ENVIRONMENTAL PROSPECTS OF "HYDROGEN" ELECTRICITY FOR TRANSPORT

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ENVIRONMENTAL PROSPECTS OF "HYDROGEN" ELECTRICITY FOR TRANSPORT

INTRODUCTION
The first electric cars were created in the USA and Scotland in 1837. Since the end of the 19th century, the development of electric cars and cars with thermal engines proceeded in parallel. At the same time, the latter were weak competitors, since electric cars had a simpler design, and in urban operating conditions their range on one battery charge (10-15 km) and speed (within 20 km/h) were quite satisfactory for consumers; in 1899, electric cars reached a speed of 106 km/h. At the end of the 19th century, 38% of all cars in the USA were equipped with electric motors, 40% with steam engines, and 22% with gasoline engines. At the beginning of the 20th century, electric cars already provided a range of 50-80 km, and a speed of up to 35 km/h. However, it was at the beginning of the 20th century that the design and characteristics of cars with internal combustion engines (ICE) were significantly improved: their speeds reached 80 km/h, and the cruising range was up to 300 km. The organization of mass production of cars and the low cost of fuel with high technical and operational indicators provided cars with an absolute advantage over electric cars [1]. In 1916, a car with a hybrid engine appeared: a gasoline engine plus an electric motor [2]. At the same time, trams began to be used in cities, and somewhat later trolleybuses; by 1960, the number of electric cars in England amounted to 26,000 units, they were used in the processes of centralized delivery of goods from retail chains to homes, transportation of parcels and mail, i.e. where high speeds and long mileage were not required; rail transport did not lag behind: electric trains were widely used in operation [3]. Since the mid-1960s, interest in electric vehicles has re-emerged (especially in the United States, Japan, Germany and England), which was due to energy and environmental issues. The latter was due to the growing number of cars, which caused pollution of the urban atmosphere with emissions of harmful substances present in the exhaust gases of internal combustion engines (gasoline, diesel, gas). In this regard, for example, in the United States in 1963 the Clean Air Act was adopted [4]. However, there was no significant expansion in the use of electric vehicles: the reason for the stagnation in the development of electric vehicle designs was the lack of new power sources with high energy capacity at a low cost [1]. In the early 2000s, interest in the use of electricity to provide movement of vehicles "got a second wind" in a number of countries around the world. And this was due not only to the desire to reduce the content of harmful substances in the air of cities from vehicles (the number of which has currently reached 1.5 billion units [5]). The second problem was the need to save non-renewable hydrocarbon fuels and, in this regard, the need to avoid dependence on hydrocarbon fuel exporting countries. Japan was the first in the world to proclaim a course for building a hydrogen economy and adopted a corresponding strategy. The country is developing two areas as a priority: the creation of distributed thermal generation on fuel cells (FC) for lighting and heating residential buildings and office premises and electric vehicles using hydrogen [6]. The "EU Hydrogen Strategy" has been published [7]: according to the document, by 2030 Europe should be covered by hydrogen gas pipelines with a length of 23 thousand km. However, during the transition period, hydrogen production from fossil fuels is allowed. It is expected that by 2050, a quarter of electricity generation will be carried out using hydrogen. Its production itself will be based on the use of wind and solar energy [8]. When considering the use of electricity to drive vehicles, attention is usually focused on the problems of using an electric motor in a vehicle. However, the overwhelming majority of electric vehicles receive electricity to recharge traction batteries (TAB) from external sources of electricity generation, produced in various ways. And at the same time, they do not attach much importance to the questions: how is this electricity obtained, from what source, what is the efficiency of electricity transmission from the places of electricity generation to the place of its use?

The first internal combustion engine, created by E. Lenoir in 1860, ran on illuminating gas - a mixture of methane, carbon monoxide, hydrogen and other combustible gases - obtained by dry distillation of coal. And at present, hydrogen is considered the most effective replacement for natural gas from an environmental point of view, since the direct combustion product of H2 is water, and the accompanying product is nitrogen oxide, as a result of the high temperature developed during the combustion of hydrogen [9]. However, there is practically no free hydrogen in nature, and its production requires electricity. Currently, about 96% of the annual world production of hydrogen is obtained from fossil fuels using technologies such as steam reforming of methane (48%), oil reforming (30%) and coal gasification (18%), which is accompanied by the formation of harmful substances with their subsequent release into the atmosphere with exhaust gases [10]. And here the question arises: how environmentally friendly will the production of hydrogen be, as well as its transportation from the place of production to the place of electricity generation? RESEARCH OBJECTIVE
Assessment of the impact on the atmosphere of using hydrogen to generate electricity in both transport and power generation plants.

