Hydrogen technology for energy needs of human settlements

Int. J. Hydrogen Energy, Vol. 12, No. 2, pp. 99-129, 1987.

0360 3199/87 $3.00 + 0.00 Pergamon Journals Ltd. © 1987 International Association for Hydrogen Energy.

Printed in Great Britain.

H Y D R O G E N T E C H N O L O G Y FOR E N E R G Y NEEDS OF H U M A N SETTLEMENTS* T. NEJAT VEZIRO~LU

Clean Energy Research Institute, University of Miami, Coral Gables, FL 33124, U.S.A.

(Receivedfor publication 17July 1986) Abstract--Hydrogen is being considered as a synthetic fuel or energy carrier for the post-fossil fuel era. It has many properties to commend itself: it compliments the nonconventionalprimary energy sources and presents them to the consumer in a convenient form; it is relatively inexpensive to produce; it can be converted to various energy forms at the consumer end with higher efficiencies than other fuels; it is renewable; and it is the lightest and cleanest fuel. It can be used in every application where fossil fuels are used today, including meeting the energy requirements of human settlements, such as cooking, water and space heating, cooling and refrigeration, lighting, powering farm implements and transportation,and electricity generation. In all these applications, it is superior to conventional fuels and other synthetic alternatives. There are already demonstration projects to show the applications of hydrogen in the domestic and transportation sectors of human settlements.

Therefore, it becomes necessary to find an intermediary or synthetic form of energy which can be produced using the nonconventional primary energy sources being considered. Many scientists and engineers believe that a hydrogen energy system could form the link between the new energy sources and the user. It is the most economical to produce, the cleanest fuel and recyclable. In the hydrogen energy system, it is envisaged that hydrogen will be produced from the new nonfossil energy sources, and will be used in every application where fossil fuels are used today, including the energy requirements of human settlements. In this system hydrogen is not a primary source of energy. It is an intermediary form of energy, a secondary form of energy, or an energy carrier. This is not a new concept. More than a hundred years ago, Jules Verne, the great French visionary, through one of the characters in his book, The Mysterious Island [2] was s a y i n g " . . , water decomposed into its primitive e l e m e n t s . . , and decomposed doubtless, by electricity, which will then have become a powerful and manageable force, . . . I believe that water will one day be employed as a fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable. Some day the coalrooms of steamers and the tenders of locomotives will, instead of coal, be stored with these two condensed gases, which will burn in the furnaces with enormous caloric power . . . I believe, that when the deposits of coal are exhausted, we shall heat and warm ourselves with water. Water will be the coal of the future." Hydrogen has the most desirable properties for a fuel. It is the lightest and the cleanest fuel. It can be converted to other forms of energy more efficiently than other fuels. It is also the most abundant element in the universe. Many stars and planets are either entirely made up of hydrogen, or contain large percentages of it.

1. I N T R O D U C T I O N Today, one quarter of the world's population, those living in the industrial countries, consume about three quarters of the world energy production. In other words, the peoples of the industrial countries have higher living standards than those of the rest of the world (i.e. the developing countries), since the gross national product per capita--which is a measure of the standard of living--is directly related to the energy consumption per capita as seen from Fig. 1 [1]. The peoples of the developing countries are aspiring and trying to improve their living standards, and hence increase their energy consumption. Presently, the earth's population is about 4.7 billion and is growing at the rate of 1.8% y-1. On the other hand, the demand for energy is growing at a much higher rate (at about 8-10% y - l ) , since the developing countries are trying to increase their energy consumption faster than the industrialized countries. Today, most of this energy demand is met by fossil fuels (i.e. coal, petroleum and natural gas). On the other hand, it is estimated that the world fossil fuel production, beginning with petroleum and natural gas, will soon start declining. Nonconventional energy sources such as solar, ocean thermal, wind, waves, thermonuclear, geothermal etc., are being considered as possible sources of energy to meet the growing demand. However, none of these new energy sources have all the desirable qualities of petroleum and natural gas. For example, some are only intermittently available, others are only available away from the consumption centres, and none can be used as a fuel for transportation.

* Presented at the United Nations Centre for Human Settlements (HABITAT) Ad Hoc Expert Group Meeting, Bangalore, India, 16-19 June 1986. 99

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Fig. 1. GNP per capita vs energy consumption per capita (1974 data). For example, the most abundant element in the sun is hydrogen. The sun's energy is produced by the fusion of hydrogen atoms or nuclei into helium. The planet Jupiter is made up of liquid and solid hydrogen. Even the interstellar space contains about 1 hydrogen molecule cm -3. On the other hand, on earth hydrogen is not abundant as a free element. It is found in natural gas in small percentages. It forms 0.2% of the atmosphere. These are very small quantities compared to the fuel needs of the world. Therefore, hydrogen must be manufactured using some primary energy source if it is to meet our fuel needs. 2. FOSSIL FUELS A N D T H E I R L I A B I L I T I E S Presently most (about 80%) of the world energy demand is met by fossil fuels. However, according to reliable estimates [3-5], the production of the fossil fuels will soon start decreasing. Figure 2 shows the projected production rates of world fossil fuels. The lower line estimates coal production if it is used as solid fuel. The middle curve is the expected rate of production of fluid fuels--petroleum and natural gas. World fluid fuel

production will reach its peak around the year 2010, and then will start decreasing. The higher curve gives the total fossil fuel production estimates, if synthetic gas and gasoline produced from coal become available. In this case, production will rise until the year 2030, and then start decreasing. The combustion products of fossil fuels are damaging the Earth's climate and environment as outlined in many recent reports, articles and books [6-30]. A n important type of pollution, air pollution, is caused mainly by fossil fuels used to obtain energy for transportation, electricity production, heat generation etc. Because of this, in the larger cities of the world, respiratory diseases are increasing and the life span is decreasing. This year alone fossil fuels will be spewing some 30 billion tons of CO2, CO, SO2, NOx, soot and ash into the atmosphere. Acid rains produced by fossil fuels are literally killing our lakes. Fish and aquatic plants can no longer live in the lakes of the Adirondack Park in northern New York state, because of the high level of acidity accumulated due to acid rains. The same thing is happening to the lakes of Canada and Sweden. Of course, acid rains do not fall over the lakes and oceans alone. They fall on our lands and cities as well. Studies show that acid rains are

HYDROGEN TECHNOLOGY FOR HUMAN SETTLEMENTS

101

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2

p-

Z O p-

o

!

t980

I t980

2000

2020

2040

CALENDAR

YEARS

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2080

2100

Fig. 2. Projected rates of production of world fossil fuels.

reducing farm and forestry products, and adversely affecting their quality. Acid rains also attack buildings and structures, causing corrosion and erosion. The damage to irreplaceable historical monuments may not be remediable at any cost. For a long time, one of the main combustion products of fossil fuels, CO2, was thought to be harmless. A recent report by Seidel and Keyes [31] blames it for the so-called "greenhouse effect". It says that the Earth's temperature has begun to rise and will continue to do so at an increasing rate. By the year 2050, it predicts mean temperature increases of 3-9°C, with the larger increases occurring in the polar regions. The report claims that this warming trend would begin altering the Earth's climate by the early 1990s. Consequently, the deserts would extend to both North and South, while agricultural lands would be displaced in the same directions and would shrink in size. Another important consequence of the rising temperatures would be the accelerated melting of the polar ice caps. As a result, sea levels would be likely to rise by 1--4 m by the year 2100, and low-lying areas of the globe--ports, coastal cities and plains--would be flooded. In addition to their environmental transgressions, fossil fuels have another fault. They are not distributed evenly among the countries of the world. This unequal distribution, together with the addiction to petroleum, is causing international problems between the suppliers of

petroleum and the consuming nations, and an increasingly intense rivalry among the super powers in their attempts to safeguard their energy supplies in the form of petroleum. The World is viewing the armed conflict in the Persian Gulf region with apprehension. Because of the large petroleum reserves of the Gulf, and the desires of the super powers to control these, the current armed conflict in the Middle East could trigger another world war. The development of nonconventional energy sources will remove this important cause of conflicts, because they are distributed more evenly around the world, and each country has one or more of the nonconventional energy sources available to meet its requirements almost indefinitely. When we consider all the detrimental effects and liabilities of petroleum and other fossil fuels, one begins to think that we are fortunate to be running out of them. If there were an interminable supply of fossil fuels, we would eventually turn this planet into a desolate graveyard. 3. N O N C O N V E N T I O N A L E N E R G Y SOURCES A N D T H E I R SHORTCOMINGS In order to make up for the depletion of fossil fuels and meet the growing world energy demand, several alternative and nonconventional primary energy sources

