ESE 3201 Gaseous Pollutants & Control 2015 (for Students)

Air Pollutants and Their EffectsTie the corresponding items togetherCO ~ Irritating to lungs

~ Contributing to tropospheric/ground level O3NOx ~ Aerosol

~ Mainly from transportation

VOC ~ Mainly from fossil fuel combustion in stationary sources

~ Erosion of buildings

PM ~ In the form of solid or liquid~ Highly water soluble

SOx ~ smoke

Air Pollutants: Carbon Monoxide (CO) Colorless, odorless, tasteless gas

Produced during incomplete combustion

77% of total CO: emitted from transportation

Form carboxyhemoglobin (COHb) in the bloodstream

An indoor air pollutant

CO & Health EffectsTypical concentration Roadway: 550 ppm Cigarette smoke: 2400 ppm Smoky bar: 2030 ppm (~ 1 hr ambient standard) Smokers [COHb]: ~ 510%

1.7% ~ 35 ppm for 1 hour 2.5%: tone signal 10%: headache 30%: fatigue, impaired judgment 60%: lost of consciousness

[COHb] in blood and symptons

CO: Effects of Exposure

Source: Seinfeld, J.H. 1986, Atmospheric Chemistry and Physics of Air Pollution, published by John Wiley & Sons, Inc., New York

Dimethyl Sulfide (CH3SCH3, 80110 ppt)

Sulfur Containing Pollutants

Carbonyl Sulfide (OCS, 500 ppt)

Hydrogen Sulfide (H2S, 450840 ppt)

Carbon Disulfide (CS2, 35120 ppt)

Carbonyl Sulfide (COS, 500 ppt)

SO2, 1500 ppt)

Wetland

Global Sulfur Emissions EstimatesSource SO2 SO42- Total Sulfur (Tg(S) yr-1)*

Fossil-fuel burning 70 2.2 7177 & industryBiomass burning 2.8 0.1 2.23.0 (1.4/1.1)Oceans (DMS) -- 40320 1525 (8.4/11.6)aWetlands (H2S,DMS, and CS2) -- -- 0.012 (0.8/0.2)Plants + soils -- 24 0.250.78 (0.3/0.2)bVolcanoes 78 24 9.311.8 (7.6/3.0)Anthropogenic (Total) 7380Natural 2540

Total 98120

*(w/o sea salta and soil dustb)Numbers in ( ) are fluxes from Northern Hemisphere/South Hemisphere. Source: Berresheim et al., 95

Anthropogenic Sulfur Emissions

Source: Dignon and Hameed (1989), Hameed and Dignon (1992), and Spiro et al. (1992)

Oxides of Sulfur (SOx) ~ 90% of the anthropogenic-related SOx emitting from

fossil fuel combustion

Transformation of SO2(g) to sulfuric acid (H2SO4):

- Reaction with hydroxyl radicals:

SO2 + OH HOSO2

HOSO2 + O2 SO3 + HO2

SO3 + H2O H2SO4

Oxides of Sulfur (SOx) Transformation of SO2(g) to sulfuric acid (H2SO4) (ctd.):

- Reaction with O2 (needs large activation energy):

2SO2(g) + O2 2SO3(g)

SO3(g) + H2O(pte) H2SO4(pte)

- Soluble in water:

SO2(g) + H2O(pte) H2SO4(pte) . (not balanced)

Neutralization reactions of SO2(g) to (NH4)2SO4:

H2SO4(pte) + 2NH3(g) (NH4)2SO4(pte)

SOx: Effects Precursor of sulfate particles Most sulfate particles in urban air: 0.20.9 m

- p visibility- easily penetrating deep in human lungs- synergistic effects

Highly water soluble: erosion of building materials

(1) Sulfur oxides:

(2) Others (e.g., H2S):

Control of Sulfur-Containing Pollutants

Pre-combustion control; pollution preventionRemoval of SO2 from rich waste stream lean waste stream Combustion Flue gas desulfurization (FGD):

