pei-fgs hgmeasurement white paper 2012

Mercury Management White Paper 2012 The Measurement and Monitoring of Mercury in Natural Gas withSorbent Traps

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 associ-ated 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. Certain oil and gas reservoirs in the United States, including at least one located in the Gulf of Mexico, are known to produce natural gas and condensate with mercury concen-trations that are orders of magnitude greater than those of typical gas reservoirs. Hydrocarbon processing facilities (oil and gas production equipment, gas pro-cessing plants, refineries and petrochemical manufacturing facilities) that handle hydrocarbons with elevated mercury concentrations are subject to an increased risk for serious occupational exposure, damage to aluminum process equip-ment and the poisoning of precious metal catalysts. Even at low to moderate concentrations mercury will accumulate in processing equipment and can cause increased exposure risks during maintenance activities.

Since 2005 Portnoy Environmental, Inc (PEI) and Frontier Global Sciences (FGS) have worked on the development of improved sampling and analysis methods for the measurement and monitoring of mercury in natural gas. This white paper presents an overview of the current industry standard methods for the measurement of mercury in natural gas and other 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.

www.pei-tx.com [email protected]

White Paper 2012 The Measurement and Monitoring of Mercury in Natural Gas James H. Vickery, Jr.2


White Paper 2012 The Measurement and Monitoring of Mercury in Natural Gas James H. Vickery, Jr. 3

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 accu-rately 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 a 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 90º 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 pres-sure 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 mer-cury in natural gas and process streams. The probe as well as the entire sample train should decontaminated to less than 10 ng/scm before installation at each sample point.

Figure 1.

Portable Insertion Probe

Typical Insertion Probe Design SpecificationsMaterial: Stainless Steel

Maximum Operating Pressure: 2500 PSIG

Maximum Operating Temperature: 225˚ F

Internal Coating: Sulfinert™

Pipe Connections: 1-inch NPT or ½-inch NPT

Sample point entry valve: Minimum diameter, 1-inch, full opening ball valve.

Integral Probe Regulator: A. Maximum Inlet Pressure: 3000 PSIG B. Maximum Outlet Pressure: 500 PSIG (pressure reduction required for mercury sampling equipment)

Sample Probe Tip: A liquid exclusion type, sintered stainless steel, Sulfinert™ coat-ed 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.

Table 1.

Figure 3.

Sorbent Trap

Sampling System

Flow Indicator�Rotameter

Dry GasMeter

Pressure�Regulator

Spiking�Port

Sorbent�Trap

Primary�By-pass Valve Vent

Filter



Sample Collection Methods Typically, mercury samples are collected from natural gas by the use of a solid sorbent trap (Figure 2). 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 ~ 800º C) onto another gold sorbent trap, and then thermally desorbed into the ana-

lyzer 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 chemicsorb to the surface of stainless and carbon steel the potential for loss of mercury to sample wetted metal components of sampling systems (Figure 3) 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 silica type coating or be made of a material that is not reactive with mercury. Conditioning (flowing sample gas through the 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 the representativeness of the col-lected samples.

Figure 2.

Sorbent Traps:

(Top) Carbon based

sorbent, and gilded

silica sorbent

White Paper 2012 The Measurement and Monitoring of Mercury in Natural Gas James H. Vickery, Jr. White Paper 2012 The Measurement and Monitoring of Mercury in Natural Gas James H. Vickery, Jr. 5


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 Modified EPA Method 30B 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-FGS 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 (7–30 days) samples.• 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.

Mercury Sampling and Analysis Methods for Gas Phase Matrices

ASTM D 6350 ISO 6978 EPA Method 30B

Standard test method for mercury sampling and analysis in natural gas by atomic fluorescence spectroscopy.

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.

Table 2.

Features of the Modified Method 30BRobust 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 com-mon 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 advan-tages 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-FGS Team The PEI-FGS 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 in Wyoming, Colorado, West Texas, South Texas, Louisiana, Mississippi, and Ala-bama. The Modified Method 30B has also been used extensively in gas processing plants and refineries including, California, Texas, New Mexico, Wyoming, Canada, and Saudi Arabia.

