Encounters

The method proposed in this monograph has a firm thermodynamic basis. For vapo/-liquid equilibria, the method may be used at low or moderate pressures commonly encountered in separation operations since vapor-phase nonidealities are taken into account. For liquid-liquid equilibria the effect of pressure is usually not important unless the pressure is very large or unless conditions are near the vapor-liquid critical region. 

This chapter presents a general method for estimating nonidealities in a vapor mixture containing any number of components this method is based on the virial equation of state for ordinary substances and on the chemical theory for strongly associating species such as carboxylic acids. The method is limited to moderate pressures, as commonly encountered in typical chemical engineering equipment, and should only be used for conditions remote from the critical of the mixture. 

These systems are solved by a step-limited Newton-Raphson iteration, which, because of its second-order convergence characteristic, avoids the problem of "creeping" often encountered with first-order methods (Law and Bailey, 1967) ... 

Both vapor-liquid flash calculations are implemented by the FORTRAN IV subroutine FLASH, which is described and listed in Appendix F. This subroutine can accept vapor and liquid feed streams simultaneously. It provides for input of estimates of vaporization, vapor and liquid compositions, and, for the adiabatic calculation, temperature, but makes its own initial estimates as specified above in the absence (0 values) of the external estimates. No cases have been encountered in which convergence is not achieved from internal initial estimates. 

Flash calculations for these mixtures usually require four to eight iterations. Cases 5 and 6 in Table 1 have feeds of this type, including noncondensable components in Case 6. Within the limits of the thermodynamic framework used here, no case has been encountered where FLASH has required more than 12 iterations for satisfactory convergence. 

The calculational procedure employed in BLIPS, when used with the particular initial phase-composition estimated included in the subroutine, has converged satisfactorily for all systems we have encountered (except very near plait points as noted). 

Before we can proceed with the choice of reactor and operating conditions, some general classifications must be made regarding the types of reaction systems likely to be encountered. We can classify reaction systems into five broad types ... 

Even if the reactor temperature is controlled within acceptable limits, the reactor effluent may need to be cooled rapidly, or quenched, to stop the reaction quickly to prevent excessive byproduct formation. This quench can be accomplished by indirect heat transfer using conventional heat transfer equipment or by direct heat transfer by mixing with another fluid. A commonly encountered situation is... 

Take note that Ft can therefore be regarded as depending only on the inlet and outlet temperatures of the streams in a 1-2 exchanger. Three basic situations can be encountered when using 1-2 exchangers (Fig. 7.8) ... 

As the amount of temperature cross increases, however, problems are encountered, as illustrated in Fig. 7i8c. Local reversal of heat flow may be encountered, which is wasteful in heat transfer area. The design may even become infeasible. 

Perhaps the most extreme situation is encountered with purge streams. Purges are used to deal with both feed impurities and byproducts of reaction. In the preceding section we considered how the size of purges can be reduced in the case of feed impurities by purifying the feed. However, if it is impractical or uneconomical to reduce the purge by feed purification, or the purge is required to remove a byproduct of reaction, then the additional separation can be considered. 

Combustion in an incinerator is the only practical way to deal with many waste streams.This is particularly true of solid and concentrated wastes and toxic wastes such as those containing halogenated hydrocarbons, pesticides, herbicides, etc. Many of the toxic substances encountered resist biological degradation and persist in the natural environment for a long period of time. Unless they are in dilute aqueous solution, the most effective treatment is usually incineration. 

The rings most frequently encountered in crude oils are those having five or six carbon atoms. In these rings, each hydrogen atom can be substituted by a paraffinic alkyl chain that is either a straight chain or branched. 

Taking into account the double bond, an olefin situation is encountered that is much more complex than that of the preceding families. For exampie, the C4Hg butene isomers have many arrangements ( B), ... 

Normally absent or in trace amounts in crude oil, products of conversion processes such as diolefins, acetylenes, etc., are encountered. Table 1.4 gives the physical properties of some of them. Noteworthy is 1-3 butadienerC ( l)... 

Molecular weight for a mixture of components such as one would encounter in petroleum cuts, the molecular weight is ... 

The most commonly encountered permanent gases are CO2, H2S, and N2 associated with gas or crude oil production and N2, CO, H2, and O2 found in refining and petrochemicals. 

The noncondensable hydrocarbons comprise the hydrocarbons having less than five carbon atoms methane, ethane, propane and butanes encountered in production refining will add the olefins and diolefins ... 

Identification of normal paraffins by chromatography presents no special problems with the exception of biodegraded crudes, they are clearly distinguished. The problem encountered is to quantify, as shown in Figure 3.14, the normal paraffin peaks that are superimposed on a background representing other hydrocarbons. 

