• Research progress on adsorption and photocatalytic degradation of formaldehyde by TiO_2 supported on activated carbon

    HUI Shien;ZHU Xinwei;WANG Denghui;LIU Changchun;School of Energy and Power Engineering,Xi′an Jiaotong Uuniversity;School of Safety Science and Engineering,Xi′an University of Science and Technology;

    Based on the increasingly serious formaldehyde pollution,the effective degradation of formaldehyde has become a practical problem urgently to be solved.Activated carbon prepared from biomass materials,coal with different metamorphic degrees and petroleum coke has the advantages of large specific surface area,high adsorption efficiency,which has significant advantages in adsorption and separation of formaldehyde pollutants.The activated carbon adsorption mechanism and modification,Ti O_2photocatalytic reaction principle,ways to improve the photocatalytic activity,Ti O_2load were reviewed,and the adsorption and degradation properties of formaldehyde on activated carbon and Ti O_2/AC were analyzed and compared,and the future research direction of activated carbon modification and Ti O_2/AC adsorptionphotocatalysis was also prospected.Activated carbon is mainly physical adsorption,which will desorb under certain pressure and temperature conditions,resulting in secondary pollution.The pore size distribution and surface acid functional group content of activated carbon can be changed by acidification modification,and the physical adsorption can be changed into physical-chemical combined adsorption,which can effectively improve the adsorption of formaldehyde molecules on the surface of activated carbon.In addition to adsorption by activated carbon,Ti O_2is non-toxic,harmless,safe and green,with high photocatalytic efficiency,and is generally recognized as an ideal material for photocatalytic degradation of pollutants such as formaldehyde.According to the photocatalytic principle of Ti O_2,pollutants such as formaldehyde can be catalyzed into CO_2,H_2O or other inorganic small molecules through two active species with strong oxidation capacity—OH and—O_2~-.However,the large-scale industrial application will be limited due to the problems of low quantum efficiency,narrow absorption range of visible light and low reusability of Ti O_2.After metal ions are doped into Ti O_2,a shallow trapping potential well of electrons and holes is formed.After nonmetallic anions replace the oxygen position of Ti O_2,the degree of structural distortion is changed,which reduces the electron-hole pair recombination to a certain extent.Semiconductor with different band gap width can be combined to form a heterojunction by compound sensitization,which can broaden the spectral response range of the compound catalyst.Ti O_2/AC adsorption and catalytic co-material prepared by supporting Ti O_2on activated carbon is conducive to solving the problem difficult recycling of catalyst.The absorption and concentration by activated carbon provides a good reaction environment for photocatalysis and improves the degradation rate.Activated carbon with specific adsorption ability can be developed by controlling activation and carbonization process.With the in-depth study of Ti O_2mechanism,Ti O_2/AC materials with high removal efficiency,large adsorption capacity,low energy consumption and selectivity are prepared to improve the preparation level of adsorption catalytic co-materials,which is conducive to the realization of the technical goal of efficient and clean degradation of formaldehyde.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 10675K]

  • Situation analysis of biodegradation of hydrophobic volatile organic compounds

    FANG Xiang;CHENG Kai;GUO Jifeng;Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region,Ministry of Education,School of Water and Environment,Chang′an University;

    With the continuous acceleration of social modernization, a large number of volatile organic compounds(VOCs) are discharged into the atmosphere in industrial production and daily life, which seriously harms the ecological environment and human health. Therefore, the emission control and degradation of VOCs have attracted wide attention. In recent years, due to the advantages of low cost, high purification efficiency, simple operation and free secondary pollution, biodegradation of VOCs has been extensively studied and applied. However, because of the low mass transfer of hydrophobic VOCs from gas phase to liquid phase, the degradation efficiency of VOCs in bioreactor is low. The influencing factors of biodegradation of hydrophobic VOCs were analyzed from the aspects of mass transfer efficiency, microbial community types and packing performance. The methods to improve the biodegradation efficiency of hydrophobic VOCs, such as the application of fungi, the addition of surfactants, the utilization of hydrophilic compounds and new biodegradation technologies, were discussed, and the research direction of biodegradation of hydrophobic VOCs in the future was prospected. It is particularly important to improve the mass transfer efficiency of pollutants in bioreactors. In the future, researches on migration and degradation mechanism of hydrophobic VOCs in biofilms should be strengthened. The degradation efficiency of VOCs by the inoculated bacteria decreases with environmental changes, such as decreasing moisture and pH. The packing in the bioreactor can affect the attachment of microorganisms and the formation of biofilm, which directly affects the degradation efficiency of VOCs. The selection and development of suitable packing can provide a good ecological environment for the growth, metabolism and biofilm development of the microbial community, and provide guarantee for the long-term stable operation of the reactor. The advantage of aerial mycelia could help fungi to absorb hydrophobic VOCs which can improve the degradation efficiency of VOCs, so as to improve the removal rate of hydrophobic VOCs. However, few fungi that can degrade hydrophobic VOCs have been found so far, more fungi that can degrade hydrophobic organic compounds should be developed in the future. Surfactants can increase their solubility by partitioning hydrophobic organic pollutants into the hydrophobic core of surfactant micelles and improve the mass transfer efficiency of hydrophobic VOCs. Compared with traditional chemical surfactants, biosurfactants are natural compounds that are more environmentally friendly, less toxic, and more easily biodegradable. Future research should pay more attention to biosurfactants. Mixing hydrophilic compounds with hydrophobic VOCs can interact with different pollutants, which improves the solubility and bioavailability of hydrophobic VOCs, but the mechanism needs to be further studied. The new bioreactor can solve the problem of low degradation efficiency for hydrophobic VOCs, such as two-phase distribution bioreactors Reactors(TPPBs),membrane bioreactors(MBR),and bioelectrochemical systems(BESs),etc.,but the cost and energy consumption of the entire degradation process are high, relevant research needs to be strengthened.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 7232K]

