Catalytic hot gas cleaning with monoliths in biomass gasification in fluidized beds. 1. Their effectiveness for tar elimination

Full-size 15 x 15 x 30 cm nickel-based monoliths are tested for tar elimination in fuel gas produced by biomass gasification in a fluidized bed at a small pilot-plant scale. The feedstocks used were mixtures of pine wood chips and "orujillo", the residue from olive oil production. Temperatures at the front or face of the monolith ranged from 820 to 956 degreesC, gas hourly space velocities in the monolith ranged from 1280 to 4550 h(-1) (normal conditions, nc), area velocities ranged from 2.7 to 7.1 m/h, and superficial or face gas velocities at the inlet of the monolith ranged from 0.34 to 1.3 m/s. Samples of gas and tar were taken before and after the monolith reactor, and variations in gas composition and tar content were determined. Using a macrokinetic model presented elsewhere, some key kinetic constants for the tar-removal reaction are calculated for the monolith and used as indexes of its activity. The effects of some important operating conditions on the activity and sometimes on the deactivation of the monolith are presented here. The intrinsic activity of the monolith for tar abatement is finally compared with those of other competing catalysts such as dolomites and commercial steam-reforming catalysts. It is concluded that these monoliths are not very high in activity, but they can operate with a fuel gas containing particulates, thereby avoiding the use of hot filters, which are problematic when used in biomass gasification.