【作者】 孙志国；

【导师】 胡国新；

【作者基本信息】 上海交通大学 ， 工程热物理， 2011， 博士

【摘要】 随着经济和社会的发展,燃煤烟气中的SO₂和NO_x造成的大气污染日益严重。如何经济有效的控制SO₂和NO_x的排放已成为科学研究的前沿。现行的烟气脱硫脱硝工艺中,湿法因其技术成熟、脱硫脱硝率高等优点而得到了广泛应用,但同时也存在着投资大、成本高、回收率低甚至造成二次污染等缺点,发展中国家对此难以接受。因此,研究并开发适合我国国情的烟气脱硫脱硝技术对解决我国的SO₂、NO_x污染问题具有十分重要的意义。本论文提出了一种腐植酸钠溶液同时吸收SO₂和NO₂的新工艺,具有成本低、能耗小、无二次污染等优点,同时副产一种复合肥料,实现了以废治废、环境保护和资源化利用。围绕该工艺的实施,开展了以下研究工作:（1）腐植酸钠复合脱硫剂（HA-Na/α-Al₂O₃）的制备及其脱硫性能研究。提出了一种新的脱硫剂HA-Na/α-Al₂O₃的制备方法,用FTIR、SEM、XRD、EDS等方法对脱硫剂进行了分析表征,并在自制的固定床上对其脱硫性能进行了实验研究,研究表明:氧化铝纤维负载腐植酸钠后,改善了氧化铝载体表面的孔结构,在氧化铝纤维表面形成了的腐植酸钠膜,该膜提高了载体氧化铝纤维的脱硫能力,在脱硫过程中起重要作用。HA-Na/α-Al₂O₃在浸渍氨水后,由于腐植酸对氨水的强吸附作用,可以减少氨损,提高氨的利用率,较长时间保持高的SO₂脱除率（≥98%）。脱硫后的产物是以硫酸铵、腐植酸铵、腐植酸钠为主的复合肥,脱硫产物经水洗后,氧化铝纤维获得再生,可循环使用。（2）腐植酸钠液相脱硫的实验及机理研究。分析了腐植酸钠脱硫的机理,在自制的鼓泡反应器上,研究了各种运行参数（如:腐植酸钠溶液浓度、pH值、温度、气流量、含氧量、SO₂入口浓度、等）对脱硫效果的影响,结果表明:腐植酸钠浓度对脱硫时间的影响较大,但对脱硫率的影响较小,0.06 g/mL为最佳浓度。提高SO₂的入口浓度可以提高SO₂气液传质的推动力。为了维持较高的脱硫效率,腐植酸钠溶液的pH值应该保持在4.5以上。随着含氧量的升高,脱硫率稍有升高。低温有利于SO₂吸收。当烟气中存在NO₂时,有利于SO₂的吸收。在最佳工况下,脱硫率可以维持在98%以上。生成的腐植酸难溶于水溶液,从脱硫液中沉淀分离、干燥后,制成肥料。脱硫后的水溶液经过腐植酸钠调节pH至中性后,可循环利用。（3）腐植酸钠溶液吸收NO₂的实验及机理研究。分析了腐植酸钠吸收NO₂的机理,并在鼓泡反应器内研究了各种运行参数对吸收NO₂的影响,结果表明:腐植酸钠溶液吸收NO₂的能力要强于同体积的水,也强于同pH值的NaOH溶液;NO₂的吸收效率会随着腐植酸钠浓度、氧含量、pH值的升高而增加。高温不利于NO₂的吸收。当烟气中NO_x的含量较低时（<0.1%）,NO_x的吸收率与氧化度成正比。SO₂与NO₂共存时,腐植酸钠溶液会优先吸收SO₂,当SO₂吸收饱和后,腐植酸钠溶液可以继续吸收NO₂,并且维持较高的吸收率。最佳工况时NO₂的吸收率可达95%以上。腐植酸钠溶液吸收NO₂的产物主要是腐植酸、硝酸钠,分离处理后可制成腐植酸复合肥。（4）腐植酸钠溶液同时吸收SO₂和NO₂的实验及机理研究。在鼓泡反应器上研究了同时吸收SO₂和NO₂的吸收率,和在不同酸碱条件下的反应生成物,还重点研究了循环水溶液对同时吸收SO₂和NO₂的影响,结果表明:在碱性环境下,当NO₂浓度由0变为340 ppm时,脱硫率从96.4%增加到97.7%,但随着NO₂浓度的进一步增加,脱硫率反而稍有下降;脱硫的主要产物是SO₄^2-和SO₃^2-。碱性环境下NO₂浓度的增加, SO₄^2-在脱硫产物中的比例逐渐减少,但在在酸性环境会逐渐增加,说明酸性条件下有利于SO₃^2-的氧化。随着NO₂的浓度增加,NO₂吸收率稍有下降。碱性时,NO₂的吸收率在有SO₂存在时比无SO₂时要稍高;吸收NO₂的主要产物是NO 3-,兼有少量NO -2。随着循环次数的增加,脱硫率稍微减小,但NO₂吸收率相应的增加。随着循环次数的增加, SO 42-、SO₃^2-、NO 3-、Na+的离子浓度整体递增,并且SO 42-和Na+的浓度远大于其它离子浓度。当循环次数由1增加到6时,循环吸收液的初始pH逐渐由10降低到8.1,但是在第6次循环以后,初始pH基本不变。循环吸收SO₂和NO₂的最后pH基本不变,维持在3.3左右。同时吸收SO₂和NO₂产物主要是硫酸根、亚硫酸根、硝酸根,经过静置分层后,腐植酸沉淀可以分离出来制成腐植酸复合肥,酸性上清液在经过腐植酸钠调节pH至中性后,可循环利用。腐植酸肥料中氧元素的含量随着循环次数的增加而不断增加,说明生成腐植酸的含氧基团不断增加,腐植酸肥料的活性进一步得到了改善。（5）腐植酸钠鼓泡塔内脱硫传质的建模与数值模拟。根据双膜理论对腐植酸钠溶液吸收SO₂的气液传质过程进行了理论分析,建立了相应的脱硫传质模型。在实验数据的基础上,确定了传质模型中的拟一级反应速率常数、气泡平均直径、气含率、气液比相面积等参数,建立了SO₂的平衡分压的多元非线性回归模型。根据该脱硫模型对腐植酸钠吸收SO₂的传质过程进行了数值模拟,并将模拟结果与实验结果进行了对比,二者吻合较好。（6）腐植酸钠溶液同时吸收SO₂和NO₂的工艺设计及经济分析。概括了喷淋塔的工作原理、工艺特点、设计原则,并据此设计、制作了适用于本研究的喷淋塔,同时还设计制作了腐植酸钠同时吸收SO₂和NO₂的工艺流程装置。实验结果显示,该工艺中SO₂吸收率可达98%以上,NO₂吸收率可达95%以上,整体效果较好。通过腐植酸钠吸收SO₂和NO₂工艺模拟实验,结果表明在优化工艺运行参数后,可以实现腐植酸钠溶液高效的同时吸收SO₂和NO₂、静置分离腐植酸沉淀、酸性水的中和、循环利用等工艺过程。对腐植酸钠脱硫工艺进行了经济评价,整体经济性较好。更多还原

【Abstract】 With the development of economy and society, the atmospheric pollution caused by SO₂ and NO₂ from the combustion of fossil fuels has been gradually more serious. Although the wet flue gas desulfurization （FGD） processes based mainly on limestone scrubbing are frequently used, they have many disadvantages such as high capital operating costs, a lager water requirement, poor quality of byproducts, and even producing second pollution, Which is difficult to accept for the developing countries. Therefore, it is important to investigate and develop the cost effective technologies of removing SO₂ and NO_x for resolving the atmospheric pollution in china.In this thesis, a novel process of simultaneous removing SO₂ and NO₂ by sodium humate （HA-Na） was proposed. This process is a resourceful type of environmental protection technology for flue gas desulfurization and denitrifcation （FGDD） and has many advantages including: （a） lower costs and energy requirements, （b） almost no waste sludge, （c） the recovery of sulfur and nitrogen as a