- XU Ji;ZHU Jialong;HU Haoquan;JIN Lijun;Institute of Coal Chemical Engineering,School of Chemical Engineering,Dalian University of Technology;
The analysis of pyrolysis products, especially in-situ detection and analysis of primary pyrolysis products is an important way to understand the mechanism of coal pyrolysis. In this paper, the application of three kinds of on-line pyrolysis coupled with mass spectrometry(MS)techniques, including thermogravimetric-mass spectrometry(TG-MS),flash pyrolysis-gas chromatography-mass spectrometry analysis(Py-GC-MS),and in-situ pyrolysis time-of-flight mass spectrometry(Py-PI/EI-TOF-MS)combined with vacuum ultraviolet photoionization(PI)and electron ionization(EI)in coal pyrolysis were reviewed, and their advantages and disadvantages were compared. TG-MS can be used to analyze the coal conversion and the escape characteristics of pyrolysis gas volatiles(especially the light components)with the pyrolysis temperature. The compositions and distribution of pyrolysis products at rapid heating rate can be acquired by Py-GC-MS. In comparison, due to the characteristic of in-situ analysis, high sensitivity, soft ionization and easy cleaning, Py-PI/EI-TOF-MS can be used to in-situ detect the primary products from individual or co-pyrolysis of coal-model compounds, raw coal and its extraction, biomass as well as waste plastics. The evolution behaviors of primary products and the catalytic pyrolysis can be also implemented. The in-situ Py-PI/EI-TOF-MS provides a promising method to understand the pyrolysis mechanism of carbonaceous organic matters in a molecular level.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2966K]
2021 04 v.27;No.134 [Abstract][OnlineView][Download 1503K] - ZHAO Xue;LUO Nanyang;HAN Zhihong;XUE Yu;HUANG Chenglyu;ZHANG Qiaoling;LYU Zhaomin;TAN Houzhang;School of Energy and Power Engineering,Xi′an Jiaotong University;Fujian Eternal Energy Management Co.,Ltd.;
In view of the problems of easy blockage and high operating costs of limestone-gypsum wet flue-gas desulfurization systems, a new type of integrated bubbling(emulsifying)wet desulfurization and dust removal system for fly ash recycling of coal-fired industrial boiler was developed. The traditional fly ash desulfurization is only used as a desulfurizer carrier and directly sprayed into the flue. By purifying the Ca~(2+) in the fly ash to prepare an alkaline slurry, wet desulfurization of fly ash can be achieved without adding other desulfurizers. At the same time, the new desulfurization system does not set nozzle device, and the "hurricane cyclone" allows the flue gas to cut the desulfurizer to form an emulsifying layer, so as to increase the reaction time and reaction area of the effect. The application results of a 14 MW industrial hot water boiler show that the new desulfurization system runs stably under high, medium and low loads, and the average inlet flue gas temperature is 100 ℃,which is 30-50 ℃ lower than the boiler exhaust temperature before the renovation, which effectively improves the thermal efficiency of the boiler. Under medium-load operating conditions, the content of SO_2 after desulfurization by the new desulfurization system is 10.9 mg/m~3,and the desulfurization efficiency is 91.2%. At the same time, the synergistic dust removal efficiency of the desulfurization system is 98.94%. After deep dust removal by wet electrostatic precipitator, the smoke concentration is 4.8 mg/m~3,which can meet ultra-low emission standards. The system fundamentally solves the traditional limestone wet desulfurization nozzle device easy blockage problem, and saves the traditional cloth bag dust collector, has low operating cost, and a good promotion prospect.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2215K] - WANG Chao;SONG Guoliang;LYU Qinggang;Institute of Engineering Thermophysics,Chinese Academy of Science;University of Science & Technology of China;University of Chinese Academy of Science;Dalian National Laboratory for Clean Energy,Chinese Academy of Science;
Circulating fluidized bed(CFB)boilers have become one of the best commercial technologies of clean coal combustion due to the advantage of inherent low cost of controlling pollutant emission. With the introduction of ultra-low emission standards, CFB combustion technology also faces huge challenges. In order to meet the ultra-low emission standards, the devices for treatment of flue gas are usually used, resulting in a significant increase in the cost of pollution treatment for CFB boiler. How to achieve ultra-low NO_x and SO_2 emissions of CFB boiler has become the research focus.The existing conventional ultra-low NO_x emission technology of CFB,ultra-low SO_2 emission technology of CFB,newly developed ultra-low NO_x combustion technology of CFB,ultra-low SO_2 emission technology in the furnace of CFB and ultra-low NO_x and SO_2 cooperative control technology of CFB were systematically discussed. The results show that high-efficiency separators cannot only improve the combustion efficiency of CFB,but also is the premise of using ultra-fine limestone for highly efficient desulfurization. The higher the separator efficiency is, the higher the CFB combustion efficiency and ultra-fine limestone desulfurization efficiency is. With the large-scale development of circulating fluidized bed boilers, the cross-section of the furnace is getting larger and larger, so how to achieve the horizontal uniform mixing of ultra-fine limestone in the large furnace becomes the first technical challenge. The technology for controlling a single gas to meet the ultra-low emission is relatively mature, but how to coordinately control NO_x and SO_2 to meet the ultra-low emission standard has become the second technical challenge. The current ultra-low emission technology in the furnace of CFB can only achieve ultra-low emissions for certain specific fuels, and however for other conventional fuels, whether NO_(x )and SO_2 can achieve ultra-low emissions still needs further deep research.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 3528K] - WANG Shiwei;JIAO Tiantian;ZHANG Yaqing;LI Xiangping;ZHANG Huawei;LIANG Peng;School of Chemical and Biological Engineering,Shandong University of Science and Technology;School of Municipal and Environmental Engineering,Qingdao University of Technology;
The main energy structure is dominated by coal in China, and the dependence of oil and natural gas resources on foreign countries has increased year by year. In order to alleviate the contradiction between supply and demand of energy and ensure national energy security, there are new challenges and opportunities for coal chemical industry in China. The indirect coal liquefaction technology based on Fischer-Tropsch synthesis is one of the effective methods to alleviate the shortage of petroleum resources and promote the clean and efficient utilization of coal resources. The post-filtration system of Fischer-tropsch synthesis slurry reactor will produce a mass of solid waste named Fischer-Tropsch synthetic wax residue, which contains 40%-60% percent paraffin. It is a kind of hazardous solid waste and is prone to generate spontaneous combustion of long-term storage. At present, the mian treatment of Fischer-Tropsch synthesis wax residue is only by mixing it with burning or burying it, which has caused a great waste of resources and security risks. In this paper, the slurry bed technology of Fischer-Tropsch synthesis, the formation of Fischer-Tropsch synthesis wax residue and the existing problems were introduced. The research progress on the recovery and utilization of Fischer-Tropsch wax residue at home and abroad was reviewed. The advantages and limitations of centrifugation, surfactant method, Superheated steam injection, ultrasonic treatment, extraction and pyrolysis technology for paraffin recovery were analyzed and compared. It is suggested that the coupling of separation technology can increase the recovery rate of paraffin on the basis of reducing the damage to the chemical structure of paraffin.The waste clay after recovering paraffin wax should be reused as construction, ceramics, rubber fillers, etc.,or recycled as fresh clay for dye adsorption and bleaching agent. It is of great significance that harmless treatment and resource utilization of wax residue can not only recycle high quality paraffin, but also alleviate resource shortage and environmental pollution. The comprehensive utilization route with the advantages of simple operation, high utilization rate, no secondary pollution and certain economic benefits, is an effective way and urgent demand for the resource utilization of Fischer-Tropsch wax residue.