結晶法是依據(jù)物料熔點 ( 結晶點 ) 的差異來實現(xiàn)其它分離方法難以完成的物料分離。由工業(yè)萘制取精萘的 生產 過程，就是利用結晶法脫除萘中的硫茚和提高萘純度。目前，國內廣泛采用的方法有動態(tài)降膜結晶法和靜態(tài)結晶法兩種，鞍鋼化工總廠采用的是動態(tài)降膜結晶法，寶鋼、上海焦化廠等采用的是靜態(tài)結晶法。 1 問題分析 我公司采用靜態(tài)分步結晶法 生產 精萘，其流程大體如下：將原料工業(yè)萘裝入結晶箱后進行快速降溫，降至 82~C 后轉為均勻降溫，以 2~C ／ h 的降溫速度冷卻至 60~C ，排放富含硫茚的第一次晶析萘油，作為中間餾分待后處理。然后結晶箱內的物料以 4~C ／ h 的速度升溫，每半小時取樣一次，測定其結晶點，根據(jù)結晶點的不同，分別排人對應餾分槽，如此進行 3 ～ 4 次分步結晶，可得到較高純度的精萘。

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，我公司生產的精萘酸洗比色一直偏高，經(jīng)常在 10 號左右。而 生產工藝 和設備與本公司大體相同的上海焦化廠，精萘的酸洗比色不超過 2 號。經(jīng)實際調研發(fā)現(xiàn)，在萘結晶過程中，晶體表面粘附有一層膠體狀不純物，如果不對它加以處理，必然將其帶人相應的餾分槽或產品槽內。我們卻忽視了這一過程，認為這些膠體狀物質可通過多次分步結晶予以分離，致使精萘產品的比色偏高。

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 改進措施 我們在改進精萘 工藝 時，在利用原有設備的基礎上，未作任何管線和設備的改動，而只是采用了三步或兩步結晶的方法，每一步由進料、預冷、結晶、排液、發(fā)汗和熔化等 6 個環(huán)節(jié)組成。

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) 進料。原料工業(yè)萘由泵裝入結晶箱。

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

(2) 預冷。通過調節(jié)結晶箱內循環(huán)介質的溫度，使結晶箱內的萘冷卻至結晶點。此時，硫茚等雜質富集于液相，萘逐步結晶于結晶管上，晶體逐漸增大。 (3) 結晶。結晶器溫度進一步降低后，結晶開始大量析出，萘以柱狀晶體構成網(wǎng)狀結晶層，硫茚存在于這些晶體周圍的液相中。此時，網(wǎng)狀晶體的密度不宜過高，以利于晶體內的液相排出。

(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。富集了硫茚等雜質的液相自流出結晶箱，排人殘液槽。

(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) 發(fā)汗。又稱部分熔化，是指逐步提高結晶箱傳熱介質的溫度，使結晶箱內的結晶逐漸被加熱，并部分熔化。隨著溫度的提高，晶體內包含的低熔點雜質首先熔化，并逐漸滲透到晶體外表面，少部分的萘也隨之熔化，晶體表面的不純物液膜逐漸被替換。熔化后的液體自流出結晶箱，排人相應的餾分槽。 (6) 熔化。當試樣的結晶點達到規(guī)程要求后，迅速加熱升溫，結晶箱內的物料全部熔化，根據(jù)需要再次進料。經(jīng)上述改進后，精萘的一級品率高達 100 ％，產品收率達 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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