distribution networks have been using local/manual control of the pipe lines to
oversee the fiscal metering process and safety standards. For this purpose, a
3-shift operation for each metering point was organized in order to keep under
control the process.
fiscal metering was made using tachometers that recorded on calibrated paper,
information regarding flow rate on fixed volume, recorded data that was later
used for manual calculation over a period of time. This offline metering
process does not provide data compatible with centralized networking
2 System description;
A new control
and fiscal system were designed, to segregate the data (fiscal and process).
Control and monitoring of the fiscal measurement is done in an automatic
fashion by the Metering Station Fiscal System. The Control System manage the
process, monitors and controls the gas
metering station, signal inappropriate operating conditions and supports
The Metering Station Fiscal System and the Control System satisfy the
centralized networking requirements, the recording of data, centralized
monitoring measurement, control and data transmission.
2.1 The metering station fiscal system
The Fiscal System has 2 different
metering devices (installed in the technologic container)
electronic equipment (installed in the instrumentation container)
The fiscal metering devices
consist of 2 parallel meter runs of 600mm, which each are equipped with a
turbine gas meter (TGM) and sensors for pressure and temperature. All meter are
connected by gas collector to ensure the same hydraulic conditions for every
meter run.The control metering installation consists of an ultrasonic gas
meter, pressure and temperature sensors. In
order to adapt to the supply situation from time to time, the load of the
individual meter runs is monitored continuously by a control and regulating
system and meter runs are switched on or off as required automatically. The
meter is operated between minimum and maximum (90%) flow rate. In order to
harmonize the recording of fiscal data, volume converters and gas chromatographs
are equipped with a serial interface pursuant to DVGW G485 'Digital
interface for gas metering devices' (DSfG interface). All thus equipped
gas meters are connected to a measurement recorder via the DSfG data bus. Remote
reading of the measurements is possible via GSM, a DSfG data connection is
hooked up to the DSfG data bus.
electronic equipment consist of flow computers with digital measurement
recorder and fiscal data transmission via GSM. Flow Computers conform to EN
12405, and corrections of the high-pressure error curve are made. Flow
computers have a DSfG interface for the transfer of fiscal and control data and
additionally are able to set up a completely independent data channel to
communicate with the control system through gateway. Online values of the gas
composition from the gas chromatograph are available via the DSfG interface.
2.2 The metering
station control system
station control system is an automation control system that monitors and
controls the gas metering station, signals inappropriate operating conditions
and supports remote-control operations. The Metering Station Control System satisfies the centralized
networking requirements, centralized monitoring operations and local operations
with process and parameters data transmission. The system insures also recording,
processing, data displaying, data transmission.
control system has the following features and characteristics:
as an open and distributed system
degree of availability;
to the international and Romanian standards;
system, centralized planning and parameters;
access protection; user friendly interface software;
The Metering Station Control System
includes the following functions:
with gas chromatograph and monitor water dew point;
data administration and transmission;
of the relational data base;
all process digital and analogue data
with easy access searching and reading mode;
functions, reports; alarm reports
control process monitoring by recording, processing and displaying all of the
data in short-and long term archives, evaluation in the form of reports and
3 Process description
The gas metering
stations are located throughout Romania
in an effort to provide gas metering along the distribution pipelines.
stations can be operated in three different operating modes:
- Manual mode (this mode is used only to start
and stop processes and equipment for maintenance;
- Auto/local mode (this mode is used to control
the process – normal operation mode);
- Auto/central mode (this mode will be used for
process monitoring and for the process control in the future).
After take off from
the main pipe there is an insulation flange, to electrical insulate the
metering station from the main pipe. In the inlet line, there is a
hydraulically operated open/close valve. The purpose of this valve is to
quickly take the metering station out of service in case of an emergency (ESD).
The inlet temperature, the inlet pressure and the pressure across the
open/close valve are measured.
During start-up the
metering station can be pressure less.
3.2. Filter separator
filter/separator module is located directly after the inlet module and before
the metering module. There are two filter/separators. One is in operation, the
other one is back-up. Each filter has two stages. The purpose is to clean the
gas from particles and hydrocarbon liquids (the gas is dry, no water present).
