WO2013107120A1 - 过饱和铝酸钠溶液晶种分解生产氢氧化铝的方法 - Google Patents

过饱和铝酸钠溶液晶种分解生产氢氧化铝的方法 Download PDF

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WO2013107120A1
WO2013107120A1 PCT/CN2012/074190 CN2012074190W WO2013107120A1 WO 2013107120 A1 WO2013107120 A1 WO 2013107120A1 CN 2012074190 W CN2012074190 W CN 2012074190W WO 2013107120 A1 WO2013107120 A1 WO 2013107120A1
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Prior art keywords
tank
seed crystal
decomposition
seed
sodium aluminate
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PCT/CN2012/074190
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English (en)
French (fr)
Inventor
苏向东
胡大乔
何力
丁元法
李丹宁
薛涛
金开胜
李勇
黄健
罗宏
刘洪波
熊永昇
李刚
谭春生
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贵州省新材料研究开发基地
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Priority to AU2012365963A priority Critical patent/AU2012365963B2/en
Priority to CA2861935A priority patent/CA2861935C/en
Publication of WO2013107120A1 publication Critical patent/WO2013107120A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/04—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom
    • C01F7/14—Aluminium oxide or hydroxide from alkali metal aluminates
    • C01F7/144—Aluminium oxide or hydroxide from alkali metal aluminates from aqueous aluminate solutions by precipitation due to cooling, e.g. as part of the Bayer process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D9/00—Crystallisation
    • B01D9/0036—Crystallisation on to a bed of product crystals; Seeding

Definitions

  • the invention relates to a process for producing alumina, in particular to a process for producing aluminum hydroxide by seed crystal decomposition of a supersaturated sodium aluminate solution, belonging to the technical field of metallurgy.
  • Bayer's production of alumina has the characteristics of simple process, convenient operation and high product quality. More than 90% of the alumina produced worldwide is produced by the Bayer process.
  • seed decomposition process which is supersaturated.
  • a large amount of aluminum hydroxide is added as a seed crystal in the sodium aluminate solution to induce crystallization and growth of the aluminum hydroxide crystal, and the supersaturated sodium aluminate solution is decomposed, and the aluminum hydroxide slurry obtained after the decomposition reaction is continued for 35 to 75 hours.
  • seed decomposition is one of the key processes to control the technical and economic indicators of alumina products.
  • the equipment used in the seed crystal decomposition process of supersaturated sodium aluminate solution is called "seed seed decomposition tank", referred to as “seed tank or decomposition tank”.
  • the production process usually consists of several to ten kinds of fractionation tanks connected in series. Work together.
  • the decomposition process in which the slurry is completely agitated in each seed tank that is, the full mixed flow
  • air is fully mixed and agitated and mechanically mixed and decomposed.
  • the seed tank with air full mixing method has simple structure, low manufacturing cost and low maintenance cost.
  • this method also has some shortcomings: a) Power consumption is large. Since the height of the seed tank is generally about 30 meters, the static pressure of the slurry is large, so the power consumption of the compressed air required for the full mixing is also large.
  • the mechanical full-mixing agitation method is to erect a mechanical agitation device with multiple layers of specially designed blades in the seeding tank without interruption.
  • this kind of strong stirring can prevent the crystals from depositing and accumulating at the bottom of the decomposition tank, the shearing force generated in the flow field of the sodium aluminate solution causes the process of crystal growth of the aluminum hydroxide to be destroyed, resulting in hydrogen which has grown crystallized.
  • the alumina particles are broken, abraded and refined, which degrades the quality of the product and is not conducive to the production of the sand-like alumina product.
  • the bulky, mechanical agitation device is also several tens of meters long, and the stirring load is large.
  • Puccini Aluminium invented the method and equipment for the production of alumina by decomposing sodium aluminate solution without agitation (CN85108251A or US4666687), which achieved energy savings with a complete agitation and reduced scarring. Phenomenon, but the invention is only applicable to cylindrical-conical small seed wells (about 1500 M 3 ), which cannot be used for large flat bottoms, arc-shaped bottoms or other seed tanks, and is solid for sodium aluminate solution. The content of the slurry is also limited to 600-700g/l, and the slurry flow rate also has special requirements.
  • the technical problem to be solved by the invention is to provide a process method for decomposing and producing aluminum hydroxide by super-saturated sodium aluminate solution with good energy-saving and consumption-reducing effect, high decomposition yield and good product quality, thereby overcoming the above prior art. Insufficient.
  • a process for producing aluminum hydroxide by seed decomposition of a supersaturated sodium aluminate solution The method only performs local agitation at the bottom of the seed crystal decomposition tank, and the agitation intensity is determined by the state in which the aluminum hydroxide particles at the bottom of the seed crystal decomposition tank can be kept in suspension to promote the high solid content of the bottom of the seed crystal decomposition tank and the ratio of the polymer to the aluminum.
  • the sodium carbonate solution diffuses and masses, and the aluminum hydroxide particles at the bottom of the seed decomposition tank are not deposited.
  • the local agitation at the bottom of the seed crystal decomposition tank may be partial agitation using air at the bottom of the seed crystal decomposition tank, or
  • the mechanical device is locally agitated at the bottom of the seed disintegration tank.
