| Coal-to-gas conversion


and secondary air heater audit. Data from these activities was then fed into RJM’s analysis of the furnace and combustion air systems. With over 10 000 MWe of gas and oil burner upgrades, RJM’s experience of assessing and analysing large utility boilers was combined with deployment of its proven Ultra-low NOx


Burner™ design to deliver the performance improvements demanded by the contract.


The importance of accurate CFD Having inputted data gathered from around the plant, RJM conducted a detailed programme of CFD analysis which enabled it to optimise the combustion system design.


It also enabled RJM’s CFD engineers to make changes to plant equipment within the virtual model. Burner design, configuration, nozzle sizes and locations, fuel and air velocity, fireball location, temperatures and emissions can all be progressively optimised as the model is run through a series of iterations.


Making incremental changes delivers step-by- step improvements each time, until the objectives of the plant’s performance upgrade are met. A successfully completed CFD programme is therefore instrumental in determining what new equipment needs to be designed, where it will be located and what the new operational settings should be to deliver the performance uplift.


Installation time-line January 2025


February 2025


SolidWorks image of the new RJM CleanAir Burner™ (Image: RJM Intermational)


CleanAir


In terms of fuel/air delivery systems, CFD can also be used to identify locations where flow improvements are required to reduce system pressure drops and, in this case at Aboño, it was used to verify how well the BFG burners would perform as pseudo-OFA (over-fire air) ports, following the conversion to gas.


First batch of burners delivered to site


Rest of burners, BFG pilot parts and ancillary components delivered to site


End February 2025 Outage begins March 2025 April 2025


May 2025 June 2025


June/July 2025 July 2025 July 2025


Installation commences First new burners installed


Installation of new components checked


Cold commissioning and first firing


Optimisation


Boiler performance tests and performance guarantees met


Hand-over to the customer


In conjunction with the CFD work, using its engineering experience and its well-proven engineering tools, RJM assessed the capability of the existing BFG burners to work in


conjunction with its new Ultra-low NOx CleanAir Burners™.


As well as assessing the ability of the BFG burners to be used as over-fire air ports for periods when BFG is not available, RJM designed further modifications to the BFG pilots to ensure BFG flame stability and performance.


Design and manufacture For this Aboño 2 project, to make the upgrade as cost-effective as possible and to minimise the duration of the outage, RJM decided to retain as many interfaces and other “non-performance critical” parts as possible and only design and


manufacture the essential “performance critical” new kit that would be required.


RJM designed and supplied 30 new ultra-low NOx


gas burners to replace the existing coal burners and 12 conversion kits to allow the gas igniters from the coal burners (that were now no longer needed) to be re-used as pilots for the BFG burners. The 12 existing BFG burners were then fully refurbished. In addition, gas pilots replaced diesel firing, thereby providing a further reduction in emissions. Meanwhile, new burner frames and refractory stuffing boxes were designed by Wood, whilst the boiler protection system was upgraded and modernised. Wood and RJM jointly supervised the installation of the gas burners and retrofitted the BFG burner pilots. Expert engineers also redesigned the superheater surfaces, whilst the tube alloys were upgraded to withstand the new operating conditions.


To accommodate the change in heat transfer characteristics arising from converting to gas firing, Wood extended the boiler economiser and conducted a remnant life assessment of the pressure parts that remained unchanged. Wood


Left: Customer inspection (Photo: RJM International)


Above: Completed burners prior to painting (Photo: RJM International)


www.modernpowersystems.com | November/December 2025 | 39


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