Clearing the air: the use of bio-oxidation for industrial air emissions control


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The wood products industry began rather ardous road to emissions control in the early 1990s with the first installation of a thermal oxidizer (an RTO) at a California MDF facility, for volatile organic compound (VOC) control.

During the ensuing years, virtually every panel board facility has had to control emissions of VOCs, and up until the last few years, always with some sort of thermal oxidizer-RTO, or a catalytic oxidizer.

The amount of natural gas that has been burned for VOC control during this time is conservatively in the billions of therms, possibly trillions, That's enough natural gas to heat hundreds of thousands of households during that period of time, not to montion the cost to the panel board industry for that natural gas.

Interestingly, biofilters also were first applied to the U.S. wood panel board industry in the easrly to mid-1990s. Three conventional bark and wood chip biofilters were installed on an oriented strand board press in the Midwest, a wet process hardboard mill in Michigan and in a particleboard mill in Gorgia. All were and are relatively successful applications and continue in operation todya. In Europe, several biofilter applications were applied to the panel wood industry in the late 1990s with modest success.

The primary issue with these 'conventional bark and wood chip' systems is that the beds must be replaced frequently, usually every 18 to 24 months because of channeling and compaction issues that cause operational problems, either loss of removal efficiency (channeling) or decrease in airflow (compaction). Biofilter system applications did not parallel the thermal oxidizer applications because of the generally mandated 90+ percent destruction efficiency (Dre) requirement specified in the first consent decrees associated with the U.S. Environmental Protection Agency's regulatory pursuit ofthe wood products industry.

Emissions of VOCs from preses could have been controlled by biofiltration, but generally not at the Dre that was mandated, and the dryer exhausts were and are too hot to be treated in a biological system without adding significant amounts of dilution air. So, for roughly 12 years, there was little or no progress on biofilter applications in the panel board industry because of the rather draconian requirement for 90+ percent Dre of the emissions stream. During that time period, more than 150 (estimated from conversations with thermal oxidizer suppliers) thermal oxidizers were installed in the industry at a capital cost of hundreds of millions of dollars and with ongoing natural gas costs of millions of dollars annually.

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