- YE Guichuan;MA Liqiang;College of Mining Engineering,Taiyuan Univerisity of Technology;School of Chemical and Environment Engineering,China University of Mining and Technology-Beijing;
Spiral separator is a kind of traditional thin flow membrane separation equipment. Due to the rapid development of mining and coal industry,as well as the urgent demand of solid waste treatment at present,spiral separator is paid attention to for its advantages of low energy consumption,simple structure,high efficiency and low operating cost. In this paper,the theoretical research progress of spiral separator was discussed,including the flow field,spiral separation process,process optimization and intelligent control of spiral separator,and the separation characteristics and application status of coal spiral separator were summarized,and the new design and application of spiral separator were introduced. For the research of flow field on the spiral separator,some new testing methods have been introduced. However,it is difficult to measure the distribution of the longitudinal velocity and radial velocity in the thin film area,especially in the inner edge at present. The numerical simulation provides a convenient method for studying the influence of structural parameters and operation parameters on the flow field,but the simulation accuracy needs to be further improved.In the research of the spiral separation process,the positron emission particle tracking technology is a breakthrough in the theoretical research of spiral separator,which is used to detect the movement of particles in the spiral separator. The numerical simulation of particle movement in the spiral separation process provides a convenient means for the qualitative analysis of the spiral separation mechanism. However,due to the neglect of many practical conditions in the simulation process,there is still a big gap between the simulation results and the test results. At present,the research on process optimization and intelligent control of spiral separator is still in its infancy. In recent years,a number of new spiral separators have been developed at home and abroad. Some progress has been made in reducing the separation density: MTI company in South Africa has developed a spiral separator with low separation density. When the production rate is reduced by about 4%,the separation density can be reduced from 1.61 g/cm~3 to 1.54 g/cm~3. Moreover,a kind of composite trough spiral separator with an ultra-low pitch to diameter ratio( inner edge cubic parabola,outer edge ellipsoid) has been designed in China. The separation density can be reduced to 1.543 g/cm~3 when the gangue is predischarged in the roughing stage. Compared with the spiral separator with the traditional parameters of an ellipse and cubic parabola,the separation efficiency of the composite trough spiral separator has been increased by 19.41% and 13.11% respectively when the ash content of clean coal is equivalent. In the future,the research focus of spiral separator is mainly to use advanced means,such as PEPT technology and numerical simulation technology,to further study the influence of structural parameters( groove shape,pitch diameter ratio,and other structural parameters) on the flow field distribution characteristics and separation process of spiral separator. Meanwhile,it is necessary to cooperate with the improvement in structure,technology,and application of new materials to improve the separation accuracy and to make a breakthrough in the scope of density control.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 9553K] - WU Ke;BAO Zhongkai;DUAN Lunbo;Huang Yu;Key Laboratory of Energy Thermal Conversion and Control,Ministry of Education,Southeast University;
The main advantages of the supercritical carbon dioxide( sCO_2) Brayton cycle as a power cycle are high efficiency,simple structure,compact system and wide heat source adaptability,which is expected to be widely used in the next generation of nuclear reactors,coal-fired power plants,waste heat recovery and renewable energy( solar energy,geothermal energy,etc.) fields. As a new type of power cycle working fluid,sCO_2 has mild critical point conditions( 31. 1 ℃/7. 38 MPa),and its physical properties change sharply near the critical point. In view of the coal-based energy structure and severe climate challenges in China,the combination of sCO_2 power cycle with oxy-fuel combustion,fluidized bed boilers,coal gasification and other technologies provides new solutions to achieve clean,efficient and low-carbon utilization of coal. In this paper,the properties of sCO_2 were firstly analyzed,then the basic principles of two types of indirect-fired and direct-fired sCO_2 Brayton cycles were introduced,and then the research progress of sCO_2 power cycle applied to coal-fired power stations was summarized. The development of sCO_2 cycle coal-fired power plant can be divided into the following two paths: ① the indirect-fired sCO_2 cycle instead of steam Rankine cycle,which is used in coal-fired power stations,and is combined with technologies such as pulverized coal boilers,circulating fluidized bed boilers,and oxy-fuel combustion; ② the direct-fired sCO_2 cycle coal-fired power station has higher efficiency and inherent carbon capture,which can compete with the IGCC power station with carbon capture and storage( CCS) system. And then a variety of technical solutions of sCO_2 power cycle applied to coal-fired power station were analyzed,including the advantages,technical challenges and development directions of different types. Next,the experimental research and heat transfer characteristics of sCO_2 in conventional round pipe,thin round pipe,micro round pipe,and printed circuit heat exchanger( PCHE) were elaborated. Also,the empirical correlations of sCO_2 flow and heat transfer in circular tubes and PCHE were summarized and analyzed. At the same time,the numerical simulation methods of sCO_2 heat transfer were presented. Finally,from the basic theory,system study and equipment development,the shortcomings of the existing research and prospects for future research were pointed out,which had reference significance for the future development of coal-fired sCO_2 cycle power station technology. The CO2 emission reduction will be the main research direction of coal-fired power station in the next few decades. The direct-fired sCO_2 cycle coal-fired power generation technology with higher efficiency and inherent carbon capture will attract more attention from academics and industry. In China,it is more practical to apply the sCO_2 Brayton cycle to coal-fired power plants. At present,there is a considerable gap between China with foreign countries on the research of sCO_2 cycle power station technology. We should rely on the technology accumulation of ultra supercritical coal-fired power plants and IGCC power plants to rapidly promote the research and development of the technology of coal-fired sCO_2 cycle power station in China.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 6077K] - LIU Hongyu;ZHANG Shouyu;SONG Xiaobing;HU Nan;SUN Mengyuan;CHANG Ming;School of Energy and Power Engineering,University of Shanghai for Science and Technology;Changchun Institute of Technology;
Biomass has great potential as a low-cost,abundant and green energy source.However,due to the high content of the alkali metal contained in biomass,there are some serious problems such as alkali slagging,ash fusion,agglomeration and corrosion during the biomass utilization process.Among those,the slagging exists in the whole process of biomass utilization and leads to the formation and growth of the agglomerates and sediments,which is extremely difficult to deal with and can bring about great harm to the boiler operation.Therefore,slagresistant biomass fuel preparation is a feasible means to achieve efficient utilization of biomass fuel.At present,in order to solve the slagging problem in the process of biomass heat conversion and utilization,the generation and conversion processes of alkali metal chlorides,sulfates,and silicates are changed by the different methods such as additives addition,co-firing,chemical pretreatment,and alloying.Among those,the high-ash-fusion-point biomass with good anti-slagging function can be produced by the mixing of additives with biomass.Here,in this paper,the existence form of alkali contained in biomass,the releasing way and the migration behavior of potassium in the process of heat conversion were introduced.Then,the mechanism of the slagging occurring during the thermal conversion of the biomas were summarized.Subsequently,the anti-slagging mechanism of the three additives including aluminum-based,calcium-based,and phosphorus-based materials during the heat conversion process of the biomass were analyzed. In general,the use of three additives have better anti-slagging performance.Among those,the phosphorus-based additive can do with the slagging occurring in the flue system and the furnace bottom of the biomass boiler.The calcium-based material can only solve the slagging occurring in the furnace bottom,but results in more serious slagging occurring in the flue system.Although the aluminum-based material can achieve similar results with that of the phosphorus-based additive,its cost is high and the performance weakens with increasing temperature.The future research of the anti-slagging biomass fuels should focus on the new additives,such as single compounds or mixed mineral additives,which can fix potassium from flue gas and react with the bottom silicate to form high ash fusion point substance.Moreover,the molding process of the biomass mixed with additives should be paid more attention to and the slag-resistant biomass briquette with high mechanical strength should be developed.Laboratory of clean carbon-based fuel conversion,USST has been engaged in the research on the high-strength slag-resistant biomass briquetteand the biomass briquette fuel with good strength and anti-slagging performance has been developed. The paper can provide some references for the research and development of the anti-slagging biomass briquette.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 6169K] - ZHU Chao;WU Pengju;WANG Yongqing;YU Xiang;OUYANG Shijie;YANG Dong;Electric Power Research Institute of State Grid Shaanxi Electric Power Company;State Key Laboratory of Multiphase Flow in Power Engineering,Xi'an Jiaotong University;
