Patent Application
20170030359
1. Field
Aspects of the present invention generally relate to a method and systems for batch change control for variable speed-driven centrifugal pumps and pump systems.
2. Description of the Related Art
Pumps and pump systems are operated in applications for different media types, for example fluids, slurries, etc., and for different batches, generally in the process industry, and in particular in the oil and gas industry, for example pipelines, refineries, tank farms, etc. Typical oil pipelines transport batches of different types of oil. Such batches include light weight oils and heavy weight oils such as for example light crude oil, diluted bitumen oil, and synthetic crude oil with wide ranges of relative densities and viscosities. Batches can be of different products and of different grades of the same product. Batch changes can occur frequently as often as several times per day.
There are different methods used to separate oil batches, for example pig separation of batches, liquid slug separation of batches, and back-to-back batch changes. When using the back-to-back batch change method, no separation equipment such as for example utility pigs, is required. Three distinct volume areas exist in the pipeline when two oil batches, for example two product grades, are flowing. The new batch and the old batch have their own unique fluid properties. The volume between the new and old batches is called the interface; the interface volume represents a mixture of the new batch and the old batch with transient fluid properties (e.g. densities, viscosities). The length of the interface in the pipeline is shortest near the point of introduction of the new batch and longest at the delivery point. Flows and velocities of the different oil batches are kept at magnitudes sufficient to maintain turbulent flow in the pipeline. With adequate turbulence, minimum mixing of the product (interface) is accomplished.
But there are hydraulic and power disturbances when heavy-to-light and light-to-heavy interfaces move into centrifugal pumps. Thus, there exists a need to minimize hydraulic and power disturbances due to viscosity and/or density transients during batch changes in order to maintain economical and safe pump operation as well as mechanical and e.g. electrical integrity of the system, in particular to control pump speed and/or discharge pressure and/or flow rate and to control a pump station discharge pressure during batch changes.
Briefly described, aspects of the present invention relate to a method and systems for batch change control for variable speed-driven centrifugal pumps and pump systems. Variable speed drives as disclosed herein includes electrical and mechanical assemblies (e.g. gear boxes, turbines).
A first aspect of the present invention provides a pump system comprising a pipeline assembly for transporting fluid; a pump assembly comprising a plurality of pumps arranged along the pipeline assembly; a pump motor assembly comprising a plurality of pump motors, for example electric pump motors, driving the plurality of pumps of the pump assembly; a control assembly for controlling speed of at least one pump motor and discharge pressure of at least one pump; and at least one interface detection meter in communication with the pipeline assembly, the interface detection meter determining properties of the fluid in the pipeline assembly, in particular in front of pump suction nozzles of the at least one pump, and the control assembly controlling the speed and/or the discharge pressure and/or flow rate of the at least one pump according to the properties determined of the fluid in the pipeline assembly.
A second aspect of the present invention provides a control system comprising at least one interface detection meter in communication with a pipeline assembly for transporting fluid; a drive assembly controlling speed of at least one pump motor powering at least one pump in communication with the pipeline assembly for transporting the fluid; and a feed forward control assembly controlling pump speed and/or discharge pressure and/or flow rate of the at least one pump, wherein a first logic control of the control assembly receives fluid data of the fluid in the pipeline assembly provided by the at least one interface detection meter, and forwards the fluid data to a second logic control for calculating speed set points and/or discharge pressure set points and/or flow rate set points for the feed forward control assembly.
A third aspect of the present invention provides a method for controlling variable speed driven pumps or pump systems comprising acquiring real-time fluid data by field instruments of a fluid travelling through a pipeline assembly, and acquiring operational data of a pump system by different units of the pump system, the pump system being operably coupled to the pipeline assembly; transferring acquired fluid data and operational data to logic controls of the pump system; processing the acquired fluid data and operational data by the logic controls; overriding basic pump controls of the pump system based on results provided by the logic controls after the processing of the acquired fluid data and operational data; and resetting the basic pump controls.
In order to facilitate an understanding of embodiments, principles, and features of the present invention, these are explained hereinafter with reference to implementation in illustrative embodiments. In particular, these are described in the context of being methods and systems for a batch change control for variable speed driven centrifugal pumps and pump systems. Embodiments of the present invention, however, are not limited to use in the described devices or methods.
The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present invention.
The pump station 100 as illustrated in
Pumps 102, 104, 106, 108 are each configured as a centrifugal pump. In this exemplary embodiment, the power for driving the pumps 102, 104, 106, 108 is provided directly by the electric pump motors 110, 112, 114, 116.
