A Guide for Midstream Process Engineers

In midstream gas processing, efficiently removing H₂S and CO₂, the “baddies” of incoming natural gas, is non-negotiable. The amine plant handles this job, and at the heart of every amine unit is one crucial step: heating the amine solution for regeneration. The question midstream engineers ask most often is simple: What is the best way to heat the amine regenerator?

In our latest “Good, Better, Best” video, we break down the three primary heating methods used in amine systems, examine their benefits and drawbacks, and explain why heating technology matters for amine solvent longevity, regenerator stability, and overall plant reliability.

Below is an expanded, engineer-focused overview of the concepts covered in the video.

Understanding Why Amine Heating Method Matters

In a typical amine plant, rich amine enters the regenerator, where heat is required to strip out the absorbed H₂S and CO₂. The reboiler delivers this energy, producing steam/vapor that rises through the column and regenerates the amine for reuse in the absorber.

Key temperature considerations:

• Typical lean amine outlet temperature: ~250°F
  
• Maximum stable film temperature for most amine solvents: ~300°F
  
• Exceeding this threshold accelerates amine degradation, corrosion, and solvent loss
  
  

This makes the type of heat source and the way heat is applied critical to protecting the amine, controlling film temperatures, and avoiding excessive thermal stress.

The Three Heating Methods: Good, Better, Best

1. Firetube Reboiler – Good

The firetube reboiler is the most common low-capital-cost option in midstream amine units. A burner fires inside a large diameter tube, transferring heat directly through the tube wall into the amine.

Advantages

• Lowest initial cost
• Self-contained (no pumps or hot oil loops)
• Simple installation and smaller footprint
  
  

Drawbacks

• High firetube metal temperatures (often around 550°F)
• Increased risk of high film temperature on the amine solution
• Essentially stagnant liquid around the tube → low heat transfer coefficient
• Higher likelihood of amine degradation
  
  

Because amine likes to be heated gently, firetubes operate close to the upper limit of acceptable temperatures. This makes them a “good” technology, functional, but not ideal for long-term solvent health.

2. Direct-Fired Amine Heater (Direct Coil) – Better

A direct-fired heater with an amine coil improves heat transfer significantly by forcing the amine through piping at high velocity.

Advantages

• Better control over heat input compared to firetubes
• Higher inside heat transfer coefficient due to flowing amine
• Reduced risk of hot spots and better film temperature distribution
• More efficient use of burner energy
  
  

Drawbacks

• More equipment than a firetube (coils, separator, connections)
• Still exposes the coil to the radiant and convection sections of a fired heater
• Higher capital cost than firetube systems
  
  

Direct-fired coils allow more even heating and better temperature control, making them a clear step up, a better midstream amine heating solution.

3. Hot Oil (Heat Medium) System – Best

Hot oil systems represent the highest level of temperature control and amine protection. Instead of direct flame exposure, heat is delivered via circulating thermal oil through a tube bundle inside the reboiler.

Advantages

• Gentle, predictable heating
  
• Typical film temperatures are far below degradation limits
• Excellent temperature control (often within ±1°F)
• Tunable system using oil temperatures around 350–400°F
  
• Dramatically reduces risk of amine breakdown
• Highly reliable and long-lived system
  
  

Drawbacks

• Higher upfront cost (heater, pumps, expansion tank)
• More components than a firetube or direct-fired coil
  
  

Despite the added equipment, the process protection and temperature precision make hot oil systems the clear winner for modern midstream amine plants.

For large, continuous midstream service, especially those processing high H₂S or requiring maximum uptime, hot oil is the best-in-class heating method.

Good, Better, Best: The Bottom Line

When comparing the three heating options for amine systems:

From an engineering and long-term OPEX perspective, Hot Oil = Best Performance for midstream amine plants.

Contact Tulsa Heaters Midstream 

At Tulsa Heaters Midstream (THM), we specialize in fired heaters, hot oil systems, and thermal solutions designed specifically for the midstream market. After decades of experience supporting amine plants in real-world field conditions, we consistently recommend hot oil heating due to its:

• Superior temperature stability
• Enhanced solvent protection
• Reduced downtime and maintenance
• Better overall lifecycle cost

While capital cost differences exist, the long-term operational benefits make hot oil systems the strongest choice for midstream professionals seeking reliability.