Learn how digital tools can assess and mitigate the impact of high hydrogen concentration events in BFG, improving energy efficiency and reducing operational costs in gas turbine operations.
By Giovanna Guzella, Kássio Nogueira Cançado, Lis Nunes Soares
Integrated steel plants face significant challenges in managing energy consumption and emissions. To generate electricity, an effective strategy involves utilizing residual gases, such as blast furnace gas (BFG). However, the variability in BFG composition, particularly hydrogen peaks, poses a risk to gas turbine integrity and energy generation efficiency.
This article explores how the ability to anticipate and promptly react to high hydrogen content events, through the use of real-time data and predictive analysis with digital tools like Viridis Performance, can enhance energy efficiency and reduce costs, avoiding electricity production shutdowns and minimizing maintenance expenses. It highlights the importance of digitalization in modern steel production and demonstrates how advanced tools can optimize energy usage and reduce environmental impact.
The role of residual gases in steel production
Steel production is energy-intensive, heavily relying on fossil fuels. The sector accounts for about 8% of global energy demand and 7% of CO2 emissions from the energy sector. In the pursuit of more sustainable production, green steel has gained momentum in recent years, which can be defined as steel produced through sustainable processes, such as using alternative energy sources, capturing and reusing CO2, recycling materials, and implementing practices and technologies that minimize greenhouse gas (GHG) emissions.
The gases generated during upstream processes in integrated steel plants have calorific value that can be reused as heat and/or electricity. Many plants recycle these gases in gas or steam electricity generation cycles. This practice makes the steel production process less harmful to the environment, as gases that would otherwise be discarded are reused and contribute to partially meeting energy needs, which minimizes demand for external energy sources, reduces greenhouse gas emissions, and lowers production costs. These and other practices have significantly reduced the energy resources required for steel production over the past 20 years.
Challenges of using blast furnace gas in gas turbines
In the blast furnace, the iron ore reduction process produces pig iron, slag, dust, and blast furnace gas (BFG). BFG can be reused in downstream processes and used as fuel in gas turbines to generate electricity. BFG contains 21-25% CO, 18-22% CO2, and 2-5% H2, with a calorific value of 700-800 kcal/Nm3. Its composition varies based on the blast furnace's operational parameters, including raw material types and volumes, as well as process conditions.
One challenge in operating with BFG is the variability in its composition, with hydrogen peaks being a concern, as these high-concentration events can damage the gas turbine's mechanical structure. This can be explained by the fact that high hydrogen concentration increases the gas flame temperature in the combustion chamber. During hydrogen peak events, when the flame temperature exceeds the recommended limit, the turbine has a reaction system that reduces power generation levels to protect the equipment. In extreme cases, where this reduction is insufficient, the turbine shuts down suddenly, which is referred to as a "trip." When this emergency shutdown is triggered, in addition to the complete halt in power generation for a certain period, the maintenance interval is shortened, increasing maintenance costs.
Methodology: evaluating hydrogen peaks
Data from a blast furnace at the studied plant were analyzed. With a real-time predictive model for the top gas composition, it would be possible to anticipate high hydrogen content events. Consequently, the operational team could prepare to react, and there would be financial gains from two perspectives: hydrogen peaks result in huge costs associated with turbine maintenance, and this could be avoided. Furthermore, the turbine would not experience a trip and would continue operating, albeit at a reduced generation level.
This study employs a mass balance approach to evaluate the factors contributing to hydrogen peaks in BFG. By analyzing real process data from a steel plant, scenarios were simulated to identify improvement opportunities and optimize power generation. Two main hypotheses were considered: hydrogen content could predominantly originate from the moisture in the steam injected into the regenerators, which subsequently blows moist air into the reactor, and the second hypothesis is that pulverized coal injection has the greatest influence on the hydrogen content in the gas.
Results obtained
Data analysis revealed that hydrogen concentrations above operational limits for 6.1% of the time led to frequent turbine shutdowns and a reduction in power generation. On average, each hydrogen peak event caused a loss of 151 MWh in power generation, with maintenance intervals shortened by 23 days due to unplanned shutdowns. Four severe events resulted in an average energy loss of 17 GWh per event. The results highlight the importance of developing predictive methods to minimize these harmful effects.
Based on the data analyzed on material composition and blast air, it was concluded that pulverized coal injection contributes approximately three times more than blast air to the generation of hydrogen peaks. Therefore, eight scenarios were developed in which the pulverized coal injection rate through the blast furnace tuyeres was varied between 190-260 kg/t of pig iron to understand the impact on the final top gas composition.
The results indicate that pulverized coal injection significantly influences the hydrogen content in BFG. Mass balances for scenarios varying the pulverized coal injection rates showed that higher injection rates increase hydrogen concentrations, confirming the hypothesis. The accuracy of the modeling was validated against data from the literature, showing consistency in the predicted gas compositions and volumes.
Implementation of predictive models
Static mass balance has some limitations as it does not consider variations in raw material composition, hot air moisture, and other parameters. A real-time predictive model for BFG composition allows proactive management of high hydrogen concentration events. Integrating this model with digital tools like Viridis Performance enables continuous monitoring and immediate adjustments to prevent turbine shutdowns. This approach not only improves energy efficiency but also reduces maintenance costs and enhances overall process reliability.
Another advantage of using the Viridis digital tool is that with real-time data, the model can be updated whenever a parameter changes, and more parameters can be considered to make the modeling more robust. In the short term, the operational team can predict high hydrogen events and react accordingly to prevent power generation shutdowns, thanks to the alert system that informs operators of the impending issue.
Moreover, in the long term, using a predictive model for gas composition would allow evaluation of changes in operational parameters, such as using different raw material suppliers like coal, iron, hematite, sinter, and pellets, which can also impact hydrogen peak formation.
Conclusion
Using digital tools to predict and manage hydrogen peaks in BFG can significantly improve energy efficiency and operational stability in steel plants. By anticipating high hydrogen concentration events, operators can take timely actions to maintain power generation and avoid high maintenance costs. Implementing these predictive models represents a critical step towards more sustainable and economically efficient steel production.
The implementation of predictive digital tools like Viridis Performance can increase efficiency, reduce costs, and make your steel plant more sustainable. Want to turn blast furnace gas challenges into energy optimization opportunities? Contact us to learn how to apply these innovative solutions to your operation.