- WANG Hanfeng;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;
Due to the existing characteristics of energy resources and the current situation of energy structure in China,it is determined in the future that it is difficult to change the role of coal as the guarantee for the safe and stable supply of energy in China. Thus,the clean and efficient utilization of coal is both an inevitable requirement of our energy revolution and effective way to prevent pollution. For a long time,China's coal-fired industrial boilers,preceded only by coal-fired power generation,are considered as the second largest coal-type pollution source,and act as one of the main sources of PM2.5 and PM10. In recent years,scientific research teams,organized by China Coal Research Institute Company of Energy,Conservation of China Coal Technology Engineering Group,has carried out the key technology research of pulverized coal industrial boilers. These technologies have been successfully applied in many large and medium cities and industrial parks and meantime,significant economic benefits,environmental protection and social benefits have been achieved. In this paper,the policy documents and industry standards in 2011 to 2019 from three aspects of steam tonnage,energy saving and emission reductionwere summarized,which were related to coal-fired industrial boilers in China. And,the continuous awareness of pulverized coal boiler policies was formed and prospects were proposed for the future potential of the industry. In general,China will continue to increase the elimination of small coal-fired boilers in the follow-up. It will be more strict for the pollutant emission standards and thus the requirements for pollution control will be higher. In the future,the following five aspects should be taken into consideration to create irreplaceable core competitiveness,including improving the level of equipment manufacturing,developing integrated control technologies,cultivating research and development teams as well as technical service agencies,promoting integration with the digital economy,and strengthening international cooperation.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 1090K]
2020 02 v.26;No.126 [Abstract][OnlineView][Download 1589K] - JIA Nan;NIU Fang;ZHOU Jianming;WANG Naiji;LIU Kangxin;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;Shanxi Jinzhong Ruiyang Gonger Co.,Ltd.;
Reverse jet combustion technology is a high-efficiency and low-pollution combustion technology,which can be applied to both gas and pulverized coal combustion.The flow characteristics are determined by the structure of reverse jet and jet velocity ratio.In this paper,the development history,research progress and development trend of reverse jet combustion technology in gas and coal-fired fields were reviewed in detail.The analysis shows that in the field of gas combustion,the reverse jet is mainly used to stabilize the flame,which is characterized by good fuel/air mixing conditions,forming a nearly uniform heat flow field and avoiding local hot spots in the combustion process.However,it is only an exploratory technology for gas turbine and aircraft engine at present.For engineering application,it is necessary to overcome some important problems,such as the reasonable control of the flow field of fuel and air in a narrow space,as well as from the simplification of the device to the enlargement of the project.In the field of coal combustion,for the pulverized coal burner,the reverse jet can form a recirculation zone with controllable components,size,shape and position.It also can directly send the pulverized coal into recirculation zone and control the residence time of pulverized coal in the recirculation zone. Compared with the traditional flame stabilization method,the technology has stronger flame stability,longer residence time and lower pollution,which is more suitable for the high efficiency of low rank coal combustion.At present,the reverse jet combustion technology coupled with other stable combustion and low nitrogen technology provides a new direction for the development of high-efficiency and clean utilization of pulverized coal,and has been applied in practical engineering.But the mechanism research is not in-depth,which limits the further development and promotion of the technology.For utility boilers,part of the primary air or burn-out air is deflected into the furnace in reverse direction,which can alleviate the velocity and temperature deviation of flue gas at the furnace exit under the mode of tangential firing.At present,the main reason is the industrial application of burnt out air tangency,but how to reasonably control the angle,momentum and number of tangency layers of burnt out air remains to be further studied.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 6177K] - WANG Xuewen;WANG Naiji;CHEN Fuzhong;LUO Wei;CUI Yuhong;ZHAO Zhenyi;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High-efficiency Mining and Clean Utilization of Coal Resources;National Key Laboratory of Efficient Utilization of Energy and Energy and Emission Reduction Technology;Jinan Thermal Group;Gansu Qingyang Xifeng Heating Power Group Co.,Ltd.;
The burner is the core component of the pulverized coal boiler.The performance of the burner is related to the degree of pulverized coal combustion and the level of pollutant discharge.The thermal test method is used to study the performance of the burner,and the obtained data are more instructive for the development of high-efficiency and low-nitrogen pulverized coal burners.From the basic principles,the advantages and disadvantages of various thermal test methods for pulverized coal combustion and the applicable places were discussed.In the flame temperature measurement,the thermocouple thermometry is simple and convenient,but its accuracy is not high and can only measure temperature at a single point at the same time,which has a large disturbance to the flame.The accuracy of air-pumped high temperature thermometry is higher than that of thermocouples,but its operation is complicated and it is easy to cause interference to the air flow.The spectrometry has sufficient accuracy and less disturbance to the flame,multi-point measurement at the same time,and the measurement can be used to reconstruct the three-dimensional temperature field,but compared with thermocouple thermometry and the air-pumped high temperature thermometry,the spectral method has complex operation and high cost.In the collection of gas-solid phase samples,the cooling sampling method is a common method for accurately collecting real-time components of the flue gas in the burner. Because the specific heat capacity of water is large,the water-cooled sampling method is the most widely used sampling method.XPS and ash tracer are common methods for measuring the chemical composition of coal char samples during pulverized coal combustion. Both can be used for quantitative analysis of solid coal char samples,but the detection focuses of the two methods are different.XPS is mainly used to analyze the composition of chemical functional groups.Trace method focuses on analyzing its elemental composition,calculating coal conversion rate,etc.XPS operation is more tedious,while the gray tracer method is simple to operate.In the detection and analysis of gas samples,a variety of gases can be measured by both electrochemical detection and infrared detection,which has strong applicability,but the infrared detection has a wider detection range.The solution absorption method is suitable for detecting the concentration of NH3 and HCN,which is tedious and difficult to capture in the measurement,and easy to be interfered by other factors,so it has fewer engineering applications.Therefore,when measuring in the field,a variety of measurement methods or multiple measurements are used as far as possible to avoid factors that may cause errors.Three-dimensional temperature field and three-dimensional atmosphere field of the pulverized coal burner in the hot state can be established through a variety of measurement methods. The pulverized coal combustion process and pollutant generation process can be studied in multiple dimensions,so as to take effective measures to control pollution.It is of great significance to the development of burners and the comprehensive treatment of pollutants from pulverized coal industrial boilers.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 3761K] - CUI Mingshuang;LI Xiaojiong;MIAO Peng;ZHENG Xiangyu;XING Wenzhao;SONG Qiang;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;Shanxi Jinzhong Huitong Heating Technology Service Co.,Ltd.;
