Simulation, optimization, and sensitivity analysis of a natural gas dehydration unit

The exploration and production of natural gas are usually accompanied by large amount of water vapor production. In order to prevent serious problems like hydrate formation that would be posed by water vapor molecules it is necessary to remove water from natural gas stream; a process called dehydration. In this study, a natural gas dehydration unit along with its diethylene glycol (DEG) recovery section, located in Iran, is simulated using a steady state flow-sheet simulator. For simulation purposes, a Redlich-Kwong-Soave equation of state with Modified-Huron-Vidal mixing rule (known as RKSMHV2 model) was applied owing to its low absolute average relative deviation percentage (AARD%) compare to the other available models. The primary aim of this research is to study the possibility of optimizing the whole process and performing a sensitivity analysis over the obtained results from the simulation. Volatile organic compounds (VOC) emission, dry gas dew point, solvent loss, and process total duty were chosen as dependent variables of the dehydration process the sensitivity of which were examined by independent variables variations like wet gas molar flow rate, solvent molar flow rate, solvent purity and water content of natural gas. The final results revealed that VOC emission is extremely sensitive to an enhancement in purity or molar flow rate of glycol while for the wet gas and water molar flow rate variations, solvent loss changes are more severe than the other dependent parameters. By taking into account all operational restrictions and assuming dry gas dew point as the key factor for the process optimization; it was revealed that a 10% increase in solvent molar flow rate is applicable in order to reduce dry gas dew point up to 6% without a significant rise in the dehydration unit's total energy consumption and VOC emission.