- MAO Jianxiong;GUO Huina;WU Yuxin;Department of Energy and Power Engineering,Tsinghua University;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua Univergity;
Biomass is a reliable low-carbon alternative fuel with the characteristics of abundant reserves and wide distribution in China. The reasonable and effective utilization of biomass is very important for the realization of low-carbon/zero-carbon emissions and the construction of the power system based on renewable energy in China, because biomass fuel also has the property of energy storage. To this end, the status and trends of biomass utilization policies and power generation technologies at abroad were systematically reviewed. An in-depth analysis of China′s future biomass utilization pathways was conducted, combined with biomass characteristics and power generation demand in China. It is concluded that the main direction of the current low-carbon development of thermal power in the world is high-efficiency coal firing power technology with biomass co-firing, which has the advantages of mature technology, low cost, and flexible utilization forms. It is a key measure for the UK,Sweden and other countries to achieve carbon neutrality, and has been developed rapidly under effective policy incentives. At present, the power efficiency of coal-fired units in China has been significantly improved, and the continuous improvement of technology to increase power efficiency can not meet the demand of substantial carbon reduction. Carbon emission reduction of coal-fired power generation needs to be carried out from both carbon reduction of raw materials and carbon sequestration of the flue gas, while biomass power generation is an effective measure to reduce carbon from raw material. On the basis of developing high-efficiency, advanced and energy-saving coal power, China should first establish and then break through, vigorously develop biomass thermal power to replace coal power, and finally realize the zero-carbon transformation of coal power. Therefore, coal power upgrading + biomass co-firing + carbon capture, utilization and storage(CCUS) is of great strategic significance to the ultimate realization of carbon neutrality by 2060 in China. The future development of biomass power generation technology in China should pay attention to three aspects: Firstly, more reasonable national regulations and incentive policies should be formulated according to the situation of biomass resources and utilization goals in China, such as carbon tax reduction under the carbon trading system, flexibility subsidies according to the blending ratio, green certificate transactions, etc.,to restrict and the co-firing of biomass in coal-fired power plants. Secondly, the biomass fuel industry should be vigorously developed, biomass processing and acquisition standards should be standardized, and a stable and reliable biomass fuel supply market should be established. The cost and quality of raw materials should be fundamentally reduced and controlled, which are also important measures to promote the healthy development of biomass utilization. At last, advanced and feasible co-firing, and even 100% burning technology should be developed. Foreign experience shows that high proportion of biomass mixing in coal-fired units is technically feasible, but there is less experience in this aspect. Technology accumulation is still needed in raw material processing and preparation, ensuring efficient combustion under the condition of large fluctuation in blending ratio, and solving corrosion and slagging on heating surfaces. The low-carbon energy system in the future will be a multi-energy complementary pattern, and the large-scale utilization of biomass will face the problem of shortage of raw materials, which means that it is necessary to promote the planting of energy crops such as shrubs and grasses on marginal land and the transformation of existing forest land. The integrated collection, storage, transportation and primary processing industrial chain of agricultural and forestry wastes and energy crops can be combined with the development strategy of agriculture, rural areas and farmers to benefit the country and the people.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 18193K]
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 1813K] - GUO Huina;WU Yuxin;WANG Xuebin;WANG Zhichao;ZHANG Man;HUANG Zhong;Department of Energy and Power Engineering,Tsinghua University;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua Univergity;School of Energy and Power Engineering,Xi′an Jiaotong University;Xi′an Thermal Power Research Institute Co.,Ltd.;
Biomass co-firing in coal-fired power plants has the advantages of low conversion cost, flexible peak shaving, and safe operation. It is an effective way for the power plant to reduce CO_2 emissions and increase the proportion of renewable energy in power generation under the carbon peaking and carbon neutrality goals. At present, the application of biomass co-firing in coal-fired units for power generation in China is still very limited. To further play the role of biomass, a clean and zero-carbon renewable energy, in the new power system, and at the same time take advantage of the flexible coal-fired units, the current status of biomass resources in China, the co-firing options of biomass with coal for coal-fired boilers, and the operation of typical co-firing projects at home and abroad were investigated in detail. It is pointed out that there is a large waste of resources, especially in agriculture and forestry. Biomass co-firing technology in coal-fired units has been widely used abroad, especially in European countries, but has not been applied to large units in China. Some challenges faced by the direct combustion coupled biomass power generation technology of coal-fired units were summarized, including the stable and low-cost biomass raw material supply and process have not yet been formed, mature technology for high-proportion co-firing has not yet been developed, contamination and corrosion on heating surfaces need to be solved urgently, the measurement standards about biomass power generation in co-firing have not yet formed a standard. To improve the flexibility of large-scale coal-fired power plants and reduce CO_2 emissions, efforts should be made in the following aspects in the future. By planting energy crops around power plants and on the marginal land, the relative unity and stability of biomass raw materials can be ensured, to avoid the influence of large changes in the properties of raw materials on the operation of the unit. It is necessary to develop high-proportion biomass co-firing technology to ensure that the blending ratio can be adjusted flexibly. Moreover, it is important to explore more advanced biomass power generation measurement methods, which will help determine reasonable subsidies and operation methods for biomass blending and accelerate the formation of a competitive, replicable and disseminated biomass power generation circular economy chain. Then, the demonstration projects according to the proportion of mixed combustion from low to high and bioenergy with carbon capture and storage technology can be carried out to gradually transition thermal power units from raw material carbon reduction to raw material decarbonization to flue gas decarbonization.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 2937K] - ZHANG Dongwang;SHI Jian;YANG Hairui;LYU Junfu;ZHANG Man;HUANG Zhong;LI Shiyuan;School of Energy and Environmental Engineering,University of Science & Technology Beijing;Department of Energy and Power Engineering,Tsinghua University;Shanghai Boiler Works Co.,Ltd.;
