The content of carbon monoxide (CO) in the raw material gas produced by the Shell pulverized coal gasification process is as high as more than 60%. This not only increases the CO shift load of the sulfur-resistant conversion system, but also may cause the occurrence of highly exothermic methanation side reactions. The catalyst bed is overheated. Therefore, how to control and suppress the first shift converter methanation side reaction and other issues, it becomes the key to whether the Shell pulverized coal gasification process can be successfully used for ammonia or methanol production.
The new process of pulverized coal gasification with low water/gas-to-sulfur conversion developed by Qingdao Lixin Chemical Co., Ltd., Guangxi Liuzhou Chemical Industry Co., Ltd., and Sinopec Group Ningbo Engineering Co., Ltd. successfully solved this problem and adopted pulverized coal gasification. The production of synthesis gas has opened up a new process approach for smooth production, energy saving and environmental protection. This technology passed the appraisal and assessment organized by the China Petroleum and Chemical Industry Association this month.
The introduction of the device encountered "methanation" obstruction Previously, in order to avoid the occurrence of methanation side reactions in the Shell pulverized coal gasification process conversion section, the design department recommended high water / gas conversion process. Therefore, of the 17 Shell pulverized coal gasifiers that have been signed in China, 15 units have adopted the high-water/gas sulfur-tolerant conversion process. Although high water/gas can suppress the methanation side reaction, because of high CO concentration and water/gas, the driving force of the reaction is large. A small amount of change in the catalyst loading will significantly affect the depth of the reaction and thus affect the bed. The hot spot temperature results in poor control of the bed temperature.
Practice has proved that some devices in the initial period of driving, due to the lower load or catalyst loading a larger margin, the first reactor appeared over-temperature phenomenon. In order to reduce the temperature of the reactor, the water/gas of the first reactor increased to more than 1.3. This not only results in a great waste of energy, but also due to a catalyst that runs under severe conditions of high water/gas and high temperature, the catalyst appears anti-vulcanization, which affects the normal production of the device.
Low-water/gas conversion new process successfully developed Qingdao Lixin Chemical Co., Ltd. has been committed to the development of sulfur-resistant conversion of new technology, as early as in 2002, the company began to pay attention to the introduction of China's Shell powder coal gasification process, and support The research and development work on the new sulfur-tolerant conversion process focuses on the side effects of methanogenesis that people are most concerned about. Through various researches on water/gas, bed hotspot temperature and airspeed, and catalyst performance, the researchers have found out the rules that affect the degree of occurrence of methanation side reactions on cobalt-molybdenum-based catalysts, as well as the low water/gas conditions. The temperature at which the lower methanation side reaction starts.
Afterwards, they conducted in-depth studies on how to transform the reaction and how to control the depth of a furnace reaction. Through kinetic calculations and verification tests on the QDB-04 catalyst, two methods for controlling the reaction depth were found. On this basis, Allied Chemical has developed a new process for low-water/gas-to-sulphur conversion of Shell coal gasification. The process makes full use of the low gas and water content of the raw materials used in Shell's waste boiler process. By controlling the water/gas in the process gas, the depth of the first reactor shift reaction is controlled, and the hot spot temperature of the bed is controlled to achieve a lower hot spot temperature. Under the conditions, that is, under the condition that no methanation side reaction occurs, the high-concentration CO part will be transformed, so that the new CO coal shell gasification process with high CO concentration can be implemented under the mild water/gas mild process conditions.
After the successful development of the new industrial process, due to the lack of industrial application performance and people's excessive concerns about the over-temperature of the methanation side-reaction, it has not immediately attracted the attention of the design department and manufacturers. Most manufacturers that use the Shell pulverized coal gasification process still use a high water/gas shift process.
Later, the Sinopec Group Company Ningbo Engineering Co., Ltd., for the shortage of steam in Guangxi Liuzhou Chemical Industry Co., Ltd., recommended to the company a low water/gas process. Guangxi Liuzhou Chemical Industry Co., Ltd. has conducted in-depth research on the pulverized coal gasification-low water/gas-to-sulfur-tolerance conversion process, and conducted in-depth and detailed exchanges with the technicians of Allenson Chemical regarding the occurrence of methanation in the first reactor. In the discussion, it was decided to select the low water/gas conversion process among the conversion devices of the ammonia conversion project, and all use the QDB type sulfur-tolerant conversion catalyst produced by Qingdao Lixin Chemical Company. So far, Shell's pulverized coal gasification low-water/gas-to-sulfur-tolerant conversion process has had its first industrial user in China, which is also the world's first industrial user.
So far, the new process has been successfully operated for 14 months at the conversion plant of the second ammonia plant of Guangxi Liuzhou Chemical Industry Co., Ltd. The results of industrial application show that the QDB-04 catalyst produced by Qingdao Allied Chemical Co., Ltd. can be used to control the reaction depth and bed hot spot temperature by controlling the reaction water/gas and bed inlet temperature. The maximum value of the water/gas reaction in the first and second stages does not exceed 0.28, the inlet temperature does not exceed 250Â°C, the hot spot temperature of the bed is 360Â°C to 380Â°C, and the CO index of each section is reasonably distributed, and the final CO outlet is less than 0.60. %, no methanation side reactions occur. The device has been operating for more than one year, which not only has a stable operation of the device but also has a significant energy saving effect. It is a very ideal process for producing methanol or synthetic ammonia with a high concentration of CO process gas.
Due to the increasingly tense impact of oil resources, China's coal chemical industry has now entered a stage of rapid development and there are many coexisting coal gasification processes. Among the many new technologies, the SCGP coal gasification process developed by the Dutch Shell Company has been applied in 17 large-scale coal chemical installations in China in less than 10 years, but the problem has followed.