Lowering stack heights from industrial units would help better control air pollution in three key ways: 1) Pollutants would remain closer to the ground and immediately impact workers, managers, and neighbors, forcing units to take action to reduce pollution. 2) Lower stacks would make pollution monitoring and enforcement easier by allowing for ambient air sampling close to ground level near units. 3) Alternative pollution control methods like fine bubble diffusers in water tanks could more efficiently trap pollutants from lower stacks compared to existing wet scrubbers. Cutting stack heights may enable exploration of better control technologies.

1. RETHINKING
STACK HEIGHTSTACK HEIGHT
By: D K Singhal, deveshksinghal@gmail.comJuly 2017

2. Stack Height
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The height of stack is an important parameter while
approving no objection certificate (NOC) to anyapproving no objection certificate (NOC) to any
industrial unit.
The stack height should not be less than a specified
mandate depending upon the boiler capacity.

3. Why So?
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The object is that the small particles of pollutants go
up in to the atmosphere and get dispersed there,up in to the atmosphere and get dispersed there,
thus diluting the pollutant level.
From the height, the pollutants may travel to distant
areas, thus getting diluted to significantly low level.
This way, these pollutants do not harm mankind.

4. Really?
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Earlier, when the mills were very less in number, this
seemed a good approach.seemed a good approach.
Earlier, when the population density was low, and
people usually lived in small villages or towns near
factories; this ensured that the pollutants may go far
away from populated places.
Earlier, when the residential buildings were usuallyEarlier, when the residential buildings were usually
single or double story, this helped in easier
spreading of pollutants.

5. But Now….
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There are many mills, often in a small proximity.
There are many high rise buildings (almost) in everyThere are many high rise buildings (almost) in every
city.
The cities have spread to even few kilometers.
Result-Result-
AIR POLLUTION RISING!

6. High Stacks
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Not only this, high stacks create several other
problems-problems-
Increased capital cost
Difficulty in assessing pollution level
Difficulty in proper monitoring of pollution
However, we shall confine ourselves towards
environmental aspects only.

7. High Stacks
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Pollution Assessment
To evaluate pollution level, you need to takeTo evaluate pollution level, you need to take
samples from a height, thus making regular
monitoring a difficult task.
What you cannot measure and monitor regularly;
you just cannot control.
Mandatory periodic monitoring cannot give clear
status about the overall performance.

8. High Stacks
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Online Monitoring Systems
To certain extent, online monitoring provide goodTo certain extent, online monitoring provide good
information about the performance, but these also
need frequent maintenance for proper
measurement.
However, these, due to very high investment have
not been mandated for all boilers.not been mandated for all boilers.
Issues related to frequent cleaning of sensor head
also need to be taken care off with these.

9. What Can be Done?
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Imagine if pollution level increases, what is the
immediate direct impact on the concerned industry?immediate direct impact on the concerned industry?
None.
If some law enforcing officer visits that time, and
monitors, action shall be taken against the unit.
But, if he does not appear that particular time….
Nothing can be done.

10. Self Monitoring
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Let us consider something else.
We still are surviving in a high pollution atmosphere.We still are surviving in a high pollution atmosphere.
What if pollution is increased by a little more?
We’d surely want to escape from that particular area.
Can we become so important for the mills that the mills
become really ready to reduce pollution so that we
stay there, with them?stay there, with them?
How?

11. Cut the Stack
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Yes. CUT the STACK.
Cut the stack height to make is lower.Cut the stack height to make is lower.
Any increase in pollutant level would immediately
impact the workers, managers, owners, visitors and
neighbors directly.
The concerned mill shall be automatically forced to
take appropriate actions to curb pollution level to
keep them there.

12. What if They Don’t?
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If a unit does not control pollution properly, workers
may not prefer to work with that unit; managersmay not prefer to work with that unit; managers
would find difficult to hire good workers or need to
pay them more.
Neighbors may also find it difficult to tolerate
increased pollution and shall make complaints, after
which appropriate action may be taken.
Presently, particulate matter being most serious
issue, a non-complying unit itself may see layers of
dust gathering on all object lying nearby in open.

13. Further Monitoring
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To monitor further, ambient air sampling can be
done at several designated places within anddone at several designated places within and
nearby the concerned unit.
Such monitoring can be done at near ground level,
say around 6ft height from ground level.
That will giver a more clear and better idea about
the pollution caused by a particular unit.the pollution caused by a particular unit.

14. Easier to Control
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In place of existing systems, lower height shall make
it easier to explore some better alternatives.it easier to explore some better alternatives.
Imagine a water tank installed with fine bubble
diffusers fed by stack emission. Would air pollution
control not be much more efficient than existing wet
scrubbers?
High NO , SO or such oxides shall also react withHigh NOX, SO2 or such oxides shall also react with
water to form weak acids which can be neutralized
by addition of alkali.

15. Easier to Control
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With such systems, a significant part of particulate
matter would also get trapped with the water, andmatter would also get trapped with the water, and
can be easily disposed off properly along with the
contaminated water in such a way that the water
gets evaporated and the solids are safely
disposed.

16. Water Use
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Here the prime object is to trap the NOX, SO2 and
particulate matter, so primary treated effluent fromparticulate matter, so primary treated effluent from
other mills may be used for this purpose; high BOD
and COD of that should not create any problems.
This way, there shall be no additional load on
existing ground water level.
Pollutants going with untreated or partially treatedPollutants going with untreated or partially treated
water to nearby river streams would also be
reduced.

17. Washing Everything
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With this scheme, everything which is emitted to
atmosphere from a boiler stack, shall be washedatmosphere from a boiler stack, shall be washed
clean.
We’d get a clean atmosphere, with easy monitoring
of pollutants discharged (on solids basis, ash content
of fuel should correlate with the pollutants
disposed).disposed).

18. Think…
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Are high stacksAre high stacks
really better, or
we should cut thesewe should cut these
into smaller ones?

19. Thank You.
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