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How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?
international journal of hydrogen energy xxx (xxxx) xxx
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How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles? Adem Ugurlu a,*, Semiha Oztuna b a b
Kırklareli University, Technology Faculty, Mechatronics Engineering Department, Kırklareli, Turkey Trakya University, Engineering Faculty, Mechanical Engineering Department, Edirne, Turkey
highlights Solar, nuclear, and electrolysis are the most environmentally friendly methods. Coal and electricity emerged as the most environmentally hazardous methods. FCVs emit lower emissions by 35.1% than SI HEVs and 49.6% than SI ICEVs in average.
article info
abstract
Article history:
Emissions variations of liquid hydrogen (LH2) production methods in liquid hydrogen
Received 14 October 2019
powered vehicles are investigated in this study. Volatile organic compounds (VOC), carbon
Received in revised form
monoxide (CO), nitrogen oxides (NOx), particulate matters (PM10 & PM2.5), sulfur oxides
20 January 2020
(SOx), and carbon dioxide (CO2) emissions, which are on well-to-wheel (WTW) basis, are
Accepted 30 January 2020
evaluated for 2013 model year’s cars in the target year of 2018. GREET software is utilized
Available online xxx
for the emissions. When the average values of all emissions are compared, hydrogen production by the solar power, nuclear, and electrolysis methods have the lowest emis-
Keywords:
sions, respectively, and hydrogen production by coal and electricity methods have the
Liquid hydrogen
highest emissions, respectively. On the other hand, it is found that in all emission types
Hydrogen production methods
and hydrogen production methods, fuel cell vehicles (FCV) emit less emission than spark
Vehicles
ignition hybrid electric vehicles (SI HEV) and SI HEVs emit less emission than spark ignition
Emissions
internal combustion engine vehicles (SI ICEV). Emissions decrease by 22.4% in SI HEVs compared to SI ICEVs, 35.1% in FCVs compared to SI HEVs, and 49.6% in FCVs compared to SI ICEVs for average of all emissions. © 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Stringent emission regulations and increasing demand for energy are pushing scientists to make progress in alternative energy sources in recent years [1e3]. Since hydrogen has an energy efficient and low pollutant structure, there are many studies in literature in which hydrogen is shown as an
alternative energy source [4e6]. Although hydrogen has the advantage that it is present in large quantities in nature since it is mainly produced from natural gas and water, it cannot be produced economically under current market conditions [7]. Research on hydrogen production methods will eliminate this disadvantage in the near future. Hydrogen vehicles, on the other hand, have become more and more popular since the
* Corresponding author. E-mail address: [email protected] (A. Ugurlu). https://doi.org/10.1016/j.ijhydene.2020.01.250 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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first hydrogen-fueled fuel cell vehicle was launched, and some internal combustion engines (ICEV) with hydrogen can be seen on the market as well as FCVs. When hydrogen is used to generate electricity in a fuel cell or burned with air, only products are water and a small amount of NOx [4e6]. High energy density and no carbon content are the main advantages of hydrogen. However, problems such as cost of production, storage problems, hydrogen embrittlement and leakage along the tank and fuel line are the main disadvantages of using hydrogen in vehicles [7]. Although most hydrogen vehicles store gaseous hydrogen in tanks such as the Ford Zetec 2.0 L [8,9] and Toyota Mirai FCV, some examples like first GM FCV Electro Van (1966), again GM HydroGen3, BMW 750 hl, and BMW Mini Hydrogen [10e12] are powered by liquid hydrogen fuel, which is stored in tanks that maintain cryogenic environment by a vacuum method [13,14]. One of the best ways to store hydrogen is in liquid state that is maintained by a liquefaction process [15], therefore LH2 is a promising part of hydrogen applications [16]. Today, liquefied hydrogen is mainly used for space applications and the semiconductor industry. Clean energy applications, such as the automotive sector, are currently contributing only a small share of this demand, and their demand may see a significant increase in the coming years [17]. LH2 is currently used for some other fields such as space applications and the semiconductor industry. There are various methods of producing liquid hydrogen. Depending on these production methods, emissions to the environment also differ. The methods of obtaining liquid hydrogen, which is usually produced in gaseous form and then liquefied, have been pointed out in literature by several studies. Hydrogen is usually produced using fossil fuels by steam reforming of natural gas. This method causes large amounts of emissions, which are mostly greenhouse gases. Approximately 48% of hydrogen demand is met by natural gas, 30% by oil products, 18% by gasification of coal, 3.9% by well-known electrolysis method, and only 0.1% by other processes [18]. Many researchers are continuously searching for environmentally friendly sources to produce hydrogen [19]. Dincer et al. [20] grouped energy types to maintain hydrogen production in four as: electrical, thermal, biochemical, and photonic. Obtaining these four energy types with renewable sources, hydrogen production can be provided in an environmentally friendly manner they concluded in their study. Lodhi [21], who is one of the earliest researchers on hydrogen production methods, analyzed hydrogen production by water dissociation in high temperature, water splitting using thermo-chemical principles, electrolysis of water, and photolysis. has been conducted by, which is considered as one of the early works. In his further study, Lodhi [22] grouped green sources in hydrogen productions as hydro, solar, wind, nuclear, and sea/ocean. He also listed green materials in hydrogen production as biomass, water (fresh or sea), and hydrogen sulfide. Lemus and Duart [23] investigated central plants in hydrogen production in terms of cost and transportation assessments. Tanksale et al. [24] reviewed catalytic methods such as sugar conversion, pyrolysis, and gasification etc. to produce hydrogen by biomass energy. Acar and Dincer [25] conducted a comprehensive investigation on hydrogen production methods of coal gasification, natural gas steam
reforming, electrolysis of water by solar or wind energy, biomass gasification, high temperature electrolysis, and thermo-chemical water splitting in terms of their costs, environment hazards, and some technical issues. Dincer and Acar [26] evaluated nineteen types of hydrogen production methods primarily thermal, electrical, electro-thermal, electro-photonic, photo-biochemical, and photonic in financial, environmental, technical performance, and social aspects. They found out that the highest global warming potentials in hydrogen production are in the methods of gasification of coal, reforming of fossil fuels, and biomass compared to others. Acar and Dincer [27] compared hydrogen production methods in a part of their study, and they concluded that photonic systems in hydrogen production have the lowest environmental hazards, while thermal systems have the € highest. El-Emam and Ozcan [28] investigated hydrogen production methods, and they found out the methods that use nuclear or geothermal energy are clean ones among others. Suleman et al. [19] studied environmental impacts of hydrogen production methods in terms of life cycle assessment (LCA). They found out that steam methane reforming (SMR) of natural gas has the highest emissions in terms of greenhouse gases, global warming potential, and abiotic depletion. On the other hand, there are many studies in the area of hazards resulting from vehicle emissions in literature. For instance, it is maintained that VOCs deteriorate ambient air quality [29e31], are significant ozone precursors that increase hazardous smog and aerosol formation to human life [32e34], irritate human organs such as eyes and lungs [35,36], and decrease agricultural products damaging the crops [37]. CO emissions, produced from incomplete combustion of hydrocarbons, are highly toxic gases that poison people even to the death in case of high amount of exposure [38]. NOx emissions, which are mainly combinations of nitric oxide (NO) and nitrogen dioxide (NO2) emitted from vehicles due to high temperature combustions, have significant hazardous effects on the environment and human health [39]. They are corrosive to the respiratory system and the skin, and if the exposure time lasts a long time they can disrupt the immune systems of humans. In addition, they are harmful to forests and surface waters when they cause acid rains reacting with nitric acid (HNO3). Furthermore, they form ozone (O3) that causes health problems in respiratory systems when they react with VOCs [40]. PM pollution in the atmosphere, main contributor of which is motor vehicles [41], has negative effects on human health [42], the air quality [43], and climate [44]. PM pollution adversely affects health not only in short-term [45] but also in long-term [46], and therefore exposure to this pollution is a worldwide problem that it appeared to be the sixth leading risk factor since 1990 [42]. Analyses show the adverse effects of PM10 emissions on health in many studies, which some of them focus on young children [47], pedestrians under bridges [48], correlations with lung cancer [49] and tuberculosis of people in especially urban areas [50], etc. PM2.5 emissions potentially increase respiratory and cardiovascular diseases in worldwide [51]. And it is estimated in a study that PM2.5 pollution on earth resulted over 8 million deaths in 2015 [52]. SOx emission, which is mainly emitted from motor vehicles, also takes its place in literature with its adverse impacts on
Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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human health, climate change, and air quality at both local and global scale [53e55]. Finally, CO2 emissions, which are actually not toxic emissions but perhaps have the worst effects for life on earth, are referenced in literature more than any emissions. The biggest environmental problem that the human race confronts in the twenty-first century is climate change, and the major cause of climate change is CO2 emissions [56e58]. In this study, production methods of liquid hydrogen have been compared in terms of their emission potentials. VOC, CO, NOx, PM10, PM2.5, SOx, and CO2 emissions emitted from SI ICEVs, SI HEVs, and FCVs depending on the liquid hydrogen production methods are examined. GREET software was used to obtain the specified emission values for the vehicles. It is sought to answer how the production method affects emissions in liquid hydrogen powered vehicles. Further research on this subject may cause new researchers to work on the subject, so as to ensure that the LH2 production is maintained more efficiently and environmentally friendly with current and new methods. This study aims to raise awareness in this direction.
