Recuperative Catalytic Oxidizers Reduce Operating Costs Because of High Energy Recovery (85-95%) and Lower Fuel Requirements

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Catalytic oxidizers are used for air pollution control systems for industrial and manufacturing processes. They destroy nearly all hazardous air pollutants (HAPS), volatile organic compounds (VOCs), and odorous emissions that are byproducts. Recuperative Catalytic Oxidizers, manufactured by HiTemp Technology, LLC , greatly reduce fuel consumption which reduces energy and operating costs by burning at a lower temperature.

Thermal Oxidizer manufactured by HiTempTechnology, LLC
Natural gas at 1600 degrees F has half the heat value than it does at 70 degrees F. Customers pay for cubic feet of natural gas, not BTUs. So when suppliers calculate a 1,000,000 BTU operating cost it is really a 2,000,000 BTU operating cost.

Theory of Operation:

RTOs (Regenerative Thermal Oxidizers) use a high-density media, such as a ceramic-packed bed still hot from a previous cycle to preheat an incoming VOC-laden waste gas stream. These preheated, partially oxidized gasses then enter a combustion chamber where they are heated by auxiliary fuel (natural gas) combustion to a final oxidation temperature typically between 760oC to 820oC (1400oF to 1500oF) and maintained at this temperature to achieve maximum VOC destruction. Temperatures of up to 1100oC (2000oF) may be achieved, if required, for very high control efficiencies of certain toxic VOCs. The purified, hot gases exit this chamber and are directed to one or more different ceramic-packed beds cooled during an earlier cycle. Heat from the purified gases is absorbed by these beds before the gases are vented to the atmosphere. The reheated, packed bed then begins a new cycle by heating another incoming waste gas stream.

If design conditions are satisfied, typically no pretreatment is required, however, in some cases, PM removal may be necessary before the waste gas enters the incinerator. This is more critical for RCOs than RTOs as RTOs tolerate PM better than RCOs. Catalysts may be “blinded” by PM coating of the catalyst so that the catalyst active sites are prevented from aiding in the oxidation of gas stream pollutants. Catalytic systems may utilize internal filters that process the air stream before it reaches the catalyst material. A sacrificial bed also can be employed to prevent PM from reaching the catalyst. Some manufacturers fluidize the catalyst beds to help pass the PM through the system (Biedell and Nester, 1995).

An RCO (Recuperative Catalytic Oxidizer) operates in the same manner as an RTO, but it uses catalyst material rather than ceramic material in the packed bed so VOCs can be destroyed at a lower oxidation temperature. An RCO uses a precious metal catalyst in the packed bed, allowing oxidation to occur at approximately 400oC (800oF). This lower temperature requirement reduces the amount of natural gas needed to fuel the VOC abatement system and the overall size of the incinerator. Catalysts typically used for VOC incineration include platinum and palladium (Gay, 1997; Biedell and Nester, 1995).

Advantages and Disadvantages of Regenerative Incinerators (Oxidizers):

Advantages of regenerative incinerators over other types of incinerators include the following (Gay, 1997; Stone, 1997; Biedell and Nester, 1995; Yewshenko, 1995):

Advantages of RTOs:

  • Lower fuel requirements because of high energy recovery (85 to 95 percent)
  • High temperature capability up to 1100oC (2000oF) provides better destruction efficiency
  •      Recuperative incinerators are generally limited to 820oC (1500oF) due to heat exchanger limitations
  •      Catalytic incinerators are generally limited to 600oC (1100oF) due to catalyst imitations
  • Less susceptible to problems with chlorinated compounds
  • Usually lower NOx emissions than thermal oxidation except when operating temperatures are above approximately 760oC (1400oF)

Advantages of RCOs:

  • Lower fuel requirements than RTOs because of lower temperatures
  • Catalyst also destroys CO in waste stream
  • Lower NOx emissions than RTOs

Disadvantages include the following (Gay, 1997; Stone, 1997):

Disadvantages of RTOs (Regenerative Thermal Oxidizers):

  • High initial cost
  • Difficult and expensive installation
  • Large size and weight
  • High maintenance demand due to number of moving parts

Disadvantages of RCOs (Recuperative Catalytic Oxidizers):

  • High initial cost
  • Difficult and expensive installation
  • Large size and weight
  • High maintenance demand due to moving parts and catalyst monitoring
  • Possible catalyst poisoning – precious metal catalysts are more resistant
  • PM often must first be removed
  • Spent catalyst that cannot be regenerated requires disposal

Other Considerations:

  • Regenerative incinerators offer many advantages for the appropriate application. Depending upon the waste stream composition, high flow, low concentration waste streams consistent over long time periods can be treated economically with either RTO or RCO systems,.
  • Pretreatment to remove PM may be necessary with either system to prevent the packed bed from clogging and or the catalyst from poisoning. In RCO units, precious metal-based catalysts usually have a longer service life and are much more resistant to poisoning and fouling than less expensive base metal catalysts (Gay, 1997).

To see a comparison of costs, please read the full article here.

Contact Stephen Parker at HiTemp Technologies, LLC for further information.

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