  • it is not limited to air agitation, mechanical agitation, etc., and its purpose is to suspend the settled solid aluminum hydroxide particles and enhance the mass transfer and non-deposition of the polymer-specific slurry in the later stage of the reaction.
  • the bottom shape of the seed crystal decomposition tank may be a flat bottom or a conical bottom or a circular arc bottom or a plurality of shape combinations or Other shaped bottoms.
  • the purpose is to collect and collect the materials at the bottom of the seed tanks of different volume and geometric shapes, and to mass transfer and transport them out.
  • the local agitation is performed at the bottom of the seed crystal decomposition tank, specifically, air is locally agitated at the bottom of the seed crystal decomposition tank, that is, Compressed air is blown in the bottom region of the seed disintegration tank for agitation.
  • the local agitation is performed at the bottom of the seed crystal decomposition tank, and specifically, the mechanical device may be used to partially localize the bottom of the seed crystal decomposition tank. Stirring, i.e., agitation using a rotating paddle in the bottom region of the seed disintegration tank.
  • the mechanical device is used for local agitation at the bottom of the seed crystal decomposition tank, specifically, at the bottom region of each seeding tank. Local agitation is carried out by using a rotating blade, and the agitation intensity can be maintained in a suspended state by the aluminum hydroxide particles at the bottom of the seed crystal decomposition tank, which is not deposited at the bottom of the seed crystal decomposition tank.
  • the present invention adopts a process-based method to study the kinetics of the chemical reaction of sodium aluminate solution by experiments, and tests the apparent activation energy of the growth of aluminum hydroxide crystals.
  • the apparent activation energy of the measured growth of aluminum hydroxide is 60. 920 kJ/mol.
  • the experimental results show that the activation energy of the aluminum hydroxide crystal growth reaction is higher. This result indicates that the crystallization reaction is dominated by the surface reaction control, so the method suitable for the diffusion process (e.g., strengthening the stirring force, etc.) does not significantly promote the crystallization reaction process of the aluminum hydroxide crystal.
  • the invention proposes to study the kinetics of the seed crystal reaction of the sodium aluminate solution and the flow characteristics of the slurry, and proposes that in the process of seed crystal decomposition, it is not necessary to fully agitate the slurry, and the local agitation flat flow decomposition method is used to realize energy saving. Process technology route. It is generally believed that the stirring can keep the aluminum hydroxide crystal particles in suspension in the sodium aluminate solution, ensure that the seed crystal has good contact with the solution, make the solution uniform, accelerate the decomposition of the solution and uniformly grow the aluminum hydroxide crystal.
  • the invention finds that the seed crystal decomposition reaction process of the industrial sodium aluminate solution is dominated by the surface chemical reaction control by measuring the apparent activation energy of the crystal decomposition of the sodium aluminate solution, and the stirring strength is not affected to the decomposition efficiency of the seed crystal.
  • decomposition efficiency is not primarily dependent on the diffusion process. Therefore, for the traditional air-mixed agitation, mechanical full-mixing agitation, and the full mixing of the draft tube, the energy can be saved by changing the overall full-mixing agitation to local agitation and flat flow decomposition.
  • the important breakthrough of the invention is to break the traditional process route that requires full mixed flow stirring in the process of seed crystal decomposition, and proposes a new process method of "local agitation + flat flow", that is, the whole full mixed flow stirring mode is changed into local agitation.
  • the mode at the bottom of the seed disintegration tank
  • the invention completely solves the accumulation by adopting local agitation in the bottom area of each seed disintegration tank without using the full mixed flow stirring method (not limited to air stirring and mechanical stirring), and adopts a reasonable design space.
  • the structure, the efficient aggregate system and the matching feed rate enable the normal transfer of the slurry, which in turn enables the series reaction of the entire seed system.
  • the invention can reduce equipment investment, realize energy saving and consumption reduction, effectively prolong the clearing cycle, and reduce maintenance cost, and at the same time, improve the Bayer method seed yield rate and product quality to some extent.
  • the partial agitating flat flow type seeding tank of the invention is a normal pressure liquid flow operation, and the liquid flow is slow and stable. This flow does not cause agitation, so that a stable dynamic balance can be established in the seed well, and the entire seed decomposition process is continuously and stably performed, and the two-phase flow of the seed decomposition can be regarded as a steady state process.
  • the slurry maintains a constant weight ratio in each horizontal section perpendicular to the axial direction, and gradually increases from the top to the bottom in the axial direction, and the kinetic conditions of the crystallization reaction are completely different from the conventional integral full mixing.
  • the stirring crystallization decomposition process technology, the reaction state is closer to the theoretical dynamics of the batch reaction.
  • the present invention has the following features: (1) The present invention does not adopt the traditional mixed agitation full-mixing mode, and only uses local agitation in the bottom region of the seed crystal decomposition tank to make it perpendicular to The properties of the solution in the same cross section in the flow direction are basically the same, so that the solid content and supersaturation of the solution are distributed in a gradient along the flow direction. During the reaction, the solid-liquid suspension slurry approximates the "flat flow", which is not only completely The back mixing phenomenon is avoided, and the kinetic conditions of the crystallization reaction of the sodium aluminate solution are completely changed, which is beneficial to increase the efficiency of the seed crystal decomposition reaction.
