Environmental and Economic Analysis of Liquefied Natural Gas And

Journal of Cleaner Production 278 (2021) 123535

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Journal of Cleaner Production

journal homepage: www.elsevier.com/locate/jclepro

Cleaner heavy transports e Environmental and economic analysis of liqueﬁed natural gas and biomethane

* Marcus Gustafsson , Niclas Svensson

Environmental Technology and Management, Department of Management and Engineering, Linkoping€ University, SE-581 83, Linkoping,€ Sweden article info abstract

Article history: Looking to reduce climate change impact and particle emissions, the heavy-duty transport sector is Received 21 April 2020 moving towards a growth within technology and infrastructure for use of liquefied natural gas (LNG). Received in revised form This opens an opportunity for the biogas market to grow as well, especially in the form of liquefied 2 July 2020 biomethane (LBM). However, there is a need to investigate the economic conditions and the possible Accepted 29 July 2020 environmental benefits of using LBM rather than LNG or diesel in heavy transports. This study presents a Available online 9 August 2020 comparison of well-to-wheel scenarios for production, distribution and use of LBM, LNG and diesel, Handling editor: Yutao Wang assessing both environmental and economic aspects in a life cycle perspective. The results show that while LNG can increase the climate change impact compared to diesel by up to 10%, LBM can greatly Keywords: reduce the environmental impact compared to both LNG and diesel. With a German electricity mix, the Biomethane climate change impact can be reduced by 45e70% compared to diesel with LBM from manure, and by 50 Natural gas e75% with LBM from food waste. If digestate is used to replace mineral fertilizer, the impact of LBM can Heavy transport even be less than 0. However, the results vary a lot depending on the type of feedstock, the electricity Liquefaction system and whether the calculations are done according to RED or ISO guidelines. Economically, it can be Life cycle assessment hard for LBM to compete with LNG, due to relatively high production costs, and some form of economic Life cycle cost incentives are likely required. © 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

1. Introduction and bus manufacturers, including Daimler (2018), Isuzu (2018), Iveco (2015), Scania (2017) and Volvo Trucks (2017). At the same Transportation of people and goods requires vast amounts of time, efforts to build up an LNG fueling infrastructure take place e.g. energy and is a major source of air pollution and greenhouse gas within the LNG Blue Corridors project (LNG BC, 2013) and through (GHG) emissions. Within the European Union (EU), there is a goal to current fueling station expansion in the Nordic countries (Gasum, reduce GHG emissions from transports by at least 60% by 2050 2019). Smajla et al. (2019) stated that LNG in heavy transports is compared to 1990, without impairing mobility (European more economic than diesel in a long perspective and that switching Commission, 2016). Around 25% of the GHG emissions from road to LNG is crucial for meeting environmental goals. transports in the EU are accounted for by commercial heavy-duty Compared to diesel, compressed or liquefied natural gas is often vehicles such as buses and trucks (EEA, 2018). Alternative propul- shown to give a certain reduction of GHG emissions from vehicles. sion technologies to reduce pollution and climate change impact Considering the whole production-to-use pathway of fuelsdu- are broadly investigated in research, including batteries, fuel cells sually referred to as well-to-wheel (WTW) analysisdSpeirs et al. and gas. When it comes to gas, liquefied natural gas (LNG) has the (2020) showed a reduction of GHG emissions with natural gas advantage of a higher volumetric energy density than compressed compared to diesel of up to 16%, Arteconi et al. (2010) reported a gas (Benjaminsson and Nilsson, 2009), which makes it feasible to GHG emission reduction with LNG of up to 10%, Borjesson€ et al. use in heavy and long-distance transports. Engines designed for (2016) showed a reduction of 2e12% for heavy-duty vehicles and methane propulsion are currently being produced by several truck Ou and Zhang (2013) found a GHG reduction of 5e10%. However, the GHG savings are limited by a lower efficiency of gas engines compared to diesel engines, by methane leakage and by the fact * Corresponding author. that natural gas is a fossil fuel. Arteconi et al. (2010) found that E-mail addresses: [email protected] (M. Gustafsson), niclas.svensson@ small-scale LNG production resulted in GHG emissions in line with liu.se (N. Svensson). https://doi.org/10.1016/j.jclepro.2020.123535 0959-6526/© 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 2 M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535

Nomenclature WS water scrubbing WTW well-to-wheel

Abbreviations Symbols

AD anaerobic digestion B0 maximum methane potential AF annuity factor CH₄ methane AS amine scrubbing CO carbon monoxide LBM liqueﬁed biomethane CO₂ carbon dioxide C3MR propane/mixed refrigerant i interest rate

GHG greenhouse gas mCH4 mass of methane emitted during storage LCA life cycle assessment mmanure mass of manure LCC life cycle cost N depreciation period LNG liqueﬁed natural gas N₂ nitrogen MCF methane conversion factor NH₃ ammonia MR mixed refrigerant NH₄-N ammonium nitrogen PM particulate matters N₂O dinitrogen monoxide RED renewable energy directive NOₓ nitrogen oxides SI spark ignition SO₂ sulfur oxides

TTW tank-to-wheel rCH4 density of methane VOC volatile organic compounds s2 variance VS volatile solids