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 1473K] - HOU Ranran;BAI Zongqing;FENG Zhihao;GUO Zhenxing;KONG Lingxue;BAI Jin;LI Wen;State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Chinese Academy of Sciences;University of Chinese Academy of Sciences;
With high content of oxygen and high thermal reactivity, lignite is an important feedstock for the preparation of high value-added chemicals, such as phenols and humic acids. The heteroatoms especially the abundant oxygen-containing functional groups(e.g. phenolic hydroxyl groups and carboxyl groups)result in the existence of a large number of hydrogen bonds in lignite. Hydrogen bonds are usually involved in thermal conversion(pyrolysis, drying and direct liquefaction)of lignite, mainly including hydrogen bonds in lignite and hydrogen bond between lignite and solvents. Those two kinds of hydrogen bonds apparently differ in geometry configuration and strength. To present, various hydrogen bonds can be figured out by experimental methods(such as volumetric swelling degree and infrared spectroscopy),as well as quantum chemistry calculations. Hydrogen bonds in coal and hydrogen bonds between lignite and solvent exist widely, and significantly affect thermal conversion of lignite, especially pyrolysis and direct coal liquefaction. Hydrogen bonds in lignite play important roles in the stabilization of macromolecular network of coal, which can promote dehydration of phenolic hydroxyl groups and carboxyl groups, as well as the low-temperature crosslinking reactions during thermal conversion and is not conducive to the formation of light products such as tar. The hydrogen bond between lignite and solvent is an important form of interaction between lignite and solvent. Its strength significantly affects the physical and chemical reactions of lignite in the process of thermal conversion, such as extraction, swelling and deoxidation. It is of great significance for the clean and efficient conversion of lignite to fully understand the existing forms and influencing factors of hydrogen bonds related to lignite, and to regulate the hydrogen bonds on this basis. To present, the main purpose of hydrogen bonds modulation is destroying hydrogen bonds which exist in lignite, so that the crosslinking reactions during thermal conversion can be suppressed to some degree. It can be realized by preheating treatment at relatively low temperature, as well as solvent pretreatment using stronger hydrogen bonds acceptors such as pyridine and ionic liquid. However, current study about hydrogen bonds formed by lignite and solvents are mainly qualitative researched, the in-situ observation and quantitative analysis of the lignite thermal conversion are lack.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 3762K] - ZHANG Jiahang;ZHU Jianguo;Institute of Engineering Thermophysics,Chinese Academy of Sciences;University of Chinese Academy of Sciences;
Coal is a major pillar of our national energy, however, the SO_2 and other pollutants released by coal combustion have caused serious damage to the environment. The organic sulfur in coal has a complex structure and diverse forms so that the research is relatively difficult. Therefore, the research on the conversion characteristics of organic sulfur in coal can provide theoretical support for the control of SO_2 pollutant emissions and achieve clean coal combustion. In order to study the conversion of organic sulfur forms in coal during the preheating process, a preheating combustion test of Shenmu bituminous coal was carried out on a 30 kW preheating combustion experiment platform. During the experiment, solid samples were taken at the measurement points, and X-ray photoelectron spectroscopy technology(XPS)and diffraction of X-rays(XRD)was used to analyze Shenmu bituminous coal and preheated semi-coke. The results show that the main forms of organic sulfur in Shenmu bituminous coal can be divided into four types: mercaptans and thioethers(32.6%),thiophenes(16.0%),sulfoxides(15.9%)and sulfones(15.3%). Inorganic sulfur includes CaSO_4,FeS_2. When the preheating temperature reaches above 800 ℃,the sulfur form and content in the preheated semi-coke change greatly compared with that in the raw coal. The inorganic sulfur in the preheated semi-coke has CaS in addition to the original types. The degree of decomposition of organic sulfur in preheated semi-coke increases with the increase in air equivalent ratio during preheating, among which mercaptans and sulfides are reduced the most due to decomposition, followed by thiophenes and sulfoxides, and the relative content of sulfones increases. The reason of the sulfones increasing is from two aspects, one is due to the discompose of other substance like mercaptans or thiophenes, and the other is due to the conversion from mercaptans to sulfones.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 4855K] - WANG Kun;LIANG Wenzheng;WANG Cuiping;School of Electrical and Mechanical Engineering,Qingdao University;College of Civil Engineering and Architecture,Shandong University of Science and Technology;
In order to explore the migration law of sulfur element and the pollutant formation in the process of coal pyrolysis, and taking Ningdong coal as the research object, X-ray photoelectron spectroscopy, ~(13)C nuclear magnetic resonance(~(13)C-NMR),industrial analysis and element analysis were used to analyze the internal element types, chemical valence states and bonding modes of Ningdong coal, and two types of low rank chemical structure models of Ningdong coal which contains sulfur but no ash and water content were constructed. After molecular dynamics annealing simulation and geometry structure optimization in Material Studio software, the chemical structure with obvious stereoscopic structure was obtained, which ensured that there were four sulfur atoms in the model box, to correctly summarize the sulfur migration path and productions during the coal pyrolysis process. After that, ReaxFF force field was used to simulate in 200 ps molecular dynamics at reference temperature of 2 500 K. It is found that the distribution of pyrolysis products is in good agreement with the reference simulation results, which proves the rationality of the model. Thus, the transformation characteristics of sulfur atoms in the form of mercaptan and thiophenol during initial period of coal pyrolysis was summarized. Although both types sulphur eventually migrate to tar products, there have different migration rates and stable chain structures. The migration of sulfur in the initial stage of coal pyrolysis corresponds to the reason of high sulfur content in coal tar during the actual low temperature coal pyrolysis. Increasing the simulation reference temperature or extending the calculation time is required to determine the deeper secondary reaction behavior of the sulfur migration during coal pyrolysis process.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 7135K] - YANG Qinlin;LIU Yongqi;TANG Xing;YAO Qiuxiang;SUN Ming;MA Xiaoxun;Shaanxi Research Center of Engineering Technology for Clean Coal Conversion,Chemical Engineering Research Center of the Ministry of Education for Advanced Use Technology of Shanbei Energy,School of Chemical Engineering,Northwest University;School of Science,Xijing University;Key Laboratory of Coal Resources Exploration and Comprehensive Utilization,Ministry of Natural Resources;
