🧪 Reactor Design – Full Summary

📌 1. Course + Mini Project Overview

What you are expected to do

You must design a complete industrial process:

• Draw a P&ID (Process & Instrumentation Diagram) → shows pipes, sensors, valves
• Dimension the system (size or capacity)
• Choose:
  • Materials
  • Pumps & valves
• Estimate:
  • CAPEX (investment cost)
  • OPEX (operating cost)
• Evaluate feasibility

💡 Core idea: This is not just theory → it’s real engineering decision-making

🧱 2. Reactor Types

Basic reactor models:

• Batch reactor → closed system, no inflow/outflow
• CSTR (Continuous Stirred Tank Reactor) → perfectly mixed, steady inflow/outflow
• PFR (Plug Flow Reactor) → flow with no back-mixing
• PBR (Packed Bed Reactor) → solid catalyst packed inside

Concept (from diagram):

• Volume changes: dV
• Flow in/out: Q, Fi

💡 Key difference:

• Batch = time-based
• CSTR/PFR = flow-based

⏱️ 3. Retention Time

• Time material spends in reactor
• Critical for:
  • Conversion
  • Reaction completion

📈 4. Reactor Sizing – Levenspiel Plots

Used to determine required reactor volume

• CSTR → larger volume needed for same conversion
• PFR → more efficient (smaller volume)

💡 Insight: PFR is usually more efficient but harder to operate

⚖️ 5. One Large vs Multiple Small Reactors

One large reactor:

✔ Simple ❌ Problems:

• Heat control 🔥
• Mixing becomes poor
• Thick walls required
• Hard to transport/build

Multiple small reactors:

✔ Advantages:

• Easier maintenance
• Can run in parallel
• One can be cleaned while others run
• More flexible

💡 Industrial reality: Parallel smaller reactors are often preferred

🔥 6. Heating (Image slides explanation)

These slides show:

• Heat supply to reactors
• Energy balance importance

💡 Why heating matters:

• Reaction rates depend on temperature
• Endothermic reactions need constant heat input

🧮 7. Example: Vinyl Chloride Production

Given:

• Endothermic reaction
• Production rate
• Efficiency
• Heat values

Goal: 👉 Calculate fuel gas required

💡 Concept: Energy balance:

• Heat needed for reaction
• Heat losses
• Furnace efficiency

🌊 8. Multiphase Reactors

Types:

• Fixed bed
• Moving bed
• Fluidized bed

💡 Key concept: Mass transfer is critical

🔄 9. Mixing (CFD)

• Mixing can be simulated using CFD (Computational Fluid Dynamics)

💡 Why it matters:

• Poor mixing = poor reaction efficiency

🌫️ 10. Mass Transfer

Key idea:

Transfer of molecules between phases

Examples:

• Gas → liquid
• Liquid → solid particle

Concept:

• Transfer happens through a film layer (δ)

💡 Important:

• Mass transfer can limit reaction rate

🧱 11. Packed Bed / Pellet Transfer

• Transfer into catalyst particles
• Internal + external resistance

💡 Interpretation: Even if reaction is fast → diffusion can slow everything down

🏗️ 12. Vessel Design

Important factors:

• Shape → cylindrical
• Material strength
• Temperature
• Pressure

📊 13. Pressure & Stress

Types:

• Hoop stress (circumferential)
• Longitudinal stress

💡 Why important: Prevent explosion or rupture

🧫 14. Fermentation (Intro)

Biological reactors using cells

🧠 15. Fermenter Design

Things to consider:

• Batch vs continuous
• Sensors:
  • pH
  • Temperature
  • Oxygen
• Mixing
• Foaming

Materials:

• Must be sterile
• Must resist corrosion

💡 Key challenge: Biology adds complexity vs chemical reactors

⚗️ 16. Enzymatic Reactors

💡 Trade-off:

• Immobilized = stable but diffusion-limited
• Free = fast but less reusable

🧼 17. Cleaning (CIP & SIP)

Steps:

1. Water wash
2. Alkaline clean
3. Rinse
4. Acid clean
5. Rinse
6. (Steam sterilization)

💡 Critical in biotech: Avoid contamination

🧪 18. Bioreactors (Image slides)

These likely show:

• Reactor setups
• Aeration
• Stirring

💡 Interpretation: Bioreactors must:

• Supply oxygen
• Remove heat
• Maintain sterility

📊 19. Batch Bioreactor Behavior

Phases:

1. Lag phase
2. Exponential growth
3. Stationary phase

💡 Product formation depends on phase

📈 20. Growth Kinetics

• Specific growth rate
• Monod equation
• Inhibition effects

💡 Insight: Growth is not only about substrate → inhibition matters

⚖️ 21. CSTR Mass Balance (Steady State)

General form: 👉 In – Out + Formation = 0

💡 Fundamental engineering equation

🔁 22. Continuous Fermentation + Membrane Filtration (MF)

Key idea:

• Cells stay inside
• Product removed continuously

👉 HRT ≠ SRT (important concept)

• HRT = liquid residence time
• SRT = cell residence time

💡 Advantage: High productivity

🧪 23. Fermentation Case Study

Goal: Produce ethanol using:

• Batch system
• Continuous + membrane system

Conditions:

• pH 5.5
• 35°C
• Yeast: Saccharomyces cerevisiae

Feed:

• Molasses (pH 8.6, 10°C)

📐 24. Design Tasks

You must:

• Draw P&ID
• Size reactors
• Select pumps/materials
• Compare costs

💡 This is your exam project core

📊 25. Batch Fermentation Results

Given:

• Final ethanol: 41.5 kg/m³
• Time: 14.9 h
• Rate: 2.79 kg/m³/h

💡 Interpretation: Slower but simpler

⚡ 26. Continuous MF Results

Different dilution rates:

• Di = 0.2 1/h
  • Moderate productivity
• Di = 1 1/h
  • Very high productivity

💡 Trade-off: Higher rate → more demanding operation

📏 27. Reactor Dimensioning

Compare:

• Batch vs continuous

Given same production: 👉 Continuous system is much smaller

💡 Key takeaway: Continuous = more efficient

📝 28. Exam Information

• Mini project + assignments
• Deadline: May 13, 2026
• Exams:
  • Biotechnology: June 3
  • Chemical Engineering: June 4

🧠 Final Big Picture

Core Engineering Themes

1. Reactor choice affects everything
2. Scaling introduces problems
3. Mass transfer can limit performance
4. Bioprocesses add complexity
5. Continuous systems are more efficient but harder

⚡ Quick Mental Map

• Reaction → Reactor type → Size → Heat → Mixing → Mass transfer → Cost → Feasibility