Stage calculations separation specifications

A wet gas reservoir produces 170,516 scf/STB of 0.646 specific gravity separator gas and 64.7°API stock-tank liquid. The separator operates at 555 psia and 89°F. The separator system is two-stage. Calculate the specific gravity of the reservoir gas. 

EXAMPLE 7-4 A wet gas produces through a three-stage separator system. The primary separator produces 61,015 scflSTB of 0,669 specific gravity gas and the second-stage separator produces 1,002 scf/STB of 0.988 specific gravity gas. Stock-tank oil gravity is 60.7°API. The primary separator operates at 900 psia and 73°F, and the second separator operates at 75 psia and 74°F. Calculate the specific gravity of the reservoir gas. 

A process stream contains light species 1 and heavy species 2. A relatively pure liquid stream containing mostly 2 is desired, obtained by a single-stage liquid/vapor separation. Specifications on die equilibrium composition are X = 0.002 and yi = 0.950. Use data given below to determine T(K) and P(bar) for die separator. Assiune diat Eq. (10.5) applies die calculated P should validate diis assmnption. Data ... 

A distillation column separates the feed stream shown below into butanes in the distillate and pentanes in the bottoms. The relative volatilities (assumed constant) and the separation specifications are also given. Use the first Fenske equation to calculate the minimum number of stages that can meet the specs at total reflux. With an average A -valuc of isopentane A 3 = 0.8, use the second Fenske equation to calculate all the component flow rates in both products. Does this value of produce component flow rates consistent with total flow rates ... 

The Lewis-Matheson method is also an equation-tearing procedure. It was formulated according to the Case I variable specification in. Table 6.2 to determine stage requirements for specifications of the separation of two key components, a reflux ratio and a feed-stage location criterion. Both outer and inner iterations are required. The outer loop tear variables are the mole fractions or flow rates of nonkey components in the products. The inner loop tear variables are the interstage vapor (or liquid) flow rates. The Lewis-Matheson method was widely used for hand calculations, but it also proved often to be numerically unstable when implemented on a digital computer. 

As an example of the procedure, consider the case of starting at the top of the column. Streams D and Lm. I and their compositions are determined by the separation specification and the assigned reflux ratio. This then provides the flow and composition of the vapor leaving the top stage N. Equation (5.3-12) gives the composition of the liquid on the top trey, Xn- The temperature of the top tray may be obtained from a dew point calculation on the vapor composition y r. 

Simple analytical methods are available for determining minimum stages and minimum reflux ratio. Although developed for binary mixtures, they can often be applied to multicomponent mixtures if the two key components are used. These are the components between which the specification separation must be made frequendy the heavy key is the component with a maximum allowable composition in the distillate and the light key is the component with a maximum allowable specification in the bottoms. On this basis, minimum stages may be calculated by means of the Fenske relationship (34) ... 

Equilibrium data and material-and heat-balances to determine the number of equilibrium stages (theoretical plates or transfer units) required for the desired separation. The required height of the column can be calculated if data are available for the specific rate of transfer of material between the two phases, expressed in terms of the plate-efficiency or the height of one transfer unit. 

Compare your answers with the laboratory measured specific volume of reservoir liquid at bubble point, 0.0353 cu ft/Ib. 13-18, The gas-liquid equilibrium calculations for a two-stage separation of a retrograde gas have been completed. Results are given below. 

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