  • Research review of co-catalytic treatment of VOCs by low temperature plasma

    HAN Fenglei;JI Chunjie;ZHANG Ziqi;ZHU Yifan;LI Dandan;ZHANG Tingting;ZHOU Shuo;GUO Wenwen;School of Chemical Engineering,China University of Petroleum;Qingdao OASIS Environmental & Safety Technology Co.,Ltd.;

    For the treatment of volatile organic compounds(VOCs) with low concentration and large flow, the traditional treatment technology has some limitations in technology and economy, and can not reach the expected results. Non-thermal plasma(NTP) technology has many advantages in the treatment of VOCs, such as low reactor treatment cost, simple reactor structure, simple operation, wide range of application, mild reaction conditions, which has received widespread attention in recent years. The experimental results show that the degradation of VOCs by single plasma has many problems such as O_3,NO_2 and organic by-products, which is easy to cause secondary pollution to the environment. The results show that the synergistic catalytic degradation of VOCs by low temperature plasma has significant effect on improving VOCs degradation rate, reducing energy consumption of reaction system and reducing harmful by-products. The NTP collaborative catalytic degradation of VOCs technology in detail was introduced, the influencing factors of NTP collaborative catalytic degradation of VOCs, the influence of different catalytic systems and discharge types on the degradation rate were summarized, and the mechanism of plasma technology and low temperature plasma co-catalytic degradation of VOCs was deduced. The synergistic effect of plasma technology and catalyst catalysis on VOCs degradation was described. Finally, the future development of this technology was prospected. The investigation shows that the current single processing technology is difficult to meet the VOCs processing requirements, a variety of technology coupling methods are widely used at home and abroad. In recent years, the combination of low-temperature plasma technology with catalytic technology plays a significant role in improving the degradation rate of VOCs, reducing the energy consumption of the reaction system and the generation of harmful by-products. This technology has feasibility and research value. At present, the research focuses on the degradation effect of pollutants by the combination mode of catalyst and low-temperature plasma, catalyst type, process parameters and other factors, but the research content is not in-depth. Plasma technology still has the disadvantages of low mineralization rate and many by-products, such as NO_x,ozone and other by-products after plasma reaction, forming secondary pollution. In addition, due to the variety of active free radicals in the low-temperature plasma generated by gas discharge and the complex chemical reaction process of VOCs degradation, the synergistic mechanism of low-temperature plasma and catalysis is still unclear, especially the basic molecular dynamics theory of plasma degradation of VOCs remains to be further studied.Therefore, focusd on intrinsically safe and industrial applications, it is necessary to put forward a set of safety evaluation theory, method and tool which is suitable for process characteristics of low temperature plasma co-catalytic governance of VOCs. And it can be used to develop risk identification and risk evaluation for the whole process system, to identify potential safety hazard, and provide improvement measures, reduce the unreasonable choice and defect in the process design to the greatest extent, and achieves the goal of safe industrial application fundamentally.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 10826K]

  • Research progress on adsorption of benzene within VOCs from coal chemical industry by electrospinning nanofibers

    FENG Yu;WU Huien;ZHOU Chuang;ZHANG Li;CUI Hong;Shanxi Xinhua Chemical Defense Equipment Research Institute Co.,Ltd.;State Key Laboratory of Clean and Efficient Coal Utilization,Taiyuan University of Technology;Taiyuan Chemical Defense Military Representative Office,Chemical Defense Military Representative Bureau of the Army Equipment Department;

    With the continuous development of coal chemical industry, the emission of pollutants associated with core coal chemical processes such as coal coking and coal gasification has become increasingly prominent, among which volatile organic compounds(VOCs) have a certain impact on China′s air quality. As one of the representatives of VOCs, benzene is poisonous and volatile, which seriously endangers the human health. In order to clearly understand the optimization direction and development status of VOCs emission control technology and provide theoretical reserves for the purification of benzene in VOCs in coal chemical industry, the relevant materials and technologies of electrospun nanofiber composites used in benzene adsorption and purification process was combed and summarized. Focusing on the main technical methods of treating benzene at present, its characteristics were analyzed, and the problems existing in the practical application of these technologies were pointed out. The advantages, action mode, types and characteristics of common adsorbents were focused on, and it is pointed out that selecting appropriate adsorbents is the core of adsorption treatment of VOCs, benzene and other pollutants. How to select, combine and improve the adsorption performance of various types of adsorbents and seek effective adsorption purification technology is a subject that needs to be continuously studied and improved. The nanofibers with porous structure, adjustable and high specific surface area and their application in the field of gas purification were introduced. From the perspective of nanofiber preparation, the basic principle, basic process and research status of electrospinning synthesis of nanofiber composites were expounded. The results shows that the advantages of electrospinning, such as simple equipment, low spinning processing cost, lots of raw materials accessible and controllable process, occupy an absolute advantage in the preparation of nanofiber technology. Compared with conventional fibers, electrospinning nanofibers have smaller size, larger specific surface area and higher porosity, which can provide a larger effective reaction area in the process of gas-solid reaction, improve the rich skeleton structure for the uniform and orderly distribution of active components. Combined with the application status of electrospinning nanofibers materials in VOCs purification, it is pointed out that there are some problems in this field, such as insufficient mechanical strength of electrospinning polymer nanofibers and carbon nanofibers, toxic and corrosive spinning solution solvents, and low electrospinning efficiency. Finally, the development direction of electrospinning nanofibers in the field of VOCs and benzene adsorption and purification was clarified: in-depth understanding and effective control of spinning process, functional expansion of spinning materials and the potential expansion of electrospinning towards industrial application.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 5056K]

