hydrocarbon world

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Mercury and mercury compounds are found in all geologic hydrocarbons

including coal, natural gas, gas condensates and crude oil. As a result,

mercury can be distributed throughout hydrocarbon production,

processing and transportation systems. Mercury and mercury

compounds present health risks to personnel performing equipment

maintenance and inspection activities, environmental risks from

atmospheric emissions and wastewater effluents and process risks to

cryogenic equipment. Oil and gas producers and processors should

understand the risks and liabilities associated with produced mercury and

develop appropriate mercury management strategies for turnarounds

including mercury mapping, exposure and medical monitoring,

turnaround management and chemical decontamination plans.

The general perception of produced mercury in hydrocarbon processing

systems has changed over the last decade, as its effect on processes has

become better understood and the science and methods of detecting

and measuring mercury in various matrices and media have advanced.

Over the last seven years our understanding of the sorption dynamics of

mercury in steel pipe and effective chemical approaches for the removal

of mercury from steel has also advanced. Since 2005, members of

Portnoy Environmental, Inc. (PEI) Mercury and Chemical Services

Group have been engaged in mercury management programmes in

hydrocarbon processing and petrochemical facilities worldwide. As part

of our ongoing efforts to mitigate the risks associated with mercury

impacted hydrocarbon processing systems, PEI’s research and

development team has focused its efforts on the improvement of

mercury sampling and analysis technologies and the development

of chemical cleaning methods and products that are effective in the

removal of mercury. PEI has deployed these methods to monitor

and remove mercury from impacted process systems including subsea

piping, natural gas processing systems and petroleum refining systems.

Mercury in Hydrocarbons

Mercury is present as a contaminant in virtually all fossil fuels,

including oil and gas. Based on available data, reported levels of

mercury present in oil and gas are extremely variable, both between

and within geographical areas.1 Some of this variability may result

from inconsistent sampling and analytical techniques and some can be

attributed to variance in geological formations. This, however, does

not account for all variations, as there can be significant differences

within a single oil or gas field. In general, average mercury levels are

relatively low, although some reported values have been extremely

high. Recent studies have concluded that mercury emissions from the

oil and gas sector (oil burning boilers in petroleum refining) in the US

represents 7 % (approximately 11 tons) of the national total mercury

emissions (158 tons) most of which (73 tons) are attributed to coal

combustion.2 The large variability in mercury content may lead to a

greater need for controls in some regions in the oil and gas sector

where mercury levels are high in comparison with those areas with

lower mercury levels. Based on available data, the volume of oil and

gas produced, refined and used globally may result in significant

mercury emissions and releases, even though they are significantly

lower than those associated with coal combustion. Mercury emissions

from coal burning power plants will most likely be regulated soon and

it is likely that emissions from hydrocarbon processing will be included.

The concentration of mercury in crude oil, natural gas and associated

liquids varies with geological and reservoir conditions with high

concentrations occurring in Southeast Asia (Thailand and Indonesia),

North Africa (Algeria), Egypt, South America (Venezuela, Bolivia), China

and the Netherlands (see Figure 1).

Partitioning of Mercury in Oil and Gas

Mercury (Hg) is a highly volatile transition metal found in the environment

in trace quantities in both elemental form and as highly toxic

organomercury compounds.3 The speciation of mercury in crude oil has

been comprehensively reviewed elsewhere.4 In brief, the complex variety

of mercury species in oil can be separated into three broad categories:

volatile mercury (including elemental mercury and dialkyl mercury);

insoluble mercury and dissolved forms (including elemental mercury, dialkyl

mercury); and mono-alkyl mercury and loosely complexed ionic mercury.

