MEASURING H2S IN CRUDE
OIL FOR QUALITY CONTROL &
TRANSPORTATION SAFETY
Wesley Kimbell
Analytical Systems Keco
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Why measure H2S in crude oil?
Safety
Industrial Process
Control
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 2
Why measure H2S in crude oil?
Safety
• Personnel
protection
• Transportation
(rail, roads,
pipelines)
Industrial Process
Control
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 3
Why measure H2S in crude oil?
Safety
• Personnel
protection
• Transportation
Industrial Process
Control
• Meet product
specifications
• Protect process
equipment
• Environmental
concern
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 4
Why measure H2S in crude oil?
•Safety
Personnel protection
1. H2S gas is toxic and deadly
2. Even H2S dissolved in crude is deadly
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 5
H2S CHARACTERISTICS
•Gas with rotten egg smell
•Specific gravity: 1.1895 vs air
•LEL 4.3%, UEL 46%
•Highly corrosive
•Toxic
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 6
Why measure H2S in crude oil?
•Safety
Personnel protection
1. H2S gas is toxic and deadly
2. Even H2S dissolved in crude is deadly
Transportation
1. Prevent car derailments
2. Corrosion
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 7
Why measure H2S in crude oil?
•Industrial Process Control
1.Meet product specifications
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 8
Why measure H2S in crude oil?
•Industrial Process Control
1.Off-spec products
2. Protect process equipment
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 9
Why measure H2S in crude oil?
•Industrial Process Control
1.Off-spec products
2.Industrial process control
3.Environmental concern
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 10
How do we measure H2S in crude oil?
Direct optical measurement of crude oil is
difficult:
•Crude oil is opaque in nature
•Complex compositional characteristics
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 11
How do we measure H2S in crude oil?
Question: What is the best method to
measure H2S in liquid samples like crude
oil?
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 12
How do we measure H2S in crude oil?
Answer: Measure the headspace
• Upon saturation, the headspace
concentration and the liquid sample
concentration are proportional
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 13
How do we measure H2S in crude oil?
Henry’s Law:
"At a constant temperature, the amount of a given gas that dissolves
in a given type and volume of liquid is directly proportional to the
partial pressure of that gas in equilibrium with that liquid."
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 14
Methods of sampling
Headspace concentration
function of:
1. Saturation time/volume
2. Temperature
3. Vapor pressure of analyte
4. Concentration of analyte
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 15
Methods of sampling
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 16
Methods of sampling
H2 S
Headspace
H2 S
H2S
H2 S
H2 S
H2 S
H2 S
Proportional
concentration
H2 S
Crude Oil
H2 S
H2 S
H2 S
H2 S
H2 S
H2 S
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 17
Methods of sampling
Goal: Extract the ‘headspace’ vapor of the
liquid sample for analysis in the gas phase
Two methods:
•‘Headspace’ stripping column
•Sample Transfer Stripper™ with
ASI Membrane Technologies (proprietary)
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 18
Methods of sampling
Headspace stripping column
Crude Oil In
~ 3 to 4 feet
Stripping Column
Stripped H2S to Detector
Crude Oil to Drain
Carrier / Stripping Gas In
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 19
Methods of sampling
Headspace stripping column
Crude Oil In
~ 3-4 feet
Stripping Column
Stripped H2S to Detector
Crude Oil to Drain
Drawbacks
• Suffers from liquid
“carry-over”
• Cleaning
requirements
• Many moving parts =
more maintenance
Carrier / Stripping Gas In
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 20
Methods of sampling
Membrane technology (proprietary)
Sample Transfer Stripper™
with ASI Membrane Technologies
by
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 21
Methods of sampling
Membrane technology (proprietary)
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 22
Methods of sampling
Membrane technology (proprietary)
H2 S
Headspace
H2 S
H2 S
H2 S
H2 S
H2 S
H2 S
ASI Membrane
Technology
H2 S
Crude Oil
H2S
H2S
H2 S
H2S
H2 S
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 23
Methods of sampling
Membrane technology (proprietary)
• Membrane physically blocks mists from
headspace vapor
• Prevents fouling of detector
• Prevents liquid “carry-over”
• Radically reduced maintenance
• Prevents in-gassing / out-gassing of H2S
• Maintains compositional representation of
the headspace vapor
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 24
Methods of sampling | Comparison
Sampling Technology:
Sample Transfer Stripper™ (STS)
with exclusive ASI Membrane Technologies
Principles incorporated
Maintenance requirements
Henry’s Law & proprietary methods
LOW
Moving parts
Cost of ownership
Accuracy
Range
Safety
Headspace stripping column
Henry’s Law
X HIGH
Plagued by frequent liquid “carry-overs”. No
STS Membrane creates ultra-clean sample for
physical block to prevent liquids from
detector & physically blocks liquids from passing contaminating detector and gas sample lines.