Gas fuel has the characteristics of easy ignition,rapid combustion and complete combustion,and its nitrogen,sulfur and ash content are low,and the content of pollutant is relatively low after combustion,which belongs to cleaner fuel.In addition,with the implementation of national gas subsidy policy,gas fuel combustion has a good development prospect in recent years.However,with the country's stricter control of air pollutants,it is very important to control the formation of nitrogen oxides in the process of gas fuel combustion.Firstly,in the paper,the production mechanism and influencing factors of different kinds of Noxwere introduced,and the control measures were put forward according to the production mechanism of different kinds of NO_x.Secondly,based on the NO_xgeneration mechanism,the low nitrogen principle and application status of gas combustion technology widely used at present were analyzed.Finally,the conclusion of this paper and the prospect of gas burner application were puts forward.It is considered that the main factors in the process of gas combustion are thermal NO_xand fast NO_x,and temperature and excess air coefficient are the main factors affecting NO_xgeneration.When the combustion temperature is higher than 1 500 ℃,the thermal NO_xincreases exponentially,and temperature is the most important factor affecting the generation of NO_x.According to the mechanism of Noxgeneration,the essence of low NO_xcombustion technology is to reduce the maximum combustion temperature,control the fuel concentration and oxygen concentration in the combustion area,which shorten the residence time of flue gas in the high temperature area,and destroy the best conditions of NO_xgeneration,and finally inhibit the generation of NO_x.These combustion technologies reduce the generation of NO_xto a certain extent,but it will destroy the whole combustion process,which causes adverse effects on the combustion and heat release process,and reduces the combustion efficiency and heat transfer efficiency,so how to solve these contradictions is an urgent problem.In practical application,it is necessary to select the appropriate combustion technology according to the demand,and at the same time,it can combine different combustion technologies to achieve the effect of stable combustion and low nitrogen.At present,the most widely used gas combustion technologies are staged combustion technology,flue gas recirculation combustion technology,flameless combustion technology and so on.Catalytic combustion technology is a promising combustion technology,which has been applied in many fields.The thermal stability and life of catalyst are the core problems limiting its wide application in industry.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 2339K] - WANG Jianpeng;DUAN Lu;WANG Naiji;LI Jie;China Coal Research Institute Company of Energy Conservation;China Coal Research Institute;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;Jinan Heating Group Co.,Ltd.;
During the increasingly serious environmental problems and the ultra-low emission implementation of coal-fired boiler,the air pollution problems caused by coal combustion and the combined effect of the flue gas desulfurization( FGD) and dust removal equipment to remove pollutants gradually has been drown great attention. The SO_2 and particulate matter released from coal combustion cause serious harm to human health and the natural environment,and it is of vital importance to control the SO_2 and particulate matter.In this paper,the development history,technical characteristics and scope of application of the wet FGD technology such as Limestone-gypsum method,ammonia method and so on,semi-dry FGD technology such as circulating fluidized bed flue gas desulfurization technology,No Gap Desulphurization technology and so on,and dry FGD technology such as Electron ray radiation desulfurization technology,activated carbon( active coke,active semi coke) adsorption desulfurization technology and so on were reviewed.The effect of the FGD system on the emission characteristics of particle was analyzed.the results show that the wet flue gas desulfurization technology has the highest SO_2 removal efficiency,especially the limestone-gypsum flue gas desulfurization technology,and the total efficiency is more than 99%.When the inlet particulate matter concentration is higher than 5 mg/m3,the technology can synergistically remove particulate matter in the flue gas,and the dust removal efficiency can reach 50%-80%.The particle size distribution before and after desulfurization is a typical bimodal distribution,and the peak value of particle size shifts to a small particle size after desulfurization,and the sulfate content increases.When the mass concentration of particulate matter at the inlet is less than 5 mg/m3,the particle concentration at the outlet may increase instead of decreasing.However,due to the disadvantages of high investment and operating cost,it is mostly used in large coal-fired units and areas with rich sources of desulfurizer,and the products of wet flue gas desulfurization also have certain economic benefits.The desulfurization efficiency of the semi-dry and dry FGD is about 60%-90%.Compared with FGD,the semi-dry and dry FGD may have a good prospect in the field of small and medium boilers such as coal-fired industrial boilers due to its low investment and operating costs,small size and water conservation.Thus,a large amount of desulfurization products and desulfurizers enter into the dedusting equipment along with the flue gas,the particle concentration at the inlet of dust removal equipment is higher than 1 000 g/m3,which causes great operating pressure for the dedusting equipment and increases the investment and operating cost.At present,there are few studies on the effects of semi-dry flue gas desulfurization technology and dry flue gas desulfurization technology on the emission characteristics of particulate matter. It is necessary to further study the influence of the desulfurization system on the particle size,composition,and morphology of particulate matter.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 5015K] - CHENG Xiaolei;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;
The reaction process of pulverized coal in reducing atmosphere has both the characteristics of combustion and gasification,which is the key factor of low-NOxcombustion for pulverized coal.The appropriate chemical reaction model is the basis for accurate simulation of the process. In this paper,the numerical simulation accuracy was studied based on the double cone burner by comparing results of EDM model,PDF model and FR/ED model under the conditions of oxidation atmosphere and reducing atmosphere.Also,by comparing with the experimental results,the chemical reaction models suitable for different reaction atmosphere were determined. The results show that,there are differences among the three models in the prediction of pulverized coal ignition position and back-flow injection distance.The ignition point of PDF model is closer to the back-flow injection nozzle of burner.For EDM model,the primary air and pulverized coal gradually burn after a period of temperature rise process,and the temperature rise process for FR/ED model is longer,and the low-temperature area of wall nearly covers half of the front cone length.When FR/ED model is used to simulate the combustion process,the average temperature is the highest,the EDM model is the second,and the PDF model is the lowest.The CO reaction is not considerd in the EDM model,and there is almost no CO in the burner. The high CO concentration area for PDF model is concentrated in the early stage of pulverized coal combustion,and the CO content at the outlet of burner is low. While The kinetic parameters of chemical reaction in FR/ED model,the high CO concentration in the whole area of pulverized coal combustion is found.Considering the effect of gasification reaction of coal and oxygen,the oxygen content in the burner simulated by FR/ED model is significantly lower than that of EDM and PDF model.When the excess air coefficient is 1.2,the oxygen content at the burner outlet is 7.0%,which is significantly lower than 11.1%of EDM model and 12. 