In today's progressive world, air pollution and greenhouse gas emissions are the most common problems in urban areas. Domestic and industrial burners significantly contribute to the production of pollution like CO and NOx. Hydrogen has genuinely great potential benefit to sustainably supply green energy to industrial areas where decarbonization is a complicated procedure. Hydrogen covers a wide range of flammability limits in air, so it is highly reactive. Hydrogen-free carbon combustion produces only water and has no unburnt (unburned) hydrocarbons (UHCs), and doesn't emit carbon dioxide (CO2). Because of the higher flame temperature and high combustion rate, NOx formation in hydrogen combustion is more in comparison with hydrocarbons like natural gas or diesel. «Hydrogen combustion» doesn't generate any soot. Engineers have been researching Hydrogen technologies recently to reduce the reaction rate and NOx formation and prevent the flame flashback phenomenon.
Consequently, a hydrogen burner, for either home heating or industrial applications, can be a master key toward a greener planet and preserve sustainability in the energy field. However, the techniques of hydrogen extraction or reservation are still a challenge. As cutting-edge technology, it needs too much support and superior cooperation between scientists, environmental activists, social leaders, and producers.
Combustion systems such as internal combustion engines, burners, gas turbines, etc., that use fossil fuels emit carbon dioxide. As a result, climate change and global warming happen. Decarbonization as a clean industrial solution is a fundamental method that enhances our production processes to reach a better environment. Fuel replacement is one of the ways to overcome this issue.
Hydrogen has great potential in decarbonizing transportation, industrial, commercial and residential sectors. The capability of hydrogen that can be generated through different renewable energy sources makes it an integral part of a renewable energy system. This way allows engineers to substitute natural gas pipelines with hydrogen to reduce carbon emissions and the dependence on fossil fuels.
The end use of this hydrogen has been a research topic for the last decades. Due to its physical properties, the extensive research literature on hydrogen flames can be found since its combustion behavior presents several particularities compared to conventional gaseous fuels. Hydrogen has a wide flammability limit in the air (4-75 vol%), low ignition energy (0.019 mJ), low density (0.0899 kg/m3), and high adiabatic flame temperature (2380 K).
Hence, various combustion devices in different sectors still require in-depth research to readapt or re-design them to ensure safe and efficient operating conditions when using hydrogen as inlet fuel. A significant challenge we have to face is using existing plants and adapting them to hydrogen fuels instead of building new facilities.
The transformation of these facilities that currently use fossil fuels with hydrogen will succeed as a society with this new particular energy source that produces fewer pollutants than the previous ones. Developing an efficient combustion technology and the least polluting possible of this fuel is necessary.
From a technical point of view, some factors must be considered that will be essential in transforming these existing plants to use hydrogen combustion, especially in its application to the boilers of electricity generation plants.
The characteristics of hydrogen in gas form have been shown in the table below:
|Density||0.0899 [kg/Nm3] (gas) / 0.0708 [kg/l](liquid)|
|Lower Calorific Value [Kcal/Nm3]||2580|
|Higher Calorific Value [Kcal/Nm3]||3050|
|Flammability Limits %Vol. in Air||4-75%|
|Detonation Limits %Vol in Air||18.3-59%|
|Specific Heat Capacity [KJ/ (kg. K)]||Cp=14.199 / Cv=10.074|
|Diffusion Coefficient [cm2/s]||0.61|
|Maximum Flame Speed [m/s]||2.8|
|Autoignition Temperature [C]||571|
The flame speed in hydrogen combustion is approximately 1.7 m/s, while the natural gas flame speed is significantly lower and around 0.4 m/s. An imbalance in the local flame and flow speeds in pre-mixed and partially pre-mixed hydrogen flames may cause a safety problem due to the high flame front velocities.
Hydrogen flame has a higher adiabatic flame temperature of about 2182 °C, while natural gas has an adiabatic flame temperature of 1937 °C. Increasing the flame temperature in hydrogen
combustion compared with natural gas or liquid fuel combustion requires upgrading the materials used to make the nozzles, flame stabilizer, and combustion chamber for higher temperatures.
