Material balance overall

The design variables originate from the design decisions. At the input/output level, the design variables define the degrees of freedom of the overall material balance. That is why it is impossible to develop a unique material balance for a process, even with the same chemistry. Table 2.3 lists some possible choices. 

The overall material balance gives the relation between the input streams, essentially raw materials, and the output streams, such as products, byproducts, purge and waste. In the first attempt, a simplified approach is useful for framing the main characteristics. Usually the assumptions are  

The preliminary material balance sets the limits for the variables of significance for process performance, namely the minimum material consumption and the maximum yield in products, and from this viewpoint is a kind of ideal material balance. 

The procedure below requires only a spreadsheet. The steps are  

Identify the inlet and outlet streams, as described before. 

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An additional separator is now required (Fig. 4.2a). Again, the unreacted FEED is normally recycled, but the BYPRODUCT must be removed to maintain the overall material balance. An additional complication now arises with two separators because the separation sequence can be changed (see Fig. 4.26). We shall consider separation sequencing in detail in the next chapter. 

Consider the single-stage phase split shown in Fig. 3.1a. Overall material balances and component material balances can be written as... 

Equation (12.29) then represents the material balance on species A, while equation (12.30) represents the overall material balance. The reaction rate... 

The entrainer recovery column takes the distillate stream, from the azeo-column and separates it into a bottoms stream of pure water, and a ternary distillate stream for recycle to column 2. The overall material balance line for column 3 is shown in Figure 19b. This sequence was one of two original continuous processes disclosed in 1915 (106). More recendy, it has been appHed to other azeotropic separations (38,107,108). 

Specify type of condenser. If total (L/i 0), compute L v from overall material balance if partial (L/i = 0), specify V] and compute L v from overall material balance. 

Compute a corresponding new set of Vj tear variables from the following total material balance, which is obtained by combining Eq. (13-74) with an overall material balance around the column ... 

Equation 1 is normally integrated by graphical or numerical means utilizing the overall material balance and the saturated air enthalpy curve. 

When the Freeman and Lewis rate constants are applied to an experimental situation and integrated. Fig. 7 results. This figure shows the same fundamental trends seen in the data. There are some differences, however. The Freeman and Lewis measurements, as presented in their Fig. 2, appear to exceed the available phenol by about 39%. This is probably one reason why Zavitsas et al. state that the Freeman rate constants do not fit the data [80], Flowever, the calculations made using their rate constants do maintain the overall material balance. As presented here, they are not as precise as they could be because the calculation interval has been set at 1 h. Flowever, they are as good as the data at this level. 

Step 7 Write an Overall Material Balance. Remember that the P2 audit focuses on a unit process, but that there are individual unit operations that make up this process. The team will need to develop a series of material balances for each unit operation, and an overall material balance about the entire unit process, to bring closure to a solution of parameters of interest. The individual or component material balances developed may be summed to give a balance for the whole process, production area, or factory. 

Assuming that the densities of the feed, the permeate and the reject are the same, one can write the following overall material balance around the module ... 

It is instructive to consider the equations specifying the system performance. Overall material balance for the RON ... 

General Material Balances. According to the law of conservation of mass, the total mass of an isolated system is invariant, even in the presence of chemical reactions. Thus, an overall material balance refers to a mass balance performed on the entire material (or contents) of the system. Instead, if a mass balance is made on any component (chemical compound or atomic species) involved in the process, it is termed a component (or species) material balance. The general mass balance equation has the following form, and it can be applied on any material in any process. 

The third term on the left side of the equation has significance in reactive systems only. It is used with a positive sign when material is produced as a net result of all chemical reactions a negative sign must precede this term if material is consumed by chemical reactions. The former situation corresponds to a source and the latter to a sink for the material under consideration. Since the total mass of reactants always equals the total mass of products in a chemical reaction, it is clear that the reaction (source/sink) term (R should appear explicitly in the equation for component material balances only. The overall material balance, which is equivalent to the algebraic sum of all of the component balance equations, will not contain any (R term. 

Perform an overall material balance and the necessary component material balances so as to provide the maximum number of independent equations. In the event the balance is written in differential form, appropriate integration must be carried out over time, and the set of equations solved for the unknowns. 

Overall Material Balance Total mass in is equal to total mass out. 

Solution An overall material balance gives -f = -I- bout- The data... 

Confirm that the solutions in Examples 11.10 and 11.11 satisfy an overall material balance. 

Check the overall material balance in all the above exercises. 

The compositions are controlled by regulating reflux flow and boil-up. The column overall material balance must also be controlled distillation columns have little surge capacity (hold-up) and the flow of distillate and bottom product (and side-streams) must match the feed flows. 

Consider the material balance for a simple binary distillation column. A simple column has one feed, two products, one reboiler and one condenser. Such a column is shown in Figure 9.5. An overall material balance can be written as ... 

Figure 7-3 Overall material balance control with intermediate material balance controls in the direction of flow.

Figure 7-4 Overall material balance control in direction opposite to flow.

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