Lecture 58: Stack Emission Monitoring using Isokinetic Sampling

Summary

This 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

00:00

🌬️ 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.

05:07

📏 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.

10:12

🔬 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.

15:19

🛠️ 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.

Keywords

💡Stack Emission Monitoring

Stack emission monitoring is the process of measuring the amount and type of pollutants released from industrial chimneys or stacks. It is crucial for ensuring that emissions do not exceed legal limits and for understanding the impact of these pollutants on the environment and human health. In the script, stack emission monitoring is the central theme, with discussions on the importance of monitoring particulate matter and gaseous components like SO2 and NOx.

💡Isokinetic Sampling

Isokinetic sampling is a method used to collect a representative sample of emissions from a stack. The technique ensures that the velocity of the gas being sampled matches the velocity of the gas in the stack, thus preventing the preferential sampling of larger or smaller particles. The script emphasizes the importance of isokinetic sampling to maintain the integrity of the sample and accurately measure emissions.

💡Particulate Matter

Particulate matter (PM) refers to a mixture of solid particles and liquid droplets found in the air. These particles can be harmful when inhaled and are regulated due to their impact on air quality and health. The script discusses the monitoring of particulate matter as a key component of stack emission monitoring, including the use of filter papers to collect samples for analysis.

💡Gaseous Pollutants

Gaseous pollutants are harmful gases released into the atmosphere, such as sulfur dioxide (SO2) and nitrogen oxides (NOx), which can contribute to acid rain and smog. The script mentions the monitoring of these gaseous pollutants as part of the stack emission monitoring process, highlighting the use of impingers for sampling these gases.

💡Sulphur Dioxide (SO2)

Sulfur dioxide is a gaseous pollutant produced by the burning of fossil fuels containing sulfur. It is a significant contributor to air pollution and respiratory problems. In the script, SO2 is specifically mentioned as one of the gaseous pollutants that can be monitored using the isokinetic sampling method, with a focus on its measurement and analysis.

💡Nitrogen Oxides (NOx)

Nitrogen oxides, collectively referred to as NOx, are a group of gases that include nitrogen dioxide and nitric oxide. They are significant pollutants that contribute to the formation of smog and acid rain. The script briefly touches on the monitoring of NOx emissions, indicating the importance of measuring these pollutants in stack emissions.

💡Thermocouple

A thermocouple is a temperature-measuring device consisting of two dissimilar metals that produce a voltage when exposed to heat. In the context of the script, thermocouples are used to measure the temperature inside the stack, which is important for accurate sampling and analysis of emissions.

💡Pitot Tube

A pitot tube is an instrument used to measure the velocity of a fluid in motion, such as the velocity of emissions coming out of a stack. The script explains the use of an S-type pitot tube for isokinetic sampling, ensuring that the sampling velocity matches the stack gas velocity for accurate measurements.

💡Rotameter

A rotameter, or flow meter, is a device that measures the flow rate of a gas. In the script, rotameters are used to regulate the flow rate of the suction pump during isokinetic sampling, allowing for the maintenance of a constant velocity and ensuring accurate sampling of both particulate matter and gaseous pollutants.

💡Quality Control

Quality control refers to the procedures and checks in place to ensure the accuracy and reliability of experimental results. The script mentions the importance of quality control in stack emission monitoring to avoid discrepancies in measurement and calculation, ensuring that the monitoring data reflects the true state of emissions.

💡Environmental Standards

Environmental standards are regulations set by governing bodies to limit the amount of pollutants that can be released into the environment. The script discusses the importance of stack monitoring to ensure compliance with these standards, such as those set by the Central Pollution Control Board (CPCB) or the Ministry of Environment, Forest and Climate Change (MOEF).

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.