In-Line Monitoring of the CO₂, MDEA, and PZ Concentrations in the Liquid Phase during High Pressure CO₂ Absorption

This article provides results of the <i>in situ</i> monitoring of carbon dioxide (CO₂) removal under high pressure. An aqueous solution of methyldiethanolamine (MDEA) promoted by piperazine (PZ) for absorption rate acceleration was used. This system is promising for natural gas purification. A predictive statistical model was built using the chemometrics method and measurements of density, pH, conductivity, sound velocity, refractive index, and Near Infra-Red (NIR) spectroscopy. The CO₂ capture rate ranged from 60% up to 96% at pressures in the absorber column ranging between 15 and 20 bar. The liquid stream composition was monitored at the low pressure part of a pileline at a location before a compressor stage. The concentrations of MDEA, PZ, and CO₂ were predicted in-line using different sets of the measurement devices during 3 days of the measurement campaign. The developed approach allowed for prediction of the concentrations with accuracies of 0.7% for MDEA, 0.4% for PZ, and 2.5% for CO₂

Online Monitoring of the Solvent and Absorbed Acid Gas Concentration in a CO₂ Capture Process Using Monoethanolamine

A method has been developed for online liquid analysis of the amine and absorbed CO₂ concentrations in a postcombustion capture process using monoethanolamine (MEA) as a solvent. Online monitoring of the dynamic behavior of these parameters is important in process control and is currently achieved only using Fourier transform infrared spectroscopy. The developed method is based on cheap and easy measurable quantities. Inverse least-squares models were built at two temperature levels, based on a set of 29 calibration samples with different MEA and CO₂ concentrations. Density, conductivity, refractive index, and sonic speed measurements were used as input data. The developed model has been validated during continuous operation of a CO₂ capture pilot miniplant. Concentrations of MEA and CO₂ in the liquid phase were predicted with an accuracy of 0.53 and 0.31 wt %, with MEA and CO₂ concentrations ranging from 19.5 to 27.7 wt % and from 1.51 to 5.74 wt %, respectively. Process dynamics, like step changes in the CO₂ flue gas concentration, were covered accurately, as well. The model showed good robustness to changes in temperature. Combining density, conductivity, refractive index, and sonic speed measurements with a multivariate chemometric method allows the real-time and accurate monitoring of the acid gas and MEA concentrations in CO₂ absorption processes

Analysis of Process Configurations for CO₂ Capture by Precipitating Amino Acid Solvents

Precipitating amino acid solvents are an alternative to conventional amine scrubbing for CO₂ capture from flue gas. Process operation with these solvents leads to the formation of precipitates during absorption that need to be re-dissolved prior to desorption of CO₂. The process configuration is crucial for the successful application of these solvents. Different process configurations have been analyzed in this work, including a full analysis of the baseline operating conditions (based on potassium taurate), the addition of lean vapor compression, multiple absorber feeds, and the use of different amino acids as alternative solvents to the baseline based on potassium taurate. The analysis is carried out with an equilibrium model of the process that approximates the thermodynamics of the solvents considered. The results show that the precipitating amino acid solvents can reduce the reboiler duty needed to regenerate the solvent with respect to a conventional MEA process. However, this reduction is accompanied by an expenditure in lower grade energy needed to dissolve the precipitates. To successfully implement these processes into power plants, an internal recycle of the rich stream is necessary. This configuration, known as DECAB Plus, can lower the overall energy use of the capture process, which includes the energy needed to regenerate the solvent, the energy needed to dissolve the precipitates, and the energy needed to compress the CO₂ to 110 bar. With respect to the energy efficiency, the DECAB Plus with lean vapor compression configuration is the best configuration based on potassium taurate, which reduces the reboiler duty for regeneration by 45% with respect to conventional MEA. Retrofitting this process into a coal fired power plant will result in overall energy savings of 15% with respect to the conventional MEA process, including compression of the CO₂ stream to 110 bar. Potassium alanate was found to reduce the energy use with respect to potassium taurate under similar process configurations. Therefore, the investigation of potassium alanate in a DECAB Plus configuration is highly recommended, since it can reduce the energy requirements of the best process configuration based on potassium taurate

Real-Time Process Monitoring of CO₂ Capture by Aqueous AMP-PZ Using Chemometrics: Pilot Plant Demonstration

A combination of analytical instrumentation and multivariate statistics is widely applied to improve in-line process monitoring. Currently, postcombustion CO₂ capture (PCC) technology often involves the use of multiamine based chemical reagents for carbon dioxide removal from flue gas. The CO₂ capture efficiency and overall process performance may be improved by introduction of the chemometrics analytical methods for flexible and reliable process monitoring. In this study, six variables were measured (conductivity, pH, density, speed of sound, refractive index, and near-infrared absorbance spectra). A compact data-collecting chemometric setup was constructed and installed at an industrial pilot plant for real-case testing. This setup was applied to the characterization of CO₂ absorption into aqueous 2-amino-2-methyl-1-propanol (AMP) activated by piperazine (PZ) as the absorption agent. A partial least-squares (PLS) regression model was calibrated and validated based on the measurements conducted in the laboratory environment. The developed approach was applied to predict the concentrations of AMP, PZ, and CO₂ with accuracies of ±2.1%, ± 3.5%, and ±4.3%, respectively. The model was constructed to include the temperature dependency in order to make it insensitive to operational temperature fluctuations during a CO₂ capture process. The setup and model have been tested for almost 850 hours of in-line measurements at a postcombustion CO₂ capture pilot plant. To provide validation of the chemometrics approach, an off-line analysis of the samples has been conducted. The results of the validation technique benchmarking appear to be consistent with values predicted in-line, with average deviations of ±1.8%, ± 1.3%, and ±3.9% for the concentrations of AMP, PZ, and CO₂, respectively

Conceptual Design of a Novel CO₂ Capture Process Based on Precipitating Amino Acid Solvents

Amino acid salt based solvents can be used for CO₂ removal from flue gas in a conventional absorption–thermal desorption process. Recently, new process concepts have been developed based on the precipitation of the amino acid zwitterion species during the absorption of CO₂. In this work, a new concept is introduced which requires the precipitation of the pure amino acid species and the partial recycle of the remaining supernatant to the absorption column. This induces a shift in the pH of the rich solution treated in the stripper column that has substantial energy benefits during CO₂ desorption. To describe and evaluate this concept, this work provides the conceptual design of a new process (DECAB Plus) based on a 4 M aqueous solution of potassium taurate. The design is supported by experimental data such as amino acid speciation, vapor–liquid equilibria of CO₂ on potassium taurate solutions, and solid–liquid partition. The same conceptual design method has been used to evaluate a baseline case based on 5 M MEA. After thorough evaluation of the significant variables, the new DECAB Plus process can lower the specific reboiler energy for solvent regeneration by 35% compared to the MEA baseline. The specific reboiler energy is reduced from 3.7 GJ/tCO₂, which corresponds to the MEA baseline, to 2.4 GJ/tCO₂, which corresponds to the DECAB Plus process described in this work, excluding the low-grade energy required to redissolve the precipitates formed during absorption. Although this low-grade energy will eventually reduce the overall energy savings, the evaluation of DECAB Plus has indicated the potential of this concept for postcombustion CO₂ capture