Mercury Management
White Paper 2015
The Measurement & Monitoring Of Mercury
In Gas-Phase Hydrocarbon Process Streams
PEI (Mercury & Chemical Services Group) and EFGS
Total Mercury Sampling and Analysis Points
AG Absorber
Regen Gas K.O
To Acid Gas Incinerator or
Acid Gas Reinjection
Dehy Feed Sep.
Regen Gas to Fuel Gas System
MDEA Regen
To AGRU Train
To Waste Water
Mercury Removal
Flash
Drum
To Waste Water
Feed Separator
Condensate
Compression
Stabilizer Column
To Liquefaction
Slug Catcher
Feed Stabilizer
Condensate
Storage
Mixing Drum
To Waste Water
MEG Compression
To Waste Water
T = 1.3 C
P = 9800 kPa
Rich MEG Flash
MEG
Storage
MEG Regen Column
2 x 50% Stream Paths
MEG Compression
Lean MEG
Copyright © 2015 Portnoy Environmental, Inc.
PEI (Mercury & Chemical Services Group) and Alliance Partner EFGS
Since 2005 PEI’s Mercury and Chemical Services Group (PEI) and Eurofins Frontier Global Sciences (EFGS)
have worked on the development of improved sampling and analysis methods for the measurement and
monitoring of mercury in natural gas and gas-phase process streams. This white paper presents an overview
of the current industry standard methods for the measurement of mercury in natural gas and gas-phase
process streams. An improved sorbent trap method based on the modification of a USEPA (United States
Environmental Protection Agency) method is also presented and compared to the current industry standard
methods. PEI and EFGS will continue to advance gas sampling technology and methods with particular
focus in the sampling of natural gas streams and gas-phase process streams at or close to the HDP and also
continue to focus on functional and molecular speciation of hydrocarbon process streams.
GLOBAL MERCURY BELTS & HOT SPOTS
GLOBAL CRUDE OIL MERCURY CONCENTRATIONS
ALGERIA 13.3 µg/kg
THAILAND
66.5 µg/kg
VIET NAM
ASIA
CANADA 2.1 µg/kg
19.5 µg/kg
NORWAY
EUROPE 8.7 µg/kg
ARGENTINA 16.1 µg/kg
COLUMBIA
3.4 µg/kg
SOUTH AMERICA 5.3 µg/kg
ALASKA 6 µg/kg
CALIFORNIA 11.3 µg/kg
TEXAS 3.4 µg/kg
LOUISIANA 9.9 µg/kg
GOM 2.1 µg/kg
593 µg/kg
220.1 µg/kg
RECENTLY DISCOVERED MERCURY HOT SPOTS +
NATURAL GAS MERCURY CONCENTRATIONS
Known Mercury Belts & Hot Spots
Recently Discovered Mercury Hot Spots
GOM Deep Shelf Gas 500 µg/Sm³
5 µg/Sm³
U.S. Mid-Continent
Western Sedimentary Basin 2 µg/Sm³* (Additional Data Pending)
Northwest Shelf >500 µg/Sm³
Marcellus Shale >1 µg/Sm³
Utica Shale >1 µg/Sm³
Introduction
The distribution of mercury throughout hydrocarbon processing systems varies and requires significant
understanding and planning prior to implementing inspection and maintenance activities. PEI and EFGS
have gained extensive recent experiences in the management of mercury across the petroleum industry
including upstream oil and gas operations, gas gathering, processing and transmission operations, and crude
oil refining operations in the Gulf of Mexico, the Gulf of Thailand, throughout the United States, Alaska,
Canada, the Middle East and Australia.
Improvements in measurement and monitoring methods for assessing mercury in process streams provide
increased confidence in measurement precision and accuracy verified with a robust well defined numerical
data quality performance criteria. Mass balance/flux studies, mercury mapping/partitioning studies and
long term monitoring programs in refineries, gas processing plants, and gas gathering systems, have led to
the development of an improved understanding of the dynamics of mercury accumulation in oil and gas
processing equipment and facilities. Understanding accumulation, distribution and the sorption dynamics
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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of mercury throughout process is instrumental in the application of improved chemical decontamination and
waste management techniques used during plant turnarounds, the clean out of gas processing equipment,
and in the decontamination of downhole equipment during well intervention operations.
Mercury in Hydrocarbons Processing Plants
Mercury is a naturally occurring trace constituent of crude oil, natural gas, and natural gas condensate.