  • the invention adopts local agitation in the bottom region of the seed crystal decomposition tank, which can effectively avoid accumulation and clogging, and provides guarantee for the normal flow transmission production of the slurry, and realizes the series reaction process of multiple decomposition tanks of the seed system. .
  • moderate agitation of the solution entering the bottom of the seed decomposition tank and having a low supersaturation is beneficial to the diffusion mass transfer during the decomposition reaction, which is beneficial to the improvement of the decomposition rate.
  • the present invention does not have a strong full-mixing agitation motion, and there is no shear force caused by strong agitation in the flow field of the sodium aluminate solution in the seed crystal decomposition tank, and the solution crystallization reaction can be similar to the "flat flow"
  • the method is smooth and continuous without causing any agitation, which provides good reaction conditions for crystal growth and agglomeration. Therefore, the growth process of aluminum hydroxide crystals will not be destroyed, and the breakage and abrasion of product particles are reduced. It is easy to obtain a large-grained alumina product.
  • the invention can realize continuous and smooth crystallization reaction without strong stirring of the tumbling solution, greatly saves energy consumption, saves production and installation cost of the reaction device, reduces equipment input and operation cost, and improves product particle size distribution, It also eliminates the disadvantages of fouling caused by the violent liquid tumbling at the top of the decomposition reaction tank, prolongs the cleaning cycle and has outstanding advantages.
  • Large flat bottom mechanically stirred sodium aluminate solution crystal The decomposition tank has become the mainstream technology at home and abroad, in which the cost of the motor and the stirring slurry is high, and daily maintenance is required.
  • the use of the invention will enable an alumina production enterprise with a design capacity of 800,000 tons to save tens of millions of equipment investment.
  • the remarkable feature of the invention is energy saving and consumption reduction, and the technology can achieve the purpose of greatly reducing energy consumption without affecting the quality and output of the product.
  • the invention can reduce the compressed air consumption by 80-90%, and save direct power consumption by 30-40% compared with the existing mechanical stirring full mixed flow stirring decomposition technology.
  • Technical and economic indicators are good.
  • the present invention can meet the process conditions required for tantalum production of a sodium aluminate solution in series with N seed crystal decomposition tanks having a solid content of less than 100 g/1.
  • the sodium aluminate solution in the present invention flows in the seed tank in the "flat flow" flow pattern, the solution in each micro element volume moves forward at the same speed, and there is no back mixing in the flow direction of the solution.
  • the composition of the solution in each section along the radial direction of the seeding groove changes little during the time course, and will not be disturbed.
  • the decomposition and crystallization reaction is continuously steady state, and the aluminum hydroxide crystal particles are uniformly distributed as the flowing solution passes through the collecting plate.
  • the ground is dispersed into a small area at the bottom and then stirred up and then transported out through the extraction pipe. Since the solid particles are concentrated to a small extent in the bottom after being aggregated, they can be efficiently transported out, making it difficult for the bottom to accumulate material. At the same time, this partial agitation plays a role in promoting localized diffusion and mass transfer in the bottom polymer ratio sodium aluminate solution, but does not affect the near-flat flow state and crystallization reaction of the low molecular ratio sodium aluminate solution in the upper part of the seed well. Dynamic conditions. In addition, the decomposition rate and product quality of sodium aluminate can be improved.
  • the reaction is carried out in the seed tank in the same condition as the pressurized liquid flow of the piston, and the reaction power is better than that in the case of sufficiently stirring into a uniform medium; on the other hand, the flow field in the seed tank is only low. Shear forces increase the agglomeration of small particle size aluminum hydroxide, which helps to obtain the smallest particle size distribution with small particles.
  • the compressed air consumption measured by the provincial energy-saving monitoring center is: The experimental group's compressed air consumption averages 14.82 m 3 /h, and the comparative group's compressed air consumption averages 205.3 m 3 /h.
  • the experimental group can save 190.48m 3 /h and save 92.78%.
  • Table 1 statistically analyzes the difference in decomposition rates between groups. The results showed that the average decomposition rate of the test group was 1.55 percentage points higher than the average of the two parallel control groups.
  • test group using the present invention is more than the comparison group (group 1 and group 2) of the previous whole agitation and full mixed flow.
  • the decomposition rate is slightly higher, and the main factors leading to the increase in decomposition rate are:
  • the local agitation flat flow decomposition mode of the present invention allows the slurry in the seeding tank to be disordered and arranged from top to bottom. At the same time, the liquid flow is slow and stable, and does not cause vigorous agitation, so that a stable dynamic balance can be established in the seed tank, so that the entire seed crystal decomposition process is continuously and stably performed.
  • the flat push flow seeding of the present invention ensures an effective reaction path or time for the slurry. Since the flat flow decomposition completely avoids the "short circuit" and “backmixing" of the slurry, the slurry entering the seed tank can be fully reacted.
  • the flat flow decomposition mode of the present invention increases the effective reaction volume in the tank.
  • the entire slurry flows in the same direction in the flat flow type branching tank, there is no dead zone in the tank, and all the volumes are utilized; and in the conventional jet compressed air full mixing and stirring type seeding tank, the air volume of the emulsified slurry is generated. Not used.
