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)

This is the Difference Between Hydrocracker and Mild Hydrocracker

🔹 Hydrocracker (Full / Conventional Hydrocracking)

• Operates at high severity conditions (high temperature & high pressure)
• Extensive cracking of heavy hydrocarbons into lighter products
• Produces large amounts of:
  • LPG
  • Naphtha
  • Kerosene
  • Diesel
• Requires high hydrogen consumption
• Uses highly active catalysts
• Goal: maximum conversion of heavy oil into lighter fuels

🔹 Mild Hydrocracker (MHC)

• Operates at lower severity conditions
• Limited or partial cracking
• Focus is mainly on:
  • Improving product quality
  • Removing sulfur, nitrogen (hydrotreating effect)
• Produces more middle distillates (diesel) and less gas
• Lower hydrogen consumption
• Goal: upgrade feedstock quality, not full conversion

🔥 Key Differences (Simple Table)

🎯 Simple One-Line Answer (for Interview)

👉 A hydrocracker performs deep conversion of heavy hydrocarbons into lighter products at high severity, while a mild hydrocracker operates at lower severity mainly to improve product quality with limited cracking.

Emergency Shutdown (ESD)

An Emergency Shutdown (ESD) is a safety procedure implemented in industries or systems to quickly and safely halt operations in response to a potential hazard, fault, or dangerous situation. The goal is to protect equipment, people, and the surrounding environment.

Key Points:

• Purpose: The purpose of an ESD system is to minimize or prevent catastrophic events like fires, explosions, system failures, or hazardous chemical spills. This is especially important in high-risk industries like oil and gas, manufacturing, power generation, and chemical plants.

• Components of an ESD system:

  • Emergency Stop Button: A physical or digital button that, when pressed, will immediately stop a system or machine to prevent harm.

  • Sensors and Monitoring Systems: These monitor for dangerous conditions such as abnormal pressure, temperature, or chemical leaks that may trigger an emergency shutdown.

  • Control Systems: Automated systems that activate in the event of an emergency, taking action to safely shut down operations without requiring manual intervention.

Common Scenarios for ESD Activation:

• Industrial Manufacturing: If machinery malfunctions or poses a risk (like overheating, mechanical failure, or fire), an emergency shutdown prevents further damage or injury.

• Power Plants: In power generation, if there’s a failure or abnormal operating condition, ESD procedures will engage to prevent equipment damage, reduce risk of fire or explosion, or protect workers.

• Oil and Gas: In the event of a gas leak, pressure surge, or equipment failure, an emergency shutdown is necessary to protect workers, prevent environmental contamination, and minimize the risk of explosions.

Types of Emergency Shutdown:

1. Automated ESD: Triggered automatically by monitoring systems based on specific thresholds, such as excessive pressure, temperature, or leak detection.

2. Manual ESD: Activated by an operator or authorized personnel through an emergency stop button or control system.

Steps Involved in an Emergency Shutdown:

1. Detection: The system identifies a dangerous condition (e.g., a pressure leak, gas buildup, or system malfunction).

2. Activation: A signal is sent to shut down operations, which could involve stopping machinery, cutting power, or diverting harmful substances.

3. Action: The system takes steps to ensure safety, such as shutting off valves, activating fire suppression systems, or bringing equipment to a safe state.

4. Recovery: After the emergency, the system may go through a controlled restart process to assess and address any damage before returning to normal operation.

Summary of Differences:

• ESD (Electrostatic Discharge): A sudden release of static electricity that can cause damage to electronic components.

• ESD (Emergency Shutdown): A safety procedure designed to stop operations in an emergency situation to protect people, equipment, and the environment.