Thread Content
Due to its advantages of high separation efficiency, low resistance, and large flux, structured packing has been widely used in industrialized devices in domestic chemical and other industries. Corrugated packing is widely used in China. The main varieties include Sulzer's CY type and BX type wire mesh corrugated packing, Mellapak series M-125~M650 orifice plate corrugated packing, and domestically developed SW-1 type and SW-2 type mesh corrugated packing. Among methanol plants with tens of thousands of t/a (two-tower process), most of them use CY type (700m2/m3) and SW-1 type (650 m2/m3), while in plants with more than 100,000t/a (three-tower process), BX (500 m2/m3) and SW-2 (450-500 m2/m3) to replace CY type and SW-1 type, both achieved good results, and SW type packing is more practical than wire mesh packing in terms of raw material cost and technical advantages. Our factory has practical experience in producing methanol using a three-tower process distillation unit at 150, 100, and 50 kt/a. Taking the 6×104t/a methanol of Shandong Shouguang Alliance Co., Ltd. as an example, its steam energy consumption of methanol is 950kg/t (see "Design and Operation of Methanol Unit Using Coal as Raw Material" written by Liu Zhichen of Shandong Shouguang Alliance Co., Ltd., "Nitrogen Fertilizer Technology" Issue 1, 2007 ； "The Development of Methanol Industry and New Progress in Process Technology" written by Xu Zhaoyu of Anhui Chemical Industry Research Institute, "Fine Chemical Raw Materials and Intermediates" Issue 6, 2007. Among the methanol units put into operation in 2005, the 40×104 t/a refined methanol plant of Lutianhua Luyuan Alcohol Co., Ltd. designed by Shanghai International Chemical Construction Company is the largest (crude methanol 1675 t/d, refined methanol 1337 t/d), production practice has proved that it is appropriate to use the SW-2 type mesh packing produced by Xuelang Chemical Filling Factory, which basically achieves the purpose of high efficiency and energy saving. In future larger methanol projects, it can be appropriately summarized and improved before selection and application. To explore low-investment and high-efficiency packings while meeting the requirements of energy saving and improving product quality, we put forward suggestions for improving tower packings and selecting more optimized tower internals (collection and redistributors) for reference and correction by design units and users. 1 Tower packing The specific surface area of the packing and the void ratio of the packing are a set of contradictions. For structured packing, the specific surface area is proportional to the efficiency. That is, the larger the specific surface area of the packing, the more theoretical plates, the higher the efficiency. However, the smaller the void ratio, the increased pressure drop, and the reduced flux per unit cross-sectional area. For example, the efficiency of the CY (700 m2/m3) type is higher than that of the BX (500 m2/m3) type, while the flux is smaller than the BX type, the same is true for the orifice plate packing, the efficiency is M450>M350>M250>M125, while the flux is opposite. SW type mesh corrugated packing is a new structured packing jointly developed by Shanghai Research Institute of Chemical Industry and Xuelang Chemical Packing Factory. It was approved in 1995 * * Appraisal by the Science and Technology Commission, won the second prize for scientific and technological achievements in 1996, and won the * * Patented, it has been used in distillation absorption in thousands of projects in more than 20 provinces and cities across the country, and is especially suitable for vacuum, normal pressure and pressurized distillation devices. SW-1 type and SW-2 type packing are based on summarizing domestic and foreign application technologies, using the value analysis method to simplify processing and save materials, so they have great practical significance. They have been widely promoted and applied in the fields of petrochemicals, medicine, fertilizers, light chemicals, environmental protection, basic organic synthesis, etc., and have achieved good social and economic benefits. The diameter of the used tower can reach more than 3m, and they have also achieved good results in the application of high melting point heat-sensitive substances such as oleochemicals. The pressure drop of SW-1 type packing is equivalent to that of orifice plate M450, and the efficiency is slightly lower than that of CY type wire mesh corrugated packing. SW-2 type packing pressure drop * * It is lower than the orifice plate M450 type, the efficiency is slightly equal to the BX type wire mesh packing, and higher than the M450 orifice plate packing. 2 Tower Internals Packed towers have been widely used in separation projects and have achieved great results. However, with efficient packing, advanced collection and redistributors and other tower internals must be matched to achieve better separation results. At present, there are generally four types of collection and redistributors at home and abroad. The first type is a sloping plate collector plus a row pipe distributor. This type is widely used in the organic chemical industry. Its advantages are large flux and relatively uniform distribution, but it is easy to block. The second type is an upper sloping plate collector, and the lower part is a secondary trough distribution. The distribution holes of this distributor are located on both sides of the sediment at the bottom, which can prevent clogging and has greater operational flexibility. However, it is difficult for each distribution trough to maintain the same plane, which affects uniform distribution. The distributor is composed of a collector and a distributor. It occupies a relatively high height in the tower. Generally, the height of a large tower is about 2m, and the cost is correspondingly high. The third type is a trough-disk type collection and redistributor. The collection and redistribution of this distributor are integrated into one. It occupies a low height and has the advantages of a trough-type distributor. It is anti-blocking and has great operational flexibility. However, this distributor needs a support ring welded to the inner wall of the tower to fix the collection distributor. Its flux is not as large as the flux of the above two distributors. In applications with large tower diameters, joist support is required. The fourth type is a tray-type collection and redistributor. This distributor does not have a support ring welded to the inner wall of the tower. A collection ring slightly smaller than the diameter of the tower is welded to the bottom plate of the distributor. A liquid collection angle is suspended on the ventilation frame. After the liquid is collected, it flows into the distribution tank, and all collection tanks are connected. The distribution holes are located on both sides of the distribution tank. The distributor can prevent blockage, has high operating elasticity, and distributes evenly. The gas flow area reaches more than 52%. There is an anti-wall flow ring on the upper part of the distributor, which can solve the wall flow phenomenon. This distributor is used in the Lutianhua 40×104t/a methanol project. The original design is 12×104t/a. After using new packing and internal parts, it can exceed 15×104t/a. Our factory has achieved satisfactory results after using nearly a thousand large and small towers. In order to meet the requirements of tower diameters above 3500mm and larger, we invented a large detachable tray liquid distributor based on the tray-type collection and redistributor (Patent No.: ZL200610088161.6). The collection main trough of this distributor is fixed to the tower wall as a beam, so that there is no need to add additional joists under the large tower diameter collection redistributor. The collection and distribution auxiliary trough is divided into blocks and is fastened and communicated with both sides of the main trough, so that the liquid in the entire distributor is connected. The collector is the same as the tray type. After the angle steel collects the liquid, it flows into the collection tank. The collection outer ring is welded to the bottom plate. The distribution holes are located on both sides of the collection auxiliary tank. The liquid is evenly distributed from the liquid guide angle steel and the liquid guide plate to the packing layer. The distributor is also welded with an anti-wall flow ring like the tray distributor to solve the tower wall flow phenomenon. The structure of the distributor is simple, compact and reasonable. All the blocks are sent into the tower through the manhole for assembly. Since there are no additional joists, the distributor can be closer to the packing layer without affecting the uniform distribution of air flow in the tower. The distributor is integrated with grooved beams, which occupies a lower height in the tower and reduces the production cost. It is an application of the tray-type distributor in large towers and maintains its original excellent characteristics. It can prevent tower wall flow, has large ventilation capacity, prevents blockage, has high operating flexibility, is low in height, has no joists at the bottom, and can arbitrarily set liquid distribution points in the case of larger tower cross-sectional areas. It is an ideal redistributor.