A _____________ heat exchanger is employed for chilling oil prior to dewaxing?
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Answer: B. Double pipe
Explanation
Double pipe heat exchangers handle viscous oils and crystallization duties exceptionally well. Their annular flow geometry provides high fluid velocities and uniform heat transfer characteristics. Specialized scrapers can be integrated to prevent wax accumulation on cold inner walls. Dewaxing lubricating oils requires chilling processes where paraffin components precipitate out. Double pipe units consist of concentric tubes allowing counter-current flow arrangements. They offer high film coefficients and handle high pressure duties better than large shells.
Petroleum refineries utilize scraped-pipe exchangers extensively in wax crystallization and solvent dewaxing units. Preventing fouling from solidified wax ensures continuous long-term operation without frequent cleaning shutdowns. Compact modular designs allow easy expansion of double-pipe systems for changing plant capacities. U-tube exchangers are prone to severe fouling when handling waxy heavy oil chilling duties. Fixed tube sheet exchangers make mechanical cleaning of wax deposits extremely difficult and impractical. Floating head exchangers are unnecessarily complex and expensive for small-duty oil chilling applications.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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