diesel, and Stettler et al. (2019) found that the GHG emissions of reductions of environmental impact compared to fossil fuels, while heavy-duty vehicles running on natural gas were equal to or up to also avoiding a competition of land between food and fuel pro- 8% higher than the emissions of equivalent diesel vehicles. Speirs duction. While large producers of biogas like Germany and Italy et al. (2020) also found that the GHG emissions could in fact in- currently use a lot of energy crops in their supply chains (EBA, crease by replacing diesel with natural gas, and Cooper et al. (2019) 2020), many EU countries even exclude energy crops in national found that the benefits of reduced climate change impact with regulations on biogas production (EurObserv’ER, 2017). natural gas could be lost if the methane emissions exceed 1.5e3.5%. The environmental impact of biomethane as a transport fuel has From a technical point of view, fossil natural gas can easily be been assessed in several studies. Shanmugam et al. (2018) exchanged for renewable biomethane, either as compressed or compared the environmental impact of LBM and diesel for heavy liquefied biomethane (LBM, also known as bio-LNG). Biomethane is trucks in Sweden, concluding that LBM is superior in 7 out of 10 produced from organic materials through fermentation (biogas) or investigated impact categories. Hagos and Ahlgren (2018) thermal processes and is treated to have a similar properties as compared the energy balance and GHG emissions of natural gas natural gas, and can therefore be regarded as one possible way and biomethane in road and maritime transports, showing that towards a more renewable gas network (Speirs et al., 2018). While biomethane can greatly reduce the WTW emissions despite a the EU market for natural gas is largely dependent on imports higher energy input. Lyng and Brekke (2019) performed a well-to- (Eurostat, 2019a; IGU, 2017), biogas and biomethane are often wheel analysis of fuels for buses and found that biomethane from produced and used domestically or even locally (Kampman et al., food waste or manure is among the vehicle fuels with the lowest 2016). Currently, the practice of using biomethane in road trans- environmental impacts on the market. Further, Natividad Perez- ports is very limited, with Sweden being the leader in Europe Camacho et al. (2019) found that biomethane can reduce the GHG (EurObserv’ER, 2017), although there is a growing interest and emissions by around 500 kg CO₂-equivalents per MWh in a life cycle policy support in many countries (Gustafsson and Anderberg, perspective compared to petrol or diesel. In addition to the envi- 2020). On average, the share of biomethane in European vehicle ronmental aspects of biomethane as a vehicle fuel, biogas and gas is about 17%, with some countries reaching close to 100% biomethane production systems typically include environmental (Hormann,€ 2020). Estimates suggest a potential steep increase in and other benefits that are not strictly tied to the production of an LBM production in Europe (Agelbratt and Berggren, 2015). energy carrier (Hagman and Eklund, 2016). For example, produc- Pa€akk€ onen€ et al. (2019) concluded that half the heavy-duty trans- tion of biogas through anaerobic digestion generates a by-product port sector in Finland could rely on biomethane by 2030. The total that can be used as a fertilizer, thus displacing an equivalent biogas production in the EU-28 has increased by a factor 10 since amount of conventional mineral fertilizer. The technical reports by the turn of the millennium, from around 70 PJ/year to over 700 PJ/ Edwards et al. (2014) and Borjesson€ et al. (2016) both note that not year (Eurostat, 2019b). While the biogas production from landfill only is the possible GHG reduction compared to diesel substantially gas and sewage sludge have been rather static in the last 15 years, larger with biomethane than with natural gas, but the climate most of this change is due to a growth in other anaerobic digestion, change impact of biomethane can even become negative if external such as energy crops, manure and food waste (Eurostat, 2019b). For effects of biogas production are included in the calculations. While the further development of biofuel production, the European Union this type of system expansion is encouraged in the ISO standards advocates second-generation, or advanced, biofuels (European for LCA (ISO, 2006a, 2006b), the EU Renewable Energy Directive Commission, 2009), which are based on non-food crops or (RED) does not allow it (European Commission, 2009). byproducts from agriculture and forestry (Sims et al., 2008). The financial conditions for production of biomethane can vary a Second-generation biofuels should thereby achieve significant lot depending on technology, scale, feedstock, energy costs, M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 3 economic incentives and other factors. Several studies have 2. Methodology assessed the economic aspects of different ways of producing biogas and biomethane, including recent publications by Lombardi The analysis consisted of two parts, as illustrated in Fig. 1:an and Francini (2020), Martín-Hernandez et al. (2020) and Gustafsson analysis of WTW environmental impact of liquefied biomethane et al. (2020a). However, comparisons against competing technol- (LBM), liquefied natural gas (LNG) and diesel, which was done ogies such as fossil fuels are less common in the literature. through life cycle assessment (LCA); and a comparison between the Pa€akk€ onen€ et al. (2019) found that in Finland, biomethane pro- WTW life cycle cost of LBM production and the market price of LNG. duction costs could be competitive with the market price of diesel, The WTW analysis was done by modelling and analyzing a set of not taking into account any possible margin for revenue from scenarios of production, distribution and use. Each scenario rep- selling the biomethane. Borjesson€ et al. (2016) found that the WTW resents a possible pathway for the fuel from resource extraction to costs of heavy-duty trucks with LBM could be comparable to diesel use in the vehicle, including all the intermediary processes to get trucks in Sweden, including taxes, but not as low as with LNG. there. The modelling process and the studied scenarios are pre- Tybirk et al. (2018) argued that it will be difficult for biomethane sented in sections 2.1 and 2.2, respectively. The data used in envi- producers to compete with the price of natural gas, especially in ronmental and economic calculations is presented in section 2.3, regions with availability of shale gas. Still, there is a need for further and the sensitivity and uncertainty analyses conducted are further studies on how factors such as technology, feedstock and scale explained in section 2.4. influence the competitiveness of biomethane as a vehicle fuel. Liquefaction of methane is a well-known concept with proven 2.1. Modelling technologies. However, they are usually designed for the scale of natural gas production. Biogas is produced in much smaller vol- The environmental impact of the scenarios was evaluated umes, and in comparison to LNG production facilities a liquefaction following ISO 14040 and 14,044 guidelines for LCA (ISO, 2006a, “ ” plant for biomethane could be considered nano-scale (Tybirk 2006b). An LCA consists of four principal steps: Goal and scope et al., 2018). Natural gas liquefaction processes worldwide are definition, Life cycle inventory (data collection), Environmental ’ mainly based on Air Products technologies with mixed refrigerant impact assessment and Interpretation of results. The boundaries condensation (IGU, 2017). The most common liquefaction tech- were set to cover the whole fuel pathway from extraction or nology for natural gas applications is C3MR, which utilizes propane collection of raw materials to combustion in the vehicle’s engine, in ₃ ₈ (C H ) and a mixed refrigerant (MR) for cooling and condensing the other words well-to-wheel (WTW). Modelling and calculations gas in two cycles (Usama et al., 2011). Gustafsson et al. (2020a) were done using SimaPro 8, a widely used tool for LCA (Goedkoop analyzed the costs, energy use and environmental impact of sce- et al., 2016). Environmental impact assessment, i.e. calculation of fi narios for production and distribution of compressed and lique ed environmental impact of the included materials and energy flows, fi biomethane, including the ve upgrading technologies described was done with the ReCiPe heuristic midpoint method (PRe, 2014), by Bauer et al. (2013) and four different technologies for liquefac- which is commonly used in LCA research studies. The assessment tion. Their results showed that the differences between the com- covered five impact categories: climate change, terrestrial acidifi- mercial upgrading technologies are quite small, except for amine cation, freshwater eutrophication, ozone formation (impact on scrubbing which uses less electricity and more heat than other technologies (Gustafsson et al., 2020a). In general, biomethane production systems are more dependent on electricity than natural gas production (Edwards et al., 2014), where part of the gas stream is often used in gas turbines for internal energy demands (Raj et al., 2016; Songhurst, 2018). This implies that the local electricity system