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Biogas from renewable electricity: Increasing a climate neutral fuel supply
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.ORCID iD: 0000-0002-0635-7372
2012 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 90, no 1, 11-16 p.Article in journal (Refereed) Published
Abstract [en]

If considering the increased utilisation of renewable electricity during the last decade, it is realistic to assume that a significant part of future power production will originate from renewable sources. These are normally intermittent and would cause a fluctuating electricity production. A common suggestion for stabilising intermittent power in the grid is to produce hydrogen through water electrolysis thus storing the energy for later. It could work as an excellent load management tool to control the intermittency, due to its flexibility. In turn, hydrogen could be used as a fuel in transport if compressed or liquefied. However, since hydrogen is highly energy demanding to compress, and moreover, has relatively low energy content per volume it would be more beneficial to store the hydrogen chemically attached to carbon forming synthetic methane (i.e. biogas). This paper presents how biogas production from a given amount of biomass could be increased by addition of renewable electricity. Commonly biogas is produced through digestion of organic material. Recently also biomass gasification is gaining more attention and is under development. However, in both cases, a significant amount of carbon dioxide is produced as by-product which is subject for separation and disposal. To increase the biogas yield, the separated carbon dioxide (which is considered as climate neutral) could, instead of being seen as waste, be used as a component to produce additional methane through the well-known Sabatier reaction. In such process the carbon could act as hydrogen carrier of hydrogen originating from water electrolysis driven by renewable sources. In this study a base case scenario, describing biogas plants of typical sizes and efficiencies, is presented for both digestion and gasification. It is assessed that, if implementing the Sabatier process on gasification, the methane production would be increased by about 110%. For the digestion, the increase, including process improvements, would be about 74%. Hence, this method results in greatly increased biogas potential without the addition of new raw material to the process. Additionally, such model would present a great way to meet the transport sector's increasing demand for renewable fuels, while simultaneously reducing net emissions of carbon dioxide.

Place, publisher, year, edition, pages
2012. Vol. 90, no 1, 11-16 p.
Keyword [en]
Biogas, Renewable energy, Intermittent power, Synthetic fuels, Sabatier reaction
National Category
Energy Systems Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-58804DOI: 10.1016/j.apenergy.2011.07.024ISI: 000297426100003Scopus ID: 2-s2.0-80055060615OAI: oai:DiVA.org:kth-58804DiVA: diva2:474836
Funder
StandUp
Note

QC 20120110

Available from: 2012-01-10 Created: 2012-01-09 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Energy systems studied of biogas: Generation aspects of renewable vehicle fuels in the transport system
Open this publication in new window or tab >>Energy systems studied of biogas: Generation aspects of renewable vehicle fuels in the transport system
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The transport sector is seen as particularly problematic when concerns about climate change and dependency on fossil energy are discussed. Because of this, bioenergy is strongly promoted for use in the transport sector, both on a European level and nationally in Sweden. Even though bioenergy is considered one of the key solutions, it is generally agreed that both supply- and demand-side measures will be needed to achieve a change to a more sustainable transport system. One of the reasons for this is the limited availability of biomass, especially agricultural feedstocks competing with food or feed production. Woody biomass, however more abundant, is also exposed to tough competition from other sectors. In this thesis, the role of biogas as a vehicle fuel in a future sustainable transport system is discussed together with the prerequisites needed to realise such a transport system. Biogas is a biofuel that could be produced in several different ways: by anaerobic digestion, which is a first-generation production route, by gasification, which is a second-generation process, and by catalytic reduction of carbon dioxide, a third-generation technology. The main focus in this thesis is on biogas produced by anaerobic digestion and the results show that there is a significant potential for an increase compared to today’s production. Biogas from anaerobic digestion, however, will only be able to cover a minor part of the demand in the Swedish transport sector. Considering biogas of the second and third generations, the potential for production is more uncertain in a mid-term future, mainly due to competition for feedstock, the possibility to produce other fuels by these processes, and the present immaturity of the technology. The limited potential for replacing fossil vehicle fuels, either by biogas or other renewable fuels, clearly shows the need for demand-side measures in the transport system as well. This thesis shows the importance of technical and non-technical means to decrease the demand for transport and to make the transport as efficient as possible. The results show that both energy-efficient vehicles and behavioural and infrastructural changes will be required. Policies and economic incentives set by governments and decision-making bodies have a prominent role to play, in order to bring about a shift to a more sustainable transport system, however, measures taken on individual level will also have a great impact to contribute to a more sustainable transport system.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiii, 67 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:54
Keyword
Anaerobic digestion, biogas, biomass, energy system, first-generation biofuels, renewable vehicle fuels, second-generation biofuels, supply- and demand-side measures, third-generation biofuels, transport system
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-105120 (URN)978-91-7501-516-3 (ISBN)
Public defence
2012-12-07, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121116

Available from: 2012-11-16 Created: 2012-11-16 Last updated: 2012-12-18Bibliographically approved
2. Energy system evaluation of thermo-chemical biofuel production: Process development by integration of power cycles and sustainable electricity
Open this publication in new window or tab >>Energy system evaluation of thermo-chemical biofuel production: Process development by integration of power cycles and sustainable electricity
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fossil fuels dominate the world energy supply today and the transport sector is no exception. Renewable alternatives must therefore be introduced to replace fossil fuels and their emissions, without sacrificing our standard of living. There is a good potential for biofuels but process improvements are essential, to ensure efficient use of a limited amount of biomass and better compete with fossil alternatives. The general aim of this research is therefore to investigate how to improve efficiency in biofuel production by process development and co-generation of heat and electricity. The work has been divided into three parts; power cycles in biofuel production, methane production via pyrolysis and biofuels from renewable electricity.

