【作者】 赵建立；

【导师】 路春美；

【作者基本信息】 山东大学 ， 热能工程， 2011， 博士

【摘要】 我国能源消费以煤为主,占据煤炭消费主导地位的燃煤发电企业成为大气污染物SO2的主要排放源。随着环保法规的日益严格,以钙基脱硫剂—石灰石为主的湿法烟气脱硫方式成为燃煤发电机组脱硫首选方案,石灰石作为自然资源,其大量消耗不可避免对环境造成很大影响。在我国众多化工企业、有色金属企业排放出大量碱性工业废渣(简称废渣)如电石渣、赤泥、白泥、碱渣及盐泥等占据大量耕地,污染当地环境,成为相关企业可持续发展的制约因素。初步研究表明,碱性工业废渣具有一定的脱硫性能,可用作湿法烟气脱硫剂,实现以废治废。但对废渣在湿法脱硫中的速率控制步骤—消溶特性及机理的认识还存在许多不完善之处,影响废渣型脱硫剂的高效应用。本文借助化学分析及XRD物相分析,利用脱硫剂湿法脱硫性能筛选系统对采集于典型行业的碱性工业废渣进行脱硫性能初步筛选。结果表明脱硫性能优良的碱性工业废渣可分为3类：1)CaCO3基废渣,如白泥、碱渣、赤泥及盐泥；2)Ca(OH)2基废渣—电石渣；3)钙基复合硅酸盐基废渣—镁渣。而粉煤灰、炉渣、高炉渣及水处理废弃物等不宜单独用作湿法烟气脱硫剂使用。废渣型脱硫剂浆液脱硫过程pH值变化分析发现,脱硫过程pH值“三阶段”特征随浆液初始pH值升高而明显。浆液初始pH值越高,浆液中自由OH-离子浓度越高,脱硫第一阶段pH变化越平缓；pH值变化率峰值的出现与浆液中脱硫剂颗粒大量溶解有直接关系,废渣初始浆液pH值越低,出现第一个pH值变化率峰值的时间越早,废渣中易参与脱硫反应的物质溶解越快。以脱硫性能优良的碱性工业废渣作为研究对象,利用pH值静态法对碱性工业废渣消溶特性进行研究,针对pH值静态法中H+浓度恒定的特点,采用改良未反应收缩核模型分析废渣消溶机理,为设计适应碱性工业废渣的脱硫系统提供基础性数据。以消溶转化率及转化速率为考察指标,探讨影响废渣消溶的关键参数如pH值、反应温度、粒径及消溶时间等对废渣消溶特性的影响。研究发现pH值对脱硫剂消溶特性有极其重要的影响,降低浆液pH值有利于废渣的溶解。转化速率分析表明,CaCO3基废渣中易溶性碱金属含量越多,消溶反应过程中初始转化速率越大,但其转化速率的衰减速度也很快。镁渣中Ca2+的初始析出是一较慢速过程,后期析出占总析出的比重较其他碱性工业废渣大,达到相同脱硫效果的时间较长。温度对各碱性工业废渣消溶特性的影响规律基本一致,转化率随温度升高而增大；与pH值对消溶的影响有所不同,反应温度变化时,转化率曲线的末端趋于重合,说明在本实验范围内,温度只会影响反应的快慢,对最终转化率的影响不大。粒径对碱性工业废渣转化率的贡献最大；粒径越小,在相同反应时间内,转化率越大。粒径减小对镁渣消溶贡献最大,Ca(OH)2基脱硫剂电石渣次之,CaCO3基脱硫剂白泥、碱渣及盐泥等最小。采用改良未反应收缩核模型分析上述废渣的消溶机理并计算其动力学参数。研究表明：CaCO3基废渣中白泥、碱渣的消溶反应由液膜扩散和颗粒表面化学反应两个阶段所控制,它们在液膜扩散控制阶段的活化能分别为11.94±0.7、4.51±0.8kJ mol-1;在颗粒表面化学反应控制阶段的活化能分别为13.69±1.3、36.34±3.1kJ mol-1.而盐泥的消溶反应由颗粒表面化学反应控制,其消溶活化能分别为9.69±1.9kJ mol-1,物相成分中易溶性碱金属盐含量少是导致这一现象的根本原因。Ca(OH)2基废渣电石渣的消溶反应由液膜扩散和颗粒表面化学反应两个阶段所控制,其消溶活化能分别为7.64±1.8kJ mol-1及14.41±1.0 kJ mol-1。钙基复合硅酸盐基废渣镁渣的消溶反应由颗粒表面化学反应控制,其消溶活化能为14.42±1.5kJ mol-1。为掌握碱性工业废渣在湿法脱硫中的脱硫性能,采用液柱冲击塔对废渣脱硫性能进行研究,利用计算流体软件对液柱冲击塔实验台进行运行参数与结构参数优化以使实验台性能达到最佳。模拟发现入口倾角对气流在塔内分布有重要影响,对本文液柱塔,烟气入口倾角为13°时,塔内的流场与流速分布最佳。多孔挡板对气流整流作用明显,孔隙率为0.5时,多孔挡板对气流整流效果最优。液滴对气流有显著整流效果。喷淋量一定的情况下,塔内风速高低直接影响液滴分布,风速越高,挡板下方液滴数目越少,但挡板上方吸收段的液滴分布在风速达一定数值后受风速影响较小。综合考虑挡板上下液滴分布、除雾器负载及引风机出力等因素后,认为塔内最佳气流速度为3m/s。利用上述模拟优化结果,搭建液柱冲击塔实验台,对影响废渣型脱硫剂湿法脱硫性能的五个主要因素浆液pH值、烟气速度、喷淋密度、液气比和入口烟气温度进行研究,并探讨了不同配比下废渣型复合脱硫剂的脱硫性能。研究表明：浆液pH值高的脱硫剂如电石渣、盐泥、白泥等,在较低浆液喷液密度时,脱硫效率对烟气流速的变化非常敏感,烟气速度增大,脱硫效率明显增加。在较高喷液密度时,脱硫效率取决于液滴分布密度,烟气速度的绕流作用轻微。对于低pH值脱硫剂,其对SO2化学反应吸收过程的推动力一定,烟气速度的变化不会对脱硫效率造成明显影响。推荐液柱冲击塔中电石渣浆液池pH值在6-7之间,循环浆液pH值在8-9之间；推荐白泥、盐泥和赤泥浆液池pH值5-6,而循环浆液pH值分别为6.5-7.5、6.5-8、6.5-8。烟气速度不变时,液气比增大脱硫效率增加；而循环浆液量保持不变,增加烟气速度,减小液气比时,液气比对Ca(OH)2基废渣和CaCO3基废渣影响不同。对电石渣,液气比减小,脱硫效率降低；对白泥、盐泥、赤泥及石灰石等脱硫剂,在烟气速度2.1-2.7m/s时,随液气比的减小,脱硫效率反呈上升趋势。CaCO3基脱硫剂烟气速度3m/s时,脱硫剂脱硫性能达到临界值,气液流场达到最佳。当液气比为16L/m3,烟气速度3m/s时,各脱硫剂可获得如下脱硫效率：电石渣97%、白泥87%、赤泥84%、盐泥91%、石灰石95%。试验范围内,随烟气入口温度增加,脱硫效率稍有增加。为拓展废渣型复合脱硫剂的应用,利用液柱冲击塔试验台对废渣型复合脱硫剂脱硫性能进行研究。以石灰石为主料的废渣型复合脱硫剂研究表明：电石渣的加入导致溶解度很低的CaSO3·1/2H2O附着在石灰石表面,阻碍CaCO3的消溶,降低复合脱硫剂的脱硫效率；石灰石、盐泥配比为8：2时,既可发挥镁对脱硫的促进作用,又可最大程度的降低Cl-对脱硫的不利影响；石灰石赤泥型复合脱硫剂随赤泥加入量增加脱硫效率基本呈下降趋势；石灰石白泥型复合脱硫剂在白泥配比变化时,脱硫效率无明显改变。以电石渣为主料的废渣型复合脱硫剂,将CaCO3基废渣与电石渣配制复合脱硫剂时需要废渣中具有脱硫后溶解度大的物质,以抵消电石渣在高pH值脱硫时所产生软垢的影响；同时要求辅料需控制含有Al3+、Fe3+的物质含量。CaCO;基废渣型复合脱硫剂研究表明,Mg2+对脱硫的促进作用与Cl-对脱硫的抑制作用使得赤泥盐泥型复合脱硫剂在赤泥、盐泥配比为7：3时脱硫效果最佳。更多还原

