Environmental and economic benefits of improving amine unit operations

Amine unit in refineries

In refinery operations, the alkanolamine system—commonly referred to as the amine unit—plays a pivotal role in extracting hydrogen sulphide (H₂S), carbon dioxide (CO₂), and mercaptans (collectively identified as acid gases) from both process gases and liquid hydrocarbon streams. For operators aiming to safeguard consistent product quality and meet environmental standards, amine units are a vital component of effective refinery management.

Their significance is growing as refinery feeds become more sour and sulphur limits for refinery products are reduced. An amine unit that is poorly operated can lead to high amine losses, poor unit reliability, amine solution contamination, off-specification products, operating headaches, and increased operating costs to the refinery.

Furthermore, 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 importans, 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.
  
  

Benefits

Conversely, there are many advantages 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.
  
  
  

Figure 1 Veolia’s electrodialysis process and photo of a dedicated amine reclaiming 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.

Figure 2 HSAS and formic acid trends

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 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 programmable 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 reclaiming for the refinery was less than 30% of the amine solution replacement cost, without considering the 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

Although amine units are not directly involved in the production of refinery outputs, they are fundamental to upholding product specifications and ensuring the safe processing of acid gases in both refinery operations and carbon capture facilities. By proactively managing key parameters and maintaining optimal amine system conditions, operators can significantly lower operational expenses and enhance reliability across refinery units. With Veolia’s Total Amine Solutions, you gain access to comprehensive technology designed to boost the dependability of your amine units, reduce energy use, trim costs, and deliver measurable environmental benefits.

If you would like to learn more about our Total Amine Solutions, please visit our website.