United States
Environmental Protection
Agency
Atmsopheric Research and Exposure 3- ,
Assessment Laboratory ^/
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-88/058 Aug. 1989
&EPA Project Summary
Application Guide for the
Source PM10 Exhaust Gas
Recycle Sampling System
Randal S. Martin, Sherry S. Dawes, Ashley D. Williamson, and William E.
Farthing
This document describes assem-
bly, operation, ami maintenance of
the Exhaust Gas Recycle (EGR) sam-
pling system. The design of the
sampling tram allows the operator to
maintain a constant flow rate through
an inertfal sampler while the gas flow
rate into the sampling nozzle is
adjusted to remain isokinetic with the
local duct velocity. This manual spe-
cifically addresses the operation of
the EGR system far determination of
stationary source PM10 emissions.
Material in the text includes: con-
struction details, calibration proce-
dures, presamplrng calculations,
sample retrieval, data reduction, and
equipment maintenance.
This Project Summary was
developed by EPA's Atmospheric
Research and Exposure Assessment
Laboratory, Research Triangle Park,
NC, to announce key findings of the
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
To ensure that a representative sample
of particulate matter is obtained from a
flowing gas stream, the sample must be
withdrawn isokinetically; that is, the gas
flow rate of the sample must be adjusted
so that the velocity in the sampling
nozzle equals that in the surrounding gas
stream. If a velocity mismatch occurs at
the nozzle, the particulate matter in the
sample gas may be selectively enriched
or depleted1; the concentration increase or
decrease will depend in part on the
particle size. This bias is avoided in EPA
Reference Method's 5 and1 17 by
specifying isokinetic sampling. To obtain
a spatially representative sample, the
duct is divided into a number of equal
area zones. The centroid of each zone is
then sampled for a fixed time interval,
and the sample flow rate is adjusted at
each centroid to be isokinetic with
respect to the local gas stream velocity.
The procedure outlined above is
satisfactory for total particulate mass
measurements. However, when sam-
pling Is conducted! with inertial particle-
sizing devices smch as cascade
impactors or sampling cyclones, an addi-
tional constraint is introduced. These
samplers must be operated at a constant
flow rate to maintain constant size cuts
for each particle size fraction. For a fixed
nozzle size, it is impossible to satisfy
both the requirements of constant
sampler flow rate and isokinetic nozzle
velocity with conventional sampling
trains.
This manual describes assembly,
operation, and maintenance of a
sampling tram that allows isokinetic
sampling while maintaining a constant
flow rate through an inertial particle-
sizing device The sampling train uses
the principle of exhaust gas recycle
(EGR). Its design allows a preselected
constant flow rate through the inertial
sampler while the gas flow rate into the
sampling nozzle is adjusted to remain
isokinetic with the local duct velocity.
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Although the potential uses of this sys-
tem are numerous, this manual spe-
cifically addresses the operation of the
EGR system for the determination of
stationary source emissions of paniculate
matter with diameter <10 nm (PM10).
However, most components of the EGR
system are independent of the type of
inertial sampler used, and the material
provided in this manual pertaining to
these components is applicable to most
sampling situations.
Details Of The EGR Sampling
Train
The design of the EGR system allows
the operator to maintain a preselected
constant flow rate through an inertial
sampler while the gas flow rate into the
sampling nozzle is adjusted at each
traverse point to remain isokinetic with
the local gas velocity. The isokinetic
sample flow rate, Qs, enters the sample
nozzle where it is mixed with a metered
flow rate of recycled exhaust gas, Qr.
The combination of these two flow rates
brings the total flow rate to the pre-
determined constant level, Qt- After pas-
sing through the inertial sampler, which
collects the larger particle size fraction
(>10 urn), through an in-stack filter that
collects the smaller PMio size fraction,
and through a heated probe, the water
vapor is removed from the gas stream by
condensation in an ice-cooled conden-
ser or impinger train. The gas stream
then enters the control console where the
total flow rate is eventually split into the
component flow rates, Qs and Qr. The
total and recycle flow rates are measured
by calibrated laminar flow elements
(LFEs). The sample flow rate is mon-
itored in the usual manner by using a dry
gas meter and calibrated orifice.
