8 Hydrogen
Although not a hydrocarbon resource, hydrogen can be used in place of or
as a complement to traditional hydrocarbon-based fuels. As an "energy
carrier,” hydrogen is clean burning, which means that when hydrogen reacts
with oxygen, either in a conventional engine or a fuel cell, water vapor is the
only emission. (Combustion with air at high temperatures will also form
nitrous oxides).
Hydrogen can be produced either from hydrocarbons (natural gas, ethanol,
etc.) or by electrolysis. Production from natural gas is often done via syngas
(see chapter 9.1.5) with up to 75-80% efficiency. Its advantage over
methane gas is that carbon dioxide can be removed and handled at a central
location rather than by each consumer, providing a cleaner energy carrier.
Hydrogen is also produced from water by electrolysis with an efficiency of
about 25% at normal conditions, to about 50% in high temperature, high
pressure processes, or in various recycling processes in the chemical
industry.
(e.g., hydrochloric acid recycled in the polyurethane process). The
energy supply can then come from a renewable source such as
hydroelectric, solar, wind, wave, or tidal, where hydrogen acts as an energy
carrier replacing batteries, to form a fully clean, renewable energy source
supply chain.
In both cases, the main problem is overall economy, distribution and storage.
Hydrogen cannot easily be compressed to small volumes, and requires quite
bulky gas tanks for storage. Also, hydrogen produced from electricity
currently has an end-to-end efficiency that does not compare well with
gasoline or electrical battery vehicles.
9.2 Emissions and environmental effects
The production, distribution and consumption of hydrocarbons as fuel or
feedstock are globally the largest source of emissions into the environment.
The total annual world energy supply of 11,000 million TOE is based 81% on
fossil fuels, and releases some 26,000 million tons of carbon dioxide plus
other gases, e.g., methane into the atmosphere.
The most serious effect of these emissions is global climate change. The
Intergovernmental Panel on Climate Change (often called the UN Climate
Panel) predicts that these emissions will cause the global temperature to rise
from between 1.4 to 6.4 ºC by the end of the 21st century, depending on
models and global scenarios.
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9.2.1 Indigenous emissions
Emissions from the industry can be divided into several types.
Discharge: Mud, shale, silt, produced water with traces of
hydrocarbons. Ballast water, polluted wastewater with
detergent, sewage, etc.
Accidental spills: Blowout, shipwreck cargo and bunker oil, pipeline
leakage, other chemicals, traces of low level
radioactive isotopes.
Emissions: CO2, methane, nitrous oxides (NOx) and sulfur from
power plants and flaring
Exposure: Toxic and/or carcinogenic chemicals
Locally, these emissions are tightly controlled in most countries by national
and international regulations, and during normal operations, emission targets
can be reached with the systems and equipment described earlier in this
document. However, there is continuing concern and research into the
environmental impact of trace levels of hydrocarbons and other chemicals on
the reproductive cycle and health of wildlife in the vicinity of oil and gas
installations.
The major short-term environmental impact is from spills associated with
accidents. These spills can have dramatic short-term effects on the local
environment, with damage to marine and wildlife. However, the effects
seldom last for more than a few years outside Arctic regions.
9.2.2 Greenhouse emissions
The most effective greenhouse gas is water vapor. Water naturally
evaporates from the sea and spreads out, and can amplify or suppress the
other effects because of its reflective and absorbing capability.
The two most potent emitted greenhouse gases emitted are CO2 and
methane. Because of its heat-trapping properties and lifespan in the
atmosphere, methane's effect on global warming is 22-25 times higher than
CO2 per kilo released to atmosphere. By order of importance to greenhouse
effects, CO2 emissions contribute 72-77%, methane 14-18%, nitrous oxides
8-9% and other gases less than 1%. (sources: Wikipedia, UNEP)
The main source of carbon dioxide emissions is burning of hydrocarbons.
Out of 29 billion tons (many publications use teragram (Tg) = million tons) of
CO2 emitted in 2008, 18 billion tons or about 60% of the total comes from oil
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and gas, the remainder is coal, peat and renewable bioenergy, such as
firewood. 11% or 3.2 billion tons comes from the oil and gas industry itself in
the form of losses, local heating, power generation, etc.
The annual emissions are about 1% of total atmospheric CO2, which is in
balance with about 50 times more carbon dioxide dissolved in seawater. This
balance is dependent on sea temperature: Ocean CO2 storage is reduced as
temperature increases, but increases with the partial pressure of CO2 in the
atmosphere. Short term, the net effect is that about half the CO2 emitted to
air contributes to an increase of atmospheric CO2 by about 1.5 ppm annually.
For methane, the largest source of human activity-related methane
emissions to atmosphere is from rice paddies and enteric fermentation in
ruminant animals (dung and compost) from 1.4 billion cows and buffalos.
These emissions are estimated at 78.5 Tg/year (source: FAO) out of a total
of 200 Tg, which is equivalent to about 5,000 Tg of CO2. Methane from the
oil and gas industry accounts for around 30% of emissions, mainly from
losses in transmission and distribution pipelines and systems for natural gas.
Figure 40. Greenhouse emissions Source: Wikipedia Commons
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There are many mechanisms affecting the overall balance of greenhouse
gases in the atmosphere. CO2 has been measured both directly and in ice
cores, and has increased from a pre-industrial value of around 250 ppm to
385 ppm today. Methane has increased from 1732 to 1774 ppb (parts per
billion).
There is no full model that describes the net effect of these changes. It is
well accepted that without CO2, methane and water vapor, the global
average temperature would be about 30 ºC colder. The current data
correlates well with a current global average temperature increase from a
pre-industrial global average of 13.7 ºC to 14.4 ºC today. The atmosphere
and seas have large heat trapping capacity, which makes their temperatures
rise. These temperature rises lag behind greenhouse gas temperature
increases. It is therefore predicted that the temperature will continue to rise
by about 1ºC even if there were no further increase in levels of CO2 and
methane.
The heat capacity of the atmosphere and seas also means that when the
temperature increases, there will be more energy stored in the atmosphere,
which is expected to drive more violent weather systems.
