One of the global problems facing mankind at the start of the 21st century is searching for alternative ways of development of power engineering. The problem is caused by two main factors: growing energy requirements of the modern society and deteriorating ecological situation on our planet.
Faced with this truly vital problem, a team of Russian experts from the KURCHATOVSKY Institute Research Center (Moscow) have initiated what they call a new hydrogen project. Its objective consists in the production of a man-made carrier of energy-pure hydrogen. The site chosen for project is the Far East and this choice is not accidental. The region possesses a wealth of mineral and raw materials resources which include tin, antimony, boron, gold, lead, fluorite and tungsten. But the development of this potential is obstructed by the absence of an adequate industrial and social infrastructures. That includes high tariffs for electricity and heating-which are 5.2 times higher than Russia's average.
The objective of the project under consideration (authors - E. Ivanov, V. Knyazev et al.)-is to develop ecologically clean production of hydrogen for the needs of power production in megapolises*. The authors of the project suggest what they call multi-grade structure including the extraction of hydrogen from water or an organic fuel and-which is especially important-from technological and domestic organic wastes. In any case the most important trends may be electrolytic production processes in combination with tidal generating stations and wind-powered stations**.
And it should be noted that electrolysis of water is one of the technologically simple methods of hydrogen production. It also makes it possible to simultaneously produce concentrated heavy water which put it in high demand in the middle of the 20th century. But the elaboration of alternative methods of heavy water production pushed electrolysis into the background because of its high energy consumption. To bring down the expenses, experts recommend in the first place to raise the temperature of the process. Another way of reducing the costs is to use relatively cheap "off-peak" electricity which can reduce by more than two times the cost of electrolysis of hydrogen.
And although the total costs of this method remain high, it will be more economically attractive in many cases (when, for example, there is no centralized power-supply system). And the electrolysis method also has some indisputable advantages. Say, when using ecologically clean renewable sources of energy (sun, wind, tides) the hydrogen obtained is also pure (-99 percent) which is necessary for a range of technological and energy processes.
At the present time electrolyzers of three basic types can be considered in terms of their practical applications: traditional water-alkaline, solid-polymer (TPE) and high-temperature hard-oxide ones. Each of them had advantages and disadvantages of its own.
The development of hard-polymer electrolyzers is associated with the advent of perforated ion-exchange membrane in the United States in 1966. Such products were primarily designed for special applications (space probes, submarines, etc.). But the high costs of such membranes (about 700 US dollars per one m2 ), its acidic properties necessitating the use of platinum metals in electric catalyzers, increased water-purity requirements and corrosion resistance of structural materials - all slowed down their production.
Hard-oxide high-temperature electrolyzers are characterized by high operating temperatures which means longer time of entry into the working regime. And that also means losses of energy, especially if the units operate
* See: V. Rusanov, "Hydrogen and Hydrogen Power Engineering", Science in Russia, No. 6, 2004. - Ed.
** See: Yu. Remizov, "Energobiological Complexes", Science in Russia, No. 2, 2004. - Ed.
with frequent intervals being combined with solar batteries.
Summing it up, an analysis of scientific and practical data indicates that the main type of electrolyzers which will be used in the near future will be the water-alkaline ones. Used in them as electrolyte are usually water solutions of caustic potash (KOH 7 and caustic soda NaOH). The material for electrodes-steel coated with a layer of nickel obtained from a nickel-zink alloy (so-called Rhenium nickel). Also effective are electrodes of metal mesh which helps considerably increase the contact surface of the electrode with electrolyte solution. In Russia alkaline electrolyzers are produced by the URALKhlMMASH Company with the capacity by hydrogen of 250 nm3 /h (under pressure of up to 6 atm) or up to 500 nm3 /h operating at atmospheric pressure). They are all functioning at current densities of less than 0.4 A/cm2 (in practice - 0.2 - 0.3 A/cm2 ) and the required energy for hydrogen production is 4.5 kWt.h/nm3 . In connection with forthcoming intense work on fuel elements one should expect in the near future considerable progress with TPE electrolytes and lesser progress with hard-oxide ones. Then the cost of the former will approach that of alkaline and that can stimulate their production.
As we said before, the Far Eastern Hydrogen Project is a regional innovative experiment aimed at the introduction of ecologically clean technologies of energy provisions for different consumers. Its main elements include the Penzhinskaya tidal power station (on the Kamchatka) with the capacity of 100 GWt; electrolysis production of hydrogen, including previous desalination of sea water; pipeline transportation of hydrogen using the energy of windmill electric stations. And each of the aforesaid projects has a number of alternatives with changing technologies of desalination, electrolysis, transportation of hydrogen etc.
The estimated average capacity of a tidal station in the Penzhinskaya Guba amounts to 87.4 GWt with the annual output of 190 TWt.h. In this version the station will be operational over not more than a quarter of a year (90 days). But in principle its maximum capacity can exceed 100 GWt at the load factor of no less than 50 percent. In that case the annual electricity output will reach 300 TWt.h. The estimated wholesale price of 1 nm3 H2 will be 0.2 dollars which is three times greater than that of the conventional motor fuel. But this is acceptable if we want to achieve the ecological cleanness of transport. The suggested volume of production - 60 bin nm3 of hydrogen a year - is sufficient for the operation of 1.0 - 1.03 mm of cars or 300 thous. buses operating on fuel elements. The length of the completion of the project is 15 years.
E. Ivanov, V. Knyazev et al. "Far Eastern Hydrogen Project", ENERGIYA journal, No. 3, 2005
Prepared by G. SATIK
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