Methodology This study emphasizes emissions from three types of vehicles: SI ICEVs, SI HEVs, and FCVs, which are mostly used when hydrogen is utilized as a fuel. Fig. 1 illustrates energy flow
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from the tank to the wheels in the form of hydrogen or motion by hydrogen in ICEVs, hybrid electric vehicles (HEV), and FCVs. In ICEVs, hydrogen is combusted in the engine, producing pressure that pushes down the pistons in the cylinders, which generate linear motion that is converted to circular motion by crank - connecting rod mechanisms and conducted to the wheels through the transmission. Differently in HEVs, the hydrogen powered engine can provide wheel rotation and/or battery charging. The engine acts like a generator, if it provides only charging to the battery. HEVs also benefit from regenerative braking, which charges the battery when the driver presses the brake pedal in certain circumstances. As to the FCVs, there is no combustion engine at all, in which vehicle movement is established through fuel cells that generate electricity for the battery of the vehicle using hydrogen. Specially designed tanks are generally used to deliver LH2 in the tank to the engine or fuel cell in gaseous state [59]. On the other hand, there are several studies in literature that investigate and compare ICEVs, HEVs, FCVs, and also electric vehicles (EV) in detail, which a further examination can be performed through the literature [60e64]. LH2 consumptions of the vehicles that are used in the analysis of this study are 31.8 mi/gal (7.4 L/100 km), 41.8 mi/gal (5.6 L/100 km), and 54.4 mi/gal (4.3 L/100 km), respectively for SI ICEVs, SI HEVs, and FCVs. In the calculation of VOC, CO, NOx, PM10, PM2.5, SOx, and CO2 emissions emitted from LH2 powered ICEVs, HEVs, and FCVs, GREET software (greenhouse gases, regulated
Fig. 1 e Energy flow by hydrogen in ICEVs, HEVs, and FCVs. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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emissions, and energy use in transportation) developed by Argonne National Laboratory [65] is used in this study. Eq. (1) demonstrates the main calculation method of the emissions that GREET software uses [66], where ðTEÞi is the total emissions of pollutant i of the energy source throughput for the given process, ðCEÞi;j is the combustion emissions of the pollutant i of the energy source j burned, ðUEÞi;j is the upstream emissions of the pollutant i of the energy source j utilized to produce and distribute the energy source to the related process, and ðECÞj is the energy consumption of the energy source j during the process. Therefore, the emissions of the energy source, which is LH2 in this study, from the production stage to the wheels of the vehicle can be calculated by the software including all the emission sources to perform these stages one by one. Depending on the production or transportation method used, the production of hydrogen also involves the consumption of oil, natural gas, etc, so, all emissions are calculated individually by the software. The units of the emission results can be optionally given in g/MJ, g/hkm, g/mi, etc. The unit g/hkm, which shows emission amount in g per 100 km travel of the vehicle, is selected in all the emissions except CO2 emission that is given in g/km. It is assumed in GREET software that the vehicles travels urban roads. In estimating the emissions of vehicles in urban roads, factors such as vehicle technology, vehicle model year, vehicle mass and dimensions, or transportation fuel have varying effects on fuel consumption of the vehicle [67]. The identical passenger vehicles are taken into consideration in the assumption of emissions in this analysis, so that to see emissions differentiation due to only the variations of hydrogen production methods. ðTEÞi ¼
Xh
i ðCEÞi;j þ ðUEÞi;j ðECÞj
(1)
j
Fig. 2 shows the scope of the study. While vehicles follow the production, transportation, operation, and recycling processes; LH2 fuel is also produced, transported, stored, filled into the vehicle tank, and consumed by the vehicle. There are
two types of emissions in the process of consuming LH2 in vehicles. The emissions that occur until the fuel is delivered to the station pump are called well-to-pump (WTP) emissions. The emissions from the filling the fuel to the vehicles and transferring to the wheels as rotational motion are called pump-to-wheel (PTW) emissions. The sum of these two emissions is called WTW emissions, which represents the scope of this study. Liquid hydrogen, which is a promising fuel in terms of increasing range in vehicles, is selected as the powering fuel for the vehicles. GREET software is based on USA as the country where hydrogen is produced and delivered to the pump for the vehicle technology of 2013 in the target year of 2018. The electricity, which contributes to the generation, liquefaction and transport of hydrogen, is also based on US electricity mix that is the sum of 33.44% natural gas-fired power generation, 28.96% coal-fired power generation, 20.31% nuclear power generation, 7.11% hydroelectric power generation, 6.85% wind power generation, 1.67% solar power generation, 0.49% biogenic waste pumped storage power generation, 0.41% oil-fired power generation, 0.41% geothermal power generation, 0.34% biomass power generation in 2018. Transmission and distribution efficiency of this electric is assumed as 95.1%. Liquid hydrogen is produced from gaseous hydrogen using this electricity in central plants or refueling stations. Variations of the emissions are presented by production methods for liquid hydrogen in figures so as to be easily compared to each other. Following liquid hydrogen production methods are evaluated in the analysis when the liquid hydrogen is produced in a central plant: from North American natural gas, from solar power, from nuclear by thermo-chemical cracking of water, from electrolysis by high-temperature gas reactor (HTGR), from coke oven gas central plants, from coal, from biomass, and from farmed trees sourced biomass. When the liquid hydrogen is produced exactly in the refueling station is also taken into consideration in the analysis, which constitutes following methods: from North American natural gas, from U.S. electricity, from
Fig. 2 e Scope of the study. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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methanol, and from ethanol. Aforementioned hydrogen production methods are also illustrated in Fig. 3 so as to give a comprehensive view. Hydrogen is produced in gaseous form in all the methods, and then it is subjected to liquefaction process. In the production of hydrogen from North American natural gas the reformation method is used that is a frequently used method to produce hydrogen [68]. Reformation here means that the atoms of the reacting gases are rearranged at the end of the reaction. In addition, the heat generated by the cooling of hot gases formed by steam reforming of natural gas is used to evaporate the water in the process, and with the reaction of CO and this water vapor, CO2 and H2 are also produced. The important point is that the hydrogen produced in this additional process can reach up to half of the amount that is produced in the whole process. In the production of hydrogen using solar power, the electrolysis method is utilized. As is known, electrolysis is the process of separating water into hydrogen and oxygen by applying direct current to water. The electrical energy required here is provided by photovoltaic cells that directly convert solar energy into electrical energy. Hydrogen production from nuclear
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energy by thermo-chemical cracking of water is carried out in three basic processes including electricity and heat production, thermo-chemical decomposition of water, and purification of hydrogen obtained. In the hydrogen production from electrolysis by high-temperature gas reactor (HTGR) method, on the other hand, nuclear energy is utilized, but hydrogen is produced by electrolysis method. Less electricity is required to split water into hydrogen and oxygen by increasing the temperature, which reduces the total energy required. Pure hydrogen can be generated from bituminous coal directly in coke oven gas central plants and after gasification of coal plants. In hydrogen production from biomass and farmed trees sourced biomass, hydrogen production takes place in two general categories: thermo-chemical and biological processes. Biomass sources are varied such as poplar, willow, switch grass, and miscanthus as of now. In the production of hydrogen at the exact spot of the fuel station, gasification of natural gas and electrolysis methods are utilized. Here, electricity needs are met from the grid (US mix.). Finally, hydrogen can be derived from methanol and ethanol by gasification method.
