Introduction to Virtual Flow Computing 

Flow measurement projects frequently face the challenge where reliable and accurate flow measurement is required for items such as fuel, flare, water injection, separator or even production allocation, but panel space and budget constraints can make using traditional dedicated flow computers prohibitive.

The answer: Use a “Virtual Flow Computer” or VFC.

Spirit IT has been a leading industry pioneer in this concept with its VFC software application as part of its eXLerate Flow Software suite.

There is no loss in the functionality compared with a traditional flow computer with increases in the areas of data storage and graphical display. Functions including; measured value of temperature, pressure density etc, accurate period totalizers, flow calculations, alarms, events, trending, communication to external systems (DCS, Pipeline Integrity, Allocation etc) and all other functionality expected to implement a custody transfer or allocation measurement point or system.

The virtual flow computing functions are implemented in a standard PC running our eXLerate VFC application. 

Field signals are gathered via standard industrial hardware controllers such as PLC’s, DCS Control Modules etc to obtain the real-time values for the associated 4-20mA analog, digital, and frequency input signals. 

These are then transferred to the PC or Server running the VFC application via standard communication protocols such as Modbus or Ethernet. This can be a single PC/server or redundant units.

Each metering stream or meter run is processed by an individual VFC calculation and presentation worksheet containing the selected choice of calculations. This includes most AGA/ISO/API/GPA calculations.

Since the VFC software internally uses double precision floating point formats throughout the entire application, high accuracy is assured for the calculated flow results.

Our VFC application uniquely runs on the Microsoft Excel platform which most of us use on a daily basis. Configuration and system changes are easily implemented without recourse to the software provider. Data is presented in a text and graphics rich environment previously not available at the flow computer level.

Highest Level of Integration

The unique combination of redundancy, HMI, flow metering calculations and report generation integrated in a single software product enables development of a complete single solution.

For the System Integrator, our approach is simple and yet flexible:

• Adding another meter run is as simple as adding just another Excel worksheet to the application and enabling communications.
• Simplified architecture - a single database is used rather than one for the supervisory functions and a small data archive in each flow computer in the system.
• Generic hardware can be purchased for field signal gathering and freely available commercial or industrial PC’s/Servers.
• No need for multiple developers licenses between various HMI and report packages.
• Significantly reduced panel requirement on multiple meter run systems make a competitive advantage.
• For the End User, flow data is gathered and presented in a clear format with all intermediate and final calculation data available for viewing, trending, reporting etc.
• All meter run and station data can be accessed from the same computer.
• Security is assured by user login and passwords.
• Remote (Client) access to the same data, displays, reports etc.
• Have the processing speeds, memory size and disk storage power of modern PC or servers that most traditional flow computers are unable to match.
• In addition to flow computing, report generation, and visualization, our platform offers additional diagnostics & performance monitoring functionality that can not be realized by a traditional flow computer.
• Reduced footprint required in the Control or Instrument Room.
• Reduces training time and costs – fewer system components to be familiar with.
• Reduces spares holding requirements and overall routine maintenance costs – Fewer system components to maintain and hold spare parts for.

Example

All that is required to implement an ultrasonic meter application, besides the meter, a pressure transmitter & temperature transmitter, is a small form-factor industrial PC running our Virtual Flow Computer application. 

This will provide all the features you would expect of a conventional flow computer, plus the integrated ultrasonic performance monitoring & diagnostics, graphical displays, trending, alarming, and reporting combined into a PC based cost-effective solution.

Both technically as well as cost-wise, this is a highly efficient solution.

Because of the flexibility, simple or complex flow computer applications can be developed as required by the customers specification. Virtual flow computing can be also used for verification, backup or check metering to complement existing flow computer systems without the need for a major installation exercise.

Features

Our VFC supports most applications and standards, for natural gas, LNG, LPG, steam, crude oil, condensate, plus many other liquids and speciality gases. Most flow meter types can be implemented as either analog, pulse or serial communication inputs.  Implementation of modern microprocessor based flow meters such as coriolis or ultrasonic using both pulse and serial data is straight forward and permits the easy implementation of diagnostic displays and graphs using the processing power and data storage size that only a PC/Server can offer.

Exporting of data either by hard/soft copy report or data transmission to customers and higher level systems is also a standard feature.

The main functions of the virtual flow computer are:

• Measurement of process variables from field transmitters through communication with the Acromag field devices, including mostly dP values from the Utility flow meters.
• Determine health status of each transmitter.
• Perform scaling for obtained process variables.
• Accept and process field I/O from the station.
• Calculate gross and line volume flow rate and standard volume flow rate bases on the flow signal of the flow meters.
• Calculate mass flow rate and energy flow rate where applicable.
• Maintain cumulative, period, daily (as well platform as pipeline time, where applicable) and maintenance totals for gross volume / line volume, standard volume, mass flow, and energy flow.
• Allow for modification of operational parameters and settings, such as alarm and deviation limits, transmitter overrides and flow meter parameters.
• Generate custody transfer + Allocation reports and other reports. In the system there will be daily quantity and quality reports, monthly quantity and quality reports, and snapshot reports implemented. Reports are stored to the disk and, when required, printed on paper.
• Archive reports, alarms and events.
• Provide a secure environment by protecting the Virtual Flow Computer from unauthorized access.
• Manage alarms. Alarms are derived from primary input signals as well as from calculated figures. Alarms are printed on the alarm printer, and stored on the hard disk. As well alarms messages as return to normal messages as acknowledgements are reported as well.

For an example of an implemented system, please check [here].