DAQ-2024-011263

H.B.220:Halogen Reductions&StandardsRecommendations
2024 Natural Resources,Agriculture,and
Environment Interim Commiee Status Report
PREPARED BY Utah Division of Air Quality
H.B.220 Background
Utah House Bill (H.B.)220 -Emissions Reduction Amendments,passed during the 2023
Utah Legislature General Session.The legislation was subsequently signed into law by
Governor Cox which directs the Utah Division of Air Quality (UDAQ)to:
1.complete an air emissions inventory of point sources that emit halogens within Box
Elder,Davis,Salt Lake,Weber,Tooele,and Utah counties,by December 31,2024;
2.complete a Best Available Control Technology emissions reduction plan to reduce
the compounds of halogens for sources within the applicable geographic area with
an implementation date of December 31,2026;and
3.provide recommendations for a state standard limiting halogen emissions.
The rst of these three elements,an air emission inventory,was published on the UDAQ’s
website in November 2023 and was presented to the legislature during the 2023 interim
session.1
This report overviews the UDAQ’s ndings for the second and third required elements,
including recommendations for an emission reduction plan for major point sources,as well
as recommendations for a state standard limiting halogen emissions.Lastly,H.B.220
directs the UDAQ to report on the status of the above to the Natural Resources,Agriculture,
and Environment Interim Committee during the November 2024 meetings.
1https://lf-public.deq.utah.gov/WebLink/DocView.aspx?id=392316&repo=Public&searchid=b4d1afc5-65c0-4c
f7-98c8-bd334965c2c9
UtahHalogen Emission Reductions &Standards•Utah Division of AirQuality 2 of 21
Utah Halogen Emission Inventory
This section provides a brief overview of halogen chemistry and the emission inventory
developed in accordance with H.B.220 Section (2)(a)and discussed in detail in the rst
report published in November of 2023.For more comprehensive information regarding the
emission inventory,please refer to that report.
Halogen Chemistry
Halogens such as chlorine (Cl2),bromine (Br2),and iodine,play an important role in
atmospheric chemistry.They are reactive species that affect the oxidative capacity of the
troposphere.The introduction of gaseous reactive halogen species,such as hydrochloric
acid (HCl),Cl2,nitryl chloride (ClNO2),Br2,bromo nitrite (BrNO2),and bromine
monochloride (BrCl),leads to the production of oxidized Volatile Organic Compounds
(VOCs),resulting in increased ozone and ne particulate matter (PM2.5)concentrations,
especially under oxidant-limited conditions.Industrial halogen emissions also play an
important role in the availability of oxidized mercury in the environment,in which
halogens directly oxidize non-water soluble elemental mercury,allowing for the water
soluble oxidized mercury to be deposited into the environment.
Halogen sources include a mix of natural and anthropogenic sources ,.Anthropogenic23
sources of halogens mainly consist of emissions from area and point sources,while natural
sources in the greater Wasatch Front include the Great Salt Lake.Sources of halogens in
Utah and their emission rates are largely unknown at this time,and current emissions
inventories for these compounds should be further resolved.An aircraft and ground-based
intensive eld study conducted by the National Oceanic and Atmospheric Administration
throughout the Northern Wasatch during a 2017 winter-time persistent cold air pool event
investigated the magnitude of industrial emissions of Cl and Br.Findings indicated that US
Magnesium,an industrial source located on the Southwest edge of the Great Salt Lake,is a
signicant source of anthropogenic halogens in the Salt Lake Valley.Aircraft observations4
collected during this study used an iodide chemical ionization mass spectrometer which
detected highly elevated levels of HCl and other halogen compounds like Cl2,Br2,and BrCl,
4 C.C.Womack,W.S.Chace,S.Wang,M.Baasandorj,D.L.Fibiger,A.Franchin,L.Goldberger,C.Harkins,D.S.
Jo,B.H.Lee,J.C.Lin,B.C.McDonald,E.E.McDuffie,A.M.Middlebrook,A.Moravek,J.G.Murphy,J.A.
Neuman,J.A.Thornton,P.R.Veres,and S.S.Brown.Midlatitude Ozone Depletion and Air Quality Impacts
from Industrial Halogen Emissions in the Great Salt Lake Basin.Environ.Sci.Technol.2023,57,5,1870–1881.
3 Simpson,W.R.;Brown,S.S.;Saiz-Lopez,A.;Thornton,J.A.;von Glasow,R.Tropospheric Halogen
Chemistry:Sources,Cycling,and Impacts.Chem.Rev.2015,115 (10),4035−4062.
2 Fu,X.;Wang,T.;Wang,S.;Zhang,L.;Cai,S.;Xing,J.;Hao,J.Anthropogenic Emissions of Hydrogen Chloride
and Fine Particulate Chloride in China.Environ.Sci.Technol.2018,52,1644−1654.
UtahHalogen Emission Reductions &Standards•Utah Division of AirQuality 3 of 21
in the plume originating from US Magnesium.The observed emissions of halogenated
compounds were representative of typical daily emissions from the facility when operating
at capacity.These levels were also associated with complete ozone depletion in the vicinity
of the plant,but increased PM2.5 and ozone formation downwind.
