Relevance: Industrial emissions of enterprises in Kazakhstan into the atmosphere amount to about three million tons per year. Non-ferrous metallurgy enterprises annually emit more than 100 thousand tons of sulfur dioxide into the atmosphere. The lack of a reliable flue gas cleaning system and the use of old methods of capturing SO2, fly ash, CO2 and other harmful air pollutants have led to an increase in their concentrations in emissions above the maximum allowable standards. Air pollution with sulfur dioxide and carbon dioxide has become one of the most serious problems. The volumes of greenhouse gases emitted have become so large that they have become the subject of intense scrutiny requiring urgent action. In this regard, the solutions developed in the work aimed at deep purification of waste gases from SO2 and CO2 with the production of commercial products seem to be extremely relevant.
Purpose: Creation of an environmentally friendly technology for the utilization of SO2 and CO2 from the exhaust gases of thermal power plants and metallurgical enterprises with the production of commercial products: elemental sulfur, biofuel and oxygen.
- – ensuring a significant reduction in sulfur emissions into the atmosphere (the residual sulfur content in gases emitted into the atmosphere after cleaning will be 0.001%) and the complete utilization of carbon dioxide to its monoxide;
- exclusion of the use of expensive materials and reagents;
- exclusion of the formation of additional solid and / or liquid waste;
- increasing energy efficiency by involving high-calorific coals with a high sulfur content in the processing;
- reducing the costs of thermal power plants and metallurgical enterprises by reducing the existing energy and material costs spent on waste gas cleaning operations;
- reducing the volume of production waste by obtaining additional commercial products – elemental sulfur or sulfuric acid and carbon monoxide;
- prevention of acid rain formation;
- ensuring stable conditions for the complex purification of waste gases from SO2 and CO2 through the use of new technical solutions («know-how »).
The results obtained for the 1st stage of the schedule:
1) The principal possibility of trapping sulfur from exhaust gases with a eutectic mixture of alkali metal carbonates, wt %: Li2CO3 - 43.5%, Na2CO3 - 31.5%, K2CO3 - 25.0% in the temperature range 450-600˚С is shown. It has been established that at low temperatures the values of the Gibbs free energy of reactions of chemical absorption of sulfur dioxide with carbonates have negative values and vary from ∆GT = - 160 kJ/mol to ∆GT = - 210 kJ/mol. The results of thermodynamic calculations are fully confirmed by experimental studies. Based on electrochemical, X-ray diffraction and XRD studies of samples obtained after the chemical absorption of sulfur from exhaust gases by carbonate melt, it was found that sulfur is almost completely (95%) removed from gases and concentrated in the melt in sulfate form.
2) The thermodynamic analysis of the reactions of interaction between the components of the carbonate-sulfate melt with natural gas has been carried out. For the first time the values of Gibbs free energy for the reaction of K2SO4 reduction by natural gas in the temperature range 400…850 ºС have been calculated. It has been established that the process of regeneration of carbonate-sulfate melts is accompanied by the release of H2S and the formation of alkali metal carbonates.
3) Based on experimental experiments, it has been established that the process of regeneration of a carbonate-sulfate melt with natural gas provides high rates of sulfate reduction and the achievement of a maximum of up to 99% sulfur recovery from the melt in the form of H2S.
4) For the first time, the kinetic regularities of the process of regeneration of a carbonate-sulfate melt with natural gas have been studied. The kinetic parameters of the K2SO4 reduction reaction with natural gas were determined: the activation energy of the reaction is E=8.7 kJ/mol, the process mechanism is described by a first-order equation, n=1. It has been established that the presence of a diffusion region does not significantly affect the rate of the reaction of potassium sulfate reduction with natural gas.
5) It has been established that the removal of sulfur from the sulfate-carbonate melt by natural gas bubbling can be carried out in the operating temperature range of the off-gas purification absorption column - 500-550 ºС. It is shown that the process of regeneration of sulfate-carbonate melt with natural gas is a relatively simple one-stage process that occurs at a fairly high rate. This makes it possible to integrate the recovery column with the absorption column, where sulfur is captured from the off-gases..
6) The removal of sulfur in the form of H2S provides considerable freedom in the choice of final commercial product, either sulfuric acid (by dry combustion of H2S) or elemental sulfur (by the Claus process), which are of considerable commercial value.
7) The developed technology can become a practical and economical method for cleaning sulfur-poor flue gases emitted by non-ferrous metal plants, which will help limit sulfur emissions into the atmosphere.