would influence the WTW performance of biomethane compared to natural gas or diesel, which (to the authors’ knowledge) is yet to be assessed in research. While there has been some previous research on the environmental aspects of LNG and LBM in transports, there is a lack of studies comparing the economic aspect. Moreover, there appears to be a lack of attention towards geographical differences in comparisons of LNG and LBM, specifically the influence on the environmental performance of the local electricity system. This paper presents an environmental and economic WTW analysis of scenarios for production and distribution of LNG and LBM for heavy- duty trucks in a European context. The comparison includes different feedstock for biogas production as well as different technologies to produce and distribute LNG and LBM, and different electricity mixes for production of LBM. As a reference, conventional diesel is also included in the comparison. Environmental impact is assessed in form of climate change, acidification, eutrophication, ground-level ozone formation and stratospheric ozone layer depletion, both with the RED method and with system expansion according to ISO. The cost of producing LBM is calculated depending on production capacity and compared to the market price of LNG. Thus, this paper provides a broad overview of the environmental and economic aspects of LNG and LBM for heavy- duty trucks, covering several possible pathways and assessing the Fig. 1. Overview of the methodology of the study. The analysis consisted of environ- influential factors. mental impact assessment and economic analysis. 4 M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 human health) and stratospheric ozone depletion. For processes Distribution of liquefied gas was done by truck with a 25-ton where specific data could not be obtaineddsuch as production of cryogenic tank. For scenarios with pressure reduction liquefac- diesel and natural gas, fuel distribution and electricity pro- tion, the gas was compressed to 60 bar and distributed via the ductiondgeneric processes from the Ecoinvent database version natural gas grid. The pressure reduction liquefaction process was 3.5 (Moreno Ruiz et al., 2018; Weidema et al., 2013) were used. assumed to produce 10% liquefied gas, while the remaining 90% These processes were selected to represent the modelled system as was considered to be used as in gaseous form in other applications closely as possible, e.g. electricity markets in specific countries (see (He and Ju, 2013). section 2.4) and distribution trucks of European standard (Euro 6). For the LBM scenarios, two sets of calculations were done, using In the life cycle cost (LCC) calculations, costs of capital, operation different system boundaries: one following the ISO standard for and maintenance and distribution for LBM pathways were LCA, and one following RED. In the ISO calculations, the use of compared to the European market price of LNG, as the equivalent digestate from anaerobic digestion (AD) as a biofertilizer were costs for LNG pathways could not be retrieved. This means that the included, and alternative handling of the substrates used in AD was LBM would have to add a revenue for sales to be able to compare considered. In the case of manure as substrate, this meant that with LNG on the same basis. However, in this study the comparison methane emissions from conventional manure handling could be is used to see how close LBM is to becoming a viable market option avoided, and a larger amount of mineral fertilizers could be in terms of price and thus the difference can be used for discussion. replaced as the AD process increases the nitrogen availability in the The LBM costs were calculated using the annuity factor (AF), with a digestate. In the food waste scenarios, the alternative waste depreciation period (N) of 15 years and a 6% interest rate (i): handling scenario was assumed to be incineration with cogenera- tion of heat and electricity, and the digestate from AD was also in ¼ i this case used as fertilizer. In the RED calculations, the environ- AF (1) 1 ð1 iÞ N mental impact of the digestate, as well as alternative waste handling and the possible gain of displacing mineral fertilizer Apart from cost for energy, operation and maintenance costs production, was not included, as RED prescribes energy allocation were assumed to be 2.5% of the investment cost. Similar economic between biogas and digestate rather than system expansion. assumptions were found in several comparable studies, including For LNG, the system boundary covered the way from raw ma- Larsson et al. (2015), Borjesson€ et al. (2016), Gustafsson et al. terial extraction to combustion in the SI engine (Fig. 3), with similar (2020a). The cost of distribution of LBM by truck was set to 1.80 pathways as for LBM. Before liquefaction, natural gas goes through V/km, including diesel, driver, truck and other related costs, plus a series of purification processes to clean it from carbon dioxide, 64.50 V/hour for loading and unloading (4 h per delivery). Distri- hydrogen sulfide and water (Ma et al., 2017). The studied lique- bution costs were based on Pettersson et al. (2006) and updated for faction technologies include C3MR and N₂ cycle liquefaction, as well inflation. The cost calculations for fueling LBM did not include costs as pressure reduction liquefaction from the gas grid. for building and operating the fueling station, only electricity for In the food waste LBM scenarios, substrate and digestate were the pump, since the same fueling stations are also used for LNG, and assumed to be transported on average 25 km between the substrate the volumes of LNG are much higher compared to LBM. The same source and the biogas plant, and between the biogas plant and the applies for distribution by gas grid. digestate recipient. An exception was made in the manure scenarios, where the biogas plant was assumed to be located at the 2.2. Studied scenarios farm, making such transports redundant. The mineral fertilizer replaced in ISO calculations was assumed to be produced further The studied WTW scenarios covered the way from raw material from the area of use, requiring a transport of 50 km. LNG and LBM to use in a vehicle in a European road transport system. The envi- were transported in a 25-ton cryogenic tank over an average dis- ronmental impact of LBM, LNG and diesel were compared on the tance of 200 km. The LNG pathways additionally included a ship basis of 1 km transport with a 40-ton long haulage truck, taking transport over 10,000 km, representing the distance between into consideration differences in fuel economy of gas and diesel Middle East (Qatar) and Western Europe (Netherlands) via the Suez engines. In the economic comparison between LBM and diesel, the Canal. Alternatively, the fuels were distributed via pipeline, over a cost of producing 1 kWh LBM was compared to the market price of distance of 200 km for biomethane and 5000 km for natural gas. 1 kWh LNG. Diesel was assumed to be produced in the Middle East and trans- For LBM, the system boundary started at collection of raw ma- ported the same way as LNG from the refinery to the area of use terial for anaerobic digestion (AD) and ended at combustion in the (Fig. 4). vehicle (Fig. 2), in a spark-ignited (SI) Otto engine. Two types of feedstock were considered for the biogas production: manure and 2.3. Data collection food waste, which are both eligible feedstock for advanced or second-generation biofuels. The biogas from the AD was assumed Energy use, costs, methane content in biogas and methane slip to be upgraded to biomethane through water scrubbing (WS) or for anaerobic digestion are listed in Table 1, and data for substrates amine scrubbing (AS) after which it was liquefied through mixed- and digestates is listed in Table 2. Data for manure were taken to be refrigerant (MR) or nitrogen (N₂) cycle, distributed by truck, the average of data for cattle and swine manure. The share of fueled and combusted in a vehicle. Alternatively, the biomethane ammonium nitrogen (NH₄-N) was assumed to be 20% higher after was distributed via a high-pressure gas grid to a pressure reduction anaerobic digestion compared to the undigested substrate. This liquefaction facility. WS is currently the most common technology value falls within intervals found in publications by Moller€ and for biogas upgrading in Europe in terms of produced volume (Prussi Müller (2012) and Sinclair et al. (2013). In accordance with the et al., 2019), while AS stands out compared to other conventional same sources, the availability of phosphorus and potassium was upgrading technologies when it comes to energy use (Gustafsson assumed to not increase through anaerobic digestion. In ISO cal- et al., 2020a). For gas upgraded through WS, an extra CO₂ polish- culations, digestate of manure was therefore assumed to replace an ing step was considered before MR or N₂ cycle liquefaction whereas equal amount (mass input) of undigested manure, plus artificial AS can meet the purity requirements for liquefaction at the cost of nitrogen fertilizer corresponding to the increased NH₄-N content, an increased energy use (Bauer et al., 2013; Karlsson, 2018). while the amounts of phosphorus and potassium were assumed to M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 5