Modeling using these observed halogen emissions shows regional PM2.5 increases of
10%−25%,with greater increases being observed closer to the plant,with notable increases
in ozone similarly observed when the halogenated plume interacts with urban nitrogen
oxide enriched air.While these ndings show an impact from halogens from US
Magnesium on local air quality concentrations in the urban areas of the Wasatch Front,
results are limited to a single winter campaign and limited plume encounters.Further
measurements are needed to constrain Utah’s emissions inventory for halogens and better
understand the impact of these species on local PM2.5 and ozone levels.
While uorine is also a halogen,it typically does not display the reactivity of the
aforementioned key halogens.Fluorine compounds are not expected to highly inuence
tropospheric ozone and particulate formation as it is typically converted into hydrogen
uoride (HF),which is highly unreactive.Therefore,uorine and its compounds were5
generally not included in H.B.220 reports and inventories.
Current Emissions Inventory
As required by H.B.220 Section 2(a),the UDAQ developed and published a halogen
emissions air inventory by compiling point source emissions inventory data from
2020-2022 into three data sets containing key halogenated compounds.The rst data set,
“Potential Halogen Point Source Inventory”,is comprised of all point sources that have the
potential to emit a halogen compound based on the literature review and internal
discussion.The second data set,“Halogen Specic Point Source Inventory”,is comprised
of currently available point source emissions which include any halogenated compound
regardless of reactivity.Lastly,the third data set,“Eight Reactive Chlorine Compound
Emissions by Facility”,is comprised of point source emissions for the eight reactive
chlorine gas compounds identied by Burklin et al.(note:only six of the eight compounds6
are currently found in the emissions inventory;phosgene and chlorodiuoromethane were
not reported by any point sources).Figure 1 below provides a summary of the point source
facilities emissions of the reactive chlorine gas compounds.
6 Burklin,C.E.,Erickson,S.Bursey,J.T.;Development of an Area and Mobile Sources Inventory for Reactive
Chlorine Compounds in Southeast Texas;Eastern Research Group,Inc.
5 Treatise on Geochemistry,Volume 4,2003,1-67.Chapter 4.02 Tropospheric Halogen Chemistry.R.von
Glasow and P.J.Crutzen.
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Utah Point Source Halogen Emission Inventory
Figure 1.Eight reactive chlorine gas compound emissions from point sources 20202022 Point Source Inventory in
tons per year).
This inventory of halogen emissions is primarily limited to chlorinated compounds and a
few brominated and iodine-containing compounds.This again highlights the gaps related
to non-chlorine and non-Hazardous Air Pollutant halogen compounds.It also highlights
the need for entirely new emission factors for these types of compounds before any
additional emissions can be calculated and added to an inventory.New emission factor
development typically takes several years to complete,if determined to be feasible.
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Best Available Control TechnologyEmissionsReductionPlan
As required by H.B.220 Section (2)(b),the UDAQ has conducted a Best Available Control
Technology (BACT)emission reduction plan for all relevant sources within the applicable
geographic region.It is important to note that the use of the term BACT in this report
differs from the regulatory denition in 42 USC §7479(3)as halogen emissions have not
historically been a regulated pollutant within the scope of this term.Therefore,the UDAQ
used the same methodology and factors when examining emission reduction technologies
and strategy,but applied this process to halogen emissions,including emissions of Cl2.As
a result,the use of the term BACT in this report,and throughout Appendix A,should be
viewed as the UDAQ’s best efforts to apply a legally dened term to the intent of the
language found in H.B.220,and may differ some from the absolute denition of BACT as
found in U.S.Code.
As demonstrated in Figure 1,only a single source,US Magnesium,has annual emissions
high enough to necessitate a BACT analysis.Currently,US Magnesium’s primary
magnesium rening operations are not operating,with operations potentially resuming in
2026.Based on the Halogen Point Source Emission Inventory from 2020-2022 (Figure 1),
when US Magnesium’s Rowley Plant is operating,it accounts for 96.9%of the eight reactive
chlorine gas compounds that were inventoried.Furthermore,US Magnesium’s emissions of
HCl and Cl2 accounted for 98.9%of the total area source inventoried halogen emissions.
From 2020-2022,Cl2 alone from US Magnesium accounted for 79.3%of all the inventoried
halogen emissions and the Rowley Plant was the producer of 99.8%of the Cl2 emissions in
the applicable geographic area.
The updated halogens BACT analysis,including an overview of US Magnesium’s processes,
and technologically and nancial feasibility assessments,can be found in Appendix A.It is
important to note that US Magnesium’s current control technologies and requirements are
considered to meet the regulatory denition of BACT found in U.S.Code,and additionally
meet the control requirements for the federal National Emissions Standards for Hazardous
Air Pollutants for a Primary Magnesium Rening facility.The BACT analysis in Appendix A7
represents an updated examination of potential control technologies and emission
reduction strategies specically for halogen emissions as required by H.B.220.