【Abstract】 The main energy consumption in China is coal. Coal fired plants are the main source of SO2 pollution because of their dominant role in coal consumption. With the environmental regulations increasingly strict, the wet flue gas desulfurization (WFGD) which main sorbent was calicium based-limestone, became the preferred desulfurization way. As one kind of natural source, the great amount of limestone consumption will influence the earth’s ecological system inevitably.While a great quantity of alkaline industrial wastes(AIW) such as carbide slag(CS), rud mud(RM), paper white mud(PWM), alkali slag(AS) and salt slag(SS) were discharged by numerous chemical companies and non-ferrous metals industries in China, which resulted in the pollution of local environment and became the constraints of the above companies in sustainable development. Previous studies proved that AIW had the ability of desulfurization, and can be used as WFGD sorbent. However, the mechanism for AIW dissolution which is one of the rate control step in WFGD has not been well acknowledged.Desulfurization behaviors of collected AIW are screened through chemical analysis, XRD analysis and comparative study. Results show that there are three kinds of sorbents which have better desulphurization properties:1) CaCO3 based sorbent such as RM, PWM, AS and SS, et al.,2) Ca(OH)2 based sorbent for example CS and 3) calcium-aluminum oxide and calcium magnesium silicate based sorbent like magnesium slag(MS). While some sorbents such as fly ash, furnace slag, blast furnace slag and water treatment waste can not be used as desulfurization sorbent alone. The pH value analysis of AIW slurries show that the higher the pH value of AIW initial slurry, the more obvious of "three stages" in desulfurization process. The concentration of free OH- is increased with the increasing of the pH value of AIW initial slurry, which makes the first stage gently. The peak value of the changing rate of pH value has direct contact with the dissolution of sorbent particles, the lower the pH value of AIW initial slurry, the faster dissolution of the desulfurization sorbent. The AIW which have better desulfurization properties are mainly mentioned in this study and their dissolution characteristics are investigated through pH static method. The dissolution mechanisms of AIW are analyzed by modified unreacted shrinking core model(MUSCM) in order to obtain the data base for designing the desulfurization systems which fit to the AIW. The key parameters which influence AIW dissolution such as pH value, reaction temperature and particle size are discussed by conversion rate and conversion rate differential. pH values have the important effect on sorbents dissolution, the lower the pH value is, the easier the AIW sorbents