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12/1/1997 | 11 MINUTE READ

New Chromium Emission Standards

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Lower MACT standards are forcing electroplaters to change their control technology...


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Recently, the EPA issued standards that limit the discharge of chromium compounds into the air from hard and decorative chromium plating and anodizing operations. The new regulations affect both existing and new chromium emission sources and all facilities that use chromium electroplating or anodizing tanks. Affected facilities must limit chromium emissions to the level of the "maximum achievable control technology," also known as the MACT standard. EPA's final rule on the MACT Standard for chromium emissions was made known in 60 Fed. Reg. 4948 (January 20, 1995).

EPA promulgated the final MACT standard for chromium emissions under amendments to the Clean Air Act, which added 189 hazardous air pollutants (HAPs) for regulation, including chromium compounds. Facilities emitting these HAPs must reach the maximum degree of emissions reduction deemed achievable. The MACT standard attempts to curtail air toxins released during certain electroplating and anodizing processes. The emissions of concern are chromium compounds mainly in the form of chromic acid mist. EPA contends chromium electroplating and anodizing tanks are significant sources of chromium emissions, and that more than 5,000 facilities perform chromium plating or anodizing.

Electroplating sources. Chromium electroplating is a process that electrochemically deposits chromium from a solution of chromic acid onto a metal or plastic part. The two processes used to plate chromium are hard plating and decorative plating. Chromium emissions result from mist produced by the electrochemical reactions. The chromium bath produces small bubbles of hydrogen and oxygen gases that burst at the surface of the plating solution, generating substantial amounts of fine mist comprised of particulates of plating solution. When more current is applied, more gassing and misting occurs. As in plating operations, chromic acid emissions are formed in anodizing tanks as a result of the evolution of hydrogen and oxygen gases.

Hard chromium plating is used to protect metal components from wear and corrosion. Industrial rollers, hydraulic cylinders and crankshafts are examples of industrial applications of hard chromium electroplating. Through the electroplating process, a thin layer of chromium is deposited on the base metal or metal alloy surface of a workpiece where resistance and hardness are important attributes. In these applications the workpiece is submerged in a chromic acid (hexavalent chromium) bath.

Decorative electroplating deposits a thin layer of chromium on base metals and plastics in applications where a bright finish and tarnish resistance are important, but wear is not. Decorative plating is used on bicycle parts, auto trim and work tools. Many decorative chromium tanks use a trivalent chromium bath.

Anodizing is an electrolytic process that produces an oxide layer on the surface of a base metal, usually aluminum, for corrosion resistance or electrical insulation. Anodizing is commonly used on aircraft parts and building structures.

Determining applicable emission limits. The MACT regulation affects all facilities that use chromium electroplating or anodizing tanks, regardless of size. The degree to which facilities are affected depends on the size and type of operation and the type of pollution control techniques. Decorative chromium operations were required to comply with the new emissions regulation by January 25, 1996. Hard chromium electroplating and chromium anodizing operations had to comply by January 25, 1997. EPA believes that the vast majority of chromium electroplaters did not upgrade their emissions equipment as required because they were not informed about the MACT standard deadlines.

In order for existing electroplating operations to evaluate their compliance requirements under the new standard, the facility must determine its regulatory status: new or existing, large or small. Existing tanks are those installed prior to December 16, 1993. All others are new. Small hard chromium facilities include those that have a maximum cumulative potential rectifier capacity (MCPRC) less than 60,000,000 amp-hr/yr. Large hard chromium facilities include those that have an MCPRC greater than or equal to 60,000,000 amp-hr/yr.

The official MCPRC for a facility is calculated as follows. The calculation assumes a maximum potential operating schedule based on operating 24 hours per day, seven days per week, 50 weeks per year for a total of 8,400 hours per year. The calculation further assumes that electrodes are energized 70 pct of the total operating time. The total installed rectifier capacity of all the tanks at a facility, expressed in amperes, is multiplied by 8,400, then by 0.7. The result is the facility's MCPRC.

