Refinery Mercury Chemical
Decontamination in Preparation
for Decommissioning 2010 – 2015
CASE STUDY
Confidential U.S. Refinery
This case study presents
Introduction
Initial mercury management strategies began in 2010 at a U.S. refinery
processing approximately 200,000 barrels of oil per day of North Slope
Crude. During maintenance and inspection activities in 2010, elemental
mercury was observed in hydrocarbon processing vessels throughout the
Solvent Extraction Unit (SEU), with interior vessel mercury vapor
a summary of mercury
management strategies
and technologies
required for mercury
concentrations greater than 500 micrograms per cubic meter (µg/m ).
3
Based on this, studies were conducted to assess the distribution/accumulation of mercury in primary process units previously scheduled for
maintenance and inspection operations. Mercury mass loading rates in
steel process systems were integrated with data from the measurement
and monitoring of mercury in process streams and wastes to develop a
robust mercury flux model. Effective mercury management and chemical
decontamination plans were developed based on the model and
chemical decontamination
of impacted hydrocarbon
processing systems in
preparation for
decommissioning.
successfully implemented in 2011.
Subsequent mercury mass flux, distribution, and chemical reduction
studies were conducted in 2013/14 to support chemical decontamination in preparation for decommissioning of
the refinery. Bench scale decontamination tests were conducted with process pipe coupons from Crude Unit 1
(operational for 20+ years) to evaluate the efficacy of mercury removal technologies. Mercury mass loading rates,
speciation, and depth profiles from test section pipe coupons were integrated with data from the measurement
and monitoring of mercury in process streams to develop an accurate mercury flux model. Understanding the
nature and distribution of mercury along with depth profiles in carbon and stainless steel process equipment
is critical to developing effective chemical decontamination and decommissioning plans. Further, understanding
mercury accumulation rates and distribution of mercury and mercury compounds is required to select the correct
decontamination and processing technologies. Shutdown plans were developed based on the new model and
implemented with complete success in May/June 2014.
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Confidential U.S. Refinery
Applications
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Throughout the oil and gas industry, the impact of mercury in produced hydrocarbons is becoming more of an
emergent issue. This is not only the case for production from certain unconventional resource plays, but also for
assets processing conventional production as they near the end of their economic life and as process systems
require decommissioning. Produced mercury contaminates multiple hydrocarbon processing systems
(i.e., upstream production assets, midstream gathering and fractionation plants, and downstream processing plants)
for which the dismantling, removal, and disposal presents unique challenges and risks to decommissioning
personnel and to ecosystems. Global conventions provide a framework and guidance for decommissioning of oil
and gas facilities’; however, specific regulatory guidance on residual mercury concentrations that can remain in
production systems (scale or complexed in steel) is not currently available. As the recycled metals value of
hydrocarbon processing plants can be considerable, it makes sense to remove mercury to an acceptable mass/
surface area that will allow for safe transportation and recycling. The planning of safe, environmentally responsible,
and cost effective maintenance and decommissioning of mercury-impacted oil and gas facilities is improved
with accurate assessment of mercury distribution and the evaluation of applicable mercury removal technologies.
Results, Observations & Conclusions
Studies indicate that the mercury mass loading potential of steel pipe, exceeds estimates reported in previously
published studies. Thermal desorption and chemical reduction bench testing indicate that the process is
reversible using various developed chemistries and methods. Also, recent thermal desorption experiments
performed on metallic test coupons in a quartz tube furnace indicate field steam-out temperatures (1000C to 2000C)
are ineffective in removing mercury from steel but may still be effective in volatilizing hydrocarbon soluble mercury
and volatile mercury species. However, these species represent the smallest fraction of the total mass of mercury
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Confidential U.S. Refinery
within the scale and steel. This can be precisely measured to quantify
mercury emissions to atmosphere from the flare during degassing and
chemical cleaning. Mercury removed from hydrocarbon processing systems
during steaming and chemical cleaning can be adsorbed on media and
removed from liquids so that the spent chemistry is rendered nonhazardous and suitable for routine disposal. Mercury vapors desorbed
during steaming of hydrocarbon process piping and vessels can also be
adsorbed/chemisorbed to various media preventing release to the
environment. Reactive fluid beds and reactive sorbent media used in
both cases remains a waste stream that must be managed as such.
Technical Contributions
Data from mercury mass flux studies, using modified and improved
methods, integrated with the results of metallic coupon mercury mass
loading, distribution and chemical reduction testing has led to the development of advanced chemical decontamination methods and chemistries
that are effective in removing 99% mercury mass and oxide scale
(depth profile 1 mm), deactivation of pyrophoric iron, and encapsulation/
removal of hydrocarbons.