0% of PDF model. The CO content at the burner outlet is 3. 5%,which is significantly higher than ～ 0% of EDM model and 0.8% of PDF model.When the excess air coefficient is 0.5,the prediction results of the EDM model for CO composition are quite different.The CO concentration at the burner outlet is 0.05%.The CO content at the burner outlet is 5.73% and 10.7%,by using PDF and FR/ED models,respectively.Through the comparison between simulation and experimental results for the oxidation atmosphere,the combustion reaction of pulverized coal mainly occurs. The prediction of temperature and CO content of EDM model and PDF model is more accurate,and the deviation of FR/ED model is larger with less deviation from the test data.Under the reducing atmosphere,the simulation results of EDM model hardly generate CO and H2,which is not suitable for reducing atmosphere,while the PDF model and FR/ED model have reasonable simulation results.The difference is mainly the generating position of reducing gas.The CO concentration at the nozzle of PDF model is higher than that at the outlet,while the CO concentration of FR/ED model increases gradually with the process of pulverized coal reaction,which is closer to the test results.Considering comprehensively,EDM model and PDF model are suitable for the simulation of biconical burner in oxidation atmosphere,and FR/ED model is suitable for the simulation in reduction atmosphere.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 2444K] - WANG Yongying;YANG Shi;ZHANG Shen;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;Jinan Heating Group Co.,Ltd.;
Possessing the advantages of burning stability and low burn-out rate,the double-cone combustion chamber with independent space is suitable for industrial boilers which start-stop frequently.with the increase of market demand for high-capacity boilers,the combustion chamber volume and number increase,and the adoption of water cooling method will lead to problems such as difficult installation and complex water system.Therefore,it is urgent to develop new cooling methods.Air cooling technology has the advantages of simple structure and combustion stability. Whether this technology can be used in the combustion chamber with independent space needs to be explored.In order to determine the combustion and wall cooling of the air-cooled combustion chamber,the three-dimensional modeling of the combustion chamber and furnace of 14 MW industrial boiler was carried out by using numerical simulation technology. The internal combustion,metal wall temperature,exit flame shape and furnace fullness were obtained under the different ratio of internal and external secondary air distribution under 50% and 100% load.The results show that: at the conditions of constant excess air coefficient,the temperature of the inner region decreases gradually with the increasing of inner secondary air ratio,the average temperature of metal wall also shows a decreasing trendwith the increase of the ratio of internal secondary air at 50% load,while first decreased and then increased at100% load,which is the result of the combined effect of combustion supporting by internal secondary air and cooling by external secondary air; With the increase of the proportion of the internal secondary air,the high temperature area of the metal wall gradually moves backward and focuses on the exit area of the back cone; when the inner secondary air ratio is 0.4,the temperature of metal wall is maximum( 930 K)at 50% load,and when the inner secondary air ratio is 0.2,the temperature of metal wall is maximum( 835 K) at 100% load.The two temperatures all appear in the behind cone,at this time,the air volume of secondary air distribution is 2 600 Nm3/h,which should be avoided.According to the maximum temperature,the wall material is selected as 0 Cr18 Ni9; The average temperature of the combustion chamber,the average temperature and maximum temperature of the metal wall under 50% load are all higher than that under 100% load,which is the working condition that air cooling structure needs to focus on.As the inner secondary air ratio increases,the length of flame increases at first and then decreases.When the internal secondary air is too small,the outlet gas velocity is small,and the external secondary air has a velocity component toward the center,and the flame is mainly concentrated in the front of the furnace.With the increase of the ratio of internal secondary air,the exit velocity increases and the flame becomes longer and thinner.However,as the proportion continues to increase,the axial speed of the external secondary air becomes smaller,and the swirl strength of the exit flame is completely determined by the secondary air.The increase of the swirl strength of the exit leads to the flame becoming shorter and thicker.Under two loads,the flame is longer when the ratio of internal secondary air is 0.4-0.5.The ratio internal and external secondary air is 0.5 ∶ 0.5,the flame's fullness in furnace is the best,the combustion situation and wall temperature in the combustion chamber are also uniform and stable,and the fullness of the flame in the furnace is the best,which is the mostsuitable working parameter for both loads.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 7322K] - ZHANG Chao;CUI Yuhong;LIU Yu;WANG Pengtao;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;
In the pulverized coal industrial boiler system,the mixer is the key equipment to realize the rapid and uniform mixing of pulverized coal and primary air.The measurement and calculation of the flow field of pulverized coal and primary air-solid two-phase flow in the air-powder mixer is of great significance to optimize the structure of the mixer,strengthen the mixing efficiency and improve the uniform and stable supply of pulverized coal.In this paper,numerical calculation and field engineering test were carried out for two kinds of air powder mixers with vertical structure and inclined structure.Based on the knowledge of geometry and topology,ICEM software was used to divide appropriate three-dimensional grids for two kinds of mixers. In the theoretical model of multiphase flow,each phase of the two fluid model in the multiphase continuum model is regarded as a continuum with mutual penetration,coupling but maintaining its own motion characteristics.Compared with the single fluid model,the two fluid model takes into account the turbulent transport of solid phase and the resistance caused by the sliding of gas-solid phases,which makes the calculation result more close to the actual situation. The basic equations of cold two fluid model are composed of conservation equation,inter phase coupling equation and closed equation,in which the inter phase coupling equation is used to represent the coupling between gas and solid momentum.In order to explore the flow field characteristics of gas-solid two phases in the mixer under different residence time,the unsteady model was adopted. In this paper,the numerical calculation and engineering test were carried out for two kinds of mixers.Based on the two-flow model of Fluent software and Schiller Naumann force coefficient model,the time-varying characteristics of the pulverized coal concentration distribution in the mixer with two different structures were studied.The negative pressure variation