Yokogawa provides an innovative automatic custody transfer
system for unmanned LNG fuel stations that uses the
STARDOM FCN controller and a cryogenic version vortex
flowmeter.
Safe installation
LNG that vaporizes and mixes with air in the proper
proportions can ignite. To prevent accidents at remote
gas stations, the controller is stored in a cabinet with an
intrinsically safe barrier.
Fleet identification
An ID file storing fleet ID information has been loaded onto
the controller and can be modified online by accessing the
controller web page. When the truck driver presses the start
button, "Enter ID number" is displayed on the local HMI.
When the fleet ID number is entered into the local HMI,
the ID number is sent to the controller and compared with
the ID information in the file. When the ID is authenticated, the
controller initiates the LNG dispensing sequence. However, if
the ID is not authenticated, an error message is displayed on
the local HMI.
Liquefied gas dispensing
1. After the ID is authenticated, the controller starts a pump
to circulate liquefied gas through the pipe until the
temperature falls low enough for single-phase liquid flow.
If this cannot be achieved within a given time frame, the
controller stops the pump, displays an "error" on the local
HMI, and returns to idle.
2. When the temperature is low enough, the controller opens
the valve and slowly ramps up the pump speed to avoid
tripping due to sudden increases in back pressure. During
the dispensing, the pressure is monitored and, if it goes
high (due to back pressure problems or the tank being
full), filling stops. If the truck has more than one tank to
fill, the local HMI prompts the driver to connect to the
next tank and continue filling. Once completed, the local
HMI displays the total amount dispensed, and a report is
created in the controller.
Flow volume measurement
The Yokogawa DY cryogenic version vortex
flowmeter handles process temperatures as low
as -200 deg C with high accuracy (liquid: ±0.75%).
Flow correction
Flow (measured by the
Yokogawa cryogenic
version vortex flowmeter)
as well as temperature and
pressure are transmitted to
the controller. The flow is
compensated to the base temperature using a customized
equation for custody transfer.
Logging file
On completion of each dispense, the corrected flow,
temperature, and pressure are saved as an Excel compatible
CSV file in the controller's compact flash memory. This log
file can be uploaded on demand to a PC using the FTP
function and can also be viewed in trend format by accessing
the controller web page.
Report file
At the end of the day, a report file is created by compiling all the
day's dispense files. As a default, two daily reports are provided.
These are (1) Daily Dispense Report: summary of the day's
dispenses, and (2) Daily Status Report: tank level and pump
usage. These reports are in Excel compatible CSV format and
are completely user definable. The created daily reports are
e-mailed to an office for billing purposes via GSM/GPRS or some
other Internet connection. Also, these reports can be uploaded
on demand to a PC using the FTP function and can be opened in
Microsoft Excel.
Web-based HMI
The following pages can be accessed at the controller URL:
Tuning Parameter Setting:
Without the modification of applications, parameters can
be set on this parameter web page. These include timer
set points, pressure set points, alarm set points, and PID
tuning parameters. Also,
data logging and report
creation configuration can
be set.
Dispense Trend:
The dispensed quantity
and historical trend can
be monitored in real time.
Site Status:
Gas station status
information such as storage
and dispensing quantity and
status can be monitored.
Alarm notification via e-mail
If an alarm occurs, the controller immediately sends to a
specified person an alarm e-mail that contains a log of all
process parameters at the time of the alarm.
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