102

T. NEJAT VEZIRO(3LU

are being considered and researched by scientists [3240], such as direct solar radiation, wind energy, ocean thermal energy, nuclear breeders, fusion reactors and geothermal energy. It may be necessary to make use of several of these primary energy sources. Of course, they do not all have to be used at the same time and/or place. Depending on the economics and availability, different mixes of the primary energies may be used in different parts of the world through different time periods. Fossil fuels on the other hand have some very useful properties, which are not all shared by nonconventional energy sources. They possess concentrated energy. They are relatively light for the amount of energy contained in them. They can be transported easily using pipelines, railcars, tankers and/or trucks. They are storable. They can be stored for long periods of time without any change in their properties. However, as outlined before, fossil fuels are not renewable. It has taken nature millions of years to produce the fossil fuels which we will be consuming in one century or so. The nonconventional energy sources, which are being considered, do not possess all the advantages of fossil fuels, although some of them, such as solar, wind and ocean-thermal, are almost unlimited and are environmentally compatible. Some are only intermittently available. For example, solar energy is only available in the daytime when the skies are clear. Even then, the intensity of solar radiation is subject to diurnal and seasonal changes. Hence, solar energy needs to be stored to meet the demand when solar radiation is not available. Some of the new energy sources are continuously available, but they are too far away from the consumption centres. For example, the best oceanthermal energy sites are the equatorial regions of the oceans. I n the case of nuclear power plants, because of the potential danger from radioactivity, it would be better to locate them away from the cities or the consumption centres. None of the new energy sources mentioned can be used as fuel for transportation with, perhaps, the exception of nuclear energy. Nuclear energy is being used to power some ships. However, it has not, as yet, proved itself commercially. None of the new energy sources, with the exception of nuclear, is transportable or storable by itself. Some are not pollution free, such as geothermal which brings out chemical pollutants, and nuclear which produces thermal pollution and radioactive waste.

4. H Y D R O G E N E N E R G Y SYSTEM The above mentioned shortcomings or drawbacks of the nonconventional energy sources point to the need for an intermediary energy system to form the link between the new primary energy sources and the energy consuming sectors or the user. In such an intermediary system, the intermediary energy form or carrier must be transportable and storable; economical to produce; and renewable and pollution free, if possible. It ought to be

independent of the primary energy sources used, so that even if the primary nonconventional energy sources are changed from time to time, the intermediary energy system remains intact. This would have the advantage of keeping the storage and transmission systems and conversion devices running on the intermediary (synthetic) fuel the same, even though the primary energy sources may have to be changed with geographic location and time. All the synthetic fuels (hydrogen, methane, methanol, ethanol, ammonia, hydrazine etc.) are candidates for the intermediary system. Among these, hydrogen meets the above prerequisites best. It is plentiful in the form of water in oceans, lakes and rivers. It is the cheapest synthetic fuel to manufacture per unit of energy stored in it. It is almost pollution free, or the least polluting of all of the synthetic fuels. Over the last decade there have been increasing research efforts to investigate the various aspects of the hydrogen energy system and its implications. Most of the research results have been presented in the proceedings of The Hydrogen Economy Miami Energy (THEME) Conference [41] and in those of the five World Hydrogen Energy Conferences [42-46] held to date. Books and reports by Bockris [47], Veziro~lu [48], Ohta [49], Williams [50] and Skelton [51] cover hydrogen production methods and utilization in some depth. Table 1 compares hydrogen (both liquid and gaseous) with gasoline and natural gas. A study of the table shows that for a given amount of energy, hydrogen weighs about one-third of the fossil fuels. But it is bulkier; for a given amount of energy, hydrogen in liquid form occupies 3.8 times the volume occupied by gasoline, and in gaseous form it occupies 3.6 times the volume occupied by natural gas. However, in practice this volume penalty is 20-50% less, since hydrogen can be converted to other forms of energy at the user end more efficiently than fossil fuels. Its high flame speed and wide flammability limits make hydrogen a very good fuel for internal combustion engines, gas turbines and jet engines. High ignition temperature and low flame luminosity make hydrogen a safer fuel than others. It is also nonpoisonous and recyclable. Figure 3 shows the proposed hydrogen energy system, forming the link between the nonconventional energy sources and the user [52, 53]. Hydrogen is produced from water using one or more of the nonconventional primary energy sources. During the changeover period, coal, a relatively abundant fossil fuel, could also be used for hydrogen production with some environmental benefits. Hydrogen can be produced by four main methods: (1) the direct thermal method, (2) the thermochemical method, (3) electrolysis and (4) photolysis. As a result of using one of these methods, water is separated into its elements, hydrogen and oxygen. Hydrogen is then transported, stored and distributed to energy consumption sectors, where it is used in every application of fossil fuels, with the exception of cases where carbon is specifically needed. After use as fuel, hydrogen turns into water vapor (by combining with oxygen)

103

H Y D R O G E N TECHNOLOGY FOR HUMAN SETI'LEMENTS Table 1. Properties of gasoline, natural gas and hydrogen Property

Gasoline

Natural gas

Hydrogen

Density (g cm -3)

0.73

0.78 x 10 3

Boiling point (°C) Lower heating value: gravimetric (kJ kg -1) volumetric (kJ m -3)

38/204

- 156

0.84 × 10 4 (gas) 0.71 x 10 -1 (liquid) -253 (20 K)

4.45 x 104 32.0 × 106

4.8 x 104 37.3 x 103

Stoichiometric composition in air (vol. %) Flammable limits (% in air) Flame speed (m s -1) Flame temperature in air (°C) Ignition temperature (°C) Flame luminosity

1.76

9.43

12.50 x 104 10.4 x 103 (gas) 8.52 x 106 (liquid) 29.3

1.4-7.6 0.40 2197 257 high

5-16 0.41 1875 540 medium

4-75 3.45 2045 585 low

1

THE HYDROGEN ENERGY SYSTEM

3

PRODUCTION

USE

2b S T O R A G E WATER

2

PRESSURIZEDGAS STORAGE

DELIVERY

METAL HYDRIDE STORAGE FOSSIL ENERGY

2a T R A N S P O R T

I

ELECTRICAL UTILITY

0

COMMERCIAL AND RESIDENTIAL

VEHICULAR TRANSPORT

NUCLEARENERGY

O

SOLAR ENERGY

CRYOGENIC STORAGE

HYDROGEN (AND OXYGEN) TRANSPORTATION

_

_

j

-

-

PIPELINE TRANSMISSION INDUSTRIAL

GEOTHERMAL ENERGY

qW" UNDERGROUND(AND UNDERWATER) STORAGE

Fig. 3. Hydrogen energy system.

WATER

104

T. NEJAT VEZIROOLU

which is recycled back to earth as rain. The oxygen produced could either be released into the atmosphere, or shipped or piped to industrial and city centres for industrial use and also for rejuvenating the polluted rivers and lakes, and in speeding up sewage treatment. Hydrogen is a very efficient energy carrier. For distances greater than 400 miles, it is cheaper to transmit energy as hydrogen through pipelines than as electricity via overhead lines. In addition, hydrogen pipelines would need very little right-of-way, take up no land area, and do away with unsightly electricity transmission lines and towers. Also, hydrogen is storable while electricity is not. In the hydrogen energy system, it is envisaged that from the production plants or the ports, hydrogen will be transmitted by means of underground pipelines to industry, buildings and homes. There, hydrogen can be used directly for industrial processes needing heat, and for space heating and cooking. For example, the combustion of hydrogen produces steam, which is used in many industries such as the paper and chemical industries. This is an elegant and efficient way of obtaining steam. Hydrogen can be used in the smelting of iron, in lieu of coal, with untold environmental benefits. The electricity needs of industry, buildings and homes can be met by fuel cells, in which hydrogen and oxygen combine, and produce electricity. Today, the conversion efficiency is of the order of 50-70%. It is expected that this figure will be improved upon with further research. Because of its ideal properties as a fuel and its lightness, hydrogen is a very good fuel for transportation. In internal combustion engines, it can be converted to mechanical energy with higher (15-20%) efficiency than fossil fuels. Additionally, hydrogen-fueled engines do not need pollution control devices and as a result conserve more energy. Because hydrogen is so much lighter than jet fuel, it considerably reduces the take-off weight of airplanes and consequently decreases the fuel consumption. With hydrogen, all the objections to supersonic transport are eliminated: there will be no damage to the ozone layer since the combustion product is water vapor, the engines will be quieter since they will be smaller, and the passenger per mile cost will be less due to energy conservation. The nonconventional energy sources are distributed more evenly around the world than fossil fuels. Each country has one or more of the nonconventional energy

sources available to it. Consequently each country will be able to produce the fuel it needs as hydrogen, using the nonconventional energy source(s) it has. As a result, an important cause of international conflicts, that of energy sources (petroleum) being concentrated in a few regions of the world, will be removed, and each country will be able to speed up its economic development by producing the fuel it needs.

