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Control Device Technology
Barrett Parker, EPA, OAQPS
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Example Control Systems
4 VOC control techniques plus capture discussion 5 PM control techniques 2 Acid gas control techniques 3 NOx control techniques
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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
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VOC Control Techniques – Carbon Adsorber
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
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VOC Control Techniques – Carbon Adsorber – Fixed Bed Schematic
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VOC Control Techniques – Carbon Adsorber – Fixed Bed Examples
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VOC Control Techniques – Carbon Adsorber
Factors affecting efficiency Presence, polarity, and concentration of specific compounds Flow rate Temperature Relative humidity
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VOC Control Techniques – Carbon Adsorber
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
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VOC Control Techniques – Carbon Adsorber
Performance indicators (continued) Inlet gas temperature Gas flow rate Inlet VOC concentration Pressure differential Inlet gas moisture content Leaks
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VOC Control Techniques – Carbon Adsorber – Manufacturer’s Specs
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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
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VOC Control Techniques – Catalytic Oxidizer
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
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VOC Control Techniques – Catalytic Oxidizer – Example Bricks
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VOC Control Techniques – Catalytic Oxidizer - Schematic
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VOC Control Techniques – Catalytic Oxidizer
Factors affecting efficiency Pollutant concentration Flow rate Operating temperature Excess air Waste stream contaminants Metals, sulfur, halogens, plastics
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VOC Control Techniques – Catalytic Oxidizer
Performance Indicators Outlet VOC concentration Catalyst bed inlet temperature Catalyst activity Outlet CO concentration Temperature rise across catalyst bed Exhaust gas flow rate
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VOC Control Techniques – Catalytic Oxidizer
Performance Indicators (continued) Catalyst bed outlet temperature Fan current Outlet O2 or CO2 concentration Pressure differential across catalyst bed
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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
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VOC Control Techniques - Condenser
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
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VOC Control Techniques – Condenser - Schematic
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VOC Control Techniques - Condenser
Factors affecting efficiency Pollutant dew point Condenser operating pressure Gas and coolant flow rates Tube plugging or fouling
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VOC Control Techniques - Condenser
Performance indicators Outlet VOC concentration Outlet gas temperature Coolant inlet temperature Coolant outlet temperature Exhaust gas flow rate Pressure differential across condenser
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VOC Control Techniques - Condenser
Performance indicators (continued) Coolant flow rate Pressure differential across coolant refrigeration system Condensate collection rate Inspection for fouling or corrosion
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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
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VOC Control Techniques – Thermal Oxidizer
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
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VOC Control Techniques – Thermal Oxidizer - Schematic
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VOC Control Techniques – Thermal Oxidizer
Factors affecting efficiency Waste gas flow rate Waste gas composition and concentration Waste gas temperature Amount of excess air
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VOC Control Techniques – Thermal Oxidizer
Performance indicators Outlet VOC concentration Outlet combustion temperature Outlet CO concentration Exhaust gas flow rate Fan current Outlet O2 or CO2 concentration Inspections
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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
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VOC Control Techniques – Capture System - Schematic
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VOC Control Techniques – Capture System
Factors affecting efficiency System integrity System flow
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VOC Control Techniques – Capture Systems
Performance indicators Enclosures Face velocity Differential pressure Average face velocity and daily inspections Exhaust Ventilation Exhaust flow rate in duct near hood Hood static pressure
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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
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PM Control Techniques – Cyclone - Schematic
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PM Control Techniques - Cyclone
Factors affecting efficiency Component erosion Inlet and outlet plugging Acid gas corrosion Air inleakage
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PM Control Techniques - Cyclone
Performance indicators Opacity Inlet velocity or inlet gas flow rate Pressure differential Inlet temperature
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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
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PM Control Techniques – Electrostatic Precipitator - Schematic
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PM Control Techniques – Electrostatic Precipitator - Schematic
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PM Control Techniques – Electrostatic Precipitators
Factors affecting efficiency Gas temperature, humidity, flow rate Particle resistivity Fly ash composition Plate length Surface area
