Comparison of combustion characteristics of petroleum coke and coal in one-dimensional furnace

The effect of primary air fraction ƒ ₁, outer secondary air swirl strength and excess oxygen coefficient on the combustion characteristics of petroleum coke, Hejin lean coal and Shenmu soft coal are researched on a one-dimensional furnace using a dual channel swirl burner. The results show that with the increase in primary air fraction ƒ ₁, the NO _x emission concentrations of both Hejin lean coal and petroleum coke increase, and the combustion worsens in the earlier stage, but the burn-out rate of Shenmu soft coal is improved. The NO _x emission concentration obtains a minimum value with an increase in ƒ ₁. The ignition and burn-out rate of petroleum coke and Shenmu soft coal are optimal when Ω_dl is minimum and Ω_dl= 0.87, respectively. However, both the NO _x emission concentration of petroleum coke and Shenmu soft coal are minimum when Ω_dl= 1.08. The increase in excess oxygen coefficient delays the ignition of petroleum coke, worsens the combustion condition and increases the NO _x emission concentration, but it greatly decreases the NO _x emission concentration of Shenmu soft coal.     

烟煤与石油焦掺混燃烧特性研究

以小型试验台上煤焦混粉燃烧试验为基础,对烟煤与石油焦的燃烧特性,混合粉的着火性能,燃烧特性,以及煤粉细度,配风条件和热负荷强度对燃烧过程的影响进行了分析研究。     

Effects of pyrolyzed semi-char blend ratio on coal combustion and pollution emission in a 0.35 MW pulverized coal-fired furnace

The effects of blend ratio on combustion and pollution emission characteristics for co-combustion of Shenmu pyrolyzed semi-char (SC), i.e., residuals of the coal pyrolysis chemical processing, and Shenhua bituminous coal (SB) were investigated in a 0.35 MW pilot-scale pulverized coal-fired furnace. The gas temperature and concentrations of gaseous species (O₂, CO, CO₂, NO_x and HCN) were measured in the primary combustion zone at different blend ratios. It is found that the standoff distance of ignition changes monotonically from 132 to 384 mm with the increase in pyrolyzed semi-char blend ratio. The effects on the combustion characteristics may be neglected when the blend ratio is less than 30%. Above the 30% blend ratio, the increase in blend ratio postpones ignition in the primary stage and lowers the burnout rate. With the blend ratio increasing, NO_x emission at the furnace exit is smallest for the 30% blend ratio and highest for the 100% SC. The NO_x concentration was 425 mg/m³ at 6% O₂ and char burnout was 76.23% for the 45% blend ratio. The above results indicate that the change of standoff distance and NO_x emission were not obvious when the blend ratio of semi-char is less than 45%, and carbon burnout changed a little at all blend ratios. The goal of this study is to achieve blending combustion with a large proportion of semi-char without great changes in combustion characteristics. So, an SC blend ratio of no more than 45% can be suitable for the burning of semi-char.     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.     

NOx and H2S formation in the reductive zone of air-staged combustion of pulverized blended coals

Low NO_x combustion of blended coals is widely used in coal-fired boilers in China to control NO_x emission; thus, it is necessary to understand the formation mechanism of NO_x and H₂S during the combustion of blended coals. This paper focused on the investigation of reductive gases in the formation of NO_x and H₂S in the reductive zone of blended coals during combustion. Experiments with Zhundong (ZD) and Commercial (GE) coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200°C–1400°C with an excessive air ratio of 0.6–1.2. The coal conversion and formation characteristics of CO, H₂S, and NO_x in the fuel-rich zone were carefully studied under different experimental conditions for different blend ratios. Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H₂S as NO reduction accelerated. Both the CO and H₂S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio. Based on accumulated experimental data, one interesting finding was that NO and H₂S from blended coal combustion were almost directly dependent on the CO concentration, and the CO concentration of the blended coal combustion depended on the single char gasification conversion.Thus, CO, NO_x, and H₂S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.     

循环流化床中石油焦与煤混合燃烧SO2排放特性研究

在一座0．5MW1循环流化床热态试验装置上进行了石油焦与煤混合燃烧试验，研究了烟气中SO2的排放特性．对于石油焦与煤不同燃料配比，不同锅炉运行参数，如过量空气系数、床温、一次风率、Ca／S比等对烟气中SO2排放浓度的影响规律进行了研究．试验表明：对不同配比的燃料，随过量空气系数和一次风率的增大，SO2排放浓度降低；对于床温有一最佳温度，其SO2排放浓度最低；随Ca／S增大，SO2排放浓度降低。     

Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine

An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO₂ concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO₂ do not vary much with hydrogen addition. The exhaust NO_x increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%.     

