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Cost Estimation using Factorial Method

Capital cost estimates for chemical process plants are usually based on purchase cost estimation for major equipment items. The accuracy of this type of estimate will depend on:

  • What stage of design has reached
  • Time the estimate is made
  • Reliability of data available on equipment cost
Factors affecting accuracy of cost estimate
Factors affecting accuracy of cost estimate

Cost Estimation using Lang Factors

The factorial method of cost estimated is often attributed to Lang. The method presented by Lang was based on study of fourteen (14) plant estimates of various sizes and types. He identified three process plant types, which are solid processing plant, fluids processing plant, and mixed fluids-solids processing plant.

The Total Installed Cost estimate was obtained by multiplying the equipment cost (purchase cost) by appropriate factors.

                Total Installed Cost = Total Equipment Cost (Purchase Cost) x f

The three factors (f) for each type of plant being:

Solid process plant                         = 3.10

Solid-fluid process plant                = 3.63

Fluid process plant                         = 4.74

The values above should be used as a guide only.

Revised Lang Factors

Peters (2004) presented revised Lang factors for various types of processing plants. However, the boundaries between the classification are not clear-cut, and considerable judgment is required in the selection of appropriate factors.

Revised Lang Factors
Revised Lang Factors


  • Perry’s Chemical Engineers’ Handbook
  • Coulson and Richardson’s Chemical Engineering Volume 6





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