through to detector. Clean only one to two times User reported constant cleaning & upkeep
per year typical
NONE
X HIGH
No moving parts
Complicated system using 85% more parts than
STS Membrane
Cost-Effective
X HIGH
Minimal maintenance means less cost
Long term expense due to cleaning &
over time
maintenance requirements
HIGH
X LOW
STS creates ultra-clean sample for analysis System fouls as liquids frequently pass through
to detector and gas sample lines requiring
frequent cleaning
PPB, PPM and up to 100% ranges with high X Low ppm ranges not reliable
precision
SAFE
X CAUTION
User potentially exposed to residual H2S when
Closed loop system for analysis and cleaning. No cleaning is required
H2S exposure to user
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 25
Method of Analysis
Difficulty of quantifying H2S in crude oil
• Crude oil is compositionally complex
• Many components interfere with H2S:
Aromatics, SO2, ethyl-mercaptan, methyl-mercaptan
and other sulfur compounds
• Crude composition changes not uncommon
• Low ppm especially a challenge
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 26
Method of Analysis
Colorimetric-Rateometric Tape Detector
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 27
Colorimetric Rateometric Tape
Detector
Advantages
Significant advantages with tape
method
• Only method inherently specific to H2S
• No complicated chemometric modeling
needed
• No need to “trick” system to minimize
interferences
• Measures only H2S, no matter the
compositional background
• Inherently accurate—measure low ppb,
ppm to 100% H2S without false
positives even in crude oil headspace
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 28
Colorimetric Rateometric Tape
Detector
Improvements to design
Significant technological advancements
to Tape Method:
•
•
•
•
•
•
Improved tape drive system
75% less parts
3-6 month tape life
Reliable and rugged
Remote diagnostics & troubleshooting
Simplest detection & most straight
forward method available
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 29
Method of analysis | Comparison
Measurement
Technology
Specific to H2S only
Accuracy
Sensor Zero Drift
Sample pressure
requirements
Range
Calibration Stability
Maintenance
Consumables
Colorimetric-Rateometric
Tape Method
UV-Absorbance
Spectrophotometry
TDL Absorbance
Spectroscopy
YES
Innately and practically free of
cross-interference. No false
positives.
X NO
Problems with mercaptans
(including naturally occurring
mercaptans), hydrogen, ammonia,
etc. giving false positives
X NO
Problems with moisture and other
sulfur components giving false
positives
± 2% of full scale typical
NO zero drift (automatic self zero,
no zero air required)
Pressure between 5 to 2,000 PSI
acceptable
±10% at 0-10ppm FS
X YES 5% in 24 hours for low ppm
ranges. Requires zero gas.
Normally requires minimum of ~150
PSI
X ± 4ppmv 0-10ppm FS
X YES. Normally requires zero gas.
PPB, PPM and up to 100%
ranges with high accuracy
X Low ppm ranges not reliable. PPB
range not possible
X Low ppm ranges not reliable. PPB
range not possible
X Unstable if process changes even
slightly. Requires calibrations
X Unstable if process changes even
slightly. Requires calibrations
X HIGH
Optics / Flow cell require frequent
cleaning
Zero gas required. Light source and
scrubber materials require
replacement. Costly.
Mirrors tend to fog or produce haze.
Requires cleaning
Long-term even in demanding
environments and process
changes
LOW
Tape change only 3 to 4 times
per year
Tape change every 3 to 6 months.
~$25 per tape reel
Normally requires minimum of ~150
PSI
Zero gas required. Scrubber (copper
nanoparticle) replaced annually or
more. Costly.
NOTE: Data based on typical manufacturers published data
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 30
Method of Analysis
Colorimetric-Rateometric Tape Analyzer
Detection of H2S concentrations by the use of H2S sensing tape
is achieved by exposing the film to an H2S sample through an
aperture in the sample flow system, called the sample
chamber. The reaction of photographic film to the light is
analogous to the way that chemically saturated H2S sensing tape
reacts to hydrogen sulfide
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 31
Method of Analysis
Colorimetric-Rateometric Tape Detector
The chemical formulation for reaction is as follows:
H2 O
Pb(OAc)2 + H2S →→→ PbS + 2HOAc
White
colored
This reaction has three characteristics which allow it to be applied
with unique analytical precision:
1. The reactants are colorless (white).
2. The product (PbS) is colored.
3. In more than a century of use, hydrogen sulfide is the only
practical reactant found that produces a colored product on
lead acetate (Pb(OAc)2 tape.
