Liquid operating variables

To calculate the equilibrium curve taking the heat of solution into accoimt, i.e., operate adiabatically with liquid temperature variable, follow the steps ... 

Liquid feedstocks for olefin production are light naphtha, full range naphtha, reformer raffinate, atmospheric gas oil, vacuum gas oil, residues, and crude oils. The ratio of olefins produced from steam cracking of these feeds depends mainly on the feed type and, to a lesser extent, on the operation variables. For example, steam cracking light naphtha produces about twice the amount of ethylene obtained from steam cracking vacuum gas oil under nearly similar conditions. Liquid feeds are usually... 

This brief discussion of some of the many effects and interrelations involved in changing only one of the operating variables points up quite clearly the reasons why no exact analysis of the dispersion of gases in a liquid phase has been possible. However, some of the interrelationships can be estimated by using mathematical models for example, the effects of bubble-size distribution, gas holdup, and contact times on the instantaneous and average mass-transfer fluxes have recently been reported elsewhere (G5, G9). 

Equation (17) indicates that the entire distribution may be determined if one parameter, av, is known as a function of the physical properties of the system and the operating variables. It is constant for a particular system under constant operating conditions. This equation has been checked in a batch system of hydrosols coagulating in Brownian motion, where a changes with time due to coalescence and breakup of particles, and in a liquid-liquid dispersion, in which av is not a function of time (B4, G5). The agreement in both cases is good. The deviation in Fig. 2 probably results from the distortion of the bubbles from spherical shape and a departure from random collisions, coalescence, and breakup of bubbles. 

To evaluate the effects of operating variables on the capacity of the gas-liquid disperser one can make the following substitutions ... 

The conditions for a complete separation of a binary mixture can be defined in terms of the Yj model parameters, which are directly related with the TMB (SMB) operating variables (fluid and solid velocities in the four sections of the TMB unit). From the constraints presented, those related to sections II and III play the crucial role on the separation performance of the TMB. It is in these central zones that the separation between the two species takes place. The role of the adjacent sections (I and IV) is to prevent cross-contamination and to allow the improvement of the continuous operation of the system by regenerating the solid and liquid phases. Taking into account these considerations, a region of complete separation in a Ym-Yn plane can be defined. Considering that the constraints concerning sections I and IV are fulfilled, the YnrYn plot is 311 important tool in the choice of best operating conditions. 

In 1974 Midwest Research Institute operated a pilot-scale multiple chamber incinerator to evaluate for EPA the operational variables for pesticide incineration (8). The system included a. pilot-scale incinerator, a three-stage scrubber system, and a scrubber water treatment system. Nine pesticides (aldrin, atrazine, captan, DDT, malathion, mirex, picloram, toxaphene, and zineb) in 15 liquid and solid formulations were studied. Destruction efficiencies generally exceeded 99.99% over a range of temperatures and retention times ( 950 to 1100°C, 1.2 to 6 s, and 80 to 160% excess air). This study also documented the generation of measurable quantities of cyanide in the incinerator off-gas during the incineration of organonitrogen pesticides. 

It would be more practical, if A in gas-sparged stirred tanks were to be directly correlated with operating variables and liquid properties. It should be noted that the definition of k a for a gas-sparged stirred tank (both in this text and in general) is based on the clear liquid volume, without aeration. 

It was shown that room-temperature molten salts derived from the combination of 1,3-dialkylimidazolium chloride and A1C13 can be used as solvents in two-phase catalytic dimerization of propene to give hexenes catalyzed by Ni(II) compounds (125). The effects of phosphane ligands coordinated to nickel and operating variables were also investigated (126). The dimerization products separate as an organic layer above the molten salt. This reaction has been carried out with n-butenes as the reactant and cationic nickel complex catalysts dissolved in organochloroaluminate liquids (127). 

The nature and sizing of equipment depends on the economic values and proportions of the phases as well as certain physical properties that influence relative movements of liquids and particles. Pressure often is the main operating variable so its effect on physical properties should be known. Table 11.1 is a broad classification of mechanical processes of solid-liquid separation. Clarification is the removal of small contents of worthless solids from a valuable liquid. Filtration is applied to the recovery of valuable solids from slurries. Expression is the removal of relatively small contents of liquids from compressible sludges by mechanical means. 

The effect of condensation upon transfer rates with application to flue-gas washing plants and cooling towers are discussed. Theoretical models were developed for determining the rate of heat and mass transfer under conditions where fog formation prevails. Derived relationships are functions of the vapor and liquid equilibria and local heat and mass transfer of driving forces. They were used for a numerical study of the amount of fog formation as a function of the operational variables of a flue-gas washing plant in which the inlet gas temperature is typically... 

