Characterization of the coal fly ash for the purpose of improvement of industrial on-line measurement of unburned carbon content

The influence of selected properties of fly ash on the measurements of an on-line analyser was described. Fly ash studied in the research originated from the pulverized coal fired boiler. The samples were taken using an inspection method within a period of 3 months. Systematic observation of the properties of the ash allowed monitoring of the work of the industrial analyzer during a relatively long period of the power plant work. Samples of coal fly ash were examined for their chemical and physical properties. Morphology was analysed by scanning electron microscopy. Unburned carbon content in fly ash was determined by using loss-on-ignition (LOI) and thermogravimetry analysis (TGA). The particle size distribution of fly ash was examined. Correlation between laboratory and on-line industrial measurements of the unburned carbon content of ash was discussed.     

Role of active sites in the steam activation of high unburned carbon fly ashes

Previous studies on carbon gasification have not included high unburned carbon content fly ashes, and therefore it remains unclear why not all fly ash carbon samples are equally suitable for activation. The concentration of active sites is well known to influence carbon gasification reactions. Therefore, the objective of this work was to investigate the effect of the concentration of active sites on the behavior of fly ash carbon samples upon steam activation. Six fly ash carbons were selected to produce activated carbons using steam at 850 °C. The concentration of active sites was determined by non-dispersive infrared analysis (NDIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). XRD analyses were also conducted to determine the crystallite size. It was observed that the concentration of active sites played a more significant effect on the surface areas of activated carbons in the carbon burn-off zone of >60%. Statistical analysis was used to relate the surface areas of activated carbon variances with carbon burn-off levels.     

回转窑煤粉浓度的测量方法

回转窑水泥厂一次风煤粉浓度测定的准确性对整个窑的标定与生产管理都有着相当重要的作用,而我们在测定中常因一次风的压力与温度影响造成较大的测量误差,根据行业中常用的测量方法提出个人的一些看法。     

燃煤式活性石灰回转窑耐火材料使用实践

燃煤式活性石灰回转窑在煅烧石灰的过程中经常出现结圈,在处理结圈的过程中由于温度的变化及结圈的脱落造成耐火材料的损坏,因此对耐火材料的强度及抗热震性提出了很高的要求,耐火材料选择是否合理关系到回转窑能否正常运转。     

回转窑下煤管喷射器合理尺寸的计算

本文结合工程实例介绍了回转窑下煤管喷射器合理尺寸的计算方法，且计算结果与实际运行参数符合，较之其它计算方法更具有实用性。     

浅析红土镍矿回转窑整体窑炉技术的施工与应用

回转窑内衬可用耐火砖砌筑,也可选用其它的耐火材料做内衬,但是近几年,随着施工方法的改进及耐火材料研发的突破,回转窑内衬开始选用整体窑炉技术。将回转窑内衬的材料选用及施工工艺相结合,此方法可以提高回转窑产能,减少热损失,取得了高效节能降耗的显著效果。     

宝钢活性石灰回转窑结圈机理研究

为了揭示宝钢石灰回转窑结圈机理,通过湿化学分析、X-射线衍射分析和扫描电子显微镜观察等手段分析了窑皮的化学组成、相组成和显微结构.高温模拟实验揭示:结圈形成条件是低熔物作为黏结相,煤燃烧后的灰分与氧化钙反应生成低熔点氧化物,这些低熔点氧化物黏结氧化钙,随着该过程进行,结圈物变厚.煤中灰分在高温下形成液相是燃煤石灰回转窑结圈的关键.     

