Estimation of separation cost

Sections 10.1 to 10.5 in this chapter are reproduced with permission from Energy and economic assessment of near-critical extraction processes, King et al. in Extraction 90, /. Chem. E. Symposium Series No. 119, 1990, pp. 165-186. 

Recent findings on the extraction of beds of particulate solids with near-critical fluids [3-6] may be summarised as follows (carbon dioxide is the solvent considered in all these studies)  

If the equilibrium solute solubility is substantial, the energy and capital costs associated with the recompressor will make a comparatively small contribution to the total separation cost when Ct and C are of similar magnitude. (C is the equilibrium concentration). This is the case, for example, with piperine which has a solubility in carbon dioxide of about 7wt % at 100 bar and 50°C. It will also be true of many other flavour and aroma compounds. In these cases capital charges associated with the extraction tower play a major part in determining the separation cost. In this situation it is reasonable to base the choice of optimum flow conditions on a maximisation of production rate 

on the other hand, the equilibrium solute concentration C is very low, leading to a correspondingly low value for Cj in equation (10.1), the energy and capital costs associated with the recompressor can become major factors in determining the separation cost. This will be seen to be the case, for example, in the hypothetical process for extracting crushed rape seed with subcritical carbon dioxide which is considered in section 10.6. It would also be true of the extraction of caffeine from coffee beans if pressure reduction was used to recover the caffeine. In cases such as these the most economic flow conditions and tower dimensions will be such that Ct is quite close to the equilibrium value C.  

2 Energy and economic assessment of near-critical extraction processes 

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To evaluate the economics of this process, a cost model has been developed to estimate the separation costs for a specific racemate [68, 69]. For this purpose, the sensitivity of the separation costs for several key process parameters have been established as compared to a base-case separation in which a purity of 99 % is required at an enantioselectivity of 1.15. The maximum solubility of the drug is set... 

A 1968 estimate of the cost breakdown for a plant with a column 4 ft dia by 15 ft high and a throughput of 200-920 tons/yr has been converted to a percentage basis in Table 15.7 because of its age. The costs are said to not vary greatly with throughput or the nature of the separation, although this analysis has been made specifically for the separation of a- and /3-pinenes. The temperature was 165°C and the solvent was Carbowax 20M. The design was based on data in a 4 in. dia column which had a capacity of 200-1500 mL/hr. 

I would like a preliminary estimate of the cost and performance of PriSm separators for the application described below... 

Table 15.11 presents data for the estimation of operating costs based on the above decomposition. The basis is the material and heat balance from flowsheeting, as well as the operating labour. This checklist can be used to compute the operating costs for profit and cash flow calculation. Note that the depreciation charge should be excluded, if it is accounted separately. 

In this chapter, methods are presented for determining capacity (or column diameter) and efficiency of some commonly used devices for vapor-liquid and liquid-liquid contacting. Emphasis is placed on approximate methods that are suitable for preliminary process design. Tray selection, sizing, and cost estimation of separation equipment are usually finalized after discussions with equipment vendors. 

Operating Cost and Economic Analysis. This section begins with a presentation of the annual costs of operating the proposed plant, that is, the cost sheet, as discussed in Section 17.2 and shown in Table 17.1. In addition to the total production cost on the cost sheet, it should provide an estimate of the cost per unit weight of the product (e.g., per lb, kg, ton, or tonne). Note that when cash flows are computed for different production rates from year to year, a separate cost sheet is required for each unique production rate. Note also that, in addition to appearing on the cost sheet, the utilities for each equipment unit and their costs should be sununarized in a separate table. 

Heavy cmde oil is widely distributed, and it is difficult to estimate reserves separate from normal cmde oil reserves or from tar sands deposits. Estimates of petroleum reserves frequendy include a large heavy oil component, which can only be produced at significantly higher cost than light oil. 

Now you can reconsider the material balance equations by adding those additional factors identified in the previous step. If necessary, estimates of unaccountable losses will have to be calculated. Note that, in the case of a relatively simple manufacturing plant, preparation of a preliminary material-balance system and its refinement (Steps 14 and 15) can usefully be combined. For more-complex P2 assessments, however, two separate steps are likely to be more appropriate. An important rule to remember is that the inputs should ideally equal the outputs - but in practice this will rarely be the case. Some judgment will be required to determine what level of accuracy is acceptable, and we should have an idea as to what the unlikely sources of errors are (e.g., evaporative losses from outside holding ponds may be a materials loss we cannot accurately account for). In the case of high concentrations of hazardous wastes, accurate measurements are needed to develop cost-effective waste-reduction options. It is possible that the material balance for a number of unit operations will need to be repeated. Again, continue to review, refine, and, where necessary, expand your database. The compilation of accurate and comprehensive data is essential for a successful P2 audit and subsequent waste-reduction action plan. Remember - you can t reduce what you don t know is therel... 

However, since fluorometric methods require sophisticated instrumentation, their applicabihty is limited because of cost. In conclusion, spectroscopic methods usually enable crude estimates of chlorophylls in an extract, but in most cases accurate and detailed analysis of a specific composition requires separation of the mixture into individual compounds using methods such as HPLC. 

Applications Membranes create a boundary between different bulk gas or hquid mixtures. Different solutes and solvents flow through membranes at different rates. This enables the use of membranes in separation processes. Membrane processes can be operated at moderate temperatures for sensitive components (e.g., food, pharmaceuticals). Membrane processes also tend to have low relative capital and energy costs. Their modular format permits rehable scale-up and operation. This unit operation has seen widespread commercial adoption since the 1960s for component enrichment, depletion, or equilibration. Estimates of annual membrane module sales in 2005 are shown in Table 20-16. Applications of membranes for diagnostic and bench-scale use are not included. Natural biological systems widely employ membranes to isolate cells, organs, and nuclei. 

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