Synthesis stream compositions

The components involved in this example are proprietary, but the results are general (Siirola, 1981). During the species allocation stage of the process synthesis procedure, it was determined that each species of a particular four-component stream was required to be relatively pure at four different destinations. The components are liquids at ambient temperatures, have about equal relative volatility differences, and form no azeotropes. Distillative separation methods were selected to resolve all composition property differences. The feed stream composition was dominated (about 70%) by the heaviest component (D). 

Zirconate pyrochlores have a low isomorphic capacity with respect tetravalent actinides. However the amount of isomorphic substitution can be increased by coupled substitution of Ca, according to the scheme 2REE = An" -i- Ca. Production of single phase ceramic can be attained only for actinide waste streams with rather simple chemical compositions. In the case of a complex waste stream composition, extra phases occur [129]. Finally, zirconate matrices require high temperatures for their synthesis. In order to prepare REE-zirconates from oxide mixtures, sintering at 1500-1600 for about 50 hours is required... 

An overview of some commercially used processes with related synthesis conditions is given in Table 3.1. The listed NH3/CO2 ratios refer to the stream composition at reactor inlet... 

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. 

The CHARMEN synthesis problem can be stated as follows Given a number Nr of waste (rich) streams and a number Ns of lean streams (frtiysical and reactive MSAs), it is desired to synthesize a cost-effective network of physical and/or reactive mass exchangers which can preferentially transfer certain undesirable species from the waste streams to the MSAs. Given also are the flowrate of each waste stream, G,, its supply (inlet) composition, yf, and target (outlet) composition, y/, and the supply and target compositions, Xj and jc for each MSA. In addition, available for service are hot and cold streams (process streams as weU as utilities) that can be used to optimize the mass-exchange temperatures. 

The composition and relative quantity of any part of the product stream returned to the reactor in admixture with the synthesis gas... 

The synthesis gas is compressed in a two-stage compressor with interstage cooling to 92.7 bar and combined with a recycle stream that is 30,660 kmol/h with a composition that is quite different from that of the synthesis gas. The inert components (nitrogen and methane) are allowed to build up to fairly high levels (24.3 mol% methane, 3.8 mol% nitrogen) so that the losses of reactants in the vent stream are kept small. The vent stream is only 893 kmol/h. 

An additional advantage of using microfluidic devices, which we do not have the space to discuss in detail here, is the absence of turbulence (Koo and Kleinstreuer, 2003). In the context of nanoparticle synthesis, turbulence gives rise to unpredictable variations in physical conditions inside the reactor that can influence the nature of the chemical product and in particular affect the size, shape, and chemical composition. In microfluidic devices, turbulence is suppressed (due to the dominance of viscous over inertial forces) and fluid streams mix by diffusion only. This leads to a more reproducible reaction environment that may in principle allow for improved size and shape control. 

Partial oxidation has more recently attracted attention because of its ability to utilize the least valuable portion of the crude oil barrel (3). Partial oxidation of residual oil generates synthesis gas with a hydrogen to carbon oxides ratio of about 1 1. To adjust the synthesis gas to the required composition, a portion of the gas stream is sent to a shift converter where CO and water are converted to hydrogen and CO2 according to the water gas shift reaction ... 

The present treatment of the conventional process will be based on the process diagram presented in Figure 1, which represents a steam reformer coupled with an ammonia synthesis plant [6], This is one of the two cases, which were considered in the project. The other was the use of the produced hydrogen as fuel in combined cycle gas turbines. In this chapter, the steam reforming part will be treated only, but some comments on the ammonia plant will be made, in view of the composition of the product stream leaving the steam reformer. 

Figure 2.14 illustrates the overall approach by pinch-point analysis. The first step is extraction of stream data from the process synthesis. This step involves the simulation of the material-balance envelope by using appropriate models for the accurate computation of enthalpy. On this basis composite curves are obtained by plotting the temperature T against the cumulative enthalpy H of streams selected for analysis, hot and cold, respectively. Two aspects should be taken into account ... 

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