Economic background of chemical integration - a case study

In this second paper on chemical integration the author refines the usual relation of total costs equals fixed plus variable costs further by splitting the fixed costs into core, true fixed and capacity related fixed costs. A set of equations for a simplified definition of the returns on investment for an entire chemically integrated complex and individual production units in the manufacturing plant is given, from which the individual contributions of diversification and of chemical integration can be deduced. An example taken from practice is given

Progress on the salmon investigation

An article detailing some of the conclusions of the salmon investigation undertaken by the author, on the River Eden and its tributaries, for the previous few years. It is proposed that seasonal changes in young salmon growth are related to water temperature variation. A figure is included showing length of fish compared to the average temperature of water in the River Eden over a two year duration. The article describes comparative work undertaken to date between three streams within the Thurso watershed and the River Eden. A table is included showing the average size of fish in each of the watercourses compared. Laboratory experiments on the effects of temperature on young salmon are outlined, as well as investigative work undertaken into the realtionship between fish scales and fish length

'Whither the Service Class Re-investigating the middle layers of employment in the 21st Century

The purpose of this working paper is to contribute towards the continuing debate on the nature of class structure in the West, recognising that occupation has constituted the central device in the construction of theoretical approaches in this area. The paper is critical of the notion that there can be a simple congruence between occupation and class, but is nevertheless committed to the view that the workplace remains a key site wherein class antagonisms are played out. Using primary data the paper explores workplace relations between research scientists and their employing organisation, a major pharmaceutical firm. It considers theoretical approaches to locating these middle layers and in particular the suggestion that they form a new service class. The paper concludes that there are weaknesses in the notion of a service class both theoretically and in practice and argues that Marxist theories of class, and labour process theories concerned with management control, have significant explanatory power when applied to the interview data presented here. Rather than witnessing the growth of a service class and the death of the working class, the paper argues, we are seeing it transformed and re-generated

Constraints in Adoption of Bio-input Usage in Cotton Cultivation

Constraints in adoption of biological inputs usage in cotton cultivation of Tamil Nadu have been identified. Among the reasons for non-adoption of bio-inputs, long-term practice has been considered as the important factor by the non-adopters (mean score, 67.18) and lack of adequate extension as the second important factor (mean score, 62.15). The probability of adoption of bio-inputs has been estimated by the multinominal logit model which has been found significant at one per cent level, based on the log-likelihood ratio test. The model has correctly predicted 78 per cent of the adopters and non-adopters. The analysis has indicated that the farmers’ perceptional characteristics are positively and significantly related to the adoption of bio-inputs, whereas storage and handling is negatively related to the adoption. Among the suggestions for enhanced bio-inputs usage, extension of subsidy has been considered as the prime suggestion by the farmers (mean score, 66.21). Cotton crop has inelastic calendar of operations, and the pest management operations are highly time bound and any delay in the availability of biological inputs would seriously hamper its adoption. Hence, the timely availability has been regarded as the second important suggestion by the farmers (mean score, 63.75).Agricultural and Food Policy,

The role of pellet thermal stability in reactor design for heterogeneously catalysed chemical reactions

For exothermic fluid-phase reactions, a reactor which is cooled at the wall can exhibit multiplicity or parametric sensitivity. Moreover, for heterogeneously catalysed exothermic fluid-phase reactions, each of the catalytically active pellets in the reactor can exhibit multiplicity. Both forms of multiplicity can lead to thermal instability and as such have to be taken into account in reactor design. Here the effect of both instabilities is quantified. To this end, simple first-order kinetics are assumed, and intraparticle resistances and reactor and particle dynamics are not considered. A one-dimensional model, consisting of microscale mass and heat balances, is chosen to describe the reactor. It is assumed that the fluid inlet temperature equals the coolant temperature. The pellet scale model is a combined mass and heat balance for the pellet and it assumes that the Chilton¿Colburn analogy holds. For its incorporation in the reactor model it is assumed that for every individual pellet heat removal to neighbouring pellets via the mutual contact spots is negligible as compared to the heat transferred to the surrounding fluid. Consequently every pellets is isolated from its neighbours. In the thermally most critical region, i.e. the hot-spot region, reactor stability is determined by three parameter groups: a dimensionless adiabatic temperature rise, an Arrhenius number or dimensionless activation temperature and the ratio of the number of heat transfer units to the number of reaction units. For pellet multiplicity, a fourth parameter group becomes significant in addition: the ratio of the reaction rate to the pellet mass transfer rate. This number depends on the pellet size. A general recipe is given which enables us to determine whether or not pellet thermal instability can become important in reactor operation. For the situation where it is significant, generalized diagrams are presented indicating which pellet sizes problems must be expected due to pellet multiplicity

The influence of the reactor pressure on the hydrodynamics in a cocurrent gas-liquid trickle-bed reactor

The influence of the reactor pressure on the liquid hold-up in the trickle-flow regime and on the transition between trickle-flow and pulse-flow has been investigated in a trickle-flow column operating up to 6.0 MPa with water, and nitrogen or helium as the gas phase.\ud \ud The effect of the gas velocity and gas density on the hold-up has been explained by means of the modified Galileo number Ga{1+ΔP/(ρlgL)}. At the transition between trickle- and pulse-flow the liquid hold-up is - for a given value of the superficial gas velocity - nearly the same at each gas density. Therefore, at elevated gas densities the transition occurs at higher liquid throughputs. From a comparison of the experiments with water-nitrogen and water-helium it has been concluded that at an equal gas density - for given values of vl and vg - the hydrodynamic behaviour is the same

Safe design and operation of fluidized-bed reactors: Choice between reactor models

For three different catalytic fluidized bed reactor models, two models presented by Werther and a model presented by van Deemter, the region of safe and unique operation for a chosen reaction system was investigated. Three reaction systems were used: the oxidation of benzene to maleic anhydride, the oxidation of naphthalene to phthalic anhydride, and the oxidation of ethylene to ethylene oxide. Predictions of the optimal yield, the operating temperature and the conversion were also subjects of our study. It appeared that for reactions carried out in a fluidized bed operating under conditions of good fluidization all models predicted the same region of safe and unique operation. For a well-designed fluidized bed only the constraint of uniqueness is affected by the reactor model chosen. Predictions of the yield, conversion and operating temperature appeared to fit slightly less well. But still a good indication can be obtained from any of the models since the deviation in the results was less then a few percent for all three reaction systems. The strongest deviations between the models occurs in the region of gas loads only slightly higher than the minimum fluidization velocity. As the heat transfer characteristics are bad at low gas loads this region is unsuitable for highly exothermic reactions where large amounts of heat have to be removed by the coolant. In the region of good heat transfer with gas loads at least several times higher than the minimum the three models predict the same results. For this reason we finally recommed the use of simple models