Tech Update: thermal oxidizer/waste heat boiler for DDGS emission control

Results show over 99% destruction of VOC's, zero opacity emissions
By | February 01, 2002
Now that the first installation of a thermal oxidizer air pollution control system for DDGS dryer emission clean up is up and running, it's a good time to review how the unit has performed. Thermal oxidation technology has been applied to thousands of industrial sources in a wide variety of industries. The nation's first urban ethanol plant was also the first ethanol plant to incorporate this technology for DDGS dryer exhaust clean up, but it will definitely not be the last.

The St. Paul, Minn. facility is a maximum 20 mmgy plant. As facilities get larger, the application of oxidizer technology will allow plants to remain minor sources of air pollution with respect to Federal Title V air permit regulations. According to Todd A. Potas of the Environmental Resource Group, it is questionable whether ethanol production facilities larger than 20 mmgy can remain minor sources of particulate and volatile organic emissions without the implementation of pollution control technology.

The MMT Environmental SIGMA series thermal oxidizer was originally selected because it provides an effective method for the control of odorous emissions. However, it soon became apparent that the oxidizer's high destruction efficiency of other pollutants such as Volatile Organic Compounds (VOC's), Hazardous Air Pollutants (HAP's), opacity, condensable and non-condensable Particulate Matter (PM/PM10) offered significant benefits to the ethanol industry. While odor destruction keeps the neighboring community happy, the destruction of other pollutants keeps the regulatory agencies happy and assures plant environmental compliance.

Results in St. Paul
The results from various stack test programs conducted on the St. Paul thermal oxidizer have proven greater than 99% destruction of VOC's and opacity emissions of zero. Also, the PM/PM10 concentrations have been reduced to less than 0.01 grains per cubic foot out the stack.
In addition to the high degree of emission clean up, the oxidizer was equipped with a waste heat recovery boiler designed and manufactured by Victory Energy Operations, LLC. As predicted, the system is providing significant thermal energy benefits to the plant compared to the existing conventional natural gas-fired boilers. The original predicted efficiency of greater than 90% was tested and confirmed in the field at the completion of the commissioning of the waste heat boiler.

With the continuing need for efficient steam generation, it is essential for the equipment to operate as efficiently as possible, while maintaining an energy balance with the plant's steam requirements. The control system which monitors the fluctuating load changes and header pressure changes must be an intricate part of the system design.

As more thermal oxidizers and waste heat boiler systems in other ethanol plants in the industry are installed, careful consideration must be given to the following key areas as a direct result of our experience with the first system installed over 8 months ago:

-Maintaining steam header pressure within +/- 5 psig range.
-Maintain steam generation to the plant while the DDG dryer is not in operation (i.e. fresh air firing).
-Maintain drum level control in the HRSG during fluctuating steam demands.
-Integration of the thermal oxidizer/ HRSG control system with the plant DCS control system.

The work continues
Now with several more systems in fabrication, ethanol developers and producers will continue to benefit from the efficiency of the package system, accroding to Viskup.

"The thermal oxidizer and the waste heat boiler package will provide guaranteed emission reduction, up to 99% destruction of odorous emissions, VOC's, HAP's, opacity emissions PM/ PM10, and steam system operation efficiencies of greater than 90%, thus lowering the overall operating costs of your plant," Viskup said.