1 ce 583 - air pollution measurements, emission estimates jeff kuo, ph.d., p.e. [email protected]
TRANSCRIPT
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Content
Representative SamplesConcentration Determination and AveragingStandard Analytical MethodsDetermine Pollutant Flow RateIsokinetic SamplingEmission FactorsVisible Emission
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Introduction to Air Pollution Measurement
Ambient monitoring vs. Source testingConcentration vs. Emission rateWhy source testing: Compliance Performance evaluation/guarantees
Problems for measurements Representative sample Correct concentration
Not an easy task
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Components of ambient or source sampling devices
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Representative Samples
Ambient MonitoringThe public has free access and C is the highest.Power, rain, constant T, easy access, safety.CO measurement: street level, downtown.
Source TestingV and C = f(t, location)Near the bend on the inside of a duct: lowFar enough down- and up-stream of disturbance>8x downstream, >4x upstreamPractically hard to achieve
AV
CAVCavg
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AV
CAVCavg
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Representative Samples…
Inlet device to exclude unwanted materials: bug screen. TSP (< 50): prior to 1987 PM10: 1987 PM2.5: 1997
Gas may condense in sampling device or reacts with the encountered solids. SO2 will react with alkaline solids on a filter, thus
increase the weight of the solids collected. Probes are heated
Grab sample: react with sample container and modify its content during transit?
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Concentration Determination
Some can be done by real-time instrument – mostly optically (light absorbance by the compound, but subject to interference).Gas containing SO2 is passed through a dilute solution of NaOH, and then the solution is thru acid-base titration. CO2 can be an interference.
SO2 + 2NaOH Na2SO3 + H2O
CO2 + 2NaOH Na2CO3 + H2O
Average C of real-time instruments (done electronically)
cdtt
Cavg1
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Averaging
Particulate (and other gases) measurements are not real-time but averaging instruments.
t)(Q
ghtfilter weiin Increase
avgC
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Averaging (Example 4.2)
A PM2.5 sampler: an inlet exclude particles > 2.5, a filter, a flow meter, and a suitable housing.Q = 16.7 L/min, t = 24 hr, wfilter = 0.0005g
C = 21g/m3 < 25g/m3 (NAAQS 24-hr average)High quality weighing and sample humidity control are critical. Can not used to assess hourly variations.16.7 L/min ~ average human breathing rate.What is our PM2.5 intake rate?
t)(Q
ghtfilter weiin Increase
avgC
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Standard Analytical Methods
EPA has standard sampling methods for various pollutants – often different for ambient monitoring than for source testing.Table 4.1: for ambient monitoring. The methods define the pollutants such as West-Gaeke method for SO2 (different from Method 6 for source testing).
For EPA, there is a reference method for each major pollutant. Equivalent methods are commonly used by local or states (simpler/cheaper).
Particulate MatterTSP is mainly for lead measurement.PM10 and PM2.5 for compliance with NAAQS.
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Standard Analytical Methods…
Pb
A TSP filter is extracted using NO3 and HCl to dissolve Pb. The extract is then analyzed by atomic absorption (AA).
SO2 (West-Gaeke method)
Known air volume is bubble through a solution of sodium tetrachloromercurate to form a complex.
The solution is treated with pararosaniline, turns into read-purple, and then determined in a colorimeter.
[HgCl4]2- + 2SO2 ---> [Hg(SO3)2]
2- + 4Cl- + 4H+
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Standard Analytical Methods…
OzoneOzone in air reacts with ethylene in a chemiluminescent reaction, measured with a photomultiplier tube.
COMeasured by nondispersive IR (NDIR) absorption. Filters are used to obtain a specific wavelength band at which CO strongly absorbs.
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Standard Analytical Methods…
Hydrocarbon (non-methane)The gas is pass through a FID (flame ionization detector) where HC burns in a hydrogen flame. Part of the sample is diverted to GC where methane is quantified. The difference is non-methane HC.
NO2
NO2 is converted to NO, which is then reacted with ozone. Light from this chemiluminescent reaction is measured.A parallel sample is run without conversion of NO2 to NO – NO reading.
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Determine Pollutant Mass/Molar Flow Rate
Pollutant molar flow rate = (molar flow rate of gas) x (pollutant molar concentration in gas)
Example 4.3: In method 6 testing of a stack, SO2 = 600 ppm, V= 40 ft/s, D = 5 ft, T = 450 oF, P = 1 atm. What is the SO2 flow rate (averaging of C and V may be needed)?
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Determine Pollutant Mass/Molar Flow Rate
hkgsg
slb
smolslbmol
s
mol
s
lbmol
scf
lbmol
AV
/1.74/6.20
/1053.4SO of rate flow Mass
/32.0/1008.7
)10600(18.1SO of rate flowMolar
53618.1
910
528)1059.2()5(
440
rate flow gasMolar
22
4
62
32
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Isokinetic Sampling
In stack sampling for particulates, one must maintain isokinetic flow into the sampling probe – the gas V inside the probe (Vn) = the gas V in the stack where the sample is taken (Vs).
Vn>Vs: gas stream will bend into the nozzle and the inertia of the particles will carry some of them past the nozzle, even though gas they were in will be collected – underestimate of C (top fig.).
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Emission Factors
Emission Factors (EPA document AP-42) Emission testing is expensive Testing not feasible (for poorly-defined source) Estimate of emission from new facilities.
EF for coal combustion w/o control equipment
Furnace Type All particles
PM10 SOx NOx CO
PC, wall-fired dry bottom
10A 2.3A 38S 21.7
0.5
PC, wall-fired wet bottom
7A 2.6A 38S 34 0.5
Hand-fired 15 6.2 31S 9.1 275
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Emission Factors –Example 4.4
Estimate emission from a 500-MW power plant. Thermal efficiency = 35%. Boiler = PC, wall-fired, dry bottom type. Pittsburgh seam coal is used (ash = 8.7%, S = 1.6%, heating value = 13,600 Btu/lb dry).Additional information about coal: Appendix C and back cover.
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Emission Factors –Example 4.4
lb/h 89.5 ton/h)9lb/ton)(17 (0.5 rateemission CO
1.78.7179ton
lb8.7)(10
rate) flow (EF)(coal rateemission eParticulat
/163/179/1058.3
10003413
)/600,13)(35.0(
500
valueheating
outputPower raten consumptio Coal
5
h
tonne
hr
ton
h
ton
hrtonnehrtonhlb
MW
kW
kWh
Btu
lbBtu
MW
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Visible Emission
If particle C is high enough, the plume becomes visible.As plume flows downstream, the plume’s opacity (optical density) decreases.Measuring opacity is easy (observers or electro-optical device), but relating opacity to mass emission rate in the plume is hard.Visual measurements of plume opacity have played a major role in air pollution control.
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Visible Emission
Professor Ringleman devised a system in 1890 – marked five grids of various densities on a piece of white cardboard (Ringleman #1 = 20% opacity, Ringleman #5 = 100% opacity) – used prior to 1970.A continued interest of using optical method. For example, large sources are often required to install in-stack electro-optical detectors for continuous monitoring.