Whereas crude oil contains a complex array of mercury species, most

of the mercury in natural gas is elemental mercury.5 Trace quantities of

Roberto Lopez-Garcia began his career as a researchassistant at PSAnalytical and currently holds a SeniorScientist position at Portnoy Environmental, Inc. (PEI)Mercury and Chemical Services Group. He is responsiblefor the development and application of measurementand monitoring technologies for mercury and toxicmetals in oil and gas processing facilities. Over the lastseven years he has focused on developing and providingsolutions for the management of mercury and toxic

metals in hydrocarbon processing facilities in North America, Europe, the Middle East,Thailand and South America. Mr Lopez-Garcia received a PhD in OrganometallicChemistry from the University of Nottingham in 2005.

E: [email protected]

Ron Radford co-manages the Mercury and ChemicalServices Group at PEI and is the Chemical CleaningDirector responsible for managing mercury managementand chemical decontamination programmes in the US andoverseas. He has 18 years of environmental remediation,consulting and industrial services experience providingspecialised services to the energy sector. He is responsiblefor managing projects/programmes including remedialconstruction, facility decontamination, regulatory

compliance programmes, chemical cleaning, toxic metals sampling and analysis,technology evaluations and remediation technology development.

E: [email protected]

a report by

Roberto Lopez-Garc ia1 and Ron Radford2

1. Chief Scientist, Portnoy Environmental, Inc. (PEI) Mercury and Chemical Services Group, London, UK; 2. Director of Chemical Cleaning Operations,

Portnoy Environmental, Inc. (PEI) Mercury and Chemical Services Group, Texas, US

Managing Mercury in Hydrocarbon Processing Plants During Turnarounds


H Y D R O C A R B O N W O R L D – V O L U M E 7 I S S U E 120

inorganic (including mercury chloride [HgCl2]), organic (including

dimethylmercury [Hg(CH3)2] and diethylmercury [Hg(C2H5)2]) and

organo-ionic compounds have been detected.5

The partitioning of elemental mercury and mercury compounds in gas

and petroleum processing is largely determined by their solubility and

physical properties. Mercury speciation in crude oil is complex with a

variety of species detected. The different species behave differently

during refining, with volatile forms partitioning into low-density fractions

such as liquefied petroleum gas (LPG) and thermally stable species that

resist volatilisation partitioning into high-density residual products such as

petroleum coke and wastewater. In natural gas, the mercury present

is almost always elemental, although trace amounts may be present as

organic complexes. Mercury in natural gas poses similar problems

to those experienced with oil during transport, storage and handling. The

solubility of mercury in petroleum liquids coupled with its volatility mean

that mercury and mercury compounds can contaminate essentially the

entire production, processing and petrochemical manufacturing systems.

Organic mercury compounds in produced gas, under normal operating

conditions, will partition to separated hydrocarbon liquids as the gas is

cooled. Therefore, if organic mercury were present in the reservoir,

it would be found primarily in condensates. Measuring dialkyl mercury

compounds in hydrocarbon liquids is complicated due to several aspects

of mercury chemistry that make it difficult to detect and quantify.

Mercury emissions and releases can occur during all phases of the

production, processing and refining of oil and gas as well as during

the use of the final products. Mercury releases can occur from the

discharge of produced water as well as from process vents and flares.

Mercury Management During Turnarounds

In hydrocarbon processing and petrochemical manufacturing, mercury in

process feeds can contaminate equipment and can segregate to sludge

and other waste streams. Steel piping and pressure vessels that are used

to transport and process produced fluids interact chemically with the

mercury species in the fluids they contain. Carbon steel is an excellent

scavenger of mercury and the appearance of mercury at downstream

processing facilities can be delayed by months or years due to scavenging

of elemental mercury by steel pipeline surfaces. In locations where

mercury is known to be present in produced reservoir fluids, rigorous

safety precautions are needed to detect mercury vapour that emanates

from steel vessels and pipes when opened for maintenance or inspection

purposes. A mercury-contaminated steel pressure vessel will emit

mercury vapour long after it has been ventilated and cleaned to remove

sludge and surface hydrocarbons. Opportunities therefore exist for

workers to be exposed to mercury and its compounds in routine repair,

maintenance and inspection activities and when handling process fluids

and waste materials. This, along with the obvious environmental issues

associated with mercury, underscores the need for comprehensive

mercury management strategies during plant turnarounds.