Virtually all geologic hydrocarbons contain measurable quantities of mercury. The concentration of mercury
in natural gas and associated liquids varies with geology and reservoir conditions with high concentrations
occurring in SE Asia (Thailand and Indonesia), North Africa (Algeria), Egypt, South America (Venezuela,
Bolivia), China, and the Netherlands and Australasia. Certain oil and gas reservoirs in the United States,
including at least one located in the Gulf of Mexico (deep shelf gas), are known to produce natural gas and
condensate with mercury concentrations that are orders of magnitude greater than those of typical gas
reservoirs. The discovery of mercury in hydrocarbons associated with several basins in the U.S. and Canada
is a relatively new occurrence and even in trace concentrations presents complicated health risks, environmental risks, and hydrocarbon processing risks to NGL and LNG plants.
Sampling and analysis methods are critical in determining a management approach and understanding risks
to personnel, products, and process. Mercury is scavenged by carbon steel and is adsorbed/chemisorbed
into the interfacial surfaces and can complex into the scale/metal grain boundary surface requiring special
chemistry and chemical application methods for mercury process system decontamination. In natural gas,
mercury may be present in elemental form and in an adsorbed state on particulates entrained in the gas
stream. In hydrocarbon liquids (e.g., gas condensate), mercury compounds may be present in the dissolved
state and again in an adsorbed state with suspended particulates. Glycol is used to separate the moisture
from the raw natural gas and during the separation process, glycol is in two different stages. In one stage
the glycol contains little or no water (lean glycol). The other stage is after the glycol has absorbed moisture
from the natural gas and in this stage is referred to as rich glycol. Recent experience from mercury mapping
projects throughout the U.S., Asia and Canada
An important part of effective mercury
indicate glycol regen streams can be highly concentrated with mercury and often flow to a thermal
management involves use of Mercury
oxidizer or directly to atmosphere. PEI and EFGS
Removal Units (MRUs). MRU performance
have developed methods and equipment for measur-
monitoring is conducted with the use of
ing mercury in this low pressure stream to quantify
advanced sampling methods intended to
quantify total mercury in gas phase streams,
mercury released to atmosphere from processing
operations.
based on EPA Methods 30B which provides
Hydrocarbon processing facilities (oil and gas produc-
the highest QA/QC protocol available.
tion equipment, gas processing plants, refineries and
Precise data is especially important when
petrochemical manufacturing facilities) that handle
assessing mercury levels in LNG facilities.
hydrocarbons with elevated mercury concentrations
are subject to an increased risk for serious occupational exposure, damage to aluminum process
equipment and the poisoning of precious metal catalysts. The presence of mercury in LNG and NGL plant
feeds and the intermittent performance of mercury removal equipment may suggest the possibility of
mercury deposition in aluminum heat exchangers. Even at low to moderate concentrations, mercury will
accumulate in processing equipment and can cause increased risks to personnel and cryogenic process
equipment.
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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Sample Point Design
The collection of representative samples is one of the most important steps in
producing analytical results that meet project data quality objectives and
accurately report mercury concentrations. The selection of the sample point
locations and the design of the sample point/probe are key components of a
sampling approach that will facilitate the collection of representative samples.
The gas sample should be collected via an insertion type sample probe located
well away from any fittings or appurtenances that may disturb laminar flow. The
industry standard rule of thumb is: Collect the sample at a distance of five (5)
inside pipe diameters away from 90° tube turns, valves, and any other discontinuities. The tip of the insertion probe should be inserted well away from the
walls of the process piping, the rule of thumb is in the middle one-third of the
process pipe. Any pressure reductions (through valves, regulators, reducers or
other fitting) should be designed so as to minimize Joule-Thompson cooling.
Additionally, the sample point entry valve should be located on the top of a
horizontal pipe run to minimize the potential for debris or liquids to enter the
sample probe. Portable insertion probes are typically used for short term
assessments of mercury in natural gas and process streams. The probe as well
as the entire sample train should be decontaminated to less than 10 ng/Sm³
The industry standard
rule of thumb is: Collect
the sample at a distance
of five (5) inside pipe
diameters away from 90°
tube turns, valves, and
any other discontinuities.
The tip of the insertion
probe should be inserted
well away from the walls
of the process piping, the
rule of thumb is in the
middle one-third of the
process pipe.
before installation at each sample point. PEI and EFGS go through a great deal
of effort to ensure sampling equipment and systems are blanked and verified to
<10 ng/Sm³ prior to deployment on new sampling projects.
