Using fast pyrolysis—gasification’s cooler, oxygenless cousin—to economically produce a bio-oil that serves as a replacement for alternative fuel oil has been a challenging endeavor. Despite its unusual properties and typically high capital and operating expenditures, however, there is increased interest around bio-oil production and utilization, and researchers and companies are achieving success in solving commercialization barriers.
One of those companies is Metso, whose technology partner, VTTTechnical Research Centre of Finland, has been working on bio-oil since 1982. Jussi Mantyniemi, general manager of technology for Metso’s power business line, says the patented, integrated bio-oil production process has three main parts, the first of which is fuel handling. This includes fuel receiving, drying of the biomass to 10 percent moisture, crushing and conveying.
Prepared fuel then enters a fluidized pyrolysis reactor where the dried biomass is pyrolysed in oxygen-free conditions. “The heat for the reaction is provided by the hot sand from the host boiler,” Mantyniemi explains. “After the reactor, in the cyclones, vapors are separated from the sand and char, which are returned to the boiler.” Vapors from the reactor are condensed to form bio-oil, and noncondensable gases are introduced to the boiler for heat and power generation.
The technology has been thoroughly tested in a process demonstration unit at VTT, as well as a 7-ton-per-day scale unit at Metso’s research and development facility in Tampere, Finland. Metso and VTT will reach a milestone this fall, with the completion of a commercial-scale production facility in Joensuu, Finland, at a facility owned by energy company Fortum. “The pyrolysis plant is integrated into the existing CHP (combined-heat-and-power) plant, and will produce 50,000 tons annually of bio-oil,” Manthyniemi says.
Previously, for proof of concept, around 40 metric tons of bio-oil was combusted in Fortum’s 1.5 MW district heating plant in Masala, Finland.
Commissioning of the plant is scheduled for this fall. Though it may serve as proof that bio-oil can be produced and used at commercial scales, there are still hurdles to robust market development.