Lecture 58: Stack Emission Monitoring using Isokinetic Sampling
Summary
TLDRThis video script delves into stack emission monitoring, a crucial process for assessing air pollutants from industrial chimneys. It covers the necessity of isokinetic sampling to accurately measure particulate matter and gaseous pollutants, detailing the equipment and procedures involved. The script also discusses the calculation of emission rates and the importance of quality control in ensuring reliable environmental data for compliance and health risk assessments.
Takeaways
- 🌐 Stack emissions are crucial to monitor for particulate matter and gaseous pollutants, as they are significant point sources of pollution.
- 🔍 Isokinetic sampling is emphasized for accurate stack monitoring because it ensures that the sampling velocity and conditions match those in the stack.
- 🛠️ The equipment for stack monitoring includes a panel box, probes, thermocouples, impinger tubes, vacuum pump, and a sampling probe.
- 📍 Sampling location is critical and should coincide with the point of velocity measurement to ensure accurate particulate concentration readings.
- 🌀 Nozzle size selection is vital for maintaining a sampling rate between 40 to 60 liters per minute, ensuring representative sampling.
- ⚖️ The mass of particulate matter collected on filter paper is measured before and after sampling, with the difference indicating the concentration of pollutants.
- 🔥 The filter paper or thimble is heated to remove moisture, ensuring accurate measurement of particulate matter free from errors.
- 📉 The volume of gas sampled is calculated using parameters like pressure difference, temperature, and barometer pressure to apply necessary corrections.
- 📊 Dust emission rate is calculated by multiplying the concentration of pollutants by the flow rate, providing a measure of total emissions.
- 🧪 Gaseous pollutants like SO2 and NOx can be monitored using impingers and specific sampling and analytical methods, such as barium-thorium titration for SO2.
- 🔄 Quality control is essential in stack monitoring to ensure the accuracy and reliability of the data collected for environmental compliance and assessments.
Q & A
What is the primary purpose of stack emission monitoring?
-The primary purpose of stack emission monitoring is to measure the levels of particulate matter and gaseous components, such as sulphur dioxide and NOx, that are emitted from large chimneys or stacks, ensuring that these emissions do not exceed the standards set by regulatory bodies like the CPCB or MOEF.
Why is isokinetic sampling emphasized in stack emission monitoring?
-Isokinetic sampling is emphasized because it ensures that the velocity, temperature, and other kinetic parameters of the sampling process match those inside the stack. This method helps to accurately represent the actual conditions of the emissions being sampled.
What are the key components of the apparatus used for stack emission monitoring?
-The key components include a panel box for pressure and flow rate measurements, probes for inserting into the stack, pilot tubes for guiding the probes, thermocouples for temperature readings, impinger tubes for gaseous components, a vacuum pump for extraction, and a sampling probe.
How is the sampling rate calculated in stack emission monitoring?
-The sampling rate is calculated using parameters such as flow rate, absolute gas temperature, absolute temperature of the metering conditions, and barometer pressure. These parameters are input into a specific equation to determine the appropriate sampling rate.
What is the significance of the location of sampling in stack emission monitoring?
-The location of sampling is significant because it should be done at the point where velocity measurements were carried out to ensure the accuracy of the particulate concentration measurements.
How is the sample recovered after the sampling process in stack emission monitoring?
-After sampling, the filter paper or thimble, which has collected the particulate matter, is carefully collected to prevent contamination. It is then weighed, and the mass of the collected dust is determined after drying in an oven at 120 degrees Celsius for about 2 hours to remove moisture.
What is the role of the rotameter in maintaining isokinetic sampling conditions?
-The rotameter is used to regulate the flow rate of the suction pump, ensuring that the velocity of the gas passing through the sampling probe matches the velocity of the emissions coming out of the stack, thus maintaining isokinetic sampling conditions.
How is the concentration of particulate matter calculated in stack emission monitoring?
-The concentration is calculated by dividing the weight difference of the filter paper or thimble before and after sampling by the volume of gas sampled. This gives the weight of particulate matter per unit volume of gas.
What is the procedure for monitoring gaseous pollutants like SO2 during stack emission monitoring?
-Gaseous pollutants are monitored by using impingers to collect samples through extraction from the sampling point in the stack. The collected sample is then analyzed in the lab, and the concentration of pollutants like SO2 is measured using specific titration methods.