Additionally,US Magnesium is currently undergoing an updated BACT process for
7 40 Fed.Reg.58,620 (October 10,2003).Subpart TTTTT—National Emissions Standards for Hazardous Air
Pollutants for Primary Magnesium Rening
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emissions of nitrogen oxides and VOCs as part of the serious ozone State Implementation
Plan for the Northern Wasatch Front.8
The halogens BACT analysis found in Appendix A examined four independent emission
reduction strategies including updating current control technologies,adding additional
control technologies,limiting production to reduce halogen emissions,and potential
changes to the process of the plant.
Based on the results of this analysis,the UDAQ recommends:
1)US Magnesium install a connection between the Chlorine Reduction Burner (CRB)
and the Chlorine Bypass Scrubber (CBS)and use the CBS to control melt-reactor
emissions during periods of CRB maintenance;
2)the full removal of maintenance limits from US Magnesium’s air permit;and
3)adding additional ongoing halogen testing requirements to US Magnesium’s air
permit including Br2,HBr,and HF.
The UDAQ has concluded that these recommendations represent the most technologically
and economically feasible options to reduce halogen emissions from the Rowley Plant,and
provide additional data as needed.
The implementation of the combined recommendations 1 and 2 would limit US
Magnesium’s currently permitted maintenance emissions by 75%.US Magnesium is
permitted to produce up to 7,500 tons of Cl from scheduled maintenance every rolling
60-month period.From a potential-to-emit perspective,implementing these
recommendations would reduce possible maintenance Cl emissions by 5,625 tons every
ve years,or 1,125 tons every year.US Magnesium generally produces far less than 7,500
tons of chlorine due to scheduled maintenance per rolling 60-month period;however,from
April 2009 to September 2022 US Magnesium produced an average of 97 tons per month of
Cl2 from scheduled maintenance.This equates to 1,167 tons per rolling 12-month period
and 5,835 tons per rolling 60-month period.Therefore,a 75%reduction in these actual
emissions represent a substantial reduction in emissions of halogenated compounds
within the Wasatch Front.While these recommendations primarily target emissions of Cl2,
the UDAQ anticipates a similar,or greater,reduction in Br2 emissions resulting from these
same recommendations.Currently,data associated with Br2 emissions from US Magnesium
is not available;however,Br2 compounds are typically more reactive than Cl emissions due
to their chemically charged state,and therefore it is anticipated that these same reduction
strategies should correspond to reduced emissions of Br2.
8 https://deq.utah.gov/air-quality/northern-wasatch-front-moderate-ozone-sip-technical-support-documentation
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US Magnesium’s air quality permit currently requires annual stack testing using EPA
Reference Method (RM)26A on the 05/06 Magnesium Chloride Bins,Spray Dryers 01-03,
Melt Reactor,Emergency Off-gas Stack,and Hydrogen Chloride Production Unit to test
and report on emissions of Cl2 and HCl.RM 26A can also be used to measure Br2,HBr,and
HF.To collect ongoing data regarding halogen compounds beyond Cl2 and HCl,the UDAQ
recommends adding Br2,HBr,and HF,to their annual stack testing requirements,all of
which can be achieved using the same RM 26A method required for current annual testing.
Additionally,the UDAQ has issued an order requiring all of these units to use RM 26A to
measure HCl,Cl2,Br2,and HBr within 180 days of achieving 90%of maximum magnesium
production,which is anticipated to occur in 2026.9
Lastly,the UDAQ has concluded that these recommendations could be achieved by
December 31,2026,if directed by the legislature to do so.
9 DAQC-932-23,dated August 31,2023
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State Standard Limiting HalogenEmissions
As required by H.B.220 Section 2(c),the UDAQ examined a potential state standard
limiting halogen emissions.Through this process,the UDAQ examined the available
literature and met with scientists specializing in halogen chemistry to understand the
current state of the science surrounding the impact of halogen emissions on air quality.
The UDAQ found that the current state of the science shows that extremely high
concentrations of halogen emissions,like those experienced at US Magnesium,directly
negatively affect air quality.Furthermore,these studies can also quantify the impacts of10
these sources on air quality.However,outside of these narrow instances of highly
concentrated emission sources,the current science is lacking in denitive and quantiable
impacts of lower level,and more broadly distributed,emissions of halogens.Outside of
these instances of highly concentrated sources,a key understanding of the tradeoff
between lowering halogen emissions and improving air quality is missing.Other
fundamental questions remain unanswered regarding halogen chemistry which are needed
in setting an appropriate state standard,including what the natural background
concentrations of halogen are,and how do background concentrations in the Wasatch
Front compare to other areas?
It is important to note that the science necessary to understand these important questions,
including appropriate thresholds for reductions,is ongoing.The UDAQ believes reliable
results needed to inform a state standard could be available in the coming years,in part
from the results of upcoming and ongoing Utah focused studies as highlighted in the Utah
Based Halogen Research section of this report below.