The real yield and composition distribution of low temperature coal tar play a key guiding role in evaluating low-temperature carbonization process of coal. In order to obtain the accurate yield of coal tar and the distribution law of light and heavy coal tar and the whole component information of coal tar, the low temperature light coal tar(LCT)and heavy coal tar(HCT)were used as raw materials, and the mixture of LCT∶HCT∶water=1∶1∶1 was heated and recombined to obtain the reconstructed coal tar(RCT),the reconstructed light coal tar(RLCT)and heavy coal tar(RHCT). In addition, the n-hexane extracts(E-CT,E-LCT,E-HCT,E-RCT,E-RLCT and E-RHCT)and insoluble residues(I-CT,I-LCT,I-HCT,I-RCT,I-RLCT and I-RHCT)were obtained by ultrasonic extraction with n-hexane, the composition structure, pyrolysis behavior, and volatile gases characteristics of extracts and residues by n-hexane ultrasonic extraction were analyzed by gas chromatography-mass spectrometry(GC-MS)and thermogravimetric-Fourier transform infrared spectroscopy(TG-FTIR)technology. The results show that the RLCT and RHCT are 24.93% and 75.08% respectively by coal tar restructuring test, n-hexane extracts are mainly composed of alkanes, aromatics and phenolic substances. Compared with E-LCT and E-HCT,the content of aliphatic hydrocarbons of E-CT decreases, acidic compounds increases instead. Compared with E-CT,the content of aromatic hydrocarbons in E-RCT significantly reduces and E-RHCT enriches aromatic hydrocarbons and acidic compounds, while the aliphatic hydrocarbons decreases to 35.05%. The composition of residue mainly contains saturates and aromatics. After recombining, the light components of I-RHCT and I-RLCT declines and residues show better thermal stability.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 5588K] - ZHENG Hongyan;HUANG Youhang;ZENG Hao;ZHAO Xiaoxu;FENG Zhihao;HOU Ranran;BAI Zongqing;Department of Chemistry and Chemical Engineering,Taiyuan Institute of Technology;State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Chinese Academy of Sciences;
Pyrolysis to recover oil accompanied by semi-coke combustion can realize the high-efficiency and staged utilization of low-rank coal, which is the research hotspot of high-efficiency utilization of low rank coal. However, because of its low volatile, the ignition temperature of semi-coke is high, and it is hard to burn out as well. The addition of flux is a promising method to improve the combustion properties of the hard-to-burn semi-coke with low volatile. In this paper, the effects of alkali(K_2CO_3)and alkaline metal(CaCO_3)on the combustion characteristics of semi-coke were studied by thermogravimetric analysis, and the activation energy of the semi-coke combustion were investigated by Kissinger-Akahira-Sunose(KAS)model. The results show that the semi-coke has the high ignition temperature and low combustion reactivity. The inherent mineral matters in semi-coke have some catalytic effects on its combustion performance. The addition of CaCO_3 has little promotion effect on the characteristics of semi-coke combustion, which indicates that CaCO_3 does not improve its combustion properties. However, compared with alkali earth metal CaCO_3,the addition of K_2CO_3 obviously lowers the ignition temperature, the peak temperature of combustion and the combustion index. At the same time, with the increase of addition ratio of K_2CO_3,the apparent activation energy of semi-coke combustion decreases obviously, which means that the addition of K_2CO_3 can apparently improve the combustion reactivity of semi-coke. 2% addition of K_2CO_3 shows the best improvement for the combustion of semi-coke in this experiment, and the dispersion effect of adding K_2CO_3 by impregnation method is better. In addition, the addition of K_2CO_3 with impregnation is more favorable for the improvement of semi-coke combustion than physical mixture.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2882K] - YAN Huaqing;ZHANG Xianlian;XU Kai;LI Hanjian;XU Jun;WANG Yi;JIANG Long;SU Sheng;HU Song;XIANG Jun;School of Energy and Power Engineering,Huazhong University of Science and Technology;Hubei Xisaishan Power Generation Co.,Ltd.;
Pressurized oxy-fuel combustion has attracted much attention, which is considered to be a more efficient and cleaner second-generation oxy-fuel combustion technology. As the first step of coal combustion, different pyrolysis conditions(pressure, atmosphere, heating rate, etc.) directly affect the physical and chemical structure of char, which in turn leads to different combustion reactivity. At present, under the conditions of pressurized oxy-fuel combustion, there is few report on the correlation between the reactivity and structural properties of char. A pressurized concentrating photothermal apparatus whose maximum heating rate could reach 80 ℃/s was independently designed and established. Two kinds of Zhundong coals, Hongshaquan(HSQ) and Wucaiwan(WCW) were selected to prepare char under different pressures(atmospheric pressure-1.5 MPa) and pyrolysis atmospheres(N_2,CO_2). The specific surface area analyzer, Raman analyzer, thermogravimetric analyzer were used to systematically investigate the influence of pressure and pyrolysis atmosphere on the structural characteristics of char and its combustion reactivity. The results show that under inert N_2 atmosphere, the char yield of HSQ and WCW coal at 1.5 MPa increase by 3.54% and 10.49%,respectively, compared with atmospheric pressure. While under CO_2 atmosphere, compared with atmospheric pressure, the char yield of HSQ coal at 1.5 MPa decreases by 16.40%,and the char yield shows opposite trends with pressure changes under two kinds of atmospheres. Under N_2 atmosphere, the specific surface area of HSQ/WCW char increases from 24.20/14.85 m~2/g to 26.27/46.19 m~2/g with the pressure increases from atmospheric pressure to 0.4 MPa. However, when the pressure continues to increase to 1.5 MPa, the specific surface area of HSQ/WCW char decreases from 26.27/46.19 m~2/g to 21.21/39.46 m~2/g. Under the same pressure, the pore structure of char prepared under CO_2 atmosphere is more developed. At atmospheric pressure and 1.5 MPa, the specific surface area of HSQ char prepared under CO_2 atmosphere is 6.46 and 9.03 times that of char prepared under N_2 atmosphere, respectively. This is also the main reason why the combustion reactivity of HSQ char prepared under CO_2 atmosphere is better than that prepared under N_2 atmosphere. With the increase of pressure, whether it is prepared under N_2 atmosphere or CO_2 atmosphere, the ratio of I_((GR+VL+VR))/I_D calculated by the peak fitting calculation of the Raman spectra of two kinds of chars gradually decreases, and the chemical structure of the chars tends to be more stable, which also make the combustion reactivity of chars prepared under high pressure decreases. However, under the same pressure, the ratio of I_((GR+VL+VR))/I_D of HSQ char prepared under CO_2 atmosphere is lower than that prepared under N_2 atmosphere. Under high pressure, the gasification reaction of CO_2 and char is enhanced, which consume more amorphous carbon, so the difference of I_((GR+VL+VR))/I_D is more obvious under two kinds of atmospheres. However, due to the dominant effect of the difference in physical pore structure, HSQ char prepared under CO_2 atmosphere has better combustion reactivity. It could be concluded that the combustion reactivity of char is affected by physical structure and chemical structure.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 3773K] - SHAN Xiangen;SHU Geping;CAO Xueping;WANG Hongxue;GAO Shansong;National Engineering Laboratory for Direct Coal Liquefaction,China Shenhua Coal to Liquid and Chemical Company Shanghai Research Institute;