In response to the increasing conflict between energy supply and demand, the development of renewable energy sources to achieve energy saving and emission reduction has become a global issue. The adoption of carbon pricing can increase the cost of coal-fired power generation and promote renewable energy generation. Biomass reserves are abundant and the net CO_2 emissions are zero, which makes it possible to realize carbon neutralization. More and more foreign countries adopt carbon pricing to promote emission reduction. The cost of coal-fired power generation with additional carbon pricing in China under different carbon pricing scenarios was analyzed, and the biomass power generation with other power generation methods was compared, making it clear that the gap between the cost of biomass direct combustion power generation and coal-fired power generation will gradually narrow as coal prices continue to rise and the urgent need to further increase carbon pricing to achieve the Paris Agreement temperature control targets. In addition, as biomass power generation technology continues to mature and improve, its operational reliability will be substantially improved, laying the foundation for the vigorous promotion of biomass power generation. Biomass power generation has a very good market prospect due to the combined economic and technical advantages.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 14507K] - HU Nan;TAN Xuemei;LIU Shijie;ZHAO Bing;GONG Taiyi;WANG Jialin;ZHANG Shouyu;School of Energy and Power Engineering,Changchun Institute of Technology;China State Key Lab of Power System,Tsinghua University;Tianjin Development Area Branch of Huadian Power International Co.,Ltd.;School of Energy and Power Engineering,University of Shanghai for Science and Technology;
Direct combustion power generation of agricultural and forestry biomass in circulating fluidized bed is the main technical route of biomass utilization. Power generation with biomass will embrace great opportunities and face more problems and challenges under the strategic goal of carbon peak and carbon neutral in China. In order to promote the development of the CFB boiler biomass power generation industry, the development status of biomass direct combustion power generation industry were investigated, the technical advantages of circulating fluidized bed boiler in biomass power generation industry were combed and the development history and key technological breakthroughs was analyzed systematically. Power generation of biomass direct combustion has developed rapidly in China and the world in recent years. The average growth rate of biomass power generation installed in China is about 20.3% each year since the 13 th Five-Year Plan. CFB combustion technology is suitable for biomass due to its wide fuel adaptability, higher combustion efficiency and lower pollutant emission. At present, high pressure and ultra-high pressure CFB boilers are commonly used in new biomass power plants, and some units are equipped with once reheat cycle. The fluidization reconstruction technology on biomass circulating fluidized bed boilers has greatly reduced the auxiliary power consumption rate of the unit and further improved the boiler efficiency. Through the optimization of combustion temperature and air volume ratio, the original emission of nitrogen oxides is effectively controlled. In view of the high content of alkali metal of biomass fuel, the problems such as contamination and blockage of heating surface can be effectively reduced by optimizing the design of convective heating surface and lowering combustion temperature, and the availability of boiler is greatly improved.The main factors restricting the development of biomass power generation industry were pointed out at present, including high operating costs, uncertainty of state subsidies and backward level of enterprise management and control.With the decline of government subsidies for biomass power generation, industrial development will be limited. In view of the poor economy of biomass pure combustion power generation, small-capacity, ultra-high parameter units including ultra-high pressure once reheat and sub-critical units should be developed, which can effectively improve the power generation efficiency. With the establishment of carbon trading system, power generation by coal coupled biomass will be further popularized.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 7053K] - HAN Jingkun;WANG Jinhan;YU Dunxi;WANG Shaozhuang;YU Xin;WU Jianqun;XU Minghou;School of Energy and Power Engineering,Huazhong University of Science and Technology;
The physical and chemical properties of biomass after torrefaction can be significantly improved, which enable the biomass to replace coal in large scale for power generation and CO_2 emission reduction. However, ash deposition and corrosion during the combustion are still urgent issues to be solved, and systematic investigations on the influence of torrefaction on the corrosion behavior of biomass combustion is rarely available. In view of this, two typical biomass, corn stalk and wheat straw, were selected to prepare their torrefied samples in a fixed-bed reactor, and the effects of torrefaction on the occurrence modes and contents of key ash-forming elements in the biomass were investigated through chemical fractionation analysis combined with ICP-MS and IC tests. Combustion tests of biomasses, two typical power coals and the blends of biomass and coal were conducted on a drop-tube furnace, and the bulk ash was collected. 12 CrMoVG steel was selected as tested alloy for corrosion tests which conducted on a horizontal tube furnace at 550 ℃. The corrosion behavior of loading ash from individual combustion under atmosphere containing HCl, and loading ash from co-combustion under atmosphere containing HCl and SO_2 were investigated. The mass increment of ash loaded-alloys after corrosion tests were weighed. The morphology and composition characteristics of the corroded samples were analyzed by SEM-EDS. Finally, the influence of torrefaction on the corrosion propensity of co-combustion of biomass and coal was revealed through corrosion tests under atmosphere with various HCl concentrations. The results indicate that the corn stalk and wheat straw contain considerable amounts of Cl and K. After torrefaction at 270 ℃,17.84% and 38.76% Cl is released from corn stalk and wheat straw while 7.78% and 20.98% S is released, respectively. The total amount of Na, Mg, K,Ca and Fe is hardly changed. A small amount of water-soluble K is transformed into ion-exchange forms, and part of water-soluble Mg and Ca are transformed into HCl-soluble forms. Under the same atmosphere, the mass increment after corrosion tests of torrefied biomass ash is slightly higher than that of the raw biomass due to the slightly increased AAEM(alkaline and alkaline earth metal) contents ash after torrefaction. Due to the presence of SO_2,the sulfate reaction is caused, and the degree of corrosion is reduced, thus the mass increment after corrosion tests of co-combustion ash is obviously lower than that of individual combustion ash. After torrefaction, the elemental composition of bulk ash from both individual combustion and co-combustion has little change, so its influence on corrosion degree is limited. However, the increase of Cl in the corrosive atmosphere can significantly promote the corrosion behavior. Benefiting that torrefaction can remove part of Cl in the biomass, torrefaction is potential to reduce the corrosion tendency during combustion.