Basic control technologies. The new emission limits are tied to the facility's choice of air pollution control techniques. Air pollution control techniques include any add-on pollution control device or chemical additive that is used to reduce chromium emissions from plating and anodizing tanks. Standards under the MACT rule are tied to three different types of control technologies that are commonly used in plating operations. The three types are packed-bed scrubbers, composite mesh-pad systems and fume suppressants.

Packed-bed scrubber (PBS) systems involve the use of an air pressure ducting system to capture chromium emissions from plating tanks that are routed through duct work that terminates in a scrubber prior to venting to the atmosphere. The PBS system is the predominant scrubber design used to control emissions of chromic acid mist from plating and anodizing operations. PBS-controlled devices consist of single- or double-packed beds that collect and accumulate chromic acid droplets. The scrubber is packed with a media, usually catalytic pieces, that capture and collect particulates of chromium through physical and chemical processes.

The composite-mesh-pad (CMP) system collects and transports chromium emissions similar to the air pressure system described previously, except the emissions are fed through a mesh blanket-type pad where the chromium particles are condensed and collected, primarily through physical means. A CMP system typically consists of several mesh-pad stages. Early stages remove large particles, intermediate stages remove smaller particles and final stages remove microscopic particles. The CMP system is effective at removing droplets and eliminating the discharge of chromic acid mist.

Fume suppressants are chemical agents added to the chromium bath to reduce the amount of chromium lost at the surface. Chemical suppressants are surface-acting compounds that are added directly to plating and anodizing baths. These chemical additives usually contain some type of agent designed to reduce misting of chromium at the bath surface rather than attempting to collect emissions prior to atmospheric discharge. Suppressants are widely used by decorative chromium electroplaters and chromic acid anodizers. In contrast, suppressants are seldom used by hard chromium platers because of their cost and effect on final product quality.

Suppressants are classified as wetting agents, foam blankets or combinations of the two. Wetting agents reduce misting by lowering the surface tension of the plating or anodizing solution, which substantially mitigates mist formation. Foam blankets generate a layer of foam across the surface of a solution, which reduces misting by entrapping chromic acid mist as it forms at the surface of the plating tank. Combination wetting agents/foam blankets reduce misting by both methods.

Specific pollution limits. The three basic control techniques previously described are used to categorize the specific emission limits required under the new MACT regulation. The limits are defined by the level of chromium discharged in the exhaust air. The emission limits are expressed as a concentration of chromium in milligrams per dry standard cubic meter (mg/dscm) of exhaust air. Owners or operators of small, existing hard chromium electroplating tanks and facilities are required to meet an emission limit of 0.03 mg/dscm of ventilation air, which is based on the application of packed-bed scrubbers. Owners or operators of large, existing hard chromium electroplating tanks are required to meet an emission limit of 0.015 mg/dscm, which is based on the use of a composite mesh-pad system. Owners or operators of small or large, new hard chromium electroplating tanks are required to meet an emission limit of 0.015 mg/dscm of ventilation air, which is based on the application of the composite mesh-pad system.

All new and existing decorative chromium electroplating tanks are required to either meet a total chromium emission limit of 0.01 mg/dscm or use a wetting-agent-type fume suppressant in the plating bath and maintain a bath surface tension less than 45 dynes/cm. All new and existing decorative chromium electroplating operations that use a trivalent chromium plating process and a wetting agent are required to notify EPA that the trivalent chromium process is being used and must provide the bath's components. Subsequent notification is required if a change is made to the bath such that a different standard applies to the tank. All new and existing chromium anodizing operations are required to either meet an emission limit of 0.01 mg/dscm or use a wetting-agent-type fume suppressant in the plating bath and maintain a surface tension less than 45 dynes/cm.

Combinations of technology and other options. The regulated entity may use another control technique, as long as the level of control is the same as or better than its requirements. For example, a facility may be able to use a fume suppressant with its existing scrubbers to meet the new MACT standard. If upgrading, a facility may use either the packed-bed or composite-mesh-pad system, as long as it meets the emissions standards.

