Chapter 18: Air Pollution Control

selective reduction

part of dry processes; may be catalytic or non-catalytic

Evaporative Controls

put in place to reduce evaporation; like putting lids on tanks containing volatile solvents, using solvents with a lower vapor vapor pressure

Adjustment of the air to fuel ratio (HC and CO)

reduce HC and CO emission

Vapor Pressure Reduction (HC and CO)

reduce loss of HCs due to evaporation

Emulsify fuel with water

reduces NOx by lowering the flame temperature

Sedimentation

remove particles large enough to settle under the force of gravity.

Regenerative system

salable product systems

1967 Air Quality Act

set federal air pollution guidelines and extended federal enforcement power 1) Required states to promulgate ambient standards and to develop state implementation plans to meet these standards 2) gave the US attorney general permission to bring an abatement action in any situation presenting an imminent and substantial danger to health.

Disadvantages of Taller Stacks

Unsightly, increase long-range transport of SOx and NOx, which fall downwind in the form of nitric and sulfuric acid.

Catalytic Incinerators

similar to thermal incinerators, but the catalyst requires less heat to achieve a given degree of removal. (less fuel at a lower temperature)

Double Alkali Process

solution of sodium bicarbonate is used to capture SO2 as NaHSO3. In an external loop, Ca(OH)2 is added to react with the NaHSO3, making CaSO3 solids and sodium sulfite (Na2SO3). The sodium sulfite is recycled to the scrubber and removes more SO2

Throwaway Product Systems

the end product has little or no commercial value and is disposed of in landfills or ponds

Vapor recovery system (HC and CO)

the process of capturing and recovering vapors. vapors are captured by methods such as chilling or scrubbing. They are then purified, and the vapors or products are sent back to the process, sent to storage, or recovered.

The Clean Air Act Amendments of 1990

11 Titles

Federal Pollution Control Legislation PL 84-159

1955: Made after the Deanery, PA lake on fire episode; authorized federal funding for research, training, and support of local air pollution agencies for 5 years.

Examples of adsorption

1: Adsorption of acidic gases (SOx, HCl, H2S, or HNO3) on alkaline solids (limestone, sodium carbonate, activated alumina) 2: Adsorption of organic chemicals by granular activated carbon or biodegradable vapors by soil beds.

Key Elements of Title 11 CAAA 1990

1: Allocated 50 million per year to provide additional unemployment under Title 3

1965 Clean Air Act Amendment ( Motor Vehicle Air Pollution Control Act)

1: Allowed secretary of Health to promulgate and enforce federal emission standards for new vehicles 2: resulted in the requirement for positive crankcase ventilation (PCV) for new autos in 1968

Key Elements of Title 9 CAAA 1990

1: Authorized research on monitoring stuff in the Adirondack region.

Key Elements of Title 4 CAAA 1990

1: Capped annual utility emissions of SO2. This was supposed to be achieved through innovative market based systems. They were given allowances or allowed to purchase emission control equipment. 2: Required EPA to be more stringent performance standards for NOx emissions and set more stringent standards for newer equipment.

Precombustion control techniques

1: Change fuels 2: Emulsify the fuel with water 3: Fuel denitrification

What are the technologically-based alternatives for air control strategies?

1: Change the production process 2: Develop an alternative product 3: Treat the air stream to remove the pollutants 4: Disperse the pollutants in sihc a way that they case no adverse effects (like building very tall stacks)

Key Elements of Title 1 CAAA 1990

1: Classified non-attainment areas and set deadlines for achieving attainment 2: Figured out how and when the federal government can set sanctions 3: Let EPA force non-attainment areas to implement controls in proportion to the severity of their air quality problem 4: Required new sources in non-attainment areas to get more than 1 for 1 emission offsets (this ratio increases with the severity of the problem)

Cyclones

1: Cyclones are typically 3-5 ft in diameter; high efficiency are smaller 2: more effective for large particles, have greater inertia, more likely to come into contact with the walls of the cyclones 3: operational problems include high pressure drop and plugging

Key Elements of Title 6 CAAA 1990

1: EPA forced to list ozone depleting substances, their ozone depleting and global warming potential, and atmospheric lifetime, within 60 days. 2: Phase out of ozone chemicals and regulated 2 classes of chemicals 3: Made EPA list safe and unsafe substitutes for class 1 and 2 chemicals; banned the use of unsafe chemicals. 4: Banned non-essential use of products using class 1 chemicals 5: Banned aerosols and non-insulating foams using Class 2 chemicals

Options for Control of Sulfur Oxide (SO2) Emissions

1: Fuel Switching 2: Coal Cleaning 3: Coal Gasification 4: Taller Stacks 5: Flue Gas Desulfurization (FSD) 6: Lime or Limestone Injection 7: Use Less Electricity

Controlling Greenhouse Gas Emissions

1: Greenhouse Gases 2: Options for controlling CO2 emissions 3: Alternative energy sources

1963 Clean Air Act

1: Let Secretary of Health publish air quality criteria and established a conference hearing procedure for interstate air pollution 2: authorized federal funds for statewide air pollution control agencies.

