- Email: [email protected]
Dual-chamber RTO oxidizers provide cost-effective VOC compliance for metal finishers and coaters
Dual-Chamber RTO Oxidizers Provide CostEffective VOC Compliance for Metal Finishers and Coaters by Brian J. Cannon Adwest
Technologies
Inc., Wellsville, N.Y; E-mail [email protected]:
egenerative thermal oxidizers, or “RTOs” as they are commonly called, can provide an affordable, low-energy usage and cost effective solution to Volatile Organic Compound 0700, solvent, and hydrocarbon compliance issues in the metal-finishing and paint coating industry. RTOs have been widely utilized and successfully installed over the past 20 years for paint spray booth, industrial finishing, metal coating, bake ovens, coating, laminating, lacquering, printing, gelcoat, circuit board, and chemical processing applications. In addition, many low-VOC vapor-venting processes, including wastewater treatment, reactor vessels, spray dryers, and air strippers, have successfully installed smaller-flow RTO systems for VOC compliance in metal and industrial finishing plants. The major advantage of RTO technology is the extremely low RTO energy usage required to convert the VOC hydrocarbons to harmless CO, and water vapor in the stack. There are no catalyst or carbon modules to replace, replenish, or worry about maintaining. Dual-bed RTOs are one of the most widely installed type of RTO and the enclosed schematic diagram (Fig. 1) illustrates the dualchamber RTO oxidizer mode of operation and flow path, which is illustrated in a forced-draft fan design. Other RTO designs are available with 1 to 9 beds or heat transfer vessels with varying degrees of higher operational and capital cost as well as higher-pressure drop compared to the twin-bed RTO design. The VOCs enter the RTO, which has been preheated on a l-hour cold startup by an external gas or oil fired burner, through a forced-draft fan system (induced draft is always an option if condensable buildup on the fan is a concern), and are directed by a dual-poppet valve
R
FLOW CONTROL
glass industry and “checker” furnaces since around 1900. Other media include the more expensive and less durable structured ceramic block or honeycomb media, which typically cost 4 to 7 times more than random packing ceramic materials. The VOCs travel up through bed #l and are preheated to 1,500”F and greater and are destroyed in the combustion chamber. The hot, purified vapors are then directed through a second bed of ceramic media, which absorbs and stores the heat given off in the combustion chamber oxidation process. The purified vapors then exit the RTO via the second poppet valve and manifold and out the exhaust stack as water vapor. What provides the unique “regenerative” heat transfer capability is the RTO flow control mechanism, which quickly reverses or switches the internal RTO flow path every 4 to 6 minutes. This regenerating flow pattern allows the ceramic media to absorb and store the BTUs of combustion to continually preheat the incoming VOCs from the finishing process. The most common flow control system is the
SYSTEM
The VOCs enter bed #l at the bottom, which contains an internally insulated vessel filled with heat transfer media rated at 95% thermal efficiency. All RTOs use a ceramic heat transfer media to store the BTUs liberated in the combustion chamber (typically 1,500 to 1,800”F) purification reaction process. The ceramic heat transfer media are typically random packing materials that have been successfully utilized for high-temperature heat transfer in the January 2003
www.adwestusa.com
Figure 1. Schematic of a dual-chamber regenerative thermal oxidizer. A: forced draft fan; 6: twin-poppet flow-control valves; C: heat exchange bed #l; D: burner/piping train; E: combustion chamber; F: heat exchange bed #2; G: exhaust stack; H: PLC controls.
53
poppet valve, which provides rapid, zero-leakage switching of the flow rate without the need for an additional purge-control module. The poppet-valve flow control is done automatically by an integral programmable logic control (PLC) system and allows bed #2 to rapidly preheat the incoming process gases after the inlet path has been switched to go to the bottom of bed #2 and up into the combustion chamber at 1,500 to 1,800”F and then back down through the ceramic media of bed #l where the BTUs are again absorbed and stored, and where the flow is finally directed to the exhaust stack. The internally insulated beds of ceramic media act as a “BTU thermal heat sink” or storage area to preheat the low-temperature VOCs entering the inlet of the RTO. This allows the RTO with 95% thermal efficiency to operate fuel-free or “self sustaining” at 3% and greater lower explosive limit (LEL) inlet solvent loadings. Figure 2 illustrates the major advantages and energy savings of typical 20,000-cfm oxidizers with 95% primary heat recovery that operates fuel free and flameless at 3% and greater LEL inlet loadings (or 83 lbkr VOC at 18,600 BTU/lb solvent heat release). Compared to RTOs
Circle 033 on reader card or go to www.thru.to/webconnect 54
Figure 2.20.000~scfm RTO self-sustaining fuel-free inlet solvent loading advantages. Note: 1. Solvent blend is 18,000 BTU/lb. 2. * denotes recuperative oxidizer always has burner at low fire as min.