For countries where coal is the main energy source,thermal power units,especially coal-fired power units,will continue to operate with low load or deep peak adjustment in the next few years. In the process of depth peak adjustment,the load of the unit deviates from the design condition,which may lead to flow instability. In this paper,the formation mechanism and influencing factors of the flow instability of ultra-supercritical units was analyzed and studied in order to provide guidance for the design of heat transfer equipment and safe variable load operation and the research methods of flow instability in ultra supercritical units were analyzed. According to occurrence characteristics,flow instability can be divided into static instability and dynamic instability. In load changing process of ultra-supercritical boiler flow system,there are flow instabilities such as density wave,pressure drop and thermal flow instability,which will have a serious impact on the normal operation of the system. The main influencing factors of flow instability include heat load distribution,pipeline structure and system flow parameters. Due to the development of analysis and calculation tools,the occurrence conditions and change rules of flow instability can be predicted accurately. A large number of experiments and numerical studies show that the lower the heat flux density is,the higher the system pressure is,the larger the inlet throttle coefficient is,and the smaller the outlet throttle coefficient is,and the more stable the system is. From the perspective of pipeline structure,the shorter the heating length is and the larger the inner diameter is,the more stable the system is,and the system with cross-connection is more stable than the system without cross-connection and the single-channel system. There are two methods to study the instability of ultra-supercritical water flow: experimental test and numerical simulation. The advantage of the experimental method is that it can focus on the actual physical system as the research object and provide valuable reference for the corresponding numerical simulation. Considering that the experimental system of water flow instability under ultra-supercritical pressure and temperature is extremely complex and requires a large amount of cost,numerical simulation has become an important research method. Numerical simulation can learn from mature two-phase boiling research results,which can easily analyze the influence law of various parameters on flow instability. For the numerical simulation of the flow instability of supercritical fluid system,the analysis methods can be divided into frequency domain method and time domain method. The disadvantage of the frequency-domain analysis method is that it can't solve the nonlinear problem well. The solution to the disappearance of the nonlinear effect of frequency-domain analysis method is to determine the amplitude of the limit cycle through the Hopf bifurcation technology. To analyse the flow instability of ultra supercritical fluid,the time domain method is most commonly used in the analysis for period of oscillation and chaotic nonlinear effect. With a series of dimensionless number,both dynamic changes and the flow instability boundary of subcritical and supercritical fluid can be effectively described.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 4226K] - ZHOU Jianming;CUI Yuhong;JIA Nan;CUI Mingshuang;ZHANG Bin;WANG Caihong;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of Coal Mining and Clean Utilization;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;
In China,pulverized coal industrial boiler has drawed lessons from the technical concepts of oil-gas boilers and German pulverized coal industrial boilers,which experiences project development,pilot test certificate and industrial demonstration.The system technology is gradually maturing.Since 2010,large-scale industrial application has been achieved.The coal-fired industrial boiler system has the advantages of high thermal efficiency and low emission of flue gas pollutants,which effectively promotes the development of coal-fired industrial boiler industry. In this paper,the technology and development of coal-fired industrial boiler were discussed,the key technologies of coal-fired industrial boiler were mainly introduced,the main technologies were compared,and the industrial application of coal-fired industrial boiler was analyzed,and finally the development direction of coal-fired industrial boiler technology was put forward.The results show that the technical system of pulverized coal industrial boiler consists of pulverized coal production,storage and supply,oil and gas ignition,combustion,boiler body,flue gas purification and automatic control system. The boiler thermal efficiency is more than 91 %,the flue gas pollutants meet the national ultra-low emission standard,and the system technology is more in line with the national coal clean utilization direction.The one-step process is adopted in the production of pulverized coal. The safe storage technology can achieve a storage capacity of 1 000 m~3 by strengthening the fluidity and safety protection measures of pulverized coal.The technology of pneumatic activation,pulse less feeding and high-speed jet dense phase conveying is adopted for feeding.The conveying resistance is less than 20 k Pa,the powder-air-solid ratio is more than 2.5 kg/m~3,the feeding accuracy is less than ±3.0 %,and the maximum feeding amount is 5 t/h.The dense phase feeding technology and equipment are widely used in the boiler feeding system.The feeding amount 2.5 t/h third-generation and fourth-generation feeders with feeding accuracy within ± 2.0% and ± 1.0% also carried out industrial verification and prototype trial production respectively,and achieved phased results.The pulverized coal burner adopts the reverse injection type reflux structure.According to its structural characteristics,the design work is carried out by simulating the air flow expansion angle,reflux area range,reflux flow,swirl intensity,temperature and velocity field,and then through practical engineering application,the design parameters are further verified and optimized,and finally the gradual amplification of the burner is realized.The natural gas/pulverized coal dual fuel burner has the functions of convenient switching and fast ignition.The air-cooled burner adopts internal and external two-stage swirl air supply combustion technology,which has the advantages of rapid ignition,stable combustion,high combustion efficiency and low initial NOxemission.With the development of pulverized coal boiler system technology,the boiler structure has gradually formed the related design and manufacturing specifications.Based on the continuous improvement of technology and equipment,the measurement and control technology is developing towards intelligence,networking and integration.Boiler flue gas desulphurization and dust removal adopts NGD high rate ash-calcium cycle desulphurization technology,which has the characteristics of small land occupation,low operating cost,and the system's desulphurization and dust removal efficiency can reach 90 % and 99.95 %,respectively,at a low molar ratio of calcium and sulfur.The low-temperature carbonbased pre-oxidation denitration coupled with NGD synergistic flue gas purification technology being developed is in the same direction as the synergistic purification of flue gas at home and abroad.The utility model has the advantages of simple process,less water consumption,reuse of waste resources,no secondary pollution,etc.,which is more suitable for flue gas purification of pulverized coal industrial boilers.The pulverized coal industrial boiler has been optimized and upgraded through key technologies and equipment in the development process,and has achieved results in the direction of large-scale,modularization and series.It has significant advantages over conventional industrial boilers in terms of energy saving,environmental protection and economy,and the technology has reached the world advanced level.In the future,with the optimization of the national energy structure,and the development and maturation of natural gas/pulverized coal boilers,low-nitrogen combustion,biomass composite semi-coke powder,and synergistic flue gas purification and other technologies,pulverized coal industrial boiler technology will become one of the main technologies for clean coal combustion.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 14547K] - ZHU Shujun;ZHU Jianguo;Institute of Engineering Thermophysics,Chinese Academy of Sciences;State Key Laboratory of High-temperature Gas Dynamics,Institute of Mechanics,Chinese Academy of Sciences;University of Chinese Academy of Sciences;
With the rapid development of China's economy,as an important basic material,the demand for cement products is huge and tends to be stable. The NO_x emission from cement production process and coal-fired power plants and automobile exhaust has become the main source of air pollution,and decomposition furnace is an effective equipment to reduce NO_x emission in cement production process.The air-staging combustion experiments were carried out in a simulated precalciner with high-temperature flue gas,and the effects of air distribution position,air distribution ratio and limestone/coal ratio on combustion and NO_xemission characteristics in cement precalciner were investigated. During the stable test,the coal feeding and air distribution of the high-temperature flue gas generator remain unchanged.At this time,the time-average temperature of the high-temperature flue gas generator is 911 ℃,and the temperature of the high-temperature flue gas produced is stable at approximately 750 ℃ . The NO_x in the high-temperature flue gas mainly exists in the form of NO and N_2O,and the concentration is 261.49×10~(-6) and 12.96×10~(-6),respectively. The high-temperature flue gas will simulate the actual flue gas from the rotary kiln into the decomposition furnace. The temperature in the upper part of the calciner( 0-2 000 mm from the top) is from800 to 1 000 ℃,which is consistent with the actual operation temperature of the calciner. NO_xin the exhaust gas mainly exists in the form of NO and N_2O. As the position of the middle air distribution moves down,the exothermic region of pulverized coal combustion moves down,while the heat absorbed by limestone in the top region changes a little,so the original heat balance is broken and the original heat absorbed is higher than the exothermic quantity,causing the combustion