Heat Integration of Two Low-Temperature Processes: Natural Gas Liquefaction and Air Separation Unit

This research aims to present a new integrated design for Natural Gas Liquefaction and two-column Air Separation Units, each of them with a capacity of 60,000 kg/h. First, each of these two selected units was simulated and optimized using Genetic Algorithm with the aim of reducing total annualized costs. Then, the streams were thermally investigated and after identifying the streams participating in the process heat transfer area, the processes were integrated. The results of the sensitivity analysis of the integrated process indicated that by increasing the outlet pressure of the C-5 compressor, increasing the outlet pressure of the VLV-5 expansion valve and increasing the flow intensity of isopentane refrigerant, the annual cost decreases and by increasing the flowrate of other refrigerant components, the annual cost increases. In the next step, the integrated process was optimized using MATLAB software. The results showed that by integrating these two processes, the amount of the power consumed in the processes increases from 46.6 to 48.5 MW. This increase in power consumption increases the operating costs of the compressors by 4%, capital costs reduce from 246.2 to $218 million, which is reduced by approximately 11%, and the total annualized cost was reduced by $1.2 million /y.