Pumps 102, 104 are powered each by a variable speed drive, also referred to as Variable Speed Drive System (VSDS). Pump 102 is powered by VSDS 122, and pump 104 is powered by VSDS 124. The variable speed drives 122, 124 are used to control speed and torque of pump motors 110, 112. In the exemplary embodiment according to
Pumps 102 (P1) and 104 (P2), which are powered by VSDS 122 and 124, are discharge pressure controlled using speeds of the motors 110 (M1) and 112 (M2). Thus, each pump 102, 104 comprises pressure transmitters 130, 132, 134, 136. Pressure transmitters 130, 132 monitor pressure head of pump 102, wherein pressure transmitter 130, also labelled as PT-1S, is arranged upstream of pump 102 and pressure transmitter 132, also labelled PT-1D, is arranged downstream of pump 102. Transmitter 132 is operably connected to VSDS 122 in order to control the discharge pressure of pump 102 using the speed of motor 110. As
The four centrifugal pumps 102, 104, 106 and 108 of pump station 100 are arranged in series. One of ordinary skill in the art appreciates that pump station 100 can comprise more or less than four pumps, for example only one pump or ten pumps. When pump station 100 comprises more than one pump, the pumps can be arranged in series and/or in parallel and/or a combination of both.
The pump station 100 further comprises field devices to measure and monitor relevant data and manipulate operation. Such field devices comprise for example flow, pressure and temperature gauges, sensors, transmitters. Pump station 100 can comprises pressure and temperatures gauges and transmitters installed along the pipeline 150 on specific locations. A supervisory control and data acquisition system, known as SCADA system, at a main control room receives all the field data and presents the data to pipeline operators through a set of screens or other type of human-machine-interface, displaying the operational conditions of the pipeline. The operator can monitor the hydraulic conditions of the line, as well as send operational commands (open/close valves, turn on/off compressors or pumps, change set points, etc.) through the SCADA system to the field. Exemplary embodiments of the present invention integrate into such an operational environment.
The pump station 100 is labelled as pump station #62 and is part of a pump system. A pump system can comprise one ore pump stations, such as for example pump station 100 as illustrated in
As described before, there are different methods used to separate oil batches. When using the back-to-back batch change method, no separation equipment such is required. Flows and velocities of the different oil batches are kept at magnitudes sufficient to maintain turbulent flow in the pipeline. With adequate turbulence, mixing of the product (interface) is kept at a minimum. But hydraulic and power disturbances start when heavy-to-light and light-to-heavy interfaces reach the inlet of a pump station.
During batch changes, behaviour of operating point 200a, 200b, also referred to as invariant flow rate set point, of a pump station, as for example pump station 100 as shown in
Reference numeral 200a labels an operating point for heavy fluid, and reference numeral 200b labels an operating point for light fluid. The x-axis labels flow rate (m3/hr) of the fluid, and the y-axis labels total pump station head required (m), also referred to as total dynamic head (TDH).
Line 230 labels a minimum flow rate, and dotted line 240 labels a maximum flow rate of the fluid. Dotted curve 250 labels a minimum pump speed curve, and curve 260 labels a maximum pump speed curve, with different speed curves 270 in between. Pump curves are dependent on viscosity of the fluid and are corrected accordingly.
For example, during a batch change the flow rate is as follows:
The transition swings of the operation point 200a/b in both cases a) and b) are the more extreme the larger the differences in density and viscosity between “heavy” and “light” are and the smaller the interface length of batch changes is. Fast changes in flow rate during transition can induce pressure surges in the pump system. Timely detection of a batch change interface in front of first pump of pump station 100 (refer to
Similarly to the pump station 100 as illustrated in
The pump station 300 is labelled as pump station #62 and is part of a pump system. A pump system can comprise one ore pump stations, such as for example pump station 300. As
As illustrated in
On the contrary to the exemplary embodiment according to
Timely detection of a batch change interface in front of pump station 300 mitigates upsets and enables optimizing operation of the pump station 300 as well as of the pump system. According to an exemplary embodiment of the invention, pump station 300 comprises a control system in order to minimize hydraulic and power disturbance due to density and viscosity transients during batch changes and in order to maintain economical and safe pump operation as well as mechanical and e.g. electrical integrity of the pump station 300 and the pump system, in particular to maintain a constant flow rate and to manage a pump station discharge pressure during batch changes. The control system includes logic, which may be implemented in hardware, software, or a combination thereof.