In order to study the direct liquefaction characteristics and product distribution of Naomaohu coal in Xinjiang, the effects of reaction temperature and reaction time on the yield of liquefied products were investigated in the 0.5 L batch autoclave with tetrahydronaphthalene as solvent, nano-iron oxide as catalyst and S as a promoter. The results show that Naomaohu coal is easy to be liquefied. When the reaction temperature just rises to 425 ℃,the conversion is up to 96.6%,and the oil yield is 56.68%. With the increase of reaction temperature and reaction time, coal conversion, hydrogen consumption, gas yield, and oil yield gradually increase, while the yield of asphaltic substances decreases and the water yield remains basically unchanged. Then, as the reaction temperature increases further and the reaction time continues to extend, the light oil will be further cracked, leading to further increase in gas yield and decrease in oil yield. When the reaction temperature is 455 ℃ and the reaction time is 80 min, the conversion rate of coal reaches 99.6%,the yields of oil, asphaltic substances, and gas are 73.42%,1.64%,and 16.61%,respectively, and the hydrogen consumption is 4.85%. According to the law of liquefaction reaction, five lumped reaction kinetic models were established. The Kinetic model parameters were obtained by using the optimization algorithm. The relative errors of the simulated and experimental values of coal conversion, asphalt substances, and oil and gas yield are 0.5%,1%,and 8%,respectively.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 4543K] - CHEN Zhihui;WU Youqing;WU Shiyong;HUANG Sheng;CHEN Dabo;SUN Shuo;GU Jiale;Department of Energy Chemical Engineering,East China University of Science & Technology;Hangzhou NiuMo Technology Co.,Ltd.;
In this paper, direct coal liquefaction residue(DCLR)obtained by mild hydroliquefaction(430 ℃)and carbonization process(410 ℃)of Hongliulin(HLL)coal was blended with other five coals to prepare crucible coke under the laboratory conditions, which was beneficial to alleviate the shortage of high quality coking coal, reduce the cost of coking, and make the utilization use of coal resources. The adhesion index of raw coal was studied, crucible cokes were prepared by using coal samples with different proportions, and the coke yield, cold strength and thermal strength of cokes were analyzed. In addition, the mechanism of DCLR addition in coal blending system was proposed. The results show that adding 5% and 10% DCLR into coal blending system can replace 12% and 18% high caking property coals respectively with coke quality promised. When the DCLR ratio increases from 5% to 10%,the crushing strength increases about 1.20%,the abrasive resistance decreases about 1.04%,the coke reactivity index increases about 3% and the coke strength after reaction increases about 2%. In addition, the addition amount of DCLR should not be too high(<15%),because the high activity and high content of inert component of DCLR may lead to a decrease in the caking property of coal blends. The optimal preparation conditions of DCLR are as follows: liquefaction temperature 430 ℃,carbonization temperature 410 ℃,1% basic iron oxide catalyst. The G index of DCLR is 68,and the adhesion is strong. Thus DCLR is suitable to be used as additive and binder for coal blending and coking. DCLR and QM can partly replace FM by interacting with each other, increase the fluidity of the metaplast, and broaden the melting temperature range of coal blending. A large amounts of gas in the system wallopes the colloidal layer, and squeezes metaplast into the pores of coal particles, so as to obtain high strength coke. In the early stage of coking, the interactions between DCLR and QM have a certain influence on the key process of coking, and increase the degree of anisotropy of coke.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 1640K] - FAN Yingjie;LIU Jinqian;MA Chen;GUO Wei;YANG Bolun;WU Zhiqiang;Shanxi Key Laboratory of Energy Chemical Process Intensifcation,School of Chemical Engineering and Technology,Xi′an Jiaotong University;Shaanxi Coal and Chemical Industry Group Co.,Ltd.;
Pyrolysis as the first step of coal quality conversion technology can achieve efficient utilization of coal under mild conditions, in which the purification of dust-containing pyrolysis gas is one of the key problems to be solved in the large-scale application of this technology. The granular bed filtration technology has the advantages of high filtration efficiency and low filter material cost. In order to investigate the filtration effectiveness of the granules moving bed for dust removal from pulverized coal pyrolysis gas, wheat was selected as the filter medium for the cold test, and silica gel powder was used as the experimental dust. The influence of various operating conditions on the filtration efficiency and dust removal efficiency were investigated on a self-designed cold test platform. The results show that the order of influencing factors of filtration efficiency following: apparent speed of wind > thickness of filtration layer >blanking speed of filter material; the filtration efficiency decreases with the increase of apparent wind speed and increases with the rise in filter layer thickness. When the thickness of the filter layer increases to more than 200 mm, the filter efficiency changes is small; while, the blanking speed of the filter material increases, the filter efficiency decreases. After the dust particle size reaches to 10 μm, the filtration efficiency can basically be maintained at 98%. Under optimized filtration conditions: the thickness of the filter layer is 300 mm, the feeding speed of the filter material is 0.002 m/s, the filtration time is 10 min, the best filtration efficiency can reach to 98.1%. The experimental results not only realize the prediction of the filtration performance of the granules moving bed at room temperature, but also provide a reference basis for designing the hot state dust removal device for pulverized coal pyrolysis.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2034K] - CAI Jin;WU Yuxin;ZHANG Man;MA Qiangqiang;LIU Qing;LYU Junfu;YANG Hairui;Key Laboratory of Thermal Science and Power Engineering of the Ministry of Education,Department of Energy and Power Engineering,Tsinghua University;Shanxi Research Institute for Clean Energy,Tsinghua University;Inner Mongolia Jingneng Kangbashi Thermal Power Co.,Ltd.;