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 32
Method of Analysis
Colorimetric-Rateometric Tape Detector
The rate (r) of this reaction (forming PbS) is as follows:
r = k Pb(OAc)2x H2S
Where k, the proportionality factor, is called the rate constant.
NOTE: The very large (more than 1000 times) concentration of Pb(OAc)2
on the H2S sensing tape simplifies the reaction as follows:
[Pb(OAc)2]0 = [Pb(OAc)2]1 – PbS1 = K2 (<.1%)
Therefore, rn = kk2(H2S - PbSn)
For simplicity:
kk2 = K
rn = K(H2S = PbSn)
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 33
Method of Analysis
Colorimetric-Rateometric Tape Detector
By maintaining a constant H2S concentration, with continuous flow of the
sample into the sample chamber, the rate of reaction equation is further
reduced to:
r = KH2S
Therefore, by maintaining the control conditions of:
1. A large quantity of Pb(OAc)2
2. Constant H2S concentration.
3. Sufficient moisture.
The rate of reaction (i.e. the rate of darkening) is linearly proportional
H2S concentration. Measuring the rate of darkening is therefore directly
equivalent to measuring the H2S concentration.
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 34
Method of Analysis
Colorimetric-Rateometric Tape Detector
The rate of reaction (i.e. the rate of darkening) is linearly proportional H2S concentration.
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 35
Method of Analysis
Colorimetric-Rateometric Tape Detector
In actual practice, the rate of darkening is determined by measuring the change in
darkness from second to second.
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 36
Method of Analysis
Colorimetric-Rateometric Tape Detector
80 PPM
tape
darkness
Y
40 PPM
b
0
0
X
time
The general equation for the lines of the graph above is:
y = ax + b
b is the zero drift or offset term in conventional equipment that is often adjusted to zero (zero
drift)
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 37
Method of Analysis
Colorimetric-Rateometric Tape Detector
80 PPM
tape
darkness
Y
40 PPM
b
0
0
X
time
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 38
Case Study
Measuring H2S for quality control
Location: In-plant study in Middle East
Participants: ASI Personnel, Customer Plant
Manager, Customer Lab Manager
Activity: Startup/commissioning and accuracy test
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 39
Case Study
Measuring H2S for quality control
Equipment:
Model 205
H2S in Crude Oil Analyzer
•
Sample Transfer Stripper™ with
ASI Membrane Technologies
(proprietary)
Colorimetric-Rateometric Tape Detector
•
Measuring Range: 0 to 80 ppm by wt.
•
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 40
Case Study
Verification of Calibration Method
Volumetric Blending Process
The calibration procedure calls for a known concentration of H2S, which is
injected into the crude sample in a container. This will cause the concentration
of H2S in the sample to read proportionally more based on the concentration
of H2S injected.
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 41
Case Study
Results
The model 205 H2S in Crude Oil Analyzer measured continuously while two
field samples were taken by lab personnel which were tested in the laboratory.
The cross reference of the readings of the analyzer and the lab results can be
seen below:
SAMPLE #/ TIME
Sample 1: 12:00
Sample 2: 15:00
ASI Prepared Standard 10
ppmw
MODEL 205
5.201 ppm/w
15.02 ppm/w
10.07 ppm/w
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
LAB
4 ppm/w
14 ppm/w
14 ppm/w
Slide 42
Case Study
Conclusion
The Model 205 H2S in Crude Oil Analyzer utilizing the membrane Sample Transfer
Stripper™ and colorimetric-rateometric tape method of detection was tested by the
plant laboratory specialists and found to be accurate.
The Volumetric Blending method of calibration was also verified for accuracy. Both the
plant engineers and Process Analyzer Engineer specialists along with ASI engineers
were very pleased with the testing method and the accuracy of the model 205 H2S in
Crude Oil Analyzer.
The Sample Transfer Stripper combined with Tape detector results in an accurate
and stable analyzer to measure H2S in crude oil:
• The analyzer maintains calibration long term (no chemometric modeling required)
• Field calibrations not required
• Zero gas not required
• Membrane stripper eliminates liquid carry over and cleanup
• Advancements in tape technology results in low maintenance
• Tape change required only 2-4 times annually
Analytical Solutions by the Sea
The 60th Annual Symposium of the Analysis Division
Galveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 43