Butter formation in the caustic scrubber and optimized operation

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The last edit to this post was made by liaifeng on 2018-7-28 at 10:29: file:///C:\Users\Administrator\AppData\Local\Temp\msohtmlclip1\01\clip_image002.gif Optimization of the alkali scrubbing tower and butter recovery. In the ethylene industry that uses petroleum as a raw material, the proper operation of the alkali scrubbing units in the compression section is a key factor determining whether the ethylene production facility can operate continuously. The formation of butter in the caustic scrubber tower tends to polymerize and form scale, which can clog the distributors and packing inside the tower, leading to tower blockage and reducing the operating cycle of the caustic scrubber tower. Furthermore, the discharge of waste lye containing large amounts of butter poses difficulties for the operation of downstream treatment facilities. The inability to recycle butter also leads to waste during production. Therefore, to better optimize the operation of the alkali scrubber and the recovery of butter, it is necessary to analyze its formation mechanism and properties. I. Reducing the formation of butter in the alkali scrubber 1. Reducing the amount of heavy hydrocarbons entering the alkali scrubber. The formation of butter occurs in two ways: one is the condensation of heavy hydrocarbons within the alkali scrubber, which leads to blockage of the trays. Second, a polymerization reaction takes place in the presence of trace oxygen to produce polymers. Reducing the amount of heavy hydrocarbons entering the alkali scrubber can fundamentally reduce the formation of butter. Therefore, a liquid separation tank can be installed between the water wash tower and the alkali wash tower; the heavy hydrocarbons that condense in this tank can be returned to the suction tank of the previous stage compressor, and then sent to the downstream system along with the hydrocarbons condensed in that suction tank. 2. Reduce the residence time of butter in the alkali scrubber. Relevant data show that there is a positive correlation between the amount of butter produced and its residence time in the alkali scrubber. Reducing the residence time of butter in the caustic scrubber can minimize butter formation and optimize the operation of the caustic scrubber. The residence time can be reduced by continuously or in multiple intermittent discharges of butter. II. Butter recovery: The heavy hydrocarbons and butter coming from the compression area enter the butter recovery system. Butter in the alkaline solution can dissolve in crude gasoline; therefore, the heavy hydrocarbons coming from the compression area can be reused to recover the butter in the alkaline solution. It is possible to reduce the amount of crude gasoline coming from the debutanizing tower, and it is also possible to recover the butter present in the alkaline solution, thereby reducing the difficulty of processing this alkaline solution in downstream systems. 1. In the waste alkali coagulator, the heavy hydrocarbons coming from the compression system, the waste alkali solution containing butter from the caustic washing tower, along with crude gasoline and washing water, are thoroughly mixed together using a mixer. Crude gasoline can dissolve the butter present in the waste alkali solution, while the washing water helps to separate the waste alkali solution and certain ions from the oil phase. Within the waste alkali coagulator, the waste alkali solution and the oil phase are separated; the oil phase overflows to the other side and is sent to the waste gasoline coagulator. The spent alkali liquid coagulator has pressure control to maintain a stable operating pressure. 2. Waste gasoline coagulator: The heavy hydrocarbons containing metal ions, along with the wash water coming from the waste alkali solution coagulator, are thoroughly mixed in a mixer; this allows the metal ions in the heavy hydrocarbons to be reduced to the desired levels. The heavy hydrocarbons are separated in the waste gasoline coagulator, and the overflow flows to the other side and enters the gasoline flash tank. The waste gasoline coalescer has pressure control to maintain a stable operating pressure. 3. The heavy hydrocarbons coming from the waste gasoline coalescer into the gasoline flash tank contain some light components with molecular weights below C3; if these light components enter the butane removal tower system, it can cause difficulties in the operation of the tower, and may ultimately result in defective products. Therefore, the heavy hydrocarbons coming from the waste gasoline condenser are flashed in a gasoline flash tank to remove the light components. Among them, the light components are sent to the front system along with the exhaust gases, while one stream of heavy hydrocarbons is pumped to the debutane tower; another stream returns via a heat exchanger to recover butter from the alkaline solution.