5. SYNTHETIC FOSSIL FUELS VS H Y D R O G E N Those who desire continuation of the present fossilfuel system claim that synthetic gasoline (or SynGas) and synthetic natural gas (or SNG) could be manufactured through use of the vast deposits of coal, oil shale, and tar sands, or even of CO2 from air and from limestone, when we run out of petroleum and natural gas. Consequently, hydrogen (gaseous and liquid) will be compared with synthetic natural gas and synthetic gasoline from the viewpoint of real economics, i.e. by taking into account production costs, utilization efficiencies and environmental effects, as well as such factors as resource conservation, transportation and capital investment [54, 55]. 5.1. Production costs

The production costs of interest here are for the large-scale production of the synthetic fossil fuels and hydrogen, so that they may meet large-scale demands. Hydrogen can be produced by several methods, using various primary energy sources. Amongst the methods are electrolytic, thermal, thermochemical, photolytic and various "hybrid" methods. Any one of the primary energy sources, including the fossil fuels, can be used as the energy source for the production of hydrogen. As the post fluid fossil fuel era is under consideration, the main fossil, fuel resource of interest would, of course, be coal. Table 2 presents the averages of large-scale production costs taken from recent literature [56-73]. In the case of hydrogen, costs are classified by the primary energy source used in production, namely coal, hydropower and others (direct solar, wind, ocean thermal, nuclear etc.), as the estimated prices also group according to this classification. All the dollar values have been

Table 2. Estimated average production costs of synthetic fuels Synthetic fuel

Estimated average Estimated average gaseous fuel cost liquid fuel cost (1986 US$ GJ -1) (1986US$ GJ -1)

Coal H 2 7.19 Hydropower H z 9.65 Other (solar, wind, nuclear etc.) H218.13 Synthetic fossil fuels 7.42 (SNG)

8.99 12.06 22.66 14.47 (SynGas)

HYDROGENTECHNOLOGY FOR HUMAN SETI'LEMENTS

105 o'

brought up to 1986 US$ by assuming an average annual inflation of 8% through 1984 and 4% between 1984 and 1986. Although gaseous hydrogen can be used in most of the applications where gaseous or liquid (and solid) fossil fuels are currently being used, there are some applieations where liquid hydrogen must be used, e.g. in rocket engines for space travel and in jet engines for air transportation. Consequently, prices of liquid hydrogen must also be considered. If conventional liquefaction methods are used, the price has to be increased by about 50% [74] over that of gaseous hydrogen. However, a revolutionary liquefaction process (magnetic liquefaction) is being developed at the Los Alamos National Laboratory [75], which has a circuit efficiency of 60% as compared with only 30% in conventional systems. Preliminary studies show that the magnetic liquefaction process will need less capital investment and less maintenance than conventional systems. It then becomes reasonable to assume a 25% add-on for liquid hydrogen produced by the new method, which could be available in the 2000s. As can be seen from Table 2, the estimated production costs of coal GH2 (gaseous hydrogen) and coal LH2 (liquid hydrogen) are lower than those for the synthetic fossil fuels, while both GH2 and LH2 from other energy sources are more expensive than the corresponding synthetic fossil fuels. In the case of hydropower hydrogen, GH2 is more expensive than SNG, but LH2 is cheaper than SynGas.

efficiencies in the stop-start type city driving as compared with fossil fuels which can only burn in rich mixtures. Hydrogen can be converted to electricity in fuel cells with much greater efficiencies [60] than is possible in thermal power plants using fossil fuels. While conversion efficiencies for the latter are in the range of 35-38 %, practical efficiencies in hydrogen fuel cells are 50-70%. In the advanced hydrogen fuel cells which are now being developed, it is expected that efficiencies will rise to 80-90%. This is an important, unique property of hydrogen, which can also increase the conversion efficiencies in transport vehicles. Even if the end use required mechanical power (such as in automobiles, buses or trucks), hydrogen fuel cell/electric motor combinations would yield far greater conversion efficiencies than an internal combustion engine running on fossil fuels. Via a fuel cell/electric motor system, hydrogen can be converted to mechanical power more than twice as efficiently as gasoline or diesel fuel. In some industrial, commercial and residential applications, such as in heating and cooling, fuels are converted to thermal energy. Experiments [82, 83] show that hydrogen can be converted to thermal energy 24% more efficiently than fossil fuels. Gas-turbine electric power plants using liquid hydrogen may have favorable efficiency benefits if cryogenic energy of LH2 is converted to useful work [84]. Using the above-described efficiency advantages of hydrogen over fossil fuels, Table 3 has been constructed. On the left-hand side, it starts with 1000 units of synthetic fossil fuel energy to meet the demands of the four main world energy-consuming sectors, namely 5.2. Utilization efficiencies transportation, commercial, industrial and residential. In comparing the fuels, it is important to compare the It then divides into sub- and sub-sub-sectors. It also gives utilization efficiencies at the user end. For utilization by the units of fossil fuel energy needed by each sector and the user, fuels are converted to various energy forms, its components. The efficiency advantages of hydrogen such as mechanical, electrical and thermal. Studies show over fossil fuels are given in the middle column, with the that in almost every instance of utilization, hydrogen can corresponding references in the next column. The be converted to the desired energy form more efficiently following column lists the units of hydrogen energy than the fossil fuels (or the synthetic fossil fuels). In necessary to produce the same end work as the fossil other words, conversion to hydrogen would result in fuels. The final column is the overall summation of the energy conservation owing to its higher utilization hydrogen energy units required by each of the sector efficiencies. components. As can be seen from the final column, 736 Investigations [76] show that, for a given number of units of hydrogen energy will suffice to do the same work passengers and a given payload, a subsonic jet passenger as 1000 units of fossil fuel energy. In other words, when airplane would use 19% less energy, if it were to use all the applications are considered, hydrogen is about hydrogen (liquid) instead of fossil-based jet fuel. In the 26% more efficient than fossil fuels. case of a supersonic jet plane, the efficiency advantage of hydrogen is even greater [77]; it is 38% better than jet fuel. 5.3. Environmental damage Research workers [78-81] have reported a wide range In calculating the cost of fuels to society, their (22~50%) of utilization efficiency advantages for hydrogen use in existing automobile internal combustion environmental effects and damages must be considered. (IC) engines. The wide variation in the reported efficien- Investigations are being conducted in many parts of the cies emanates from the fact that the lower figure applies world to estimate those damages. Effects of fossil to the engine alone, while the higher figure applies to the fuel-produced acid rains and COz on the environment automobile under city driving conditions. As hydrogen were discussed earlier in this paper. Pollution elements can burn in lean fuel/air mixtures as well as in rich have many dangerous effects on human beings [85]. mixtures, it can cause large improvements in fuel-use They cause heart disease, strokes, acute respiratory

T. NEJAT VEZIRO(3LU

106

Table 3. Utilization efficiency comparison between fossil fuels and hydrogen

Energy sector

Fossil energy consumption by sector (Arbitrary units) I

/

Transport

250

"~

L Industrial

Commercial

Residential World totals:

300

150

300

End-use energy form/ sub-sector Road (IC engine) Road (fuel cell) Rail (fuel cell) Sea (IC engine) Sea (fuel cell) Air (subsonic) Air (supersonic)

Fossil energy consumption by end-use (Arbitrary units)

He energy consumption I-I2 efficiency by end-use advantage (Arbitrary 100(r/s-rh)/7/e units) (Percentage) Reference

120

22

[81]

