THE use of steam for industrial purposes 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 notes.
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 a supercritical phase to drive power generation efficiency, and to then consider carbon capture and storage; as well as novel combustion systems to drive overall boiler thermal efficiency.
Mix of old and new
Williams observes that the local boiler fleet is best described as “legacy” plant – evidenced by the very 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 element (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differentiator between South African boilers and those used in North America and Europe is the use of coal, which has been replaced by alternative fuel sources, particularly gas.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.
The use of steam is widespread across various industries including pulp and paper, textiles, healthcare, air conditioning, laundry services, mining, medical manufacturing, power generation, desalination, wood board manufacture and chemical manufacturing where it is used in cooking, heating, cleaning, sterilising, curing, evaporating, raw materials preparation, drying, setting and turbine-driving processes.
Williams notes that, in South Africa, efforts to improve local industries such as the food and textile sectors could certainly see an increased demand for steam.
The right boiler for the job
Williams explains that there are two main types of boilers: those with a fire tube design, which is essentially a cylindrical vessel containing water, with tubes passing through it that carries hot flue gas through the inside of the tubes. Heat transfers through the tubes to the body of water on the outside of the tubes, eventually creating steam. Water tube boilers contain less water volume per unit of steam output, featuring upper and lower steam drums connected by boiler tubes. Water boils within the tubes, with steam rising to the top of the boiler into the steam drum.
There is also the option of a combined water tube and fire tube design.
Williams adds that optimising efficiencies and understanding a client’s current and future operational requirements are critical when selecting a boiler: “The decision needs to be robust and defensible in terms of longer-term business strategy. These assets are expensive to buy, operate and maintain – and have potentially long service lives if well maintained, so a selection error can impact on many fronts for a long time.”
Partnership
AES claims to be the ‘perfect partner’ in making such a decision, with many years of experience across numerous industries, operations and energy plants, equipping the company to provide the necessary on-the-ground capex, opex and other insights. After engaging with a client to understand the company’s overall objectives, AES can provide an overview of workable steam boiler alternatives – and assist in clarifying the technicalities of each.
“We can then assist with the execution of a project on a turnkey basis – or combine the turnkey project with an operations and maintenance SLA which covers a longer-term contract period (of at least three years). AES can provide a solution while being fully accountable to clients around their operational outcomes,” Williams concludes.
