International Biomass Conference & Expo: Harnessing value from MSW

By Anna Austin
Posted May 4, 2010 at 4:27 P.M. CNT

Different biomass gasification technologies produce different results, and which one a buyer should select largely depends on what they desire to do with the synthesis gas, according to Karl Schoene, CEO of InEnTec.

Schoene was a waste-to-energy panel presenter at the International Biomass Conference & Expo in Minneapolis, May 4-6. After discussing basic gasification processes, he outlined several factors to consider when selecting an appropriate gasification technology. "How the syngas will be used sets the requirement," he emphasized. "If you're using a catalyst bed it has to be very clean. If you're doing a direct burn, you don't want a lot of halogens. You also have to know the contents of the feedstock beyond hydrocarbons and carbohydrates as it affects what goes into the residual solids."

InEnTec owns a Plasma Enhanced Melter technology that utilizes a fixed bed down draft gasifier. The produced syngas is much cleaner than updraft processes in terms of light vaporizables, according to Schoene, and is very suitable for use with catalytic conversion to liquid fuel products. He said PEM is highly tolerant to heavy metals and other difficult contaminates, produces a recyclable solid residual, and possesses low cooling water requirements and a scalable design.

Fellow panelist Scott Hughes, chief operating officer for Visiam, described his company's biomass treatment and waste recovery as a technological breakthrough. "We can take mixed municipal solid waste (MSW) and recover all of the resources to utilize for other applications," he said.

Visiam's Vacuum Explosion Process VEP, is patented and proven for the separation of organics from MSW and increasing the yield rates of processed biomass, said Hughes. Visiam built a 250 ton per week pilot plant at Shakopee, Minn., in 2005, and has successfully tested 15 different feedstocks. "One of the things that we've seen is that by running regular yard waste through the vessel, there's about a 30 to 40 percent increase in sugar fermentation," he said.

Hughes said a typical system, operating five days per week in 75-minute cycles, could serve a community of about 20,000 to 30,000 people but could be further scaled up.

Larry Link, consultant for Novaspect, touched on aspects of combustion optimization of MSW. "A big thing we need to focus our efforts on is reducing emissions at waste incineration plants," he said. "We need less corrosive gases, less emissions, and less ash disposal."

Waste incineration plants face many challenges, such as measuring the weight of the fuel going into the plant, variations in Btu content, bridging, clogging and uneven conveyor fills, Link pointed out. He said there are two main areas for optimization, one being bed management. "You must maintain a continuous depth across the bed-not even but continuous, in order to respond to load changes," he said. "If it's too thick of a bed, there will be problems with the undergrade air getting through and you may get slagging on top of the bed. If the bed gets too thin, holes will be blown in it and the grate temperatures will be affected."

The air system-undergrate and overfire air- is the second optimization area, according to Link. "Most refused derived fuel units have been retrofitted and because of that, the overfire air systems aren't adequate," he said. "A correct and coordinated ratio of overfire to undergrate air is critical for good combustion, and only requires minor changes for fuel variations after initial set up."

Roger Nichols, president of eNRG Solutions, echoed Schoene's notions of the importance of being particular when evaluating gasification technologies. "All gasifiers aren't alike," he said. The gasifier eNRG owns was designed by ICM Inc. and converts MSW into steam, electricity, heat or biofuels. A typical 18 MW 500-ton-per-day system has no visible emissions, a wet electrostatic precipitator on the back end to produce a very clean syngas, minimum fuel size reduction requirements, waste heat recovery and a 27 by 12 foot footprint, Nichols said.

Nichols pointed out that the amount of MSW generated each year is increasing along with the population. "MSW amounts increase yearly, and landfills are closing rapidly around the nation," he said. "Waste utilization is an area seeing a lot of activity right now. With concerns of controlling greenhouse gases, modern approaches [to processing waste] are required, as incineration is now perceived as a ‘dirty' process. We're going to run out of land space, so sooner or later we'll have to deal with it."