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 15546K] - XIAO Haiping;WANG Mingwei;GUO Zhengwang;LI Yan;YAN Dahai;Energy Power and Mechanical Engineering Department,North China Electric Power University;Research Institute of Solid Waste Management,Chinese Research Academy of Environmental Sciences;
The boiler collaborative treatment technology of coking solid waste realizes the heat resource recovery. The CO combustion test of raw coal, biochemical sludge and tar pulverized coal was carried out on a 480 t/h pulverized coal boiler to evaluate the environmental harm of the collaborative utilization of coking solid waste. The flue gas, slag, fly ash and ammonium sulfate were sampled and analyzed to study the emission characteristics of various pollutants and their impact on the environment under the mixed combustion condition. The results show that the combustion is stable and the fluctuation of various operating parameters is small when the mixing ratio of coal, biochemical sludge and tar pulverized coal is 100.0∶3.0∶1.5. Naphthalene and acenaphthylene in low ring(2-3 ring) polycyclic aromatic hydrocarbons are the main components of 16 PAHs, and the monomer contents of other PAHs are low. The total toxic equivalent concentration of PAHs in flue gas is 71.3 ng/m~3, and the concentration of PAHs in solid samples is lower than 0.5 mg/kg. The concentration of dioxins in flue gas is 0.004 3 ng/m~3, which is 61.3% lower than that in blank condition. The concentration of dioxins in solid samples are lower than 2.0 ng/kg. All organic matter emissions under collaborative working condition meet the standards. The mass ratio of Cr and As in biochemical sludge are 3.6 and 26 times of that in raw coal, resulting in the mass ratio of Cr and As in mixed fuel increased by 21.1% and 63.1%, respectively, and other heavy metals do not increase significantly. More than 90% of Cr and As exist in fly ash, about 2%-4% in slag, and only a small part in flue gas and ammonium sulfate. The Cr content in flue gas is 6.69 μg/m~3, which decreases by 45.2% compared with blank condition, and the As content is below the detection limit. The leaching experiment of solid samples such as slag, fly ash and ammonium sulfate show that the leaching mass concentrations of Cr and As in solid samples are lower than 4 mg/L and 0.1 mg/L, respectively and there is no environmental risk in the leaching of heavy metals. The emission concentrations of pollutants in the test process are lower than the current standard limit in China, and the environmental risk of boiler collaborative treatment technology is controllable, which provides a reference for the harmless utilization of coking solid waste.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 5412K] - ZHAO Xiaojun;WANG Xuebin;SUN Jinyu;XUE Dongfa;Nandian Synthesis Energy Utilization Co.,Ltd.;MOE Key Laboratory of Thermo-Fluid Science and Engineering, Xi′an Jiaotong University;
Biomass, as a renewable source with zero carbon emission, is regarded as a promising alternative fuel to coal. Coupling combustion with pulverized coal is one of the key technologies to realize the utilization of biomass. In order to study the influence of pulverized coal coupling combustion of biomass, the coupling combustion of biomass in a pulverized coal boiler of 300 MW power station was numerically simulated, and the effects of biomass mixing ratio and powder feeding temperature on the parameters in the furnace were discussed. The results show that as the proportion of biomass increases, the oxygen consumption in the furnace decreases, and the concentration of CO and char decreases, while the NO_x emission increases at outlet. A lower temperature input of biomass only causes a slight increase of oxygen concentration and a decrease of CO concentration in the main combustion area, which has no significant change to the parameters in the furnace. It means that a slight adjustment of biomass feeding temperature could not cause a significant influence for combustion in the furnace.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 16181K] - LIU Ruidong;ZHUO Xiaohui;MA Lun;CHENG Qiang;LUO Zixue;ZHOU Huaichun;Sichuan Zhongdian Fuxi Electric Power Development Co.,Ltd.;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;School of Electrical and Power Engineering,China University of Mining and Technology;
Biomass co-firing in coal-fired power plants has the advantages of low conversion cost, flexible peak shaving, and safe operation, which has a positive effect on carbon emission reduction and can realize the efficient utilization of biomass. At present, a large number of experiments and simulation studies have been carried out on the blending of sludge and other substances in coal-fired boilers, but there are few numerical simulation studies on the blending of distiller′s grains in coal-fired boilers. In order to study the influence of blending distiller′s grains in coal-fired boilers on the temperature field, component concentration field and NO_x emission in the furnace, the mixed combustion of pulverized coal and distiller′s grains was simulated by numerical simulation and the vortex dissipation model in computational fluid dynamics software FLUENT. The results show that the simulation method is reliable. Under full load, the simulated outlet oxygen, carbon content of fly ash and NO_x emission are in good agreement with the experimental results under the same conditions. The simulation results of 0,3%,6%,8% and 10% of the mass fraction of distiller′s grains show that the ignition distance near the nozzle of the burner is shortened, but the overall temperature field of the furnace does not change significantly. The concentration distribution of O_2 in the furnace is not significantly affected by the blending of distiller′s grains, the concentration of H_2O is increased near the burner nozzle due to the influence of distiller′s grains water content. Blending distiller′s grains have a significant impact on NO_x emission, which is the result of the interaction of reducing atmosphere caused by the nitrogen content of blending fuel and the release of biomass volatiles.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 14030K] - ZHANG Xiaotao;ZHANG Chengyu;LIU Haoming;BAI Linrui;WANG Aijun;School of Electric Power,North China University of Water Resources and Electric Power;