dissolute. According to dissolution conversion rate differential, the higher pH value the CaCO3 based AIW initial slurry has, the higher the initial conversion rate, while its decay rate is faster also. The magnesium slag need more time to obtain the same desulfurization effect compared to other AIW because the separating of Ca2+ is a slower process. Conversion rate increases with the increasing of reaction temperature although the final curves of conversion rate closed to each other. This proves that reaction temperature affect the reaction velocity only and has slightly influence on final conversion rate. Particle sizes contribute to the AIW conversion rate. The smaller the particle size is, the higher the conversion rate in the same reaction time. According to the decending order, the contributions to AIW dissolution because of the decreasing of particle size are as follows:magnesium slag, Ca(OH)2 based AIW and CaCO3 based AIW.The dissolution mechanisms of CS, RM, PWM, AS, SS and MS are analyzed by MUSCM and their kinetic parameters are calculated. Results show that the dissolution reactions of PWM, AS and CS are under control of film diffusion and particle surface chemical reaction. The activation energies of PWM, AS and CS in film diffusion control step are 11.94±0.7,4.51±0.8 and 7.64±1.8kJmol-1, respectively. While in surface chemical reaction control step the activation energies are 13.69±1.3,36.34±3.1 and 14.41±1.0 kJ mol-1, respectively. The dissolution reactions of SS and MS are controlled by surface chemical reaction and their activation energies are 9.69±1.9and 14.42±1.5 kJ mol-1, respectively. The optimal operation and configuration parameters of impinge stream scrubber experimental bench are gained through CFD simulation analysis. The inlet angle has important effect to the distribution of gas flow in scrubber, when the inlet angle is 13°, the optimal flow and gas velocity distribution can be got. Perforated baffle has the obvious impact on gas flow straightening as the porosity is 0.5. Droplets have significant influence on gas flow straightening. To a given spray flow, droplets distribution have direct contact with gas velocity in scrubber, the higher the velocity is, the lower number of droplets under the baffle, however, the droplets distribution above the baffle are influenced slightly by gas velocity when it is above 3m/s. the optimal gas velocity 3m/s is got by taken the amount of droplets above and under the baffle, demister load and induced draft fan output into account.The impinge stream scrubber experimental bench is established, based on the above simulation results. The five main parameters such as pH value, gas velocity, spray density, liquid gas ratio and inlet gas temperature which influence the AIW sorbents wet desulfurization performances are investigated. The desulfurization behaviors of