Fig. 2. Schematic view of the modelled WTW scenarios for LBM. Going from the left to the right, each of the indicated pathways represent a possible scenario from production to end user: biogas production, upgrading to biomethane, liquefaction and distribution, fueling and combustion in vehicle engine. The color and weight of the lines indicate the state (gas/liquid) and methane content at that part of the pathway. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the Web version of this article.)

Fig. 3. Schematic view of the modelled WTW scenarios for LNG. Going from the left to the right, each of the indicated pathways represent a possible scenario from production to end user: gas extraction and processing, liquefaction and distribution, fueling and combustion in vehicle engine. The color and weight of the lines indicate the state (gas/liquid) and methane content at that part of the pathway. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the Web version of this article.)

Fig. 4. Schematic view of the modelled WTW scenario for diesel. be unchanged compared to the alternative waste handling and the digestate (Lantz et al., 2009), and 1% was assumed to be emitted were left out of the calculations. In the food waste scenarios, the in the form of N₂O(De Klein et al., 2006). The remaining ammonium digestate was assumed to replace mineral fertilizer corresponding in the digestate was modelled as emission to soil. Methane emis- to the total NH₄-N content of the digestate. sions from digestate spread on agricultural land were assumed to Spreading of the digestate was assumed to cause 10% higher be negligible in relation to methane emissions from biogas pro- emissions of ammonia (NH₃) and dinitrogen monoxide (N₂O) duction (Amon et al., 2006; Tufvesson et al., 2013). The share of compared to mineral fertilizers (Tufvesson et al., 2013). The NH₃ biogas ﬂared in the AD plant due to occasional mismatch between emissions to air were set to 5% of the total ammonium content of biogas production and demand was set to 5%. Internal heat demand 6 M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535