  • the local agitating flat flow type seeding tank (test group) of the present invention is compared with the conventional jet compressed air full mixing stirring seeding tank (comparative group 1 and comparison group 2).
  • the grain crystal morphology is relatively close, but the fine-grained grain distribution is reduced.
  • the above test results show that the decomposition rate of the supersaturated sodium aluminate solution of the present invention is improved, and the particle size is also improved, and the obtained aluminum hydroxide crystal particles are crystallized in a regular shape, and the shape is regular, and the surface fine particles are less adhered.
  • the extended hexagonal crystal which is decomposed by the full mixed flow method of the conventional jet compressed air is broken, the edges are broken, the edges are broken, and a large amount of fine particles adhere to the surface.
  • these fine particles are caused by the damage of the crystal due to the large shear force in the flow field; it is also possible that the growth of the secondary nucleus adheres to it.
  • Example 1 The cylindrical-flat bottom structure is used to mechanically stir the seeding troughs, each of which has a diameter of 14 m, a height of 35 m, and a tank volume of 4500 m 3 .
  • a layer of rotating blades is used for local agitation.
  • the agitation intensity is maintained at the bottom of the seed crystal.
  • the aluminum hydroxide particles at the bottom of the tank can be kept in suspension and not at the bottom of the seed crystal decomposition tank.
  • the raw deposits shall prevail, and the rest shall be carried out in accordance with the daily production operation regulations of the alumina plant.
  • the withdrawal rate of the seed discharge end of the seed tank is greater than the interference sedimentation speed of the solid particles in the solution.
  • the manner of material extraction can be, but is not limited to, compressed air, mechanical pumps, or manufacturing liquid level differences.
  • this example only arranges a layer of blade near the bottom of the seeding tank, which not only reduces the load on the motor, but also reduces the load. Electrical consumption, but also reduces the manufacturing difficulty of rotating shafts, bearings and other components.
  • the air-mixing seeding tank is a cylindrical-conical bottom structure, each of which has a diameter of 8. 2 m, a height of 29.7 m, and a tank volume of 1300 m 3 .
  • Compressed air is blown in the bottom area (or the end of the discharge) of each seeding tank for local agitation.