  • Research progress of VOCs adsorption by biochar material

    HUANG Yuping;WANG Denghui;HUI Shien;LIU Changchun;School of Energy and Power Engineering,Xi′an Jiaotong Uuniversity;School of Safety Science and Engineering,Xi′an University of Science and Technology;

    Volatile organic compounds(VOCs) have attracted wide attention because of their serious harm to the ecological environment and human health. VOCs treatment technologies mainly include incineration, condensation, adsorption and catalytic oxidation, among which adsorption is considered to be an efficient and economical control strategy with its low cost, stable effect and renewable adsorbents. As a green, cheap and easily available carbon adsorption material, biochar has become a research hotspot.The basic adsorption characteristics of biochar were introduced, and the advantages and disadvantages of different preparation and modification methods were compared. The effects of specific surface area, pore characteristics and functional groups on VOCs adsorption by biochar were analyzed, and the mechanism of VOCs adsorption by biochar was discussed. The raw materials of biochar come from a wide range of sources, and the structural properties of biochar will be affected by the differences in the type, content and composition of raw materials, thus affecting its adsorption capacity. Biochar has rich functional groups and complex pore structure. Generally, the biochar prepared by conventional pyrolysis at appropriate temperature has high yield and good structural properties. At present, the significant modification methods of biochar include physical modification and chemical modification, and the modified biochar has high VOCs adsorption properties. In general, the larger the specific surface area of biochar is, the better the adsorption performance is; the larger the pore size is, the more favorable for the adsorption of macromolecular VOCs is, but when the pore size is much larger than the diameter of VOCs molecules, the intermolecular adsorption weakens; the smaller the pore size is, the more favorable for the adsorption of small molecules VOCs is, but too small pore size will also increase the diffusion resistance of VOCs. The biochar have better adsorption properties due to the larger specific surface area, appropriate pore size and targeted modification according to the polarity of the adsorbed VOCs gas. The adsorption mechanism of biochar on VOCs mainly includes the adsorption of carbonization zone and the distribution of non-carbonized organic matter. The distribution is the main mechanism when the carbonization temperature is less than 300 ℃. The larger the specific surface area is, the more developed the pore structure is, which is more conducive to physical adsorption; Chemisorption is generally achieved through the formation of chemical bonds(such as hydrogen bond, π—π). Multi-component VOCs will have competitive adsorption, and the gas with strong adsorption affinity will replace the gas with weak affinity. The research of biochar in related fields is mainly focused on the experimental stage in the laboratory. Due to the problems of raw material transportation and secondary pollution, biochar adsorption is not yet mature in industry. The future research direction of biochar adsorption of VOCs is developing targeted modified biochar, new environment-friendly biochar composites, reducing the production cost of biochar materials and conducting simulation research at the molecular level.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 8947K]

  • Progress of VOCs terminal treatment technology and some points on its application in purification of flue gas from coal-fired power plant

    ZHAO Zishu;ZUO Xin;ZHAO Dan;XU Ximeng;SHI Jiahui;DING Hui;School of Environmental Science and Engineering,Tianjin University;

    Volatile organic compounds(VOCs) is the prominent precursors to environmental problems such as PM_(2.5) and photochemical smog, are one of the targets for improving air quality in China during the 14 th Five-Year Plan period. Currently, the emission reduction of VOCs is a hot issue in air pollution control. As the main primary energy source in China, coal consumption is still dominant in the power industry. Coal is a major contributor to VOCs emissions. However, there are few studies and engineering practices for VOCs management in the flue gas of coal-fired power plants. Based on the introduction of the typical emission characteristics of VOCs in flue gas from coal-fired power plants, the current research status of existing terminal recovery and destruction technologies for VOCs was summarized and the characteristics, applicable conditions, and latest research progress of the technologies including adsorption, absorption, biodegradation, photocatalysis, low-temperature plasma, catalytic oxidation and ozone oxidation methods were introduced. Under the background of China′s carbon emission reduction era and collaborative emission reduction of air pollutants, the research direction of VOCs purification technology for flue gas from coal-fired power plants was prospected. Adsorption and catalytic oxidation technologies are suitable for the treatment of VOCs in the flue gas of coal-fired power plants with high air volumes and low concentrations. Adsorption possesses a relatively low selectivity and can adsorb various VOCs. The research of adsorption technology mainly focuses on exploring the adsorption mechanism, designing efficient adsorbents, and dissecting the adsorption behavior of VOCs in complex flue gas environment. The catalytic activity of the catalyst is affected by many factors, such as support, metal loading, preparation method and so on. Developing efficient and stable catalysts is the key to catalytic oxidation technology. The research on the synergistic catalytic oxidation of VOCs and NO_x has achieved remarkable results under medium and high temperature. It is still necessary to further probe into the synergistic catalytic mechanism, reaction by-products and competitive adsorption. Normal temperature catalytic oxidation technology can realize the high-efficiency degradation of VOCs with complex structure and various types at room temperature, solve the problems of high energy consumption, poor safety and deactivation at high temperature of traditional catalytic oxidation technology, reduce flue gas treatment cost and promote zero carbon emission. It has a good application prospect for purifying VOCs in flue gas of coal-fired power plants. The combination of normal-temperature catalytic oxidation technology for VOCs with existing flue gas treatment equipment and developing synergistic catalytic processes of multiple pollutants will be the development trend for controlling VOCs in flue gas from coal-fired power plants.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 13795K]

  • New progress on sulfur resistance of VOCs combustion catalysts

    WU Dongxia;CHENG Hang;HU Jiangliang;HOU Jiancai;CHANG Liping;WANG Jiancheng;BAO Weiren;Key Laboratory of Coal Science and Technology,Ministry of Education and Shanxi Province,Taiyuan University of Technology;State Key Laboratory of Clean and Efficient Coal Utilization,Taiyuan University of Technology;

