Decarbonization: are we going the right way? – Hydrogen technology solutions

Decarbonization: are we going the right way?

Now there is a lot of talk about decarbonization, with an emphasis on
carbon emissions. But few people talk about water vapor, which has an even more
disastrous effect. Have you forgotten or is it not time yet?

Decarbonization: are we going the right way?

The transition to hydrogen energy is justified by the need to reduce carbon dioxide emissions into the atmosphere. This process is called decarbonization.

It is known that an increase in the concentration of carbon dioxide in the Earth’s atmosphere leads to an increase in the average air temperature, that is, “global warming”.

To encourage the decarbonisation process, the European Union plans to adopt a so-called” carbon tax ” on all imported goods.

In July last year, analysts at KPMG calculated the likely losses of Russian exporters in the event of the introduction of the fee. In the worst-case scenario, it will appear as early as 2022 and will affect both direct and indirect emissions. Then the suppliers will pay 50.6 billion euros until 2030. In the basic scenario, the tax will be introduced in 2025 and will only apply to direct emissions, which will cost Russian exporters 33.3 billion euros. The most positive scenario assumes the appearance of a tax in 2028, in which case manufacturers will pay $ 6 billion.

With the development of hydrogen energy, carbon dioxide emissions into the atmosphere will decrease and water vapor emissions will increase, since energy and water vapor are released during the reaction of hydrogen and oxygen.

It is believed that water vapor is harmless to humans and the environment.

Is there a link between water vapor and the greenhouse effect?

Water vapor and the greenhouse effectWater in the Earth's atmosphere contains:

  • — in the form of steam (water gas formed during the evaporation of water)
    — – in the liquid state (cloud elements in the form of water drops, raindrops),
    — in the frozen state (cloud elements in the form of ice crystals, snowflakes, hailstones).A distinctive feature of water from other components of the Earth’s atmosphere is that its content in the atmosphere is constantly changing.

Decarbonization: are we going the right way?The water content in the Earth's atmosphere depends on:

  • — air temperature,
    – the state of the evaporating surface.In the Arctic countries, the air temperature is very low, so the atmosphere contains a very small, difficult to measure, amount of water – that is, the air is dry. In hot countries, where the evaporation process is very intense, on the contrary, the amount of water in the Earth’s atmosphere can reach 4% and the air is very humid.

The higher the air temperature, the more water vapor can be contained in the air.

Does water vapor dissolved in the air affect the climate, and if so, can its effect be compared with that of carbon dioxide?

Below are excerpts from the publications of foreign researchers of the influence of water vapor on the climate of our planet:

“The importance of water vapor in climate regulation is undeniable. It is the dominant greenhouse gas that holds the Earth’s heat more strongly than other substances.”
“Water vapor is the most important greenhouse gas. Carbon dioxide is the second most important greenhouse gas.”
“The authors found that in the case of clear sky, the contribution of water vapor in the reflection of the long-wave radiation is 75 W/m2, while carbon dioxide – 32 W/m2.”
“Water vapor is the dominant greenhouse gas, the most important source of infrared opacity in the atmosphere”.
“The dominant role of water vapor as a greenhouse gas seen for a long time”.
“Generally speaking, water vapor is the only atmospheric absorber of infrared radiation.”

“In society, only carbon dioxide is known as a greenhouse gas. In reality, water vapor makes a more significant contribution to the increase in atmospheric temperature.”

The burning of natural gas

Natural gas consists of a mixture of marginal hydrocarbons such as methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), pentane (C5H12) and hexane (C6H14), as well as a small amount of inert gases.

The characteristics of natural gas, such as density and heat of combustion, can be determined with great accuracy using the characteristics of the first four homologs. The general formula for the reaction of marginal hydrocarbons with oxygen is as follows:

SpN(2n+2) + 0.5 (3n+1)O2→ nCO2 + (n+1) H2O,

where n is the number of carbon molecules and the ordinal number of the homolog of the hydrocarbon.

Consider gorenje reaction equations for the first four homologues of hydrocarbons C1, C2, C3 and C4, which are in the gaseous state under atmospheric conditions.

 

When n=1

CH4 + 2O2 → CO2 + 2 H2O

(i.e., 1 mole of methane, when combined with 2 moles of oxygen, forms 1 mole of carbon dioxide and 2 moles of water vapor).

When burning one kilogram of methane (CH4), 50 MJ of thermal energy is released, as well as 2.75 kg of carbon dioxide (CO2) and 2.25 kg of water vapor (H2O), that is, water vapor emissions into the atmosphere are slightly lower than carbon dioxide emissions.

When n=2

C2H6 + 3,5O2 → 2CO2 + 3 H2O.

When burning one kilogram of ethane (C2H6), 47.8 MJ of thermal energy is released, as well as 2.93 kg of carbon dioxide (CO2) and 1.8 kg of water vapor (H2O), that is, the mass fraction of water vapor in the combustion products of ethane is less than when burning methane.

When n=3

C3H8 + 5O2 → 3CO2 + 4 H2O.

When n=4

C4H10 + 6,5O2 → 4CO2 + 5 H2O.

