Hydrogen Energy: Challenges and Prospects / Edition 1 available in Hardcover
Hydrogen Energy: Challenges and Prospects / Edition 1
- ISBN-10:
- 085404597X
- ISBN-13:
- 9780854045976
- Pub. Date:
- 12/14/2007
- Publisher:
- RSC
Hydrogen Energy: Challenges and Prospects / Edition 1
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Hydrogen Energy
Challenges and Prospects
By D.A.J. Rand, R.M. Dell
The Royal Society of Chemistry
Copyright © 2008 The Royal Society of ChemistryAll rights reserved.
ISBN: 978-0-85404-597-6
CHAPTER 1
Why Hydrogen Energy?
From time immemorial, mankind has burnt wood in order to keep warm and to cook food. With the discovery of coal and the development of mining engineering, a new source of fuel, of higher calorific value, became available. As populations expanded and became urbanized, wood was less readily accessible and coal assumed greater importance for heating purposes. Following the introduction of rotative steam engines in the 1780s, coal was used as the prime source of energy for the production of mechanical power. Steam engines propelled ships, railway locomotives and traction engines and also provided a universal means for generating power in factories and on farms.
Late in the 19th century, the internal combustion engine was developed. Liquid petroleum was exploited – first in North America and then across the world – and was refined to provide fuels for both petrol and diesel engines. With its greater efficiency and convenience, this new technology soon replaced steam engines for most applications. Consequently, in many countries the use of coal declined (at least in percentage terms), while that of petroleum grew rapidly.
Since the mid-20th century, natural gas fields have been found in abundance. Some of the gas is associated with oil wells, but exists on its own in other places. Where oil wells are remote from centres of population, the gas was initially seen as a by-product that had no commercial value and was therefore flared. This situation changed with the development of technology for liquefying natural gas and conveying it to market by road or by sea in cryogenic tankers. Thus, once considered to be a waste product associated with oil, natural gas is now regarded as a prime fuel. With improvements in offshore drilling technology, it became possible to seek and access reservoirs in ever-deeper waters. Often these were located conveniently close to customers, e.g., in the North Sea and the Gulf of Mexico, for the gas to be delivered by pipeline. The result is that much of the developed world has now adopted gas as the preferred fuel for space heating and cooling, for use in industry and for electricity generation. Starting with wood (a form of biomass), mankind has moved to fossil fuels – first to coal, then to petroleum and latterly to natural gas – to provide the energy needed by society. Electricity also is a useful, but secondary, form of energy since it is manufactured from primary energy sources. In the mid-1950s, commercial nuclear power was added to the range of primary energy sources.
Fossil fuels are laid down over geological time and, once used, cannot be replaced on any realistic time-scale. These fuels represent the world's energy capital. By contrast, many renewable (sustainable) forms of energy, i.e., those derived from wind, solar or marine (tidal, wave, ocean) sources, must be used as they are produced; otherwise, they are wasted. Other 'renewables' may have some storage element associated with them: biomass can be stored for short periods, while hydro energy is contained in mountain lakes or reservoirs held back by dams. Geothermal energy, like fossil fuels, is retained underground until it is required. Renewables comprise the world's current account in energy. As in financial matters, where it is easier to raid the capital account than work hard to earn money for the current account, so it is easier and cheaper to dig or drill for fossil fuels than it is to extract useful energy from renewable sources. In essence, although renewable energy is widely available, the world faces major problems in harnessing this resource — many of the forms of this energy are small-scale, diffuse and, as yet, hardly cost-competitive with fossil fuels. Moreover, those that generate electricity directly have no storage component.
