Mass pinch analysis

Martinez-Hemandez, E., Sadhnkhan, J. and Campbell, G.M. (2013) Integration of bioethanol as an in-process material in biorefineries nsing mass pinch analysis. Appl. Energy, 104, 517-526. 

As can be seen from Fig, 3.7, the pinch decomposes the synthesis problem into two regions a rich end and a lean end. The rich end comprises all streams or parts of streams richer than the pinch composition. Similarly, the lean end includes all the streams or parts of streams leaner than the pinch composition. Above the pinch, exchange between the rich and the lean process streams takes place. External MSAs are not required. Using an external MSA above the pinch will incur a penalty of eliminating an equivalent amount of process lean streams from service. On the other hand, below the pinch, both the process and the external lean streams should be used. Furthermore, Fig. 3.7 indicates that if any mass is transferred across the pinch, the composite lean stream will move upward and, consequently, external MSAs in excess of the minimum requirement will be used. Therefore, to minimize the cost of external MSAs, mass should not be transferred across the pinch. It is worth pointing out that these observations are valid only for the class of MEN problems covered in this chapter. When the assumptions employed in this chapter are relaxed, more general conclusions can be made. For instance, it will be shown later that the pinch analysis can still be undertaken even when there are no process MSAs in the plant. The pinch characteristics will be generalized in Chapters Five and Six. 

Integration of heat and power Mass integration to prevent waste Pinch analysis, source sink diagrams... 

Pinch analysis can optimize the combined heat and mass exchanger network and chemical reactor systems with heat exchangers. 

This paper has presented and tested a design philosophy for the synthesis of mass exchange networks whereby an MINLP approach is integrated with pinch analysis tools. At the heart of the integration is the use of pinch-based total cost targets to evaluate the optimality of MINLP solutions and driving force diagrams to identify different initial solution structures. 

The target for the flow rate of purified CO to make the whole network feasible is found from COj pinch analysis. The mass balance of the purifier assumes 98% CO recovery. The purified stream is added to the table of source data for the analysis, and its flow rate is varied until a pinch point and only positive values are shown in the surplus diagram. The pinched purity profile and CO surplus diagram after the introduction of the purification unit are shown in Figure 9.10. Figure 9.10a shows that the target for the lowest amount of 92% (by mass) CO stream is 5164kgh", in order to make the whole network feasible. 

Another problem of significance is the optimum policy of water recycling. This subject is in itself substantial and cannot be handled here. An economical approach involves optimal allocation of streams, both as flow rates and contaminant concentration. The analysis may be performed systematically with tools based on the concept of water pinch and mass-exchange networks . This subject is treated thoroughly in specialized works, as in the books of El-Halwagi [19] and Smith [20]. A source-sink mapping technique developed around the acrylonitrile plant may be found in the book of Allen and Shoppard [21]. 

For high Da the column is dose to chemical equilibrium and behaves very similar to a non-RD column with n -n -l components. This is due to the fact that the chemical equilibrium conditions reduce the dynamic degrees of freedom by tip the number of reversible reactions in chemical equilibrium. In fact, a rigorous analysis [52] for a column model assuming an ideal mixture, chemical equilibrium and kinetically controlled mass transfer with a diagonal matrix of transport coefficients shows that there are n -rip- 1 constant pattern fronts connecting two pinches in the space of transformed coordinates [108]. The propagation velocity is computed as in the case of non-reactive systems if the physical concentrations are replaced by the transformed concentrations. In contrast to non-RD, the wave type will depend on the properties of the vapor-liquid and the reaction equilibrium as well as of the mass transfer law. 

The annual total cost was analyzed considering 3 variables (i) total water flowrate (see Fig. 5a, b) (ii) freshwater flowrate (see Fig. 5c) and (ii) water reuse flowrate (see Fig. 5d). This evaluation was done considering the total annual cost variation respect to the total flowrate into two steps. First, an interval of water reuse possibilities was observed, according to Fig. 5a, in which the total water flowrate varies from 132.7 to 132.85 t h In this interval the total cost decreased linearly until the minimum Pinch flow rate. Below the 132.7 t h there are no viable reuse networks. In a second analysis it was observed that above 132.85 t h the total annual cost increased, as can be observed in Fig. 5b. It means that in this interval there are no possibilities of reuse and the process operation is between the minimum necessary limits for the key component mass transfer until the maximum available value to the industrial plant operation. 

Practically, all the experimental mass transfer rate data available in the literature are for unpinched conditions the reason being of course that experiments near pinches are very hard to carry out. Furthermore, a large fraction of the theoretical analysis in the literature refers to the irreversible limit, which is, of course, as far away from a pinch as possible. The following question arises how much of the available information is useful for predicting mass transfer rates near a pinch, i.e. under those conditions which are the most relevant for industrial design ... 

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