The crystal growth rate of calcium carbonate at conditions of hydrate inhibition in gas processing systems

摘要

The injection of inhibitors for corrosion and gas hydrate formation duringtransportation of wet gas/condensate in steel pipelines strongly affect the tolerancefor produced formation water. The elevated alkalinity downstream of the injectionpoint, combined with calcium ions from the produced formation water, might result inthe precipitation of calcium carbonate. This paper reports on a study of growth ofcalcium carbonate in mixtures of ethylene glycol (MEG) and water at temperatures of40 and 70°C. Our previous findings (Flaten and Andreassen, 2007) show thatcalcium carbonate precipitated in MEG contains the metastable polymorphs vateriteand aragonite in addition to the thermodynamically stable calcite. In the present studythe effect of MEG and temperature on the growth rate has been determined for allthree polymorphs, paying special attention to vaterite. The effect of the scalinginhibitor sodium triphosphate was investigated with respect to vaterite. The resultsshow that increased contents of MEG reduce the growth rate constant of the vateriteat both temperatures investigated, from kg = 3.2 to 0.2 nm/s for 0-70wt% MEG at40°C and from kg = 4.0 to 0.7 nm/s for 0-70wt% MEG at 70°C. The growth rateconstant for calcite was significantly lower and decreased from kg = 0.7 to 0.05 nm/sfor 0-50wt% MEG at 40°C. The growth rate constant of aragonite was reduced fromkg = 0.9 to 0.4 nm/s for 0-50wt% MEG at 40°C. The scaling inhibitor sodiumtriphosphate pentabasic was found to inhibit the growth of vaterite at 40°C forconcentrations of 1-20 ppm present in solutions both with and without MEG.