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亚熔盐介质蒸发结疤形成机制与工艺优化
Alternative TitleScale Mechanisms of Sub-molten Salt Liquor and Process Optimization in the Evaporation
郭涛
Subtype博士
Thesis Advisor张懿
2014-04
Degree Grantor中国科学院研究生院
Degree Discipline环境工程
Keyword分解母液   蒸发   碳酸钠   结垢   亚熔盐介质
Abstract蒸发是氧化铝行业平衡水量和排除杂质盐类的重要工序,在蒸发设备不断改进和创新的过程中,结疤问题始终是困扰蒸发的一大难题,也是造成能耗增加的主要原因。亚熔盐氧化铝清洁生产技术,可以实现低铝硅比铝土矿的高效利用,并可从赤泥中进一步回收氧化铝和氧化钠,是实现赤泥资源化利用的可行性工艺。高苛碱浓度铝酸钠溶液蒸发技术与单元操作控制是实现亚熔盐氧化铝清洁生产技术的重要步骤。本文重点研究高苛碱浓度铝酸钠溶液蒸发过程中碳酸钠的析出规律及影响因素,并试验了不同蒸发设备的蒸发运行情况,为亚熔盐介质的高效循环提供理论支撑和设备选型依据。 本论文主要创新性成果如下: (1)首次研究了120℃下NaOH-Al(OH)3-Na2CO3-H2O体系的相平衡,测定了不同温度、不同分子比的铝酸钠溶液中碳酸钠的溶解度,并利用聚焦光束反射测量仪(FBRM)测量了蒸发条件下碳酸钠的介稳区,为高苛碱浓度铝酸钠溶液蒸发提供了理论依据。 (2)研究了Ca2+和Na2SO4对蒸发过程中碳酸钠结晶成核的影响规律,首次发现了Ca2+对碳酸钠成核的抑制作用。Ca2+的存在,可使Na2CO3在更高苛碱浓度铝酸钠溶液中保持稳定,降低降膜蒸发器Na2CO3结疤的可能性。 (3)利用MSMPR结晶技术研究了110℃下铝酸钠溶液蒸发过程中Na2CO3的结晶动力学,依据粒数衡算方程,计算出不同进料浓度和平衡浓度条件下Na2CO3的生长速率和其他动力学参数。 (4)研究了外加热自循环蒸发器、强制循环蒸发器蒸发不同苛碱浓度铝酸钠溶液的运行效果,Na2CO3大量析出的低苛碱浓度段的蒸发,结垢较快,高苛碱浓度段的蒸发,结垢缓慢。亚熔盐介质的蒸发循环,宜采用两段蒸发流程。 (5)研究了脱硅剂、苛碱浓度、温度、氧化铝浓度等因素对脱硅效果的影响,确定了结晶前液苛碱浓度为550 g/L时水合铝酸钠结晶的最低硅量要求为:结晶6 h后结晶母液的分子比高于26,SiO2浓度低于2.8 g/L;结晶20h后结晶母液的分子比高于26,SiO2浓度低于3.7 g/L。 (6)优化了现有的蒸发工艺,采用降膜蒸发器出料与拜耳法赤泥溶出液混合析盐—蒸发—结晶工艺,使Na2CO3在进入后续蒸发器之前大量析出,同时提高了降膜蒸发器出料的分子比,降低了铝酸钠的过饱和度,避免了Na2CO3和铝酸钠在加热面的结垢。溶液分子比提高后,沸点降低,蒸发所需的饱和蒸汽的压力降低,可进一步减轻蒸发器的腐蚀,降低蒸发能耗。
Other AbstractEvaporation of caustic liquor is a vital unit in alumina refinery, in which redundant water and salt impurities brought in during the other unit can be excluded. For the main reason of increasing energy consumption, scaling of the heating surface is a major challenge persecuting the evaporation equipments with continuous improvement and innovation. Sub-molten process for alumina cleaner production, developed for leaching diasporic bauxite with low A/S ratio, has been a feasible process with recycling utilization of red mud by further extraction of Al2O3 and Na2O from red mud. The evaporation technology of sodium aluminate solution with high concentrated alkaline and unit operations are the key process to realize the sub-molten process for alumina cleaner production. The rules and effects of crystal of sodium carbonate in the evaporation process of sodium aluminate solution with high concentrated alkaline were systematically investigated for a theoretical basis for the high efficient cycle of the sub-molten liquor. The running of the evaporation equipment was obseverd in order to provide the selection basis of the key evaporators. The innovative achievements were exhibited as follows: (1) The phase diagram of the NaOH?Al(OH)3?Na2CO3?H2O quaternary system at 120 degree centigrade was studied for the first time. Solubilities of Na2CO3 in sodium aluminate solution with varied molar ratio (MR) at different temperature and the metastable region of sodium carbonate in the evaporation process of sodium aluminate solution monitored by Focused Beam Reflectance Measurement (FBRM) by were determined, which could be provided as theoretical foundation for the evaporation of high concentrated alkaline sodium aluminate solution. (2) The effects of calcium ion and sodium sulfate on the nucleation of sodium carbonate in the evaporation process were investigated, and the inhibitive effect of calcium ion on the primary nucleation of sodium carbonate in the evaporation process of sodium aluminate solution was first reported. The present of calcium ion, can reduce the scaling probability of sodium carbonate on the heating surface of the falling falm evaporator by keeping sodium carbonate stable in higher concentrated alkaline sodium aluminate solution. (3) The crystallization kinetics of sodium carbonate at 110 degree centigrade in the evaporation system were investigated in a steady-state MSMPR (Mixed Suspension Mix Product Removal) crystallizer. The volume growth rates and other kinetic parameters of sodium carbonate at varied feed concentrations and equilibrium concentrations were calculated on the basis of population balance equation. (4) Different concentrated alkaline sodium aluminate solution evaporated in external heating circulation evaporator and forced circulation evaporator was studied. The sodium aluminate solution with special concentrated alkaline during which large amounts of sodium carbonate precipitated caused scaling fast, and that with higher concentrated alkaline seldom scaled. It could be better to use two-stage evaporation process for the cycle of sub-molten liquor. (5) The effects of desilieonization agent, alkaline concentration, temperature and alumina concentration on the desiliconization of sodium aluminate solution were investigated. To make the MR of the sodium aluminate solution (560 g/L) higher than 26 after monosodium aluminate hydrate (MAH) crystal after six hours or twenty hours, the content of SiO2 was required below 2.8 g/L and 3.7 g/L respectively. (6) The current evaporation process was optimized and a new process that is mixed precipitation of the mother liquor from the falling film evaporator and the leaching liquor of red mud-evaporation-crystallization was proposed. In the new process, large amounts of sodium carbonate was precipited before the mix liquor was pumped to the latter evaporation, and supersaturation of MAH in mixed liquor is higher than that from the falling film evaporator by increasin
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15544
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
郭涛. 亚熔盐介质蒸发结疤形成机制与工艺优化[D]. 中国科学院研究生院,2014.
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