Energy-saving and environmentally-benign integrated ammonia production system

In this work, an integrated conversion system of coal to ammonia (NH3) is developed with the objectives of total energy efficiency maximization and process simplification. The system integrates drying, chemical looping hydrogen production, cryogenic nitrogen separation, NH3 synthesis, and power generation. Due to this integration, the total exergy destruction from each individual process, as well as the whole system, can be reduced significantly, leading to high energy efficiency. Several operating parameters, including mass fraction of oxygen carrier, reduction temperature, oxidation temperature, operating pressure, and conversion per pass during NH3 synthesis are evaluated. Low-rank coal with a flowrate of 100 t h−1 (moisture content of 65.5 wt% wb) is used as the feedstock, while Fe2O3 is adopted as an oxygen carrier. From the results, the system shows high total energy efficiency (NH3 production and total energy efficiencies of 58% and 60%, respectively) and significant system simplification. Higher Fe2O3 mass fraction lowers the total flowrate of circulated material in the chemical looping module. Moreover, lower reduction temperature and higher combustion temperature are preferred due to lower amount of circulated material in the chemical looping module. Conversion per pass of 40% during NH3 synthesis leads to largest NH3 production amount, which is 40 t h−1.