Shenhua’s world’s first MTO unit uses domestically produced butter inhibitors
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This post was last edited by lsl343952854 on 2013-7-1 22:13. Domestic butter inhibitors are now being used in the world’s largest coal-to-olefins (MTO) plants. As of March 12, the 1.8 million tons per year MTO unit using a new domestic butter inhibitor had been operating steadily for 15 days. Trial results showed that in the MTO unit of the Baotou Coal Chemical Branch of Shenhua Coal-to-Oil Chemical Co., Ltd., by stopping the supply of inlet deoxidizer and butter inhibitor to the alkali scrubber tower, the amount of butter generated in that tower was reduced by 25.73%, and both energy consumption and material usage in the alkali scrubbing system were significantly decreased. Shenhua’s MTO unit is the world’s first and currently the largest MTO unit of its kind. Lummus, the U.S.-based company that holds the patents for the separation technology in its alkaline washing system, specified that the most advanced imported butter inhibitors available today must be used, along with oxygen scavengers, in order to meet the requirements of the process design. Therefore, since the successful operation of this unit in August 2010, the olefin separation unit has been continuously fed with both imported deoxidizers and butter inhibitors. To reduce production costs and achieve full domesticization of coal-to-olefins technology in China, Shenhua Baotou Coal Chemical Branch decided to trial a new type of butter inhibitor developed and produced by Beijing Sibole Science and Technology Research Institute. This product has multiple functions, including inhibiting aldehyde condensation, suppressing the polymerization of reactive olefins, cleaning and dispersing dirt, and removing oxygen. By being injected at a single point in the caustic scrubber tower for coal-derived olefins, it can also significantly improve the performance of that scrubber tower. The technical staff at Sibole Research Institute, taking into account the actual operating conditions of China’s first coal-to-olefins plant, provided a \"one-stop\" solution for use and injection. By eliminating the original imported steam-heated injection system and using only 2/3 as much inhibitor as the imported version, the amount of butter formed in the waste alkali solution at the bottom of the alkaline washing tower was reduced by 25.73% compared to before, resulting in annual savings of over 1.8 million yuan. It is understood that butter inhibitors are key additives for the long-term stable operation of large-scale coal-to-olefins plants. In the MTO olefin separation system, the alkali scrubber is a very important component; it not only prevents the formation of butter compounds in the conversion gas, but also plays a key role in removing acidic corrosive gases such as CO2 and H2S from the same gas. If a large amount of butter is generated in the alkali washing system, it will directly lead to an increase in the pressure inside the alkali washing tower, a decline in the efficiency of alkali washing, and an increase in the amount of waste alkali discharged. This in turn results in excessive COD levels in the waste alkali stream downstream, and in severe cases it can even cause blockages in the alkali washing tower, forcing the entire plant to stop operating for maintenance – thereby severely affecting the long-term stable operation of the whole system.
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The separation system of Shaanxi Yanchang China Coal Yulin Energy Chemical Co., Ltd.’s 1.5 million tons per year ethylene production facility via catalytic cracking (DCC) has been operating steadily for nearly 80 days since the use of domestically produced butter inhibitors began on August 25th. The results of use show that, with the same dosage, the domestic agent reduces the amount of butter formed in the waste alkali solution at the bottom of the caustic scrubber by 1/3; it also leads to a significant increase in the temperature of the reboiler at the bottom of the caustic scrubber. Moreover, the cost of the agent is reduced by more than 35%, allowing the facility to save over 3.6 million yuan in purchasing costs each year. This DCC unit was put into operation in July 2014; it is currently the largest industrial DCC facility in China. Integrating a range of advanced technologies from home and abroad, it was constructed under the general contract of Sinopec Engineering Construction Co., Ltd., with Shaanxi Huajian Engineering Co., Ltd. responsible for the installation work. The process for producing ethylene via catalytic cracking of DCC consists of multiple units, including reaction, regeneration, purification, and cryogenic separation. When atmospheric-pressure feed oil is atomized with steam and fed into a riser reactor to undergo catalytic cracking in contact with hot regenerated catalyst, the high content of dienes in the high-temperature reaction products makes it very easy for polymerization to occur, leading to blockages in pipes, trays, and reboilers. This in turn makes it difficult to control the operation of the alkali scrubber in the subsequent separation system, and this has become a major bottleneck for the long-term stable operation of DCC units. As specified by the patent holder, since the completion and operation of this project, imported butter inhibitor products have been used in the alkali scrubber, and imported deoxidizer products have also been added to the top of the alkali scrubber. The newly developed environmentally friendly and multi-functional butter inhibitor, independently created by the Beijing Sibole Science and Technology Research Institute, possesses functions such as polymerization inhibition, antioxidant action, cleaning and dispersion, as well as metal passivation. It not only offers good cost-performance but also eliminates the need for additional oxygen scavengers, achieving two goals at once – **reducing the energy and material consumption of the equipment. According to industry experts, the DCC process utilizes heavy feedstocks for catalytic thermal cracking to produce low-carbon olefins; this not only expands the sources of raw materials for ethylene production but also reduces the average cost of ethylene by about 25% compared to existing naphtha cracking plants in China. The successful development of a new domestic butter inhibitor tailored to this process provides a guarantee for the industrial application and promotion of the DCC technology package.
Since last year, Yulin Energy Chemical Company has made great efforts to implement the group company’s \"16 measures for increasing revenue and reducing costs.\" It has sought ways to cut costs through technological innovation, and has gradually advanced the localization of these three types of materials; repeated tests have yielded significant results. Recently, the reporter learned from the company’s olefins division that since the domestic production of butter inhibitors for the DCC and DMTO units was achieved, these units have been operating stably, resulting in annual savings of over 10 million yuan. Butter inhibitors are agents that control (reduce) the amount of butter produced during the alkaline cleaning process. During operation of the DCC unit, when atmospheric-pressure feed oil is atomized with steam and then fed into the lift tube reactor to come into contact with hot regenerated catalyst for catalytic cracking, polymerization can easily occur, leading to blockages in pipes, trays, and reboilers, and thereby making it difficult for the unit to operate stably over extended periods of time. Since its completion and commissioning, the DCC unit at Yulin Petrochemical has been using imported butter inhibitors as specified by the patent holder, and it is also necessary to add imported deoxidizing agents to the alkali scrubber tower. Last August, after the installation was equipped with a new type of environmentally friendly, multi-functional butter inhibitor developed by a domestic company, the caustic scrubber operated smoothly; there was no longer any need to add oxygen scavengers, and energy consumption was significantly reduced. Since its commissioning in 2014, the imported catalysts used in the DMTO unit have been sufficient to meet the requirements of the production process. However, these reagents are acidic, causing corrosion to the pipelines; they also result in high maintenance costs and have a significant impact on the stable operation of the auxiliary systems. Since the use of domestic catalysts in this device last September, its production has been stable, and the reagent has reduced pipe corrosion, demonstrating good performance. It is reported that after the use of domestically produced butter inhibitors in the DCC and DMTO units, the annual cost savings can reach over 11 million yuan, based on the designed dosage levels, resulting in significant improvements in cost efficiency. (Zhong Guofei)