稻壳循环流化床燃烧特性研究

在一座循环流化床燃烧试验装置上进行了稻壳的燃烧试验.通过热重分析得到稻壳的着火特性.试验发现:稻壳在流化床燃烧中,飞灰含碳量较高,燃烧效率低于预期值.试验得到了二次风率、空气过剩系数、床温和一次风量等对飞灰含碳量的影响规律.结果表明,在空气过剩系数保持不变的条件下,随着二次风率的增加,飞灰含碳量呈下降趋势;随着空气过剩系数的增加,飞灰含碳量先减小后增大,存在一最佳值,使得飞灰含碳量最小;随着床温的增加,飞灰含碳量逐渐减小;随着一次风量的增加,飞灰含碳量呈上升趋势.     

稻壳内混式循环流化床燃烧试验研究

在循环流化床燃烧试验台上对稻壳的燃烧特性进行了冷热态试验研究,冷态试验确定了稻壳与河砂按一定比例掺混后的临界流化风速与单一稻壳的流化风速基本一致,且稻壳流化范围较窄.通过热态试验确定了适合稻壳燃烧的流化速度应为1～2.5 n/s,同时为提高稻壳燃尽效率应尽量提早给入一部分二次风.试验结果表明,一二次风比例为7∶3时可以...     

循环流化床锅炉原煤掺烧稻壳初探

通过对循环流化床锅炉在原煤中掺人部分稻壳燃烧的研究和试验，使得大量的稻壳得到合理利用，解决了稻壳污染环境的问题。     

循环流化床锅炉在原煤燃料中直接掺稻壳初探

我国东北水稻种植区由于大量水稻壳造成了环境污染,减少这种污染是重要的环保课题。本文介绍了在CFB中煤与稻壳的混合燃烧技术,并分析了这种技术所带来的经济效益。     

循环流化床净煤燃烧技术

本文概括了国内外循环流化床锅炉及循环流化床电站锅炉的发展状况，说明了循环流化床燃烧技术是减小低环境污染、提高燃烧效率的理想方法，并为今后的研究提出了几点建议。     

循环流化床燃烧技术及分析

循环流化床（ＣＦＢ）技术是一门新兴的发展极为迅速的洁净煤燃烧技术。本文从其燃烧特性及ＳＯ２和ＮＯｘ的排放特性出发,对一些基本原理进行了介绍和分析,在此基础上对当前世界上ＣＦＢ锅炉的主要的炉型以及我国ＣＦＢ锅炉发展现状进行了简要介绍。     

燃用稻壳流化床锅炉的燃烧特性研究

本文介绍了在热态流化床试验台上进行的燃用稻壳的试验结果。     

燃煤循环流化床锅炉改燃稻壳的试验研究

对一台燃煤循环流化床锅炉进行了改烧稻壳试验,试验结果表明循环流化床锅炉燃烧稻壳是成功的,能够减少排放,节约能源,保护环境,具有良好的社会和经济效益,推广应用前景广阔.     

循环流化床锅炉燃烧技术在工业锅炉改造中的应用

本文介绍了循环流化床燃烧技术的发展与特点以及在工业锅炉改造中的应用,并结合典型实例进行介绍,对中小型锅炉改造具有一定的指导意义。     

Assessment of the rice husk lean-combustion in a bubbling fluidized bed for the production of amorphous silica-rich ash

Rice husk lean-combustion in a bubbling and atmospheric fluidized bed reactor (FBR) of 0.3 m diameter with expansion to 0.4 m in the freeboard zone and 3 m height was investigated. Experiment design - response surface methodology (RSM) - is used to evaluate both excess air and normal fluidizing velocity influence (independent and controllable variables), in the combustion efficiency (carbon transformation), bed and freeboard temperature and silica content in the ashes. Hot gases emissions (CO₂, CO and NO_x), crystallographic structure and morphology of the ash are also shown. A cold fluidization study is also presented. The values implemented in the equipment operation, excess air in the range of 40-125% and normal fluidization velocities (0.13-0.15 Nm/s) show that the values near the lower limit, encourage bed temperatures around 750 °C with higher carbon transformation efficiencies around 98%. However, this condition deteriorated the amorphous potential of silica present in the ash. An opposite behavior was evidenced at the upper limit of the excess air. This thermochemical process in this type of reactor shows the technical feasibility to valorize RH producing hot gases and an amorphous siliceous raw material.     

