1



## Review of Draft EPA Test Methods 201A and 202 relat ed to the Use of High Temperature and Out-of-Stack Collec tion
Methods

Introduction

Southern Research Institute (SRI or Southern) was ta sked by Eastern Research Group, under contract to EPA (Work Assignment No. 3-05, Contract No. EP-D-07-064) to review and provide advice on two issues related to proposed revisions to Meth od 201A. The first deals with the reduction or elimination of cyclone thread galling resulti ng from exposure of PM10 and PM2.5 cyclones to high temperature sources. The second deals w ith the possibility of locating the cyclone(s) outside the duct to be sampled and using heated pr obes to convey the sample stream to the sizing device(s) which would be maintained at a suitabl e temperature.



### Reduction or Elimination of Cyclone Thread Galling

Stainless steel should be OK for temperatures to 1,200 ° F. If such cyclones are to used, one (or both) of each of each mating thread surfaces should hav e a hard chrome plating applied and a high-temperature anti-seize compound should be used. For h igher temperature applications Southern has constructed samplers of both Hastelloy, and Haynes 230 alloys. A Haynes 230 alloy sampler has been used successfully at temperatures as high as 1,840 ° F and the specifications of the alloy suggest that it should be good to about 2,500 ° F. These samplers all used bolt-together rather than screw-together assemblie s. Details on one such impaction-type sampler can be found in “Development of Particle Size Test Methods for Sampling High Temperature and High Moisture Source Effluents” prepared fo r the California Air Resources Board (NTIS PB95-170221). 1 The latter document also describes a method for making gaskets for use at high temperatures. Fairly straight-forward modifications of the PM10 and PM2.5 cyclone designs should be possible to allow the same ty pe of assembly of the cyclones. This may necessitate larger sampling port diameters. Boron nitride i s an excellent anti-seize compound for this application. (Paint a thin slurry of boron nitride on the bolts before assembling the sampler. Use “break-away” bolts to facilitate disassembly in c ase the bolt threads gall. Over-torqueing
such bolts causes them to break at the bolt head withou t damaging the flanges.



### Locating the Cyclone(S) Outside the Duct to Be Sampled

Locating the cyclone(s) outside the duct to be sampled c an be done only if the transport losses for particles in the size range of interest are low e nough that the measurement results would not be materially affected. These losses would be caused by deposition primarily by impaction in the sampling nozzle and (at the flow rates used in PM10 and PM2. 5 sampling) settling losses in horizontal probes.

In order to use extractive sampling, the sampling nozzle will have to turn the gas stream through

a 90 ° angle before the sample enters the probe. Losses in such nozzles for even given particle size depend on the gas velocity, the gas viscosity, and th e diameter of the tubing from which the
nozzle is constructed. Losses in nozzles occur as a re sult of mechanical deposition in the straight section of the nozzle immediately downstream of the n ozzle inlet 2 and, in the case of Method 52

or similar nozzles, in the bend(s) used to turn the sampl e stream to enter the probe. Losses in the straight (entry section) of the nozzle are ignored h ere because they would be expected to be comparable to losses in the nozzles called for by the cur rent PM10 sampling method. As a test of the feasibility of using extractive sampling for PM10 sam pling, a set of calculations were carried out for based on sampling a source in which the gas was s tandard air at a temperature of 300 ° F. Figure 1 shows a plot of the velocity at which sampling wo uld be isokinetic at the PM10 flow

rate (0.61 acfm or 17 lpm) at these conditions.

Figure 1. Isokinetic velocity versus nozzle diameter for PM10 flow rate at 300 F in standard
air.

Particle losses in bends are dominated by impaction of pa rticles on the “back side” of the bend.
Particles that have too much inertia to allow them to f ollow the flow streamlines will continue moving toward the back wall of the bend as the gas turns, an d if the inertia is great enough, they will contact the wall and be subject to capture. The pe netrations through bends can be calculated from empirical relationships developed by Pui, et al., as follows:

P = 10 -0.963Stk

For 90° bends where Stk (the particle Stokes number), is calculated in each case based on the tube diameter and gas velocity immediately upstream of th e bend. 3 0 5 10 15 20 25 30 35 40 45

2 3 4 5 6 7 8 9 10
Nozzle Diameter, mmGas Velocity, m/s3

Selecting two test cases, using velocities of 10 m/s and 20 m/s, which span the range of gas velocities commonly encountered in the field, losses we re calculated for the bends in tubes having the corresponding nozzle diameters in Figure 1. Fi gure 2 shows a plot of the results as percent penetration by particle size for each case.