METHODS
Research method - analytical

RESULTS AND DISCUSSION

Hydrogen production: "50 shades" of color
The most common fuel is hydrocarbons CnHm, which, when burned, forms oxidation products such as carbon monoxide CO (carbon monoxide), carbon dioxide CO2 (aka carbon dioxide), and products of incomplete oxidation of hydrocarbons CaHb. "Claims" to CO are due to the fact that this gas, when inhaled, displaces oxygen from the blood, leading to suffocation, and among CaHb there are carcinogenic (for example, benzopyrene C20H12), provoking the development of cancer [11]. Carbon dioxide is currently classified as a "greenhouse gas" (see below).
Of all possible gaseous fuels, only hydrogen does not contain carbon, therefore, hydrogen can be considered the most environmentally friendly gas from the very beginning, the direct combustion product of which is water:
Н2 + О2 + Т oC H2O + N2 (1)
A by-product of hydrogen combustion (as with combustion of any type of fuel) is nitrogen oxide NO, provided that 2000 оС is reached during combustion [9]. It can also be added that in case of hydrogen leaks from the fuel tank, there will be no pollution of the environment, unlike the evaporation of diesel fuel, gasoline, as well as natural and petroleum gases.
But hydrogen in its pure form is practically not found, it is part of numerous chemical compounds, the most famous of which is water H2O. Accordingly, obtaining hydrogen in its pure form requires energy expenditure. The cost factor is one of the main ones determining the demand for hydrogen as an energy source on an industrial scale. Therefore, the transition to hydrogen energy means large-scale production of hydrogen, its storage, distribution, transportation. Therefore, at "low" prices for traditional motor fuel, hydrogen technologies will be economically unattractive. However, at "high" prices, the picture changes significantly: hydrogen in centralized production based on natural gas, coal and nuclear energy requires lower costs compared to traditional technologies for producing fuels for internal combustion engines [12]
To simplify the determination of the method of production and comparison of the degree of impact on the environment, it was proposed to take as a basis the degree of environmental friendliness of the corresponding technology: the more carbon dioxide CO2 is released during the production of hydrogen, the less environmentally friendly the corresponding technology is. And each such technology was given a "color" definition [13]:
- "White" hydrogen (natural, golden, geological) - naturally produced or present in the earth's crust;
- "Green" hydrogen is the most environmentally friendly of those produced, since it is obtained by electrolysis of water H2O and provided that electricity comes from renewable energy sources (RES), such as wind, solar energy, hydropower, respectively, there are no CO2 emissions;
- "Yellow (orange)" hydrogen is also obtained by electrolysis, but the source of energy is nuclear power plants (NPP). There are no CO2 emissions, but the method is not completely environmentally friendly due to the large emission of water vapor due to the cooling of hot water coming from the reactors using cooling towers;
- "Grey" hydrogen is produced by steam reforming of methane CH4, i.e. the feedstock for this reaction is natural gas;

- "Turquoise" hydrogen is produced by decomposing CH4 into hydrogen and solid carbon by pyrolysis (high-temperature action with a lack of oxidizer). This production yields a relatively low level of carbon emissions, which can be either buried or used in industry, for example, in the production of steel or tires, and thus does not enter the atmosphere;
- "Emerald" hydrogen is produced by decomposing biomethane and natural gas using thermal plasma electrolysis;
- "Blue" hydrogen is produced by steam reforming of methane, but with the condition of carbon capture and storage, which reduces carbon emissions by about 2 times. This technology for producing hydrogen is very expensive;
- "Brown" hydrogen is produced by gasification of brown coal to form synthesis gas (syngas): a mixture of carbon dioxide, carbon monoxide, hydrogen, methane and ethylene, as well as a small amount of other gases;
- "Black" hydrogen, for which coal is the feedstock.
Currently, about 96% of the world's annual hydrogen production is obtained from fossil fuels using technologies such as steam methane reforming (48%), oil reforming (30%) and coal gasification (18%). However, the most common process for producing hydrogen from methane (reforming process) is based on the following reactions:
CH4 + H2O = CO + 3H2 (2)
CH4 + 2H2O = CO2 + 4H2 (3)
CO + H2O = CO2 + H2, (4)
the product of which is carbon dioxide.
In a hydrogen plant with a capacity of one million m3 H2 per day, about 0.3-0.4 million standard cubic meters of CO2 are emitted into the atmosphere daily. At the same time, CO2 capture imposes approximately 25-30% additional costs on hydrogen production [14].
A method that allows us to do without the use of fossil fuels is water electrolysis: the process of splitting water into its constituent elements - hydrogen and oxygen - using electric current. However, to implement this process, in addition to electricity, water is also needed, and purified water at that. Thus, to obtain 1 ton of hydrogen by electrolysis, an average of 9 tons of purified water is required, and to obtain 1 ton of purified water, 2 tons of the original (unpurified) water are needed. Thus, to obtain 1 ton of hydrogen, 18 tons of water are needed, and taking into account various losses, this will be 20 tons [15]. Currently, hydrogen production from non-renewable resources such as coal and natural gas is dominant in the world [16]. About 95% of the hydrogen produced is produced by methods based on fossil fuels, and the production of hydrogen from water using electricity and biomass is only 4% and 1%, respectively. About half of all hydrogen produced comes from natural gas (NG) gasification and thermal catalytic processes, followed by heavy oils, petroleum and coal. The reaction between NG and steam in a catalytic converter splits off hydrogen atoms, producing carbon dioxide as a by-product. The use of fossil fuels to produce hydrogen must be coupled with carbon capture systems. Hydrogen can also be produced from methanol or gasoline, although CO2 is again an unwanted by-product. Hydrogen production from low- and zero-carbon energy sources, including renewable electricity, biomass and nuclear energy, could be a long-term goal of a hydrogen utopia [17].