99

25

133

[60]

11

15

84

[60]

8

25

22

[81]

21

15 25 25

84 19 38

[60] [76] [77]

8 21 18

Heat Electricity (fuel cells)

250

24

[83]

145

50

84

[60]

65

Heat Electricity (fuel cells)

110

24

[83]

89

40

84

[60]

22

Heat Electricity (fuel cells)

250

24

[83]

202

50

84

[60]

27

H2 energy consumption by sector (Arbitrary units)

186

210 ~ 111

229

1000

infections, chronic respiratory infections, tissue destruction and cancer. Carbon monoxide, absorbed in red blood cells (forming carboxyhaemoglobin), affects a person's ability to coordinate his or her activity. The traces of lead in blood cells of children were found to be closely correlated with the amount of lead in gasoline. If inhaled for long periods---particularly in large concentrations---gasoline vapors can have damaging effects on the brain. Also to be considered are accidental suffocations, poisonings caused by CO emissions in confined spaces and loss of work days [86-88]. Although human diseases caused by pollution are costly in terms of medical care and treatment expenses, these expenses do not cover the mental damage, human discomfort and unhappiness that may be involved. Oil spills in seas and oceans by various kinds of ships, and particularly those caused by tanker accidents, pollute the waters and shores causing costly damages. The oil spill from the tanker Amoco Cadiz, which in 1978 ran aground off the coast of Brittany while carrying 60 million gallons (some 228 million 1) of crude oil, caused damages in the neighborhood of $1.5 billion [12]. Another disaster, in November 1982, of the Globe Asimi while carrying 4.8 million gallons (some 18 million 1) of boiler fuel off the Baltic Sea coasts of the Soviet Union, is reported to have cost $900 million. Accidents occurring at off-shore oil rigs also produce substantial

736

pollution, while ballast water habitually discharged by tankers is another menace. Also, fresh water resources suffer [89J--mainly because of acid rains. Strip mining is yet another culprit, damaging farmlands and forests. It is reported by Taylor [28] that the U.S. Government will have to spend $19 billion (in 1982 dollars) in the period 1980-89 for land reclamation. This amount is apparently needed to correct the damages caused by strip mining. Additionally, it is estimated that, during the same period, an equal amount will be similarly spent by industry. Detailed estimates of the fossil fuel damage on various elements of the Biosphere are presented in Table 4. The table indicates the type of damage, reference, and the damage per unit of modified fossil fuel consumption, which is defined as the total of the petroleum and coal consumption plus one-third of the natural gas consumption, as it has been assumed that the environmental damage caused by natural gas is one-third that of the liquid or solid fossil fuels. As can be seen from Table 4, the total environmental damage of fossil fuels is $8.26 GJ -z, which is quite a large figure. This is what society pays, in addition to the market prices, for using fossil fuels. On a world-wide basis, it amounts to about US$1613 billion, or 12.7% of the world's projected total Gross Domestic Product in 1986. It should be noted that the figure of $8.26 GJ -1

107

HYDROGEN TECHNOLOGY FOR HUMAN SETI'LEMENTS Table 4. Estimates of fossil-fuel damage

Type of damage

References

Damage per unit of fossil-fuel energy (1986 $ GJ -~)

1. Effect on humans (loss of working time, medical expenses, deaths) 2. Effect on fresh water resources/sources (loss of fish, damage to drinking water) 3. Treatment of lakes (treatment by powdered lime) 4. Effect on farm produce, plants and forests (acid rains, ozone) 5. Effect on animals (domesticated or wildlife) 6. Effect on buildings (historical, commercial and residential) 7. Effect on coasts and beaches (oil-spills, ballast discharge) 8. Effect of ocean rise (coastal protection) 9. Effect of strip-mining (land reclamation) Total damage:

[86-88]

3.86

[22, 89]

1.93

[11] [15, 21, 89]

0.06 0.57

ought actually to be greater, as it does not include the costs of human discomfort and any induced climatic changes. On the other hand, hydrogen is the cleanest fuel we know. Hydrogen itself, and its combustion product water vapor, are neither poisonous nor polluting. They do not cause acid rains, acid smog or the Greenhouse effect. 5.4. Effective cost In order to compare the synthetic fuels under consideration, we could define a societal (effective) cost, which takes into account the production cost, utilization efficiency and environmental cost, as follows: S = ( e + E) r/f/r/s

(1)

where S is the societal cost of the synthetic fuel per unit of energy, P is the production cost, E is the environmental cost, and r/f/r/s is the utilization ratio (i.e. the fossil-fuel utilization efficiency divided by the syntheticfuel utilization efficiency).

[89] [18] [12] [89] [28]

0.49 0.83 0.09 0.31 0.12 1986 $8.26

Using the above equation with the data developed earlier, Table 5 has been prepared to give the societal costs of the four synthetic fuels which are being compared. In the calculations it has been assumed that the environmental damage caused by SNG is two-thirds that of SynGas, one-third being due to the environmental damage at the coal (or other hydrocarbon) based production plant, and one-third due to the environmental damage at the user end. In the case of hydrogen obtained from coal, one-third of the environmental damage has been assessed as the environmental damage at the production plant. This is due to the fact that it is easier to control and reduce the pollutants in a large central plant than in the small distributed energy conversion devices at the user end. It can be seen from Table 5 that hydropowerproduced gaseous hydrogen has the lowest effective cost, and SynGas the highest effective cost. When the gaseous synthetic fuels are compared, the o r d e r - starting with the lowest effective cost--is hydropower GH2, coal GH2, SNG and other GH2. When the liquid synthetic fuels are compared, the order is coal LH2, hydropower LH2, other LH2 and SynGas.

Table 5. Effective cost of synthetic fuels

Fuel SNG GH2

Coal Hydropower Other

SynGas LH2

Coal Hydropower Other

Production cost (1986 $ GJ -~)

Environmental damage (1986$ GJ 1)

Utilization efficiency ratio rh/r/s

Effective cost (1986 $ GJ -~)

7.42 7.19 9.65 18.13 14.47 8.99 12.06 22.66

5.51 2.75 --8.26 2.75 ---

1.00 0.74 0.74 0.74 1.00 0.74 0.74 0.74

12.93 7.36 7.14 13.42 22.73 8.69 8.92 16.77

108

T. NEJAT VEZIROQLU

5.5. Conservation and capital investment In addition to the effective or real costs calculated above, the synthetic fuels could be compared with regard to the conservation which they can effect, and the capital investment they require. In Sub-section 5.2 above, it was shown that the weighted overall utilization of hydrogen is 26% better than that of fossil fuels. As a result, to produce the same end-work, the energy conservation devices become smaller if they run on hydrogen rather than on fossil fuels. For example, the generating system of a power plant, the jet engine of an airplane, the automobile engine etc., would be smaller if they used hydrogen rather than a fossil fuel. In addition, the structures or frames to which they are attached would be smaller, as the energy-conversion devices would be lighter. Consequently, there would be savings in the material resources (such as metals, wood, plastics etc.) needed to build the energy conversion systems, as well as in primary energy resources. Assuming a linear relationship between the resources expended and the utilization efficiencies, the resourceconsumption factor for hydrogen becomes 0.74 if that for the fossil fuels is taken as unity. In other words, if 1 unit of resources is consumed when the energy carrier is the fossil fuels, only 0.74 unit of resources would be consumed when the energy carrier is hydrogen. This is an important saving in resources; indeed, hydrogen could be labeled as the most energy- and resourceconserving fuel. Of course, the above discussion refers to the energyconversion devices and related structures. However, the savings would propagate beyond them. For example, there would be savings in transportation costs of the resources, and also in storage costs etc. Hence, the savings in the energy sector would produce savings in other sectors. If the capacity of a production plant (including an energy-conversion system) is doubled, the capital investment needed does not double, but increases roughly as ~/2. In other words, the capital investment is proportional to the square root of the size. Applying this to the energy-conversion plants, if one unit of capital

investment is needed for a fossil-fuel using plant or device, (0.74/1)!/2 = 0.86 unit of capital investment will be needed for a hydrogen-using plant of similar capacity. This represents a 14% saving in capital investment in favor of hydrogen-using plants or devices. 5.6. Comparison with real economics In order to compare the real economics of the post-petroleum (and natural gas) era energy systems, two possible scenarios have been assumed. (1) The present system will continue and the energy needs will be satisfied by the use of synthetic hydrocarbons in the ratio of 50% SNG and 50% SynGas (the synthetic fossil fuel system). (2) Alternatively, the conversion to hydrogen will take place, whereby 20% of energy needs will be met by LH2 and 80% by GH2, while one-half of the hydrogen will be produced by hydropower and the other half by direct solar, ocean thermal and wind sources (solar-hydrogen system). Table 6 compares the real economics of the two energy systems. It gives the average effective costs for large-scale fuel production, resource consumption factors and the capital requirement factors. It can be seen that the solar-hydrogen system will result in a 39% saving in effective cost, will save 26% in resource consumption, and will require 14% less capital than the synthetic fossil fuel system.

