In the production process of epichlorohydrin, hydrochloric acid generated from by-product hydrogen chloride after absorption by water is highly corrosive, which greatly shortens the life of metal heat exchanger. Therefore, in the production of epichlorohydrin, the heat exchangers related to hydrogen chloride medium are all corrosion resistant graphite heat exchangers. Block hole graphite heat exchanger
The use of graphite heat exchanger in the production process can not only effectively exchange heat, reduce energy consumption, but also improve the yield of related materials, thus reducing material consumption. The application of graphite heat exchanger in the production of epichlorohydrin can save the steam consumption of the cyclization reactor, and increase the reaction yield of dichloropropane.
Heat conduction effect.
In the temperature range of 480.7J/(m.h. ℃), the thermal conductivity of graphite is greatly reduced compared with ordinary alloys. For example, the 304 stainless steel is 58.69J/(m.h. ℃). Therefore, the thermal resistance of graphite with the same thickness is smaller than that of stainless steel, and it can also transfer heat more. Although the thermal resistance of the pipe wall in the heat transfer process is far less than that between the fluid and the dirt, its influence can not be ignored sometimes.
Long life.
In hydrochloric acid, a strong corrosive medium, the corrosivity of even corrosion-resistant alloys is 0.1mm/a, while that of graphite is almost zero. Therefore, the life of graphite heat exchanger is significantly longer than that of metal heat exchanger under strong corrosion environment, and it is still in normal use up to now, which is a good example. The metal heat exchanger of other posts shall be blocked or replaced.
Although the cost of graphite heat exchanger is relatively high, from the user's use, the graphite heat exchanger in the epichlorohydrin unit does not have the problem of leakage of heat exchange tubes due to corrosion, and the damage is mainly caused by accidental damage. However, the metal heat exchanger often needs to be plugged even under other medium conditions, and it needs to be replaced frequently under acidic medium conditions, which will lead to frequent shutdown. If the shutdown lasts for two days at a time, the direct loss caused by replacing the pipeline or heat exchanger will not be counted, and the indirect loss caused by plugging or replacement of the unit alone will be as high as 2.5 million yuan. It can be seen that the graphite heat exchanger not only has good heat exchange effect, but also has strong corrosion resistance, It has a long service life, prevents the shutdown of the unit due to frequent plugging or replacement of the heat exchanger, and enables the chemical plant to achieve long-term and stable operation. It is worth promoting and improving in the chemical and petrochemical industries.
Description of electricity use.
During transportation and installation, the graphite heat exchanger shall be handled with care, and shall not collide with the ground or other hard materials, let alone be knocked with hard objects. The principle of "caution and slowness" shall be followed during startup and shutdown. The process and relevant precautions are described as follows:
(1) Start the step.
Water filling: first open the vent valve at the outlet of circulating water, then open the connecting valve between the outlet and inlet of circulating water, and slowly open the inlet valve to control the flow. Shutdown: slowly close the inlet valve first, then close the outlet valve, open the drain valve and vent valve, and discharge all the cooling water.
(2) Description.
Before using the equipment, it is required to exhaust the air in the equipment. B. The switching of inlet valve shall be slow. ② In winter, all the circulating water in the heat exchanger shall be drained to prevent freezing. The working pressure shall not fluctuate abnormally during operation. Once the fluctuation is found and cannot be eliminated immediately, the equipment or system shall be shut down.
In a word, because graphite heat exchanger has high corrosion resistance, heat resistance and good heat transfer effect, it can avoid frequent shutdown due to plugging or temporary replacement of heat exchanger tubes under the corrosive medium conditions that metal heat exchanger cannot meet. However, its cost is relatively high, so factors such as using medium, service life and actual economic benefits should be comprehensively considered when selecting, and then determine whether to choose. In addition, due to the low impact strength of graphite, relevant operating procedures shall be strictly followed during transportation, installation and specific operation, and the fluctuation of operating pressure shall be noted to prevent the accidental damage of graphite heat exchanger caused by abnormal pressure fluctuation, thus making graphite heat exchanger more widely used in chemical production with poor medium conditions.
