstream pressure (P1<220 psig). While the worker regulator 20 is operating normal (i.e., throttling gas flow) to maintain downstream pressure (P2) at the preferred 160 psig, the low and dropping upstream pressure will eventually cause a flow reversal in the gas linei.e., backflowwhen P1<P2 is achieved. The upstream pressure sensor 31, which is set to 220 psigi.e., below the lowest preferred normal upstream pressure of 230 psigis triggered and signals the pressure controller 30 and/or the trigger valve 28 which then sends a loading pressure to the monitor valve 26. The monitor control valve 26 is actuated to a full-closed position, thereby preventing reverse flow in the gas line 100.
[0034] The control valve 26 is able to close much earlier than a check valve of the prior art (see FIG. 1), thereby preventing a greater loss of product. The control valve 26 may be a pressure regulator but must have a guaranteed physical close to be used in the disclosed system 10.
[0035] The monitor control valve 26 used for the disclosed system 10 may be either a rotary control valve or a linear control valve as manufactured and sold by Assignee, VRG Controls, LLC. (see https://www.vrgcontrols.com/control-valves). Further, while all the embodiments illustrated are directed to a natural gas supply line, it should be understood that the principles of the invention can be more broadly applied to most any fluid delivery system where reverse flow presents an issue.
[0036] The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the broader aspects of applicants' contribution. The actual scope of the protection sought is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.