The results obtained for the 2nd stage of the schedule:
1) Based on the study of the scientific foundations of the electrolysis of carbonate-oxide melts of alkali metals and the results of complex laboratory studies, the possibility of implementing the technology of electrolysis of carbonate-oxide melts of alkali metals with the production of commercial biofuel (CO) and pure oxygen is substantiated.
2) On the basis of thermodynamic and electrochemical analyzes of lithium carbonate electrolysis, new data were obtained on the implementation of the process with the production of CO. The possibility of utilizing CO2 to CO during the electrolysis of lithium carbonate is shown. It has been established that in long-term experiments (more than 100 hours) the Faraday efficiency of the process of electrochemical reduction of CO2 to CO at 900 °C is close to 100%, and the thermodynamic efficiency at 100 mA/cm2 is at least 85%.
3) It has been established for the first time that the electrolysis of the Li2CO3/Li2O melt, which initially contains <2 mol % Li2SO4, at 900 °C, makes it possible to obtain CO and elemental sulfur in the cathode space. It is shown that the Li2SO4 decomposition potential measured under these conditions is only 0.15 V, and at a cathode current density above 1 A/cm2, the sulfur reduction current is limited by diffusion. Because sulfur is constantly being removed from the cathode portion of the cell, sulfur-contaminated CO2 sources can be used to convert CO2 to CO during the electrolysis of molten lithium carbonate.
4) Studies have been carried out to study the stability of Li2CO3/Li2O melts under electrolysis conditions, and for the first time the pressures of CO2 vapors over melts of various compositions have been determined. It has been established that for a mixture with a Li2O mole fraction of 0.06, at a temperature below 1173 K, the equilibrium pressure of CO2 is less than 20 kPa, and rapidly decreases with decreasing temperature and increasing the content of Li2O in the melt.
5) New data on the equilibrium values of the partial pressure of CO2 over Li2CO3 + Li2O melts of various compositions (the mole fraction of Li2O is from 0.02 to 0.06) at temperatures from 1073 to 1248 K have been obtained. The values of the equilibrium constant for the decomposition reaction of Li2CO3 and the values of the thermodynamic functions - enthalpies and entropies. It has been established that within the limits of the change in the mole fraction of Li2O in the melt in the range 0.02 ≤ ХLi2O ≤ 0.06, the values of enthalpy and entropy remain constant up to experimental error and are: ΔH = 275±5 kJ/mol and ΔS = 179± 4 J /(mol×K). For the Li2O mole fraction below 0.02, the values of both ΔS and ΔH decrease sharply with decreasing oxide concentration in the melt.
6) The selection of wear-resistant materials for the manufacture of the electrolytic cell was carried out, the choice of material for the electrolytic cell was substantiated. Systematic studies have been carried out to study the wear resistance of electrically insulating materials depending on the exposure time in carbonate-sulphate melts and temperature changes. New data on the wear resistance of various ceramic materials (MgO, ZrO2, BeO2) in aggressive carbonate-sulphate melts at 900°C have been obtained. It has been established that ceramics based on MgO practically does not react with the melt and is suitable for creating current inputs for electrodes that are resistant to high temperatures and aggressive media. It is shown that a coating consisting of lithium zirconate appears on the surface of a ceramic material made of ZrO2, when it is held in a melt at 900°C, the thickness of which increases with an increase in the holding time in the melt. The established fact limits the use of ceramics based on ZrO2 for the manufacture of an electrolyzer and protection of current inputs, due to the threat of ensuring the long-term structural stability of ceramics. Ceramics based on beryllium oxide experience severe corrosion even with a short duration of exposure in the melt (2 hours), which makes it unsuitable for use as an insulating material.
7) Experiments were carried out on the electrolysis of lithium carbonate with the production of CO. Recommendations were issued, optimal parameters and modes of the electrolysis process were established. On the basis of experimental experiments, the choice of material for the manufacture of the electrolyzer and electrodes was made. The possibility of coating a titanium electrode with a protective TiC coating 10 microns thick is shown. It has been established that electrolysis can be carried out continuously, producing pure CO with a thermodynamic efficiency of at least 96%.
Based on the results of comprehensive studies, the optimal technological parameters and modes of the electrolysis process were established:
- Initial electrolyte - Li2CO3/Li2O (mole fraction of Li2O, XLi2O = 1-8 % mol.).
