A global shift toward low-carbon pathways strongly promotes the idea of switching to green hydrogen in order to meet climate goals.
However, the predominance of grey hydrogen derived from fossil fuels must be acknowledged and addressed. However, it is expected that the use of grey hydrogen will continue to be critical until the green hydrogen value chain is mature enough to be commercialized.
Coal gasification and steam methane reforming (SMR) are the two primary processes currently contributing to the majority of the hydrogen produced globally. Figure 1 can be used to get an idea of how much hydrogen is being produced around the world.
Natural gas or hydrocarbons can be used in the steam methane reforming (SMR) process to produce industrial hydrogen at the lowest possible cost. Almost half of all hydrogen produced in the world comes from this method. With a Technology Readiness Level (TRL) of 9, the method’s efficiency is somewhere between 70 and 80 percent. There are two stages to the SMR procedure. Using high-temperature steam (700-1000 oC under 14-20 atmospheres of pressure) and a catalyst (usually nickel), natural gas undergoes a thermochemical reaction to produce hydrogen, carbon monoxide (CO), and carbon dioxide (CO2). The CO and steam are then reacted to produce CO2 and additional hydrogen in a water-gas shift reaction.
Pressure swing adsorption removes CO2 and other impurities from the gas stream, such as sulphur (S), chlorine (Cl), and carbon oxides, to produce 99.99 percent pure hydrogen.
Using steam reforming, other fuels like ethanol, propane, and gasoline can be converted into hydrogen. Coded grey hydrogen is the result of steam methane reformation. SMR’s energy consumption and CO2 emissions to hydrogen production ratio are two of the process’ drawbacks. Approximately 9-12 kilograms of CO2 are released for every kilogram of hydrogen produced.
Coal gasification is responsible for about one-eighth of all hydrogen production worldwide. Gasifiers in which steam and oxygen are present heat and compress carbon-based feedstock (such as coal) to produce syngas (a gas mixture of carbon monoxide, hydrogen gas, and oxygen gas) that can then be used to generate electricity or heat a building. The amount of water, CO2 and methane that can be produced with the syngas depends on the gasification technology used. A water-gas shift reactor is used to convert syngas into hydrogen and CO2 by reacting CO in the gas with water. Afterwards, two hydrogen and three carbon atoms are separated from the rest of the mixture.
Brown hydrogen is the color code for the hydrogen produced by coal gasification. The technology has a technology readiness level of 8 and a higher carbon footprint of around 60% to 70%. About 18-20 kilograms of CO2 are released for each kilogram of hydrogen produced using this method.
Methane Pyrolysis is the process by which natural gas methane is thermally decomposed. Compared to SMR, this is a new technology that can produce hydrogen with a lower carbon footprint. Methane is thermally split into solid carbon and gaseous hydrogen in this process. Methane is heated to between 1,100 and 1,200 degrees Fahrenheit in a liquid bubble column without the use of a catalyst. A catalyst can be used to lower the temperature. Recent years have seen the use of molten metals such as titanium, nickel-bismuth, and copper-bismuth, as well as molten salts such as potassium bromide and sodium bromide in liquid bubble column reactors as catalysts for the production of chemical compounds. When it comes to methane pyrolysis, iron catalysts are considered the most stable at 700-1000 degrees Celsius.
Packet-bed reactors, fluidized bed reactors, fluid wall reactors, molten salt reactors, and other types of reactors can be used for the catalytic decomposition of methane. When it comes to methane pyrolysis, the fluidized-bed reactor is the most common option. Turquoise hydrogen is the code name given to the hydrogen produced using this method.
Carbon dioxide-free hydrogen is produced with this method, unlike methods that use fossil fuels as feedstock. The pyrolysis of methane has a 58 percent success rate. It is possible to permanently store the carbon dioxide produced as a byproduct. As a result of this soot buildup, operational efficiency and the catalyst surface deactivation occur within a short period of time, which is a major problem with the process.
The SMR process is currently used to produce the vast majority of the hydrogen consumed in India. There has been an increase in interest in the production of hydrogen using the electrolysis method that has been discussed in previous blogs. The production of hydrogen using fossil fuels is expected to remain a significant portion of the market in the near future, due to the readiness and efficiency of the processes. India’s green hydrogen ambitions can be complemented by low-carbon production alternatives like methane pyrolysis and SMR and coal gasification with technologies like Carbon Capture Utilization and Storage (CCUS).
