Libmonster ID: UA-12096
Author(s) of the publication: Viktor PETRENKO, Pavel ALEXEYEV

by Viktor PETRENKO, Dr. Sc. (Phys. & Math.), Pavel ALEXEYEV, Dr. Sc. (Phys. & Math.), National Research Center "Kurchatov Institute", Moscow, Russia

Such electron accelerators as betatrons, microtrons, synchrotrons, linear accelerators and the like are usually associated in our mind with physical experiments unlocking the riddles of the microworld and elementary particles. But these setups can be--and are being--used for practical purposes as well. They are quite cost-effective-say, in boosting the heat stability of cables or polymer pipes, and in sterilization of disposable medical syringes. True, their wide industrial uses (say, in cement production) may look exotic. But what if we look into the morrow?

стр. 26

CONVENTIONAL APPROACHES

For all the headway made in the information science, micro- and nanoelectronics and other trend-setting branches, conventional techniques used in obtaining building materials, power resources, metals and mineral fertilizer from natural raw materials will hold on for quite some time. Among technologies based on traditional energy carriers and fuels of greatest significance are those involving dehydrogenation of hydrocarbons, leaching as well as decomposition of water, carbonates, sulphides, alumina and other substances. To get the end product one has to make use of heat-treating, chemical and metallurgical processes. They are indispensable to the production of cement, mineral fertilizer, aluminum, soda and other essentials. The source material is processed in heat-treating furnaces.

Dating from the 19th and 20th centuries, such techniques remain essentially the same in this time and age, too. Their further efficacy is hampered by certain basic characteristics proper to conventional methods. First, unrenewable natural fuel has to be burned in huge amounts, as high as 40 percent of the raw material mass. Second, the heat treatment process has a very low efficiency factor equal to 25 percent on the average. Third, a significant ecological pressure, all that in the teeth of measures to cut it back (such environmental hazards as ash, heavy metals, carbon monoxide, carbon and nitrogen oxides, sulphides and other pollutants); further-more, heat dissipation all around. Just one example: here in Russia we burn up as much as 20 mln tons of natural fuel to produce 50 mln tons of cement a year. Thereby the escaping flue gases (twenty million tons overall) mix with conversional carbon dioxide (yet another 20 mln tons!) released into the atmosphere by and large.

Yet another problem: a considerable amount of impurities in the end product because the heat-treated raw material contacts the fuel and the inside lining of furnaces. This impairs the quality of the final product. Also, the high specific quantity of metal per furnace has to be reckoned with.

And last comes the extensive and high-cost infrastructure, such as fuel depots, large tracts of land under enterprises (say, just one rotary kiln with an annual output of 60,000 tons of quicklime takes up an area of 6,000 m2). Add waste disposal, the high proportion of unskilled labor and related facilities.

Such chemical enterprises have dim prospects. To add insult to injury, their wear-out is universal countrywide. According to the data supplied by the ISKITIMCE-MENT Company in the Novosibirsk Region of Siberia, the wear of the fixed assets at most quicklime and cement producing enterprises tops 70 percent, with 93.5 percent of kilns and furnaces in service for more than 30 years.

It is not much to say, therefore, that conventional technologies are largely a spent asset. An all-out mod-

стр. 27

ernization of related industries is urgent on the basis of new scientific and engineering approaches, in particular, by replacing natural fuels with more efficient energy carriers. Although it may look extravagant, a beam of charged particles, namely fast (accelerated) electrons, is a way out.

A GLANCE AT RADIOCHEMISTRY

In keeping with the present-day level of radiation chemistry and high-energy chemistry, we distinguish several consecutive stages of radiation/matter interaction: the physical one in the 10-18 to 10-15 s range; the physico-chemical (when the process comes to an end 10-11 s after a particle has passed through a substance), and the chemical stage proper that is 10""' seconds and longer. Electrons give off their energy, first of all, to form atomic and molecular ions; second, they spend their energy on knocking out secondary electrons with energies sufficient for ionization of several atoms and molecules more; third, part of their energy goes for excitation* of atoms and molecules; and last, it is spent on

* According to quantum mechanics principles, atoms and molecules are stable only in certain steady states corresponding to definite energy values. The lowermost energy state is known as a basic one, with the rest considered excited ones. Changing from one steady state to another, an atom also changes the structure of its electron shell.--Ed.

bremsstrahlung (braking radiation). Leaving aside particulars, we must say that in condensed media (where each elementary particle rubs shoulders with many other particles and interacts with them) plasmons take form, that is collective excitations, with their energy in the 15 to 25 eV kind of localizing on individual molecules which, ionized, pass into high-excitation states. The lifetime of collective excitations is between 10""' and 10-15 seconds.

Present toward the end of the physical stage are molecular ions, electrons, "ordinary" molecules as well as superexcited molecules and ions. At this point the irradiated substance is not equilibrated thermally and is heterogeneous spatially, for the newly formed particles generate microregions several nanometers along the track of ionizing particles; such microregions are noted for their high local concentration. Next, at the physicochemical stage, "ordinary" molecules break down, and superexcited ones get self-ionized. By the end of this stage the substance attains thermal equilibrium.