Additionally,a central component to any standard is the ability to determine compliance
through widely available,standardized testing.Therefore,the UDAQ examined the
availability of approved reference testing methods for the array of halogenated
compounds included within the inventory.In the regulatory space,these methods are
typically federally promulgated RM’s,such as RM 26A.The UDAQ found that while some
approved RM’s do cover certain halogen compounds,many of the halogenated11
compounds inventoried are not covered under existing RM testing protocols.The UDAQ
further found that measuring many of these compounds can be extraordinarily difficult,
11 See RM 26A,13,13A,and 13B.
10 C.C.Womack,W.S.Chace,S.Wang,M.Baasandorj,D.L.Fibiger,A.Franchin,L.Goldberger,C.Harkins,D.
S.Jo,B.H.Lee,J.C.Lin,B.C.McDonald,E.E.McDuffie,A.M.Middlebrook,A.Moravek,J.G.Murphy,J.A.
Neuman,J.A.Thornton,P.R.Veres,and S.S.Brown.Midlatitude Ozone Depletion and Air Quality Impacts
from Industrial Halogen Emissions in the Great Salt Lake Basin.Environ.Sci.Technol.2023,57,5,1870–1881.
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and the instrumentation needed is in limited supply.As a result,verifying compliance with
a comprehensive state standard limiting halogen emissions would be difficult,and limited
in scope relative to the array of known halogen compounds.At this time,the scope,time,
and costs associated with the development of standardized RM’s to support a state
standard is beyond both the extent and funding associated with H.B.220.
Ultimately,any emission reduction standard must be based on sound science and
standardized reference measurement methods must be available for determining
compliance.The UDAQ has determined that these two critical pieces of information
necessary to set an appropriate and veriable standard are currently lacking.As a result of
these missing components,the UDAQ cannot make a recommendation for a state standard
limiting halogen emissions at this time.However,in the absence of being able to make a
recommendation for a state standard,the UDAQ recommends the following:
1)continue to invest in,and encourage scientic studies necessary to ultimately set an
appropriate state standard;and
2)revisit the prospect of a state standard through the legislative process again in the
future when the state of the science can support setting such a standard.
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Utah Based Halogen Research
Halogen Measurement Studies
In collaboration with Utah State University,the UDAQ conducted a three-phase sampling
study to better understand the levels,spatial distribution,and temporal variation of select
halogens (HCl,HBr,pCl,pBr)along Utah’s Wasatch Front.Measurement locations include
15 sampling sites distributed around the Great Salt Lake and along the Wasatch Front
urban corridor,with sampling occurring over three sampling phases.
The study included sampling during the winter of 2022-2023,summer of 2023,and winter
of 2023-2024.US Magnesium has not been producing magnesium since the winter of 2022
so the study did not capture halogens during magnesium production periods.Concurrent
seasonal ambient measurements of bromine oxide,nitrogen dioxide radicals,and
formaldehyde were also collected by the University of Colorado at one of the 15 sampling
stations.When complete,these studies will help constrain the spatial variability of select
halogens,identify potential hotspots along the Wasatch Front and better model the
impacts of halogens on air quality along the Wasatch Front.
2024 Utah Summertime Ozone Study USOS
To determine factors and key precursor chemical
species leading to ozone exceedances along the
Wasatch Front,the National Oceanic and Atmospheric
Administration conducted an intensive eld
measurement campaign in summer 2024 throughout
the Wasatch Front.Through funding from the UDAQ,
observations were collected using a combination of
aircraft,mobile (i.e.instrumented vehicle),and xed
ground-site measurements.Collected measurements
will be used to help determine the spatial distributions,
speciation,and likely sources of ozone precursor
emissions including halogenated compounds.These
measurements will also be leveraged in photochemical
modeling of the study time period.The role of
halogens (Cl2,Br2,and potentially iodine compounds),
Utah HalogenEmissionReductions&Standards •UtahDivision ofAir Quality 11 of 21
their sources (both industrial and natural sources,such as the Great Salt Lake)and their
impact on ozone formation are specic goals of the campaign.
Researchers from a number of local,regional,and federal entities also participated in the
USOS campaign,each providing funding through sources independent of the funding
provided by UDAQ,representing a signicant amount of matching contributions to the
effort.Collaborators from Colorado State University,the University of Wyoming,and
Montana State University collected supplemental measurements using a National Science
Foundation funded mobile laboratory.Weber State funded a collaboration with Aerodyne
Research to measure aerosol composition,including halogens,at the UDAQ Hawthorne
ground site.Researchers from NASA Jet Propulsion Laboratory brought ozone lidar
instruments to the region,and a group from National Institute of Standards and
Technology measured gaseous species including HCl.NOAA Air Resources Lab contributed
mobile measurements of ozone precursors,and collaborators from the University of Utah
and the State University of New York added to both mobile and ground-based platforms.
Instruments measuring BrO and other species from the University of Colorado at Boulder
were deployed at ground sites and on aircraft.Lastly,the UDAQ provided additional
funding to Utah State University and Weber State to measure ozone proles using drones
and to sample halogens around the lake,respectively.The joint efforts of these institutions
will help maximize the understanding of factors leading to ozone formation along the
Wasatch Front and will help rene emissions inventories,including Utah’s halogens source
inventory.
