Application Note
Energy & Chemicals

Calculation of Natural Gas Calorific
Value with the Agilent 990 PRO MicroGC SystemAuthorJie Zhang
Agilent Technologies, Inc.

Abstract
This Application Note gives a functionality introduction of the Agilent 990 process(PRO) Micro GC on how to autonomously analyze and calculate the natural gas
energy content.

Introduction
Natural gas is an important energy
resource. It is widely used in different
industries to melt, dry, bake, and glaze
a product. General households use itfor cooking, heating, and lighting. Itcan also be used as fuel for vehicles.
The chemical energy of natural gas
is released by the reaction of thenatural gas with oxygen. The tradeof natural gas is mainly determinedby its energy content. Usually, gas
chromatography (GC) analysis ofnatural gas is used to estimate its
energy content.
Several organizations, such as theGas Processors Association (GPA),
which collaborates with the American
Petroleum Institute, ASTM international—
formerly American Society of Testingand Materials—and the International
Organization for Standardization (ISO)have developed different standards forcalculation of natural gas energy basedon the individual compound energy
values and other physical constants.
The 990 process (PRO) Micro GC canwork as an intelligent process GC toquickly analyze the composition of anatural gas stream, then automaticallymake onboard calculations of its
energy content according to the above
mentioned standards.
With the assistance of Agilent
PROstation software, a user canload predefined energy calculation
methods (following GPA/ATSM/ISO/GOST standards) to the 990 PRO
Micro GC. With the completion of each2

chromatography analysis, the 990 PRO
Micro GC generates the normalized
mole concentration of each targetedcomponent, then autonomously feeds
them to an internal energy content
calculation process. Finally, a reportfor the analyzed gas stream can begenerated with information on energy
content, including total superior/inferior
calorific value (depending on water
existing in either the liquid or gaseousstate), density, relative density, andWobbe index.
This Application Note demonstrates thecomposition analysis and calorific value
calculation of natural gas by the 990 PRO
Micro GC.

Experimental
Simulated natural gas was analyzed ona two-channel Agilent 990 PRO MicroGC. Channel 1 is a 10 m Agilent J&W
CP-PoraPLOT U backflush channel
for nitrogen, methane, carbon dioxide,and ethane analysis. Channel 2 is a
6 m Agilent J&W CP-Sil 5CB straightchannel for propane, isobutane, butane,
2,2-dimethylpropane, isopentane,pentane, and hexane analysis.
The 990 Micro GC used has PRO andenergy meter licenses. The PRO license
enables the autonomous runningof the instrument at prescheduled
time and onboard data processing,including integration, identification, andquantitation based on the preloaded
method. The energy meter license
enables the automatic onboard
calculation of fuel gas energy content
based on the PRO GC quantitation result.

Table 1 lists the analytical methods
used for natural gas composition
analysis. The composition of the gas
sample is tabulated in Table 2. The
analytical parameters were prewritten
into the 990 PRO Micro GC mainboard
with assistance of Agilent PROstation
software. The external standard
calibration curve for each targetedcomponent was developed using
PROstation.
Table 1. Configuration and analytical conditions ofthe Agilent 990 PRO Micro GC.
The Agilent 990 PRO Micro GC Parameters
10 m Agilent J&W
CP-PoraPLOT U,
backflush

6 m Agilent J&W
CP-Sil 5 CB,
straight

30 seconds

30 seconds

Injector
Temperature

110 °C

110 °C

ColumnPressure

200 kPa

175 kPa

ColumnTemperature

80 °C

70 °C

11.3 seconds

NAChannel Type
SamplingTime

Backflush
Time

Table 2. Composition of simulated natural gas.
CompoundNitrogen

Concentration (mol%)
2.04%

Carbon Dioxide

3.12%

Ethane0.575%

Propane0.084%

Isobutane

0.011%

Butane0.011%

2,2-Dimethylpropane

0.0106%

Isopentane

0.0097%

Pentane0.011%

Hexane0.0102%MethaneBalance

The normalization method wasdefined and written into the mainboard
together with the calibration and energy
calculation methods prior to the realsample analysis. When the analysis
was initiated, the PRO GC deploys thesemethods for onboard data collection
and calculation to generate energy
information about the sample. In thisapplication, the calculation method
was developed based on ISO standard
6976-2016 as shown in the method
setting (Figure 1).