temperature in the top zone to drop. At this time,the reaction time of coal combustion and limestone decomposition becomes longer in reducing atmosphere,which leads to more sufficient reduction of NO_x.However,calcium oxide( Ca O) produced by limestone decomposition,as an intermediate product,can promote the formation of NO,and its reaction time also promotes the formation of NO. On the other hand,limestone is used as a catalyst in the reduction of NO by char and volatiles,the reduction of NO is weakened due to the decrease in temperature in the top zone of the decomposition furnace. To sum up,the final emission concentration of NO is the combined result of the above reactions. As the position of air distribution moves down,the effect of those changes on NO production becomes more obvious,so the concentration of NO emission increases gradually. When the ratio of the first air flow rate to the second air flow rate is reduced,the coal combustion rate and limestone decomposition rate in the upper part of the calciner decrease,and the proportion of pulverized coal combustion and the proportion of undecomposed limestone in the lower part of the calciner increases,but the heat absorption increase of limestone is higher than the heat release of combustion increase,so the whole temperature of calciner decreases. The concentration of NO in the calciner is determined by the oxidation and reduction processes catalyzed by limestone. The concentration of CO in the tail increases and the concentration of NO in the flue gas decreases with the decrease of the first stage air flow rate. When the ratio of limestone to coal increases,the temperature in the calciner decreases gradually. With the increase of the amount of limestone powder,the CaO concentration produced by thermal decomposition of limestone in the calciner increases,and the NO reduction reaction is more intense,and the NO concentration decreases gradually. The increase of limestone powder and the decrease of calciner temperature lead to the increase of CO concentration in the tail.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 2848K] - FU Peifang;GONG Xueqi;ZHANG Bin;LIU Yang;GONG Yusen;XU Tianyao;State Key Laboratory of Coal Combustion,School of Energy and Power Engineering,Huazhong University of Science and Technology;
It is very important to study the ignition characteristics of pulverized coal for the design and operation of nozzle and chamber in a pressurized gasifier.In this paper,the ignition characteristics of three types of coal sample were studied by using pressurized thermogravimetry.According to the principle of energy conservation in the process of heating up and Semenov's TET theory,a novel method by processing PTG curve and obtaining ignition temperature,namely the inflection point method was proposed,which was compared with the empirical tangent method.The influences of pressure,oxygen concentration,heating rate,volatile content and particle sizes were discussed.The results show that the ignition temperature range of pulverized coal is from the initial ignition temperature( Ti) to the ultimate ignition temperature( Tig),and the location of tangential point determined by the environmental heat transfer conditions is the only definite condition.The high heating rate of high-temperature industrial furnaces corresponds to the ultimate ignition temperature; during the pressurized combustion of pulverized coal in fixed bed,heterogeneous ignition occurs,and the ignition temperature increases slightly with the increase of volatile content; in the pressure ranges of 0.1-1.0 MPa and 3-5 MPa,the ignition temperature decreases with the increase of pressure,which is much lower than that under atmospheric combustion,but increases slightly at the pressure range of 1-3 MPa.The effect of oxygen volume fraction on ignition temperature is similar to that of atmospheric pressure.With the increase of oxygen volume fraction,the ignition temperature decreases.Although the quick oxidation of pulverized coal under pressure and the ignition temperature obtained by the inflection point method is close to that obtained by the empirical tangent method,the tangent method cannot respond to the change of environmental conditions,and the empirical tangent method cannot give satisfactory results under normal pressure.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 2276K] - ZHANG Ping;CHEN Lujian;JIANG Hua;ZHANG Man;XU Wei;LIU Shi;YANG Hairui;LYU Junfu;Guotou Panjiang Power Generation Co.,Ltd.;State Key Laboratory of Power Systems,Department of Energy and Power Engineering,Tsinghua University;
Large proportion of coal slime co-combustion in CFB boilers is an effective means to treat low quality coal such as coal slime. A one-dimensional chamber model was used to simulate the operating conditions of a CFB boiler with different proportions of coal slime co-combustion. The effects of blended coal slime ratio on the average particle size in CFB boiler furnace,the residence time of particle in furnace and the material concentration of upper furnace were studied,and the optimal operation condition on flow regime under the condition of large proportion of coal slime was determined. The simulation results show that increasing the proportion of coal slime can increase the material circulation flow rate and the residence time of particles in the intermediate size range( 0.1-0.3 mm) in the furnace,and improve the burnout rate of fuel. Increasing the proportion of coal slime can increase the particle concentration of upper furnace,which is beneficial to improve the heat transfer in the upper part of the furnace,reduce the temperature of the furnace,and control pollutants.Based on the operation data of large proportion of coal slime co-combustion in a 300 MW circulating fluidized bed boiler unit in Panbei Power Plant,the effects of proportion of coal slime co-combustion on bed temperature,exhaust gas temperature,carbon content of bottom slag and fly ash were analyzed. When the boiler load is at 300 MW,the bed temperature obviously decreases after the blended coal slime being burned,the carbon content of the fly ash and the smoke exhaust temperature increase with the proportion of blended coal slime increased,and the carbon content of the bottom slag decreases with the proportion of blended coal slime increased. In order to achieve the goal of large proportion of coal slime co-combustion,it is recommended to control the coal particle size of gangue,and it is necessary to strengthen the tail soot blowing or adjust the tail heating surface appropriately.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 1619K] - PENG Chao;LAN Yanbing;ZOU Chun;CAI Lei;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;School of Environmental Science and Engineering,Huazhong University of Science and Technology;
Carbon dioxide emission is one of the main reasons for the greenhouse effect. Oxy-fuel combustion has an extensive research prospect as an effective carbon emission reduction and storage technology.The ignition temperature of pulverized coal in oxy-fuel combustion in coal-fired power plants is an important indicator of burner design and operational safety,which has complex correlations with the composition of coal,coal particle size,and the atmosphere of combustion. Therefore,the research of the ignition temperature prediction model of pulverized coal oxy-fuel combustion is very meaningful. In this study,the ignition temperatures of five coal samples were measured in dropper furnace under 30%,35%,40%,50%,60%,70%,80%,90% and 100% volume fraction of O_2 in CO_2 atmosphere.The relationship between coal ignition temperature and the oxygen concentration and the composition of pulverized coal was analyzed.The research finds that the coal ignition temperature decreases significantly with the increase of oxygen concentration,and the degree of decrease is higher when the coal sample contains more volatile.A machine learning sample base with 45 sets of coal ignition temperature in the experiment and 69 sets of ignition temperature collected from recent year' s research with the same measurement was established.The ultimate analysis and proximate analysis of the pulverized coal,the coal particle size and the oxygen volume fraction were selected as the input features,and the ignition temperature was the target output,a random forest model optimized by genetic algorithm( GA-RF model)was constructed and the ignition temperature of pulverized coal in oxy-fuel combustion was accurately predicted,with the accuracy of R~2>0.99,RMSE<16,MAE<8.The feature importance of ignition temperature shows that the ignition temperature increases immediately when the H content is over 5%,which is proved by the existing ignition data of pulverized coal.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 5991K] - TONG Sheng;WANG Zhizhou;KANG Yaqian;LYU Yuan;NIU Yanqing;Guodian Power Development Co.,Ltd.;Xi'an Research Institute of China Coal Technology & Engineering Group;State Key Laboratory of multiphase flow in Power Engineering School of Energy and Power Engineering,Xi'an Jiaotong University;
