2023-12-07
Air Pollution Part 4 – Reduction Methods
With all said about emissions of pollutants in preceding blogs, it should also be noted that there are multiple methods available and in frequent use to reduce the emissions at their sources, both of gaseous substances and particulates.
Addressing Particulates
To start with the latter, there are cyclones, electrostatic filters, and fabric filters that can catch the particles before being emitted.
A coarse method to reduce dust levels is to use cyclones, significantly applied in cement production but also in other contexts. The raw gas is forced into a funnel-shaped device where the gas is made to rotate. The particles in the flue gas are pushed by centrifugal forces and gravity towards the bottom and the clean gas exits at the top. Electrostatic filers can be used to further reduce the particulate levels in the flue gas. The dust-laden flue gas passes high-voltage electrodes causing particles to be charged. Collector plates with reverse voltage then captures particles by electrostatic attraction. Fabric filters can also be used to further reduce the particulate levels. In fabric filters, also known as “bag houses”, the flue gas is forced through filters (bags) where the particles are captured.
Reduction of Gaseous Pollution
When it comes to gas-phase pollutants, the combustion temperature can be tuned for example by exhaust gas recirculation (EGR) to minimise the combustion reactions leading to excess levels of pollutants being formed. SO2, HCl and some other pollutants can be made to react with lime or a lime slurry in a scrubber, leading to formation of solid material (for example plaster) which can be deposited. The resulting wastewater can be neutralised and cleaned. NOX emissions can be reduced by reactions with ammonia (or more precisely, usually urea) in the presence of a catalyst, forming nitrogen and water.
Exhaust gas recirculation, particulate filters, and catalytic reduction is applied both to stationary sources and in vehicles. Examples of the application of reduction methods in industrial contexts are given in the blog Pollutant Reduction Control and Continuous Emissions Monitoring at Waste-to-Energy Plants.
However, the best way of reducing the levels of air pollution is of course to not generate the pollution at all. This is a challenge given the rising demand for energy around the world and that a lot of energy production still comes from combustion of fossil fuels. Nevertheless, it’s a challenge we must face and manage.
More to read
If you want to dive deeper into the matter of industrial emissions, you can read more about it in the article Pollutants in Emissions to Air – What’s in the Smoke? The monitoring of industrial emissions is discussed in Continuous Emissions Monitoring – What, Why, and How?, and more information on surveillance of ambient air quality can be found in Air Quality Monitoring.