The exhaust flue gas from a circulating fluidized bed boiler with low nitrogen combustion should be cleaned once again when NO_x concentration exceeds the emission limit. Flue gas purification process mainly includes SNCR denitrification and SCR denitrification.In order to identify the most economical and suitable denitrification technology for circulating fluidized bed combustion conditions, the techno-economic analysis model was suggested and the techno-economic index for two cases was predicted under the condition of full load. The results indicate that reductant price, catalyst price and annual operating time are the main factors affecting the denitrification cost. The price of urea is the most sensitive to the cost of SNCR denitrification, and the sensitivity of liquid ammonia to the cost of SCR denitrification is greater than that of the catalyst. When operating cost and total cost of SNCR denitrification technology are relatively low, NO_x concentration can be required below 140 mg/m~3 and 228 mg/m~3. Based on the inlet NO_x concentration of 200 mg/m~3,the economic comparison between two cases shows that when the price of urea is lower than 3 402 yuan/ton, the total cost of SNCR denitrification technology is lower. When the unit price of liquid ammonia is higher than 3 300 yuan/ton, the total cost of the SNCR denitrification technology is more economical. Within the research fluctuation range of catalyst and annual operating time, the total cost of SNCR denitrification technology is always the lowest and the most economical. SNCR-SCR combined denitration technology has no economic advantage, and the total cost is the highest when the inlet NO_x concentration is 151-273 mg/m~3. Ultra-low emission circulating fluidized bed boiler technology can improve the economy of SCR denitrification technology and SNCR denitrification technology, and make the advantages of SNCR denitrification technology more prominent.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 4614K] - SHI Zhaochen;WANG Guishan;WANG Xuebin;CHEN Yongqiang;YU Wei;MIAO Yanjun;PENG Yonghong;TAN Houzhang;Department of Thermal Engineering,Xi′an Jiaotong University;Huichao New Energy Technology Co.,Ltd.;China Chemical Saiding Ningbo Engineering Co.,Ltd.;
Coal chemical gasification process produces a large number of gasification fine slag, which does not meet the national and industrial standards of building mixed raw materials due to its high carbon content and large burning loss. Because of the lack of effective large-scale consumption mode, gasification fine slag with huge output has become an important problem restricting the sustainable development of coal chemical enterprises at the present stage. Through the mechanism study of the preheating and decarbonization process of a constant temperature preheating and decarbonization device for low volatile and low calorific value fuel, the constant temperature thermogravimetric test is carried out by using the thermogravimetric experimental platform to simulate the internal combustion process of the constant temperature preheating and decarbonization device for low volatile and low calorific value fuel, so as to compare and analyze the combustion characteristics of particle size graded gasification fine slag under different preheating temperatures and different combustion atmospheres. It is found that the gasification fine slag samples begins to oxidize rapidly when oxygen is introduced, and the burnout time is between 6.6-9.4 min at 900 ℃ and 10% O_2,and 3.7-5.6 min at 900 ℃ and 21% O_2. Under the condition of controlling the NO_x value within the specified range, the oxygen concentration in the combustion zone can be appropriately increased to shorten the burnout time. With the increase of preheating temperature, the average weight loss rate of gasified fine slag samples with the same particle size grading increases regularly, while the burnout time decreases regularly. The increase of preheating temperature can improve the burnout characteristics of gasified fine slag, and the combustion zone temperature can be appropriately raised to achieve faster burnout under the safe operation of the equipment. Under different combustion atmosphere and preheating temperature, with the increase of particle size of gasification fine slag, the weight loss increases, the burnout time increases regularly, and the average weight loss rate decreases regularly. Therefore, the preheating and decarburization device needs to reasonably adjust the residence time of materials according to the particle size of materials in order to achieve full burnout.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2970K] - FAN Yilin;WANG Zhichao;WANG Yikun;ZHANG Man;YAO Wei;ZHANG Guangcai;WU Yuxin;Department of Energy and Power Engineering,Tsinghua University;Xi′an Thermal Power Research Institute Co.,Ltd.;
With the proposal of China's carbon peak in 2030 and carbon neutralization target in 2060,it has become a necessary constraint for power generation industries to continuously reduce greenhouse gas emissions while developing energy. Biomass co-firing technology can reduce CO_2 emissions effectively and increase the share of green energy. However, the practical application of co-firing in China's existing coal-fired power plants is still little. Under the current background, economy is the main problem restricting the development of biomass co-firing in China. With the withdrawal of government subsidy, the application of this technology to power generation is facing great challenges. But the carbon tax trading may bring a new turn for the economy of biomass co-firing. In this case, a technical and economic model of power generation with biomass co-combustion was established, the technical potential of replacing coal installed capacity by co-combustion technology was evaluated, and the economic feasibility of biomass co-combustion was studied under the background of carbon tax trading considering different constraints. The results show that the cost balance of biomass co-combustion can be achieved when the standard coal price is 780 yuan/t, carbon tax is 60 yuan/t and biomass price is 450 yuan/t. The sensitivity analysis of parameters shows that under the given heat value, the impact of standard coal price increase of 100 yuan/t is basically the same as biomass price decrease of 50 yuan/t or carbon tax increase of 36 yuan/t on additional cost. The heating value based biomass price, standard coal price and carbon tax all have important influence on the economic feasibility. The lower heating value based biomass price and the higher carbon tax ratio are conducive for the coal price to achieve the profit and loss balance point of co-combustion and pure coal combustion. Because the price of biomass per unit calorific value, coal price, transportation cost and other factors have a positive impact on the economy of co-firing, the economy of co-firing must be determined based on the specific parameters of each power plant.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 1663K] - ZHAO Xiaojun;SUN Jinyu;XUE Dongfa;LIU Yi;Nandian Synthesis Energy Utilization Co.,Ltd.;
