Recovery processing schemes

The arrangement of light ends separation facilities is an important factor in overall refinery economics. The development of the optimum scheme for a particular application often involves postulation of a number of alternatives and comparison of the economics for each. 

The Hj/400°FVT streams from each system are sent to separate flash drums where the bulk of the Cj and lighter material is removed. The virgin and cat cracker streams from the flash drums go to separate debutanizers while the Powerformer stream goes to an absorber-deethanizer followed by a debutanizer. The Q and lighter overhead streams from the virgin and cat cracker debutanizers are sent to this absorber- deethanizer for final deethanization. In the flow scheme shown this tower does not have a separate lean oil. It is called an absorber-deethanizer because the Powerformer stream serves in part to absorb the Cj and C4 components in the streams from the debutanizers. A separate lean oil stream is added in cases where higher Q and Q recoveries are justified. 

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Modijications to the Recope Cycle. The recovery system is a principal capital cost in a kraft mill. Consequently, any recovery process that is less expensive to build can improve pulping economics. There have been numerous attempts to improve the kraft recovery process. Two examples are the direct alkaline recovery scheme (DARS) and the autocausticizing scheme using sodium borates (37). Both schemes eliminate the lime loop of the conventional kraft mill. As of 1996, neither is commercially used. 

The Claus process is the most widely used to convert hydrogen sulfide to sulfur. The process, developed by C. F. Claus in 1883, was significantly modified in the late 1930s by I. G. Farbenindustrie AG, but did not become widely used until the 1950s. Figure 5 illustrates the basic process scheme. A Claus sulfur recovery unit consists of a combustion furnace, waste heat boiler, sulfur condenser, and a series of catalytic stages each of which employs reheat, catalyst bed, and sulfur condenser. Typically, two or three catalytic stages are employed. 

Recovery Process. Figure 5 shows a typical scheme for processing sodium chlodde. There are two main processes. One is to flood solar ponds with brine and evaporate the water leaving sodium chlodde crystallized on the pond floor. The other is to artificially evaporate the brine in evaporative crystallizers. Industrial salt is made from solar ponds, whereas food-grade salt, prepared for human consumption, is mosdy produced in the crystallizers. 

There are numerous applications in solvent recovery processes where evaporation equipment are employed. Figure 14 provides an example of a process scheme for toluene-di-isocyanate recovery. This is an example of continuous vacuum evaporation of distillation residues. 

Another example in the polymers industry is illustrated in Figure 17, which is a process aimed at the batch drying of waste residue with solvent recovery. In this application liquid or viscous waste solutions are pumped into a batch dryer where they are dried under vacuum to a solid granular residue. Vaporized water and solvent are recovered by condensation and then separated by gravity. The process scheme is flexible, offering a range of temperatures and vacuum levels for treating... 

In comparison with classical processes involving thermal separation, biphasic techniques offer simplified process schemes and no thermal stress for the organometal-lic catalyst. The concept requires that the catalyst and the product phases separate rapidly, to achieve a practical approach to the recovery and recycling of the catalyst. Thanks to their tunable solubility characteristics, ionic liquids have proven to be good candidates for multiphasic techniques. They extend the applications of aqueous biphasic systems to a broader range of organic hydrophobic substrates and water-sensitive catalysts [48-50]. 

In rhodium hydroformylations, highly efficient separation and recovery of catalyst becomes imperative, because of the very expensive nature of the catalyst. Any loss, by trace contamination of product, leakage, or otherwise, of an amount of rhodium equivalent to 1-2 parts per million (ppm) of aldehyde product, would be economically severe. The criticalness of this feature has contributed to some pessimism regarding the use of rhodium in large hydroformylation plants (63). However, recent successful commercialization of rhodium-catalyzed processes has proved that with relatively simple process schemes losses are not a significant economic factor (103, 104). 

Most of the toluene and xylenes have their origin in catalytic reforming or olefins plants. From there, the processing schemes vary widely from site to site. The schematic in Figure 3-6 captures most of the variations, although its hard to portray that some plants separate the BTXs from each other early in the scheme while others do it at varying places downstream of an aromatics recovery unit. 

Refinery cat reformers produce a reformate stream with aromatics. That stream, with or-without the benzene-laden scream from the olefins plant, can be split apart in the various processing schemes in the BTX recovery facility. 