Why is quality control important in stack emission monitoring?
-Quality control is important to ensure that the monitoring values are accurate and consistent with real-world conditions. Without strict adherence to guidelines and protocols, the data collected may not reflect the true levels of pollution, leading to incorrect assessments and decisions.
Outlines
🌬️ Stack Emission Monitoring Basics
This paragraph introduces the importance of stack emission monitoring for air pollutants, focusing on both particulate matter and gaseous components. It outlines the need for isokinetic sampling to ensure accurate measurements, which involves matching the velocity and other kinetic parameters of the sampling nozzle to those within the stack. The paragraph also mentions the significance of monitoring emissions to comply with standards set by environmental regulatory bodies such as the CPCB or MOEF. The equipment used for stack monitoring, including a panel box, probes, thermocouples, impinger tubes, and a vacuum pump, is briefly described. The role of stacks in dispersion and dilution of pollutants is highlighted, emphasizing the necessity of understanding emissions to prevent ground-level concentration from exceeding prescribed limits.
📏 The Procedure and Equipment for Stack Sampling
The second paragraph delves into the specifics of stack sampling, including the selection of sampling location and nozzle size to ensure an appropriate sampling rate between 40 to 60 liters per minute. It discusses the importance of calculating the sampling rate using various parameters such as flow rate, absolute gas temperature, and barometric pressure. The paragraph also describes the dual-stream sampling procedure for capturing temperature and velocity data alongside particulate matter collection. The recovery process of the sample, including the careful handling of filter paper and the removal of moisture through oven drying, is outlined. The calculation of gas volume sampled and the determination of particulate concentration by weighing the filter paper before and after sampling are explained. Additionally, the paragraph covers the calculation of dust emission rate and the use of impingers for gaseous pollutant monitoring, specifically for SO2 and NOx, detailing the sampling and analysis process.
🔬 Quality Control in Stack Emission Monitoring
This paragraph emphasizes the critical role of quality control in ensuring the accuracy of stack emission monitoring. It discusses the potential for discrepancies in values and calculations if strict guidelines and mandatory procedures are not followed. The paragraph also introduces a short video from the air pollution laboratory at the Department of Civil Engineering, IIT Roorkee, which provides a visual demonstration of the isokinetic sampling method for particulate matter and gaseous components. The video showcases the experimental setup used for stack monitoring, including the stack monitor, vacuum pump, thermocouple sampler, pitot tube, and rotameters, each serving a specific purpose in the sampling process.
🛠️ Isokinetic Sampling Technique and Instrumentation
The final paragraph provides a detailed explanation of the isokinetic sampling technique, which is essential for accurate stack emission measurements. It describes the use of a pitot tube to measure the velocity of stack emissions and the importance of maintaining the same velocity during sampling. The paragraph explains the use of two rotameters to control the flow rate for particulate matter (SPM) and gas sampling, ensuring the isokinetic condition is met. Additionally, it discusses the use of a probe with a filter assembly for collecting suspended particles while allowing gas to pass through. The paragraph concludes with the significance of stack monitoring for compliance with emission standards, dispersion modeling, and health risk assessment, highlighting the importance of this knowledge for environmental engineers.
Mindmap
Keywords
💡Stack Emission Monitoring
💡Isokinetic Sampling
💡Particulate Matter
💡Gaseous Pollutants
💡Sulphur Dioxide (SO2)
💡Nitrogen Oxides (NOx)
💡Thermocouple
💡Pitot Tube
💡Rotameter
💡Quality Control
💡Environmental Standards
Highlights
Discussion on the importance of stack emission monitoring for particulate matter and gaseous components.
Introduction to isokinetic sampling as a method for stack emission monitoring.
Explanation of the need for stack monitoring to ensure compliance with environmental standards set by CPCB or MOEF.
Description of the role of stacks in dispersion and dilution of pollutants.
Details on the apparatus and equipment used for stack emission monitoring, including panel box, probes, and vacuum pump.
Importance of selecting the correct nozzle size and calculating the proper sampling rate for accurate measurements.
Procedure for sampling rate calculation using parameters like flow rate, temperature, and barometer pressure.
Process of sampling procedure involving two streams for temperature, velocity, and particulate matter collection.
