Encyclopedia of Environmental Science and Engineering, Volume I and II

STACK SAMPLING 1103

Other methods 2A through 2H are used for specific

conditions.

Test Method 3

Test Method 3 is used to determine the oxygen (O 2 ) and

carbon dioxide (CO 2 ) concentration from combustion gas

streams for the determination of molecular weight.

The method can also be used for other processes where

compounds other than CO 2 , O 2 , CO or N 2 are not present in

concentrations that will affect the results significantly. The

O 2 and CO 2 can then be used to calculate excess air, molecu-

lar weight of the gas, or to correct emission rates as specified

by various subparts of 40 CFR Part 60. Method 3 can also be

used to determine carbon monoxide when concentrations are

in the percent range.

Two types of analyzers can be used depending on the use

intended for the data. Both analyzers depend on the absorp-

tion of components in the combustion gases by specific

chemicals. The Orsat Analyzer sequentially absorbs CO 2 ,

O 2 , and CO. The change in sample volume is measured with

a gas burette after each absorption step. Potassium hydrox-

ide solution is used to absorb CO 2 , forming potassium car-

bonate. When no further change in volume is noted, the

difference from the starting volume is the amount of CO 2

present. Since the starting volume in the burette is usually

100 ml, the difference in ml is also the concentration of

CO 2 in percent. The absorbent solution for O 2 is a solution

of alkaline pyrogallic acid or chromous chloride. The CO

absorbent is usually cuprous chloride or sulfate solution.

The Fyrite type analyzers are available for either CO 2 or

O 2 , however they do not provide the accuracy of the Orsat

Analyzer, using Method B.

Test Method 3A

Test Method 3A is an instrumental method for determin-

ing O 2 and CO 2.

From stationary sources when specified in the applicable

regulations. Calibration procedures are similar to those dis-

cussed in Method 6C.

Test Method 3B

The Orsat analyzer is required for emission rate correc-

tions and excess air determinations. Concentration values

from 3 consecutive analyses must differ by no more than

1

Dt

Dn

TYPE S PITOT TUBE

SAMPLING NOZZLE

x > 1.90 cm (3/4 in.) for Dn = 1.3 cm (1/2 in.)

(a) BOTTOM VIEW: SHOWING MINIMUM PITOT-NOZZLE SEPARATION.

SAMPLING NOZZLE

SAMPLING PROBE

Dt

TYPE S PITOT TUBE.

NOZZLE OPENING

IMPACT PRESSURE

OPENING

STATIC PRESSURE

OPENING

(b) SIDE VIEW: TO PREVENT PITOT TUBE FROM INTERFERING WITH

GAS FLOW STREAMLINES APPROACHING THE NOZZLE, THE IMPACT

PRESSURE OPENING PLANE OF THE PITOT TUBE SHALL BE EVEN

WITH OR DOWNSTREAM FROM THE NOZZLE ENTRY PLANE

FIGURE 5 (a) Bottom view: showing minimum pitot-nozzle separation. (b) Side view: to prevent

pitot tube from interfering with gas flow streamlines approaching the nozzle, the impact pressure

opening plane of the pitot tube shall be even with or downstream from the nozzle entry plane.

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