Air Pollution Control (APC) Methods for MSW incinerations Flashcards
What needs to be removed after incineration?
1) Fly ash
- composed by particles pneumatically transported by the gaseous flow
2) Acids and acid Precursors
- sulphur dioxide (SO2), Nitrogen oxides (NOx), Hydrochloric Acid (HCl)
3) Dioxins
4) Typical metals
- arsenic, beryllium, thallium, cadmium, chromium antinomy, silver
Types of Air Pollution Control (APC) Systems
1) Wet systems
2) Dry Systems
3) Wet / Dry systems
What are particulates?
particle density in the flue gas from incinerators measured in mg per dry normal m^3
What options are there for particle removal?
1) Gravity separation
2) Impaction devices
3) Centrifugal Separation
4) Filtration
5) Electrostatic Separation
6) Wet Scrubbing
How are dry Particles removed?
1) Impaction using baffles and screens
2) Centrifugal separation using cyclone separators
3) Filtration using fabric filters
4) Electrostatic Precipitators
How are wet particulates removed?
- wet methods employ water as a medium and include:
1) Impaction Tray columns
2) centrifugal separation using wet cyclones
3) particulate wetting using a venture reason similar units
4) Particulate conditioning of wetting using a collision scrubber
5) Wet electrostatic precipitator
What is a Venturi Scrubber?
High velocity induced by the reduction in size at the throat of a venturi will shear water introduced and form a fine spray of water droplets which will remove particulates by entrainment.
What are Advantages and Disadvantages of Venturi Scrubbers?
(+) Simple and rugged
(-) High pressure drop to remove some microparticles to required emission levels and therefore not very energy efficient.
How is acid gas removed?
Gases such as HCl, SO2, HF
Wet or dry methods available
Wet methods have higher efficiency but produce wastewater which requires treatment
What is a Packed Tower?
Work by transferring pollutants from the gas stream into liquid steam.
Cylindrical column of ceramic or plastic.
Relatively low water consumption
What is Dry Injection and why is it used?
To avoid wastewater treatment a completely dry APC system is employed.
A neutralising agent (typically lime) is introduced in powder form.
What is an Electrostatic Precipitator?
Electric currents used behind plates to attract unwanted pollutants.
After collected they are washed off by water.
What is the problem with chlorinated organics?
Chlorinated organics when burned in air, will produce hydrogen chloride gas and some chlorine gas.
The amount of Cl2 in the flue gas is proportional to the incineration temperature and amount of excess air.
The aim is to maximise HCl content and minimise Cl2 because HCl is very soluble in water and can easily be removed by a wet APC system.
Why are mist eliminators used?
Flue gas from an incinerator will contain a significant amount of water.
To remove this water mist eliminators are employed.
What is a stack?
A stack is used to disperse the flue gas into the atmosphere.
When designing a stack it is important to take into account prevailing wind direction
