结晶法是依据物料熔点 ( 结晶点 ) 的差异来实现其它分离方法难以完成的物料分离。由工业萘制取精萘的 生产 过程，就是利用结晶法脱除萘中的硫茚和提高萘纯度。目前，国内广泛采用的方法有动态降膜结晶法和静态结晶法两种，鞍钢化工总厂采用的是动态降膜结晶法，宝钢、上海焦化厂等采用的是静态结晶法。 1 问题分析 我公司采用静态分步结晶法 生产 精萘，其流程大体如下：将原料工业萘装入结晶箱后进行快速降温，降至 82~C 后转为均匀降温，以 2~C ／ h 的降温速度冷却至 60~C ，排放富含硫茚的第一次晶析萘油，作为中间馏分待后处理。然后结晶箱内的物料以 4~C ／ h 的速度升温，每半小时取样一次，测定其结晶点，根据结晶点的不同，分别排人对应馏分槽，如此进行 3 ～ 4 次分步结晶，可得到较高纯度的精萘。

The crystallization method is based on the difference in the melting point (crystallization point) of materials to achieve material separation that is difficult to achieve by other separation methods. The production process of producing refined naphthalene from industrial naphthalene involves the use of crystallization to remove thionines from naphthalene and improve its purity. At present, there are two widely used methods in China: dynamic falling film crystallization and static crystallization. Ansteel Chemical Plant uses dynamic falling film crystallization, while Baosteel and Shanghai Coking Plant use static crystallization. 1. Problem analysis: Our company uses the static stepwise crystallization method to produce refined naphthalene, and the process is generally as follows: the raw industrial naphthalene is loaded into a crystallization box for rapid cooling, and then cooled to 82~C before switching to uniform cooling. The cooling rate is 2~C/h to 60~C, and the first crystallization naphthalene oil rich in sulfur indene is discharged as an intermediate fraction for post-treatment. Then, the materials inside the crystallization box are heated at a rate of 4~C/h, and samples are taken every half hour to determine their crystallization points. According to the different crystallization points, they are arranged in the corresponding distillation tanks. This process is carried out 3-4 times in steps to obtain high-purity refined naphthalene.

然而，我公司生产的精萘酸洗比色一直偏高，经常在 10 号左右。而 生产工艺 和设备与本公司大体相同的上海焦化厂，精萘的酸洗比色不超过 2 号。经实际调研发现，在萘结晶过程中，晶体表面粘附有一层胶体状不纯物，如果不对它加以处理，必然将其带人相应的馏分槽或产品槽内。我们却忽视了这一过程，认为这些胶体状物质可通过多次分步结晶予以分离，致使精萘产品的比色偏高。

However, the color ratio of the refined naphthalene pickling produced by our company has been consistently high, often around the 10th. The production process and equipment of the Shanghai Coking Plant, which is roughly the same as our company, do not exceed the acid washing color ratio of No. 2 for refined naphthalene. Through actual research, it has been found that during the crystallization process of naphthalene, there is a layer of colloidal impurities adhered to the surface of the crystal. If it is not treated, it will inevitably be taken into the corresponding distillation tank or product tank. We have overlooked this process and believe that these colloidal substances can be separated through multiple stepwise crystallization, resulting in a higher color ratio of the refined naphthalene product.

2 改进措施 我们在改进精萘 工艺 时，在利用原有设备的基础上，未作任何管线和设备的改动，而只是采用了三步或两步结晶的方法，每一步由进料、预冷、结晶、排液、发汗和熔化等 6 个环节组成。

2 Improvement Measures: When improving the naphthalene refining process, we did not make any changes to the pipeline and equipment based on the original equipment, but only adopted a three-step or two-step crystallization method, each step consisting of six steps: feeding, pre cooling, crystallization, liquid discharge, sweating, and melting.

(1) 进料。原料工业萘由泵装入结晶箱。

(1) Feed. The raw material industrial naphthalene is pumped into a crystallization box.

(2) 预冷。通过调节结晶箱内循环介质的温度，使结晶箱内的萘冷却至结晶点。此时，硫茚等杂质富集于液相，萘逐步结晶于结晶管上，晶体逐渐增大。 (3) 结晶。结晶器温度进一步降低后，结晶开始大量析出，萘以柱状晶体构成网状结晶层，硫茚存在于这些晶体周围的液相中。此时，网状晶体的密度不宜过高，以利于晶体内的液相排出。

(2) Pre cooling. By adjusting the temperature of the circulating medium in the crystallization chamber, the naphthalene in the crystallization chamber is cooled to the crystallization point. At this point, impurities such as thionines are enriched in the liquid phase, while naphthalene gradually crystallizes on the crystallization tube and the crystal size gradually increases. (3) Crystallization. After the temperature of the crystallizer further decreases, a large amount of crystallization begins to precipitate, and naphthalene forms a network of crystalline layers in columnar crystals. Thiindene exists in the liquid phase around these crystals. At this point, the density of the network crystal should not be too high to facilitate the discharge of the liquid phase inside the crystal.

(4) 排液。富集了硫茚等杂质的液相自流出结晶箱，排人残液槽。

(4) Drainage. The liquid phase enriched with impurities such as sulfur indene flows out of the crystallization chamber and is discharged into the residual liquid tank.

(5) 发汗。又称部分熔化，是指逐步提高结晶箱传热介质的温度，使结晶箱内的结晶逐渐被加热，并部分熔化。随着温度的提高，晶体内包含的低熔点杂质首先熔化，并逐渐渗透到晶体外表面，少部分的萘也随之熔化，晶体表面的不纯物液膜逐渐被替换。熔化后的液体自流出结晶箱，排人相应的馏分槽。 (6) 熔化。当试样的结晶点达到规程要求后，迅速加热升温，结晶箱内的物料全部熔化，根据需要再次进料。经上述改进后，精萘的一级品率高达 100 ％，产品收率达 90 ％左右。

(5) Sweating. Also known as partial melting, it refers to gradually increasing the temperature of the heat transfer medium in the crystallization box, so that the crystals inside the crystallization box are gradually heated and partially melted. As the temperature increases, the low melting point impurities contained within the crystal first melt and gradually penetrate the outer surface of the crystal. A small amount of naphthalene also melts, and the impure liquid film on the crystal surface is gradually replaced. The melted liquid flows out of the crystallization box and is discharged into the corresponding distillation tank. (6) Melt. After the crystallization point of the sample meets the requirements of the regulations, it is quickly heated and heated up, and all materials in the crystallization box are melted. Feed again as needed. After the above improvements, the first grade yield of refined naphthalene is as high as 100%, and the product yield is about 90%.

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This article is provided by a refined naphthalene manufacturer for assistance. For more related content, please click on http://www.jnjdbc.cn I hope this article can be helpful to you. Thank you for reading!