Table 1: Typical Insertion Probe Design Specifications
Material: Stainless Steel
Maximum Operating Pressure: 2500 PSIG Maximum Operating Temperature: 225°F
Internal Coating: Sulfinert™
Pipe Connections: 1-inch NPT or 1/2-inch NPT
Sample Point Entry Valve: Minimum diameter, 1-inch, full opening ball valve.
Integral Probe Regulator:
A.
B.
Maximum Inlet Pressure: 3000 PSIG
Maximum Outlet Pressure: 500 PSIG
Sample Probe Tip: A liquid exclusion type, sintered stainless steel, Sulfinert™ coated
probe tip is used during the mercury sampling phase as a precaution to help minimize
the potential of a liquid slug pushing liquids into the sampling system.
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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Sample Collection Methods
Typically, mercury samples are collected from natural gas and process streams by the use of solid sorbent
sample traps. Two standard methods for the measurement of mercury in natural gas (ASTM D6350 and ISO
6978) both specify gold in the form of gilded silica as the solid sorbent for the collection, via amalgamation,
of mercury from a sample gas stream. After sample collection, both procedures specify a double amalgamation step whereby the mercury is thermally desorbed (sorbent trap heated to ~ 800° C) onto another gold
sorbent trap, and then thermally desorbed into the analyzer cell, and analyzed by either Cold Vapor Atomic
Fluorescence Spectrometry (CVAFS), or Cold Vapor Atomic Absorption Spectrometry (CVAAS). The sample
collection process is the most difficult and critical aspect of accurately quantifying mercury concentrations in
gas phase streams. Mercury can form amalgams with many metals and alloys commonly used in gas
sampling systems including stainless steel, brass, copper, nickel, chromium and aluminum.
Due to the potential for amalgamation, and the tendency for mercury to adsorb, and chemisorb to the
surface of stainless and carbon steel the potential for loss of mercury to sample wetted metal components of
sampling systems is significant. To minimize this loss, all sampling system components that come into
contact with the sample gas should be heated and have their sample-wetted surfaces coated with a high
temperature silica coating or be made of a material that is not reactive with mercury. Conditioning (flowing
sample gas through a system for a period of time before active sampling) of installed sampling equipment
including the sample probe is recommended as a means of minimizing mercury sorption/desorption effects
that can adversely affect representativeness of collected samples. Conditioning times may vary and depend
on many factors but typically range from 12 to 24 hours.
Table 2: Mercury Sampling & Analysis Methods for Gas Phase Matrices
» ASTM D 6350
Standard test method for
mercury sampling and analysis
in natural gas by atomic
fluorescence spectroscopy.
» ISO 6978
» EPA METHOD 30B
Natural Gas, determination
of mercury, Part 3: Sampling
of mercury by amalgamation
on gold/platinum alloy.
Determination of total vapor
phase mercury emissions
from coal fired combustion
sources using carbon
sorbent traps.
While both of these methods perform reasonably well, they lack a well defined QA/QC component for the
validation of the precision and accuracy of the field sampling procedures. Also, since the double amalgamation process results in the desorption of all of the collected mass from a single trap into the analyzer at once,
the sampler must limit the amount of mercury mass loading on the trap so that the upper range of the
analytical instrument is not exceeded. This limits the sample time and the sample volume.
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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PEI and EFGS have used EPA 30B
independently and in conjunction
with both ISO 6978 and ASTM D6350
methods on over 100 sites globally
(upstream, midstream and at
downstream processing plants).
Modified EPA Method 30B
Sampling of potentially wet gas streams is encountered in upstream processing environments such that
sampling and analytical methods require consideration to generate precise gas-phase mercury measurements. A combination of two sampling and analysis methods can help insure accurate and reliable results.
An effective approach is to use ISO Method 6978-3, using gilded silica bead sorbent traps with onsite
analysis, and a modified version of EPA Method 30B using chemically impregnated activated carbon sorbet
sample traps with offsite analysis. Since gilded silica sample traps are mass limited and can be affected
negatively by hydrogen sulfide, a series of gold samples traps run as simultaneous duplicates with breakthrough traps are recommended to determine mercury mass loading and sample durations for the more
stable long term carbon sample traps. Upon completion of sampling, Method 30B carbon sample traps are
analyzed offsite using acid digestion analysis via EPA Method 1631. Data is subsequently assimilated and
integrated with field measurements and laboratory data to calculate total mercury concentrations and
associated QA/QC parameters (see table 4 and 5).
