The future of energy is undergoing a significant transformation, with hydrogen emerging as a promising, eco-friendly fuel source. The growing global demand for hydrogen is driven by its ability to generate water as its only byproduct during combustion, with minimal carbon dioxide emissions, depending on its production method. However, integrating hydrogen into various applications presents unique challenges, particularly when it comes to combustion systems. In this article, we explore how radiant wall burner technology is addressing the issues associated with introducing hydrogen fuels into combustion processes.
The Importance of Hydrogen Fuel
The significance of hydrogen fuel lies in how it is generated. Hydrogen production methods can be classified into several categories, where the most common are blue hydrogen, grey hydrogen, and green hydrogen. Blue hydrogen is produced by steam methane reforming (SMR) and captures the resulting CO2 emissions. Grey hydrogen, on the other hand, is produced without capturing CO2 emissions. Green hydrogen, which holds the most promise for sustainability, is generated using renewable energy sources like wind or solar energy to power electrolysis processes.
High Hydrogen Usage in Certain Applications
While there is a growing interest in using hydrogen as a fuel, certain applications have been using high levels of hydrogen for years. For example, in the production of ethylene from ethane feedstock, off-gases contain 70-85% hydrogen, which is used as fuel for cracking furnaces.
Challenges of Hydrogen Combustion
Integrating high volumes of hydrogen into existing combustion systems is not a straightforward transition. Hydrogen, in its natural state, is a gaseous element with low density, making it prone to leaks from piping systems. It also possesses unique properties compared to conventional hydrocarbon fuels, including a high heating value on a mass basis but a low heating value on a volume basis due to its low density. This low volumetric heating value results in higher volumetric flow rates and higher fuel gas pressure, leading to specific design challenges.
Moreover, hydrogen has a higher flame speed and ignition temperature compared to many common fuels, making it more susceptible to flashback and necessitating design adjustments. However, hydrogen combustion offers advantages, such as the absence of carbon, leading to reduced emissions of soot, carbon monoxide (CO), and unburned hydrocarbons.
Design Considerations
To address the complex combustion characteristics of hydrogen, burners may need to be capable of firing on both natural gas and high-hydrogen fuels, which can complicate their design and operation. This is particularly relevant when using SMR for hydrogen production. Burners that are designed to fire on hydrogen are initially started up with natural gas, until the SMR process is established and hydrogen is being produced. This means that burners may need to be capable of firing on both natural gas and fuels containing a high level of hydrogen. As the combustion characteristics between hydrogen an other fuels can be significantly different, this could complicate burner design concept and operation.
Challenges for Premixed Process Burners
Traditional premix burner designs are susceptible to issues when using high levels of hydrogen in the fuel mix. Challenges include:
- Flashback: Hydrogen’s considerably higher flame speed increases the risk of flashback, leading to internal combustion inside the burner and potential destruction.
- Thermal NOx: The higher adiabatic flame temperature of hydrogen can influence thermal NOx emissions, requiring evaluation on a case-by-case basis.
- Noise Level: Increasing fuel gas pressure generates higher noise levels.
- Air Aspiration: Air aspiration in premixed burners is dependent on fuel gas pressure, which can affect combustion efficiency.
Introducing WALFIRETM Technology
To overcome these limitations, John Zink Hamworthy has developed WALFIRE Radiant Wall Burner for process heaters, specifically targeted for high-temperature applications such as ethylene cracking furnaces. WALFIRE operates as a diffusion-style burner, where air and fuel gas are not premixed before combustion. This eliminates the risk of flashback, ensuring safe operation regardless of hydrogen concentration in the fuel gas. The technology uses the furnace’s negative pressure to aspirate air, making it independent of fuel gas pressure and composition, thus simplifying fuel quality adjustments during operation.
Case Study: Petrochemical Plant in the US
A petrochemical plant in the US experienced high maintenance intervals and frequent flashback when using ultra-low NOx (ULN) radiant wall burners in an ethylene cracking furnace. By replacing these wall burners with WALFIRE burners, the plant widened its operating window, eliminating flashback risk, and reduced maintenance requirements while maintaining emissions performance.
Conclusion
Integrating high levels of hydrogen into combustion systems can significantly reduce or eliminate CO2 emissions compared to conventional hydrocarbon fuels. However, the unique properties of hydrogen pose challenges that require innovative solutions. Technologies like WALFIRE demonstrate the ability to safely embrace hydrogen as a fuel source, paving the way for a greener and more sustainable energy future. As the demand for hydrogen continues to grow, creative combustion solutions are essential for a cleaner and more environmentally friendly world.