The filters are,
during normal operation, pressurized together with the inlet module. All hand
valves must be opened at start-up. The hand valves have no control have no
control system interaction. When the hand valves of the filter separator are
closed, the inlet module is pressurized. Across each filter there is a pressure
difference transmitter, if the filter is in operation the pressure drop is
between 0.15 and 0.5 bar. The control system can generate alarms to indicate
that it is time to change the filter separator.
3.3. Gas metering
The purpose of the
metering module is to measure the quality and the quantity of the gas. The
metering module is placed directly after the filter/separator module and before
the flow control module.
Each station has 2
or 3 metering lines: Either 1 or 2 main metering lines and always 1 backup
redundant line. If a station has 2 metering lines, then each line has a 100%
capacity. If a station has 3 metering lines, each line has 50% capacity.
The sample take off
for the gas chromatograph is located at the inlet of the metering module. After
the gas chromatograph water dew point, inlet pressure and temperature are
measured. The line is then split into either 2 or 3 lines. Each metering line
has a motor operated valve at the beginning and end of the line.
After the inlet
valve of the gas metering module, a strainer is located which provides
measurement of the differential pressure. If the differential pressure over the
strainer becomes grater than a set value, then an alarm is generated and the
back-up metering line will automatically be started.
After the strainer,
ultrasonic and turbine flow meters are placed, each with its own temperature
and pressure measurement, for fiscal purposes. When the flow rates differ with
more than a set value, the software application triggers an alarm.
module is placed behind the metering module and before the outlet module. The
function of the regulator module is to regulate the gas flow with protection
for high pressure and high flows for each individual metering line.
module consists of 2 control valves with block valves in front and behind each
control valve. During normal operation only one control valve is active, the
other one being in stand-by (closed). On the inlet of the regulator module
there is also a pressure transmitter.
In operation, when
the outlet pressure is higher then the inlet pressure, the flow through the
metering station must be stopped using the active control valve. The valve must
be ramped to close. As long as the inlet pressure does not become higher then outlet
pressure, the control valves are kept closed and locked in a mode that disables
application allows setting of a tuneable value for the maximum output of the
The outlet module
is the last part of the metering station. After the outlet module, an
insulation flange is passed connecting the station back to the main pipe, to
electrically insulate the metering station from the main pipe. In the outlet
line there is a hydraulic operated open/close valve. The purpose of this valve
is to quickly take the metering station out of service in case of an emergency.
The module also contains also pressure transmitters, temperature sensors and
pressure measurement across the open/close valve. The hydraulically operated
valve has a bypass circuit which consists of 2 ball valves with an electrically
operated solenoid valve in between, in order to equalise pressure across the
hydraulically operated valve before opening.
3.6. Automatic start-up &
The station is able
to start-up automatically when the operator gives the start command. Actions
taken during automatic start-up:
inlet and outlet module; The inlet is pressurized up to the metering line inlet
valves. The outlet line is pressurized up to the control valve.
pressurize the line between the metering run and the control valve, the control
valve is opened to a tuneable value and immediately closed again
secondary metering line
3.7. Emergency Shut Down
An emergency shut
down (ESD) can be initiated by hand switches, manual call points. When
activated the ESD cuts the power using safety relays to the valves and motor of
the hydraulic packages as well as to the magnetic bypass valves in the inlet
and outlet module.
After ESD reset,
the station shall come back in a state from which it cannot start straight
after ESD reset. Station start will be an operator action.
Aggregated output data from the gas metering station include gas quality
flow information (quantitative information),
energy measurement (aggregated information of the equivalent of gas quality and
quantity) and are arranged in tables and charts.
implementation of this system insurers online fiscal metering information, autonomous
operation of the metering and distribution process that provide a human free
operation of the distribution network.
Metering Station control and fiscal systems increase the gas throughput, lower
the loses caused by the unavailability of the distribution network, increase by
a factor of 100 the MTBF and offer a high level of automation of the gas
► The Metering Station offers in a technologic container: filters and
separators, metering section, regulating section, sampling points section,
instrumentation section, diesel generator, condensation and storage tank.
The metering station control system is an automation control
system that monitors and controls the gas metering station, signals
inappropriate operating conditions and supports remote-control operations.
►The system offers the possibility of real-time
monitoring of the gas quality and quantity, fiscal monitoring, error monitoring
and automatic emergency shutdown procedures.
► The system was designed to work interconnected
with other gas metering stations and also with central level processing
hardware and software, allowing access to information, at different decisional