Catalytic hot gas cleaning with monoliths in biomass gasification in fluidized beds. 4. Performance of an advanced, second-generation, two-layers-based monolithic reactor

After several years of research with a single-layer-based monolithic reactor, a new, second-generation monolithic reactor was designed, manufactured, set-up, and tested for tar and NH3 elimination from a real gasification gas. This gas was produced in an upstream bubbling fluidized-bed biomass gasifier at small pilot-plant scale (5-10 kg/h) and operated under conditions close to those used in large pilot and commercial units. The life of the monolith, which is more important in this application than its activity, is dependent basically on the longitudinal profiles of temperature in the entire monolithic reactor which must be optimal, avoiding very high and very low temperatures at the front and at the exit, respectively, of the monoliths. The longitudinal profile of temperature was modified and approached the optimal profile by dividing or partitioning the total air flow to the entire gasification plant into four different flows: two (first and second flows) to the gasifier (bottom and freeboard) and two (the third and fourth flows) to the monolithic reactor, to reheat the gasification gas before it enters the two layers of monoliths. Through the use of an optimal distribution of the air, the performance of the monolithic reactor was good and tar contents as low as 150 +/- 50 mg/N-3 were obtained in the tests reported here.