Ongoing Utah Based Higher Education Research
In addition to the intensive eld campaigns described above,there are several ongoing
research projects being conducted at universities located in Utah.These projects include
improving modeling associated with halogen chemistry in the atmosphere,understanding
halogen sensitivity as it relates to health-based air quality standards,and a study funded
by the National Science Foundation's Atmospheric Chemistry Program in which
researchers from the University of Utah,Utah State University,Brigham Young University,
and the University of Nevada (Reno)will further examine the role halogens play in
oxidizing and depositing mercury into the environment.
The results of these projects could be critical components in understanding the
relationship between emissions of halogens and establishing an appropriate state
standard.As this research progresses,it has the potential to inform the tradeoffs between
lowering emissions and improving air quality.
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Conclusions
In accordance with H.B.220,the UDAQ has developed:
1)an air emissions inventory of point sources that emit halogens in Box Elder,Davis,
Salt Lake,Tooele,and Utah counties;
2)recommendations for a Best Available Control Technology plan to reduce
compounds of halogens in the same applicable geographic region with the
implementation date of December 31,2026;and
3)recommendations for a state standard limiting halogen emissions.
All three of these elements have been made publicly available on the UDAQ’s web page.
For a Best Available Control Technologies plan to reduce compounds of halogens in the
applicable geographic region,the UDAQ recommends that:
1)US Magnesium installs a connection between the CRB and the CBS and use the CBS
to control melt-reactor emissions during periods of CRB maintenance;
2)the full removal of maintenance limits from US Magnesium’s air permit;and
3)adding additional ongoing halogen testing requirements to US Magnesium’s air
permit including:Br2,HBr,and HF.
For a state standard limiting halogen emissions,the UDAQ recommends:
1)continued investment in scientic studies necessary to ultimately set an appropriate
state standard;and
2)revisit the prospect of a state standard through the legislative process again in the
future when the state of the science can support setting such a standard.
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Appendix AUS Magnesium BACTEmissionReductionPlan
Introduction
The following analysis was conducted by the Utah Division of Air Quality (UDAQ)and includes a Best Available Control
Technology (BACT)analysis for an emission reduction plan to reduce compounds of halogens in the applicable
geographic area outlined in H.B.220 Emission Reduction Amendments.The definition of BACT as defined in 42 USC §
7479(3)can be simplified to a requirement that limits emissions from a major point source.From the scope of new source
review permitting,BACT is what a source will implement to control emissions.The term BACT used in this report differs
slightly from the regulatory definition as defined in the CFR as halogen emissions have not historically been a regulated
pollutant within the scope of this term.Therefore,the same methodology and factors were used when examining emission
reduction technologies and strategy,but this process was applied to halogen emissions,including emissions of Cl2.The
UDAQ has analyzed four control technologies and emission reduction strategies which are used to develop the emission
reduction plan for point source pollution of halogens.
Based on the Halogen Point Source Emission Inventory from 2020-2022,US Magnesium’s (USM)Rowley Plant12
accounts for 96.9%of the eight reactive chlorine gas compounds that were inventoried.Since the USM Rowley Plant
produces the overwhelming majority of the inventoried halogen emissions in the area of concern,this analysis focuses on
ways to limit halogen emissions from the plant.The same inventory also shows that hydrogen chloride (HCl)and chlorine
gas (Cl2)accounted for 98.9%of the total area source inventoried halogen emissions.From 2020-2022,Cl2 alone
accounted for 79.3%of all the inventoried halogen emissions and USM’s Rowley Plant was the producer of 99.8%of the
Cl2 emissions in the inventoried locations.As a result of the lack of available emission data for other halogenated
compounds,this analysis focuses on Cl2.It is assumed that strategies which reduce Cl2 emissions would also reduce other
halogenated compounds such as bromine (Br2),bromine monochloride (BrCl),and hydrogen bromide (HBr).This
assumption could be verified after the installation or implementation of an emission reduction strategy through on-site
testing.
The four control technologies and emission reduction strategies discussed in this analysis include:(1)updating current
control technology to reduce halogen emissions from the plant;(2)adding additional control technology to reduce halogen
emissions from the plant;(3)limiting production to reduce halogen emissions from the plant;and (4)changing the process
of the plant.The first two options are considered control technologies,while the second two are considered emission
reduction strategies.
US Magnesium Background
There are two primary processes which produce excess Cl2 at USM’s Rowley Plant.During the final stages of the13
refinement,molten magnesium chloride (MgCl2)salt is transferred to electrolytic cells and magnesium (Mg)is separated
from Cl2.The anode gas chlorine produced from the electrolytic cells is piped to the chlorine plant where some is liquified
and some is recycled for other use at the plant.The remaining chlorine tail gas from the chlorine plant passes through
13 Tripp,Thomas G.(2009)“Production of magnesium from Great Salt Lake,Utah USA,”Natural Resources and Environmental
Issues:Vol.15,Article 10.
