Sulfuric Acid Mist Sampling and Controlled Condensate (NCASI Method 8a) Testing

Criteria Pollutants and MACT related air toxics such as Mercury and HCl get a lot of attention in the field of air-quality analysis and emissions testing (stack testing), but other, less-known pollutants can and do cause issues for facilities. Sulfuric Acid Mist (H2SO4) is one such pollutant.

 

Sulfuric acid emissions

Sulfuric acid emissions have traditionally been measured using EPA Method 8. This method utilizes the principle of selective solvent absorption (SSA) and captures sulfur trioxide (SO3) and H2SO4 in an isopropyl alcohol (IPA) solution, and SO3 in a low concentration of hydrogen peroxide. A drawback to this method, however, is that it was developed and originally promulgated to determine SO3/H2SO4 emissions from stationary sources in the absence of other particulate matter. The principal drawback is the absence of a filter to effectively remove PM and other pollutants prior to the capture of H2SO4 in IPA. This can lead to interference from a number of filterable particulates and other pollutants, such as ammonia, and may result in emissions reading much higher than expected, making it difficult to achieve compliance with the emissions standards.

 

NCASI Method 8a

NCASI Method 8a, originally Conditional Test Method (CTM)-013, was developed as an alternative to EPA Method 8, and uses a heated quartz filter for capturing particulates, thereby eliminating the potential for interference from particulate sulfate and other interference. For sources that are having trouble with obtaining low emissions of H2SO4, and particularly those that have been using ammonia-injection control technology, the use of this method can result in a significant reduction in reported emissions from the source, by removing these varying interferences.

The quartz filter is maintained at temperatures above 500 degrees F, allowing the gaseous SO3/H2SO4 to pass through and be selectively condensed in a temperature-controlled condenser. The condenser cools the flue gases below the dew point of the SO3/H2SO4, but above the dew point of water, eliminating the potential for interference from SO2. The method was developed and validated as an alternative for determining sulfuric acid emissions from combination boilers and recovery furnaces equipped with dry particulate control devices, and tested extensively on kraft recovery furnaces. It was specifically approved by the EPA for use on recovery furnaces in 1996.

 

Potential Issues

There are two potential issues with utilizing this method. The first is that it utilizes special equipment that not many testing firms have. The equipment costs several thousand dollars, which creates a large up-front cost to conducting tests using this method. The second is that the method is not specifically approved for any units other than recovery furnaces, and compliance tests performed by this method must be approved by state regulators on a case-by-case basis.

 

Call in the Professionals

ESS, an air-testing firm out of Wilmington, North Carolina, has the equipment and experience to conduct this test method for facilities that are currently or potentially regulated for H2SO4. ESS has requested and received variances from state regulators for use on biomass boilers, paper mills, and ceramic kilns for compliance-level testing. In all cases so far, the use of this alternative method has greatly improved the reported emissions of H2SO4, and helped our clients achieve compliance with the emissions standards their units are subject to.

If your facility is expected to be regulated for sulfuric acid mist, you need a testing partner that can achieve the best results. Give ESS a call today at  (910) 799-1055.

Overcoming the Stack Testing Challenges of PM and Method 201a

Stack Test MethodologiesParticulate Matter (PM) is the term for solid or liquid particles found in the air – more accurately referred to as aerosols. Worldwide, most atmospheric aerosol particles (approximately 90%) are produced by ‘natural’ processes such as grinding and erosion of land surfaces resulting in dust, salt-spray formation in oceanic regions, biological decay, forest fires, chemical reactions of atmospheric gases, and volcanic injection. The balance of the PM is anthropogenic in source – from industry, agriculture, transport and construction. Particulate size, elemental breakdown and color can vary significantly between the many sources.

PM can have high levels of toxicity and is considered by the Clean Air Act as one of the Criteria Pollutants. Originally, the focus has been on Total Suspended Particulates (TSP), but over the past decade the EPA has put a greater emphasis on the measurement of smaller particles, those less than 10 and 2.5 microns in diameter (PM10 and PM2.5). This is due to the greater health risk associated with the smaller particles, which are capable of reaching into the lower regions of the respiratory system.

