Nov-2022

Environmental and economical benefits of improving amine unit operations (ERTC)

Amine unit in refineries - The alkanolamine system in a refinery, better known as the ‘amine unit’, is used to remove hydrogen sulphide (H₂S), carbon dioxide (CO₂), and mercaptans (collectively referred to as acid gases) from process gas and liquid hydrocarbon streams.

Donato Vinciguerra
Veolia Water Technologies & Solutions

Article Summary

Amine units are an essential part of the refinery operation to maintain product quality and environmental compliance. Their importance is increasing as refinery feeds become more sour and refinery product sulphur limits are lowered. A poorly operated amine unit can result in high amine losses, poor unit reliability, amine solution contamination, off-specification products, operating headaches, and increased operating costs to the refinery.

Also, for post-combustion CO₂ capture from flue gas, the amine-based CO₂ capture system is commercially the best available technology today. There is currently a worldwide R&D effort taking place to improve this technology mainly to reduce the high energy penalty of this technology and focus on reduction in the degradation products.

Challenges
Despite their importance, amine unit operations are often not well understood or operated optimally. This is due to several factors, including:
• Amine units enable a refinery to make a profit but do not directly produce a profitable product
• The various parts of an amine unit are typically spread out across different operating units: lean amine solvent is typically pumped to absorber towers in the process units containing the production fluids, then rich amine is pumped back to the stripper tower for acid gas removal, so control of the entire circuit is not straightforward.
• Many refinery amine units are operated well beyond their original design capacities.
• Amine systems are often robust enough to maintain refinery product quality, even when operating far from either original design or best operating practices.

Conversely, there are many benefits that can be realised by improving amine unit operations, such as:
• More consistent product quality, resulting in reduced frequency of ‘event-driven’ activities to blend off or retreat episodic off-spec products
• Lower energy costs
• Reduced costs for filters, activated carbon, and replacement amine
• Improved reliability that lowers equipment replacement/repair costs
• Improved operation of the sulphur plant by providing a more consistent feed quality to this unit.

Amine units tend to accumulate thermally stable amine salts (HSAS), which cause issues like corrosion, fouling, loss of efficiency, foaming, operational instability, and excessive loss of amine solvent. Best practices indicate that the maximum allowable concentration of HSAS is 2.0% wt in the amine solution. A key aspect of successfully operating an amine unit for optimal performance is a good amine management programme. This involves monitoring the condition of the amine solution and managing the feed quality, operating conditions, and the amine solvent itself to avoid issues associated with highly contaminated or degraded amine.

Case study
A refinery in Europe had a high HSAS concentration (>5.0% wt as methydiethanolamine, MDEA) and a formate content greater than 15,000 ppm, which caused corrosion problems, fouling, and an excessive loss of amine solvent. Veolia Water Technologies & Solutions performed the reclaiming of amine solvent using a custom-built mobile electrodialysis (ED) unit.

Veolia’s ED technology provides several advantages: when in stable operation and if there is no necessity to perform a cleaning procedure, a mobile ED unit can stay in operation for several days or weeks, and the waste stream generated is a neutral salt solution. Additionally, during this period, no water is introduced into the amine stream, except for a ‘flush’ sequence required before a clean in place (CIP).

A lean amine stream was passed through the reclaiming unit, sending back the reclaimed stream to the amine unit. The effluent generated in the reclaiming process (brine formed by neutralised stable salts) was sent directly to the refinery wastewater plant without causing any negative impact. The double ED mobile unit is fully automated by a programmabale logic controller (PLC) System + human machine interface (HMI). Flow rates, temperatures, conductivities, and pressures are controlled and measured automatically during operation. The system will be monitored and controlled by a single operator per shift without exclusive dedication, given the degree of automation.

At the end of operation, 850 m³ of amine solution was reclaimed. A 90% reduction in formate content was achieved, down to 1,500 ppm – below our control guideline of 2,000 ppm. The HSAS was reduced to 0.5% wt. Amine losses throughout the regeneration process were less than 1% wt, based on total system volume.

The cost of the reclaiming for the refinery was less than 30% of the amine solution replacement cost, without considering disposal costs of the contaminated amine. The total saving for the refinery was more than $400K (US). The reclaiming mobile unit has wide applicability and can be successfully used for different types of amine solvent, including MDEA, monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), formulated solvents, and others.

Veolia can also offer a dedicated amine reclaiming unit to customers. This ED unit can be put into continuous feed & bleed operation (at lower capacity) to keep HSAS at a continuous low level operated by Veolia.

Conclusion
While amine units do not directly contribute to producing the products from a refinery, they are an essential unit operation to maintain product specification and to safely handle the acid gases in the refinery operation and carbon capture plants. Attention to operating parameters, amine system condition, and performance can minimise operating costs and improve refinery unit reliability and operations. Veolia’s total amine solutions will provide a full scope of technology to increase the reliability of amine units, reduce the energy footprint, and lower operational costs and the environmental footprint.

This short article originally appeared in the 2022 ERTC Newspapers, which you can view HERE