12
https://lf-public.deq.utah.gov/WebLink/DocView.aspx?id=392316&repo=Public&searchid=b4d1afc5-65c0-4cf7-98c8-bd334965c2c9
Utah Halogen Emission Reductions &Standards•Utah Divisionof Air Quality 14 of 21
destruction equipment before being released to the atmosphere.The melt-reactor process requires an excess of Cl2 to
facilitate the conversion of magnesium oxide (MgO)to MgCl2.The offgas of the melt and reactor cells is sent to
destruction equipment before being released to the atmosphere.
The primary control technology used by USM to reduce Cl2 is a chlorine reduction burner (CRB).The CRB has a
suggested destruction efficiency of 99.2%.The CRB receives the tail gas from the chlorine plant and the offgas from the14
melt-reactor process and converts Cl2 into HCl .USM uses a chlorine bypass scrubber (CBS)to control Cl2 emissions
when the chlorine plant or the CRB are not operating.The CBS has a suggested destruction efficiency of 95%.If the
chlorine plant is down,the CBS receives all of the anode gas chlorine from the electrolytic cells.If the CRB is down,the
CBS receives all of the tail gas from the chlorine plant.The CBS uses ferrous chloride (FeCl2)as a scrubbing agent and
converts Cl2 into ferric chloride (FeCl3)which is recycled at the plant.
USM utilizes very efficient control technology and has methods in place to capture Cl2 emissions in the event that the
chlorine plant is down.However,the CRB regularly has scheduled maintenance and needs to be completely rebuilt
roughly once every three to five years.During periods of CRB downtime,the chlorine tail gas from the chlorine plant is
routed to the CBS,but the Cl2 emissions from the melt-reactor process are not controlled.So,when the CRB is down,
USM continues operation and Cl2 emissions from the melt-reactor process are not captured by any control technology,
resulting in fully uncontrolled emissions from the melt-reactor process.
Because of USM’s unique refining process,USM’s Approval Order (AO)and Title V Operating Permit contain a
maintenance emission limit.A maintenance emission limit is unique to USM and not found in any other approved permits
issued by UDAQ.Once the Mg refining process is running,there is no way to quickly stop production without threatening
refined magnesium and other valuable resources.Furthermore,because of the nature of the refining process and the
chemical compounds used,the plant is continually undergoing different forms of maintenance and repair.The CRB needs
to be completely rebuilt roughly once every three to five years depending on throughput,but numerous smaller occasions
of downtime occur on a consistent basis.The idea of the maintenance limit was to allow USM to continue operation and
not exceed their rolling 12-month Cl2 limit during periods of unforeseen maintenance and during periods when the CRB is
being rebuilt.
Currently,USM’s plant-wide Cl2 emissions are limited to 3,300 tons per rolling 12-month period.USM’s Cl2 emissions
from maintenance are limited to 7,500 tons per rolling 60-month period.The first requirement of USM’s AO is as follows:
II.B.1.a The following plantwide emission limits shall not be exceeded:
A.Plant-wide chlorine emissions shall not exceed 3,300 tons per rolling 12-month
period.Emissions from scheduled maintenance shall not be included in
calculating compliance with the plant-wide chlorine limit
B.Chlorine emissions from maintenance shall not exceed 7,500 tons per rolling
60-month period.
[R307-401-8]
14 For emission calculation purposes,USM uses 98%efficiency and adjusts the efficiency of the CRB to include downtime.
Utah Halogen EmissionReductions&Standards •Utah DivisionofAir Quality 15 of 21
Below is a detailed examination of the four control technologies and emission reduction strategies outlined in the
introduction of this analysis,including:(1)updating current control technology to reduce halogen emissions from the
plant;(2)adding additional control technology to reduce halogen emissions from the plant;(3)limiting production to
reduce halogen emissions from the plant;and (4)changing the process of the plant.
1)Updating Current Control Technology
One possible way to update current control technology is to create a physical connection between the CRB and the CBS.
Therefore,during periods of CRB downtime,Cl2 emissions that would have been previously uncontrolled could be routed
to the CBS which often has excess scrubbing capacity.While the CBS would not be able to control all of the CRB
scheduled maintenance emissions since it also handles chlorine plant downtime and chlorine tail gas emissions,USM has
suggested it could control 75%of the CRB downtime Cl2 emissions.This would represent a significant reduction in Cl2
emissions during CRB downtime.
Over the last five years USM has reported that scheduled maintenance events accounted for 44 tons of Cl2 per month (528
tons per year (tpy))and 3,263 tons of Cl2 per rolling 60-month period.Since April 2009,based on USM’s Chlorine
Emission Reports submitted to the UDAQ,on average,scheduled maintenance events accounted for 97 tons of Cl2 per
month (1167 tpy)and 5,280 tons of Cl2 per rolling 60-month period.A 75%reduction in Cl2 emissions from scheduled
maintenance would greatly reduce halogen emissions from USM’s Rowley Plant and would predominantly stop periods of
uncontrolled Cl2 release into the atmosphere.
A conservative look at the last five years of data (July 2018 -July 2022)suggests this control technology update would
result in a reduction of 33 tons of Cl2 per month (396 tpy)and 1,980 tons of Cl2 per rolling 60-month period.USM has15
estimated that the cost of this project would cost approximately $204,000.This equates to $515/ton of Cl2 removed which
the UDAQ deems economically feasible.Therefore,this control option would be considered a viable emission reduction
strategy.