Technique for sample recovery and ensuring no external particulate matter contamination.
Method for calculating the concentration of pollutants by weighing filter paper before and after sampling.
Use of impingers for gaseous pollutant sampling and monitoring of SO2 and NOx emissions.
Demonstration of the sampling setup in the air pollution laboratory of the civil engineering department at IIT Roorkee.
Explanation of the isokinetic sampling principle and its importance in maintaining constant velocity for accurate measurements.
Role of rotameters in controlling the flow rate to maintain isokinetic conditions during sampling.
Procedure for measuring stack temperature and ambient temperature using a thermocouple sampler.
Calculation methods for determining dust emission rate and concentration of pollutants.
Quality control measures to ensure accurate monitoring and adherence to mandatory procedures.
Conclusion emphasizing the significance of stack monitoring for environmental compliance, dispersion modeling, and health risk assessment.
Transcripts
Hello friends, as you know these days we are discussing about lab based experiments
or field based experiments to monitor different air pollutants. So, today we will discuss about
stack emission monitoring using isokinetic sampling. So, what are the emissions from the
stack if you want to measure like particulate matter or gaseous components, so how do we
measure these emissions, that is very important stack monitoring is very important.
So, in this particular presentation we will first discuss about what is the need,
why it is so important, then the principle of the sampling method for stack monitoring,
what are the apparatus or equipment which are used for the sampling in stack monitoring and
what is the procedure, then how do we recover the sample so that we can analyze in the lab,
then how do we estimate the concentrations, what are the procedures of the calculation
and the particulate matter as well as gaseous pollutants can be measured.
So, first we will discuss about particulate pollution monitoring method and then briefly
we will also touch about gaseous pollutants like sulphur dioxide,
we have given one example otherwise NOx emissions can also be monitored and explained, then after
quality control related brief discussion we will show you the video which will further explain how
this sampling is done at the stack emissions and we will conclude.
So, as you know these stacks which are quite large size chimneys where pollutions are coming
as a kind of point source emissions you can say, so they are important in the sense because earlier
they were used for giving the pressure difference in the draft velocity otherwise later on it was
found that stacks also help in dispersion of the pollutants, so you can send directly
it also helps in dilution of the pollutants and reducing the concentration at the ground level.
So, we should know how much emission is coming out of it because if there are so many stacks
and emissions are multiplying then maybe even if they are diluting, ultimately the ground level
concentration may exceed the standards which are prescribed by CPCB or MOEF Ministry of
Environment Forest and Climate Change. So, we need to monitor the emissions
from the stacks that is the important thing and the particulate matter or the gaseous components,
their properties like velocity, temperature, humidity and the concentration of particular
pollutants, whether it is particulate matter or gaseous components we can measure and the
importance is because the pollution if we do not measure and we do not compare then we cannot judge
how much pollution is coming from those stack, so stack monitoring is very important thing.
Now, if you talk about like the principle of sampling method for particulate matter
monitoring, then this is basically the isokinetic sampling method which is given lot of emphasis,
because in this we have to ensure that the velocity, temperature and other parameters are
the same as it is in the stack, means the nozzle which we will be using for extracting the sample,
so the velocity and the flow rate etc, all these kinetic parameters must be the same
which goes into the probe or the nozzle which is in the entire stack, so that is the isokinetic
fundamental thing which we should ensure. If we look into the apparatus or equipment which
is used for this stack emission monitoring then basically it is like panel box, on front side
you can see the pressure, the measurement of the pressure difference and the flow rate etc,
on the back side we have out and inlet or those where we will put those probes you can say and
then these pilot tubes which are used for guiding the probes etc, thermocouples are also there, then
impinger tubes are needed for gaseous components basically so that we can have the knowledge about
how much NOx or SOx are there, then vacuum pump is there for extraction, this is the sampling probe
which is inserted in the stack basically. So, you can see there are other parts like
filter paper or thimble which is known, then the thimble holder, nozzle is also there,
then heated filler box, stopwatch is there and other parts of this equipment which are shown in
CPCB manual basically you can go through that to learn more.
Then there are important aspects like location of sampling, the sample which is collected so
that sample for particulate concentration shall be done where velocity measurement
were carried out basically, that particular point is very important. The nozzle size is selected
so that we can provide this meter sampling rate between 40 to 60 liter per minute, so that kind of
nozzle size must be there, calculation of proper sampling rate is also very important which is done
with the help of like gas meter for each sampling point before starting the test.
