Gas cleaning process optimization

Case study

Gas cleaning process optimization

SO₂ emissions control optimization in iron ore pelletizing using Advanced Process Control

A leading pellet plant in Sweden implemented ABB Ability™ Expert Optimizer to stabilize gas cleaning system operation, predict and mitigate SO₂ excursions, while reducing emission levels and operational costs.

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Customer challenges
  • Chemical process complexity
  • Parallel reactors variability
  • Resource consumption issues

Out solution

Benefits

  • SO2 emissions decrease
  • Improved water exhaust, less buildup
  • Reduced operator workload

Gas cleaning process challenges in the pellet plant

Pelletizing plants face significant challenges in maintaining sulfur dioxide (SO₂) emissions within regulatory limits due to the complex and dynamic nature of the process. During the conversion of iron ore fines into pellets for steel production, variations in the sulfur content of raw materials and fuels, together with fluctuations in process temperature, air distribution, and gas flow, lead to unpredictable SO₂ formation and release.  Gas cleaning systems such as scrubbers and electrostatic precipitators play a crucial role, but their efficiency can vary with gas temperature, humidity, and reagent quality. Control room operators must simultaneously balance production rate, fuel efficiency, pellet quality, resource consumption, and emission compliance—objectives that often conflict.

Chemical process complexity

The SO2 absorption process relies on precise chemical reactions between calcium carbonate (CaCO3) or calcium hydroxide (Ca(OH)2) and sulfur dioxide. Managing these reactions optimally requires balancing multiple variables including lime slurry concentration, water consumption, flow rates, temperature, and residence time. The chemical complexity made it difficult for operators to maintain consistent performance across varying operating conditions.

 

Reactor variability

The plant operates dual reactors for SO2 absorption, each with different characteristics and performance profiles. Variability between reactors, combined with fluctuating feed gas compositions and flow rates from the pelletization process, created unpredictable emissions patterns and buildup in the reactors. Operators struggled to maintain stable emissions and water exhaust while avoiding excessive lime consumption.

 

Emission deviations

Under operator control, daily SO2 emissions showed wide variability around the operating targets, creating uncertainty in operational planning.

 

Because all these variables interact in nonlinear and time-dependent ways, manual control strategies often forced operators to adopt conservative operating margins to ensure compliance under all circumstances. This presented a strong case for the implementation of Advanced Process Control (APC) strategies capable of predicting emissions, coordinating multivariable interactions, and dynamically optimizing process performance while maintaining robust environmental compliance.

The solution

ABB conducted a comprehensive fingerprint technical consultancy to evaluate the potential for advanced process control implementation. Based on this assessment, ABB Ability™ Expert Optimizer was deployed to optimize the gas cleaning process using model predictive control (MPC) technology to:

  • Predict emission behavior based on real-time process conditions
  • Optimize lime slurry dosing to maintain emissions within target range
  • Balance multiple objectives including emission control, reagent consumption, and water usage
  • Adapt to process variability across both reactors automatically
  • Maintain stable operation despite fluctuations in feed gas composition
SO2-emission-control-gas-cleaning-optimization-apc

Key benefits and impact

"After two weeks of APC implementation, we saw a clear statistical improvement: SO₂ emissions dropped by 14.8%, and water exhaust became more stable and controlled. These early results are promising, but long-term monitoring is essential to confirm sustained benefits.“ 
Site process engineer

The implementation of ABB Ability™ Expert Optimizer at the iron ore pellet plant in Sweden delivered promising results across environmental, economic, and operational dimensions. After more than two weeks of APC implementation, both SO₂ and H₂O exhaust performance improved significantly, with a clear statistical difference between APC-ON and APC-OFF states:

  • SO₂ emissions decreased by 2.34 g/ton, representing an improvement of approximately −14.8%.
  • Water exhaust also improved, dropping by 0.32 Vol%, with enhanced stability and tighter control. This reduction is beneficial as it helps prevent buildup in the reactors.

However, the data was collected over a short period with frequent process changes. Long-term monitoring is needed to fine-tune APC parameters and confirm sustained SO₂ reduction and reactor buildup effects.

Reduced operator workload for emissions management

The system is set to free operators from constant emissions management tasks, enabling them to focus on other critical activities while the predictive control algorithms automatically adapted to process variability across dual reactors and fluctuating feed gas conditions.

Possible future work and expansion

The success has established a proven foundation for potentially expanding advanced process control to other areas of the mining and metals value chain, including ABB Ability™ Expert Optimizer solutions for crushing, grinding, pelletization, and induration processes, demonstrating that environmental excellence and economic efficiency can be achieved simultaneously.

 

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If you’re interested in learning how similar APC strategies can help you tighten emissions control and optimize performance, fill in the contact form below to connect with our process optimization experts.

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