  • the agitation intensity of the alumina particles at the bottom of the seed crystal decomposition tank can be kept in suspension and not deposited at the bottom of the seed crystal decomposition tank.
  • the rest shall be implemented in accordance with the daily production operation regulations of the alumina plant.
  • the withdrawal rate of the seed discharge end of the seed tank is greater than the interference sedimentation speed of the solid particles in the solution.
  • the manner of material extraction can be, but is not limited to, compressed air, mechanical pumps, or manufacturing liquid level differences.
  • Example 3 The cylindrical-multi-cone bottom combined air agitating seeding tank, each seeding tank has a diameter of 15m, a height of 35m, and a tank volume of 5500m 3 ; each cone bottom (or the discharge end) in the bottom area of each seeding tank.
  • the compressed air is blown in for local agitation, and the agitation intensity is maintained in a suspended state at the bottom of the seed crystal decomposition tank, and is not deposited at the bottom of the seed crystal decomposition tank, and the rest is performed according to the daily production operation regulations of the alumina plant.
  • the withdrawal rate of the seed discharge end of the seed tank is greater than the interference sedimentation speed of the solid particles in the solution.
  • the manner of material extraction can be, but is not limited to, compressed air, mechanical pumps, or manufacturing liquid level differences.

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Abstract

一种过饱和铝酸钠溶液晶体分解生产氢氧化铝的方法，其中仅在晶种分解槽底部进行局部搅动，搅动强度以晶种分解槽底部的氢氧化铝颗粒能保持悬浮状态为准，以促进晶种分解槽底部高固含、高分子比铝酸钠溶液的扩散传质，并使晶种分解槽底部的氢氧化铝颗粒不产生沉积。

Description

过饱和铝酸钠溶液晶种分解生产氢氧化铝的方法 技术领域
本发明涉及一种生产氧化铝的工艺方法， 特别是一种过饱和铝酸钠溶液晶种分解生产 氢氧化铝的工艺方法， 属于冶金技术领域。
背景技术
拜耳法生产氧化铝具有流程简单、 作业方便、 产品质量高的特点。 目前全世界生产的 氧化铝 90%以上是用拜耳法生产的。 在拜耳法生产氧化铝的过程中， 过饱和铝酸钠溶液添 加晶种进行分解反应是重要的工序之一， 通常称为 "晶种分解工序"， 简称 "种分工序"， 是在过饱和铝酸钠溶液中添加大量的氢氧化铝作为晶种， 进行氢氧化铝晶体的诱导结晶和 长大， 使过饱和铝酸钠溶液分解， 分解反应持续 35〜75h后得到的氢氧化铝浆料， 进行液 固分离并按颗粒大小进行分级， 分解后所得的粗颗粒氢氧化铝经洗涤、 脱水后即获得氧化 铝产品； 细颗粒的氢氧化铝返回分解流程继续用做晶种。 因此， 晶种分解是控制氧化铝产 品技术经济指标的关键工序之一。 过饱和铝酸钠溶液晶种分解工序中所采用的设备称为 "晶种分解槽"， 简称 "种分槽或分解槽"， 生产过程通常是由几个至十几个种分槽串联在 一起进行。