- Electrodes: cathode - titanium; anode - graphite.
- The distance between the electrodes is 50 mm (laboratory setting).
- Current density:
– at the cathode - 1 A/cm2;
– at the anode - 50 mA/cm2.
- Duration of electrolysis - continuous process.
- Electrolysis temperature - 900 ºС.
- Products of electrolysis:
– at the cathode - CO gas (at least 98%) and elemental sulfur (if present in gases);
– at the anode - pure oxygen.
- Process efficiency - not less than 96%.
- Composition of gas supplied for utilization, % (vol.): 5 SO2, 15 CO2, 3 O2, 77 N2.
List of performers:
- Dosmukhamedov Nurlan Kalievich - Scientific adviser
- Egizekov Maksut Gusmanuly - Chief Researcher
- Kaplan Valery Aronovich - Leading Researcher
- Zholdasbay Yerzhan Yesenbayuly - Senior Researcher
- Kurmanseitov Murat Bauyrzhanuly - Senior Researcher
- Argyn Aidar Abdilmalikuly - Researcher
List of publications:
- Kaplan V., Dosmukhamedov N., Zholdasbay E., Daruesh G., Argyn A. Alumina and Silica Produced by Chlorination of Power Plant Fly Ash Treatment // JOM. – 2020. – Vol. 72(10). – P. 3348–3357. (Web of Science, Scopus, Q-2, Процентиль-84-й.) DOI
- Досмухамедов Н.К., Каплан В.А., Даруеш Г.С. Инновационная технология комплексной переработки золы от сжигания угля // Уголь. – 2020. – №1. – С. 58-63. (Scopus, Q-3, Процентиль-30-й.) DOI
- N. Dosmukhamedov, G. Daruyesh Products from coal combustion – additional extraction source of valuable metals // Vestnik KazNRTU. – 2020. – Vol.2 (138). – P. 333-342
- Досмухамедов Н.К., Даруеш Г.С., Жолдасбай Е.Е. Особенности поведения компонентов золы в условиях хлорирующего обжига // Международный журнал прикладных и фундаментальных исследований. – 2020. – № 2. – С. 97-98. (РИНЦ, IF-0,58)
- N. Dosmukhamedov, V. Kaplan Flue gas purification from SO2 and NOx using molten mixture of alkali metal carbonates // International Journal of Coal Preparation and Utilization. – 2021. – P. 1-12. (Web of Science, Scopus, Q-3, Процентиль-58-й.) DOI
- Досмухамедов Н.К., Каплан В.А., Жолдасбай Е.Е., Даруеш Г.С., Аргын А.А. Выделение железа в железосодержащий продукт из золы от сжигания Экибастузских углей // Уголь. – 2021. – №1. – С. 56-61. (Scopus, Q-3, Процентиль-30-й.) DOI
- Досмухамедов Н.К., Егизеков М.Г., Жолдасбай Е.Е., Курмансейтов М.Б., Аргын А.А. Поведение NOx при очистке отходящих газов ТЭС карбонатным расплавом щелочных металлов // Международный журнал прикладных и фундаментальных исследований . – 2021. – № 1. – С. 30-35. (РИНЦ, IF-0,58)
- Досмухамедов Н.К., Каплан В.А., Жолдасбай Е.Е., Курмансейтов М.Б., Аргын А.А. Электрохимическое восстановление CO2 до СО в условиях электролиза карбоната лития при 900 ºС
- // Международный журнал прикладных и фундаментальных исследований. – 2021. – № 3. – С. 59-66. (РИНЦ, IF-0,58)
- Досмухамедов Н.К., Каплан В.А., Жолдасбай Е.Е., Курмансейтов М.Б., Аргын А.А. Егизеков М.Г.
- Технологические опыты по утилизации СО2 с получением товарных продуктов // Международный журнал прикладных и фундаментальных исследований. – 2021. – № 9. – С. 95-99. (РИНЦ, IF-0,58)
- Dosmukhamedov N.K., Zholdasbay E.E., Kurmanseitov M.B., G., Argyn A.A. Kinetic parameters of the process of regeneration of carbonate-sulphate melt with natural gas // Gornyi Zhurnal Kazakhstana. – 2021. – №1. – P. 34-40.
- Досмухамедов Н.К., Егизеков М.Г. Условия устойчивого развития медной промышленности. Теория. Эксперимент. Практика. Монография. – 2021. – 308 с.