Cost estimation unit operations

Three flow sheets with consistent assumptions, and using commercially available equipment where possible, were developed. The flow sheets and mass and energy balances were used to generate sized equipment lists. Estimated costs for unit operations are based on industry databases for materials and labour, and on the estimates of technical experts from associated research and development programmes. Installation costs, including labour and field bulk materials, were estimated on a subsystem basis. 

Operating Labor The cost of operating labor is the second largest item of expense in the manufac turing cost. Labor requirements for a process can be estimated from an intelhgent study of the equipment flow sheet, paying careful attention to the various primaiy process steps such as frac tionation, filtration, etc. The hourly wage rate should be that currently paid in the company. Once the number of persons reqiiired per shift has been estimated for a particular production rate, the annual labor cost and the labor cost per unit of production can be estimated. 

Instrument and Plant Air Systems. A typical setup for a large plant could include three to four 50% instrument air compressors and two 100% plant air compressors, with steam drives for normally operated units and electrical drives for spares. Common practice would provide an interconnection to allow makeup from plant air into instrument air, but not vice versa, and two sets (two 100% driers per set—one on-stream and one regenerating) of 1007c instrument air driers. Two main receivers on instrument air near the compressors with several minutes holdup time and satellite receivers at process trains would be likely and proper for feasibility cost estimating. 

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... 

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. 

Sources of data on costs were discussed in Chapter 6 and materials of construction in Chapter 7. This chapter covers sources of information on manufacturing processes and physical properties and the estimation of physical property data. Information on the types of equipment (unit operations) used in chemical process plants is given in Volume 2, and in the Chapters concerned with equipment selection and design in this Volume, Chapters 10, 11 and 12. 

The chemical process industries are competitive, and the information that is published on commercial processes is restricted. The articles on particular processes published in the technical literature and in textbooks invariably give only a superficial account of the chemistry and unit operations used. They lack the detailed information needed on reaction kinetics, process conditions, equipment parameters, and physical properties needed for process design. The information that can be found in the general literature is, however, useful in the early stages of a project, when searching for possible process routes. It is often sufficient for a flow-sheet of the process to be drawn up and a rough estimate of the capital and production costs made. 

Two advantages of this approach would be the minimized capital and operating costs, along with minimal space requirements. The best process (for iron removal) would probably be chemical precipitation with lime through a rapid mix, flocculation, and DAF step. DAF size requirements would be in the range of a 300- to 350-ft2 unit. Total costs for operation and maintenance of the preliminary treatment facility using an interest rate of 10% over 10 years are estimated at 0.44/1000 gal. A summary of the capital and operating cost estimates is presented in Table 8.2. 

Since both the direct and phased approaches offer, at least in principle, equal promise for ultimate success (i.e., comprehensiveness and complete characterization), it is worthwhile to examine their relative resource requirements. Several studies were conducted with the objective of comparing the costs of direct and phased (with elimination of low priority streams) sampling and analysis approaches. (2,3] A number of processes were evaluated during these studies and the results for two unit operations — a limestone wet scrubber and full-scale low-Btu coal gasifier — are taken as examples. The scrubber involved seven feed or waste stream sampling sites. The gasifier contained 70 identifiable stream sampling points. The total estimated costs for both processes by both approaches are shown in Table I. 

Approximately 47% of the costs associated with operating this technology are for labor, and the bulk of the remainder derives from purchasing the 2 million Detoxifier unit (D104654, pp.19-20). It should be kept in mind that these estimates are in 1991 dollars and that the machine used was a company prototype. 

A cost analysis was also done for the hypothetical treatment of 22,000 tons of contaminated soil using the existing THC treatment plant. The total estimated unit cost for this operation is 147 (1993 U.S. dollars) per ton. The breakdown of costs by technology is as follows ... 

When the attractiveness of new products is evaluated, either for submitting an offer or for inclusion in the R D program, manufacturing costs have to be estimated on the basis of a laboratory synthesis procedure. This is best done by breaking down the process into unit operations, the standard costs of which have been determined previously. Care has to be taken to estimate the time required for each step of a process. Thus a liquid-liquid extraction can take more time than the chemical reaction. The capability of a fine-chemical company to make dependable manufacturing cost forecasts is a distinct competitive advantage. 

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