Most authorities attribute the rise in the mean global temperature over recent years to the combustion of fossil fuels that has grown steadily since the Industrial Revolution. The concentration of carbon dioxide in the atmosphere has risen steadily from 280 — 300ppmv in the 18th century to 360 — 380ppmv today, an increase of around 25%. Carbon dioxide is known to absorb infrared radiation re-emitted from the Earth and is a principal 'greenhouse gas'; see Section 1.2. The progressive move from coal to oil and then to natural gas represents 'decarbonization' of fuels and is desirable in that it results in less carbon dioxide release per unit of energy produced. Natural gas (methane) has four atoms of hydrogen per carbon atom and is the limit of decarbonization without going all the way to hydrogen, which is obviously a carbon-free fuel; see Figure 1.1. The idea of introducing hydrogen as the universal vector for conveying renewable forms of energy, and also as the ultimate non-polluting fuel, is encapsulated in idealized form in Figure 1.2. This proposition is commonly known as the 'Hydrogen Economy'. The upper part of the diagram is generally referred to as the transitional phase, during which hydrogen is produced from fossil fuels; the lower part relates to the long-term, post fossil-fuel, age when hydrogen will be manufactured from renewable energy sources and used as a storage medium and as a super-clean fuel.
There is, however, a problem with the concept of a sustainable Hydrogen Economy. Within our present span of vision, renewables alone do not afford a path to a carbon-free future because they are difficult to harvest on a large scale and, as noted above, breakthroughs in cost must be achieved if these sources are to supplant fossil fuels and become commonplace. Also, there is often local opposition to the construction of renewable facilities such as hydroelectric dams or wind generators, which may spoil areas of scenic beauty or interfere with natural habitats. The counter proposition of increasing the deployment of nuclear power, which is not usually regarded as renewable energy but at least is carbon-free, is unpopular in many quarters because of concerns over radioactive waste. Nevertheless, some countries already rely on nuclear power to provide an appreciable percentage of their domestic electricity requirements, e.g., France (78%), Sweden (46%), Ukraine (45%) and Korea (36%).
Hydrogen is the most abundant element in the universe. It is a major component of stars, including the Sun, whose heat and light are produced through the nuclear-fusion process that converts hydrogen into helium. Elemental hydrogen does not occur in significant amounts on Earth and energy has to be supplied in order to extract it from water or fossil fuels. Hydrogen is therefore not a primary energy source but a secondary energy vector. Energy from primary sources can be stored in hydrogen by decomposing water using chemical, thermal or electrical energy.
The various primary energy sources that can be used for the production of hydrogen and potential applications for this energy vector are summarized schematically in Figure 1.3. In the near-term, it is probable that hydrogen will, as now, be derived principally from fossil fuels, since this is the most economic route.
Economic development and poverty eradication depend on secure and affordable energy supplies. Although reserves of conventional oil and gas are diminishing relatively rapidly, other fossil fuels (heavy oils, tars, coal) are widely distributed and can meet the need for energy security in the medium-term, even though they are environmentally challenging and more costly to process. Technology, driven by the right incentives, offers possible answers to the environmental problems. For example, 'clean coal technology' (see Section 2.7, Chapter 2) is designed to use coal in a more efficient and cost-effective manner while enhancing environmental protection through the capture and storage of emissions, principally carbon dioxide.
As an energy-storage medium that is manufactured from a primary energy source, hydrogen may be used to convey energy to where it may be utilized. In this respect, it is analogous to electricity, which is also a secondary form of energy. Hydrogen and electricity are complementary: electricity is used for a myriad of applications for which hydrogen is not suitable, whereas hydrogen, unlike electricity, has the attributes of being a fuel and an energy store. These two energy vectors are, in principle, inter-convertible; electricity may be used to generate hydrogen by the electrolysis of water, while hydrogen may be converted to electricity by means of a fuel cell. It should be noted, however, that such electrochemical devices are less than 100% efficient and there is a significant loss of useful energy in the inter-conversion. Nevertheless, as discussed in Chapter 6, the realization of a Hydrogen Economy is linked irrevocably with that of the fuel cell.