Table 1 off-gas was assumed to be treated through catalytic oxidation, Data used in modelling of environmental impact and life cycle costs of anaerobic converting 95% of the methane to carbon dioxide and water (Herbst digestion. et al., 2010). The electricity demand for gas sweetening and dehy- Parameter Value Unit dration was considered to be 10% of the electricity demand for € Electricity 30a MJ/ton substrate liquefaction (Honig et al., 2019), which was set to 0.26 kWh/kg LNG. Heat 90a MJ/ton substrate This value is in line with data reported by Yoon et al. (2009) and b Methane content 60% CNPC (2019), and only slightly higher than the 0.23 kWh/kg re- c Methane slip 0.5% ported by Hajji et al. (2019). For LBM production, a German elec- Investment cost 240e340d V/m3 reactor volume tricity mix was assumed in the default case, and other alternatives a (Lantz et al., 2009). were included in a sensitivity analysis. Road transports were b (Rasi et al., 2007). c (Lantz and Bjornsson,€ 2016). considered to be done with gas vehicles in the gas scenarios (using d (Lantz, 2013). LNG in the LNG pathways and LBM in the LBM pathways) and with diesel vehicles in the diesel scenario. Tank-to-wheel (TTW) emissions from combustion of the studied fuels (Table 4) were based on for the AD plant, as well as for AS upgrading, was assumed to be emission data for heavy freight trucks from Stettler et al. (2019). covered through combustion of raw biogas with 95% efficiency The SI gas engines were considered to require 18% more energy per (Lantz et al., 2009; Tufvesson et al., 2013). km than the diesel engines (Borjesson€ et al., 2016; Gustafsson et al., In the scenarios where manure was used as a feedstock, the AD 2020b): 3.24 kWh/km, compared to 2.74 kWh/km for diesel process was assumed to reduce methane emissions compared to (Gustafsson et al., 2020b). conventional handling of manure by 90% (Tufvesson et al., 2013). In the economic analysis, the cost for producing LBM was The amount of methane emissions from manure was calculated compared to the European market price of LNG, which was found to through: have varied between 4 and 10 USD/mmBtu over the last five years, or 0.012 to 0.030 EUR/kWh (YCharts, 2019). m ¼ m ,VS,B ,MCF,r (2) CH4 manure 0 CH4 where mmanure is the amount of manure (kg), VS is the share of 2.4. Sensitivity and uncertainty analysis volatile solids (%), B0 is the maximum methane production of the 3 substrate (m /kg), MCF is the methane conversion factor (%), rCH4 is Electricity use for production of LBM was modelled with elec- the density of methane (kg/m3) at normal temperature and pres- tricity mixes representative for Germany, UK, Italy and Sweden, in sure and mCH4 is the amount of methane emitted during storage order to investigate the sensitivity with respect to how the elec- (kg). B0 was set to 0.345 (average between dairy cattle and swine tricity is produced. Germany, UK and Italy are the three largest manure) in accordance with Gavrilova et al. (2006), and MCF to biogas producers in Europe, while Sweden currently has the largest 3.5% (Tufvesson et al., 2013). market for biomethane as a transport fuel (EurObserv’ER, 2017). In In the scenarios where food waste was used as a feedstock, the the Ecoinvent database version 3.5 (updated 2018), the major alternative waste handling was considered to be combustion with components of the studied electricity mixes are: lignite (28%), hard energy recovery, with heat and electricity efficiencies of 74% and coal (22%) and nuclear power (18%) in the German mix; hard coal 21%, respectively (Hamelin et al., 2014), and a lower heating value (34%), natural gas (28%) and nuclear power (21%) in the UK mix; of 20 MJ/kg dry matter (Davidsson et al., 2007). As the food waste in natural gas (34%), hydropower (26%) and hard coal (18%) in the these scenarios was used for biogas production rather than energy Italian mix; and hydropower (45%) and nuclear power (43%) in the production, equivalent amounts of heat and electricity were Swedish mix (Table 5)(Moreno Ruiz et al., 2018; Weidema et al., considered to be produced from natural gas. 2013). Considering the fact that electricity is exported and im- Data for the other processes included in the studied scenar- ported between different countries in Europe, these scenarios serve iosdgas upgrading, liquefaction and fuelingdare listed in Table 3. more to illustrate the difference between contrasting electricity Internal electricity demand for LNG production was assumed to be systems than to represent the situation in either of the four covered with gas turbines, using part of the gas flow (Raj et al., countries. 2016; Songhurst, 2018), with an efficiency of 40% (Siemens, 2016). For climate change impact, the level of uncertainty in the results The production of natural gas was assumed to have a methane slip was assessed through Monte Carlo analysis, which constructs an of 1%, similar to water scrubber biogas upgrading. In both cases, the interval based on probability functions and the combined

Table 2 Data for substrates and digestates used in modelling of anaerobic digestion. The table shows the used values (average) as well as the Intervals found in literature.

Substrate type TS, % VS of TS, % Methane yield, m3/ton VS Total N, kg/ton NH₄-N in digestate, % of N

Manure 8 80 290 3.9 67 Cattle 8.5e9a,b,c 80a 213e240a,d 2.6e4.3a,b,e,f,g 54e67e,g Swine 7.3e8a,b 80a 268e450a,d 3.1e5.9a,b,e,f 68e81a,e Food waste 22 (18e28)h 90 (87e94)h 360 (275e461)a,h,i 5.2 (3.1e7.5)a,e,h,j 70 (60e80)e,j

a (Carlsson and Uldal, 2009). b (Kirchmann and Witter, 1992). c (Walsh et al., 2012). d (Gavrilova et al., 2006). e (Sinclair et al., 2013). f (Moller€ and Müller, 2012). g (Lukehurst et al., 2010). h (Banks et al., 2018). i (Davidsson et al., 2007). j (Ljung et al., 2012). M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 7

Table 3 Data used in modelling of environmental impact and life cycle costs of pathways for biomethane and natural gas.

Process Electricity Heat Water Chemicals Methane content Methane slip Investment cost

MJ/MJ gas MJ/MJ gas m3/kg gas kg/kg gas % % V/(Nm3/h)

Water scrubber 0.039a 4.5E-04a 6.0E-05a 98%a 1%a 1,490e5,820a Amine scrubber 1,630e3,300a Gas grid quality 0.023a,b 0.017b 6.1E-05a 6.1E-05a 99.8%a,b 0.06%a,b Liquefaction quality 0.034b 0.017b 6.1E-05a 6.1E-05a 99.995%a,b 0.06%a,b Catalytic oxidation of off-gas 0.008a BG cleaning for liquefaction 0.015b 99.995%b 1,400e2,600a NG cleaning for liquefaction 0.002c Mixed-refrigerant cycle liquefaction (BG) 0.058b,d 99.995%b 0%e 4,650e21,000f Nitrogen cycle liquefaction (BG) 0.072b 99.995%b 0%e 8,025a C3MR cycle liquefaction (NG) 0.019g,h 99.995%b 0%e Nitrogen cycle liquefaction (NG) 0.043i 99.995%b 0%e Pressure reduction liquefaction 0.001j Fueling, LBM/LNG 0.0003k

a (Bauer et al., 2013). b (Karlsson, 2018). c (Honig€ et al., 2019). d (Cryo Pur, 2019). e (Tybirk et al., 2018). f (Olgemar and Partoft, 2017). g (Yoon et al., 2009). h (CNPC, 2019). i (Cryostar). j (Patterson et al., 2011). k (Heisch, 2012).

Table 4 Tank-to-wheel emission factors for a heavy-duty truck running on diesel or CNG (SI engine). Based on data from Stettler et al. (2019).