    Volatile organic compounds(VOCs) are important precursor of fine particulate matter(PM_(2.5)) and O_3 compound pollutants. VOCs pollution control has been listed as one of the important tasks in Chinese "13 th Five Year Plan" environmental protection management. The “14 th Five Year Plan” further pointed out that it is necessary to strengthen the management of urban air quality, promote the collaborative control of PM_(2.5) and O_3,and accelerate the comprehensive treatment of volatile organic compounds emissions. Among various VOCs treatment technologies, catalytic combustion is the most effective method for VOCs treatment because of its wide range in the treatment concentration and no secondary pollution. However, there are usually a certain amount of sulfur compounds in the organic waste gas from coal chemical industry, coking plants, petroleum refineries and other industrial sources in the practical application process, which can interact with the catalyst to cause sulfur poisoning of the catalyst. Therefore, it is of great significance to control and design the catalyst and improve the sulfur tolerance of the catalyst for the treatment of VOCs. By analyzing the mechanism about the catalytic combustion of VOCs the important role of active oxygen in the process of catalytic combustion of VOCs was pointed out. The mechanism about sulfur poisoning of the catalyst was analyzed. The main causes about sulfur poisoning of the catalyst were given. According to the combustion mechanism and sulfur poisoning mechanism of the catalyst, four ways to improve the sulfur tolerance of the catalyst were summarized. Meanwhile, the characterization techniques of sulfur tolerance catalyst were given. On the basis of the global research status and technical level, the difficulties in the synthesis of sulfur tolerant catalysts and the future research focus were pointed out. There are three reaction mechanisms for the catalytic combustion of VOCs. The type of active oxygen is related to the reaction mechanism, and the type and concentration of active oxygen are closely related to the sulfur resistance of the catalyst. Therefore, it is of great significance to determine the catalytic reaction mechanism, analyze the type of active oxygen species and improve the oxygen reduction ability of the catalyst for the sulfur resistance of the catalyst. According to the sulfur poisoning mechanism of the catalyst, sulfides competed with VOCs to occupy the adsorption active sites, the active sites are reduced, and the catalyst is inactivated; sulfur compounds react with catalyst components to form sulfate, which blocks catalyst channels and covers catalyst active sites, resulting in sulfur poisoning of the catalyst. By introducing promoters, the acid and alkalinity of the catalyst can be adjusted, and the weak acidity of the catalyst can weaken the adsorption of sulfide. By introducing promoters and adding sulfating supports, the interaction between active components and sulfide can be weakened, and the acidification of active components can be weakened. The coexistence of water and sulfide in the catalytic combustion system can prevent the deposition of sulfate radical on the catalyst surface. The wet sulfate catalyst containing a large number of surface hydroxyl groups has higher surface acidity, thus promoting catalytic activity. The sulfur resistance of the catalyst can be improved by improving the oxidation-reduction performance of catalyst, inhibiting the adsorption of sulfide, weakening the interaction between sulfide and catalysts and controlling the composition of raw gas.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 6660K]

  • Research and construction of safety assessment methodology for VOCs treatment projects

    YANG Zhonglin;XIE Qiang;HAO Zhengping;ZHOU Hongyang;School of Chemical and Environmental Engineering,China University of Mining and Technology-Beijing;National Engineering Laboratory for VOCs Pollution Control Material & Technology,University of the Chinese Academy of Sciences;

    In recent years, accidents occur frequently in VOCs treatment installations and processes, resulting from the fact that there is not developed safety assessment methodology available for design, construction, and operation of VOCs purification projects. The intrinsic characteristics of VOCs treatment projects was discussed, a survey of theory, method and tools for safety assessment of chemical processes was conducted, the similarities and differences between VOCs treatment projects and chemical processes were figured out. On this basis, combined with the characteristics of VOCs treatment engineering, the chemical safety evaluation method is selected and revised. A VOCs treatment engineering safety evaluation system of integrating safety check list(SCL),hazard and operability study(HAZOP),risk matrix, layer of protection analysis(LOPA),fault tree analysis(FTA) and shock wave overpressure calculation is preliminarily constructed, and the information sharing mode is determined. The initial event frequency and consequence severity obtained from HAZOP analysis can be used as the data source of risk matrix analysis, and the assessment of accident risk level by risk matrix can figure out more serious accidents for further LOPA analysis. Besides, the initial events identified by HAZOP can also provide accident events for FTA analysis. This safety assessment methodology is targeted for VOCs treatment project, combines several safety assessment methods closely and efficiently share data among methods, and the assessment process is systematic, efficient and hierarchy.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 5415K]

  • Improvement and evaluation of sampling system for volatile organic compounds in coal combustion

    CAO Qingquan;XU Jingying;LYU Yue;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;School of Energy and Power Engineering,Huazhong University of Science and Technology;

    The existing volatile organic compounds(VOCs) sampling standards are mostly for simple environments and small molecular compounds, and lack sampling methods for coal-fired flue gas with high humidity, high dust and complex composition. Based on the existing sorbent adsorption-thermal desorption-gas chromatography mass spectrometry sampling standard HJ 734—2014 "Stationary source emission-determination of volatile organic compound-sorbent adsorption and thermal desorption gas chromatography mass spectrometry method",five kinds of VOCs including acetone, hexane, toluene, ethylbenzene, and 1-decylene, and coal-fired simulated flue gas were sampled by the improved sampling system to investigate the effects of different sorbents, moisture and other flue gas components on VOCs sampling and analysis. The results show that the adsorbent tubes filled with porous polymer adsorbent(Tenax TA) and sulfur molecular sieve adsorbent(Sulficarb) have relative standard deviations of 0.01%-2.04%,and standard average recoveries are more than 80%,which are more suitable for the sampling of VOCs from coal combustion. The ash removal device or water removal device in the sampling system has little impact on VOCs, which can ensure the accuracy and effectiveness of the data in the sampling process. Without the sampling system, the presence of moisture, NO and SO_2 in the simulated flue gas can have a negative impact on the average and weight recovery rate of VOCs, among which 1-decene is greatly affected by the flue gas environment and the average recovery rate only reaches 36%. When the mass concentrations of NO and SO_2 vary from 16 to 621 mg/m~3 and 40 to 1 326 mg/m~3,respectively, the sampling system can well reduce the impact of moisture, NO and SO_2 on the simulated flue gas, which can provide a reference for the sampling in actual coal-fired power plants.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 12515K]

