Experimental study on NOx emissions of pulverized bituminous coal combustion preheated by a circulating fluidized bed

This study investigated nitrogen oxide (NO_x) emissions of pulverized coal combustion preheated by a circulating fluidized bed (CFB). During the test process, high-temperature fuel preheated in a CFB was burned in a down-fired combustor (DFC). The effect of air distribution on NO_x emissions was studied in the DFC, including three types of secondary air nozzle structures, five secondary air ratios, and three tertiary air position arrangements. Under stable conditions, the conversion ratio of fuel-nitrogen to N₂ in the CFB was 41.4%, which resulted in lower NO_x emissions in the platform. In this study, secondary air could be injected into the combustor at the top (annular) or through the side wall (circular) of the DFC, both with high combustion efficiency. This means that the secondary air is completely separated from the burner, and burner structure is greatly simplified. NO_x emissions from secondary air nozzle structures of center, annular, and circular ports were 565.66, 345.45, and 220.38 mg/Nm³ (@6% O₂) respectively. NO_x emissions initially decreased then increased with increases in secondary air ratio with the annular nozzle structure. NO_x emissions could be further inhibited by rationally arranging tertiary air positions.     

Experimental investigation of NOx emissions during pulverized char combustion in oxygen-enriched air preheated with a circulating fluidized bed

An experimental investigation on NO_x emissions of pulverized char combustion in oxygen-enriched air was carried out in a new test system consisting of a circulating fluidized bed (CFB) and a down-fired combustor (DFC). In this paper, the pulverized char combustion characteristics and NO_x emission characteristics in the air conditions, the local oxygen-enriched air conditions in the CFB and the overall oxygen-enriched air conditions were studied. The results show that when the primary air oxygen concentration increased from 21.0% to 24.6% and to 28.2%, the ratio of fuel-nitrogen converted to nitrogen in the CFB increased from 39.7% to 45.0% and to 50.8%, respectively. This finding indicates that the preheating process in the CFB was one of the important reasons why the preheating combustion technology could significantly reduce NO_x emissions. Compared with the air combustion conditions, the NO emissions decreased to almost half of the original emissions when only the primary air oxygen concentration increased. On this basis, the NO emissions increased slightly when the air oxygen concentration was also increased in the DFC. Under these conditions, the variations in the char combustion efficiency were consistent with the variations in the temperature distribution. The feasibility and superiority of integrating the preheating combustion technology and oxygen-enriched air combustion technology are verified.     

大型循环流化床锅炉NO_x排放的研究

近年来循环流化床锅炉技术得到了迅速发展.基于由国内某锅炉厂生产并投运的大型循环流化床锅炉的实际运行及试验数据,对锅炉的NOx排放特性进行了分析和研究.分析了锅炉的NOx排放量与锅炉负荷,空预器进口氧量,上、下二次风配风量及配风方式,燃料特性及脱硫剂之间的关系.研究表明:锅炉运行过程中应合理调整燃烧工况,以优化运行,减少污染物排放.研究为电厂循环流化床锅炉的优化和调整运行参数提供借鉴和参考,从而实现锅炉NOx排放的环保达标.     

Experimental Study on an On—Line Measurement of High Temperature Circulating Ash Flux in a Circulating Fluidized Bed Boiler

A new kind of measuring method that may be used to measure high temperature circulating solid particles flux in a circulating fluidized bed boiler is studied in this paper. The measuring method is founded on the principle of thermal equilibrium. A series of cold tests and hot tests were carried to optimize the structure and collocation of water-cooling tubes and showed that the method had the advantage of simple, accurate, reliable and good applicability for on-line usage in a circulating fluidized bed boiler.     

循环流化床锅炉燃烧系统动态特性分析

根据循环流化床锅炉(CFBB)的工作特点以及燃烧系统输入和输出过程变量间的耦合关系,讨论了CFBB的蒸汽压力和床温的动态特性。认为引起蒸汽压力变动的主要原因在于燃料量(内扰)和汽轮机调门的变化(外扰);而影响床温变化的主要因素是给煤量、风量、物料循环量的变动,并从传热和燃烧过程分析了这些因素间的相互耦合关系。这对CFBB燃烧自动控制系统的设计与调试,以及整个控制系统的可靠运行都至关重要。     

