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COURSE MODULE ON
STATIONARY SOURCE SAMPLING AND ANALYTICAL METHODS
FOR GASEOUS POLLUTANTS
FOR
INDUSTRIAL POLLUTION PREVENTION AND CONTROL (IPPC)
DR. AMBEDKAR INSTITUTE OF PRODUCTIVITY
MADRAS
PREPARED BY
V.S.S.Bhaskara Murty Director (Environment)
Dr Ambedkar Institute of Productivity National Productivity Council, Chennai
1995
1.0 INTRODUCTION
Many industrial processes, such as Smelters, Fertiliser plants
fossil fuel combustions etc. emits gaseous air pollutant. The gas
sampling method constitutes the collection of representative gas
sample from the parent gas stream in a suitable absorbing media
and analysing the grab samples by wet chemical analysis.
The representative gas samples are collected through the sampling
port from any point across the cross section of the duct since
the gas composition is uniform. However proportional sampling
techniques have to be implemented if the source is unsteady and
vary with time.
Most frequently measured gas components viz. sulfur dioxide
(SO2), sulfur trioxide (SO3), acid mist, Nitrogen Oxides NOx) are
described below.
2.0 SULFUR DIOXIDE AND SULFUR TRIOXIDE
CPCB has prescribed emission standards for SO2 and SO3 for
different industrial operations as given in the Annexure-1. For
sulfuric acid manufacture these two gas components are analysed
combinedly interms of SO2 and in addition acid mist concentration
is another important parameter. The emission load of SO2 has
importance in calculating the minimum stack height requirements
of industrial operations.
2.1 PRINCIPLE AND APPLICABILITY
The basic problem is to detect SO2 in the presence of SO3 and
H2SO4. Therefore the latter components first must be removed
from the sample. The sulfur dioxide is then absorbed in a
hydrogen peroxide solution and eventually is determined
quantitatively by titration with barium perchlorate or barium
chloride. Thorin is used as a color indicator for this
titration.
2.2 INTERFERENCES
Metal sulfates, phosphates, sulfuric acid mist, and cations which
complex with the thorin indicator or coprecipitate with barium,
interfere but can be eliminated by proper use of a filter.
2.3 SAMPLING TRAIN
The sampling train is similar to that of particulate sampling as
shown in Fig-1 except for the dust collecting thimble holder
which is replaced by a set of midget impingers for the absorption
of the gaseous components.
2.3.1 Sampling probe: A short sampling probe Pyrex or quartz is
used to prevent condensation prior to sample collection. Quartz
of Pyrex glass wool is placed in the entry of the probe to
prevent particulate matter from entering the scrubbers.
Alternatively a midget bubbler stuffed with glass wool is placed
at the end of the sampling probe along with the gas absorption
equipment. The particulate matter contains sulfates and also
other impurities which may precipitate with barium or complex
with the thorin indicator. Acid mist is also removed at this
point.
2.3.2 Absorption equipment: The sample collector consists of
three midget impingers (Fig-2) placed in an ice bath. The first
midget impinger contains 100 ml of 80% isopropyl alcohol
solution. This removes the SO3 and any carry over H2SO4 from the
filter. Some glass wool is placed at the top of the midget
bubbler to act as a filter and thus preventing any H2SO4 mist
from carrying over into the following midget impingers. The gas
stream becomes saturated with the isopropyl alcohol vapor, which
inhibits the oxidation of SO2 to SO3 because the alcohol is more
readily oxidized.
The SO2 is removed in the next two midget impingers, which
contain 100 ml each of hydrogen peroxide solutions. SO2 is
absorbed in the impingers and converted to form H2SO4.
2.3.3 Flow metering: Finally the gases are passed through silica
gel drying column to protect the Dry Gas Meter which follow it.
To achieve the optimum absorption efficiency, the sampling flow
rate has to be set at a minimum constant flow rate of 2 lpm with
the help of rota meter and the needle valve.
2.3.4 Vacuum pump: Since the sampling flow rates are very low
the pressure drop across the sampling train is around 10 to 15
mmHg and hence a small capacity vacuum pump is enough for such
purpose.
2.4 GLASSWARE & REAGENTS
The following reagents and glass ware have to be kept ready in
the laboratory for analysis of the field samples.
2.4.1 Glassware: - Glass wash bottle to hold the deionized water - Polyethylene storage bottles for storing impinger samples prior to analysis. - Transfer pipettes: 5 ml and 10 ml sizes with 0.1 ml divisions and 25 ml size with 0.2 ml divisions - Volumetric flasks : 50 ml, 100 ml and 1000 ml - Burettes : 5 ml and 50 ml - Erlenmeyer flask : 125 ml - Dropping bottle for indicator solution.
2.4.2 Reagents:
2.4.3 deionized distilled water
2.4.4 Hydrogen peroxide,(3% solution): Prepare by diluting 100
ml of 30% hydrogen peroxide to 1 liter with deionized water.
Caution: the 30% H2O2 is a strong skin irritant which is not
noticeable until a few minutes after the injury occurs. This
solution must be prepared daily.
2.4.5 Isopropyl alcohol,(80% solution): Prepare by mixing 80 ml
of isopropyl alcohol with 20 ml of deionized water. This
solution is stable.