Size distribution of unburned carbon in coal fly ash and its implications

A set of nine coal fly ashes, obtained from various US utilities, were fractionated by standard dry-sieving techniques. The carbon contents of the different size fractions were measured, and the nature of the carbon particles was microscopically examined. Significant differences were found in the distribution of carbon in class F and class C ashes. The ‘foam index’ test is commonly used for quick evaluation of the suitability, with respect to air entrainment, of pozzolanic additives for concrete. This test measures adsorption of air entraining admixtures (AEAs) by the carbon in the fly ash. Application of this test to the different ash fractions confirmed that the smallest particle size fractions of ash make the major contribution to AEA adsorption. The carbon from class F ash has a comparable capacity for AEA adsorption as carbon from class C ash, when compared on a surface area basis. What makes the class C carbons apparently ‘worse’ is the fact that they have much higher surface areas than class F carbons (and it is only by virtue of the low carbon mass in most class C ashes that problems with these ashes are not more common). The importance of accessibility of the surface is also clearly seen from these results.     

2014年度石灰回转窑技术发展报告

对2014年石灰回转窑发展状况进行分析,制定了大型石灰回转窑技术主要考核指标,阐述了石灰回转窑在2014年的新技术和当前存在的主要问题,并对2015年石灰回转窑发展的技术前景进行了展望。     

The influence of carbon particle type in fly ashes on mercury adsorption

Recent research has shown that certain fly ash materials produced in coal combustion for power generation have an affinity for the mercury compounds present in flue gases. However, the exact nature of Hg-fly ash interactions is still unknown and the different variables that influence mercury adsorption need to be identified. In this work the microscopic components of fly ashes derived from the combustion of different types of feed blends of different coal rank and mercury adsorption were investigated. The aim of this research was to establish relationships between Hg retention and the type of unburned carbons present in various fly ashes. The fly ashes and fly ash fractions studied were used as sorbent beds for high mercury concentrations, conditions in which mercury retention is highly favored. From the results obtained it was confirmed that the role of the unburned carbon components in mercury capture may depend, among other factors, on the type of unburned carbon. Fly ashes capture different species of mercury depending on their nature and the type of anisotropic particles.     

Characterization of unburned carbon present in coarse gasification ash

Depending on the mode of operation and quality of the feed material, discrete unburned carbon particles are evident in coarse gasification ash emanating from a commercial gasifier. Black, partially reacted carbon particles in the size range −13 + 4 mm were randomly hand picked from grab sample following a gasifier shutdown. These particles were classified into three major categories namely: unburned carbon, carbonaceous shale, and “shrinking core” particles. The unburned carbon particles were further macroscopically subdivided into remnant “coal” particles, solid carbon, layered carbon, and porous carbon. The unburned carbon particles were characterized using a petrographic analysis, reflectance analysis, chemical analysis, TGA mass loss curves, pore volume and surface area, and mineral characterization. The carbon particles were compared to the feed coal. The petrographic-based characterization technique as developed for the characterization of coarse unburned carbon particles indicated that remnant coal, devolatilised coal, highly porous isotropic carbon, dense anisotropic carbon, and variations in-between occurred in the coarse gasification ash sample.     

Fly ash and coal char reactivity from Thermo-gravimetric (TGA) experiments

The purpose of this research is to determine the reactivity of a sample of high carbon fly ash obtained from a circulating fluidized bed (CFB) gasification system and benchmark it against three other chars prepared at different pyrolysis temperatures in a laboratory drop tube furnace (DTF).Isothermal and non-isothermal thermo-gravimetric (TGA) experiments were used to determine sample reactivities. Structural analysis tests were carried out to establish the influence of the pore characteristics and Scanning Electron Microscope (SEM) pictures were taken for sample morphology. In-spite of high (BET) surface area and pore volume; reactivity parameters such as activation energy, kinetic rate coefficient, half life, burnout temperature and time proved the fly ash to be the least reactive. The low reactivity is associated with its carbon thermal deactivation. Non-isothermal tests also show the fly ash to be heterogeneous in composition. Of all the samples, the char prepared in the laboratory at the lowest pyrolysis temperature was the most reactive.     