- Wet-throwaway- Double alkali- Dry throwaway- Wet-dry throwaway- Adsorption/absorption

Removal of S from natural gas and petroleum

Unit of sulfur content emitted:

Pre-combustion control: Fuel switching: p 30-90% emission; blending; temporary Compliance coal or low-sulfur coal:

Control of SO2: Pre-combustion Control

% or mass of SO2 emitted per heat energy delivered

- Meeting NSPS without control: [emission] < 1.2 lb/MBtu (0.5 g/MJ) (NSPS: new source performance standard)

- Organic bound: chemical/biological treatment- Inorganic form: washing to remove pyrite (FeS2),

p ash content

Control of Rich SO2 in Waste GasesResource Recovery

for smelting ores:SO2 + 0.5O2 vanadium catalyst SO3;SO3 + H2O o H2SO4

Cost-effective if (a) SO2 concentration is high enough(b) the chemical conversion leads to marketable

products (H2SO4)

Combustion control: Fluidized-bed combustion (FBC):

Control of Lean SO2 in Waste Streams

CaCO3 + SO2 + 0.5 O2 o CaSO4 + CO2 ~ 90% p of S

Advanced Pressurized Fluidized-Bed Combustion (PFBC)Source: http://www.engineering-4e.com/systems.htm

Flue gas desulfurization (FGD)- Often used for coal/oil power plantsProcesses: - Wet-throwaway: limestone, hydrated lime/quicklime- Double alkali (DA): sodium (bi)carbonate (Na2CO3, NaHCO3)- Dry-throwaway: Boiler injection (CaCO3/Ca(OH)2); Boiler/flue gas injection (Na2CO3 or NaHCO3)

- Wet-dry: spray dryers (SD)- Regenerative adsorption/absorption: Regenerableadsorbents or absorbents



CaCO3 + SO2 + 2H2O o CaSO32H2O ~ 90% p of SCaO + SO2 + 2H2O o CaSO32H2O ~ 95% p of S

1. Expensive2. Corrosion, scaling, plugging problems3. n amounts of water used4. Sludge treatment: CaSO3 CaSO4 thickening

vacuum filtration

Disadvantages of wet scrubber:

(CaCO3 CaO (porous materials) + CO2)heat

Wet-throwaway process (limestone), Wet Scrubber:

Wet-throwaway processes (Quicklime/hydrated lime):- An alternative to limestone in wet-throwaway processes

- CaO (burned lime/quicklime) hold tank hydrated to Ca(OH)2- More reactive than CaCO3 because of higher surface area

- More expensive because of additional steps


Eashwar Ranganathan

Na2CO3 + SO2 o Na2SO3 + CO2- To solve the problems of wet scrubbing

- Solubility of sodium salts >> solubility of calcium salts

liquid w/o solid particles regenerated with CaO/CaCO3

Na2SO3 + CaCO3 + 0.5O2 o CaSO4 + Na2CO3 (in hold tank)CaSO4 can be precipitates

Control of Lean SO2 in Waste StreamsDouble alkali scrubber

Control of Lean SO2 in Waste StreamsDouble alkali scrubber

(Source: Air Pollution Control Engineering by Noel De Nevers, McGraw Hill, 95)

Control of Lean SO2 in Waste StreamsScrubber

Taken from www.induscoenviro.com/img/scrubber1.jpg


Taken from www.mikropul.com/products/wscrub...turi.gif


Taken from www.q-net.net.au/~legion/scrubber.jpg


CaCO3 CaO CaSO3 CaSO4

Disadvantages of dry system1. More expensive by requiring excess of lime/limestone2. Increase in solid waste3. Less efficient than wet-throwaway (DA)4. Mainly based on empirical tests

dried at high temp. SO2 O2

Dry-throwaway process:

Spray dryers (SD): dispersion from high-pressure gas atomizing nozzle for heat-sensitive products (e.g., SO2-containing flue gases) more like wet-lime scrubber partly like dry sorbent injection


