As the original equipment manufacturer (OEM) of hundreds of steam boilers in Africa, Babcock played a part in the build of one of South Africa’s largest power stations, focusing mainly on the construction of the high-pressure (HP) piping systems. When one of the steam air heaters was damaged, the Babcock crew was awarded the contract to undertake repairs. These involved specialised rigging and welding expertise. The steam air heater repaired is a multi-row fin tube heat exchanger, consisting of three tube bundles and two bypass dampers installed in the air ducting of the boiler.
Tommy Scheepers, Senior Piping Engineer at Babcock, explains the significance of the rotary air preheater. In combination with the steam air preheater, it works sequentially to control both primary and secondary air temperatures before the air enters the boiler furnace through the burners. Precise control of the combustion air temperature is crucial in regulating the combustion process, ensuring efficient burning to minimise environmental emissions.
The damaged steam air heater could not be removed from the plant as that would have required extensive and costly rigging, together with additional structural support to maintain the integrity of the boiler ducting. Consequently, the replacement of the fragile nine-metre-long finned tubes had to be performed on the tubes individually in situ. Specific rigging methodology, routes and lifting aids were identified and developed prior to the replacement.
Before starting the refurbishment work, the Babcock crew had to remove the existing damaged finned tubes from the steam air heater frames inside the ducting. This involved cutting out and removing the connecting auxiliary steam and condensate drain piping to provide access for rigging activities on the outside of the ducting. The inlet and outlet air chambers were also removed, followed by the removal of the steam headers and tube sheets.
The air heater finned tubes are made from carbon steel with embedded aluminium spiral fins. These finned tubes are sourced offshore, with related delays in supply and high costs. The style of tube used is required for efficient heat transfer between the internal steam-heated tubes and the secondary air flowing over the fins.
Scheepers explains that special precautions were taken to prevent any damage to the fragile finned tubes during handling, rigging and installation, bearing in mind the consequences for the team in terms of time, cost and quality of the overall repair. “The handling of these delicate materials in a confined area required meticulous planning, sequencing and control of all actions by the staff involved during the replacement process, making this a complex and detailed undertaking,” Scheepers says.
Babcock Construction Manager, Luis Ferraz De Almeida, emphasises the company’s commitment to providing safe and effective solutions throughout the lifecycle of power plants. Babcock is renowned for its expertise in welding special creep-resistant alloy steels, and the front-end design of steam generation plants and pressure equipment.
"Our customer had confidence in Babcock's boiler knowledge and in-house expertise, which assured them that we could perform this specialised steam air heater replacement project successfully within the specified timeline," adds Ferraz De Almeida.
As an original equipment manufacturer with over 130 years’ experience, Babcock has the expertise to design, build, maintain and operate complex and critical steam-generation infrastructure. Its products and services additionally include boiler cleaning and optimisation, ash handling, wet and dry flue gas desulphurisation, bubbling and circulating fluidised bed boilers, and industrial and chemical recovery boilers.
With its specialised expertise, Babcock has consistently provided advanced world-class power generation and environmental technology solutions to industrial and utility customers in South Africa. It has helped businesses optimise operations and reduce environmental impacts, assisting them in aligning their operations to contribute to global decarbonisation and climate change objectives.
For more information visit: www.babcock.co.za
