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.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
6 March 2008
- Meeting paper published:
28 May 2008
- Revised manuscript received:
20 June 2008
- Manuscript approved:
8 August 2008
- Published online:
27 August 2009
- Version of record:
25 November 2009
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