Prior to performing equipment maintenance and inspection on mercury

impacted process equipment during a turnaround or shutdown, it is

necessary to understand the type and distribution of mercury throughout

the plant. This is not always the case though; sometimes mercury is

discovered during a turnaround without the benefit of this understanding.

In these instances turnaround management teams can decide to: proceed

with the turnaround using high levels of personal protective equipment

(PPE), extensive exposure monitoring and reactive waste management

planning or postpone the turnaround until an understanding of the type

and distribution of mercury can be obtained. The latter option is preferred

but not always feasible. The required mercury management strategies in

both instances are similar and discussed in this article.

Mercury Mass Flow Assessments

It is helpful to have an understanding of how mercury can be

distributed in hydrocarbon processing systems, which also includes

an understanding of mercury chemistry and how mercury reacts with

steel surfaces. In hydrocarbon liquids, dissolved mercury occurs in its

elemental form (Hg°), as organic (dialkyl, monoalkyl) mercury – Hg(CH3)2,

Hg(C2H5)2, methylmercury chloride (HgCH3Cl) – and as inorganic

(HgCl2) forms. In addition, produced liquids and some process streams

contain suspended mercury compounds, such as mercury sulphide

(HgS), which can be a significant fraction of the measured total

mercury concentration. Temperature, pressure and chemical changes

13.3 μg/kgAlgeriaThailandVietnamAsiaCanadaNorwayEuropeArgentinaColumbiaSouth AmericaAlaskaCaliforniaTexasLouisianaGOM

593 μg/kg66.5 μg/kg

220.1 μg/kg2.1 μg/kg






GOM deep shelf gasUS Mid-ContinentWestern sedimentary basin

500 μg/Sm35 μg/Sm3

1 μg/Sm3 (additional data pending)

Global Crude Oil Mercury Concentrations

Known mercury belts and hot spots Recently discovered mercury hot spots

Recently Discovered Mercury Hot Spots and Natural Gas Mercury Concentrations

Figure 1: Global Mercury Belts and Hot Spots

GOM = Gulf of Mexico.


H Y D R O C A R B O N W O R L D – V O L U M E 7 I S S U E 1 21

throughout hydrocarbon processing systems allow mercury to change

from one chemical form to another.

Mercury mass flow assessments are used to quantify the gain or loss of

mercury across a plant or an entire process unit and each individual

process vessel. Analytical results from gas and fluid streams can identify

process vessels and groups of process vessels with process streams that

have elevated mercury concentrations and increased mercury mass gain or

loss, either accumulating mercury or adding mercury to the process fluids.

In some cases surrogate sample data may need to be used to complete

the mercury mass flow balance. Mercury mass flow assessments help

guide the turnaround team by providing mercury speciation and

distribution data that are used to develop mercury management plans,

exposure monitoring plans, chemical decontamination plans and waste

minimisation plans (solids, liquids and vapours). The photograph (see

Figure 2) depicts a process unit at a refinery where the mercury mass and

distribution were determined before the turnaround, providing valuable

data needed to complete the turnaround safely and on schedule.

Mercury Exposure Monitoring

Oil and gas processing equipment and appurtenances contaminated

with mercury require stringent safety precautions and exposure

monitoring procedures to mitigate risks to personnel during inspection

and maintenance activities. For example, one square metre of steel

holding 1 gram (g) of mercury can potentially contaminate 40,000

cubic metres (m3) of air to a concentration >25 µg/m3 of mercury.6 It is

easy to underestimate mercury exposure risks before and during

turnarounds for several reasons:

• Precise mercury concentrations in process streams are often unknown.

• Speciated forms of mercury in process streams and products are

rarely known.