There are some basic factors in alkylation which should be considered in addition to the catalyst, feed stock, and normal operating variables. Although thermal alkylation can be accomplished without the presence of a catalyst, essentially all commercial processes today employ a catalyst. The alkylation reactions considered here normally take place in the liquid state. Sufficient pressure is therefore required to insure that the hydrocarbons in the reactor remain in the liquid state. This is only partially true for the autorefrigeration process, where cooling of the reaction zone takes place as a result of vaporizing some of the light hydrocarbons in the reactor. The ethylbenzene reaction is also an exception, since it normally takes place in the partial vapor state, especially when the feed contains considerable ethane. The alkylation reaction is exothermic, and this heat of reaction must be removed from the reaction zone. This heat can be removed by cooling coils, by vaporization of hydrocarbons, or in the effluent stream. 

Walcher W, Toll H, Ingendoh A, et al. Operational variables in high-performance liquid chromatography-electrospray ionization mass spectrometry of peptides and proteins using polyjstyrene-divinylben-zene) monoliths./. Chromatogr. A. (2004) 1053 107-117. 

The conditions of the gas feed may or may not vary, but is normally taken as given. The column pressure is normally fairly constant. The main operational variable is the amount of MSA required the more solvent that is used, the more gas will be absorbed. However, the more liquid is present in the column, the wider the column needs to be, which will make the column more expensive. As for distillation, a trade-off therefore exists between operation and design. 

Crude oil is heated to temperatures at which it thermally cracks into gasoline and distillate products and lower-molecular-weight gases. This liquid cracking process is referred to as visbreaking. A schematic of the process and the effect of operating variables on performance is shown in Fig. 19-12. 

In order to determine the relative importance of mass-transport processes in gas-liquid-solid-reactions, it is recommended to measure the global reaction rate as function of catalyst concentration w (keeping all other operating variables constant). With the assumption of spherical catalyst particles, the specific surface of the catalyst can be calculated as... 

Determine the turbulent power number for impeller geometry. Power number N P is a dimensionless variable [5] which relates impeller power P to such operating variables as liquid density p, agitator rotational speed N, and impeller diameter D as follows ... 

Two studies have been concerned with measurement of the interfacial area obtained by agitation of liquid-liquid systems. Each of these investigations relied on the use of a photoelectric probe which measured the light transmission of the two-phase dispersion. Vermeulen and co-workers (V2) made measurements in two geometrically similar, baffled vessels of 10- and 20-in. diameter. They used a very simple four-blade paddle-like stirrer, with a tank-to-impeller diameter ratio of about 1.5, and a 0.25 blade-width/impeller-diameter ratio. The impeller was located midway between the top and bottom of the vessel, which had a cover and was run full. Impeller speeds varied from about 100 to 400 r.p.m. A wide variety of liquids was employed. Volume fractions of dispersed phase varied from 10% to 40%. The mean droplet diameters observed ranged from 0.003 to 0.1 cm. The results were correlated with a mean deviation of about 20% by an empirical equation relating the specific interfacial area near the impeller to several system and operating variables as follows ... 

Pavlushenko et al. (P2) studied the suspension of screened fractions of sand and iron ore in a variety of liquids, with a 1-ft. diameter unbaffled vessel filled to a depth of one foot. Square-pitch three-blade propellers of 3-, 4-, and 5-in. diameter were used, and most of the observations were made with a 1 to 4 weight ratio of solids to liquid. Thief samples were taken at various levels in the vessel. In some cases, the contents did not become uniform at any impeller speed in other cases the contents became uniform at some impeller speed and remained so at higher speeds in a third type of behavior, the upper part of the vessel reached the over-all vessel average and then exceeded it as impeller speed was increased. Using the observations from the second and third types of behavior, a critical speed was defined as the lowest impeller speed at which the solids concentration at each level, or in the upper layers of the liquid, was equal to the over-all average solids concentration. This critical speed Nc in revolutions per second had the following relation to the operating variables ... 

These ideas of impeller flow, head and power input as related to operating variables have some merit for a qualitative description of the effects of the operating variables on the process. However, it requires extensive experience, and usually actual experiments, to decide whether a system performance is favored by a particular combination of flow and head. (Rushton and Oldshue (R12) note that high values of Q/3Care preferred for blending and solid suspension, low ratios for liquid-liquid and gas-liquid operations.) This approach still requires the systematic study of impeller speed and diameter as process variables. 

Temperature and pressure are not considered as primary operating variables temperature is set sufficiently high to achieve rapid mass-transfer rates, and pressure is sufficiently high to avoid vaporization. In liquid-phase operation, as contrasted to vapor-pliase operation, the required bed temperature bears no relation to the boiling range of the feed, an advantage when lieat-sensitive stocks are being treated. 

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