law in the mixer with different pulverized coal dropping amount was measured by using the testo 425 thermal anemometer.The results show that when the residence time in the vertical structure of the mixer increases from 0.25 s to 1 s,the phenomenon of particle deposition at the bottom of the mixer always exists,that is to say,there is a long dead angle area of particle flow,and for the inclined structure of the air-powder mixer,when the residence time is greater than 0.3 s,the particle concentration in the mixer basically drops to zero,which better avoids particles at the bottom of the mixer.This structure is of great significance to strengthen the mixing of pulverized coal and reduce the fluctuation of feed.The results of engineering tests under different blanking amount show that when the feed quantity is large,the average negative pressure in the vertical structure of the mixer is small,almost close to the positive pressure,and there is a phenomenon of intermittent positive pressure powder spraying,so the negative pressure of the air-powder mixer under high blanking amount is insufficient,which is easy to cause large feed fluctuation.However,the average negative pressure of the inclined mixer is still greater than-1 000 Pa,and there is no phenomenon of powder spraying.Compared with the vertical structure,the inclined mixer has a stable and wide range of negative pressure changes,which can better overcome the phenomenon of large feed fluctuation.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 6417K] - ZHANG Xin;CHEN Long;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;
The flame velocity is about 60-200 m/s at the nozzle of the high velocity coal combustor.The flame is long and the convective heat exchange ratio between the flame and membrane wall is increased in the furnace,which comes into being a uniform temperature field without local over-heating and slagging by the traditional low velocity pulverized coal burner.Taking 14 MW high-speed pulverized coal burner as the research object,the key factors liked swirl intensity and secondary air temperature on the combustion of pulverized coal in the burner were studied and the structural optimization design was carried out in this article according to the combustion characteristics of pulverized coal in the burner by way of numerical simulation.The study about swirl intensity shows that the shape of recirculation zone changes little when the swirl intensity increases from 2.2 to 3.7.The recirculation zone starts from the jet of primary duct to the swirl vane,and the recirculation zone surrounds the primary duct.The maximum return flow is near the primary air nozzle,and the farther away from the primary air nozzle is,the smaller the return flow is.The swirl intensity has little effect on the maximum recirculation flow ratio which is around0.45 kg/s and the effect of swirl strength on the return flow becomes larger when the distance from the jet is more than somewhere L/H<0.35.It appears that the recirculation flow ratio increases as the swirl intensity gets stronger and the ratio is from 0.17 kg/s to 0.30 kg/s at the end of the recirculation flow zone.The results shows that flame is 150 m/s at the nozzle of the combustor with moderate swirl intensity which is proportional to the swirl intensity of the secondary air at the inlet of the combustor.The swirl intensity at the nozzle is 0.10-0.28.The fuel and oxygen is hierarchical distribution which means the nozzle center is fuel-rich and oxygen-lean.The study shows that the concentration of combustible component at the middle of the nozzle decreases when the swirl intensity increases. Concentration of CO、H2 and coke is deducing from 11% to 10%,1.65% to 1.40% and 0.14% to 0.11%,respectively.The oxygen concentration at the nozzle edge is deducing from 13% to 10%.At the same time,the study shows that it has little difference on the oxygen and combustible gas distribution when the swirl intensity is increased from 3.2 to 3.7,indicating that the effect of swirl strength on combustion is weakened.In order to study the effect on combustion of secondary air temperature,the three different temperatures such as 0,100 and 200 ℃ were set and studied.The result shows that when the temperature of secondary air increases,the carbon conversion in the combustor is increased by 20% to 65%while the reaction time is deduced from 0.15 s to 0.11 s.Central air is arranged when it comes to structural optimal design of the combustor.The swirl condition of the central air and 3 kinds of conditions were studied.The results show that the combustible gas at the middle of the nozzle is dropped within a radius less than 75 mm when central air is added in the combustor.The oxygen concentration is increased when the central air is direct flow as the jet flow is rigid and can get to the middle of the nozzle.The swirl central air has little effect on the oxygen distribution at the nozzle but the effect of reducing the concentration of combustible components is better than that of the DC center wind.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 13187K] - NIU Fang;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;
Pulverized coal high-efficiency and low-nitrogen combustion technology is a hot spot in the field of coal utilization.As a core equipment of the pulverized coal boiler,it is very important to study the design principle and technology of pulverized coal burner suitable for multiple coal types and wide load conditions.The mechanism of reverse jet steady combustion is mostly applied in the field of aero-engines and gas turbines,and rarely used in the field of pulverized coal combustion.Therefore,the studies on the influence of the pre-combustion chamber on the flowfield characteristics of the swirl burner are available,however,there are few studies about the influence on the flow field of the reverse-jet swirl burner.In this paper,In order to explore the influence of precombustion chamber on the flow field characteristics of a reverse swirl pulverized coal burner,and taking a 20 t/h reverse jet swirling burner as a prototype,a cold burner model was built based on the isothermal modeling principle.Then,with the help of streamer method,the flow field test and analysis were carried out via hot-wire anemometer.The results show that the annular shape of the backflow area will not be changed in the presnece of the pre-combustion chamber.By contrast,the recirculation zone,formed within the burned and featured by low axial velocity and high turbulence intensity,is beneficial to pulverized coal ignition. For the aera of X/D < 1. 3,the area of backflow area is prohibited due to the existence of pre-combustion chamber,which is conected to the squeezing effect of the conical pre-combustion chamber on the airflow. While for 1.3<X/D<2.3,the existence of the precombustion chamber promotes the formation of the reflux zone due to the effect of the combustion chamber.In case of X/D>2.3,the effect of pre-combustion chamber on the internal flow field can be ignored.The widest part of the recirculation zone is reduced from 0.97 D to 0.86 D under the action of the pre-combustion chamber.At the same time,the maximum relative recirculation rate is moved from the cross section X/D = 1 to 1. 6 and the relative recirculation rate is decreased from 1. 17 to 0. 99. The existence of pre-combustion chamber has a great influence on the axial mean velocity and turbulence distribution in the secondary air zone. Under the condition of no pre-combustion chamber,in the region of X/D<0.6,the peak values of velocity and turbulence appear; in the region of X/D>1.6,the peak values disappear,and the inner and outer secondary air are completely mixed; under the condition of pre-combustion chamber,in the region of X/D<0.6,the velocity increases along the radial direction,and the turbulence decreases along the radial direction; in the region of X/D>1.6,the velocity and turbulence are evenly distributed along the radial direction.The existence of pre-combustion chamber is beneficial to the stable combustion of pulverized coal in recirculation zone.It plays the role of rapid ignition of pulverized coal and stable combustion of low volatile coal in engineering application.In addition,the over-temperature or coking phenomenon of the pre-combustion chamber will be prevented by the pre-combustion chamber wall with large air velocity and strong rigidity,which is expected to prolong the trouble-free operation time and overall service life of the pulverized coal burner.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 3899K] - DUAN Lu;WANG Shipu;China Coal Research Institute Company of Energy Conservation;China Coal Research Institute;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;