Electricity generation at stations
In the structure of electricity production in all regions of the world, thermal power plants are in the lead. The exception is Latin America, where preference is given to hydroelectric power plants, which is due to the natural conditions of this region. The largest electricity producers: China - 29.0% of the world's output, the USA - 16.0%, India - 5.8%, Russia - 3.9%, Japan - 3.7% and the rest of the world - 41.5%. At the same time, for different regions of the world, the source of electricity generation are stations of different operating modes, and these figures differ significantly (Table 1) [16, 17].

Table 1
Structure of electricity generation

Taking into account the volume of electricity generation, it follows that 1) Electricity is mainly generated at thermal power plants (TPP) and 2) the main sources are the combustion of coal (due to China) and natural gas (due to the USA); Russia's share in terms of natural gas use is small, since Russia's contribution to global electricity generation is 7 times less than China's contribution and 4 times less than the USA's contribution. As for the focus on renewable energy sources, the utilization rate of installed capacities, for example, wind generators, is only 25%, which is due to the vulnerability of these types of electricity generation to natural disasters [18].
Thus, at present, electricity generation at stations is accompanied by large emissions into the atmosphere of hydrocarbon fuel combustion products: coal and natural gas.

Greenhouse effect
The greenhouse effect is a phenomenon of secondary heating of the atmosphere by long-wave (infrared) radiation from the planet's surface, returned back to the surface by some gases in the atmosphere. The greenhouse effect is determined by the difference between the average temperature of the planet's surface (plus 15 °C) and its radiation temperature in space ("minus" 18 °C). Accordingly, the greenhouse effect is equal to plus 33 °C. With an increase in the greenhouse effect, the surface temperature rises while maintaining a constant radiation temperature. This effect is caused by the presence of so-called "greenhouse gases" (GHG) in the atmosphere: carbon dioxide CO2, methane CH4, nitrous oxide N2O, hydrofluorocarbons HFC, perfluorocarbons PFC and sulfur hexafluorides SF4. [19]. Despite the lowest greenhouse activity, the greatest influence on the creation of the greenhouse effect is exerted by carbon dioxide, the mass emission of which into the atmosphere is the greatest - 68% of the total emission of all GHG, which is why CO2 is considered to have the greatest "greenhouse activity". And it is by the amount of formed CO2 that hydrogen production technologies are classified. Methane is in second place in greenhouse activity. However, water vapor was not included in the number of GHGs (it is difficult to say why), although water vapor has a significantly higher greenhouse activity compared to CO2: the greenhouse effect is up to 78% due to water vapor and only 22% by carbon dioxide, the contribution of other gases is significantly less [20, 21]. At the same time, the relative content of water vapor in the atmosphere is 0.2-2.5%, and carbon dioxide 0.03-0.05%; the relative content of other greenhouse gases does not exceed 3∙10-4%.[22, 23].

