Desulfurization characteristics of slaked lime and regulation optimization of circulating fluidized bed flue gas desulfurization process--A combined experimental and numerical simulation study

Circulating fluidized bed flue gas desulfurization(CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics(CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^(-1)for the atomized water flow, 70 kg·s^(-1)for circulating ash flow, and 0.56 kg·s^(-1)for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.

Experimental Studies on a Circulating Fluidized Bed for Flue Gas Desulfurization

The tests of flue gas desulfurization were carried out on a circulating fluidized bed reactor in which the flue gas had different velocities at different sections. The SO 2 removal efficiency could be as high as 80% when Ca/S molar ratio was 1 1 and a small amount of water was sprayed into the reactor by a two phase (gas liquid) system nozzle.

Cold-modeling study of a circulating fluidized bed reactor for flue gas desulfurization (FGD)

Short residence time of the sorbent in the gas stream and formation of a dense layer of reaction product surrounding its surface influence the sulfur removal efficiency. A practical means of improving the process performance is to employ fluidized bed reaction in replacement of entrained bed reaction on normally used in cool side desulfurizaiton. This paper describes cold modeling study of a circulating fluidized bed reactor. Several aspects of the problem are discussed: fluidization behavior of CaO, attrition of the sorbent and solids entrainment from the fluidized bed. Mechanisms and key controlling parameters are identified, and an integral model based on rate of attrition and mass balance is developed for predicting steady state mass flows and particle size distributions of the system. A process flow scheme is finally presented for conducting desulfurization tests in the second stage of the study.

SO_2 emission characteristics from co-firing of petroleum coke and coal in circulating fluidized bed

Combustion and sulfur retention experiments of mixed fuel of petroleum cokeand coal were conducted on a pilot-scale circulating fluidized bed (CFB) combustor with the thermalinput of 0. 6 MW. The effects of several parameters, such as the primary air percentage, excess aircoefficient, bed temperature, Ca/S molar ratio and mass ratio of petroleum coke to coal on SO_2emission were verified. Experimental results show that when the ratio of petroleum coke to coal inthe mixed fuel increases, the SO_2emission increases. The maximum SO_2 emission appears when purecoke burns. The SO_2 concentration in flue gas reduces with the increase in the primary airpercentage, excess air coefficient and Ca/S molar ratio for all kinds of fuel mixtures. Therangebetween 830 t and 850 t is the optimal temperature for sulfur retention during co-firing ofpetroleum coke and coal with the mass ratio R of 1 and 3 in CFB.

The Carbonation Behaviors of Limestone Particle in Oxygen-Fuel Circulating Fluidized Bed O₂/CO₂Flue Gas

Limestone powder is still applied as SO2 sorbent in emerging oxygen-fuel circulating fluidized bed boiler, but its carbonation in O2/CO2 flue gas is an unclear problem. For a better understanding of carbonation behaviors, the tube furnace heating system was built for simulating circulating fluidized bed boiler flue gas by regulating the supply of O, CO2, N2, SO2 and H2O, and Carbonation reaction was tested. Thermal gravimetric analysis and scanning electron microscopy were used. It was found that carbonation is closely related to temperature, CO2 concentration, impurities, water vapor, and cycle times;high temperature can promote carbonation process;high concentration of CO2 can inhibit the chemical reaction stage speed of carbonation process, but it has little effect on the final conversion rate;water vapor can increase the final conversion rate of carbonation;the cycle times will reduce the activity of carbonation. The presence of carbonation turns the traditional boiler flue gas indirect desulfurization model into indirect desulfurization mechanism which does not have a negative impact on SO2 removal efficiency.

