Flowsheet Cycle

Clearly, the time chart shown in Fig. 4.14 indicates that individual items of equipment have a poor utilization i.e., they are in use for only a small fraction of the batch cycle time. To improve the equipment utilization, overlap batches as shown in the time-event chart in Fig. 4.15. Here, more than one batch, at difierent processing stages, resides in the process at any given time. Clearly, it is not possible to recycle directly from the separators to the reactor, since the reactor is fed at a time different from that at which the separation is carried out. A storage tank is needed to hold the recycle material. This material is then used to provide part of the feed for the next batch. The final flowsheet for batch operation is shown in Fig. 4.16. Equipment utilization might be improved further by various methods which are considered in Chap. 8 when economic tradeoffs are discussed. 

The process engineer identifies heat exchange equipment in a process by the operation or function it serves at a particular location in the flow cycle. For example, the bottom vaporizer on a product finishing distillation column is usually termed Finishing Column ReboUer E-16, or Reboiler E-16 the overhead vapor condenser on this column is termed Condenser E-17 etc. The usual operations involved in developing a process flowsheet are described in Table 10-11, or Chapter 1, Volume 1. 

It is clear that the illustrated flowsheet is quite flexible. As shown, pulses can be produced by a 6-way valve. The valves are electrically actuated so a cycled feed can easily be produced. A separate mixture preparation apparatus has been built, so that preparing the various mixtures needed is quick and simple. 

Collector PL520 was selected as the final collector due to its low-frothing properties. After selection of the collector, a series of final locked cycle tests were conducted using the flowsheet shown in Figure 21.10. The final reagent scheme is shown in Table 21.13. 

A depressant system developed for beneficiation of Ta/Nb-Zr ores involves oxalic acid-hydro fluoro silicic acid and depressant SHQ. SHQ is a mixture of a low-molecular-weight acrylic acid and condensation product of disulphonic acid (Suspendol PKK, manufactured by Cognis, Germany). After the development of the final reagent scheme, a series of locked-cycle tests were performed using the flowsheet shown in Figure 23.7. 

Figure 23.7 Final flotation flowsheet used in the continuous locked-cycle tests.

The second part deals with applications of solvent extraction in industry, and begins with a general chapter (Chapter 7) that involves both equipment, flowsheet development, economic factors, and environmental aspects. Chapter 8 is concerned with fundamental engineering concepts for multistage extraction. Chapter 9 describes contactor design. It is followed by the industrial extraction of organic and biochemical compounds for purification and pharmaceutical uses (Chapter 10), recovery of metals for industrial production (Chapter 11), applications in the nuclear fuel cycle (Chapter 12), and recycling or waste treatment (Chapter 14). Analytical applications are briefly summarized in Chapter 13. The last chapters, Chapters 15 and 16, describe some newer developments in which the principle of solvent extraction has or may come into use, and theoretical developments. 

Many variants of the Purex (Plutonium Uranium Reduction Extraction) process23S based on TBP extraction have been developed but a basic outline flowsheet is illustrated in Figure 38. This shows the so-called early split flowsheet most commonly used in existing plants. It involves the separation of the uranium and plutonium using two different back-extractant streams during the first solvent extraction cycle. Additional solvent extraction cycles are then carried out independently on the uranium and plutonium streams to effect further purification. An alternative arrangement is the iate split flowsheet used at the Cap La Hague plant in France, and the... 

Windscale II plant in the UK. In this the uranium and plutonium are back-extracted together in a first cycle of decontamination. They are then separated in a second cycle of solvent extraction and independent back-extraction. The factors affecting the choice of flowsheet type have been reviewed and criticality control is an important consideration in the process design.286... 

More recently a flowsheet has been developed which employs 30% TBP/OK as the solvent.349-446 447 This involves the use of an acid feed to the first cycle to assist in zirconium decontamination and suppress hydrolysis. An acid-deficient partition cycle then follows in which the U-Th separation is effected. A pilot plant (JUPITER) has been constructed at Julich in Germany to process Th02/U02 fuel using this flowsheet. Although a complete separation of thorium, uranium and FPs is possible using TBP in the Thorex process,448 alternative approaches... 

FIGURE 1.8 Conceptual flowsheet of GANEX with a single cycle DIAMEX-SANEX process. 

FIGURE 1.9 Conceptual flowsheet of ARTIST for advanced fuel cycle. 

