A comparative study of a fluidised bed reactor and a gas lift loop reactor for the IBE process: Part I. Reactor design and scale down approach

For the continuous production of isopropanol-butanol mixtures by immobilised Clostridium spp. (the IBE process) two reactor types were studied: a fluidised bed reactor with liquid recycling (FBR) and an external loop gas lift reactor (GLR). A large scale design (50–65 m³) was made for both reactors. A regime analysis, by evaluating the time constants for e.g. mixing and conversion, identified the ruling regime. Via the scale down approach two representative model reactors were developed: a 10 dm³ FBR reactor (H/D=25, D=0.08 m) and a 15 dm³ external loop GLR (H/D = 12.5, D_r=D_d=0.08 m). For both reactors the hydrodynamical behaviour and the total reactor performance were studied and are described in parts II and III of this study.     

Olefins from Syngas

Although the chemical industry is at present in a depressed state, this situation need not be permanent. The volume of raw materials used by the industry is already gigantic, but will grow even larger when the industry revives. A large part of the raw materials consists of lower olefins, at present produced from petroleum. The dependence of the chemical industry on this feedstock has been a weak point in the past, and there is no assurance of a continued supply in the future.     

Deviation of residual stress patterns in 52 100 bearing steel due to inherent microstructural transformations after rolling contact

A previous publication proved empirically that residual stresses in 52 100 bearing steel are caused mainly by microstructural transformations during rolling contact. It also introduced a model estimating the magnitude of residual stresses resulting from microstructural transformations. The results from this model prompted this study because the model showed a discrepancy between the measured results and the magnitude of the estimated residual stresses derived from the model. This study uses metallurgical analysis and modeling to explain why the measured and estimated magnitudes of residual stresses did not coincide. Metallurgical analysis explains the roles of retained austenite transformation and martensite decay in the ultimate magnitude of residual stresses at the surface of the bearing balls after rolling contact. The model estimates the magnitude of expected residual stresses due to martensite decay and suggests the number of cycles that bearing balls can operate under the beneficial effects of compressive residual stresses without spalling.     

Microstructural modelling of grain-boundary stresses in Alloy 600

The stress distribution in a random polycrystalline material (Alloy 600) was studied using a topologically correct microstructural model. The distributions of von Mises and hydrostatic stresses, which could be important factors when studying the intergranular stress corrosion cracking, at the grain vertices were analysed as a function of microstructure, grain orientations and loading conditions. The grain size, shape, and orientation had a more pronounced effect on stress distribution than the loading conditions. The stress concentration factor was higher for hydrostatic stress (1.7) than for von Mises stress (1.5). Hydrostatic stress showed more pronounced dependence on the disorientation angle than von Mises stress. The observed stress concentration is high enough to cause localized plastic microdeformation, even when the polycrystalline aggregate is in the macroscopic elastic regime. The modelling of stresses and strains in polycrystalline materials can identify the microstructures (grain-size distributions, texture) intrinsically susceptible to stress/strain concentrations and justify the correctness of applied stress state during the stress corrosion cracking tests.     

An indirect method for transfer function estimation from closed loop data

An indirect method is introduced that is able to estimate consistently the transfer function of a linear plant on the basis of data obtained from closed loop experiments, even in the situation where the model of the noise disturbance on the data is not accurate. Moreover, the method allows approximate identification of the open loop plant with an explicit and tunable expression for the bias distribution of the resulting model.