Reprinted from Pollution Equipment News, October 2005

SILOXANES EMISSIONS CASE STUDY

Background
Siloxane-family constituents are composed of various combinations of silicon and organic compounds, with examples such as decamethyltetrasiloxane and decamethylcyclopentasiloxane.  These contaminants are often present in landfill gases and wastewater treatment digester gases.  Where municipalities or companies seek to harvest the high BTU content of these gases via combustion turbines and boilers, these contaminants can cause enormous maintenance costs and downtime for the power-generation equipment.

The siloxanes are present generally as ultra-fine particulate, with mean diameter far less than 1 micron.

Alternatives
Alternatives for siloxanes control include the following control technologies:

• Carbon adsorption beds;
• Baghouse/fabric filter;
• APC Technologies’ Ultra-High Efficiency Filter (UHF™) system.

Comparison of Alternatives
For siloxanes control, the UHF™ system provides good removal efficiency (e.g., 85%+ control) on the ultra-fine particulate, i.e., at 0.01 to 1 microns mean diameter, versus 20%-40% control efficiency range for a fabric filter baghouse or cartridge collector. 

Compared to a carbon bed for this application, the UHF™ removes the siloxanes without the aforementioned problems of carbon bed plugging, heavy equipment weight and large size, and high replacement costs of activated carbon adsorption beds.  Another major issue with carbon adsorption is that it is non-selective and will simultaneously remove organic gases from the gas stream, thereby reducing the BTU value of the gas

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