Wet Gas Scrubbers
Spray Dry System
In the mid 1990’s, Fowlerex developed a spray dry adsorption system which combined one process, many years of experience on both industrial spray drying and emission control. This initial system was designed for sulphur dioxide removal using hydrated lime (CaOH) slurry. Spray dry scrubbing today is responsible for abatement of many diverse pollutants.
PROCESS
DESCRIPTION
Hot, untreated gas enters the top of the spray-dryer absorber through the gas disperser. Here, the hot pollutant-laden gas mixes intimately with an atomised absorbing solution (lime, KOH, NaOH, ammonia, etc). Simultaneously, water evaporates from the droplets as the pollutant gas is absorbed, leaving a dry waste powder.
The dried powder is removed at the base of the absorber and through the following particulate collector (either an electrostatic precipitator or a baghouse, which is the preferred option).
From here it can be conveyed to a waste hopper and, eventually, away to a landfill. The power can also be partially recycled to obtain maximum yield from the active absorbent. This process removes any airborne particulate matter at the same time.
The cleaned gas passes from the particulate collector through an induced draft fan and then out to the atmosphere.
DRY
SCRUBBING V. WET SCRUBBING
The advantages of the spray-dry system over a wet system are many. They include:
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There is no wet/dry interface where serious corrosion generally occurs. This means no special reactor linings are required, such as alloys or plastics, reducing the reactor construction cost.
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Removal efficiencies can be above 90% using several different reagents.
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No ancillary equipment (thickness, dewaterers, etc) is required to treat the waste product, as a dry power is produced, not a wet sludge.
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The flue gas typically requires no re-heating.
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Various absorbents can be used as the system is flexible. In other words, a different absorbent may be used to remove more of a certain pollutant gas if a future need arises.
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Plant construction costs are cheaper as there are fewer components. Operational costs are also generally cheaper.
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A low pressure drop across the system allows for a smaller induction fan, which is situated in a dry, clean gas stream.