with 90% heat recovery (% LEL and 166 lb/hr VOC fuel free), catalytic oxidizers with 60% (10% LEL) and thermal oxidizers with 70% (18% LEL) and thermal afterburners (53% LEL) the RTO with 95% heat recovery provides substantial short- and longer-term energy savings due to the high level of heat transfer. RTOs also provide a reliable and flexible VOC
Circle 034 on reader card or go to www.thtu.tolwebconnect Metal Finishing
ACM ServicesCompany abatement solution for halogenated compounds typically found in the chemical and paint finishing industries, as the RTO ceramic heat exchange media provide long-life operation and are resistive to acid and corrosion attack that historically has plagued metallic recuperative heat exchangers or catalyst units. RTO oxidizers can also be designed to accommodate operation from low inlet concentrations of 0.8% LEL to up to 25 LEL solvent levels, which provide for automatic operation for custom coating and finishing plants who do a variety of lowto high-solvent coatings. Most dual-bed RTOs are available in skid-mounted modules from l,OOO- to over 75,000-scfm air flow rates. For larger paint booth flow rates, hybrid concentrator systems with a smaller RTO have been successfully utilized for flows from 75,000 to over 300,000. Typically, concentrators provide a 1O:l or greater concentration ratio with zeolites, which means that a 200,000-scfm concentrator will have a 20,000-scfm RTO on the end of the system for final VOC control. The RTO system can provide 99% VOC destruction through the
CompleteIonExchange Resinsand RegenerationServices
IonExchange Resin Regeneration l
Systems l Service l Sales
Figure 3. A 61,000-scfm dual-chamber RTO at a Midwestern paint finishing facility for automotive wheel components.
entire range of solvent loadings as well as flowrates from the maximum, down to the minimum flow conditions, which typically are one fourth or one fifth the maximum flow rate and would then use an optional variable frequency drive on the RTO fan system if process flow conditions vary, Other RTO oxidizer system options, features, and project evaluation factors to consider are: Turnkey installation-outside, platform, or roof mounted?
inside,
ground,
Interconnecting process to RTO ductwork requirements with inspection doors
410=420-8001 www.acmix.com FOO6
Approved
Circle 073 on reader card or go to www.thru.to/webconnect January 2003
55
High solvent operation of the RTO heat exchange system to 25% LEL Special halogenated RTO designs if halogen compounds are present Exhaust stack height requirements above nearest roofline)
(usually 10 ft
Telemetry software for client’s record keeping RTO and process operation Possible air-to-air or chilled air secondary recovery prior to going to stack Custom-designed and/or classified or drive enclosures
of
energy
duty controls
Future expandability-will you need more RTO flow capacity in the near future? Do I purchase or lease the RTO system? Are extended RTO service and annual inspection packages/services available? How much RTO experience does each vendor have and do they specialize in RTOs? Who builds the RTO? Does my vendor have his own dedicated shops or is all work contracted out? Quantification or measurement of process airflows, solvent loadings at the maximum/minimum and design conditions, and the required state and federal EPA requirements While capital cost is always a major, if not the most important, criteria for any VOC abatement system evaluation, the dual-chamber RTO systems have been available with prices at or below most catalytic and thermal recuperative oxidizers for the past 15 years. Prior to this, many RTOs cost 2 to 4 times greater than other VOC control technologies. The low dual-chamber RTO capital cost is due to the lower cost RTO ceramic media and compact modular designs compared to traditional stainless steel and high alloy tubular shell-and-tube or plate-type heat exchangers that have expensive materials of construction that require high labor content for welding and assembly. Most Adwest dual-chamber RTO systems from l,OOO- to 75,000-cfm sizes are shop-assembled and insulated on compact skidmounted modules (Fig. 3) that help keep the RTO capital and turnkey installation costs lower than other RTO and oxidation technologies and designs. There are other RTO designs that require extensive field assembly and installation and this can drastically drive up the cost of oxidizer systems. Mechanical RTO oxidizer installation can typically be accomplished in usually 1 to 3 days and, while
56