Fig. 3 e Hydrogen production methods. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Results and discussion WTW VOC emissions emitted from SI ICEVs, SI HEVs and FCVs according to GREET software are presented in Fig. 4. Liquid hydrogen production methods of North American natural gas, solar power, nuclear by thermo-chemical cracking of water, electrolysis by high-temperature gas reactor, coke oven gas central plants, coal, biomass, farmed trees biomass, again North American natural gas, U.S. electricity, methanol, and ethanol are demonstrated as NG, SP, N, Es, COG, C, B, FTB, NG, El, M, and E, respectively. Emissions are given in g/100 km for each vehicles and liquid hydrogen production methods. As seen from the figure, lower VOC emissions are emitted from the vehicles when the liquid hydrogen is produced by solar power and nuclear power in central plants. Emissions from vehicles when using liquid hydrogen produced by natural gas in a central plant are also lower values compared to other production methods. When liquid hydrogen is produced in a refueling station, the lowest VOC emissions are from natural gas method. The highest VOC emissions, on the other hand, are seen in vehicles that use liquid hydrogen produced from refueling stations by ethanol method. When liquid hydrogen is produced in central plants, the highest VOC emissions are seen in coke oven gas method. As to the emission variations among vehicle types, FCVs are the most environmental friendly vehicles. FCVs have almost no VOC emissions when they powered by liquid hydrogen produced by solar power, nuclear power, and electrolysis. So as SI ICEVs totally and SI HEVs partially are powered by consuming liquid hydrogen in their internal combustion engines, SI ICEVs have the highest VOC emissions. SI HEVs emit lower VOC emissions due to their additional electric motors that are powered by batteries recharged by the internal combustion engine of the vehicle operating at the most efficient engine speed and also by the energy recovered during braking of the vehicle. Average VOC emissions of vehicles according to the method in which liquid
hydrogen is produced in central plants are 3.90 g/hkm for North American natural gas method, 1.14 g/hkm for solar power method, 1.34 g/hkm for nuclear by thermo-chemical cracking of water method, 1.37 g/hkm for electrolysis by high-temperature gas reactor method, 9.87 g/hkm for coke oven gas central plants method, 5.58 g/hkm for coal method, 3.93 g/hkm for biomass method, and 4.35 g/hkm for farmed trees biomass method. When liquid hydrogen is produced in refueling stations, average VOC emissions from vehicles that use this hydrogen are 5.06 g/hkm for North American natural gas method, 5.76 g/hkm for U.S. electricity method, 7.80 g/hkm for methanol method, and 17.45 g/hkm for ethanol method. WTW CO emissions from SI ICEVs, SI HEVs and FCVs according to GREET software are presented in Fig. 5. As can be seen, CO emissions are drawing different graphs than VOC emissions. For all liquid hydrogen production methods, the average CO emissions emitted by vehicles using this fuel are very close to each other as 28.39 g/hkm for North American natural gas method, 22.51 g/hkm for solar power method, 23.32 g/hkm for nuclear by thermo-chemical cracking of water method, 23.44 g/hkm for electrolysis by high-temperature gas reactor method, 29.17 g/hkm for coke oven gas central plants method, 25.17 g/hkm for coal method, 28.78 g/hkm for biomass method, and 28.43 g/hkm for farmed trees biomass method in central plants, and 34.93 g/hkm for North American natural gas method, 37.12 g/hkm for U.S. electricity method, 31.45 g/hkm for methanol method, and 38.00 g/hkm for ethanol method in refueling stations. CO emissions in SI ICEVs and SI HEVs are very close to each other, whereas CO emissions in FCVs are very slight. Average CO emission value in FCVs is 5.04 g/hkm for all liquid hydrogen production methods, which constitutes a little part of total average CO emission of 29.22 g/hkm for all vehicles and liquid hydrogen production methods. WTW NOx emissions from SI ICEVs, SI HEVs and FCVs according to GREET software are presented in Fig. 6 for different
Fig. 4 e VOC emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Fig. 5 e CO emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods. liquid hydrogen production methods. Liquid hydrogen gives more NOx emissions in vehicles when it is produced in refueling stations instead of central plants. As to liquid hydrogen consuming vehicles, FCVs emit lowest NOx emissions for all production methods. SI HEVs emit lower NOx emissions than SI ICEVs also discovered from the figure. When liquid hydrogen is produced by the solar power method, the lowest NOx emissions are maintained for all vehicles. Nuclear and electrolysis methods also have little more NOx emissions than that of solar power method. Average NOx emissions emitted from the vehicles are 15.54 g/hkm for North American natural gas method, 5.04 g/hkm for solar power method, 6.13 g/hkm for nuclear by thermo-chemical cracking of water method, 6.29 g/hkm for electrolysis by high-temperature gas reactor method, 15.99 g/hkm for coke oven gas central plants method, 16.70 g/hkm for coal method, 18.07 g/hkm for biomass
method, and 14.91 g/hkm for farmed trees biomass method in central plants, and 23.15 g/hkm for North American natural gas method, 33.40 g/hkm for U.S. electricity method, 19.93 g/hkm for methanol method, and 38.39 g/hkm for ethanol method in refueling stations. WTW PM10 emissions of SI ICEVs, SI HEVs and FCVs depending on liquid hydrogen production methods according to GREET software are presented in Fig. 7. As clearly understood from the figure, when solar power, nuclear, and electrolysis methods are used to produce liquid hydrogen in central plants, SI ICEVs, SI HEVs, and FCVs that use this liquid hydrogen emit nearly zero PM10 emissions. In contrast, when liquid hydrogen is produced using especially the coke oven gas central plants method, SI ICEVs, SI HEVs and FCVs emit very high PM10 emissions at decreasing rates. FCVs have the lowest PM10 emissions for all liquid hydrogen production
Fig. 6 e NOx emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Fig. 7 e PM10 emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
methods. Average PM10 emissions of the vehicles are 1.69 g/hkm for North American natural gas method, 0.04 g/hkm for solar power method, 0.11 g/hkm for nuclear by thermochemical cracking of water method, 0.12 g/hkm for electrolysis by high-temperature gas reactor method, 11.71 g/hkm for coke oven gas central plants method, 5.27 g/hkm for coal method, 1.28 g/hkm for biomass method, and 1.36 g/hkm for farmed trees biomass method in central plants, and 1.77 g/hkm for North American natural gas method, 5.20 g/hkm for U.S. electricity method, 2.18 g/hkm for methanol method, and 7.44 g/hkm for ethanol method in refueling stations. WTW PM2.5 emissions of the vehicles according to GREET software are presented in Fig. 8. PM2.5 gives a similar image compared to PM10 emissions in the figure. However PM2.5 emission levels have been almost 50% lower than that of PM10. Similarly, SI HEVs have lower PM2.5 emissions than SI ICEVs