Each variable speed driven pump among pumps 302, 304, 306, 308 comprises respective suction pressure transmitters 330, 334, 338, 342 and discharge pressure controllers 332, 336, 340, 344, which monitor and control the discharge pressure of a respective pump 302, 304, 306, 308. At least one or two pumps of the pump station 300 are variable speed driven and discharge pressure controlled, wherein one pressure transmitter is arranged upstream of the pumps and one pressure controller is arranged downstream of the pumps. For example, variable speed driven centrifugal pump 302 can comprise pressure transmitter 330 (PT-1S), pressure controller 332 (PT-1D), variable speed driven centrifugal pump 302 can comprise pressure transmitter 334 (PT-25), pressure controller 336 (PT-2D), variable speed driven centrifugal pump 306 can comprise pressure transmitter 338 (PT-35), pressure controller 340 (PT-3D), and variable speed driven centrifugal pump 308 can comprise pressure transmitter 342 (PT-45), pressure controller 344 (PT-4D). The exemplary pump station 300 is designed so that all pumps 302, 304, 306, 308 have closed loop discharge pressure controllers e.g. 384, 386 that can be activated when powered from VSDSs 322, 324 and de-activated when powered direct online from the utility 320. Feed forward control during batch change shall take place only on variable speed driven pumps within the pump assembly. VSDSs 322, 324 can drive any pump 302, 304, 306, 308 and when driving a specific pump, the respective pressure controller is assigned to that specific pump and operably coupled to VSDSs 322, 324 so that discharge pressure control is achieved for any pump driven by a VSDS.
Fast and accurate measurement of the properties of the fluid transported in pipeline 350 is prerequisite for a fast acting control system in order to predict interface during a batch change in first pump 302 at the pump station 300. Issues caused by delayed fluid property measurements are avoided by using e.g. a multi-variable clamp-on interface detection instrument 380 with sufficient sampling at rates such as five times per second. The instrument 380 can be for example a clamp-on transit-time ultrasonic meter. Such an ultrasonic meter is for example a device named SITRANS FUH1010® manufactured by Siemens. The instrument 380 ensures precise and timely sampling of flow rate, density and viscosity by sensoring sonic velocities and temperature of the media in the pipeline 350. The pump station 300 can comprise one or a plurality of interface detection meters 380 installed at desired locations along the pipeline 350. Typically, a pump station comprises at least one interface meter 380 installed in front of first pump 302 of the pump station 300. The optimal location of the interface meter 380 downstream of pump station 360 and upstream of pump station 300 depends on the feed forward control requirements (refer to pump suction L).
The control system encompasses comprehensive control loops including sensors, transmitters, logic software, actuators and electrical supply and analogue/digital signal interfaces. In general, logic software applications calculate (e.g. based on sensor readings, plant condition data, and system design data) the optimal transition of pump operating points from start to end of a batch change. The results are implemented to override basic control parameters and set points of the pump station.
The pump station 300 comprises feed forward logic and/or model-based predictive logic in order to supplement or override basic control commands and/or data of the pump station 300, and feed back control loops comprising a plurality of logic controllers 382, 384, 386. Logic control 382 is operably coupled between interface detection instrument 380 VSDSs 322, 324, and flow controller 396, also labelled FC. Logic control 382 comprises feed-forward control functionality and/or model-based predictive logic in order to supplement or override basic control commands of the pump station 300. Models applied include batch detection application, viscosity corrected pump curves, ultrasonic signal compensation, etc. and overriding set points and/or controller parameter of VSDS controls 388, 390 and/or flow controller 396, and/or discharge controller, e.g. 384, 386.
The interface detection instrument 380 provides sonic velocities and temperature of the fluid in the pipeline 350. In an exemplary embodiment, the interface detection instrument 380 can be configured such that it also determines and/or calculates flow rate and/or density and/or viscosity of the fluid in the pipeline 350. Alternatively, viscosity and/or density can be calculated in logic control 382 instead of being provided by the interface detection instrument 380. The logic control 382 controls the VSDSs 322, 324 and/or flow controller 396 by adjusting the speed set points and/or control parameter of each VSDS 322, 324, and/or set point and control parameter of pressure controls e.g. 384, 386, and/or set point and control parameter of flow controller 396 according to the properties, in particular viscosity and/or density, of the fluid in the pipeline 350 based on viscosity corrected pump curves of pertinent pumps. Other examples for an interface detection instrument 380 are viscosity meters and/or density meters or many other meters capable of providing viscosity and/or density information of a fluid in timely manner.
Pump station 300 further comprises logic controls e.g. 384, 386, and/or 396, wherein each logic control 384, 386, 396 comprises logic functionality, for example a PID controller. In the event of a batch change, manipulated variables (output) and/or control parameters and/or set points of these controllers 384, 386, and/or 396 are overridden by control logic 382. After the batch change, these logic controllers 384, 386, 396 are re-started accordingly and the control logic 382 is set idle.
Pump station 300 further comprises logic controls e.g. 388, e.g. 390, 392. These logic controls e.g. 388, e.g. 390, 392 override logic controls e.g. 384, 386 and/or the set point of logic control 396 by means of results/output of logic control 382, if applicable during a batch change.
