1114 STACK SAMPLING
The EPA Test Method 18 write-up and the QA Handbook
Section 3.16 contain detailed instructions for sampling,
analysis and calibrations, along with a list of references for
many organic compounds of interest. Both should be read
in detail before the Method is attempted. Testing should be
performed only by personnel trained and experienced with
source sampling and gas chromatography. Audit samples are
available for many compounds through EPA’s Emissions,
Monitoring and Analysis Division.Test Method 19Test Method 19 is not a stack test method. Instead, it contains
procedures for measuring the sulfur content of fossil fuels.
It also contains extensive procedures for calculating emis-
sion rates for particulates, nitrogen oxides (NO x ) and sulfur
dioxide (SO 2 ) and for calculating SO 2 removal efficiency, all
for electric utility steam generators. These calculations are
based on sulfur in fuel measured by this method, on stack
gas concentrations measured by the appropriate methods,
and by ultimate fuel analyses (determination of the major
elemental constituents in samples).
The sulfur content in fuel, either before or after pretreat-
ment, is determined using ASTM procedures specified in
this method. The primary consideration is the representative-
ness of the sampling procedure. The SO 2 removal efficiency
of the pretreatment is calculated by the standard (in-out)(in)
procedure, in which the 5% values are corrected for the gross
caloric value of the fuel to compensate for changes in mass
related to the S removal. SO 2 removal attributed to the flue
gas desulfurization unit is calculated in the same way, but
without need for correction. Overall percent removal is cal-
culated from them.
Many regulations prefer particulate, SO 2 , and NO x emis-
sion rates to the heat input to the boiler, as “pounds/million
Btu.” In order to calculate these values, the emission rates
must be corrected by so-called F factors to account for the
different heat content of the fuel and the excess combustion
air. This method includes detailed procedures or calculating
F factors from ultimate analyses and average F factors for
various fuels. It also includes procedures for correcting for
moisture and for combining various results together.
Finally, Method 19 describes procedures for combining
the SO 2 emission rates calculated before and after a control
device for determining removal efficiency.Test Method 20Test Method 20 is used for determining the nitrogen oxide
(NO x ) emission rate from stationary gas turbines. Since
measurement of oxygen (O 2 ) or carbon dioxide (CO 2 ) is
needed in order to calculate NO x emissions, this method
also includes procedures for their determination. Finally, the
method includes provisions for calculating sulfur dioxide
(SO 2 ) emissions based on Method 6 measurements of SO 2
and diluent measurements from this method.
The basic principles of this method is that a gas sample
is extracted from eight or more traverse points, filtered,stripped of moisture, and fed to automatic NO x and diluent
analyzers. The results of the instrument readings are then
used to calculate the NO x and/or SO 2 emission rates.
The sampling train begins with a heated probe, a calibra-
tion valve (where calibration gases can be added instead of
stack gas), a moisture trap, a heated pump, an automatic ana-
lyzer for either O 2 or CO 2 (to indicate the amount of excess
air in the exhaust stream ), a NO 2 to NO converter (to ensure
the inclusion of all NO x molecules in the analysis), and a
NO x analyzer.
The method includes detailed specifications for the
calibration gases and for the analyzers. All of the calibra-
tion gases must be either traceable to National Institute of
Standards and Technology Standard Reference Materials
(NIST SRMs) or must be certified in a manner speci-
fied in the method. The analyzers must be able to pass a
calibration check and must be subjected to a response time
determination. The NO x monitor must pass an interference
response check (to ensure that high levels of CO, CO 2 , O 2 ,
and/or SO 2 will not interfere in its performance). In addi-
tion, the NO 2 to NO converter must be checked with cali-
bration gases to ensure that the conversion will be stable at
peak loading.
Before conducting the actual NO x and diluent measure-
ments, a sampling rate and site must be selected and a pre-
liminary diluent traverse performed. Site selection is both
important and difficult. The method presents some factors
to be considered, such as turbine geometry and baffling,
but leaves to the testing team the selection of a representa-
tive location. The guidance provided in section 6.1.1. of the
method should be read carefully before a site is selected. The
preliminary traverse is then performed, sampling for a period
of one minute plus the instrument response time at each of
at least eight points (The number of points, between eight
and 49, is determined by a calculation procedure included
in the method) for the purpose of selecting the eight sam-
pling points exhibiting the lowest O 2 concentration or the
highest CO 2 concentration. Those are the points expected to
show the highest NO x concentrations and are the eight to be
sampled for both NO x and diluent.
Three test runs constitute a test at each load condition
specified in the regulation. A run consists of sampling at
each designated traverse point for at least one minute plus
the instrument response time.
The measured CO 2 and NO x values are then averaged
algebraically and corrected to dry conditions using data
from a Method 4 traverse. The CO 2 concentration is cor-
rected to account for fuel heat input by using an F factor
obtained from Method 19 (either from the Table there or by
calculation based on ultimate analysis). Both NO x and dilu-
ent concentrations are then corrected to 15% O 2 (to ensure
consistent comparison with regulatory standards). Finally,
the emission rates are calculated using the corrected concen-
trations. The most sensitive portion of Method 20 is the cali-
bration and operation of the diluent analyzer, as the diluent
concentration strongly affects the NO x corrections. All of the
procedures should be attempted only by trained personnel
using appropriate equipment.C019_003_r03.indd 1114C019_003_r03.indd 1114 11/18/2005 11:07:17 AM11/18/2005 11:07:17 AM