The use of steam for industrial purposes, including the cold chain, dates back to the Industrial Revolution and, even in the wake of the fourth industrial revolution and with the proliferation of artificial intelligence (AI), steam boilers remain the unsung heroes of contemporary production and the ‘chameleons’ of manufacturing, as a recent blog describes them. Part 1 of a two-part series.
Dennis Williams, commercial director at steam and boiler operations and maintenance service provider, Associated Energy Services (AES) explains: “The science behind steam use and heat transfer is fundamental to many processes, and will remain a requirement for many industries into the future. The mode of steam generation might change and the fuels might change, but steam will be needed.
Accordingly, the evolution of industrial process steam boilers has included upgraded control systems and instrumentation. The fundamentals of the ‘boiler’ part of the system where energy is transferred from combustion flue gases into the water to generate steam has been well established for many years. The focus has shifted to optimising combustion, improving efficiency, aiding operability (reaction time, load following capability, turndown) and improving emissions (reducing CO² and NOx).
When it comes to Eskom power-station sized utility boilers, change has centred on boiler materials and design – with the aim of increasing generation steam pressure to supercritical phase to drive power generation efficiency, and to then consider carbon capture and storage (CO2 capture options; as well as novel combustion systems to drive overall boiler thermal efficiency.
‘Steamy’ mix of old and new
The burning question around steam boilers is undoubtedly, has South African industry kept up?
Williams observes that the local boiler fleet is best described as “legacy” plant – evidenced by the buoyant second hand/refurbished steam boiler market. This is because older boilers are extremely robust and, with proper operation and care, can last between 20 and 40 years.
“There are, however, ways for the combustion elements (energy input mechanism) to be evolved via retrofits on control systems, fuel switches or technology replacements,” he suggests.
New fuels have also ushered in various changes, with more gas-fired, biomass and novel fuel systems being implemented, to facilitate the use of (previously) inefficiently used resources to drive circular operating systems.
However, the main differentiator between South African boilers and those used in North America and Europe is the use of coal, which has been replaced by alternative fuel sources, particularly gas.
“On larger scale plants, there has been a lot of activity in fluidised bed systems, including bubbling and recirculating fluidised bed boilers. Their lower combustion temperature has a positive effect on NOx generation and the technology is suited to solid fuels. Fluidised bed boilers have also been used in a few limited applications in South Africa, but the substantial capital investment cost has detracted from this,” he continues.
Williams believes that steam is so enduringly popular primarily because it is an extremely useful and excellent heat transfer mechanism: “It contains both latent and sensible heat energy and can deliver substantial quantities of energy in smaller flows than alternative heat transfer mechanisms relying solely on sensible energy (temperature). Steam can therefore ensure that temperature within a system is very accurately and effectively controlled.
Source: AES