air quality exam 2 SO2

CEE4504

health impacts of SO2

respiratory illness especially children and elderly

what does SO2 contribute to forming

acid rain and particles

what is the harm of acid rain

damages plants and buildings, acidifies soil, lakes, and streams

most of the global sulfur is from

humans anthropogenic

other places sulfur comes from

ocean, volcanoes, biomass burning, soil/vegitation

where does anthropogenic sulfur come from

vehicles(3), electricity generation (1), fossil fuel and industrial processes (2)

anthropogenic sources of sulfur

combustion: fuel S + O2 → SO2
coal inorganic S
pyrite, sulfate minerals, organic S, crude oil, natural gas if H2S is high it is sour gas
Sulfide ore smelting

emission controls

fuel switching, fuel desulfurization, remove SO2 from exhaust

three types of industrial S exhaust

1. reduced sulfur

2. concentrated SO2

3. Dilute SO2

reduced sulfur H2S industrial exhaust

natural gas, by products from oil refining, fuel from coal gasification

concentrated SO2 from industrial exhaust

metal smelting converting SO2 to H2SO4

dilute SO2 from industrial S exhaust

coal and oil burning convert to gypsum and put in wallboard

H2S collecting absorption tower

absorption tower, collecting gas with some liquid medium, for H2S use water but have to add alkali to make it soluable

H2S removal reaction

react H2S with controlled amount of air and form elemental sulfur, claus process, sulfur can be sold after production or landfilled, too much O2 forms SO2

claus process too much O2 forms SO2

H2S + 0.5 O2 → S + H2O how it should work
H2S + 1.5 O2 → SO2 + H2O

concentrated SO2 stream

gas stream from smelting gets oxygen to form SO3 and then add water to from H2SO4b

by products from concentrated So2 stream

H2SO4, inexpensive industrial acid with many uses like fertilizer, must have SO2 conc >4%, other factors to consider is distance to market, transportation costs, and investment cost

dilute SO2 recovery?

not concentrated enough for profitable recovery, most commonly treated using flue gas desulfurization (FGD), comes from coal or oil burning facilities like power plants CFPP

flue gas desulfurization classifications

once through (throwaway) or regenerable, wet, dry

once through (throwaway) FGD

SO2 permanently binds to sorbent spend sorbent is disposed of as waste or utilized as a by product

regenerable FGD

so2 is released from sorbent may be further treated to yield H2SO4 or liquid SO2

wet FGD

wet slurry waste or by products and flue gas is saturated with waterd

dry FGD

dry waste or by products flue gas is not saturated

most commonly used FGD

limestone wet scrubbing

less commonly used FGD

regenerable due to expense, may have future with simultaneous removal of NOx and SO2

Limestone forced oxidation FGD

air in effluent holding tank EHT forces oxidation of SO3 2- to SO42-, produces gypsum to sell as wallboard, pile or landfill can remove 95% and more SO2

limestone inhibited oxidation FGD

no air blower which can be cheaper, forms CaSO3 which is landfilled, efficient for high sulfur coals or salable gypsum not required, Thiosulfate S2O32- added to slurry to prevent oxidation of SO32- to SO42- in absorber

lime scrubbing using CaO(s) or magnesium enhanced lime FGD

MgSO3 more soluble can increase pH more, increase SO2 uptake, both more reactive than limestone, smaller tower less pump cost, CaO more expensive than limestone

dual alkali FGD

uses alkaline materials besides limestone lien sodium carbonate Na2CO3 or sodium bicarbonate NaHCO3, solubility much higher, increased pH, more SO2 uptake, smaller

lime and limestone used to treat scrubber effluent and regenerate alkali

advantage of dual alkali FGD

reduces scaling and lower maintenace cost

disadvantages of dual alkali FGD

reagents expensive, treatment of sodium salts

seawater process FGD

utilizes natural alkalinity to neutralize SO2, seawater spray, no precip of solids discharge SO42- which is already in seawater, cl causes corrosion issues, and location issues need to be close to ocean

once through dry FGD

about 88% efficiency, 14% of all FGD in US 8% of worlds FGD, dry waste produced which is easier disposal, fewer problems with corrosion and scaling, particles produced are collected by PM control deviceO

dry scrubbing/furnace sorbent injection

dry sorbent or flue, CaSO4 and unreacted sorbent leaves with flue gas and is collected in PM control device

advantage of dry scrubbing FGD

lower capital cost and maintenance cost, collect PM and SO2 simultaneously

disadvantage of dry scrubbing

high reagent cost, lower utilization efficiency, need to inject extra reagents

lime spray dryer/wet-dry scrubber FGD

wet lime slurry is atomized, SO2 dissolves in water and reacts with dissolved Ca(OH)2, water evaporates quickly forming particles dry before reaching walls or bottom bin

advantage of lime spray dryer FGD

lower capital cost and maintenance collect PM and SO2 simultaneouslyd

disadvantage of lime spray dryer

risk of bind the baghouse/fabric

similarities of SO2 and NOx

both criteria air pollutants, both cause acidic deposition and contribute to acid rain, both lead and contribute to formation of PM, both have large sources from coal combustion

differences between SO2 and NOx

NOx→ troposphere leads to O3, Emission mechanisms, pollution control strategies/methods