ALKALI-METAL EMISSION FROM FILTER ASH AND FLUIDIZED-BED MATERIAL FROMPFB GASIFICATION OF BIOMASS

The alkali metal emission from materials collected in a PFB biomass ga sification pilot plant has been characterized. Samples of SiC filter a sh and fluidized bed particles from different operating conditions wer e subjected to a constant heating rate up to 1000 degrees C in a nitro gen atmosphere, and the alkali metal emission was monitored continuous ly by a surface ionization technique. For all samples, two characteris tic emission intervals are identified. In the range 100-500 degrees C, a small fraction of the alkali metal content is emitted. Above 600 de grees C, the alkali metal release increases sharply and the rise is cl ose to exponential up to 900 degrees C. For fluidized bed particles, t he alkali metal emission is significantly lower for agglomerates compa red to material used during 1 day, which is attributed to the formatio n of less volatile compounds. For the filter ash samples, the alkali m etal emission is enhanced in samples collected after longer filter cle aning intervals, indicating that the formation of a filter deposit imp roves the alkali capture efficiency.