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As the implementation of hydrogen blended with natural gas as a sustainable alternative to pure natural gas gains momentum, the requirement to upgrade existing equipment and add new thermal processing systems with this equipment and technology is vital.
As hydrogen fuel becomes more of a viable option in thermal processing and manufacturing processes, equipment upgrades and technology additions will ensure quick response, expandability, leak detection, safety, compliance and more.
Consider four important elements for the proper design of an H2-fuel-management system to incorporate hydrogen fuel blending to handle combustion technology, blending analysis and emission control for ease of implementation in the manufacturing process.
1. Blending ratio for carbon reduction:
The mixing of H2 with natural gas can significantly reduce greenhouse gas emissions since the combustion of H2 produces no greenhouse gases; it reduces carbon oxides (COx), sulfur oxides (SOx), nitrogen oxides (NOx) and particulate matter emissions.
Measurement and control of the gas blends throughout all the manufacturing processes for safety, homogeneity of phases and accuracy of the blends is essential in keeping with sustainability goals, while being economically feasible. Obtaining trending data to manage these processes is also very useful both for quality, quantity and ensuring product integrity and process functionality.
Figure 1 shows how the blending ratio between methane and hydrogen effects the CO2 reduction.
Since H2 has a much lower calorific value than methane, but higher flame propagation, the optimum blend of hydrogen and methane is application specific. Studies have indicated that a hydrogen blend of 10%-30% by volume to methane is a good ratio between performance and safety.
Nevertheless, H2 may not blend in a homogeneous manner. Therefore, proper phase control. pressure, temperature, concentration and flow must all be taken into consideration to ensure the best blend for the application.
2. Flame properties
When looking at proper burner design — one vital component to consider is the different flame characteristics that a hydrogen flame exhibits vs. a natural gas flame.
This includes flame speed, temperature, geometry and heat-release patterns.
Flame speed is defined as the speed at which the combustion reaction progresses relative to oxygen and fuel. Therefore, a properly mixed ratio of fuel and oxygen within the burner tube is essential for consistency and efficiency. This, of course, will be different for different blend ratios.
It all depends on pressure, temperature and heat-transfer requirements and more.
Figure 2 shows the relative speed of a hydrogen flame compared to other fuels:
Figure 2: Flame Speed Table. Hydrogen is nearly 10 times faster than other conventional fuels.
In general, combustion intensity increases with hydrogen content due to the flame speed. Flames will tend to be shorter and more compact. Other conditions should remain the same. This will dictate the modifications and/or new burner designs that will be needed to handle H2 flames.
3. Emissions:
As the flame temperature of hydrogen is higher than methane, there is the potential for an increased amount of nitrogen oxides or NOx emissions.
During combustion, the flame temperature and the amount of nitrogen in the air are contributing factors to NOx levels2.
Therefore, the increased flame temperature of hydrogen can increase the NOx emissions in comparison to burning natural gas.
In general, the NOx will be lower if the burner pressure is high, leading to higher velocity and more entrainment of the products of combustion within the flame.
4. Safety
For combustion to take place, fuel, air (oxygen) and a source of ignition are needed.
The lower and upper flammability limits represent the percentage of fuel and air mixture required for ignition. For hydrogen, the lower limit is 4% and the upper limit is 75%. Compare this with natural which is 7% and 20%.
Figure 4: The large flammable range of hydrogen makes controlling the combustion of hydrogen more difficult than natural gas.
This means that hydrogen will burn with lower and higher amounts of air present compared to natural gas.
Figure 4 shows the flammability range between hydrogen and other common combustible fuels.
This wide range of flammability makes controlling the combustion of hydrogen more difficult than natural gas.
Even a small amount of hydrogen in air can be combustible. Nevertheless, hydrogen is a small molecule and is prone to leakage quicker than methane or other conventional fuels. It will escape through piping quicker and absorb in the atmosphere fast. This can be good or bad, depending on the situation.
Therefore, proper safety considerations, fast monitoring and control need to be implemented to ensure viability and protection.
Hydrogen is a viable alternative to methane as a combustion technology. It is cleaner, burns well and is a by-product of many conventional fuel systems (i.e. Green, Grey, Blue or Purple sources).
As the hydrogen economy expands, hydrogen equipment (i.e. burners and other thermal processing systems) are expected to play a pivotal role in decarbonizing industries and households. Advanced burner design, such as smart monitoring systems and hybrid burners that can switch between hydrogen and natural gas, are improving safety and efficiency. It is therefore critical to understand the factors that go into proper design of these systems now and into the future.
Elementale Enterprises assists organizations in selecting the best technical and economical process and measurement solutions to optimize all facets of their hydrogen processes, ensuring adherence to proper safety protocols while transforming their plants. The company provides guidance on choosing the best technologies to enhance overall plant efficiency, ensure proper operations, maintain product quality and remain competitive while meeting ESG goals.
For more information, visit Elementale Enterprises.
