Elsevier

Applied Energy

Volume 252, 15 October 2019, 113461
Applied Energy

Evaluation of biofuel production integrated with existing CHP plants and the impacts on production planning of the system – A case study

https://doi.org/10.1016/j.apenergy.2019.113461Get rights and content

Highlights

  • Regional combined heat and power (CHP) plants are integrated with bioethanol supply.

  • The influence of polygeneration on production planning of CHP plant is investigated.

  • Three extreme cases related to transportation system are developed and investigated.

  • Integration and power supply from rooftop panels affect production planning of system.

  • Use of hybrid cars is the optimal approach concerning fuel use, cost, CO2 emissions.

Abstract

The increasing atmospheric CO2 concentration has caused a transformative shift in global energy systems, which is contributing to an increased use of renewables. Sweden is among the countries trying to shift to a fossil-fuel-free system in all energy sectors. This paper addresses the fuel demand and supply in the transportation sector in the county of Västmanland in Sweden. A Mixed Integer Linear Programming optimization model is developed to minimize cost in the studied system. The model is further used to investigate the influence of three different scenarios on production planning of regional Combined Heat and Power (CHP) plants: (1) straw-based biofuel production integrated with existing CHP plants to fuel combustion engine vehicles, (2) use of electric vehicles, and (3) use of hybrid vehicles fueled by both electricity and bioethanol. Potential solar power generation from rooftop solar cells is also included in the model. The energy system in scenario 2 is found to have the highest overall system efficiency; however, a large amount of power needs to be imported to the system. Hybrid vehicles can potentially reduce the electricity import and CO2 emissions compared to the current situation. Electricity production from rooftop solar collectors could provide the energy needs of the vehicles during summer, while regionally produced straw-based bioethanol integrated with CHP plants can satisfy the fuel needs of the vehicles in winter. This approach could affect the production planning of CHP plants, result in less fuel use and increase the share of renewable resources in the regional transportation system.

Introduction

Utilization of fossil fuels in energy systems is the main source of global Greenhouse Gas (GHG) emissions [1]. The burning of fossil-based fuels in the transportation system also presents a major challenge. In Sweden, for instance, most vehicles are fueled by petrol or diesel. One solution to reduce the use of fossil fuels and mitigate CO2 emissions is to move towards a renewable-based energy system. According to Swedish statistics (SCB) [2], around 6.3% of the total net power generation in Sweden in 2015 was dependent on renewable-based fuels. Fossil fuels have been replaced with biomass-based feedstock such as wood in most energy plants in Sweden; the share of renewable fuels for heat production reached 83.5% in 2015. In the transport sector, the share of biofuels has increased by around 8% over a period of five years from 2011 to 2015 [3]. During the same period, the number of petrol-fueled cars in the domestic transport sector had decreased by more than 13%; However, utilization of Electric Vehicles (EVs) and hybrid cars, which are fueled with biodiesel or bioethanol, has approximately tripled [4]. Despite trends of increasing use of biofuel cars, the transportation system still relies on fossil fuels as the main energy source. Therefore, implementation of further CO2-emissions-reduction approaches in the energy system is needed.

Application of biomass-based fuels in vehicles together with increased use of EVs and hybrid cars is among the potentially effective solutions to meet the Swedish government’s target for the energy system in 2030, which aims for a transportation system that is independent of fossil fuels [5]. This means that the use of petrol and diesel as transport fuels needs to be substituted with biomass-origin fuels such as ethanol and methanol, or electricity. Several studies have been carried out to find suitable renewable-based alternatives to replace conventional fossil-based transport fuels. Aldenius et al. [6] investigated the impacts of using renewable fuels such as biogas and bioethanol in public transportation vehicles such as buses in European countries, by looking at the motivations and challenges that might occur in applying this approach. Improved air quality and reduction of GHG emissions were two of the most important motivations, according to the evaluation in this study, while biomass availability and the required increase in biofuel production were pointed out as big challenges. Turner et al. [7] proposed ternary blends of gasoline, bioethanol and biomass-origin methanol (GEM) that can be used in flex-fuel vehicles. Regarding the climate impacts and economic point of view, Lantz et al. also investigated the biofuel supply from straw [8]. The test results from these two studies showed that the proposed fuel could increase utilization of ethanol in road traffic and displace petrol from the transportation system and simultaneously reduce emissions. Börjesson et al. [9] evaluated the potential raw material production for biofuel supply and the competition for land use for food and biofuel production. The results of the study reveal that the potential production of raw material depends on various technical and environmental factors. Development of conversion technologies for more energy- and cost-efficient biofuel production systems have been proposed as a possible solution. Another study was carried out by Onat et al. [10], investigating the use of hybrid vehicles in the transportation sector in the US. Hybrid electric cars (HEVs), plug-in hybrids (PHEVs) and EVs were compared across 50 US states with respect to regional driving patterns and the sources of power production, including solar energy. Based on the energy mix considered in the study and the Life Cycle Analysis (LCA) results, EVs were found to be the best option in terms of CO2 emissions, whereas HEVs and PHEVs had the highest energy efficiency. Different scenarios were developed in a study in Brazil by De Souza et al [11], in which petrol-fueled vehicles, biofuel cars and hybrid vehicles were compared with respect to their environmental impacts. The study showed that sugarcane-based bioethanol could be applied directly as transport fuel or used in power plants to produce electricity for hybrid vehicles. Both of these strategies would reduce GHG emissions; however, utilization of hybrid vehicles would have the lowest environmental impacts.

