Control Device Technology

1. Control Device Technology Barrett Parker, EPA, OAQPS

2. Example Control Systems • 4 VOC control techniques plus capture discussion • 5 PM control techniques • 2 Acid gas control techniques • 3 NOx control techniques

3. 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

4. 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

5. VOC Control Techniques – Carbon Adsorber – Fixed Bed Schematic

6. VOC Control Techniques – Carbon Adsorber – Fixed Bed Examples

7. VOC Control Techniques – Carbon Adsorber • Factors affecting efficiency • Presence, polarity, and concentration of specific compounds • Flow rate • Temperature • Relative humidity

8. 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

9. VOC Control Techniques – Carbon Adsorber • Performance indicators (continued) • Inlet gas temperature • Gas flow rate • Inlet VOC concentration • Pressure differential • Inlet gas moisture content • Leaks

10. VOC Control Techniques – Carbon Adsorber – Manufacturer’s Specs

11. 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

12. 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

13. VOC Control Techniques – Catalytic Oxidizer – Example Bricks

14. VOC Control Techniques – Catalytic Oxidizer - Schematic

15. VOC Control Techniques – Catalytic Oxidizer • Factors affecting efficiency • Pollutant concentration • Flow rate • Operating temperature • Excess air • Waste stream contaminants • Metals, sulfur, halogens, plastics

16. 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

17. VOC Control Techniques – Catalytic Oxidizer • Performance Indicators (continued) • Catalyst bed outlet temperature • Fan current • Outlet O2 or CO2 concentration • Pressure differential across catalyst bed

18. 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

19. 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

20. VOC Control Techniques – Condenser - Schematic

21. VOC Control Techniques - Condenser • Factors affecting efficiency • Pollutant dew point • Condenser operating pressure • Gas and coolant flow rates • Tube plugging or fouling

22. 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

23. VOC Control Techniques - Condenser • Performance indicators (continued) • Coolant flow rate • Pressure differential across coolant refrigeration system • Condensate collection rate • Inspection for fouling or corrosion

24. 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

25. 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

26. VOC Control Techniques – Thermal Oxidizer - Schematic

27. VOC Control Techniques – Thermal Oxidizer • Factors affecting efficiency • Waste gas flow rate • Waste gas composition and concentration • Waste gas temperature • Amount of excess air

28. 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

29. 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

30. VOC Control Techniques – Capture System - Schematic

31. VOC Control Techniques – Capture System • Factors affecting efficiency • System integrity • System flow

32. 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

33. 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

34. PM Control Techniques – Cyclone - Schematic

35. PM Control Techniques - Cyclone • Factors affecting efficiency • Component erosion • Inlet and outlet plugging • Acid gas corrosion • Air inleakage

36. PM Control Techniques - Cyclone • Performance indicators • Opacity • Inlet velocity or inlet gas flow rate • Pressure differential • Inlet temperature

37. 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

38. PM Control Techniques – Electrostatic Precipitator - Schematic

39. PM Control Techniques – Electrostatic Precipitator - Schematic

40. PM Control Techniques – Electrostatic Precipitators • Factors affecting efficiency • Gas temperature, humidity, flow rate • Particle resistivity • Fly ash composition • Plate length • Surface area

41. PM Control Techniques – Electrostatic Precipitator • Performance indicators • Outlet PM concentration • Opacity • Secondary corona power (current and voltage) • Spark rate • Primary power (current and voltage)

42. 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)

43. 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

44. PM Control Techniques – Electrified Filter Bed - Schematic

45. 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

46. PM Control Techniques – Electrified Filter Bed • Performance indicators (continued) • Pressure differential • Gas flow rate • Outlet PM concentration • Opacity

47. 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)

48. PM Control Techniques – Fabric Filter - Schematic

49. PM Control Techniques – Fabric Filter • Factors affecting efficiency • Filter media • Abrasion • High temperature • Chemical attack • Gas flow • Broken or worn bags • Blinding

50. PM Control Techniques – Fabric Filter • Factors affecting efficiency (continued) • Cleaning system failure • Leaks • Re-entrainment • Damper or discharge equipment malfunction • Corrosion