2.4.6 Thorin indicator: [1-(0-arsonophenylazo) -2-naphthol-3,
6-disulfonic acid, disodium salt (or equivalent)]. Prepare by
dissolving 0.2 grams in 100 ml of deionized distilled water. It
should be stored in a polyethylene container since it tends to
deteriorate if stored in glass.
2.4.7 Barium perchlorate (0.01N): Prepare by dissolving 1.95
grams of barium perchlorate, Ba(ClO4)2 3H2O in 200 ml of
deionized water. Then dilute to 1 liter using isopropyl alcohol.
Alternatively, dissolve 1.22 grams of barium chloride,
BaC12.2H2O, in 200 ml deionized water and then dilute to 1 liter
with the isopropyl alcohol. The normality of this solution
should be standardized with standard sulfuric acid.
2.4.8 Sulfuric acid standard (0.01N): Purchase or standardize
to + or - 0.0002 N against 0.01 NaOH which has previously been
standardized against primary standard grade potassium acid
phthalate.
2.5 SAMPLING PROCEDURE
This method determines only the concentration in the gas stream.
The volumetric flow rate of the stack must be determined
according to EPA methods 1 and 2. The same sampling port which is
used for the velocity monitoring can be used for the gaseous
sampling. Eventhough the gas composition is uniform across the
cross section of the duct, it is advised to collect the sample at
the centroid of the duct or not closer than 200mm to the duct
wall.
The sampling train is assemble as shown in the Fig-1 and leak
tested by plugging the probe inlet and pulling 300mmHg vacuum.
Observing the dry gas meter, the leakage rate should not exceed
1% of the desired sampling rate. If the leakage is severe, each
joint of the train should be inspected and the leak test
performed again. A thin film of silicone grease often helps to
make the joints leak tight.
The impingers are filled with the reagents as given in 5.2. The
initial reading of the DGM is recorded and a sampling flow rate
of 2 lpm is maintained at the rotameter. In case of unsteady
source conditions, " proportionate sampling" is implemented by
introducing the Pitot tube in to the duct along with the sampling
probe and the sampling flow rate varies with the variations in
the velocity of the gas stream. Gas samples are collected for a
minimum period of 20 to 30 minutes and the final DGM reading,
meter temperature and pressure are recorded.
At the end of the sampling disconnect the sampling probe from
impingers and flush the impingers with about 10 litres of
atmospheric air by turning on the vacuum pump. It is necessary to
transfer the entrapped SO2 in the first impinger and absorbed in
the following impingers. Transfer the contents of the impingers
into the polythene bottles and continue sampling for next set of
samples. A minimum of two samples have to be collected to get
consistent and representative data.
2.6 ANALYTICAL PROCEDURES
2.6.1 Sulfur Trioxide (SO3): Transfer the sample from the first
impinger to a 100ml volumetric flask and make up to the mark with
distilled, deionized water. SO3 is absorbed by water and forms
H2SO4. Pipette a 10 ml aliquot to a 125-ml Erlenmeyer flask and
add 40 ml of isopropanol and 2 to 4 drops of the Thorin indicator
solution. The solution will then have a yellow-orange color.
The sulfuric acid is titrated against standardized barium usually
as the perchlorate or chloride. Thorin is used, which acts to
complex, and excess barium is added, thus giving a color
indicator. Titrate to a pink end point with the 0.01 N barium
perchlorate and record results.
During the titration the barium is consumed by the sulfate and
forms, in the presence of isopropyl alcohol, a gelatinous type of
precipitate which equilibrates rapidly. At the first presence of
any excess barium, a pink barium-thorin complex forms indicating
that all of the sulfate has been consumed. The determination of
the end point by the color change may take some practice on the
part of the analyst; it is less vivid than some other
calorimetric indicators but nonetheless proves to be quite
adequate.
The standard laboratory procedure of using a blank of deionized
water should be used for all sets of samples, allowing any
systematic error due to the reagents or procedures to be
accounted for.
2.6.2 Sulfur Dioxide (SO2): Transfer the samples from the two
midget impingers in to two 100ml volumetric flasks separately and
make up to the mark with distilled water. The SO2 has been
oxidized to SO3 with H2O2 and hydrolyzed to form sulfuric acid in
the impingers. Follow the same analytical procedure as given in
2.6.1 for the samples in both the impingers separately to check
the absorption efficiency and to ensure that there is no escape
of SO2 along with the gas.
2.7 DATA ANALYSIS
2.7.1 Volume of the gas sampled: The difference of the initial
and final readings of DGM gives the gas volume sampled at meter
temperature (Tm) and Pressure (Pm) conditions. This can be
further converted to normal conditions as
Tn x Pm Qn = Qm --------- . . . (1) Tm x Pn Where Qn .. Volume of gas sample under normal condition, NM3 Qm .. Volume of gas sample under meter conditions, M3 Tn .. The absolute gas temperature at normal conditions,298 oK Tm .. The absolute dry gas meter temperature, oK Pn .. The absolute pressure at normal conditions, 760 mmHg Pm .. The absolute pressure at the gas meter, mmHg 2.7.2 SO3 concentration:
The concentration of SO3 in the gases is determined using the
following expression:
(A-B) x V x N x 40 CSO , mg/NM3 = ----------------------- . . . (2) 3 v x Qn
Where A .. Volume of the Ba(ClO4)2 consumed by the sample aliquot,ml B .. Volume of the Ba(ClO4)2 consumed by the blank,ml v .. Volume of the aliquot,ml V .. Volume of the absorbing solution,ml N .. Normality of Ba(ClO4)2 48 .. Equivalent weight of SO3, gm/gm mole 2.7.3 SO2 concentration:
The concentration of SO2 in the gases is determined using the
same expression for SO3 by replacing the equivalent weight with
36 gm/gm mole. The average concentration of SO2 is estimated by
considering the arithmetic average of both the impinger readings.