Key Elements of Title 3 CAAA 1990

1: Listed 189 toxic air pollutants for which emission must be reduced. 2: Directed EPA to issue Maximum Achievable Control Technology Standards (MACT) for 40 source categories 3: EPA must look at the risk levels to determine whether additional controls are needed to reduce risks 4: Est. a Chemical Safety Board to investigate accidental releases of extremely hazardous chemicals, and required each industrial plant to have plans for preventing and managing accidental spills of toxic pollutants. 5: Required EPA to issue rules to manage air pollution from hospitals, municipal, commercial, and industrial incinerators.

1977 Clean Air Act Amendments

1: Made amendments to the 1970 amendments, mostly relaxing deadlines 2: Authorized EPA to designate non-attainment areas and require any new emissions be offset or more than offset by reductions in existing emissions. Also adopted the bubble policy 3: gave EPA the authority to take steps to insure prevention of significant deterioration of the air quality in areas designated by the EPA

Key Elements of Title 2 CAAA 1990

1: Made stricter emissions for CO, HCs, and NOx 2: Required car makers to reduce emissions resulting from refueling and evaporation 3: Required reduction in fuel volatility and sulfur content 4: Required cleaner gas in the 9 cities with the worst ozone problem 5: Required more alcohol-based oxygenated fuels to be made and sold in 41 areas where the federal CO standards is greater during winter 6: Est a clean car program in CA 7: Delayed diesel particulate standards for urban buses 8: Required EPA to regulate air toxics from mobile sources 9: Required 26 areas with the dirtiest air quality to adopt a program to limit emissions 10: Banned lead from use in motor vehicle fuels

salable product systems (Swenson)

1: Magnesium Oxide Process 2: The Wellman-Lord Process 3: The Aqueous Carbonate Process

electrostatic precipitators or ESPs

1: Particles passed through a high voltage field, causing particles to become more negatively charged. 2: There are no more moving parts and able to remove finer particles than cyclones 3: efficiency increases with increasing voltage 4: Disadvantages include the possibility of ozone production due to corona discharge at high voltages.

Combustion Modification Technologies

1: Reducing available oxygen at critical stages of combustion 2: Lowering the peak flame temperature 3: Reducing the residence time during which oxidation of nitrogen takes place.

Energy Policy and Conservation Act of 1975

1: Required car maker's fleet to reach 27.5 mpg by 1985 2: Required 75% domestic content in US made cars. (Due in part to an effort to protect US jobs.)

Key Elements of Title 5 CAAA 1990

1: Required states to develop permit programs similar to the NPDES program for water 2: Permits must include all applicable Clean Air Act requirements

Key Elements of Title 8 CAAA 1990

1: Sources within 25 miles of a shore had to meet the same standards as the shore 2: Est. programs to monitor and improve air quality along the Mexican border 3: Provided 8 million for studies involving visibility impairment

Throwaway products/disposable products (Swenson)

1: The Lime Process 2: The Limestone Process 3: Spray Absorber or dry scrubber 4: Sodium Carbonate Process

Advantages of lime/limestone FDG

1: Well developed process 2: Retrofitted to existing systems 3: Capital costs are low relative to other options 4: Particulate material (fly ash) is removed simultaneously

Filters

1: made of loosely woven material with a high void ratio 2: remove particles by interception and impaction, which may be aided by electrostatic attraction 3: Often used in a baghouse. Can be cleaned using mechanical shaking 4: Problems include fabric deterioration, clogging and high pressure drops 5: major advantage is that they can remove very small particles.

Alternative Fuels and Vehicles

1: reformulated fuels 2: biofuels (ethanol) 3: Electric vehicles and hybrids 4: Hydrogen and Liquefied Petroleum Gas 5: Fuel Cells

1970 Clean Air Act Amendments (CAAA) (1-2)

1: required EPA to issue national air quality criteria to promulgate national primary and secondary standards. NAAQS States were required to make plans to meet those standards 2: Starts in 1975: Required EPA to establish national emission standards for new light duty monitor cars. Plans for reducing HC (hydrocarbons), NOx, and CO (Carbon Monoxide) emissions by 90%

Spray towers

1: spray (water or oil) is directed downward through an up flowing air stream carrying particles. 2: efficiency of spray tower increases as: relative velocity increases, particle diameter and density increases, liquid injection rate increases 3: ADVANTAGES: better removal than cyclones and ESPs and no clogging 4: DISADVANTAGE: Decreased plume buoyancy, production of a liquid waste, corrosive enviro