Picture taken from class.fst.ohio-state.edu/Dairy_T...-141.gif

Control of Lean SO2 in Waste Streams Spray dryers (SD):

Taken from www.niro.com/NIRO/cmsresources.n...ber2.gif

Control of Lean SO2 in Waste Streams Regenerative Systems: Adsorbents/absorbents can be regenerated Concurrent removal of SOx and NOx: still under study

ReagentsCaCO3 Ca(OH)2 Na2CO3 NaHCO3 Regenerablelimestone hydrated lime sodium sodium bi- adsorbents/

Process (quicklime) carbonate carbonate absorbents----------------------------------------------------------------------------------------------------Wet-throwaway Limestone / Lime scrubbing

DA DA DA

Dry-throwaway Boiler Boiler lime Boiler or flue Boiler or fluelimestone injection injection injectioninjection

Wet-dry SD SD SD

Regenerative Many kinds, producing SO2 or S or H2SO4. Some control both SO2and NOx.


Removal of sulfur from natural gas streams:

H2S(g) H2S (l) H+ + HS- o add alkali remove H+

Control of Sulfur in Natural Gas & Petroleum

Removal of sulfur from hydrocarbon fuels:

H2S + O2 o S (inert, harmless) + H2O(Undesirable oxidation: H2S + 3/2 O2 o SO2 + H2O)HC-containing S + H2 catalysts (Ni/Co) HCs + H2S

Reduction Elemental Oxidation Oxidationform 1st step 2nd step

----------------------------------------------------------------------------------------------------High pressure+ reaction with O2, (1) atmospherehigh temperature+ at (1) high temperatures (2) catalytic reactor hydrogen gas + catalyst. (2) low temperaturesBiological processes (low pressuresand temperatures).

NH3 N2 NO NO2H2S S SO2 SO3

Reactions of Nitrogen and Sulfur: ComparisonElementary oxidation & reduction

Reaction( with water) Reaction (with NH4+ or other cations)----------------------------------------------------------------------------------------------------Rate depends on atmospheric Rate depends on [atmospheric cations]moisture content

HNO3 nitrate particles

H2SO4 sulfate particle

Reactions of Nitrogen and Sulfur: ComparisonAdditional Reactions

Nitrogen Containing Pollutants

N2O- Colorless- Almost completely from natural sources- Long residence time | 120 years- Important Green-house gas

NH3- Emitted from natural & anthropogenic sources

N2O, NOx, HNO3, and NH3

NO2 and Ozone NO2

irritating the lungs, causing bronchitis and pneumonia, and lower resistance to respiratory infections

NOx + OHx HNO3

hQNOx + volatile organic compounds photochemical oxidants

Photochemical smog pollutantsO3: chest constriction & irritation of mucous membranes

Others: PAN (peroxyacetylnitrate), HCHO, acrolein, etc. causing irritation of eyes and respiratory systems (coughing),

Thermal NOx Prompt NOx Fuel NOx

(Source: Air Pollution Control Engineering by Noel De Nevers, McGraw Hill,95)

Control NOx: Formation

During the 1st part of combustion Mainly converted from original form in fuel Carbon bearing radicals

Control NOx: Prompt NOx

CH + N2 HCN + N

N + O2 NO + O

HCN + O2 NO

HCN + NO N2

Most of the fuel nitrogen is converted in the flame to HCN, subsequently converted to NH or NH2.

Control NOx: Fuel NOx

NH + O2 NO + H2O, or NH + NO N2 + H2ONH2 + O2 NO + H2O, or NH2 + NO N2 + H2O

[NOx] from fuel depends on [NO]/[O2] ratio in the flame zone At high-temp. zone of flame, if [O2] p [NO] p Usually, 20-50% of fuel nitrogen is converted to NOx,

depending on (1) furnace conditions, and (2) chemical nature of nitrogen in fuels.