长期以来， 在铝酸钠溶液晶种分解工序中， 一直采用的是在每个种分槽内整体搅动浆 液， 即全混流的分解工艺方法。 目前普遍应用的是空气全混搅拌分解和机械全混搅拌分解 两种方式。 采用空气全混搅拌方式的种分槽结构简洁、 制造成本低， 维护费用少， 然而， 该方式也存在一些不足之处： a) 动力消耗大。 由于种分槽槽体高度一般在 30米左右， 浆 液静压很大， 因此为满足全混搅拌所需压縮空气的消耗动力也较大。 b) 种分槽内容易产 生结疤， 特别槽顶结疤严重， 脱落后易堵塞出料管， 造成沉槽重大生产事故。 c)易产生浆 液 "短路"、 "返混"现象， 使刚进入种分槽的低分子比浆液的分解动力下降。 d ) 用空气 搅拌时精液吸收其中的 C02使部分苛性碱变为碳酸碱， 不利于晶种分解。机械全混搅拌分解 方式是在种分槽中竖立设置一个带有多层特殊设计桨叶的机械搅拌装置不间断地进行搅 拌。 这种强力搅拌虽然可以防止结晶体在分解槽底部沉淀堆积， 但铝酸钠溶液流场内产生 的剪切力一方面会使氢氧化铝结晶长大过程遭到破坏， 造成已结晶长大的氢氧化铝颗粒被 破碎、 磨蚀、 细化， 使产品质量下降， 不利于砂状氧化铝产品的产出。 另外， 由于分解槽 体积庞大、 机械搅拌装置也长达几十米， 搅拌负荷较大， 因此不仅对搅拌系统的搅拌轴、 搅拌桨叶等构件的制造要求较高， 而且能耗也较大， 制造安装成本昂贵， 运行维护费用高。 一台直径 14米、 高 35米的种分槽需配置一台 75千瓦的搅拌电机和变速箱， 成本比较昂 贵； 而且电机连续运转， 不停产、 不停止， 需要消耗大量电能。 多年的生产实践证明， 不 论是空气全混搅拌还是机械全混搅拌，都会造成上、下层液体之间相互混杂（俗称 "短路")， 降低了输送到种分槽内的铝酸钠溶液过饱和度， 使反应效率下降； 同时强烈的全混流搅动 也造成了产品粒度下降。 法国皮奇尼铝公司在 1985 年发明了 "无搅拌情况下分解铝酸钠 溶液制造氧化铝的方法和设备" （CN85108251A或 US4666687)， 其采用完全取消搅拌的方法 实现了节能， 同时减弱了结疤现象， 但该发明只适用于圆柱-圆锥形的小型种分槽（1500 M3 左右）， 无法用于大型的平形底、 圆弧形底或其他种分槽， 而且对铝酸钠溶液的固含也限 制在 600-700g/l以内， 浆料流速也有特别要求， 因此， 其适用范围受到很大的局限， 根本 无法满足当前晶种分解技术发展对大容量 (4000M3以上）、 高固含（800-1000g/l )分解装备 的要求， 并且由于该发明完全取消了搅拌， 在种分槽的底部易产生大量积料， 引发沉槽事 故， 中断生产流程。
发明内容
本发明所要解决的技术问题在于提供一种节能降耗效果好、 分解产出率高、 产品质量 好的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法， 从而克服上述现有技术的不 足。
为解决上述技术问题， 本发明采用如下的技术方案： 一种过饱和铝酸钠溶液晶种分解 生产氢氧化铝的工艺方法。 该工艺方法仅在晶种分解槽的底部进行局部搅动， 搅动强度以 晶种分解槽底部的氢氧化铝颗粒能保持悬浮状态为准， 以促进晶种分解槽底部高固含、 高 分子比铝酸钠溶液的扩散传质， 并使晶种分解槽底部的氢氧化铝颗粒不产生沉积。
上述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法中， 所述的在晶种分解槽 底部进行局部搅动可以是采用空气在晶种分解槽的底部进行局部搅动， 或者是采用机械装 置在晶种分解槽的底部进行局部搅动。 但不限于空气搅动、 机械搅动等， 其目的是让沉降 下来的氢氧化铝固体颗粒悬浮起来以及加强对反应后期高分子比浆料的扩散传质和不沉 积。
前述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法中， 所述晶种分解槽的底 部形状可以是平形底或锥形底或圆弧形底或多种形状组合形底或其它异形底。 其目的是为 适合不同容积和几何外形种分槽底部物料的汇集收拢、 集中搅动传质后输送出去。 前述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法中， 所述的在晶种分解槽 底部进行局部搅动， 具体说是采用空气在晶种分解槽的底部进行局部搅动， 即在晶种分解 槽的底部区域吹入压縮空气进行搅动。
前述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法中， 所述的在晶种分解槽 底部进行局部搅动， 具体说还可以是采用机械装置在晶种分解槽的底部进行局部搅动， 即 在晶种分解槽的底部区域采用旋转桨叶进行搅动。
前述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法中， 所述的采用机械装置 在晶种分解槽的底部进行局部搅动， 准确说， 是在每台种分槽的底部区域采用一层旋转桨 叶进行局部搅动， 搅动强度以晶种分解槽底部的氢氧化铝颗粒能保持悬浮状态， 不在晶种 分解槽底部产生沉积为准。
本发明的技术原理： 本发明采用基于过程特征的方法， 通过实验对铝酸钠溶液晶种分 解化学反应动力学过程进行研究， 并测试计算氢氧化铝晶体长大的表观活化能， 分析了搅 拌传质作用对反应过程的影响。测得的氢氧化铝长大的表观活化能在 60. 920kJ/mol。 实验 结果表明， 氢氧化铝晶体长大反应的活化能较高。 该结果说明结晶反应以表面反应控制为 主导， 因此适用于扩散过程的方法 （如加强搅拌力度等） 对氢氧化铝晶体的结晶反应过程 无明显促进作用。 相反， 提高搅拌强度的结果只能造成已长大晶粒的破碎和磨蚀， 从而影 响产品质量和浪费能量。 总体而言， 在溶液分解动力不足的时候， 如分子比高时， 采用一 定的搅拌和适宜的搅拌强度有助于铝酸根阴离子的扩散传质； 而在分子比低时， 溶液分解 动力大， 可以减弱或取消搅拌。 因此， 在反应的过程中， 合理配置搅拌位置和采用不同的 搅拌方式， 将对提高产品产率与质量、 减少能耗、 降低生产成本有很大帮助， 更能提高氧 化铝生产企业的经济效益和产品竞争力。 特别地， 在晶种分解过程的氢氧化铝晶体长大阶 段取消或减弱搅拌是可行的。