2.8.0 SUMMARY
Laboratory analysis is completely wet chemical and several
hazardous solutions are used. For example extreme care must be
used when working with the 30% hydrogen peroxide solution. This
strong oxidant is a harsh skin irritant, the effect of which is
unnoticed until about 5 minutes after exposure.
3.0 ACID MIST CONCENTRATION
Acid mist from sulfuric acid plant emissions is sampled by
isokinetic sampling techniques using a glass fibre thimble since
the acid mist also persists in different droplet sizes. The
sampling train similar to particulate matter concentration
measurements is employed for acid mist sampling as shown in
Fig-3.
For analysis the thimble is thoroughly washed with distilled
water and the resultant solution is titrated against Ba(ClO4)2 as
given in 2.6.1. The concentration of acid mist is calculated by
using the same (2) for SO3 estimation by replacing the equivalent
weight by 49 gm/gm mole.
4.0 NITROGEN OXIDES (NOx)
Nitrogen oxides mainly consisting nitrogen dioxide (NO2) and
nitrous oxide (NO) forms by the combustion reactions. Combustion
temperatures up to about 600oC NO2 formation is maximum. Normally
in industrial operations where the combustion temperatures are
about 1000oC, Nitrogen Oxides comprise of about 90-95% of NO and
remaining NO2. CPCB has prescribed standard procedure for
sampling and analysis of NOx based on the method EPA-7. However
CPCB has not yet prescribed any standards for the NOx emissions.
However NOx is a dominant pollutant in atmospheric reactions and
formation of secondary pollutants.
4.1 PRINCIPLE AND APPLICABILITY
The sample is removed by a grab sampling technique. It is
captured in a 1-litre grab pipette or a 1-litre evacuated flask
which contains an absorbing solution of hydrogen peroxide and
sulfuric acid which converts the NOx (except N2O) in the captured
gas to HNO3 in solution. The amount of nitrate in solution is
determined by the phenoldisulfonic acid method. The amount of
nitrate (NOx) is then determined by calorimetric comparison to
standard solutions of potassium nitrate.
4.2 INTERFERENCES
Phenoldisulfonic acid (PDS) forms a strong color complex with NOx
and no interferences are reported.
4.3.0 SAMPLING TRAIN
The sampling train for collection and analysis of NOx samples by
grab pipette is shown in Fig-4. Quartz or Pyrex wool is packed in
the glass probe to prevent particulate matter from entering the
flask. A vacuum pump draws the gas sample through the grab
pipette. The sampling flow rate is adjusted at 2 lpm by a needle
valve so that there is excessive vacuum build up in the grab
pipette.
The method EPA-7 suggest evacuated flask method as shown in
Fig-5. The stopcocks and the T-bore insure the proper sequence
for evacuating, purging and sampling. A high capacity vacuum
pump pulls the vacuum in the flask up to a maximum of 70 mmHg
(absolute). The evacuated flask as a part of the sampling train
is connected to the source and with the help of the T-bore the
sample is drawn in to the flask. The accuracy of measurement
depends on the maximum vacuum created in the sample flasks. If
the vacuum pump has no enough capacity to draw the vacuum it is
suggested to use the grab pipette method which can produce the
results with acceptable range of error.
4.4.0 GLASSWARE, EQUIPMENT AND REAGENTS 4.4.1 Glassware - Beakers or casseroles, 250 ml - Volumetric pipettes, 1, 2 and 10 ml - Transfer pipette, 10 ml with 0.1 ml divisions - Volumetric flasks : 100 ml for each sample; 1000 ml for standard - Graduated cylinder, 100 ml with 1.0 ml divisions 4.4.2 Equipment - Steam bath - Spectrophotometer, measurement at 420 nm - Analytical balance, measure to 0.1 mg. 4.4.3 Reagents - Concentrated H2SO4 - 3% H2O2
- Distilled water - 1 N NaOH solutions (add 40 g NaOH in distilled water and dilute to one liter) - Red litmus paper - Phenoldisulfonic acid (PDS) - Potassium nitrate
4.5.0 SAMPLING PROCEDURES
4.5.1 Laboratory procedure
The volume of the flask/grab pipette must be determined. This is
done by filling the flask/grab pipette with water and then
measuring the volume of water with a graduated cylinder. Record
the volume on each flask/grab pipette.
The absorbing solution is prepared by adding 2.8 ml of
concentrated H2SO4 to 1 liter of distilled water. To this mixed
solution, add 6 ml of 3% hydrogen peroxide. Fresh solution
should be prepared weekly and protected from heat or sunlight.
4.5.2 Field procedure
This method determines only the concentration in the gas stream.
The volumetric flow rate of the stack must be determined
according to EPA methods 1 and 2.
Three repetitions are required per test and two grab samples are
required per source. These two samples should be taken over a
two-hour interval, if the process characteristics are not known.
