Online cleaning with caustic scrubber cleaners – a new source of economic growth for MTO plants

Thread Content

This post was last edited by liaifeng on 2018-9-3 11:16. In the field of coal chemical engineering, olefin separation units play a crucial role as links between different processes; they are key components for the success of coal-to-olefins projects. The product gas from the MTO unit, after being compressed in the second stage by the product gas compressor, enters a water scrubber to remove any entrained oxides, and then goes into an alkali scrubber where strong alkalis are used to eliminate any acidic gases carried along. Water washing and alkali washing are pre-treatment processes for the product gas before it enters the distillation system; they help to prevent substances such as polymers and dry ice from blocking the distillation system or contaminating the product. The Shenhua Baotou coal-to-olefins project has a capacity of 1.8 million tons per year for coal-to-methanol production, 600,000 tons per year for methanol-to-olefins production, 300,000 tons per year for polyethylene production, and 300,000 tons per year for polypropylene production. Since December 2015, the alkali scrubber has gradually started to become clogged, and as the operating cycle of the plant lengthened, this clogging problem became increasingly severe. Especially in the strong alkali section, the downcomer becomes severely clogged, and the liquid dropping capacity of the trays continues to decline. As the liquid dropping capacity in this section keeps dropping, the circulation volume in that area also has to be reduced continuously in order to prevent the alkali solution from accumulating on the trays. As of February 3, 2016, the circulation rate in the strong alkali section had been reduced from 60 t/h to 4.5 t/h, while the pressure difference in that section increased from 10 KPa to 21 KPa ； When the circulation rate in the medium-alkaline section was 60 t/h, the pressure difference rose to a maximum of 18 KPa; even after reducing the circulation rate to 55 t/h, the pressure difference still reached 13.7 KPa ； The circulation rate in the weakly alkaline section can still be maintained at 60 t/h, but the pressure difference also increases from 10 kPa to 13.8 kPa. After blockage occurred in the caustic scrubber tower, the plant tried various methods such as increasing the dosage of butter inhibitor, reducing the alkalinity level in the caustic scrubber tower, carrying out segmented hot water flushing, and using xylene for washing, but none of these methods proved effective. Before trying the alkali scrubber cleaner, the strong-alkali section was already unable to circulate effectively, and the medium-alkali section also showed significant blockages, with a tendency for the situation to worsen, severely affecting the normal operation of the plant.  RedSain Solutions – Alkali scrubber cleaner for online cleaning. In response to this issue, Tianjin RedSain New Material Development Co., Ltd. developed, based on the characteristics of petrochemical and coal chemical industries, a patented product – TRD-1F Alkali Scrubber Cleaner – to address the problem of reduced operation cycles caused by alkali scrubbers. This cleaner not only helps to prevent the formation of butter during the alkaline cleaning process, but its efficient dispersing components also enable the removal and dispersion of polymers adhering to the tray surfaces; these polymers are then discharged along with the waste alkaline solution, thereby restoring the cleaning efficiency of the alkali scrubber. This allows for online cleaning of scrubbers that have suffered from blockages, thus extending the operation cycle of the equipment. 1. Features of TRD-1F alkali scrubber cleaner: a. High cost-performance; it utilizes a multi-component system that effectively prevents the polymerization and scaling of unsaturated hydrocarbons and aldehydes, which may aggregate or dissolve during the alkali scrubbing process of the product gas. The various components work together synergistically, enabling a significant improvement in the effectiveness of the product even when used in small quantities ； b. It has good compatibility; it is miscible with water and alkaline solutions, and it also works well with the materials used in the caustic scrubber. This allows it to exert its inhibitory effect effectively, while preventing the condensation reaction between the aqueous and oily phases in the caustic scrubber, thus completely stopping the formation of butter ； c. It possesses a very strong ability to disperse scale, which can effectively reduce the pressure difference in the tower caused by polymer deposition there, thereby ensuring the normal operation of the equipment ； d. Easy to refill, can be refilled using existing equipment ； e. It can be cleaned online, allowing the alkali scrubber to be cleaned without shutting down operations ； f. Environmentally friendly, free of halogens and heavy metal ions, with no adverse effects on downstream processing procedures or product quality. 