以TG-FTIR分析煤与油棕榈空果串富氧混烧特性

棕榈空果串(EFB)作为一种生物质废料,如能将其回收利用作为锅炉燃料将具有极大潜力。本研究利用TG-FTIR分析Adaro煤与生质料EFB在富氧混烧工况下的特性。热重分析仪记录样品在加热过程中的重量损失,而FTIR则分析其释放的气体产物。该实验将Adaro coal+30%EFB样品在18%O₂/82%CO₂、Air(21%O₂/79%N₂)、21%O₂/79%CO₂、30%O₂/70%CO₂四种工况下进行燃烧。每组实验均是以升温速率10°C/min从40°C加热到900°C。TG热重分析表明与O₂/N₂工况相比,O₂/CO₂条件下CO₂气体对燃烧有抑制作用,且富氧燃烧工况下氧浓度越高,燃烧特性越好。FTIR分析释放的气体主要是CO₂,CO和H₂O。实验最后也使用了SEM和EDS进行残留固体分析。     

O_2/CO_2和O_2/N_2气氛下煤粉燃烧的着火性能和NO_x排放特性

采用Fluent软件模拟煤粉在O_2/CO_2、O_2/N_2气氛下的燃烧情况,对比2种气氛下煤粉的着火性能及NO_x的排放特性,并模拟O_2/CO_2气氛下氧气含量对不同粒径(18,79μm)煤粉燃烧情况的影响,重点研究煤粉燃烧的着火距离。结果表明:氧气含量相同时,与O_2/N_2气氛相比,O_2/CO_2气氛下18μm煤粉(超细煤粉)的着火距离较大,79μm煤粉的着火距离较小;在O_2/CO_2气氛下,随着氧气含量的增加,2种粒径的煤粉着火距离都减小,且当氧气含量较低时,着火距离随氧气含量变化较大,NO的析出及其峰值位置提前。     

流化床O_2/CO_2气氛对烟煤焦反应速率的影响研究

流化床O_2/CO_2燃烧是实现煤炭清洁利用及近零碳排放的有效技术之一.为进一步探究工业流化床O_2/CO_2燃烧条件下的煤颗粒燃烧机制,本研究在小型流化床试验台上,通过在线测量流化床出口烟气中O_2和CO的浓度,深入考察了O_2/CO_2取代O_2/N2后,不同的床层温度(800~900℃)、O_2浓度(4%~10%)及颗粒粒径(2~8 mm)下的烟煤焦燃烧特性.实验结果表明:O_2/CO_2气氛下,煤焦反应速率随床层温度的升高、O_2浓度的升高和颗粒粒径的降低而增加;煤焦燃烧反应由O_2扩散控制,气化反应由反应动力学控制;相较于O_2/N2气氛,低床温下,O_2/CO_2气氛下的O_2扩散速率降低是煤焦反应速率改变的主要原因;高床温下,除O_2/CO_2气氛下O_2的扩散速率降低外,煤焦气化反应对煤焦反应速率的影响同样不可忽略.     

柴油在O2/CO2环境下的燃烧特性分析

为了降低柴油机NO_x和碳烟(soot)的排放,对基于O_2/CO_2环境的柴油机燃烧新模式进行了研究,运用KIVA-3V软件对柴油在定容燃烧弹内模拟发动机上止点的燃烧过程进行了数值仿真,对定容燃烧弹内柴油燃烧压力曲线进行了数值模拟分析,最后在定容燃烧弹上对正常空气环境下和O_2/CO_2浓度为50%/50%环境下的柴油燃烧过程进行了可视化研究.仿真结果表明,柴油在O_2/CO_2环境下的着火延迟时间相比在正常空气环境下要有所缩短;随着喷油压力的增高,柴油的雾化混合效果变好,燃烧更加充分,使得容弹内柴油的最大燃烧压力升高.定容燃烧弹可视化试验表明,柴油在O_2/CO_2环境下可以进行预混合自燃及扩散燃烧,同时得到的理想"瓢"型火焰图像表明柴油在O_2/CO_2环境下可以稳定燃烧.     