TTW emissions, kg/kg fuel

CO₂ CO CH₄ N₂O PM VOC NOx Diesel 6.87E-02 8.16E-05 e 1.69E-06 2.71E-07 1.81E-07 1.35E-04 LNG (SI) 5.85E-02 1.90E-04 5.04E-05 2.04E-07 1.87E-07 1.58E-06 1.50E-05

Table 5 distance for the LBM pathways. The availability of biogas upgrading Energy sources in electricity production mixes in Germany, UK, Italy and Sweden. plants with respect to maintenance is generally quite high, around Based on data from Ecoinvent 3.5 (Moreno Ruiz et al., 2018; Weidema et al., 2013). 95% (Bauer et al., 2013; Patterson et al., 2011; Persson, 2003), which Share of production mix, % was therefore used as one scenario. To account for possible limiting Energy source Germany UK Italy Sweden factors (e.g. access to substrate, variations in demand), a lower utilization rate of 50% was also evaluated. For distribution by semi- Hard coal 22 34 18 0.3 fi Hydropower 5 3 26 45 trailer, the distance was varied between 0 km ( lling station adja- Natural gas 7 28 34 0.2 cent to production plant) and 400 km (double the default value). Nuclear power 18 21 0 43 Oil 0.3 0.2 5 0.1 Peat 0 0 0 0.1 3. Results and analysis Wind 11 9 7 8 Biogas 6 0 5 0 Wood chips 2 5 2 3 3.1. Environmental impact assessment Blast furnace gas 0.4 0 1 0.2 Coal gas 0.1 0 0.3 0 Fig. 5 shows the climate change impact per km of the studied Geothermal 0 0 2 0 pathways of diesel, liquefied natural gas (LNG) and liquefied bio- Lignite 28 0 0.4 0 methane (LBM) with biogas from manure, divided into impact from different processes and with error bars indicating the 95% confi- dence interval of the uncertainty analysis. The best-performing uncertainty of all parameters. Parameter values were varied using a liquefaction technology for LBM is liquefaction by pressure reduc- lognormal distribution, where the value of a parameter lies be- tion of methane from the high-pressure gas grid. Out of the two off- s2 tween the mean value divided by the variance ( ) and the mean grid technologies, mixed-refrigerant (MR) liquefaction has a lower s2 value multiplied by (Weidema et al., 2013). Most parameters energy use and climate change impact than nitrogen cycle lique- s2 were considered to be fairly reliable and representative and was faction, both for LNG (C3MR) and for LBM. For biogas upgrading, set to 1.1. A higher value, 1.2, was used for parameters regarding the amine scrubbing gives a slightly lower climate change impact than AD process (electricity and water use, amount of digestate) and for water scrubbing, due to a lower electricity use. s2 transports, as they were assumed to vary more. For methane slip, Compared to diesel, LBM from anaerobic digestion (AD) of was set to 1.5. manure can reduce the WTW climate change impact of driving a In the economic calculations, a sensitivity analysis was done by 40-ton long haulage truck by 45e70%, calculated according to the varying the utilization of production capacity and the distribution Renewable Energy Directive (RED). If the digestate from AD is 8 M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535

Fig. 5. Climate change impact of diesel, LNG and LBM well-to-wheel pathways. The LBM pathways are based on biogas from anaerobic digestion of manure and electricity use is modelled with a German electricity mix. assumed to replace mineral fertilizer in agricultural applications (in and WS þ N₂ and AS þ pressure reduction for LBM, respectively. line with ISO standard for life cycle assessment), the climate change Among the LBM scenarios, AS þ pressure reduction had the lowest impact even becomes negative, equivalent to a reduction of impact and WS þ N₂ had the highest throughout all of the included 100e125% compared to diesel. For LNG, the WTW climate change impact categories. For the LNG scenarios, it varied which one had impact is comparable to or slightly higher (5e10%) than diesel. This the highest and which one had the lowest impact, but the differ- is mainly due to the higher efficiency of the diesel engine, resulting ences were quite small and C3MR was always slightly lower than N₂ in a higher energy demand in the LNG and LBM scenarios (18% liquefaction. higher per km). Overall, the Swedish electricity mix results in the lowest envi- The processes contributing the most to the climate change ronmental impact for the LBM scenarios, followed by Germany, impact of the LBM scenarios, apart from the possible negative Italy and UK. Another general observation is that the ISO method impact of digestate, are electricity for AD, upgrading and liquefac- gives lower results than the RED method, except in terms of acid- tion and methane leakages. The uncertainty intervals are ±25e35% ification, where the situation is the opposite, and eutrophication, for the LNG scenarios, and around ±40e80% for LBM scenarios, where there is almost no difference between ISO and RED. The much due to the high variance of methane leakages (s2 ¼ 1.5), but largest difference is seen in the climate change and stratospheric also the variance of factors related to substrate and digestate ozone depletion impact categories. handling (s2 ¼ 1.2). The climate change impact is lower for all the LBM pathways The climate change impact of the pathways of LBM from food than for LNG and diesel. The lowest impact is achieved with a waste, as well as diesel and LNG, is shown in Fig. 6. Just as with Swedish electricity production mix, followed by Italy, UK and manure-based biogas, pipeline distribution and pressure reduction Germany in close competition. As previously seen in Figs. 5 and 6, liquefaction gives the lowest climate change impact for LBM, and electricity use accounts for a large share of the climate change MR results in lower impact than N₂ for both LNG and LBM. impact of the LBM pathways, and the use of digestate as fertilizer Using a substrate with a higher methane yield, such as food can greatly reduce the impact. Thus, most scenarios with LBM from waste, the WTW climate change impact reduction compared to manure have a negative climate change impact with ISO calcula- diesel can be as high as 50e75% with RED calculations. With ISO tion, except for WS þ N₂ with a German (manure, food waste), calculations, the reduction compared to diesel is 80e105%. The Italian (food waste) or UK (food waste) electricity production uncertainty intervals are ±15e40% for the LBM scenarios. The lower system. potential methane leakage compared to the manure-based path- The potential acidification impact of the studied LBM scenarios ways greatly reduces the uncertainty. is comparable to LNG and diesel if calculations are done according Fig. 7 shows the impact on climate change, acidification, to RED, and higher if the ISO method is employed. The difference eutrophication, ground-level ozone formation and stratospheric between the four electricity production mixes is smaller than in the ozone depletion of diesel, LNG and LBM pathways for different climate change category. The main contributing process to acidifi- electricity mixes. The LNG and LBM pathways shown are the ones cation are electricity use and transports. With system expansion that were found to have highest and lowest environmental impact according to ISO, the avoided production of mineral fertilizer in all categories: C3MR liquefaction and pressure reduction for LNG, compensates for some of these factors, but this effect is outranked M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 9

