A simple mathematical predictive tool for estimation of a hydrate inhibitor injection rate

Abstract

The formation of hydrates in production, processing facilities and pipelines has been a problem to the natural gas industry, that cost several millions of dollars. Therefore, an understanding of the inception of hydrate formation is necessary to overcoming hydrate problems. The aim of the first step of this study is to develop a simple-to-use correlation for predicting hydrate-forming conditions of sweet natural gases. This simple correlation estimates hydrate formation pressure of sweet natural gases for pressures up to 40 000 kPa and temperatures between 260 K and 298 K as well as molecular weights in the range of 16 to 29. In the next step, novel empirical correlations are developed to predict the required MEG weight percent in the rich solution and the flow-rate for desired depression of the gas hydrate formation temperature. These correlations are generated for a natural gas with relative density of 0.6 at pressures of 3, 5, 7, and 9 MPa, which are applicable to wet gas temperatures of 20, 30, 40, and 50 °C. In order to extend the application of these correlations to wide ranges of natural gas mixtures with specific gravities of up to 0.8, two generalized correction factors are also provided. The accuracy of this simple method is compared with the simulation results obtained by commercial software which showed excellent agreement. In all cases the error percent was approximately 2% and 5% for predicting hydrate formation temperature depression and MEG injection rate, respectively. The fitted equations developed in this study can be of immense practical value for the engineers and scientists to have a quick check on hydrate formation condition of natural gases with or without presence of inhibitor without opting for any experimental measurements. In particular, chemical and process engineers would find the simple equations to be user-friendly with transparent calculations involving no complex expressions.