褐煤在鼓泡流化床和循环流化床燃烧的汞迁移试验研究

对褐煤在小型电加热鼓泡流化床和小型电加热循环流化床中燃烧时的汞迁移特性进行了对比试验研究,重点考察了不同燃烧工况对汞迁移特性的影响。试验结果表明,炉膛温度和给煤量增加,鼓泡流化床和循环流化床的烟气总汞HgT均增加,飞灰颗粒汞含量Hg(p)均减少,并且循环流化床的烟气总汞HgT值均低于相同燃烧工况的鼓泡流化床值,循环流化床的飞灰颗粒汞含量Hg(p)值均高于相同燃烧工况的鼓泡流化床的值;流化风速增加,循环流化床的烟气总汞HgT减少,飞灰颗粒汞含量Hg(p)增加,鼓泡流化床烟气总汞HgT增加,飞灰颗粒汞含量Hg(p)减少。     

Experimental study on cotton stalk combustion in a circulating fluidized bed

This paper summarizes the results of an experimental study on cotton stalk (CS) combustion in a circulating fluidized bed. The mixing and fluidizing characteristics of binary mixture of CS with 10–100 mm in length and alumina bed material with a certain size distribution in a cold test facility were studied. The results show that CS by itself cannot fluidize, and adding inert bed material can improve the fluidization condition. CS can mix well with alumina at fluidization number N = 3–7. As N is more than 7, there will exist a little more segregation. The study concerning combustion characteristics of pure CS was performed on a circulating fluidized bed with a heat input of 0.5 MW. The effects of fluidizing velocity, secondary air flow and gas flow to the loop seal on the bed temperature profiles were investigated. Although there is a little more segregation at N higher than 7 in the cold tests, the hot experimental results indicate that slight segregation has little effect on the steady combustion of the dense region. In this study, the concentrations of major gaseous pollutants (CO, SO₂ and NO) in flue (stack) gas were measured.     

Characteristics of co-combustion of anthracite with bituminous coal in a 200-MWe circulating fluidized bed boiler

The effect of co-combustion of Vietnamese anthracite with Australian bituminous coal on the performance of a commercial circulating fluidized bed boiler was observed in the Tonghae thermal power plant.The temperature in the cyclone exit of the boiler increased slightly, which caused a decrease in the desulfurization efficiency as the co-combustion ratio of the bituminous coal increased from 40 to 100%. The unburned carbon fraction also increased. Consequently, the fine particles of the bituminous coal had lower combustion reactivity than those of the anthracite.NO_x emissions decreased as the bituminous coal ratio increased, although the fraction of nitrogen in the bituminous coal was higher than that in the anthracite. However, the emission of dust was found to increase due to an increase in the amount of CaO and MgO in the fly ash, which could lower the efficiency of the electrostatic precipitator.From these results, we concluded that the complete switch from the anthracite to Australian bituminous coal was possible, although the efficiency and the operation stability became lower than before. Additionally, as a future study, it is necessary to monitor the instability of the temperature increase and its effect on the prolonged clinker formation in the boiler.     

石油焦循环化床燃烧技术的应用

石油焦循环流化床燃烧是石油化工企业解决石油焦出路的主要途径。文章介绍了石油焦的燃烧特性和国内外纯浇石油焦循环流化床锅炉及其运行存在的问题，指出了石油焦循环流化床锅炉设计应重点研究的热力参数和关键技术，为石油焦循环流流化床燃烧技术的发展提出了一些合理化的建议。     

Numerical simulation on pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed

High temperature air combustion is a prospecting technology in energy saving and pollutants reduction. Numerical simulation on pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed was presented. The down-fired combustor, taken as the calculation domain, has the diameter of 220 mm and the height of 3000 mm. 2 cases with air staging combustion are simulated. Compared the simulation results with experimental data, there is a good agreement. It is found that the combustion model and NOx formation model are applicable to simulate the pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed. The results show that there is a uniform temperature profile along the axis of the down-fired combustor. The NOx emissions are lower than those of ordinary pulverized coal combustion, and the NOx emissions are 390 mg/m3 and 352 mg/m3 in Case 1 and Case 2, respectively. At the range of 300-600 mm below the nozzle, the NO concentration decreases, mainly resulting from some homogeneous reactions and heterogeneous reaction. NO concentration has a little increase at the position of 800 mm below the nozzle as the tertiary air supplied to the combustor at the position of 600 mm below the nozzle.     

循环流化床锅炉燃用无烟煤的运行分析

通过对循环流化床锅炉设计和运行时床温、给煤点位置、分离器形式、循环倍率及返料器等关键问题的分析，介绍了循环流化床锅炉如何调整才能适应无烟煤的燃烧。     

The simulation of influence of different coals on the circulating fluidized bed Boiler’s combustion performance

The combustion performance of the boiler largely depends on the coal type. Lots of experimental research shows that different fuels have different combustion characteristics. It is obvious that fuel will change the whole operating performance of Circulating Fluidized Bed Combustion (CFBC). We know even in a pilot-scale running boiler, the measurement of some parameters is difficult and costly. Therefore, we developed the way of simulation to evaluate the combustion performance of Chinese coals in CFB. The simulation results show that, different coals will result in different coal particle diameter and comminution depending on their mineral component and the change will affect the distribution of ash in CFBC system. In a word, the computational results are in accordance with experimental results qualitatively but there are some differences quantitatively.     

