InterGroup was engaged by Top Energy to clean two pre-heaters at the Ngawha Generation site as part of a critical maintenance program aimed at restoring operational efficiency. Over time, scaling inside the heat exchanger tubes had significantly reduced heat transfer capacity by nearly 50%, impacting overall performance and power generation stability for the Far North region.
Works took place during a tight shutdown period, requiring precise planning and execution to meet deadlines without compromising safety or quality.
Team preparing pre-heater for automated high-pressure cleaning at Ngawha Generation site.
What We Did
We began with a detailed assessment using as-built plans provided by Top Energy to gain thorough understanding of the project’s scope and complexity. Each exchanger vessel contained 1,520 seamless SA789 tubes, each measuring 18.28 meters in length and one inch in diameter. Operating at approximately 50% capacity, the exchangers showed moderate scaling, softened slightly by regular caustic washing performed by Top Energy.
To address the issue, we carried out automated high-pressure water jetting and employed a fleet of high-pressure pumps. Custom brackets were designed and installed to secure the cleaning equipment to the exchanger faces, which measured approximately 2.35 meters in diameter. This allowed for efficient and controlled cleaning of all tubes without causing damage to the equipment.
Throughout the process, we adhered to strict safety protocols – including confined space entry procedures, full PPE, continuous ventilation, atmospheric monitoring and emergency rescue readiness.
Heat exchanger tubes after cleaning – restored to near-design efficiency.
Use of Industry-Leading Automated Technology
To maximise efficiency and safety during the cleaning process, InterGroup deployed our StoneAge Sentinel AutoBox 3L equipped with Sentinel Smart Technology. This hands-free system enables precise tube cleaning using triple, dual, or single flex lances – delivering up to 30% faster performance compared to traditional methods.
By integrating automated cleaning technology with our high-pressure pumping systems, we achieved exceptional results – restoring 95% of the original heat transfer capacity and reducing pressure drop by 90%. This approach not only improved operational efficiency but also minimised manual handling risks, reinforcing our commitment to innovation and safety in critical infrastructure projects.
StoneAge Sentinel AutoBox 3L in operation for hands-free tube cleaning at Ngāwhā Generation Plant
Meeting complex Challenges
The project presented several challenges. First, the level of scaling had caused a dramatic increase in pressure drop across the exchangers (from the designed 0.5 bar to 3.5 to 3.7 bar) creating operational inefficiencies and requiring a robust cleaning solution. Additionally, the work had to be completed within a limited shutdown window, meaning there was no room for delays. InterGroup drew on our nationwide expertise and our innovative automated cleaning technology to overcome these challenges.
By combining careful planning, custom engineering solutions and precise execution, we ensured the cleaning process was completed safely, efficiently and ahead of schedule.
One of our technicians tightening flange bolts during heat exchanger cleaning to ensure safe and efficient operation
Project Results
Heat transfer capacity was restored to 79.14 MW, achieving 95 percent of the original design specification, as compared to 45.14 MW before cleaning. Pressure drop was reduced from 3.5–3.7 bar to 0.35 bar, a 90 percent improvement. These results returned the system to near-design efficiency and improved generation stability for the Far North region. The project was completed safely and within the defined shutdown window.
Client Feedback
Top Energy expected a solution that would restore performance close to design capacity within a very limited shutdown window, while maintaining strict safety and environmental standards.
InterGroup delivered on these expectations – combining innovative automated cleaning technology with precise planning and skilled execution. The improvements achieved exceeded performance goals and ensured long-term operational reliability.
“Estimated thermal exchange is now approximately 95% of the original designed capacity.”
– Top Energy