Omar Campos Ferreira:
Advisor of the Secretariat of Science and Technology, MG, Brazil
The substitution of the economy based on fossil fuels (coal, petroleum and natural gas) by the economy based on hydrogen arouses optimistic expectations fed by epithets like “clean fuel”, “unlimited availability”, “declining production costs”, etc. However, hydrogen, like electricity, is not a primary energy source, since it does not exist in a free state in large quantity. Obtaining hydrogen means to extract it from some natural substance using a primary source of energy. In any conversion there are losses related to the leak of energy from the system evaluated by the Conservation Law and to dissipation, a form of loss evaluated by the Entropy Law, of subtle application. In general, conversion is justified by the large commodity and safety associated with its use, by the better production quality, by the decrease of immediate damage to the environment, etc.
The cost of the secondary form is necessarily higher than that of the corresponding primary one, so that to lower the cost of obtaining the secondary form means to render this cost close to the cost of the original form of energy. Therefore, the introduction of a new conversion technology like that of hydrogen must be preceded by studies concerning the present and future benefits and costs of it.
Hydrogen can be liberated through various processes like water vapor reaction with mineral coal coke or charcoal from which results hydrogen the (H2) and carbon monoxide (CO) mixture known as water gas; in a second reaction, the monoxide reacts with the vapor in the presence of a catalyst, liberating more hydrogen and carbon dioxide (CO2) that is absorbed together with the impurities. Another way is the so-called natural gas reform that consists of its reaction with water vapor at high temperature in the presence of a catalyst. A third way is eletrolysis of water in which hydrogen and oxygen are separated by the passage of electric current through an acid, base or salt solution.
Electrolysis has been the preferred way of obtaining high purity hydrogen, without the simultaneous liberation of carbon compounds, therefore satisfying environmental requirements. For industrial uses, no high purity degree is required and so the natural gas reform, in general of hydrocarbons and other chemical substances, mainly alcohols, is a convenient option.
The fuel cell that would be the basic conversor in the new economy is a variation of the chemical battery, continuously loaded, in which hydrogen and oxygen exchange electrons with platinum electrodes, generating an electric current in an external circuit. So it is a conversor of chemical energy into electrical energy that replaces the traditional route based on combustion that starts a thermodynamic cycle, transforming thermal energy (of the combustion products) into mechanical energy used, among other ends, to drive an electricity generator.
Since the fuel cell is only a component in the conversion chain, its advantages and disadvantages must be evaluated in this context, especially in what concerns the electricity generation process necessary for the electrolysis. The applications already foreseen for the hydrogen cell are distributed generation of electricity and electric engines for driving vehicles.
Distributed generation has the advantage of decreasing the electric energy loss in transmission and distribution besides giving alternatives for supplying electricity in situations of crisis in the main system. The centralized generation by large hydraulic power plants interconnected by a transmission network is the predominant mode in Brazil. The hydraulic electricity generation cost in Brazil is one of the lowest in the world due to the abundance of water and favorable coast topography. Along with the development of the national economy, the best sites regarding hydraulic power plants installations are occupied and generation costs rise, giving room to alternatives. The 2001 supply crisis has called the attention of the authorities and of specialists to the vulnerability of the hydraulic electric system due in part to low investments in new reservoirs and in transmission lines. Furthermore, the loss of energy in transmission has grown regularly since the eighties when the last large change in the system has been carried out concerning the prepation for the electricity generated in Itaipu.
The occurrence of these circumstances had the merit of recovering proposals for complementing the large interconnected system with generation distributed in small hydraulic electric power plants and in co-generation of electricity and process vapor for industry (chemical, sugar and alcohol, food and beverage, paper and cardboard, steel…) and, in a smaller scale, for the service sector. The sum of the potentials related with these alternatives already fully developed represents about 40% of the presently installed power, a quantity sufficient for preparing without rush the introduction of new primary sources for electricity generation, like natural gas in combined cycle or any other that might be developed. Furthermore, the hydraulic potential is far from exhausted since it is estimated that the installed power could still grow 70% until the competion for the uses of land and waters favors the other generation alternatives. In this context, the hydrogen cell is only another alternative restricted to local demand and it seems unrealistic, in the next decades, the proposal of distribution of generation to smaller loads such as apartment buildings and uni-familiar residences. The image of a citizen generating his/her own electricity does not fit the configuration of the national economy that does not even favors solar energy for water heating, one of its elementary applications.