Sorbent Traps FGS custom makes carbon type traps with National In-stitute of Standards and Testing (NIST) traceable spiked section mercury mass. The analytical system used is a sorbent trap acid digestion method based on the prin-ciples of EPA Method 1631. This method has 17 years of proven laboratory testing.

Table 4.

Table 3.

Modified Method 30B: Three Section Sorbent Trap

Mod. Method 30B: 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 ≤ 20% of A-Section Hg MassFor Hg concentration ≤ 1 µg/dcm

Average Recovery Between 75% and 125% for Hg(0)

≤ 10% RD mass for Hg concentration > 1 µg/dcm

≤ 20% RD or 0.2 µg/dcm absolute difference for Hg concentrations ≤ 1 µg/dcm

A-Section B-Section C-Section



Sorbent Trap Mercury Sampling Methods Comparison

Feature Comparison Modified Method 30B ISO 6978 ASTM D6350

Analytical Detection Method

Acid Digestion- CVAFS

Combustion-CVAAS

Thermal Desorption- CVAFS

Thermal Desorption- CVAFS

Lower Detection Limit

0.001 µg/scm

0.001 µg/scm

0.001 µg/scm

0.001 µg/scm

Number of Analyses From One Zample

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 (dilu-tion of extract)

No limit Limited by instrument saturation

Limited by instrument saturation

Sample Collection Duration

8 – 168+ hours, depend-ing on Hg loading

8 – 168+ hours, depend-ing 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

Table 5.



Figure 3.

MAK II™ Mercury

Sampling System

Flow Schematic

Sampling System and Equipment The PEI-FGS team uses the MAK II™ Mercury Sampling Systems manufactured by the PEI subsidiary, Measurement and Monitoring Solutions.

The MAK II™ Mercury Sampling Systems are designed and manufactured expressly for the natural gas industry for the collection of mercury samples from high-pressure natural gas. MAK II™ 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.

MAK II™ Sorbent Trap Sampling System

TO PLANT

SAMPLE GAS SUPPLY LINEPI

M

VENTS TOATMOSPHERIC STACK

PI TI TI

PI TI TI

PI TI TI

BYPASS LINE

SORBENTTRAP (TYP)

(CLASS 1 DIV 1 HEATED ENCLOSURE)

HEATED SAMPLING ENCLOSUREAND CONTROL PANEL

(FIREPROOF METERING ENCLOSURE)METERING PANEL

SAMPLE GAS VENT LINE

ADJUSTABLESAMPLE PROBE

D

D

D

FL

BYPASS LINE

��

FL

FL

FL

FL

M

M

M

Figure 4.

MAK II™ Sorbent Trap Sampling System



Each MAK II™ 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 (¼-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 con- nectors and power cords (see Figure 4); and, 4) A sample gas metering unit consisting of prec- sion control flow meters, calibrated dry gas meters and ¼-inch braided stainless steel hoses for con- nection to the heated sampling enclosure (Figure 4).

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 pur-poses all electrical components (heated sampling enclo-sure, regulators, and heat traced sample lines) are rated for Class 1 Division 1 service (Figure 3).

MAK II™ with Gold TrapsMAK II™ with Carbon Traps


Contacts

James ‘Vic’ Vickery

Vice President, and

Technical Director of Mercury

and Chemical Services Group

Portnoy Environmental, Inc.

1414 W. Sam Houston Pkwy. N.

Suite 170

Houston, TX 77043 USA

281-536-0899

www.pei-tx.com

[email protected]

Bob Brunette

Frontier Global Sciences, Inc.

11720 N. Creek Pkwy. N.

Suite 400

Bothell, WA 98011 USA

206-660-7307

www.frontiergeosciences.com/

[email protected]

Roberto Lopez-Garcia

Chief Scientist


London, England

44-7791904-977

www.pei-tx.com

[email protected]

Ron Radford

Director of Chemical

Cleaning Operations


1414 W. Sam Houston Pkwy. N.

Suite 170

Houston, TX 77043 USA

713-503-6803

www.pei-tx.com

[email protected]

The MAK II™ Mercury Sampling Systems have proven their reliability, precision and robustness in the toughest environments. The design includes features and components that make it the most reliable, maintenance free, easily operated, and flexible mercury in gas sampling system available in the industry.


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