Vapor stream compositions

Stream Lq is an absorbent used to absorb heavier components in a light hydrocarbon vapor stream Vg in a five-stage absorber. The absorbent and inlet vapor stream compositions, and the component relative volatilities are given below ... 

Now, we need to turn to converting the concentrations into appropriate units. Since the total flowrates are given in terms of mass, a unit that expresses the concentration in terms of mass of the components would be most useful. The vapor stream compositions are given as mass percents, which works well with the units of flow. However, the liquid phase concentration given in terms of a molarity is not useful for finding a mass flow rate of ethanol (or of water). Hence we must convert the concentration to something more useful. 

Vapor stream compositions that do not reflect the heavier components in the sample. Half the pentane and most of the hexane condense out in the gas sample bladder, as the bladder cools waiting for the chemist to run the gas through the chromatograph. 

The temperature and composition of each feed stream and the stream ratios are specified along with a common feed pressure (significant only for the vapor stream) and the flash pressure. For an isothermal flash the flash temperature is also specified. Resulting vapor and liquid compositions, phase ratios, vaporization equilibrium ratios, and, for an adiabatic flash, flash temperature are returned. 

NTU (Number of Transfer Units) The NTU required for a given separation is closely related to the number of theoretical stages or plates required to cariy out the same separation in a stagewise or plate-type apparatus. For equimolal counterdiffusion, such as in a binary distillatiou, the number of overall gas-phase transfer units Nqg required for changing the composition of the vapor stream from yi to yo is... 

Detonation arresters are typically used in conjunction with other measures to decrease the risk of flame propagation. For example, in vapor control systems, the vapor is often enriched, diluted, or inerted, with appropriate instrumentation and control (see Effluent Disposal Systems, 1993). In cases where ignition sources are present or pre-dic table (such as most vapor destruct systems), the detonation arrester is used as a last-resort method anticipating possible failure of vapor composition control. Where vent collec tion systems have several vapor/oxidant sources, stream compositions can be highly variable and... 

For partial condenser systems, the pressure can be controlled by manipulating vapor product or a noncondensible vent stream. This gives excellent pressure control. To have a constant top vapor product composition, the condenser outlet temperature also needs to be controlled. For a total condenser system, a butterfly valve in the column overhead vapor line to the condenser has been used. Varying the condenser cooling by various means such as manipulation of coolant flow is also common. 

Both liquid and vapor products are withdrawn, with liquid reflux composition being equal to liquid product composition. Note that on an equilibrium diagram the partitd condenser liquid and vapor stream s respective compositions are in equilibrium, but only when combined do they represent the intersection of the operating line with the 45° slope (Figure 8-14). 

It is undesirable in the North Sea to have more than two product streams—crude oil, and gas--leaving the production platform. All of the components contained in the producing well stream must leave the platform, or be consumed as fuel. Depending on the well stream composition, it is possible a combination of low crude oil vapor pressure and gas hydrocarbon dewpoint specifications, with limitations in separation selectivity, may result In a third product stream of intermediate (NGL) compo-nents which cannot be put into either the oil or gas streams. As previously discussed, a separate NGL pipeline system or offshore storage and loading of NGL will be uneconomic in the North Sea, and this factor will tend to encourage development of North Sea oil pipeline systems on a high vapor pressure crude basis. 

For the Statfjord well stream composition It Is capable of producing a crude oil meeting vapor pressure requirements for offshore tanker loading and also a gas with a hydrocarbon dewpoint suitable for pipeline transmission. 

Table 1 gives the components present in the crude DDSO and their properties critical pressure (Pc), critical temperature (Tc), critical volume (Vc) and acentric factor (co). These properties were obtained from hypothetical components (a tool of the commercial simulator HYSYS) that are created through the UNIFAC group contribution. The developed DISMOL simulator requires these properties (mean free path enthalpy of vaporization mass diffusivity vapor pressure liquid density heat capacity thermal conductivity viscosity and equipment, process, and system characteristics that are simulation inputs) in calculating other properties of the system, such as evaporation rate, temperature and concentration profiles, residence time, stream compositions, and flow rates (output from the simulation). Furthermore, film thickness and liquid velocity profile on the evaporator are also calculated. 

