Design of a compact dilution sampler for stationary combustion sources

Transcription

1 Design of a compact dilution sampler for stationary combustion sources Xinghua Li, Shuxiao Wang, Lei Duan and Jiming Hao Department of Environmental Science and Engineering Tsinghua University, Beijing, China A&WMA International Specialty Conference: Leapfrogging Opportunities for Air Quality Improvement May 10-14, 2010, Xi an, China

2 Outline Background Tsinghua s compact dilution sampler Conclusion

3 Background PM emitted from combustion sources are an important contributor to urban ambient PM, especially for PM2.5. Contribution to urban ambient PM from combustion sources can be generally categorized as consisting of primary and secondary particles. Primary particles are emitted directly from sources According to source-level sampling methods, PM from source can be classifed as filterable and condensible particles. Secondary particles form in the atmosphere through the reaction of numerous compounds, such as SO2,NOx and VOCs

4 US EPA method 17 and method 5 collect filterable particles Using an in-stack filter according to method 17, solid and liquid particles present at the stack T are captured on the filter. Chinese national standard GB/T for PM sampling from stationary sources is similar to method 17 Background

5 Background US EPA method 202 collects condensible particles. The amount of material collected in a series of impingers in an ice bath downstream of an in-stack filter and includes both fine particles which pass through the filter and vapors that condense at the T of the gas leaving the impingers. It tends to overestimate condensible particles. The combination of method 17 and method 202 can collect both filterable and condensible particles

6 Dilution sampling methods are widely used to simulate the cooling and dilution processes after hot flue gas leaving the stack In dilution sampling methods, hot emissions are rapidly cooled and mixed with cleaned ambient air after leaving a stack. The rapid cooling and dilution promote gases to nucleate homogeneously and heterogeneously or condense on pre-existing particles, as in the ambient environment. It can collects both filterable and condensible particles Background CIT Dilution Sampling System (Hidemann et al., 1989)

7 Background DRI Dilution System Based on CIT design

8 Background US EPA s conditional method CTM 39

9 Compact dilution sampler Background GE Energy Compact Dilution Samplers (England et al., 2007)

10 Tsinghua s compact dilution sampler Inlet part First dilution system Pressurized air First diluter Venturi flowmeter Valve Second dilution system Dilution air Venturi flowmeter Second diluter valve Residence chamber Sampling part Stack Cyclone Venturi Second diluter Sampling part Residence chamber Pressurized air First diluter redundant gas Valve Dilution air redundant gas

11 Dilution sampler First diluter Dekati Diluter DI-100 The operation principle of the diluter is based an ejection type dilution. Pressurized dilution air is conducted into the diluter through an ejector cavity. The underpressure caused by the dilution air flow draws the sample through the nozzle.

12 Dilution sampler Second diluter The second diluter is an enclosed cylinder with a perforated cone inside. The sample gas from the first diluter is introduced into the inside of the cone. The dilution air is forced through the apertures of the cone into the inside and then mixes with the sample flow. sampling gas from first diluter Dilution air Mixing zone Dilution air

13 Dilution sampler The dilution ratio (DR) of the first diluter is 8 The DR of second diluter is 2.5~6 The total DR of the two stage diluters ranges from 20 to 50. A regulator valve, attached at the exhaust pipe of the first diluter, is used to regulate gas flow rate of outlet into the second diluter. A regulator valve, attached at pipeline of the second dilution air, is used to regulate dilution air rate of the second diluter

14 Dilution sampler Residence time, 100L/min, about 80s Temperature, cooling unit, less than 40 o C RH is less than 60%, dilution air is dryed by desiccant.

15 Dilution sampler Calibration of the venturi flowmeter

16 Dilution sampler Sampling gas and dilution gas were mixed well

17 Check the DR Dilution sampler In the field measurement, DR T =DR 1 xdr 2 DR 1 DR 1 of the first diluter was according to the sheet supplied by Dekati DR 2 Q1 sampling gas of the outlet of the first diluter, Q2 second dilution air In the lab, we use standard gas (NO 2 992ppm) to check the DR, flue gas analyzer was used to masure NO 2 in the chamber RSD The results is 7.4%

18 Particle loss Dilution sampler Hildemann, et al. 1989

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20 Flow chart for measurement emissions from biofuel combustion stack Flue gas analyzer Dilution sampler ELPI Aethalo meter PM 2.5 sampler (Teflon) PM 2.5 sample r(quartz) 20L Tedlar bag DNPH Impinger 1L Tedlar bag Canister CO 2 CO CH 4 NMTHCs and N 2 O analysis NMHCs analysis Carbonyls analysis SO 2, NO x and NH 3

21 Conclusions The combination of two stage diluters shortens the length of mixing section. The size of the residence chamber is reduced by decreasing the nominal flow rate through the aging section to 100 L/min. The decreased size of the sampler is suitable for field test. The sampling gas is pressured into the residence chamber and the air pressure in the chamber is micro-positive. The un-collected redundant gas was discharged through pressure-equalizing port attached at the lower part of chamber automatically, which will keep the unit stable.

22 Thanks for your attention!