In order to investigate the effects of different types of gas and re-burning nozzle downward inclination angle on the combustion process of boiler, based on the FLUENT software, an ultra-supercritical 660 MW boiler was selected as the research object, and the re-burning gas coupled coal-fired combustion model has been built to transform the boiler. A reburning zone was added at the upper part of the main combustion zone. The effects of different kinds of gas reburning and different reburning nozzle downdip angles on boiler temperature field, CO, CO_2,O_2 components and NO_x emissions were studied. The results show that, the re-burning gas will make the main combustion zone temperature lower, and the flue gas temperature in the re-burning zone and the burnout zone increase. With the addition of re-burning gas, the center of the furnace flame moves up, and the temperature of the outlet flue gas also increases. The re-burning results in the increase of CO concentration at the furnace outlet, but the decrease of the concentration of O_2 and CO_2 and the significant decline of NO_x emissions. Compared with the pure coal condition, the NO_x emission reductions of straw gas, methane and biogas are 20.1%,26.2% and 25.2% respectively. The proper downward slope of the re-burning nozzle can improve the intensity of the flow field in the furnace, enhance the combustion effect of the boiler, and increase the residence time of the re-burning fuel in the re-burning area, and effectively reducing the NO_x emission at the furnace outlet. When the downward inclination angle is 15°,the emission reduction effect is the best. The NO_x emissions during re-burning of straw gas, methane and biogas are decreased by 31.73%,35.66% and 33.85%,respectively. The research methods and conclusions of this paper have certain realistic reference significance for the research and application of biomass gas and coal blending utilization in large coal-fired boilers.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 22519K] - WANG Fei;ZHANG Sheng;WANG Lihua;College of Energy Engineering,Zhejiang University;Shanghai Chengtou Wastewater Treatment Co.,Ltd.;
Incineration is widely used as the mainstream way to achieve the rapid reduction and harmless disposal of sludge in China, and with the aim of "double carbon" emission reduction plan, co-combustion of sludge with coal can realize the carbon emission reduction and the clean incineration of sludge. However, there are still many problems in slagging, combustion pollutant emission and technical economy. The basic physical and chemical characteristics, water content distribution, coal quality index, and drying technologies of sludge were analyzed. The advantages and disadvantages of three technical routes of co-combustion of sludge with coal, i.e.,direct co-combustion, co-combustion of sludge dried directly by flue gas, and co-combustion of sludge dried indirectly by steam, were thoroughly analyzed based on the typical co-combustion projects. The results show that direct co-combustion of wet sludge is faced with poor combustion stability and low disposal capacity, and the combination of drying and co-combustion can achieve a large disposal capacity and ensure the combustion stability. Considering the problems of high dust explosion risk and large demand for flue gas in the direct drying of sludge by flue gas, co-combustion of sludge dried indirectly by steam is a better choice with good combustion performance. Among sludge indirect-drying technologies, paddle drying and rotary disc drying have high thermal efficiency, low dust production, and small floor area. Due to the existence of viscosity during sludge drying, it is necessary to select an appropriate drying model to analyze the heat and mass transfer process. Based on the operation practice of typical co-combustion projects in China, it is found that when the blending ratio of sludge is well controlled, co-combustion technology can not only ensure high combustion thermal efficiency, but also meet the emission standards of pollutants including conventional pollutants, heavy metals and dioxins. In terms of national policy, it is urgent to clarify and refine corresponding policies, e.g.,the pollutant emission standard, power generation subsidy standard, and carbon emission reduction accounting standard, to promote the development of co-combustion of sludge with coal.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 7970K] - LI Yuan;GUO Zhicheng;ZHAO Xinping;MAO Rui;CEN Kefa;Rundian Energy Science and Technology Co.,Ltd.;State Key Laboratory of Clean Energy Utilization,Zhejiang University;
Co-combustion of steam desiccation sludge with coal is a technical measure for large scale sludge disposal, but the effect of steam desiccation sludge co-combustion on unit energy consumption characteristic is unclear. The performance test of co-firing coal and sludge dried by steam was conducted in a 350 MW coal-fired power unit. The effects of steam desiccation sludge on boiler thermal efficiency, steam turbine heat rate, auxiliary power consumption ratio, energy consumption rate were studied. During the test, the treatment amount of raw sludge was set at 8.00 t/h, and the moisture content of the raw sludge was dried from 80% to 60% and 40% respectively by sludge dryer. The results show that the unit energy consumption rate has an increasing trend when the power unit blends with steam desiccation sludge. The decrease of boiler efficiency is mainly due to the increase of sensible heat loss in exhaust flue gas and unburned carbon heat loss in residue. The steam consumption during sludge desiccation leads to the increase of the steam turbine heat rate. The increase of power consumption of fan system and desulfurization system causes the increase of the auxiliary power consumption ratio primarily. The higher the degree of sludge drying is, the smaller the decrease of boiler efficiency is, the greater increasing extend of the steam turbine heat rate is, and the smaller increasing extend of the auxiliary power consumption ratio is. When the sludge moisture content is dried from 80% to 40%,the net fuel consumption rate reduces slightly, whose variation reduces from 2.039 g/kWh to 1.904 g/kWh. As the power unit blends with raw sludge, the decrease of the boiler thermal efficiency and the increase of the auxiliary power consumption ratio are the main factors causing the increase of energy consumption rate. As the power unit blends with steam desiccation sludge, the increase of the steam turbine heat rate is the key factor leading to the increase of energy consumption rate. This study provides the theory and data support for evaluating the energy consumption of the power generation coupled with steam desiccation sludge.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 13031K] - KE Xiwei;SUN Guorui;HUANG Zhong;GONG Taiyi;YANG Hairui;LYU Junfu;ZHANG Man;Department of Power and Energy Engineering,Tsinghua University;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua University;Tianjin Development Area Branch of Huadian Power International Co.,Ltd.;
