Controlling hydrocarbon dew point and water dew point of natural gas using Aspen HYSYS

Abstract

A great attention is subjected to the environmentally friendly natural gas. Compared to other fossil fuels, natural gas is a cleaner burning due to the lower emission of carbon dioxides into the air. Removal of associated hydrocarbons from natural gas streams plays an important role to sell and to achieve the pipeline specification of natural gas. To satisfy the specification of pipelines, the hydrocarbon dew point and water dew point of natural gas must be controlled below the pipeline operating conditions to prevent many problems: two-phase flow and hydrate formation in the system. The main purpose of this paper is to simulate the gas plant process to study the effect of natural gas composition and changing in differential pressure of Joule–Thomson expansion valve on the obtained values of hydrocarbon, water dew points, and cricondentherm temperature.The results of process simulation using Aspen HYSYS have shown that the control of hydrocarbon dew point, water dew point, and cricondentherm of natural gas is achieved through increasing the Joule-Thomson valve differential pressure. There is an inverse relation between increasing Joule-Thomson valve differential pressure (∆p) and hydrocarbon dew point, water dew point, and cricondentherm to meet the specification of gas pipeline transmission. Increasing differential pressure (∆p) from 14 bar to 24 bar causes a decrease in hydrocarbon dew point, water dew point from −1 to −26°C and from 0 to −18°C, respectively. Cricondentherm is also decreased from 4 to −12°C by increasing differential pressure (∆p) from 14 to 24 bars. The operating conditions at differential pressure below 14 bar is not advisable because cricondentherm temperature does not meet the specification of gas pipeline transmission and hence lead to many problems. Careful adjustment of the operating conditions of gas processing plant is very important by making such simulations to choose the optimum operating conditions which meet gas pipeline transmission.