So, this is the calculation procedure for sampling rate basically where there are different
parameters like flow rate, then the sampling rate, absolute gas temperature, absolute temperature
of the metering conditions, then barometer pressure all these parameters are noted and
we use those parameters here in this particular equation to calculate the sampling rate.
And if we talk about the sampling procedure basically so the two streams are there, one
is like giving the temperature related, velocity related values, other one is giving us where this
particulate matter will be collected, so the two streams you can look into in this procedure.
So, the sample is recovered when we have done the sampling so we need to collect that filter paper
basically and we have to make sure that there is no addition of the particulate matter from
outside, so we need to keep it in a proper way and then the mass of the dust collected on this filter
paper or thimble is to be weight basically and it should be kept in oven about 2 hours at 120
degree Celsius to remove any kind of error which could be because of some moisture etc, so the
before and after the sampling the way is taken and then the difference as in this high volume sampler
case we have already seen, how the difference of these two values gives us the concentration.
Well, so when we calculate the volume of the gas which has been sampled basically,
so we need this particular relationship where pressure difference is there, volume of the
gas sample at dry gas meter conditions and the temperature etc, so that correction can
be applied according to their unit and then this gives the value of gas sample basically.
This value is used for like to divide this weight difference and it will give
the concentration, concentration means weight divided by the volume flow rate, so this
equation can be used for that purpose. Then if you want to calculate the dust emission
rate then we have to multiply it with the flow rate Qs, so that can give the emission rate.
So, we know the concentration as well as the emission rate and if you want to use
this particular device for monitoring the gaseous pollutant that is also possible
by using some impingers, so for SO2 or NOx. So, for SO2 we have given some information so that
gas sampling is done through extraction from the sampling point where we are using the probe
in the stack basically, so in this case of SO2 sulphuric acid mist including the sulphur trioxide
and the sulphur dioxide are separated so that there is no error, the SO2 fraction is measured
by the barium-thorium titration method. And there are reagents which are
used for this particular purpose and deionized distilled water, then isopropanol, then hydrogen
peroxide, 3 percent all these stuff is being used for that calculation and sampling method.
Then the procedure is shown in this particular figure, a schematic diagram you can see here,
so the sample is collected and then sample is recovered and then it is analyzed in the
laboratory. So, here you collect the sample it goes through these impingers and it is absorbed
and then it is taken to the lab. Calculation is done in this case also
as we have done particulate matter, so this is the, these are the temperature,
then the volume and this calibration factor, pressure related factor all these parameters
are to be used for gas volume calculation. Then the concentration, so concentration is to
be calculated by this particular relationship where volume of barium standard titrant used
for the sample is used and similarly for the blank is used so that difference can be noted
and other the like dry volume, volume of the sample this kind of values are to be
used for this particular relationship. Also the quality control is important as we
have seen in each experiment we have to follow the strict guidelines or
those mandatory procedure or protocol so that quality is ensured, otherwise the monitoring
values can be different, and calculation may also be different than what is the real one.
So now we present a short video which will give you better perspective about
how the sampling of gaseous components or particulate matter is to be done using the
isokinetic sampling method and this video has been recorded in air pollution laboratory of civil
engineering department IIT Roorkee, so enjoy the video please.
Good morning friends, I welcome you in another experiment of our subject air pollution and
control and in today's experiment I am going to explain you the method of sampling of emissions
which are coming out from the stacks and that is called as the stack monitoring and
for that we use the stack monitor and stack monitoring is generally used when we are
going into the power plants or industries and the emissions which are coming out from the
height of the different height of the stacks. So, from those stacks through which the emissions
are coming out we measure the how much of the particulate and polluting gases are there
which are coming out from the emissions of these stacks.
So, this is the experimental setup that we use for measurement of emissions from the stacks
and first of all I will explain you the different component of this device.
So, basically like we have seen in our previous experiments also, like we have to suck the ambient
air to measure the pollutants or particular matter inside it, so here also we need to have a suction
device. So, here you can see this is the stack monitor and to suck the ambient air we have here
a vacuum pump which is connected through this hose and it is attached at this point, so when we start
this vacuum pump it sucks the air through this instrument, so this is the suction pump part and
this stack monitor is having the different components.