useful sulfur-containing nitrogen fertilizer, and （d） the simultaneous removal of SO₂ and NO₂. Therefore, it is hopeful to be used in a large scale. For developing the novel process, investigations were conducted in this thesis as following:（1） Preparation of HA-Na/α-Aluminum （α-Al₂O₃） and its desulfurization properties.A new composite adsorbent of HA-Na/α-Al₂O₃ for FGD was prepared using the impregnation method. The desulfurization property of the adsorbent was studied in a fixed-bed. The experimental results show that the HA-Na-coating on theα-Al₂O₃ fibers improved the property ofα-Al₂O₃ support for FGD. On the other hand, the HA-Na-coating on the adsorbent of HA-Na/α-Al₂O₃ impregnated with ammonia （NH4OH） played an important role in enhancing the desulfurization property of a-Al₂O₃. Due to the strong adsorption capability of HA-Na, more NH4OH was adsorbed in the adsorbent of HA-Na/α-Al₂O₃ the longer a high SO₂ conversation rate was maintained. In addition, the desulfurization products can be flushed fromα-Al₂O₃ fibres and make into the compound fertilizer consisting of ammonium sulfate [（NH4）2SO4], ammonium humate （HA-NH4）, and HA-Na. the recycling use ofα-Al₂O₃ fibres was also easily achieved. （2） Experiment and mechanism research of FGD by HA-Na solution.Experiments were carried out to examine the effect of various operating parameters, such as the HA-Na concentration, pH, temperature, gas flow rate, O₂ concentration, SO₂ inlet concentration, and NO₂ coexiting with SO₂, on the SO₂ absorption efficiency and breakthrough time in a lab-scale bubbling reactor. The experimental results indicate that the HA-Na concentration significantly influences the breakthrough time but has little effect on the SO₂ absorption efficiency. The breakthrough time increases with the HA-Na concentration reaching 0.06 g/mL, and after this value, it begins to decrease. The SO₂ absorption efficiency maintains 99% when pH is above 4.5. The low temperature is favorable to SO₂ absorption. The increase of the SO₂ inlet concentration improves the mass transfer of SO₂ and accelerates the SO₂ consumption rate. NO₂ coexisting with SO₂ can promote SO₂ absorption because it may speed up oxidation of sulfite to sulfate. HA-Na solution shows great performance in SO₂ absorption, and the SO₂ absorption efficiency can be above 98% in the optimal condition. Moreover, the desulfurization products can be made into the humic acid （HA） compound fertilizer, and recycling water can be obtained in this desulfurization process.（3） Experiment and mechanism research of removing NO₂ from flue gas by HA-Na solution.The effects of various factors like the HA-Na concentration, NO₂ inlet concentration, temperature, O₂ concentration, the oxidation extent （the NO₂ volume fraction in NO_x） and SO₂ coexiting with NO₂, have been investigated in a bubbling rector The experimental results show that the NO₂ absorption efficiency is increased with HA-Na concentration, O₂ concentration, and pH. The low absorption temperature is favorable to the absorption of NO₂. The inlet NO₂ concentration has not significant effect on the NO₂ absorption efficiency. It is concluded that SO₂ coexisting with NO₂ may go against removing NO₂ until SO₂ concentration is saturation in HA-Na solution. The NO_x absorption efficiency is proportional to the oxidation extent when the NO₂ concentration is lower than 0.1% in flue gas. HA-Na solution has strong NO₂ absorption capability, and the NO₂ absorption efficiency can be above 95%. Moreover, the denitrification products can be made into the HA compound fertilizer.