Fig. 6. Climate change impact of diesel, LNG and LBM well-to-wheel pathways. The LBM pathways are based on biogas from anaerobic digestion of food waste and electricity use is modelled with a German electricity mix.

by ammonia emissions from the biofertilizer. The LNG scenarios 3.2. Economic analysis have a lower acidification impact than diesel. The eutrophication impact is higher than LNG and diesel for Fig. 8 and Fig. 9 show the WTW life cycle cost of LBM scenarios, most of the LBM pathways with a German or UK electricity pro- depending on production capacity, compared to the market price duction system, but comparable or lower with Swedish or Italian range of LNG. In Fig. 8 the LBM production is assumed to be at 95% of electricity. The LNG scenarios have a higher or equal impact to the design production capacity, and in Fig. 9 the utilization rate is set diesel. The German electricity production system has a much to 50% of the capacity. It is clear from these figure that LBM pro- higher eutrophication impact per kWh electricity than the others (a duction has to reach a rather large scale to be able to compete with factor 4, 6 and 112 compared to UK, Italy and Sweden, respectively). natural gas without economic incentives. The lower end of the nat- Apart from the electricity, the processes contributing the most to ural gas price range appears to be out of reach for most biomethane eutrophication in the LBM scenarios are the transports. With sys- technologies, where amine scrubber (AS) and biogas based on food tem boundaries according to ISO, the use of biofertilizer to replace waste is the one that gets closest, although this comparison does not mineral fertilizer contributes with a small reduction of the eutro- include a sales margin for the LBM. At a production capacity of phication impact, whichdwith a Swedish electricity mixdis 120 GWh/year and 95% utilization, this scenario reaches a cost of enough to result in a negative impact. 0.028 EUR/kWh (Fig. 8). At times when the natural gas price is high, Looking at ground-level ozone formation, the impact is lower even WS þ MR with biogas from food waste might be cost-efficient for the LBM scenarios than for LNG and diesel, except for a few cases enough to be competitive, at least at a capacity of 100e120 GWh/ with a UK, Italian or German electricity production system. LNG has year or more. For the manure scenarios, the production cost at a higher impact than diesel with pressure reduction liquefaction, 100e120 GWh/year is still more than twice as high as the LNG price, but lower than diesel with C3MR liquefaction. The lowest impact is around 0.050e0.057 EUR/kWh, which means that some form of seen for LBM scenarios with biogas from food waste. The impact of incentive is necessary for this type of production to be feasible. If the the LBM scenarios is mainly due to carbon monoxide emissions production capacity is only utilized to 50% (Fig. 9), the specificin- from combustion in the vehicle’s engine. vestment costs rise and all LBM scenarios end up with production The impact on stratospheric ozone depletion is much lower for costs higher than the LNG price. For the scenario with AS and food nearly all LBM scenarios compared to LNG and diesel, especially waste, the life cycle cost at 120 GWh/year capacity increases to 0.035 with system expansion. The variations between different electricity EUR/kWh, while the costs for the manure scenarios reach mixes is relatively small, but in many cases the Swedish mix gives 0.077e0.084 EUR/kWh at the same plant size. the lowest impact. With a German or Italian electricity mix and In the scenarios presented, the LBM is distributed 200 km by calculations according to RED, the LBM pathway impact is com- semitrailer, and the distribution cost is about 3 EUR/MWh, or 0.3 parable to LNG, but still lower than diesel. The processes causing eurocent per kWh. If the LBM were to be fueled locally rather than the most ozone layer depletion are the transports and the elec- being transported from the production site, this cost could be dis- tricity for AD, upgrading and liquefaction. The LNG scenarios all regarded. In that case, the cheapest LBM technology would reach a have a lower impact compared to diesel. cost of 0.025 EUR/kWh at 120 GWh/year production capacity and 10 M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535

Fig. 7. Environmental impact of LBM and LNG pathways compared to diesel in different electricity systems, based on country mix. From top to bottom: Climate change, terrestrial acidiﬁcation, freshwater eutrophication, ozone formation (human health impact) and stratospheric ozone depletion.

95% utilization, while WS þ MR with biogas from food waste would 120 GWh/year, and the cost for AS þ MR with biogas from food nearly match the higher end of the LNG price range (0.030 EUR/ waste at 120 GWh/year would go up to 0.031 EUR/kWh. kWh) at 120 GWh/year. If, on the other hand, the distribution range The rest of the costs for LBM are shared between AD, upgrading were twice as large (400 km), this would not occur even at and liquefaction. All speciﬁc investment costs decrease with a M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 11

Fig. 8. Life cycle cost of producing LBM as a function of yearly production capacity, compared to market price of LNG, when LBM production is at 95% of the design capacity.