Key Elements of Title 7 CAAA 1990

1: upgraded criminal violations from misdemeanors to felonies 2: added new criminal sanctions for endangerment, related to air pollution 3: Authorized penalties up to $200,000

Noncatalytic Selective Reduction

2 processes that employ ammonia or urea as a reductant; but the reaction is carried out at high temperatures rather than under the influence of a catalyst

Schemes for NOx reduction

3 Schemes: 1: Reduction before combustion by reducing 2: reduction during combustion by modification 3: reduction after combustion by gas treatment

1970 Clean Air Act Amendments (CAAA) (3-4)

3: Required EPA to set national emission standards for new stationary sources 4: Required EPA to establish national emission standards for hazardous air pollutants (NESHAPS) to regulate all sources of hazardous pollutants not included in the primary standards.

1970 Clean Air Act Amendments (CAAA) (5-6)

5: States could obtain primacy if their programs met minimum federal guideline requirements; EPA was given authority to preempt states not making satisfactory progress. 6: Private citizens given the right to sue states or the EPA to prevent lax enforcement

coal gasification

A process whereby coal is turned into a gas (mainly CO2 and H2) and all the sulfur and nitrogen compounds are removed.

Major advantage of the Double Alkali Process

Absorption into the alkaline solution is very rapid, since dissolution of a solid is not required in the scrubber itself.

CAAA 1990 Title 4

Acid Deposition Control (looks to obtain a permanent 10 million ton reduction in SO2, NOx, and acid rain)

thermal incinerators

Afterburners; used to destroy organic chemicals by oxidizing them to CO2 and H2O.

CAAA 1990 Title 3

Air Toxics (regulating more air toxics; originally, only 7 pollutants had previously been regulated under the NESHAPS regulations)

Oxidation or Reduction

Alteration of a chemical state of a pollutant by adding or withdrawing electrons. Enhanced by catalysts or means of heating

CAAA 1990 Title 1

Attainment and Maintenance of NAAQS (national ambient air quality standards); provisions for representing federal strategies for improving urban air quality

Why do air pollution control devices tend to relatively small devices?

Because polluted air streams can not easily be collected and transported to a central treatment facility. The devices are intended to remove pollutants from single stacks, tail pipes and other processes.

lime vs limestone

Both work well and the overall costs are comparable. Scrubbing efficiency is greater with lime, but lime is worse with regards to scaling. Lime also results in greater production of calcium sulfite solids. They are difficult to dewater and oxidize to the sulfate form. Use of limestone slurries results in high maintenance requirements for grinding equipments and piping.

Developments of the 1990 Clean Air Act Amendments

Bush administration issue 2 regulations targeting power plant emissions, aimed at SO2 and NOx, and mercury. Started discussion on regulating CO2 emissions.

Greenhouse Gases

CO2, CH4, N3O, CFCs (some), HFCs, PFCs, Methane and CO2 receive most attention

CAAA 1990 Title 9

Clean Air Research

Lime or Limestone Injections

Coal and limestone are crushed, then burned together, removing the SOx and other acidic gases that are removed by the limestone as the coal is burned. The coal and limestone can be burned in fluidized bed combustion (FBD).

catalytic converter (HC and CO)

Control HC and CO emission by oxidizing them to carbon dioxide.

Forced Oxidation

Converts sulfite to sulfate, making solids easier to handle.

Use Less Electricity

Decreases coal burning and emissions of SO2.

CAAA 1990 Title 11

Employment Transition Assistance

CAAA 1990 Title 7

Enforcement

When is source control a preferred option in reference to air pollution control?

For anthropogenic pollutants, since it is impractical to treat air at the point of use.

Fuel Denitrification

Hydrodesulfurization of fuel oil also removes nitrogen, but is very expensive in comparison with combustion modification techniques. This is used because nitrogen binds to organic compounds, making it harder to remove.

Major advantage of dry scrubbers

It does not completely humidify the flue gas. It shows promise for use with high sulfur coals.

Lime Process

Lime is slaked with water to form a slurry of Calcium Hydroxide (Ca(OH)2), which reacts (in a scrubber) with SO2 to form hydrated calcium sulfite (CaSO3) and calcium sulfate (CaSO4)

CAAA 1990 Title 8

Miscellaneous Provisions

CAAA 1990 Title 2

Mobile Sources; even though the cars built today emit less VOC and NOx than before, there are more cars being made and driven. The growth in number of cars in urban areas is so high that it's a huge problem

Interception

Occurs when a particle, under the influence of Brownian motion (diffusion) or carried tangentially near the surface, touches the surface (where it usually adheres as a result of physical or chemical forces)

CAAA 1990 Title 5

Operating Permits

Single Alkali Process

Released SO2 can be converted to sulfuric acid.