Fox, O.D., Jones, C.J., Birkett, J.E. et al. 2006. Advanced PUREX flowsheets for future Np and Pu fuel cycle demands. In Separations for the Nuclear Fuel Cycle in the 21st Century. Lumetta, G.J. et al. Eds. ACS Symposium Series Vol. 933, American Chemical Society, Washington, DC, pp. 89-102. 

Birkett, J.E., Carrott, M.J., Fox, O.D. et al. 2007. Controlling neptunium and plutonium within single cycle solvent extraction flowsheets for advanced fuel cycles. J. Nucl. Sci. Technol. 44 (3) 337-343. 

Laurinat, J.E. 2006. SASSE modeling of first cycle neptunium(VI) recovery flowsheet. WSRC-TR-2006-00104, Rev.0. 

FIGURE3.14 TODG A/TBP process flowsheet tested at the FZ J on a surrogate PUREX raffinate. (Courtesy of Modolo, G., Asp, H., Vijgen, H., Malmbeck, R., Magnusson, D., Sorel, C., Global 2007 Advanced Nuclear Fuel Cycles and Systems, September 2007, Boise, ID.)... 

An(III) from Ln(III) in a two-cycle flowsheet. In the first cycle, Ln(III) and An(III) are coextracted by 0.2 M ZS-HDBP dissolved in 30% TBP/Isopar-L and, in the second cycle, the An(III) are selectively stripped by a diethylenetriamine-A, N,N, N",N"-pentaacetic acid (DTPA) solution, while the Ln(III) are consecutively stripped by a mixture of nitric acid and hydrogen peroxide. DFs greater than 100 are expected by calculations, and less than 5% Ln(III) contamination is assumed (233, 234). 

After a few years of storage, the main radioactive heat emitters in HLW are 90Sr and 137Cs. In addition, extremely long-lived actinides—neptunium, plutonium, americium, and curium—should be collected for transmutation in the future. Therefore, different flowsheets can be proposed for waste processing. It is possible to extract each radionuclide in the special extraction (sorption) cycle, for example, uranium and plutonium in the PUREX process, and after that, minor actinides (MAs) by the TRUEX process,4 strontium by the SREX process,5,6 and cesium by sorption7 or extraction.8... 

The flowsheet of the UREX process, developed in the United States, includes the following extraction cycles (1) separation of uranium and technetium, (2) separation of plutonium, (3) separation of cesium and strontium, (4) separation of MAs and Rare Earth Elements (REE), and (5) group separation of MA from REE metals.9,10 Flowsheet development in Europe11 includes a modified PUREX process and, after that, the DIAMEX process for separation of MAs and lanthanides, the SANEX process for separation of MAs from lanthanides, and a special cycle for Am/Cm separation. Cesium and strontium will be in the raffinate of the DIAMEX process, and this raffinate will be vitrified, or cesium can be preliminarily extracted.12... 

FIGURE 6.3 DIAMEX-SANEX flowsheet with organophosphorus acid regeneration in extraction cycle. (From Heres, X., Ameil, E., Martinez, I., Baron, P., Hill, C., Extractant separation in Diamex Sanex Process. Presentation on Global 07 conference. With permission.)... 

The CEA has sponsored the ATALANTE conferences to provide an international forum for presentation and discussion of the advances for future fuel cycles and waste management that are needed for sustainable development of nuclear energy. Abstracts of the papers from the Avignon (2000) and Nimes (2004) conferences are available on the web at www-atalante2004.cea.fr. They demonstrate that centrifugal contactors are being used for flowsheets covering various nuclear processes. 

A third stream is another pseudostream, which is attached on the red arrow at the bottom of the vessel called Reactor Product (required) (see Fig. 4.22). This pseudostream represents the contents of the reactor at the end of the batch cycle. Note the blue arrow pointing out of the vessel in Figure 4.22. This can be used as a product stream that is withdrawn from the vessel during the batch cycle. For example, a pressure controller can be used to withdraw a vapor stream to hold the pressure in the reactor. Figure 4.23 shows the flowsheet with the three streams attached to the RBatch reactor. Remember that the charge and product streams are required connections for the reactor. 

Brown, L.C., R.D. Lentsch, G.E. Besenbruch, K.R. Schultz (2003), Alternative Flowsheets for the Sulfur-Iodine Thermochemical Hydrogen Cycle , AIChE Journal, April. 

---