Review of Capital Costs Cp = Purchased equipment cost = f(capacity variable) Bare module cost (CBM)= Cp x FBM(materials, pressure) Cost of Process Unit = (CBM )CE Index fcurr floc Location Time Currency Total Project Cost = Process Units + Offsites + Contingency + Contractor’s Fee Contingency = 5 to 40% depending on class of estimate Utility Costs GD Ulrich, Chemical Engineering, 1992, Vol 2, pp 110 • Updated costs using same calculation method as text Cu = Cost of utility per unit, e.g. $/kWh or $/kJ cooling Cu = Capital equipment and labor expenses + Energy related expenses Cu = a·CE Index + b·Cf Cf = Price of fuel, $/GJ EXAMPLE PROCESS • Deutsche Texaco AG Isopropanol Process Unit (Hydrocarbon Processing, November, 1981) • Application: Process for the manufacture of 99.9% min. purity isopropanol (IPA) from 90-99% propylene IPA Process Description • The direct hydration of isopropylene to isopropanol is carried out in a trickle-bed reactor using an ion exchange catalyst • Liquid propylene is mixed with preheated water, then charged as a supercritical mixture to the top of a fixed-bed reactor, and allowed to trickle downward over a bed of ion exchange resin • Intensive mass transfer occurs between the liquid and vapor phases in the reactor at 130-160C and 1200-1500 psig IPA Process Description (Cont.) • Aqueous alcohol and unconverted propylene are separated in a high-pressure separator • The liquid phase is passed to a low-pressure separator, then charged to a distillation column. Di-isopropyl ether (a byproduct) is removed from the top of the column. • The bottom stream is sent to a second column, which removes isopropanol as an azeotropic mixture in the overhead stream • The water from the bottom of the column is desalted by ion exchange and recycled to the reactor. Azeotropic isopropanol is further purified by distillation, after adding benzene to break the azeotrope Raw Materials • Raw Material Consumption: 0.746 ton propylene/ton IPA • Conversion:93.4% wt of propylene to IPA 5.0% wt of propylene to di-isopropyl ether 1.6% wt of propylene not reacted or lost • Conversion per pass = 75% • Costs: A 100,000 tonne/yr plant requires battery limits investment of $13.8 million (1981) and uses 1 supervisor and 4 operators Utilities for IPA • Utility requirements per tonne of IPA (99.9% purity) are: – – – – – – – Cooling water, USG T 7 C Process water, USG Low pressure steam, GJ Electricity, kWh Med. pressure steam, GJ Chemicals + catalysts, $ Catalyst life, months 1000 80 7.4 115 0.525 2.8 8 • Calculate the cost per unit product for a 60,000 t/yr plant.
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