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Five capital-cost-estimation programs are compared using a set of case studies
Capital cost assessment is an integral part of process design when building or expanding a chemical process plant. It is required to provide project analysis and evaluation, to select among alternative designs, to plan the appropriation of funds and to serve as a basis for project cost control. Capital cost estimation is also important for an engineerng student's final design project.
The accuracy of capital cost estimates depends on the available design details, the accuracy of the cost data, as well as the time available to prepare estimates. The generally accepted classification of capital cost estimates (Table 1) is published by the Association for the Advancement of Cost Engineering (AACE International). Currently, several methods and associated computer programs exist for estimating capital cost, and they provide mainly study or preliminary estimates (Table 1; Class 4).
An evaluation and comparison of the computer programs available for capital cost estimation provides a better understanding of both their use and the methods behind them. This article arose out of a systematic effort by the authors to apply and analyze several programs available for capital cost estimation. The goals of this effort were to evaluate available cost estimation programs, apply the programs to case studies of plant design and to analyze the cost estimates for different types of equipment.
Five programs are discussed here - CapCost, EconExpert, AspenTech Process Economic Analyzer (AspenPEA), Detailed Factorial Method (DFP) and Capital Cost Estimation Program (CCEP). They were evaluated using seven case studies taken from textbooks. The selected case studies involve petroleum refining, petrochemical and biopharmaceutical processes. The cost estimates are compared and analyzed at both the equipment and plant levels to uncover the relative strengths of each of the programs used.
Estimation methods
Capital cost estimation methods in various process design reference books range from simple order-of-magnitude schemes to more detailed module costing and factorial methods. Common methods for preliminary capital cost estimation are based on the Lang factor method, the detailed factorial method and the module costing method. Most available cost estimation programs in the open literature use one of these methods.
In the Lang factor method [1], plant capital cost is determined by multiplying the sum of the...