  • Distribution and emission characteristics of VOCs in flue gas of CFB boiler

    WANG Jianguo;ZHU Meng;LU Shaohua;ZHANG Xiaoguang;Hebei Jiantou Xuanhua Thermal Power Co.,Ltd.;Hebei Ji-Yan Energy Science and Technology Rsearch Institute Co.,Ltd.;

    In order to understand the distribution and emission of volatile organic compounds(VOCs) in flue gas of circulating fluidized bed(CFB) boiler, as well as the treatment effect of flue gas treatment device, the whole process concentration monitoring of CH_4,non-methane total hydrocarbon(NMHCs) and a variety of typical VOCs components in flue gas of a 200 MW CFB boiler unit was carried out. The contents of CH_4 and NMHCs in three solid samples of coal burning, fly ash and slag were analyzed. The results show that the mass concentrations of CH_4 and NMHCs in the flue gas at the entrance of SCR are 0.65 and 6.63 mg/m~3 respectively under 100% and 50% load of CFB boiler units, and the mass concentrations of CH_4 emission and NMHCs after a series of flue gas treatment devices are 0.14-0.18 and 1.05-1.43 mg/m~3,respectively. The total VOCs content in coal sample is 49 979.65 mg/kg, while only a small amount of VOCs remains in fly ash and slag. The flue gas of CFB boiler unit is mainly benzene series with carbon atomic number ≥6,such as benzene, toluene, ethylbenzene, p/m-xylene, styrene, o-xylene and hydrocarbons represented by n-hexane. SCR denitration system and bag filter have better treatment efficiency for VOCs in flue gas. After all pollutant treatment equipment, the total VOCs mass concentration discharged through the chimney is 1.19-1.61 mg/m~3,and the total VOCs synergistic removal efficiency is 77.88%-78.64%. The overall removal effect of existing flue gas treatment facilities can meet the corresponding discharge requirements.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 4128K]

  • Research progress of low-NO_x combustion technology for boilers

    WANG Jing;LIAO Changjian;WANG Haibo;JIN Ping;LIU Zhiyu;MENG Fanfei;Dalian Research Institute of Petroleum and Petrochemicals,China Petroleum and Chemical Corporation;

    With the increasingly strict national requirements for nitrogen oxide(NO_x) emissions, improving the level of NO_x control has become a research focus in environmental protection field.The NO_x generation mechanism of boilers was summarized, the characteristics of low-NO_x combustion technologies was analyzed, mechanism characteristics and appliation of oxy-fuel combusiton was discussed. The results show that NO_x formation mechanism is quite complex, which is closely related to fuel characteristics, oxygen content, nitrogen content, temperature, boiler structure and so on. Based on the different formation mechanism, the NO_x produced in boilers can be divided into five types: fuel-NO_x,thermal-NO_x,prompt-NO_x,NNH route and N_2O-intermediate route. Different low-NO_x combustion technologies or their combination can be applied to reduce NO_x emission of different boilers. Low-NO_x combustion technology has the advantages of diversified types, wide adaptability and low cost, which is one of the important technologies to realize NO_x emission reduction. At present, the widely used low-NO_x combustion technologies include air staged combustion technology, fuel staged combustion technology and flue gas recirculation technology. A wealth of operation experience has been accumulated for air staged combustion technology, which is suitable for boiler renovation projects, but the NO_x emission reduction effect is limited and the problems of inadequate combustion and corrosion cannot be ignored.For fuel staged combustion technology, the NO_x emission reduction effect is significant when gas fuels represented by natural gas are used as reburning fuels, and it is more suitable for new boilers. It is easy to retrofit the existing boilers for flue gas recirculation technology, but the combustion stability and efficiency is not very good. The NO_x emission reduction effect of flue gas recirculation technology is so limited when used alone that it should be combined with other technologies simultaneously. Nevertheless, the ultra low NO_x emission can be realized by emerging technologies such as MILD combustion, porous medium combustion, oxy-fuel combustion and MILD oxy-fuel combustion, thus having a very wide application prospect. MILD combustion technology has the advantages of good combustion stability, high combustion efficiency and low NO_x emission. MILD combustion can be achieved for gas, liquid and powder solid fuels in both fully premixed and air unpreheating conditions. It also has significant advantages for the combustion of low calorific value fuels. Porous media combustion technology has the characteristics of high combustion efficiency, low NO_x emission and wide lean combustion limit are, which can realize combustion of low calorific value gas fuels such as blast furnace gas, biomass gas and VOCs. As a clean combustion technology, oxyfuel combustion technology can achieve ultralow pollutant emissions and carbon capture at the same time, of which the economic and social benefits are of great worth. Combining the advantages of MILD combustion technology and oxy-fuel combustion technology, MILD oxy-fuel combustion is a new and efficient technology that can achieve near zero pollutant emissions for fossil fuels such as coal or natural gas.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 16574K]

  • Development and prospect of coal gasification technology in China

    WANG Lifeng;China Mining Products Safety Approval and Certification Center,China Coal Technology & Engineering Group;