most are installed on the ground outside, many clients occasionally install their RTOs indoors or on the plant rooftop or on a platform above the spray booths and ovens to conserve space. In summary, the dual-chamber RTO oxidizers can provide metal and paint finishers with a reliable and lower-cost VOC abatement project than most other technologies available. Less capital cost, less natural gas or propane energy usage, less NOx byproducts (especially with the flameless, zero-NOx RTO design), less fan horsepower, and less installation time and cost due to the shop assembly. When selecting an RTO supplier, always evaluate the fan, burner combustion air blower, and burner natural gas/oil usage as there are many differences in operating costs that you will continue to see over the life of the RTO system. Many rotary RTO systems require the running of 3 large fans (main fan, combustion air blower fan, and rotary valve purge fan) while many others only require a single main process fan to operate. It is important to make sure that all RTO vendors are quoting a true 95% thermally efficient heat recovery system at full flow rate, as a 3 or 5% lower efficiency heat exchanger can cost you up to a 2 to10 times greater energy cost. Last, but not least, every finisher should evaluate vendors with a proven track record and extensive installations in the VOC abatement market. If a vendor’s selling price seems too low to be true, it probably is. One thing is certain and that is energy costs for natural gas, propane, fuel oil, and electricity will all continue to increase in the future. One needs to evaluate and look at a specific VOC-abatement system not as a one time purchase but as a 15to 20-year energy investment over the life of the dual-chamber RTO system. BIOGRAPHY
Brian J. Cannon has 26 years in the sales, installation, design, and marketing of RTO oxidizer systems and has been the Sales Director of Adwest Technologies, headquartered in Anaheim, Calif., MF since 1993.
Metal Finishing
Technologies
Inc., Wellsville, N.Y; E-mail [email protected]:
egenerative thermal oxidizers, or “RTOs” as they are commonly called, can provide an affordable, low-energy usage and cost effective solution to Volatile Organic Compound 0700, solvent, and hydrocarbon compliance issues in the metal-finishing and paint coating industry. RTOs have been widely utilized and successfully installed over the past 20 years for paint spray booth, industrial finishing, metal coating, bake ovens, coating, laminating, lacquering, printing, gelcoat, circuit board, and chemical processing applications. In addition, many low-VOC vapor-venting processes, including wastewater treatment, reactor vessels, spray dryers, and air strippers, have successfully installed smaller-flow RTO systems for VOC compliance in metal and industrial finishing plants. The major advantage of RTO technology is the extremely low RTO energy usage required to convert the VOC hydrocarbons to harmless CO, and water vapor in the stack. There are no catalyst or carbon modules to replace, replenish, or worry about maintaining. Dual-bed RTOs are one of the most widely installed type of RTO and the enclosed schematic diagram (Fig. 1) illustrates the dualchamber RTO oxidizer mode of operation and flow path, which is illustrated in a forced-draft fan design. Other RTO designs are available with 1 to 9 beds or heat transfer vessels with varying degrees of higher operational and capital cost as well as higher-pressure drop compared to the twin-bed RTO design. The VOCs enter the RTO, which has been preheated on a l-hour cold startup by an external gas or oil fired burner, through a forced-draft fan system (induced draft is always an option if condensable buildup on the fan is a concern), and are directed by a dual-poppet valve
R
FLOW CONTROL
glass industry and “checker” furnaces since around 1900. Other media include the more expensive and less durable structured ceramic block or honeycomb media, which typically cost 4 to 7 times more than random packing ceramic materials. The VOCs travel up through bed #l and are preheated to 1,500”F and greater and are destroyed in the combustion chamber. The hot, purified vapors are then directed through a second bed of ceramic media, which absorbs and stores the heat given off in the combustion chamber oxidation process. The purified vapors then exit the RTO via the second poppet valve and manifold and out the exhaust stack as water vapor. What provides the unique “regenerative” heat transfer capability is the RTO flow control mechanism, which quickly reverses or switches the internal RTO flow path every 4 to 6 minutes. This regenerating flow pattern allows the ceramic media to absorb and store the BTUs of combustion to continually preheat the incoming VOCs from the finishing process. The most common flow control system is the
SYSTEM
The VOCs enter bed #l at the bottom, which contains an internally insulated vessel filled with heat transfer media rated at 95% thermal efficiency. All RTOs use a ceramic heat transfer media to store the BTUs liberated in the combustion chamber (typically 1,500 to 1,800”F) purification reaction process. The ceramic heat transfer media are typically random packing materials that have been successfully utilized for high-temperature heat transfer in the January 2003
www.adwestusa.com
Figure 1. Schematic of a dual-chamber regenerative thermal oxidizer. A: forced draft fan; 6: twin-poppet flow-control valves; C: heat exchange bed #l; D: burner/piping train; E: combustion chamber; F: heat exchange bed #2; G: exhaust stack; H: PLC controls.
