June
2016
HYDROCARBON
ENGINEERING
25
analyser method continues
to provide the hydrocarbon
processing industry with an
online analytical method
with precision and bias data
2 - 5 times better than other
analytical techniques for
total sulfur measurements.
As a recent development,
ABB adjusted the injection
valve type from a liquid to a
vapour, and developed a
specific and dedicated H
2
S
measurement analytical
module that provides a
system capable of measuring
both H
2
S and total sulfur in
the same analytical oven
and detector.
For hydrogen sulfide measurements (outlined in
40CFR60 Subpart Ja), there are two options:
n
n
PGC5000B class oven or PGC5007 with additional H
2
S
measurement option.
§
§
A direct measurement of H
2
S in fuel gas with a
measurement range of 0 - 300 ppm.
§
§
This analytical method uses a sample injection with
backflush and selector to eliminate interference with
a flame photometric detector for H
2
S.
§
§
Sulfinert-treated hardware for chemical inertness and
measurement accuracy.
§
§
Fuel gas stream isolation from flare gas sulfur
excursions.
§
§
Zero potential of cross contamination when flare gas
sulfur exceeds 300 ppm.
§
§
Separate and independent daily validation and CGA
audit analyses.
§
§
Total sulfur and direct H
2
S measurement from the
same oven.
n
n
Standard PGC5007B total sulfur analyser.
§
§
The EPA has approved the use of a total sulfur
analyser for the H
2
S measurement provided it can
meet a 0 - 300 ppm measurement range. Since the H
2
S
content in fuel gas will always be less than the total
sulfur reported from the flare gas, this analyser can
also be used to confirm the H
2
S measurement.
§
§
Measurement can be made using the total sulfur analyser
system designed for the flare gas stream. Due to the
broad range of measurement, the total sulfur analyser
above can be used to assess compliance with the short
term 162 ppmv H
2
S concentration in the fuel gas.
§
§
Both sulfur measurements can be made within a single
analyser. One PGC5007B can satisfy the 0 - 300 ppm
H
2
S and the 1.1 - 1.3 times the maximum anticipated
total sulfur requirements.
§
§
Lower overall cost of ownership.
Net heating value
For the net heating value, a recommended analyser model is
PGC5000B (Btu measurement). There are direct measurements
of the hydrocarbons in the fuel gas and a net heating value is
calculated from the results.
n
n
Sample injection, hydrocarbon separation and
measurement using a multiport TCD.
n
n
The measurements are used to calculate the net
heating value of the fuel gas stream.
n
n
Chromatography designed to eliminate any potential
water interferences on the Btu value.
n
n
Multiple ASTM methods and GPA calculation
packages available.
n
n
Common analytical technology and hardware to the
PGC5007B total sulfur analyser.
n
n
Complete analytical solution for the entire flare
monitoring package.
n
n
Parallel method of analysis to the total sulfur (TS)
application.
Taking into account the data presented in Table 1,
application option one, based on two B class ovens
represents the most compact solution for meeting the
three measurements. Application option two outputs
the H
2
S as part of the total sulfur measurement. In both
cases, the second B class oven is dedicated to the Btu
calculation. Application option three distributes the
analysis among three independent ovens, for the
maximum measurement control and isolation. Dedicated
sample valves enable automatic switch to low, mid
and high measuring ranges. The PGC5000 series
provides a flexible platform, which allows different
application options for meeting the H
2
S, total sulfur and
Btu analysis.
Conclusion
Process gas chromatographs provide an efficient and accurate
solution for online and automatic sampling, and analysis of
flare effluents. Ensuring operational safety, measurement
accuracy and reliability, and low cost of ownership, this
analytical method has proven to be particularly useful in an
environment of increasingly stringent standards for process
heaters and flares at petroleum refineries.
Acknowledgement
The ABB Lewisburg Process Analytics Team also provided
contributions to this article.
Table 1.
Flare gas analysis – application summary
Application
option
Total sulfur application method H
2
S application method Btu
oven
Number of
ovens
1
Two internally switched ranges
Total sulfur = TS (0 - 5000 ppm)
Total sulfur = TS (5000 - 100%)
Other ranges possible to satisfy the
1.1 - 1.3 x requirement
Directly measured
component:
H
2
S (0 - 300 ppm)
Yes Two B ovens
2
Three internally switched ranges
H
2
S measured as TS (0 - 300 ppm)
Total sulfur = TS (300 - 5000 ppm)
Total sulfur = TS (5000 ppm - 100%)
Other ranges possible to satisfy the
1.1 - 1.3 x requirement
Measured as total sulfur
Reported H
2
S (0 - 300 ppm)
Yes Two B ovens
3
Two internally switched ranges
Total sulfur = TS (0 - 5000 ppm)
Total sulfur = TS (5000 ppm - 100%)
Other ranges possible to satisfy the
1.1 - 1.3 x requirement
Directly measured
component:
H
2
S (0 - 300 ppm)
Yes Three B
ovens