Experimental and mechanism studies on simultaneous desulfurization and denitrification from flue gas using a flue gas circulating fluidized bed

The oxidizing highly reactive absorbent was prepared from fly ash,industry lime,and an oxidizing additive M.Experiments of simultaneous desulfurization and denitrification were carried out in a flue gas circulating fluidized bed(CFB).The effects of influencing factors and calcium availability were also investigated on the removal efficiencies of desulfurization and denitrification.Removal efficiencies of 95.5%for SO2 and 64.8%for NO were obtained respectively under the optimal experimental conditions. The component of the spent absorbent was analyzed with chemical analysis methods.The results in- dicated that more nitrogen species appeared in the spent absorbent except sulfur species.A scanning electron microscope(SEM)and an accessory X-ray energy spectrometer were used to observe micro-properties of the samples,including fly ash,oxidizing highly reactive absorbent and spent absorbent.The simultaneous removal mechanism of SO2 and NO based on this absorbent was pro- posed according to the experimental results.

Geldart C类脱硫灰颗粒在环流耦合提升管内稳定流动特性

我国CO_(2)的排放中70%来自工业领域,故工业过程的碳捕集对实现“双碳目标”十分关键。工业烟气中往往含有的硫氧化物会腐蚀设备并使后续脱碳等过程使用的催化剂中毒。因此,工业烟气的深度脱硫技术对后续的CO_(2)捕集或提纯过程至关重要。循环流化床半干法烟气脱硫因具有脱硫效率高、无污染、停留时间可控等优点受到广泛关注。循环流化床脱硫工艺中作为脱硫剂的脱硫灰颗粒为典型Geldart C类颗粒。由于C类颗粒的强黏附性,其在循环流化床操作中容易结块,从而影响装置稳定运行。为了强化脱硫灰颗粒在循环流化床内的流动稳定性,提出了环流强化的耦合提升管反应器的概念,并自行设计搭建了一套导流筒内径100 mm、高度300 mm,外筒内径160 mm、高度760 mm,输送段内径75 mm、总高度12.6 m的环流耦合提升管。在U_(g)=4 m/s、G_(s)=45 kg/(m^(2)·s),U_(g)=7 m/s、G_(s)=25 kg/(m^(2)·s)的操作条件下,考察了环流段的压力分布、标准差以及功率谱密度。当环隙区气速为0.4 m/s时,环流流动能够实现稳定、连续的密相环流流动。在C类颗粒形成稳定流动基础上,讨论了环流耦合提升管内的流动特性分布规律,包括固含率和颗粒速度。实验发现,环流流动的设计可以强化C类颗粒的流动特性,大幅提高耦合反应器内C类颗粒脱硫灰固含率,并实现了C类颗粒循环流态化装置的稳定运行。同时,这些研究结果可以为C类颗粒新型循环流态化反应器设计提供参考。

适应330MW循环流化床锅炉灵活运行的脱硫自动控制系统分析与实践

内蒙古京海煤矸石发电有限责任公司330MW循环流化床锅炉原脱硫系统存在自动运行品质差、脱硫剂单耗高、脱硝脱硫协调性差、烟气测量仪表自检滞后性大等问题。在超低排放改造过程中,通过采取炉内脱硫自动主控逻辑设计与调试、串级控制系统及多变量前馈的设计与优化,炉内4套给料系统和炉外2套给料系统的自动联锁启停控制设计与优化等措施,有效地解决了上述问题,同时对比了优化前后机组快速变负荷期间SO2控制情况及脱硫剂单耗用量。该研究内容可对同类型机组脱硫自动控制设计和投运提供参考。

基于烧结工序的半干法烧结废气脱硫脱硝工艺节能减排研究

传统的烧结废气治理方法往往能耗较高,不仅增加了企业的生产成本,还加剧了能源资源的紧张局面。对此,基于传统半干法脱硫脱硝技术进行改进,提出一种半干法循环流化床脱硫除尘与中低温选择性催化还原技术结合的综合技术。经实验分析表明:该研究技术下节约的电力约是改进前半干法工艺的2.47倍,是湿法脱硫+SCR脱硝技术的1.97倍;基于研究技术的烧结废气处理工艺耗气量最低,平均每天耗气量约为0.34 m^(3)/t,改进前的半干法工艺技术的平均每天耗气量为0.74 m^(3)/t,湿法脱硫+SCR脱硝技术下平均每天耗气量为0.72 m^(3)/t。由此得出,改进后的半干法工艺可以达到烧结废气处理中节约能耗的效果。

