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Efficiency of heat and work in a regional energy system
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, Faculty of Science & Engineering.
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: urn:nbn:se:liu:diva-162605DOI: 10.3384/lic.diva-162605ISBN: 9789179299347 (print)OAI: oai:DiVA.org:liu-162605DiVA, id: diva2:1377104
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
List of papers
1. Active Management of Heat Customers Towards Lower District Heating Return Water Temperature
Open this publication in new window or tab >>Active Management of Heat Customers Towards Lower District Heating Return Water Temperature
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 10, article id 1863Article in journal (Refereed) Published
Abstract [en]

The traditional way of managing the supply and return water temperatures in a district heating system (DHS) is by controlling the supply water temperature. The return water temperature then becomes a passive result that reflects the overall energy efficiency of the DHS. A DHS with many poorly functioning district heating centrals will create a high return water temperature, and the energy efficiency of the DHS will be affected negatively in several ways (e.g., lower efficiency of the flue gas condenser, higher heat losses in pipes, and lower electricity production for a DHS with combined heat and power (CHP)). With a strategic introduction of low-grade heat customers, the return water temperature can be lowered and, to some extent, controlled. With the heat customers connected in parallel, which is the traditional setup, return water temperatures can only be lowered at the same rate as the heat customers are improved. The active management of some customers can lower the return water temperatures faster and, in the long run, lead to better controlled return water temperatures. Active management is defined here as an adjustment of a domestic heating system in order to improve DHS efficiency without affecting the heating service for the individual building. The opposite can be described as passive management, where heat customers are connected to the DHS in a standardized manner, without taking the overall DHS efficiency into consideration. The case study in this article shows possible efficiency gains for the examined DHS at around 7%. Looking at fuel use, there is a large reduction for oil, with 10-30% reduction depending on the case in question, while the reduction is shown to be largest for the case with the lowest return water temperature. The results also show that efficiency gains will increase electricity production by about 1-3%, and that greenhouse gas (GHG) emissions are reduced by 4-20%.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
district heating; system perspective; low-grade district heating; return water temperature
National Category
Energy Engineering
Identifiers
urn:nbn:se:liu:diva-158821 (URN)10.3390/en12101863 (DOI)000471016700042 ()
Note

Funding Agencies|Swedish District Heating Association; Fjarrsyn (district heating and cooling research programme)

Available from: 2019-07-16 Created: 2019-07-16 Last updated: 2019-12-11
2. System Perspective on Biogas Use for Transport and Electricity Production
Open this publication in new window or tab >>System Perspective on Biogas Use for Transport and Electricity Production
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
Keywords
District heating; system perspective; electric buses; biogas; smart energy systems
National Category
Energy Systems
Identifiers
urn:nbn:se:liu:diva-162625 (URN)10.3390/en12214159 (DOI)
Available from: 2019-12-11 Created: 2019-12-11 Last updated: 2019-12-11Bibliographically approved

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