From these expressions, it can be seen that when the number of the homologue of a hydrocarbon increases, a larger volume of oxygen is required for its complete oxidation, while a larger volume of carbon dioxide and water vapor is released than when methane is burned. The volume of CO2 released during the combustion of hydrocarbons is proportional to the ordinal number of the homologue, and the water vapor is n+1. When methane is burned, twice as much water vapor is released as carbon dioxide, and when the proportion of “heavy” hydrocarbons in the burned gas increases, this proportion decreases.

Combustion of hydrogen and methane

Let’s compare the amount of greenhouse gas emissions from the combustion of hydrogen and methane, which is the main component of natural gas.

When two hydrogen molecules combine with one oxygen molecule, two water molecules are formed. The reaction of combining hydrogen and oxygen is accompanied by the release of energy.

2*H2 + O2 → 2*H2O + energy (1)

When burning one kilogram of hydrogen (H2), 120 MJ of thermal energy and 9 kg of water vapor (H2O) are released.

When one methane molecule is combined with two oxygen molecules, two water molecules and one carbon dioxide molecule are formed. The reaction of methane and oxygen compounds is accompanied by the release of thermal energy.

CH4 + 2*O2 → 2*H2O + CO2 + thermal energy (2)

When burning one kilogram of methane (CH4), 50 MJ of thermal energy is released, as well as 2.75 kg of carbon dioxide (CO2) and 2.25 kg of water vapor (H2O), that is, 5 kg of greenhouse gases.

To produce 120 MJ of thermal energy, you will need to burn 2.4 kg of methane. At the same time, 6.6 kg of carbon dioxide and 5.4 kg of water vapor, that is, 12 kg of greenhouse gases, will enter the atmosphere.

The data from the above calculations are summarized in Table 2.

Table 2

Mass of the burned gas

Allocation of thermal energy,

MJ

Weight water vapor

Weight

carbon dioxide

Total mass of greenhouse gases
1 kg of hydrogen (H2O) 120 9 kg – 9 kg
2.4 kg methane (CH4) 120 5.4 kg 6.6 kg 12 kg

 

From this calculation, it can be seen that when the same amount of energy is obtained, the total greenhouse gas emissions from methane combustion are 30% higher than those from hydrogen combustion.

At the same time, water vapor emissions from natural gas combustion are 40% lower than from hydrogen combustion.

From the publication /3/ it can be seen that the effect of water vapor on the greenhouse effect is 2.3 times higher than the effect of carbon dioxide.

If we take this fact into account, the greenhouse effect of burning 1 kg of hydrogen will be comparable to the burning of 2.4 kg of methane. That is, when the same amount of energy is released, the effect of hydrogen and methane on the greenhouse effect is commensurate.

At the same time, according to the publications of foreign mass media (mass media), it can be concluded that only carbon dioxide affects the increase in the greenhouse effect!

In /7 / it is reported that research conducted by scientists from the University of Miami Rosenstiel School of Marine and Atmospheric Science confirmed that water vapor in the troposphere – the layer of the atmosphere located between the Earth’s surface and extending to an altitude of 5-20 km – will play an increasing role in climate change in the future.

Researchers from Florida reported that the increasing amount of water vapor in the atmosphere is caused by human activity.

If this is the case, then along with reducing carbon dioxide emissions into the atmosphere, it is also necessary to control water vapor emissions.

Sources of water vapor emissions

As noted above, when using hydrocarbon gases such as methane, ethane, propane, and butane, water vapor is generated along with carbon dioxide emissions.

In thermal and nuclear power engineering, the working fluid involved in the generation of electrical and thermal energy is water vapor, for the condensation of which various types of cooling towers are used, as well as direct-flow cooling with water from rivers, lakes and reservoirs.

In 2008, direct-flow cooling was banned in the design and construction of new power plants in Russia.

So-called ” wet ” cooling towers are sources of water vapor emissions into the atmosphere.

“Dry” cooling towers, as well as air condensing units (VCS), can reduce water vapor emissions in the energy sector.

Hydrogen-the fuel of the future

As noted above, replacing natural gas with hydrogen as a fuel does not reduce the greenhouse effect if the steam generated by the combustion of hydrogen-containing gas is not condensed.

This also applies to fuel cells, in which electrical energy is generated electrochemically, since water vapor is formed at the outlet of the fuel cell along with electrical energy.

That is, in the transition to hydrogen energy, it is necessary to stimulate not only technologies that reduce carbon dioxide emissions into the atmosphere, but also water vapor.

References

  1.  “Climate Modeling through Radiative-Convective Models”, Ramanathan & Coakley, Reviews of Geophysics and Space Physics (1978).
  2.  “Atmospheric Radiation: Theoretical Basis”, Goody & Yung, Oxford University Press (1989, 2nd edition).
  3.  “The Importance and Nature of the Water Vapor Budget in Nature and Models”, Lindzen, Climate Sensitivity to Radiative Perturbations: Physical Mechanisms and Their Validation (1996).
  4.   “Earth’s Annual Global Mean Energy Budget”, Kiehl & Trenberth, Bulletin of the American Meteorological Society (1997).
  5.  “The Radiative Signature of Upper Tropospheric Moistening”, Soden, Jackson, Ramaswamy, Schwarzkopf & Huang, Science (2005).
  6.  “Radiation and Climate”, Vardavas & Taylor, Oxford University Press (2007).
  7.  «Rising Levels of Human-Caused Water Vapor in Troposphere will Intensify Climate Change Projections”, Rick Panpaleo, (2014)