Clean sweep
Many fired heaters operate below their design potential due to progressive fouling in the convection section. This case study examines how a large US Gulf Coast refinery restored lost performance in its delayed coker unit (DCU) heaters using robotic cleaning technology (Rovex), following a data-driven thermal efficiency evaluation that quantified the opportunity and projected return on investment (ROI)
Prior to execution, the refinery engaged in a complimentary fired heater thermal efficiency evaluation to assess current operating performance against design intent. The evaluation identified significant convection section under-performance across three terrace-wall DCU heaters, processing approximately 100,000bpd. The study highlighted measurable inefficiencies, including reduced heat recovery, elevated flue gas temperatures, and increased reliance on radiant section duty. Importantly, it also quantified the financial upside of restoring convection performance, providing a clear business case for intervention.
THE IMPACT OF CONVECTION SECTION FOULING
Fouling within convection tube banks is a well-understood but often under-estimated issue in fired heaters, particularly in coking-prone services such as DCUs. Deposits restrict heat transfer, forcing higher firing rates to maintain target process temperatures. Over time, this leads to:
- Increased fuel consumption and operating costs
- Elevated tube metal temperatures and higher coking rates
- Greater thermal stress
- Reduced operational flexibility
At the subject refinery, convection sections were operating well below design duty in all three heaters. Traditional cleaning methods, including chemicals, hydro-blasting, and dry ice, had been deployed previously, but with inconsistent and incomplete results due to unknown fouling characteristics, limited access and complex tube geometries.
LIMITATIONS OF CONVENTIONAL CLEANING APPROACHES
Manual and semi-mechanical cleaning techniques present several challenges in modern fired heaters:
- Safety exposure: Many methods require confined space entry
- Incomplete coverage: Dense tube arrangements limit access
- Inconsistent results: Cleaning effectiveness varies across passes
- Operational disruption: Extended downtime may be required
These limitations often result in only partial performance restoration, leaving significant efficiency gains unrealised.
ROBOTIC CLEANING WITH ROVEX
To address these challenges, the refinery deployed Rovex by TubeTech, a robotic convection cleaning system designed for high-coverage, repeatable cleaning in complex geometries. Operating remotely, Rovex eliminates the need for confined space entry while enabling precise and consistent cleaning across accessible tube surfaces.
Key features of the Rovex system include:
- Full-surface cleaning in tight tube configurations
- 90-95% coverage of convection surfaces
- Real-time visual verification via onboard cameras
- Controlled, repeatable cleaning methodology
The project scope included cleaning across three convection sections, each with four tube coils approximately 70 feet long. Additional access ports were installed to ensure complete coverage.
OPERATIONAL EXECUTION
The cleaning project was completed over nine shifts with zero safety incidents and no delays to the turnaround schedule. Remote operation allowed work to proceed efficiently while maintaining strict safety standards.
Following cleaning, a post-project evaluation was conducted to validate performance improvements and quantify gains relative to pre-cleaning conditions.
RESULTS: CONVECTION DUTY RECOVERY
The cleaning intervention delivered a substantial recovery in convection section performance across all three heaters. Table 1 summarises the measured improvements. Notably, these gains were achieved while operating at higher process outlet temperatures, confirming that the improvement was driven by restored heat transfer rather than changes in operating severity.
BROADER PERFORMANCE BENEFITS
Beyond convection duty recovery, the refinery observed a range of measurable operational improvements:
- Fuel efficiency: Increased by approximately 1 percentage point
- Flue gas temperature reduction: 93°F (52°C)
- Stack temperature reduction: 26°F (14°C)
- Fuel gas savings: ~4.0 MMBtu/hr (~1.17 MW)
- CO2 emissions reduction: ~1,870 tonnes per annum
From a thermal management perspective, reduced radiant heat flux lowered tube metal temperatures and decreased coking propensity, contributing to improved reliability and extended run length. Additionally, the plant gained operational flexibility, with the ability to shift between maximising throughput and minimising fuel consumption depending on economic conditions.
RELIABILITY AND MAINTENANCE IMPLICATIONS
The restoration of convection section performance had a direct impact on heater reliability. Run length is expected to increase by up to 5%, translating to more uptime between turnarounds. This improvement is particularly valuable in DCU operations, where unplanned downtime carries significant economic penalties.
The repeatability and scalability of robotic cleaning also support a more proactive maintenance strategy. Rather than relying on reactive interventions, operators can incorporate convection cleaning into planned maintenance cycles, preserving efficiency over the long term.
This case study demonstrates that convection section fouling represents a significant but recoverable source of efficiency loss in fired heaters. Through the combination of a data-driven thermal efficiency evaluation and advanced robotic cleaning, the refinery was able to restore heat transfer, reduce fuel consumption, and improve overall heater reliability.
For operators facing similar challenges, the first step is understanding the true performance gap. A comprehensive thermal efficiency evaluation can identify bottlenecks, quantify potential gains, and provide a clear pathway to improvement, often with compelling payback.
Larry Emch is senior director of technical sales at IGS.
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