W. de Jong

Selective production of hemicellulose-derived carbohydrates from wheat straw using dilute HCl or FeCl3 solutions under mild conditions. X-ray and thermo-gravimetric analysis of the solid residues

The present work explores the combined production of hemicellulose-derived carbohydrates and an upgraded solid residue from wheat straw using a dilute-acid pretreatment at mild temperature. Dilute aqueous HCl solutions were studied at temperatures of 100 and 120°C, and they were compared to dilute FeCl(3) under the same conditions. Comparable yields of soluble sugars and acetic acid were obtained, affording an almost complete removal of pentoses when using 200 mM aqueous solutions at 120°C. The solid residues of pretreatment were characterized showing a preserved crystallinity of the cellulose, and a almost complete removal of ash forming matter other than Si. Results showed upgraded characteristic of the residues for thermal conversion applications compared to the untreated wheat straw.

Thermochemical conversion of brown coal and biomass in a pressurised fluidised bed gasifier with hot gas filtration using ceramic channel filters, measurements and gasifier modelling

Biomass (wood and Miscanthus pellets) and Rhenish brown-coal were gasified using a 1.5 MWth (max.) pressurised fluidised bed gasification (PFBG) installation. NOx precursor and tar emissions were studied by varying process parameters like the fuel type, pressure, temperature and air factor. Carbon conversions were well above 80%. Fuel-nitrogen conversion into NH3 was mostly above ca. 50%. Fuel-nitrogen conversion into HCN was significantly lower. Results were in-line with comparable investigations with bottom feeding. Measurements of the gas composition for Miscanthus gasification were compared with a steady-state model based on elementary reaction chemistry and heterogeneous gas-char reactions related to the emission of nitrogen species. A flash pyrolysis model (FG-DVC-biomass version) was applied to determine the initial yields. Measurements and model simulation results were in reasonably good agreement.

Coal gasification and combustion of LCV gas

Experiments were performed on the gasification of bituminous coal with air and steam in a 2·5 kW atmospheric fluidized bed. Thermal conversion efficiencies, the retention of sulphur and the conversion of fuel nitrogen to NH3 were determined for various oxygen-to-carbon ratios (equivalence ratios between 0·58 and 0·82), with and without limestone in the bed. The conversion efficiency increased with increasing equivalence ratio, while the conversion of fuel-nitrogen to NH3 decreased with increasing equivalence ratio. The sulphur conversion without the addition of limestone increased with increasing equivalence ratio. As expected, the presence of limestone in the bed led to increased sulphur retention, more so at the high and low ends than at intermediate values of the range of equivalence ratios. In addition, limestone adversely affected thermal conversion efficiency and increased the conversion of fuel-nitrogen. The low calorific value (LCV) fuel gas, produced by the AFBG, was combusted in a cyclone combustor at atmospheric pressure. Stable combustion of the LCV fuel gas was possible down to a calorific value of 1·57 MJ/m3n. The combustion efficiency in the atmospheric topping combustor varied between 98·72 and 99·96%. Nearly 60% of the NH3 in the fuel gas was converted to NO in the combustor.

Thermochemical Gasification of Biomass: Fuel Conversion, Hot Gas Cleanup and Gas Turbine Combustion

Air-blown fluidized bed biomass gasification integrated with a gas- and steam turbine combined cycle (BIGCC) is a potentially attractive way to convert biomass into electricity and heat with a high efficiency.