• Mercury toxicity is gradual and generally produces no immediate

impairment that can be attributed to a specific occupational

exposure event.

• Mercury in vapour form is colourless and odourless and often not

included in monitoring programmes if it is not observed visually in

liquid elemental form.

• Available field mercury vapour analysers are subject to

environmental and chemical interferences found in hydrocarbon

processing environments and can generate false or under-reported

mercury concentrations.

Plant Environmental, Health and Safety (EHS) personnel should

understand the limitations of field portable mercury vapour analysers

and develop policies designed to ensure the health and safety of

workers based on rigorous chemical analysis of the process streams and

ambient air monitoring in work areas. With this information, exposure

to mercury can be managed using conventional PPE, engineering

controls and chemical decontamination. Data generated during

mercury mass flow assessments is invaluable when developing facility

and turnaround management plans. Organic mercury is significantly

more toxic than inorganic mercury and having this information before

a turnaround allows EHS personnel to design appropriate exposure

monitoring plans. Mercury exposure monitoring plans during

turnarounds should include detailed personnel/area sampling plans,

data quality objectives, selection of similar exposure groups, medical

surveillance for at-risk personnel and mercury awareness training.

Mercury Chemical Decontamination of Process Equipment

The incorporation of mercury into steel surfaces, its accumulation in

sludge and other deposits along with the condensation of mercury

in equipment can lead to situations during turnarounds, which require

special procedures and precautions. In these situations, removal of

mercury from equipment may be necessary to protect workers, to protect

equipment integrity and to ensure environmental compliance. There is

some debate regarding the potential for mercury to diffuse into the steel

matrix through some mechanism other than adsorption and

chemisorption.7 Thermal desorption tests show a substantial amount of

mercury is desorbed at 200 °C indicating mercury strongly adsorbs or

chemisorbs to steel surfaces.7 Generally speaking, for in-service process

equipment going back into service in a mercury contaminated system, it

is not practical or necessary to remove adsorbed or chemisorbed mercury

from all interfacial steel surfaces.8 Mercury chemical decontamination

objectives must be decided during turnaround planning so the

appropriate chemistry, decontamination methods and verification

analyses are selected. For example, if the goal is for limited entry into a

vessel for a short duration then removal of residual surface hydrocarbon,

hydrocarbon soluble mercury and surface oxide scale followed by venting

may be sufficient to meet objectives. If the goal includes extended entry

into vessels contaminated with mercury then more concentrated

oxidising agents and chelants can be used to remove a higher mercury

mass per area such that work can be performed in modified level D or C

PPE. Equipment scheduled for decommissioning and metals recycling

may require a more aggressive approach. Chemical cleaning results

based on sequential digestions of representative test coupons, removed

by cold cutting sections ofcontaminated pipe, indicate that 50% or more

of the measured mercury mass in the steel can be removed by employing

inhibited acids/chelants. Thermal desorption testing of steel coupons can

also be used to determine baseline and post-verification mercury mass

concentrations. Determining the removal mass depends on local

environmental regulations, waste disposal regulations, selected metals

recycling vendor permits and final disposition of the equipment.

Successful mercury chemical decontamination of process equipment

depends on accurate analytical data to design chemistries and chemical

application phases appropriately to meet a range of project objectives.

The chemical process flow diagram (see Figure 3) depicts vapour phase

Figure 2: Refinery Solvent Extraction Unit


H Y D R O C A R B O N W O R L D – V O L U M E 7 I S S U E 122

and cascade phase chemical flow paths using surfactant and chelant

based chemistries to decontaminate a process tower during a

turnaround to allow extended entry in lower levels of PPE. A critical

component of chemical decontamination is monitoring progress in the

treatment process so that decisions can be made to increase chemical

concentrations, temperatures and residence times. A field analytical

method to measure total mercury concentrations in the applied

chemistries provides a means of monitoring the reaction efficiency and

overall required residence times. Chemical treatment sequence as well

as the verification methods should be determined during turnaround

planning and should consider:

• the safety of the personnel implementing the chemical

cleaning/inspection programme;

• safety and effectiveness of selected chemical phases;

• data quality objectives; and

• waste minimisation after the chemical cleaning programme.

