Max temperature at CDU fired heater outler

1. Typical CDU Furnace Outlet Temperature (COT)
Normal operating range: 340–370°C
Some units push to: 350–380°C

👉 This is the industry “safe zone” for atmospheric CDU.

⚠️ 2. Absolute Upper Limit (Before Cracking/Coking)

Once you go beyond design:

Around ~380°C+ → thermal cracking starts increasing
Above ~400°C → serious coking risk
Absolute extreme (rare, short-term): ~390–400°C max

Why?

Crude components (resins/asphaltenes) thermally decompose
Coke forms inside furnace tubes → pressure drop ↑ → tube hot spots → failure risk
Refiners avoid this deliberately (this is why VDU exists instead of higher CDU temp)
🧠 3. Key Insight (Important for You)

You cannot maximize diesel by just increasing temperature.

Because:

Higher temperature → more cracking → gas + naphtha, NOT diesel
Diesel yield depends more on:
Cut point optimization
Flash zone conditions
Reflux/pumparound
Stripping efficiency

👉 Overheating actually reduces diesel selectivity

⚙️ 4. What Controls Your REAL Temperature Limit

Your actual max is NOT a fixed number—it depends on:

✅ Crude type (Egina specifics)
Medium crude → moderate coking tendency
Likely safe ceiling: ~365–375°C
✅ Furnace design
Coil metallurgy
Heat flux (critical)
Residence time
✅ Velocity & steam injection
Higher velocity → less coke
Steam dilution → reduces partial pressure
✅ Run length target
1–2 years run → conservative temp
Short campaign → you can push slightly higher
📊 5. Practical Recommendation (For Your Goal: Max Diesel)
🔹 Safe operation range:

👉 350–370°C (optimal)
👉 370–375°C (aggressive but still controlled)

🔹 Avoid:

❌ >380°C continuous operation
❌ Trying to “force vaporization” of heavy ends

💡 6. Better Ways to Increase Diesel Yield (Instead of Temp)

If your goal is diesel maximization, do this:

Increase overflash (3–5%)
Optimize cut point (AGO endpoint)
Improve side stripper steam
Adjust flash zone pressure (slightly lower)
Optimize pumparound heat removal

👉 These give more diesel without coke risk

🧾 Final Answer

👉 For Egina crude in CDU:

Recommended max: ~370°C
Aggressive upper limit: ~375°C
Do NOT exceed: ~380°C (high coking risk)