Electricity generation in the world is mainly provided by burning coal and natural gas. As a result, both products of incomplete combustion (partially oxidized hydrocarbons and methane in their original form, as well as coal in the form of soot) and products of complete combustion (CO2 and H2O) are released into the atmosphere. Although methane decomposes in the atmosphere much faster than CO2, in the first 10 years after the emission of CH4, its greenhouse activity is approximately 80 times stronger than that of CO2 [23]. When generating electricity at nuclear power plants, which makes up a significant share on the scale of such regions as the USA, Russia and Europe, even in this case there is a large emission of water vapor H2O from cooling towers during the cooling of water used to cool the reactors. It should be noted that each ton of steam emitted from the cooling tower into the ground layer of the atmosphere, where the "greenhouse effect" is formed, is equivalent in terms of the "greenhouse effect" to 360 kg of carbon dioxide. Accordingly, for every kWh of electricity generated at nuclear power plants, 3.6 kg of water vapor is emitted into the ground layer of the atmosphere. [24]. Thus, if hydrogen is burned at a thermal power plant instead of hydrocarbon fuel, water vapor is released into the atmosphere - a substance that enhances the "greenhouse effect". And although the emission of combustion products and hydrocarbon fuel occurs at a distance from the places of predominant population residence, due to the transboundary movement of air masses, all these emissions, both in their original form and in the form of acids, will have an impact on both populated areas and forest lands and agricultural fields.

Electricity generation in transport
There are three methods for driving an electric motor in vehicles: 1) using hybrid motor units (HMU), when the ICE provides recharging of the HBU using a generator, 2) recharging of the HBU from an external source and 3) recharging of the HBU from fuel cells [25]. Electric vehicles usually provide smooth operation, good acceleration when starting from a standstill and require less maintenance than vehicles with ICE. However, electric vehicles have three problems compared to cars: mileage on one charge, infrastructure and recharging time.
In the case of using HMU, the emission of combustion products into the atmosphere is natural. To reduce air pollution in this case, it is possible to use hydrogen as an alternative fuel. The organization of the working process in this case is ensured by introducing hydrogen into the intake manifold, where it will mix with air, and already in the form of a hydrogen-air mixture enter the engine cylinders. And the further course of the ignition and combustion process will depend on the ignition method: either from a spark plug or as a result of compression of the mixture by a piston - in this case, the HCCI process (Homogeneous Charge Compression Ignition) is implemented [25]. But when implementing the HCCI process, the stability of the engine is low [26, 27]. However, harmful substances (carbon monoxide, dispersed particles, partially oxidized hydrocarbons) are still present in the engine exhaust gases as a result of combustion of lubricating oil entering the combustion chamber. Nitrogen oxides are also present in the exhaust gases: the result of oxidation of nitrogen by oxygen (both components are present in the air) under the influence of high temperature during the combustion of hydrogen. The range on one charge of an electric vehicle is determined by two factors: the capacity of a fully charged battery pack and the efficiency of its electric transmission. For most electric vehicles, the following ratio is valid: 3.0-6.0 km / (kW h) due to TAB. In this case, energy consumption depends on such factors as the temperature of the TAB (it is desirable to maintain a constant temperature), maintaining the climate in the cabin (the consumption for heating or cooling the cabin depending on external conditions), driving style (each driver has his own style: some are calm, some are aggressive), operating conditions (electric cars have an advantage in city traffic with frequent braking and stops, when, thanks to regenerative braking, the TAB is recharged.

Recharging. Most electric vehicles can be charged using AC power from a wall outlet (120 V or 240 V), and some can be charged using DC power. However, since the batteries can only store DC current, the AC current must be converted to DC before it can be used to charge the vehicle using an on-board charger. With a 110-120 V grid, a battery charge of about 60 km can be provided in 8-13 hours. The charging speed is then limited by the amount of electricity available at the wall outlet, not the capacity of the vehicle's on-board charger. However, higher battery discharge levels require proportionally longer charging times. With a 220-240 V grid and increasing the amperage to 80 A (depending on the vehicle), charging times can be reduced by a factor of 10. However, this maximum charging rate is rarely achieved, as the AC-to-DC conversion capacity becomes the limiting factor.[28] Thus, recharging of electric vehicles from external sources requires a developed infrastructure of charging stations and the electric vehicles themselves, capable of providing charging in a short time and having a high capacity. Otherwise, the use of electric vehicles will be limited to one locality and will require a lot of time. Recharging at night from a home power grid is only possible in private homes - how to implement this in multi-story buildings seems difficult. Given the size of large cities, the "greenest" motorized type of transport at present is public electric transport: trams, trolleybuses, metro, electric buses. The more people regularly use public rather than personal motorized transport, the lower the specific emission of pollutants per person in the city will be, and as technology develops, various types of shared transport, that is, shared on-demand, will also find wider application [29].

