Journal of Natural Gas Chemistry 18(2009) 453–457 A novel correlation for estimation of hydrate forming condition of natural gases Alireza Bahadori ∗ , Hari. B. Vuthaluru Department of Chemical Engineering, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia [ Received April 20, 2009; Revised May 13, 2009; Available online November 19, 2009 ] Abstract An inherent problem with natural gas production or transmission is the formation of gas hydrates, which can lead to safety hazards to produc- tion/transportation systems and to substantial economic risks. Therefore, an understanding of conditions where hydrates form is necessary to overcome hydrate related issues. Over the years, several models requiring more complicated and longer computations have been proposed for the prediction of hydrate formation conditions of natural gases. For these reasons, it is essential to develop a reliable and simple-to-use method for oil and gas practitioners. The purpose of this study is to formulate a novel empirical correlation for rapid estimation of hydrate formation condition of sweet natural gases. The developed correlation holds for wide range of temperatures (265 – 298 K), pressures (1200 to 40000 kPa) and molecular weights (16-29). New proposed correlation shows consistently accurate results across proposed pressure, temperature and molecular weight ranges. This consistency could not be matched by any of the widely accepted existing correlations within the investigated range. For all conditions, new correlation showed average absolute deviation to be less than 0.2% and provided much better results than the widely accepted existing correlations. Key words gas hydrate; correlation; natural gas 1. Introduction A gas hydrate is an ice-like crystalline solid called a clathrate, which occurs when water molecules form a cage- like structure around smaller guest molecules. The most com- mon guest molecules are methane, ethane, propane, isobutane, normal butane, nitrogen, carbon dioxide, and hydrogen sulfide [1,2]. It should be noted that normal butane does form a hy- drate, but is very unstable [3]. It has been assumed that normal paraffin molecules larger than normal butane are nonhydrate formers [4,5]. While many factors influence hydrate forma- tion, the two major conditions that promote hydrate formation are (1) the gas being at the appropriate temperature and pres- sure, and (2) the gas being at or below its water dew point. Other factors that affect hydrate formation include mixing, kinetics, type of physical site, surface for crystal formation, agglomeration and the salinity of the system. For the optimal design of gas production systems, it is im- perative that hydrate formation can be adequately predicted. There are numerous methods available for predicting hydrate formation conditions in natural gas systems. The most reliable of these models requires a gas analysis. However, if the gas composition is not known, even the previous methods can- not be used to predict the hydrate formation conditions, and the Katz (1945) gravity chart [6] can be used to predict the approximate pressure and temperature for hydrate formation. Therefore, there is an essential need to develop a simple-to- use method for appropriate prediction of hydrate formation conditions of natural gases. 2. Methodology to develop new correlation The required data to develop this correlation includes the reported data for hydrate formation condition of natural gases as well as temperature and pressure. In this work, the hy- drate formation condition is predicted rapidly by proposing a novel correlation, which has been developed, based on newly proposed numerical model [7,8]. The following methodology has been applied to develop this correlation. Firstly, hydrate formation temperatures are correlated as a function of pressure for various molecular weights. Then, the calculated coefficients for these polynomials are correlated as a function of molecular weight. The derived polynomials are applied to calculate new coefficients for Equations (1) and (2) ∗ Corresponding author. Tel: +61 8 9266 1782; Fax: +61 8 9266 2681; E-mail: Alireza.bahadori@postgrad.curtin.edu.au Copyright©2009, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. All rights reserved. doi:10.1016/S1003-9953(08)60143-7