Flow rate flowchart

Figure 6.7 is a popular flowchart for determining steam flow rate, pipe size, steam pressure, or steam velocity in a given pipe. Using this chart, the designer can determine any one of the four variables listed above when the other three are known. In solving a problem on the chart in Fig. 6.7, use the steam-quantity lines to intersect pipe sizes and the steam-pressure lines to intersect steam velocities. Here are two typical applications of this chart. 

Some valve manufacturers use the valve-flow coefficient C for valve sizing. This coefficient is defined as the flow rate, in gal/min, through a valve of given size when the pressure loss across the valve is 1 lb/in2. Tabulations such as Table 6.19 and flowcharts such as Fig. 6.9 incorporate this flow coefficient and are somewhat easier to use. Their accuracy equals that of the flow-coefficient method. 

Suppose you have balanced a process and the amount or flow rate of one of the process streams is n. You can scale the flowchart to make the amount or flow rate of this stream by multiplying all stream amounts or flow rates by the ratio n2/ni, You cannot, however, scale masses or mass flow rates to molar quantities or vice versa by simple multiplication conversions of this type must be carried out using the methods of Section 3.3b. 

Choose a basis of calculation—an amount or flow rate of one of the feed or product streams—and then draw and label the flowchart. 

We will arbitrarily choose a basis of 100 kg of the 20% feed solution. (We could also have chosen a flow rate of 100 Ibm/min of the 8% product solution or 10 tons of diluent water. The final results do not depend on the basis chosen since we are only asked to find ratios of stream amounts.) The flowchart appears as follows ... 

The flowchart is completely labeled if you can express the mass or mass flow rate (or moles or molar flow rate) of each component of each stream in terms of labeled quantities. Labeled variables for each process stream should therefore include either... 

Every component mass flow rate in every process stream can be expressed in terms of labeled quantities and variables. (Verify this statement.) For example, the flow rates of toluene (kg T/h) in the feed, overhead, and bottom streams are, respectively. 0.55mi, 2(1 - yB2). and mT3 The flowchart is therefore labeled completely. 

Write expressions for the quantities requested in the problem statement. In terms of the quantities labeled on the flowchart, the quantities to be determined are m2 (the overhead product mass flow rate), m3 = mss + mxs (the bottom product mass flow rate), xq = mB3/ 3 (the benzene mass fraction in the bottom product), and xt = 1 -. rs (the toluene mass fraction). Once we determine m2. B3, and mx3, the problem is essentially solved. 

A labeled flowchart of a continuous steady-state two-unit process is shown below. Each stream contains two components. A and B, in different proportions. Three streams whose flow rates and/or compositions are not known are labeled 1,2. and 3. 

A process stream on a flowchart is completely labeled if values or variable names are assigned to one of the following sets of stream variables (a) total mass flow rate or total mass and component mass fractions (b) mass flow rates or masses of each stream component (c) total molar flow rate or total moles and component mole fractions and (d) molar flow rates or moles of each stream component. If a total amount or flow rate or one or more component fractions are known for a stream, use (a) or(c) to incorporate the known values into the labeling. If neither the total nor any fractions are known, using (b) or (d) (component amounts or flow rates) often leads to easier algebra. Volumetric quantities should be labeled only if they are either given or requested in the problem statement. A flowchart is completely labeled if every stream is completely labeled. 

A basis of calculation for a process is an amount or flow rate of one of the process streams. If two or more stream flow rates or amounts ate given in the problem statement, they constitute the basis of calculation. If one is given, it may be assumed as a basis but it may also be convenient to assume another basis and then scale the flowchart to the specified value. If no flow rates or amounts are given, assume one as a basis, preferably an amount of a stream with known composition. 

Draw and completely label a process flowchart. Include in the labeling the molar flow rates and SO2 mole fractions of the gas streams and the mass flow rates and SO2 mass fractions of the liquid streams. Show that the scrubber has zero degrees of freedom. 

If a PVT calculation is part of a material balance problem and a volume (or volumetric flow rate) is either given or required for a process stream, label both n (or h) and V (or V) on the flowchart and count a density relationship (for solids and liquids) or an equation of state (for gases) as an additional relation in the degree-of-fireedom analysis. 

It is advisable to determine the molar amounts or flow rates of the components of all feed and product solutions before drawing and labeling the flowchart. In this case... 