典型建筑木材的燃烧特性分析

基于典型建筑木材的元素分析、工业分析和组分分析,利用锥形热量仪开展了燃烧特性试验,分析了四种木材的燃烧特性。在较低辐射温度下(564°C),水曲柳因较高的水分含量和较低的木质素含量使原料表面的实际温度低于辐射温度,促进了焦炭的形成,使着火时间延迟为770s;随着辐射温度增加至782°C,原料表面温度达到了纤维素的热裂解温度,水曲柳在260s后开始热解形成大量挥发分,并迅速燃烧释放热量,获得了最大的热释放速率(442.5k W/m~2)。松木、樟木和杉木的着火时间和热释放速率相近,但都明显小于水曲柳,小分子气体CO和CO_2的析出也比较平缓;随着辐射温度的增加着火时间缩短,热释放速率增加,燃烧进行得更充分,但燃烧强度仍弱于水曲柳。     

低碳经济下电厂O2/CO2煤粉燃烧技术的应用

电厂O_2/CO_2煤粉燃烧技术是一种新型的煤粉燃烧技术,它采用纯氧和再循环烟气代替空气组织煤粉的燃烧,也被称作富氧燃烧技术或氧气/烟气再循环技术。本文介绍了O_2/CO_2燃烧技术国内外发展现状;阐述了电厂O_2/CO_2煤粉燃烧技术的特点,并以某电厂600MW亚临界四角切圆一次中间再热控制循环汽包炉对其特点进行了计算分析。研究表明:电厂O_2/CO_2煤粉燃烧技术是一种经济、高效、节能、环保的燃烧技术,正处于试验研究阶段。在低碳经济下,电厂O_2/CO_2煤粉燃烧技术的应用有利于推进国家节能减排目标的实现,符合建设资源节约型、环境友好型社会的要求。     

不同褐煤在O_2/CO_2条件下燃烧特性的实验研究

利用热重分析仪,系统地研究了霍林河褐煤、印尼1#褐煤和印尼2#褐煤在空气和O2/CO2条件下的燃烧特性,比较了不同褐煤样品在燃烧过程中失重与温度和时间的关系.实验结果表明,褐煤在O2/CO2条件下的燃烧特性与空气条件下的燃烧特性存在明显的区别,富氧燃烧条件下CO2分压力的大小影响褐煤的反应活性.     

N_2和CO_2对煤燃烧全过程灭火效能的对比研究

为掌握N_2和CO_2防治煤燃烧全过程的不同效果,采用自主研制的煤自燃氧化程序升温和煤明火燃烧实验装置,分别对平煤八矿煤样进行了通入相同流量N_2和CO_2抑制煤低温氧化过程和熄灭煤明火燃烧过程实验,测定了煤低温氧化阶段的耗氧速率、CO和CH_4产生率、煤有焰燃烧阶段的温度场温度、标志性气体(O2,CO和CH_4)组分和热释放速率的变化规律.结果表明:相比于煤在纯空气条件下的燃烧,在煤低温氧化阶段,通入CO_2时煤的耗氧速率、CO和CH_4产生率比通入N_2时更低;在煤有焰燃烧阶段,通入CO_2时煤温上升速度、耗氧量、热释放速率以及CO和CH_4产生量的下降速度比通入N_2时更低;在煤阴燃熄灭阶段,通入CO_2时煤温、CO和CH_4产生量下降速度比通入N_2时的更高,而通入CO_2时的耗氧量和热释放速率比通入N_2时的更低,说明CO_2比N_2具有更好的防治煤燃烧全过程的能力.     

二氧化碳在盐碱水中溶解及溢出的实验研究

实验室条件下,将空气、体积分数1%CO_2、5%CO_2、100%CO_2分别通入实验室制备盐碱土-水混合样(#1)、现场取样盐碱水(#2)、黄河水(#3)3种样品中,考察了不同样品中pH值的变化以及不同温度下CO_2的溢出速率。研究结果表明:#1通入100%CO_2,pH值降低到6.62后变化速率趋于平缓,有效地中和土壤碱性同时避免了因通入CO_2而带来的土壤酸化问题,CO_2的溢出速率随着温度的增加而加快,24h后基本达到平衡,pH值不再上升;#2和#3通入100%CO_2后pH值分别降低到5.51和5.43,当温度达到40℃时,20h后CO_2基本全部溢出,样品呈中性,并随着温度的升高,CO_2溢出速率加快。本实验为实际利用烟气CO_2精准释控改造盐碱地提供了基础数据。     

富氧条件下煤燃烧特性的热重分析实验研究

为研究氧气浓度变化对煤燃烧特性的影响规律,利用热重分析对4种煤样在不同氧气体积浓度(21%、30%、40%、70%、100%)条件下的燃烧特性进行实验研究,根据实验结果分析氧气浓度对不同煤样燃烧动力学参数的影响.结果表明:随着氧气浓度的增大,煤样的着火温度及燃烬温度均呈下降趋势,且燃烬温度相对于着火温度下降得更快,煤粉...     