have, and FCVs have lower than SI HEVs. The least PM2.5 emission causing liquid hydrogen production methods are solar power, nuclear, and electrolysis all in central plants. On the other hand, the most PM2.5 emission causing liquid hydrogen production methods are coke oven gas method in central plants and ethanol method in refueling stations. Average PM2.5 emissions emitted from the vehicles that use liquid hydrogen according to the production methods are 1.00 g/hkm for North American natural gas method, 0.03 g/hkm for solar power method, 0.08 g/hkm for nuclear by thermochemical cracking of water method, 0.08 g/hkm for electrolysis by high-temperature gas reactor method, 5.15 g/hkm for coke oven gas central plants method, 0.96 g/hkm for coal method, 0.90 g/hkm for biomass method, and 0.95 g/hkm for farmed trees biomass method in central plants, and 0.97 g/hkm for North American natural gas method, 2.26 g/hkm for
Fig. 8 e PM2.5 emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Fig. 9 e SOx emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
U.S. electricity method, 1.24 g/hkm for methanol method, and 4.09 g/hkm for ethanol method in refueling stations. WTW SOx emissions of SI ICEVs, SI HEVs and FCVs depending on liquid hydrogen production methods according to GREET software are presented in Fig. 9. SOx emissions have the highest levels in g/hkm when compared to VOC, CO, NOx, PM10, and PM2.5 emissions. While solar power, nuclear, and electrolysis methods in central plants to produce liquid hydrogen cause minimum SOx emissions in SI ICEVs, SI HEVs, and FCVs, electricity method in refueling stations have the highest SOx emission potential in the same vehicles. Since the electricity in the electricity method is met from the US electricity mix, we see that US produce its electricity by SOx emissions causing sources. For all the methods, SI HEVs have
higher SOx emissions than FCVs, and lower SOx emissions than SI ICEVs. Average SOx emissions from the vehicles when using liquid hydrogen depending on the production methods are 18.44 g/hkm for North American natural gas method, 0.01 g/hkm for solar power method, 0.70 g/hkm for nuclear by thermo-chemical cracking of water method, 0.80 g/hkm for electrolysis by high-temperature gas reactor method, 29.40 g/hkm for coke oven gas central plants method, 5.94 g/hkm for coal method, 33.52 g/hkm for biomass method, and 37.63 g/hkm for farmed trees biomass method in central plants, and 21.42 g/hkm for North American natural gas method, 70.85 g/hkm for U.S. electricity method, 25.08 g/hkm for methanol method, and 37.61 g/hkm for ethanol method in refueling stations.
Fig. 10 e CO2 emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Finally, WTW CO2 emissions of SI ICEVs, SI HEVs and FCVs depending on liquid hydrogen production methods according to GREET software are given in Fig. 10. CO2 emissions are given in the unit of g/hkm as be usually given in literature. Solar power, nuclear and electrolysis methods to produce liquid hydrogen in central plants cause nearly zero CO2 emissions in the vehicles. Also farmed trees biomass and biomass methods to produce liquid hydrogen in central plants cause very low CO2 emissions in vehicles. However, coal method in central plants, electricity in refueling stations, and coke oven gas method in central plants have the highest CO2 potentials when the liquid hydrogen that is produced by these methods, respectively. Average CO2 emissions from the vehicles when using liquid hydrogen depending on the production methods are 224.1 g/hkm for North American natural gas method, 0.4 g/hkm for solar power method, 5.4 g/hkm for nuclear by thermo-chemical cracking of water method, 6.1 g/hkm for electrolysis by high-temperature gas reactor method, 310.5 g/hkm for coke oven gas central plants method, 502.2 g/hkm for coal method, 28.2 g/hkm for biomass method, and 28.8 g/ hkm for farmed trees biomass method in central plants, and 261.7 g/hkm for North American natural gas method, 410.4 g/ hkm for U.S. electricity method, 314.9 g/hkm for methanol method, and 188.2 g/hkm for ethanol method in refueling stations.
Conclusion Hydrogen is used safely in areas such as oil refining, glass purification, semiconductor production, aerospace applications, fertilizer production, welding, annealing and heat treatment of metals, pharmaceutical industry, and hydrogenation of unsaturated fatty acids in vegetable oils, and it attracts more and more attention of scientists day by day. Vehicle powering is one of the most important areas where hydrogen is utilized as fuel. When hydrogen is used in vehicles in liquid form, refueling time and vehicle range significantly increase. The emission changes that occur when conventional or alternative fuels are used in vehicles have been investigated in many studies in the literature. In this study, the effects of hydrogen production methods on emissions are investigated and compared for liquid hydrogen powered SI ICEVs, SI HEVs, and FCVs. As understood from the emissions variations, following items can be concluded from the study: The lowest values of all emissions are seen in the method that liquid hydrogen is produced by solar power in central plants. The highest values of VOC, CO, and NOx emissions are seen in the method that liquid hydrogen is produced by ethanol in refueling stations. The highest values of PM10 and PM2.5 emissions are seen in the method that liquid hydrogen is produced by coke oven gas in central plants. The highest values of SOx emissions are seen in the method that liquid hydrogen is produced by electricity in refueling stations.
The highest values of CO2 emissions are seen in the method that liquid hydrogen is produced by coal in central plants. All the lowest values in emissions belong to FCVs, and all the highest values are encountered in SI ICEVs. Average of all emissions in SI HEVs is 22.4% lower than that of SI ICEVs, that of FCVs is 35.1% lower than that of HEVs, and that of FCVs is 49.6% lower than that of SI ICEVs.
Nomenclature B C CE CO CO2 COG E EC El Es EV FCV FTB GREET
Biomass Coal Combustion emissions Carbon monoxide Carbon dioxide Coke oven gas central plants Ethanol Energy consumption U.S. electricity Electrolysis by high-temperature gas reactor Electric vehicle Fuel cell vehicle farmed trees biomass Greenhouse gases, regulated emissions, and energy use in transportation HEV Hybrid electric vehicle Nitric acid HNO3 HTGR High-temperature gas reactor ICEV Internal combustion engine vehicle LCA Life cycle assessment LH2 Liquid hydrogen M Methanol N Nuclear by thermo-chemical cracking of water NG Natural gas NO Nitric oxide Nitrogen dioxide NO2 Nitrogen oxide NOx Ozone O3 Particulate matter with a diameter of 10 mm PM10 Particulate matter with a diameter of 2.5 mm PM2.5 PTW Pump-to-wheel SI HEV Spark ignition hybrid electric vehicle SI ICEV Spark ignition internal combustion engine vehicle SMR Steam methane reforming Sulfur Oxide SOx SP Solar power TE Total emissions UE Upstream emissions VOC Volatile organic compound WTP Well-to-pump WTW Well-to-wheel Subscripts i Pollutant j Energy source
Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles? Adem Ugurlu a,*, Semiha Oztuna b a b
Kırklareli University, Technology Faculty, Mechatronics Engineering Department, Kırklareli, Turkey Trakya University, Engineering Faculty, Mechanical Engineering Department, Edirne, Turkey
highlights Solar, nuclear, and electrolysis are the most environmentally friendly methods. Coal and electricity emerged as the most environmentally hazardous methods. FCVs emit lower emissions by 35.1% than SI HEVs and 49.6% than SI ICEVs in average.
