Control Device Technology Barrett Parker, EPA, OAQPS.

Control Device Technology

Barrett Parker, EPA, OAQPS

Example Control Systems

4 VOC control techniques plus capture discussion

5 PM control techniques

2 Acid gas control techniques

3 NOx control techniques

VOC Control Techniques – Carbon Adsorber

General description– Gas molecules stick to the surface of a solid– Activated carbon often used as it

Has a strong attraction for organics Has a large capacity for adsorption (many pores) Is cheap

– Silica gel, activated alumina, and zeolites are also used


General description (continued)– 3 types – fixed bed (most common), moving

bed, and fluidized bed– Typically appear in pairs – one adsorbing

while other desorbs– Used for control as well as recovery– Regenerated via steam, hot gas, or vacuum– Work best if molecular weight of compound

between 50 and 200

VOC Control Techniques – Carbon Adsorber – Fixed Bed Schematic

VOC Control Techniques – Carbon Adsorber – Fixed Bed Examples


Factors affecting efficiency– Presence, polarity, and concentration of

specific compounds– Flow rate– Temperature– Relative humidity


Performance indicators– Outlet VOC concentration– Regeneration cycle timing or bed

replacement frequency– Total regeneration stream flow or vacuum

profile during regeneration cycle– Carbon bed activity – Bed operating and regeneration

temperature


Performance indicators (continued)– Inlet gas temperature– Gas flow rate– Inlet VOC concentration– Pressure differential– Inlet gas moisture content– Leaks

VOC Control Techniques – Carbon Adsorber – Manufacturer’s Specs

VOC Control Techniques – Catalytic Oxidizer

General description– Waste gas gets oxidized to water and

carbon dioxide – Catalyst causes reaction to occur faster and

at lower temperatures– Saves auxiliary fuel


General description (continued)– Catalysts allow lower operation temperatures

(~ 650 to 1000°F)– Catalyst bed generally lasts from 2 to 5 years

Thermal aging, poisoning, and masking are concerns

– Excess air is added to assist combustion Residence time and mixing are fixed during design Only temperature and oxygen can be controlled

after construction

VOC Control Techniques – Catalytic Oxidizer – Example Bricks

VOC Control Techniques – Catalytic Oxidizer - Schematic


Factors affecting efficiency– Pollutant concentration– Flow rate– Operating temperature– Excess air– Waste stream contaminants

Metals, sulfur, halogens, plastics


Performance Indicators– Outlet VOC concentration– Catalyst bed inlet temperature– Catalyst activity– Outlet CO concentration– Temperature rise across catalyst bed– Exhaust gas flow rate


Performance Indicators (continued)– Catalyst bed outlet temperature– Fan current– Outlet O2 or CO2 concentration

– Pressure differential across catalyst bed

VOC Control Techniques - Condenser

General description – Gas or vapor turns to liquid via

Lowering temperature or Increasing pressure

– Used as pretreatment to reduce volumes– Used to collect and reuse some solvents


General description (continued)– Two types – contact and surface

condensers No secondary pollutants from surface type More coolant needed for contact type

– Chilled water, brines, and CFCs used as coolants

– Efficiencies range from 50 to 95 percent

VOC Control Techniques – Condenser - Schematic


Factors affecting efficiency– Pollutant dew point– Condenser operating pressure– Gas and coolant flow rates– Tube plugging or fouling


Performance indicators– Outlet VOC concentration– Outlet gas temperature– Coolant inlet temperature– Coolant outlet temperature– Exhaust gas flow rate– Pressure differential across condenser


Performance indicators (continued)– Coolant flow rate– Pressure differential across coolant

refrigeration system– Condensate collection rate– Inspection for fouling or corrosion

VOC Control Techniques – Thermal Oxidizer

General description– Waste gas turns to carbon dioxide and water– Operating temperatures between 800 and

2000°F– Good combustion requires

Adequate temperature Turbulent mixing of waste gas with oxygen Sufficient time for reactions to occur Enough oxygen to completely combust waste gas


General description (continued)– Only temperature and oxygen concentration

can be controlled after construction– Waste gas has to be heated to autoignition

temperature Typically requires auxiliary fuel

– Common design relies on 0.2 to 2 seconds residence time, 2 to 3 length to diameter ratio, and gas velocity of 10 to 50 feet per second

