Final Report: Microdischarge-Based Multimetal Emission Monitoring SystemEPA Contract Number: EPD04015
Title: Microdischarge-Based Multimetal Emission Monitoring System
Investigators: Herring, Cy
Small Business: Caviton Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2004 through August 31, 2004
RFA: Small Business Innovation Research (SBIR) - Phase I (2004) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Air Quality and Air Toxics , SBIR - Air Pollution
Caviton, Inc., has developed a novel method for the detection of trace quantities of metals as well as other pollutants and chemicals. This method utilizes a microplasma, in which the chemical of interest is excited. The excited chemical emits light, which then is coupled to a spectrometer through an optical fiber. The light given off by any excited chemical is characteristic, resulting in a “fingerprint” that can be used for unambiguous identification. This light is separated into discreet wavelengths in the spectrometer and then analyzed by computer.
Caviton microdischarge sensors are rugged, contain no moving parts, can withstand high temperatures (1,100°C), and require little power for operation. These qualities make them ideal for use in the harsh environments found in smokestacks, boilers, and burners. Additionally, the sensors are real time and sense all metals simultaneously.
The goal of this research project was to determine the detection limits for mercury, lead, nickel, cadmium, and selenium in backgrounds of helium, nitrogen, and air. Helium initially was used as an inert background gas to determine the range of emission lines emitted by the metals. Then, nitrogen and air were added. Nitrogen and oxygen can provide interference by transferring energy from the metals before they emit light. The metals (or metal compounds) were heated in an oven until the vapor pressure was high enough that metal emission could be detected by the microdischarge device contained in the same test cell. The temperature at which metal vapors first appear can be used to determine the concentration of metal present, giving a detection limit.
Caviton detectors were capable of detecting mercury, nickel, lead, cadmium, and selenium in a background of helium. Nickel, cadmium, and selenium were detected in air, with detection limits around 1 part per million. Mercury and lead were not detected in a background of air because of energy transfer to nitrogen or oxygen. Mercury detection was sensitive (60 parts per billion) in helium, and with a cold trap or a gold film trap, this technique could be used for continuous monitoring of mercury emissions. A summary of the Phase I findings is presented in Table 1.
Table 1. Detection limits for five metals used in this study with different backgrounds (units are in parts per million.)
* The cadmium data are not in equilibrium because of residual oxygen in the test chamber, causing falsely high calculations of the number density.
** NiCl2 decomposed with oxygen present and the nickel never reached the vapor phase.
Microdischarge detection of trace metals is a powerful technique,with the potential to replace existing technologies with rugged, reliable equipment at a fraction of the cost. Sensitive detection of mercury, nickel, lead, selenium, and cadmium were shown in this study. Caviton also has demonstrated detection of aluminum, copper, silver, and chromium in the past. It is anticipated that all metals can be detected with this technique simultaneously, with similar detection limits. The detection limits in this study likely will be improved, and Caviton currently is investigating a wide range of sample collection options.
These detectors can withstand high heat and harsh environments, making them ideal for use in smokestacks, burners, and boilers as continuous emissions monitors. These systems can be made in a portable package for field measurements of trace metals. Another advantage of Caviton microdischarge detectors is that they can be applied to oxidized metals, organically bound metals, salts, or elemental metals because of the high energy of the discharge, which breaks down chemicals into their atomic constituents.
A complete instrument will consist of a cold trap or other continuous sampling system to collect metals, a microdischarge detector, a spectrometer, and a computer for analysis. These systems will be compact, require little power, and will be simple to operate, with the sampling and data processing all automated. Systems will cost far less than current x-ray fluorescence machines, and have higher sensitivity to metals.