Heat Exchanger Fouling and Rubby Formation

Heat Exchangers as Critical Unit Operations in Methanol Plants

In methanol plants, fouling observed in downstream heat exchangers often originates in the Auto-Thermal Reformer (ATR), as a consequence of catalyst degradation mechanisms such as Rubby Formation.

This phenomenon occurs when impurities and hot spots inside the ATR weaken the catalyst support, triggering a chain of effects that propagate far downstream into critical equipment such as heat exchangers.

Figure 1 illustrates a practical example: on the right, a degraded catalyst pellet deactivated by Rubby Formation; on the left, silica deposits inside a heat exchanger tube. Together, they demonstrate how a localized reaction in the ATR can propagate downstream, affecting plant reliability.

In chemical engineering, heat exchangers are one of the most important Unit Operations for energy recovery and process efficiency.

When fouling occurs, the overall heat transfer coefficient drops, forcing higher temperature differences and increasing energy consumption.

For a general overview of heat transfer as a unit operation, refer to the article Heat Transfer in Chemical Engineering.

What Is an Auto-Thermal Reformer (ATR)?

An Auto-Thermal Reformer (ATR) is a key reactor used in methanol, hydrogen, and ammonia production plants. Its role is to convert light hydrocarbons (such as natural gas) into syngas — a mixture of hydrogen (H₂), carbon monoxide (CO), and carbon dioxide (CO₂).

Unlike a conventional steam reformer, the ATR combines two reactions inside a single vessel:

• Partial oxidation of hydrocarbons with oxygen (exothermic).
• Steam reforming with water vapor (endothermic).

The heat released by partial oxidation balances the energy required by steam reforming, making the process “auto-thermal.”

Advantages of ATR technology include:

• Compact design compared to large steam reformer furnaces.
• Ability to operate with a flexible steam-to-carbon ratio.
• Production of syngas with a suitable H₂/CO ratio for methanol synthesis.

This is why the ATR is often described as the heart of the methanol front-end process.

What Is Rubby Formation in Methanol ATR?

Rubby Formation is a degradation process that takes place within the catalyst bed of the ATR.

Impurities such as silica, alkalis, chlorine, and sulfur react with the alumina support of the catalyst under high-temperature hot spots.
The outcome is the formation of low-melting aluminosilicate phases, which progressively damage the catalyst structure.

Key consequences include:

• Gradual deactivation of nickel and loss of catalytic activity.
• Sintering and fragility of the catalyst bed.
• Release of fine silica particles into the syngas stream.

How Rubby Formation Impacts Heat Exchangers

The silica particles released in the ATR are transported downstream, where they deposit on heat exchanger tubes. This fouling layer drastically reduces thermal conductivity and impairs the exchanger’s ability to generate steam efficiently.

Operational impacts include:

• Reduced heat transfer efficiency.
• Increased gas outlet temperature from exchangers.
• Lower steam generation capacity.
• In critical cases, the need to derate the entire methanol plant to protect equipment.

Operational Mitigations

In methanol plants, several mitigation approaches have been adopted to limit the impact of Rubby Formation.

Among them, Steam Washing has proven effective in restoring heat exchanger performance.

This method involves increasing steam flow while slightly reducing oxygen, raising the S/C ratio up to ~2.2, and boosting linear velocity inside exchanger tubes to dislodge silica deposits.

The procedure is continued until downstream silica concentration stabilizes, confirming removal of transportable particles.

In addition to steam washing, controlling impurity levels and optimizing ATR operating conditions are also considered effective strategies to prevent the recurrence of Rubby Formation.

Other approaches reported in industry include the use of catalyst formulations with higher resistance to aluminosilicate formation, as well as periodic monitoring of silica levels downstream of the ATR.

Conclusion

Rubby Formation in ATR is not only a catalyst degradation issue — it creates a chain of operational challenges that extend to heat exchangers and overall plant reliability.

By combining preventive measures (impurity control, optimized ATR operation) with corrective actions like Steam Washing, plants can mitigate fouling, maintain energy efficiency, and sustain stable methanol production.

Ing. Ivet Miranda

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