Scrubber Systems: Pollution The Essential Role of Control Equipment in Ensuring Cleaner Air
Scrubber System |
What are Scrubber Systems?
Scrubbers are air pollution control devices that work as filtration systems for
industrial exhaust streams. They operate by directing gas or air streams laden
with particulates through various liquid sprays. The pollutants make contact
with the scrubbing liquid and get eliminated from the emission stream before it
leaves the scrubber chamber through the exit stack.
How do Scrubber Systems work?
The basic principle of a scrubber is that the exhaust gas stream loaded with
pollutants is brought into contact with the scrubbing liquid so that the
pollutants in gas or particulate form react or bind with the liquid. There are
different scrubber designs based on the type of pollutants and the technique
used to maximize contact between gas and liquid. Some common scrubber
technologies include:
Venturi scrubbers: Uses a high velocity Venturi throat to create turbulent Scrubber
System action. The flue gas accelerates through the constricted
throat where scrubbing liquid is injected. The mist droplets provide a very
large gas-liquid contact area.
Packed bed scrubbers: Consist of a long cylindrical vessel filled with packing
material like plastic or ceramic saddles/rings. The exhaust gas flows through
the packed bed while the scrubbing liquid trickles downward counter-currently.
Good contact results in efficient removal of particulates.
Spray tower scrubbers: Comprises of a tall tower through which the waste gas
flows upwards as spraying nozzles introduce the scrubbing liquid in the form of
droplets falling downward. Counter-current contact facilitates pollutant
removal.
Cyclonic scrubbers: Utilise centrifugal force to improve contact between the
swirling gas stream and scrubbing liquid droplets. Cylindrical shaped units with
tangential inlets impart rotational motion causing particles to impact liquid
films on walls.
How effective are scrubbers?
The pollutant removal efficiency of a scrubber depends on parameters like
gas-liquid contact effectiveness, solubility/reactivity of pollutants,
liquid-to-gas ratio and residence time. Most scrubbers are capable of removing
over 90% of particulate matter and some gaseous pollutants like SO2, HCl
depending on the liquid chemistry.
Multiple scrubbers may need to be installed in series or a combination of wet
and dry techniques employed to meet stringent emission norms. Modern scrubber
controls with advanced designs, monitoring and intelligent process control can
extract over 99% contaminants from waste streams in industries like power
generation, mineral processing, waste incineration etc.
Scrubbers in coal power plants
Coal-fired power plants are one of the largest industrial applications of
scrubbers for flue gas desulfurization (FGD). Coal contains significant sulfur
content which upon combustion forms SO2. Releasing this as a gas can cause acid
rain. FGD scrubbers use a slurry of limestone/lime to chemically react with SO2
as the flue gas passes through spray towers.
The alkaline liquid neutralizes SO2 converting it into insoluble solid gypsum.
This byproduct is then extracted from the scrubber bottom. Most coal plants
today have wet FGD systems with efficiencies above 90% to meet tightening
environmental regulations. Dry FGD systems using dry sorbent injection are also
gaining popularity due to advantages like lower capital costs and footprint.
Uses of scrubbers in other industries
Besides power generation, scrubbers find widespread application across many
commercial and industrial sectors:
- Cement plants use venturi/packed bed scrubbers with hydrated lime slurry to
control particulate and gaseous emissions from kilns and mills.
- Incinerators at waste processing facilities employ scrubbers to scrub acid
gases like HCl from combustion flue before discharging into atmosphere.
- Metal smelting and mineral processing industries deploy wet scrubbers with
alkali solutions for removal of contaminants like heavy metals and acid mist
from furnace gases.
- Chemical process industries and refineries utilize scrubbers charged with
solvents and alkalis for absorbing gaseous pollutants released from reactor
vents/stacks.
- Water/wastewater treatment deploys scrubbers for neutralizing odorous
gases/vapors through chemical/biological scrubbing processes.
Scrubbers are indispensable air pollution control devices helping various
industries comply with environmental norms on emission of particulate matter,
acid rain precursors and toxic gases. Advancing scrubber technologies continue
delivering higher pollutant removals while reducing costs, footprint and
consumable requirements for a sustainable future.
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