Double alkali process for removal of sulfur dioxide from gas streams
An improved double alkali process is disclosed which is useful for the removal of sulfur dioxide from gas streams, especially waste gas streams derived from coal-fired plants which also contain entrained fine particles of ash which contain alkali, which process comprises leaching soluble alkali from said entrained fine particles to establish an aqueous alkali scrubbing solution, scrubbing the resulting gas stream with said scrubbing solution, which circulates between said leaching and scrubbing steps, followed by bleeding off a portion of the resulting scrubber effluent to a regeneration system wherein the alkali scrubbing solution is regenerated. The scrubber effluent contains a relatively higher amount of alkali bisulfite and regeneration is in two main stages: a first stage wherein the alkali bisulfite is oxidized to alkali sulfate with formation of sulfuric acid followed by reaction of the acid with a calcium carbonate slurry to produce insoluble calcium carbonate and carbon dioxide gas; and a second stage wherein lime is added and reacts with the alkali sulfate to form insoluble calcium sulfate and alkali hydroxide. After thickening and filterhing the reaction product of the second stage regeneration step, alkali carbonate is added thereto in a clarifier in a softening step (i.e., to remove dissolved calcium as a solid) which forms an overflow containing alkali hydroxide which is recycled to the scrubbing step and an (insoluble) calcium carbonate slurry which in turn is recycled to the first stage regeneration reaction. The primary advantage of the present invention is the total elimination for any alkali make-up to the system. This is accomplished by forming in situ the alkali scrubbing solution using the alkali contained in the entrained fine particles carried to the scrubber.
- Assignee:
- AirPol, Inc.
- Patent Number(s):
- US 4452766
- OSTI ID:
- 6435335
- Country of Publication:
- United States
- Language:
- English
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AQUEOUS SOLUTIONS
ASHES
CARBON COMPOUNDS
CARBONACEOUS MATERIALS
CARBONATES
CHALCOGENIDES
CHEMICAL REACTIONS
COAL
COMBUSTION PRODUCTS
DESULFURIZATION
DISPERSIONS
DISSOLUTION
ENERGY SOURCES
FLUE GAS
FOSSIL FUELS
FOSSIL-FUEL POWER PLANTS
FUELS
GASEOUS WASTES
HYDROGEN COMPOUNDS
HYDROXIDES
LEACHING
MATERIALS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
POWER PLANTS
PROCESS SOLUTIONS
REGENERATION
REMOVAL
RESIDUES
SCRUBBING
SEPARATION PROCESSES
SOLUTIONS
SULFATES
SULFITES
SULFUR COMPOUNDS
SULFUR DIOXIDE
SULFUR OXIDES
THERMAL POWER PLANTS
WASTE PRODUCT UTILIZATION
WASTES