With the development of new mercury removal chemistries came the
development of new analytical methods to measure the performance of
these chemistries during chemical decontamination and processing
(waste minimization). Laboratory and field trials of the analytical method led to an improved understanding of
economical and efficient mercury waste minimization processes effective in removing mercury, metals,
hydrocarbons and other contaminates.
Mercury mass loading, distribution, and chemical reduction bench scale studies are a key component of evaluating
decontamination chemistries/methods and identifying the most cost effective technology for application
to mercury-impacted hydrocarbon process systems. In an effort to better understand and quantify the adsorption/
desorption of mercury in steel and process, technical modifications to PEI’s Mak2™ sampling systems were
designed to allow for connection to plant flare systems to quantify mercury emissions from steaming and
chemical cleaning operations.
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Confidential U.S. Refinery
Crude Oil Laboratory Comparison
The appearance of mercury at processing facilities can be delayed by months or years due to scavenging of mercury
by steel pipeline surfaces. It should be noted that this refinery is located around 500 miles from the supply and
that the first Turnaround where condensed elemental mercury and volatile mercury was recorded in process
systems was in 2010. A previous Turnaround performed in 2005 on the SEU made no record of observed mercury.
Although no mention was made of mercury in the 2005 Turnaround, process stream sampling and analysis was not
performed to verify the presence of mercury in process streams or equipment, however, mercury sampling was not
standard at the refinery at that time. A laboratory comparison was performed on crude oil composite samples
collected from the inlet feed to gain visibility into mercury concentrations and trends in crude oil processed by the
refinery. There was some slight variability in the data reported from the three laboratories sourced for the study
(4 to 6 parts per billion [ppb]) however those concentrations are in the range of a previous study performed in 2004.
Conclusions could not be made to support the duration of pipeline equilibrium or that new production could have
caused a substantial increase in crude oil mercury concentrations; however, mercury accumulates and concentrates
in process systems and data from recent mass flux studies support the conclusion that 4 - 6 ppb mercury in inlet
feeds is sufficient to produce process stream concentrations >1,000 ppb.
Lean Solvent
Naptha 2
Extractor
Naptha 2 Raffinate
Naptha 2
Extractor Stripper
892.14 ppb
Rich Solvent
Naptha Feed
STAB 2 BTMs
V-04303
5.47 ppb
V-04305
Naptha Feed
STAB 1 BTMs
V-04308
0.73 ppb
OVHD Recycle
205.87 ppb
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Confidential U.S. Refinery
Mercury Mass Flux, Distribution & Chemical Reduction Studies
Turnaround and decommissioning planning should consist of attempts to determine the extent and type of
mercury contamination present in process systems. Routine mercury assessment sampling and analysis along
with mass flux studies performed throughout the life cycle of an asset provides invaluable information required
for decontamination and decommissioning planning. Data from mercury mass flux studies integrated with the
results of metallic coupon mercury distribution, depth profiles, and chemical reduction studies provides planners
visibility into the process system and the means to design/modify select cleaning chemistries, chemical cleaning
flow paths, temperatures, and residence times based on accumulation rates, results of functional and molecular
speciation, and process design restrictions.
Two separate mass flux studies (Jan 2011 and Aug 2013) were
performed to understand the mercury sorption and distribution
dynamics associated with process systems scheduled for
decontamination/decommissioning. In that time, the mass
flow rate balance of the SEU in 2014 (process feeds vs.
process outputs) indicated a potential mercury accumulation
rate of 0.0003 lbs per hour, which was an order of magnitude
more accumulation than in 2011. Also, the concentration of
mercury in the naphtha feeds to the SEU increased from around 5 ppb in 2011 to around 9 ppb in 2014, resulting
in approximately 10 pounds of mercury being introduced into the process per year. Both mass flux studies clearly
identified mercury sinks in the SEU as well net gains in mercury in process fluids as they moved through the system.
As part of the mass loading study to support the 2014 chemical decontamination, a chemical reduction study
was performed to focus on the development of chemistry effective in removing oxide scale, hydrocarbons, and
mercury from steel. Once distribution, depth profiles, speciation, and mass loading per surface area had been
established (test section from C4 stream piping downstream of crude column overhead receiver), select test
coupons were subjected to 10 chemical formulations and evaluated for mercury mass removal efficacy. For each
chemistry tested, two coupons (primary and duplicate) were inserted into a Silconert™-treated stainless steel
chemical reaction chamber and subjected to each test case chemistry for predetermined residence times.
