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Thermochemical gasification of biomass can produce low, medium and high calorific value gases. The characteristics, applications and potential of the different processes and reactor types are discussed. The introduction of biomass gasification on a large or intermediate scale for the production of power, synthetic natural gas (SNG), methanol etc. will depend on developments in coal and (municipal) solid waste gasification and on the price of biomass. Biomass - and especially wood - is a clean fuel and, therefore, its direct combustion using modern equipment will be a strong competitor for energy generation via gasification. Gasification is also attractive for small scale, power and power-heat generation and developments necessary for its widespread acceptance are discussed. It is further concluded that, on the small and intermediate sc...
In many processes in the chemical industry mass transfer accompanied with reversible, complex chemical reactions in gas-liquid systems are frequently encountered. In point of view of design purposes it is very important that the absorption rates of the transferred reactants can estimated sufficiently accurate. Moreover, mass transfer phenomena can also affect substantially important process variables like selectivity and yield. Therefore large amounts of research effort has been invested in describing these processes and in the development of models that can be used for the calculation of the mass transfer rates and other parameters. The description of the absorption of a gas followed by a single first order irreversible reaction is simple and straightforward. For all mass transfer models, e.g. film, penetration and surface renewal re...
A review is given of gasification processes for solid fuels with special emphasis on waste gasification. Although the co-current moving bed gasifier has not been under consideration for a long time, it offers interesting possibilities for waste gasification. Some operational data are given. Two potential applications are discussed—gasification of agricultural waste (maize cobs) in the rural areas of Tanzania and municipal waste gasification.
The height of an overall transfer unit has been evaluated in a gas—solid packed column at trickle flow by measuring column performance during steady state adsorption experiments. Results have been interpreted with an extraction model: mass transfer and axial dispersion in both phases. Using Bodenstein numbers for the gas and solid phases from a previous investigation the height of a true transfer unit has been calculated. The column was filled with dumped Pall rings, the solid phase was a freely flowing catalyst carrier, and the gas phase was air at ambient conditions containing freon-12 as adsorbing component. At low gas velocities column performance is entirely determined by axial dispersion but at higher gas velocities mass transfer limitations become important. For conditions of practical importance the height of a true transfer ...
The rate of oxidation of H2S by O2 over synthetic sodium faujasite zeolites to produce elemental sulphur has been studied at partial sulphur lo
The oxidation of H2S by O2 producing elemental sulphur has been studied at temperatures of 100–300°C and at atmospheric pressure in a laboratory-scale gas-solid trickle-flow reactor. In this reactor one of the reaction products, i.e. sulphur, is removed continuously by flowing solids. A porous, free-flowing catalyst carrier has been used which contains a NaX zeolite acting as a catalyst as well as a sulphur adsorbent. In order to describe mass transfer in the trickle-flow reactor, a reactor model has been developed in which a particle-free, upflowing gas phase and a dense, downflowing gas-solids suspension, the so-called trickle phase, are distinguished. Within the trickle phase, diffusion of the reactants parallel to reaction in the catalyst particles takes place. The mass transfer rate from the gas phase to the trickle phase has been...
The reaction between CO2 and tertiary alkanolamines (MDEA, DMMEA, TREA) has been studied in aqueous solutions at various temperatures. Also the absorption of CO2 in a solution of MDEA in ethanol has been studied. Reaction kinetics have been established by chemically enhanced mass transfer of CO2 into the various solutions. The experiments were performed in a stirred vessel with a horizontal interface which appeared to the eye to be completely smooth. The reaction of CO2 with tertiary amines can be described satisfactorily with the base-catalysis mechanism proposed by Donaldson and Nguyen (1980). Also attention has been paid to the influence of reversibility and small amounts of impurities (primary and secondary amines) on the measured mass transfer rate. For the reaction rate constant, k2, of the reaction between carbon dioxide and ter...
Absorption rates of H2S and CO2 in several aqueous alkanolamines in a cocurrent downflow fixed-bed reactor operated in the pulse flow regime have been measured in order to obtain information on the potential selectivity and on the mass transfer parameters. From these experiments it can be concluded that this type of reactor seems to be very suitable for the selective removal of H2S from acid gases. It was not possible to derive correlations which are always valid for the calculation of the mass transfer parameters in laboratory-scale contactors. The results of the present study in combination with the data published in the literature were correlated with only one unknown parameter in which the influence of the physical properties of the system and the shape and material of the packing were combined. This parameter has to be determined...
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