6. H Y D R O G E N T E C H N O L O G Y F O R H U M A N SETTLEMENTS As mentioned earlier, hydrogen can be used in every application which uses fossil fuels today, including the energy for human settlements [90], such as heating and cooling for comfort, hot water for bathing and washing, cooking and refrigeration for food preservation, lighting and electricity, as well as energy for residential transportation. Of course, before hydrogen can be used to meet these needs, it must be produced, stored, transported and distributed.

Table 6. Comparison of fuels re real economics

Energy system scenario (a) Synthetic fossil-fuel system 50% SNG + 50% SynGas (b) Solar-hydrogen system: 20% LH2 + 80% GH2 (I/2 hydropower, V2 direct solar, ocean thermal, wind)

Effective cost (1986 $ G J- l)

17.84 (1) 10.79 (0.61)

Resource consumption factor

Capital requirement factor

1

1

0.74

0.86

109

HYDROGEN TECHNOLOGY FOR HUMAN SE'ITLEMENTS

6.1. Production In the hydrogen energy field, most research projects are concerned with hydrogen production---economical and efficient ways of producing hydrogen [41-49, 9199]. For a post-fossil fuel era, the main primary energy sources of interest are nuclear energy, direct solar radiation, wind energy, ocean thermal energy and geothermal energy. In the case of human settlements in urban areas, hydrogen should be produced in central energy plants--using any one or more of these primary energy sources, depending on the availability, and the raw material, water. With hydro, wind and ocean thermal energies, the electrolysis method of hydrogen production should be used, since these primary energies can initially be converted to electricity more conveniently than any other energy form. With direct solar and nuclear either electrolysis or the thermochemical method could be used to produce hydrogen. With solar energy, the direct thermal method can also be used to dissociate water to hydrogen and oxygen at high temperatures--3000 K or higher. This is the most efficient hydrogen production method; however, there is the difficult problem of keeping hydrogen and oxygen from combining again as the temperatures are lowered. Various ways are being pursued to separate hydrogen and oxygen, such as centrifuging, diffusion and magnetic separation. For most human settlements, hydrogen could be produced through a photovoltaic-electrolyzer system, small h y d r ~ d . c , generator--electrolyzer system, wind--d.c, generator--electrolyzer system or through biological systems. Some of these systems or their

components, using advanced technologies, are now being commercialized. A California company* is offering sun tracking and concentrating photovoltaic modules for electricity and heat generation. SUNTREK800-MSEPG has a net operative area of 76 m 2, and is rated at 7 kWep peak electric power plus 45.8 kWth heat output. It is claimed that the electricity generated will cost 2.85 cents per kWh, while nuclear and coal electricity would cost 7.75 and 9.93 respectively. A Belgian companyt is offering a new alkaline bipolar electrolyzer using inorganic ion-exchange membranes. Its specifications indicate a thermal efficiency of 90% or better. These are all very encouraging developments for the introduction of hydrogen energy. Then there are hydrogen-producing photosynthetic and anaerobic bacteria, which are especially suited for rural hydrogen production, though large-scale bacteria farms could also be conceived to meet the requirements of urban settlements. Herlevich and Karpuk [71] report of a hydrogen-producing photosynthetic bacteria (Rhodopseudomonas capsulata) with quite a high light-tohydrogen conversion efficiency of 5%. The bacteria are capable of metabolizing waste effluents. It is suggested that the conversion efficiency could further be increased using genetic engineering. Nitsch [100] has estimated cost of solar produced (in North Africa) hydrogen for Europe, and has compared these with the estimated prices of fossil fuels (see Fig. 4). * MSEPG Solar Power Corporation, 10635 Scripps Ranch Blvd, San Diego, CA 92131, U.S.A. ? Hydrogen Systems n.v./s.a., Jan van Rijswijcklaan 17, B-2018 Antwerpen, Belgium.

D = 30 YEARS

~,

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198o

2600

2o'Io

H~ BY PHOTOVOLTAICS H~ BY SOLARTOWER

2(J2o

2o'ao

2040

TIME (YEARS)

Fig. 4. Comparison of solar hydrogen cost (including transport from North Africa to Europe) with fossil fuel cost as a function of interest rate (I), life time (D), and price escalation of fossil fuels (p).

110

T. NEJAT VEZIRO~LU

It can be seen that the cost of hydrogen is expected to decrease progressively and fall below that of fossil fuels early in the next century. Of course, as pointed out earlier, if utilization efficiency and environmental damage are considered, then hydrogen is already the most economical fuel. 6.2. Storage After hydrogen is produced, it must be stored. Several surveys and studies [41--49, 101-106] have been conducted in order to determine better, safer and more economical methods of hydrogen storage for given conditions. For large-scale storage or for the requirements of urban human settlements, the recommended method is the underground storage of hydrogen in aquifers, depleted petroleum and natural gas reservoirs and man-made caverns resulting from mining and other activities. This method is already being utilized in some countries. Gaz de France has stored hydrogen-rich refinery by-product gases in an aquifer structure near Beynes, France. Imperial Chemical Industries Ltd stores their hydrogen in salt mine caverns near Teesside, England. Hydrogen losses due to diffusion and pumping is estimated to equal about 3% of the hydrogen stored. For small-scale storage (e.g. homes in rural settings where hydrogen is produced at individual homes using solar energy, wind energy, small hydro power, etc.), the recommended method is the storage of hydrogen in hydriding metals or alloys. When a hydride is formed by the chemical combination of hydrogen with a metal, an element or an alloy, heat is generated. In other words, the charging or absorption process is exothermic. Conversely, the discharging or desorption process is endothermic, i.e. heat must be supplied to a hydride in order to liberate hydrogen from it. These processes can be represented by the following chemical relationships: charging or absorption: M + xH 2 --) MHEx + heat

(2)

discharging or desorption: MHz~ + heat ~ M + xH2

6.3. Transmission and distribution Stored hydrogen must be transported to the consumption centres. Although it is possible to transport hydrogen on a small scale as pressurized gas in high pressure containers and as liquid in insulated containers, the most

Table 7. Comparison of hydrogen storage media

Medium MgH2* MgNiH4 VH2 FeTiH1.95 TiFeoTMno.2H1.9 LaNisH7 R.E.NisH6.5 Liquid H 2 Gaseous Hz (100 atm) N-octane

Hydrogen content (wt %)

Storage capacity (g m1-1 of vol.)

7.0 3.16 2.07 1.75 1.72 1.37 1.35 100 100

0.101 0.081

* Starting alloy 94% Mg-6%Ni. t Refers to H only in metal hydrides.

(3)

where M represents the hydriding substance, a metal, an element or an alloy. The rate of these reactions increases with increasing surface area. Therefore, in general, the hydriding substances are used in powdered form to speed up the reactions. Using the above described properties of hydriding materials, hydrogen can be stored in homes. Figure 5 shows such a storage system filled with a granular hydriding material. The basic storage module is a shell and tube heat exchanger. Granular material is contained on the shell side, and heat is removed and added through tubes spaced throughout the bed of granules, for the storage and extraction of hydrogen, respectively. The heat needed could be obtained through solar collectors, through storing the heat of the hydriding reaction or through combustion of hydrogen. The bed of granules contains an inlet/outlet header connected to porous metal tubes in the tank. This arrangement allows hydrogen to be added and extracted without movement of the granules. Table 7 gives a comparison of some hydriding substances with liquid hydrogen, gaseous hydrogen and N-octane. As can be seen from the table, all the hydriding substances shown there can store hydrogen atoms more densely than is possible with liquid hydrogen. Another advantage of storing hydrogen in hydriding substances is that a hydride tank would result in almost no fire hazard, which is not true for a pressurized hydrogen gas tank or a gasoline tank.