The final, chemical stage witnesses oxidation of metals and formation of stable products as a result of respective reactions.

So, the action of electron beams on a substance ends in the same result as heating, with the energy "invested"--directly and practically in full--into molecular dissociation processes. This process accounts for the shifting of chemical reaction equilibrium toward lower temperatures. That is to say, an electron-irradiated substance does not have to be heated as much as it is in heat-treating furnaces with the use of conventional technologies.

WHAT ELECTRONS DO WE NEED?

The efficiency of electron/substance interaction depends on the energy of electrons and the intensity of a beam. The above-described processes of dissociation and ionization are effective already at 100 keV. The MeV value is considered to be an upper boundary, for any further increase of this energy will induce radioactivity through photonuclear reactions. An increase in the energy of fast electrons also results in a greater increase of the thickness of the irradiated layer of a substance. Simultaneously, however, fast electrons lose more of their energy on bremsstrahlung and, as a result, this poses problems for radiation protection. Thus, the choice of the above upper boundary is a compromise with respect to such factors as the thickness of the irradiated layer of a substance, energy losses of electrons on bremsstrahlung and the constraints imposed by acceleration facilities. Electron accelerators developed at the

стр. 28

Budker Nuclear Physics Institute of the RAS Siberian Branch in Novosibirsk* seem to be best for practical application. Such accelerators have been designed and built by teams headed by Dr. Vadim Auslaender (ILU series) and Rustam Salimov (ELV series). For as long as forty years these setups have been shipped to customers in many countries. The ILU accelerators operate in an alternating high-frequency electric field and are designed for work in the 0.7÷5 MeV range and at beam intensity as high as 50 kW. The ELV accelerators work on direct current within the 0.2 to 2.5 MeV range at beam intensity up to 400 kW. Both types are simple in design and have a long service life. Fully automated, they are radiation safe and have efficiency as high as 90 percent! It is possible to assemble several acceleration modules into one. This will allow to expand output siz-ably and provide for its flexibility by switching on or off individual component units.

The Budker Institute is closely involved with the upgrading of its electron accelerators and building up the energy of accelerated beams. Such setups are used for a variety of technological purposes, say, for purification of effluent industrial gases, decontamination of sewage, for modification of substances, in the paint and varnish industry, and so forth.

Although our country is a pioneer in developing such setups, their wide-scale use is realized abroad in the main. For instance, China has purchased around 50 plants like that in Novosibirsk. But they are important to us as well, especially in hydrometallurgy**, oil processing, in the production of lime, cement, chemical fertilizer, soda and many other essential materials.

FROM PETROCHEMISTRY

ON TO CARBONATE PROCESSING

Let us look into some of the above areas and begin with the radiothermal cracking of heavy fractions of oil.

Today oil refineries upon the extraction of light fractions (gasoline, kerosene, etc.) have to dispose of the remaining heavy fractions (up to 30 percent), for the available cracking techniques are unable to cope. But this problem can be solved, as shown by recent experiments (results obtained in 2009) involving powerful electron beams (20 kW, 2.5 MeV) and carried out by research institutes affiliated with the RAS Siberian

See: A. Skrinsky, "Cognition of Matter", Science in Russia, No. 6, 2007.--Ed.

** Hydrometallurgy-extraction of metals from ore concentrates and industrial wastes by means of water solutions of chemical reagents (leaching) and subsequent electrolysis as well as other techniques.--Ed.

Branch--the Institute of Solid State Chemistry and Mechanochemistry (Novosibirsk), the Budker Nuclear Physics Institute, the Oil Chemistry Institute (Tomsk), and Vorozhtsov Institute of Organic Chemistry. These experiments have proved the possibility of high-speed radiothermal cracking of different hydrocarbons at low temperatures. A cost-effective technology of cracking could be developed for powerful electron accelerators (800 kW, 5 MeV), efficient at temperatures lower than with conventional techniques.

Other research centers are showing an interest in these new methods. For instance, the Moscow-based Institute of Technical Physics and Automation (ROSATOM Corporation) is planning to adopt these very approaches.

Another line involves hydrometallurgical technologies for the breaking down of uranium, gold-bearing, platinum and other hard ores*. To leach out the constituent components one makes use of solutions of acids, alkalis and salts containing oxidizing and reducing agents. This

* See: N. Laverov et al., "Gold and Platinum of Sukhoi Log", Science in Russia, No. 1, 2001.--Ed.

стр. 29

process can be stepped up with the aid of catalytic and other special additives, oxygen and live steam blow. Yet all these techniques call for more high-energy and material costs.

In 2003 we proposed to use beams of fast electrons for modifying the mechanical characteristics of ore components and for triggering chemical reactions in leaching solutions. This idea was backed by MINATOM (ROSATOM) State Corporation, with the Moscow-based Research Institute of Chemical Technology turning to this job. At first it was done at our "Kurchatov Institute" center on the high-current accelerator Fakel ("Torch"), and then continued at the RAS Institute of Nuclear Research--its accelerator generating 5 kW beams with the energy of electrons as high as 7 MeV. As suggested by colleagues from the Chemical Technology Institute, we focused our experiments on intensifying chemical reactions for ferric iron, the most effective uranium oxidant.