Co-combustion of sludge and other fuels such as coal in the circulating fluidized bed(CFB) boiler is an effective way to reduce, harmless and resource sludge treatment. To understand the influence of sludge co-combustion on the material balance and operation performance of a large-scale CFB boiler, taking a 330 MWe subcritical CFB boiler as the research object, the material balance characteristics after sludge mixed combustion were predicted and analyzed with the help of one-dimensional CFB mathematical model. Then, the boiler operation performance under co-combustion condition was analyzed in combination with some field test data. Model calculation results show that in the mixed fuel of raw coal gangue and coal slime(the mass fraction of coal slime is 15%),if 10% mass fraction of sludge is added by replacing part of the coal gangue, the particle size of fly ash and bottom ash will change little, while the circulating ash size may be slightly increased. Meanwhile, the solid circulation rate will increase by nearly 30%,from 9.2 kg/(m~2·s) to 11.8 kg/(m~2·s),the average pressure drop across dilute phase zone as well as the particle suspension density will increase by about 35%,and the share of fly ash in the total discharging ash will increase by about 1.5 percentage points. Besides, the residence time of solid particles inside furnace can also be extended. In addition, the field test results under different boiler loads(from 50% to 100% load) reveal that when 10% mass fraction of sludge is mixed in the feeding fuel, the bed temperature has dropped by about 10 ℃,the exhaust gas temperature has raised within 3 ℃. The steam temperatures at the outlet of primary superheater and primary reheater have increased, while the temperature rise is within 10 ℃ at most boiler loads, and the outlet steam temperature of in-furnace platen superheater has slightly decreased by 2-15 ℃. The results in this paper indicate that the co-combustion of sludge with coal is beneficial to improving the solid circulation performance of the CFB boiler to some extent, moreover, the convection heat transfer in tail flue may be enhanced, while the heat transfer coefficient of the platen heating surfaces in furnace may decrease. However, on the whole, for the wide load range, if the blending ratio of sludge in the mixed fuel is not high, the changes of boiler steam parameters are small, which has little impact on the overall operation performance.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 17276K] - SHI Mingzhe;LEI Kai;ZHANG Rui;School of Energy and Power Engineering,Nanjing University of Science and Technology;
Due to the rapid growth of sludge discharge in recent years and serious pollution to the environment, improving the utilization level and harmless treatment capacity of sludge has become a research hotspot. The coupling combustion of coal and sludge has become an effective measure on reduction, harmless and resource disposal of sludge. A coal power plant coupled with sludge incineration system based on circulating flue gas was proposed, sludge was incinerated in an incinerator instead of being added to the pulverized coal boiler, and the high-temperature circulating flue gas of the pulverized coal boiler was used to promote sludge incineration.The combustion characteristics and heavy metal migration characteristics of sludge in the system were studied by tube furnace, thermogravimetric analyzer and X-ray fluorescence spectrum analyzer.The effects of moisture content on combustion characteristics and the effects of furnace temperature and gas composition on the heavy metal migration characteristics of sludge were analyzed. The results show that the increase of moisture content brings negative effects on sludge combustion and the increase of furnace temperature is conducive to the conversion of strongly volatile heavy metals into gaseous state, thereby reducing the residual rate. The increase of O_2 volume fraction brings different effects on the residual rate of different heavy metal. The increase of volume fraction of CO_2 will increase the residual rate of heavy metal because high concentration of CO_2 would decrease the combustion temperature, and the heavy metal is converted to stable metal oxides and decrease the porosity of residual chars. On the contrary, the increase of H_2O volume fraction decreases the residual rate of heavy metal because the presence of H_2O improves the combustion temperature and porosity of chars.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 10199K] - ZHANG Zili;SUN Guang;DUAN Lunbo;National Industrial Boiler Quality Inspection Center,Fujian Boiler & Pressure Vessel Supervision and Investigation Institute;School of Energy and Environment,Southeast University;Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,Southeast University;
Co-combustion of sludge with coal is expected to improve the comprehensive combustion behavior of fuel, and promote reduction, harmless disposal, and resource utilization of sludge. Much study has been done on the combustion and co-combustion characteristics of sludge and coal, but the research on the occurrence of N and S in fuel and its effect on the release characteristic and control of pollutants during co-combustion is still insufficient. The co-combustion characteristics, interaction, and kinetic behavior of Xuzhou bituminous coal and municipal sewage sludge using a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer(TG-FTIR) were carried out. In addition, the occurrence of N and S elements in fuel and its thermal transformation behavior were studied. The results show that a significant interaction occurred during the co-combustion of Xuzhou bituminous coal and municipal sewage sludge at 300-750 ℃,improving the co-combustion performance. The ignition and burnout temperature decrease with the increasing proportion of municipal sewage sludge. The kinetic results show that the activation energy of the co-combustion process is between both of the single samples. The reaction mechanism of mixed combustion of a small amount of sludge is close to that of coal. In the sewage sludge sample, pyrrolic-N and quaternary nitrogen are the main N-containing species. A large amount of NH_3 and HCN emission are released due to its decomposition. As for bituminous coal, pyrrolic-N is the main N-containing species, and its decomposition leads to the emission of NO and HCN. The N-containing gaseous release intensity during co-combustion is lower than that of coal or sewage sludge mono-combustion. Sulfone sulfur, and non-aromatic sulfur are the main S-containing species in sewage sludge. Meanwhile, organic sulfur in sewage sludge decomposes below 400 ℃,resulting in a large amount of SO_2 released. The S-containing species exist in coal mainly as the formation of sulfate(66.24%) and pyrite(21.97%),thiophene sulfur(11.79%),which is contributed to the SO_2 released at high temperature(350-650 ℃) due to the higher thermal stability of its sulfur compounds.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 19722K] - JIANG Mengyan;ZHANG Zili;SUN Guang;DUAN Yuanqiang;DUAN Lunbo;Sinochem Quanzhou Petrochemical Co.,Ltd.;National Industrial Boiler Quality Inspection Center,Fujian Boiler & Pressure Vessel Supervision and Investigation Institute;School of Energy and Environment,Southeast University;Southeast University Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,Southeast University;