回转窑内煤粉燃烧及气体分布的数值模拟研究

运用CFD数值模拟的方法 ,研究回转窑中煤粉燃烧及气体分布。冷态模拟结果显示窑内产生中心回流区、内回流区和外回流区;热态模拟,结合温度场对窑中各气体分布进行详尽的说明。     

石灰回转窑的技术特点及发展前景

回顾了2013年度石灰回转窑的建设情况以及回转窑的技术进步和技术特点,并重点介绍了1 000t·d-1回转窑焙烧系统。指出了回转窑存在的主要问题和解决办法。回转窑技术成熟、产品质量好、燃料适应能力强,今后的发展前景较好。     

High energy syngas production by waste tyres steam gasification in a rotary kiln pilot plant. Experimental and numerical investigations

This paper presents experimental and numerical results on steam gasification of waste tyres in a rotary kiln pilot plant. Both the process performance and the gas features have been evaluated varying the feeding ratio (FR), defined as the steam/tyres mass ratio. First, several experimental tests have been performed. Then, the obtained experimental results have been used to verify the consistency of a numerical model developed with the aid of the commercial code ChemCAD®. Once done, the effect of increasing the FR on the gas energy content has been evaluated.Numerical results showed that the gas energy content increases as the FR increases as well, achieving a maximum value for FR = 0.33 that produced a gas which composition N₂ free is (H₂ = 52.7%_vol, CO = 18.1%_vol, CO₂ = 7.0%_vol, CH₄ = 22.2%_vol) in correspondence of which the lower heating value (LHV) is equal to 29.5 MJ kg_gas⁻¹. Higher FR values do not produce a further increase of the gas energy content, rather require a greater amount of input energy for heating the steam from the atmospheric to the process temperature.     

Mixing large and small particles in a pilot scale rotary kiln

The mixing of solid alternative fuel particles in cement raw materials was studied experimentally by visual observation in a pilot scale rotary kiln. Fuel particles were placed on top of the raw material bed prior to the experiment. The percentage of particles visible above the bed as a function of time was evaluated with the bed predominantly in the rolling bed mode. Experiments were conducted to investigate the effects of fuel particle size and shape, fuel particle density, rotary kiln fill degree and rotational speed. Large fuel particles and low-density fuel particles appeared more on top of the bed than smaller particles and high-density fuel particles. Fuel particle dimensions and sphericity were important parameters for the percentage of visible particles. Increasing bed fill degree and/or increasing rotational speed decreased the percentage of particles visible on top of the bed.Results can be up-scaled to industrial conditions in cement rotary kilns and show that even relatively large fuel particles will predominantly be covered by raw material after less than 30 s in the rotary kiln. This affects the heating and combustion mechanisms for the fuel particles.     

国产耐火材料在新型干法水泥窑上的使用

介绍了新型干法水泥回转窑用内衬材质的选择原则、施工时应注意的事项及使用过程中所取得的一些经验体会。认为按实际情况不断调整生产工艺、强化工艺管理是回转窑耐火材料使用寿命明显提高的主要措施     

回转窑轴线、轮带直径测量仪的研制

从测量原理、系统组成、关键技术、实际应用等方面阐述了一种大型回转窑轴线测量系统，研制的测量系统具有结构简单、安装测量方便、精度高、可已忆存贮和通讯等特点。     

Characterization of unburned carbon from ash after bituminous coal and lignite combustion in CFBs

This paper deals with the characterisation of carbon (UC) from bottom ash (BA) and fly ash (FA) samples from two fluidised-bed power stations burning bituminous coal and lignite. The laboratory results for the carbon determinations and its mass balances are evaluated. Chemical and mineral analyses and textural characteristics (specific surface area and pore-size distribution) are presented. Depletion/enrichment of selected elements (S, Cl, V, Cr, Ni, Cu, Zn, As, Se, Sb, Hg, and Pb) in carbon from the bottom ash are compared with both ash compostions. The strong positive relationships between the concentrations of some trace element contents (Hg, Se, As, Cu, Ni, V and Cl) in fly ash with the content of carbon and the specific surface area of FA are presented and expressed by regression equations with very high correlation coefficients. Laser ablation-ICP-MS has been used to obtain an insight into element distributions within carbon grains from the bottom ash.