2. • The main pollutants are:-
• SPM, etc.
• The gases emitted from the stack impair the
composition of the atmosphere. Thus causes
air pollution. Therefore, analysis & monitoring
of pollutants is done.
• A stack is a structure for venting hot flue gases or smoke
from a boiler, stove, furnace or fireplace to the outside
• These are typically vertical to ensure that the gases flow
smoothly through them.
• The height of stack plays an important role in their ability to
transfer flue gases and it varies for different industries.
• The dispersion of pollutants at a higher altitude helps
reduce the influence of pollutants in the surroundings.
• In the case of chemically aggressive output, the tall stack
allows partial or complete self- neutralization of chemicals
in the air before they reach the ground.
• The dispersion of pollutants over a large area reduces their
concentration in compliance with regulatory limits.
4. STACK EMISSION MONITORING
• Stack monitoring is
performed by inserting a
measuring device into the
stack to obtain a sample of
• The purpose of stack
sampling is to determine
the quantity, quality & the
type of pollutants emitted
from a specific source,
efficiency of the pollutant
collector & to determine
an appropriate design for
air pollution control
5. Devices for general use
• They are used to determine accurately the volume of
the gas collected. They are fitted with manometers and
thermometers to indicate the pressure and temperature
of the gas stream sampled.
• These are tubes suitable for penetrating into the gas
stream and should be constructed of materials which are
noncorrosive and which can withstand special
• Also, they should be constructed of materials which do
not react with the substances to be sampled.
6. Therefore, they should be made of stainless steel or
preferably of glass or quartz.
• A probe should have suitable length and diameter.
• To ensure isokinetic sampling conditions, the opening
of the probe should face the gas stream to be sampled.
• Any suction device which has the required volumetric
capacity can be used. Vacuum pumps driven by electric
motors are very commonly used.
8. Selection of Sampling location and Minimum
Number of Traverse Points
• Select the sampling location at any cross section of the stack
at least eight stack diameters downstream (8D) and two stack
diameters upstream (2D) from any point of flow disturbance
(bend, expansion, contraction, visible flame, or stack exit)
• Cross section of stack is divided into a number of equal areas
where traverse points are located
• Determine the number of traverse points required.
Inside diameter of stack or duct (m) Number of points
I.D. ≤ 0.3 4
0.3 ≤ I.D. ≤ .6 8
0.6 ≤ I.D. ≤ 1.2 12
1.2 ≤ I.D. ≤ 2.4 20
2.4 ≤ I.D. ≤ 5 32 8
9. Location of traverse points on circular cross section
For circular stack divide the cross section into equal parts by two
right-angle diameters, locate half the traverse points symmetrically
along each diameter.
12. • For stack having dia. > than 0.61 m , no traverse point shall be
located within 2.5 cm of stack wall.
• For stack diameters < than 0.61 m , no traverse point shall be
located within 1.3 cm of stack wall.
• If any traverse points falls within 2.5/1.3 cm of stack wall,
relocate them away from stack wall.
• For elliptical stacks having unequal perpendicular diameter,
separate traverse points shall be calculated along each
• Use same traverse points and locations for velocity and
13. Location of sampling port
• To ensure laminar flow, 8D- 2D
i. Number of sampling port – min. 2 ports are required, so that full
cross- sectional area of stack can be covered for measurements.
ii. Dimensions of sampling port – standard flanged pipe of 0.10 m
inside diameter with 0.15 m bolt circle diameter. Port should
extended outward from the exterior stack wall not less than
40mm, installed at height between 0.90 and 1.2 m above the
floor of working platform.
iii. Platform – If two ports are required at 90o , half of stack
circumference and If four ports are required, entire
circumference ; minimum platform width shall always be 1.2 m
iv. Platform access – caged ladder, stairway, rooftop
v. Platform loading – support load of at least three men and
vi. Power supply – At platform and stack base 13
15. Iso-kinetic sampling
• Obtaining representative particulate sample
• Kinetic energy of gas stream in stack should be equal to
kinetic energy of gas stream through the sampling nozzle
• If sampling velocity is greater than velocity in duct tube will
suck extra particles, collecting higher percentage of smaller
particles, the sampling will have a lower mass concentration
• If the sampling velocity is less than velocity in duct then tube
will became pressurized and particles will want to be expelled
from the tube. The particles more easily dispelled are small
particles resulted into collection of larger particles ,PM has a
higher mass conc.
