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Energy system evaluation of thermo-chemical biofuel production: Process development by integration of power cycles and sustainable electricity
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
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 [en]
Biomass, Gasification, Methane, SNG, Power to Gas, Pyrolysis
National Category
Energy Systems Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-105814ISBN: 978-91-7415-835-9 (print)OAI: oai:DiVA.org:kth-105814DiVA: diva2:572354
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
List of papers
1. Increased Power Generation by Humidification of Gasification Agent in Biofuel Production
Open this publication in new window or tab >>Increased Power Generation by Humidification of Gasification Agent in Biofuel Production
2010 (English)In: World Renewable Energy Congress XI, 2010Conference paper, Published paper (Refereed)
Abstract [en]

The second generation biofuels are based on gasification of waste and non-food crops. A mix of oxygen and steam is used as gasification agent. A drawback when mixing the two pure streams of oxygen and steam is that exergy is lost. The gasification process is often pressurized; which implies that both the oxygen and the steam must have higher pressure to enable feeding. The gasification process is therefore one of the main internal steam uses. However, if the steam injected can be replaced or decreased in pressure level, power generation could be significantly increased. This study shows that the power penalty can be reduced by humidification of the gasification agent compared to steam injection. The power penalty can be reduced by more than 10% when using humidification process. The power penalty is reduced by even more, 18-25%, when also using a pre-humidifier driven by latent heat recovered after the methanisation.

Keyword
Humidification, Gasification Agent, SNG
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-29248 (URN)
Conference
World Renewable Energy Congress XI 25-30 September 2010, Abu Dhabi, UAE
Note
QC 20110128Available from: 2011-01-28 Created: 2011-01-28 Last updated: 2012-11-27Bibliographically approved
2. Integration of Hybrid Cycles in Bio-Methanol Production
Open this publication in new window or tab >>Integration of Hybrid Cycles in Bio-Methanol Production
(English)In: Environmental Impact of Energy SystemArticle in journal (Other academic) Submitted
Abstract [en]

In bio-based methanol production approximately 60% of the biomass energy content is converted into methanol, the remaining part can be recovered as thermal heat. Efficient utilization of the thermal heat is difficult in stand-alone methanol plants. The overall efficiency is to a large extent dependent on the further conversion of power due to the significant quantity of excess heat. Heat can be recovered in a steam cycle but due to poor steam data energy efficiency is low. This paper therefore proposes the integration of a natural gas fired gas turbine. Simulations of the hybrid cycle in methanol production have shown good improvements. The total electrical efficiency is increased by 1.4-2.4 percentage points, depending on the fuel mix. The electrical efficiency for the natural gas used in the hybrid plant is 56-58%, which is in the same range as in large-scale combined cycle plants. A bio-methanol plant with a hybrid power cycle is therefore a competitive production route for both biomass and natural gas.

Keyword
Bio-Methanol, Biomass, Gasification, Hybrid Cycles, Polygeneration
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-29249 (URN)
Note
QS 20120326Available from: 2011-01-28 Created: 2011-01-28 Last updated: 2012-11-27Bibliographically approved
3. Integration Feasibilities for Combined Cycles in Biofuel Production
Open this publication in new window or tab >>Integration Feasibilities for Combined Cycles in Biofuel Production
2011 (English)In: Proceedings of the 24th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2011, Nis University , 2011, 3498-3508 p.Conference paper, Published paper (Refereed)
Abstract [en]

The aim of this paper is to evaluate the opportunities for gas turbine integration into biofuel production. When producing biofuels via gasification, a significant amount of the input of chemical energy is converted to reaction heat. A steam cycle is therefore used to recover the heat to useful power, but despite that, the plant often remains net users of electricity. To further enhance the production several studies suggest integration of gas turbines, often fired with offgas from the fuel synthesis. The excess of low level heat in the gas turbine exhaust is successfully integrated in the steam cycle which creates integration synergies. Gasification of biomass for fuel synthesis generally implies that oxygen is used as gasification agent. Despite the synergies in the joint steam cycle, the positive effects are outweighed by the energy penalty from oxygen production. Conclusively, serial production of biofuel and power is not beneficial. More interesting is the integrating of a parallel, air-blown gasifier to produce syngas for the gas turbine. Also the natural gas fired gas turbines have successfully been integrated.

