How to Determine Metals Emissions by EPA Method 29
By Ed Wallace, Project Chemist, Kelso, WA
EPA Method 29 measures hazardous air pollutant (HAP) emissions from stationary sources for mercury and other metals. The Clean Air Act (CAA) requires all major sources to meet HAP emission standards reflecting the application of maximum achievable control technology (MACT). These sources include industrial, commercial, and institutional boilers and process heaters. The other metals to be tested are antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, manganese, nickel, phosphorus, selenium, thallium and zinc.
Before the laboratory testing by Method 29 begins, a sample of the exhaust from the combustion process is withdrawn isokinetically from the source. Particles in the exhaust are deposited in a probe and heated filter. The metals and mercury in the gaseous emissions are recovered in a series of impingers containing aqueous acidic solutions of peroxide. The gas is passed through a further set of impingers containing acidic permanganate that are only analyzed for mercury. The filter, probe rinses, and impinger catches are carefully transferred to bottles for shipment to the lab.
At the laboratory, the volumes of the solutions are measured to allow the calculation of the weight of analyte per cubic meter of gas sampled. The metals in the particulate are calculated from the filter and the probe rinse (called the front half). The metals and part of the mercury in the gas are measured from the acidified peroxide impinger catches collected after the filter (aka back half). The rest of the mercury is collected in the acidic permanganate impingers.
By using ICP/MS to measure the metals content (except for phosphorus, which is best quantified using optical ICP), the lowest possible reporting limits can be achieved.
Typically, the metals are found in the front half particulate, with only about 10 to 20% of the metals detected in the back half impingers. The mercury tends to be in the particulate (front half) and in the precipitate from the permanganate impingers. Only a small amount of mercury is present in the acidified peroxide impingers.
With care in setting up the impinger train, attention to leak detection, thorough rinsing of the probe after sample collection and proper combing of the bottles at the laboratory, method 29 provides a reliable assessment of the metals in the flue gas.
Tags: antimony, arsenic, barium, beryllium, CAA, cadmium, chromium, Clean Air Act, cobalt, copper, emissions, EPA, EPA Method 29, HAP, hazardous air pollutant, impingers, lead, leak detection, manganese, Mercury, Metals, Method 29, nickel, particulate, permanganate, phosphorus, selenium, stationary sources, thallium, zinc