Due to high content of alkali metals such as Na and K in Zhundong coal and biomass,there will be related problems of ash in the combustion process,and it is easy to slag and deposit on the heating surfaces in the combustion process,resulting in high-temperature corrosion of metal tube,which will affect the heat exchange efficiency and use safety of metal tube bundles.In serious cases,it can lead to tube explosion and threaten the normal and safe operation of the boiler.In this paper,the high-temperature corrosion test under simulated flue gas was conducted on metal materials of 15 CrMoG and T91 and the deposition corrosion of alkali metal salt on the surface of heating surface was simulated by KCl coating method. The morphology and composition of corrosion products were analyzed by SEM,EDS and XRD,and the effects of metal materials,corrosion time and reaction temperature on the high temperature corrosion of alkali metal chloride were studied.The results show that the KCl coating on the metal surface aggravates the high-temperature corrosion,and the alkali metal chloride can effectively intensify the high-temperature corrosion of the metal materials.Under various corrosion time and reaction temperature,the weight gain and thickness of corrosion layer of metal material 15 CrMoG are greater than that of T91,indicating that the corrosion resistance of T91 is greater than that of 15 CrMoG.With the increase of reaction time,the weight and thickness of corrosion increase gradually,while the corrosion rate decreases gradually. Compared with the corrosion time between 20-48 h,the corrosion rate is faster when the corrosion time is less than 20 h and the corrosion curve generally conformes to the parabolic law. The main reason for the decrease of corrosion rate in the later stage of corrosion is that high-temperature corrosion will lead to the formation of dense oxide film covering the metal substrate surface,which has a protective effect on the metal and slows down the occurrence of corrosion.With the increase of reaction temperature,the corrosion is intensified.When the temperature is lower than 500 ℃,the slope of the curve is smaller and the corrosion rate is lower; when the temperature is higher than 500 ℃,the slope of the curve is obviously increased and the corrosion rate is faster.The trend of temperature corrosion thickening curve is basically the same as that of weight increase curve and the corrosion curve is in accordance with parabola law.With the increase of temperature,the chemical reaction rate of alkali metal corrosion has an exponential relationship with the temperature.With the increase of temperature,the number of active molecules participating in the corrosion reaction increase,and the corrosion reaction rate is accelerated rapidly.It can be seen from the corrosion micrograph that before corrosion,the metal matrix structure is complete and the surface is smooth.After corrosion,the contact surface between the metal and the corrosion layer appeares uneven structure.With the increase of corrosion time,the thickness of the corrosion layer increases gradually. According to the results of SEM-EDS,the main components of the corrosion products of the two kinds of metal materials are Fe and O.Combined with XRD peak spectrum identification,the corrosion products of the metal materials are mainly in the form of Fe_2O_3.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 6697K] - XIE Qiang;LIANG Dingcheng;LIU Jinchang;School of Chemical and Environmental Engineering,China University of Mining and Technology-Beijing;
Resources of low rank coal with high content of alkali and alkaline earth metals( AAEM) are rich in China. The serious problems,including slag-bonding,staining,erosion and agglomerating in boiler and gasifier,are caused due to high AAEM in coal. Meanwhile,low-rank coal is often characterized by particular features,such as high moisture content,high oxygen content,high volatile content,low caloric value and ease of spontaneous ignition,which bring great difficulties to its storage,transportation and utilization.Pyrolysis can produce high-quality fuel and high value-added chemical raw materials. Besides,pyrolysis can also be considered as the initial stage and/or paralleling part of coal combustion,gasification and liquefaction,and the reactions and behaviors in coal pyrolysis play an important and even decisive role in the thermal conversion of low rank coal. In the paper,a critical survey of investigation into coal pyrolysis and characterization of char derived from coal pyrolysis was presented,with emphasis on the influence of AAEM on coal pyrolysis. The results show that the apparatus and equipment used for pyrolysis study in labs and the set of experimental parameters are far from that in the process of modern coal chemical industry,and the representativeness of Semicoke sample is not strong enough to guide the research results of pyrolysis. The occurrence mode and separation method of AAEM in coal need to be improved and new extraction reagents need to be screened and tried. Although the behavior of AAEM in coal pyrolysis is basically grasped,there is not an effective method to reduce the harm of AAEM in coal thermal conversion process. Thus,safe,efficient and clean utilization of high AAEM low rank coal awaits researching and developing further.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 3249K] - YAN Tinggui;BAI Jin;KONG Lingxue;DAI Xin;LI Huaizhu;GUO Zhenxing;BAI Zongqing;LI Wen;School of Chemistry and Chemical Engineering,Guizhou University;State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Chinese Academy of Sciences;Shougang Group research Institute of Technology;Beijing Key Laboratory of Green Recyclable Process for Iron & Steel Production Technology;
As the requirements for conversion rate and production efficiency in coal conversion industry further improving,the thermal conversion process of coal tends to be performed in converter with high temperature and high pressure. In the high-temperature and highpressure combustion furnaces and gasifiers with slag tapping,the minerals in coal are completely melted into slag and then discharged. For an entrained-flow gasifier with slag tapping and a water-cooled wall,the melting temperature of coal ash is required to be lower than the operating temperature,and the viscosity of the molten slag ranges from 2.5 to 25.0 Pa·s. Moreover,the fluctuation of viscosity with temperature should be small in the operating temperature range. The melting temperature and the viscosity-temperature characteristics of coal ash during gasification are the key factors affecting the flowing of slag. The development of traditional testing methods for ash melting temperature was reviewed and analyzed in this paper. The principle of standard methods in various countries is to determine the melting temperature by the deformation of the compacted sample during the heating process. However,the melting temperature alone cannot provide enough information to achieve fine control of modern large-scale gasification processes,and the full-stage testing of the coal ash melting process helps to guide the actual production more accurately. A few qualitative and quantitative studies of the melting process by researchers in various countries show that the deformation temperature in the melting temperature is not the real temperature at which the coal ash starts to melt. In view of the deposition and sintering problems of coal ash,the start temperature of shrinking and the initial formation temperature of the liquid phase that predicted by thermodynamic calculation helps to predict the temperature at which coal ash may deposit or sinter more accurately. At present,the test of viscosity-temperature characteristics still relies on the high-temperature rotational viscosimeter,which is time-consuming and complex. Therefore,a simpler and time-saving method is used to quickly screen the viscosity-temperature characteristics of suitable feedstocks. In addition to the experimental methods,the application of simulation calculation methods is more and more widely used in the study of coal ash fluidity. Through thermodynamic calculations and molecular simulation methods,it is possible to obtain mineral composition and microstructure changes of the melt that are difficult to measure in experiments. The non-equilibrium method in molecular dynamics can simulate the shear thinning process of complex fluids more accurately,thereby the obtaining viscosity calculation results are closer to the experimental values. Not only does the use of non-equilibrium methods improve the accuracy of the calculation results,but also increases the complexity of the calculation and the time required for the calculation. At present,there are not many choices of calculation models for the coal ash system. Therefore,the complexity of the system and the accuracy of the calculation results should be considered comprehensively when using the simulation calculation methods. With the further study of the melting process and the general application of simulation calculation methods,the mechanism of the change for macroscopic property presented in experiment will be easier to be clarified through the microstructure changes,which in turn will help optimize existing simulation calculation methods and parameters.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 4033K] - HU Fating;WANG Xueyun;MAO Xuefeng;LI Junfang;ZHAO Peng;Coal Chemistry Branch of China Coal Research Institute;State Key Laboratory of Coal Mining and Clean Utilization;National Energy Technology and Equipment Laboratory of Coal Utilization and Emission Control;
Direct coal liquefaction technology is an important way to promote the clean and efficient utilization of coal,alleviate the contradiction between oil supply and demand,and ensure the energy security in China.In order to fully understand the whole process of coal liquefaction reaction mechanism,kinetics,catalyst and technology,and promote the rapid progress of basic research of coal direct liquefaction technology and the development of new technology,the research results of the mechanism,reaction kinetics,catalyst and liquefaction process of the hydrogenation liquefaction were introduced. In this paper,the coal liquefaction processes of German IGOR,Japan NEDOL and Shenhua in China were mainly introduced,and the development history and characteristics of these typical coal liquefaction processes were analyzed.The development trend of direct coal liquefaction to oil technology were pointed out.The hydrogenation liquefaction reaction of the coal is a free radical reaction mechanism,which is a comprehensive result of a series of sequential reactions and parallel reactions,and includes pyrolysis of coal,hydrogenation of free radicals,removal of impurity atoms and condensation reaction,etc.In general,the sequential reaction is dominant.With the help of modern analytical methods and experimental methods such as isotope tracing,in situ detection,plasma and microwave rapid heating,the research on the production rate of free radicals,the active hydrogen production rate and the quantitative transfer mechanism of free radical is helpful to further understand and accurately elucidate the mechanism of coal hydrogenation and liquefaction.Using different research methods,the various kinetic models for different coal types,catalysts,process conditions and hydrogen supply solvents have been established in various countries. The kinetic models range from single-component to two-component and multi-component,from continuous reaction,parallel reaction to complex network reaction,from the initial one-step reaction to the later more reasonable multi-stage reaction. The models are becoming more and more complex and closer to industrial applications. The multi-component " lumped" reaction kinetic model based on the different stages of the reaction will be the main direction for the development of coal hydrolique reaction kinetics in the future.By means of the advanced analysis means and the treatment method,it is the development trend in the future to establish the model of the coal liquefaction dynamics law under different conditions.With the help of hightech such as nano-synthesis and plasma,it is an effective method for the preparation of highly active catalysts by controlling the compatibility of components,reducing the particle size of catalyst and optimizing the preparation method. The future development trend of direct coal liquefaction is to strengthen the rational configuration and optimization integration of the system,pay attention to the mild liquefaction and classification transformation of coal,optimize the product structure,and develop the coupling technology of direct and indirect liquefaction.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 9659K] - WANG Xueyun;HU Fating;WANG Guangyao;Coal Chemistry Branch of China Coal Research Institute;State Key Laboratory of Coal Mining and Clean Utilization;National Energy Technology and Equipment Laboratory of Coal Utilization and Emission Control;
