8.3 Emissions Control Technologies and Regulations

Emissions control technologies are crucial for reducing harmful pollutants from combustion processes. From catalytic converters to selective catalytic reduction systems, these innovations transform toxic gases into less harmful substances, improving air quality and public health.

Regulations like the Clean Air Act and international standards drive the development and implementation of emissions control technologies. Continuous monitoring systems ensure compliance, while ongoing research aims to further reduce environmental impact and meet increasingly stringent emissions limits.

Catalytic Emissions Control Technologies

Catalytic Converters and Their Operation

Top images from around the web for Catalytic Converters and Their Operation

• 

  Catalytic converter - Wikipedia View original

  Is this image relevant?

• 

  Catalysis · Chemistry View original

  Is this image relevant?

• 

  Catalysis | Chemistry View original

  Is this image relevant?

• 

  Catalytic converter - Wikipedia View original

  Is this image relevant?

• 

  Catalysis · Chemistry View original

  Is this image relevant?

1 of 3

Top images from around the web for Catalytic Converters and Their Operation

• 

  Catalytic converter - Wikipedia View original

  Is this image relevant?

• 

  Catalysis · Chemistry View original

  Is this image relevant?

• 

  Catalysis | Chemistry View original

  Is this image relevant?

• 

  Catalytic converter - Wikipedia View original

  Is this image relevant?

• 

  Catalysis · Chemistry View original

  Is this image relevant?

1 of 3

• Catalytic converters transform harmful exhaust gases into less harmful emissions
• Contain precious metal catalysts (platinum, palladium, rhodium) coated on a ceramic honeycomb structure
• Convert carbon monoxide (CO) to carbon dioxide (CO2)
• Transform hydrocarbons (HC) into water vapor (H2O) and CO2
• Reduce nitrogen oxides (NOx) to nitrogen gas (N2)
• Three-way catalytic converters simultaneously handle CO, HC, and NOx
• Require precise air-fuel ratio control to function effectively
• Operate most efficiently at temperatures between 400°C and 800°C

Selective Catalytic Reduction (SCR) Systems

• SCR systems reduce NOx emissions in diesel engines and power plants
• Inject a reductant (urea solution or ammonia) into the exhaust stream
• Reductant decomposes into ammonia (NH3) when heated
• NH3 reacts with NOx over a catalyst to form N2 and H2O
• Typical catalysts include vanadium oxide, zeolites, or metal-exchanged zeolites
• Can achieve NOx reduction efficiencies of 70-95%
• Require careful control of reductant injection to avoid ammonia slip
• Commonly used in heavy-duty diesel vehicles and industrial applications

Diesel Particulate Filters (DPF) and Regeneration

• DPFs capture and store particulate matter (PM) from diesel exhaust
• Consist of a honeycomb structure made of ceramic or silicon carbide
• Alternate channels are plugged, forcing exhaust through porous walls
• Trap soot particles while allowing gases to pass through
• Require periodic regeneration to burn off accumulated soot
• Passive regeneration occurs at high exhaust temperatures during normal operation
• Active regeneration involves injecting fuel to raise exhaust temperature
• Can reduce PM emissions by over 90% when functioning properly

Combustion Modification Technologies

Exhaust Gas Recirculation (EGR) Systems

• EGR reduces NOx formation by lowering combustion temperatures
• Recirculates a portion of exhaust gas back into the engine intake
• Dilutes the intake air with inert exhaust gases
• Lowers oxygen concentration in the combustion chamber
• Reduces peak combustion temperatures, inhibiting NOx formation
• Can be cooled (cooled EGR) for greater effectiveness
• Typically controlled by an EGR valve based on engine operating conditions
• May slightly increase fuel consumption and particulate emissions

Low NOx Burners and Combustion Optimization

• Low NOx burners modify the combustion process to reduce NOx formation
• Implement staged combustion to create fuel-rich and fuel-lean zones
• Fuel staging introduces fuel in multiple stages to control combustion
• Air staging supplies combustion air in stages to reduce peak temperatures
• Flue gas recirculation mixes exhaust gas with combustion air
• Often combined with overfire air systems for further NOx reduction
• Can achieve 30-50% NOx reduction in industrial boilers and furnaces
• Require careful design to maintain combustion efficiency and stability

Flue Gas Desulfurization (FGD) Technologies

• FGD systems remove sulfur dioxide (SO2) from flue gases
• Wet scrubbers use a limestone slurry to absorb SO2
• Dry scrubbers inject a dry sorbent (lime or sodium bicarbonate) to react with SO2
• Wet FGD can achieve SO2 removal efficiencies of 95% or higher
• Dry FGD typically achieves 80-90% SO2 removal
• Produce gypsum as a byproduct, which can be used in construction materials
• Require significant capital investment and ongoing operational costs
• Widely used in coal-fired power plants to meet emissions regulations

Emissions Regulations and Standards

Clean Air Act and National Ambient Air Quality Standards

• Clean Air Act establishes the framework for air pollution control in the United States
• Enacted in 1970, with major amendments in 1977 and 1990
• Authorizes EPA to set National Ambient Air Quality Standards (NAAQS)
• NAAQS set limits for six criteria pollutants (CO, lead, NO2, O3, PM, SO2)
• Requires states to develop State Implementation Plans (SIPs) to meet NAAQS
• Establishes New Source Performance Standards (NSPS) for new or modified sources
• Implements the National Emissions Standards for Hazardous Air Pollutants (NESHAP)
• Addresses acid rain, ozone depletion, and mobile source emissions

International Emissions Standards and Compliance

• Euro emissions standards regulate vehicle emissions in the European Union
• Progressively tightened from Euro 1 (1992) to current Euro 6 standards
• Set limits for CO, HC, NOx, and PM emissions from various vehicle types
• California Air Resources Board (CARB) sets stringent emissions standards
• CARB standards often exceed federal requirements and influence national policy
• Many states adopt CARB standards under Section 177 of the Clean Air Act
• Best Available Control Technology (BACT) required for major new or modified sources
• BACT determination considers technical feasibility and economic reasonableness

Emissions Monitoring

Continuous Emissions Monitoring Systems (CEMS)

• CEMS provide real-time data on pollutant concentrations in exhaust streams
• Measure gaseous pollutants (NOx, SO2, CO) and particulate matter
• Use various analytical techniques (infrared absorption, chemiluminescence)
• Include sampling systems, analyzers, and data acquisition systems
• Require regular calibration and quality assurance procedures
• Data used for regulatory compliance, process control, and emissions trading
• Enable rapid response to emissions exceedances or equipment malfunctions
• Increasingly integrated with advanced data analytics and predictive maintenance