0.096 0.090 0.089 0.090 0.070 0.007

Energy density: Heat of combustiont (cal g-l) (cal m1-1 of vol.) 2373 1071 701 593 583 464 458 33900 33900 11400

3423 2745 3245 3050 3051 3050 2373 244 8020

HYDROGEN TECHNOLOGY FOR HUMAN SETTLEMENTS

111

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HYDRIDE BED (H a STORAGE )

Fig. 5. Hydrogen storage hydride tank. economical large-scale transportation of hydrogen is by pipelines. There are already hydrogen pipelines operating in Europe and in the States [107, 108]. Air Products and Chemicals, Inc. operates a hydrogen pipeline in Texas. It consists of 96 km of underground pipes, which range in size from 10 to 30 cm. Pipeline pressure is obtained by compressors at the hydrogen production site, and no intermediary compressors are used. The Imperial Chemical Industries of England has a 16 km above-ground hydrogen pipeline system in Teesside. Chemische Huls of F. R.G. and L'Air Liquide of France have a hydrogen pipeline system extending some 550 km and consisting of 10-30 cm diameter pipes. As a result of the foregoing commercial operations, there exists a wealth of experience and information for safe operation of hydrogen pipelines. Figure 6 compares energy transmission costs by different carriers [109]. As can be seen from the figure, hydrogen transmission costs are somewhat higher than those of natural gas (CH4) due to higher compression

costs resulting from hydrogen's low density, but much lower than electricity transmission costs both for overhead and underground modes of transmission. Hydrogen in human settlements, whether it is produced and stored in situ or arrives by pipeline, must be distributed to the use points. The Institute of Gas Technology has conducted an extensive study [110] to determine suitable piping, valves, fittings, meters, materials and lubricants for such a hydrogen distribution system (see Fig. 7). The results indicate that the pipings and components used in natural gas home distribution systems should be adequate for hydrogen delivery as well. The meters would need larger volumetric capacity and adjustments. Hydrogen did not affect the mechanical and physical properties of metallic or elastomeric materials of system components. There were some indications that plastic products, lubricants and adhesives were somewhat affected by exposure to hydrogen. Although the overall hydrogen-to-natural gas volumetric leaks ratio could range from about 2.9 to 3.5,

112

T. NEJAT VEZIRO(~LU 1000

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I 103

104

280MW

4

105

2800MW FLOW Gd/HR

Fig. 6. Energy transport costs (1975 $).

energy loss from leakage would be similar. Hydrogen leaks would not ignite spontaneously without an ignition source. 6.4.

Electricity generation

Energy requirements of some basic domestic activities, such as lighting, sewing, ironing, receiving radio and television broadcasts, pumping well water etc., can be met better by electricity. As the standard of living rises, electricity can also provide the electromotive force for domestic appliances such as air conditioners, refrigerators, water heaters, clothes washers and dryers, cooking ranges and ovens, dish washers, trash compactors, food mixers, electric shavers, hair dryers, etc. Hence, it is important that electricity must be generated to meet the energy requirements of some or all of these domestic activities. Hydrogen, again, is the most suitable fuel for electricity production. It can be converted to electricity in fuel cells--which are not subject to Carnot cycle limitations--with efficiencies higher than any other fuel. Figure 8 shows a schematic diagram of a fuel cell [50]. It

has two electrodes separated by an electrolyte. The electrolyte can be a basic solution of sodium or potassium hydroxide; an acidic solution, perhaps of phosphoric acid; or one of the various solid ceramic or polymeric solids that carry electric current in the form of hydroxyl ions or hydrogen ions. At the anode, hydrogen gas reacts to produce hydrogen ions, H ÷, and electrons. The electrons are driven through the external circuit producing d.c. electricity, where they can do work, and finally to the cathode, where they react with the oxygen (from the air or from an oxygen supply) and the electrolyte to produce hydroxyl ions, O H - . In the electrolyte, the hydroxyl ions and the hydrogen ions react to produce pure water. The water is then removed from the cell. In the United States several 40 kW phosphoric acid fuel cells are being tested in homes and apartments, achieving combined thermal and electric efficiencies of up to 80% [111]. It is expected that further research work will increase the conversion efficiencies to 8590%. European and Japanese companies are also experimenting with fuel cells. A fuel cell, about the size of an air-conditioning unit, would meet all the electric

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conjunction with a heat source, such as solar heat or waste heat. If passed through a turbine or expansion engine, hydrogen moving from one hydride tank to the other could produce mechanical and electrical power. Figure 9 [112] illustrates such a scheme proposed for electric power generation. It consists of three tanks containing the same kind of bydriding substances (in this case, lanthanum nickel 5 alloys). During the first cycle, hydrogen driven off from the desorption tank (Tank 1)

114

T. NEJAT VEZIRO(~LU

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HYDROGEN TECHNOLOGY FOR HUMAN SETTLEMENTS by means of solar heat (or heat from any other source) passes through the expansion turbine producing electricity, and then at a lower pressure is absorbed by the lanthanum nickel 5 alloy in Tank 2 producing heat at 104°F. In this case, the heat is produced at a lower temperature (and not at the temperature 212°F of the desorption process) since hydrogen is at a lower pressure after passing through the turbine. The heat produced in the absorption tank (Tank 2) is rejected to the environment through the water cooling system. The water cooling system also helps to cool down the cooling tank (Tank 3) from 212 to 104°F, as it was the desorption tank in the previous cycle. In the second cycle, through a system of piping and valves, the tanks are displaced one step to the left in the diagram, i.e. the cooling tank becomes the absorption tank, the absorption tank becomes the desorption tank, and the desorption tank becomes the cooling tank. Then, the cycle is repeated. Using this method, low quality heat could be converted to electricity.

6.5. Space heating and cooling Once the electricity is generated, using fuel cells or otherwise, it could then be used for heating through electrical resistance heaters, for cooling through conventional electric air-conditioning systems, and for heating and cooling through conventional reverse cycle air-conditioning systems. If d.c. electricity is generated, then d.c. motors and d.c. controls must be used in the above stated heating and cooling systems. Another, and perhaps more efficient way of achieving space cooling would be to use hydrogen in lieu of natural gas in the conventional absorption cooling systems. It would only be necessary to make some adjustments to the burners. For space heating hydrogen could be used in lieu of natural gas in steam boilers for producing circulating steam [113]. However, there is a better and more efficient way of producing steam through hydrogen, i.e. using an Aphodid steam generator. In such a steam generator, hydrogen burns with oxygen producing pure steam at quite high temperatures of 6000°F. Then an appropriate amount of water is added to this high temperature steam in order to bring the steam temperature down so that the boiler, piping and fitting materials can withstand it. This is a very efficient way of producing steam, as there are no flue gases going up the chimney and carrying away some 25-35 % of the heat. If hydrogen is produced by electrolyzers, then the oxygen needed would be readily available. Another way of producing space heating would be through the use of wall units of catalytic hydrogen combustors, which make use of the property of hydrogen to combine with oxygen--in the presence of a catalyst such as platinum or palladium--in an exothermic reaction without a flame [114-116]. Figure 10 shows such a catalytic combustor. It consists essentially of a set of two porous plates. One has the role of gas distributor

B

(CQtalyt*c p l a t e

115 (Distributor)

A

)

,

H z inlet

Fig. 10. Wall catalytic combustor. and the second is the catalytic bed. A conti'olled flow of hydrogen passes, by forced convection, through the set of two plates and reacts in a layer of a certain thickness at the external surface of the plate with the atmospheric oxygen permeating into the layer by molecular diffusion. The heat of reaction is transferred to the surrounding area by radiation and convection. The combustion rate and the resulting temperatures depend upon the rate of hydrogen supply and the active surface area of the catalyst. Room heaters could operate at relatively low temperatures and could be hung on the wall, covered with formica or other panel materials. Catalytic heating efficiencies are extremely high---close to 100%. If solar heat or waste heat is available, then hydrogen, together with hydriding substances, can be used for heating and/or air conditioning. Figures 11 and 12 [112] show how one of the proposed systems works. The system consists of four hydride tanks, a solar collector, and a number of heat exchangers for the air in the building and for the outside atmosphere. Tank 1 is connected to Tank 3 with a hydrogen pipe in order to allow the movement of hydrogen from one tank to the other. Similarly, hydride Tanks 2 and 4 are connected with a hydrogen pipe. Heat exchangers (including solar collector) and the hydride tanks are connected by water-carrying pipe circuits or loops, through a series of switches or valves, so that a hydride tank in a given water circuit (loop) can be replaced by another hydride tank. Tanks 1 and 2 contain calcium nickel 5 (CaNis) hydriding substances while Tanks 3 and 4 contain lanthanum nickel 5 (LaNis) hydriding substances. When the system works as a heater, the connections for Cycle 1 are as shown in Fig. 11. The solar heat is carried to Tank 1 by means of water at about 212°F and drives the hydrogen off the calcium nickel 5 hydride (CaNisH4) in Tank 1 to the lanthanum nickel 5 in Tank 3. In Tank 3, lanthanum nickel 5 hydride (LaNisH6) and heat at 104°F are produced. The water circuit carries this heat to the building heat exchangers and heats the air in the building. At the same time, the water in the last loop (R.H.S. loop) absorbs heat at 46°F from the ambient