Overview of combustion and gasification of rice husk in fluidized bed reactors

Rice is cultivated in more than 75 countries in the world. The rice husk is the outer cover of the rice and on average it accounts for 20% of the paddy produced, on weight basis. The worldwide annual husk output is about 80 million tonnes with an annual energy potential of 1.2 × 10⁹ GJ corresponding to a heating value of 15 MJ/kg. India alone generates about 22 million tonnes of rice husk per year. If an efficient method is available, the husk can be converted to a useful form of energy to meet the thermal and mechanical energy requirements of the rice mills themselves. This paper provides an overview of previous works on combustion and gasification of rice husk in atmospheric bubbling fluidized bed reactors and summarizes the state of the art knowledge. As the high ash content, low bulk density, poor flow characteristics and low ash melting point makes the other types of reactors like grate furnaces and downdraft gasifiers either inefficient or unsuitable for rice husk conversion to energy, the fluidized bed reactor seems to be the promising choice. The overview shows that the reported results are from only small bench or lab scale units. Although a combustion efficiency of about 80% can normally be attained; the reported values in the literature, which are more than 95%, seem to be in higher order. Combustion intensity of about 530 kg/h/m² is reported. It is also technically feasible to gasify rice husk in a fluidized bed reactor to yield combustible producer gas, even with sufficient heating value for application in internal combustion engines. A combustible gas with heating value of 4-6 MJ/Nm³ at a rate of 2.8-4.6 MW_th/m² seems to be possible. Only very little information is available on the pollutant emissions in combustion and tar emissions from gasification. The major conclusion is that the results reported in the literature are limited and vary widely, emphasizing the need for further research to establish suitable and optimum operating conditions for commercial implementations.     

Transformation characteristics of Na and K in high alkali residual carbon during circulating fluidized bed combustion

In this study, the transformation characteristics of sodium (Na) and potassium (K) during combustion of Zhundong coal gasification fly ash in circulating fluidized bed (CFB) reactors were investigated by examining gasification fly ash (TCf) from a 0.1-MW CFB test system. Experimental results indicated that TCf was rich in Na and K, with water-soluble and insoluble Na the main Na forms. Insoluble K was the major K form in TCf, accounting for 70.6% of total K. Reactor bed temperature exerted important effects on Na release during combustion such that, as bed temperature increased, the proportions of Na in bottom and circulating ash decreased while the Na in fly ash increased. Hydrochloric acid-soluble and insoluble Na in ash accounted for a large fraction of total Na. However, insoluble K was the principle K form in ash and bed temperature showed little influence on K release and distribution in ash during combustion. With decreased flue gas temperature, the Na content in deposition ash initially increased, then decreased, and eventually stabilized, while the K content in deposition ash was basically unchanged. Agglomeration of ash particles occurred during combustion, being more apparent at higher gas temperatures, and the agglomerates were rich in Na, K, sulfur (S), chlorine (Cl), and calcium (Ca). Deposition ash Na was mainly contained NaCl and Ca/Na sulfates. The enrichment of these salts as well as of Ca sulfate in ash was the main cause of ash agglomeration and deposition.     

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     

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.     

