Overhead product yield

As you read the subsequent chapters in this book, please recall the picture of the vodka still. Keep in mind that the origin of the reflux is the vapor generated from burning firewood beneath the big can. This concept is the key to understanding how distillation towers function. You cannot have more reflux without increasing your reboiler duty, unless you are willing to sacrifice the overhead product yield. And if extra reflux results in more heavy components in the overhead, the trays are flooding. 

Fluid coking (Fig. 4) is a continuous process that uses the fluidized soflds technique to convert atmospheric and vacuum residua to more valuable products (12,13). The residuum is converted to coke and overhead products by being sprayed into a fluidized bed of hot, fine coke particles, which permits the coking reactions to be conducted at higher temperatures and shorter contact times than they can be in delayed coking. Moreover, these conditions result in decreased yields of coke greater quantities of more valuable Hquid product are recovered in the fluid coking process. 

Petroleum products may be treated with various solvents for the removal by selective solubility of undesirable constituents or for the recovery of by-products. The solvent and solute must be separated to yield the desired product and to recover the solvent for reuse. The solvents normally boil at a lower temperature than the products from which they are to be removed and so are generally distilled off as overhead products. The pipe stills used for this service may be single-stage or multi-stage units, depending on the service involved. Some solvents can be removed by the use of steam heated stills. In other cases, the high temperature required necessitates the use of fired heaters and vacuum towers. 

The equipment required for the production of cumene is almost identical to that shown in Fig. 1. The recycle column takes the recycle benzene overhead while the cumene is removed as an overhead product of the rerun column. Table VIII shows typical yields from cumene operation. 

In the fourth step, the preprocessor generates plant performance data for the FCC, gas oil hydrocracker, motor reformer and BTX reformer. For each of these process units, the preprocessor calls the appropriate process simulator which computes the usage of equipment and utilities, product yields, and product properties for all base and alternate operations specified by the user. For all of the FCC operations, the feed properties are those of the atmospheric plus vacuum gas oil from the base crude mix blended with a specified fraction of deasphalter overhead. 

Step 1. For this process we must be able to set the production rate of vinyl acetate while minimizing yield losses to carbon dioxide. During the lifetime of the catalyst charge, catalyst activity decreases and the control system must operate under these different conditions. To maintain safe operating conditions, the oxygen concentration in the gas loop must remain outside the explosivity region for ethylene. The azeotropic distillation column must produce an overhead product with essentially no acetic acid and a bottoms product with no vinyl acetate. The absorber must recover essentially all of the vinyl acetate, water, and acetic acid from the gas recycle loop to prevent yield losses in the CCf removal system and purge,... 

The washed alkylate is fed to a series of three distillation columns where benzene, ethylbenzene, and diethyl benzene-triethyl -benzene mixtures are removed as overhead products. The benzene is recycled to the benzene drying column before feeding again to the alkylator. The diethyl benzene mixture is recycled to the transalkylator. The bottoms from the last column is what we call "flux oil." This consists mainly of diphenylethanes. The amount of this material is good measure of the overall process yield. 

The flowchart shown here depicts a multi-unit separation process. Three liquid streams are mixed adiabatically the product stream is pumped through a heater to a distillation column, and the overhead product from the column is partially condensed to yield liquid and vapor products. Using the blocks MIX (mix two streams to form a third), PUMP, HEAT, DISTILL, and CNOS, construct a block diagram for the simulation of this process. 

The heat of reaction is removed by excess ethylene leaving the reactor as an overhead stream. Ethylene is cooled and recycled to the reactor along with fresh ethylene feed. The reaction is conducted under an oxygen-free, anhydrous environment to prevent deactivation of the catalyst. The reaction is maintained at 80°C in order to minimize the potential isomerization of butene-1 to butene-2. Ethylene conversion is about 20 percent per pass and the assumed product yield from this process are 95 percent butene-1 and 5 percent butene-2. 

The overhead product of the third column is an azeotropic mix of higher alcohols, cyclohexane and water which is fed to a second phase separator. The light phase in this separator, consisting essentiaUy of cyclohexane, is recycled to the second column whereas the aqueous phase is fed either to the first column or to the first phase separator. The diagram does not show the equipment to handle the cyclohexane and to remove the residual alcohol from the waste water. This plant arrangement yields a product containing less than 0.1 wt. % of water. 

A fifty percent vaporized feed (Xg = 0.40) is to yield an Xo and Xg of 0.95 and 0.05. The columns internal reflux at the top (L/V) is 0.818. A side stream is taken from the second stage from the top at rate equal to that of the overhead product. Find the total number of stages and the appropriate mole fractions associated with the side stream. The system s vapor-liquid equilibrium data are... 

The owner specifies the ASTM distillations for the side-streams down through heavy distillate and the ASTM end point of the overhead product. He may also specify the ASTM initial point of the atmospheric gas oil, but, if not, this shall be determined by the designer. The designer must also determine the TBP cut point between the overhead and the lightest sidestream. These specifications are used to estimate yields by the following procedure. 

A third alternate is to yield the overhead product as two phases, their composition being determined by making a flash calculation at the appropriate temperature dictated by the available cooling media at this maximum operating pressure level. 

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