No gap desulfurization( NGD) has great prospects for the pulverized coal industrial boilers due to low investment and operating costs,saving space,saving water and refraining from the colored plume.However,the investigations reported mainly pay attention to the reaction process of desulfurization and its influence factors.It's still unclear about the flow field and the energy consumption inside the NGD reactor.Based on the entropy generation theory,a model for quantitatively predicting the energy consumption inside a NGD reactor was established.The energy consumption results from the heat loss of flue gas and the flow of viscous fluid.The energy consumption of flow is mainly attributed to the turbulent dissipation and fluid friction near the wall.In addition,the potential energy should not be neglected at the pressure drop of inlet and outlet as the NGD reactor is usually higher than 20 m.Thus,the pressure drop of NGD reactor can be attributed to the potential energy,turbulent dissipation and fluid friction near the wall.The numerical investigation was carried out for a NGD reactor from a 30 t/h pulverized coal industrial boiler by using CFD method.And the energy consumption and distribution inside the NGD reactor was analyzed by using the energy consumption model based on the CFD data.The results show that the CFD method and the energy consumption model can precisely predict the inlet and outlet pressure drop of NGD reactor with the deviations of 0.4% and 9.6% compared with the measured data,respectively.Therefore,CFD method and energy consumption analysis model can accurately predict the energy consumption caused by viscous fluid flow in the desulfurization reactor.The flow of viscous fluid is the main factor of energy consumption because the ratios of energy consumption due to the flow of viscous fluid and heat loss are 96.2% and 3.8%.It can be seen that viscous fluid flow plays a leading role in the energy consumption of NGD,and the pressure drops due to the change of potential energy,the turbulent dissipation and the fluid friction near the wall are 237.6,347.4 and 57.5 Pa respectively,indicating that the turbulent dissipation is the main factor for the energy consumption.The NGD reactor is divided into the middle part of speed-up zone and the underpart of flue gas inlet zone.Because the energy dissipation in the viscous fluid flow comes from the friction dissipation caused by the velocity difference of different flow layers,the energy consumption depends on the velocity gradient of fluid flow.The high velocity and the high non-uniform flow field inside the middle part of speed-up zone results in the highest entropy generation due to turbulent dissipation per volume. Therefore,although its volume accounts for only 3.6%,the ratios of entropy generation inside the middle part of speed-up zone is 53.8% with a small part of volume.The ratios of entropy generation and volume inside the upper part of main reaction zone are 40.1% and 88.3% with a low velocity and relatively homogenous flow field.The entropy generation increases with position with a low average velocity and a high non-uniform flow field inside the underpart of flue gas inlet zone.The ratio of entropy generation is 6.1% and the ratio of volume is 13.1%.It can be seen that the energy is mainly consumed in the upper part and the middle part.And,it will be most useful to decrease the energy consumption by modifying the middle part.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 12089K] - LI Meijun;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 Emision Control;
As a renewable energy,biomass is clean,low-carbon,easy to obtain and ignite,which has a higher volatile content,lower sulfur and nitrogen content,and belongs to carbon neutral substance,but it has a lower energy density.Blending biomass in a large proportion in pulverized coal( biomass/pulverized coal mass ratio is greater than 5/5) can effectively improve the ignition characteristics of pulverized coal,make the carbon emission level close to burning natural gas,and significantly decrease the pollutant emissions,finally can achieve the goal of energy conservation and emission reduction.At present,the study of the co-combustion characteristics of biomass and pulverized coal at low mixing ratios( less than 5/5) is mainly focused on.It is necessary to study the co-combustion characteristics of biomass and pulverized coal at the large mixing ratio,such as corn stalks,rice stalks and corn cobs,which is common in the north of China.In this paper,thermogravimetric analysis techniques were adopted to study the co-combustion characteristics of the pulverized coal and different biomass( corn straw,rice straw,and corn cob) at different mixing ratios( 5/5,6/4,7/3 and 8/2). The effects of biomass species and mixing ratios on the ignition temperature,burn-out temperature,interaction,and combustion characteristic index of the mixed fuel were analyzed and the optimal blending ratio for different biomass was determined.The results show that the effect of the blending ratio on the weight loss curve of the mixed fuel is corn stalk,corn cob,and rice straw,in order from large to small. As the blending ratio increases,the maximum weight loss rate gradually increases in the first stage and the combustion process moves forward,and gradually decreases in the second stage,which is due to the relative increase of volatile matter and the relative decrease of coke.Compared to pure coal powder,the ignition and burn-out temperatures of the mixed samples are reduced by approximately 100 ° C and 60 ° C,respectively.With the increase of the blending ratio,the ignition temperature of the corn cob gradually decreases,and the corn stalks and rice stalks decrease and then increase,and both reach the minimum at 7/3. The burn-out temperature shows a downward trend,and the decline range is corn stalk,corn cob,and rice straw,in order from large to small.Corn straw and rice stalks have poor burnout performance at 8/2.The mixed fuels interact to varying degrees,and the interaction is the synergy effect between the promotion and inhibition of biomass.So the three kinds of biomass have a large inhibitory effect on pulverized coal combustion at 5/5; if the corn straw and rice stalks are at 7/3,and corn cob is at 6/4 and 8/2,the promotion effect is great.At the same time,the combustion characteristics index of the three biomass is much larger than that of pulverized coal.As the blending ratio increases,the combustion characteristics index of corn cob changes the most and reaches a maximum at 8/2,and is almost the same at 6/4 and 7/3.The change of rice stalk is the smallest and reaches the maximum at 7/3. The corn stalk is almost the same and reaches the maximum at 7/3 and 8/2.When the blending ratio changes in a small range,the combustion characteristic index does not change largely.This may be because the combustion characteristic index is not only related to the ignition temperature and burn-out temperature,but also to the reaction rate of the sample during its main combustion process.However,the reaction intensity of pulverized coal in coke combustion stage is higher than that in biomass volatilization stage,which makes the mixed samples with different mixing proportion appear the above phenomenon.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 10836K] - LUO Wei;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;
