Thermodynamic Analysis of an Ammonia Synthesis Process Based on Brayton Cycle

摘要

The paper develops a new ammonia synthesis process based on Brayton cycle, successfully solving the problem of low heat recovery efficiency of reaction heat by conventional Rankine cycle. In the new process, a gas turbine expander is introduced to drive the multistage compressor coaxially instead of raising steam in a waste heat boiler to drive a steam turbine. Such a process represents a typical reaction-separation system with a recycle stream and cold separation of the product from the recycle loop. Through thermodynamic analysis, it is found that the ammonia synthesis system has the innate convenience and conditions to use the actual improved Brayton cycle. Moreover, since the cold separation is always influenced by gas-liquid equilibrium of pure ammonia, absorption separation is integrated in the process to achieve better use of the reaction heat, which can be driven by the low temperature heat. Flow sheets of the new process are described with the pressure and temperature parameters according to the actual operation conditions. For this special case, thermodynamic calculation and analysis are carried out by a software. The calculated results show that the expansion work is much larger than the required compression work. Even if the utilization efficiency is relatively low, the output work can meet the need of gases compression.