article info
abstract
Article history:
Emissions variations of liquid hydrogen (LH2) production methods in liquid hydrogen
Received 14 October 2019
powered vehicles are investigated in this study. Volatile organic compounds (VOC), carbon
Received in revised form
monoxide (CO), nitrogen oxides (NOx), particulate matters (PM10 & PM2.5), sulfur oxides
20 January 2020
(SOx), and carbon dioxide (CO2) emissions, which are on well-to-wheel (WTW) basis, are
Accepted 30 January 2020
evaluated for 2013 model year’s cars in the target year of 2018. GREET software is utilized
Available online xxx
for the emissions. When the average values of all emissions are compared, hydrogen production by the solar power, nuclear, and electrolysis methods have the lowest emis-
Keywords:
sions, respectively, and hydrogen production by coal and electricity methods have the
Liquid hydrogen
highest emissions, respectively. On the other hand, it is found that in all emission types
Hydrogen production methods
and hydrogen production methods, fuel cell vehicles (FCV) emit less emission than spark
Vehicles
ignition hybrid electric vehicles (SI HEV) and SI HEVs emit less emission than spark ignition
Emissions
internal combustion engine vehicles (SI ICEV). Emissions decrease by 22.4% in SI HEVs compared to SI ICEVs, 35.1% in FCVs compared to SI HEVs, and 49.6% in FCVs compared to SI ICEVs for average of all emissions. © 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Stringent emission regulations and increasing demand for energy are pushing scientists to make progress in alternative energy sources in recent years [1e3]. Since hydrogen has an energy efficient and low pollutant structure, there are many studies in literature in which hydrogen is shown as an
alternative energy source [4e6]. Although hydrogen has the advantage that it is present in large quantities in nature since it is mainly produced from natural gas and water, it cannot be produced economically under current market conditions [7]. Research on hydrogen production methods will eliminate this disadvantage in the near future. Hydrogen vehicles, on the other hand, have become more and more popular since the
* Corresponding author. E-mail address: [email protected] (A. Ugurlu). https://doi.org/10.1016/j.ijhydene.2020.01.250 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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first hydrogen-fueled fuel cell vehicle was launched, and some internal combustion engines (ICEV) with hydrogen can be seen on the market as well as FCVs. When hydrogen is used to generate electricity in a fuel cell or burned with air, only products are water and a small amount of NOx [4e6]. High energy density and no carbon content are the main advantages of hydrogen. However, problems such as cost of production, storage problems, hydrogen embrittlement and leakage along the tank and fuel line are the main disadvantages of using hydrogen in vehicles [7]. Although most hydrogen vehicles store gaseous hydrogen in tanks such as the Ford Zetec 2.0 L [8,9] and Toyota Mirai FCV, some examples like first GM FCV Electro Van (1966), again GM HydroGen3, BMW 750 hl, and BMW Mini Hydrogen [10e12] are powered by liquid hydrogen fuel, which is stored in tanks that maintain cryogenic environment by a vacuum method [13,14]. One of the best ways to store hydrogen is in liquid state that is maintained by a liquefaction process [15], therefore LH2 is a promising part of hydrogen applications [16]. Today, liquefied hydrogen is mainly used for space applications and the semiconductor industry. Clean energy applications, such as the automotive sector, are currently contributing only a small share of this demand, and their demand may see a significant increase in the coming years [17]. LH2 is currently used for some other fields such as space applications and the semiconductor industry. There are various methods of producing liquid hydrogen. Depending on these production methods, emissions to the environment also differ. The methods of obtaining liquid hydrogen, which is usually produced in gaseous form and then liquefied, have been pointed out in literature by several studies. Hydrogen is usually produced using fossil fuels by steam reforming of natural gas. This method causes large amounts of emissions, which are mostly greenhouse gases. Approximately 48% of hydrogen demand is met by natural gas, 30% by oil products, 18% by gasification of coal, 3.9% by well-known electrolysis method, and only 0.1% by other processes [18]. Many researchers are continuously searching for environmentally friendly sources to produce hydrogen [19]. Dincer et al. [20] grouped energy types to maintain hydrogen production in four as: electrical, thermal, biochemical, and photonic. Obtaining these four energy types with renewable sources, hydrogen production can be provided in an environmentally friendly manner they concluded in their study. Lodhi [21], who is one of the earliest researchers on hydrogen production methods, analyzed hydrogen production by water dissociation in high temperature, water splitting using thermo-chemical principles, electrolysis of water, and photolysis. has been conducted by, which is considered as one of the early works. In his further study, Lodhi [22] grouped green sources in hydrogen productions as hydro, solar, wind, nuclear, and sea/ocean. He also listed green materials in hydrogen production as biomass, water (fresh or sea), and hydrogen sulfide. Lemus and Duart [23] investigated central plants in hydrogen production in terms of cost and transportation assessments. Tanksale et al. [24] reviewed catalytic methods such as sugar conversion, pyrolysis, and gasification etc. to produce hydrogen by biomass energy. Acar and Dincer [25] conducted a comprehensive investigation on hydrogen production methods of coal gasification, natural gas steam
reforming, electrolysis of water by solar or wind energy, biomass gasification, high temperature electrolysis, and thermo-chemical water splitting in terms of their costs, environment hazards, and some technical issues. Dincer and Acar [26] evaluated nineteen types of hydrogen production methods primarily thermal, electrical, electro-thermal, electro-photonic, photo-biochemical, and photonic in financial, environmental, technical performance, and social aspects. They found out that the highest global warming potentials in hydrogen production are in the methods of gasification of coal, reforming of fossil fuels, and biomass compared to others. Acar and Dincer [27] compared hydrogen production methods in a part of their study, and they concluded that photonic systems in hydrogen production have the lowest environmental hazards, while thermal systems have the € highest. El-Emam and Ozcan [28] investigated hydrogen production methods, and they found out the methods that use nuclear or geothermal energy are clean ones among others. Suleman et al. [19] studied environmental impacts of hydrogen production methods in terms of life cycle assessment (LCA). They found out that steam methane reforming (SMR) of natural gas has the highest emissions in terms of greenhouse gases, global warming potential, and abiotic depletion. On the other hand, there are many studies in the area of hazards resulting from vehicle emissions in literature. For instance, it is maintained that VOCs deteriorate ambient air quality [29e31], are significant ozone precursors that increase hazardous smog and aerosol formation to human life [32e34], irritate human organs such as eyes and lungs [35,36], and decrease agricultural products damaging the crops [37]. CO emissions, produced from incomplete combustion of hydrocarbons, are highly toxic gases that poison people even to the death in case of high amount of exposure [38]. NOx emissions, which are mainly combinations of nitric oxide (NO) and nitrogen dioxide (NO2) emitted from vehicles due to high temperature combustions, have significant hazardous effects on the environment and human health [39]. They are corrosive to the respiratory system and the skin, and if the exposure time lasts a long time they can disrupt the immune systems of humans. In addition, they are harmful to forests and surface waters when they cause acid rains reacting with nitric acid (HNO3). Furthermore, they form ozone (O3) that causes health problems in respiratory systems when they react with VOCs [40]. PM pollution in the atmosphere, main contributor of which is motor vehicles [41], has negative effects on human health [42], the air quality [43], and climate [44]. PM pollution adversely affects health not only in short-term [45] but also in long-term [46], and therefore exposure to this pollution is a worldwide problem that it appeared to be the sixth leading risk factor since 1990 [42]. Analyses show the adverse effects of PM10 emissions on health in many studies, which some of them focus on young children [47], pedestrians under bridges [48], correlations with lung cancer [49] and tuberculosis of people in especially urban areas [50], etc. PM2.5 emissions potentially increase respiratory and cardiovascular diseases in worldwide [51]. And it is estimated in a study that PM2.5 pollution on earth resulted over 8 million deaths in 2015 [52]. SOx emission, which is mainly emitted from motor vehicles, also takes its place in literature with its adverse impacts on
Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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human health, climate change, and air quality at both local and global scale [53e55]. Finally, CO2 emissions, which are actually not toxic emissions but perhaps have the worst effects for life on earth, are referenced in literature more than any emissions. The biggest environmental problem that the human race confronts in the twenty-first century is climate change, and the major cause of climate change is CO2 emissions [56e58]. In this study, production methods of liquid hydrogen have been compared in terms of their emission potentials. VOC, CO, NOx, PM10, PM2.5, SOx, and CO2 emissions emitted from SI ICEVs, SI HEVs, and FCVs depending on the liquid hydrogen production methods are examined. GREET software was used to obtain the specified emission values for the vehicles. It is sought to answer how the production method affects emissions in liquid hydrogen powered vehicles. Further research on this subject may cause new researchers to work on the subject, so as to ensure that the LH2 production is maintained more efficiently and environmentally friendly with current and new methods. This study aims to raise awareness in this direction.