compound AIW sorbents are discussed also. Desulfurization efficiency is very sensitive to the change of gas velocity when the slurry has a high pH value. Under high spray density conditions, desulfurization efficiency is dependent on droplets distribution, while the flow around action of gas has slightly influence. To the low pH value sorbents, the changing of gas velocity has no significant effect on desulfurization efficiency because of the certain driving force of chemical sorption to SO2. It is recommended that to CS slurry tank the optimal pH value is 6-7, while the circulating slurry pH value is 8-9. To PWM, AS and RM slurry tank, the slurry tank pH vaule is 5-6, while the circulating slurry is 6.5-7.5,6.5-8 and 6.5-8, respectively.Desulfurization efficiency increases with the increasing of lquid gas ratio when gas velocity is stable, while the decreasing of the lquid gas ratio has different effects on Ca(OH)2 based and CaCO3 based AIW sorbents when increasing gas velocity. To CS sorbent, the lower the lquid gas ratio is, the lower the desulfruzation efficiency. While to PWM, RM, AS and limestone sorbents, the desulfurization efficiency rises with the decreasing of lquid gas ratio when gas velocity is 2.1-2.7m/s. The critical desulfurization properties and optimal gas liquid flow can be obtained to CaCO3 based AIW sorbents when gas velocity is 3m/s. When liquid gas ratio is 16L/m3 and gas velocity is 3m/s, the desulfurization efficiencies of CS, PWM, RM, AS and limestone are 97%,87%,84%,91% and 95%, respectively.The desulfurization efficiency is slightly increased with the increasing of inlet temperature under the experimental conditions.The properties of three kinds of compound desulfurization AIW sorbents are conducted in impinge stream scrubber such as limestone primary type, CS primary type and CaCO3 based AIW type.The mixing of CS in limestone results in CaSO3·1/2H2O adhering to the surface of limestone particles because of its low solubility, which will decrease the dissolution of CaCO3. When the compound ratio of limestone and AS is 8:2, the improvement of magnesium and the lowest negative effect of Cl- to desulfurization process can be got. Desulfurization efficiency of limestone-RM type sorbents decreases with the increasing compound ratio of RM. The desulfruzation efficiency of limestone-PWM type changes slightly regardless of the variation of PWM compound ratio.To CS primary type compound desulfurization sorbents, it is the quantity of high solubility material after desulfurization and Al3+, Fe3+concentration in AIW that are the two key factors when choosing CaCO3 based AIW as supplementary material in sorbents.Results on CaCO3 based AIW type show that, the best compound ratio 7:3 of RM-AS type compound sorbent is got because of the improvement of Mg2+ and the inhibition of Cl- to desulfurization process.更多还原