Co-combustion of sludge and coal in circulating fluidized bed(CFB) boilers can not only realize its reduction disposal, but also be used as alternative fuel to reduce the use of coal and realize resource utilization. The effects of operating parameters such as different blending ratio, primary air ratio, and excess air ratio on the combustion efficiency and gaseous pollutant emission of municipal sewage sludge and Xuzhou bituminous coal were investigated on a 0.3 MW_(th) circulating fluidized bed pilot plant. The existing forms and transformation characteristics of nitrogen and sulfur in coal and sludge were discussed, and the components and melting characteristics of fly ash in the process of co-combustion of coal and sludge were analyzed. The XPS results indicate that N mainly exists in the form of pyrrole nitrogen(90.58%) and quaternary nitrogen(9.42%) in sludge. In the bituminous coal, N mainly exists in the form of pyrrole nitrogen. The S in sludge is mainly organic sulfide, while S in bituminous coal mainly is the stable inorganic sulfate. The NO emission decreases while the SO_2 emission increases when the proportion of sludge increases during the co-combustion process. The NO emission decreases but barely influence SO_2 emission with increasing the secondary air ratio. The NO and SO_2 emissions increase while the CO emission decreases when the excess air ratio increases from 1.2 to 1.4. When the proportion of sewage sludge increases from 0 to 100%,the unburned carbon in fly ash increases from 8.09% to 28.26%,while the combustion efficiency decreases from 99.23% to 87.76%. Co-combustion sludge with coal can also decrease the melting temperature of fly ash.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 20649K] - WANG Cuiping;LIANG Wenzheng;WANG Kun;GEORGY Ryabov;ZHAO Rongyang;SHAN Mingxuan;YUE Guangxi;Clean Energy Lab,College of Civil Engineering and Architecture,Shandong University of Science and Technology;College of Mechanical & Electrical Engineering,Qingdao University;All Russian Thermal Engineering Institute(VTI);Department of Energy and Power Engineering,Tsinghua University;
The low carbon emission and utilization of municipal sludge is an important guarantee for the construction of "waste free city" and coping with global climate change. Chemical looping combustion/gasification technology can realize the sludge pyrolysis, combustion and carbon capture by looping of oxygen carrier between sludge fuel and air reactors. The cheap and readily available iron-based oxygen carrier was used to carry out the chemical looping combustion of municipal sludge. In order to explore the pyrolysis mechanism of municipal sludge at the initial stage of chemical looping combustion based on the iron-based oxygen carrier, the X-ray optoelectronic energy spectroscopy, ~(13)C solid nuclear magnet and the proximate analysis, elemental analysis were used here to determine the type, the chemical valence state and bonding mode of the typical municipal sludge, so as to determine the chemical structure of molecular groups. Two structural models of sludge independent pyrolysis and oxygen carrier surface pyrolysis with AlFeO_3 as oxygen carrier were constructed in this paper. The molecular dynamics simulations by the reaction force field(ReaxFF MD) is mainly simulated under the two influence factors of heating rate and pyrolysis temperature. The simulation results show that, under different heating rates, the products of sludge independent pyrolysis are mainly organic gas, and the too higher heating rate is not conducive to the pyrolysis of sludge molecular groups, 16 K/ps is suitable. The increase of the pyrolysis temperature and the presence of the oxygen carrier both promote the pyrolysis of the sludge structure and reduce the generation of the tar oil. Without the oxygen carrier, the N mainly migrates into the heavy tar at different heating rates to participate in the subsequent combustion reaction.The pyrolysis temperature has little effect on the generation of the nitrogen-containing products. But the presence of Fe-based oxygen carrier promptes the generation of nitrogen-containing active groups, and then produces NO,while part of NO will be reduced into N_2. The S elemental mainly migrates into the small molecular fragments or precipitates in the form of H_2S.Therefore, iron based oxygen carriers improve the pyrolysis rate of solid fuels, and have a tendency to reduce the production of tar, reduce the generation of nitrogen oxides, but have little impact on sulfur dioxide emissions.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 15682K] - SHI Bingquan;SHI Mingzhe;ZHANG Rui;School of Energy and Power Engineering,Nanjing University of Science and Technology;Zibo Chenyue Baoshan Environmental Protection Technology Co.,Ltd.;
The technology of coal fired coupled waste incineration power generation can make full use of the existing coal fired units and environmental protection facilities, co-processing waste, reduce waste-to-energy costs, improve the scale of waste treatment, and reduce the coal consumption of coal fired power, increase the proportion of non-fossil energy utilization. At present, there are three coupling modes in coal-fired coupled waste incineration power generation technology: flue gas side coupling, fuel side coupling and steam side coupling. In order to study the coupled incineration power generation technology, a coupling transformation scheme based on a 220 t/h tangentially pulverized coal boiler was proposed. Among them, the pulverized coal in the pulverized coal boiler of the system before transformation is burned alone, accounting for 100% of the total input calorific, and after the transformation, the waste calorific replaces 5% and 10% of the total input calorific, while the pulverized coal accounts for 95% and 90% of the total input calorific. The combustion conditions before and after the transformation were analyzed by Fluent simulated. The results show that the flue gas side coupling transformation will make the boiler flow field more complex, and the higher the proportion of waste replacing coal calorific is, the more obvious the impact is; the average temperature of the furnace section is affected by the coupled flue gas volume. The average flue gas temperature at the outlet section increases with the increase of the calorific ratio of waste to coal. The flue gas outlet temperature is 1 366.9 K when pulverized coal is burned alone before the transformation. After the transformation, the average flue gas outlet temperature of the 5% waste to coal calorific ratio system increases to 1 409.9 K,and the average flue gas outlet temperature increases to 1 420.1 K when 10%;the NO concentration at the furnace outlet increases with the increase of the calorific proportion of waste replacing coal. Compared with the separate combustion of pulverized coal before the transformation, the NO emission concentration of the 5% waste replacing coal calorific proportion system after the transformation increases by 6.3% and 13.0% when the proportion system is 10%;the SO_2 concentration at the furnace outlet decreases with the increase of the calorific proportion of waste replacing coal. Compared with that before the transformation, the SO_2 concentration of the 5% waste replacing coal calorific proportion system after the transformation decreases by 40.9%,and that of the 10% proportion system decreases by 41.4%.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 31598K] - ZHOU Ke;LI Yinlong;LI Minghao;LU Xiaoyu;YANG Dong;Xi′an Thermal Power Research Institute Co.,Ltd.;State Key Laboratory Institute of Multiphase Flow in Power Engineering,Xi′an Jiaotong University;