Combustion characteristics and synergy behaviors of biomass and coal blending in oxy-fuel conditions: A single particle co-combustion method

Co-combustion biomass and coal can effectively reduce the emission of CO₂. O₂/H₂O combustion is regarded as the next generation of oxy-fuel combustion technology. By co-combustion biomass and coal under oxy-fuel condition, the emission of CO₂ can be minimized. This work investigates the co-combustion characteristics of single particles from pine sawdust (PS) and bituminous coal (BC) in O₂/N₂, O₂/CO₂ and O₂/H₂O atmospheres at different O² mole fractions (21%, 30% and 40%). The experiments were carried out in a drop tube furnace (DTF), and a high speed camera was used to record the combustion process of fuel particles. The combustion temperature was measured by a two-color method. The experiments in O₂/N₂ atmosphere indicate that the particles from pine sawdust and bituminous coal all ignite homogeneously. After replacing H₂O for N₂, the combustion temperature of volatiles of blended fuel particles decreases, while the combustion temperature of char increases. The ignition delay time in O₂/H₂O atmosphere is shorter than that in O₂/N₂ or O₂/CO₂ atmosphere. The combustion temperature of volatiles of blended fuel particles increases as the mass fraction of bituminous coal increases, while the combustion temperature of char of blended fuel particles is higher than that of biomass or bituminous coal. The ignition delay time of blended fuel particles increases with the increasing mass fraction of bituminous coal, and the experimental ignition delay time of blend fuel particles is shorter than the theoretical one. These reveal a synergy during co-combustion process of pine sawdust and bituminous coal.     

Influence of organic and inorganic properties of coal-shale on spontaneous combustion liability

Coal and coal-shale undergo low-temperature oxidation when exposed to air, potentially leading to spontaneous combustion. Coal-shale found in association with coal seams vary considerably in their intrinsic properties and spontaneous combustion liability index. Fourteen coal-shale samples collected from four different coal mines in Witbank Coalfield, South Africa, were experimentally investigated. The influence of coal-shale intrinsic properties and spontaneous combustion liability indices (determined by the Wits-Ehac Index and the Wits-CT Index) were established. The liability indices indicate relationships with the intrinsic factors and thus, identifying the major intrinsic factors affecting liability toward spontaneous combustion in these coal-shale samples. The XRF analysis indicated that the coal-shale samples are rich in SiO₂, Al₂O₃ and Fe₂O₃, while the XRD showed that same coal-shale samples are generally dominated with kaolinite and quartz. The coal-shale occurred in association with medium Rank C bituminous coal and contained varying proportion of macerals. The Wits-Ehac Index was unable to reliably determine liability indices of some coal-shale samples, and hence the Wits-CT Index was developed. The results obtained from the characterisation tests may be used as a tool to predict the spontaneous combustion liability in carbonaceous material and may serve as a reference when comparing coal-shale from different coal mines.     

Chemical looping combustion of coal in interconnected fluidized beds

Chemical looping combustion is the indirect combustion by use of oxygen carrier. It can be used for CO2 capture in power generating processes. In this paper, chemical looping combustion of coal in interconnected fluidized beds with inherent separation of CO2 is proposed. It consists of a high velocity fluidized bed as an air reactor in which oxygen carrier is oxidized, a cyclone, and a bubbling fluidized bed as a fuel reactor in which oxygen carrier is reduced by direct and indirect reactions with coal. The air reactor is connected to the fuel reactor through the cyclone. To raise the high carbon conversion efficiency and separate oxygen carrier particle from ash, coal slurry instead of coal particle is introduced into the bottom of the bubbling fluidized bed. Coal gasification and the reduction of oxygen carrier with the water gas take place simultaneously in the fuel reactor. The flue gas from the fuel reactor is CO2 and water. Almost pure CO2 could be obtained after the con- densation of water. The reduced oxygen carrier is then returned back to the air reactor, where it is oxidized with air. Thermodyanmics analysis indicates that NiO/Ni oxygen carrier is the optimal one for chemical looping combustion of coal. Simulation of the processes for chemical looping combustion of coal, including coal gasification and reduction of oxygen carrier, is carried out with Aspen Plus software. The effects of air reactor temperature, fuel reactor temperature, and ratio of water to coal on the composition of fuel gas, recirculation of oxygen carrier par- ticles, etc., are discussed. Some useful results are achieved. The suitable tem- perature of air reactor should be between 1050―1150℃and the optimal temperature of the fuel reactor be between 900―950℃.     

