Feb-2007

Advances in amine reclaiming

Why there is no excuse for operating a dirty amine system. The benefits of reclaiming amine systems are trumpeted by many and doubted by others.

Arthur L Cummings, Glen Smith and Dennis K Nelsen, MPR Services

Article Summary

Removing the contaminants generally results in smoother operations. Various methods of removing contaminants from amine solutions have been developed and improved over the years, primarily because of the enthusiasm of the users of reclaiming services. Suspended solids and hydrocarbons have been routinely dealt with by filtration and absorption technologies for longer than anyone can remember, but other contaminants have only relatively recently been targeted. Heat stable salts (HSS) were rarely spoken of 15 years ago, but are now universally known as an operational concern. Of the several potential chemical degradation products of amines, only HEEU and BHEEU (ureas formed by MEA and DGA, respectively) have had a long-standing routine way of dealing with them. As analytical capabilities improved, more and more contaminants can be identified and have become of interest. Amino acids (bicine, HES, and others) have received particular interest because of their strong contribution to corrosion. In recent years, amides, diamines, ureas and oxazolidones have become common targets of reclaiming efforts. Amides and oxazolidones have been converted back to useable amine. Over the last 15 years, reclaiming services have become available, employing a variety of technologies to remove contaminates. These are reviewed and compared.

Introduction
Operators of acid gas scrubbing units are continually challenged to maintain and increase throughput as feedstocks change and product specs tighten. Amine systems (scrubbing units employing alkanolamine solvents) have been scrutinised more and more closely over the last 15 to 20 years, because of capacity, throughput and costs concerns. Twenty years ago, amine reclaiming consisted of built-in particle filtration and activated carbon units and, for MEA and DGA systems, a built-in thermal reclaimer. Now, operating companies can purchase mobile reclaiming services and permanent add-on reclaiming units for an ever-increasing array of dissolved, entrained and suspended contaminants anywhere in the world. What has changed? Why the rise in the perceived need for reclaiming and what is now available to meet that need?

Product specifications and environmental concerns have also changed. Lower sulphur specs in finished products coupled with sourer feed stocks press ever-increasingly on the capacity of amine systems.^1,2

Amine system downtime and upsets have a more visible connection to throughput and profits. Disposal of contaminated amine is hindered by fewer available options and higher costs. For many refineries, reclaiming is becoming the only option.

Reclaiming — removing the contaminants from amine solvents — generally results in smoother operations, which, more and more visibly, translates to improved bottom line. Table 1 shows the bottom-line benefits of reclaiming to low impurity levels that four refiners documented. The positive effects of reclaiming seen by these refiners included reduced amine losses/consumption/ replacement, reduced anti-foam usage, reduced foaming, reduced filtration costs, reduced heat exchanger fouling, reduced amine unit operating costs, fewer production curtailments, fewer upsets of wastewater treatment plant, record crude, coker, cracker runs, increased overall production, ability to run sourer crude, and increased sulphur production.

About 15 years ago, as mobile reclaiming services began to be available, only a few brave operators could be induced to try reclaiming their amine. However, the reclaiming resulted in such dramatically improved operations that they realised that amine reclaiming had to be a necessary part of their future. The previously rarely mentioned HSS became a term that amine system engineers had to know. Replacing traditional “bleed and feed” (disposal of contaminated amine and replacing it with new amine) are services of ion exchange, distillation and electrodialysis for dissolved salts and degradation products along with filtration and absorption for suspended solids and hydrocarbons.^3,4,5  All these technologies have been improved and are more available than ever before as permanent on-site installations, temporary on-site mobile services, and as off-site services.

A review of the current state of reclaiming options is overdue. This paper is a review of advances and limitations of reclaiming options organised by contaminant type.

Reclaiming methods
There are fundamentally two approaches to reclaiming contaminated amines: remove the contaminant from the solvent, and remove the solvent with or from the contaminant. A third approach, sometimes used in place of reclaiming, employs additive to negate or cover a particular symptom of a contaminant. Examples of the first approach include ion exchange, electrodialysis, filtration and adsorption. The second approach includes “bleed and feed” and distillation. The third approach includes addition of caustic, corrosion inhibitors or antifoaming agents.⁶