石灰立窑代焦型煤燃烧特性的实验研究

在SDTQ600差热-热重联用仪上对石灰立窑代焦型煤试样进行了热重分析,研究了不同升温速率对其燃烧特性的影响,并以5℃/min的升温速率将型煤、焦炭和无烟煤块煤试样进行对比。利用马弗炉研究了单颗粒代焦型煤的燃烧速率。结果表明,代焦型煤的燃烧过程经历了干燥预热、挥发份析出、碳粒燃烧和残碳燃尽4个阶段;随着升温速率的增加,代焦型煤燃烧各阶段的反应时间缩短,反应速率加快;当升温速率由5℃/min提高至10和15℃/min时,代焦型煤的着火时间由28.12min下降至14.01和10.13min,其燃尽时间也由36.82min下降至27.59和22.47min。通过对比,型煤在着火、稳燃性能及综合燃烧特性方面最好,而燃尽性能居中;代焦型煤、焦炭与无烟煤块煤3种试样的综合燃烧指数分别为53.25×10-9、30.14×10-9和11.53×10-9。燃烧温度对型煤燃烧速率影响较小,而型煤尺寸对后期燃烧速率影响较明显,减小型煤尺寸可增大燃烧速率;相同条件下,代焦型煤的燃烧速率低于焦炭而高于无烟煤块煤。实验结果可为石灰立窑型煤代焦提供指导。     

富氧燃烧条件下煤焦特性研究

以大同烟煤为研究对象,在高温携带流模拟反应器上,利用平流火焰燃烧器制取真实富氧燃烧气氛下的煤焦,对不同停留时间下制取的煤焦进行工业分析,讨论停留时间对煤焦的燃尽率、固定碳和挥发份的含量的影响,当停留时间超过94ms时,煤焦的各种参数保持不变.利用热重分析仪进行煤焦的燃烧实验,讨论不同O2/CO2(20/80、30/70和40/60)气氛对煤焦燃烧特性的影响,并采用Coats - Refern法计算煤焦的活化能和指前因子等动力学参数,460～660℃范围内,背景气氛O2/CO2为30/70时煤焦的活化能和指前因子数值最大,为进一步研究煤焦在富氧燃烧气氛中的燃烧反应提供理论依据.     

石油焦燃烧特性研究

石油焦是炼油工艺的副产品,具有低灰分和一定挥发分及高热值的特性,还含有相当多的硫、氮元素和钒、镍等碱金属元素,这些成分在石油焦燃烧时会造成锅炉内腐蚀和污染。在石油焦的利用上,通过燃烧回收热量仍然是主要途径。分别在220t/h煤粉锅炉上和热输入率为0.5MW的循环流化床热态实验装置上进行了石油焦与煤的掺烧实验研究。经过实验对比,认为利用循环流化床技术将石油焦与煤混烧是一种高效、清洁利用石油焦的有效方法。     

循环流化床中石油焦与煤混合燃烧温度场研究

石油焦是炼油工艺的副产品．具有低灰分、一定挥发份和高热值的特性。焦中含有相当多的硫、氮元素和钒、镍等碱金属元素．这些成分在石油焦燃烧时可造成锅炉内腐蚀和沾污。经过技术对比认为：利用循环流化床燃烧技术将石油焦与煤混合燃烧是高效、清洁回收利用石油焦的有效方法。本文在热输入率为0．5MW的循环流化床热态试验装置上进行了石油焦与煤掺混燃烧炉内温度场研究,分析了石油焦与煤不同燃料配比,不同锅炉运行参数,如一次风率、过量空气系数、Ca／S比和给料量等对炉内温度场分布的影响规律。     

低低温电除尘及高效电源协同烟气处理技术的应用

为研究低低温电除尘及高效电源协同烟气处理技术的应用效果,以一循环流化床锅炉为研究对象,通过试验方法,对协同烟气处理技术投运前后烟气中的粉尘颗粒特性及排放质量浓度进行了测量及对比,并对该技术投运后的经济性进行了分析。结果表明:协同烟气处理技术投运后,机组排放的粉尘质量浓度由49.5 mg/m³降低至10.7 mg/m³,可显著提高除尘器的除尘效率;可降低机组供电标煤耗2.835 g/(kW·h),年节煤量1473.5 t;可进一步减少CO₂,SO₂,NO_x及粉尘等污染物的排放;可节约用电160 kW·h/h,每年节约电量6.16×10⁵ kW·h。     

Effects of EGR on combustion process of DI diesel engine during cold start

Experiments on the effects of external and internal exhaust gas recirculation (EGR) on combustion and emission performance during a cold start process were investigated in a 135 single-cylinder DI diesel engine. Combustion was improved during the initial ignition cycles by introducing internal or external EGR. The addition of an appropriate amount of internal or external EGR can promote the combustion stability significantly. However, excessive amounts of external EGR could lead to extremely unstable combustion or even misfiring. An appropriate amount of internal or external EGR decreased smoke opacity effectively during a cold start. External EGR reduced NO_x emissions effectively while internal EGR led to an increase in NO_x emissions due to thermal effects.     

