Hydrogen

Hydrogen is a “building block” product of remarkable industrial interest and it is indicated as energy carrier of increasing relevance. Hydrogen is found naturally in hydrogen-rich compounds; it cannot be extracted like natural gas or oil, but needs to be released by applying energy. On the one hand, this represents a drawback because the process requires the input of primary energy carriers like coal, natural gas or biomass, of electricity or high temperatures. The advantage is that a wide range of different feedstocks and energy sources can be used for hydrogen production. It can be manufactured form a wide range of energy sources and in particular from fossil feuls, biofuels by thermochemical way and form water by electrolytic way. Currently, the main sources for the next two or three decades will remain fossol fuels and in particular the natural gas.

The synthesis gas is a mixture of hydrogen and carbon monoxide; it may contain carbon dioxide together with some nitrogen and other inert gases, depending form the used source and the production process. Synthesis gas may be manufactured by coke and biomass gasification, by steam reforming or partial oxidation of hydrocarbons, usually natural gas.

Today, “hydrogen economy” is high on the political agenda and on the priorities of agencies funding research. Hydrogen is claimed to replace hydrocarbons and to provide a clean fuel with no carbon emissions for use in stationary and mobile applications as well. Fuel cells will play a key role for both applications. However, hydrogen is an energy carrier, not a fuel.

The world energy production is dominated by fossil fuels as energy sources. It amounted to 88% in 2003 with oil responsible for 37%. the energy consumption is growing fast in Asia (7% in 2003), and China has become the world’s second largest consumer of oil behind the United States. The proven reserves of oil are concentrated in the Middle East(63%) and those of natural gas in the Middle East (41%) followed by Russia. Coal is more evenly distributed between Asia, Europe and North America.

With the present world production, the oil reserves known today would be used up within about 40 years. This figure should be considered with care. It does not include reserves still to be discovered and it does not include the changes in consumption (for instance the growth in Asia). It has been emphasized the need for flexibility in the energy network and the need the for alternative fuels. Oil is the most versatile of the fossil fuels with high energy density and ease of transportation.

The power industry is very flexible to feedstocks. Coal can be transported over long distance to big centralized power plants close to deep water harbors. Natural gas in large quantities is provided by pipeline or as liquefied natural gas (LNG). The automotive sector represents a special challenge as the energy conversion is strongly decentralized. So far oil derived products have been the solution, but in view of the limited reserves, a number of alternative fuels are being considered, such as LPG, natural gas, methanol, DME, ethanol, bio-diesel, Fischer-Tropsch synthetic fuels, and hydrogen.

Biofuels represent a sustainable response for liquid fuels. It may be based on ethanol and bio-diesel derived from conventional agricultural products or from synfuels via gasification of biomass.

As an example, the manufacture of ethanol from biomass requires the use of fossil energy that for methanol from corn, the ratio of the energy from ethanol divided by the amount of no renewable energy to produce it is only slightly above one if no other waste of the process are used to recover energy. This energy is used for fertilizer, harvesting, transportation, and processing. Ethanol may be produced more efficiently from sugar cane when the bagasse ia also to produce heat, as in Brazil, but it remains a challenge to find routes converting cellulose into ethanol.

Comparing the alternative fuels with conventional oil-derived fuels is a comparison against a moving target, since technologies for making and using conventional fuels are developing as well.

In locations with high natural gas prices, the energy efficiency becomes critical and the feedstock costs may amount to 2/3 of the total production costs. This means that the potential for reduction in hydrogen production costs are limited if energy costs are high.

H₂ relevance and applications 

The development of hydrogen production technologies requires indentification of potential markets and the constraints associated with those markets.

For non-carbon-dioxide-emitting hydrogen production technologies (nuclear, renewable, and fossil with carbon dioxide sequestration), restrictions on carbon dioxide emissions to the atmosphere are an important factor in the increasing potential size of a future markets. Existing and potential hydrogen markets were indentified as follows.

Industrial: The two major industrial markets for hydrogen are fertilizer production (ammonia), steel, methanol and H₂ for cracking and hydrodesulfurization. All nitrate fertilizers require hydrogen in their production processes. Some but not all steel production processes require hydrogen. These are large-scale facilities that match large-scale hydrogen production systems.

Vehicle: Transportation requirements can be met with different fuels(methanol, dimethyl ether,F-T fuel or gasoline,diesel, jet fuel and in the future H₂ itself). Each fuel requires different amounts of hydrogen in the production process and has different economics of scale.

Power: Hydrogen is a candidate for power production, particularly as a vector for storage and use for production when necessary.

Commercial: Hydrogen is being considered for commercial applications in buildings with the co-generation of power and heat.

With interest in its practical applications dating back almost 200 years, hydrogen energy use is hardly a novel idea. What is new is the confluence of factors since the mid-1990s that increase the attractiveness of hydrogen energy economy. Those factors include persistent urban air pollution, demand for low or zero-emission vehicles, the need to reduce foreign oil imports, carbon dioxide emissions and global climate change, and the need to store renewable electricity supplies. These considerations are not confined to a single nation or region, and make hydrogen a virtually ideal energy carrier that is abundantly and equitably available to humanity.

The interest on hydrogen-based energy systems surged in response to the first oil crisis and the growing concerns about environmental issues. The advantages are the hydrogen nearly zero emissions, its potential role in reducing greenhouse gases (improving air quality), reducing climate changes and the possibility of local production on the basis of a variety in fuel cells and the possibility to produce hydrogen form non-fossil sources or clean fossil fuels(fossil fuel combustion in combination with coke capture and storage-CCS) could reduce greenhouse gas emissions from the energy system. Currently, most hydrogen production technologies for energy purposes (large-scale and low cost) are still in the laboratory phase or at best in the demonstration phase. Natural gas plays an important role, almost all transition scenarios start with small-scale production of hydrogen from natural gas via steam reforming (SR), possibly in combination with electrolysis. In long term, literature shows three different possible configurations of the large-scale hydrogen energy system:

-  large scale production of hydrogen from fossil sources, mainly coal and natural gas;

-  a situation with climate constraints, when a fossil based hydrogen system can be combined with CCS (coke capture and storage);

-  renewable hydrogen production, based on biomass gasification, direct solar thermal hydrogen production and electrolysis from solar or wind electricity.

These configurations do not necessarily exclude each other. The costs of producing hydrogen consist largely of feedstock and investment costs. Future hydrogen production costs are generally assumed to be lower than current values as a result of technology development. For small-scale, SR costs are generally significantly higher than that of large scale, but some authors except cost declines down to the large scale reformers.