The method, referred to as Modified Method 30B is based on the EPA reference method (30B) for the measurement of total vapor phase mercury in flue gases. The Modified EPA Method 30B was developed by the PEI-EFGS
team to provide industry clients with a method that:
• Includes a rigorous, performance based QA/QC protocol that validates the accuracy and precision
of the sample collection procedures
• Utilizes sorbent traps with an increased mercury loading capacity useful for continuous monitoring
through the collection of long term samples that provide an integrated average mercury concentration
• (7-30 days) samples depending on mercury mass loading rates and other operational factors
• Minimizes the loss of mercury to sampling system components
• Is highly portable and robust enough for deployment at remote locations and in harsh weather conditions
• And is relatively unaffected by gas stream contaminants such as H2S, CO2, and hydrocarbon mists
PEI and EFGS have used EPA 30B independently and in conjunction with both ISO 6978 and ASTM D6350
methods on over 100 sites globally (upstream, midstream and at downstream processing plants).
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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Table 3: Features of the Modified Method 30B
»
»
»
»
»
Robust QA/QC protocol with numerical performance criteria (Table 4) for the evaluation of the precision and
accuracy of the sample collection process. NIST traceable spiked sorbent traps.
Sorbent media with increased mass loading capacity, unaffected by common natural gas contaminants such as
acid gases, H2S scavengers and corrosion inhibitors as well as entrained hydrocarbon mists
Long-Term Sampling Capability: Large mercury loading capacity (up to 50,000 micrograms per trap) allows for
a longer sampling period and a larger total volume of sample gas. Improved representativeness.
Acid digestion of carbon based traps allows multiple analytical runs of the sample, and the ability to archive the
sample extract for future analysis. Gold trap samples allow for one analytical run only.
Streamlined sample collection procedures, which is one of the primary advantages of the Modified Method 30B.
This approach eliminates the expense and effort associated with the setup, calibration and maintenance of an
analyzer in the field.
The PEI-EFGS Team
The PEI-EFGS team began field testing the method in 2005 on natural gas production platforms offshore
Texas and natural gas collection and transmission lines both offshore and onshore extending from South
Texas to Alabama. To date the Modified Method 30B has been used in natural gas fields throughout the U.S.
Asia and Australia. Modified Method 30B has also been used extensively in gas processing plants and
refineries including, California, Texas, New Mexico, Wyoming, Alaska, Canada, and Saudi Arabia.
Sorbent Sample Traps for Total Mercury and Functional
Speciation of Mercury
EFGS custom makes carbon type traps with National Institute of Standards and Testing (NIST) traceable
mercury mass spiked sections. The analytical system used is a sorbent trap acid digestion method based on
the principles of EPA Method 1631 (proven over 17 years of laboratory testing). Recently PEI/EFGS have
been using selective capture functional speciation sorbent sample traps using a modified version of EPA
30B. This modified version employs a particulate trap and a specialized sorbent trap designed to selectively
capture oxidized gaseous mercury and a sorbent trap to selectively capture elemental gaseous mercury.
Functional speciation of mercury in gas phase streams includes a) particulate bound mercury (PHg), b)
elemental mercury and c) ionic mercury. Functional and molecular speciation of mercury in process streams
is critical to developing appropriate mercury management plans and MRU design.
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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Production Flow Tests and Drill Test
Sampling and Analysis
Accurate concentrations of mercury in reservoir fluids are important to
process and facility design (production platforms, FPSOs and LNG
plants). The exact concentration of mercury in newly discovered
reservoirs is often under reported. Measurements of mercury at
the surface during flow test may not reflect actual concentrations
since tubing and other metallic surfaces are not equilibrated but
more importantly sampling equipment and methods may not be
Mak2 system depicted during molecular speciation (DMHg)
sampling during a dehydrator regen cycle. PEI uses proprietary
selective capture sorbent sample traps for DMHg speciation
sampling and analysis.
designed to minimize the chemical effects of mercury during the
sampling process. Additionally, well flow test equipment may
contribute to biased high mercury concentrations depending on
duration of use, location, mercury sorption loading of interior
process surfaces and other factors. To obtain precise representative
samples an integrated average mercury concentration measured by
collection of a larger sample volume using heated (250 °F) mercury
inert wetted sampling components with accurate volumetric measurement is required. Since gilded silica quartz sample traps are
affected negatively when used in upstream sampling environments
carbon sorbent sample traps that are unaffected by hydrogen sulfide
and other gas contaminates are recommended (see Table 4 –
modified EPA 30B).