17. Stack Temperature and Velocity Measurement
• Temperature- Has a digital pyrometer and thermocouple.
• Velocity- A digital pressure cell (for measurement of pressure
in mm of H2O) along with pitot tube.
Extension for pitot
18. Stack Temperature and Velocity Measurement
• APM 602
• Temperature- Has a digital pyrometer and thermocouple.
• Velocity- An inclined cum vertical manometer along with pitot
19. Temperature Measurement
• Thermocouple is connected with the Pyrometer
• Switch on the pyrometer to measure the Ambient
• Insert the thermocouple sensor into the stack
through sampling port
• Allow the temperature to stabilize for atleast 10
• Record Stack temperature (Ts) from pyrometer
• Remove the thermocouple
• Hold the sensor by its handle, it is likely to be hot.
20. Stack gas velocity determination
• Connect two ends of the manometer marked “pitot” to ends
of Pitot tube (pitot end which has mark is connected to ‘+ve’
end of manometer)
• Manometer sets to zero before hoses are connected
• Insert pitot tube into stack keeping marked end of the tube
facing the air stream
• Plug the clearance between the port hole walls and pitot tube
with asbestos wool to prevent air flow through port hole
• Orient the pitot tube axis and search best alignment (highest
• Note the manometer reading at various traverse points
• Disconnect the pitot tube when entire cross-section of stack
has been traversed
23. i. Stack gas velocity
V = k x (Stack Temperature x Pressure difference)1/2
where, V = Air velocity (m/sec)
k = Pitot tube constant (0.1973)
24. ii. Stack gas volumetric flow Rate
Qs = V x 60 x 1000 x Tm/Ts x A
Qs = Flow rate (lpm)
V = Velocity of stack gases (m/sec)
A = Cross - sectional area of nozzle (m2)
Tm= Absolute ambient gas temperature (K)
Ts = Absolute stack gas temperature (K)
• Stainless steel (SS 304) with sharp tapered leading edges.
• Minimum recommended internal diameter is 7 mm.
• Select the nozzle size which provides meter sampling rate up
to 30 LPM.
• Nozzle Sizes :-
1/2 12.58 12.4 x 10-5
3/8 8.60 5.8 x 10-5
1/4 6.32 3.1 x 10-5
1/8 3.10 7.5 x 10-6
26. Sampling Period for Particulate matter
• A minimum of 1 m3 of dry gas has been withdrawn
• The mass of particulate matter amounts to atleast 20
percent of the mass of the filtering medium in the
• Sampling period should be of lesser duration in
heavy dust concentrations.
• Too short time may give unreliable results and too
long a time may cause resistance of sampling train to
exceeds capabilities of vacuum pump.
27. Handy Stack Sampler APM-620
• The SPM is trapped and collected in a Filter media
• Various gaseous pollutants are absorbed in suitable reagents,
then analysed subsequently by simple wet chemistry methods
to determine the concentrations.
28. Handy Stack Sampler APM-620
i. Nozzles : A set of 4 stainless steel nozzles with internal diameter of
12.5mm, 98.6 mm, 6.3 mm & 3.1 mm.
ii. Filter Holder : Stainless steel (SS 304), Suitable to hold (a) cellulose
filtration thimble (size 28mm lD X 100mm long) (b) glass micro fibre
thimble (size 19mm lD X 90mm long)
iii. Sampling Probe : Made from SS 304 , 0.3m and 1 m in length
iv. Impingers : 2 No. (240 ml) and 3 No. (120 ml) borosilicate glass
impingers with Ball socket joints accommodated in ice tray.
v. Rotameter : Used for flow measurement, Plastic body rotameter , 0
– 30 lpm for particulates and 0-3 lpm for gaseous pollutants
vi. Dry Gas Meter : Mechanical Type with a range of 40 lpm flow rate.
vii.Vacuum Pump : Monoblock Rotary Vane type, oil lubricated, 0.5 HP
single phase motor (230V) with 50 lpm free flow capacity
29. Filter media - Thimbles
• Paper thimbles – used at temp. up to 150o C
• Alundum thimbles – able to withstand high temp. up to 550o C
high wet strength, chemical resistance
• Glass fibre thimbles – used in heavy dust loading conditions,
able to withstand 550o C of temperature