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13The purpose of the study was to investigate the influence of torrefaction on the grindability of wheat straw. 14 Straw samples were torrefied at temperatures between 200 ˚C to 300 ˚C and with residence times between 0.5 to 15 3 hours. Spectroscopic information obtained from ATR-FTIR indicated that below 200 ˚C there was no obvious 16 structural change of the wheat straw. At 200-250 ˚C hemicelluloses started to decompose and were totally 17 degraded when torrefied at 300 ˚C for 2 hours, while cellulose and lignin began to decompose at about 270-300 18 ˚C. Tensile failure strength and strain energy of oven dried wheat straw and torrefied wheat straw showed a clear 19 reduction with increasing torrefaction temperature. In addition, Hardgrove Grindability Index (HGI) of wheat 20Page 2 of 23 straw torrefied at different conditions was determined on a standard Hardgrove grinder. Both results showed an 21 improvement of grindability in the torrefaction temperature range 250-300 ˚C, which can be well explained by 22 the findings from FTIR analysis. At a torrefaction temperature of 260 ˚C and with a residence time of 2 hours, 23 wheat straw samples produced similar HGI values as coal (RUKUZN) with 0% moisture content. Under this 24 condition, the Anhydrous Weight Loss (AWL%) of the wheat straw sample was 30% on dry and ash free basis 25 (daf), and the higher heating value of the torrefied wheat straw was 24.2 MJ kg -1 (daf). The energy loss 26 compared to the original material was 15% (daf). 27

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Fertilizer quality of ash and char from incineration, gasification and pyrolysis of a single municipal sewage sludge sample were investigated by comparing composition and phosphorus (P) plant availability. A process for post oxidation of gasification ash and pyrolysis char was developed and the oxidized materials were investigated as well. Sequential extraction with full elemental balances of the extracted pools as well as scanning electron microscopy with energy dispersive X-ray spectroscopy were used to investigate the mechanisms driving the observed differences in composition and P plant availability in a short-term soil incubation study. The compositional changes related mainly to differences in the proximate composition as well as to the release of especially nitrogen, sulfur, cadmium and to some extent, phosphorus (P). The cadmium load per unit of P was reduced with 75-85% in gasification processes and 10-15% in pyrolysis whereas no reduction was observed in incineration processes. The influence on other heavy metals was less pronounced. The plant availability of P in the substrates varied from almost zero to almost 100% of the plant availability of P in the untreated sludge. Post-oxidized slow pyrolysis char was found to be the substrate with the highest P fertilizer value while ash from commercial fluid bed sludge incineration had the lowest P fertilizer quality. The high P fertilizer value in the best substrate is suggested to be a function of several different mechanisms including structural surface changes and improvements in the association of P to especially magnesium, calcium and aluminum.

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Results from five experimental campaigns with Low Temperature Circulating Fluidized Bed (LT-CFB) gasification of straw and/or municipal sewage sludge (MSS) from three different Danish municipal waste water treatment plants in pilot and demonstration scale are analyzed and compared. The gasification process is characterized with respect to process stability, process performance and gas product characteristics. All experimental campaigns were conducted at maximum temperatures below 750°C, with air equivalence ratios around 0.12 and with pure silica sand as start-up bed material. A total of 8600kg of MSS dry matter was gasified during 133h of operation. The average thermal loads during the five experiments were 62-100% of nominal capacity. The short term stability of all campaigns was excellent, but gasification of dry MSS lead to substantial accumulation of coarse and rigid, but un-sintered, ash particles in the system. Co-gasification of MSS with sufficient amounts of cereal straw was found to be an effective way to mitigate these issues as well as eliminate thermal MSS drying requirements. Characterization of gas products and process performance showed that even though gas composition varied substantially, hot gas efficiencies of around 90% could be achieved for all MSS fuel types.

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