Fuel cells (FC) are devices for converting the chemical energy of fuel into electrical energy, they provide electricity generation due to oxidation-reduction transformations of reagents coming from outside, as a result of which the batteries are recharged. Hydrogen and air are used as reagents (the latter as a source of oxygen, which is cheaper than using pure oxygen). Unlike a battery, which discharges while it is used to power electrical components, FCs act as constantly working energy sources as long as they are supplied with fuel. It is expected that the hydrogen fuel cell will be able to overcome the shortcomings of electric vehicles, making hydrogen the transport fuel of the future.
The main problems of FC vehicles are associated with high production and operating costs, with a lack of electrical capacity for hydrogen production and the safety of its use [23]. Improvement of the FC itself and infrastructure elements are decisive factors for the commercialization of hydrogen as a motor fuel in motor vehicles.
Hydrogen can be transported in a vehicle in a fuel tank. However, the low volumetric energy density of hydrogen under ambient conditions requires its storage in high-pressure cylinders with an operating pressure of up to 20.0-70.0 MPa, but even at the highest pressure, the energy density of hydrogen is only 4.4 MJ/l versus 31.6 MJ/l for gasoline. When using liquefied hydrogen (cooled to minus 253 °C), its energy density increases to 8.0 MJ/l. However, the compression and liquefaction processes themselves require energy expenditure: during liquefaction, energy consumption is from 25 to 45% of the energy of the liquefied hydrogen [30], which causes additional consumption of hydrogen and, accordingly, natural resources for its production, as well as the emission of harmful substances and greenhouse gases into the atmosphere.

CONCLUSION
The main source of atmospheric pollution in populated areas, especially large cities, is transport, the number of which in the world has currently reached almost 1.5 billion units. Almost all transport is equipped with internal combustion engines (ICE), which use hydrocarbon fuel as fuel: diesel, gasoline, as well as natural and petroleum gas. During the combustion of these fuels, both harmful substances and so-called "greenhouse" gases (mainly carbon dioxide and methane) are formed, which are emitted into the atmosphere with the exhaust gas flow.
The use of hybrid motor units (HMU) in cars, which are a combination of an ICE and an electric motor, will reduce the emission of harmful substances and "greenhouse" gases into the environment. The use of hydrogen as fuel in ICE will further reduce the emission of harmful substances, but will increase the emission of water vapor, which is three times more greenhouse than carbon dioxide. The transition completely to electric motors will completely eliminate such emissions.
However, hydrogen in its free form in nature, similar to, for example, natural gas, practically does not exist, and hydrogen production is provided by processing hydrocarbon fuels, more than 90% of natural gas. As a result, both harmful substances and "greenhouse" gases are formed, which enter the atmosphere and, due to transboundary air mass flows, spread over many hundreds and thousands of kilometers, polluting huge territories. Electric motors operate by recharging traction batteries (TAB). In this case, TAB recharging is possible due to the operation of the internal combustion engine (as part of the GMU), from external power grids, from fuel cells (installed on an electric vehicle). The presence of an internal combustion engine causes the emission of harmful substances and "greenhouse" gases into the atmosphere, including in the case of using hydrogen as a fuel. The operation of fuel cells using hydrogen as a fuel is environmentally friendly. However, if hydrogen leaks from the fuel tank (located on board the vehicle), it may form free hydrogen radicals when exposed to solar ultraviolet radiation, which can deplete the ozone layer. Due to the low volumetric energy density of hydrogen, it can be transported in compressed (up to 70.0 MPa) or liquefied (cooled to minus 253 °C) form, which requires corresponding energy expenditure: during liquefaction, the energy consumption is from 25 to 45% of the energy of the liquefied hydrogen. In the case of transporting hydrogen in a chemically bound form as part of liquid hydrides (mainly ammonia and methanol), it is necessary to ensure the transportation of the hydride carrier to the end users, followed by the return of the dehydrated carrier back to the chemical plant for loading with hydrogen. Both in the case of transportation and when using carriers, they can enter the atmosphere. Electricity generation at power plants worldwide is currently provided (almost 60%) by burning coal and natural gas, which is accompanied by the formation of harmful substances and "greenhouse" gases. When generating electricity at nuclear power plants (about 10%), large volumes of water vapor are released into the atmosphere (due to the cooling of the reactor cooling water in cooling towers). Electricity generation using solar panels and wind generators (about 16%) depends on natural conditions and is characterized by a high level of instability, which allows their installed capacity to be used by no more than 25%.

About the authors

Alexey Kulchitskiy

Author for correspondence.
Email: ark6975@mail.ru
ORCID iD: 0000-0001-9609-0829
SPIN-code: 6807-8316

Доктор технических наук

Специалист по сертификации конструкторского подразделения

References

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