For vehicle propulsion through electric engines we have in Brazil a situation similar to distributed generation. The use of fuel oil in the individual transport, as an additive to gasoline (anhydrous alcohol) and as unique fuel (hydrated alcohol) has promoted a notable efficiency gain in engines (from 25% in A gasoline engines to 30%, on the average, in gasoline C and hydrated alcohol engines) and has reduced the emission of chemical pollutants (CO and HC have dropped to 30% between 1979 and 1989) with relatively low investments gladly carried out by the car industry since the fuel modification has permitted to maintain the vehicle production. Furthermore, alcohol has allowed the reduction of greenhouse gases emission, permiting the Brazilian fleet to have the lowest emission indexes in g/km. Environmental problems exist in the metropolitan regions, for which specific solutions exist as well (generalization of subways, for example).
However, at the end of the eighties, a new regulation regarding emissions was issued, based on European indexes and applicable in the whole country. In order to follow this regulation it was necessary to introduce electronic control in the engines, valid for alcohol vehicles too, as a preliminary measure for the introduction of the catalyst for treating emissions in the exhaust pipe. The cost of the innovation is estimated to be between 20 and 30 billion dollars in 15 years. It was not evaluated the effect of this investment, should it be applied in improving the collective transport in the metropolitan regions.
The automotive sector is an appropriate mean to disseminate innovations due to the fascination that people have for individual transport and to the marketing techniques used by the car industry and by the car salers. Therefore, it is predictable that the cell-engine system will be rapidly disseminated in all the car fleet, with or without environmental or economical motivations. Considering the present fuel consumption in the individual transport and supposing a 60% efficiency gain by using hydrogen, about 40TWh/year of electricity consumption would be necessary to supply the demand corresponding to hydrogen, that is, about 12% of hydraulic electricity presently generated would be used for individual transport. In the future, we might be generating electricity in thermo-electric power plants (including nuclear plants) for this purpose, what would correspond to substitute the diffuse emission source (the fleet of internal combustion engine vehicles) by the concentrated source of the thermo-electric plants.
The imminent exhaustion of petroleum will be followed, in the medium term, by that of natural gas, converting into fatality the use of nucleo-electric energy, economically unresolved, in order to prevent nuclear weapons proliferation, and ecologically under suspicion, as the problem of safe final disposal of the reactor waste has not been solved yet.
Following the evolution of the nuclear industry, we have seen its fast penetration in the sixties and seventies followed by the so-called “nuclear moratorium”, the abandonment of the main programs for developing breeder reactors. The reactors now in operation, called burners, are energetically wasteful since less than 1% of the fissile uranium (U235) participates in the conversion. So the Brazilian reserves, evaluated in 100 thousand recoverable tons of U3O8 would generate 160 TWh/year during 30 years, the time necessary to amortize the nuclear plant investment, representing less than 1/3 of the average annual demand predicted for that period, assuming the average annual rate of 3% for growth of demand (in the last decade the average growth rate was 4% annually). Therefore it does not seem wise to plan the production of H2 based on nuclear energy in Brazil.
New technologies call the popular attention because we are used to relate them with progress since they come from countries with more advanced economies. However we could invert the rationale without disrespecting logic by saying that countries with more advanced economies are compelled to develop new technologies because they have consumed the natural resources that have permitted them to maintain the economy working with simpler technologies. Therefore, technology development seems to be an imperative for the accomodation of society to the progressive environmental degeneration. It is also interesting to observe that the technology transfer to less developed countries helps to amortize its cost faster.
New technologies will fatally come but they should be introduced after thorough and careful examination of its social, economical and environmental repercussions,
in the context of simpler technologies already developed in the country.
Graphic Edition/Edição Gráfica:
Tuesday, 11 November 2008.