A 75 t/h biomass circulating fluidized bed(CFB) boiler burns mixed fuels for long time, including eucalyptus bark, wood tail, wood board, bamboo, and industrial composite board. On the high-temperature superheater and low-temperature superheater, a severe slagging phenomenon was observed during actual operation. As a result, it's critical to investigate the slagging mechanism of mixed biomass fuels while considering the characteristics of various biomass fuels. The slagging samples from a biomass CFB boiler's high-temperature superheater and low-temperature superheater were collected firstly. Following that, the physical and chemical properties of the collected samples were investigated by analyzing the ash composition and ash fusion temperatures. The results show that among the biomass used in the boiler, bamboo, wood tail and wood board have high calcium and potassium content, with approximately 30% CaO content and more than 10% K_2O content. Eucalyptus bark contains high silicon and aluminum, with an ash content of SiO_2 as high as 62.4%. Industrial composite board and wood tails have high levels of chlorine, and the chlorine content in the ash is 0.67% and 0.865%,respectively. In addition to bamboo and Industrial composite board, others have high ash fusion temperatures with a soften temperature above 1 200 ℃. The slagging samples from high-temperature superheater area have a layered structure: the outer layer of the slagging sample is hard, the middle layer contains white KCl crystals and fine particles, and the outer layer of slagging and ash particles are made of Ca_2Al_2SiO_7,SiO_2,KCl, Ca_2MgSi_2O_7. The low-temperature superheater's outer slagging samples have the same composition as the high-temperature superheater's. However, white KCl crystal content in the middle layer is higher, which is related to the condensation and precipitation of KCl vapor in the flue gas.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 5973K] - LIU Lu;LI Pengfei;CHENG Pengfei;LIU Yaowei;HU Fan;LIU Zhaohui;ZHENG Chuguang;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
Flameless combustion is one of the new high-efficiency and low-pollutant combustion technologies widely concerned in recent years. Due to the volumetric combustion zone with relatively low reaction rate and typically medium or low temperature region in flameless combustion, it is necessary to consider the turbulence-chemistry interaction coupled with detailed reaction mechanisms in numerical simulations to improve the prediction accuracy of the combustion and NO formation. In this paper, the high-fidelity numerical simulations on the flameless combustion of pulverized coal and NO formation were performed based on the dynamic adaptive chemistry mechanism. The dynamic adaptive mechanism simplification algorithm was adopted to realize the local reduction of the in-house-developed nitrogen-containing skeletal mechanism during simulation. It is found that compared with the simulation with a skeletal mechanism, the dynamic adaptive chemistry can obtain nearly three times calculation acceleration without sacrificing the accuracy. And the prediction accuracy of in-furnace NO formation is significantly improved relative to the traditional NO post-processing simulation method. After experimental validation, the distributions of typical in-furnace nitrogen-containing precursors such as HCN and NH_3 were obtained. The key information on nitrogen conversion, such as fuel nitrogen conversion pathway, active species and reactions in the furnace, were further analyzed. The results show that the NO formation from pulverized coal flameless combustion mainly depends on NH_3,HCN,and N_2O intermediates, while NCO and HNO are the key intermediate components. HCN is converted to NO mainly by the HNCO/CN and NCO paths. NH_3 is converted from HNCO,and is further converted to NH_2 and HNO,and finally leads to NO formation. The N_2O path mainly participates in the NO reduction and is insignificant to the NO formation. CH_3CN is also an important intermediate component for NO formation, which can be converted to NO by the NCO path.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 7938K] - WANG Xiaolong;ZHANG Feilong;WANG Li;XU Xinwei;ZHANG Yixiang;WANG Xuebing;TAN Houzhang;CHN Energy Shendong Coal Group Co.,Ltd.;School of Energy and Power Engineering,Xi′an Jiaotong University;
The high-concentration pulverized coal burner can stabilize the combustion and significantly reduce NO_x emissions, which is a very economical and environmentally friendly combustion technology. Its primary wind speed has a very important impact on the ignition delay in the furnace, the stability of pulverized coal combustion and the NO_x emissions. In order to determine the primary wind speed suitable for the new high-concentration coal pre-combustion low-nitrogen burner, and provide guidance for the on-site experiment and actual operation of the burner, ANSYS Fluent software was used to simulate and calculate the influence of primary wind speed on the combustion stability of pulverized coal and NO_x emissions. In this paper, a grid-independent test was performed first, and a 25 t/h full-scale pulverized coal industrial boiler was tested to verify the accuracy of the model. The numerical simulation results show that the new high-concentration coal pre-combustion low-nitrogen burner can form two recirculation zones in the pre-combustion chamber and the furnace. The recirculation zone in the pre-combustion chamber ensures stable combustion of pulverized coal, and the recirculation zone in the furnace reduces NO_x. When the primary wind speed is too low, the later mixing of primary and secondary air weakens, the combustion of pulverized coal is unstable, and NO_x emission increases slightly. Also, when the primary wind speed is too high, the mixing of the secondary air and the pulverized coal is weakened, and the combustion of pulverized coal is unstable, resulting in a significant decrease in the coke conversion rate and a significant increase in NO_x emissions. The primary wind speed increases from 17 m/s to 20 m/s, and the NO_x concentration in the outlet section increases by about 10%. An appropriate primary wind speed can not only stabilize the ignition and combustion of pulverized coal, but also achieve low NO_x emissions. The best primary wind speed of the burner studied is between 14-17 m/s.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 6171K] - LIU Shihai;LYU Sichen;HAO Hao;LI Chunyu;ZHOU Lu;MA Honghe;College of Electrical and Power Engineering,Taiyuan University of Technology;Institute of Coal Chemistry,Chinese Academy of Sciences;
Various low-NO_x combustion technologies, such as air-staged, are currently widely used in coal-fired boilers to reduce NO_x concentration at furnace outlet. However, in practical application, these technologies cause sulfidation corrosion of the boiler water-wall, and affect the safe operation of pulverized coal boiler. In order to accurately predict the concentration of H_2S near the boiler water wall, the gas-phase kinetics software Chemkin software was used to evaluate and simplify the established detailed reaction mechanism model of H_2S generation. First, in this paper, the coupling between the detailed reaction mechanism model of sulfur species and the detailed reaction mechanism of C/H/O was verified, which showed that GRI-3.0 could better predict the concentration distribution of important components in pulverized coal-fired boiler with air-staged. Then, the coupling mechanism model was taken as the initial mechanism and compared with other detailed sulfur reaction mechanisms. The results show that the detailed reaction mechanism model of sulfur species in our research group can better describe the evolution of gaseous sulfur species during pulverized coal combustion, and CS_2 is considered as an important sulfur species to better predict the concentration distribution of sulfur species. Finally, by comparing the simplified results, the result obtained by the directed relation graph with error propagation(DRGEP)is selected as the simplified reaction mechanism model of the sulfur species, including 15 species and 28 reactions, which has been verifying in the temperature range of 1 373-1 673 K. The results show that reduced mechanism model can be applied to the prediction of the sulfur species concentration distribution during the fuel-rich combustion of pulverized coal.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 6345K] - YAN Jingchong;YANG Qitong;ZHANG Li;FANG Hongxin;LEI Zhiping;LI Zhanku;SHUI Hengfu;Anhui Province Key Laboratory of Coal Clean Conversion and High Value-added Utilization,School of Chemistry & Chemical Engineering,Anhui University of Technology;School of Computer Science and Technology,Anhui University of Technology;Anhui Costar Biochemical Co.,Ltd.;