循环流化床锅炉燃烧系统的优化控制研究

为提高循环流化床炉内脱硫效率以减小床温波动,采用反馈控制的脱硫燃烧系统,并针对其床温波动大的问题,加入床温变化率和炉内CaO含量以对其进行优化,得到基于前馈-反馈的优化控制系统。经对比仿真后,与实测数据相比,该优化控制系统能快速降低炉膛出口SO2的含量及其波动性,且可有效控制床温变化,改善床温波动,验证了该优化控制系统的脱硫效果好、成本低。

循环流化床燃煤锅炉的SO_2和NO_x排放的试验和数值计算

文中采用数值模拟和试验相结合的方法来研究煤种对循环流化床燃烧(CFB)燃烧 SO2 和 NOx 排放的影响。在1.5MWth CFB 试验台上分别做了 5 种煤燃烧的 SO2和 NOx排放试验,根据所建 CFB 锅炉脱硫脱氮数学模型和已建与煤种相关的 CFB 锅炉总体数学模型,对该试验台炉膛内 5种煤 SO2 和 NOx 的生成和脱除进行数值模拟,其结果和试验结果吻合良好。结果表明,煤种决定 CFB 锅炉脱硫效率及 SO2和 NOx的排放。

循环流化床烟气脱硫机理研究

对影响脱硫效率的关键因素进行了分析，同时进行了实验验证．认为水分的蒸发是主要影响因素，而流化床的运行温度和床内的相对湿度则是影响循环床脱硫效率的主要运行参数．对排烟循环流化床的床料进行了电镜扫描分析，结果表明，床料的再循环，一方面为脱硫剂的再循环提供了载体，另一方面，扩大了脱硫反应的面积。

循环流化床富氧燃烧SO_2排放和石灰石脱硫特性研究

在50kW循环流化床燃烧试验台上进行了大同煤在O2／CO2气氛下未添加石灰石和添加石灰石的富氧燃烧试验，试验各工况进口的氧气浓度为25％～50％，燃烧温度为850-950℃。试验研究的目标是获得燃烧温度和进口氧气浓度等参数对循环流化床富氧燃烧过程中SO2的排放特性和石灰石的脱硫特性的影响。试验研究表明：未添加石灰石时，SO2的排放量随着燃烧温度的升高而升高，随着进口氧气浓度和过氧系数的升高而降低。在相同[Ca]／[S]情况下，石灰石的最高脱硫效率所对应的燃烧温度在900℃。随着进15氧气浓度的增加，石灰石的脱硫效率显著提高，在[Ca]／[S]为3的条件下，进口氧气浓度从25％增加到50％，石灰石的脱硫效率从39．0％增加到83．5％。

脱硫塔气固两相流场优化的数值模拟研究

循环流化床脱硫塔是一种用于锅炉尾部烟气的干法脱硫技术。由于实际脱硫塔尺寸庞大,给实验研究带来困难且成本很高,该文采用数值模拟的方法对多种方案进行比较,能够便利、深入地对塔内流场进行研究。并根据拟建的循环流化床脱硫塔实际结构和运行参数,通过数值模拟方法对塔内气固两相流场进行了模拟,发现和揭示了塔内流场所存在的不均匀性。为将塔内流场调节均匀,在所建立的数值模拟平台上对大量设想的调节方案进行了尝试、比较和筛选。最终结果表明,通过改变文丘里管直径、加装直导流板或弯曲导流板均可以将流场调节均匀,达到理想状态。

循环流化床内烟气脱硫模拟分析

基于气固两相流双流体模型及床内浆滴蒸发和SO_2吸收过程的分析,该文发展了循环流化床烟气脱硫过程的双流体/蒸发脱硫模型。采用恢复系数修正颗粒与颗粒团、壁面之间碰撞影响,合理解释固相含率沿径向分布特性;引入颗粒相湍能和湍能耗散率描述颗粒团的脉动过程,分析不同表观气速和颗粒循环量时床内颗粒相轴向速度沿径向变化规律,及颗粒团形成和脉动对浆滴蒸发和脱硫效果的影响。分析指出颗粒团的形成可减小浆滴蒸发速度,增强脱硫效果。