The gasification reactions of char have an important influence on combustion and pollutant formation under the condition of deep air-staging. In this paper,the influence of char gasification on the combustion and NO_xemission characteristics of pulverized coal under the condition of SR1 from 1.2 to 0.6 by the method of drop-tube furnace experiment and numerical calculation. Compared with the experimental data of the drop-tube furnace and the results of the traditional model and the improved model( considering char gasification),it can be seen that the traditional model has some defects in the prediction of reducing atmosphere of air-staged combustion,and the improved model is more consistent with the experimental results. The results of the experiment and the caculation of the improved model show that under the condition of deep air-staging,the main combustion zone is extremely anoxic,and the combustion process changes from the initial volatile ignition( R1 and R2) and incomplete char oxidation( R4) to the combustion state dominated by char gasification reaction( R5 and R6). At this time,a large amount of CO is generated,and the high concentration of CO_2 is consumed gradually until the end of reduction zone. With the addition of exhausted air,the oxygen content increases,CO is rapidly consumed( mainly R2),and CO_2 is gradually generated. The NO_xemission characteristics under the air classification condition are as follows: the NO_xconcentration near the burner is high; With the formation of reducing atmosphere,the NO_xlevel remains low after a certain degree of decline; And with the addition of burnout air,there is a certain degree of " rebound",which is caused by the rapid oxidation of some nitrogen intermediates that are not completely reduced after the addition of burnout air when the reduction zone is end.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 3715K] - YANG Shi;China Coal Research Institute Company of Energy Conservation;China,State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;
With increasingly strict monitoring of air pollutant emissions in China,Nitrogen oxide control technology has been widely used in various fields of industrial production.As a direct and simple nitrogen oxide emission control technology,oxygen-enriched air combustion technology has been used in gas-fired boilers and internal combustion engines.However,it is rarely used in coal-fired boilers.In order to verify the NO_xreduction effect of oxygen-enriched air combustion technology in pulverized coal industrial boilers,Shenfu bituminous coal was used as fuel,and the two-stage dropper tube furnace test system was used to simulate the actual situation of pulverized coal combustion in the boiler.The NO_xemission characteristics of oxygen enriched air staged combustion of bituminous coal were studied by using the hot test method,and the NO_xemission was compared with that of single-stage air supply and air staged combustion.The effect of key factors,such as temperature of main combustion zone,ratio of secondary air( expressed as excess oxygen coefficient in main combustion zone) and oxygen concentration of secondary air,on NO_xemission were investigated. The results show that,compared with single stage air and air-staged combustion,the NO_xremoval effect of oxygen enriched air staged combustion is much more significant.When the main combustion zone temperature is in the range of 1 200-1 500 ℃,The NO_xemission reduction ratio of oxygen-enriched air staged combustion is 6-12 percentage points higher than that of graded air combustion.Under the condition of oxygen enriched air staged combustion,and as the increase of the main combustion zone temperature,the coal combustion is more completed and the fuel nitrogen is decomposed into a large number of intermediate products such as NHi,HCN,etc,which makes the reducibility of the atmosphere in the main combustion zone enhanced and the proportion of NO_x reduced increased.Therefore,NO_xemission is reduced and the proportion of NO_xemission reduction is on the rise; the ratio of secondary air in oxygen enriched air staged combustion has a significant impact on NO_xemission.With the increase of excess oxygen coefficient in the main combustion zone,NO_xemission is reduced first and then increased.Therefore,there is an optimal ratio of secondary air to minimize NO_xemission concentration.When the temperature of the main combustion zone is 1 300 ℃,the optimum excess oxygen coefficient is about 0.58.When the temperature of the main combustion zone is 1 500 ℃,the optimum excess oxygen coefficient is about 0.55.At a certain excess air coefficient in the main combustion zone,increasing the concentration of secondary air oxygen can prolong the residence time of coal particles in the main combustion zone,and local oxygen-enriched environment is formed on the surface of the coal particles to promote the coal combustion,thereby enhancing the reducibility of the atmosphere in the main combustion zone and reducing the generation of NO_x.Therefore,when the secondary air oxygen concentration is the range of 21%-31%,NO_xemission decreases with the increase of the secondary air oxygen concentration. As the oxygen concentration of the secondary air gradually increases,the decreasing trend of NO_xemission gradually slows down.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 2326K] - LI Hui;YANG Shi;ZHOU Jianming;China Coal Research Institute Company of Energy Conservation;National Coal Resource High Efficient Mining and Clean Utilization;National Key Lab of Energy and Coal High Utilization,Energy Saving and Emission Reduction Technology and Equipment;
Semi-coke is the product of low-rank coal pyrolysis at low temperature. The price of pulverized semi-coke is lower than that of bituminous coal which is the commonly used in industrial pulverized coal boiler. If semi-coke can be used as the fuel of industrial pulverized coal boiler,the applicable fuel range of the coal-fired industrial boiler will be widen. Besides,the market competitiveness of coal-fired industrial boiler can be enhanced. Because of the low volatile content and a high fixed carbon content,semi-coke needs a higher temperature for ignition and steady combusiton. What's more,the decrease of NO_xemission is a also a technical problem. The NO_x emission properties of semi-coke air-staged combustion was studied in two-stage drop-tube furnace to realize steady combustion in pulverized coal industrial boiler and low NO_xemission of semi-coke. In this paper,the NO_xemission law of semi coke air non-staged combustion was studied.The influence of fuel-rich zone temperature( 1 000-1 400 ℃) and excess air coefficient( 1.0-1.3) were explored to give a comparison with the following air-staged combustion experiment. In semi-coke air-staged combustion experiment,the influence of the fuel-rich zone temperature( 1 000-1 400 ℃) and the ratio of secondary air( 0.4-0.8) were explored. Besides,the burn-out rate,NO_x decrement rate and microscopic pore structure and morphology of air-graded combustion ash were analyzed to reach a comprehensive conclusion. It can be concluded from the non-staged combustion experiment that under the condition of air non staged combustion,and when the ratio of exhaust air to air distribution is 0,the NO_xemission increases rapidly with the fuel-rich zone temperature increasing. When the excess air coefficient increases,the NO_xemission increases rapidly first,and then the increase becomes slowly when excess air coefficient is over 1.15.It can be concluded from the air-staged combustion experiment that when the ratio of secondary air changes from high to low under the same temperature of the main combustion zone,the NO_xemission shows a trend of rapid decline and slow recovery,and the burnout first increases rapidly and then tends to be gentle. The optimal ratio of secondary air is 0.56,when the NO_xemission concentration is under120 mg/m3,and the burn-out rate and the decrease rate of NO_xare all at a high value.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 2201K] - PAN Hao;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of Coal Mining and Environmental Protection;National Energy Technology and Equipment Laboratory of Coal Utilization and Emission Control;
