Framing¶
This notebook captures process framing decisions, assumptions, and tradeoffs in a reusable format.
Decision question¶
For an ethanol-to-olefins concept model, should we prioritize conversion yield or utility intensity in the next design iteration?
System boundary and basis¶
- Boundary: feed conditioning -> reactor -> separation -> product storage
- Basis: 100 kmol/h dry ethanol feed
- Products of interest: ethylene and propylene
Baseline assumptions (explicit)¶
- Single-pass ethanol conversion = 92%
- Ethylene selectivity = 78% of converted carbon
- Column pressure drop = 0.25 bar per major separation train
- Steam cost = $11/GJ
- Electricity cost = $70/MWh
First-pass checks¶
Check 1: Carbon reasonableness¶
- Converted ethanol carbon = 100 x 2 x 0.92 = 184 kmol C/h
- Ethylene carbon to product = 184 x 0.78 = 143.5 kmol C/h
- Result is plausible because it leaves room for byproducts and purge losses.
Check 2: Utility leverage¶
- At baseline, reboiler duty dominates OPEX sensitivity.
- A 10% duty reduction has larger cost effect than a 1-point selectivity change in this setup.
Preliminary decision¶
Prioritize utility intensity reduction in the next iteration, while holding selectivity above 75%.
What could reverse this decision¶
- If measured selectivity drops below 72%
- If steam price falls below $6/GJ
- If downstream purity specs tighten and force higher reflux ratios
Mindsets demonstrated¶
Rubric snapshot (example)¶
- Problem framing: 4/4
- Assumption quality: 3/4
- Quantitative discipline: 3/4
Evidence requested next week¶
- One sensitivity run on steam cost (+/-30%)
- One sensitivity run on selectivity (70-82%)
Next in sequence: Assumption Failure Map
Appendix¶
Archived course-specific HTML export: Aspen appendix.