The studies of bio-based methanol plants showed that steam power generation has a key role in the large-scale biofuel production process. However, a large portion of the steam from the recovered reaction heat is needed in the fuel production process. One measure to increase steam power generation, evaluated in this thesis, is to lower the steam demand by humidification of the gasification agent. Pinch analysis indicated synergies from gas turbine integration and our studies concluded that the electrical efficiency for natural gas fired gas turbines amounts to 56-58%, in the same range as for large combined cycle plants. The use of the off-gas from the biofuel production is also a potential integration option but difficult for modern high-efficient gas turbines. Furthermore, gasification with oxygen and extensive syngas cleaning might be too energy-consuming for efficient power generation.

Methane production via pyrolysis showed improved efficiency compared with the competing route via gasification. The total biomass to methane efficiency, including additional biomass to fulfil the power demand, was calculated to 73-74%. The process benefits from lower thermal losses and less reaction heat when syngas is avoided as an intermediate step and can handle high-alkali fuels such as annual crops.

Several synergies were discovered when integrating conventional biofuel production with addition of hydrogen. Introducing hydrogen would also greatly increase the biofuel production potential for regions with limited biomass resources. It was also concluded that methane produced from electrolysis of water could be economically feasible if the product was priced in parity with petrol.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. v, 68 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:59
Keyword
Biomass, Gasification, Methane, SNG, Power to Gas, Pyrolysis
National Category
Energy Systems Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-105814 (URN)978-91-7415-835-9 (ISBN)
Public defence
2012-12-14, Sal E3, Osquarsbacke 14, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20121127

Available from: 2012-11-27 Created: 2012-11-27 Last updated: 2012-11-27Bibliographically approved
3. Power to gas: Bridging renewable electricity to the transport sector
Open this publication in new window or tab >>Power to gas: Bridging renewable electricity to the transport sector
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Globally, transport accounts for a significant part of the total energy utilization and is heavily dominated by fossil fuels. The main challenge is how the greenhouse gas emissions in road transport can be addressed. Moreover, the use of fossil fuels in road transport makes most countries or regions dependent on those with oil and/or gas assets. With that said, the question arises of what can be done to reduce the levels of greenhouse gas emissions and furthermore reduce dependency on oil? One angle is to study what source of energy is used.

Biomass is considered to be an important energy contributor in future transport and has been a reliable energy source for a long time. However, it is commonly known that biomass alone cannot sustain the energy needs in the transport sector by far.

This work presents an alternative where renewable electricity could play a significant role in road transport within a relatively short time period. Today the amount of electricity used in road transport is negligible but has a potential to contribute substantially. It is suggested that the electricity should be stored, or “packaged” in a chemical manner, as a way of conserving the electrical energy. One way of doing so is to chemically synthesize fuels. It has been investigated how a fossil free transport system could be designed, to reach high levels of self-sufficiency. According to the studies, renewable electricity could have the single most important role in such a system.   

Among the synthetic fuels, synthetic methane (also called synthetic biogas) is the main focus of the thesis. Hydrogen is obtained through water electrolysis, driven by electricity (preferable renewable), and reacted with carbon dioxide to produce synthetic methane. The concept of the mentioned process goes under the name Power to Gas. The electricity to fuel efficiency of such a process reaches about 50 %, but if utilizing excess heat produced during the electrolysis and the reaction, the total process efficiency can reach much higher levels.

The economics of the process is as important as the technology itself in terms of large scale implementation. The price of electricity and biogas are the most important influences on the economic viability. The minimum “spread” between purchase and selling price can be determined to obtain a general perception of the economic feasibility. In this case biogas must be sold about 2.6 times higher than purchased electricity per kWh.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. v, 50 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:2
Keyword
transport, renewable electricity, synthetic fuels, energy, power to gas
National Category
Chemical Engineering Energy Engineering
Identifiers
urn:nbn:se:kth:diva-111457 (URN)978-91-7501-597-2 (ISBN)
Presentation
2013-01-14, Biblioteket/Seminarierummet, Teknikringen 42, plan 6, Stockholm, 13:00 (English)
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Supervisors
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Formas
Note

QC 20130111

Available from: 2013-01-11 Created: 2013-01-11 Last updated: 2013-01-11Bibliographically approved

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