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PM Control Techniques – Electrostatic Precipitator
Performance indicators Outlet PM concentration Opacity Secondary corona power (current and voltage) Spark rate Primary power (current and voltage)
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PM Control Techniques – Electrostatic Precipitator
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)
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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
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PM Control Techniques – Electrified Filter Bed - Schematic
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PM Control Techniques – Electrified Filter Bed
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
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PM Control Techniques – Electrified Filter Bed
Performance indicators (continued) Pressure differential Gas flow rate Outlet PM concentration Opacity
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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 to 140 dB, on line)
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PM Control Techniques – Fabric Filter - Schematic
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PM Control Techniques – Fabric Filter
Factors affecting efficiency Filter media Abrasion High temperature Chemical attack Gas flow Broken or worn bags Blinding
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PM Control Techniques – Fabric Filter
Factors affecting efficiency (continued) Cleaning system failure Leaks Re-entrainment Damper or discharge equipment malfunction Corrosion
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PM Control Techniques – Fabric Filter
Performance indicators Outlet PM concentration Bag leak detectors Outlet opacity Pressure differential Inlet temperature Temperature differential
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PM Control Techniques – Fabric Filter
Performance indicators (continued) Exhaust gas flow rate Cleaning mechanism operation Fan current Inspections and maintenance
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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
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PM Control Techniques – Wet Scrubber - Schematic
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PM Control Techniques – Wet Scrubber
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
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PM Control Techniques – Wet Scrubber
Performance indicators Pressure differential Liquid flow rate Gas flow rate Scrubber outlet gas temperature Makeup / blowdown rates Scrubber liquid solids content (PM)
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PM Control Techniques – Wet Scrubber
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)
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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
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Acid Gas Control Techniques – Dry Injection - Schematic
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Acid Gas Control Techniques – Dry Injection
Factors affecting efficiency Dry sorbent injection rate Emission stream gas temperature Residence or reaction time Degree of turbulence Other PM control device used factors
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Acid Gas Control Techniques – Dry Injection
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
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Acid Gas Control Techniques – Dry Injection
Performance indicators (continued) Inlet gas / process exhaust temperatures Exhaust gas flow rate Other PM control device used indicators
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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
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Acid Gas Control Techniques – Spray Dryer - Schematic
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Acid Gas Control Techniques – Spray Dryer
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
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Acid Gas Control Techniques – Spray Dryer
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
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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
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NOx Control Techniques – Selective Catalytic Reduction - Schematic
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NOx Control Techniques – Selective Catalytic Reduction
Factors affecting efficiency Catalyst activity Masking or poisoning Space velocity (gas flow rate divided by bed volume) Excess ammonia or urea slip
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NOx Control Techniques – Selective Catalytic Reduction
Performance indicators Outlet nitrogen oxide concentration Ammonia / urea injection rate Catalyst bed inlet temperature Catalyst activity Outlet ammonia / urea concentration Catalyst bed outlet temperature
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NOx Control Techniques – Selective Catalytic Reduction
Performance indicators (continued) Inlet gas flow rate Fuel sulfur content Pressure differential across catalyst bed
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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
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NOx Control Techniques – Non Selective Catalytic Reduction
Factors affecting efficiency Catalyst activity Masking or poisoning Space velocity (gas flow rate divided by bed volume) Catalyst material
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NOx Control Techniques – Non Selective Catalytic Reduction
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
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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
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NOx Control Techniques – Water or Steam Injection - Schematic
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NOx Control Techniques – Water or Steam Injection
Factors affecting efficiency Water quality Quantity of water injected Combustor design Combustor materials Turbine load cycle
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NOx Control Techniques – Water or Steam Injection
Performance indicators Outlet nitrogen oxide concentration Water to fuel ratio Fuel bound nitrogen concentration
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