VOC Control Techniques – Thermal Oxidizer - Schematic


Factors affecting efficiency– Waste gas flow rate– Waste gas composition and concentration– Waste gas temperature– Amount of excess air


Performance indicators– Outlet VOC concentration– Outlet combustion temperature– Outlet CO concentration– Exhaust gas flow rate– Fan current– Outlet O2 or CO2 concentration– Inspections

VOC Control Techniques – Capture System

General description– Total efficiency is product of capture and

control device efficiencies– Two types of systems

Enclosures and local exhausts (hoods)

– Two types of enclosures Permanent total (M204) – 100% capture efficiency Nontotal or partial – must measure capture

efficiency

VOC Control Techniques – Capture System - Schematic

VOC Control Techniques – Capture System

Factors affecting efficiency– System integrity– System flow

VOC Control Techniques – Capture Systems

Performance indicators– Enclosures

Face velocity Differential pressure Average face velocity and daily inspections

– Exhaust Ventilation Face velocity Exhaust flow rate in duct near hood Hood static pressure

PM Control Techniqes - Cyclone

General description– Particles hit wall sides and fall out– Often used as precleaners

Especially effective for particles larger than 20 microns

– Inexpensive to build and operate– Can be combined in series or parallel

PM Control Techniques – Cyclone - Schematic

PM Control Techniques - Cyclone

Factors affecting efficiency– Component erosion– Inlet and outlet plugging– Acid gas corrosion– Air inleakage

PM Control Techniques - Cyclone

Performance indicators– Opacity– Inlet velocity or inlet gas flow rate– Pressure differential– Inlet temperature

PM Control Techniques – Electrostatic Precipitator

General Description– Charged particles are attracted to plates

and removed from exhaust gas– Two types

Dry type use mechanical action to clean plates Wet type use water to prequench and to rinse

plates– High voltages are required– Multiple sections (fields) may be used– Efficiencies up to 99% can be obtained

PM Control Techniques – Electrostatic Precipitator - Schematic

PM Control Techniques – Electrostatic Precipitators

Factors affecting efficiency– Gas temperature, humidity, flow rate– Particle resistivity– Fly ash composition– Plate length– Surface area


Performance indicators– Outlet PM concentration– Opacity– Secondary corona power (current and

voltage)– Spark rate– Primary power (current and voltage)


Performance indicators (continued)– Inlet gas temperature– Gas flow rate– Rapper operation– Fields in operation– Inlet water flow rate (wet type)– Flush water solids content (wet type)

PM Control Techniques – Electrified Filter Bed

General description– Charged particles are deposited on pea

gravel– Three parts

Ionizer system Filter bed Gravel cleaning and recirculation system

PM Control Techniques – Electrified Filter Bed - Schematic


Factors affecting efficiency– Glaze build up on ionizer or gravel– Temperature

Performance indicators– Ionizer voltage and current– Filter bed voltage, current, and

temperature– Inlet gas temperature


Performance indicators (continued)– Pressure differential– Gas flow rate– Outlet PM concentration– Opacity

PM Control Techniques – Fabric Filter

General description– Particles trapped on filter media, then

removed– Either interior or exterior filtration systems– Up to 99.9% efficiency– 4 types of cleaning systems

Shaker (off-line) Reverse air (low pressure, long time, off line) Pulse jet (60 to 120 psi air, on line) Sonic horn (150 to 550 Hz @ 120 to 140 dB, on line)

PM Control Techniques – Fabric Filter - Schematic


Factors affecting efficiency– Filter media

Abrasion High temperature Chemical attack

– Gas flow– Broken or worn bags– Blinding


Factors affecting efficiency (continued)– Cleaning system failure– Leaks– Re-entrainment– Damper or discharge equipment

malfunction– Corrosion


Performance indicators– Outlet PM concentration– Bag leak detectors– Outlet opacity– Pressure differential– Inlet temperature– Temperature differential


Performance indicators (continued)– Exhaust gas flow rate– Cleaning mechanism operation– Fan current– Inspections and maintenance

PM Control Techniques – Wet Scrubber

General description– Particles (and gases) get trapped in liquids

Inertial impaction and diffusion

– Liquids must contact pollutants and dirty liquids must be removed from exhaust gas

– Four types Spray; venturi or orifice; spray rotors; and

moving bed or packed towers

PM Control Techniques – Wet Scrubber - Schematic


Factors affecting efficiency– Gas and liquid flow rate– Condensation of aerosols– Poor liquid distribution– High dissolved solids content in liquid– Nozzle erosion or pluggage– Re-entrainment– Scaling


