Extraction energy costs

This operation is essential for the extraction of butadiene contained in a steam-cracked C4 cut by means of cuprous ammonium. It is not absolutely necessary in the case of extractive disrillation. In this case, however, hydrogenation pretreatment significantly improves the operating conditions of the separation step, and helps to raise the recovery rate of polymerization grade butadiene. Indeed, this leads to a reduction of its losses as a diluent for acetylenic compounds in the effluent rich in these compounds and separated by extraction. Energy costs are reduced simultaneously ... 

Many industrial processes begin with a leaching step, yielding a slurry that must be clarified before solvent extraction. The solid-liquid separation is a costly step. The solvent extraction of unclarified liquids ( solvent-in-pulp ) has been proposed to eliminate solid-liquid separation. The increased revenue and reduced energy cost make this an attractive process, but many problems remain to be solved loss of metals and extractants to the solid phase, optimization of equipment design, effluent disposal, etc. 

In the area of extracting solutes from aqueous solutions, many systems have been screened in feasibility tests that have used carbon dioxide as a solvent. A partial list of the solutes includes ethanol, acetic acid, dioxane, acetone, and ethylene glycol. The reason for these efforts has been potential low energy costs compared with distillation and the environmental advantages of using carbon dioxide. 

A 4-month vapor extraction project in which the soil was heated to 160°F would require approximately 200,000 Bm/yd. According to the vendor, the energy cost for electricity-provided heat would be about 6.00/yd. For natural gas and propane, the cost would be lowered to 1.00 and 1.60/yd, respectively (D15838X, p. 2). 

Because of its low cost, nonhazardous chemical nature, and low critical temperature, carbon dioxide has been used in many applications. A commercial process to remove caffeine from coffee, using supercritical C02 as the solvent, is shown in Fig. 17. While actually a liquid-solid extraction process, it demonstrates principles involved in SCFE. A commercial SCFE process has been reported for recovery of hydrocarbon liquid from heavy oil. As compared with conventional propane deasphalting, this SCFE process can reduce capital and energy costs. 

Concentration. Clarified filtrates, centrates, or column eluates are usually too dilute for use in their specific applications, thus, substantial amounts of water must be removed. This can be achieved by evaporation or by ultrafiltration. Concentration methods used in industrial settings, such as evaporation, which is done under vacuum, and solvent extraction, may or may not be suitable for dewatering proteins because of their potential for thermal or chemical denaturation, and due to high energy costs associated with evaporation. The benefit of evaporation is that nonvolatile compounds that may stabilize the proteins are retained. 

The results of the calculations for each process with the mentioned extraction and separation pressures and temperatures are ranked according to their overall energy cost. Table 1 and Table 2 show the ten Process 1 and Process 3 variants whose energy costs are lowest. 

Energy costs K for supercritical fluid extraction of hops with C02 according to Process 1. 

Figure I shows the overall costs K for Process 3 as a function of the separation pressure p for extraction temperatures between 40 and 100C. As the separation pressure increases, the overall costs K decrease. The saving in mechanical work outweighs the effect of more unfavourable separation conditions at higher separation pressures. The process is more efficient because no heating is necessary, and ftirthermore, simple pressure release results in a temperature favourable for separation. The same trend is observed when energy costs for mechanical work are about 25 % higher or lower, i. e. 0.10 DM/kWh or 0.16 DM/kWh..

A priori it would seem that liquid-liquid extraction with the almost negligible energy costs associated with the transfer of one material in a liquid solution (preferentially from one solvent to another) would be always more economical than vaporization in terms of energy. However, since the added solvent usually has to be separated subsequently from both the extract layer and the raffinate layer by distillation, these thermal costs for the overall separation may be substantial. 

Current estimates of the available reserves and further resources of uranium and thorium, and their global distribution, are shown in Figs. 5.44-5.50. The uraruum proven reserves indicated in Fig. 5.44 can be extracted at costs below 130 US /t, as can the probable additional reserves indicated in Fig. 5.45. Figure 5.46 shows new and unconventional resources that may later become reserves. They are inferred on the basis of geological modelling or other indirect information (OECD and IAEA, 1993 World Energy Council, 1995). The thorium resource estimates are from the US Geological Survey (Hedrick, 1998) and are similarly divided into reserves (Eig. 5.47), additional reserves (Fig. 5.48) and more speculative resources (Fig. 5.49). The thorium situation is less well explored than that of uranium the reserves cannot be said to be "economical", as they are presently mined for other purposes (rare earth metals), and thorium is only a byproduct with currently very limited areas of use. The "speculative" Th-resources may well have a similar status to some of the additional U-reserves. 

Karlovic et al. (79) examined the aqueous enzymatic extraction of com germ oil. Hydrothermal pretreatment, grinding, and enzymatic treatment of corn germ improved extraction efficiency. Although the energy cost for enzymatic com germ oil extraction was lower than that of the conventional extraction, the enzyme cost made the process more expensive (79). 

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