Using a turbine expander to recover exothermic reaction heat - a case study on a phthalic anhydride process

J. Perold, I.L. Greeff, K.J. Ptasinski, F.J.J.G. Janssen

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Phthalic anhydride (PA) is produced from alkyl-substituted- or multinuclear at. compds. such as o-xylene or naphthalene by partial oxidn. With reaction enthalpies as high as -1 793 kJ/mol naphthalene reacted, there are many opportunities for energy recovery making these systems attractive for process integration research. The prodn. of PA from naphthalene is used to investigate two energy recovery schemes. The first is a Rankine cycle that uses steam, raised during the cooling of the reactor, to produce power. The second also includes a turbine expander at the reactor exit. It expands hot reactor product gases to deliver addnl. power and reduces the pressure of the reactor product before it enters the sepn. section. Simulation results showed that, under certain operating conditions, the steam cycle alone could not supply the feed compression power requirement. However, when a turbine expander is included in the process, all of the power requirements can be fulfilled and as much as 2 651 Mj/ton PA can be exported for use elsewhere. Unlike power generation from fossil fuels, no carbon dioxide is emitted to the atm. when an expansion turbine is used. Savings in CO2 emissions between 0.46-0.75 ton CO2/ton PA are estd. for this unit. An exergy anal. showed that the thermodn. loss of the process with the second energy recovery scheme is 4.5% lower than that of the first. The reason being that power can be recovered when expansion takes place in a turbine instead of an isenthalpic expansion valve.
Original languageEnglish
Pages (from-to)1-14
JournalSouth African Journal of Chemical Engineering
Volume13
Issue number2
Publication statusPublished - 2001

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