Biogas webinar details condensation removal, upgrading options
The American Biogas Council held a webinar May 9 detailing the intricacies and available options for biogas upgrading. The webinar, “ABCs of Biogas Upgrades: Options, Steps and Standards,” featured three primary speakers: Bernie Sheff, president of UTS Residuals Processing LLC; Chris Marinucci, control systems integration manager for O’Brien & Gere; and Sean Mezei, president of Flotech-Greenlane North America.
Marinucci explained the importance of reducing moisture in a biogas stream, emphasizing that condensation removal is important. “It is important to understand that if you are going to be pushing biogas very far, you need to get the water out of it,” Sheff said.
Marinucci talked about a biogas facility operating in the Northeastern U.S. “Because we’re dealing with freezing temperatures, we needed to remove the moisture and get the dew point (in the biogas stream) so that we didn’t worry about freezing pipes down the road,” he said. The biogas stream needs to travel 500 feet and because of the temperatures, the facility installed a glycerol chiller with two heat exchangers. While the first heat exchanger provided the primary moisture removal services, the resulting cold gas stream headed for a boiler needed to be reheated with a second heat exchanger. “A little bit of extra mechanical equipment helped to actually save energy and make the process run more smoothly,” Marinucci said.
Marinucci also advised developers and operators to consider how the biogas will be used. “You aren’t continually turning processes on and off,” he said.
After the condensation in the biogas stream has been treated, the next area of concern, according to Sheff, is the upgrading process that removes particulates and unwanted gases. The most common method is water scrubbing, which uses a cold stream of water to absorb carbon dioxide from the methane stream. Although the process is widely used in most biogas systems in Europe, there are other alternatives. Amine scrubbers offer a chemical absorption option and are currently used in oil fields to remove odors. Although the process is efficient, it does require heat to dry the amine for reuse.
Pressure swing adsorption (PSA) is another option and is commonly used in the chemical industry. The process includes a tank filled with absorption material and the biogas stream. After adding pressure, the CO2 in the biogas stream clings to the material. After depressurization, the methane in the tank clears out, allowing removal of the gas. With PSA approaches, however, the resulting tail gas can contain up to 50 percent methane, so Sheff recommends planning for tail gas use ahead of time. Membrane technologies and even cryogenic gas applications are also a possibility for upgrading purposes.
Future ABC webinars will feature discussions on end-use applications of biogas streams.