Natural Gas Dehydration with Aspen Hysys Validation of the CPA Property Package

ACKNOWLEDGEMENT  

ABSTRACT 

INTRODUCTION  

OBJECTIVE  

Natural Gas Dehydration 

TEG  

PROCESS DESCRIPTION  

Modeling the Dehydration Process in Aspen HYSYS 

Aspen Report of Absorber and Regenerator 

Model Configuration  

Run a Case Study to Identify 

Possible Process Improvements 

Graph and Results  

Conclusion  

References

Abstract

Dehydration process is an important focal unit in offshore gas processing to avoid industrial problems accompanied by hydrated gas processing and pipeline transport system such as corrosion and hydrates formation. The gas dehydration process has been entirely simulated and optimized in Aspen HYSYS V8.8 using cubic plus association equation of state thermodynamic package and compared to the simulation results obtained by using glycol package which is developed particularly for gas dehydration modeling. 

Mathematical models for the prediction of water content, gas and solvent temperatures of the absorber of a natural gas glycol dehydration facility were developed. The models developed contain contributions from bulk and diffusion flows, however only the effect of diffusion on the process occurring in the absorber was studied. The developed models were second order partial differential equations. The Laplace transform technique was applied to obtain analytical solutions of the model equations. The models were validated using the plant data from an SPDC TEG unit in Gbaran Ubie, Bayelsa State. The results showed a reasonable agreement between the model predictions and industrial plant data. The model predicted the amount of water in the gas stream at the end of the absorption process very  accurately with a deviation of 0%., the gas and solvent temperatures with deviations of 1.584% and 2.844% respectively. These results show that diffusion alone can be use to accurately model the absorption process. The effects of certain process variables such as residence time, gas inlet water content, mass and thermal Diffusivities of the gas on the performance of the absorber was studied. 

Natural gas is an important energy source among other sources of fossil fuels. It is usually produced saturated with water vapor under production conditions. The dehydration of natural gas is very essential in the gas processing industry to remove water vapor. Water vapor in natural gas stream, poses threat to process facilities if the dew point temperature is not properly controlled. Dehydration of natural gas is the process removal of the water that is associated with natural gases. The mixtures of water in natural gas can cause the problems for the production operation, transportation, storage and use of the gas. The four major methods of dehydration are absorption, adsorption, gas permeation and refrigeration. The process of dehydration by using TEG is absorption, involves the use of a liquid desiccant to remove water content from the gas. 

The objective of this experiment is to carry out a simulation on TEG dehydration unit using AspenHYSYS process software. This is important in an FPSO since the removal of water from natural gas is necessary before processing, and due to the fact that Natural gas from the reservoir contains large amount of water which can cause several problems to downstream processes and equipment. TEG was used because it has gained nearly universal acceptance as the most cost effective of the glycols due to its superior dew point depression, operating cost and operational reliability. The composition of the natural gas has been provided on a water-free basis, therefore to ensure water saturation it was mixed 

with water before entering the first unit operation. The units involved in this simulation are; Contractor, Regenerator, Valve, Component splitter, Cooler, Stripper and Splitter, alongside with an adjust logical tool which was used to find the point at which water is just formed (dew point with a temperature of -13.67Oc). At the end of the converged simulation, 89.92 wt% methane was recovered at a flow rate of 9177kg/hr. which might have resulted due to loss of some of the gases at certain stage of the process. 

Keywords: Dehydration process optimization; gas dehydration process simulation; natural gas thermodynamics