Assignment #2
Ethylene Oxide Plant — Level 2 Conceptual Design
Electronic Submission due 6 am September 21, 2016
Context
This assignment will give practice in Conceptual Design Levels 0-2 with emphasis on Level 2. We strongly encourage that you work collaboratively on Task 3 Level 2 Decisions as you can benefit from alternative points of view and the associated discussions even if you don’t make the same eventual decision. However, Task 4 material balance development and associated calculations including Task 5 EP are to be performed and submitted independently.
Learning Objectives
Below 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 diagrams
7. Students will be able to work in a team environment
Background:
Ethylene oxide (EO) is the simplest cyclic ether. It is quite reactive because its highly strained ring can be opened easily, which makes it one of the most versatile and widely-used chemical intermediates in the Chemical Process Industries. Ethylene oxide itself is used 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 polyester fibers, 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.
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 psia through the following exothermic reaction:
C2H4 + ½ O2 ? 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 S to 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 X
for 0.04 < X < 0.40
where 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 / lb
The plant will be designed to operate 8100 hr/yr
Raw Materials Specifications:
99.5% Ethylene (0.5% CH4) (250 psia, 25 °C) $0.27 / lb
99.5% O2 (0.5% Ar) (250 psia, 25 °C) $0.12 / lb
or Air (21% O2, 79% N2) ambient conditions no cost
Task 1
The 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 2
Explain 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 4
Construct 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 5
Determine the Economic Potential – Level 2 (EP2) for your Design. Construct an appropriate graphical summary of EP2 vs. (and potentially as a function of) your Design Variable(s). Discuss the outcome in terms of next steps and any insight gained.
Submission: Due before 6am on September 16, 2016
There 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 2 Checklist
2. The Assignment 2 Pre-reflection
3. The Body of the work
4. A references section, formatted using ACS citation format
5. 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.
Preparing and Submitting Assignments
This document takes students step-by-step through the process of preparing and submitting an assignment for Dr. Burrows’ classes.
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Where will I find assignments posted?
Normally, just open the Assignments folder of the course webpage.
Notice that these documents contain a list of assigned tasks or problems followed by a checklist (sometimes the checklist is a separate document).
________________________________________Submitting assignments – the absolute, no exceptions rules:
• You must follow all format requirements.
• You must complete a pre-reflection and a post-reflection for each submission (see below).
• You must answer all questions and complete all tasks listed in an assignment’s description.
• You must complete the checklist/template provided for each assignment (non-shaded items).
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General Format Requirements
You will encounter format requirements throughout your professional career, and these requirements will vary by organization. This course requires you to follow all of the format instructions below (as well as the table format and plotting format requirements later in the document) for each submission – including assignments, lab reports, projects, reworked exams, and any other submission (the rare exceptions will be identified as exceptions). If you do not follow format requirements, your grade might be decreased, you might receive an NI and be required to rework the assignment, or – if the formatting has severe deficiencies – you might receive an NC and be required to do a makeup assignment. This can seem harsh, but many industrial, professional, and government organizations refuse to even look at documents submitted to them that do not follow every format requirement. You can build a sense of professional skill (and avoid these penalties) if you prepare your work carefully and check that it meets format requirements.
• Print or write hard-copy submissions on ONE SIDE of the paper ONLY. Print computer-generated work in black on white 8½ ? 11-inch sheets, using 10-point or 12-point fonts. Use MS-Word® or a compatible document application for all work except for extensive calculations, which you may usually write out by hand. Prepare hand-written work on either white printer paper or on green or tan engineering computation paper – do not use loose leaf paper or paper torn from a spiral notebook.
• All submissions must have their checklist at the front (checklists are provided for all submissions). Do not change the checklist formatting.
• Staple hard copy submissions with fewer than 10 pages; for hard-copy submissions of 10 or more pages, secure a steel binder clip (typically black, with fold-down handles) in the upper left corner. Please use an appropriately sized clip – normally a “mini-size” clip. Do not use wire or plastic paper clips, as they fall off too easily.
• Type the submission date and the student/team name on the upper right corner of each page (including any handwritten pages) after the checklist page. Assignment files usually come with a template that includes the name, team number and date in the header; you only need to fill them out.
• Page numbers must appear on the bottom of each submitted page after the checklist. Assignment files come with a template that includes page numbering. If you do not use the template, format the footer in your own MS-Word® document to include a page number.
• All work must look neat and readable, and must pass spelling and grammatical error checks; handwritten work must have few erasures and no crossing-out. Hard copy printing must be crisp and clear – I should not be able to tell that your printer is running out of ink or toner. Use printer settings for black and white, NOT gray-scale! Some printers print gray as a combination of colors – you want your grays to have only black ink/toner.
• For a submission that contains a set of problems or tasks, start each new problem or major task on a new page. (This may take some judgment. A major task is normally one that itself requires several pages to complete. Consider a major task as equivalent to a chapter in a book)
• Use a computer to generate all plots and essentially all diagrams. If necessary, make sketches and hand-drawings of any kind (e.g., process flow diagrams) using a straightedge (and other drawing tools as needed).
• Each table, and figure/plot must have a number (e.g. “Table 1: …”), and a descriptive caption (more on this below).
• Complete numerical results require correct signs, correct units, and the correct number of significant digits, in addition to the correct numerical value.
• Use super- and subscripting for quantities and chemical formulas, e.g., 1.15?105 instead of 115000 or 115,000 or 1.15×10(5) or 1.15*10^5 or 1.15e5, and CO2 instead of CO2.
• Use an equation editor for equations, and use the display form rather than the linear form. The Ms Word equation editor is OK, but MathType works much better.
• Give proper citations for all sources used. This includes equations, conversations with the instructor, TA, or classmates (“name, personal communication”), and Internet sources. Cite Internet or print sources as recommended by the American Chemical Society’s ACS Style Guide . NOTE: If you access a source via the Internet that actually exists in print (e.g., accessing the CRC Handbook online edition), you must cite the print version. This is addressed in detail later in this document.
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The Pre-Reflection
Most professions expect their members to engage in self-reflection. Your professor uses the process described here for her research and academic work, and intends that you develop your self-reflection skill, an important component of lifelong learning.
Before beginning an assignment, step outside of the work itself and consider what you’re about to do. Write this pre-reflection in the first person (“I/we think that …”). Imagine the response you might make to someone who asks you what you think about the assignment, after you’ve read it but before you’ve started wo