The development of indirect coal liquefaction technology is an effective way to alleviate the shortage of oil and promote the clean utilization of coal. In this paper,the early classical F-T synthesis reaction mechanisms,such as carbide mechanism,CO insertion mechanism,intermediate polycondensation mechanism,and recent proposed C2 active species mechanism,carbide theory of resorption of dilute hydrocarbons,network reaction mechanism and so on were introduced. The rationality and limitation of these reaction mechanisms were pointed out. The characteristics and research progress of F-T synthetic reaction kinetic model such as CO consumption rate kinetic model and detailed kinetic model were discussed. The kinetics model of CO consumption can predict the conversion of CO well without considering the growth process of carbon chain. The detailed dynamic model contains the reactant consumption rate and product distribution information,but its reliability is based on the F-T synthesis reaction mechanism. The characteristics of iron-based catalysts and cobalt-based catalysts in industry as well as the research progress in phase transition and catalytic mechanism were reviewed. The research and development progress of new catalysts such as composite catalysts,multi-metal catalysts and new support catalysts were discussed. In this paper,the development course of coal indirect liquefaction process at home and abroad was introduced. The problems and improvement measures in industrial application were analyzed. The characteristics and technological process of indirect coal liquefaction developed by Shanxi Coal Chemical Institute and Yankuang Mining Group in China were emphatically discussed. The research focus and development direction of F-t synthesis reaction mechanism,reaction kinetics,catalyst and coal indirect liquefaction process in the future were discussed and prospected.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 5150K] - LI Shuangshuang;QIN Zhihong;YANG Xiaoqin;CHEN Qiang;School of Chemical Engineering and Technology,China University of Mining and Technology;
Supercapacitor has the advantages of high power density,long life and low production cost,which is considered to be one of the most promising energy storage systems. However,the practical application of supercapacitors is prevented due to its low energy density.Because the stored energy is directly proportional to CV2,the energy density of the supercapacitor can be increased by increasing the capacitance " C" of the material or the operating voltage window " V" or both. Organic electrolytes with wide potential windows in batteries have poor ionic conductivity,high cost,and easily cause environmental problems. Therefore,in order to improve the energy density,an electrode material with a high specific capacitance should be used. Therefore,the design of suitable electrode materials with high specific capacitance has become a research hotspot. As a supercapacitor electrode material,Ni(OH)_2 has attracted more and more attention in recent years due to its outstanding theoretical capacity,low cost,natural richness and easy synthesis. However,since Ni(OH)_2 has a low conductivity and a small surface area,its capacity is deteriorated severely. Carbonaceous materials are electrode materials for electric double layer supercapacitors,and their energy storage mechanism depends on the dissociation of the electrode surface and the adsorption of electrolyte ions. It is widely used due to its good conductivity,abundant raw materials,low cost,and high electrochemical stability. Therefore,it is necessary to make composite of Ni(OH)_2 with a highly conductive carbonaceous material to improve the capacitance performance. In this paper,the synthesis of Ni(OH)_2-based materials was reviewed,especially for the synthesis of Ni(OH)_2 combined with different carbonaceous materials to improve their cycle stability and rate performance as electrode materials.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 3249K] - DU Juntao;NIE Yi;LYU Jiahe;MA Jiangkai;JIA Huina;ZHANG Minxin;SUN Yikai;ZHENG Shuangshuang;BAI Lu;Zhengzhou Institute of Emerging Industrial Technology;Institute of Process Engineering,Chinese Academy of Sciences;School of Chemical Engineering,Dalian University of Technology;School of Chemical Engineering,Zhengzhou University;
MCMB has the advantages of good lithium ion dispersion,conductivity and mechanical stability,which is a widely used anode material of lithium ion battery with excellent comprehensive performance. However,the low theoretical specific capacity is a key factor for restricting its development. In order to obtain MCMB based anode materials with excellent performance,the modification of MCMB and its composite materials have become the focus of current research and development. So,the effect of microstructure design on electrochemical properties of MCMB lithium-ion battery anode materials was discussed,such as carbon structure,surface interface and composite materials.The influence of carbon structure microstructure design on the electrochemical performance of MCMB was discussed from the aspects of carbon stacking structure type,carbon layer order,carbon layer interlayer spacing and sphere particle size. It is concluded that MCMB with a disordered layer structure generates less internal stress during charging and discharging,and the carbon structure is relatively stable,thereby it has excellent cycle stability. MCMB with a large number of micropores or a large carbon layer spacing,can increase the migration rate of lithium ions in the electrode and provide more lithium storage space during charging and discharging,which often shows excellent charge and discharge specific capacity and rate performance. MCMB with the small particle size has a shorter lithium ion migration path,but the specific surface area of the electrode material will also increase accordingly,which show better rate performance and relatively poor reversible specific capacity and the attenuation of charge discharge efficiency.The influence of surface interface carbon layer modification on the electrochemical properties of MCMB was discussed from the aspects of surface interface modification,coating and doping modification. The literature indicates that the surface carbon layer modification can increase the electrolyte compatibility specific surface area of MCMB with electrolyte,promote the contact area of electrolyte and the lithium storage capacity,and improve the electrochemical performance of lithium ion battery anode materials. In addition,the MCMB surface coating a layer of amorphous carbon can avoid direct contact between its surface and the electrolyte,reduce the electrochemical side reactions and increase the reversible specific capacity. From the aspects of carbon active material composites and non-carbon active material composites,the influence of the microstructure design of the composite materials on the electrochemical performance of MCMB was discussed. The carbon active material can decrease the carbon layer structure order inside the MCMB,which can reduce the internal stress caused by the lithium ion insertion process and improve the cycle stability. Non-carbon active materials can induce MCMB to form a more ordered carbon layer structure and increase its specific surface area,improve the contact ability and the lithium insertion performance between MCMB surface and electrolyte molecules,which is conducive to improving the reversible specific capacity,cycling performance and rate performance of MCMB anode. MCMB possesses the specially structural characteristics,such as the high carbon layer spacing and the multiple defect sites,which is also conducive to the free extraction of sodium ions. When MCMB is applied to sodium ion batteries,it often shows good reversible specific capacity,cycle stability,and rate performance. Similarly,the irregularly oriented layered structure of MCMB has a high specific surface area after activation,so MCMB can be applied to the electrode materials of supercapacitors. Finally,the application of MCMB as lithium ion battery anode materials was prospected. With the development of high-performance lithium ion battery electrode materials,the research focus of MCMB anode materials would be to design the MCMB nanocomposite materials from the perspective of microstructure.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 1422K] - ZHANG Tiankai;WANG Qi;ZHANG Yongfa;Key Laboratory of Coal Science and Technology,Ministry of Education and Shanxi Province,Taiyuan University of Technology;
