| 英文摘要 |
Determination of particulate matter emissions from stationary sources is the most complicate and challenging task among all environmental sampling and analytical procedures. It is speculated that the dust concentration measurement is affected by the interactions among exhaust velocity, temperature, humidity, aerosol concentration, aerosol size distribution, type of sampling equipment and level of experience of the sampling team. this program can be used to identify the factor(s) contributing to the variability of measurements. The primary goal is to enhance the proficiency of stack particulate measurement.
The backbone of the proficiency testing system was built in 1997. A humidity generation system and a heater were added in the following years. This system simulating a stack is composed of an inlet filtration unit, a 15-Hp blower, a 13.4 m height, 60 cm diameter stainless steel duct, and an outlet filtration unit, as shown in Figure 1. The blower is capable of propelling the face velocity up to 15 m/sec. A Palas Powder Disperser is used to generate aerosol particles. A heater of 750 kW with a PID feedback system is used to control the temperature of the exhaust gas. A 120 kW steam generator is used to change the humidity of the exhaust gas, i.e., water content ranging from 2 % to 10 %. The major operation parameters include dust feeding rate, temperature, relative humidity, and fan rotation speed. Duct velocity ranging from 4 to 11 m/secand PM concentration ranging from 72 to 481 mg/m3 are randomly set for stack sampling team taking the test. In addition to velocity and aerosol concentration, blind gas samples of different combination of CO2, CO, O2 were also prepared for the sampling team to perform Orsat analysis. Statistical analysis is carried out each year after the completion of the proficiency testing program.
After 10 years of operation, the proficiency testing program has been proven to be effective providing a quantitative way to grade the performance of the sampling teams. The measurement errors on duct velocity has been decreasing from 24.5% down to 8.5% since the launch of this program. The errors committed by the stack sampling teams on PM measurements are also decreasing, from 22.2 % down to 13.4 %, a bit higher than that of velocity measurement because of the error propagation. The more rigorous requirements by EPA authority are expected to drive the participants of stack sampling to concentrate more on all fundamentals, and further reduce the measurement errors in the future.
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