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00//~0/, Fig. 13. Hydrogen/hydride water pumping system. atmosphere and carries it to Tank 4. This heat drives off the hydrogen from the lanthanum nickel 5 hydride in Tank 4 to the calcium nickel 5 alloy in Tank 2. In Tank 2, calcium nickel 5 hydride and heat at 104°F are produced. The water loop of Tank 2 then carries the heat to the heat exchangers to heat the building. The whole operation of moving hydrogen from Tanks 1 and 4 to Tanks 3 and 2 takes about 2 min. At the end of this period, the hydride tanks are switched from one loop to the other (Cycle 2) as shown in Fig. 12. Now, the solar heat and the ambient heat are used to drive off the hydrogen in Tanks 2 and 3 to Tanks 4 and 1. Then, the heat produced during the absorption processes in Tanks 1 and 4 is carried by means of circulating waters to the heat exchangers for heating the building. After this, the cycles are repeated. When the system works as an air conditioner, the building heat exchangers are placed in the 46°F water loop, while the outside heat exchangers are placed in the 104°F water loops. During Cycle 1, the water in the 46°F loop removes the heat from the air in the building, and through desorption and absorption processes, the heat is moved to the ambient atmosphere via the 104°F water loops. Two minutes later, during the second cycle, the solar heat and the building heat move the hydrogen off the Tanks 2 and 3 to Tanks 4 and 1, and continue to remove the heat from the building to the outside atmosphere.

6.6. Water heating Four of the space heating methods described above could also be used for producing hot water for the needs of the human settlements, viz. (1) using conventional electrical resistance water heaters, (2) using hydrogen in lieu of natural gas in conventional gas water heaters, (3) using catalytic hydrogen heaters, and (4) using an Aphodid steam generator. A water heater operating on a flame-type hydrogen burner would have an efficiency of 70%, whereas a natural gas water heater has an efficiency of about 60% [117]. If an Aphodid-type steam-hot water generator is used, then the conversion efficiency would be nearly 100%. In addition to the above methods, the waste heat from air-conditioning systems could be used for water heating, and of course in the tropical and sub-tropical regions of the earth solar energy could be used for producing hot water quite economically, 6.7. Waterpumping One of the basic needs of human settlements is water. If there is no city water available, then--in general-underground water is used. Hydrogen could be used in several ways to pump the underground water up. One way is to use hydrogen generated electricity with a conventional water pump. Another way is to couple a

T. NEJAT VEZIRO~LU

118

conventional pump to a hydrogen fueled internal combustion engine. If solar heat or waste heat is available, then a hydrogen/hydride system could be used for water pumping. Figure 13 illustrates such a system [118]. Hot water produced by solar (or waste) heat and cold water obtained from the well are supplied alternately to a heat exchanger in a metal-hydride bed by means of two sequentially operated valves. Hydrogen gas released from the bed during the heating phase of the cycle inflates a rubber bladder in the well, lifting water through the upper check valve. Ground water then flows into the well through the lower check valve, deflating the bladder and forcing hydrogen back into the hydride bed during the cooling phase, returning the system to its starting position. 6.8.

Cooking

One of the basic energy needs of human settlements is for cooking--in cooking ranges, ovens etc. There are three possible ways for hydrogen to provide the required energy. One method is to use conventional electric cooking appliances if hydrogen electricity is available. Another method is to use hydrogen in lieu of natural gas in conventional gas cooking appliances [82, 119]. In

burners of such appliances (atmospheric burners), all air for combustion is taken from the surrounding atmosphere at atmospheric pressure, and hydrogen is supplied at a relatively low pressure. Usually the hydrogen gas is passed through an orifice (see Fig. 14a), which serves to meter flow and accelerate the velocity of hydrogen. When it enters the mixing tube, it entrains air drawn in through a series of orifices near the base of the burner. In the mixing tube, hydrogen and air are mixed together and then passed through small holes, which are called burner ports. When the gas mixture issues from the port, it is ignited and a flame appears. The atmospheric air diffuses into the flame to complete the combustion. The flame does not propagate back through the burner port because the speed of the issuing gas mixture is adjusted to be greater than the flame speed of the hydrogen/air mixture. A suitable catalytic igniter could be used to initiate combustion. In another type of the proposed atmospheric hydrogen burners (see Fig. 14b), hydrogen-air mixing is inhibited by blocking all primary air. Then a stainless steel wire mesh is placed around the bunaet ports. The placement of the wire mesh in a proper configuration will allow a gradual mixing of hydrogen and air throughout the operating flow rates of the burner design. A hydrogen-rich condition exists in close proximity of the

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ttYDROGEN TECttNOLOGY FOII, I IUMAN SETTLEMENTS burner, with the oxygen concentration increasing when moving away from the burner head. If the stainless steel material is properly configured, there will be a region immediately surrounding the burner openings, consisting of an inflammable hydrogen concentration. This region, referred to as the inflammable zone, will move in and out of the burner head depending on the hydrogen flow rate. A proper burner design would incorporate sufficient stainless steel material so as to ensure that the inflammable limit zone is always located within the outside perimeter of the stainless steel material. The stainless steel also provides a very important secondary function in addition to the mixing inhibiting function. A t high temperatures, stainless steel is an excellent catalyst for hydrogen combustion. Shortly after ignition, the temperature of the stainless steel is raised by hydrogen combustion to the region where catalysis begins to occur. A t this point, the hydrogen in the inflammable zone begins to react with the dilute quantities of oxygen present through the action and on the surface of the stainless steel catalyst. In this manner, a controlled reaction occurs in the inflammable zone where mixture limitations will not permit the rapid combustion of hydrogen which would occur under normal conditions. Consequently, peak combustion temperatures are maintained below the threshold level for NOx formation. The third method is to use catalytic combustion of hydrogen for providing thermal energy for cooking. The

119

primary advantage of catalytic combustion is that combustion can be carried out without a flame and the production of nitrogen oxides from the air is negligible at temperatures below IO00°F. They transfer more usable heat to food. Temperature ranges are much wider and can be adjusted much more finely, and the heat is distributed more evenly over the entire burner surface. A catalytic burner is self starting, requiring no pilot, glow coil or spark ignition. Ignition takes place when the hydrogen gas contacts the catalyst (typically a very thin coating of platinum). Catalytic hydrogen combustor efficiencies are 85%, while those of flame burners are 70%, both of which are much higher than those for natural gas flame burners (viz. 60%). Figures 15a-c present photographs of a hydrogen flame cooking range, a hydrogen catalytic combustor cooking range and a hydrogen barbeque. 6.9. Potable water It was mentioned earlier in Sub-section 6.4 that in fuel cells in addition to electricity pure water is produced as a by-product. The amount of the water produced depends on the electricity consumption. The average household electricity consumption could vary from a low of 7 kWh per day to 70 k w h per day, depending whether a developing or industrial country is being considered and whether electricity is used only for lighting or for most of

Fig. 15a. Hydrogen flame stove top.

120

T. NEJAT VEZIROGI~U

Fig. 15b. Hydrogen catalytic combustor stove top.

