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

A model for a countercurrent gas—solid—solid trickle flow reactor for equilibrium reactions. The methanol synthesis

The theoretical background for a novel, countercurrent gas—solid—solid trickle flow reactor for equilibrium gas reactions is presented. A one-dimensional, steady-state reactor model is developed. The influence of the various process parameters on the reactor performance is discussed. The physical and chemical data used apply to the case of low-pressure methanol synthesis from CO and H2 with an amorphous silica—alumina as the product adsorbent. Complete reactant conversion is attainable in a single-pass operation, so that a recycle loop for the non-converted reactants is superfluous.\ud \ud In the following article the installation and experiments for which this theory was developed will be described

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

Safe design of cooled tubular reactors for exothermic multiple reactions: Multiple-reaction networks

The model of the pseudo-homogeneous, one-dimensional cooled tubular reactor is applied to a multiple-reaction network. It is demonstrated for a network which consists of two parallel and two consecutive reactions. Three criteria are developed to obtain an integral yield which does not deviate more than a chosen fraction from the maximum yield that can be obtained in an isothermal reactor. The criteria enable us to choose relevant design and operating conditions for the safe execution of a reaction network in a tubular reactor. The method is illustrated for the production of maleic anhydride by air oxidation of benzene

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

The use of the chemical method for the determination of interfacial areas in gas-liquid contactors

The interfacial area achem in a gas-liquid contactor as determined by the chemical method deviates from the true geometrical interfacial area ageo, because the overall conversion of the gas phase reactant represents an incorrect average if bubble sizes and residence times are not uniform. The deviations of achem fromageo become larger the broader the distribution τb/db and the higher the overall conversion ΩA of the reactant in the gas phase. Model calculations, which take into account both the effect of gas phase backmixing as well as the effect of bubble coalescence on the deviation of achem from ageo, are performed for a mechanically agitated gas—liquid reactor and a bubble column at practical micro- and macromixing conditions. For a gas-liquid model reaction, which is first-order in the gas phase reactant, it is found that: (1) for a mechanically agitated reactor the error in achem will always be smaller than 10% if ΩA is lower than 0.99, and (2) for a bubble column the error in achem will be smaller than 20% for most practical applications if ΩA is lower than 0.99. Gas-liquid model reaction systems with absorption of CO2 in alkanolamine solutions are recommended for the determination of interfacial area in gas—liquid contactors

Safe design and operation of tank reactors for multiple-reaction networks: uniqueness and multiplicity

A method is developed to design a tank reactor in which a network of reactions is carried out. The network is a combination of parallel and consecutive reactions. The method ensures unique operation. Dimensionless groups are used which are either representative of properties of the reaction system or exclusively of the design and operating variables. In a plot of the optimal yield vs the dimensionless operating temperature the region is indicated where operation under conditions of uniqueness is feasible. The method is illustrated with an example: the air oxidation of benzene of maleic anhydride