    As a key technology for clean and efficient utilization of coal resources, coal gasification technology has developed rapidly in recent years. The important role of coal gasification technology in energy utilization and development in China was summarized, the current development context of coal gasification technology application in China was introduced, and the mainstream fixed bed gasification technology, fluidized bed gasification technology and entrained bed gasification technology were compared. The characteristics and applications of various gasification technologies were summarized, the experience and lessons of coal gasification technology application in China were pointed out, the future development trend of new gasification technology and mainstream coal gasification technology was forecasted. It is proposed that China′s coal gasification technology has gradually changed from extensive in the early stage to connotation intensive development stage. Under the background of "carbon peaking and carbon neutrality goals",the development direction of coal gasification technology mainly foucus on improving the overall efficiency of the gasifier, broadenning the adaptability of coal types, improving the production capacity of a single furnace of the gasifier, reducing the risk of shutdown, ensuring the reliability of the device, reducing the impact of gasification technology on the environment, and strengthening coal gasification technology integration with new coal chemical industry.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 1252K]

  • Composition structure and properties of four narrow fraction Fisher-Tropsch waxes

    XIE Haodong;YU Yanan;ZHANG Shengzhen;JIANG Chenguang;KANG Shanjiao;ZHANG Fan;CHEN Shengli;College of Chemical Engineering and Environment,China University of Petroleum;National Institute of Clean-and-Low-Carbon Energy;College of Mechanical and Transportation Engineering,China University of Petroleum;

    The Fischer-Tropsch synthesis crude waxes, which were produced by indirect coal liquefaction demonstration units from China Energy Ningxia Coal, were separated into four narrow fraction waxes by solvent extraction coupled with fractional crystallization. The composition, structure and properties of the four narrow fraction waxes were investigated by Gas Chromatography(GC),Fourier Transform Infrared Spectroscopy(FT-IR),Differential Scanning Calorimetry(DSC),Thermogravimetric Analysis(TG) and other characterization methods. The results show that the four narrow fraction waxes are similar to each other in composition, with a normal distribution of carbon numbers and mainly composed of long-chain alkanes. With the increase of molecular weight of the narrow fraction waxes, their melting point, crystallization enthalpy, degree of branching of alkane and thermal stability all show an increasing trend. It can be concluded that solvent extraction coupled with fractional crystallization can obtain refined waxes products with different melting points according to requirements so that the crude waxes with low added value can be better separated.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 9651K]

  • Concept of carbon cycle based on co-gasification of carbon containing waste and coal and analysis of carbon emission reduction potential

    LIU Zhen;CI Donghui;FANG Xinhui;LI Wenhua;Department of Energy and Power Engineering,Tsinghua University;National Institute of Clean-and-Low-Carbon Energy;

    China has the largest coal production and consumption in the world. A large amount of CO_2 is discharged due to the development and utilization of coal. In order to help realize the clean transformation and utilization of coal, the CO_2 emissions of coal-fired power generation and coal gasification to methanol process was analyzed. The CO_2 emissions from coal-fired power generation process and coal to methanol production process with coal gasification as the core were calculated. Through the analysis and calculation, in the coal gasification to methanol process, about 37% of carbon from the raw coal enters the product, which can achieve a certain proportion of "chemical carbon fixation". The CO_2 concentration in the syngas produced in the coal gasification process is high. Coal gasification to methanol process is easier to achieve large-scale and low-cost carbon capture and storage than coal-fired power generation. Based on the co-gasification of carbon containing waste and coal, the concept of carbon cycle is put forward. It is a very potential carbon emission reduction technology to use gasifiers to deal with all kinds of carbon containing waste in a coordinated manner, so as to realize cross system carbon recycling and save the use of raw coal. Take 1 million t/a coal direct liquefaction project for example, the reduction of CO_2 emission is about 1.23 million tons every year by the gasification of carbonaceous wastes. CO_2 emission reduction consists of three parts. Part I is about 0.58 million tons, due to about 50% of carbon from the coal liquefaction residues are entered the asphalt product. Part II is about 0.30 million tons, due to 10% raw coal for hydrogen production is placed by coal direct liquefaction residues raffinate. Part III is about 0.35 million tons by avoiding the direct combustion of coal direct liquefaction residues raffinate. If this method extends to the coal chemical industry, it can save about 23.91 million tons of raw coal in China and reduce 37.10 million tons CO_2 emission potentially in 2019.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 7331K]

  • Potassium migration and release during torrefaction and combustion of corn straw

    CAO Qingsi;CHEN Yun;LIU Siyu;HE Yong;ZHU Yanqun;WANG Zhihua;CEN Kefa;State Key Laboratory of Clean Energy Utilization,Zhejiang University;Zhejiang Zheneng Electric Power Co.,Ltd.;

    In order to research the transformation of potassium in the torrefaction and the release law of subsequent combustion process of straw biomass, corn straw was pretreated in a tubular furnace, and the release rate of potassium and the conversion of different classes of potassium were measured by fractional extraction combined with ICP-AES after torrefaction at different temperature. A multi-point LIBS system was used to measure the release of potassium during the burning of corn straws in real time. The results show that the higher torrefied temperature is, the stronger the activity of organic functional groups is, and the more H_2O-soluble potassium is converted into organic potassium. The release of different classes potassium of torrefied samples in the volatilization and the char stage are significantly different in the subsequent combustion. During the combustion of corn straw torrefied at low temperature, the release peak of devolatilization is high and the total amount of devolatilization is large, less is released during char combustion, which is related to potassium enrichment and porosity of samples. The release concentration and release rate of high temperature torrefied corn straw in devolatilization stage are low. In the char combustion stage, the release of more is related to less volatile matter and higher ash. The proportion of H_2O-soluble K in corn straw before and after baking is the largest, and the release rate of H_2O-soluble K is close to the total K release rate during burning, indicating that the release of H_2O-soluble K plays a leading role in the total K release rate.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 13069K]

