Natural Gas Dehydration Using Supersonic Separators with a Novel Design
Authors: Haghighi Mohammad , Abedinzadegan Abdi Majid , Hawboldt Kelly 
Published: May 2013

Supersonic separators are compact devices capable of separating condensables of gaseous mixtures. Of special interest is the application of these separators in the dew point control of natural gas. Many researchers as well as industry pioneers have invested in the study of these separators in the past two decades and various prototypes as well as field ready models have been introduced. All of these designs are based on the concept of a swirling flow in a supersonic nozzle. The current work was initiated to investigate possible alternate designs.

In this paper, preliminary studies of an alternate design of the supersonic separators based on inducing centrifugal separation using a U-shaped diffuser is presented. Computational Fluid Dynamics models were used to simulate the design, predict the flow dynamics of the gaseous mixture, and compare to the conventional swirl type design. A bench scale experiment was set up to verify the CFD models. It was concluded that the CFD technique is a valuable and reliable tool for the study of these separators. Moreover, it was shown that potentially more efficient separation with a higher rate of pressure recovery can be achieved with the proposed design when compared to the conventional designs.

Introduction

Natural gas is one of the most important sources of energy in the world. At a current rate of over 120 trillion cubic feet per year, it accounts for over 25% of the world's primary energy consumption. Furthermore, in the drive for cleaner fuels, the demand for natural gas is forecast to grow 1 to 3.5% per year for the next 20 years (EIA, 2012). This ever growing demand for natural gas has led to the exploration and development of unconventional reservoirs (e.g. Shale gas, deep water, and the Arctic). However, with these new sources come new challenges, this is particularly true of offshore and harsh environments that limit recovery, storage, and transportation options to bring the gas to market. The key challenge is the limited space on offshore platforms for gas treating. To bring the gas to market, contaminants such as water, carbon dioxide, and sulphur compounds, among others must be removed. However, the bulk of the platform is required for oil recovery, limiting space for the large equipment needed for gas treatment. In addition, energy requirements and waste streams generated in typical gas treatment systems further limit these systems. To bring the gas to market under these conditions requires the development of equipment with a small footprint. Supersonic separators, where removal of contaminants is accomplished through centrifugal forces, do not require chemical solvents and are relatively compact, therefore a more suitable gas conditioning system for offshore. Supersonic separators have been used for selective dew pointing of natural gas with respect to water and/or hydrocarbons (Okimoto et al., 2000; Brouwer et al., 2003; Alfyorov et al., 2005). The supersonic separator is a compact device capable of removing contaminants from natural gas with little loss of thermal energy and/or hydrodynamic head by combining the principles of gas expansion and cyclonic separation.