Oxidative degradation and ignition of loose-packed straw beds

Oxidative degradation and ignition of straw and rain-leached straw were inv estigated at a laboratory scale. Leaching reduced the ash content (by about 50 wt.%), in particular chlorine and potassium, and caused some swelling. A loose-packed bed (density 50 kg/m(3)) was exposed to a forced flow (veloc ities in the range 0.34-1.9 m/s) of hot air (temperatures in the range 540- 890 K). Degradation rates became significant for bed temperatures of about 500 K. However, the ignition temperatures were only slightly higher, hence oxidative degradation is a slow process, resulting in maximum conversions o f about 50 wt.% (slightly lower for leached straw). Ignition temperatures i ncreased, as the heating conditions were made more severe, and were lower f or untreated straw, compared to leached straw. The ignition times were init ially shorter and then longer for untreated straw, as the solid heating rat e was increased. These results are due to a lower reactivity of leached str aw, as a consequence of the partial ash removal, and its swelling, which mo difies the heat transfer conditions across the bed. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.