Material balance optimization

Although dynamic responses of microbial systems are poorly understood, models with some basic features and some empirical features have been found to correlate with actual data fairly well. Real fermentations take days to run, but many variables can be tried in a few minutes using computer simulation. Optimization of fermentation with models and reaf-time dynamic control is in its early infancy however, bases for such work are advancing steadily. The foundations for all such studies are accurate material Balances. 

Isoprene does not participate in the reaction under the above-optimized conditions. The combination of Ni(cdt) and c-Cy3P promotes the reaction. Unfortunately, however, the reaction results in a very complex mixture consisting of 1 1 and 1 2 adducts of acetaldehyde and isoprene. The 1 1 adducts (8a,b) are the minor products (Eq. 2) [12]. Except for 8e, all the products are out of material balance (vide supra, requiring one molecule of H2) and it is difficult to give any mechanistic rationale for their formation. 

Figure 26.53 presents a superstructure for the design of an effluent treatment system involving three effluent streams and three treatment processes17. The superstructure allows for all possibilities. Any stream can go to any effluent process and potential bypassing options have been included. Also, the connections toward the bottom of the superstructure allow for the sequence of the treatment processes to be changed. To optimize such a superstructure requires a mathematical model to be developed for the various material balances for the system and costing correlations included. Such a model then allows... 

The unit ratio material balance is often included in the scope. For discussion of this, see Chapter 4. Any information that might be useful for designing equipment of optimizing operating conditons should also be included. 

In many cases the optimization of the energy exchange systems may require a modification of the proposed operating conditions as well as the material balance. 

In this chapter, we first consider uses of batch reactors, and their advantages and disadvantages compared with continuous-flow reactors. After considering what the essential features of process design are, we then develop design or performance equations for both isothermal and nonisothermal operation. The latter requires the energy balance, in addition to the material balance. We continue with an example of optimal performance of a batch reactor, and conclude with a discussion of semibatch and semi-continuous operation. We restrict attention to simple systems, deferring treatment of complex systems to Chapter 18. 

At macroscopic level, the overall relations between structure and performance are strongly affected by the formation of liquid water. Solution of such a model that accounts for these effects provides full relations among structure, properties, and performance, which in turn allow predicting architectures of materials and operating conditions that optimize fuel cell operation. For stationary operation at the macroscopic device level, one can establish material balance equations on the basis of fundamental conservation laws. The general ingredients of a so-called "macrohomogeneous model" of catalyst layer operation include ... 

The energy optimization VIP is most beneficial for processes where energy and related capital expense are a relatively large fraction of the total operating cost. The benefits result in reduced energy requirements and environmental emissions in balance with project economics. This VIP should be implemented in the feasibihty phase (FEL-2) when preliminary PFDs and heat and material balances are available. 

A significant part of developing a model used for other than determining static sets of heat and material balances (which are sufficient for some model objectives, such as providing the basis for new plant design) is specifying which variables are independent and which are dependent. Far more variables are dependent variables than are independent in essentially all models. For simulation and optimization... 

Control objectives for a chemical process originate from certain regulation tasks (i.e. product quality control, material balance control, safety, environmental regulations, etc.) and economic objectives (i.e. optimizing the economic performance). Such a classification of control objectives automatically formulates the different design activities for the regulatory and optimizing control structures. 

Also Senkan et al. (6) and Schehl et al. (3) have shown that for methanation, the material balance equation can be solved independently of the energy balance equation in diffusion-limited cases, because the effects of temperature variation on gas properties essentially cancel each other. It is therefore justified to consider the isothermal model for the purpose of yield optimization. 

At the end of the Level 4, the result is a close-to-optimum process flowsheet together with a consistent material balance. The next levels will have as a goal the solution of the problems related with the optimal use of energetic resources and material utilities, as well as with waste minimization and plantwide process control. 

The economic potential may be used to optimize the flowsheet with respect to the material balance. After Level 4 the mass-balance envelope is closed by completing the synthesis of reaction and separation systems. The economic potential EP4 becomes ... 

The second issue regards the optimal plantwide material balance. It is clear that the raw materials must be fed only in amounts required by the target production and selectivity. The control structure of fresh feeds should allow flexibility, within predefined limits, both in production rate and selectivity, but avoiding large variation of recycles that might upset some units (snowball effect). 

Optimizing product recovery (material balance optimization)... 

Material balance optimization. Figure 3.1a shows the concentration of the light key at the distillate and bottoms at a fixed separation S, where... 

Figure 3.2 Material balance optimization at a fixed separation S (or reflux ratio). (Reprinted by permission. Copyright Instrument Society of America, 1978, from...

The optimization described so far is referred to as material balance optimization, or D versus B optimization. At a fixed separation, the capital and utility costs of the column are relatively insensitive to the... 

Figure 3.3 Material balance optimization at a fixed separation S, Numbers marked on curve show the percent recovery of light component in the distillate stream. (Reprinted with permission from W, R, Fiaher, M. F. Doherty, and J. H. Douglas, Ind. Eng. and Chan. Proc. Deg. and Deuel., Vol, 24, p. 805, Copyright (1985), American Chemical Society.)...

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