Improving carbon dioxide capture efficiency of amine processes using advanced measurement technologies

Efforts to reduce emissions of carbon dioxide (CO₂) are expanding around the world. For example, captured CO₂ is diverted for direct utilization in various chemical processes, or processed for sequestration/storage, ensuring it does not contribute to climate change.

In this article, we will concentrate on the most common capture process: liquid amine absorption (Figure 1), showing ways to make this process more effective and efficient through strategic use of process instrumentation.

Figure 1: This article focuses on liquid amine absorption, used in various industrial sites.

The amine process runs continuously and involves chemical absorption, where a gas stream containing CO₂ is placed in contact with a liquid solvent containing amines. CO₂ is absorbed by the amine solution, allowing CO₂ lean gas to exit at the top. CO₂ rich amine is sent to a desorber to strip CO₂ and recycle the lean amine back into the process.

Applying instrumentation

As with any process, the primary objective is to optimize energy and performance, while maintaining safety. Accurate measurements for timely actions are critical in meeting these objectives. In an amine treating process, there are several critical measurements that need to be monitored and controlled to ensure efficient CO₂ capture, process safety and solvent longevity. These include flow, pressure, temperature and chemical composition.

Mass balance — Carbon capture must be regarded as an extension of the main process producing CO₂ rich gas because the two must respond in tandem to any operational changes. Amine flow must match both overall gas flow and CO₂ concentration to optimize removal efficiency, while minimizing solvent consumption and costs. The optimal measurement in this case is direct mass, for example with a Micro Motion Coriolis Mass Flowmeter (Figure 2). This provides data to perform mass balance across the entire system. In addition to ensuring the correct ratio of solvent to gas, it allows for effective measurement of CO₂ in each of its phases: liquid, gas and supercritical for pipeline transport.

Figure 2: Data from Micro Motion Coriolis Mass Flowmeters can be used to perform a direct mass balance on the process, and it is one of the few technologies able to measure CO₂ in all three phases; gas, liquid and supercritical state.

Heat exchangers — Heat exchanger performance, especially the lean-rich amine heat exchanger, and accurate steam measurement around the stripper, can significantly contribute to reducing energy consumption, thereby improving process efficiency. Minimizing energy consumption and maintenance costs start with equipping heat exchangers with the right measurement technologies since there are many distributed throughout the unit. A 2% restriction in throughput due to fouling can waste up to 10% of total energy input, making efficient monitoring essential. Non-intrusive devices — such as Flexim FLUXUS Ultrasonic Flowmeters, Rosemount X-Well Technology and WirelessHART-enabled instruments (Figure 3) — simplify installation, while optimizing performance.

Figure 3: Proper instrumentation is essential for detecting heat exchanger fouling and ensuring optimal efficiency. These include devices such as Emerson’s Rosemount 848T Wireless Temperature Transmitters, Rosemount X-well Technology, Rosemount 3051SFC Wireless Compact Flowmeters and Rosemount 3051S Wireless DP Transmitters, ensuring precise temperature and flow control throughout the unit.

Steam management — Accurate steam supply and control is required to heat amine solvent and efficiently extract CO₂. Using a compensated flow measurement, either DP or Vortex (Figure 4), provides significantly better measurement accuracy, allowing for better mass and energy balance, reducing process variability.

Figure 4: Rosemount 8800 Series Vortex Flowmeters (left) use a shedder bar design with an integral temperature sensor. The Rosemount 3051S MultiVariable Transmitter (right) can improve accuracy on steam measurements two-fold by compensating for pressure and temperature variations.

Monitoring corrosion — The corrosiveness of amines, which are known to be aggressive towards carbon steel, and CO₂, due to its ability to create carbonic acid, are areas of concern for maintenance departments. Corrosion potential increases with increasing amine concentration and CO₂ loading. Wall thickness measurement sensors (Figure 5) can be installed throughout a unit on pipe and vessel walls to monitor metal thickness continuously. Data from these sensors can be transmitted via WirelessHART to an automation or asset management host system so engineers can make decisions in real-time, with the data historized for analysis. Host systems can also trigger an alarm when wall thickness has reached a safety threshold.

Figure 5: Emerson’s Rosemount Wireless ET310 Corrosion and Erosion Transmitters can be mounted permanently at strategic points on piping and vessels. Analytics software can develop a heat map of corrosion activity simultaneously across a facility or unit, and plant personnel can use this information to evaluate overall maintenance efforts.

Amine solvent quality and CO₂ integrity — Real-time monitoring of amine solvent composition and CO₂ is critical for determining solvent degradation and process efficiency (Figure 6). Over time, amines can degrade due to oxidation, thermal breakdown or reaction with impurities.

Figure 6: Measuring online density with a Micro Motion Compact Density Meter (top), or if preferred with a Flexim FLUXUS H721 Non-Intrusive Ultrasonic Flowmeter (middle), amine make-up rate can be managed to achieve desired CO₂ capture efficiency. These measurements allow for reduced lab quality work and improved safety by eliminating manual rounds. At the same time monitoring CO, CO₂ and water using a NDIR (non-dispersive infrared) analyzer (bottom) ensures efficiency of the amine treatment process.

When monitoring amine composition, manual sampling can introduce safety risks and process inefficiencies. By monitoring amine density or concentration, along with CO₂ concentration, in near real-time, operators gain an accurate view of amine condition and carbon dioxide capture rates. This technology improves operational efficiency and safety.

Absorption and desorption — Pressure and temperature play an important role in both absorption and desorption (Figure 7). As absorption is especially impacted by the gas partial pressure, measurement of this variable is critical in managing absorption efficiency. Temperature has an even bigger role in process efficiency since the reaction between amines and CO₂ is temperature sensitive. In addition, temperature plays a significant role in ensuring a good heat balance across the process. Knowing temperature distribution across the entire length of the absorber and desorber is important in managing the process.

Figure 7: The Rosemount 848T Temperature Transmitter (top) provides a cost-effective way of getting accurate temperature measurements along the length of the absorber and stripper. A non-intrusive option, such as the Rosemount 648 Wireless Temperature Transmitter with Rosemount X-Well Technology (bottom), provides a quick temperature addition measurement to the lean/rich amine heat exchanger. All these measurements can be used to improve energy efficiency and improve the efficiency of the absorber and stripper.

Minimizing complexity

An amine capture unit is part of the larger CCUS value chain, stretching all the way from the initial process or combustion application, to final underground storage or other ultimate disposition. Putting these processes together so all steps function optimally from end-to-end often requires outside help from the outset to create an effective system. Emerson’s Engineered Solutions Team can assist in any and all phases of a project, including:

System software and services for monitoring and process control.
Flow meters and flow computers for process and custody transfer.
Analyzers for process gas and emissions.
Gas chromatographs for purity evaluation.
Corrosion and erosion monitoring.
Consultation, and more.

As a global innovator, Emerson has a deep legacy of solving the most complex challenges facing process plants and related facilities. We combine advanced technologies, industry-leading expertise and an insatiable curiosity about the world around us to create sustainable solutions.

Emerson’s vision for industrial architecture is built on a consistent, cohesive software ecosystem from intelligent field devices to the edge, and to the cloud. This approach integrates operations to make all data instantly accessible, understandable and usable for analytics, innovation and performance improvement.