If the process is known to be steady, then the time can be
shortened. Clean justification of this modification should be
included in the final report.
4.5.2.1 Grab pipette: Connect the grab pipette (Fig-4) to the
sampling probe and the vacuum pump through the rotameter and
needle valve. Set the sampling flow rate at 2 lpm. Insert the
sampling probe into the duct, open both the stop cocks of the
pipette and allow purging for about 5 minutes with the process
gas. Close the stop cocks at the out let of the pipette first and
the second one immediately so that there is no evacuation of the
gas from the pipette or the gas collection is under vacuum.
4.5.2.2 Sampling in evacuated flask: Pipette 25 ml of absorbing
solution into a sample flask. Insert the flask valve stopper
into the flask with the valve in the "purge" position. Assemble
the sampling train as shown in Fig-5 and place the probe at the
sampling point. Turn the flask valve and the pump valve to their
"evacuate" positions. Evacuate the flask to at least 70mmHg
absolute pressure. Turn the pump valve to its "vent" position
and turn off the pump. Check the manometer for any fluctuation
in the mercury level. If there is a visible change over the span
of one minute, check for leaks. Record the initial volume,
temperature, and barometric pressure. Turn the flask valve to its
"purge" position, and then do the same with the pump valve.
Purge the probe and the vacuum tube using the squeeze bulb. If
condensation occurs in the probe and flask valve area, heat the
probe and purge until the condensation disappears. Then turn the
pump valve to its "vent" position. Turn the flask valve to its
"sample" position and allow sample to enter the flask for about
15 seconds. After collecting the sample, turn the flask valve to
its "purge" position and disconnect the flask from the sampling
train. Shake the flask for 5 minutes.
4.6.0 Analytical procedure
4.6.1 Recovery: This method specifies a minimum sample
absorption time of 16 hours. Margolis and Driscolls
theoretically predicted a 97% recovery would require 28.7 hrs.
Hence the absorption process is the slowest step in the NOx
procedure. The samples may be returned to the laboratory in the
flask/pipette and kept in a cool and dark place for a minimum
period of 24 hrs.
4.6.2 Analysis: After the absorption period shake the contents
of the flask/pipette for 2 minutes. The contents of the flask are
then transferred to 100 ml china dish. The flask/pipette is
rinsed with two small portions of distilled water (10 ml). An
accompanying blank of absorbing solution, along with an equal
amount of rinse, is also processed. Then 1.0 N NaOH is added to
the absorbing solutions until they are alkaline to litmus paper.
Evaporate the solution to dryness on a steam bath and then cool.
Add 2 ml phenoldisulfonic acid solution to the dried residue and
dissolve all the residue thoroughly using a glass rod. Make sure
the solution contacts all the residue. Add 1 ml distilled water
and 4 drops of concentrated sulfuric acid. Heat the solution on
a steam bath for 3 minutes with occasional stirring if any
undissolved matter presents. Cool, add 20 ml distilled water,
mix well by stirring, and add concentrated ammonium hydroxide
drop wise with constant stirring until alkaline to litmus paper.
Transfer the solution to a 100 ml volumetric flask and wash the
beaker three times with 4 to 5 ml portions of distilled water.
Dilute to the mark and mix thoroughly. If the sample contains
solids, transfer a portion of the solution to a clean, dry
centrifuge tube, and centrifuge, or filter a portion of the
solution. Measure the absorbance/extintion of each sample in a
spectro photometer at 420 nm using the blank solution as a zero.
Read the amount of NO2 value "m" correspond to the
absorbance/extintion value from the standard calibration grab
drawn following the procedure given in 4.6.3. Dilute the sample
and the blank with a suitable amount of distilled water if
absorbance falls outside the range of calibration.
4.6.3 Calibration
The standard solution is prepared by dissolving 0.5495 g of KNO3
in distilled water and diluting to 1 liter. The working solution
is prepared by diluting a 10-ml portion of the standard solution
to 100 ml; 1 ml of this solution then is equivalent to 25 ug of
NO2. The calibration curve is prepared by adding 0.0 to 16.0 ml
of standard solution to a series of china dishes. To each dish
add 25 ml of absorbing solution and follow the same analytical
procedure given in 4.6.2. A calibration graph (Fig-6) is then
drawn in micro grams of NO2 per sample versus
absorbance/extintion at 420 nm.
4.7.0 DATA ANALYSIS
4.7.1 Sample gas volume in evacuated flask
The sample volume at normal conditions is calculated by the
following expression.
a) For Evacuated flask _ _ | | | Pf Pi | Tn Vn = (Vf-Va) x |----- - ---- | x -- | Tf Ti | Pn |_ _| b) For Grab pipette Ps x Tn Vn = (Vf-Va) x --------- Pn x Ta Where
Vn .. Dry sample volume at normal conditions, ml Vf .. Volume of flask and valve, ml Va .. Volume of absorbing solution, 25 ml Pf .. Final absolute pressure of flask, mmHg Pi .. Initial absolute pressure of flask, mmHg Ps .. Absolute stack pressure, mmHg Ta .. Absolute ambient temperature, oK Tf .. Final absolute temperature of flask, oK Ti .. Initial absolute temperature in flask, oK
The calibration curve is used in conjunction with the following
expression to determine stack gas concentration. m x 1000 CNOx,mg/NM3 = ---------- Vn Where CNOx .. Concentration of NOx as NO2 (dry basis), mg/NM3 m .. Micro gram of NO2 from the calibration graph
4.8 SUMMARY
The NOx field test can be conducted easily by one person. In
fact this field test can be run at the same time as other
pollutant tests. Thus if a team of 2 or 3 people is conducting
an isokinetic particulate matter test, the NOx samples can be run
concurrently.