Place, publisher, year, edition, pages
Nis University, 2011
Keyword
Biofuel, Biomass, Combined Cycle, Hybrid, Polygeneration, Syngas
National Category
Energy Engineering Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-105547 (URN)2-s2.0-84903647615 (Scopus ID)978-866055016-5 (ISBN)
Conference
24th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2011, Novi Sad, Serbia, 4 July 2011 through 7 July 2011
Note

QC 20121123

Available from: 2012-11-23 Created: 2012-11-22 Last updated: 2015-04-22Bibliographically approved
4. Bio-methane via fast pyrolysis of biomass
Open this publication in new window or tab >>Bio-methane via fast pyrolysis of biomass
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, no SI, 440-447 p.Article in journal (Refereed) Published
Abstract [en]

Bio-methane, a renewable vehicle fuel, is today produced by anaerobic digestion and a 2nd generation production route via gasification is under development. This paper proposes a poly-generation plant that produces bio-methane, bio-char and heat via fast pyrolysis of biomass. The energy and material flows for the fuel synthesis are calculated by process simulation in Aspen Plus®. The production of bio-methane and bio-char amounts to 15.5. MW and 3.7. MW, when the total inputs are 23. MW raw biomass and 1.39. MW electricity respectively (HHV basis). The results indicate an overall efficiency of 84% including high-temperature heat and the biomass to bio-methane yield amounts to 83% after allocation of the biomass input to the final products (HHV basis). The overall energy efficiency is higher for the suggested plant than for the gasification production route and is therefore a competitive route for bio-methane production.

Keyword
Bio-methane, Bio-oil, Biomass, Pyrolysis, SNG, Synthetic natural gas
National Category
Energy Engineering Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-105552 (URN)10.1016/j.apenergy.2013.01.002 (DOI)000329377800044 ()2-s2.0-84884207011 (Scopus ID)
Conference
4th International Conference on Applied Energy (ICAE), July 01-04, 2012, China
Note

QC 20131205. Updated from submitted to published.

Available from: 2012-11-23 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
5. Bio-methane upgrading of pyrolysis gas from charcoal production
Open this publication in new window or tab >>Bio-methane upgrading of pyrolysis gas from charcoal production
2013 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 3, 66-73 p.Article in journal (Refereed) Published
Abstract [en]

This article presents a novel route for bio-methane synthesis utilizing pyrolysis gas from charcoal production. It is a retrofit option that may increase overall process efficiency in charcoal production while adding a valuable product. The pyrolysis gas from charcoal production can be used for bio-methane production instead of burning, while the required heat for the charcoal production is supplied by additional biomass. The aim is to evaluate the energy efficiency of bio-methane upgrading from two types of charcoal plants, with and without recovery of liquid by-products (bio-oil). Aspen simulations and calculations of the energy and mass balances are used to analyse the system. The yield of bio-methane compared to the import of additional biomass is estimated to be 81% and 85% (biomass to bio-methane yield) for the syngas case and the pyrolysis vapour case, respectively. When the biomass necessary to produce the needed electricity (assuming ηel = 33%) is included, the yields amount to 65% and 73%. The results show that the suggested process is a competitive production route for methane from lignocellulosic biomass.

Keyword
Bio-methane, Biomass, Charcoal, Pyrolysis, SNG
National Category
Energy Engineering Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-105563 (URN)10.1016/j.seta.2013.07.001 (DOI)2-s2.0-84882580667 (Scopus ID)
Note

Updated from "Submitted" to "Published" QC 20140218

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved
6. Biogas from renewable electricity: Increasing a climate neutral fuel supply
Open this publication in new window or tab >>Biogas from renewable electricity: Increasing a climate neutral fuel supply
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.

Keyword
Biogas, Renewable energy, Intermittent power, Synthetic fuels, Sabatier reaction
National Category
Energy Systems Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-58804 (URN)10.1016/j.apenergy.2011.07.024 (DOI)000297426100003 ()2-s2.0-80055060615 (Scopus ID)
Funder
StandUp
Note

QC 20120110

Available from: 2012-01-10 Created: 2012-01-09 Last updated: 2017-12-08Bibliographically approved
7. The competitiveness of synthetic natural gas as a propellant in the Swedish fuel market
Open this publication in new window or tab >>The competitiveness of synthetic natural gas as a propellant in the Swedish fuel market
2013 (English)In: Energy Policy, ISSN 0301-4215, E-ISSN 1873-6777, Vol. 52, 810-818 p.Article in journal (Refereed) Published
Abstract [en]

The road transport sector today is almost exclusively dependent on fossil fuels. Consequently, it will need to face a radical change if it aims to switch from a fossil-based system to a renewable-based system. Even though there are many promising technologies under development, they must also be economically viable to be implemented. This paper studies the economic feasibility of synthesizing natural gas through methanation of carbon dioxide and hydrogen from water electrolysis. It is shown that the main influences for profitability are electricity prices, synthetic natural gas (SNG) selling prices and that the by-products from the process are sold. The base scenario generates a 16% annual return on investment assuming that SNG can be sold at the same price as petrol. A general number based on set conditions was that the SNG must be sold at a price about 2.6 times higher per kWh than when bought in form of electricity. The sensitivity analysis indicates that the running costs weigh more heavily than the yearly investment cost and off-peak production can therefore still be economically profitable with only a moderate reduction of electricity price. The calculations and prices are based on Swedish prerequisites but are applicable to other countries and regions.

Keyword
Synthetic natural gas, Economiv feasibility, Sabatier reaction
National Category
Energy Engineering Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-105565 (URN)10.1016/j.enpol.2012.10.049 (DOI)000313775100072 ()2-s2.0-84870695799 (Scopus ID)
Note

QC 20130205

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2017-12-07Bibliographically approved

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