Coal resources is rich in China,but at present,the traditional utilization methods,mainly including combustion,pyrolysis and gasification,have some problems such as waste of resources,environmental pollution and low economic benefits,and the energy structure with coal as the theme will not change in a short period of time. Therefore,clean and efficient utilization is the foothold and primary task of coal resources in the new era. On the other hand,carbon nanotubes have excellent properties in mechanics,electricity and thermotics due to their unique one-dimensional structure,which makes them widely used in the fields of composite materials,electronic materials and energy materials. However,the problem of high preparation cost of carbon nanotubes is prominent,which severely limits its large-scale application. At present,it is urgent to develop new and environmentally friendly carbon nanotubes preparation technology. The above two problems can be well solved by the large-scale and low-cost coal-based carbon nanotubes preparation technology at the same time. Based on the literature,in this paper,the influence of reaction materials,discharge atmosphere and catalyst on the direct preparation of carbon nanotubes by arc discharge method and plasma jet method was analysed,and the influence process of raw materials,catalyst,reaction temperature,heating rate and reaction atmosphere on the preparation of indirect carbon nanotubes by chemical vapor deposition method was discussed. It is found that in arc discharge and plasma jet methods,the type of raw materials plays an important role in the production of carbon nanotubes,the discharge atmosphere has an significant influence on the type of carbon nanotubes,and the catalyst has great effects on both the production and type of carbon nanotubes. In the chemical vapor deposition method,the type of raw materials has a major impact on the morphology,aspect ratio and order degree of carbon nanotubes,the catalyst can make a big difference to the growth process of carbon nanotubes,the reaction temperature and heating rate will influence on the diameter change and type of carbon nanotubes,and the reaction atmosphere can change the catalytic effect of the catalyst. In addition,in this paper,the types and characteristics of the growth mechanism of carbon nanotubes in the direct and indirect preparation of coal-based carbon nanotubes were summarized: the growth process of carbon nanotubes in the direct preparation technology conformed to the fragment growth mechanism,while the growth process of carbon nanotubes in the indirect preparation technology could be divided into four types: gas-liquid-solid( VLS),gas-solid-solid( VSS),gas-phase nucleation( VPN) and ladder type. Analysis shows that the further research should be carried out on the following aspects: the process of preparing carbon nanotubes from cheap raw materials such as coal,coal pyrolysis gas and commercial gas is investigated,so as to establish and improve the relationship system between raw materials and carbon nanotubes products,and the new and efficient preparation technology of coal-based carbon nanotubes catalyst is developed. The growth models of new carbon nanotubes are established,so as to further enrich and improve the carbon nanotubes growth model system further.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 4624K] - QU Zhibin;SUN Fei;PI Xinxin;QIE Zhipeng;GAO Jihui;School of Energy Science and Engineering,Harbin Institute of Technology;
The coal consumption of power generation in China is nearly 2 billion tons annually. Although SO_2 emissions have been controlled at ultra-low emission level by the wet limestone-gypsum flue gas desulfurization( WFGD) technology,the problems of large consumption of H_2O as well as the difficulty in disposing the low-value by-product CaSO_4 make traditional WFGD technology face the sustainable development dilemma. By contrast,SO_2 removal based on carbon materials is regarded as one of alternative technologies to WFGD due to the advantages of low H_2O consumption,less water consumption,recycling of pollutants,eco-friendliness as well as high-value utilization of by-product. Herein,the research progress of sulfur removal and resource utilization based on the adsorption and catalysis of carbon materials was reviewed. The key technical links in the process of desulfuration by using carbon materials were discussed. Finally,the directions for future research for sulfur removal and resource utilization were proposed. The mechanism of SO_2 adsorption catalytic reaction and the product migration path in carbon materials were discussed. The effects of pore structure,functional group and metal oxide loading on the adsorption and conversion of SO_2 as well as by-product migration were discussed. The results show that the adsorption and conversion of SO_2 as well as by-product migration can occur in hierarchical pore; Doping non-carbon elements such as nitrogen and oxygen can change the electronic structure of carbon surface and further adjust the processes of adsorption as well as catalytic oxidation of SO_2 in carbon materials. Therefore,oriented construction of hierarchical pore structures and functional groups is an efficient method to strengthen the adsorption and transformation of SO_2 and improve the desulfurization performance of carbon materials. The regeneration of saturated carbon materials and the pathways of sulfur resource utilization were analyzed. Particularly,the factors that may influence the conversion of SO_2 to sulfur by carbothermal reduction were discussed. Thermal regeneration faces the problems of high energy consumption and serious loss of quality. Washing regeneration has the problems of low efficiency and poor cycling desulfurization capacity. Efficient regeneration requires effective matching of pore structures of different sizes to enhance the diffusion and transportation processes. Among all kinds of desulfurization by-products,sulfur owns the advantages of low quality,high value,convenient storage and transportation,which is an ideal goal of resource recovery. The regulation of the activity and selectivity of carbon-based reductant is the key to achieve efficient sulfur generation. Low-cost preparation methods of high-performance coal-based activated coke was analyzed. The method that could prepare activated coke with hierarchical pore structures was particularly discussed. The preparation of traditional columnar activated coke has complicated preparation process and high cost and microporous distribution of pore structure. The prepared columnar activated coke only owns micropores,leading to the problems of large internal diffusion resistance,low internal surface utilization,and poor SO_2 removal and regeneration performance. The preparation of broken or granular activated coke is able to reduce the cost of preparation of activated coke and achieve deep regulation of the pores of activated coke,but the improvement of structural stability( strength) is the key for its application. Through catalytic activation,coal blending and catalytic graphitization,the desulfurized active coke with both high activity and high structural stability is expected to be prepared.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 14286K] - LI Yunjia;LI Changming;LIU Zhouen;GAO Shiqiu;XU Guangwen;YU Jian;State Key Laboratory of Multi-phase Complex Systems,Institute of Process Engineering,Chinese Academy of Sciences;University of Chinese Academy of Sciences;Key Laboratory on Resources Chemicals and Materials of Ministry of Education,Shenyang University of Chemical Technology;
The flue gas from pyrolysis and coking industry is always in low temperature range and contains high content of water vapor as well as other other pollutants such as tar and carbon black,making the traditional flue gas purification technology for power plant unsuitable for the pyrolysis and coking fields. In order to provide new ideas and references for the technology upgrade of end-stage flue gas treatment in pyrolysis and coking processes,the latest application progress of the promising end-stage flue gas purification technology was summarized. Accordingly,the two relatively mature coking flue gas purification technical routes were dry desulfurization/bag filter dedusting/low temperature denitrification and integrated desulfurization and denitrification of activated coke. Although the integrated technology of catalytic ceramic fiber filter has been successfully applied in glass industry abroad,it was still not long for its application in the field of coking flue,deserving more attention for potential risks. In addition,oxidation coupling wet absorption technology was not widely used in industry due to its serious secondary pollution. After analyzing the existing problems of the current technologies,solutions were proposed with clear research directions and upgrading routes for the further development of these technologies. To improve the process of dry desulfurization/bag filter dedusting/low temperature denitrification,the further research will mainly focus on treatment of desulfurization ash,recovery of spent catalysts and in-depth process optimization. Researches on integrated desulfurization and denitrification of activated coke should focus on the evolution of activated coke characteristics in multiple cycles,control of carbon loss during regeneration and recovery of waste coke powder. Potential issues of integrated technology of catalytic ceramic fiber filter need be further examined,such as ammonia escape,catalyst deactivation and blocking tube by tar. Finally,combining the characteristics of pyrolysis coking flue gas,it was concluded that the key to the pyrolysis coking flue gas purification was the coupling of low temperature denitrification technology and other pollutant control technologies,and the further development trends will be the integrated purification,simple maintenance of equipment and low operating costs of flue gas purification products and technologies.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 3899K] - SHI Chaoting;CAI Jun;REN Qiangqiang;WU Huixing;MA Haijun;Institute of Engineering Thermophysics,Chinese Academy of Sciences;University of Chinese Academy of Sciences;Dalian National Laboratory for Clean Energy;Ningxia Tianzonghongguang Waste Heat Power Generation Technology Co.,Ltd.;