Figure 2 shows penetration versus particle diameter for simple 90 ° bend nozzles at the PM10 flow rate (isokinetic at gas velocities of 20 m/s and 10 m/s respectively). The gas conditions used were those for standard air at a temperature of 300 F.

As can be seen from Figure 2, losses in the bend would in these cases be too large to be acceptable for PM10 measurement in both cases and might b e marginally acceptable for use for
PM2.5 measurement.

Method 5 nozzles are effectively three 90 ° bends in series. Thus losses for Method 5 (“button hook”) nozzles would be expected to be even greater than those for the cases of simple 90 ° bends used in the calculations for Figure 2. The projected cut diam eter (D 50 ) for Method 5 nozzles sampling isokinetically at the PM10 flow rate are shown below at two gas stream velocities at the same conditions used in Figure 2. These results indi cate that Method 5 nozzles would be totally unsuited for either PM 10 or PM2.5 sampling.

Gas Velocity, m/s Nozzle ID, mm 90 ° Bend D50, μ m M5 D50, μ m 10 6.15 6.4 3.56

20 4.32 3.7 2.05

Figure 2. Penetration versus particle diameter for simple 90 ° bend nozzles at the PM10 flow

rate (isokinetic at gas velocities of 20 m/s and 10 m/s respecti vely)

.4

Figure 3. Penetration versus particle diameter for a 2.44 m long, 1.27 cm ID (8 foot long, 0. 5 inch ID) horizontal tube at the PM10 flow rate for the same gas conditions used in the previous examples.



### Probe Losses

Probe losses versus particle size were calculated using the model developed by Fan, et al. 2 , for
the same PM10 flow conditions used in the discussions a bove for sampling nozzles. A plot of the results are shown in Figure 3.

As can seen from the Figure 3, probe losses for a probe of the size modeled here would not be expected be of much consequence compared to nozzle losses. Losses in sampling nozzles and transport systems are discussed more thoroughly by Farthing, e t al. in “Instrumental Monitoring of Particulate Mass Emissions from Stationary Source s.” 4



### Conclusions

Extractive sampling probably cannot be allowed in the case of measuring PM10 emissions but might be acceptable, at least in many cases, for PM2.5 s ampling at dry sources. Losses in extractive systems preclude their use in measuring PM10 emis sions and make it impossible to account for dissolved or suspended droplets larger than about 3 um to 4 um in the case of wet
sources for both PM10 and PM2.5. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0.1 1 10 100
Particle Diameter, micrometersPercent Penetration 4.32 mm

6.15 mm5



### References

1. McCain, Joseph. D. and C. S. Fowler. Development of Pa rticle Size Test Methods of Sampling High Temperature and High Moisture Source Effluent s. Final Report on California Air Resources Board Contract A132-084, June, 1994. NTIS PB95-170221.

2. Pui, David Y. H., Francisco Romay-Novas, and B. Y. H. Liu. Experimental Study of Particle Deposition in Bends of Circular Cross Section. Aeros ol Science and Technology. 7:301-315,
1987.

3. Fan, Bijian, Andrew R. McFarland, and N. K. Anand. Aero sol Particle Losses in Isokinetic Sampling Probe Inlets. Environmental Science and Techno logy. 26:390-394, 1992.

4. Farthing, William E. , J. D. McCain, A. D. Williamson , R. R. Wilson, T. R. Snyder, and L. G. Felix. Instrumental Monitoring of Particulate Mass Emissions from Stationary Sources. Southern Research Institute Final Report on Cooperative Agreement No. 822049 with EPA Methods Research and Development Division, Atmospheric Research and Exposure Assessment Laboratory, Research Triangle Park, NC 27711, EPA Project Officer: Thomas E. Ward, April 1999.