  • Analysis of emission characteristics of particulate matter and organic pollutants from coal-fired power plant

    LIN Guohui;YANG Fuxin;LI Zhenghong;ZHAO Xu;TAN Houzhang;Zhejiang Juhua Thermal Power Co.,Ltd.;MOE Key Laboratory of Thermo-Fluid Science and Engineering,Xi′an Jiaotong University;School of Energy and Power Engineering,Xi′an Jiaotong University;

    The emission of pollutants in coal combustion process, especially organic pollutants, has received increasing attention. Based on the particulate matter sampling system, the filterable particulate matter(FPM),condensable particulate matter(CPM) and organic pollutants were measured and studied at the inlet and outlet of desulfurization tower(WFGD),wet electrostatic precipitator(WESP) and wet phase transition agglomeration system(WPTA) in a 280 t/h coal-fired unit. The pollutant removal characteristics of the devices were analyzed. The results show that CPM accounts for 80.94%-90.16% of the total particulate matter concentration. WFGD,WESP and WPTA can effectively reduce the emission of total particulate matter, and the total removal efficiency reaches 78.58%. The concentrations of polycyclic aromatic hydrocarbons(PAHs) in CPM are 64.17-126.40 μg/g, while the content of PAHs in FPM is only 7.52-11.21 μg/g. From the qualitative analysis of the organic compositions in CPM,it is found that alkanes are the main components, accounting for 42.11%-59.94% of the total organic matter, followed by esters, and other organic compounds, including aromatic hydrocarbons, acids, alcohols, ketones, et al.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 9588K]

  • Effect of calcium alkali on ammonia desorption in fly ash

    TANG Xiao;XU Renbo;MA Yunlong;ZHANG Fajie;ZHAO Hong;WANG Lele;YU Jie;SUN Lushi;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;Huaneng Dalian Power Plant;Suzhou Branch of Xi′an Thermal Power Research Institute Co.,Ltd.;

    In order to solve the technical problem of residual ammonium bisulfate(ABS) in SCR fly ash in China, alkaline and acidic fly ash were selected as the test materials, and the two kinds of fly ash were added with water to remove ABS,and the effect of internal alkali/alkaline earth metals in fly ash on the removal of ABS was studied; on this basis, a certain amount of calcium-based alkali and water were added to explore the effect of this method on ammonia desorption in fly ash. The results show that adding a small amount of water to the ash and stirring at room temperature can promote the release of part of the ammonia in the alkaline ash, while the acid ash releases very little ammonia. Adding 1% Ca(OH)_2,2% H_2O to acid and alkaline ash, more than 95% of the ammonia in the ash is removed after stirring 5 minutes. Under the same conditions, the effect of CaO on ammonia removal in fly ash is slightly worse than Ca(OH)_2. Compared with the heating method, the alkali addition method is carried out at room temperature, and little water is added, so the ash is easy to dry. The test device for ammonia removal in ash based on the alkali addition method has a good deamination effect. For fly ash containing 300×10~(-6) ABS,the addition of 1% Ca(OH)_2 and 2% H_2O can remove 75% ABS from fly ash by mixing with a mixer without heating treatment. After heating treatment, the ammonia in the ash is further removed, and the ammonia removal rate can reach more than 90%,which can ensure that that the content of ammonia in ash is less than 100 mg/kg after treatment, and will not have an adverse impact on subsequent utilization

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 16903K]

  • Preparation of cement-based composite materials by using decarbonized coal gasification slag

    LI Yanjun;YAN Ruizhen;WANG Jiancheng;HAN Dongxiao;FAN Panpan;School of Construction Management,Shanxi Vocational University of Engineering Science and Technology;College of Civil Engineering,Taiyuan University of Technology;State Key Laboratory of Clean and Efficient Coal Utilization,Taiyuan University of Technology;

    To explore the feasibility of using decarbonized coal gasification slag(DGSP) as supplementary material in concrete, the decarbonized coal gasification slag powder, fly ash(FA) and steel slag powder(SSP) were employed to replace cement to prepare the mortar and concrete samples. The workability and mechanical properties were studied. Meanwhile, the chemical composition, mineral composition and micro morphology of the powders were analyzed by using X-ray fluorescence(XRF) spectrometer, X-ray diffraction(XRD) and scanning electron microscope(SEM). The results show that, the existence of globular vitreous body in FA and SSP helps to improve the flowability of the mixture. The slump of the fresh concrete with DGSP slightly reduces to 210 mm with slump flow to 500 mm, due to the rough and porous surface of the particles, resulting in much more water demand, which still meet the working requirements. Moreover, the compressive strength of all the specimens increases with the curing age, in particular, each group reaches over 70% of the designed strength value at 3 d age. The strength of the specimens with SSP increases significantly due to the early hydration of silicate minerals in the powders, while fly ash contains a certain amount of lime and gypsum, which helps to stimulate the activity of glass, and activates the hydration of vitreous materials in FA. Especially, the strength of the specimens with DGSP at 28 d exceeds the designed value by 23%,due to the delayed vitreous hydration next to the hydration of cement, leading to the improvement of the later strength of the concrete. It is explicit that the higher the mass coefficient of the particles is, the higher the activity and compressive strength of the mortar is. However, the compressive strength of the concrete is not only influenced by the activity of the powders. The surface of decarburized gasification slag powder has many edges and corners, which enhances the adhesion between slag powder particles and cement paste, and the flexural pressure ratio of mortar specimen is relatively the highest, leading to the increase of the ratio of bending-compressive strength of the specimens with DGSP by 50% compared with the group of ordinary portland cement at 7 d, and 78% at 28 d.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 32839K]

  • Low level calorific value and uncertainty of waste in MSW incineration power plant

    XU Kai;ZHONG Ping;SONG Jinshi;MENG Guixiang;HAN Guoqing;CAO Shoufeng;Suzhou Branch of Xi′an Thermal Power Research Institute Co.,Ltd.;

