Control Device Technology

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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
Manufacturers 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 1000F)
• 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 2000F
• 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
• Face velocity
• 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 550 Hz _at_ 120 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 1100F

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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 1500F

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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