The salt deposition problem in catalytic fractionation towers
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This post was last edited by Final Fantasy on 2010-4-22 at 14:06. The distillation tower in our workshop starts to form salt deposits within a few months – are there any effective ways to prevent this?
Confirm salt formation? Consider the ammonia injection port; changing it doesn’t necessarily lead to salt formation. Let’s talk about the phenomenon
Reducing the salt content in the raw materials improves the efficiency of electrodesalination; salt formation inhibitors can also be added (by continuously adding such inhibitors, it is possible to prevent salts such as ammonium chloride from accumulating inside the tower, thereby avoiding salt formation within the distillation tower). It will move in the direction of the heavier components, that is, toward the lower part of the tower. During this process, the ammonium chloride deposits in the tower are gradually saturated by the salt formation inhibitor. Salt-forming inhibitors can form a strong bond with the metal surface, gradually separating ammonium chloride from it. Ammonium chloride will be carried away by the liquid flow and exit along with the product.)
The FCC unit in our facility experienced salt deposition on two occasions in previous years, mainly due to washing； Salt formation in the distillation column occurs mainly in the upper part of the column, primarily as NH4CI ； Main phenomena: high pressure drop across the entire tower, high dry point of crude gasoline, low diesel yield, instability, and difficulty in controlling quality ； The main reason for this is that the temperature at the top of the column is too low – lower than the dew point temperature corresponding to the moisture pressure at that level. As a result, steam condenses into water, which then reacts with NH3 and HCl present in the oil and gas to form an NH4Cl solution. This solution, along with the liquid phase, flows downward layer by layer, gradually becoming more concentrated and crystallizing, thus leading to salt formation ； The main treatment methods are: reducing the reaction load, washing with top-loop reflux or cold reflux along with softened water, and removing water by diesel extraction ； Prevention methods: Appropriately increase the top temperature to a level higher than the dew point temperature corresponding to the moisture pressure at the tower top; reduce the amount of ammonia added to the atmospheric and vacuum distillation unit; and enhance the operation of electrodesalination.
Measures to reduce salt deposition in the catalytic fractionation tower: 1. Keep the salt content in the raw materials within the specified limits, and improve the desalination efficiency of electrodesalination； 2. Determine the appropriate dew point temperature based on the water vapor partial pressure at the top of the catalytic fractionation tower; during operation, keep the temperature at the top of the tower above the dew point temperature ； 3. Control the heat extraction load at the upper part to prevent water from being carried back by the top circulation ； 4. Produce as little diesel with a low freezing point as possible, in order to avoid frequent changes in the temperature at the upper part of the system. 5. During startup and in case of accidents, control the volume of slurry circulation properly to ensure effective washing of the catalyst, and prevent the catalyst from accumulating in the downcomers, which could increase the likelihood of salt formation ； 6 can modify the structure of the downcomer to enhance its resistance to salt crystallization.
Proper operation of atmospheric and vacuum electrodesalination is essential; the main solution is washing with water
1. Control of salt content in the raw materials. 2. Control of salt content in the steam. 3. Control of the temperature at the top of the tower to ensure that no water is carried along in the overhead stream!
The usual solution is to wash the fractionation tower; if done properly, it can be considered as part of on-the-job training, with little impact on operations. If a long-term solution is desired, a buffer tank can be added to the top circulation system; you can search online for details, as there is information available on that topic. It seems that the oil refinery in Xinjiang has already implemented this approach!
Forgot, sorry – here it is: http://bbs.hcbbs.com/thread-294692-1-1.html:loveliness:
Strengthen electrodesalination in the atmospheric and vacuum distillation units; wash the distillation columns promptly after salt formation occurs
The person on the 4th floor explained it in great detail. The original poster can refer to this. In essence, salt formation occurs when the operating temperature at the top of your tower is too low, which leads to the deposition of NH4Cl and disrupts normal operation. The solution is to wash with warm water. The first preventive method is front-end control, with improved management of raw materials ； Second, improve operations on one’s own by appropriately raising the tower top temperature ； Third is prevention by adding additives.