When retrofitting and upgrading boilers, operational experience, technical knowledge of different boiler types, operating conditions and water treatment count. Through operating 79 boilers, AES knows what works and what does not. This equips the company as South Africa’s go-to industrial steam operations and project company to share insights and make invaluable recommendations.
Motivation for boiler retrofits
“Retrofitting a boiler is like upgrading some components on a car rather than replacing its entire engine,” explains AES commercial director, Dennis Williams.
“New control systems improve fuel efficiency, emissions and load response without changing the boiler’s original pressure rating. The right upgrades deliver meaningful performance improvements while extending the delivery of value through existing assets.”
He points out that the main motivations for applying a retrofit or upgrade to an existing boiler could include:
• Unworkability of obsolete instrumentation and equipment, and non-availability of spare parts such as SCADA, PLC, control modules and electronic components.
• Incompatibility with updated technology in management systems, for example, collection of site operating data, process management and efficiency tools.
• Efficiency impacts due to obsolete design of air preheater or economiser components, combustion and control system design, fuel management, and air distribution system designs.
• Inability to comply with emissions targets because of ageing and poorly performing emission abatement plant.
• Desire to reduce carbon footprint through a fuel switch where combustion system can be changed.
Additional considerations include maintenance of boiler steam output due to changes in combustion, and emission abatement systems that require changes to draught management through the boiler, as well as improved electrical efficiency through applying latest technology on electrical motors and drives, better boiler operability by improving a boiler’s ability to respond to load changes and operate with lower emissions.
“Retrofits such as boiler control systems, combustion systems, burners and flue gas upgrades, can improve boiler combustion and overall efficiency, mirroring the benefits of a new plant with its better operating efficiency, yet unfortunately, also high capex requirements,” Williams notes.
An example of the potential payback is a 15% improvement in efficiency with a 13,1% reduction in fuel intensity per ton of steam generated, following the retrofit of a boiler control and steam load balancing system on a fast-moving consumer goods client site featuring multiple boilers.
Benefits included access to operating data from the boiler house for overall plant management insight and planning, and a reduction of between
First-hand insights
Regarding boiler modifications, Williams says AES has assessed a range of combustion and burner systems. “Through engagement with original equipment manufacturers, site visits and reviews of client reference plants, AES has gained first-hand insight into pyrolysis, gasification, biofuel combustion and other technologies that can often be retrofitted to package boilers for fuel switching.”
AES has also developed an in-house control system that supports boiler combustion, overall efficiency and load-following performance. It can incorporate load-balancing systems to distribute steam demand across multiple operating boilers. The system is continually reviewed, adjusted and optimised to ensure the most effective combustion technology is applied.
In addition, AES installs and operates emissions-abatement solutions such as bag filters and electrostatic precipitators or ESPs and has first-hand experience with alternative systems. “AES has access to an advanced cyclone particulate-emission abatement plant that achieves flue-gas particulate loading below 120 mg/Nm3.” This technology is more
To retrofit, or not
Williams stresses that retrofitting differs significantly from legally required pressure-vessel maintenance and repairs, such as welding repairs and tube replacements.
A complete boiler replacement is only necessary when an asset has limited remaining life and there is clear value in buying a new unit. “When addressing emissions, if a retrofit can achieve the same outcomes, and changes can be made to control systems, combustion systems and burners on an existing boiler, then that would negate almost all of the benefits of a new boiler,” he continues.
Replacement might also not be considered where an asset’s days are numbered. This applies when the wall thickness on the pressure parts of an older boiler is compromised through rusting of the outer shell or internal pitting corrosion due to poor water treatment. “This may render boilers non-compliant in terms of their originally designated steam pressure and temperatures.
In such cases, professional engineering experts can perform the necessary design calculations, while an approved inspection authority can assess whether the boiler’s affected areas can be repaired or whether the operating pressure should be reduced so the boiler can continue operating,” Williams advises.
Using a boiler designed to operate at 20 bar as an example, he explains that if there is a case for de-rating and recertifying the boiler to a lower maximum pressure, the reduced steam pressure must still meet the client’s needs. “If they do not require 20 bar steam, this remains workable. If they do, the boiler must be replaced.”
Safety and legal compliance
Another safety aspect entails ensuring that a new liquid or gas burner installed in a boiler has the correct flame shape and size to prevent impingement of the flame onto the boiler’s metal surfaces. Flame adjustment and setup is needed to prevent localised overheating and possible failure.
Steam plant safety requirements in South Africa and boiler compliance requirements go hand in hand. Adjustments must be undertaken in alignment with the legal requirements such as Pressure Equipment Regulations.
Changes impacted by legal and design restrictions require signoff by approved and professional parties. Third party oversight and approvals are critical, and over the years, AES has worked closely with approved inspection authorities, as well as metallurgical and engineering design professionals, to evaluate each situation according to its merits.
Safety is one area where AES will not compromise: “If we arrive on site and find that an asset is not signed off legally to be operational, we will immediately shut it down. It is absolutely critical that clients understand legislative requirements in terms of boilers as pressure vessels, and safety around these is strictly non-negotiable,” Williams concludes.
For more information contact AES,
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