In recent years, the rapid development of renewable energy has raised the demand for flexible operation of the power supply system. Deep peaking of coal-fired units will become the norm in the coming years. The flexibility modification of coal-fired generating units is an important step to resolve the conflict between thermal power and new energy development. In order to improve the deep peaking capability of coal-fired generating units, the coupling technology of coal-fired power generation and thermal storage was proposed. The coupling technology can achieve thermal-electrolytic coupling, enhance the deep peaking ability and flexible operation characteristics of the unit, and provide more space for new energy to access the grid. For the coupled coal-fired power generation-thermal storage technology, three types of physical thermal storage technologies that can be applied to coal-fired units, namely hot water thermal storage, phase change filled bed thermal storage and molten salt thermal storage were presented, and the characteristics of the three types of thermal storage technologies were analyzed and the research direction of the three physical heat storage technologies in the future was put forward. The indicators for evaluating the thermal performance of energy storage devices were summarized, including thermal storage and discharge power, dimensionless temperature, richardson number and thermal storage and discharge efficiency. A model for calculating the peaking capacity of the coupled coal-fired power generation-thermal storage system was also established, and the electro-thermal characteristics of the coal-fired power generation unit were coupled with the calculation model of the thermal storage system, so as to analyze the peaking capacity of the coupled coal-fired power generation-thermal storage system. A reasonable operation mechanism for the coupled coal-fired power generation-heat storage system was proposed, and the thermal performance indicators for evaluating the coupled system were established, namely the thermal efficiency of the heat storage process, the heat release process and the whole process, and the peak regulation capacity and peak regulation margin of the system. A comprehensive electric and thermal dispatch model of the coupled coal-fired power generation-heat storage system was constructed, which included the objective function and dispatch constraints. The scheduling constraints include power balance constraint, heat supply constraint, renewable energy output constraint, electric power constraint, thermal power constraint, climbing speed constraint, heat storage capacity constraint and heat storage capacity constraint. The integrated electric and thermal model of the coupled coal-fired power generation-thermal storage system is used as a decision-making tool for the scheduling system to reasonably arrange the system operation planning after the configuration of thermal storage, which provides an operation planning strategy for the power system. The coupled coal-fired power generation-thermal storage technology utilizes the flexibility of thermal energy utilization of thermal storage technology to adjust the system heat supply in a timely manner according to fluctuations in external thermal load, effectively meeting the thermal demand at different times, increasing the peaking capacity of coal-fired generating units, achieving the purpose of enhancing the level of renewable energy consumption of the integrated system, shifting peaks and filling valleys, and building a new type of power supply system.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 5326K] - GAO Zhengping;TU Anqi;LI Tianxin;DUAN Lunbo;Inner Mongolia Power Research Institute Branch,Inner Monglia Power (Group) Co.,Ltd.;Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,Southeast University;
Under the background of global carbon emission reduction, the carbon-free fuel industry faces both great opportunities and challenges. Ammonia, as an alternative of fossil energy, has the advantages of mature industrial production technology, easy storage and transportation, and zero carbon emission, et al. The research and application of ammonia fuel is one of the promising pathway to improve China′s traditional energy structure and achieve carbon emission reduction target. However, there are still some remaining problems in ammonia combustion, such as unstable combustion, low laminar flame velocity and high NO_x emission. Therefore, the research on ammonia combustion technology is urgently needed. Combined with the recent achievements of ammonia combustion technology at home and abroad, the burning characteristic of the ammonia as a fuel and chemical reaction kinetics were reviewed. Specifically, the research progress of ammonia fuel in different applications including gas turbines, internal combustion engine, fuel cell and boiler were introduced. Compared with traditional fuels such as hydrogen and methane, the ammonia laminar flame velocity is low and the reaction activity is weak, which brings challenges to the optimization design of burner. For different mixing systems, the rich kinetic models of ammonia chemical reactions were established, laying the foundation for ammonia combustion applications. Pure ammonia combustion tests have been completed for ammonia-fueled gas turbines and combined with SCR devices, the lower NO_x emissions can be achieved, The combustion performance of ammonia in the combustor is further optimized by technologies such as mild combustion and liquid ammonia injection. The research results show that ammonia can be blended in internal combustion engines by mixing in a large proportion, and when the blending ratio is less than 60%,the lower emissions can be achieved. The feasibility of mixed combustion of 20% ammonia can be proved by the experiment of small proportion mixed combustion of ammonia and coal. The effect of different injection locations on emissions was explored. The problems of current ammonia combustion technology research were pointed out and the future development focus direction was prospected. It is pointed out that ammonia/hydrogen fuel system is the focus of future research, and in the field of gas turbine and internal combustion engine, technologies such as burner design, injection strategy optimization will greatly improve the combustion performance of ammonia, and ammonia/coal blending boiler experiments are urgently needed.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 7734K] - WANG Yikun;DENG Lei;WANG Tao;WANG Zhichao;LI Yang;JIA Zhaopeng;ZHOU Fei;Huaneng Yangtze Enviromental Technology Co.,Ltd.;State Key Laboratory of Multiphase Flow in Power Engineering,Xi′an Jiaotong University;Huanneng Laiwu Power Generation Co.,Ltd.;Xi′an Thermal Power Research Institute Co.,Ltd.;Xi′an TPRI Boiler & Environmental Protection Engineering Co.,Ltd.;
