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Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
MEASURING H2S IN CRUDE OIL FOR QUALITY CONTROL & TRANSPORTATION SAFETY
Wesley Kimbell Analytical Systems Keco
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 2
Why measure H2S in crude oil?
Safety Industrial Process Control
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 3
Why measure H2S in crude oil?
Safety
• Personnel protection
• Transportation (rail, roads, pipelines)
Industrial Process Control
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 4
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 5
Why measure H2S in crude oil?
•SafetyPersonnel protection
1. H2S gas is toxic and deadly2. Even H2S dissolved in crude is deadly
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 6
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 7
Why measure H2S in crude oil?
•SafetyPersonnel protection
1. H2S gas is toxic and deadly2. Even H2S dissolved in crude is deadly
Transportation3. Prevent car derailments4. Corrosion
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 8
Why measure H2S in crude oil?
•Industrial Process Control1.Meet product specifications
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 9
Why measure H2S in crude oil?
•Industrial Process Control1.Off-spec products2. Protect process equipment
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 10
Why measure H2S in crude oil?
•Industrial Process Control1.Off-spec products2.Industrial process control3.Environmental concern
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 11
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 12
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 13
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 14
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 15
Methods of sampling
Headspace concentration function of:
1. Saturation time/volume2. Temperature3. Vapor pressure of analyte4. Concentration of analyte
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 16
Methods of sampling
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 17
Methods of sampling
Headspace
Crude Oil H2S
H2S
H2S
H2S
H2SH2S
H2S
H2SH2S
H2S
H2S
H2S
H2S
Proportionalconcentration
H2S
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 18
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 19
Methods of sampling
Carrier / Stripping Gas In
Crude Oil In
Crude Oil to Drain
Stripped H2S to Detector
~ 3 to 4 feet
Str
ipp
ing C
olu
mn
Headspace stripping column
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 20
Methods of sampling
Carrier / Stripping Gas In
Crude Oil In
Crude Oil to Drain
Stripped H2S to Detector
~ 3-4 feet
Str
ipp
ing C
olu
mn
Headspace stripping column
Drawbacks• Suffers from liquid
“carry-over”
• Cleaning requirements
• Many moving parts = more maintenance
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 21
Methods of sampling
Membrane technology (proprietary)
Sample Transfer Stripper™with ASI Membrane Technologiesby
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 22
Methods of sampling
Membrane technology (proprietary)
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 23
Methods of sampling
Membrane technology (proprietary)
ASI MembraneTechnology
Headspace
Crude Oil H2S
H2S
H2S
H2S
H2SH2S
H2S
H2SH2S
H2S
H2S
H2S
H2S
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 24
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 25
Methods of sampling | Comparison
Sampling Technology: Sample Transfer Stripper™ (STS)with exclusive ASI Membrane Technologies
Headspace stripping column
Principles incorporated Henry’s Law & proprietary methods Henry’s Law
Maintenance requirements LOW
STS Membrane creates ultra-clean sample for detector & physically blocks liquids from passing through to detector. Clean only one to two times per year typical
X HIGH Plagued by frequent liquid “carry-overs”. No physical block to prevent liquids from contaminating detector and gas sample lines. User reported constant cleaning & upkeep
Moving parts NONE No moving parts
X HIGHComplicated system using 85% more parts than STS Membrane
Cost of ownership Cost-Effective Minimal maintenance means less cost over time
X HIGHLong term expense due to cleaning & maintenance requirements
Accuracy HIGHSTS creates ultra-clean sample for analysis
X LOWSystem fouls as liquids frequently pass through to detector and gas sample lines requiring frequent cleaning
Range PPB, PPM and up to 100% ranges with high precision
X Low ppm ranges not reliable
Safety SAFE
Closed loop system for analysis and cleaning. No H2S exposure to user
X CAUTIONUser potentially exposed to residual H2S when cleaning is required
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 26
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 27
Method of Analysis
Colorimetric-Rateometric Tape Detector
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 28
Colorimetric Rateometric Tape DetectorAdvantagesSignificant 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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 29
Colorimetric Rateometric Tape DetectorImprovements 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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 30
Method of analysis | Comparison
NOTE: Data based on typical manufacturers published data
Measurement Technology
Colorimetric-Rateometric Tape Method
UV-Absorbance Spectrophotometry
TDL Absorbance Spectroscopy
Specific to H2S only
YES Innately and practically free of cross-interference. No false positives.
X NOProblems with mercaptans (including naturally occurring mercaptans), hydrogen, ammonia, etc. giving false positives
X NO Problems with moisture and other sulfur components giving false positives
Accuracy ± 2% of full scale typical ±10% at 0-10ppm FS X ± 4ppmv 0-10ppm FS
Sensor Zero Drift NO zero drift (automatic self zero, no zero air required)
X YES 5% in 24 hours for low ppm ranges. Requires zero gas.
X YES. Normally requires zero gas.
Sample pressure requirements
Pressure between 5 to 2,000 PSI acceptable
Normally requires minimum of ~150 PSI
Normally requires minimum of ~150 PSI
Range
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
Calibration Stability
Long-term even in demanding environments and process changes
X Unstable if process changes even slightly. Requires calibrations
X Unstable if process changes even slightly. Requires calibrations
Maintenance
LOWTape change only 3 to 4 times per year
X HIGH Optics / Flow cell require frequent cleaning
Mirrors tend to fog or produce haze. Requires cleaning
Consumables
Tape change every 3 to 6 months. ~$25 per tape reel
Zero gas required. Light source and scrubber materials require replacement. Costly.
Zero gas required. Scrubber (copper nanoparticle) replaced annually or more. Costly.
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 31
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 32
Method of Analysis
Colorimetric-Rateometric Tape Detector
The chemical formulation for reaction is as follows: H2OPb(OAc)2 + H2S →→→ PbS + 2HOAcWhite 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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 33
Method of Analysis
Colorimetric-Rateometric Tape DetectorThe 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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 34
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 35
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 36
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 37
Method of Analysis
Colorimetric-Rateometric Tape Detector
tape darkness
Y
80 PPM
40 PPM
Xtime
b
00
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 38
Method of Analysis
Colorimetric-Rateometric Tape Detector
tape darkness
Y
80 PPM
40 PPM
Xtime
b
00
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 39
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 40
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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 41
Case Study
Verification of Calibration MethodVolumetric 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 SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 42
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 MODEL 205 LABSample 1: 12:00 5.201 ppm/w 4 ppm/wSample 2: 15:00 15.02 ppm/w 14 ppm/w
ASI Prepared Standard 10 ppmw
10.07 ppm/w 14 ppm/w
Analytical Solutions by the SeaThe 60th Annual Symposium of the Analysis DivisionGalveston Island Convention Center, Galveston, Texas, USA; 26th – 30th April 2015
Slide 43
Case Study
ConclusionThe 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