Methodology This study emphasizes emissions from three types of vehicles: SI ICEVs, SI HEVs, and FCVs, which are mostly used when hydrogen is utilized as a fuel. Fig. 1 illustrates energy flow
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from the tank to the wheels in the form of hydrogen or motion by hydrogen in ICEVs, hybrid electric vehicles (HEV), and FCVs. In ICEVs, hydrogen is combusted in the engine, producing pressure that pushes down the pistons in the cylinders, which generate linear motion that is converted to circular motion by crank - connecting rod mechanisms and conducted to the wheels through the transmission. Differently in HEVs, the hydrogen powered engine can provide wheel rotation and/or battery charging. The engine acts like a generator, if it provides only charging to the battery. HEVs also benefit from regenerative braking, which charges the battery when the driver presses the brake pedal in certain circumstances. As to the FCVs, there is no combustion engine at all, in which vehicle movement is established through fuel cells that generate electricity for the battery of the vehicle using hydrogen. Specially designed tanks are generally used to deliver LH2 in the tank to the engine or fuel cell in gaseous state [59]. On the other hand, there are several studies in literature that investigate and compare ICEVs, HEVs, FCVs, and also electric vehicles (EV) in detail, which a further examination can be performed through the literature [60e64]. LH2 consumptions of the vehicles that are used in the analysis of this study are 31.8 mi/gal (7.4 L/100 km), 41.8 mi/gal (5.6 L/100 km), and 54.4 mi/gal (4.3 L/100 km), respectively for SI ICEVs, SI HEVs, and FCVs. In the calculation of VOC, CO, NOx, PM10, PM2.5, SOx, and CO2 emissions emitted from LH2 powered ICEVs, HEVs, and FCVs, GREET software (greenhouse gases, regulated
Fig. 1 e Energy flow by hydrogen in ICEVs, HEVs, and FCVs. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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emissions, and energy use in transportation) developed by Argonne National Laboratory [65] is used in this study. Eq. (1) demonstrates the main calculation method of the emissions that GREET software uses [66], where ðTEÞi is the total emissions of pollutant i of the energy source throughput for the given process, ðCEÞi;j is the combustion emissions of the pollutant i of the energy source j burned, ðUEÞi;j is the upstream emissions of the pollutant i of the energy source j utilized to produce and distribute the energy source to the related process, and ðECÞj is the energy consumption of the energy source j during the process. Therefore, the emissions of the energy source, which is LH2 in this study, from the production stage to the wheels of the vehicle can be calculated by the software including all the emission sources to perform these stages one by one. Depending on the production or transportation method used, the production of hydrogen also involves the consumption of oil, natural gas, etc, so, all emissions are calculated individually by the software. The units of the emission results can be optionally given in g/MJ, g/hkm, g/mi, etc. The unit g/hkm, which shows emission amount in g per 100 km travel of the vehicle, is selected in all the emissions except CO2 emission that is given in g/km. It is assumed in GREET software that the vehicles travels urban roads. In estimating the emissions of vehicles in urban roads, factors such as vehicle technology, vehicle model year, vehicle mass and dimensions, or transportation fuel have varying effects on fuel consumption of the vehicle [67]. The identical passenger vehicles are taken into consideration in the assumption of emissions in this analysis, so that to see emissions differentiation due to only the variations of hydrogen production methods. ðTEÞi ¼
Xh
i ðCEÞi;j þ ðUEÞi;j ðECÞj
(1)
j
Fig. 2 shows the scope of the study. While vehicles follow the production, transportation, operation, and recycling processes; LH2 fuel is also produced, transported, stored, filled into the vehicle tank, and consumed by the vehicle. There are
two types of emissions in the process of consuming LH2 in vehicles. The emissions that occur until the fuel is delivered to the station pump are called well-to-pump (WTP) emissions. The emissions from the filling the fuel to the vehicles and transferring to the wheels as rotational motion are called pump-to-wheel (PTW) emissions. The sum of these two emissions is called WTW emissions, which represents the scope of this study. Liquid hydrogen, which is a promising fuel in terms of increasing range in vehicles, is selected as the powering fuel for the vehicles. GREET software is based on USA as the country where hydrogen is produced and delivered to the pump for the vehicle technology of 2013 in the target year of 2018. The electricity, which contributes to the generation, liquefaction and transport of hydrogen, is also based on US electricity mix that is the sum of 33.44% natural gas-fired power generation, 28.96% coal-fired power generation, 20.31% nuclear power generation, 7.11% hydroelectric power generation, 6.85% wind power generation, 1.67% solar power generation, 0.49% biogenic waste pumped storage power generation, 0.41% oil-fired power generation, 0.41% geothermal power generation, 0.34% biomass power generation in 2018. Transmission and distribution efficiency of this electric is assumed as 95.1%. Liquid hydrogen is produced from gaseous hydrogen using this electricity in central plants or refueling stations. Variations of the emissions are presented by production methods for liquid hydrogen in figures so as to be easily compared to each other. Following liquid hydrogen production methods are evaluated in the analysis when the liquid hydrogen is produced in a central plant: from North American natural gas, from solar power, from nuclear by thermo-chemical cracking of water, from electrolysis by high-temperature gas reactor (HTGR), from coke oven gas central plants, from coal, from biomass, and from farmed trees sourced biomass. When the liquid hydrogen is produced exactly in the refueling station is also taken into consideration in the analysis, which constitutes following methods: from North American natural gas, from U.S. electricity, from
Fig. 2 e Scope of the study. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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methanol, and from ethanol. Aforementioned hydrogen production methods are also illustrated in Fig. 3 so as to give a comprehensive view. Hydrogen is produced in gaseous form in all the methods, and then it is subjected to liquefaction process. In the production of hydrogen from North American natural gas the reformation method is used that is a frequently used method to produce hydrogen [68]. Reformation here means that the atoms of the reacting gases are rearranged at the end of the reaction. In addition, the heat generated by the cooling of hot gases formed by steam reforming of natural gas is used to evaporate the water in the process, and with the reaction of CO and this water vapor, CO2 and H2 are also produced. The important point is that the hydrogen produced in this additional process can reach up to half of the amount that is produced in the whole process. In the production of hydrogen using solar power, the electrolysis method is utilized. As is known, electrolysis is the process of separating water into hydrogen and oxygen by applying direct current to water. The electrical energy required here is provided by photovoltaic cells that directly convert solar energy into electrical energy. Hydrogen production from nuclear
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energy by thermo-chemical cracking of water is carried out in three basic processes including electricity and heat production, thermo-chemical decomposition of water, and purification of hydrogen obtained. In the hydrogen production from electrolysis by high-temperature gas reactor (HTGR) method, on the other hand, nuclear energy is utilized, but hydrogen is produced by electrolysis method. Less electricity is required to split water into hydrogen and oxygen by increasing the temperature, which reduces the total energy required. Pure hydrogen can be generated from bituminous coal directly in coke oven gas central plants and after gasification of coal plants. In hydrogen production from biomass and farmed trees sourced biomass, hydrogen production takes place in two general categories: thermo-chemical and biological processes. Biomass sources are varied such as poplar, willow, switch grass, and miscanthus as of now. In the production of hydrogen at the exact spot of the fuel station, gasification of natural gas and electrolysis methods are utilized. Here, electricity needs are met from the grid (US mix.). Finally, hydrogen can be derived from methanol and ethanol by gasification method.
