Inhibitor Selection for Iron-Scale Control in MEG Regeneration Process

Abstract

Summary The formation of iron-containing scale because of highly dissolved iron content and increased pH (≥ 8.5) has been observed in a monoethylene glycol (MEG) regeneration system. The control of iron-scale deposition under these harsh conditions causes recurring problems in the reboilers, requires frequent filter change-outs, and remains a challenge to the field. To investigate this problem, a modified corrosion-testing apparatus was employed to replicate the iron-scale formation. It evaluates the performance of selected chemicals under realistic field conditions (specifically, low pH caused by carbon dioxide dissolution; higher pH because of carbon dioxide boiling off from the reboiler; and alkali addition for corrosion control). Both pH and iron levels (including dissolved iron, ferrous iron Fe2+, and total iron) were closely monitored. Additional digital photos were taken at various stages. There are several challenges associated with the inhibition of iron scale in systems with a high iron level (≥ 150 ppm), high MEG content (≥ 60%), and high pH (≥ 8.5). These factors contribute to incompatibility and poor inhibition by conventional inhibitor species. A number of scale-inhibitor (SI) products, scale dissolvers, and blends were tested under aerobic or anaerobic conditions. One product greatly reduced the rate of scale formation and indefinitely delayed scale formation at higher dosage. This product also showed the capability to redissolve deposits already present in the system. Evaluation of iron-scale inhibitor is a challenge because of the debatable iron-poisoning effect and the lack of a standard laboratory method. In this paper, the propensity of various iron deposits (e.g., iron carbonate and insoluble iron/inhibitor complex) is discussed. Moreover, the formation of a soluble iron/inhibitor complex is quantified. This could have important implications for the remediation of iron-containing scale.