Regulated facilities should realize that users of trivalent chromium are subject to far less reporting and emission requirements than are users of chromic acid baths. This is because the hexavalent form of chromium found in chromic acid is carcinogenic and toxic. Although it is associated with decreased lung functions, the trivalent form of chromium is less toxic.

Regulated entities should examine whether their processes can use trivalent chromium instead of chromic acid to lower emissions and avoid the regulatory requirements associated with hexavalent chromium.

Progress has been made in developing technology to control or eliminate emissions from plating and anodizing tanks. One new technological development worth considering eliminates emissions of hexavalent chromium through sealable hoods or covers installed over plating bath tanks that contain the mist created during electroplating operations. Since such sealed control devices do not emit chromic acid from inside the building to the atmosphere, the air emission standards for electroplating and anodizing do not apply. Although the price of retrofitting tanks with sealable hoods is costly, when compared to installation and maintenance of control technology required under the MACT standard, some facilities may elect to spend the extra money to avoid regulation altogether.

Notification and testing requirements. EPA required all facilities with existing tanks to submit an initial notification on or before July 24, 1995, which required potentially regulated facilities to report their location, rectifier capacity and other information. New and reconstructed sources with initial start-up after January 25, 1995, were required to notify EPA of the actual start-up date within 30 calendar days. After January 25, 1995, no one may begin construction on new or used sources without submitting a notification.

Each facility must participate in a one-time initial performance test to determine whether it meets the emission limit for its type of operation. The one-time test was required by July 23, 1996, for decorative chromium platers and by July 24, 1997, for hard chromium platers and chromium anodizers to demonstrate they are meeting the emissions limit for their type of operation. All regulated entities must notify EPA in writing of their intent to conduct this one-time test at least 60 calendar days before the scheduled test date to allow EPA to observe. Facilities required to complete performance testing must use EPA test methods 306 and 306A for measuring the chromium concentration discharged to the atmosphere. Test results must be disclosed to EPA no more than 90 days after the test is performed.

Entities subject to the MACT Standard must submit a Notification of Compliance Status Form within 90 days after any required initial performance test or no later than 30 days after the compliance date if testing is not required. This form requires the regulated entity to report the type of test method used to determine the facility's compliance and the pollution control equipment used.

Costs of compliance. According to EPA, the average electroplating shop is a small business with annual sales greater than $1,000,000. Most of these facilities are located near residential areas. EPA estimates the average price to purchase a packed-bed scrubber or a composite-mesh-pad system ranges from $27,000 to $186,000, depending on the size of the operation. Annual maintenance costs range from $10,000 to $45,000 for a PBS system, $14,000 to $84,000 for a CMP system and $1,000 to $17,000 for suppressants.

The initial compliance test costs about $1,150 per stack if a facility performs the test in-house or $4,500 per stack if a contractor is used. On average, the annual cost for monitoring, recordkeeping and reporting is $2,300 per facility.

Industry concerns and insights. The plating industry is particularly concerned with that portion of the regulation that imposes chromium emission limits on platers and anodizers. The remainder of the rule imposes less intrusive work practice requirements regarding pollution control, equipment maintenance, compliance monitoring, recordkeeping, notification and reporting.

According to EPA, the high toxicity of chromium compounds and the close proximity of many shops to residential areas warrant regulation of all sources, even small businesses. EPA estimates that full compliance will result in a reduction of about 173 tons of chromium emitted into the air annually, or about a 99 pct reduction from the current level. It also believes the economic impact to the industry will be minimal. However, electro-platers question both the cost and benefit assertions of EPA.

EPA believes the MACT regulation will cause the closure of 37 to 60 of the 1,170 small operations. It also believes the economic impact in terms of small business closures will result in less than five pct of all small operations going out of business as a result of these regulations. EPA estimates that the annual control costs of compliance are about $19,000, or less than two pct of average annual sales. However, the electroplating industry believes these figures are grossly understated. EPA further calculates that product price increases resulting from implementation of the most costly control option generally will be less than one pct.



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