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Project Evaluation 2012

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Project Evaluation 2012

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Dimensional Cost Exponents for Novel Processing Equipment

Cost-capacity equations have been used for rapid cost estimation in the process industries for decades. The most common use is for the whole of plant' cost adjustment where typically the basis is tonnage and an exponent of 0.6 is used. The use of the 0.6 exponent is commonly known as the six-tenths rule and is an aggregate indicator of the economy of scale of individual equipment types.A number of cost engineering practitioners have developed and in some cases published equipment-specific exponents. These are based on cost-critical dimensions (power, surface area, length, pressure, etc), rather than tonnage (mass flow rate) alone. The equipment specific exponents can increase the accuracy of the cost estimate substantially; however while the body of knowledge is extensive it cannot encompass all equipment types in the process industry, particularly that of novel equipment. This leads to the incorrect application of equipment-specific exponents, or a default to the six-tenths rule. Both methods often lead to imprecise cost estimates.This paper groups and analyses these exponents based on their dimensional root and develops new dimension-based exponents. It was found that mass flow rate, kinetic power, volume and volumetric flow rate closely adhere to the six-tenths rule, while all other dimensions - mass, thermal power, surface area, diameter and pressure, generated unique exponents. The dimension of length adhered to the six-tenths rule however the data set did not yield satisfactory results. It is felt that this is due to the multi-dimensional character of conveyors that are the main feature of the data set, and is therefore not a reliable, single source of information for scale-up.Dimension-specific exponents can be applied to novel process equipment in the absence of equipment-specific exponents. The method is demonstrated using an example of innovative equipment and the boundaries for correct application and expected accuracy are discussed.CITATION:Kingsbury, A B, Mnch, A and Bland, J, 2012._x000D_
Dimensional cost exponents for novel processing equipment, in Proceedings Project Evaluation 2012 , pp 189-194 (The Australasian Institute of Mining and Metallurgy: Melbourne).
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  • Published: 2011
  • PDF Size: 0.174 Mb.
  • Unique ID: P201204024

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