Research On Co-combustion Characteristics And Combustion System Optimization Of Large Proportion Pyrolysis Semi-coke Mixed With Bitumious Coal

As the main energy and industrial raw material,coal plays a very important role in energy system.Although the proportion of new energy in the energy system has increased recently,the pillar position and ballast role of coal will not change in a short term.At present,coal is still directly combustion for power generation and industrial heating,which produces a large amount of NOx and CO₂and leads to environmental problems such as acid rain and greenhouse effect.Pyrolysis of raw coal to produce oil and gas products,and the remaining solid semi coke is used for power generation.This graded utilization of coal technology is one of the important ways for clean and efficient utilization of energy in the future.Pyrolysis semicoke is not suitable for direct combustion because of its poor ignition and burnout characteristics,unstable combustion and large amount of NOx.The mixed combustion of pyrolysis semi coke and high volatile bituminous coal is a new combustion technology.The characteristics of easy ignition and burnout of bituminous coal can make up for the defect that pyrolysis semi coke is difficult to burn alone.The development of burner suitable for large-scale mixing of bituminous coal and pyrolysis semi coke is an important prerequisite for the realization of this technology.In this thesis,the technical route of gradually enlarging the experimental scale is adopted,and the small-scale test of the laboratory device is used to analyze the combustion characteristics and NOx emission characteristics of pyrolysis semi coke and bituminous coal.The experimental results are used to guide the design and development of the burner.The cold state test is used to study the concentration dilution separation and central reflux characteristics of the burner,and the combustion characteristics and pollutant emission characteristics of the burner are verified through the pilot test.Finally,the research results are applied to the300MW pulverized coal boiler,The application of large-scale blending of bituminous coal with pyrolytic semicoke in utility boilers will provide reference for the large-scale application of pyrolytic semicoke in the future,contribute to the realization of the grand goal of"double carbon"proposed by China,and promote the clean and efficient cascade utilization of coal.Thermogravimetric analyzer is used to analyze the basic characteristics of raw coal semi coke bended combustion.Shenmu raw coal pyrolysis semi coke and Shenhua bituminous coal are selected for mixed combustion.In addition,Wangqu lean coal,Wulagai lignite and Shenmu semi coke are selected for mixed combustion to analyze the influence of coal quality on mixed combustion characteristics.According to the thermogravimetric analysis and derivative thermogravimetric analysis curves in the experiment,the ignition,steady combustion,burnout characteristics under different operating conditions and the reaction kinetic parameters under low temperature conditions were obtained.The results show that the combustion characteristics of semi coke are similar to that of lean coal,and semi coke is more suitable for blending combustion with bituminous coal.Increasing the blending ratio of semi coke from 20%to 50%will lead to poor combustion characteristics,lower weight loss,higher ignition temperature and worse combustion stability.With the increase of the proportion of semi coke,the reaction activation energy of the mixed fuel gradually increases,and the change trend of frequency factor and activation energy is the same.The fitting relationship between the proportion of semi coke and the activation energy and frequency factor is obtained by analyzing the experimental data.A settling furnace was used to study the mixed combustion characteristics of pyrolytic semi coke and coke in the high temperature range of 1200℃-1400℃,and the reaction kinetic parameters at high temperature were obtained.The results of combustion experiments show that the mixing ratio of semi coke,oxygen concentration,reaction temperature and the content of fixed carbon in coke all affect the carbon conversion,and they also affect each other.The carbon conversion increased with the increase of oxygen content from 0.5%to 10%,and with the increase of reaction temperature from 1473K to 1673K.As the blending ratio of semi coke increases from 0 to 100%,the carbon conversion first increases and then decreases.NOx emission has the characteristics of synchronous change with the carbon conversion rate.When the blending ratio of semi coke is 30%,the carbon conversion rate and NOx emission reach the maximum.A reduction in the fixed carbon content of the fuel will result in a reduction in the NOx emission value.The concentration of reactive oxygen and the mixing of semi coke affect the nitrogen no conversion of coke.In the low oxygen range,when 0.5%<O₂<1%,the nitrogen no conversion rate of coke is higher than that of carbon,and the mixing proportion of semi coke has little effect on the nitrogen no conversion of coke.In the range of high oxygen content,when 5%<O₂<10%,the nitrogen no conversion rate of coke is lower than that of carbon,and the mixing proportion of semi coke has an obvious effect on the nitrogen no conversion of coke.With the increase of the proportion of semi coke,the activation energy first decreases and then increases.When the proportion of semi coke is 30%,the activation energy is the largest.With the increase of oxygen content,the activation energy decreased gradually.The frequency factor and the activation energy have a similar change law.In order to improve the mixing combustion characteristics of semi coke and bituminous coal,a central recirculation Dense dilute pulverized coal burner was developed by combining cold state test and numerical simulation.The results show that the burner has better concentration ratio characteristics when the 1-5 angles of concentrator blades are 23°,35°,35°,45°and 50°respectively.The arrangement of bluff bodies and combustion stabilizing teeth forms an obvious central recirculation zone at the nozzle to strengthen the initial ignition and combustion stabilizing characteristics of pulverized coal.The pilot scale test of Shenhua bituminous coal and semi coke blended combustion was carried out on a 10MW level tangential firing test-bed to explore the effects of semi coke blending ratio and burnout air rate on boiler efficiency and NOx emission,and to verify the comprehensive performance of the burner.The test results show that the furnace temperature decreases gradually along the furnace height direction.Increasing the burnout air rate will lead to a small decrease in the furnace temperature,and increasing the mixing ratio of semi coke will reduce the furnace temperature.The change of the burn out air rate has a significant impact on NOx emission.Increasing the burn out air rate will reduce the NOx emission level.Increasing the mixing ratio of semi coke has little effect on NOx emission,and the effect of burnout air rate needs to be comprehensively considered.The burner has good burnout characteristics and fuel adaptability.Under the conditions of different semi coke mixing ratio,the boiler combustion efficiency always maintains a high level.When the semi coke mixing ratio is 50%,the combustion efficiency is basically unchanged,and the NOx emission does not change significantly.In addition,the numerical simulation software is used to simulate the thermal test conditions.The simulation results have similar change rules with the test results,which verifies the accuracy of the test results.At the same time,there is a certain gap between the two,indicating that the influencing factors of the test conditions are more complex.Based on the results of pilot test,the burner of a 300MW subcritical pulverized coal boiler in a power plant was reformed,and the combustion test of large-scale mixed combustion of semi coke was carried out.The effects of semi coke mixing ratio,reaction oxygen content,peripheral air valve opening,sofa air rate,air distribution mode on combustion characteristics and NOx emission were studied.A large-scale mixed pyrolysis semi coke technology of bituminous coal suitable for industrial application was proposed.The test results show that the combustion performance of the central recirculation dense dilute pulverized coal burner is stable.Changing the operating parameters,the furnace temperature changes little,NOx emission fluctuates in a small range,and the boiler efficiency is always at a high level.When the proportion of mixed combustion of semi coke is increased to 50%,the boiler efficiency is basically unchanged,and the NOx emission does not increase significantly...