23-Chem-A5 Chemical Plant Design and Economics · December 2019
Question 5 of 6: Categories of Plant Storage Facilities
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exams / EGBC — December 2019 — 16-Chem-A5 Chemical Plant Design and Economics. Three-hour closed-book examination; one aid sheet (both sides) and an approved Sharp/Casio calculator are permitted. Six questions are printed and any five constitute a complete paper (each worth 20 marks); all six are solved below for completeness. The two calculation questions (Q3, Q4) are worked with explicit engineering-economy factors; the four discussion questions (Q1, Q2, Q5, Q6) are answered as structured lists with supporting description, as the paper directs.
Reference texts: M. S. Peters, K. D. Timmerhaus & R. E. West, Plant Design and Economics for Chemical Engineers (5th ed., McGraw-Hill) — profitability measures (rate of return, incremental analysis), straight-line depreciation, after-tax cash flow, and the anatomy of a process/economic study; R. Turton, R. C. Bailie, W. B. Whiting & J. A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes (4th ed., Prentice Hall) — the process flow diagram and its information content, equipment/economics; G. Towler & R. Sinnott, Chemical Engineering Design (Coulson & Richardson Vol. 6, 2nd ed.) — utilities, offsites and storage; O. Levenspiel, Chemical Reaction Engineering (3rd ed.) and H. S. Fogler, Elements of Chemical Reaction Engineering — reactor scale-up. Engineering-economy factors follow the standard notation $(A/P,i,n)$ and $(P/A,i,n)$; as the question specifies straight-line depreciation, that method is used throughout (rather than the Canadian CCA declining-balance system).
Question 5: Categories of Plant Storage Facilities (20 marks)
Overview. Storage is a principal offsite function. Storage facilities are classified first by function (where the material sits in the supply chain) and second by storage method / vessel type, which is dictated by the physical state, volatility, toxicity and reactivity of the chemical stored. In the Canadian setting the design and separation of these facilities follow the applicable provincial fire code, CSA standards and, for spill containment, provincial and federal environmental regulations.
(A) Categories by function.
Raw-material (feedstock) storage. Holds incoming feedstocks and reagents — crude oil, naphtha, natural-gas liquids, acids, caustic, solvents, ores/minerals — and buffers the plant against interruptions in supply and against the mismatch between delivery batches and continuous consumption.
Intermediate / in-process (surge or buffer) storage. Holds partly processed streams between units so that upstream and downstream sections can be shut down or run at different rates independently; typical contents are reaction intermediates and recycle streams.
Product (finished-goods) storage. Holds on-specification product — fuels, polymers, fertilizers, specialty chemicals — to decouple production from shipping and to allow blending and quality certification before dispatch.
By-product and waste storage. Holds saleable by-products and, separately, wastes and off-spec material awaiting treatment or disposal.
(B) Categories by storage method / vessel type and the chemicals stored.
Atmospheric fixed-roof (cone-roof) tanks. For liquids of low vapour pressure and high flash point — water, heavy fuel oil, diesel, lube oils, many aqueous and non-volatile organic chemicals, caustic solutions.
Floating-roof tanks (external or internal floating roof). For volatile liquids with appreciable vapour pressure; the roof floats on the liquid to suppress evaporative “breathing” losses and vapour-space fire risk — crude oil, gasoline, naphtha, and volatile solvents.
Pressurised storage (spheres and horizontal “bullet” vessels). For gases liquefied under pressure at ambient temperature — LPG (propane, butane), anhydrous ammonia, chlorine, vinyl chloride and similar liquefied gases.
Refrigerated / cryogenic storage. Insulated tanks that keep a liquefied gas at low temperature and near-atmospheric pressure — LNG, liquid ethylene, refrigerated ammonia, and cryogenic liquid oxygen and nitrogen.
Gas holders and high-pressure gas storage. Gas holders (gasometers) and high-pressure bottles/spheres for gaseous products — hydrogen, fuel gas, and inert gases.
Bulk-solids storage. Silos, bins, hoppers and covered warehouses or stockpiles for particulate solids — catalyst, coal, ores, limestone, polymer pellets, fertilizers, salts and solid additives.
Packaged (small-quantity) storage. Drums, intermediate bulk containers, cylinders and bags for specialty chemicals, catalysts, additives and small volumes of hazardous reagents, held in dedicated warehouses.
Special / segregated storage. Diked (bunded) and inert-blanketed tanks for hazardous, toxic, corrosive or oxygen-sensitive chemicals; nitrogen blanketing for flammable or air-sensitive liquids; and heated, insulated tanks for materials that are viscous or that freeze at ambient temperature — molten sulphur, waxes, phenol, concentrated phosphoric acid.
The quantity of storage provided for each category is an economic and safety decision: more storage adds capital cost and inventory but improves plant availability and shipping flexibility.
