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Chemical EngineeringDesign and Professional Skills B
Second assignmentM A N U F A C T U R E O F S T Y R E N E

Assignment 2 – Monday 28/01/13

You have a provisional flowsheet for a process to manufacture 30 ton/h of styrene from ethylbenzene. This is described below. (It may differ in some details from the one you developed last term – but if so, you should use the version described here, so that all groups are working with the same, correct process.)

For Assignment 2 of DPS-B, you will complete a team-based report on a Hazard Study 1 of the styrene manufacturing process described below. Please make sure to submit your group report at 11 am on 11th March 2013 (week 10) in CHE-124. There is a strict page limit of 15 pages – so use space efficiently, for example by putting information in tables. The Reference list at the end of the report and the Page of Content will not count towards the 15 pages. Any extra information can be included as an appendix and it will not be part of the 15 pages limit.

This exercise will be peer-assessed: along with your group report, you must submit a completed peer-assessment form, signed and agreed by all members of the team. Also you must include the Records of Meetings forms which should show the action required by each member of the group and if the actions were completed.

To succeed at this project, you will need to divide the work between group members. You can work on different parts of the exercise as individuals, but you will also need to communicate your findings to the rest of the group. Some sections will be influenced by results from many other sections; these will require group meetings. You should also meet up to discuss progress – if some tasks are taking longer than expected, you can transfer manpower from other tasks.

You would be well advised to keep records of your group meetings, to make sure that everyone understands their duties. At each meeting, review the previous actions given, to check that progress is being made. This will also be useful in agreeing on peer-assessment allocations. (For these allocations, do not be shy about noting which group members have contributed most, but also give all members a chance to contribute. If you have some group members who are not contributing at all, please alert your Personal Tutor of this before the end of the exercise.)

Process description

Overview: This process manufactures 30 ton/h of styrene by the dehydrogenation of ethylbenzene. Gas-phase catalytic reactors are used, with recycle of unreacted ethylbenzene. Steam is added as a heat source, to reduce the partial pressure of reactants and to minimise catalyst fouling. The reactor product is used to preheat the reactor feeds, then condensed. Water is separated using a decanter, and the organic components are separated by distillation.

Reactors: Pure ethylbenzene (EB) is supplemented with the recycle from the top of the EB column (see below), which contains small amounts of styrene and methylbenzene, and is then mixed (using in-line mixing in the pipeline) with 10% of the steam (at 3 barg pressure and 150(C). This is passed through heat exchangers in which the EB is vaporised and the steam/EB vapour mixture is heated to ~530(C by heat exchange with the reactor product. The remaining 90 % of the steam is superheated first to 350(C in a heat exchanger using the reactor product and then to 800(C in a gas-fired superheater. This is then mixed with the steam/EB mixture immediately before it enters the reactor. At this point, the steam/EB ratio is about 1.5/1 by mass.

The combined flow of EB and steam enters the reactor at 670(C. The catalyst is mostly Fe2O3, (with some KOH and Cr2O3) in 5 ( 5 mm cylindrical pellets. The steam does not react with the EB, but it helps to provide the necessary heat of reaction. It also reduces the partial pressure of styrene and improves the conversion of EB to styrene. A pressure of ~40 kPa...
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