The NOx laboratory procedure is lengthy, requires a number of
steps and analysis must be performed by a qualified chemist or
laboratory technician. Errors may arise due to improper
procedures and deterioration of reagents.
The velocity traverse must be run concurrently with this NOx
test. Also the pertinent process information for the sampling
period is essential. Remember, the NOx concentration data may
only be part of what is needed to determine compliance.
Regulations are sometimes stated on the basis of pounds per
million BTU's input or pounds per ton of process weight.
5.0 OTHER GASEOUS COMPONENTS
The sampling and analytical procedures for other frequently
encountered gases like Ammonia, Urea (dust), Fluorides are given
in Annexures 6 to 8.
ANNEXURE -
DIFFERENT INDUSTRIAL EMISSION STANDARDS FOR
GASEOUS POLLUTANTS - PRESCRIBED BY CPCB ------------------------------------ 1. SULFURIC ACID MANUFACTURE ---------------------------------------------------------------- Process Sulphur dioxide Acid mist emission emission ----------------------------------------------------------------- Single conversion 10 Kg/tonne of 50 mg/Nm3 Single absorption concentrated (100%) acid produced Double conversion 4 Kg/tonne of 50 mg/Nm3 Double absorption concentrated (100%) acid produced. ---------------------------------------------------------------- 2.0 NITRIC ACID --------------------------------------------------------------- Standard for oxides of nitrogen, NOx 3Kg of Nox per tonne of weak acid (before concentration) produced. --------------------------------------------------------------- 3.0 OIL REFINERIES: ----------------------------------------------------------------- Process Emission Limit ----------------------------------------------------------------- Standard for sulphur dioxide Distillation 0.25 Kg/Te of feed* (Atmospheric Plus Vacuum) Catalytic Cracker 2.5 Kg/Te of feed Sulphur Recovery Unit 120 Kg/Te of Sulphur in the feed --------------------------------------------------------- * Feed indicates the feed for that part of the process under
consideration only. 4.0 COKE OVEN ----------------------------------------------------------------- Standard for Carbon monoxide 3.0 kg/T of coke produced ----------------------------------------------------------------- 5.0 POWER GENERATION BOILERS ----------------------------------------------------------------- ----------------------------------------------------------------- Boiler size Stack height ----------------------------------------------------------------- Standard for Sulphur dioxide control (through stack height) Less than 200 MW H = 14 (Q) 0.3 200 MW to less than 500 MW 220 meters 500 MW and more 275 meters ----------------------------------------------------------------- Q = Sulphur Dioxide emission in kg/hr H = Stack height in meters 6.0 STACK HEIGHT FOR COAL FIRED BOILERS --------------------------------------------------------- Capacity of Steam generation Stack height --------------------------------------------------------- 1. Less than 2 tons/hour Two and a half times (or 2.6 MT/day of coal used) the neighboring building height of 9.0 m whichever is more 2. More than 2 tons/hr to 5 tons/ 12.0 m hour (or 2.6 MT/day to 6.5 MT/day of coal used) 3. More than 5 tons/hr to 10 tons/ 15.0 m hour (or 6.5 MT/day to 13 MT/ day of coal used)
4. More than 10 tons/hr to 15 tons 18.0 m /hour(or 13 MT/day to 19.5 MT/day of coal used) ----------------------------------------------------------------- Contd .... --------------------------------------------------------- Capacity of Steam generation Stack height --------------------------------------------------------- 5. More than 15 tons/hr or 20 tons 21.0 m /hour (or 19.5 MT day to 26.0 MT/day of coal used) 6. More than 20 tons/hr to 24.0 m 25 tons/hour (or 26 MT/day of coal used) 7. More than 25 tons/hr to 30 27.0 m tons/hour (or 32.5 MT day 39 MT/day of coal used) 8. More than 30 tons/hour (or 30.0 m or using the than 39 MT/day of coal used) formula H=14) where H=minimum stack height required in metres. Q is sulfur dioxide emissions in kg/hr, whichever is more) --------------------------------------------------------
ANNEXURE - 2
MODEL PROBLEM FOR SULFUR DIOXIDE AND SULFUR TRIOXIDE ANALYSIS AND ESTIMATION
------------------------------------------------------------ 1.0 A Fertiliser plant has a 100 TPD sulfuric acid plant producing concentrated sulfuric acid (98%) through DCDA process. Source emission monitoring was conducted at the stack located at the end of the second absorption column. The flow rate of the gases was measured to be 12,500 NM3/hr at 52oC following the EPA standards methods 1 to 4. 1.1 Sulfur trioxide and sulfur dioxide samples were collected and analysed by EPA standard method 6. The data collected are as follows: Volume of the gas sample collected = 50 lit DGM temperature = 35oC Vacuum at DGM = 14 mmHg Volume of the absorption media for SO3 estimation = 98 ml Volume of the absorption media for SO2 estimation = 192 ml Volume of the aliquot for both SO2 & SO3 analysis = 20 ml Ba(ClO4)2 consumption by SO2 aliquot = 9.8 ml Ba(ClO4)2 consumption by SO3 aliquot = 3.5 ml Ba(ClO4)2 consumption by blank = 1.2 ml Ba(ClO4)2 normality = 0.00987N Atmospheric pressure = 740 mmHg Calculate the concentrations of SO2 and SO3 in the emissions and also check whether the emissions comply with emission regulations.