Temperature dependence on reaction of CaCO3 and SO2 in O2/CO2 coal combustion

The temperature dependence on the reaction of desulfurization reagent CaCO₃ and SO₂ in O₂/CO₂ coal combustion was investigated by thermogravimetric analysis, X-ray diffraction measurement and pore structure analysis. The results show that the conversion of the reaction of CaCO₃ and SO₂ in air is higher at 500–1 100 °C and lower at 1 200 °C compared with that in O₂/CO₂ atmosphere. The conversion can be increased by increasing the concentration of SO₂, which causes the inhibition of CaSO₄ decomposition and shifting of the reaction equilibrium toward the products. XRD analysis of the product shows that the reaction mechanism of CaCO₃ and SO₂ differs with temperature in O₂/CO₂ atmosphere, i.e. CaCO₃ directly reacts with SO₂ at 500 °C and CaO from CaCO₃ decomposition reacts with SO₂ at 1 000 °C. The pore analysis of the products indicates that the maximum specific surface area of the products accounts for the highest conversion at 1 100 °C in O₂/CO₂ atmosphere. The results reveal that the effect of the atmosphere on the conversion is temperature dependence.     

Greenhouse gas emissions from shallow uncovered coal seams

This study discusses a method of quantifying emissions from surface coal mining that has been trialled in Australia. The method is based on direct measurement of surface emissions from uncovered coal seams in mine pits, concurrent measurement of residual gas content of blasted coal in mine pits, and measurement of pre-mining gas content of the same seam from cores retrieved from exploration boreholes drilled away from active mining. The results from one of the mines studied are presented in this paper. In this mine, the pre-mining gas content of the target seam was measured using cores from an exploration borehole away from active mining. Gas content varied from 0.7 to 0.8 m³/t and gas composition varied from 16% to 21% CH₄ (84–79% CO₂). In-pit measurements included seam surface emissions and residual gas content of blasted and ripped coal. Residual gas content varied from 0.09 to 0.15 m³/t, less than twofold across the mine pit. Composition of the residual gas was in general 90% CO₂ and 10% CH₄, with slight variation between samples. Coal seam surface emissions varied from 1.03 to 7.50 mL of CO₂-e per minute and per square meter of the coal seam surface, a sevenfold variation across the mine pit.     

An experimental study of the effect of ionic liquids on the low temperature oxidation of coal

Fourier transform infrared spectroscopy (FTIR) and constant heating rate experiments were performed to study the low temperature oxidation of coal treated by an ionic liquid, 1-allyl-3-methylimidazolium chloride. The inerting effect of the ionic liquid toward the low temperature oxidation process is discussed. The results show that: (1) The hydroxyl content associated with hydrogen bonds, the aliphatic methyl content, the methylene group content, and the ether oxygen bond content are reduced in the treated coal. At the same time the content of aromatic CC bonds is constant but these chemical bonds weaken and some substituted aromatic hydrocarbon content increases while other types decrease. This demonstrates that (AMIm)Cl dissolves and destroys the coal surface microstructure; (2) The oxygen consumption of the treated coal is less than what is seen in raw coal. The CO, CO₂, C₂H₄, and C₂H₆ content from the treated coal is reduced compared to the untreated coal; (3) The apparent activation energy for the oxidizing reaction is different in the treated and raw coals. Micro-structural changes and macroscopic gas production allow us to conclude that (AMIm)Cl can effectively inhibit low temperature oxidation of coal.     

