Air Pollution Control & Industrial Hygiene

• The content covers techniques for air pollution control and industrial hygiene.

Introduction

• Focuses on emissions to the atmosphere, including their sources.

Control of Mobile Combustion Sources

• Examines the combustion reaction itself.
• Discusses emission reduction methods.
• Outlines preventive solutions like improving combustion reaction.
• Advocates using alternative fuels.
• Focuses on palliative solutions involving catalysts.

Combustion Reaction

• This is a process where heat is added to combustible material until it reaches its ignition point.
• This produces oxidation of reduced carbon compounds, releasing energy.
• Requires a fuel (solid, liquid, or gas), a comburent (pure oxygen, air), and a diluent (Nitrogen).

Fuel-Air Ratio

• Ratio is measured in mass or moles.
• AFR = mair / mfuel, where AFR is the air-fuel ratio, mair is the mass of air, and mfuel is the mass of fuel.

Lambda Factor

• Lambda (λ) = AFR / AFRstoich
• λ > 1 indicates a lean mixture.
• λ < 1 indicates a rich mixture.
• Temperature increases the rate of oxidation, but also leads to greater fuel consumption.
• Residence time is a function of combustion chamber geometry, gas stream flow and temperature.

Emission Reduction Methods

• Active solutions (preventive) focus on avoiding pollutant formation by optimizing processes and using good quality fuel.
• Passive solutions (palliative) focus on preventing pollutants from reaching the atmosphere through carter and fuel tank vapor retention systems, catalysts, and traps or particulate filters.

Use of Alternative Fuels

• Biofuels are liquid at room temperature and burn easily, producing heat.

Methanol (M) and Ethanol (E)

• Both can be obtained from corn.
• Both can be used in vehicles.

Hydrogen

• Does not generate CO or CO2.

Hydrogen storage

• Stored in liquid form at -253 °C.
• Formed by the electrolysis of water.

Biodiesel

• It is esterified vegetable oil (rapeseed oil).
• Produces less soot and SO2 emissions than diesel.

Exhaust Gases in Diesel and Gasoline Engines

• Diesel engines produce proportionally more water (H2O), O2, and Nitrogen with approx. 67% (N2) and gasoline is approx. 71% (N2).
• Gasoline engines produce proportionally more hydrocarbons NOX and CO2.

Diesel Engine: Emissions Control

• CO and HC are catalyzed by oxidation that produces CO2 and H2O.

Oxidation Catalysts

• Assist in filtering diesel particulate

Selective Catalytic Reduction (SCR)

• NOx is treated with ammonia (NH3) to produce nitrogen (N2) and water (H2O).

Gasoline Engine: Emission Control

• Three-way catalytic converters are used.

Catalytic Converter

• Simultaneously facilitates oxidation of hydrocarbons (HC) and carbon monoxide (CO), as well as the reduction of nitrogen oxides (NOx).
• Reduction Catalysts: CuO, Cr2O3 resulting in products N2 and O2.
• Oxidation Catalysts: Pt, Pd, Rh; products are CO2 and H2O.

Control of Stationary Combustion Sources

• Focuses on gas cleaning processes and removing particulate matter through different means.

Gas Cleaning Processes

• Oxidation involves direct flame, thermic, or catalytic incineration for CO and VOC removal.
• Absorption uses absorption towers to transfer pollutants to a liquid absorber; VOCS, SOX, NH3, Cl2, and HCI are removed.
• Adsorption utilizes adsorption towers to transfer pollutants to a solid surface; VOCS, CO, HC, NOX and SOXI, are removed.

Direct Flame Incineration

• Gases are burned in a combustion chamber.
• Used to treat large volumes of combustible gases.
• Achieves a flame temperature of 1300 °C, can lead to the formation of nitrogen oxides.

Thermal Incineration

• Waste gases are burned completely in a combustion chamber.
• Used for low concentrations of combustible gases.
• Operates at temperatures between 550 and 800 °C.

Catalytic Incineration

• Gases are forced through a catalytic bed to increase the rate of oxidation.
• Operates at lower residence times and temperatures (225-340 °C) than thermal incineration.
• Catalyst are noble metals in a bed of alumina.

Absorption Towers

• Use a damp absorbent or dissolution in countercurrent to retain gas pollutants.

Adsorption Towers

• Use solids to retain gases by surface phenomena.
• Common solids include activated carbon, active alumina, magnesium oxide, or molecular sieves.

Processes to Remove Particulate Matter

• Involves dry collectors, wet collectors, filters, and electrostatic precipitators.

Removal From a Gaseous Effluent

• Dry Collectors: Use gravitational settling chambers (dp > 50 μm) and cyclones (dp 5-25 μm).
• Wet Collectors: Use chamber scrubbers (dp > 10 μm) and cyclonic scrubbers (dp > 2.5 μm).
• Filters: Use fabric filters (dp > 0.5 μm).
• Electrostatic Precipitators (or electrofilters): (dp 200-0.05 μm).

Gravitational Settling Chambers

• Introduce gas into a large section chamber to slow it down.
• Increase residence time to allow sedimentation particles.
• They are low in maintenance and are of simple design.

Cyclones

• They form a current inside.
• Particles lose energy.
• Treated performance rate is 50-80 %.

Cyclone Efficiency

• Increases with increasing force acting on particles.
• F ~ dv * vgas / rc (dp = particle diameter, Vgas = gas velocity, rc = Cyclone radius).

Chamber Scrubbers

• Where gas containing particles collides with drops of washing liquid (dp > 10 μm).

Cyclonic Scrubbers

• They are similar to dry cyclones, but spray washing liquid.
• Drops of liquid with particles are subjected to centrifugal force.

Inertial Cleaning Separators

• Uses the energy of the gas stream to spray the washing liquid.
• Has an achievable performance rate of 100 %.

Venturi Scrubbers

• Have an achievable dp of 8-0,5 μm.

Fabric Filters

• Gaseous particles are retained in a porous material.

Electrostatic Precipitator

• Application of electric shock that ionizes gas molecules, causing particles to acquire a charge.
• Operate at high temperatures up to 450 °C and are high-performance.

Industrial Hygiene

• Includes a consideration of Occupational exposure limit values .

Occupational Exposure Limits

• These are reference values for the assessment and control of the risks.
• Pertain specifically to inhalation of chemical agents.
• They are meant to protect the health of workers.
• The document on the "Professional Exposure Limits for Chemical Agents in Spain" includes values that have been adopted by the National Institute of Safety and Health at Work for 2023 and which have been approved in February 2023, by the National Commission for Safety and Health at Work.

Threshold Limit Value (TLV)

• The Threshold Limit Value (TLV) and Biological Exposure Indices (BEIs) are used as indicators of exposure.
• Acetone TLV-TWA is 500 ppm, Urine: 40 mg/l.
• Emission is measured as elemental carbon.
• Benzene TLV-TWA is 1ppm.

Biological Exposure Indices (BEIs)

• BEIs are reference values for biological indicators (BI).
• BEIs with respect to chemical exposure, biological monitoring measures the concentration of a chemical marker in a human biological media.
• Biological indicators of dose are parameters that measure the concentration of the chemical agent.
• Biological indicators of effect. can identify reversible biochemical alterations from chemical agent exposure.