1.2 The acid mist sample in the emissions was also collected following the method EPA-8 and the collected data are as follows: Volume of the gas sample collected across the duct through isokinetic sampling = 345 lit DGM temperature = 35oC Average vacuum recorded in the DGM = 18 mmHg Volume of the sample after thible wash = 250 ml Volume of the aliquot for analysis = 50 ml Ba(ClO4)2 consumption by the aliquot = 4.6ml Ba(ClO4)2 consumption by blank = 1.2 ml Ba(ClO4)2 normality = 0.00987N Calculate the concentrations of acid mist in the emissions and also check whether the emissions comply with emission regulations. 2.0 SOLUTIONS: 2.1 Estimation of SO3 Volume of the gas sample collected = 50 lit Under normal conditions, Qn 0.05 x 726 x 298 Qn = ----------------- = 0.046 NM3 760 x 308 Concentration of sulfur trioxide is calculated by (A-B) x V x N x 40 CSO , mg/NM3 = --------------------- . . . (2) 3 v x Qn
Where A .. Volume of the Ba(ClO4)2 consumed by the sample aliquot,ml B .. Volume of the Ba(ClO4)2 consumed by the blank,ml v .. Volume of the aliquot,ml V .. Volume of the absorbing solution,ml N .. Normality of Ba(ClO4)2 48 .. Equivalent weight of SO3, gm/gm mole (3.5-1.2) x 98 x 0.00987 x 40 CSO , mg/NM3 = -------------------------------- 3 20 x 0.046 = 96.7 or 29.6 ppm SO3 emission load = SO3 conc. x emission flow rate = 96.7 mg/NM3 x 12,500 NM3/hr = 1.21 kg/Hr H2SO4 manufacture = 100 TPD (98%) = 98 TPD (100%) = 4.08 T/Hr 1.21 SO emission factor = ---- = 0.3 kg/T of 100% acid 3 4.08 2.2 Estimation of SO2 Concentration of sulfur dioxide is calculated by
(A-B) x V x N x 32 CSO , mg/NM3 = --------------------- . . . (2) 2 v x Qn Where A .. Volume of the Ba(ClO4)2 consumed by the sample aliquot,ml B .. Volume of the Ba(ClO4)2 consumed by the blank,ml v .. Volume of the aliquot,ml V .. Volume of the absorbing solution,ml N .. Normality of Ba(ClO4)2 32 .. Equivalent weight of SO2, gm/gm mole (9.8-1.2) x 192 x 0.00987 x 32 CSO , mg/NM3 = -------------------------------- 2 20 x 0.046 = 567 or 434 ppm SO2 emission load = SO2 conc. x emission flow rate = 567 mg/NM3 x 12,500 NM3/hr = 7.09 kg/Hr 7.09 SO emission factor = ---- = 1.74 kg/T of 100% acid 2 4.08 SO2 emissions are satisfying the CPCB standards of 4kg of SO2 per T of 100% sulfuric acid produced. 2.3 Estimation of Acid mist
Volume of the gas sample collected = 345 lit Under normal conditions, Qn 0.345 x 722 x 298 Qn = ----------------- = 0.317 NM3 760 x 308 Concentration of sulfuric acid mist is calculated by (A-B) x V x N x 48 C H SO mist, mg/NM3 = --------------------- 2 4 v x Qn Where A .. Volume of the Ba(ClO4)2 consumed by the sample aliquot,ml B .. Volume of the Ba(ClO4)2 consumed by the blank,ml v .. Volume of the aliquot,ml V .. Volume of the absorbing solution,ml N .. Normality of Ba(ClO4)2 48 .. Equivalent weight of H2SO4, gm/gm mole (4.6-1.2) x 250 x 0.00987 x 48 CSO , mg/NM3 = -------------------------------- 2 50 x 0.317 = 25.4
ANNEXURE - 3
MODEL PROBLEM FOR NITROGEN OXIDES ANALYSIS AND ESTIMATION ------------------------------------------------------------ A) PROBLEM A source sampling test was conducted on a 200 KVA diesel generator set. The flue gas analysis reveals 13% - CO2, 1.0% - CO and 5% - O2. Flue gas temperature measured to be 370oC. The samples for nitrogen oxide analysis were collected in an evacuated flask. The collected samples were analysed by Phenol Disulfonic Acid method following the standard EPA - 7 method. The analysis data are as follows Volume of the evacuated flask,ml : 960 Absolute flask pressure before sampling,mmHg : 70 Absolute stack pressure,mmHg : 735 Atmospheric pressure,mmHg : 740 Ambient temperature,oC : 35 Volume of the absorbing solution,ml : 25 Dilution ratio : 1:2 Extintion reading : 0.348 Corresponding NO2 value from calibration graph, ug : 350 NO2 quantity considering dilution, ug : 700 Calculate the concentration of NOx in the DG set exhaust gases in mg/NM3. B) SOLUTION Concentration of the NOx using evacuated flask method and with the given data can be calculated by using the following equation