本发明通过对铝酸钠溶液晶种反应动力学过程和浆料流动特性的研究， 提出了在晶种 分解过程中无须全混流搅拌浆料， 而采用局部搅动平推流分解方式来实现节能的工艺技术 路线。 一般认为， 搅拌能使氢氧化铝晶体颗粒在铝酸钠溶液中保持悬浮状态， 保证晶种与 溶液有良好的接触， 使溶液均匀， 加速溶液的分解并使氢氧化铝晶体均匀地长大。 本发明 通过测定铝酸钠溶液晶种分解的表观活化能发现： 工业铝酸钠溶液的晶种分解反应过程是 以表面化学反应控制占主导， 提高搅拌力度对晶种分解效率影响不大， 说明分解效率主要 不是取决于扩散过程。 因此对于传统的空气全混搅拌、 机械全混搅拌以及导流筒全混搅拌 等种分过程， 可以通过改变整体全混流搅拌为局部搅动平推流分解来实现节能。 本发明的重要突破就是打破了以往在晶种分解过程中需要全混流搅拌的传统工艺技 术路线， 提出了 "局部搅动 +平推流" 的新工艺方法， 即将整体全混流搅拌模式变为局部 搅动模式 (在晶种分解槽底部）， 使晶种分解过程从整个全混流的模式变为近于 "平推流" 模式。 本发明在不采用全混流搅拌方式 (不限于空气搅拌和机械搅拌）的前提下， 通过在每 个晶种分解槽底部区域内采用局部搅动的方式彻底解决了积料， 并通过设计合理的空间结 构、 高效的集料系统和匹配的提料速度实现浆料的正常传输， 进而实现整个种分系统的串 联反应过程。本发明可减少设备投资、 实现节能降耗、有效延长清槽周期、 降低维护费用， 同时， 在一定程度上提高了拜耳法种分产出率和产品质量。
本发明的局部搅动平推流种分槽是一种常压液流操作， 液流缓慢、 平稳。 这种液流不 引起搅动， 因而可在种分槽中建立起稳定的动力平衡， 整个晶种分解过程连续、 稳定地进 行， 晶种分解的两相流动可以看作是稳态过程。 浆料在此状态下， 在垂直于轴向的每一水 平截面上保持恒定的重量比， 并沿轴向从上至下逐渐增大， 结晶反应的动力学条件完全不 同于传统的整体全混搅拌式结晶分解工艺技术， 反应状态更接近于间歇反应的理论动力学 性质。
本发明的有益效果： 与现有技术相比， 本发明具有以下特点： （1 ) 本发明不采用传统 整体搅拌的全混流方式， 仅在晶种分解槽底部区域采用局部搅动， 使在垂直于流动方向上 同一横截面内溶液的性质基本保持一致，使溶液的固含、过饱和度沿流动方向呈梯度分布， 反应过程中固 -液悬浮浆料近似于 "平推流"， 这样不仅完全避免了返混现象， 也完全改变 了铝酸钠溶液结晶反应的动力学条件， 有利于提高晶种分解反应效率。 （2) 本发明在晶种 分解槽底部区域采用局部搅动的方式， 可有效避免积料、 瘀堵， 为料浆的正常流动传输生 产提供保证， 实现种分系统多个分解槽的串联反应过程。 同时， 对于进入晶种分解槽底部 反应后期、 过饱和度较低的溶液 (其分子比 较高)进行适度的搅动， 有利于分解反应过程 中的扩散传质， 有利于分解率的提高。 （3) 本发明由于没有强烈的全混流搅拌运动， 晶种 分解槽内的铝酸钠溶液流场中不存在强力搅拌引起的剪切力， 溶液结晶反应能够以似近 "平推流" 的方式平稳、 连续进行而不会引起任何搅动， 为晶体的长大、 附聚提供了良好 的反应条件， 因此氢氧化铝晶体长大过程不会遭到破坏， 减少了产品颗粒的破碎、 磨蚀现 象， 易于得到粒度较大的氧化铝产品。 （4) 本发明无需强烈搅动翻滚溶液即可实现结晶反 应的连续平稳进行， 大大节约了能耗， 节省了反应装置的制作和安装成本， 减少设备投入 和运行成本并改善了产品粒度分布， 同时还消除了分解反应槽顶部由于液体剧烈翻滚而造 成结垢的弊端， 延长了清理周期， 具有突出的优点。 大型平形底机械搅拌式铝酸钠溶液晶 种分解槽目前已成为国内外的主流工艺技术， 其中电机和搅拌浆费用高， 还需日常维护保 养。 采用本发明将会使一个设计产能 80万吨的氧化铝生产企业节约几千万元的设备投资。
本发明的显著特点是节能降耗， 该技术在不影响产品的质量和产量前提下可以实现大 幅度降低能耗的目的。 与现有喷射空气全混流搅拌分解技术相比， 本发明可降低压縮空气 耗量达 80-90%， 与现有机械搅拌全混流搅拌分解技术相比， 节约直接电耗 30-40%， 技术 经济指标良好。
本发明的主要技术特点：与现有技术比较，本发明能够满足铝酸钠溶液在固含 lOOOg/1 以下 N个晶种分解槽串联生产所需的工艺条件。 本发明中的铝酸钠溶液以 "平推流"流型 在种分槽中流动时， 每一微元体积里的溶液以相同的速度向前移动， 在溶液的流动方向上 不存在返混且沿种分槽径向每一个截面上溶液组成在时间进程中变化很小， 不会被打乱， 分解结晶反应连续稳态进行， 氢氧化铝结晶颗粒随流动溶液通过集料板时被均匀地分散到 底部一个小的面积内后被搅动扬起， 再通过提料管道输送出去。 由于经过集料后， 固体颗 粒被集中到底部小范围内， 能被有效地输送出去， 使底部不易产生物料堆积。 同时， 这种 局部搅拌对底部高分子比的铝酸钠溶液起到了促进局部区域扩散传质的作用， 但不影响种 分槽上部低分子比铝酸钠溶液的近平推流状态和结晶反应的动力学条件。 此外， 铝酸钠的 分解率和产品质量可得到提高。 一方面， 反应是在种分槽内等同于活塞加压液流条件下进 行的， 其反应动力要比充分搅拌成均一介质情况为好； 另一方面， 种分槽内流场内仅为低 剪切力， 增加了小粒度氢氧化铝的集聚， 有助于得到含小粒子最少的粒度分布。
为验证本发明的技术效果， 申请人进行了以下工业试验： 在国内某氧化铝厂 40万吨 种分生产线上采用本发明技术制作了 14台锥形底 Φ 8. 2mX 29. 7m种分槽串联形成一条完整 的生产线作为实验组， 同时平行的两条采用全混搅拌技术的生产线作为对比组。
统计结果： （1 ) 压縮空气消耗。
经省级节能监测中心测定认证压縮空气消耗量为： 实验组压縮空气消耗量平均 14.82 m3/h,对比组压縮空气消耗量平均 205.3m3/h。实验组可节约风量 190.48m3/h，节能 92.78%。
(2) 和分解率变化
表 1统计分析了各组之间分解率的差别。 结果显示， 试验组的平均分解率比平行的两 个对比组的平均值高出 1.55个百分点。
表 1 本发明与全混搅拌工艺分解率比较 分解率 /% 分解率提高绝对量 /%
对比组
试验组 对比 1组 对比 2组 对比 1组 对比 2组 对比均值 均值
51. 71 50. 57 50. 38 50. 47 1. 14 1. 33 1. 23
