Research Note 95-6: Topic = Particle-Size Test Methods for Emissions

No. 95-6
March 1995
RESEARCH NOTES
California Environmental Protection Agency Brief Reports to the Scientific and Technical
Air Resources Board Community

Research Division, John R. Holmes, Ph.D., Chief P.O. Box 2815, Sacramento CA 98512

Particle-Size Test Methods for Sampling High- Temperature and High-Moisture Sources

Source sampling equipment and procedures were developed for determining the particle size distribution of effluents that are high in temperature or high in moisture. Sources of these types have frequently been encountered that are or may be subject to regulation, but which have been difficult or impossible to test. Suitable methods for sampling these sources are described in this study, which was performed by Southern Research Institute.

Background:

Under California's toxic air contaminant (TAC) program, the ARB provides assessments of facilities that emit TACs. The particle size distribution of the emissions is an important factor, because this is used to calculate a deposition rate, which in turn is used for assessing risk. The particle size distribution must also be known in order to determine control efficiency because control measures often include limits that are based on emission rate and control efficiency.

High-temperature environments (above 1300 degrees F) are difficult to test because of the need for equipment that can withstand high temperatures. In the case of high-moisture environments, the moisture promotes the formation of droplets that can overload the sampling system or wash the sample off the collection surfaces.

Examples of high-temperature sources include uncontrolled hospital and municipal waste incinerators, landfill gas-burning flares, and effluent from cement kilns and illicit drug incinerators. Examples of high-moisture sources include scrubbers used in pulp and paper manufacturing and steam generators used in thermally enhanced oil recovery.
Methods: ARB's cascade impactor methodology for sizing of particles was modified for sampling of both high-temperature and high-moisture gas streams. In both cases, large drops and/or particles are collected in adaptations of a right-angle precollector. In the wet stream sampling, the remaining droplets are passed to the impactor through a heated inlet tube, where they are evaporated to dryness. In the high temperature case, the sampled gases are passed through an air-cooled tube until they are cool enough for collection in a standard impactor.

The high-moisture particle size measurement apparatus developed in this project is the same as that required for ARB's Method 501 (Determination of Size Distribution of Particulate Matter from Stationary Sources), with additions. A University of Washington Pilat Mark V cascade impactor was used. The additions include a liquid droplet precollector, a heated interconnecting tube, a heating jacket for the impactor body, thermocouples, and temperature controllers. The liquid droplet precollector is an EPA right-angle precollector modified to include greater internal volume, permitting collection of relatively large amounts of water. Prior to sampling, power is applied to the heaters to bring them to optimal operating temperatures.

The high-temperature particle size measurement apparatus developed for this project is also a modification of ARB's Method 501. A Pilat Mark V cascade impactor was used. The additions include a high-temperature precollector using a Hayes high-temperature "super-alloy" that allows operation up to 2000 degrees F, a sheathed air-cooled probe (also fabricated with a Hayes alloy), a heating jacket for the impactor body, thermocouples with braided ceramic insulation, temperature controllers, and a blower to provide cooling air for the probe. Operation of the high-temperature sampler requires pre-heating of the impactor and equilibration of the inserted portion of the probe. Participation of at least two people is recommended for the insertion and removal. An hour-long cool-down period is recommended after removal of the apparatus from the high-temperature source.

Demonstration tests were conducted at two sites. The wet source was a stack downstream of a scrubber that is used to control emissions from a medical waste incinerator, and the high-temperature source was the exhaust of a flare burning landfill gas. The size distribution for particles less than 50 micrometers in diameter was determined.
Results: Before fabricating the new sampling equipment, the investigators produced a review of the fundamentals of basic particle sizing techniques, including optical and inertial methods, that will be of value to many researchers and commercial source sampling companies. After completing the demonstration tests, the contractor developed wet-source and high-temperature sampling proce-dures and a computerized data reduction system for the cascade impactor.

During sampling at the wet source, stack temperatures averaged about 160 degrees F, and the moisture content ranged from 30 to 35 percent. Most of the final dry particulate matter collected was smaller than one micrometer in diameter, and the evaporative residues from the precollector were all quite small (a few micrograms). The method appeared to perform well.

During sampling at the high-temperature source, gas temperatures at the flare ranged from 1650 to 1840 degrees F. No significant collection of particles was expected from the landfill gas combustion, and none was found for the sampling times employed (two hours). Overall, the method and the hardware performed well.
Significance and Application: The contractor has provided source testing procedures based on the outcomes of this study. ARB intends to propose the newly designed methods as official ARB source-test methods.

The results provide important new tools for ARB's Monitoring and Laboratory Division to test sources as requested by the Stationary Source Division. With these tools, ARB will be able to better assess health risks represented by exposure to emissions from several stationary sources.
Related Projects: Assessment of Combustion Sources That Emit Polychlorinated Dioxins and Furans, Polycyclic Aromatic Compounds, and Other Toxic Compounds, ARB Contract No. A832-124, January 1992, by Midwest Research Institute, reports results of source sampling at recycled waste oil combustion facilities, and at drum reconditioners. Improved Methods for PAH Combustion Source Sampling, ARB Contract No. A932-098, by the California Department of Health Services, Environmental Health Laboratory Branch, reports on the development of a new reduced-artifact dilution sampling system to assist in assessing stationary combustion sources that emit polycyclic aromatic hydrocarbons.

This research was conducted under contract with Southern Research Institute (ARB Contract No. A132-084). Comments or questions can be directed to the contract manager, Ralph Propper, by mail, FAX (916) 322-4357, phone (916) 323-1535, or e-mail: rpropper@arb.ca.gov. For an index of Research Notes, call (916) 445-0753 or FAX (916) 322-4357.
Copies of the research report upon which this Note is based can be ordered from:
National Technical Information Service
5285 Port Royal Rd
Springfield VA 22161
Request NTIS No. PB95-170221
Title: Development of Particle Size Test Methods for Sampling High Temperature and High Moisture Source Effluents
Author: Joseph D. McCain