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System Perspective on Biogas Use for Transport and Electricity Production
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-2860-1820
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 21, article id 4159Article in journal (Refereed) Published
Abstract [en]

Linköping municipality has managed biogas driven buses in the regional transport system since 1997 and all buses in the municipality have run on biogas since 2015. Biogas is a renewable fuel and by replacing fossil fuels it can help to lower net CO2 emissions. However, Internal Combustion Engines (ICE) in buses still have a rather low efficiency, in the range of 15–30%. If the combustion of biogas instead takes place in a combined cycle gas turbine (CCGT) efficiency could be higher and heat losses reduced. This could be a feasible solution if the transport system instead used electric buses charged with electricity generated by the CCGT. This article has a top-down perspective on the regional transport system and the regional district heating system (DHS) in Linköping municipality. Two alternative systems are compared regarding CO2 emissions, electricity production and component efficiencies. The first system that is studied is in operation today and uses locally produced biogas in the ICE buses. In parallel the combined heat and power (CHP) system delivers electricity and heat to households in the region. The second system that is studied is a system with electric buses and a CHP system that uses biogas in the CCGT to deliver electricity and heat to the regional power grid and DHS. The study shows that emissions would be reduced if biogas use is changed from use in ICE buses to use in the CCGT in the CHP-DHS. Improved biogas use could lower CO2-eq emissions by 2.4 million kg annually by using a better fuel-energy pathway.

Place, publisher, year, edition, pages
Basel: MDPI, 2019. Vol. 12, no 21, article id 4159
Keywords [en]
District heating; system perspective; electric buses; biogas; smart energy systems
National Category
Energy Systems
Identifiers
URN: urn:nbn:se:liu:diva-162625DOI: 10.3390/en12214159OAI: oai:DiVA.org:liu-162625DiVA, id: diva2:1377229
Available from: 2019-12-11 Created: 2019-12-11 Last updated: 2019-12-11Bibliographically approved
In thesis
1. Efficiency of heat and work in a regional energy system
Open this publication in new window or tab >>Efficiency of heat and work in a regional energy system
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

One of the largest flows of energy in Swedish municipalities is the fuel-energy flow through the regional combined heat and power (CHP) plant. The customer products from this flow are mainly electricity to the electricity grid and heat to the building sector. There are many ways to describe and examine this fuel-energy flow, and there are many perspectives. This thesis presents one perspective. It is a top-down, analytical and numerical perspective on the efficiency of heat and work in a regional energy system. The analysis focus on the present situation in Linköping municipality and aims at describing the energy efficiency improvement potential. Three subsystems are considered, the regional production of electricity, the regional production of heat, and the regional public transport by bus. These three systems are physically all heat engines i.e. engines that derive work and/or heat from fuel combustion processes. It is important to notice that the analysis in this thesis does not describe the theoretical improvement potential, that potential is considerably higher than the implementable potential, but of no practical use. Instead the analysis is as far as possible based on real world measured efficiencies and efficiency values of best practice (Best available technology).

The analysis shows that hardware investments at the CHP plant can improve the electricity generation efficiency and thereby reduce CO2 emissions. The investments are in high pressure turbines, medium pressure turbines and preheaters. The size of the improvement is hard to quantify because it depends partly on unknown factors in the surrounding electricity market. In the studied system CO2 reduction could be as high as 40 - 60 %.

The regionally produced biogas would be used more efficiently if it were used in the local combined cycle gas turbine instead of being used in internal combustion engines in buses. The buses would instead be electrically driven. This use of biogas would create a better integrated fuel-energy flow and reduce heat losses.

Another improvement is to reduce the system temperatures in the district heating system. The study shows that the efficiency gains, because of lower system temperatures, would increase electricity production by about 1 – 3%, and that greenhouse gas emissions would be reduced by 4 – 20%. However, these improvements are dependent on demand side investments in the district heating system and are therefore slow to implement.

Abstract [sv]

Ett av de största energiflödena i svenska kommuner är bränsle/energi-flödet genom det regionala kraftvärmeverket. De konsumentprodukter som detta energiflöde producerar är främst uppvärmning av bostäder och elkraft. Det finns många sätt att beskriva och utvärdera detta bränsle/energi-flöde och det finns många olika perspektiv. Det här arbetet analyserar energiflödet med en analytisk ”top-down” metod. Analysen utgår ifrån den nuvarande situationen i Linköpings kommun och avser att belysa den förbättringspotential som finns med avseende på systemets verkningsgrad. Tre delsystem har studerats, det regionala systemet för värmeproduktion, det regionala systemet för elproduktion och det regionala kollektivtrafiksystemet för innerstadstrafik med buss. Dessa tre system är fysikaliskt värmemotorer d.v.s. de är system som nyttjar termisk energi från förbränningsprocesser för att utföra ett arbete och/eller generera värme. Det är viktigt att notera att analyserna i detta arbete inte avser att beskriva en teoretisk förbättringspotential. Analyserna avser istället att belysa den praktiska, implementerbara, förbättringspotentialen. Därför har arbetet så långt som möjligt utgått ifrån uppmätta data och numeriska värden på verkningsgrader ifrån redan existerande anläggningar eller tekniska komponenter.

Analyserna visar att hårdvaruinvesteringar i det lokala kraftvärmeverket skulle öka elproduktionen och därigenom sänka koldioxidutsläppen. De investeringar som skulle behöva göras är investeringar i högtrycksturbiner, mellantrycksturbiner och förvärmare. De sänkta koldioxidutsläppen är svåra att kvantifiera eftersom de delvis beror på okända faktorer på den omgivande elmarknaden. Reduktionen av koldioxidutsläppen skulle kunna vara så stor som 40 - 60 %.

Den lokalt producerade biogasen skulle användas mer effektivt om den användes i den lokala gaskombi-anläggningen istället för att användas som bussbränsle som är det nuvarande användningsområdet för detta bränsle. Bussarna skulle istället kunna ersättas med elbussar. En sådan förändring av biogas-användningen skulle innebära ett bättre integrerat energisystem med lägre värmeförluster.

En annan möjlig förbättring av kraftvärmesystemet är att sänka returtemperaturerna i fjärrvärmesystemet. Analyserna visar att elverkningsgraden skulle förbättras 1 – 3 % och att koldioxidutsläppen skulle kunna minska med 4 – 20 %. Dessa förbättringar skulle däremot kräva investeringar på kraftvärmesystemets kundsida och bedöms därför vara långsamma att implementera.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. p. 61
Series
Linköping Studies in Science and Technology. Licentiate Thesis, ISSN 0280-7971 ; 1863
National Category
Energy Systems
Identifiers
urn:nbn:se:liu:diva-162605 (URN)10.3384/lic.diva-162605 (DOI)9789179299347 (ISBN)
Presentation
2019-12-16, ACAS, A-building, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2019-12-11 Created: 2019-12-11 Last updated: 2019-12-11Bibliographically approved

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