Waste Minimisation During Plant Turnarounds

When feasible, the most effective approach for managing mercury is

to remove mercury from process feeds. Mercury removal units are

available for naphtha feeds, condensates and natural gas but the

technology to remove mercury from crude oil is not commercially

available at this time. Waste minimisation strategies should be a part

of pre-turnaround planning so waste minimisation systems can be

designed to meet project objectives and applicable environmental

regulations. Mercury can be removed from spent chemical cleaning

liquids and turnaround condensates such that they are rendered

non-hazardous and suitable for routine disposal at plant wastewater

facilities. There are a variety of technologies to choose from and

selection depends on project goals, costs, and treatment schedule.

Sorbent media used in these processes will remain a hazardous waste

stream and should be sampled and characterised per applicable

regulations. Also, filtration and adsorption units used in the waste

minimisation process should be chemically decontaminated before

demobilisation to the companies that provided them. Mercury and

hydrocarbons can also be removed from vapour streams and waste

gases generated during turnarounds preventing release to the

atmosphere. Chemically impregnated sorbents are used successfully in

this application and treatment units can be monitored for

breakthrough. As with fluid treatment systems this equipment

should be chemically decontaminated before leaving the site. When

monitoring breakthrough on these systems careful consideration

should be given to the instruments used since most of the field mercury

vapour analysers are subject to interferences from gases contained in

these vapour streams.

Conclusion

Mercury management during turnarounds requires some forward

thinking to determine the type and distribution of mercury

throughout hydrocarbon processing plants, process units and

pipeline systems to minimise worker exposure, and develop

appropriate turnaround management, chemical decontamination

and waste minimisation strategies. n

Cascade ChemInlet 165 F

SP 01Top 2 Inch Valve <1 μg/m3

8”8”

SP 02TR 20 MW<1 μg/m3

TCV 6,650 GalV 4305 6’ ID x 66’6” T/T

Operating Temp.260º F

Operating Temp.277º F



20”

20”

6”

V-04309

E-04308A

E-04308B

E-04308C

E-04308D

E-04308E

E-04308F

E-04400A

E-04400B

Steam/ChemInjection 225 F


E-04305


Figure 3: Naptha 2 Extract Stripper Chemical Process Flow Diagram

1. Wilhelm SM, Bloom N, Mercury in petroleum, Fuel Processing Technology, 2000;63(1):1–27.

2. Wilhelm SM, Avoiding exposure to mercury during inspectionand maintenance operations in oil and gas processing, Process Safety Progress, 1999;18(3):178–88.

3. Carnell PJH, Mercury Matters, Hydrocarbon Engineering,2005;10:37–40.

4. Wilhelm SM, Liang L, Kirchgessner D, Identification and

Properties of Mercury Species in Crude Oil, Energy Fuels,2005;20:180–6.

5. Wilhelm SM, Mercury in petroleum and natural gas:Estimation of emissions from production, processing, andcombustion, US EPA, 2001. Available at: http://purl.access.gpo.gov/GPO/LPS34680 (accessed 7 June 2012).

6. Zettlitzer M, Kleinitz W, Mercury in steel equipment used fornatural gas production - amounts, speciation and penetration

depth, Oil Gas European Magazine, 1997;23:25–30.7. Wilhelm SM, Nelson SM, Interaction of Elemental Mercury

with Steel Surfaces, JCSE 2010;13 (preprint 38).8. Hase B, Radford R, Vickery V, Mercury in Hydrocarbon Process

Streams: Sampling/Analysis Methods, Exposure Monitoring,Equipment Decontamination and Waste Minimization,Presented at: 110th American Fuel & PetrochemicalManufacturers Annual Meeting, California US, 12 March 2012.

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