Many forms of renewable energy are manifest as electricity, which is used immediately it is generated. For applications that require a portable fuel (e.g., road transportation), it would be necessary to convert this form of renewable energy to a chemical fuel, for example methanol or hydrogen, which could be used in an internal combustion engine or re-converted back to electricity in a fuel cell to drive an electric vehicle. In energy terms, this would be a grossly inefficient process and uneconomic under most conditions. Generally, it would be better to utilize electricity derived from renewables directly since the energy lost in local distribution of electricity is comparatively small. There may, however, be exceptions to this rule. One situation might be on islands or in isolated communities where there is plenty of renewable energy in the form of wind or solar electricity, but no means of storing it from times of surplus to times of peak demand. Hydrogen could then provide an energy store and later be reconverted to electricity, although this approach to storage would be in competition with batteries or standby diesel generators. Another exception might be in countries such as Norway or Iceland, where there is an abundance of cheap hydro or geothermal electricity, some of which could be converted to hydrogen for use in road vehicles, ships, etc. Ultimately, when fossil fuels are really scarce and expensive and when renewable energy technology has become economically competitive, it may prove practical on a much wider basis to convert renewable electricity to hydrogen fuel. But that day may yet be distant. The International Energy Agency (IEA) has forecast that renewables (excluding nuclear and hydro) will still account for only 10% of world energy supply by 2030; of this, more than half is expected to be derived from biomass. Meanwhile, it is perfectly feasible to manufacture hydrogen from all types of fossil fuel and this is likely to be the route forward in the medium-term to a sustainable future, always provided that technologies for carbon capture and storage become available; see Chapter 3.
Before embarking on a discussion of hydrogen production and utilization (in later chapters), it is pertinent to consider the forces that drive the present international push for hydrogen energy and why it is that many people view the Hydrogen Economy as the fulfilment of an environmental dream for the long-term future. The four key 'drivers' are:
• national security of energy supplies;
• climate change (global warming);
• atmospheric pollution;
• electricity generation.
These drivers, which are examined in detail below, are inter-related in a complex fashion in an increasingly complex world. First, however, we should consider briefly the many obstacles that have to be surmounted before a Hydrogen Economy can become a reality. The obstacles fall into a number of different categories, as follows:
Institutional
• the difficulty in a free market of building and sustaining consensus on a long-term energy policy for a nation;
• the short time horizon of many politicians and much of industry;
• the inflexibility of the existing energy infrastructure and the long time-scale associated with effecting major changes to energy supply and usage;
• the lack of a hydrogen infrastructure and the huge cost of introducing one;
• the large scale of hydrogen production required to make a national impact and the inability of present-day electrolyzers even to approach this scale;
• the small-scale and present cost of generating electricity from most renewable forms of energy;
• the little near-term market demand for hydrogen as a fuel.
Technical
• technological barriers associated with the production, distribution and utilization of hydrogen – starting from coal and lower-grade fossil fuels with capture and storage of the carbon released as carbon dioxide;
• the problems of producing hydrogen efficiently and affordably using clean technology;
• the lack of a satisfactory hydrogen-storage medium, particularly for mobile applications (vehicles);
• the present limited performance, reliability and lifetime of fuel cells especially for mobile applications.
Regulatory
• concerns over the safety aspects of hydrogen installations and, in the case of vehicle refuelling, possible widespread use by the general public;
• the absence of internationally consistent codes and standards to ensure hydrogen safety and to facilitate its commercialization;
• the task of training and certifying mechanics, technicians and others involved in implementing hydrogen energy.
Financial
• the requirement for huge amounts of capital, including risk capital, to establish a hydrogen infrastructure;
• the need to reduce system costs to compete with traditional fuels and, for mobile applications, with internal combustion engines;
• the present high cost of fuel cells, particularly when compared with engines.