_ _ | | | Pf Pi | Tn Vn = (Vf-Va) x |----- - ---- | x -- | Tf Ti | Pn |_ _| m x 1000 CNOx,mg/NM3 = ---------- Vn Where Vn .. Dry sample volume at normal conditions, ml Vf .. Volume of flask and valve, ml Va .. Volume of absorbing solution, ml Pf .. Final absolute pressure of flask, mmHg Pi .. Initial absolute pressure of flask, mmHg Ps .. Absolute stack pressure, mmHg Ta .. Absolute ambient temperature, oK Tf .. Final absolute temperature of flask, oK Ti .. Initial absolute temperature in flask, oK CNOx .. Concentration of NOx as NO2 (dry basis), mg/NM3 m .. Micro gram of NO2 from the calibration graph _ _ | | | 735 70 | 298 Vn = (960-25) x |----- - -----| x --- | 308 308 | 760 |_ _| = 792
700 x 1000 CNOx,mg/NM3 = ---------- Vn = 884
----------------------------------------------------------------- S No. C O N T E N T S Page No. ----------------------------------------------------------------- 1.0 Introduction . . . . . . . . . . . . . 1 2.0 Sulfur Dioxide and sulfur trioxide (EPA - 6) . . 1 3.0 Acid mist concentration (EPA - 8) . . . . . . . 10 4.0 Nitrogen oxides estimation(EPA -7) . . . . . . . 12 5.0 Other gases . . . . . . . . . . . . . . . . 21 ANNEXURES 1 Emission standards for gaseous pollutants - CPCB . . . . 22 2 Model problem and calculation for analysis of SO2 & SO3 . . . . 25 2A Computerised data sheets for SO2 analysis . . . 30 3 Model problem and calculation for analysis of NOx . . . . 31 3A Computerised data sheets for NOx analysis . . . 33 4 Sampling and analysis of ammonia emissions. . . 34 5 Sampling and analysis of Urea emissions . . . 41 6 Sampling and analysis of Fluoride emissions . . 46 7 Sampling and analysis of H2S and CS2 . . . . . 51 8 References . . . . . . . . . . . . . . . 58 -----------------------------------------------------------------
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ANNEXURE - 7
SAMPLING AND ANALYSIS HYDROGEN SULFIDE AND CARBON DISULFIDE ___________________________________________________________ 1.0 PRINCIPLE:
The gas containing hydrogen sulfide and carbon disulfide is
initially passed through cadmium chloride solution. Hydrogen
sulfide reacts with cadmium chloride and precipitated as cadmium
sulfide which is quantitatively estimated by iodometric
titration. Subsequently the gas containing only carbon disulfide
is passed through potassium hydroxide solution where CS2 froms
potassium xanthate which is estimated quantitatively by
iodometric tritration.
2.0 SAMPLING EQUIPMENT AND THE CHEMICALS: 2.1 EQUIPMENT FOR SAMPLE COLLECTION: Sampling probe: Sampling probe made of corrosion resistant material like quartz or stainless steel Quartz wool filter: About 10mm - 15 mm dia and 150 mm long heated quartz wool filter Five Glass impingers: Mid-jet impingers of 250 ml capacity Ice bath: Leak proof ice bath to accomodate five impingers Suction pump:
To facilitate 60 lit/hr flow rate. Gas volume meter: Suitable for 60 lit/hr flow rate. Thermometer: To measure the gas temperature at the Gas volume meter. Barometer: To measure the atmospheric pressure at the sampling site. 2.2 GLASS WARE FOR ANALYSIS: Burette: 25ml capacity with 0.05 ml minimum graduations - 2 Nos Erlenmeyer Flask: 300 ml capacity, Wide mouth with ground stopper joint.- 6 Nos 2.3 CHEMICALS: All chemicals should be of Analytical grade should be used.
Cadmium chloride solution: 25g of cadmium chloride is dissolved
with 900 ml of double distilled water in 1.0 lit volumetric
flask. Add 20 ml of 0.5N NaoH and make it upto 1.0 lit.
Iodine solution: 0.1N and 0.01N Iodine solutions
Sodium thiosulfate solution: 0.1N Sodium thiosulfate solution.
Acetic acid: 100 ml of acetic acid is diluted to 1000 ml with
double distilled water in a volumetric flask.
Starch solution: 1.0g of starch dissolved in 100ml of double
distilled water.
Potassium Hydroxide: 5 gm of KOH dissolved in 2-3 ml of
distilled water, cooled in ice bath and make it to 100 ml with
absolute alcohol/methy alcohol.
Phenolpthaline indicator:
3.0 SAMPLING TRAIN
The sampling train is similar to that of EPA -5 for particulate
sampling except for the dust collecting thimble holder which is
replaced by a set of midget impingers for the absorption of the
gaseous components as given in Fig - A.
3.1 Sampling probe: A short sampling probe Pyrex or quartz is
used to prevent condensation prior to sample collection. Quartz
of Pyrex glass wool is placed in the entry of the probe to
prevent particulate matter/water droplets from entering the
impingers. Alternatively an additional midget bubbler stuffed
with glass wool is placed at the end of the sampling probe along
with the gas absorption equipment.