2. Cleaning Solution: ReidSain Corporation conducted technical discussions regarding this product with Shenhua Baotou Company, and was invited to carry out experiments using its alkali scrubber cleaner and butter dispersant. The results of these experiments showed that the alkali scrubber cleaner produced by our company is effective at dispersing the butter that forms inside the alkali scrubbers, and it received unanimous approval from Baotou Company. Therefore, in order to prevent further deterioration of blockages in the alkali scrubber towers, the Shenhua Baotou Olefins Plant used our company’s alkali scrubber tower cleaner for online cleaning from February 3, 2016, to March 2, 2016. The test was carried out in two phases. In the first phase, the weakly alkaline section and the moderately alkaline section were cleaned; larger amounts of caustic cleaner were injected into these sections to gradually remove the grease from the tray surfaces, and the cleaning effect was observed ； In the second phase, emphasis is placed on cleaning the strong-alkali section; the amount of cleaner injected into this section is increased, while the amounts injected into the medium-alkali and weak-alkali sections are reduced. The trays are cleaned from bottom to top to prevent a large amount of butter on the trays in the strong alkaline section from falling off and accumulating with the butter attached to the lower trays. 3. Cleaning efficiency: During the trial use of the alkali scrubber cleaner TRD-1F, the circulation volume in each alkali section increased, while the pressure difference across the various sections of the alkali scrubber remained stable or even decreased. This significantly improved the operation of the facility and ensured its proper functioning ； Especially in the strong alkali section, the circulation rate was gradually increased from 4.5 t/h to 22 t/h, while the pressure difference dropped from around 20 KPa to around 19 KPa. The maximum circulation rate of the alkaline solution in this section continued to increase; both the pressure difference and the liquid level remained stable, with no occurrence of liquid carryover. This fully demonstrates the cleaning effect of the detergent used in the caustic scrubber tower. The state of the butter in the waste alkali solution discharged from the alkali washing tower shows that it is bright red in color, in a slightly foamy liquid state; upon standing, an oil layer with good fluidity forms ； Before trying the cleaning agent, the butter in the spent alkaline solution was dark red in color, paste-like in texture, highly viscous, and had poor flow properties. This shows that the alkali cleaning tower detergent can effectively reduce the molecular weight of butter and improve its formation state, thereby facilitating subsequent processing. After a month of testing the caustic scrubber cleaner, the performance of the caustic scrubber has improved significantly, and it was effectively cleaned. After trial use, as the circulation rate of the alkaline solution in the medium-to-strong alkali section was gradually increased, the original upward trend in the pressure difference across various alkali sections was significantly suppressed, and an effective reduction in the pressure difference in the strong alkali section was achieved. Meanwhile, during the trial period of the caustic scrubber cleaner, it ensured an excellent caustic scrubbing effect for the product gas, enabling the caustic scrubber unit to operate safely, at full capacity, stably, and efficiently; the quality of the product received high praise from Shenhua Baotou Company. 4. Economic value: The annual profit of Shenhua Baotou coal-to-olefins project is approximately 300 million yuan. Online cleaning procedures ensured the proper maintenance of the equipment, extending its operational life by four months; the cleaning agents used in the caustic scrubbers played a key role in this. In summary, the caustic scrubber cleaner developed and produced by Tianjin Ruide Sain New Material Development Co., Ltd. exhibits excellent capabilities in suppressing the formation of butter deposits as well as in cleaning such deposits. It enables the online cleaning of clogged caustic scrubbers, addressing the issue of short operation cycles that often arise in MTO units. This product offers a new solution for coal-based olefin manufacturers, ensuring the safe, efficient, stable, and optimal operation of MTO units and creating new opportunities for profit growth. It has broad application prospects and the potential to generate significant economic benefits.