（4） Simultaneous removal of SO₂ and NO₂ from flue gas by HA-Na solution.This study relates to the SO₂/NO₂ absorption efficiency and products of simultaneous removing SO₂ and NO₂ in a bubbling reactor, especially the effect of recycled water on the SO₂/NO₂ absorption. Under alkaline conditions, the sulfate content in S-containing compound decreases with the increase of NO₂ concentration, whereas there is a contrary result under acidic conditions. Whether the absorption liquid is alkaline or acidic, the presence of NO₂ improves the SO₂ absorption into HA-Na solution. The NO₂ absorption efficiency in the presence of SO₂ is more than that in the absence of SO₂.The NO₂ absorption efficiency decreases slightly with the increase of NO₂ concentration, and NO 3- is the main byproduct of absorption of NO₂.The NO₂ absorption efficiency can be improved with the cycle number rising due to the increasing amount of sulfite. Although all the ion concentrations of Na⁺, SO₄^2-, SO₃^2-, and NO 3- have a gradual increase as the cycle number rises, the ion concentrations of SO₄^2- and Na+ are far more than that of the other ions, which results in a slight decrease of the SO₂ absorption efficiency. However, the initial pH of HA-Na solution prepared by recycled water decreases from 10 to 8.1 with the cycle number increasing from 1 to 10, whereas the final pH remains almost constant （3.3）. The SO₂ absorption efficiency is above 98% and the NO₂ absorption efficiency may reach above 95% in the optimal condition in this process. The chief byproduct is a compound fertilizer consisting of HA, sulfate, and nitrate. The oxygen content in the byproducts increases with the cycle number rising, which indicates that the O-containing functional groups of HA is increased and the activity of HA is improved by oxygenolysis.（5） Modeling and numerical simulation of mass transferring for FGD by HA-Na in bubbling reactor.According to the double-film theory, the theoretical analysis of gas-liquid mass transfer process for absorption of SO₂ by HA-Na solution was carried out, and the mass-transfer model was established. The parameters in this model were determined on the basis of experimental results, such as pseudo-first-order rate constant, average bubble diameter, gas holdup, and specific gas-liquid interfacial area. The nonlinear regression model of SO₂ equilibrium pressure was constructed by the losopt-software. According to the SO₂ mass-transfer model, the SO₂ mass-transfer during the FGD by HA-Na was numerical simulated, and the simulated result is in agreement well with the experimental result.（6） Design and make the spray absorber and process units for the simultaneous removal of SO₂ and NO₂ process by HA-Na solution.According the working principle, process characteristics and design principle of spray absorber, the spray absorber and process units for removing SO₂ and NO₂ by HA-Na solution were designed and made. The results show the simultaneous removal of SO₂ and NO₂ process by HA-Na has a better performance on the whole, and the SO₂ absorption efficiency is above 98% and the NO₂ absorption efficiency is above 95% in the optimal condition. During this process, not only the high SO₂/NO₂ absorption efficiency, but also the precipitation separation of by-products, the neutralization and recycling of acidic water solution can be achieved. The economic evaluation of FGD process by HA-Na was also carried out, and this process has good economy.更多还原