循环流化床锅炉设计方法探讨

阐述了目前国内外循环流化床锅炉的最新发展趋势 ,重点分析了循环流化床锅炉燃烧室和飞灰循环系统的设计 ,综合考虑了商用循环流化床锅炉的运行数据和前人的一些设计方法 ,在此基础上提出了作者认为合理的一套设计方案     

循环流化床锅炉的现状及发展

循环流化床燃烧技术是一种清洁煤燃烧技术,以这种燃烧技术设计的锅炉具有较好的可靠性、经济性和环保性。分析了循环流化床锅炉旋风分离器的形式和整体布置的发展与改进,指出第三代采用方形分离器、冷却型紧凑布置的循环床燃烧技术将成为将来的发展方向。     

循环流化床锅炉优点分析

循环流化床锅炉因具有燃料适应性广、负荷调节性强以及环保性能优良而日益得到人们的重视,并且是传统技术所无法实现的,正是由于这些技术优点,使循环流化床锅炉得以快速发展和广泛应用.     

Experimental Study and Modelling of Char Combustion under Fluidized Bed Conditions

INTRODUCTIONMailyexperimentshavebeendonetostudytheconversionbehaviorofdifferentcoalsundervariousreactorsandconditions.Someauthorshaveproposeddetailedmodelsfromobservedresults,orfromthealreticalaspects.Twotypemodelsaredevelopedtopredicttheconcelltrationprofilesforthegaseousspeciesaroundaburningcharparticled].In'single--film'models,thecarbonreactdirectlywithoxygentoformCOorCOb.In'double--film'modelsitisassumedthattheoxygendiffusingtowardsthepaxticleisconsumedbeforeitreachesthesuxface.Thep…     

RDF在流化床中燃烧生成NOx的试验研究

对2种N元素含量不同的RDF物料在流化床中燃烧的排放物NOx的生成量进行了研究。试验表明：RDF在流化床中能完全燃烧，能满足燃烧系统运行要求；炉膛内NOx的生成量与炉膛温度分布基本相同；在相同工况下，含N元素多的RDF产生的烟气中NOx浓度大；过量空气系数、二次风加入都能改变NOx生成量，且含N元素多的RDF受这2个因素的影响大一些，而含N元素少的RDF基本不受影响。     

Operation control of circulating fluidized bed boilers

The heat balance of different circulating fluidized bed boiler designs is investigated for variations in input parameters, such as specific flue-gas amount and ash content of the fuel. A simple model and a corresponding diagram are developed to describe the boiler behaviour when conditions deviate from the nominal ones. The model shows how the furnace temperature is influenced in different ways in different boiler designs by changes of furnace heat transfer and of the mass flow of particles and flue gases. The model results are verified by measurements in one type of boiler. Finally, it is shown how the desired stable furnace temperature and stable heat flux distribution are in conflict during variations of the input parameters. As a consequence, a two-dimensional boiler control strategy is suggested.     

Experimental study on Egyptian biomass combustion in circulating fluidized bed

The present study investigates the combustion of four kinds of biomass in a circulating fluidized bed. The combustion chamber is a steel cylinder with 145 mm inner diameter and 2 m height. Tests were conducted on wheat straw, sawdust-wood, cottonseed burs, and corncobs. Excess air was varied for each fuel. Temperature, heat flux and gas emissions were measured along the combustion chamber and at the chimney inlet. Results showed that sawdust-wood produces the highest values of CO emissions (about 3000 mg/Nm³). On the other hand, cottonseed burs produce the lowest values of CO emissions (about 250 mg/Nm³). The SO₂ emissions were very low in all tests (less than 20 mg/Nm³). The lowest emission value occurred at an excess air ratio (EA) of 1.24 except for cottonseed burs where it was 1.4.     

循环流化床掺渣锅炉运行技术

循环流化床锅炉作为一种高效、节能、低污染的环保锅炉 ,越来越被中小型化肥厂所接受和认可。但其影响燃烧的因素较多 ,尚处在不断完善之中。本文就WZ - 35 3.82 -M9型循环流化床锅炉掺烧炉渣的运行情况 ,在点火及各参数的调整方面作了一定的技术总结。