Process parameters (temperature, dissolved iron, pH, residence time, total mercury, flow, Re number) were
collected every 20 minutes for the duration of the chemical test. Precise measurements, weights, and microscope
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Confidential U.S. Refinery
photos were taken of each coupon during inventory into the laboratory and post chemical testing. Several test
case chemistries removed hydrocarbon, oxide scale, and mercury from the surface to 1 millimeter in 4 hours at a
temperature of 500C. This is significant as mercury mass loading rates were around 70 grams/m2 which equated
to around 35 milligrams of mercury per test coupon that had to be affected by the chemistries. The test case
selected and deployed for the full scale chemical cleaning program in 2014 had an efficacy of up to 99%, coupon
mass loss of 2%, and depth of scale penetration of 0.51 millimeters. Chemistries used in this study included
Chemical Decontamination
99.66
Deposition of mercury, and its
compounds, can occur by adsorption,
51.57
99.71
41.97
57.53
41.51
39.88
45.61
FORMULATIONS
99.88
EFFICACY OF TEST
99.84
% HG REMOVAL
.........................
modifications to existing proprietary formulations as well as some new formulations.
chemisorption, precipitation, and/or
condensation. The amounts of
elemental mercury and its compounds
in processed fluids affect all of these
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CHEMICAL TEST FORMULATION #
mechanisms. The uptake of mercury
in steel is primarily through adsorption
and chemisorption into the scale,
making both carbon and stainless
steel excellent mercury scavengers. With some effort this process can be reversed depending on many factors
(what goes in can come out). However, mercury complexed and incorporated into steel surfaces is not easily
affected by typical hydrocarbon chemical decontamination chemistries and methods. Since 2005 the research
group at PEI has concentrated efforts on understanding sorption dynamics of mercury in steel pipe and in the
development of effective chemical decontamination solutions.
On a scale, some chemistries are more effective than others for decontaminating
mercury from hydrocarbon process systems and each requires careful consideration before use. Generally strong oxidizers and acids are the most effective
but come with corrosion risks and can require additional processing steps to
remove mercury from spent fluids. Mercury can be oxidized by oxidants
including halogens, hydrogen peroxide, nitric acid, and concentrated sulfuric
acid. Using any of these options for mercury chemical decontamination in high
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Confidential U.S. Refinery
concentrations coupled with heat should only be attempted by qualified chemical and industrial services companies.
If the objective is strictly related to health and safety (e.g., for inspection), the target may be to convert mercury to
a non-volatile species rather than removal. If the goal is to meet disposal requirements, the decontamination process
may be designed to convert mercury to a non-soluble species so as to meet leachate criteria. Total mercury removal
is possible for systems scheduled for abandonment and decommissioning but as the chemicals used for this purpose
are aggressive to mercury, they typically are to other metals as well. Less aggressive chemistries (aqueous noncorrosive surfactant/chelants blends) are easy to process but depending on mercury mass loading rates and
mass removal objectives can require higher temperatures, increased residence times and multiple application
technologies and cost more. Reactive chemistries react with mercury to form water soluble (ionic mercury halides)
or insoluble mercury (HgS) or otherwise combine with metal ions. Since mercury is soluble in hydrocarbons to
a certain extent (around 2 ppm), various surfactants and solvents are also effective in dissolving mercury and
removing organic solids.
Generally, total mercury removal from a hydrocarbon processing systems
Total mercury removal
is possible for systems
scheduled for abandonment
and decommissioning,
but as the chemicals
used for this purpose
are aggressive to mercury,
is not considered unless the system is scheduled for abandonment and
decommissioning or process risk reduction is required. For example, the
Turnaround in 2011 required systems with mercury accumulation rates
ranging from 1 to 100 lbs per year to be decontaminated to allow for
extended maintenance activity over a 10-day period. Chemistry selected
for this purpose was non-corrosive and designed to remove hydrocarbon
soluble and particulate mercury and form soluble and insoluble mercury
salts. The selected formulations of surfactants and chelants were applied
in vapor phase and cascades phase over 12 to 24 hours with success in
reducing interior mercury concentrations from around 1,000 µg/m3 to
<1 µg/m3 as continuously monitored from systems over the duration of
they typically are to
maintenance. The goal for the 2014 SEU decontamination was decon-
other metals as well.
tamination in preparation for decommissioning, which generally requires
99% mercury mass removal to allow components to be processed at a
metals recycler or reused at another processing facility. Chemistry
selected for this purpose was a blend of surfactants (encapsulate metal ions and hydrocarbons), mineral acids,
corrosion inhibitors, penetrants, and chelants with a hydrogen sulfide scavenger.
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Confidential U.S. Refinery
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In both cases (mercury decontamination for reuse and decontamination for decommissioning), continuous performance sampling and analysis was performed to provide guidance on the effectiveness and duration of each
chemical phase. Assimilation of this data provides an approximate total mass of mercury removed from each system.