2)Adding Additional Control Technology
There are several possible ways to utilize additional control technology to reduce halogen emissions for USM’s Rowley
Plant.The first control option would be the installation of a secondary CRB.The plant would effectively operate two
CRBs at the same time,utilizing the secondary CRB whenever the primary CRB requires maintenance.While this would
allow for a 99.2%reduction in maintenance emissions,well above the 75%identified in option 1 above,it would require a
large energy impact.A CRB takes between 5-30 hours to start up.Maintenance at USM’s Rowley Plant is often required
without days of notice,thus in order to be used effectively,the secondary CRB would need to run continually on standby.
During peak production USM has estimated that a CRB can use between 250,000 and 400,000 million cubic feet (MMCF)
of natural gas annually.Running a secondary CRB would roughly double this fuel usage.This control option would
reduce annual Cl2 emissions by 517 tpy.However,because of the increased fuel combustion and resulting criteria16
pollutant emissions,the UDAQ does not recommend this control from an economic,energy,and environment standpoint.
A second option is to use two separate sites for CRBs.USM rebuilds their CRB roughly once every five years.Instead of
waiting until the CRB needs to be rebuilt,USM could begin rebuilding a second CRB in a separate site prior to the
primary CRB’s complete deterioration.This would still require the large initial capital costs associated with a secondary
CRB,yet some of these costs would be nullified since USM already rebuilds the CRB once every five years.Once the two
16 Determined using USM’s data from the last five operational years and a secondary CRB efficiency of 98%.
15 Expanding this control to data back to April 2009,the 75%control on maintenance emissions would cause an average reduction of
73 tons of Cl2 per month (873 tpy)and 3,960 tons per rolling 60-month period.
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sites are set up,USM would be able to rebuild one CRB,use it for roughly five years,rebuild the next CRB,and
effectively switch between the two.This control would reduce Cl2 emissions associated with the periods during which the
CRB is being rebuilt.However,because the CRB is only rebuilt roughly once every five years,the UDAQ does not
recommend this option due to the large capital costs associated with it.
A final option is to install and use a scrubber designated specifically for periods of scheduled maintenance.Instead of
using the CBS which USM has conservatively estimated can only control 75%of Cl2 emissions during maintenance,USM
could add a scrubber dedicated solely for this purpose.The chlorine maintenance scrubber could be connected to the CRB
and control any downtime emissions by 95%.This control would be 20%more efficient than establishing a connection
between the CRB and the CBS and would reduce Cl2 emissions by an additional 106 tons per year.In order to justify this
additional reduction,the cost of the control technology would need to be around $1 million to be viewed as17
economically feasible.Because a chlorine scrubber is estimated to cost substantially more than $1 million,the UDAQ
does not recommend this option.
3)Limiting Magnesium Production
A different approach to reduce USM’s halogen emissions is to limit the plant’s production.If less magnesium is being
produced,then less Cl2 will be produced from the electrolytic cells,and less Cl2 will be produced from the melt-reactor
process.However,since the liquefaction process which occurs at the chlorine plant and because of the recycling of the Cl2
which occurs at the plant,the Cl2 reduction is hard to estimate and may not be one-to-one.For the purposes of this
analysis,the UDAQ has assumed that if magnesium production was cut in half,the tail gas from the chlorine plant and the
offgas from the melt reactor process are also cut in half .Using these assumptions,if USM reduced magnesium18
production by half,their Cl2 emissions would also be cut in half.
Currently USM is not limited by any magnesium production limit and as of October 2022 USM has not been operating
magnesium production in any capacity.The most straightforward way to limit USM’s production would be to reduce the
Cl2 limits in the USM’s AO and Title V permit.A substantial reduction in the Cl2 Limit would force USM to limit
production by some degree.The UDAQ does not recommend this strategy as USM is the only magnesium producer of
refined primary magnesium ore in the United States.Magnesium is a strategic resource and limiting production could
have a large impact on USM’s revenue and the availability of a critical resource utilized in a wide array of industries.
Furthermore,a large reduction in production would not be an economically feasible way of reducing emissions.
4)Changing Refining Process
USM has spent the last 50 years updating and improving their magnesium refining process.MgCl2 occurs naturally in the
Great Salt Lake.The natural magnesium concentration in the lake is about 0.45%by weight and the natural Cl2
concentration in the lake is about 7%by weight .A large portion of USM’s refining process involves creating a19
concentrated MgCl2 brine through solar evaporation.Because of the nature of the compound which occurs naturally in the
Great Salt Lake,Cl2 will always be a byproduct when magnesium is refined.At this time,the UDAQ is not aware of any
ways to modify USM’s refining process to reduce halogen emissions,and therefore cannot recommend this strategy.
19 Tripp,Thomas G.(2009)“Production of magnesium from Great Salt Lake,Utah USA,”Natural Resources and Environmental
Issues:Vol.15,Article 10.
18 In reality,the tail gas from the chlorine plant would probably be much less than half if USM desired to continue to produce liquid
chlorine at normal production rates.
