When it comes to making the correct choice of thermal carrier for production optimisation, boiler operations and maintenance service provider AES’s Commercial Director Dennis Williams believes many questions must be asked: “These include how the energy is being used, if its supply should be outsourced, and if it is the right fit for every manufacturing process,” he says.
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A steam header with multiple process steam offtakes.
“Other pertinent questions would be how much of the facility is aligned with steam and how much with another thermal carrier? What are the implications of switching those? If changes are made, could the cost of production be reduced and quality improved?” he continues, advising that the best place to start is by fully understanding the company’s primary product, and the potential roles of different thermal carriers in the production process.
Steam and multiple-use challenges
Steam remains the most user-friendly thermal carrier. Inert, non-toxic and safe, it minimises dangers such as product contamination or fire in the event of a leak, which can happen with thermal oil, which is highly flammable and operates at high temperatures. Therefore, from a process safety management perspective, steam is a good choice. Furthermore, steam can be generated across a range of pressures, and heating can be tightly controlled.
In the event of the thermal carrier of choice being steam, and in an ideal world, a single steam user has a consistent load demand and operates continuously. In reality, it is more common to have to manage a dynamic steam plant operation, featuring multiple users, which requires strong technical skills, good communication and close attention to optimise results, emphasises Williams.
Understanding the process comes first when setting out to achieve efficient, optimal steam generation and thermal energy supply across a multi-use site, he notes: “This is critical to determine the energy flows required in terms of timing, tonnages, pressures, variability profiles and condensate return generated. These factors form an overall operational ‘map’ of the variation in demand and load on the steam plant.”
AES then determines the best operational strategy, including when to start which assets, specific boilers’ load profiles at particular times, and the management of risk in the event of equipment challenges or breakdowns. Site-specific operating procedures (SSOPs) are optimised based on the plant's configuration and user requirements.
AES’s Remote Monitoring System (RMS) gathers steam generation plant data and records critical operational monitoring parameters. This data is essential to monitor boiler efficiency and steam quality,” Williams explains.
The focus is not only on minimising steam use to achieve energy requirements, but also on maximising the percentage and quality of condensate return to save water and recover heat.
Additionally, pivotal Process Safety Management (PSM) within a multi-user environment requires consistent practices across multiple boilers: “We must ensure safe operation for multiple boiler plants, multiple combustion devices, more hot surfaces, more maintenance and variations thereof if using different boiler designs, fuels or combustion systems,” Williams points out.
Alternatives to steam
Pressurised hot water: Williams says that lower temperature requirements of 120 to 150°C do not require steam. Instead, by using a pressurised water heater, the water temperature will rise to the desired level without boiling and flashing to steam. This process is widely used in companies such as breweries. Another example is when cleaning a plant or equipment.
Gas and hot air: The textile and paper industries use gas and hot air extensively. “In the paper industry, there is a hood over the main paper cylinder, which is heated using gas. The flame is not fired onto the paper. Instead, it is used to heat the air directly in front of the burner flame. A flue gas-air mixture radiates onto the paper surface to dry out the last bit of moisture,” Williams explains.
Alternatively, manufacturing or processing companies can use a combination of thermal carriers. For example, in the food production sector, an AES client that manufactures coffee and coffee creamer utilises gas and steam-heated air to dry the product.
Thermal oil: Thermal oil is widely used in the textile sector, where it is circulated through stenters and other textile machinery to provide the required temperatures for fabric heat treatments. “Thermal oil, therefore, has specific applications, where higher temperatures can be achieved than when using a typical industrial process steam application,” Williams points out.
Making the right choice
“Decision-makers could unlock far more lasting and meaningful savings by carefully analysing key issues such as sustainability and efficiency,” he continues, adding that many companies are now integrating different thermal processes, including across multi-use sites, into one fully optimised system.
However, the capital outlay will differ across thermal carriers, with decisions influenced by the selection of the fuel and associated technology.
In summary, when considering thermal carrier changes or upgrades – including across multi-use sites -Williams warns against price-based procurement and recommends a longer-term, value-based approach: “It is about deriving maximum value from the production process and achieving optimal operational performance, margin and end-product,” he concludes.
AES is a leading steam and boiler operations and maintenance (O&M) service provider that operates in the power generation, chemical, plastics and rubber, timber, pulp and paper, textiles, food and beverage, and mining sectors of South Africa. The company helps industrial plants optimise their energy production processes and achieve best-practice energy use, including reduced downtime, efficient and cost-effective fuel combustion, extended plant life, energy resource diversification, and a smaller carbon footprint.
