Elster EnCal 3000, Technical Documentation Manual, Page: 27 / 118

EnCal 3000 page 21
5 Functional Description
5.1 Gas Quality Module(s)
5.1.1 Function
The EnCal 3000 Controller is a device for indicating and controlling the measurement of the gas quality (GQ) of natural
gases by the gas chromatograph (GC) of the same name (EnCal 3000 Gas Chromatograph). The GC uses the different
adsorptions rates of the individual components contained in the sample gas, which are separated from each other on
their way through the integrated GC column.
Each component’s concentration is measured at the end of the column by a
detector. Each piece of gas quality data (e.g. superior heating value or relative density) can then be calculated based on
the mole fraction of each individual component. The gas quality data is determined in the GC according to ISO 6976
4
and
transferred to the EnCal 3000 Controller at the end of each analysis together with the values of the component fractions.
Another variable is derived from these direct variables in the EnCal 3000 Controller: the methane number (Mn).
A variable that can also be derived is the hydrocarbon dew point. It indicates the temperature at which the first
hydrocarbons condensate. The gas will partly become fluid below this temperature. All components are completely
gaseous above this temperature. The hydrocarbon dew point is indicated in Kelvin and can be determined for a
parameterized pressure or the current online pressure. In case the current online pressure is used, an upper pressure
limit can be parameterized. If the current value is above this limit, the dew point is determined for the parameterizable
substitute pressure value.
The dew point calculation is an additional option that must be purchased and activated with a license key in the
parameterization. The following basic requirements also apply to the use of this option:
The chromatograph must be able to measure all higher components up to n-nonan (C9). This is why the dew point
calculation can only be performed in combination with the C9+ version of the EnCal 3000 Gas Chromatograph.
The chromatograph must be parameterized accordingly for the application. A corresponding Modbus table
5
and a
corresponding application
6
are necessary in particular. Furthermore, the GC should be able to identify the benzol
(C6H6, benzene), cyclohexane (C6H12), methylcyclohexane (C7H14) and toluene (C7H8) components separately
from the other components so that the dew point calculation is as accurate as possible.
After the EnCal 3000 Controller has been switched on, it establishes the communication to the EnCal 3000 Gas
Chromatograph and starts to permanently poll new analysis results. As soon as new analysis results are available they
are indicated. Therefore, make sure to switch on the gas chromatograph about 30 s before the controller.
You can restart the controller during the operation of the gas chromatograph as the gas chromatograph continues the
parameterized measurement series independently. After a restart the controller indicates the last valid analysis results
from before the restart until the first valid analysis after the restart has been completed and the results have been
transferred. It may happen, however, that an analysis is being completed during the restart period of the controller. In this
case the corresponding results are not transferred.
A prerequisite for starting the measuring operation is that the helium carrier gas is applied with sufficient pressure. The
gas chromatograph contains an electronic pressure regulator that determines whether the inlet pressure is sufficient.
Another prerequisite for the operation to start is that the two modules of the gas chromatograph must have reached the
respective parameterized operating temperature. The warm-up time of a cold device can take up to 30 minutes. The gas
chromatograph waits until the operating temperature has been reached before starting to measure. Not until then can the
controller indicate valid measurements.
Observe the temperature of the gas chromatograph in the Instrument status display of the RGC 3000 (PC) software of
the EnCal 3000 Gas Chromatograph (cf. Chapter 3.2 in the EnCal 3000 Gas Chromatograph Software Manual).
4
T1 = 25°C (combustion reference temperature), T2 = 0°C (volume reference temperature)
5
See Chapter 4.8 in the EnCal 3000 Software Manual
6
See Chapter 3.7 in the EnCal 3000 Software Manual