The carbon emission of units can be greatly reduced by the power generation of coal-fired units mixed with hydrogen rich fuel. It is expected to be an important way for coal-fired units to achieve carbon emission reduction in the future. A thermal calculation and analysis of 300 MW power plant were studied based on the energy conservation law. The influence of the unit′s mixed combustion mass ratio of 20%-100% NH_3 power generation on the coal-fired unit under different working conditions was analyzed through the boiler thermal check calculation. The results show that after coupling with 20%-100% NH_3,the theoretical combustion temperature decreases linearly, the flue gas temperature at he economizer exit reduces slightly, the temperature of exit flue gas rises, the boiler thermal efficiency decreases by 0.31-2.04 percent points, the attempering water consumption increases, and the original heating surface can meet the requirment of heat exchange. Through adding the specific burner, the NO_x emssion can achieve the same level as that of the original boiler, and the maximum annual emission reduction is about 1.12 million tons of CO_2. The induced draft fan needs to be expanded, which has little impact on the original air supply system, denitrification and desulfurization system. It may be necessary to adjust the low-temperature flue gas waste heat recovery system and investigate the wet electrostatic precipitator or other new system to reduce the aerosol emission.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 12807K] - NIU Tao;ZHANG Wenzhen;LIU Xin;HU Daocheng;WANG Tiankun;XIE Yan;WANG Heyang;Yantai Longyuan Power Technology Co.,Ltd.;China Energy Investment Co.,Ltd.;GD Power Development Co.,Ltd.;School of Mechanical Engineering,Tianjin University;
China is a country dominated by coal-fired power generation. In order to reduce the CO_2 emissions of coal-fired power plants, it is important to develop low-carbon alternative fuels and corresponding combustion technologies. Compared with hydrogen, ammonia has considerably lower storage and transportation costs, and is safer and more reliable. Thus, it is considered as a better energy carrier and carbon-free fuel. It is a more practical and feasible technical route to reduce CO_2 emission of coal-fired boilers at this stage by replacing part of pulverized coal with ammonia and cofiring coal with ammonia in the boiler. In order to examine the technical feasibility of ammonia cofiring in coal-fired boilers, the world′s largest 40 MW_(th) ammonia-coal cofiring test facility equipped with a full-scale ammonia-coal cofiring burner and ammonia supply system was designed and fabricated, and the cofiring tests of 0-25% ammonia cofiring ratios(calorific value) were conducted on this facility.The results show that the boiler can establish stable ignition and combustion at all ammonia cofiring ratios, and the char burnout of ammonia cofiring cases is better than that of pure coal combustion cases. With air-staging combustion, the boiler NO_x emission can be controlled lower than that of coal combustion case at high ammonia cofiring ratios. However, at overfire air rates higher than 20%,the further increase of overfire air rate has no significant effect on the NO_x emission, but significantly increase the boiler CO emission and the unburned carbon content in fly ash, and hence, reduce the boiler efficiency. Therefore, there is an optimal overfire air rate at which both the NO_x emission and char burnout can be kept at low level. The boiler excess O_2 level also has significant impacts on boiler NO_x and NH_3 emissions. With the decrease of excess O_2,the boiler NO_x emission decreases significantly, while the NH_3 emission increases rapidly. Thus, there is an optimal range of excess O_2 within which the boiler NO_x and NH_3 emissions can be both kept at low level. The industrial scale test in this paper verifies the feasibility of ammonia-coal cofiring technology in coal-fired boilers, reveals the key parameters that affect boiler NO_x emission and fuel burnout, and provides a promising technical advancement direction for the coal-fired power plants to achieve signification reduction of CO_2 emissions.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 12637K] - MA Lun;FANG Qingyan;ZHANG Cheng;CHEN Gang;WANG Xuebin;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;School of Energy and Power Engineering,Xi′an Jiaotong University;
As a hydrogen-rich carbon-free fuel,ammonia has the advantages of high energy density,low cost,and safe storage and transportation.Pulverized coal co-firing with ammonia can reduce CO_2emissions during coal combustion.Taking a 20 k W settling furnace (ammonia is injected from the high temperature zone of pulverized coal flame) as the research object,the coupled ammonia combustion characteristics and NO generation law of pulverized coal under deep air classification was carried out.By the numerical simulation,the effects of the ammonia co-firing ratio (0,10%,20%,30%),ammonia combustion zone excess air coefficient (1.08,0.96,0.84,0.72),and the ammonia injection location (0.5,0.6,0.7,1.0 m) on combustion characteristics and NO formation behavior in a 20 k W drop tube furnace with a deep-air staging condition (the ammonia is injected into the high temperature coal-flame zone) were investigated.The results show that compared with pure pulverized coal combustion,pulverized coal co-firing with ammonia increases the carbon content in fly ash and reduces NO emissions.The carbon content in fly ash increases and NO emissions decrease with the further increase of the ammonia co-firing ratio.Considering the combustion economy and NO emissions,the ammonia co-firing ratio with approximately 20%is more appropriate.When the excess air coefficient in the ammonia combustion region is more than 1,the excess of oxygen promotes the reaction of NH_3+O_2→NO+H_2O+0.5H_2,and amounts of NO are generated.When the excess air coefficient in the ammonia combustion region is less than 1,the incomplete-burning ammonia plays a reducing role,which is conducive to the reaction of NH_3+NO→N_2+H_2O+0.5H_2,and the formation of NO is inhibited effectively.Considering comprehensively,it is suggested that the excess air coefficient in the ammonia combustion region is maintained at approximately 0.96,which can not only meet the high-efficiency combustion of pulverized coal,but also effectively inhibit the formation of NO during the ammonia combustion process.The farther the ammonia injection location is from the pulverized coal flame zone,the higher the fly ash carbon content and NO concentration is.It is recommended that the ammonia injection location should be as close as possible to the pulverized coal combustion flame zone.
2022 03 v.28;No.139 [Abstract][OnlineView][HTML全文][Download 49338K] 下载本期数据