钙基脱硫灰低温增湿脱硫的TGA模拟实验研究

以石灰石为脱硫剂，在热天平中研究了其高温脱硫产物在低温（60～150℃）条件下的增湿脱硫特性，探讨了水活化温度、活化水量和高温脱硫时间对脱硫灰低温增湿脱硫能力的影响．结果表明，在合适的水活化增湿条件下，高温脱硫产物中的残留氧化钙水合生成氢氧化钙的转化率可以达到90％以上，具有较强的潜在再脱硫能力．增湿活化温度越低，高温脱硫时间越短，越有利于低温脱硫反应；随着活化水量的增加，低温脱硫反应的钙利用率先提高后降低，活化水量存在一个最佳值．

循环流化床锅炉超低排放技术研究

循环流化床(CFB)锅炉能够比较清洁地燃烧各种固体燃料,但其如何适应新的国家环保标准,实现SO2及NOx污染物的超低排放,需作进一步研究。结合CFB锅炉工程实例,根据煤折算硫分的高低和挥发分高低,分别提出了CFB锅炉深度脱硫及脱硝的技术方案,并对关键技术进行了分析讨论。研究结果表明:针对不同煤种采取相应措施后,CFB锅炉SO2排放值可小于100 mg/m3,NOx排放值可稳定在100 mg/m3以下;对于烟煤等高挥发分煤种,若结合SNCR技术,CFB锅炉NOx排放值可达到小于50 mg/m3的超低排放水平。

循环流化床锅炉组合脱硫系统运行策略研究

通过循环流化床锅炉炉内脱硫与尾部烟气湿法脱硫相结合的组合式脱硫方式,燃煤电站SO2排放可以达到新的国家标准。基于燃煤SO2产生及脱除过程中系统平准化运行成本最低的原则,提出了一种组合脱硫系统运行状态选择策略模型。对某300MW循环流化床锅炉组合脱硫系统计算表明:采用w(Szs)表征电站燃煤的含硫量,基于w(Szs)高低将燃煤分为6类。I类煤种,系统宜仅运行CFB炉内脱硫;III类、V类煤种,系统宜仅运行FGD湿法脱硫;II类、IV类、VI类煤种,系统宜采用CFB和FGD同时运行的组合脱硫方式。石灰石单价、脱硫石膏单价、以及上网电价对系统运行状态影响较大,工业水单价影响较小。通过敏感性分析可知,上网电价对平准化运行成本影响程度最大;石灰石单价远高于工业水单价的影响程度;而脱硫石膏售价增加有利于降低平准化运行成本。组合脱硫系统运行状态需要根据实际运行参数进行确认。

循环流化床脱硫器文丘里式入口对流动特性的影响

以循环流化床脱硫反应器为研究对象,所建的实验装置采用了工业上最新应用技术———文丘里管气体分布器,对文丘里扩散段和提升管内的速度场进行了测量,用速度分布不均匀度的概念详细讨论分析了气体轴向速度沿径向位置的分布和轴向发展规律,并与数值模拟解进行了对比.研究结果表明,装置的侧向进口结构和回料管的存在严重影响提升管底部气体速度分布的均匀性,提升管底部产生了不良的气体流动行为,在回料管一侧,甚至出现了旋涡,提升管段的稳定流动区域远离提升管的进口端.

循环流化床脱硫塔内流场及气固分离特性数值模拟

应用气固两相双流体模型结合颗粒动力学理论,对内置分离器循环流化床脱硫塔内气固两相流中的气相湍流流动和颗粒相脉动流动进行了数值模拟。模拟得到脱硫塔内颗粒相、气相速度和浓度径向分布。利用FFT方法分析了颗粒质量流率振幅图,结果表明,利用数值模拟方法能够很好地预测不同内部构件条件下塔内分离效率。内置分离器有利于强化内部循环,减轻外部除尘设备负荷。气力输送条件下,脱硫塔内呈环核流动,有利于防止壁面结垢和提高脱硫塔的运行稳定性。模拟得到的结果与实验值基本吻合,为化学反应模拟奠定了基础。