For investigation of the feasibility of cofiring high sodium coals(HSC) mixed with coal gangues(CG) to inhibit fouling and slagging of coal ash, thermogravimetric analyzer and fixed bed reactor were used to evaluate the cofiring performance and effect on Na fixation in coal ash. By comparison of Na content in ash before and after combustion, the effect of cofiring on Na fixation was evaluated. By comparing the differences of weight loss and mass change rate between theoretical and experimental combustion, the synergistic of cofiring was confirmed. The results show that the Na forms in HSC mainly consist of H_2O-soluble, HCl-souble and NH_4Ac-soluble Na, while the Na-containing compounds cannot be detected with XRD analysis before and after combustion. Cofiring effectively enhances the residual of Na-containing compounds in ash, the Na retention in ash increases by 50%-75% through cofiring 10% CG with 90% HSC,thus verifying the effectiveness of Na fixation in ash. Meanwhile, cofiring enhances the combustion rate and reduces the peak temperatures of the mixed fuel, and shows obvious synergistic effect. By further optimizing cofiring conditions, it is expected to realize synergistic, efficient and safe conversion of HSC and CG,which favors the energy conservation and emission reduction undoutedly.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 5156K] - CHEN Chongming;DANG Zhiguo;CHE Kai;HAN Zhongge;ZHANG Lijun;State Grid Hebei Electric Power Research Institute;Hebei Guohua Cangdong Generation Co.,Ltd.;
Coal-fired power plants is the main source for mercury emission. In order to characterize the removal characteristics of mercury, a 660 MW coal-fired unit was taken as an example. The migration and transformation characteristics of mercury in selective catalytic reduction equipment(SCR),electrostatic precipitator(ESP),flue gas desulfurization(FGD) and wet electrostatic precipitator(WESP)was systematically studied under 500 MW and 600 MW. The results show that the mercury mass balance rate in test locations are 72.01%-90.05% and 79.14%-96.36% respectively, which verify the accuracy of test results. Flue gas mercury is the main discharge form, followed by ash and gypsum. The proportions of mercury emission from FGD waste water and slag account for a small proportion. The conversion rate elemental mercury to oxidized mercury and particulate mercury by SCR catalysts is beyond 40%,but the total mercury reduction is insignificant, and higher ammonia consumption can reduce the conversion rate. ESP can remove all particulate mercury, but the total mercury removal efficiency is less than 33.73% because of lower removal of elemental and oxidized mercury. Because reduction effect of HSO_3~- is stronger for oxidized mercury to element, the elemental mercury concentration increases more obviously under 600 MW condition. And the cumulative removal efficiency of oxidized mercury by FGD and WESP reaches over 91%. Total mercury reduction by all the environmental protection facilities is more than 59%. However, collaborative lowest removal efficiency of elemental and oxidized mercury are 6.16% and 94.12% by downstream facilities of SCR,which indicate that mercury oxidation by SCR is the key to reducing mercury emission. Finally, the total mercury concentration in exhaust gas is less than 3.66 μg/m~3,which is below the national emission standard.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2869K] - MAO Rui;LI Yuan;REN Liming;ZHANG Ping′an;CHEN Xinke;MA Lun;FANG Qingyan;Rundian Energy Science and Technology Co.,Ltd.;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
Reducing the flue gas temperature deviation is one of the characteristics of tower boiler, but the flue gas temperature deviation still exists in the actual operation, and there is still a lack of detailed research on its formation mechanism. In this paper, a 660 MW tangentially fired tower boiler was used to study the characteristics of flue gas flow field deflection and temperature deviation in the penal heating surface area under rated working conditions. Three cases with different flue structures and heating surface layout were designed and analyzed, and the smoke temperature deviation mechanism was deeply and carefully studied.. The results show that the deviation characteristics of simulation are consistent with the experimental values and actual operation deviation characteristics, and there are obvious flow deflection and temperature deviation in the area of penal heating surface. The velocity and temperature in the left area were significantly higher than those in the right area. With the increase of height, the flue gas temperature deviation in the left and right region increases firstly and then decreases, and reaches the maximum near the entrance of the third-stage superheater. The mechanism of flow field deflection and gas temperature deviation is as follows: First, after the gas rotates and rises into the pipe penal, it is constrained by the pipe penal, and the velocity component perpendicular to the direction of the pipe penal turning around, causing gas near the left wall flowing to the forward wall, and gas near the right wall flowing to the back wall. Then, because the flue gas outlet at the top of the furnace is asymmetrically arranged on the rear wall, under the suction of the downstream induced draft fan, gas near the left wall first inclines to the forward wall, then turns to the back wall, and is more centered in the area of the penal heating surface. On the contrary, gas near the right wall is first inclined to the back wall, and then is drained away by the draft fan along the back wall, resulting in a serious deflection of the flow field and a large scale of reflux.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 17509K] - CHEN Bo;CAO Gehan;HUANG Yaji;YUE Junfeng;XU Wentao;WANG Ya′ou;LI Yuxin;JIN Baosheng;Jiangsu Frontier Electric Power Technology Co.,Ltd.;Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,Southeast University;