A flowchart for a program to implement this procedure is shown in Figure P8.1. Write the program and test it by estimating the flash lank temperature and product stream flow rates (mol/s) and compositions (mole fractions) for the flash vaporization of one mol/s of an equimolar mixture of n-pentane (A) and n-hexane (B), if the feed temperature is llOX and the tank pressure is 1.0 atm. 

To perform energy balance calculations on a reactive system, proceed much as you did for nonreactive systems (a) draw and label a flowchart (b) use material balances and phase equilibrium relationships such as Raoult s law to determine as many stream component amounts or flow rates as possible (c) choose reference states for specific enthalpy (or internal energy) calculations and prepare and fill in an inlet-outlet enthalpy (or internal energy) table and (d) calculate AH (or AC/ or A/C), substitute the calculated value in the appropriate form of the energy balance equation, and complete the required calculation. 

Suppose the oxygen gas fed to the reactor and the oxygen in the coal combine with all the hydrogen in the coal (Reaction 3) and with some of the carbon (Reaction 2), and the remainder of the carbon is consumed in Reaction 1. Taking a basis of 1.00 kg coal fed to the reactor and letting o equal the moles of O2 fed, draw and label a flowchart. Then derive expressions for the molar flow rates of the four outlet gas species in terms of hq. (Partial solution h2 = 51,5 - no.)... 

In labeling the flowchart, we have taken advantage of the fact that CO and H2 remain in stoichiometric proportion throughout the process, which cuts down on the number of unknown variables that must be defined if the flow rate of CO is n, the flow rate of H2 must be 2h,. However, this also means that we cannot write independent balances on these two species. We must therefore allow for no more than two independent material balances on each process unit when we do the degree-of-freedom analysis, rather than the three that would normally be allowed when three species are involved in a process. 

The time-dependent mass flow rate is calculated numerically. In doing this the entire process is represented by a sequence of time intervals. Within each of these all quantities are considered as constant. The calculation procedure is shown in the flowchart of Fig. 10.9. Figure 10.10 presents the results. 

Column 2 is a sinple distillation that can be designed by the methods discussed in Chapter 4. Column 1 is considerably more cortplex, but the bubble-point matrix method discussed in Chapter 6 can often be adapted. Since the system is nonideal and K values depend on the solvent concentration, a concentration loop is required in the flowchart shown in Figure 6-1. Fortunately, a good first guess of solvent concentrations can be made. Solvent concentration will be almost constant in the middle section and also in the bottom section except for the reboiler. In the top section of the column, the solvent concentration will very rapidly decrease to zero. These solvent concentrations will be relatively unaffected by the tenperatures and flow rates. The K values can be calculated from Eq. (2-35) with the activity coefficients determined from the appropriate VLE correlation. Process simulators are the easiest way to do these calculations (see appendix to Chapter 81. 

Absorbers, like flash distillation, are equivalent to very wide boiling feeds. Thus, in contrast with distillation, a wide-boiling feed (sum rates) flowchart such as Figure 2-13 should be used. The flow rate loop is now solved first, since flow rates are never constant in absorbers. The energy balance, which requires the most information, is used to calculate new temperatures, since this is done last. Figure 12-13 shows the sum-rates flow diagram for absorbers and strippers when K = K (T, p). If K = Kj (T, p, Xj, X2,. .. Xj,) a concentration correction loop is added. The initial steps are very similar to those for distillation, and usually the same physical properties package is used. 

The fresh feed to the process flows at a rate of60,000 kg/h and contains 25.0 mole% isobutane. 25.0% butylene, and 50.0% -buiane. which is chemically inert in this process. The fresh feed combines with three separate recycle streams, as shown in the flowchart, and the combined stream enters the reactor. Essentially all of the butylene fed to the reactor is consumed. A portion of the reactor effluent is recycled to the reactor inlet and the remainder passes to a decanter, in which the aqueous (sulfuric acid) and hydrocarbon phases are allowed to separate. ITie acid is recycled to the reactor, and the hydrocarbons pass to a distillation column. ITie overhead from the column contains iso-octane and n-butane, and the bottoms product, which is recycled to the reactor, contains only isobutane. The stream entering the reactor contains 200 moles of isobutane per mole of butylene, and 2 kg of 91 wt% H2S04(aq) per kg of hydrocarbon. ITie stream obtained by combining the fresh feed and isobutane recycle contains 5.0 moles of isobutane per mole of butylene. 

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