Assignment #2

 

Ethylene Oxide Plant — Level 2 Conceptual DesignElectronic Submission due 6am  September21, 2016

ContextThis assignment will give practice in Conceptual Design Levels 0-2 with emphasis on Level 2. We strongly encourage that you work collaboratively on Task 3Level 2 Decisionsas you can benefit from alternative points of view and the associated discussions even if you don’t make the same eventual decision. However,Task 4material balance development and associated calculations including Task 5 EP are to be performed and submitted independently.  Learning ObjectivesBelow is the set of Learning Outcomes for CHE 432; this project addresses the highlighted portion of the Learning Outcomes: 1. Students will be able to apply concepts from previous chemical engineering courses to synthesize processes.2. Students will be able to analyze chemical processes for economic viability.3. Students will be able to utilize concepts from conceptual design to minimize work in uneconomical designs.4. Students will be able to size process equipment based on specified flows and compositions 5. Students will be able to obtain equipment cost for a design 6. Students will be able to develop flow diagrams7. Students will be able to work in a team environment

Background:Ethylene oxide (EO) isthe simplest cyclic ether. It is quite reactive because itshighly strained ring can be opened easily, which makes it one of the most versatile and widely-usedchemical intermediatesin the Chemical Process Industries.  Ethylene oxide itself isused as a disinfectant, sterilizing agent, and fumigant, although these direct product applications represent only about 2% of worldwide production.  Ethylene oxide’s most important uses are as an intermediate in production of ethylene glycol and for the manufacture of polyesterfibers, with lesser uses as an intermediate in production of other ethylene oxide derivatives, amines, and poly(ethylene glycols).
Your assignment as described further below is to perform a complete Level 2 Conceptual Design and analysis for a commercial-scale process to produce ethylene oxide. The Process Basis is given below, although there is one decision (Task 1) that must be made before it is completed.

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Level 0: Process Basis V1.0
Reaction Pathway and Process Window:Ethylene oxide is produced through vapor-phase direct partial oxidation over an alumina-supported Ag catalyst at temperatures from 200 – 300 °C and pressures ranging from 150 to 300 psiathrough the following exothermic reaction:
C2H4+½O2C2H4O
Undesirable complete combustion also takes place as follows:
C2H4+   3 O2   2 CO2     +   2 H2O
At sufficiently low conversion(< 40%) and “lean” reactor feed composition (O2 : ethylene < 0.5), the sequential combustion of the ethylene oxide produced from the first reaction is not observed.  Small amounts of acetaldehyde (typically less than 0.1%) and even less formaldehyde are also formed; these undesirable byproducts can safely be ignored at the current level of design detail.
In the absence (at this point) of reaction kinetics data, we use an empirical fit of selectivity Sto the desired product: EO selectivity is empirically related to the conversion through the following correlation:
S (mol EO / mol ethylene converted)  =  0.96- 0.82 Xfor    0.04 < X < 0.40where X is the ethylene molar conversion.
The supported Ag catalyst is irreversibly poisoned by S-containing gases.  Acetylene also acts as a reversible poison through coking reactions.  Under normal operation in the absence of poisons, modern commercial catalysts have an operating lifetime of 2-5 years, with gradual activity degradation due to thermal sintering (agglomeration) of the Ag crystallites, which reduces the active surface area available to drive the reactions.
Product Specifications:13,750 lb/hr Ethylene Oxide 99.97% purity $1.04 / lbThe plant will be designed to operate8100 hr/yr
Raw Materials Specifications:99.5% Ethylene (0.5% CH4) (250 psia, 25 °C) $0.27 / lb99.5% O2 (0.5% Ar) (250 psia, 25 °C) $0.12 / lbor Air (21% O2, 79% N2)  ambient conditions no cost

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Task 1The process can be implemented either with air as the source of O2, or with purified O2 from an air separation plant. Although the reaction pathway is not changed by the choice of air vs. purified O2, this choice will have significant ramifications in process design and ultimately in the economics of the project.Construct a table that summarizes the point-by-point relative advantages of one approach over the other as you perceive them at this early stage.  Based on the entries in your table, complete the Level 0 Design by making the decision: air-based or O2-based process?and succinctly explain your choice.
Task 2Explain why “Continuous” is the best Level 1 Decision: Batch or Continuous?
Task 3 Complete a Level 2 Conceptual Design of the EO Process.  Document your efforts by first presenting the Level 2 diagram that accurately represents your decisions, and then succinctly explain the rationale for all of your decisions in logical sequential order.
Task 4Construct a Stream Table for your Design of Task 3 as a function of your chosen Design Variable(s). Be sure to clearly document the development of the entries in the table.  Choose one set of quantitative values for your Design Variable(s) and include a table of numerical values as an example calculation in units of lbmol/hr.
Task 5Determine the Economic Potential – Level 2 (EP2) for your Design. Construct an appropriate graphical summary of EP2vs. (and potentially as a function of) your Design Variable(s).  Discuss the outcome in terms of next steps and any insight gained.

Submission: Duebefore 6am onSeptember 16, 2016There are no minimum or maximum page requirements for this assignment. You must follow all of the requirements given in the Assignment Requirement document posted in the folder with this document.If you need to scan in work that is handwritten, make sure it is extremely neat and well annotated (i.e., describe what you are doing!).
Submit through the Blackboard link in a single MS-Word document, in the following order:1. The Assignment 2Checklist 2. The Assignment 2 Pre-reflection 3. The Body of the work4. A references section, formatted using ACS citation format5. Any Appendices you choose to include. 6. The Assignment 2 Post-reflection
Email submissions will not be accepted under any circumstances. Late work will receive a grade of NC (i.e., zero). Conditions for rework/makeup are given in the Polices & Info portion of the Blackboard site.
Reminder regarding permissible collaboration:You are required to submit only your own keystrokes – that means that you may not share Excel, Word, or other files containing your work for the assignment.

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