From an emissions sampling standpoint, this has increased the importance of quantifying emissions in specific size ranges, rather than the analysis of total filterable particulate (by EPA Method 5). The most widely accepted methodology for determination of PM10 and PM2.5 from stationary sources is Method 201a. This isokinetic method requires some of the same sampling equipment as Method 5, but includes the addition of sizing cyclone(s) upstream of the PM filter. What is not as well-known are the multiple challenges and limitations with Method 201a that can hamper testing or even make it unfeasible. Many of these challenges can be mitigated but require knowledge of the stack condition prior to the sampling date. Some of these major challenges are summarized below.

Test Port Size – As mentioned, the method requires a particular set of equipment: a probe (equipped with special pitot tube extensions and temperature sensor), in-stack PM sizing cyclone(s) and a nozzle. The cyclone and nozzle combination required for the method are typically stainless steel, inflexible, and have a wide circumference, often wider than the test ports installed in some of the older stacks. Method 5, typically, only requires 4″ test ports, but the 201a equipment requires a test port of 6″ minimum to fit the sampling probe inside, so a facility that is not prepared for 201a testing may find that its test ports are too small and testing cannot take place. Further, if the test port is long, an 8″ (minimum) test port may be required to prevent the nozzle from scraping the inside of the port wall. We urge our clients to properly verify test port configuration prior to our arrival on-site.

Moisture Level of the Stack (Saturated Stacks) – If water droplets are present in the stack, it is not possible to utilize the Method 201a cyclone. The spherical nature of PM is assumed when utilizing the Method 201a cyclone. If moisture is present, this can cause conglomerations of the PM and also cause the PM to stick to the cyclone walls. Additionally, the moisture-laden aerosol mists do not act spherically – thus biasing the results. The EPA-accepted measurement of fine particulates in saturated stacks is Method 5/202, which adds the total filterable PM and the condensable particulate matter (CPM). Although the US EPA has defined PM10 (or 2.5) in a saturated stack as the sum of the PM + CPM, it is clearly an overestimation of the stack emissions.

Temperature of the Stack – Another challenge with the method is dealing with the heat of the gas stream inside of the stack. If the stack gas temperature is over 30 degrees C (85 F), then the Facility must account for the measurement of CPM by Method 202. Therefore, PM10 (or 2.5) is measured as the sum of the filterable fine fraction plus the CPM.

Some of the equipment used in typical 201a trains has a temperature limit of approximately 260 degrees C (500 F) before problems occur with seizing, galling, or thermal breakdown. The method can be used at temperatures of up to 1,371 degrees C (2,500 F) but, in order to do this, it requires the usage of specialty high-temperature resistant material, which generally must be procured or prepared beforehand, and which can drastically influence the price of the testing.

Other Sampling Options/Purpose of Sampling – ESS frequently conducts engineering testing for clients evaluating flue gas streams for particulate matter. The analysis of such streams can provide useful information to control device manufacturers, efficiency experts, and boiler engineers. Although EPA Methodology is required for demonstration of compliance, ESS typically recommends other sampling methodologies for engineering testing.

Such methodologies can include isokinetic sampling on specialty media and analysis utilizing x-ray diffraction, computer-controlled scanning, electron microscopy, or GC/MS scanning. ESS frequently provides in-depth particulate analyses including particulate sizing and elemental composition. Depending on the goals of the sampling, ESS will propose the best methodology to meet your required outcome.  Read more about Stack Test Methodologies ESS is qualified to conduct.

Summary – These factors – port size, stack moisture level, flue gas temperature, and the purpose of the sampling – are all important considerations for your PM test series. The Method 201a/202 test takes more preparation than many other emissions test and requires more communication between the facility and the professional stack testing company being used for the conduct of the test.