3.2 Absorption equipment: The sample collector consists of four
midget impingers placed in an ice bath. The first two midget
impingers contain 100 ml of calcium chloride solution. This
removes the H2S. To ensure efficient absorption a second
impinger with 100 CaCl2 is placed. Two impingers with 100 ml
each of alcoholic potassium hydroxide are placed in series to
absorb carbon disulfide. A fifth impinger in series is preferred
to trap the liquid droplets. It is essential to keep the the
implinger set in ice/chilled water bath to prevent the escape of
CS2 while sampling.
3.3 Flow metering: Finally the gases are passed through silica
gel drying column to protect the Dry Gas Meter which follow it.
To achieve the optimum absorption efficiency, the sampling flow
rate has to be set at a minimum constant flow rate of 2 lpm with
the help of rota meter and the needle valve.
3.4 Vacuum pump: Since the sampling flow rates are very low the
pressure drop across the sampling train is around 10 to 15 mmHg
and hence a small capacity vacuum pump is enough for such
purpose.
4.0 SAMPLING AND ANALYTICAL PROCEDURE:
4.1 SAMPLING:
The first two impingers are filled with 100ml each of cadmium
chloride solution. The following two impingers are filled with
100 ml each of potassium hydroxide. The fifth imger is kept
empty to trap any carry over moisture droplets. Gas sample is
drawn through the probe and the quartz filter and bubbled through
the impingers. A sampling flow rate of 1.0 lpm is maintained. If
the sample time is limited then the flow rate has to be increased
accordingly. Generally the sample volumes of 30 to 50 lit are
being collected to get the repersentative data. However it
should be ensured that the absorption is completed in the first
impinger itself and the quantity of gas component in the second
impinger is negligible.
Cadmium chloride is white turbid solution and when it reacts with
H2S it becomes yellow precipitate. The strength of the color
depends on the amount of cadmium sulfide forms and care should be
taken that the sampling should be stopped before the solution the
second impinger turns pale yellow.
The reaction of CS2 with KOH can also be observed by changing its
color to pale yellow with high concentrations. care should be
taken that the second following impinger should not change its
color.
4.2 ANALYSIS:
4.2.1 Hydrogen Sulfide, H2S:
The solution from the impingers are transfered independently in
to two iodometric flasks. Add 20 to 50ml of 0.1N iodine depending
on the quantity of CdS in the solution. Add 25 ml of 10% acetic
acid, close the stoppers and keep the flasks in dark for about 10
to 15 mts. Titrate the solution with standardised 0.1N Na2S2O3
till pale yellow and add two drops of stacrch to get dark blue
color. Continue the titration till it becomes colorless. Repeat
the titration for blank starting with cadmium chloride solution
and following the same analytical procedure parallely. Record
both the sample and blank readings.
4.2.2 Carbon Disulfide:
Transfer the contents in two 250ml Erlenmeyer flask and cool the
sample in chilled water for 10 to 15 mts. Neutralise the
solution with 10% acetic acid using phenolpthaline as indicator.
Add starch and titrate with 0.01N iodine solution till the buff
color end point appears. Repeat the procedure with blank.
5.0 CALCULATIONS: 5.1 HYDROGEN SULFIDE (H2S) Concentration of H2S in the gas sampled is calculated by the following equation (Yo - Y) x 1.702 C H2S = ----------------- Vn
Qm x Pm x Tn Q = -------------- n Pn x Tm Where C H2S .. Concentration of H2S in the sample gas, mg/NM3 Yo .. Consumption of 0.1N sodium thiosufate by the blank Y .. Consumption of 0.1N sodium thiosufate by the sample Qn .. Sample gas volume at normal conditions,NM3 (25oC,760mmHg) Qm .. Sample gas volume, M3 P , T .. Pressure and temperature n n under normal condition (25oC,760mmHg) 1.702 .. mg of H2S per ml 5.2 CARBON DISULFIDE (CS2) Concentration of CS2 in the gas sampled is calculated by the following equation (P - Po) x 0.38 C CS2 = ----------------- Qn Qm x Pm x Tn Q = -------------- n Pn x Tm Where C CS2 .. Concentration of H2S in the sample gas, mg/NM3 Po .. Consumption of 0.1N Iodine by the blank P .. Consumption of 0.1N Iodine by the sample
Qn .. Sample gas volume at normal conditions,NM3 (25oC,760mmHg) Qm .. Sample gas volume, M3 P , T .. Pressure and temperature n n under normal condition (25oC,760mmHg) 0.38 .. mg of CS2 per ml 6.0 RANGE OF APPLICABILITY: Minimum quantity .. 0.05 mg Minimum concentration .. 1.0 mg/Nm3 ( 50 L sample volume) Standard deviation .. 0.5 mg/NM3 at 25 mg/NM3
ANNEXURE - 9
REFERENCES
1. Air Pollution - Vol - III, 3rd edition, A.C.Stern, Academic Press, New York 2. Emission regulations - Part-III, Comprehensive Industry Document Series, COUINDS/20/1984-85 - CPCB, New Delhi 3. EPA-Code of Federal Regulations, Title-40: Standards of Performance for new Stationary Sources - reference methods 4. Industrial source sampling, D.L. Brenchley et.al, Ann arbor Publishers, Inc., Michigan 5. Hand book of air pollution analysis, II edition - Roy.M.Harison et.al., University Press, Cambridge.
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