Biofuels can be generated from different types of biomass through different conversion technologies. The energy yield in a standalone biofuel plant is relatively low and varies depending on the type of conversion process and the input biomass. For example, the maximum bioethanol energy yield of the fermentation process is around 35%, based on the raw biomass [5], and the residual energy from biomass will appear as waste heat.

Jonker et al. [12] developed an optimization model for a regional sugarcane-based ethanol industry in Brazil to minimize the production cost and GHG emissions from ethanol plants through expansion of biomass supply in the region by 2030. In another study, it was argued that the land use for farming sugarcane as a biomass-based source for ethanol production could increase GHG emissions due to the conversion of forests for sugarcane cultivation. Therefore, an alternative land change, such as utilization of degraded pasture lands for sugarcane production, would reduce the negative impacts on land use and emissions [13].

Due to competition between food and energy supply, restrictions in cultivation areas and use of biomass resources, it is important to use the available energy as efficiently as possible, especially in ethanol production processes, where the production efficiency is low. One possible solution is to integrate bioethanol production with a Combined Heat and Power (CHP) plant in a polygeneration system [5], [14]. In such a system, the by-products from a biofuel plant can be used in a CHP unit to produce heat and electricity. The waste heat from the fermentation process can also be transferred to the district heating network.

The present study evaluates a polygeneration system, with biofuel production integrated with existing CHP plants, and the impacts on production planning of the system. The system interacts with power production from local renewable resources, including rooftop solar collectors and hydropower. The integration of bioethanol production with regional CHP plants in the county of Västmanland in Sweden is used as a case study. Three different scenarios are developed for the regional transport sector, in which the vehicles including passenger cars, trucks, buses and motorcycles are fueled by 1) straw-based bioethanol (cars with combustion engines), 2) electricity (EVs), and 3) a combination of electricity and biofuel (in hybrid vehicles). The reduction in CO2 emissions and the balance between supply and demand in the system are included in the investigation.

Polygeneration refers to a system, in which multiple energy products, such as power, heat and biofuels can be produced. A common example of a polygeneration system is bioethanol production that is integrated with CHP plants to increase the power and heat supply in the system or the overall system efficiency. Several studies have been done on biofuel production and the importance of polygeneration design in energy systems. For example, Salman et al. [15] investigated methanol production through integrated gasification with a local CHP plant in Sweden. Similarly, the performance of an existing CHP plant and the influence of lingocellulosic ethanol yield in a regional polygeneration system was evaluated by Starfelt et al. [14], [16]. The alternatives to achieve a fossil fuel-free system including the transportation sector in the Mälardalen region in Sweden were addressed and evaluated by Dahlquist et al. [17]. These studies assessed the impact of integrating ethanol production into an existing CHP plant, concerning the efficiency of the system; the results showed that polygeneration design of the energy system would improve the overall efficiency of the system compared with standalone biofuel production.

Similar studies were done in [5], [18], investigating the effects of integrating ethanol production into the district heating network. Song et al. [19] studied the feasibility of increased production efficiency by integration of biofuel production with CHP plants at regional level in Sweden, and Daianova et al. [20] evaluated the potential for biofuel production from available straw in a small municipality in central Sweden. Another study [21] presented a techno-economic analysis to investigate the influence of different parameters such as feedstock cost and petrol price on a local integrated CHP with straw-based biofuel production, comparing the results with standalone biofuel plants. These studies together show that integration could lead to a significant decrease in production cost. Moreover, application of waste and renewable-based resources in an integrated energy system can reduce the regional GHG emissions.

The focus of these investigations is predominantly on evaluating the influence of a polygeneration strategy on CO2 emissions, the system cost and overall system efficiency. However, there are few studies that analyze the potential for feedstock supply for biofuel production and the influences on production planning of plants. Moreover, they are generally done either at small scale, such as for a city, or at large scale, for a country [20], [22], [23]. Grahn et al. [24] estimated that the potential biofuel production at national level in Sweden would reach about 26 TWh in 2030 through expansion in the biofuel production capacity. This production corresponds to a maximum biofuel share of 79% of total energy use in the Swedish transportation system in 2030. In a similar study, Ekman et al. [25] investigated the feasibility of biofuel production from agricultural residues in Sweden and examined the key technical factors in the conversion of biomass to biofuels.