17 A cost of $1 million would equate to $9,434/ton of Cl2 removed.
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Conclusions and Recommendations
After examining possible control technology and emission reduction strategies,the UDAQ has concluded that requiring
USM to create a connection between the CRB and the CBS and using the CBS to control melt-reactor emissions during
periods of maintenance when possible,is the most technologically and economically feasible option to reduce halogen
emissions from the Rowley Plant.
This control technology would limit USM’s currently permitted maintenance emissions by 75%.USM is permitted to
produce up to 7,500 tons of Cl2 from scheduled maintenance every rolling 60-month period.From a potential-to-emit
perspective,implementing this technology would reduce possible maintenance Cl2 emissions by 5,625 tons every five
years,or 1,125 tons every year.USM generally produces far less than 7,500 tons of Cl2 due to scheduled maintenance per
rolling 60-month period,however from April 2009 to September 2022 USM reported producing an average of 97 tons per
month of Cl2 from scheduled maintenance.This equates to 1167 tons per rolling 12-month period and 5,835 tons per
rolling 60-month period.A 75%reduction in these emissions would still represent a substantial reduction in emissions of
halogenated compounds.
Figure 1 shows USM’s maintenance,non-maintenance,and plant-wide total (which includes maintenance and
non-maintenance emissions)Cl2 emissions.Figure 1 uses monthly reports from USM from April 2009 to February 2024.
Figure 1.US Magnesium reported chlorine emissions in tons per year.
In the past 15 years,USM reported emitting over 500 tons of Cl2 in a single month eight times.In October 2011,USM
reported emitting 1,562 tons of Cl2,of which 1,505 tons were categorized as scheduled maintenance.As of October 2022,
USM has not reported any Cl2 emissions from the Rowley Plant.Figure 2 shows USM’s maintenance,non-maintenance,
Utah Halogen Emission Reductions &Standards•Utah Divisionof Air Quality 18 of 21
and total Cl2 emissions if maintenance emissions were reduced by 75%,as would be achieved if the recommended control
option were to be installed.Figure 2 uses the same monthly data reported by USM from April 2009 to February 2024,but
applies a 75%reduction to maintenance emissions as would be achieved if these emissions were controlled by the CBS
during periods of maintenance as recommended.
Figure 2.US Magnesium reported chlorine emissions in tons per year with a 75%reduction of maintenance emissions.
If the recommended control was implemented in April 2009,the 75%reduction in maintenance emissions would have
kept USM from producing over 500 tons of Cl2 in any single month.In the month of October 2011,USM would have
produced roughly 433 tons of Cl2 instead of 1,562 tons of Cl2.Figure 3 shows USM’s 12-month rolling totals.The chart
indicates the source-wide 12-month rolling total (which includes both maintenance and non-maintenance emissions),the
non-maintenance 12-month rolling total,and the non-maintenance 12-month limit of 3,300 tons of Cl2.
Utah Halogen Emission Reductions &Standards•Utah Divisionof Air Quality 19 of 21
Figure 3.US Magnesium Chlorine Rolling Total chlorine emissions in tons per year.
The 12-month reported non-maintenance emissions (in red)show that the USM generally produces less than 2,000 tons of
Cl2 from non-maintenance emissions from the plant.This is substantially less than the 3,300 tons of Cl2 which they are
permitted to produce from non-maintenance operation.However,if non-maintenance and maintenance emissions were
combined into a plant-wide 12-month rolling total (in blue),USM clearly would have exceeded the 3,300 tons rolling total
for roughly a year long period between 2017 and 2018.Figure 4 shows USM’s 12-month rolling totals if the
recommended controls were in-place and 75%reduction in maintenance emissions was applied.Figure 4 uses the same
reported data,but applies a 75%reduction to maintenance emissions.The 12-month reported non-maintenance emissions
(in red),remain the same in both Figure 3 and Figure 4.
Utah HalogenEmissionReductions&Standards •UtahDivision ofAir Quality 20 of 21
Figure 4.US Magnesium chlorine rolling total chlorine emission in tons per year with a 75%reduction in maintenance
emissions.
Figure 3 and Figure 4 illustrate how a 75%reduction in maintenance emissions affects the plant-wide Cl2 emissions.
Without the recommended control,USM’s combined maintenance and non-maintenance Cl2 emissions would have
exceeded the 3,300 tons for roughly a year long period between 2017 and 2018.With the recommended control and the
associated 75%reduction in maintenance emissions,the plant-wide Cl2 emissions would have remained below 3,000 tons
for each of the past 10 years.
As the 75%maintenance emission reduction resulting from implementing the CBS to control emissions from the
melt-reactor process during periods of maintenance would have limited plant-wide Cl2 emissions at the Rowley Plant to
under 3,000 tons per rolling 12-month period for each of the last 10 years,the UDAQ further recommends that the
maintenance limit be removed for USM’s AO and Title V permit.By rerouting Cl2 emissions to the CBS during periods
when the CRB is down,USM would be able to continue normal operation and while remaining below their annual limit of
3,300 tons of Cl2.
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