During combustion:- Emitted [NOx] n with

Control NOx During Combustion

n peak temperature, n time at high temperature, n [O2] at high temperature

- Peak temperature depends on (1) fuel and oxidizer used, (2) flame size, (3) degree of fuel-air premix, and (4) amounts of fuel-air preheat

During combustion:Control NOx During Combustion

- Peak temperature


Low NOx burner / Two-stage combustion:1st stage: low excess air


p [O2] and max. temp. p [NOx] formed

2nd stage: - w/ excess air; - the max. temp. from the 1st stage is low enough to p [NO] formed

- Often add extra fuel (e.g., CH4) without N

Modify Combustion / Combustor Design


Disadvantages: (1) n fuel consumption, (2) n [CO] emissions, and (3) larger burner.

Low NOx burner / Two-stage combustion (ctd.):Modify Combustion / Combustor Design


prevent fuel-rich p thermal NOx and prompt NOx

[NOx] formed v fuel nitrogen

Low NOx burner / Flue gas recirculation (FGR):

When fuel gas is employed: through mixing + excess air

Modify Combustion / Combustor Design


If oil is employed: prompt NOx

From mobile emission sources:Adding reducing agents:2NO + 2CO pt-rh catalysts N2 + 2CO2

Control NOx Post-Combustion

3-way catalytic converter

Taken from images.gasgoo.com/MiMwMDRfMDA0Iz...rter.jpg

Chemical Treatment of Combustion Exhaust Gases

Air-to-fuel ratio & Catalytic Converter PerformanceC

onve

rsio

n ef

ficie

ncy

(%)

Air-to-fuel ratio

(Source: Introduction to Environmental Engineering and Science by G.M. Masters, Prentice Hall, 2008)

Control of NOx Post-Combustion

14.8:1 14.9:1

(Source: Introduction to Environmental Engineering and Science by G.M. Masters, Prentice Hall, 97)

Control of NOx Post-CombustionAir-to-fuel ratio for vehicle emission control

From stationary emission sources:(1) Selective catalytic reduction (SCR) w/ reducing reagents:


6NO + 4NH3 o 5N2 + 6H2O4NO + 4NH3 + O2 o 4N2 + 6H2O2NO2 + 4NH3 + O2 o 3N2 + 6H2O

Note: @ temp. > 1800oF, NH3 + O2 o NO + 1.5H2Odominates over other reactions



(3) Scrubbing w/ solution of NaOH & KMnO4- Expensive electrochemical regeneration of KMnO4- More suitable for small-scale processes

From stationary emission sources (ctd.):(2) Selective noncatalytic reduction (SNCR)


Preventing artificial dilution of exhausts before release: - depending on dilution of excess air;- standard limit/regulation based on O2% in the exhaust

(Max. 6-7% of O2, by volume)

Other units: mg/m3, lb/106 Btu, g/GJ, Pg/kcal

Regulating NOx in Exhausts

Most abundant photochemical oxidants, in addition to formaldehyde (HCHO), peroxybenzoyl nitrate (PBzN), peroxyacetyl nitrate (PAN), and acrolein (CH2CHCOH)

Health effects of photochemical pollutants

O3: chest constriction & irritation of mucous membranes

Others (PAN, HCHO, acrolein, etc.): irritation of eyes and respiratory systems (coughing),

Photochemical Reactions: Ground Level O3

NO-NO2-O3 photochemical reaction sequenceN2 + O2 2NO2NO + O2 2NO2NO2 + hv NO + OO + O2 + M O3 + MO3 + NO NO2 + O2


When RCOO + NO RCO + NO2(RCOO & RCO : VOC radicals)

Concentrations measured in Los Angeles, CA, USA, Jul. 19, 1965

Source: U.S. HEW, 1970, Air Quality Criteria for Carbon Monoxide, AP-62, National Air Pollution Control Administration, Washington, DC

Air Pollutants and Ground Level O3

Why and how do VOC emissions aggravate ground level [O3]?


Tropospheric chemical reactions! To reduce [O3]: p both VOCs and NOx

ESE 3201 Gaseous Pollutants & Control 2015 (for Students)

Documents

Transcript of ESE 3201 Gaseous Pollutants & Control 2015 (for Students)