China is the largest cement producer and consumer in the world,and NO_x emission from cement industry has become the third largest emission source since thermal power generation and transportation,which is one of the main reasons causing the haze weather in China. With the improvement of NO_x emission standards in the cement industry,more and more attention has been focused on the low NO_x emission control technologies for coal-fired cement kilns. In order to clearly understand the optimization direction of the common low NO_x emission control technology and the development status of the new low NO_x emission control technologies in the cement industry,and provide references for cement enterprises to achieve ultra clean and green production,the conventional and emerging low nitrogen denitration technologies used in coal-fired cement kilns were summarized and analyzed in this paper. Firstly,in the view of the conventional low nitrogen denitrification technologies in coal-fired cement kilns,the principles,characteristics and application status of these technologies were stated according to the classification of before,during and after the burning of the fuel,and the problems encountered in practical application were further pointed out. And the combined application of various low NO_x emission control technologies before,during and after combustion were also introduced briefly. Secondly,in the view of the emerging low nitrogen denitrification technologies with two-step NO_x reduction method as representative,in this paper,the nitrogen reduction principles and research status of these methods were focused on. And the denitrification efficiencies,research and application status of various low NO_x emission control technologies in cement industry were compared and summarized. Facing the increasing severe situation of emission reduction,it is imperative to carry out the deep denitration work in the cement industry. To this end,in combination with the principles,characteristics and problems of various common low NO_x emission control technologies,the combined application of low nitrogen control technologies during combustion and after combustion were proposed to achieve the purpose of cost reduction and efficiency increase in the cement industry,and some feasible plans for the reconstruction of existing production lines and the construction of new production lines were put forward. Considering the nitrogen reduction principle and development status of various new low NO_x emission control technologies,the future research and efforts of the low NO_x emission control technologies in the cement industry were pointed out. In the future,the development of low NO_x emission control technology in cement industries should pay attention to improving the carbon reduction capacity in reduction atmosphere,and the optimization of the existing technology and the exploration of new technologies should be carried out with the stimulation of carbon reduction capacity as the core. Besides,it was pointed out that the application of precise measurements and control equipment with automation and intelligence should be considered in order to give full play to the denitrification effect of low NO_x emission control technologies with all-round monitoring and feedback system related indicators.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 2576K] - QU Jiangshan;ZHANG Jianbo;SUN Zhigang;YANG Chennian;SHI Da;LI Shaopeng;LI Huiquan;Key Laboratory of Green Process and Engineering,Institute of Process Engineering,Chinese Academy of Science;National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology;University of Chinese Academy of Science;Sinopec Ningbo Technology Research Institute Co.,Ltd.;School of Resources and Civil Engineering,Northeastern University;
The energy structure characteristics of rich coal,poor oil and little gas,the actual situation of high external dependence of oil and natural gas,and the attention to the efficient and clean utilization of coal in China give the coal chemical industry development opportunities. As a leading technology in coal chemical industry,coal gasification technology is developing rapidly in China. With the large-scale promotion of coal gasification technology,the storage and production of coal gasification slag become larger and larger,which has caused serious environmental pollution and waste of land resources,and has adversely affected the sustainable development of coal chemical enterprises. The treatment of coal gasification slag is imminent. The background of coal gasification technology,the generation of gasification slag and its environmental problems,and the basic characteristics of coal gasification slag were introduced. The research progress on utilization of coal gasification slag at home and abroad was reviewed,including construction and building materials( aggregate,gelling material,wall material,non-burnt brick),soil and water restoration( soil improvement,water body repair),residual carbon utilization( residual carbon properties,residual carbon upgrading,cycle blending combustion),high value utilization( catalyst carrier,rubber-plastic filler,ceramic material,silicon-based material),etc. Suggestions for comprehensive utilization of coal gasification slag were proposed.The coal gasification slag is mainly composed of SiO_2,Al_2O_3,CaO,Fe_2O_3 and C. The residual carbon content of gasified fine slag is higher than that of coarse slag. The main mineral phase of coal gasification slag is amorphous aluminosilicate,which is mixed with quartz,calcite and other crystalline phase. The chemical composition characteristics are rich in silicon,aluminum,carbon resources and the special mineral phase composition is the basis for the recovery and utilization of coal gasification slag. At present,the large-scale utilization of coal gasification slag is mainly focused on construction materials and ecological treatment. However,its characteristics of high carbon content and high impurity content lead to low incorporation of construction materials,unstable quality,and serious secondary pollution caused by ecological control. The economic and environmental benefits are poor. In terms of resource utilization,combined with the characteristics of coal gasification slag resources,it has attracted extensive attention in the development and utilization of carbon materials,the preparation of ceramic materials,and the preparation of aluminum/silicon based products. Although the economic benefits are relatively significant,they are all in the stage of laboratory research or expanding test. There are many problems,such as high cost,complicated process,difficult control of impurities,small downstream market and so on,which cannot realize large-scale utilization. In order to improve the economic benefits of enterprises and solve the environmental problems of enterprises,combined with the current situation of large coal gasification slag heap,large production volume,and urgent treatment,as well as the special properties rich in aluminum,silicon and carbon resources,it is suggested that the idea of comprehensive utilization of coal gasification slag is to solve the environmental problems of enterprises mainly by scale consumption and to increase the economic benefits of enterprises supplemented by high-value utilization. It is an effective way and urgent demand to develop a comprehensive utilization technology route of coal gasification slag with simple process,strong adaptability and certain economic benefit.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 3413K] - WANG Min;WANG Hui;YANG Hairui;LIU Hanhui;SUN Jianwei;College of Energy Science and Engineering,Harbin Institute of Technology;Department of Energy and Power Engineering,Tsinghua University;
In order to realize the green utilization of Zhundong coal ash,the process of preparing Al_2O_3 and SiO_2 from Zhundong coal ash was designed. The optimal process conditions was determined,and the degree of different factors on the extraction rate were carrieed out by SPSS bivariate analysis. Zhundong coal—Jiangjunmiao was used as raw coal,and ash samples was prepared using a muffle furnace to simulate the static combustion of a pulverized coal furnace after crushing.. Through the composition analysis and elemental analysis of the coal ash,it is found that SiO_2 accountes for 48.84%,and Al_2O_3 accounted for 31.26%. The coal ash sample was prepared according to the standard,and the sample was analyzed by SEM. The stickiness is serious,so mechanical grinding is performed before experiment.The Al_2O_3 was prepared from coal ash by ammonium sulfate roasting method which was divided into roasting process and acid leaching process.Because the filtrate contained a large amount of impurities such as iron and calcium,impurities were removed by using the pH adjustment method and the effect of removing impurities was checked. The impurity removal rate is almost 100%. Alkali leaching process and multiple CO_2 separation process were used to prepare SiO_2 from the aluminum slag. In the calcination process of aluminum extraction,the optimum experimental conditions of various factors were determined by the change curve. The results show that the calcination temperature is 600 ℃,the calcination time is 60 min,and the roasting ratio is 1 ∶ 6. In the acid leaching process of aluminum extraction process,the best experimental conditions are temperature 60 ℃,time 20 min,H_2SO_4 0.2 mol/L,and liquid-solid ratio 50. The slag was analyzed by SEM and XRD. It is found that aluminum extraction slag contains a large amount of silicon and calcium elements,and the Si loss after aluminum extracting is 7.64% by the RIR method.The optimum experimental conditions for the alkali leaching process are temperature 60℃,time 30 min,NaOH_3 mol/L,liquid-solid ratio 70,and the SiO_2 extraction rate is 99%. Multiple CO_2 separation method can meet the requirements of different SiO_2 content purity. The optimum alkali leaching conditions are p H = 9. 5,CO_2 aeration rate 24 m L/min,NaOH 0.2 mol/L,and liquid-solid ratio 80. Through the bivariate correlation analysis,the effects of various factors on the Al_2O_3 extraction rate,SiO_2 extraction rate and H_2SiO_3 precipitation rate are obtained which are roasting temperature > roasting time > roasting ratio,acid leaching time>acid leaching temperature>H_2SO_4 concentration>acid leaching liquid-solid ratio,alkali immersion liquid-solid ratio>alkali leaching temperature>NaOH concentration> alkali leaching time,pH> liquid-solid ratio> Na OH concentration>CO_2 aeration rate.Through the economy and feasibility analysis,the research can effectively realize the green utilization of Zhundong coal ash.( NH_4)_2SO_4 is re-extracted from the filtrate after aluminum extraction to realize the reuse of production raw materials. The Na_2CO_3 solution after the CO_2 separation process can be causticized by adding lime to realize the recycling of Na OH in the extraction process. In addition to the production of Al_2O_3 and SiO_2,additional products such as Na_2SO_4 can also be obtained.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 23185K] - PENG Siwei;HE Xuwen;BAI Yuyong;GU Xiaobing;LIU Haiyang;Datang Environmental Industry Group Co.,Ltd.;School of Chemical & Environmental Engineering,China University of Mining and Technology-Beijing;
