* Corresponding author: Tel.: #31-15-278-2823; fax: #31- 15-278-3422. E-mail address: paulienh@sepa.tudelft.nl (P.M. Herder) Int. J. Production Economics 64 (2000) 311}318 A concurrent engineering approach to chemical process design Paulien M. Herder*, Margot P.C. Weijnen Department of Systems Engineering and Policy Analysis, Group of Industrial Systems and Environmental Resources, Delft University of Technology, P.O. Box 5015, 2600 GA Delft, Netherlands Abstract Much confusion still surrounds the concurrent engineering design concept in the chemical engineering world. The conventional hierarchical design method is compared to the concurrent engineering concept, and it is shown that the CE concept particularly improves the way a chemical design engineer deals with `external factorsa that in#uence a process design. A framework is introduced to easily identify and classify these external factors. Through a number of industrial case studies, the current design methods have been analyzed, and improvements are identi"ed. The #exibility of the plant can be improved by using a concurrent approach.  2000 Elsevier Science B.V. All rights reserved. Keywords: Chemical process design; Concurrent engineering; Hierarchical design; Flexibility 1. Introduction In industrial practice, the design of a new chem- ical plant or the retro"t (redesign) of an already existing plant is usually executed according to the hierarchical engineering method as described by Douglas [1,2]. The hierarchical method is used by process engineers in many di!erent companies and taught at many universities. Interviews that were held with process engineers in several di!erent companies, showed, however, that the hierarchical method has one major drawback. It is encountered in the e!ectiveness of dealing with the so-called external factors. Here we will address this draw- back and investigate whether a concurrent engin- eering approach will better incorporate external factors into the design process and into the "nal design of the plant. 2. External factors During the design process of a chemical plant, the design engineer has to account for numerous external factors. We de"ne external factors as `factors that in#uence the design process or the design of the plant, but cannot be manipulated by the process design engineer, thus posing either constraints or opportunities to the designera. External factors di!er from the `basic design criteriaa or `basis of designa of a plant, which is a well-de"ned list preceding each design project, in the sense that the basis of design contains only a subset of all possible external factors. 0925-5273/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 7 3 ( 9 9 ) 0 0 0 6 8 - 7