The effect of oyster shell powder and rice husk ash on the pyrolysis of rice husk for bio-oil

The aim of this study was to investigate the effect of oyster shell powder (OSP) and rice husk ash (RHA) on the pyrolysis of rice husk (RH) for bio-oil. The present study focuses on the effect of catalysts on pyrolysis of RH for bio-oil and the quantity of bio-oil produced. The results showed that both OSP and RHA could improve the yield and quality of bio-oil, and the catalytic effect of OSP was better than that of RHA. With the content of the two catalysts increased, the net increase range of bio-oil yield decreased gradually. With 3 wt.% of OSP or 2 wt.% of RHA, the yield of bio-oil achieved to 57.06% and 56.07% respectively, which increased by 6.03% and 4.20% compared to that of single pyrolysis of rice husk. Both OSP and RHA can increase the bio-oil heating value and decrease the acid value. With the presence of 1–5 wt.% of OSP or RHA in the RH pyrolysis process, the heating value of the bio-oil can be increased by 5.04–10.25% and 4.32–5.78%, the acid value of the bio-oil can be decreased by 5.30–13.54% and 9.81–33.01%, respectively. OSP was better than RHA on the heating value improvement, while RHA was superior to OSP in decreasing the acid value. The gas chromatography/mass spectrometry (GC-MS) analysis of bio-oil composition indicated that the formation of phenols, acids and ketones compounds were inhibited and alcohols and furan compounds were promoted with the addition of OSP and RHA catalysts. The study made the catalytic pyrolysis process more favorable for the production of high heating value fuel.     

Thermodynamic analysis of hydrogen rich synthetic gas generation from fluidized bed gasification of rice husk

In the present work, the generation of hydrogen rich synthetic gas from fluidized bed steam gasification of rice husk has been studied. An equilibrium model based on equilibrium constant and material balance has been developed to predict the gas compositions. The equilibrium gas compositions are compared with the experimental data of the present group as well as of available literature. The energy and exergy analysis of the process have been carried out by varying steam to biomass ratio (ψ) within the range between 0.1-1.5 and gasification temperature from 600 °C to 900 °C. It is observed that both the energy and exergy efficiencies are maximum at the CBP (carbon boundary point) though the hydrogen production increases beyond the CBP. The HHV (higher heating value) and the external energy input both continuously increase with ψ. However, the hydrogen production initially increases with increase in temperature up to 800 °C and then becomes nearly asymptotic. The HHV decreases rapidly with increase in temperature and energy input increases. Therefore, gasification in lower temperature region is observed to be economical in terms of a trade off between external energy input and HHV of the product gas.     

Effect of rice husk co-combustion with coal on gaseous emissions and combustion efficiency

Investigation on co-combustion of Lakhra coal and rice husk blends was carried out in a drop tube furnace to measure its impact on flue gas emissions and carbon burnout. According to experimental results, the emissions of NO and SO₂ were higher in case of combustion of Lakhra coal compared to coal?–rice husk blends combustion. The emissions of CO decreased rapidly at higher furnace temperatures beyond 900°C. Minimum of CO emissions were nearly 45 ppm while SO₂ and NO emissions were found to be 554 and 120 ppm, respectively, for 15% biomass blending ratio and at exit furnace temperature of 1000°C. The unburnt carbon was found to be reduced significantly with an increase in furnace temperature and blending ratio. The study has shown that blending of rice husk would be a useful option to minimize SO₂ and NO emissions during combustion of Lakhra coal.     

Sulfation phenomena in fluidized bed combustion systems

Fluidized bed combustors (FBCs) are noted for their ability to capture SO₂ in situ via direct reaction with Ca-based sorbents. However, despite more than 30 years of intensive study of sulfation processes in atmospheric FBC boilers and numerous laboratory studies, there are still many uncertainties and disagreements on the subject. In particular, the mechanisms of the sulfation reaction are still not properly understood, and there is dispute over the explanation of the well-known temperature maximum for optimum sulfur capture found in FBC boilers. This paper discusses these points of contention and suggests the most probable mechanisms and explanations for the various phenomena seen with sulfur capture, based on current literature and personal experimentation.