53
poppet valve, which provides rapid, zero-leakage switching of the flow rate without the need for an additional purge-control module. The poppet-valve flow control is done automatically by an integral programmable logic control (PLC) system and allows bed #2 to rapidly preheat the incoming process gases after the inlet path has been switched to go to the bottom of bed #2 and up into the combustion chamber at 1,500 to 1,800”F and then back down through the ceramic media of bed #l where the BTUs are again absorbed and stored, and where the flow is finally directed to the exhaust stack. The internally insulated beds of ceramic media act as a “BTU thermal heat sink” or storage area to preheat the low-temperature VOCs entering the inlet of the RTO. This allows the RTO with 95% thermal efficiency to operate fuel-free or “self sustaining” at 3% and greater lower explosive limit (LEL) inlet solvent loadings. Figure 2 illustrates the major advantages and energy savings of typical 20,000-cfm oxidizers with 95% primary heat recovery that operates fuel free and flameless at 3% and greater LEL inlet loadings (or 83 lbkr VOC at 18,600 BTU/lb solvent heat release). Compared to RTOs
Circle 033 on reader card or go to www.thru.to/webconnect 54
Figure 2.20.000~scfm RTO self-sustaining fuel-free inlet solvent loading advantages. Note: 1. Solvent blend is 18,000 BTU/lb. 2. * denotes recuperative oxidizer always has burner at low fire as min.
with 90% heat recovery (% LEL and 166 lb/hr VOC fuel free), catalytic oxidizers with 60% (10% LEL) and thermal oxidizers with 70% (18% LEL) and thermal afterburners (53% LEL) the RTO with 95% heat recovery provides substantial short- and longer-term energy savings due to the high level of heat transfer. RTOs also provide a reliable and flexible VOC
Circle 034 on reader card or go to www.thtu.tolwebconnect Metal Finishing
ACM ServicesCompany abatement solution for halogenated compounds typically found in the chemical and paint finishing industries, as the RTO ceramic heat exchange media provide long-life operation and are resistive to acid and corrosion attack that historically has plagued metallic recuperative heat exchangers or catalyst units. RTO oxidizers can also be designed to accommodate operation from low inlet concentrations of 0.8% LEL to up to 25 LEL solvent levels, which provide for automatic operation for custom coating and finishing plants who do a variety of lowto high-solvent coatings. Most dual-bed RTOs are available in skid-mounted modules from l,OOO- to over 75,000-scfm air flow rates. For larger paint booth flow rates, hybrid concentrator systems with a smaller RTO have been successfully utilized for flows from 75,000 to over 300,000. Typically, concentrators provide a 1O:l or greater concentration ratio with zeolites, which means that a 200,000-scfm concentrator will have a 20,000-scfm RTO on the end of the system for final VOC control. The RTO system can provide 99% VOC destruction through the
CompleteIonExchange Resinsand RegenerationServices
IonExchange Resin Regeneration l
Systems l Service l Sales
Figure 3. A 61,000-scfm dual-chamber RTO at a Midwestern paint finishing facility for automotive wheel components.