The physicochemical principles of interaction of electrons with water solutions are the same as for gases and solid bodies. Yet reactions proceed much more vigorously in water solutions, for their radiolysis* gives rise to leaching ions and ion complexes alongside free oxygen, hydrogen peroxide, alkalis and other impurities. Extensive chemical chain reactions may proceed there

* Radiolysis-radiolytic decomposition under the effect of ionizing radiation.--Ed.

as well. In our experiments we have come up with situations when the liquid suddenly splashed out of the vessel where it was irradiated as a result of these reactions. Such phenomena have to be taken into account in technologies involving the electronic initiation of leaching reactions.

We came forward with a schematic design of a setup for metal extraction. It provides for a flow of solution or pulp, a receptacle and a tray (chute) feeding the liquid into the accelerator's zone of radiation. The feed rate of the solution or pulp is regulated by changing the up and down position of the receptacle under the tray; the thickness of their layer should not be above the range of an electron path in the medium (at 1 MeV in aquatic media it approaches 4 mm).

Yet another line of research relates to the decomposition of carbonates. We might as well note that the invig-oration of chemical reactions in leaching solutions and the decomposition of solid body molecular components under the action of electronic radiation are essentially one and the same process qualitatively, barring a few minor details. Carbonates are most needed in the production of lime, cement, aluminum, chemical fertilizer, soda and other essential materials. Works published as far back as the 1980s and 1990s cite experiments on radiolysis of certain solid substances made, in particular, by Dr. Alexei Pikayev of the Frumkin Institute of Physical Chemistry and Electrochemistry in Moscow;

стр. 30

Shorthand of a setup for metal extraction from ore: 1-accelerator, 2-vessel for source solution, 3-electron beam, 4-tray, 5-receptacle for irradiated solution.

they examine mechanisms implicated in the radiochemical decomposition of chlorates and bromates. In their structure and energy of molecular bonds these compounds come closest to carbonates. That is why, proceeding from the similarity principle, we can say: acted upon electrons, carbonates will break up in the same fashion as chlorates and bromates.

A setup realizing the radiothermal principle of the molecular breakdown of carbonates and their caking with clinker* additives may be analogous to the above setup for liquid heterogeneous systems. Only the tray is replaced with a closed-loop laminar conveyor with a regulated feed rate, and the radiation zone has to be enclosed within a cap linked to pump-down and conversion gas disposal facilities. The thickness of an atomized layer of carbonate raw material should not exceed the range of an electron path at a given energy value (by our estimates, given the electron beam power of 400 kW, the output of carbonate breakdown will reach 17.6 tons daily).

WHAT EXPERIMENTS HAVE SHOWN

As proved experimentally, the high-rate radiothermal cracking of hydrocarbons (paraffins, high-paraffin oil, flux, tar) at temperature ca. 350ºC is quite possible after all. The conversion of paraffin raw material to light cuts at boiling point <200ºC is above 70 percent. The output at boiling point <300ºC is equal to 57 percent for saturated hydrocarbons, it is 31 percent for unsaturated hydrocarbons, and 11 percent for other hydrocarbons.

As proved experimentally, irradiation with fast electrons at the absorbed dosage rate** 2.3 kGr's increases the degree of radiation-caused oxidation of ferrous iron in a sulphate solution (concentration of iron, 1 g/1; that of sulphuric acid, 5 g/1) to 95 percent just in 30 seconds, i.e. at the overall absorbed dose of 69 kGr. This means that an accelerator generating a 400 kW beam at power 1 MeV makes it possible to obtain 21 tons of leaching solution per hour. This absorbed dosage value could hold for other analogous solutions as well, since irradiation-caused chemical processes are of similar nature.

Two teams of Leningrad and Novosibirsk research scientists pioneered in devising methods for obtaining

* Clinker-here, an intermediate product in cement production.--Ed.

** Absorbed dosage (dose) rate-a ratio of the absorbed dose of radiation within a definite time interval to the interval itself; measured in grays per second (Gr/s).--Ed.

cement clinker from calcium carbonate in a beam of fast electrons. Back in 1976 Drs. Iosif Abramson, Boris Volkonsky and other Leningraders as well Acad. Vladimir Boldyrev, Dr. Vadim Auslaender and other scientists of Novosibirsk gained positive results in their experiments. Using fast electrons on model samples they obtained cement and registered a lower equilibrium temperature. Unfortunately this breakthrough achievement won no support from the state and then from big business.

As we see it, work on substituting an electron carrier for natural fuel will provide incentives for comprehensive research all down the line and in future could be instrumental in eliminating the oldtime technologies of burning up vast amounts of natural fuel and discharging hothouse gases into the atmosphere. Ecologically safe and pure industries will be born in the wake of such modernization.

The authors wish to express their gratitude to Dr. Nikolai Znamensky of the "Kurchatov Institute" Research Center for his support of our work, and to a leading expert of the same center, Alexander Arefyev, for taking part in experiments.

Illustrations supplied by the authors


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