So first of all I will tell you this is the thermocouple
sampler and this long road is there so the purpose of this road is like when we are going to
measure the temperature inside the stack we have to insert this probe into the stack through the
sampling port and this probe or thermocouple is connected through this pipe at this point, so this
is the thermocouple for measurement of temperature inside the stack as well as ambient air.
Another component of this instrument is your pitot tube this is called as S type of pitot
tube and the purpose of this pitot tube is to measure the velocity and
the fundamental principle or the physics which are used in this sampling is called as
isokinetic sampling, what is the isokinetic? Basically like when we are sampling the
emissions through the stack whatever the velocity of the emissions which are coming
from the stack or coming out from the stack the same velocity should be maintained when we are
sampling the sample through this probe of the pitot tube, if the velocity is different
then it will not be isokinetic sampling. So, in order to maintain uh the constant velocity
or the isokinetic sampling so that like velocity which are coming out from the stack and which
is passing through this of the gas should have a constant value or it is the same value so we have
this rotameter here through which we can regulate, so this is your pitot tube for measurement of
the velocity of the stack emission and it has a long probe, so we just insert it through the
port wherever we are doing the sampling in the stack and it has a two pipes here and which
are connected here in the stack sampler. So, what is the purpose of this two pipe?
When we are keeping this pitot tube like this then if from bottom to up it is the gas which
is coming out then it has a two probe so there will be some difference in the pressure, like
coming the velocity of the gas which is coming up here it will be higher and here it will be lower,
so the difference of these two will be here and using this fundamental equation of the
pitot tube we will be able to measure the velocity because by using the pressure drop.
So, this is the purpose of the pitot tube to measure the velocity in the stack.
So, until now I have tell you the temperature through the temperature probe or thermocouple
using which we can measure the temperature inside the stack as well as outside and through
the pitot tube we are able to measure the velocity of the stack emissions.
So, now as I said like we need to maintain the isokinetic sampling, now how do we do this
and in order to do this like we have to have a rotameters, so here you can see in this
device we have a rotameter, two rotameter, one is corresponding to the SPM and one is corresponding
to gas, the purpose of saying this for SPM like when we are doing the sampling for SPM or
suspended particular matter then we maintain the flow rate through this and when we are measuring
the gases only then we control the flow rate through this.
Now, how what is the purpose of controlling? The purpose of controlling is like when we are
measuring the velocity through the pitot tube we can use the formula and estimate the velocity and
then we can calculate the flow rate, now that flow rate if we are able to control through the
suction pump and through regulating here then by regulating that flow rate we will be able
to maintain a constant velocity and therefore this will ensure the isokinetic condition of sampling.
And so this is the purpose of these two rotameters and here we have another opening
and the purpose of this opening is like when we are doing for the sampling of particles along
with gas then we use this probe, actually this probe is having at the front a filter assembly
through which when the stack emissions is coming and it is passing through the filter, so whatever
the dust particle or suspended particles that will be collected inside the filter and only
gas will be allowed to pass, so this probe is used when we are doing sampling of SPM also.
And this probe will be connected at this point, so for measurement of stack temperature
we use the probe and when we also use this switch, so when this switch is on for the
stack temperature, the temperature of stack will be recorded and when we are using this switch
to switch up so that the ambient temperature will be recorded from here, so this is how
using this switch we can measure the stack temperature as well as the ambient temperature.
Professor: So, on this basis we can calculate all those parameters whether particulate
matter or SO2 you know the procedure sampling as well as calculation.
So, in conclusion we can say that these kind of methodologies or instruments can be used for
measurement of gaseous and particulate pollution which is emitting out of a particular stack and
those values are very much required because there are norms how much pollution emission standards
are there which has to be met, so we can compare with the help of those particular monitoring data,
those monitoring data are also used for dispersion modeling purpose, health risk assessment, etc.
So, stack monitoring is very important activity and environmental engineers
they should know the methodology how to do stack monitoring, so this is the explanation about the
stack sampling, stack emission sampling and the calculation. I hope you have enjoyed this
so thank you for your kind attention. And these are the references where we have
taken matter and thanks again and see you in the next lecture.
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