52. 06 49. 84 50. 29 50. 06 2. 22 1. 77 2. 00
51. 85 50. 27 50. 34 50. 31 1. 58 1. 51 1. 55 同比条件下， 采用本发明的试验组比采用以往整体搅拌、 全混流的对比组 （1 组、 2 组） 的分解率稍高， 导致分解率提高的主要因素为：
a) 本发明的局部搅动平推流分解方式使种分槽内浆液的 没有混乱， 由上至下有序排 布。 同时液流缓慢、 平稳， 不引起剧烈搅动， 因而可在种分槽中建立起稳定的动力平衡， 使整个晶种分解过程连续、 稳定地进行。
b) 本发明的平推流种分槽保证了浆液的有效反应路径或时间。由于平推流分解完全避 免了浆液的 "短路"与 "返混" ， 使进入种分槽中的浆液能充分反应。
c) 本发明的平推流分解方式使槽内的有效反应容积增大。平推流种分槽中整个浆液向 同一方向流动， 槽内没有死区， 全部容积均被利用； 而在传统的喷射压縮空气全混搅拌式 种分槽内， 生成乳化状浆液的空气体积没有被利用。
(3) 氢氧化铝的粒度分布
在粒度分布方面， 采用本发明的局部搅动平推流种分槽 （试验组） 与传统喷射压縮空 气全混搅拌种分槽 （对比 1组、 对比 2组） 相比在各个分段上的晶粒结晶形貌比较接近， 但细粒度晶粒分布减低。
以上试验结果表明， 采用本发明的过饱和铝酸钠溶液的分解率有了提高， 粒度也得到 了改善， 得到的氢氧化铝晶体颗粒结晶规整， 形状规则， 表面细碎粒子黏附较少。 而采用 传统喷射压縮空气整体搅拌的全混流方式分解产出的延长六边形晶体则棱角破损， 边缘折 断， 表面有大量细碎粒子黏附。 这些细碎粒子一方面是由于流场内存在较大剪切力致使晶 体破损所致； 同时也可能是次生晶核生长黏附于其上。
下面结合具体实施方式对本发明作进一步的说明。
具体实施方式
实施例 1。 采用圆柱-平形底结构机械搅拌种分槽， 每台种分槽直径为 14m， 高 35m， 槽体容积 4500m3。 在每台种分槽的底部区域 （或出料末端） 采用一层旋转桨叶进行局部搅 动， 搅动强度以晶种分解槽底部的氢氧化铝颗粒能保持悬浮状态、 不在晶种分解槽底部产 生沉积为准， 其余按氧化铝厂日常生产操作规程要求执行。 种分槽出料端的提料速度大于 溶液中固体颗粒的干涉沉降末速。 提料的方式可采用但不限于压縮空气、 机械泵或制造液 位差等方式。 与原来沿搅拌轴设置多层桨叶 （一般五层） 的全混搅拌方式相比，该实例仅 在靠近种分槽底部的位置配置一层浆叶， 不仅减轻了电动机的负荷， 降低了用电消耗， 而 且还降低了旋转轴、 轴承等构件的制造难度。
实施例 2。采用圆柱-圆锥形底结构空气搅拌种分槽，每台种分槽直径为 8. 2m，高 29. 7m, 槽体容积 1300m3。 在每台种分槽的底部区域 （或出料末端） 吹入压縮空气进行局部搅动， 搅动强度以晶种分解槽底部的氢氧化铝颗粒能保持悬浮状态、 不在晶种分解槽底部产生沉 积为准， 其余按氧化铝厂日常生产操作规程要求执行。 种分槽出料端的提料速度大于溶液 中固体颗粒的干涉沉降末速。 提料的方式可采用但不限于压縮空气、 机械泵或制造液位差 等方式。
实施例 3。 采用圆柱-多锥底组合空气搅拌种分槽， 每台种分槽直径为 15m， 高 35m， 槽体容积 5500m3; 在每台种分槽底部区域的每个锥底 （或出料末端） 吹入压縮空气进行局 部搅动， 搅动强度以晶种分解槽底部的氢氧化铝颗粒能保持悬浮状态、 不在晶种分解槽底 部产生沉积为准， 其余按氧化铝厂日常生产操作规程要求执行。 种分槽出料端的提料速度 大于溶液中固体颗粒的干涉沉降末速。 提料的方式可采用但不限于压縮空气、 机械泵或制 造液位差等方式。
本发明的实施方式不限于上述实施例， 在不脱离本发明宗旨的前提下做出的各种变化 均属于本发明的保护范围之内。

Claims

权 利 要 求 书
1、 一种过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法， 其特征在于： 仅在晶种分 解槽的底部进行局部搅动， 搅动强度以晶种分解槽底部的氢氧化铝颗粒能保持悬浮状态为 准， 以促进晶种分解槽底部高固含、 高分子比铝酸钠溶液的扩散传质， 并使晶种分解槽底 部的氢氧化铝颗粒不产生沉积。
2、 根据权利要求 1 所述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法， 其特征 在于： 所述的在晶种分解槽底部进行局部搅动是采用空气在晶种分解槽的底部进行局部搅 动， 或者采用机械装置在晶种分解槽的底部进行局部搅动。
3、 根据权利要求 1或 2所述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法， 其 特征在于： 所述晶种分解槽的底部形状为平形底、 锥形底、 圆弧形底、 多种形状组合形底 或其它异形底。
4、 根据权利要求 2 所述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法， 其特征 在于： 所述的在晶种分解槽底部进行局部搅动是采用空气在晶种分解槽的底部进行局部搅 动， 即在晶种分解槽的底部区域吹入压縮空气进行搅动。
5、 根据权利要求 2 所述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法， 其特征 在于： 所述的在晶种分解槽底部进行局部搅动是采用机械装置在晶种分解槽的底部进行局 部搅动， 即在晶种分解槽的底部区域采用旋转桨叶进行搅动。
6、 根据权利要求 5 所述的过饱和铝酸钠溶液晶种分解生产氢氧化铝的工艺方法， 其特征 在于： 所述的采用机械装置在晶种分解槽的底部进行局部搅动， 是在每台种分槽的底部区 域采用一层旋转桨叶进行局部搅动， 搅动强度以晶种分解槽底部的氢氧化铝颗粒能保持悬 浮状态， 不在晶种分解槽底部产生沉积为准。
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