Regional biofuel production depends on the availability of feedstock. Local ethanol production in Sweden is lower than the demand. Therefore, a large share of the ethanol demand is satisfied by biofuel imports [21]. The weather conditions are one reason for the low domestic production. Cultivation of different energy crops in suitable locations in the country, bearing in mind the Swedish climate and landscape, would be a possible solution to increase the available feedstock for local production of biofuels. The feedstock used for biofuel production is divided into three categories: the first category includes sugarcane and corn- which are among the most common resources used in bioethanol technology in Brazil and the USA- and food residues such as cooking oil, wheat and barley; the second category includes wood and agricultural residues such as straw and municipal waste; and the third category includes algae. This paper considers straw-based bioethanol production. The cereal straws considered are wheat, oats and barley, as these are the most common type of cereals cultivated in the region.

The objective in most of the studies mentioned above is to improve the production process in existing production units. There are few investigations on production planning of energy plants at large scale that consider the key parameters in the supply chain. There is also a shortage of studies on potential biofuel production at the regional scale with consideration of trends in the system. Due to increased utilization of biomass-based fuels in the energy system and low energy density of this type of feedstock, it is important to evaluate the energy system at local and regional level and to estimate the potential energy supply under the regional conditions, including the yearly variations in demand.

Studies conducted on transportation systems and transport fuels mostly investigate only passenger cars in road traffic. This paper, however, maps transport fuel use in the county of Västmanland in central Sweden and considers the potential transformation of the regional transportation system including passenger cars, motorcycles, trucks and buses with increased application of renewable energy sources such as biomass and solar energy.

Section snippets

Methodology

To perform the analysis and develop the future scenarios, a case study is carried out for Västmanland. The investigation uses energy use profiles and regional production of transportation fuels from 2015, the studied year. The research methods include data collection and optimization modeling for the case study. Data on regional energy use and production of power, heat and fuels from available resources were collected from official statistics for Sweden, which are provided by authorities such

Results and discussion

Of 154,522 vehicles of different types including passenger cars, trucks, motorcycles and buses in the regional road transport, around 7000 vehicles were fueled by ethanol in the base scenario for 2015. According to the estimated data for cereal straw production in Västmanland and the energy content of straw (see Table 2), the potential bioethanol production is around 950 GWh, which indicates that there is high potential in local production of bioethanol from regionally cultivated cereals.

Conclusion

In this study, integration of bioethanol production with CHP plants and renewable resources such as hydropower and rooftop PV collectors have been modelled and investigated. The production strategy of the system, considering the production cost, fuel price and availability, power imports, and CO2 emissions have been analyzed to identify the optimal energy system.

Estimation of available straw in the region shows that the potential production of biofuel from locally available cereal straw might

Acknowledgements

This study is part of the SYDPOL project, which is funded by the Co-operation program on fuel based power and heat production SEBRA. Energiforsk, Swedish Energy Agency, Mälarenergi and Eskilstuna Energi och Miljö are acknowledged for their funding and contributions to the project. The authors would also like to acknowledge Muhammad Abdullah Zafar for his assistance in providing some of the data sources.

References (51)

  • D. Djuric Ilic et al.

    District heating and ethanol production through polygeneration in Stockholm

    Appl Energy

    (2012)
  • L. Daianova et al.

    Evaluation of a regional bioenergy system with local production of biofuel for transportation, integrated with a CHP plant

    Appl Energy

    (2012)
  • P. Börjesson et al.

    Agricultural crop-based biofuels – resource efficiency and environmental performance including direct land use changes

    J Clean Prod

    (2011)
  • A. Elfasakhany

    Performance and emissions of spark-ignition engine using ethanol–methanol–gasoline, n-butanol–iso-butanol–gasoline and iso-butanol–ethanol–gasoline blends: a comparative study

    Eng Sci Technol an Int J

    (2016)
  • Environmental and Energy Study Institute (EESI). Fossil Fuels. EESI 2018....
  • SCB. År I korta drag (year in brief) (in Swedish), Report No. EN 11SM 1601;...
  • SCB. Fordon 2015. Trafa 2016. http://www.trafa.se/globalassets/statistik/vagtrafik/fordon/fordon_2015.pdf [accessed...
  • Swedish Energy Agency. Statistical Database. SCB 2015....
  • M. Lantz et al.

    Biogas and ethanol from wheat grain or straw: Is there a trade-off between climate impact, avoidance of iLUC and production cost?

    Energies

    (2018)
  • Börjesson P, Lundgren J, Ahlgren S, Nyström I. Dagens och framtidens hållbara biodrivmedel (Today’s and future...
  • E. Dahlquist et al.

    Alternative pathways to a fossil-fuel free energy system in the Mälardalen region of Sweden

    Int. J. Energy Res.

    (2007)
  • H. Song et al.

    A dynamic model to optimize a regional energy system with waste and crops as energy resources for greenhouse gases mitigation

    Energy

    (2012)
  • Daianova L, Thorin E, Yan J, Dotzauer E. Local production of bioethanol to meet the growing demands of a regional...
  • M. Börjesson et al.

    Biofuel futures in road transport – a modeling analysis for Sweden

    Transp Res Part D Transp Environ

    (2014)
  • M. Grahn et al.

    Prospects for domestic biofuels for transport in Sweden 2030 based on current production and future plans

    Adv Bioenergy Sustain Chall

    (2015)
  • Cited by (0)

    View full text