Table 4: Three Section Sorbant Trap
MODIFIED METHOD 30B: Three Section Sorbent Trap
A-Section
B-Section
C-Section
QA/QC Performance Criteria
A-Section
B-Section
C-Section
Duplicates
QA/QC Test or
Specification
Primary Collection
Breakthrough
Spiked
(Field Recovery Test)
Duplicate Agreement
Acceptance
Criteria
95% of Total
Collected Mass
≤ 10% of A-Section Hg Mass
For Hg concentration > 1 µg/dcm
Average Recovery Between
75% and 125% for Hg(0)
≤ 10% RD mass for Hg
concentration > 1 µg/dcm
≤ 20% of A-Section Hg Mass
For Hg concentration ≤ 1 µg/dcm
≤ 20% RD or 0.2 µg/dcm
absolute difference for Hg
concentrations ≤ 1 µg/dcm
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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Table 5: Sorbent Trap Mercury Sampling Methods Comparison
Feature Comparison
Modified Method 30B
ISO 6978
ASTM D6350
Analytical Detection
Method
Acid DigestionCVAFS
CombustionCVAAS
Thermal DesorptionCVAFS
Thermal DesorptionCVAFS
Lower Detection Limit
0.001 µg/scm
0.001 µg/scm
0.001 µg/scm
0.001 µg/scm
Number of Analyses
From One Sample
Multiple
1
1
1
Sample Collection
Phase QA/QC
Yes
Yes
No
No
NIST Traceable Standard
Yes
Yes
No
No
Sorbent Trap Hg Mass
Loading Limit
No limit (dilution
of extract)
No limit
Limited by instrument
saturation
No limit
Sample Collection
Duration
8–168+ hours,
depending on
Hg loading
8–168+ hours,
depending on
Hg loading
Limited by Hg mass
loading (typically
less than 4 hours)
Limited by Hg mass
loading (typically
less than 4 hours)
Sample Gas Volume
Up to 10,000
liters
Up to 10,000
liters
<500 liters
<500 liters
Analysis On-site
No
Yes
Yes
Yes
PEI Sampling Systems and Equipment
The PEI-EFGS team uses the Mak2™ Mercury Sampling Systems manufactured by PEI in the U.S., U.K. and
Thailand. The Mak2™ Mercury Sampling Systems are designed and manufactured expressly for the hydrocarbon processing industry for the collection of mercury samples from high-pressure gas-phase process
streams. Mak2™ systems meet all of the requirements for mercury sampling equipment specified in the
most recent versions of ASTM (American Society of Testing Methods), ISO (International Standards Organization) and EPA standard methods for the sampling and analysis of mercury. In addition, the procedures and
equipment that PEI uses are consistent with those procedures detailed and recommended in the Gas
Research Institute’s publication GRI-94/0243.2.
The Measurement & Monitoring Of Mercury In Gas-Phase Hydrocarbon Process Streams
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Each Mak2™ Sampling Unit Consists of Four Primary Components:
1.
A portable insertion type sampling probe (stainless steel, Sulfinert™ treated, 2500 psig MAOP)
2.
A heat-traced Sulfinert™ treated sample gas line (1/4-inch stainless steel)
3.
A heated sampling enclosure consisting of three sample trains with heated pressure regulation and
sampling manifold, sample train control valves, primary and secondary bypass, and Class 1
Division 1 heater and thermostat with explosion proof connectors and power cords
4.
A sample gas metering unit consisting of precision control flow meters, calibrated dry gas meters
and ¼ inch braided stainless steel Teflon™ lined hoses for connection to the heated sampling enclosure
All wetted surfaces of the sampling apparatus are treated with Sulfinert™ coating, a high-temperature silica
coating process designed to minimize the sorption or adherence of mercury to the sample-wetted surfaces. For
safety purposes all electrical components (heated sampling enclosure, regulators, and heat traced sample lines)
are rated for Class 1 Division 1 service.
Mak2™ Deployment
PEI has deployed 2 each complete Mak2 mercury sampling systems and CVAFS analyzers to our alliance partners
CR Asia, Rayong Thailand base of operations and CR Australia Perth facility for use throughout southeast Asia and
Australia (including offshore assets throughout the northwest shelf).
Mercury & Chemical Services
Ron Radford
Dr. Darrell Gallup
Bob Brunette
Vice President (MCS Group)
Technical Director
Vice President
+1 (713) 503-6803
+1 (707) 480-5508
+1 (206) 660-7307
+66 098 495 5474
[email protected]
RobertBrunette@eurofinsus.com
[email protected]
www.pei-tx.com
www.frontiergeosciences.com
www.pei-tx.com
Copyright © 2015 Portnoy Environmental, Inc. All Rights Reserved.
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