The Dawa ammonia production and liquid nitrogen-based tail gas purification and recycling project was successfully commissioned on the first attempt

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The Dawa Ammonia Production Company’s project for recycling exhaust gas through liquid nitrogen washing was successfully commissioned in one attempt. Author/Source: Yunnan Dawa Ammonia Production Co., Ltd. Date: 2022-02-07. Clicks: 15. Recently, this project was brought online successfully in just one attempt; it achieves the goal of fully replacing the use of hot air furnaces in the coal grinding system to burn crude syngas for coal dust drying, by enabling the catalytic conversion and combustion of exhaust gas using liquid nitrogen. The project for the recovery and utilization of tail gas through liquid nitrogen washing took three months from the start of civil engineering work on September 30, 2021, to its successful commissioning. Patent technology developed jointly by Kunming University of Science and Technology and Yunnan Tianan Chemical Co., Ltd. was employed in this project; this technology introduces a new method for staged catalytic oxidation of tail gas using liquid nitrogen to transfer heat. The heat-inert gases generated can be used in place of hot air to burn crude syngas for the drying of coal powder. The core of this technology lies in the establishment of a system for steady heat transfer and the development of efficient, specialized catalysts. At the beginning of the project construction, a system was adopted for assigning a dedicated project manager, with regular project meetings and supervision meetings held to enhance coordination and communication in the project’s implementation. Under the meticulous management of the project team and the careful organization of the construction contractor, various stages of the project—including site surveying, civil engineering construction, steel structure installation, equipment installation, and pipeline installation—were carried out efficiently and in an orderly manner. On December 20, various specialties, construction units, and supervision units were organized to carry out the “three inspections and four determinations” checks prior to the trial operation. By December 25, more than 30 issues identified as part of these checks had been resolved, allowing the project to proceed with the intermediate handover and enter the full-scale trial production phase. Building on the successful first trial operation of the liquid nitrogen-based tail gas recovery project on December 31, 2021, the plant was restarted by introducing gas and feeding materials at 17:30 on January 29, 2022. After adjustment, all process parameters remained stable. The liquid nitrogen-washed exhaust gas was subjected to catalytic combustion to produce high-heat, qualified thermally inert gas, which was then introduced into the coal grinding system, thereby completely stopping the production of crude syngas in that system. The pilot operation of the liquid nitrogen-based tail gas washing and recovery system was successful; the coal grinding system of the gasification unit will save 3,000 Nm3 of crude syngas per hour. Approximately 240 million Nm3 of low-calorific-value fuel coal can be recovered each year through this process, generating 291,108.54 million kJ of heat, while also saving 12,070 tce. This leads to an increase in synthetic ammonia production of around 8,621 tons, resulting in annual economic profits of 22.59 million yuan. The liquid nitrogen-based tail gas recovery project is one of the initiatives aimed at enhancing the comprehensive capabilities of large-scale ammonia production facilities. It will further optimize the company’s production structure, create new sources of profit growth, and leverage the company’s advantages in the ammonia synthesis industry chain as well as in production technology. Through circular production methods and integrated facility design, it is possible to achieve recycling of products and by-products as well as more efficient production processes, thereby reducing energy consumption and overall production costs and enhancing the company’s competitiveness in the market. The completion and operation of this project will reduce the consumption of clean, low-pressure nitrogen by the coal grinding system, thereby further cutting nitrogen usage costs. It also enables the effective recycling of liquid nitrogen used for gas washing, eliminating completely the energy waste and CO2 emissions resulting from the combustion of fuels treated with liquid nitrogen. This facilitates the comprehensive recovery and utilization of low-grade energy, which holds great practical significance for the company’s efforts to reduce energy consumption and emissions, improve efficiency, and establish a green factory.