440t_h CFB锅炉掺烧石油焦二氧化硫排放特性研究

在440 t/h大型循环流化床锅炉上进行了燃烧不同比例煤和石油焦混合燃料时二氧化硫排放特性的试验研究。研究了燃烧不同比例的混合燃料、炉膛温度、过量空气系数和钙硫摩尔比对二氧化硫排放特性的影响。研究结果表明,过量空气系数和钙硫摩尔比的增加可以降低二氧化硫排放浓度。存在一个最佳脱硫温度,二氧化硫排放浓度最低,对于各种混合燃料最佳脱硫温度应在830～850℃之间。     

中心风对径向浓淡旋流煤粉燃烧器燃烧的影响

通过冷态PDA试验,研究了中心风对燃烧器出口气固流动特性的影响;并结合1台670t/h锅炉的工业性试验,说明了中心风对径向浓淡旋流煤粉燃烧器的燃烧有很重要的调节作用,为设计和运行提供了参考依据。图10参4     

锅炉氧煤无焰燃烧技术分析

氧煤燃烧是一种全新燃烧方式,将氧煤燃烧器的表观氧气浓度从30％提高到50％、将O2/CO2混合气改变为纯氧气与再循环CO2烟气分离、将喷嘴速度从50m/s左右提高到200 m/s左右组织炉膛烟气形成高倍率内循环,从而在炉膛内实现高温低氧的氧煤无焰燃烧状态,氧煤无焰燃烧技术能实现煤粉高效燃烧和较低NO浓度排放的统一,锅炉...     

Industrial-scale investigations on effects of tertiary-air declination angle on combustion and steam temperature characteristics in a 350-MW supercritical down-fired boiler

Industrial-scale experiments were conducted to study the effects of tertiary air declination angle (TDA) on the coal combustion and steam temperature characteristics in the first 350-MW supercritical down-fired boiler in China with the multiple-injection and multiple-staging combustion (MIMSC) technology at medium and high loads. The experimental results indicated that as the TDA increased from 0° to 15°, the overall gas temperature in the lower furnace rose and the symmetry of temperature field was enhanced. The ignition distance of the fuel-rich coal/air flow decreased. In near-burner region, the concentration of O₂ decreased while the concentrations of CO and NO increased. The concentration of NO decreased in near-tertiary-air region. The carbon in fly ash decreased significantly from 8.40% to 6.45% at a load of 260 MW. At a TDA of 15°, the ignition distances were the shortest (2.07 m and 1.73 m) at a load of 210 MW and 260 MW, respectively. The main and reheat steam temperatures were the highest (557.2°C and 559.4°C at a load of 210 MW, 558.4°C and 560.3°C at a load of 260 MW). The carbon in fly ash was the lowest (4.83%) at a load of 210 MW. On changing the TDA from 15° to 25°, the flame kernel was found to move downward and the main and reheat steam temperatures dropped obviously. The change of TDA has little effect on NO_x emissions(660–681 mg/m³ at 6% O₂). In comprehensive consideration of the pulverized coal combustion characteristics and the unit economic performance, an optimal TDA of 15° is recommended.     

运行参数对锅炉煤粉着火燃烧和飞灰含碳量影响的数值研究

为了达到锅炉的优化运行以保证煤粉气流及时着火和充分燃尽，采用IPSA两相流动模型和煤粉燃烧综合模型，在不同的一次风率和煤粉细度的工况下，对1台350MW锅炉煤粉燃烧过程进行了数值模拟，得出了炉内燃烧器区域以及出口处烟气温度场和燃烧产物的组分浓度分布。分析了一次风率和煤粉细度对煤粉着火燃烧和飞灰含碳量的影响规律，并确定了优化的运行参数。结果表明：一次风率对煤粉气流的着火影响较大，而对出口处烟气温度、氧量以及飞灰含碳量影响较小。煤粉细度对煤粉气流的着火、燃烧以及燃尽均有较大影响。图8表2参9     

链条炉中推迟配风方式的特性研究

采用气相色谱法研究了某6.5 t/h链条炉在3种不同配风方式(尽早配风、均匀配风和推迟配风)下煤层表面各气体组分沿链条长度的分布规律。结果显示:尽早配风和推迟配风相对均匀,配风整体氧量水平较低,推迟配风在煤燃烧的中后期促进焦碳燃烧,集中释放出大量CO和CO2,而且固体碳转化为气态碳(CH4,CO,CO2)的量最大,这说明其煤层燃尽率最高。对炉膛内气相燃烧的数值模拟进一步表明,推迟配风还有利于新型双人字型炉拱在前拱下部形成火焰漩涡,直接冲刷新煤,保证和加速新煤的引燃。     

燃煤电站锅炉富氧燃烧技术研究进展综述

富氧燃烧技术是未来实现燃煤电站锅炉CO2捕集和存储可能采取的技术路线之一,但是煤粉在普通空气和CO2气氛条件下的燃烧及传热传质特性有很大的区别,因此有必要对煤粉富氧燃烧技术进行深入的研究。通过总结富氧燃烧技术的最新研究进展,并与传统燃煤电站锅炉空气燃烧技术进行比较,从传热特性、煤的反应性以及污染物排放特性3个方面介绍了富氧燃烧的特点,为将来工业应用做好技术储备。