Assume that two streams leave the process a liquid water stream at rate ndotUq and a vapor stream at rate ndotvap. Apply mole balances around the cooler to calculate the exit composition of the vapor phase. 

In case of heat removal or addition, there is no q-line. In such a case, the second point thet is used to construct the minimum-reflux component balance line is the point on the equilibrium curve representing the compositions of the liquid and vapor stream leaving the heat-addition or heat-removal stage. 

For a total condenser, the vapor composition used in the equilibrium relations is that determined during a bubble point calculation based on the actual pressure and liquid compositions found in the condenser. These vapor mole fractions are not used in the component mass balances since there is no vapor stream from a total condenser. It often happens that the temperature of the reflux stream is below the bubble point temperature of the condensed liquid (subcooled condenser). In such cases it is necessary to specify either the actual temperature of the reflux stream or the difference in temperature between the reflux stream and the bubble point of the condensate. 

Reactive distillation is in theory a simpler process than extractive distillation, but it has yet to be demonstrated experimentally. There are two key differences between reactive and extractive distillation. First, unlike the extractive process, the HI, azeotrope is not broken, so the composition in both the liquid and vapor phases is the same. Second, the reactive process must be conducted under pressure. Figure 4.7 shows a schematic of the reactive distillation flow sheet, and the processing conditions are listed in table 4.4. In this process, azeotropic HI, is distilled inside a pressurized reactive column and the HI gas within the HI vapor stream is decomposed catalytically, resulting in a gas mixture of HI, Ij, H2, and H2O. To accomplish this, the HI feed from Section I is first heated to 262°C from 120°C and is then fed into the reactive column. At the bottom of the column, the HI is brought to a boil at around 310°C, and this boiling HI vapor results in an equilibrium vapor pressure of 750 psi inside the distillation column. 

Inside the column a liquid stream flows downward and a vapor stream rises. At each point in the column some of the liquid vaporizes and some of the vapor condenses. The vapor leaving the top of the column, which contains 97 mole% benzene, is completely condensed and split into two equal fractions one is taken off as the overhead product stream, and the other (the reflux) is recycled to the top of the column. The overhead product stream contains 89.2% of the benzene fed to the column. The liquid leaving the bottom of the column is fed to a partial reboiler in which 45% of it is vaporized. The vapor generated in the reboiler (the boilnp) is recycled to become the rising vapor stream in the column, and the residual reboiler liquid is taken off as the bottom product stream. The compositions of the streams leaving the reboiler are governed by the relation... 

A vapor stream that is 65 mole% styrene and 35 mole% toluene is in equilibrium with a liquid mixture of the same two species. The pressure in the system is 150 mm Hg absolute. Use Raoull s law to estimate the composition of the liquid and the system temperature. 

A hydrocarbon mixture is distilled, producing a liquid and a vapor stream, each with a known or calculable flow rate and composition. The energy input to the distillation column is provided by condensing saturated steam at a pressure of 15 bar. At what rate must steam be supplied to process 2000 mol/h of the feed mixture ... 

Benzene (B) and chlorobenzene (C) are being separated in a distillation column. Vapor and liquid streams, each containing both species, are fed to one of the trays of the column, and liquid and vapor streams are taken off the tray. The tray functions as an ideal stage (see Problem 6.63) the effluent streams are in equilibrium at temperature T and pressure P, with compositions related by Raoult s law. Equation 6.4-1. 

It is convenient to carry out the analysis in terms of equilibrium stages. In an equilibrium stage (theoretical plate), the liquid and vapor streams leaving the stage are taken to be in equilibrium, and their compositions are determined by the vapor-liquid equilibrium relationship for the system (see Chapter 8). In terms of equilibrium constants... 

In an equilibrium flash process, a feed stream is separated into liquid and vapor streams at equilibrium. The composition of the streams will depend on the quantity of the feed vaporized (flashed). The equations used for equilibrium flash calculations are developed in this section, and a typical calculation is shown in Example 11.1. 

These equations are linear, with slopes L/V and L /V. They are referred to as operating lines and give the relationship between the liquid and vapor compositions between stages. For an equilibrium stage, the compositions of the liquid and vapor streams leaving the stage are given by the equilibrium relationship. 

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