Transferability of Kinetic Inhibitors Between Laboratory and Pilot Plant
Authors: Lederhos J.P. , Sloan E.D. 
Published: December 2007

This work concerns the transferability of hydrate kinetic inhibition results between two small bench scale apparatuses and a pilot scale flow loop. Industrial use of hydrate kinetic inhibitors depends on the transferability of the results between the lab, pilot plant, and field. Experimental data are presented showing the transferability of hydrate kinetic inhibitor results between two bench scale apparatuses at the Colorado School of Mines (CSM) and an industrial pilot scale flow loop. The transferability was based in terms of the amount of subcooling observed for each apparatus. The kinetic inhibitors tested (PVCAP and VC-713) were discovered at CSM and shown to be economic alternatives to thermodynamic inhibitors such as methanol.

Introduction

The problem of hydrate blockage of flow channels has been of major importance to the energy industry since the discovery of hydrates in gas pipelines. Every year an operating expense greater than $500 million is devoted to hydrate prevention via methanol injection. Offshore, insulation expense to prevent hydrates is $1 million per mile of subsea pipeline. Such economics have led to substantial hydrate research, mostly in the area of thermodynamic prevention.

Over the last decade, hydrate research has witnessed a transition from time-independent (thermodynamic) studies to time-dependent (kinetic) studies. Significant advances have been made in the area of hydrate kinetic inhibition in the past five years. In particular, hydrate kinetic inhibitors have been found which prevent hydrate growth for a time exceeding, for example, the typical residence time of free water in a gas pipeline.

Recently, the hydrate kinetic inhibitors poly(N-vinylcaprolactam) (PVCap) and poly(N-vinylpyrrolidone/Nvinylcaprolactam/N, N-dimethylaminoethylmethacrylate) (VC-713), discovered at CSM, were both shown to be economic alternatives to traditional thermodynamic inhibitors. This was based on gas consumption data from a bench scale apparatus located at CSM. The performance of these two kinetic inhibitors in terms of subcooling is reported in this work for two small bench scale apparatuses and an industrial pilot scale flow loop. In addition, the transferability of the results between the apparatuses is reported.

Young suggested that of the methods of evaluating the performance of the kinetic inhibitors subcooling and the study of hydrate particle size and morphology are the best. The amount of subcooling is defined as the equilibrium temperature minus the operating temperature. Kinetic inhibitors increase the tolerated amount of subcooling over that observed for the non-inhibited system before hydrate formation. The methods of rate of formation, total amount of hydrate formed, and induction time were considered to be dependent on the physical configuration of the apparatus. To date, there have been only four studies reporting the hydrate kinetic results for aqueous mixed systems in terms of subcooling.

The most comprehensive of these studies was reported by Reed et al. for the effect of cooling rate and flow rate on the hydrate subcooling. Reed reported results showing that variations in the cooling rate from 0.6 to 5.6 C/hr had less than a 1.1 C effect on subcooling. The results were based on flow loop results for a gas/condensate/sea water system. In addition, Reed et al. found that the subcooling was only weakly affected by flow rate.

Experimental Apparatuses and Procedures The two bench scale apparatuses used in this work were the CSM high pressure and sapphire screening apparatuses. The high pressure apparatus consisted of a 300ml autoclave reactor submersed in a temperature controlled water bath. A standard charge of 60g of aqueous solution and 30g of liquid condensate were used. P. 173