The SO_2 and NO_xproduced by coal fired boiler are important components of air pollutant.With increasingly serious environmental situation,the national environmental protection rules put forward higher requirements for the emission standards of both utility boiler and middle and small industrial boiler. The flue gas purification system of pulverized coal fired industrial boiler has large inertia by using manual control mode,which can not meet the latest environmental standards.In view of these problems,combined with limited pollutant emission modification project of certain Shendong boiler station,an integrated pollutant emission control system based on programmable logic controller( PLC) and ethernet was designed.The optimal control logic of desulfurization and denitration system were proposed through analyzing process flow of certain systems.The desulfurization system was on the basis of original NGD system,the storage and transportation device of desulfurizer was added,and the automatic desulfurizer supplying and regulating control logic based on ash calcium circulation and humidification activation of desulfurization system were proposed.By installing ozone generator and conveying unit,denitration system was implemented with SNCR-Ozone cooperative method,then the cascaded start-up and automatic addition control logic were designed.Control system was deployed with distributed hardware,then subsystems of desulfurization,SNCR,and ozone system were configured based on optimized control logic using SIEMENS SIMATIC series PLC.The Ethernet network is used to build the communication subnet and share the internal data of each subsystem,so as to enable interlock protection and the tracking response of the desulfurization and denitrification system to the boiler load.The results show that the control system is able to maintain SO2 concentration below 100 mg/m3 in 10 min after the boiler started,and keep the value under the preset limit at variable load. During continuous operation of several boilers,the average consumption time of desulfurizer surge bins is about 80 min,the average supply time is about 4.5 min,and the average waiting time is about7 min,which ensures the nonstop supply of the desulfurizer.The control system starts SNCR and ozone system in succession after the boiler started,adjusts dosing quantity of urea and ozone automatically,and maintains NO_xconcentration below 100 mg/m~3 in 20 min. Compared with that before the transformation,the SO_2\ NO_xemission of the station decreases significantly in long period operation,the concentration of which reduces from 100-200 mg/m~3 to 50-100 mg/m~3; according to operation data during 80 h,the average SO_2 emission concentration value decreases from 163. 55 mg/m~3 to 72. 54 mg/m~3,meanwhile the average NO_xemission concentration value decreases from160.85 mg/m~3 to 71.06 mg/m~3,which meets the national and local environmental standards.In addition,the fluctuation of pollutant emission is also reduced compared with that before the transformation,and the standard deviation of SO_2 concentration value decreases from21.04 to 18.14,meanwhile the standard deviation of NO_xconcentration value decreases from 25.09 to 15.84.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 11305K] - LI Ting;China Coal Research Institute Company of Energy Conservation;
In order to achieve the coordinated removal of multi pollutants and avoid the problems of wet absorption process,a semi dry flue gas multi pollutant integrated removal process was proposed based on the combination of low temperature oxidation denitrification and ash calcium cyclic desulfurization and dust removal.The NO removal experiment on pollutants integration removal process of oxidation coupled ash-calcium cycle was carried out.The calcium absorption characteristics of calcium based absorbers for NO_xat low temperature were investigated in fixed bed and liquid-phase experimental device.The de NO_xeffect was verified on gas-fast-bed industrial test device.The results show that the absorption rate of NO_2 calcium base is 20%-30% in fixed bed,under the conditions of 70-80 ℃,O25%,RH 40%-60%.The average denitrification rate of liquid absorption is more than 90%,at NO_2 concentration 200×10~(-6),Ca( OH)_2 suspension concentration 1%,70 ℃,O_2 content of 5%.Reaction temperature and relative humidity are the key factors affecting the absorption of NO2.Under the experimental conditions,the lower the reaction temperature is and the higher the relative humidity is,the higher the removal rate of NO_2 by calcium based absorbers is; the change of NO_2 initial concentration in the low concentration range has little effect on the denitrification effect.Under the condition of inlet NO concentration 231-423 mg/m3,absorption reaction temperature75 ℃,oxidation temperature 140 ℃,[O_3]/[NO]0.9-1.8,the NO_xcalcium absorption rate is 83%-89%,NO oxidation rate 74%-97%,and the total de NO_xrate 66%-87%in the industrial test device.The oxidation rate and denitration rate increase with the increase of [O_3]/[NO],and the concentration of NO and NO_xat the outlet of the device decreases after oxidation.Therefore,in a certain range,the higher [O3]/[NO]is,the better the denitration effect is,but the ozone escape increases. In actual operation,the reasonable process parameters should be selected according to the site conditions.According to the denitration products IR results,NO_2 reacts with Ca( OH)_2 to form nitrate and nitrite.The de NO_xrate of the three methods is as follows: wet method( liquid absorption) > semi dry method( gas fast bed) > dry method( fixed bed),and the gas fast bed is close to liquid-phase.The results are mainly affected by the way of humidification,that is,the existence and relative amount of liquid water are the key factors affecting the absorption reaction. This is because the reaction form between NO_2 and Ca( OH)_2 will change from gas-solid heterogeneous reaction to rapid ionization reaction in the presence of water.Therefore,the more moisture and relative humidity in the reactor is,the higher the absorption rate and the denitrification rate is.The lowest NO_xemission concentration is 30 mg/m~3,reaching the ultra-low emission level.It realized the high-efficiency collaborative removal of multi-pollutants in the same device.The flue gas purification technology with oxidation coupled with ash calcium circulation is suitable for the treatment of small and medium-sized coalfired flue gas,and has a broad application prospect.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 6006K] - CHEN Fuzhong;Jinan Thermal Group;
Based on the circulating desulfurization with high ratio of ash and calcium( No Gap Desulphurization) of Shendong 30 t/h coalfired industrial boiler,and in order to further find the desulfurization process and mechanism,the influence of different factors on the desulfurization efficiency was studied.In this paper,the sulfur content and water content of desulfurizer in different positions were detected by drilling and sampling along the reactor firstly.The results show that the water content and sulfur content in desulfurizer decrease and increase respectively with the desulfurizing reaction,which indicate that water is very important for desulfurizing reaction.In the presence of water,the desulfurizing reaction changes from gas-solid two-phase reaction to liquid-phase reaction between ions,and the desulfurization reaction rate increases significantly.At the same time,with the desulfurization reaction,the reaction products in the desulfurizer increase,so the sulfur content increases. Secondly,the change of composition and content of flue gas along the reactor is detected. According to the change rate of desulfurization efficiency per unit distance on the reactor,the desulfurization process is divided into