Because of the difficulty in capturing all the fractions, a more
accurate method of determining mercury mass loss is by
thermal desorption or acid digestion of select steel from
process and comparison to the average mercury mass
loading per surface area pre-chemical application. Another
verification method which PEI is pioneering with two other
global oil and gas companies is XRF analysis, which with
correct software and custom calibration standards is
yielding promising results.
Spent Chemistry & Vapors Processing
Chemical and processing procedures can be applied to
spent fluids and condensates such that the materials are
rendered non-hazardous and thus suited for non-hazardous
disposal. Medias used for encapsulation, reaction, or
chemisorption and filters used for colloidal particulate
removal during processing still need to be characterized
and managed based on results of waste characterization.
Some commercial mercury removal systems are targeted at vapor phase treatment and some are targeted at liquids.
Vapor phase treatment systems primarily consist of sulfur-impregnated carbon, metal sulfide on carbon or alumina,
and regenerative molecular sieve (zeolite) onto which is bonded a metal that amalgamates with mercury. Liquid
removal processes consist of iodide impregnated carbon, metal sulfide on carbon or alumina, and silver on zeolite
mole-sieves. Functional and molecular mercury speciation are not only important to developing effective chemical
decontamination plans but are as important to planners to design effective processing systems.
In both cases (mercury decontamination for reuse - 2011 and decontamination for decommissioning - 2014), vapors
and fluids were processed to: a) minimize mercury emissions to atmosphere, and b) remove mercury and other
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Confidential U.S. Refinery
contaminates from spent chemistries and condensates. A new innovative active fluid bed was designed and
installed prior to solid media beds to minimize media change-outs. This new approach has exceptional mass
loading potential and cost benefits and, when coupled with a solid media system, performs extremely well.
As with chemical decontamination, continuous performance sampling and analysis are required to provide guidance
on the effectiveness and duration of each phase of processing. As a means of determining how accurate the field
analysis methods can be, an instrument detection limit study was performed with the field analyzer on each
chemical formulation selected for the 2011 and 2014 events. In addition, field duplicates and laboratory triplicates
were analyzed for compliance of processing.
A total of 100,000 gallons of spent chemistry/condensates were processed (average pre-processing concentration
of 500 ppb mercury) during the 2011 Turnaround to <7 ppb mercury. As the chemistry used during the 2014
Shutdown was more complex (thus removing significantly more iron and mercury) additional processing steps
were required to completely neutralize and process 400,000 gallons of spent chemistry/condensates with average
mercury concentrations ranging from 500 ppm to less than 4 ppb mercury.
Compliance Monitoring Of Flare
As a chemical element, mercury is not destroyed by a thermal oxidizer, but is only converted to other chemical
forms. Although steaming equipment may remove some volatile mercury species and hydrocarbon soluble
mercury, the temperatures are too low to affect complexed mercury in steel. Many hydrocarbon processing plants
are located near environmentally sensitive areas and mercury emissions from steaming to flare and materials
processing should be considered and mitigated.
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Confidential U.S. Refinery
A considerable amount of mercury can be released to the atmosphere from steaming and chemical cleaning
mercury contaminated systems during Turnarounds and Shutdowns. Therefore, during both the 2011 turnaround
and 2014 Shutdown, mercury emissions to atmosphere were quantified and recorded for compliance.
This is a complicated and challenging vapor stream to sample and required certain modifications to PEI’s Mak2™
mercury sampling systems. Measurements have shown that mercury vapor concentrations during active steaming
and chemical cleaning can range from <1.0 µg/m3 to >6,000 µg/m3, while condensate concentrations can range
from <1.0 to 200 µg/L. The higher mercury concentrations are measured during chemical cleaning as mercury
is oxidized and volatile mercury is released from scale and substrate surfaces. The total amount of mercury
released to the atmosphere from crude oil processed in the U.S. is about 11 tons, which is around 7 percent of the
U.S. total (158 tons annually). It should be noted that Turnaround waste streams (e.g., fluids, vapors and gases)
and other potential sources of mercury were not included in the aforementioned atmospheric emissions; therefore,
these potential additional sources should be considered when developing a mercury management strategy.
(Note: Planners should also consider at the conclusion of chemical decontamination for preparation of decommissioning that the flare-line will likely also require mercury decontamination.)
PEI – Mercury & Chemical Services
DeBusk (DSG)
Ron Radford
Dr. Darrell Gallup
Ian Bonner
Alan Noack
Vice President (MCS Group)
Technical Director
Chemical Cleaning Manager
Project Manager
(713) 503-6803
(707) 480-5508
(281) 450-0242
(713) 301-0914
Thai Cell: +66 098 495 5474
[email protected]
[email protected]
[email protected]
[email protected]
www.debusksg.com
www.pei-tx.com
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