Rethinking stack height
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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.
Rethinking stack height
- 1. RETHINKING STACK HEIGHTSTACK HEIGHT By: D K Singhal, deveshksinghal@gmail.comJuly 2017
- 2. Stack Height 2 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? 3 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? 4 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…. 5 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 6 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 7 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 8 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? 9 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 10 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 11 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? 12 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 13 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 14 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 15 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 16 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 17 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… 18 Are high stacksAre high stacks really better, or we should cut thesewe should cut these into smaller ones?
- 19. Thank You. 19