    According to the FDBR standard and the principle of uncertainty, the calculation method of low heat value(LHV) of municipal solid waste(MSW) incineration power plant was introduced, and the uncertainty calculation model of LHV of MSW was constructed. Taking a 935 t/d MSW incineration boiler as the research object, the LHV of MSW was calculated and analyzed, and the uncertainty of LHV test was evaluated. The results show that the matching degree of the LHV of MSW into the furnace and the designed LHV of the MSW incineration power station directly affects the operation state of the MSW incineration boiler. The tracking and analysis of the LHV of MSW should be strengthened. Compared with the MSW sample test, the performance test method can better reflect the real situation of LHV of MSW into the furnace. According to the FDBR standard, the average value of the LHV of the furnace waste during the performance testing can be accurately obtained, and the test accuracy is high. However, the operator is still unable to adjust the running state of the unit in real time according to the furnace waste. The real-time prediction of the LHV of the furnace waste is still the focus of the current stage. The measurement uncertainty of superheated steam mass flow, municipal solid waste mass flow, flue gas volume flow at economizer outlet, slag loss on ignition, economizer inlet feed water temperature, superheated steam temperature, air temperature in the middle section of primary air preheater, the ratio of wet furnace slag, economizer outlet flue gas temperature accounts for 99.3% of the uncertainty of LHV of waste into the furnace. Improving the measurement accuracy of these nine parameters can ensure the test quality of the LHV of MSW.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 2125K]

  • Synthesis of citric acid modified hydroxyapatite by hydrothermal method and its performance of defluoridation in mine water

    ZHAO Jiaxin;LI Wenbo;WANG Jikun;China Coal Research Institute;CCTEG China Coal Research Institute;

    In order to improve the dispersibility of hydroxyapatite, hydrothermal method with citric acid as chelating agent was used to prepare hydroxyapatite with improved dispersibility and citric acid was added to improve the dispersion of the sample, reduce the grain size, and adsorb fluorine ions in simulated water samples. The main parameters of hydrothermal synthesis of hydroxyapatite were optimized by single factor test and response surface method. Hydroxyapatites with different ratio of citric acid were characterized by five techniques such as: X-ray Diffraction(XRD),Fourier Transform Infrared Spectroscopy(FT-IR),Scanning Electron Microscope(SEM),Nitrogen Adsorption/Desorption Experiment and Energy Dispersive Spectrometer(EDS). The results show that the addition of citric acid will significantly affect the micro morphology of hydroxyapatite in nano scale. Box-Behnken design with three-levels and three-factors has been applied to determine the optimal parameters such as hydrothermal time(4-8 h),temperature(140-160 ℃),citric acid dosage(0.5%-1.5%) on removal of fluoride from simulated solution. The results show that the optimal conditions are 147 ℃ of hydrothermal temperature, eight hours of hydrothermal time, and 0.5% of citric acid addition. Under the best process conditions, nano hydroxyapatite with high dispersion is successfully obtained. For simulated water samples(fluorine ion concentration is 6 mg/L),the fluoride removal efficiency reaches 44.6%,The fluoride removal capacity is 2.678 mg/g, which is higher than the test value of commercially available hydroxyapatite under the same test conditions(1.437 mg/g). According to thermodynamic parameters, adsorption of fluoride is a spontaneous process(ΔG~0<0) with reduced endothermic(ΔH~0<0) and increased entropy(ΔS~0>0).The kinetic simulation of fluoride absorption by hydroxyapatite is conformed to pseudo second-order kinetics. The prepared hydroxyapatite samples were made into particles and evaluated by continuous adsorption device. The fluoride concentration in the effluent remained below 1.0 mg/L for 9 days, which means the hydroxyapatite made in lab has a significant removal effect of fluoride.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 26118K]

  • Preparation of composite flocculant and its application in high turbidity mine water

    MA Bo;LIN Zhiwei;SUN Chao;WANG Wenqian;ZHANG Chunhui;Ecological Environment Monitoring Center of Qingyang;College of Chemistry and Environmental Engineering,China University of Mining and Technology-Beijing;

    In view of the traditional flocculants used in the pretreatment process of high turbidity mine water,there are problems such as low efficiency,large dosage,and difficulty in removing turbidity and emulsified oil.Inorganic-organic composite flocculants was used to coagulation and sedimentation treatment of mine water to achieve the goals of high efficiency,environmental protection and greenness.The effect of flocculant on the removal of turbidity and emulsified oil under different dosage,temperature and p H conditions was studied through indoor simulation test.The results show that the removal effect of composite flocculant (PFS-P) is better than that of polyferric sulfate(PFS) and cationic polymer P(AM-DMDAAC-OM).When the dosage is 60-75 mg/L,the temperature is 20℃,and the p H=7,the removal effect is the best.The removal rate of turbidity reaches 99.3%-99.7%,and the remaining turbidity is only 3.1-7.4 NTU.The removal rate of emulsified oil is about 75.24%,and the remaining oil content is 7.0 mg/L.The analysis results of FT-IR,XRD and TEM show that the inorganic and organic flocculants are effectively combined.The ionic bond in AM interacts with the SO_4~(2-)bond of PFS to connect,and the composite flocculant finally presents a network structure under the action of the adsorption bridging.Under the action of Fe(Ⅲ) hydroxyl complex,long-chain organic molecule adsorption and neutralization,and net trapping and sweeping action of composite flocculant,it can effectively remove turbidity and oil in water.The preparation of composite flocculants and their simulated wastewater treatment tests provide theoretical references for the engineering application of coagulation and sedimentation treatment of high turbidity mine water.

    2022 02 v.28;No.138 [PaperDigest][OnlineView][HTML全文][Download 23734K]
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