PARTICLE BREAKAGE IN THE CYCLONES OF FLUIDIZED BED SYSTEMS

A breakage model is developed to predict the change in particle size distribution of brittle materials that undergo mechanical stress in gas cyclones. The breakage probability depends on the cyclone inlet gas velocity, solids load, particle size, and a material-specific constant. The model is validated with data from experiments on a laboratory gas cyclone with aluminum oxide and iron oxide. The results are applied to calculate the particle size distribution of a chemical looping combustion process with iron ore as oxygen carrier

CHALLENGES WITH THE COUPLING OF FLUIDIZED BEDS FOR CHEMICAL LOOPING COMBUSTION

In the present work the system of interconnected fluidized bed reactors of a Chemical Looping Combustion (CLC) process is simulated in pilot plant scale and 100 MWth scale. Attrition models, derived from small scale laboratory experiments, are employed to predict the behavior of a large scale CLC process in terms of attrition and oxygen carrier (OC) losses. Realistic circulation mass flows of OC are calculated and the sources of the losses are further investigated. Different arrangements of cyclones are evaluated for their potential to improve the solids recovery. For example the introduction of a second-stage cyclone separation for the air reactor reduces the OC losses significantly

Catalyst Attrition in the CFB Riser

Catalyst attrition in the CFB riser was experimentally investigated in a pilot scale CFB system consisting of a 400 mm diameter riser with a height of 15 m, a return leg and a two-stage cyclone separation. The catalyst loss of the CFB system was measured. In order to discern between attrition occurring in the cyclones and in the riser the system was simulated by a population balance approach which takes the separation efficiency of the cyclone system into account. On the basis of the experimental investigation an empirical correlation for catalyst attrition in the CFB riser has been developed which accounts for the influence of the gas velocity and the catalyst mass in the riser

The Influence of Carbon Stripper Efficiency on CO2 Capture Rate in a Chemical-Looping Combustion Process for Solid Fuels

In the present work a Chemical-Looping Combustion process for solid fuels is simulated on the 100 MWth scale. The coal is gasified inside the fuel reactor by recirculated CO2 and H2O. A carbon stripper downstream of the fuel reactor is used to reduce the carryover of char from the fuel to the air reactor. The influence of the carbon stripper on the CO2 capture rate is investigated. The results demonstrate the significance of the carbon stripper in this process

Glucose sensing based on the intrinsic fluorescence of sol-gel immobilized yeast hexokinase

In this study, we investigated measurements of the intrinsic fluorescence of yeast hexokinase as an assay for glucose and immobilization of the enzyme in a silica sol-get matrix as a potential in vivo glucose sensor for use in patients with diabetes. The intrinsic fluorescence of hexokinase in solution (excitation = 295 nm, emission = 330 nm) decreased by 23% at a saturating glucose concentration of 1 mM (K-d = 0.3 mM), but serum abolished the glucose-related fluorescence response. When entrapped in tetramethylorthosilicate-derived sol gel, hexokinase retained activity, with a 25% maximal glucose-related decrease in intrinsic fluorescence, and the saturation point was increased to 50 mM glucose (K-d = 12.5 mM). The glucose response range was increased further (to 120 mM, K-d = 57 mM) by a covering membrane of poly(2-hydroxyethyl) methacrylate. Unlike free enzyme, the fluorescence responses to glucose with sol-gel immobilized hexokinase, with or Without covering membrane, were similar for buffer and serum. We conclude that fluorescence monitoring of sol-gel entrapped yeast hexokinase is a Suitable system for development as an in vivo glucose biosensor. (c) 2005 Elsevier Inc. All rights reserved