Biogas is such a renewable alternative, and there is potential to increase the biogas production in the world.
In recent decades, many countries have increasingly been upgrading biogas to vehicle fuel. In the last few years, the interest has also increased in liquefying biogas for heavier transports. Biogas can also be a raw material for other fuels by gasifying the biogas, for example Fischer-Tropsch fuels, methanol, dimethyl ether and hydrogen. Vehicle fuels that can be produced from biogas, their technological maturity and their respective potentials as substitutes for fossil fuels in the transport system. A common factor for all of them is that they are most often produced from fossil fuels. Compressed and liquefied methane are the only fuels being commercially produced using biogas. The other fuels all have strengths that both compressed and liquefied methane lack, for example the possibility of emission-free fuel cell vehicles. However, they are all less mature technologies than compressed and liquefied methane. The greatest short-term potential is thus for expanded use of biogas as compressed and liquefied biomethane.
Over 80% of the energy supply in the world in 2017 came from fossil sources [
Citation1]. To avoid undesirable global warming, this current fossil regime must be transformed into one that is based on renewable energy. However, in contrast to fossil fuels, there is not yet any easy way to produce huge amounts of storable and easily utilizable renewable fuels from a single source. In 2018, less than 20% of the energy used in the European Union (EU) came from renewable sources, and a variety of different raw materials and energy carriers had to be used to achieve even that limited share [
Citation2]. A system of different raw materials and energy solutions that work together to solve the problem must thus be developed to achieve a global, large-scale transition to renewable energy.
Biogas, which is a methane and carbon dioxide mix produced by anaerobic digestion of biomass, is one alternative that could be a part of this system. Biogas is especially interesting as an alternative fuel since it is not only a renewable fuel, but because biogas production also can help solve other societal problems – mostly by improving waste treatment, but also through positive secondary effects like improvement of soil structures [
Citation3,
Citation4] and reduced use of mineral fertilizers [
Citation5,
Citation6]. Many different biomass sources can be used to produce renewable methane, and all countries have at least some potential to produce biogas, but only 0.2% of the total primary world energy supply came from biogas during 2014 [
Citation7]. However, the biogas potential in the world from just waste (i.e. urban waste, agro-industry and sewage sludge) has been estimated to around 3% of the fossil fuel use in 2017.
In most countries, biogas is primarily used for producing electricity and heat. However, biogas can also be used for other purposes, such as for producing vehicle fuels. Biogas is in many countries increasingly being upgraded to compressed biomethane (CBG), as a renewable version of compressed natural gas (CNG) for use in especially cars and buses. During the last few years, there has been an increased interest in liquefied biomethane (LBG) for use in heavier transports instead of liquefied natural gas (LNG). There are also other options available. Apart from CBG and LBG, biogas can also be used to produce syngas, which in turn can be used to produce renewable versions of fuels such as hydrogen, methanol or DME. These fuels have different characteristics and potentials than CBG and LBG, which might make them suitable for other parts of the renewable energy system that needs to be developed. However, like compressed and liquefied methane, they are currently all produced from primarily fossil fuels.
The purpose of this study is to contribute with an overview and an increased understanding of fuels that can be produced from biogas and their potential to be used as a substitution for fossil energy in the transport sector. The study answers the following research questions:
- For what purpose have the different fuels been developed?
- What strengths and weaknesses do these fuels have?
- How far have the fuels come in their development, and how are they produced and used today?
A literature inventory was made to be able to identify what possible fuels can be produced from biogas and their potentials. This inventory was wide and included both academic literature and grey literature, newspaper articles and reports from companies based on previously found newspaper articles, depending on where information could be found. In some cases, especially with the alternative fuels that are less mature and used, information is scarce and hard to access. Some journal articles, such as one by Ahmadi Moghaddam et al, had previously studied either one or several of the possible biogas-based fuels. Such overview articles were used to create an overview of the alternatives and their strengths and weaknesses. Journal articles were also used to show the historical context of the fuels and what the current research is focused on. Grey literature, such as governmental or organizational reports, e.g. [
Citation18,
Citation19], were valuable sources for statistics on the different fuels and applications as well as on new or planned developments. Newspaper articles were used to find information on recent developments, such as decisions to build new production sites. This information were then corroborated by the company’s annual report or their homepage.
A bibliometric search for each fuel was conducted to complement the inventory. This was done to get an indication of how the interest in the fuels developed throughout the years. The bibliometric search was performed using the Scopus database, and the search looked in the titles, keywords and abstracts for the terms presented. Several of the fuels, for example hydrogen, are common in chemical production and the distinction of adding the word ‘fuel’ to the search terms was considered needed. However, it was assumed that there was no need to add the word ‘fuel’ to the search terms when doing the bibliometric search of CBG and LBG since methane gas used for other purposes is not usually compressed or liquefied. In most cases, the figures produced from the bibliometric search were cut off around the year 2000, since after then, the number of hits rapidly increased for all search terms, which made it hard to distinguish the earlier interest.
See:
https://www.tandfonline.com/doi/full/10.1080/17597269.2020.1821571
Biogas is competitive, viable, and generally a sustainable energy resource due to abundant supply of cheap feedstocks and availability of a wide range of biogas applications in heating, power generation, fuel, and raw materials for further processing and production of sustainable chemicals including hydrogen, and carbon dioxide and biofuels. The capacity of biogas based power has been growing rapidly for the past decade with global biogas based electricity generation capacity increasing from 65 GW in 2010 to 120 GW in 2019 representing a 90% growth.
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