Material balance recycle

Life cycle assessment, energy and raw material balances, recycling and reuse Reduction of emissions during the production and the use of wood-based panels... 

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. 

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). 

Closed-Circuit Milling In closed-circuit miUing the taiUngs from a classifier are mixed with fresh feed and recycled to the miU. Calculations can be based on a material balance and an expUcit sohi-... 

Simple combinations of reactor elements can be solved direc tly. Figure 23-8, for instance, shows two CSTRs in series and with recycle through a PFR. The material balances with an /i-order reaction / = /cC are... 

As can be seen for infinite recycle ratio where C = Cl, all reactions will occur at a constant C. The resulting expression is simply the basic material balance statement for a CSTR, divided here by the catalyst quantity of W. On the other side, for no recycle at all, the integrated expression reverts to the usual and well known expression of tubular reactors. The two small graphs at the bottom show that the results should be illustrated for the CSTR case differently than for tubular reactor results. In CSTRs, rates are measured directly and this must be plotted against the driving force of... 

The reuse or recycling of wastes can reduce the amount of freshwater and raw materials required for a process. While looking at the inputs to unit operations, think about the opportunities for reusing and recycling outputs from other operations. Note that if reused wastes are not properly documented, double-counting may occur in the material balance, particularly at the process or complete plant level that is, a waste will be quantified as an output from one process and as an input to another. 

The material balance in a constant volume chemostat is derived based on cell balance as shown in the following equations. Material balance in a chemostat with recycle, pcell ... 

The material balance around the mixing point of a loop reactor is given by Equation (4.21) for the case of constant fluid density. How would you work a recycle problem with variable density Specifically, write the variable-density counterpart of Equation (4.21) and explain how you would use it. 

The application of a selective pyrolysis process to the recovery of chemicals from waste PU foam is described. The reaction conditions are controlled so that target products can be collected directly from the waste stream in high yields. Molecular beam mass spectrometry is used in small-scale experiments to analyse the reaction products in real time, enabling the effects of process parameters such as temperature, catalysts and co-reagents to be quickly screened. Fixed bed and fluidised bed reactors are used to provide products for conventional chemical analysis to determine material balances and to test the concept under larger scale conditions. Results are presented for the recycling of PU foams from vehicle seats and refrigerators. 12 refs. 

The objectives of this study were to compare the yields of cold-pressed essential oil, water consumption, material balance and efficiency of the process in a typical citrus peel oil recovery plant with and without recycling system. The different emulsions and aqueous discharges from these processes were also characterized. 

Table 1. Material balance in the non-recycling and recycling lemon peel oil recovery systems...

Without recycle, the material balances on a series of processing steps can be carried out sequentially, taking each unit in turn the calculated flows out of one unit become the feeds to the next. If a recycle stream is present, then at the point where the recycle is returned the flow will not be known as it will depend on downstream flows not yet calculated. Without knowing the recycle flow, the sequence of calculations cannot be continued to the point where the recycle flow can be determined. 

The solution of more complex material balance problems involving several recycle loops is discussed in Chapter 4. 

Material balance calculations on processes with by-pass streams are similar to those involving recycle, except that the stream is fed forward instead of backward. This usually makes the calculations easier than with recycle. 

The procedure is based on the theory of recycle processes published by Nagiev (1964). The concept of split-fractions is used to set up the set of simultaneous equations that define the material balance for the process. This method has also been used by Rosen (1962) and is described in detail in the book by Henley and Rosen (1969). 

Hint start the material balance at the reactor inlet (after the addition of the recycle streams) and use a basis of 100 kmol/h benzene at this point. 

Two other problems that fit this category are calculating the number of stages in a multicomponent distillation problem, and obtaining the material balance when complicated recycle operations occur. 

Sherrington (S10) has presented a static model of the granulation loop operating in the snowballing mode. The model combines the solution phase theory in Eq. (106) with the material balance across the granulator. The recycle ratio defined as recycle/raw solid feed, is given by... 

If the assumption that the contaminant mass in the wastewater is relaxed, then the additional raw material in the form of the contaminant mass has to be accounted for. The wastewater in this case not only supplements the water in the raw material, but also any other raw materials used in product formulation. The raw material balance given in constraint (8.1) is reformulated to account for the additional raw material source. Constraint (8.1) is split into a water balance and a raw material balance for the other components required in product formulation. The water balance is given in constraint (8.52). The balance for the other components used in the product formulation is given in constraint (8.53). Due to the fixed ratio of water and other components in product formulation and the fixed batch size, the amount of water and the amount of other components are fixed. Therefore, in constraints (8.52) and (8.53) the amount of water and amount of other raw material is fixed. The water balance, in constraint (8.52), states that the amount of water used in product is comprised of freshwater, water from storage and directly recycle/reused water. Constraint (8.53), the mass balance for the other components, states that the mass of other components used for product is the mass from bulk storage, the mass in directly recycled/reused water and the mass in water from storage. 

Plug flow reactor (PFR) with recycle. The recycle reactor is characterized by a non-zero value of R, that is the ratio between the mass flow rate of the recycled stream and the feeding rate Q. The material balance reads for this case as... 

A recycle PFR, operating at steady-state for the reaction A +. . - products, is shown schematically in Figure 15.6, together with associated streams and terminology. At the split point S, the exit stream is divided into the recycle stream (flow rate RqJ and the product stream (flow rate q,), both at the exit concentration cA1. At the mixing point M, the recycle stream joins the fresh feed stream (flow rate q0, concentration cAo) to form the stream actually entering the reactor (flow rate (1 + R)q0, concentration ca o)-The inlet concentration c Ao may be related to cAo, cA1, and R by a material balance for A around M ... 

The volume of the recycle PFR may be obtained by a material balance for A around the differential control volume dV. Equating molar flow input and output, we obtain... 

Notation and material balances for recycle operation are stated in problems P4.06.01 and P4.06.02. An adiabatic operation is studied in P4.06.08. 

A yeast is cultivated in a CSTR with partial recycle of the product. Effluent from the reactor has concentrations Cx and Cs and goes to a separator where a product stream, F, has concentrations 0.3CX and Cs. The recycle stream, R, likewise has concentration Cs and a material balance on X as Recycle = (F+R)CX -0.3FCX = (0.7F+R)CX = RCxr (1)... 

This establishes the recycle concentration if desired. Material balance on the cell production with zero in the fresh feed,... 

---