Removal of the access door to the catalytic oxidizer reveals five catalyst blocks.

Catalytic oxidation is an effective method of destroying volatile organic compounds (VOCs) in an effluent stream. Particulate matter, however, cannot be destroyed by catalytic oxidation. Therefore, if there is particulate matter in an effluent stream to be destroyed with a catalyst, the particulate matter must be destroyed before reaching the catalyst bed.

One cause of catalytic oxidizer failure is an undetected buildup of unburned particulate matter on the face of the catalyst bed. If a lump of particulate matter catches fire, it will burn a hole in the catalyst bed says, Jim Morrissey, president of Conversion Products Inc., a maker of catalytic oxidizers in Hayward, Calif. The company uses a proprietary combustion/mixing chamber to inject particulate into the flame envelope at a high velocity. While the velocity is well above the maximum “cross velocity” recommended by burner manufacturers, the flame envelope maintains the standard configuration that it normally has when there is no impingement of the external pollutant stream.

A catalytic oxidizer from Conversion Products uses a proprietary combustion/mixing chamber to inject particulate into the flame envelope at a high velocity.

Because of the lower incineration temperature with a catalytic oxidizer, the burner is smaller and the actual cubic feet per minute is less than with a conventional thermal oxidizer. The result is a catalyst body and burner system that cost less than a thermal system. However, most precious-metal catalysts have platinum as their major constituent and platinum is expensive. Currently, the price of platinum is about 25 percent higher than that of gold on the precious-metals market. Although a catalyst body and burner system are less expensive, the added expense of the platinum catalyst results in a catalytic oxidizer having a higher total capital cost than a thermal oxidizer. The question then is: If the destruction ratio is the same, why invest in a higher capital cost catalyst oxidizer?

According to Morrissey, the answer is simple: significant fuel savings.

Morrissey says that when Conversion Products was asked recently to submit a proposal to a chemical company requiring the destruction of ethyl acetate, he submitted a set of calculations that compared the costs of a catalytic oxidizer system with that of a thermal system so the customer could see the advantages of using a catalytic oxidizer.

The analysis showed the following:
  • Effluent flow rate: 1,200 scfm.
  • Effluent entering temperature: 100°F (38°C).
  • Required Destruction Ratio: 99 percent.
  • Fuel cost: $8.50 per million BTU.
  • Thermal incineration temperature: 1,400°F (760°C).
  • Catalytic incineration temperature: 625°F (329°C).
  • Increased capital cost for catalytic: $44,500.
  • Firing rate for thermal: 3.0 million BTU/hr.
  • Firing rate for catalytic: 1.3 million BTU/hr.
  • Annual hours worked: 3,700.

Catalyst manufacturers prepare a curve for each formulation and pollutant that is to be destroyed. If the pollutant is CO, for example, the curve would show how much of the CO is being converted to CO2 at any temperature. The catalyst manufacturer asks the user for the required destruction ratio, which is set by the customer’s local air quality board. For instance, if 95 percent of the CO has to be destroyed, the catalyst maker enters the CO curve at 95 percent and then looks at where the 95 percent line intersects the curve. The engineer follows the line down the X-axis and reads off the temperature necessary to destroy 95 percent of the CO.

Given those conditions, Morrissey demonstrated the following calculations:
  • Thermal annual cost: 3,700 x 3.0 x 8.50 = $94,350
  • Catalytic annual cost: 3,700 x 1.3 x 8.50 = $40,885
  • Annual savings in fuel cost: $53,465
  • Recovery period: $44,500 / $53,465 x 12 = 10 months
The chemical company chose the catalytic system, Morrissey says, adding that the customer found further savings by purchasing a shell-and-tube heat exchanger system from Conversion Products to preheat the effluent before entering the oxidizer. During final test, Conversion Products ran its catalytic oxidizer at the specified temperature for a minimum of four continuous hours. During testing, the company recorded burner performance by measuring CO, NOX, sulfur compounds and oxygen content, and took surface temperature readings to be sure they met the 125°F (52°C) target.

Morrissey says the customer’s project engineer witnessed the final testing along with the personnel who would be operating the oxidizer. This gave the operators the opportunity to observe the process and train on the equipment, he says.

For more information on Conversion Products’ catalytic oxidizers, go to