Fig. 9. Life cycle cost of producing LBM as a function of yearly production capacity, compared to market price of LNG, when the LBM production is at 50% of the design capacity. larger scale, particularly for liquefaction and for upgrading by with previous studies by e.g. Shanmugam et al. (2018) and Borjesson€ amine scrubbing. Thus, the division of costs between different et al. (2016)dthat liquefied biomethane (LBM) can indeed contribute processes varies with the production capacity. The costs for AD are to reduced environmental impact from heavy-duty vehicles, not higher with manure as feedstock than with food waste, as more least in terms of climate change impact. However, attention must be substrate is treated per kWh biogas produced. With AS the share of given to the type of feedstock used and how the electricity used in costs for AD are higher than with WS, partly because AS requires biomethane production is generated, which is clear from Fig. 7. With less electricity and partly because biogas from the AD is assumed to a lower share of fossil fuels and a lower carbon intensity in electricity be used for producing process heat for the AS. production, LBM comes out even better in the comparison with LNG, as the LBM scenarios to a higher degree are dependent on electricity. 4. Discussion Conversely, the environmental impact of LBM can be quite high if it is produced with electricity from fossil energy sources. However, the Judging from current trends in policy (Gustafsson and Anderberg, climate change impact is still lower compared to LNG and diesel even 2020) and use of biomethane in road transports (Hormann,€ 2020), it in electricity systems with a high share of fossil fuels. seems clear that biomethane from second-generation energy sour- While LBM was found to greatly reduce the climate change ces will have an important place in the work towards cleaner impact compared to diesel, the WTW scenarios with LNG resulted transports. The results of the present study further showdin line in up to 10% higher climate change impact than diesel. This goes 12 M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 against findings of e.g. Arteconi et al. (2010) (up to 10% lower would amount to up to 0.08 EUR/kWh if the biogas is produced from climate change impact) and Ou and Zhang (2013) (5e10% lower manure and is upgraded and liquefied, which is almost double the impact), but is supported by results from e.g. Stettler et al. (2019) existing support (for manure-based biogas) (Westlund, 2019). Such (up to 8% higher climate change impact) and Cai et al. (2017) support systems could turn the competition around and stimulate an (1e8% higher impact). As pointed out by e.g. Speirs et al. (2020) increased production of biomethane, although the exact effects on and Cooper et al. (2019), this has to do with the rate of methane the production in Sweden or other countries would need further leakage as well as the inferior fuel economy of SI gas engines. Thus, investigation. these are two areas of possible technological improvement which can help reduce the environmental impact of vehicles using LNG as 5. Conclusions well as LBM. System boundaries and the way in which byproducts are This paper has presented an environmental and economic well- considered can greatly affect the outcome of the calculations in life to-wheel analysis of production and distribution pathways of LBM cycle assessment (LCA), as also shown by e.g. Borjesson€ et al. (2016). and LNG for heavy-duty trucks, including different feedstock for Biomethane produced through AD can be considered to have a biogas production, different production technologies and different positive environmental impact in many impact categories, due to electricity mixes. The main findings of the study were: the possibility of displacing mineral fertilizers by utilizing the digestate. However, spreading digestate on agricultural land is not By replacing diesel with LBM, it is possible to greatly reduce the always on option, in which case this type of system expansion is not WTW environmental impact of heavy-duty trucks in terms of possible. For example, Dutch regulations do not allow the use of climate change, acidification, eutrophication, ground-level digestate to replace mineral fertilizer (Pfau et al., 2017). There could ozone formation and stratospheric ozone depletion, thus also be other reasons, e.g. economic, for not using the digestate, achieving cleaner heavy transports. With a German electricity which would make the RED guidelines more appropriate for mix, the climate change impact can be reduced by 45e70% with calculating the environmental impact. The ISO method, on the LBM from manure, and by 50e75% with LBM from food waste, other hand, shows what is possible to achieve with a larger system not including the use of digestate. In electricity systems with thinking where both the biogas and the digestate from AD are higher shares of renewable energy, the climate change impact of valued and utilized. LBM is even lower. Although an LCA can cover many aspects of environmental If digestate from biogas production is considered to replace impact, it does not fully reflect all the effects of a complex socio- mineral fertilizer, in accordance with ISO standards for life cycle technical system such as biogas production. Particularly in a local or assessment, the climate benefits of using LBM instead of diesel regional perspective biogas solutions can give many benefits, are even larger. With LBM from manure, the climate change including e.g. waste treatment, increased resource efficiency, impact could be reduced by 100e125%, and with LBM from food increased yield from agriculture and rural area development waste by 80e105%. (Hagman and Eklund, 2016). A complete analysis of a biogas system Using LNG instead of diesel in heavy-duty trucks does not would either have to include qualitative elements, for example a reduce the WTW climate change impact, but can rather increase multi-criteria analysis, or some way of converting qualitative values it by up to 10%, due to a lower engine efficiency. into quantitative ones, similar to methods for putting a price on air The environmental impact of LBM is greatly influenced by the pollution, noise and traffic congestions (Bångman and Nordlof,€ type of feedstock used, how the required electricity produced 2016). and whether calculations are done according to ISO or RED The best-performing liquefaction technology was found to be guidelines. pressure reduction of methane from the high-pressure gas grid. Although there are clear environmental incentives to use LBM, it This is of course provided that the production facility is connected seems difficult to compete economically with the price of LNG, to the gas grid, which is often not the case in some of the Nordic due to higher specific production costs. countries (Sweden, Finland, Norway). Furthermore, as shown by Gustafsson et al. (2020a), adding propane to the biomethane to In order for LBM to compete against LNG and other fossil fuels, increase the heating value when injecting it to the gas grid, as has some type of economic support is likely to be required. The sometimes been custom, greatly increases the environmental investigation of how such economic incentives should be formed impact of this technology and should be avoided. It should also be and what changes might be needed in current practices is however taken into account that the share of the gas that can be liquefied left for future studies. It could also be relevant to look into the with this technology is limited to around 10e15% (see e.g. He and possibility to capture and store or use CO₂ from biogas production, Ju, 2013; Tan et al., 2016), leaving most of it to be used in gaseous and what effects that could have on the environmental and eco- form. Thus, it would not be the technology of choice if the aim is to nomic performance of biogas systems. only produce liquefied gas. In the economic comparison of LBM and LNG, natural gas has the CRediT authorship contribution statement advantage of that it exists in large volumes and requires relatively cheap processes to obtain a high-energy fuel, while biogas is pro- Marcus Gustafsson: Conceptualization, Methodology, Software, duced at a much smaller scale with higher specific costs. Based solely Validation, Formal analysis, Investigation, Data curation, Writing - on the costs for production and distribution, LBM would not be able original draft, Writing - review & editing, Visualization. Niclas to compete with the average market prices of LNG. Considering that Svensson: Conceptualization, Writing - review & editing, Visuali- the LBM producers would also like to have a certain margin for zation, Supervision. revenue, it is not realistic that a fair competition would be achievable without economic incentives. The economic calculations by Declaration of competing interest Borjesson€ et al. (2016) suggest that the WTW costs of LBM are more or less in line with market prices of LNG and diesel with the Swedish The authors declare that they have no known competing taxation system. A recent enquiry commissioned by the Swedish financial interests or personal relationships that could have government suggested a support package for biogas production that appeared to influence the work reported in this paper. M. Gustafsson, N. Svensson / Journal of Cleaner Production 278 (2021) 123535 13

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