Fig. 3 e Hydrogen production methods. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Results and discussion WTW VOC emissions emitted from SI ICEVs, SI HEVs and FCVs according to GREET software are presented in Fig. 4. Liquid hydrogen production methods of North American natural gas, solar power, nuclear by thermo-chemical cracking of water, electrolysis by high-temperature gas reactor, coke oven gas central plants, coal, biomass, farmed trees biomass, again North American natural gas, U.S. electricity, methanol, and ethanol are demonstrated as NG, SP, N, Es, COG, C, B, FTB, NG, El, M, and E, respectively. Emissions are given in g/100 km for each vehicles and liquid hydrogen production methods. As seen from the figure, lower VOC emissions are emitted from the vehicles when the liquid hydrogen is produced by solar power and nuclear power in central plants. Emissions from vehicles when using liquid hydrogen produced by natural gas in a central plant are also lower values compared to other production methods. When liquid hydrogen is produced in a refueling station, the lowest VOC emissions are from natural gas method. The highest VOC emissions, on the other hand, are seen in vehicles that use liquid hydrogen produced from refueling stations by ethanol method. When liquid hydrogen is produced in central plants, the highest VOC emissions are seen in coke oven gas method. As to the emission variations among vehicle types, FCVs are the most environmental friendly vehicles. FCVs have almost no VOC emissions when they powered by liquid hydrogen produced by solar power, nuclear power, and electrolysis. So as SI ICEVs totally and SI HEVs partially are powered by consuming liquid hydrogen in their internal combustion engines, SI ICEVs have the highest VOC emissions. SI HEVs emit lower VOC emissions due to their additional electric motors that are powered by batteries recharged by the internal combustion engine of the vehicle operating at the most efficient engine speed and also by the energy recovered during braking of the vehicle. Average VOC emissions of vehicles according to the method in which liquid
hydrogen is produced in central plants are 3.90 g/hkm for North American natural gas method, 1.14 g/hkm for solar power method, 1.34 g/hkm for nuclear by thermo-chemical cracking of water method, 1.37 g/hkm for electrolysis by high-temperature gas reactor method, 9.87 g/hkm for coke oven gas central plants method, 5.58 g/hkm for coal method, 3.93 g/hkm for biomass method, and 4.35 g/hkm for farmed trees biomass method. When liquid hydrogen is produced in refueling stations, average VOC emissions from vehicles that use this hydrogen are 5.06 g/hkm for North American natural gas method, 5.76 g/hkm for U.S. electricity method, 7.80 g/hkm for methanol method, and 17.45 g/hkm for ethanol method. WTW CO emissions from SI ICEVs, SI HEVs and FCVs according to GREET software are presented in Fig. 5. As can be seen, CO emissions are drawing different graphs than VOC emissions. For all liquid hydrogen production methods, the average CO emissions emitted by vehicles using this fuel are very close to each other as 28.39 g/hkm for North American natural gas method, 22.51 g/hkm for solar power method, 23.32 g/hkm for nuclear by thermo-chemical cracking of water method, 23.44 g/hkm for electrolysis by high-temperature gas reactor method, 29.17 g/hkm for coke oven gas central plants method, 25.17 g/hkm for coal method, 28.78 g/hkm for biomass method, and 28.43 g/hkm for farmed trees biomass method in central plants, and 34.93 g/hkm for North American natural gas method, 37.12 g/hkm for U.S. electricity method, 31.45 g/hkm for methanol method, and 38.00 g/hkm for ethanol method in refueling stations. CO emissions in SI ICEVs and SI HEVs are very close to each other, whereas CO emissions in FCVs are very slight. Average CO emission value in FCVs is 5.04 g/hkm for all liquid hydrogen production methods, which constitutes a little part of total average CO emission of 29.22 g/hkm for all vehicles and liquid hydrogen production methods. WTW NOx emissions from SI ICEVs, SI HEVs and FCVs according to GREET software are presented in Fig. 6 for different
Fig. 4 e VOC emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Fig. 5 e CO emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods. liquid hydrogen production methods. Liquid hydrogen gives more NOx emissions in vehicles when it is produced in refueling stations instead of central plants. As to liquid hydrogen consuming vehicles, FCVs emit lowest NOx emissions for all production methods. SI HEVs emit lower NOx emissions than SI ICEVs also discovered from the figure. When liquid hydrogen is produced by the solar power method, the lowest NOx emissions are maintained for all vehicles. Nuclear and electrolysis methods also have little more NOx emissions than that of solar power method. Average NOx emissions emitted from the vehicles are 15.54 g/hkm for North American natural gas method, 5.04 g/hkm for solar power method, 6.13 g/hkm for nuclear by thermo-chemical cracking of water method, 6.29 g/hkm for electrolysis by high-temperature gas reactor method, 15.99 g/hkm for coke oven gas central plants method, 16.70 g/hkm for coal method, 18.07 g/hkm for biomass
method, and 14.91 g/hkm for farmed trees biomass method in central plants, and 23.15 g/hkm for North American natural gas method, 33.40 g/hkm for U.S. electricity method, 19.93 g/hkm for methanol method, and 38.39 g/hkm for ethanol method in refueling stations. WTW PM10 emissions of SI ICEVs, SI HEVs and FCVs depending on liquid hydrogen production methods according to GREET software are presented in Fig. 7. As clearly understood from the figure, when solar power, nuclear, and electrolysis methods are used to produce liquid hydrogen in central plants, SI ICEVs, SI HEVs, and FCVs that use this liquid hydrogen emit nearly zero PM10 emissions. In contrast, when liquid hydrogen is produced using especially the coke oven gas central plants method, SI ICEVs, SI HEVs and FCVs emit very high PM10 emissions at decreasing rates. FCVs have the lowest PM10 emissions for all liquid hydrogen production
Fig. 6 e NOx emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Fig. 7 e PM10 emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
methods. Average PM10 emissions of the vehicles are 1.69 g/hkm for North American natural gas method, 0.04 g/hkm for solar power method, 0.11 g/hkm for nuclear by thermochemical cracking of water method, 0.12 g/hkm for electrolysis by high-temperature gas reactor method, 11.71 g/hkm for coke oven gas central plants method, 5.27 g/hkm for coal method, 1.28 g/hkm for biomass method, and 1.36 g/hkm for farmed trees biomass method in central plants, and 1.77 g/hkm for North American natural gas method, 5.20 g/hkm for U.S. electricity method, 2.18 g/hkm for methanol method, and 7.44 g/hkm for ethanol method in refueling stations. WTW PM2.5 emissions of the vehicles according to GREET software are presented in Fig. 8. PM2.5 gives a similar image compared to PM10 emissions in the figure. However PM2.5 emission levels have been almost 50% lower than that of PM10. Similarly, SI HEVs have lower PM2.5 emissions than SI ICEVs
have, and FCVs have lower than SI HEVs. The least PM2.5 emission causing liquid hydrogen production methods are solar power, nuclear, and electrolysis all in central plants. On the other hand, the most PM2.5 emission causing liquid hydrogen production methods are coke oven gas method in central plants and ethanol method in refueling stations. Average PM2.5 emissions emitted from the vehicles that use liquid hydrogen according to the production methods are 1.00 g/hkm for North American natural gas method, 0.03 g/hkm for solar power method, 0.08 g/hkm for nuclear by thermochemical cracking of water method, 0.08 g/hkm for electrolysis by high-temperature gas reactor method, 5.15 g/hkm for coke oven gas central plants method, 0.96 g/hkm for coal method, 0.90 g/hkm for biomass method, and 0.95 g/hkm for farmed trees biomass method in central plants, and 0.97 g/hkm for North American natural gas method, 2.26 g/hkm for
Fig. 8 e PM2.5 emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Fig. 9 e SOx emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods.