These barriers present a formidable challenge and it is necessary to develop a strategy for an integrated approach to overcoming them. Whilst petroleum and natural gas remain widely available and relatively inexpensive, it will prove difficult for hydrogen energy to compete on a favourable cost basis. Competition will be possible if/when premium fossil fuels fail to meet market requirements and become very much more expensive, or when concern about climate change leads to the introduction of high taxes for the liberation of carbon dioxide into the atmosphere. The various impediments to the introduction of hydrogen, as listed under the above four broad categories, must always be borne in mind when proposing hydrogen as a universal solution to present-day energy problems.
1.1 Security of Energy Supplies
The total primary energy supply throughout the world has increased from 6035 Mtoe in 1973 to 11 059 Mtoe in 2004, a rise of 83% in 31 years, and is projected by the IEA to reach 16 500 Mtoe by 2030, a further 49% on the 2004 level; see Table 1.1. This increase is a result of growth in the world population and a general rise in prosperity. There is a well-established link between the gross domestic product (GDP) of a nation and its energy consumption, although nations are now trying hard to break this link.
The growth in demand for different fuels and energy sources from 1973 to 2002 and projected through to 2030 is plotted in Figure 1.4. It is expected that fossil fuels will account for most of the increase in energy supply between 2002 and 2030. These data demonstrate the magnitude of the task facing mankind and the time-scales involved in substituting renewable, sustainable energy for a significant fraction of the fossil fuel consumed.
In looking ahead to 2030, it is predicted that the percentage of the world energy market supplied by oil will not change greatly with respect to that of 2002. By contrast, in percentage terms: gas will rise, coal will decline slightly and nuclear will fall significantly as old nuclear stations are retired and not replaced. In many ways, these forecasts are counter-intuitive, in the light of declining reserves of oil and gas and the economic growth of China and India with their vast reserves of coal. They are, however, the considered view of the IEA, the world's leading authority, and reinforce the competition bound to be faced by renewable forms of energy and the difficulty of introducing the Hydrogen Economy on this time-scale. Naturally, these projections to 2030 are only forecasts, albeit made by experts, and may be proved wrong by future events.
Many geologists and petroleum engineers are of the opinion that the Earth's ultimate reserves of petroleum are around 2 × 10 12 barrels, of which over 40% has been used already. The concept of 'reserves' is open to debate and some authorities opt for 3 × 1012 barrels. Nevertheless, it is claimed that over 90% of all available oil has been discovered and mapped. Some important oil-producing regions (e.g., USA, North Sea) have passed their peak production rates and are in decline; others are expected to peak within 10 years; see Figure 1.5. Moreover, the rate at which oil is being pumped (28 × 10 barrels in 2003) greatly exceeds the rate at which new reserves are found.
Even when new oil fields have been identified, substantial investment of time and money is required, particularly offshore in deep water, before extraction can begin. It is important to distinguish between reserves in place and excess production capacity available at short notice. Among the major producing countries, only Saudi Arabia has excess capacity (about 3 × 10 barrels per day ~4% of world consumption) that could be brought into use quickly. Elsewhere, the exploitation of fresh reserves will require substantial investment and concern has been expressed that the necessary capital may not be available.
(Continues...)
Excerpted from Hydrogen Energy by D.A.J. Rand, R.M. Dell. Copyright © 2008 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Table of Contents
Why Hydrogen Energy?; Hydrogen from Fossil Fuels and Biomass; Carbon Sequestration; Hydrogen from Water; Hydrogen Distribution and Storage; Fuel Cells; Hydrogen-fuelled Transportation; Hydrogen Energy: The Future?What People are Saying About This
This is an excellent text, which gives a comprehensive description of the technologies associated with the introduction of the hydrogen economy and more importantly a similarly comprehensive and balanced coverage of the complex and often contradictory issues surrounding hydrogen energy. Written at a level that has something for everyone. The Book is more than just a text, it is a wide ranging analysis of the twin issues facing the global energy industry. I urge everyone who has an interest in energy or hydrogen, from student to policymaker to read this book. I certainly learned a great deal from reading it, in fact i wish i had written it.