As in all things, experience is the key to success. ESS has conducted hundreds of tests for PM, CPM, PM10 and PM2.5 since 1979 and has the knowledge and experience to provide reliable and acceptable results for your engineering or compliance test program. If you require PM/PM10/PM2.5 testing – or other air emissions sampling services – give ESS a call today: 888-363-0039

Stack Testing Methods

Stack Testing Methods

Stack Testing Methods

Whether for engineering purposes or for compliance with EPA regulations, source emissions testing — or stack testing — is an important part of a facility’s operations.

When conducting your stack test the methods used to conduct the testing must be understood and followed carefully, in order to obtain reliably accurate data that will be accepted by the EPA to show compliance.  These methods have been set by the EPA, and are available for public review on the EPA website, which has been linked at the bottom of this article.

A full understanding of each and every method is a long and difficult process that will often require the assistance of specifically trained engineers such as can be found in an experienced stack testing organization.

However, it is helpful to have a basic understanding of some of the more common types of stack testing methods, and for that purpose we have compiled a short list of commonly analyzed pollutants, and the EPA-approved methods used to test for them.

Particulate Matter (PM): EPA Methods 5, 201a, 202 – Particulate matter, also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. PM is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.  Particulates are categorized by size.  “Inhalable coarse particles,” such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter. “Fine particles,” such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller.  The smaller the particles the more hazardous they are, as they are more easily absorbed.

  • Method 5 is used to determine filterable particulate matter. The PM mass, which includes any material that condenses at or above the filtration temperature (248 +25oF) is determined gravimetrically.
  • Method 201a is used to measure filterable particulate matter (PM) emissions equal to or less than a nominal aerodynamic diameter of 10 micrometers (PM10) and 2.5 micrometers (PM2.5). You cannot use this method on a wet source.
  • Method 202 is used to measure condensable particulate matter. Method 5 and 201a only measure particulate matter that condenses at or above 248oF. Method 202 is used in conjunction with the above methods to account for PM emissions that condense below 248oF.

Gaseous Emissions (SO2, NOx, CO): EPA methods 3a, 6c, 7e and 10 – This is a catch-all term for a variety of air pollutants that are emitted in gaseous form.  The most common, according to the EPA, are:

  • Carbon monoxide (CO): EPA method 10 — A colorless, odorless gas emitted from combustion processes.  Particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources.
  • Nitrogen dioxide (NO2): EPA method 7e — One of a group of highly reactive gasses known as nitrogen oxides (NOx), also including nitrous acid and nitric acid. NO2 forms quickly from emissions from vehicles, power plants, and off-road equipment. It contributes to ground-level ozone, and fine particle pollution.
  • Sulfur dioxide (SO2): EPA method 6c — One of a group of highly reactive gasses known as “oxides of sulfur.”  The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%).  Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment.

Each of these methods uses a continuous instrumental analyzer to determine emissions, and requires mobile laboratories or access to climate controlled shelters. Real time results using these methods are available on a ppmvd basis.

Multiple Metals (As, Be, Cd, Cr, Pb, Hg, Ni): EPA Method 29 – This method can be used to determine emissions of 17 different metals, including mercury. Method 5 can be run in the same train to determine filterable particulate emission at the same time. Metals are found naturally in the environment, but also in manufactured products.  The most commonly tested metals include Lead, Mercury, and Arsenic.

Special Note on CEMS RATA: Many facilities use a system know as a CEMS, or Continuous Emissions Monitoring System, that provides continuous feedback on emission levels and act as a substitute for regular stack testing.  These CEMS units are subject to a 3rd party check known as a Relative Accuracy Test Audit, or RATA, to guarantee that it is reading emission levels accurately.   (See info on CEMS Testing)

For how to conduct the methods themselves, there is information available on the EPA website, in an index format, at the following webpage: http://www.epa.gov/region1/info/testmethods/

We invite you to contact Environmental Source Samplers (ESS) to learn more about our stack testing services.  Visit www.ESSKnowsAir.com or call 888-363-0039.

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