Fig. 15c. Hydrogen barbeque.

t IYDROGEN TECt INOI-OGY FOR t IUMAN SETTLEMENTS the appliances and climate control. Consequently, assuming a fuel cell efficiency of 70%, the pure water produced could vary between 2.5 and 25 1 day -1. This amount of water could meet the potable water needs for drinking and/or cooking purposes, especially in areas where potable water might not be available or might be too expensive to obtain. 6.10. Refrigeration It is important to have refrigerators for human settlements in order to keep groceries, food stuffs and food products fresh. If electricity is available, then one way of obtaining refrigeration is to use conventional electric refrigerators. A second method of refrigeration would be to use the hydrogen flame heating of the refrigerant, in lieu of natural gas heating, in the conventional "Servel" type gas refrigerators. These units operate without moving parts, thereby resulting in quiet operation, long life and low maintenance. A third method of refrigeration would be to use hydrogen catalytic combustion heating of the refrigerant in lieu of natural gas heating. This would further improve the energy conversion efficiency and conserve fuel (hydrogen).

6.11. Wasteheat storage Any heat, such as waste heat, solar heat and geothermal heat, can be stored as potential hydrogen hydriding energy by supplying the heat to a hydride as shown in the following relationship: waste heat + hydride --+ hydriding substance + hydrogen

121

However, if utility electricity or home-produced electricity is not available, then hydrogen could be used to obtain illumination in a way similar to that of gas camping lanterns. It involves a low temperature combustion process of hydrogen for illumination called candoluminiscence [121]. In this process the light emission is generated by molecules, ions and atoms in a phosphorous material coating, excited by the hydrogen flame. 6.13. Electricitypowered appliances/equipment Some household appliances, equipment and gadgets need electricity to provide their energy, since they are dependent on electric motors and/or electronics to function. Such equipment includes sewing machines, clothes washing machines, dishwashers, food mixers, electric shavers, electric tooth brushes, electric saws and electric drills (for repairs), radios, televisions and sound systems (for recreation and education). This equipment would then run on either utility electricity and/or home produced electricity. 6.14. Electricityandfuel powered appliances/equipment Some household appliances, equipment and gadgets could run on either electricity or a fuel or a combination of both. Such equipment includes clothes dryers and irons, in addition to climate control systems and water heaters covered earlier. In such cases hydrogen heat, produced either through flame combustion or catalytic combustion, could be used to dry clothes and to heat irons.

(4)

Whenever heat is needed, hydrogen released can be supplied back to the hydride, releasing the hydriding reaction heat stored in the hydrogen, viz., hydrogen + hydriding substance --+ hydride + heat (5) If the hydrogen is supplied to the hydriding substance at the same pressure as it was released, then the heat released will be at the same temperature (or slightly lower because of the hysteresis effect) as that of the waste heat. However, by increasing the pressure of the hydrogen supplied, the temperature of the heat released can be increased; and by reducing the hydrogen pressure, the temperature of the heat released can be reduced. In other words, hydriding substances and hydrogen can be used as heat pumps [120], as well as for heat storage. The above outlined properties of hydrogen/hydride systems can be utilized in low grade heat requiring operations, such as water heating, space heating and hydrogen discharging from hydride storage. 6.12. Lighting Of course, electricity is the most convenient energy carrier for providing energy for lighting systems.

6.15. Domestic transportation/farm implements Hydrogen is a clean and efficient fuel for obtaining mechanical power through internal combustion engines. In consequence, a large amount of research work has been done on the use of hydrogen fueled internal combustion engines in cars, buses and farm tractors [78-82,122-126]. In order to eliminate preignition some researchers used water injection and the others used liquid hydrogen. Various methods of on-board hydrogen storage have been studied, such as pressurized gas, metal hydrides and liquid hydrogen. Because of the potential of high utilization efficiencies, the application of fuel cells to provide power for vehicles--through electric motors--has caught the attention of several researchers [60,127-130]. However, fuel cells need more room than internal combustion engines. As a result their first applications will probably be in bigger vehicles, i.e. trucks and buses. Figures 16a and b show a liquid hydrogen fueled passenger car developed by Furuhama of the Musashi Institute of Technology, Tokyo, Japan and its liquid hydrogen storage system. Figure 17 shows a minibus, having metal hydride storage, developed by DaimlerBenz A.G. of Stuttgart, F.R.G. It has three hydride storage tanks, which are used to provide heating and

122

T. NEJAT VEZI RO~LU

Fig. 16a. Suzuki car converted to run on liquid hydrogen.

HYDROGEN TECHNOI.OGY FOR IIUMAN SEq~FI.EMENTS cooling for the bus, in addition to storing hydrogen fuel for the engine. Figures 18a and b show a photograph of the Jacobsen tractor and its hydrogen system developed by the Billings Energy Corporation of Provo, Utah, U.S.A. 6.16. Hydrogenhome Some researchers have considered and developed fully integrated energy systems for homes to run on hydrogen. One, named "Hydrogen Homestead", has actually been built [82]. Figure 19 shows the energy system of the Billing Hydrogen Homestead. Figure 20 shows the energy system concept for a hydrogen home proposed by Buchner and Saufferer [131]. 7. SAFETY Mainly because of the accident to the airship Hindenburg, there is a belief among many people that hydrogen is a dangerous fuel. On the other hand, scientific studies comparing hydrogen with other fuels show that it is one of the safest fuels [85, 132-137]. There are several reasons for this conclusion. One is the comparison of fire dangers and damages therefrom. Because of their functions, all the fuels can burn, and therefore start

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fires. However, a hydrogen fire is less dangerous than a fossil-fuel fire, since a hydrogen flame has very low luminosity and radiates very little heat, while fossil fuel flames have higher luminosity and radiate intense heat. As a result, objects which are not inside a hydrogen flame are not affected, whereas objects which are close to fossil-fuel flames can be badly burned and damaged. In the Hindenburg accident, there were some 100 people in the gondola of the dirigible. When the fire started, 35 jumped to the ground and died. The other 65 remained in the gondola until it touched the ground. They walked out unharmed, as they were not affected by the radiation from the hydrogen flames. On the other hand, in the worst disaster of aviation history, when two jumbo jets (one of Pan Am, the other of KLM) collided on a runway in the Canary Islands, more than 400 people died. Although most of them were not inside the flames, because of the intense radiation they were mortally burned. If these planes had been running on hydrogen, most of the passengers could have been saved. There is another safety problem with fossil fuels: they and their combustion products are poisonous. If one drinks gasoline or breathes natural gas or combustion products of fossil fuels, the outcome can be fatal. Every year thousands of people around the world die from carbon monoxide poisoning. On the other hand, if one

COLD AIR WARM AIR

1 HIGH TEMPERATURE HYDRIDE STORAGE TANK, HEATED BY EXHAUST GAS (AUXILIARY HEATER) 2 LOW TEMPERATURE HYDRIDE STORAGE TANK, HEATED BY EXHAUST GAS (WATER CONDENSATION) ;3 LOW TEMPERATURE HYDRIDE STORAGE TANK WITH UQUID HEAT EXCHANGE (AIR CONDITIONING) Fig. 17. Mini-bus running on gaseous hydrogen with hydride storage, and hydrogen/hydride heatingcooling system.

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Fig. 18a. Hydrogen fueled Jacobsen tractor.

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HYDROGEN

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breathes hydrogen or its combustion product (water vapor), there are no harmful effects: both are nonpoisonous. This property of hydrogen makes it especially suitable for use in human settlements. There is one problem with hydrogen: being the lightest of all elements, it can leak more easily than gasoline or natural gas. H o w e v e r , today's technology is able to provide the hydrogen industry with pipes, valves, fittings and related equipment, which are manufactured to close tolerances to make them leak-proof. The U.S. National Space Administration, N A S A , is the world's largest hydrogen-user. So far as we are aware, they have not had any accident of consequence related to hydrogen. 8. C O N C L U S I O N It has been shown that when all factors are considered, hydrogen is the best fuel for meeting the energy requirements of human settlements, including both household and transportation applications. It has the highest utilization efficiency, is the most compatible with the environment, the most cost-effective, the most energy conserving and the most resource conserving fuel. The technology exists for near term applications of hydrogen. With further research and d e v e l o p m e n t work, there should be improvements in utilization efficiencies and cost. Acknowledgements--The assistance of M. Akcin, E. Amado, Z. Arnavut, G. EI-Jrushi, V. EI-Osta, D. G. Pressley, A. Raffle and C. Robu of the University of Miami is gratefully acknowledged.

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73.

74.

75. 76. 77. 78.

79.

80.

81.

82. 83. 84.

85.

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