Recycle of information

The need for simultaneous solution of the design equations implies that there is a recycle of information. Choice of an outlet stream composition as a design variable in... 

If for a set of equations an order of solution exists such that there is no need for the simultaneous solution of any of the equations, the system is said to be acyclic , no recycle of information. 

For many design calculations it will not be possible to select the design variables so as to eliminate the recycle of information and obviate the need for iterative solution of the design relationships. 

Sequential-modular programs in which the equations describing each process unit (module) are solved module-by-module in a stepwise manner and iterative techniques used to solve the problems arising from the recycle of information. 

In the previous section we addressed some of these issues in the context of physical versus empirical models. These issues are also intertwined with the question of model verification what kinds of data are available for determining that the model is a valid description of the process Model building is an iterative process, as shown by the recycling of information in Figure 2.2. 

When the temperature at the outlet of the exchanger on the feed side is specified, the duty of the exchanger is defined and there is no recycle of information. The model thus solves very quickly, but it is necessary to check the results to see that the exchanger design makes sense. 

Measuring process parameters on full-scale plants is notoriously difficult, but is needea for control. Usually few of the important variables are accessible to measurement. Recycle of material makes it difficult to isolate the effects of changes to individual process units in the circuit. Newer plants have more instrumentation, including on-line viscosimeters [Kawatra and Eisele, International ]. Mineral Processing, 22, 251-259 (1988)], mineral composition by on-line X-ray fluorescence, belt feeder weighers, etc., but the information is always incomplete. Therefore it is helpful to have models to predict quantities that cannot be measured while measuring those that can. 

The outlet streams from a unit can feed forward to other units, or backward (recycle). An information flow diagram for a process consisting of three units, with two recycle streams is shown in Figure 4.7. The nomenclature defined in Figure 4.6 is used to show the stream flows. 

Once a consumer has purchased a material made of a polymer, the likelihood of it being recycled is dramatically reduced. In the United States there are three resins that are commonly recycled polyethylene, polypropylene, and polyethylene terephthalate, SPI (The Society of the Plastics Industry) recycling codes, found on the bottom of food containers, provide the consumer with information as to the recyclability of the material. Table 17,1 lists these codes. 

SFA for China Including Processes of Informal Recycling for the Year 2005. 324... 

In previous sections, the most common ways of informal recycling have been introduced. It is known that a computer is not entirely recycled and that it is divided into the most interesting elements before going to the informal recycling processes as reported by Chi et al. [21]. The selection of the interesting elements takes place during the physical dismantling process already introduced in Sect. 3.5. 

The use of a deuterium tracer in this research makes it possible to obtain new information regarding the reactions involved in the formation of these compounds. Since reactions of this type result in a loss of hydrogen donor capability of the solvent, research in this area is important to improve the efficiency of coal hydroliquefaction and the recycleability of the solvent. 

Only a small amount of information has been released by Shell about the recovery and recycle of the special P,0 bound Ni catalyst. Obviously, the overall operation of the SHOP plants is economical but one has to keep in mind that the non-homogeneously catalyzed parts of Shell s integrated system of processes use inexpensive, heterogeneous catalysts. It is to be expected that a large part of these catalysts can be disposed off without any recycling - neither of the metal content nor of the supports. 

From a computational viewpoint, the presence of recycle streams is one of the impediments in the sequential solution of a flowsheeting problem. Without recycle streams, the flow of information would proceed in a forward direction, and the cal-culational sequence for the modules could easily be determined from the precedence order analysis outlined earlier. With recycle streams present, large groups of modules have to be solved simultaneously, defeating the concept of a sequential solution module by module. For example, in Figure 15.8, you cannot make a material balance on the reactor without knowing the information in stream S6, but you have to carry out the computations for the cooler module first to evaluate S6, which in turn depends on the separator module, which in turn depends on the reactor module. Partitioning identifies those collections of modules that have to be solved simultaneously (termed maximal cyclical subsystems, loops, or irreducible nets). 

To execute a sequential solution for a set of modules, you have to tear certain streams. Tearing in connection with modular flowsheeting involves decoupling the interconnections between the modules so that sequential information flow can take place. Tearing is required because of the loops of information created by recycle... 

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