BBe it the recent carbon tax legislation passed by the South African government or the introduction of ‘green’ import tariffs by the European Union (EU), the South African manufacturing sector is facing significant sustainability challenges, according to Dennis Williams, Commercial Director of Associated Energy Services (AES), a leading operations and maintenance services provider to the steam and boiler industry.
As the debate over emissions, affordability and “green” taxes on exports to the EU intensifies, Williams points out that it is not yet clear how emissions will be measured, whether improvements to existing energy plants will be recognised by the relevant authorities or whether manufacturing companies will be forced to switch entirely to alternative fuels.
“This would certainly be a blow to South African manufacturers who still rely on fossil fuels,” he notes.
Solid debate on energy efficiency
AES believes that a company’s path to sustainability begins with maximizing what can be achieved with existing energy assets.
“By controlling combustion and ensuring it is extremely responsive to the changing needs of each production plant, both costs and emissions can be optimised. However, different fuel types respond differently to fluctuating steam demands. For example, because gas combustion systems offer a high turndown range, they respond extremely quickly. Solid fuel combustion systems such as coal and biomass respond more slowly to changes in steam demand,” he explains.
He adds that there is only a certain amount of solid fuel in the incinerator at any one time and that, therefore, any change in the demand for steam requires a change in the amount of fuel supplied to the furnace as well as the amount of oxygen required to maintain effective combustion.
“The problem arises when you have several boilers running and suddenly there is a significant peak in steam demand. Under normal automatic control they ramp up to follow that peak and eventually catch up. But when that subsides there is enormous thermal inertia in those boilers. It is very difficult to counteract that quickly and this is wasteful in terms of the ability to burn coal effectively.”
Load balancing
AES’s load balancing system allows multiple solid fuel boilers to work together to provide steam effectively and efficiently when needed. The key to this is understanding a company’s steam load. When it is constant and changes only gradually, loads are easy to track. Unfortunately, sudden spikes and dips in steam demand are harder to control.
A coordinated approach using the overall load balancing control system effectively coordinates the steam demand of the various boilers and ensures optimization of online capacity to meet demand efficiently and effectively, recommends Williams: “We control how each of these boilers is synchronized to follow the load – and how it is reduced when the load drops. This system achieves optimized efficiency and improves the plants’ ability to control pressure by applying analytics to sequence demand changes and effectively sequence the boiler loads.”
The era of “smart”, data-driven steam
These systems are highly data-driven. Setpoint inputs are carefully adjusted to ensure the tightest possible steam pressure control band is achieved so that steam pressure remains stable. Key metrics in the operating model can be adjusted to meet the unique needs of each site – and to account for the number of boilers whose load needs to be balanced.
In addition, instruments are particularly important when it comes to measuring the efficiency of combustion based on the components of the flue gas coming out of the boiler: “We rely on the carbon dioxide and oxygen levels to tell us if we have too much or too little fuel or oxygen to get the right reaction. This is all based on data,” explains Williams.
AES’s Remote Monitoring System (RMS) works hand in hand with its load balancing module, he adds.
“The two share some instruments and data streams. Through the RMS and its web interface, AES and our customers can see what is happening from an operational perspective.”
Although components such as variable speed drives (VSDs) allow more precise control of elements such as boiler stacks and fans than before, and data is also often used to continuously manage these systems, human intervention remains important.
“To set up the system, you still need someone who understands exactly what you are trying to achieve. In certain circumstances, a certain level of intervention and supervision by qualified and experienced operations and maintenance personnel is still required. An example of this is the knowledge to ensure the correct bed depth in the stoker, which other automated systems have failed to achieve,” claims Williams.
A more balanced future
The benefits of load balancing include better control over combustion processes and steam quality – as well as lower fuel consumption and ultimately lower CO2 or eco-tax payments.
Williams believes that AES and its customers will need to work even more closely together in the future to achieve sustainability goals while increasing efficiency and minimizing costs:
“The introduction of green taxes, whether by European or local authorities, will lead to an increasing need for accurate monitoring and load balancing among our customers, and the data or metrics that enable this. We are already carrying out various assessments for different fuel types and load balancing options for customers,” he concludes.