Due to hydrogen’s higher flame temperature than conventional fuels such as natural gas, NOx pollutant emission will increase up to 3 times. Therefore, it is necessary to use various approaches to reduce NOx pollution, such as using FGR, steam injection, and staged combustion.
According to methane and hydrogen stoichiometric equations, it has been reported that for methane and hydrogen, 0.31 and 0.24 kg of air is needed per Megajoule of energy, respectively. This amount is 30% less air than methane combustion. Because of the high flammability limit of hydrogen, less excess air is needed.
Hydrogen flame has low radiation in the infrared range rather than ultraviolet; scanners capable of measuring ultraviolet waves should be used for flame detection. Frequency scanners are suggested to improve safety.
Note: flame invisibility will be decreased when using FGR.
According to ATEX rules, hydrogen is classified as gas group IIC. Therefore, the equipment used is selected based on Zone 1/Group IIC requirements. EExd explosion-proof equipment will be sufficient to prevent hazards from hydrogen gas leaks.
Heating hydrocarbon molecules can produce hydrogen in a process called hydrogen “conversion.” In this process, hydrogen is obtained from natural gas. With an electric current, water decomposed into oxygen and hydrogen in an electrolysis process. Algae and bacteria use sunlight as an energy source to produce hydrogen in certain conditions.
In general, hydrogen extraction methods are classified into fossil and non-fossil sources.
1. Hydrogen production from non-fossil sources
2. Production of hydrogen from fossil sources
Today 98% of all hydrogen produced worldwide is obtained from fossil fuels.
According to the extraction method, hydrogen is placed in the following categories:
With renewable energies, water is electrolyzed, and the water molecule is decomposed into hydrogen and oxygen molecules. This method uses a direct electric current and two electrodes, producing hydrogen gas in the cathode and oxygen gas in the anode. The hydrogen gas produced during this process is twice the amount of oxygen. Also, the obtained hydrogen contains some moisture and impurities (1-2%), so to make the hydrogen purer and reduce the oxygen concentration, hydrogen can be passed through the platinum catalyst to reduce the oxygen amount to 1 ppm.
Its dew point can be minimized by passing the gas through molecular sieves to remove moisture from hydrogen gas. Since the hydrogen in this method from renewable sources and its by-products do not risk the environment, the hydrogen produced in this method is called green hydrogen.
Hydrogen production using the natural gas reforming process with steam is one of the world’s most common and economical hydrogen production methods. During the reformation, Natural gas is heated in the presence of catalyst and steam. As a result of this reaction, methane molecules are broken into carbon monoxide and hydrogen.
Carbon monoxide can be separated from hydrogen with a water-gas shift reaction (WGSR). WGSR can be achieved by passing carbon monoxide through certain oxides like Fe2O3. The steam reforming method problem is the production of by-products such as carbon monoxide and carbon dioxide, which are all greenhouse gases. Depending on the natural gas quality, 9 to 12 tons of carbon dioxide are produced per Ton of hydrogen.
The hydrogen is called gray hydrogen if carbon dioxide is released into the atmosphere. Else carbon dioxide is separated and stored; the hydrogen produced is called blue hydrogen.
Brown hydrogen comes from brown coal or petroleum (it takes millions of years to produce brown coal from peat deposits). Black hydrogen is also made using bituminous coal (a substance similar to bitumen).
Today, studies on hydrogen burners have achieved a mixture of about 20% of hydrogen and 80% of natural gas in the forced draught, Nozzle mixed, pre-mixed, and post-mixed burners. The flashback phenomenon may occur in higher combustion ratios.
Toward the edge of technology in combustion science, research is being carried out in our R&D department to create reliable combustion of pure hydrogen fuel without the problem of flashback. As a result, we are proud that our high technology-hydrogen-ready burners are working well, with the lowest amount of emission according to international standards.