| With the deepening exploitation and utilization, high quality coking coal appears severe shortage. And part of the low-quality coking coal with high sulfur content cannot be used reasonably. Therefore, the present research focuses on finding out an efficient method of removing surfur from coal. In this paper, we mainly study on microwave irradiation desulphurization technology.This paper is aimed at different regions of coking coal. The occurrence of mineral and organic sulfur in coal was characterized by XRD, XPS and XANES. Vector network analyzer has been used to analyze the microwave dielectric response of coal and model compounds in 0.1～6GHz and 6-16GHz, and the influence of moisture, minerals and organic sulfur model compounds on the macroscopic dielectric properties of coal samples is investigated. The related properties of sulfur model compounds were calculated by Materials studio software, which provide the study of the chemical reactivity of different sulfur compounds, the breaking difficulty of carbon-sulfur bond and the special effects of the sulfur bonds in the microwave alternating electromagnetic field. Based on the above research, the research on microwave desulfurization test of high-sulfur coking coal has been carried out.The main research conclusions obtained are as follows:1. The content of organic sulfur in high sulfur coking coal sample is about 70%～80% of total sulfur. Organic sulfur in coal is mainly composed of mercaptan, sulfoether, thiophenes, sulfoxides and sulfones, in which thiophenes are the majority reaching 50%～70% while sulfone sulfuris is in low content. The content of inorganic sulfur in coal is low and is mainly in the shape of pyrite.2. The dielectric properties of coal, the main minerals in coal and selected small molecule sulfur-containing model compounds are tested by vector network analyzer. The results show that the real part of relative complex permittivity of low ash coking coal is between 3.0～4.0, the loss angle tangent is more than 10-2, and the coal is lossy dielectric. The complex dielectric constant of coking coal will increase with the improvement of metamorphic grade of the coking coal. And the ash content in coal has a great impact on dielectric properties. In the test, the larger the ash content is the higher dielectric parameter values will be. The dielectric parameter value of water, pyrite and montmorillonite is ten times higher than coal. And the complex permittivity of galena and kaolinite is slightly higher than that of dry low ash coal. The dielectric parameter value of calcite, carbonate, gypsum and quartz varies little from coal. The complex permittivity of quartz in the selected minerals is the smallest. When mixing high permittivity material with low ash clean coal, the dielectric parameter value of the composite sample will be greatly increased. However, mixing low permittivity material the value changes little. In the material of sulfur-containing model compounds with similar structure and good symmetry, the higher the content of sulfur is the stronger the material storage polarization microwave energy in the microwave field will be. Some of the organic sulfur compounds have relatively obvious model absorption peak appeared in the frequency range of 8-12GHz, and which show that the absorption ability of microwave energy is higher.3. By cavity resonance method, the results of the dielectric properties tests of coal samples shows that the interaction of coal samples and microwave at 915MHz is stronger than at 2450MHz. When the temperature is between 30℃ to 300℃, the permittivity and loss tangent of coal will change with the increase of temperature, which can reach the max value at 100℃.4. Analysis of quantum mechanics simulation software shows that C-S bond in organic sulfur molecules is a weak bond, and it will give priority to fracture when there is energy input. The C-S bond in the ring structure or C-S bond where C atom comes from a ring structure is more stable than C-S bond in the chain structure. That is, the C-S bond in the thiophene is the most stable of all. By Mulliken atomic charges analysis, S atom is charged negatively because it is easy to accept electrons transferred from C atom or H atom nearby. Therefore, it is vulnerable to be attacked by electrophilic reagents. Study on typical small molecules sulfur-containing model compounds in external electric field shows that the reaction of electric field on the chemical bonds has directivity.The effect of electric filed can increase or decrease bonding capability between the atoms. Bonding in the direction of electric field has more influence on bonding capability than perpendicular to the bond direction of the electric field. When the electric field direction along with the C-S bond direction, the length of C-S bond will decrease and the bond order will increase. While the electric field direction along with the S-C bond direction, the length of C-S bond will increase and the bond order will decrease. Electrons within molecules move directionally under the effect of electric field and change the density of electron cloud and charge distribution of the atoms. The state density distribution of atomic orbital also changed at Fermi level affecting the activity of sulfur atom. The vibration of the molecules, dipole moment and energy gap changes along with different directions of electric field. The process of Hydrogen sulfide generated by sulfur transfer in thiophene is also influenced by directions of electric field. In the course of reaction, energy and potential barrier changes a little under the effect of electric field.5. The results of microwave irradiation experiment of high-sulfur coking coal show that, with all other factors being equal, the effects of microwave desulfurization at 915MHz are slightly better than that at 2450MHz. Because of a high thiophenic sulfur content in coal, in the condition of low temperature desulfurization effect is ineffective, and desulfurization degree is 7.5%. After irradiation, the content of inorganic sulfur, thioalcohol and thiophenic sulfur decreases while sulfoxide and sulfone increases and other forms of sulfur (e.g., thiophene) translate into sulfoxide sulfur. Desulfurization with microwave and oxidizing agent show that: good desulfurization effect was achieved when the frequency is 2450MHz, microwave irradiation power is 560W-700W, irradiation time is 4mins and the ratio of acetic acid and hydrogen peroxideis 1:1.Desulfurization degree of Xinyu coal is 29.50%, Wuhai coal is 39.54% and has a greater damage to caking property of coal. Desulfurization with microwave and NaOH show that: when microwave irradiation power is 560W, irradiation time is 8mins and caustic soda solution is 5mol/L, the desulfurization rate of Xinyu coal is 20.63% and Wuhai coal is 29.53%. And it has less damage to caking property of coal during microwave assisted alkali desulfurization. |
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