Spontaneous combustion influenced by surface methane drainage and its prediction by rescaled range analysis

This study established numerical modeling using COMSOLTMto examine the influence of horizontal location and drainage ability of surface borehole on spontaneous combustion in longwall working face gob. Rescaled Range Analysis(R/S analysis) was employed to investigate the chaos characteristic of N_2/O_2 ratio from a surface borehole in 10416 working face gob, Yangliu Colliery, China. The simulation results show that there is always a circular ‘‘dissipation zone" around the drainage borehole and an elliptic ‘‘spontaneous combustion zone" in deep gob. Little influence was found on spontaneous combustion zone on the intake side of the gob but the width of spontaneous combustion zone in middle gob is enlarged, while the depth of spontaneous combustion zone near the return side is reduced. The R/S analysis indicates that the influence of surface borehole on spontaneous combustion can be divided into two stages by the chaos feature of N_2/O_2: safety drainage stage and spontaneous combustion initiating stage. It can be concluded that the methane drainage from gob through surface borehole can intervene in the distribution of spontaneous combustion zone in gob and the chaos feature of N_2/O_2 from surface borehole can effectively reflect coal spontaneous combustion condition in gob.     

Effect of CO2 on coal P-wave velocity under triaxial stress

As P-wave velocity is sensitive to the variations in coal reservoir parameters, it is possible to monitor the injected CO₂ through P-wave velocity during CO₂ sequestration in coal. However, the effects of CO₂ on the coal P-wave velocity under triaxial stress are not clearly discerned. In the present study, different boundary conditions and gases were utilised to investigate the factors affecting the P-wave velocity after the interaction of coal with CO₂. Experiments with helium indicated that the pore pressure primarily affected the P-wave velocity by altering the effective stress. Experiments with CH₄ and CO₂ indicated that matrix swelling induced-cleats porosity decline significantly promoted P-wave velocity. Moreover, CO₂ caused a wider scale and severe weakening of coal matrix than CH₄, thereby significantly decreasing the P-wave velocity, and the decline in P-wave velocity increases with vitrinite content. Furthermore, experiments under different boundary conditions showed that with the boundary condition having more constraints, the decrement of pore pressure on P-wave velocity is more weaken, whereas the improvement of matrix swelling on P-wave velocity is more evident. This study contributes to understanding the mechanism of effect of CO₂ on P-wave velocity under triaxial stress condition and provides guidance for monitoring CO₂ sequestration in coal.     

CO2–H2O–coal interaction of CO2 storage in coal beds

In order to study the physical and chemical reaction after CO₂ injected into coal beds at different condition. The physical and chemistry reaction among CO₂, H₂O and coal was studied, and the influence on permeability and porosity of coal beds was carried out. The experimental method was used, so did the basic theory of mineralogy, coal petrology, geochemistry, analytical geochemistry and physical chemistry. In this experiment, the changes of mineral and permeability of coal and water quality were observed through CO₂ solution reacting with different coal samples. The differences could be found out by comparing the properties and microcrystalline structure before and after the reaction. There are three results were carried out: First, the content of carbonate in coal beds decreases because of the dissolution reaction between carbonate minerals and CO₂ solution, and precipitation is formed by reaction of chlorite and orthoclase. Second, the result that permeability and porosity of coal beds are improved after the reaction is proposed. Third, the initial permeability of different coal samples plays a great role on the reaction, and the improvement of permeability is not obvious in the samples which have too low or too high permeability, and the improvement is good in medium permeability (0.2–3 mD).     

Component fractionation of temporal evolution in adsorption–desorption for binary gas mixtures on coals from Haishiwan Coal Mine

Adsorption–desorption experiments on CO₂–CH₄ gas mixtures with varying compositions have been conducted to study the fractionation characteristics of CO₂–CH₄ on Haishiwan coal samples. These were carried out at constant temperature but different equilibrium pressure conditions. Based on these experimental results, the temporal evolution of component fractionation in the field was investigated. The results show that the CO₂ concentration in the adsorbed phase is always greater than that in the original gas mixture during the desorption process, while CH₄ shows the opposite characteristics. This has confirmed that CO₂, with a greater adsorption ability has a predominant position in the competition with CH₄ under different pressures. Where gas drainage is employed, the ratio of CO₂ to CH₄ varies with time and space in floor roadways used for gas drainage, and in the ventilation air in Nos.1 and 2 coal seams, which is consistent with laboratory results.