U.S. electricity method, 1.24 g/hkm for methanol method, and 4.09 g/hkm for ethanol method in refueling stations. WTW SOx emissions of SI ICEVs, SI HEVs and FCVs depending on liquid hydrogen production methods according to GREET software are presented in Fig. 9. SOx emissions have the highest levels in g/hkm when compared to VOC, CO, NOx, PM10, and PM2.5 emissions. While solar power, nuclear, and electrolysis methods in central plants to produce liquid hydrogen cause minimum SOx emissions in SI ICEVs, SI HEVs, and FCVs, electricity method in refueling stations have the highest SOx emission potential in the same vehicles. Since the electricity in the electricity method is met from the US electricity mix, we see that US produce its electricity by SOx emissions causing sources. For all the methods, SI HEVs have
higher SOx emissions than FCVs, and lower SOx emissions than SI ICEVs. Average SOx emissions from the vehicles when using liquid hydrogen depending on the production methods are 18.44 g/hkm for North American natural gas method, 0.01 g/hkm for solar power method, 0.70 g/hkm for nuclear by thermo-chemical cracking of water method, 0.80 g/hkm for electrolysis by high-temperature gas reactor method, 29.40 g/hkm for coke oven gas central plants method, 5.94 g/hkm for coal method, 33.52 g/hkm for biomass method, and 37.63 g/hkm for farmed trees biomass method in central plants, and 21.42 g/hkm for North American natural gas method, 70.85 g/hkm for U.S. electricity method, 25.08 g/hkm for methanol method, and 37.61 g/hkm for ethanol method in refueling stations.
Fig. 10 e CO2 emissions of SI ICEVs, SI HEVs, and FCVs by liquid hydrogen production methods. Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250
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Finally, WTW CO2 emissions of SI ICEVs, SI HEVs and FCVs depending on liquid hydrogen production methods according to GREET software are given in Fig. 10. CO2 emissions are given in the unit of g/hkm as be usually given in literature. Solar power, nuclear and electrolysis methods to produce liquid hydrogen in central plants cause nearly zero CO2 emissions in the vehicles. Also farmed trees biomass and biomass methods to produce liquid hydrogen in central plants cause very low CO2 emissions in vehicles. However, coal method in central plants, electricity in refueling stations, and coke oven gas method in central plants have the highest CO2 potentials when the liquid hydrogen that is produced by these methods, respectively. Average CO2 emissions from the vehicles when using liquid hydrogen depending on the production methods are 224.1 g/hkm for North American natural gas method, 0.4 g/hkm for solar power method, 5.4 g/hkm for nuclear by thermo-chemical cracking of water method, 6.1 g/hkm for electrolysis by high-temperature gas reactor method, 310.5 g/hkm for coke oven gas central plants method, 502.2 g/hkm for coal method, 28.2 g/hkm for biomass method, and 28.8 g/ hkm for farmed trees biomass method in central plants, and 261.7 g/hkm for North American natural gas method, 410.4 g/ hkm for U.S. electricity method, 314.9 g/hkm for methanol method, and 188.2 g/hkm for ethanol method in refueling stations.
Conclusion Hydrogen is used safely in areas such as oil refining, glass purification, semiconductor production, aerospace applications, fertilizer production, welding, annealing and heat treatment of metals, pharmaceutical industry, and hydrogenation of unsaturated fatty acids in vegetable oils, and it attracts more and more attention of scientists day by day. Vehicle powering is one of the most important areas where hydrogen is utilized as fuel. When hydrogen is used in vehicles in liquid form, refueling time and vehicle range significantly increase. The emission changes that occur when conventional or alternative fuels are used in vehicles have been investigated in many studies in the literature. In this study, the effects of hydrogen production methods on emissions are investigated and compared for liquid hydrogen powered SI ICEVs, SI HEVs, and FCVs. As understood from the emissions variations, following items can be concluded from the study: The lowest values of all emissions are seen in the method that liquid hydrogen is produced by solar power in central plants. The highest values of VOC, CO, and NOx emissions are seen in the method that liquid hydrogen is produced by ethanol in refueling stations. The highest values of PM10 and PM2.5 emissions are seen in the method that liquid hydrogen is produced by coke oven gas in central plants. The highest values of SOx emissions are seen in the method that liquid hydrogen is produced by electricity in refueling stations.
The highest values of CO2 emissions are seen in the method that liquid hydrogen is produced by coal in central plants. All the lowest values in emissions belong to FCVs, and all the highest values are encountered in SI ICEVs. Average of all emissions in SI HEVs is 22.4% lower than that of SI ICEVs, that of FCVs is 35.1% lower than that of HEVs, and that of FCVs is 49.6% lower than that of SI ICEVs.
Nomenclature B C CE CO CO2 COG E EC El Es EV FCV FTB GREET
Biomass Coal Combustion emissions Carbon monoxide Carbon dioxide Coke oven gas central plants Ethanol Energy consumption U.S. electricity Electrolysis by high-temperature gas reactor Electric vehicle Fuel cell vehicle farmed trees biomass Greenhouse gases, regulated emissions, and energy use in transportation HEV Hybrid electric vehicle Nitric acid HNO3 HTGR High-temperature gas reactor ICEV Internal combustion engine vehicle LCA Life cycle assessment LH2 Liquid hydrogen M Methanol N Nuclear by thermo-chemical cracking of water NG Natural gas NO Nitric oxide Nitrogen dioxide NO2 Nitrogen oxide NOx Ozone O3 Particulate matter with a diameter of 10 mm PM10 Particulate matter with a diameter of 2.5 mm PM2.5 PTW Pump-to-wheel SI HEV Spark ignition hybrid electric vehicle SI ICEV Spark ignition internal combustion engine vehicle SMR Steam methane reforming Sulfur Oxide SOx SP Solar power TE Total emissions UE Upstream emissions VOC Volatile organic compound WTP Well-to-pump WTW Well-to-wheel Subscripts i Pollutant j Energy source
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Please cite this article as: Ugurlu A, Oztuna S, How liquid hydrogen production methods affect emissions in liquid hydrogen powered vehicles?, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.250