Constrained only by the ability to condition the solution to the guideline levels of conductance and contamination, the AQUATECH System is a versatile unit operation in a wide variety of industry areas. In addition to our commercial stainless steel pickling acid recovery plant and the specialty metals waste recycling described above, AQUATECH Systems has developed and patented numerous other process schemes including ... 

Fig. 15.18. General process scheme for the production of methanol from renewable resources. (Reprinted from S. Stucki, A. Schuler, and M. Constantinescu, Coupled C02 Recovery from the Atmosphere and Water Electrolysis Feasibility of a New Process for Hydrogen Storage, Int. J. Hydrogen Energy, Vol. 20, p. 654, Fig. 1,1995. Reproduced with permission of the International Association for Hydrogen Energy.)...

Van Sint Annaland [28] proposed a four-step process for propane dehydrogenation coupled with combustion of methane or propane the phases of the process are illustrated in Fig. 1.15. Different process schemes are possible, depending on the sequence of the phases within one cycle. In any case, the complete cycle is symmetric, which is favorable with respect to heat recovery. 

A complete process scheme for regeneration and reuse of spent final rinse water from an electroless plating operation has been developed by Wong et al. [105]. It includes (i) pre-treatment by microfiltration, UV irradiation, carbon adsorption (ii) heavy metal removal by nanofiltration and (iii) polishing using an ion exchange mixed bed. The results of a pilot study showed that high quality product water with an overall water recovery of 90% could be produced with an estimated payback period of less than 18 months. 

In order to compare the economics as well as the overall C02 emissions from each schematic studied in this joint venture, a reference case was analyzed. The reference case included only the process steps associated with coal gasification, shift, and hydrogen purification, but none of the steps associated with C02 sequestration or coalbed methane recovery. Three other process schemes were examined in this study and compared to the reference case. Figure 1 depicts simplified process flow diagrams for the reference case and the other three schemes (note the overall heat integration for each scheme is not shown). The top portion of the figure shows the process steps that are the same for each scheme up to hydrogen purification, while the operations inside the dashed boxes represent the steps that differ between the four cases. 

Finally, it must be noted that the predictive evaluation scheme as presented has recently been verified and confirmed by carrying out migration tests using PET bottles produced from a challenge-test-accompanied recovery process (Franz and Welle 1998). 

The DBBP extraction scheme provides excellent decontamination of plutonium and americium from all the other metals in the neutralized CAW solution. Kingsley(7) reports that distribution ratios for Fe3+, Al3+, Ca2+, and Mg between 30 vol% DBBP-CCI4 and neutralized CAW are, respectively, 0.11, <0.003, 0.025, and <0.0005. Primarily because of entrainment but partly because of extraction, small amounts of aluminum, iron, and sodium accompany 21tlAm into the dilute HNO3 strip solution. Richardson(9 ) in nonradioactive tests of the countercurrent DBBP 2 1Am recovery process observed decontamination factors in the range 80-180 for iron and in the range 2 x 103 - 1.5 x 105 for aluminum. 

The product BX, with decreased content of impurities, is obtained in column I. Carried out in column II is the combined process of separation and recovery of the AX and BX mixture from the ion exchanger and resin regeneration. The process scheme is shown in Fig. 3. For complete displacement of the ions separated by the auxiliary C ions in column II it is necessary [7] that the ratio of solution and ion exchanger flow inputs should satisfy the condition... 

Selective separation of strontium from calcium at significant SrCl2 concentration levels up to 2 g/L was obtained with KB-4 carboxylic add exchanger employed in a Higgins-type contactor [246]. The pilot unit for strontium recovery from seawater in the closed (and practically waste-free) processing scheme was constructed in the Okhotsk Sea region (Sakhalin power station). The data obtained with the new pilot plant have shown that several components will be recovered simultaneously from seawater. The unit is estimated to produce more than 150 kg of SrCOj, more than 5000 kg of KNOj, and about 2 kg of RbNOj [15]. However, recovery of strontium is still uneconomical. Its cost is expected to become comparable to that of strontium produced from traditional, land-based sources. 

Table 3 shows an example of the comparative performances of these three processes. All of them can produce a 99+% N2 enriched product gas. The two zeolite processes also produce a 85-90% O2 enriched product gas. The O2 product purity of the carbon sieve process is, however, low. This shows that different adsorbents can be married with different process schemes to obtain similar product purities but different process performances (recovery, productivity, product pressure, etc.). 

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