entire range of solvent loadings as well as flowrates from the maximum, down to the minimum flow conditions, which typically are one fourth or one fifth the maximum flow rate and would then use an optional variable frequency drive on the RTO fan system if process flow conditions vary, Other RTO oxidizer system options, features, and project evaluation factors to consider are: Turnkey installation-outside, platform, or roof mounted?
inside,
ground,
Interconnecting process to RTO ductwork requirements with inspection doors
410=420-8001 www.acmix.com FOO6
Approved
Circle 073 on reader card or go to www.thru.to/webconnect January 2003
55
High solvent operation of the RTO heat exchange system to 25% LEL Special halogenated RTO designs if halogen compounds are present Exhaust stack height requirements above nearest roofline)
(usually 10 ft
Telemetry software for client’s record keeping RTO and process operation Possible air-to-air or chilled air secondary recovery prior to going to stack Custom-designed and/or classified or drive enclosures
of
energy
duty controls
Future expandability-will you need more RTO flow capacity in the near future? Do I purchase or lease the RTO system? Are extended RTO service and annual inspection packages/services available? How much RTO experience does each vendor have and do they specialize in RTOs? Who builds the RTO? Does my vendor have his own dedicated shops or is all work contracted out? Quantification or measurement of process airflows, solvent loadings at the maximum/minimum and design conditions, and the required state and federal EPA requirements While capital cost is always a major, if not the most important, criteria for any VOC abatement system evaluation, the dual-chamber RTO systems have been available with prices at or below most catalytic and thermal recuperative oxidizers for the past 15 years. Prior to this, many RTOs cost 2 to 4 times greater than other VOC control technologies. The low dual-chamber RTO capital cost is due to the lower cost RTO ceramic media and compact modular designs compared to traditional stainless steel and high alloy tubular shell-and-tube or plate-type heat exchangers that have expensive materials of construction that require high labor content for welding and assembly. Most Adwest dual-chamber RTO systems from l,OOO- to 75,000-cfm sizes are shop-assembled and insulated on compact skidmounted modules (Fig. 3) that help keep the RTO capital and turnkey installation costs lower than other RTO and oxidation technologies and designs. There are other RTO designs that require extensive field assembly and installation and this can drastically drive up the cost of oxidizer systems. Mechanical RTO oxidizer installation can typically be accomplished in usually 1 to 3 days and, while
56
most are installed on the ground outside, many clients occasionally install their RTOs indoors or on the plant rooftop or on a platform above the spray booths and ovens to conserve space. In summary, the dual-chamber RTO oxidizers can provide metal and paint finishers with a reliable and lower-cost VOC abatement project than most other technologies available. Less capital cost, less natural gas or propane energy usage, less NOx byproducts (especially with the flameless, zero-NOx RTO design), less fan horsepower, and less installation time and cost due to the shop assembly. When selecting an RTO supplier, always evaluate the fan, burner combustion air blower, and burner natural gas/oil usage as there are many differences in operating costs that you will continue to see over the life of the RTO system. Many rotary RTO systems require the running of 3 large fans (main fan, combustion air blower fan, and rotary valve purge fan) while many others only require a single main process fan to operate. It is important to make sure that all RTO vendors are quoting a true 95% thermally efficient heat recovery system at full flow rate, as a 3 or 5% lower efficiency heat exchanger can cost you up to a 2 to10 times greater energy cost. Last, but not least, every finisher should evaluate vendors with a proven track record and extensive installations in the VOC abatement market. If a vendor’s selling price seems too low to be true, it probably is. One thing is certain and that is energy costs for natural gas, propane, fuel oil, and electricity will all continue to increase in the future. One needs to evaluate and look at a specific VOC-abatement system not as a one time purchase but as a 15to 20-year energy investment over the life of the dual-chamber RTO system. BIOGRAPHY
Brian J. Cannon has 26 years in the sales, installation, design, and marketing of RTO oxidizer systems and has been the Sales Director of Adwest Technologies, headquartered in Anaheim, Calif., MF since 1993.
Metal Finishing