Figure 1. Settings of the calorific value calculation method based on ISO standard in Agilent PROstation
software.

3

Results and discussion
Figures 2a and 2b show thechromatograms generated on channel 1
and channel 2 for simulated natural
gas sample. The peaks were integrated
onboard according to the integration
parameters optimized for each analyticalchannel. The integration result wasused to generate the quantitation result
for each target component basedon the prewritten ESTD curves. The
concentration normalization was madeover two analytical channels for all target
components according to the settingin the normalization table (Figure 3).
Then, the normalized concentrations
were used for onboard calorific value
calculation according to predefinedenergy calculation methods.

Figure 2a. Chromatogram of N2 /methane/CO2 /ethane on 10 m Agilent J&W CP-PoraPLOT U backflush
channel.

Figure 4 shows the quantitation andenergy content calculation results for thesimulated natural gas. The “energy” partshows the standard which is followed
for calculation, and the key physicalproperties required to be calculated in
the standard, such as compressibility,
relative density/density, superior/inferior
heating value in molar/weight/volume
units, and Wobbe index. The types ofproperties shown in the report vary
according to the standard requirement.
The quantitation results based on
chromatography analysis are shownin the bottom of the report. Both theESTD concentration and normalized
concentration are reported. The report
was generated in Agilent PROstation
software as soon as eachchromatography separation was finished.
The analysis cycle under the applied
conditions in this work is approximately
90 seconds from sampling to separation
and report generated. If continuous flowmode is used, the analysis cycle time canbe further reduced to 60s.

4

Figure 2b. Chromatogram of C3-C6 hydrocarbons on the 6 m Agilent J&W CP-Sil 5 CB channel.

Figure 3. Normalization table settings for natural gas analysis in this work.

Figure 4. Energy content calculation report generated by the Agilent 990 PRO Micro GC.

5The 990 PRO Micro GC works as a“detector” or “sensor” for natural gas
stream analysis. PROstation software isused to•Develop methods, including
analytical, qualitative andquantitative method, and energy
content calculation method•Set the automation mode•Define how to output the results

All these “commands” are written tothe mainboard by PROstation. In thereal analysis, the Pro Micro GC canrun by itself without connection to thePROstation software. The quantitation
result and energy content will not be
displayed in the format shown here if
PROstation software is not connected.
Instead, the results can be displayed ina scrollable way on the touch screenof the 990 PRO Micro GC, as shown in
Figure 5. Additionally, the result can beoutput through FTP in .txt file or using
Modbus protocol to other terminals formonitoring and recording. Analog output

is another approach to produce analysis
results in voltage or current signal
through a connection to the extension
analog board (Figure 6). The conversionof analog signal and the quantitation
result or energy contents can bepredefined and loaded on the PRO GC
mainboard.

Figure 5. The calorific value calculation results
displayed on the touch screen of the Agilent 990
PRO Micro GC.

Figure 6. Agilent 990 PRO Micro GC connection with extension board for analog output of analysis results.

www.agilent.com/chem
This information is subject to change without notice.
© Agilent Technologies, Inc. 2019
Printed in the USA, October 9, 20195994-1374EN

Conclusion
This Application Note demonstrates
natural gas composition analysis andenergy content calculation by theAgilent 990 PRO Micro GC. The PRO
license and energy content license areactivated on the 990 PRO Micro GC toenable automated fuel gas composition
analysis and energy content calculation.
The analysis process from sampling,
separation, quantitation to calorificvalue calculation and result output, areautonomously executed according to
the prewritten method and automation
mode on the PRO Micro GC mainboard.
The energy calculation methods aredeveloped with compliance to different
international standards, including ASTM,ISO, GPA, and GOST standards. All
methods are developed in PROstationand then downloaded to the 990 PRO
Micro GC for its independent andautomated operation. The energy
content calculation results can be shown
on a local touch screen or outputtedthrough FTP, Modbus, and analog signal
for monitoring and recording.