Membrane PSA: [Weekly Topic] {May 9, 2011} How is pressure swing adsorption used in the ammonia synthesis industry?

Reply to 1# Air separation main cooler: Haha, the teachers are too modest! With such a great post, no one wants to share their insights! The student would first say a few words in a cursory manner; the term “cursory” is used because what these students say comes from research in literature, and they have no actual research experience or hands-on experience in this area! I hope all the teachers can give me more guidance! I also hope that the original poster won’t consider the students’ replies as spam; there are sections on this topic in the students’ graduation projects, and they are very eager to learn about it as well. Thank you! The basic principle of pressure swing adsorption is to utilize the fact that the adsorption capacity, adsorption strength, and adsorption rate of adsorbents for different gases vary with pressure. Under conditions where the adsorbent preferentially adsorbs certain components, pressure is applied to adsorb the more easily adsorbable components in the mixture (usually through physical adsorption); when the pressure in the adsorption bed is reduced, these adsorbed components are desorbed, thereby regenerating the adsorbent. An alternating cyclic operation of two or more towers is employed to achieve continuity in the process. This method features a simple process flow, strong adaptability of the equipment, a CO2 content of less than 0.2% after purification, easy operation, high automation level due to DCS control, no need for complex pretreatment systems, and no issues related to equipment corrosion or environmental pollution. In particular, the two-stage pressure swing adsorption patent technology, which has emerged as a result of continuous technological innovations in recent years, offers advantages such as a simpler process, greater flexibility in operation, lower operating costs, and a higher degree of automation. Compared to traditional methods such as NHD, modified carbon-propane method (PC), modified MDMEA method, and modified thermal potassium-alkali method, it is capable of replacing existing wet carbonation systems. The entire investment can be recovered within less than two years. As energy shortages become more severe, the advantages of this two-stage pressure swing adsorption patent technology in terms of energy savings and coal reduction become even more apparent. The pressure swing adsorption process has been developed in China for 20 years. Initially, its low technical level and low yield led to difficulties in its adoption; over time, the technology was improved to increase yields. Chengdu Tianli Chemical Technology Co., Ltd. introduced a two-stage vacuum extraction process, which resolved the issue of limited adoption due to low yields. As a result, numerous pressure swing adsorption units were installed across the country to replace the older processes. With the goal of continuous innovation, and through rigorous experimentation, a revolutionary transformation was carried out on the pressure swing adsorption decarburization process, resulting in significant improvements in the recovery rate of the product and in reducing energy consumption. At present, many companies in China are using the full-purge pressure swing adsorption process for carbon removal: Hubei Zhijiang Sanning Chemical Co., Ltd. operates a pressure swing adsorption carbon removal unit that processes 30,000 NM3/h of shift gas (for the production of liquid ammonia); Liaoning Fengcheng Fertilizer Factory has a pressure swing adsorption carbon removal unit that handles 21,000 NM3/h of shift gas (for liquid ammonia production); Hunan Anxiang Fertilizer Factory uses a pressure swing adsorption carbon removal unit capable of processing 1,500 NM3/h of shift gas (for liquid ammonia production). Among these, the units with an annual production capacity of over 160,000 tons include Inner Mongolia Wulashan Fertilizer Factory’s pressure swing adsorption carbon removal unit that processes 96,000 NM3/h of shift gas, and Hunan Dangyang Huahua Chemical Co., Ltd.’s unit that handles 88,000 NM3/h of shift gas. The carbon dioxide content in the purified gas is generally around 0.2% (by volume), while the hydrogen recovery rate is above 99.5% (by volume) and the nitrogen recovery rate is above 98% (by volume). There is no power consumption associated with these equipment.

Currently, PSA is mostly used in the decarburization sections of small and medium-sized ammonia synthesis plants. The effect is also very good. Currently, some large-scale ammonia synthesis purification units are showing a tendency toward low-temperature methanol washing. However, PSA decarburization still has much room for development in ammonia synthesis systems.

I checked some information, and PSA has three main applications in the production of ammonia: (1) Using PSA to purify the feed gas used in ammonia synthesis, by removing impurities such as CO and sulfides from it； (2) PSA-concentrated ammonia synthesis off-gases, such as CO concentration and hydrogen recovery, etc ； (3) In the production process of raw gas for ammonia synthesis, PSA can be used in new processes for oxygen-enriched gas generation from coal and petroleum coke, as well as from natural gas, in order to achieve goals such as saving raw materials and increasing production