Knowledge of physical properties of fluids is essential to the process engineer because it enables him to specify, size or verify the operation of equipment in a production unit. The objective of this chapter is to present a collection of methods used in the calculation of physical properties of mixtures encountered in the petroleum industry, different kinds of hydrocarbon components, and some pure compounds. 

The DIPPR is a research organization sponsored by the AlChE (American Institute of Chemical Engineers). Its objective is to develop a thermophysical data bank for the components most frequently encountered in the chemical industry. 

Other kinds of liquid-liquid equilibria are encountered in processes such as alkylation, where anhydrous hydrofluoric acid (HF) is partially soluble in hydrocarbons. 

The properties of the solids most commonly encountered are tabulated. An important problem arises for petroleum fractions because data for the freezing point and enthalpy of fusion are very scarce. The MEK (methyl ethyl ketone) process utilizes the solvent s property that increases the partial fugacity of the paraffins in the liquid phase and thus favors their crystallization. The calculations for crystallization are sensitive and it is usually necessary to revert to experimental measurement. 

For vehicles, special attention is most often focused on the knocking potential encountered at high motor speeds in excess of 4000 rpm for which the consequences from the mechanical point of view are considerable and lead very often to mechanical failure such as broken valves or pistons, and rupture of the cylinder head gasket. Between RON and MON, it is the latter which better reflects the tendency to knock at high speeds. Conversely, RON gives the best prediction of the tendency to knock at low engine speeds of 1500 to 2500 rpm. 

Hydrocarbons generally have very low electrical conductivities and manipulation of these fluids creates electrostatic charges that can result in fire or explosions. This problem is encountered with gasoline and kerosene. 

Once an exploration well has encountered hydrocarbons, considerable effort will still be required to accurately assess the potential of the find. The amount of data acquired so far does not yet provide a precise picture of the size, shape and producibility of the accumulation. 

Even if all of the elements described so far have been present within a sedimentary basin an accumulation will not necessarily be encountered. One of the crucial questions in prospect evaluation is about the timing of events. The deformation of strata into a suitable trap has to precede the maturation and migration of petroleum. The reservoir seal must have been intact throughout geologic time. If a leak occurred sometime in the past, the exploration well will only encounter small amounts of residual hydrocarbons. Conversely, a seal such as a fault may have developed early on in the field s history and prevented the migration of hydrocarbons into the structure. 

In some depositional environments, e.g. fluviatile channels, marked differences in reservoir thickness will be encountered. Hence the assumption of a constant thickness, or a linear trend in thickness across the field will no longer apply. In those cases a set of additional maps will be required. Usually a net oil sand (NOS) map will be prepared by the production geologist and then used to evaluate the hydrocarbon volume in place. 

Hence we need to combine the two maps to arrive at a net oil sand map (3). The odd shape is a result of that combination and actually it is easy to visualise at the fault the thickness of oil bearing sand will rapidly decrease to zero. The same is the case at the OWC. Where the net sand map indicates 0 m there will be 0 m of net oil sand. Where the channel is best developed showing maximum thickness we will encounter the maximum net oil sand thickness, but only until the channel cuts through the fault or the OWC. 

Different plant operating conditions (steady load, load variations, startups / shutdowns) have been encountered during the monitoring period. Electrical load, steam pressure and steam temperature values vs time have been acquired and stored during the entire period. At the same time, the RMS values of the acoustical background noise were have been continuously checked and stored, thus providing a quick check of proper instrumentation condition and a correlation between variations of plant parameters and the acoustical behaviour of the components. 

Homogeneity of data. Homogeneous data will be uniform in structure and composition, usually possible to describe with a fixed number of parameters. Homogeneous data is encountered in simple NDT inspection, e.g. quality control in production. Inhomogeneous data will contain various combinations of indications from construction elements, defects and noise sources. An example of inhomogenous data are ultrasonic B-scan images as described in [Hopgood, 1993] or as encountered in the ultrasonic rail-inspection system described later in this paper. 

When implementing CBR systems one has to able to define and implement the methods to distinguish between data from different classes. This is a more difficult problem than when constructing a simple data classifier, as the important parameters cannot be simply determined based on a set of examples. One has to have some a-priori knowledge about the important features that distinguish various data classes, as well as anticipate possible data forms that can be encountered during future inspections. This may necessitate the use of more features to describe the problem than a comparable classifier would use. When determining the data... 

Some of the problems often encountered during ultrasonic inspection of plane specimens are also found on cylindrical specimens. For example, problems associated with the directional characteristic of the ultrasonic transducer. Furthermore, the discontinuity influences the shape and propagation direction of a reflected pulse, causing wave mode transformation. In addition, the specimen influences the shape and amplitude of the reflected pulse by sound absorption. 

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