H. Rapoport et al., RETROFIT DESIGN OF NEW UNITS INTO AN EXISTING PLANT - CASE-STUDY - ADDING NEW UNITS TO AN AROMATICS PLANT, Computers & chemical engineering, 18(8), 1994, pp. 743-753
The design of a process plant generally follows recursive steps of syn
thesis, analysis, and evolution. Retrofit design makes changes or addi
tions to the plant in order to achieve expanded and/or more economical
operation. A retrofit design algorithm which was developed in this st
udy, uses a process synthesis approach with heuristic rules based on e
ngineering experience, detailed process calculations and detailed econ
omical evaluations leading to an optimal design. This approach was tes
ted extensively and successfully on the flowsheet of an existing aroma
tics plant. The intervention of experienced engineering judgment leads
to improved and more profitable retrofit design or to the optimal cho
ice between alternate downstream process additions. Cascading distilla
tion towers and reactors, maximal utilization of processing unit capac
ities, and the reuse of superseded equipment improves the economics of
the design. A grassroot design of the whole plant will in most cases
be more economical than constructing an initial small plant and then e
xpanding it gradually. Economical failure can result from poor guesses
of future prices of feedstocks and products. It was shown for the pla
nt studied in this paper by redesign under historical conditions that
the added value of the chemicals in the good years made up for the poo
rer performance in bad years