Investigation of methane hydrate formation in a recirculating flow loop: Modeling of the kinetics and tests of efficiency of chemical additives on hydrate inhibition

Gas hydrates can be formed when light gases, such as the components of natu ral gas, come into contact with water under particular conditions of temper ature and pressure. These solid compounds give rise to problems in natural gas and oil industry because they can plug pipelines and process equipment. To prevent hydrate formation methanol and glycols are commonly and extensi vely used as inhibitors. Today, the thermodynamic equilibria of hydrate formation are well known, bu t the kinetics of gas hydrate formation and growth has to be studied in ord er to find means of controlling these processes and to explore the mechanis ms or hydrate formation that follows non equilibrium laws. The present work deals with the kinetics of methane hydrate formation studi ed in a laboratory loop where the liquid blend saturated with methane is ci rculated up to a pressure of 75 bar. Pressure is maintained at a constant v alue during experimental runs by means of methane gas make-up. First the effects of pressure (35-75 bar), liquid velocity (0.5-3 m/s), liq uid cooling temperature ramp (2-15 degrees C/h), and liquid hydrocarbon amo unt (0-96%), on hydrate formation kinetics are investigated. Then a new method is proposed to predict firstly the thermodynamic conditio ns (pressure and temperature) at the maximum values of the growth rate of m ethane hydrate and secondly the methane hydrate growth rate. A good agreement is found between calculated and experimental data. Finally the evaluation of the efficiency of some kinetic additives and some surfac tants developed to avoid either nucleation or crystal growth and agglomerat ion of methane hydrates is tested based on the proposed experimental proced ure.