¦POWER GENIUS GENERATOR: Power at the Covington gasification plant is produced via a General Electric Organic Rankine Cycle generator. PHOTO: PHG ENERGY
city to dispose of about 10 tons of urban wood waste and 2 tons of sewer sludge each day, or 360 tons per month. In a nutshell, PHGE’s plant design includes wood chipping and material handling, chip and sludge mixing and drying, gasification conversion of the feedstock to gas, a thermal oxidizer and an oil heater to provide heat power for a General Electric Clean Cycle heat-to-power Organic Rankine Cycle generator. Direct use of the ORC generator to produce power from a gasification plant was pioneered this year through a research and development project PHGE completed with General Electric. While just bringing the project on line is exciting—commissioning should be complete by late October—the successful installation is particularly noteworthy because it will likely lead to larger projects, which have traditionally utilized updraft gasifiers.
Up with Downdraft “For larger gasification projects, updraft gasifiers have been prevalent, as downdraft gasifiers have traditionally been limited in size and deemed not scalable,” Koczaja says. “[However] downdraft gasifiers offer easy operation and low operation and maintenance costs—very few moving parts—power density, and a cleaner gas as their output.” The cleaner gas is a result of air being drawn downward through the feedstock, in the same direction the biomass is moving. Main reactions occur in a throat-like constriction area where the tars and volatile gases are passed through a hot bed of char and broken down into carbon monoxide and hydrogen, at a much higher temperature than in an updraft gasifier. As a result, downdraft gasifiers produce cleaner gas. Through focused R&D, PHGE has been able to develop a line of gasifiers that maintain the benefits of downdraft while overcoming the issue of scalability. Rather than scaling up and then looking at symptoms to try to correct them, PGHE approached the core problem—the geom22 BIOMASS MAGAZINE | OCTOBER 2013
Published on Oct 7, 2013