1106 STACK SAMPLING
Condenser
The condensation of the water vapor serves two purposes:
first, it prevents condensation in the dry gas meter and the
vacuum pump. Second, the collected condensate is used
to determine the water vapor content in the stack gases.
This collection is considered quantitative if the exit gases
are maintained below 20ºC (68ºF). Four Greenburg-Smith
impingers are connected in series and placed in an ice bath.
The first, third, and fourth impingers are modified by remov-
ing the tip and replacing it with a straight piece of glass.
One hundred ml of water is placed in the first and second
impingers. The third is left empty and the fourth is filled
with 200 to 300 grams of silica gel, at least some of which
is the indicating type that turns from blue to pink when it is
spent. The silica gel is usually put into a preweighed bottle
before the start of testing. After use, it is returned to the same
bottle and the weight difference is recorded.
After the sampling is complete the total water collected is
determined by measuring the liquid in the first three imping-
ers and subtracting the starting 200 ml. Any oil film or color
of the water should be noted. Added to the liquid water col-
lected is the weight gain of the silica gel. The color of the
silica gel should be noted after sampling; if it all has changed
to pink, all of the water passing through the train water may
not have been collected.Meter System
The metering system is used to withdraw isokinetically a
measured quantity of gas from the stack. A vacuum pump
is used to withdraw the sample. There is a vacuum gauge
located before the vacuum pump. A dry gas meter capable of
2% accuracy is used to measure the gas sample volume. Two
thermometers, one at the meter inlet and one at the outlet, are
used to measure the gas temperature. To maintain isokinetic
sampling rates, it is important to know the gas flow rate. This
is done by measuring the pressure difference across an ori-
fice in the exit from the dry gas meter.
The meter must be calibrated before initial use against
a wet test meter. Then after each field use the calibration is
checked at one point with either a wet test meter or critical
orifice. The calibration check can not deviate from the ini-
tial reading by more than 5%. The metering system should
be leak checked from the pump to the orifice meter prior to
initial use and after each shipment.Nomograph
The sampling rate necessary to maintain isokinetic conditions
is dependent on the conditions in the stack (i.e. water content,
average molecular weight of the gas, temperature, velocity,
and pressure) and at the meter (i.e. temperature and pres-
sure). The correct sampling rate is determined from the above
parameters. The sampling rate is controlled by selecting the
nozzle size and regulating vacuum. They serve as the course
and fine adjustment of sampling rate. An initial velocity tra-
verse is done to determine the stack conditions. A nomograph,
special slide rule, or computer program is used to select an
appropriate nozzle size to allow the fine adjustments of the
vacuum pump to cover the expected range. This is necessarybecause the vacuum pump has a limited range. Because the
stack velocity can change during the run, the operator must
be able to rapidly recalculate the desired flow rate through the
meter. The slide rule and computer can also be used to correct
rapidly for changes in temperatures and pressures.SamplingThe first step in determining particulate emissions is the
selection of the sampling site and number of traverse points
by Method 1. The following are the steps to perform particu-
late sampling:1) Set up the equipment as shown in Figure 5.
2) Do initial traverse to determine appropriate
nozzle.
3) Install nozzle.
4) Leak check from nozzle to vacuum pump.
5) Insert probe into stack and heat probe and filter.
6) Start traverse maintaining isokinetic sampling.
7) After traverse, leak check equipment.
8) After cooling, clean probe, nozzle and front of
filter housing. Transfer filter to a petri dish.
9) Determine the amount of water collected.
10) Calculate the isokinetic variation. It must be
within 10%.
11) Evaporate acetone from probe and nozzle washes
and weigh.
12) Desiccate or oven dry the filter to constant weight.
13) Calculate the particulate emissions in the required
units.The EPA Test Method 5 write-up contains detailed instruc-
tions, along with a list of references. It should be read in
detail before the Method is attempted. As with all of these
methods, testing should be performed only by trained and
experienced personnel using equipment and materials
designed for this purpose.Test Method 5ATest Method 5A is used to determine particulate emissions
from the Asphalt Processing and Asphalt Roofing Industry.
This method differs from Method 5 in only two aspects:1 The glass fiber filter is maintained at 42º 10ºC
(108º 18ºF).
2 Trichloroethane is used to wash the probe and
front half of the filter housing instead of acetone.
This may be evaporated at 38ºC.Test Method 5BTest Method 5B is used to determine the non-sulfuric acid par-
ticulate matter from stationary sources. This method is very
similar to Method 5 except that the filter housing is kept at
160º 14ºC (320º 25ºF) during the sample collection and
dried at the same temperature for six hours. This volatilizesC019_003_r03.indd 1106C019_003_r03.indd 1106 11/18/2005 11:07:16 AM11/18/2005 11:07:16 AM