three stages: constant speed section,deceleration section and quasi balance section.The desulfurization reaction rate of first two stages is fast,which is the key section of desulfurization reaction.The SO_2 removed accounts for 90% of the total SO_2. Therefore,It is a effective method to improve the desulfurization efficiency by strengthening the first two desulfurization stages.Finally,the engineering test was carried out on the NGD desulfurization unit to study the influence of the humidification water quantity,initial concentration of SO_2 and the mixing ratio on the desulfurization efficiency.Finally,the results are as follows: the humidification water quantity increases,the initial concentration of SO_2 decreases,and the proportion of hydrated lime increases,which is equivalent to the increase of the initial concentration of the desulfurization reactant,and promotes the desulfurization reaction to the right,and the desulfurization reaction rate increases in the initial stage,so the final desulfurization efficiency shows an increasing trendy.However,due to the limitation of pore structure and active substance content of desulfurizer,there are optimal technological conditions for desulfurizing reaction to make full use of the effective substances in desulfurizer.According to the variation of desulfurizing efficiency,the optimal range of humidification water quantity,initial concentration of SO_2 and mixing ratio is finally determined,which are 0.14-0.27 t/h,350-550 μL/L and 3 ∶ 1-2 ∶ 1 respectively.At this time,the variation of desulfurizing efficiency is 28.81%,25.87% and 10.55% respectively.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 5666K] - WANG Zhiqiang;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of Mining and Environmental Protection;National Energy Technology and Equipment Laboratory of Coal Utilization and Emission Control;
Coking in coal-fired boilers will cause great harm to the safety and economy of boiler operation.Therefore,it is important to analyze the factors affecting coking of coal-fired boilers and effectively prevent coking in coal-fired boiler. In practical application,different preventive measures can be taken for different factors affecting coking of coal-fired boiler.It is found that the melting temperature of coal ash,particle size of coal,combustion atmosphere of boilers,primary and secondary air force field,thermal loads of boiler section and boilers are the factors that affect the coking of coal-fired boilers. In order to solve the problem of large area combustion coking in precombustion chamber,furnace and convection heating surface in a specific pulverized coal boiler,based on combustion coking mechanism of coalfired boilers,the measures of by adjusting combustion atmosphere,increasing secondary air rigidity,reducing the pulverized coal particle size,replacing the pulverized coal were taken to analyze coking phenomenon under different conditions. The conclusion is that the types of coal and the particle size are the factors affecting the combustion coking of this specific pulverized coal boiler.The micro morphology and element composition of the coking block as well as the composition of different coals were analyzed by SEM-EDS,the coal quality and ash composition between the coal powder currently used in the on-site sampling boiler and Sunjiacha coal powder were compared and analyzed,and the slagging discrimination index was calculated according to the ash composition.The melting temperature of coal ash used in the boiler is relatively low.The softening temperature Ts is 1 170 ℃,less than 1 200 ℃ .It is called fusible coal and easy to slag and belongs to a typical kind of easily coking coal.The calculation results of slagging discrimination index show that 4 indexes are evaluated as " serious",1 index is evaluated as " medium",meaning high slagging tendency.In general,the change of coal type and the low melting temperature of the coal are the essential factors affecting the combustion coking of the boiler.To further solve practical problems,the acid-base equilibrium of coal ash was destroyed to increase the melting temperature and the particle size was refined by the following methods,5%quartz was blended into the coal to increase the content of Si O2 and thus increase the melting temperature of the coal to 1 280 ℃,and the temperature would be increased by 110 ℃ .The frequency of pulverized coal mill was turned up from 19 Hz to 22 Hz to increase the sieving rate of pulverized coal particle size( 200 mesh) from 70% to 85%.Eventually,the boiler ran smoothly and the coking condition is improved significantly.Overall,the combustion adjustment measures achieve good results and relevant experience are available for reference.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 10670K] - LIU Zhenyu;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of Coal Mining and Clean Utilization;National Energy Technology and Equipment Laboratory of Coal Utilization and Emission Control;
The quantitative measurement of feeding parameters is an important prerequisite for automatic regulation of boiler. At present,most kinds of direct measuring equipment have limited applicability to industrial boilers due to the influence of concentration measuring range,cost and other factors.However,some of the sensor data of boiler have a significant relationship with the feeding system.In order to explore the feasibility of using these sensor data to calculate feed parameters,the sensor data of a 58 MW boiler in tianjin huayuan were collected at a frequency of 1 Hz.Under the condition of controlling other variables,the data related to the feed such as the weight of the intermediate bin,the total pressure of the primary air,the speed of the air lock valve,the pressure of the furnace and the oxygen content of the flue gas were screened out,and the relationship between the absolute value and standard deviation of the above variables and the feed parameters were quantitatively calculated by the least square method and the determination coefficient method.The results indicate that When the feeding valve of the intermediate bin is closed,the average feeding quantity within 300 s of the feeder can be calculated by weighing the middle bin with high accuracy.If the filling rate and filling density of the air lock valve are fixed,the feeding quantity can be accurately calculated by using the feeding speed of the air lock valve.The feeding curve at low speed conforms to this assumption.With the increase rate of the rotational speed,the marginal value of the feed decreases at the edge of the quadratic curve,and there are individual differences in the decline rule.The calculation of the total primary air pressure is a differential pressure method,and when the total primary air pressure is used to calculate the feed quantity,the adjusted determination coefficient R_(Adj)~2>0.98,and the calculation accuracy is very high.The disadvantage is that the coefficient k needs to be calculated based on the cumulative operation data of each device.The fluctuation of negative pressure in furnace can better reflect the fluctuation of feed,but the accuracy is lower than the total pressure of primary air.When the sampling time is 30 s,the standard deviation of supply-the standard deviation of furnace pressure R_(Adj)~2 reaches its maximum value of 0.890 1.The R2 Adjof the feedstock-oxygen consumption reached a maximum value of 0.296 1 at the sampling time of 200 s,and the R_(Adj)~2 of the standard deviation of feed-standard deviation of oxygen consumption reached its maximum value of 0.640 8 at the sampling time of 10 s.It indicates that oxygen consumption is of medium reliability in inferring feed fluctuation,while inferring feed quantity is of poor reliability,which may be related to the instability of the boiler pulverized coal mixing ratio is not stable,resulting in the unit weight of pulverized coal calorific value fluctuations.
2020 02 v.26;No.126 [Abstract][OnlineView][HTML全文][Download 3170K]
2020 02 v.26;No.126 [Abstract][OnlineView][Download 1751K]