Benzene,toluene,ethylbenzene and xylene( BTEX) are typical refractory organic pollutants in coal chemical wastewater,which are usually difficult to be removed by traditional chemical oxidation technology.In this experiment,a porous ozone catalyst was prepared independently and the catalyst was characterized and analyzed.The best reaction conditions of degradation of BTEX by ozone catalytic oxidation were studied,and the excitation of free radicals in different reaction systems was compared.Based on this,the mechanism of the removal of BTEX by the ozone catalytic oxidation method was explored,which provided a theoretical basis for the technical application of BTEX in actual treatment process. The analysis results of XRD show that the porous ozone catalyst contains alumina and silica,and the catalyst contains compounds with a zeolite structure.XPS analysis results show that the synthesized catalyst contains Si,O,Cu,Fe,Mn,Al and other elements.The SEM results show that the catalyst is composed of many irregular small powders and its surface is very fluffy. The stacked multi-stage structure makes the catalystporous. The specific surface area analysis shows that the catalyst is porous with a specific surface area of 20.8 m~2/g,and the pore diameter is mainly concentrated at 3.8 nm.The experimental results of ozone-catalyzed oxidation of BTEX with this catalyst show that the degradation effect of BTEX is the best when the reaction temperature is 30 ℃,the solution pH is 8,the ozone dosage is 3.5 mg/L and the catalyst dosage is 5 g/L.In this reaction system,the removal rate of organic matter is 99.1%,and the removal rates of benzene,toluene,ethylbenzene and xylene are 95. 6%,98. 2%,100% and 100%,respectively. The ESR analysis results show that the excitation intensity of hydroxyl radicals and superoxide radicals in ozonation system is significantly higher than that in ozonation system. Because the catalysts prepared in this study contain Al,Fe,Mn and Cu oxides,which makes the valence states of supported metal oxides change each other during the catalytic reaction. The transferred electrons can promote the decomposition of ozone molecules,thus the more free radicals can be produced.Ozone catalytic oxidation is dominated by hydroxyl radicals,superoxide radicals and catalyst adsorption as a synergistic action to efficiently remove typical organic pollutants BTEX in coal chemical wastewater.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 3747K] - ZHU Tao;YUAN Qiancheng;JIN Xinrui;YE Zefu;HOU Yiming;School of Chemical & Environmental Engineering,China University of Mining & Technology-Beijing;Shanxi Gemeng US-China Clean Energy R&D Center Co.,Ltd.;Gemeng International Energy Co.,Ltd.;
In recent years,the emission permit system is vigorously carried out in China. Thermal power industry,as a national pillar industry and a large water user,has not been paid much attention to water pollutants during the implementation of the system. The relevant statistical data of thermal power wastewater is unclear,and the discharge performance is vague,which makes it difficult to be included in the emission trading system. Since thermal power generation in China gradually entered the mature period in 2008,the water use for thermal power enterprises in various provinces and cities has formed the obvious regional features since the mature period. In order to better carry out discharge license system in accordance with the requirements of " control of pollutant discharge permit system implementation plan",based on the regional water resources situation,the typical provinces( Shandong and Guangdong) were choosed to emphatically analyze the present situation of coal waste water. According to the 2015 national provincial environmental statistics,the water pollution factor characteristics of the thermal power industry in selected region were sorted out. Firstly,the related water indicators of thermal power enterprises were defined. Thermal power plants need a large amount of cooling water to cool the unit. The difference in cooling methods determined the difference in cooling water amount of thermal power plants. The enterprise's cooling technology was determined according to the three indicators. Secondly,the two main types of discharge directionwere determined. Finally,the treatment efficiency of water pollution factors was compared. The characteristic water pollution factors were selected. The performance evaluation of thermal power industry wastewater was carried out,including wastewater emissions performance calculation and main water pollution discharge performance factor calculation.each region according to the performance calculation results of its own in the thermal power industry water use and emissions problems targeted policy,the implementation of the thermal power wastewater discharge permit system was dedicated to provide with basic support. The results show that the total emission control of thermal power enterprises should be based on the discharge performance of waste water The purpose of the wastewater discharge performance evaluation and regional characteristic research is to explore the association between power and waste water discharge,and hydrological conditions of the region,generation efficiency and cooling method. The level of wastewater treatment in water shortage areas below is lower than that in water resource area,which can lead to the aggravation of bad water.The corresponding wastewater treatment policies can be formulated to find a balance point between the emissions trading and investment balance on wastewater treatment equipment. The obstacles existing in emission trading at the present stage are summarized. The water pollutants in thermal power industry are not taken seriously,resulting in inaccurate emission statistics,which brings difficulties to formulate policy; The Internet real-time monitoring platform has not been established,so the water quality and quantity discharged by thermal power enterprises cannot be monitored in real time. The pollution source tracking method is adopted to urge the non-conforming enterprises to rectify and give priority to promoting the emission reduction of water pollutants through emission right trading. the wastewater discharge performance shows that the situation varies greatly among different regions. Considering that the drainage basin is the main source of wastewater discharge,it is based on the drainage basin division. Government agencies put forward total reduction requirements to enterprises with higher performance,and enterprises with lower performance were given preferential policies on emission trading.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 7146K] - SUN Xuefeng;WANG Qiang;YAN Shijian;LI Luming;WU Dongyin;Xinjiang East Hope New Energy Co.,Ltd.;School of Energy and Power Engineering,Xi'an Jiaotong University;
Zhundong Coal Field is located in Xinjiang Changji Hui Autonomous Prefecture,which is currently the largest packaged coal field in China. However,Zhundong Coal is prone to coking during the combustion process of boilers. Kaolin is usually mixed to ease coking. In a 350 MW unit burning Zhundong coal,after the coal was burned with kaolin in a boiler,the amount of dust particles and dust carried by the flue gas increased,which resulted in the serious ash accumulation in the SCR denitration system and a significant increase in ammonia injection. The air preheater was blocked by ammonia hydrogen sulphate,which made the unit unable to run stably for a long period. After compared with the domestic boilers of multiple units of the same type,it is found that the denitration system has ash deposits in the denitrification steering room,over the catalyst,and the air preheater inlet slope. Aiming at the existing problems,by the calculation and analysis of setting the correct model and incorrect installation model modeling,the optimal design of the deflector layout,the CFD flow field distribution,the optimization of the SCR system deflector design,and the combination of sonic and steam soot blowers and the optimization and upgrading of ammonia injection grid were performed. Using Testo 480 anemometer measured wind speed test,it was found that the original deflector of the denitration flue was unreasonable in design and construction and installation deviation; the horizontal section of the original deflector has a large span and insufficient support,resulting in the guide plate to collapse and deform and affecting the distribution of the flue gas field. The coal burned by the boiler is high-sodium coal. To prevent the boiler from coking and adding kaolin,the amount of fly ash particles and dust in the flue gas is increased,and the fly ash is quite sticky. It is easy to deposit on the flue deflector and the flue wall. Therefore,it is proposed to optimize the deflectors inside the denitrification system,add sonic sootblower to the ash-prone parts of the denitration system,upgrade the number of ammonia injection grid nozzles and ammonia air mixer,and carry out boiler SCR test work on thermal adjustment and optimization of denitrification and ammonia spraying. Through relevant work,the relative standard deviation of the flue gas field of the SCR flue gas system was optimized by 5%,and the consumption of liquid ammonia was reduced by 45% under the same load. The problems of ash accumulation in the denitration system and the blockage of the air preheater were completely solved to achieve the stable operation of the full load of the unit. After the boiler was shut down for half a year after long-term operation,it was found that the ash deposits of up to 1 m in the flue of the previous denitration system were completely resolved,and the catalyst surface was clean and free of debris,which solved the problem of ash accumulation in the denitration system. At the same time,the blockage problem of the air preheater of the boiler was completely solved by cooperating with the measures to improve the comprehensive temperature of the cold end of the air preheater.At the same time,the economic benefits are significant,which can save 700 000 yuan in liquid ammonia costs,1 million yuan in fan power consumption,800,000 yuan in maintenance and cleaning of dust and overhaul,and 200,000 yuan in air preheater cleaning and treatment costs. The comprehensive cost saving is 2.7 million yuan/year,and the expected effect is achieved to realize the safe and economic stable operation of the unit group leader cycle.
2020 01 v.26;No.125 [Abstract][OnlineView][HTML全文][Download 9172K] 下载本期数据