Lower Explosive Limit (LEL) Monitoring for Estimating Mass Removed

Since 2000, TerraTherm has removed over three million pounds of organic contaminants from the sites we have treated. Many of these sites had yielded too much mass to economically use granular activated carbon as the vapor treatment method. Therefore, we often use thermal oxidizers, using gas and the fuel value of the contaminants to treat the vapors at temperatures of 1500°F (816°C) or higher.

The National Fire Protection Agency has mandated continuous monitoring of vapors entering oxidizers when those vapors are expected to be over the 25% Lower Explosive Limit (LEL). Additionally, thermal oxidizers generally have a safe upper operable limit of 50% LEL. An LEL meter measures the amount of energy in the vapor at the inlet of the oxidizer.

During a recent project where the primary constituents of concern were Volatile Organic Compounds  and Reduced Sulfur compounds, concentrations were so high that vapors were expected to occasionally exceed 100% LEL.

For this project, two LEL meters were used to guide safe operations and monitor the mass flux of contaminants. The first meter sampled a diluted slip stream and provided an estimate of the percent LEL in the raw vapors, guiding the dilution air flow control so the oxidizer inlet remained under 50% LEL. The second meter monitored the diluted influent to the oxidizer, yielding data on the mass removed from the subsurface.

This approach was used to successfully operate the oxidizer within desired limits, and provided valuable data on mass removal rates and trends during the operational period.

If you have any questions about LEL monitoring, or data management please don’t hesitate to reach out to me at pwood@terratherm.com.

About Nate Bierschenk

Nate Bierschenk began working at TerraTherm, Inc. in 2012 as a Marketing Assistant. Since then, Nate has grown into a more technical role and is currently Technical Sales Specialist servicing the Southeast. In addition, Nate is the service line sales lead for TerraTherm's new on-site thermal offering, the Heated-Box or HB1100 approach.
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