Based on information relating to density and/or viscosity of the fluid in the pipeline, the logic control 382 detects timely batch changes. During a batch change, the logic control 382 predicts optimal pump and pump system operation based on design limits and actual operational data and constraints (e.g. including electro-mechanical system data) and/or actual viscosity corrected pump curves (refer to
In further exemplary embodiments, the logic control 382 calculates the speed set points for VSDSs 322, 324 and/or set points and parameters of discharge pressure controllers e.g. 384, 386, and/or set points for flow controller 396 derived dynamically from a multi-dimensional system of equations or lookup tables based on viscosity corrected pump system curves, design limits, actual operational constraints and conditions of pump and pump system (e.g. including electro-mechanical systems). The calculated speed and/or discharge pressure control parameter and/or set points and/or flow rate set points are functions of multiple variables, for example:
Fluid density and viscosity, compressibility factors,
Volumetric flow rate,
Crude assays and pump curves,
Pressure and temperature of fluid,
Suction/discharge pressure of pumps and pumps systems,
Batch interface length, and
Theoretical and calculated actual pump efficiencies.
As noted before, each of the pumps 302, 304, 306, 308 can be operated on/off. For example, according to flow rate of fluid in pipeline 350 and discharge pressure of pumps 302, 304, 306, 308, one or more of the pumps may be switched off because the flow rate and discharge pressure is such that not all of the pumps are needed. When the flow rate and discharge pressure requirements increase, the pumps can be switched on again.
The control logic of the control system comprises at least the following functionalities:
Essentially, the control system of pump station 300 monitors the flow rate of the fluid in the pipeline 350 as well as density and viscosity of the fluid in real time. A fluid interface of a batch change can be detected and speed set points for the VSDSs 322, 324 and/or set points and parameters for discharge pressure controls e.g. 384, 386 are automatically adapted when the fluid interface enters each pump 302, 304, 306, 308 of the pump station 300. The control system also calculates correct station pressure set points for at least pumps 302, 304, and discharge pressure controllers e.g. 384, 386 and/or flow controller 396 for non-batch change conditions. The control system mitigates the transient effects on the hydraulic and power systems when batch changes occur, in particular when batch changes with oil viscosity changes occur. The control system as described in
The control circuit as illustrated in
The described control system can be integrated into new pump stations or pump system when being installed (refer to for example
Plug-and-play device 440 processes pump suction information such as for example fluid temperature 422, fluid density 426, fluid flow rate 424 provided by interface detection meter 420 and suction pressure information 428 provided by pressure transmitter 438, as well as pump discharge information 410, 412 provided by pressure transmitter 432 and/or flow controller 430. Pump system 400 further comprises logic controls 434, 436, which override existing logic control 410 and/or set points of logic control 430 by means of results/output of logic control of feed forward controller 444, if applicable during batch change detection 442.
Step 510 of method 500 comprises acquisition of real-time fluid data (e.g. temperatures, flow rates, pressures, sonic velocities, densities, viscosities, etc.) from field instruments and operational data (e.g. real-time, set points, design book, maintenance, condition monitoring) from unit control, station control, SCADA, Manufacturing Execution Systems, Enterprise Resource Planning Systems, etc., or other systems connected for example by secure internet. In step 520, acquired data are transferred to logic controls of a pump station or pump system. The logic controls include, but are not limited to (see step 530):
Scaling, filtering, inter-conversion, correcting, compensating, etc.,
Data reconciliation,
Batch change detection,
Feed forward control by calculating,
Coordinating with similar logic controllers on other pump units and systems.
Step 540 includes forwarding and overriding the results/output of the logic controls (refer to steps 520, 530) of the pump station or pump system to pump basic controls (pressure, flow, etc.), and forwarding and overriding results/output of feed forward controller to other pumps and outside systems (for example unit control, station control, SCADA, Manufacturing Execution, Enterprise Planning, or other systems connected for example by secure internet). In step 550, when a batch change is over, basic pump controls, e.g. discharge pressure controller and/or flow rate controller are reset.
The proposed control system optimizes by means of logic application (mathematical algorithm) based on plant, design data (incl. viscosity corrections of pump curves) the transition upsets of operations, minimizes the transition time and maintains safe pump and plant operation by processing timely interface sensor signals in order to predict new operation set points and control parameters, as well as optimal path of transient operation. This includes switching discrete pumps on/off and adjusting speed of pumps as well as overriding, ramping set points and control parameters of basic controls, if applicable. The mathematical algorithm includes—but is not limited to—algebraic equations, ordinary differential equations, partial differential equations, mixed integer equations, and a combination thereof.
The described control system can be integrated into new pump stations 300 or pump system when being installed, referred to as so called Greenfield projects, or can be installed as plug-and-play system as retrofit application into existing infrastructure, referred to as so called Brownfield projects.
While embodiments of the present invention have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.