The direction of economic development and policy orientation has promoted the upgrading of coal-fired boilers in thermal power plants towards the direction of intelligence. The combustion efficiency of coal-fired boiler is an important indicator to measure the operating status of boiler. In order to meet the requirements of real-time calculation of boiler thermal efficiency, the following methods are used to calculate the boiler efficiency with the help of the daily measurement data of the power plant: Firstly, the corresponding combustion and operation characteristics of the boiler were analyzed; Secondly, according to the extracted features, the preprocessing methods of eliminating outliers, steady state discrimination, and similarity processing were carried out to generate better training samples. Finally, the neural network algorithm improved by genetic algorithm was used to establish the calculation model among the boiler exhaust temperature, fly ash carbon content and coal ash content. The calorific value of the coal into the furnace was calculated by using the proportional relationship between the calorific value of coal and the theoretical air volume, and the calculated value was used in the inverse balance calculation model of the boiler thermal efficiency. The calculation results show that the predicted value of the neural network model can meet the requirements of engineering calculation. The calculated exhaust gas temperature, fly ash carbon content and coal ash content can be used in the calculation of boiler efficiency to realize real-time dynamic boiler efficiency calculation. The change of the calculated boiler efficiency is approximately the same as that of the actual evaporation change. When the actual evaporation capacity of the boiler decreases, the efficiency of the boiler will decrease. When the actual evaporation capacity of the boiler is maintained above 60% of the rated evaporation capacity, the boiler efficiency is easily maintained at a high level.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2207K] - PAN Fei;ZHU Jianguo;LIU Jingzhang;University of Chinese Academy of Sciences;Institute of Engineering Thermophysics,Chinese Academy of Sciences;
In the process of preheating combustion of circulating fluidized bed, the combustion process of the preheated fuel in the down-fired combustor(DFC)is very important. In order to study the flow characteristics and combustion characteristics of the preheated fuel in the DFC,the computational fluid dynamics software Fluent was used, combined with experimental methods, to test and simulate the combustion process of the preheated fuel in the DFC under different secondary air nozzles. the differences in flow characteristics, temperature characteristics, component concentration distribution characteristics and nitrogen oxide emission characteristics under different air distribution methods were compared. The results show that during the combustion process of the preheated fuel in the DFC,the secondary air can entrain the flue gas and reflow in the upper part of the down-fired combustor to dilute the reactants, and the recirculation area is larger when the air is distributed at the central nozzle. Under different air distribution modes, the temperature distribution is different. The peak temperature in the DFC is 1 459 K when the air is distributed at the annular nozzle, while the temperature peak is 1 555 K when the central nozzle is distributed. At the same time, when the air is distributed at the annular nozzle, the high temperature area is smaller and the temperature distribution is more evenly. When the air is distributed at the annular nozzle, the mixing of preheating fuel and secondary air is more sufficient, and the reaction between high temperature gas and air is more intense, which is helpful to the ignition and heating of fuel. When the air is distributed at the central nozzle, the concentration of CO and H_2 at the top of the DFC is higher, which helps to reduce NO_x. What′s more, a higher temperature promotes the gasification reaction, forming a reducing atmosphere, which is conducive to further reduce NO_x. When the central nozzle is used for air distribution, more nitrogen oxides are reduced, the NO_x emission in the tail flue gas is 107×10~(-6). When the annular nozzle is used for air distribution, the NO_x emission is 121×10~(-6).
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 4733K] - MA Fangru;WEI Bo;MAIERHABA·Abudoureheman;WANG Jianjiang;LI Xian;WANG Xuebing;Key Laboratory of Coal Clean Conversion and Chemical Process,Xinjiang University;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;School of Energy and Engineering,Xi′an Jiaotong University;
The acid-base ratio and Si-Al ratio of coal ash are the key factors affecting coal ash properties. Adding additives to coal or using mixed coal to adjust coal ash fusing characteristics by changing the ratio of SiO_2 to Al_2O_3 is an important means to improve the ash and slag problems in the high temperature coal conversion process. In order to analyze the influence of the change of Si-Al ratio on the microstructure of coal ash system and obtain the theoretical mechanism of the change of macroscopic properties, the radial distribution function(RDF),mean coordination number(CN),degree of polymerization, distribution of oxygen and other microstructures in CaO-SiO_2-Al_2O_3 system were simulated and calculated when SiO_2/Al_2O_3 increased from 0.5 to 3.1 based on first principles at 1 600 ℃. The results show that: when SiO_2/Al_2O_3 increases from 0.5 to 3.1,Si—O has a stable four coordination structure and the average bond length is 1.61×10~(-10) m; the average bond length of Al—O is 1.75×10~(-10) m, the coordination number of Al—O is relatively stable, and the coordination number decreases with the increase of Si-Al ratio. Si and Al are network formers in the silicate system of synthetic coal ash. As SiO_2/Al_2O_3 increases from 0.5 to 3.1,Q~4 and Q~5decrease gradually, forming Q~2 and Q~3 with low degree of polymerization. Among them, Q~4 and Q~5decrease by about 23% and 10% respectively and Q~3 and Q~2 increase by about 14% and 11% respectively. A large number of [SiO_4]~(4-) and [AlO_4]~(5-)are destroyed, the degree of polymerization is reduced, the disorder is increased, and the network structure is destroyed, resulting in the decrease of ash fusibility. With the increase of Si-Al ratio, O_t and O_b decrease gradually, and O_(nb) increases significantly. Among them, O_b and O_t decrease by about 7% and 13% respectively, and O_(nb) increases by about 18%. The network structure of the system is destroyed, and the loose network structure makes the system more prone to collapse at high temperature. The macro performance is that the melting temperature of coal ash is reduced, and it is easier to produce low-temperature eutectic.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 2118K] - WANG Meng;SHA Yufei;WANG Xiaolu;LIU Quansheng;ZHOU Huacong;College of Chemical Engineering,Inner Mongol University of Technology;
Using humic acid extracted from lignite as raw material, a copper-humic acid catalyst(Cu-HAs)was prepared by hydrothermal method, and the structure of the catalyst was characterized by FTIR,XRD,XPS,and SEM. The catalyst was used to catalyze the oxidation of benzyl alcohol. The preparation conditions of the catalyst, such as the ratio of copper acetate monohydrate to humic acid, aging temperature, aging time, etc.,were investigated, and the effects of different reaction conditions on the catalytic activity of the copper-humic acid catalyst for the oxidation of benzyl alcohol were discussed. The results show that the catalyst has good catalytic activity under the conditions of temperature 30 ℃ and aging time 3 h. The conversion of benzyl alcohol is 71% and the yield of benzaldehyde is 68.6%. When the reaction temperature increases to 110 ℃ and the reaction time is prolonged to 3 h, the conversion of benzyl alcohol can reach to 91.3%,and the yield of benzaldehyde can reach to 87.8%. The recyclability of the catalyst and the general applicability for different substrates were also investigated. The results shows that the yield and conversion of Cu-humic acid catalyst remain basically unchanged after 6 cycles, indicating that the catalyst can be reused and have good stability. The prepared catalyst can catalyze the selective oxidation of alcohols with different structures, and the yields can reach more than 90% for the different substrates under the optimized conditions.
2021 04 v.27;No.134 [Abstract][OnlineView][HTML全文][Download 10330K] -
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