Taller Stacks

Releasing the plume at a higher altitude allows for greater dispersion before the plume reaches the ground, lowering the maximum ground level concentrations.

Coal Cleaning

Removing impurities from coal to increase efficiency and reduce pollution.

Flue Gas Desulfurization (FGD)

Scrubbing of the air to remove SOx (or when burning municipal solid waste to remove HCl)

Spray Absorber or Dry Scrubber

Slurry of lime or soda ash (Na2CO3) is atomized into the flue gas to absorb SO2; the droplets are dried by the flue gas and collected as dry particles

Limestone Process

Slurry of limestone (CaCO3) is used in a scrubber to remove SO2 as CaSO3 and CaSO4 hydrates

Magnesium Oxide Process

Solution of Magnesium Oxide (MgO) traps SO2 and converts it to MgSO3; the SO2 is then extracted and converted to sulfuric acid

Sodium Carbonate Process

Solution of Na2CO3 is sprayed into the flue gas to absorb the SO2, converting it to Sodium Bisulfite (NaHSO3)

Wellman-Lord Process

Solution of Na2SO3 is used to scrub SO2, formin NaHSO3. The scrubbing liquor, containing NaHSO3, is used to drive off water and SO2, regenerating the NA2SO3 solution. The released SO2 can be converted to sulfuric acid or to elemental sulfur.

Venturi Scrubber

Squeeze down size of pipe so increase velocity through water High efficiency, but expensive Particle > 1 micrometer Requires maintenance

CAAA 1990 Title 6

Stratospheric Ozone and Global Climate Protection

CAAA 1990 Title 10

Support for Disadvantaged Business Concerns

Fuel Switching

Switch from soft coal with a high sulfur content to low sulfur coal; a change from one fuel to another.

Maximum Achievable Control Technology (MACT)

The best technology available for reducing the output of especially toxic industrial pollutants. Standards based on performance of the top 12% of facilities in a given source category.

Salable Product Systems

Yield a potentially marketable material such as elemental sulfur, sulfuric acid, or fertilizer base compounds. Systems will produce gypsum as an end product may be considered either throwaway or salable product systems, depending on purity, quality and site specific market.

Adsorption

accumulation of a substance at a surface or interface. Air pollutants are usually adsorbed on solid materials.

Positive Crank Ventilation (HC and CO)

achieved by means of a PCV valve. They eliminate HC emissions due to blowby.

Bubble Policy

allows a plant to measure emissions as an average of all emission points from that plant

Acid Precipitation Act of 1980

also known as Title 7 of Energy Security Act; started the National Acid Precipitation Assessment Program to study acid rain authorized funding to study acid rain over 10 years

Wet processes

for NOx removal representing natural extensions of processes originally developed for SOx removal.

Adsorption (1)

applicable to a wide range of organic chemicals, usually at low concentrations

Non-selective reduction

application of a catalytic converter; limited to stationary reciprocating engines, not yet applicable for coal fired utilities

non-attainment areas

areas with significant air pollution problems, areas not meeting their standards, according to the EPA

Federal Pollution Control Legislation PL 86-493

authorized the Public Health Service to investigate the effects of motor vehicle emissions

Adjustment of the air to fuel ratio (NOx)

can reduce NOx emissions to a limited extent

3 Way Converter (NOx)

employ catalyst containing approximately 0.1% platinum, 0.01% rhodium, 2% NiO, and Ce2O3. They oxidize HC and CO and reduce NOx.

diesel engine

internal-combustion engine that burns fuel by using heat produced by compressing air; produce lower HC and CO

wet ESPs

less commonly used than dry ESPs and scrubbers, well suited for treating some types of emissions

Biofilters

living material or an organism that captures and biologically degrades pollutants.

Change fuels

lower nitrogen fuel

Selective Catalytic Reduction (SCR)

most popular FGT process in international utility use, employs ammonia.

Moving Source Standards

national emission standards

Impaction

occurs when an air stream carrying particles changes direction and the momentum (inertia) of the particle is such that it deviates from the stream line and strikes (impacts) the surface

Settling Chambers

only effective for removing relatively large particles. Also useful for pretreating an air stream to remove coarse particles before the air enters a downstream treatment device.

Non-regenerative systems

throwaway product systems; these systems predominate

Absorption

transfer of a constituent from one phase into another phase (usually liquid) in which the constituent is uniformly dispersed.

Photocatalytic Processes

use both raidant energy (UV radiation) and a catalyst (titanium dioxide) to oxidize organic contaminants

Scubbers

used to remove inorganic chemicals (HCl or H2S) and can sometimes be used to remove organic vapors, especially in soluble water