Hydrogen is considered the ideal raw material for a sustainable energy market transformation. However, some questions still await answers. Where will we get our hydrogen? Will we use the gray, blue, turquoise or green variant in the distant and not-so-distant future? Green hydrogen is produced using renewable energy sources and often generated via water electrolysis.
However, one of the biggest obstacles to using the gas, most of all in transportation, is its poor conversion efficiency. From the 100 kilowatt-hours of clean power fed to an electrolyzer, only 32 will end up in the fuel tank.
The remainder is lost during electrolysis, compression, delivery, and ultimately, during fuel cell conversion. By contrast, the efficiency of all-electric vehicles is around 73 percent . This article will discuss the option of producing renewable hydrogen from biogas via steam reforming. A crucial advantage of this pathway is its astonishing efficiency. Compared to water electrolysis, biogas-sourced hydrogen has a cutting edge – in more ways than one.
Biogas facilities produce biogas from both biogenic waste and sustainable raw materials. Around 90 percent of the gas is fed to distributed cogeneration plants, thus producing both electricity and heat. The other 10 percent is processed into biomethane. In 2019, around 9,500 biogas systems were up and running in Germany, feeding 31.9 terawatt-hours into the national power grid [1, 3].
Yet, biogas is more than just a source of electricity and biomethane. Via steam reforming, the methane-rich gas can also be used to manufacture green hydrogen, whereby a catalyst refines and separates the hydrogen from the gas stream. Steam-reforming natural gas, with subsequent pressure-swing adsorption to remove impurities, is currently the most common hydrogen production method in all corners of the globe . Small reformers, such as those required for CHP biogas plants, are already commercially available, indicating tried-and-true technology can be tapped immediately.
Bright prospects for the hydrogen industry
Biogas-sourced hydrogen can significantly improve energy efficiency. Instead of generating 31.9 terawatt-hours of electricity a year, German biogas plants could switch to steam reforming to produce around 58 terawatt-hours, or 1.7 billion kilograms of hydrogen annually (see fig. 1). By contrast, PV systems in Germany produced 47.5 terawatt-hours in 2019, and the country’s total PV generating potential would be only around 33 terawatt-hours’ worth of hydrogen [2, 3].
read more in H2-international August 2020
M.Sc.Prof. Herbert Pfeifer; both for RWTH Aachen, Aachen, Germany
Dr. Joachim G. Wünning, WS Wärmeprozesstechnik GmbH, Renningen, Germany