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Clean hydrogen is of the greatest interest in addressing the climate crisis, with the recognition that hydrogen could play a crucial role in economy-wide decarbonization, particularly in the transportation and industrial sectors including sustainable fuels, iron & steel, ammonia and chemicals, and more.1 Hydrogen is an extremely clean energy carrier, as its consumption produces only water; it also has a high energy density by mass. Hydrogen can be used to power fuel cells or combusted in a hydrogen turbine to generate electricity, and could also serve as clean transportation fuel.
The first Energy Earthshot, the Hydrogen Shot launched in 2021, seeks to reduce the cost of clean hydrogen by 80% to $1 per kilogram in 1 decade. This is an ambitious initiative, since current costs of clean hydrogen are much higher. For example, electrolytic generation of hydrogen using renewable electricity costs at least $6 per kilogram.
Worldwide, about half of all hydrogen production is from reforming of natural gas (mainly steam methane reforming or SMR), with the remainder deriving from gasification of liquid and solid feedstocks such as coal, petcoke, and petroleum residuals, from oil as a byproduct, and with a few percent from electrolysis. Syngas from gasification already contains a significant amount of hydrogen, which can be increased through water gas shift (WGS) and separated into a pure hydrogen product meeting industry product quality standards. There are several conventional hydrogen separation processes, with the well-proven and moderate cost pressure swing adsorption (PSA) methods commonly chosen. PSA has the ability to produce high purity (99.9%) hydrogen at near feed pressure; however, relatively high hydrogen concentration in feed gases is required for its economics to remain favorable.
For either natural gas reforming or gasification routes, hydrogen production costs are lower than the electrolytic route, but the challenge is that the carbon footprint of conventional hydrogen production is large, as shown in the following table:
|
|
Hydrogen product (kg/h) |
CO2 product (kg/h) |
CO2 emitted in stack gas (kg/h) |
Carbon intensity kg CO2/kg H2 |
|---|---|---|---|---|
|
SMR w/ 90% capture |
25,700 |
227,600 |
25,300 |
1.0 |
|
Coal gasification w/ 90% capture |
25,700 |
456,700 |
49,300 |
1.9 |
Carbon Intensities of SMR and Coal Gasification-based Hydrogen Production (with 90% capture)
If all CO2 produced in these processes is emitted, and CO2 footprint ranges from about 10 to 20 times the mass of the hydrogen produced. Only 0.7% of fossil fuel-based hydrogen production is currently performed in conjunction with carbon capture and storage.2
The gasification route to hydrogen presents an opportunity to use low-cost and liability feedstocks including biomass, solid wastes, and waste coal, which could help reduce the environmental costs and liabilities of solid waste disposal and legacy waste impoundments. Carbon-neutral biomass feedstocks significant reduce the carbon footprint of gasification, and combined with high levels of carbon capture facilitated by high syngas concentrations of CO2 and hydrogen characteristic of efficient gasification processes, production of clean hydrogen from gasification could be a compelling option in the emerging decarbonized economy.
Hydrogen