Performance indicators– Pressure differential– Liquid flow rate– Gas flow rate– Scrubber outlet gas temperature– Makeup / blowdown rates– Scrubber liquid solids content (PM)


Performance indicators (continued)– Scrubber inlet gas and process exhaust gas

temperature (PM)– Scrubber liquid outlet concentration (Acid

gas)– Scrubber liquid pH (Acid gas)– Neutralizing chemical feed rate (Acid gas)– Scrubber liquid specific gravity (Acid gas)

Acid Gas Control Techniques – Dry Injection

General description– Sorbent reacts with gas to form salts that

are removed in a PM control device (fabric filter)

– Hydrated lime and sodium bicarbonate often used as sorbents

Acid Gas Control Techniques – Dry Injection - Schematic


Factors affecting efficiency– Dry sorbent injection rate– Emission stream gas temperature– Residence or reaction time– Degree of turbulence– Other PM control device used factors


Performance indicators– Outlet acid gas concentration– Sorbent feed rate– Fabric filter inlet temperature– Sorbent carrier gas flow rate– Sorbent / carrier gas nozzle pressure

differential– Sorbent specifications


Performance indicators (continued)– Inlet gas / process exhaust temperatures– Exhaust gas flow rate– Other PM control device used indicators

Acid Gas Control Techniques – Spray Dryer

General description– Alkali sorbent slurry turns acid gas into PM

that is collected by a control device– Slurry is usually lime and water

Acid Gas Control Techniques – Spray Dryer - Schematic


Factors affecting efficiency– Slurry feed rate– Residence or reaction time– Emission stream gas temperature– Slurry reactor outlet temperature– Slurry droplet size– Other PM control device used factors


Performance indicators– Outlet acid gas concentration– Alkali feed rate to slurry mix tank– Water feed rate to slurry mix tank– Slurry feed rate and droplet size– Spray dryer inlet gas / process exhaust

temperature– Other PM control device indicators

NOx Control Techniques – Selective Catalytic Reduction

General description– Ammonia or urea is injected into exhaust

streams with plenty of oxygen to reduce nitrogen oxide to nitrogen and oxygen

– Efficiency ranges from 70 to 90 percent– Catalysts made from base and precious

metals and zeolites– Operating temperatures range from 600 to

1100°F

NOx Control Techniques – Selective Catalytic Reduction - Schematic


Factors affecting efficiency– Catalyst activity– Masking or poisoning– Space velocity (gas flow rate divided by

bed volume)– Excess ammonia or urea slip


Performance indicators– Outlet nitrogen oxide concentration– Ammonia / urea injection rate– Catalyst bed inlet temperature– Catalyst activity– Outlet ammonia / urea concentration– Catalyst bed outlet temperature


Performance indicators (continued)– Inlet gas flow rate– Fuel sulfur content– Pressure differential across catalyst bed

NOx Control Techniques – Non Selective Catalytic Reduction

General description– Low oxygen exhaust gas transforms via

catalytic reaction to water, carbon dioxide, and nitrogen

– Catalysts made from noble metals– Efficiency ranges from 80 to 90 percent– Operating temperatures range from 700 to

1500°F


Factors affecting efficiency– Catalyst activity– Masking or poisoning– Space velocity (gas flow rate divided by

bed volume)– Catalyst material


Performance indicators– Outlet nitrogen oxide concentration– Catalyst bed inlet temperature– Catalyst activity– Catalyst bed outlet temperature– Inlet gas flow rate– Pressure differential across catalyst bed– Outlet oxygen concentration

NOx Control Techniques – Water or Steam Injection

General description– Water or steam injected in combustion

zone reduces temperature and nitrogen oxide formation

– Only thermal nitrogen oxides reduced– Reductions range from 60 to 80 percent– Water must be atomized

NOx Control Techniques – Water or Steam Injection - Schematic


Factors affecting efficiency– Water quality– Quantity of water injected– Combustor design– Combustor materials– Turbine load cycle


Performance indicators– Outlet nitrogen oxide concentration– Water to fuel ratio– Fuel bound nitrogen concentration

Control Device Technology Barrett Parker, EPA, OAQPS.

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Transcript of Control Device Technology Barrett Parker, EPA, OAQPS.