For the purposes of this method, an
in-stack cyclone is the recommended
PM-io sampler based upon the research
to date. The candidate classifier must be
shown, in laboratory calibrations, to
satisfy specific collection efficiency
criteria. The PM-io sampler specifically
described in this manual and known to
meet these criteria is the commercially
available version of Cyclone I, the first
stage of the Southern Research Institute
(SRI)/EPA five-stage series cyclone.
The cyclone is available in a variety of
outer dimensions and styles from differ-
ent commercial sources. The critical
inner dimensions, however, are standard-
ized to the original design parameters.
Laboratory calibrations have shown
Cyclone I produces a 10-nm fraction-
ation at a flow rate of approximately 0.5
dscfm; the precise flow rate depends on
local stack conditions.
A range of nozzle sizes suitable for
isokinetic sampling at varying recycle
rates should be available. Because
inertia tends to cause deposition of
particles in the PM^ size range in
bends, only straight sampling nozzles
should be used. "Gooseneck" or other
nozzle extensions designed to turn the
sample gas flow 90°, as in Methods 5
and 17, should not be used. The EGR
sampling nozzle designed for use with
Cyclone I is attached to the stainless
steel cyclone body with a flange plate or
straight pipe threads. The recycled ex-
haust gas enters the nozzle through a
1/4-in. side entry tube and fills an
annular region around the sample inlet
tube. The temperature of the recycle
gas is monitored near the EGR nozzle to
ensure isothermal mixing of the recycle
and sample gases.
Procedures
Initial calibration of the components of
the EGR system is essentially the same
as a Method 5 or 17 sampling train with
the exception of the flow metering
system. In the EGR train, the total and
recycle LFEs must be calibrated in
addition to the dry gas meter and sample
orifice. The total flow rate LFE may be
calibrated simultaneously with the dry
gas meter and the sample orifice
Calibration of the recycle flow rate LFI
requires an additional, separate step
Pretest and posttest calibration checks o
the flow metering system an
recommended.
Pretest calculation of sampling para
meters for operation of the system in
volves determining target pressure differ
entials (AH, AP(, APr) for a range of pos
sible velocity pressures, APve|, and stacl
temperatures. An approximate solutior
of the governing equations provides ace
eptable agreement with the exact solutior
and allows calculation of these para
meters in a few simple steps.
Operation of the sampling train is th«
same as Method 5 except that valve
settings must be adjusted for two flow
rates (Q( and Qs). Recovery of the
collected sample after a run is dependen
on the type of sampling device used
For Cyclone I, a combination of brushmc
and rinsing with a suitable solvent u
required to quantitatively recover the
larger size fraction. The PM10 size
fraction is recovered by simply removing
the filter from the filter holder.
Test data reduction and analysis
requires the same calculations outlined ir
Method 5 (gas meter volume, water frac-
tion, percent isokinetic) with the addition
of average flow rate calculations (Qt, Qs,
Qr) and cyclone cut diameter, D50
Acceptance criteria for test data is per-
cent isokinetic in the range 100 ± 10%
and cyclone D$Q in the range 10 ± 1 \im.
Conclusions
The EGR sampling system allows the
operator to maintain a preselected con-
stant flow rate through an inertial sam-
pling while adjusting the gas flow rate
into the sampling nozzle at each traverse
point to remain isokinetic with the local
gas velocity. This allows determination
of stationary source PM^ emissions
within the constraints placed on total
emissions by Method 5.
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Randal S. Martin, Sherry S. Dawes, Ashley D. Williamson, and William E. Farthing
are with the Southern Research Institute, Birmingham, AL 35255.
Thomas £ Ward is the EPA Project Officer (see below).
The complete report, entitled "Application Guide for the Source PM10 Exhaust Gas
Recycle Sampling System," (Order No. PS S9-789 856/AS; Cost: $21.95, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-88/058
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