Chemical Absorption System Research Articles

Exergy and economic analysis of the trade-off for design of post-combustion CO2 capture plant by chemical absorption with MEA

CO2 abatement strategies are crucial in any industrial cluster. In post-combustion capture solutions, the high-energy consumption and the cost associated with the operation are the main drawbacks. In this work, a chemical absorption system using a 30% MEA solution was modeled to process 3,240 t/h of flue gases with 12% CO2 content, and evaluated for design insights and their potential cost reduction and fewer energy losses, thus providing a screening tool for design and scale-up. Thermodynamic analysis showed that regulating the inlet temperature of the stripper column was pivotal in decreasing exergy destruction and heat consumption. A trade-off analysis allowed tracing their influence on system metrics, with absorber parameters being critical. Nevertheless, minimizing the Levelized Cost of CO2 Capture proved to be a more suitable metric for decision-making compared to either heat consumption or exergy efficiency. Solutions were ranked based on TOPSIS tool, which confirmed the most relevant design parameters. The potential operational expense savings (20 USD/t CO2), and thermodynamic improvement (52%), were achieved. Although capture cost values are within the expected industrial range for mature capture technologies (70 USD/t CO2), these are still far away from current taxes and levers for curbing emissions.

Waste heat recovery and cascade utilization of CO2 chemical absorption system based on organic amine method in heating season

In this paper, we proposed a waste heat recovery route of CO2 chemical absorption systems, which can realize waste heat recovery and cascade utilization in heating season. Simulation methods were used to study carbon capture systems and absorption heat pump, experimental methods were used to study the contact heat transfer characteristics of packed tower, and three organic amine solutions were involved: MEA (2-Aminoethanol), MEA& MDEA (N-Methyldiethanolamine) and AMP (2-Amino-2-methyl-1-propanol). The outlet gas temperature of carbon capture system is 47.7 °C∼58.8 °C, the temperature of lean solution is 73.3 °C∼95.0 °C, the absorption heat pump can increase the return water from 40 °C to 85 °C∼97 °C, the heat transfer end difference between flue gas and water in packed tower can be less than 1.0 °C. The system can achieve energy conservation and CO2 emission reduction effect, over 80% of the solution waste heat were recovered, the two-stage gas waste heat recovery process can improve boiler efficiency by over 19%.

Bubble dynamics and mass transfer enhancement in split–and–recombine (SAR) microreactor with rapid chemical reaction

In this study, a split–and–recombine (SAR) microreactor which is composed of convergent–divergent arc channel and rectangular obstacles was designed, and its enhancement characteristics in gas–liquid rapid chemical absorption system were explored. In the SAR microreactor, the deformation, splitting, stretching and breakup of bubbles are monitored by a high–speed camera. Accordingly, the bubble velocity pulsation caused by SAR structure is analyzed. The squeezing mechanism for bubble breakup located on the front surface of the obstacle is revealed. Two breakup patterns, namely complete and partial breakup, are observed, and the mass transfer performance is highly related to them. The mass transfer enhancement factor (Eka) of SAR structure increases with gas/liquid flow rate in complete breakup pattern while decreases in partial breakup pattern. The increase of gas–liquid flow rates and the number of SAR units, or slower reaction rate strengthens the velocity fluctuation and bubble breakup, resulting in an increase in Eka, with a maximum value of 2.74. Overall, the SAR microreactor performs comparable to Corning Advanced Flow Reactor in term of mass transfer energy efficiency. This work guides the application of SAR microreactor in rapid gas–liquid chemical reaction system.

Mass transfer intensification mechanism of Al2O3 sphere packing in a rotating packed bed

In this work, the gas–liquid mass transfer performance of rotating packed bed (RPB) with Al2O3 sphere packing, in term of volumetric liquid-side mass transfer coefficient (kLae), was investigated by CO2-NaOH chemical absorption system. The adsorption performance of Al2O3 spheres was also evaluated by an ink adsorption method. Results showed that the kLae values of RPB with Al2O3 sphere packing were higher than those of RPB with nonporous sphere packing, and over one magnitude order higher than those of trickle bed reactor (TBR) with Al2O3 sphere packing. The ink adsorption, film diffusion and pore diffusion rates of Al2O3 spheres have been greatly improved under the high gravity field, and it has been found that the surface tension was the main driving force of ink adsorption. Moreover, the adsorption kinetics was investigated and the experimental data fitted well with the pseudo-first-order adsorption kinetics model.

A machine learning model for predicting the mass transfer performance of rotating packed beds based on a least squares support vector machine approach

Rotating packed beds (RPBs) have been widely noted due to its superior gas-liquid mass transfer performance compared to conventional packed bed for CO2 absorption. The overall volumetric gas-side mass transfer coefficient (KGa) is selected as one of the key parameters for the screening and evaluation of RPBs. Existing theoretical and semi-empirical models for the KGa are easy to be used but have a poor accuracy and generalization ability. In this paper, a machine learning model based on least squares support vector machine (LSSVM) is developed to predict the KGa more accurately for CO2-NaOH chemical absorption system in different types of RPBs. Unlike the conventional prediction models, the input parameters are selected by multiple correlation analysis in the model establishment. Then, the proposed model is comprehensively evaluated by using four evaluation indicators, including determination coefficient, mean relative error, Root mean square error and standard deviations. The results show that the proposed model has the prediction performance with R2 = 0.9808 and RMSE = 0.0055 for testing set. In addition, the model performance is compared with the multiple nonlinear regression and artificial neutral networks. The results show that the proposed model has a superior performance for predicting the KGa of CO2 absorption in RPBs.

Techno-economic assessment of calcium and magnesium-based sorbents for post-combustion CO2 capture applied in fossil-fueled power plants

This work evaluates the most relevant techno-economic performances of calcium and magnesium-based sorbents used in high temperature solid looping cycles for post-combustion CO2 capture applied in fossil power generation. The evaluated power plants generate 1000 MW net electricity with 90% CO2 capture rate. As fuels, natural gas was assessed for combined cycle power plants since coal and lignite were assessed for super-critical power plants. As comparison benchmark systems, the correspondent plants with non-capture feature and with carbon capture using reactive gas–liquid absorption were also assessed. As the results show, both calcium and magnesium carbonate looping concepts applied in solid fossil fuel super-critical plants induce lower carbon capture energy penalty compared to the reactive gas–liquid absorption by about 1–2.2 net efficiency percentage points. The Calcium Looping (CaL) cycle shows higher net power efficiency than the Magnesium Looping (MgL) cycle by about 1–1.4 net percentage points. In case of natural gas combined cycle plants, the chemical absorption system has higher net power efficiency than CaL and MgL systems by about 4–6 percentage points. The key economic indicators (e.g., electricity production cost, CO2 capture costs etc.) show that both evaluated carbonate looping systems perform better than amine-based chemical scrubbing.

CO2 Absorption Performance and Electrical Properties of 2-Amino-2-methyl-1-propanol Compared to Monoethanolamine Solutions as Primary Amine-Based Absorbents

Two CO2 chemical absorption systems using 2-amino-2-methyl-1-propanol (AMP) and monoethanolamine (MEA) aqueous solutions are qualitatively compared in terms of absorption performance and electrical...

Catalytic syngas production from carbon dioxide of two emission source scenarios: techno-economic assessment

We designed process alternatives for syngas production from carbon dioxide (CO2) based on two emission source scenarios: flue gas (FG) in power plants vs. blast furnace gas (BFG) in ironmaking and steelmaking plants. In the both scenarios CO2 is separated through a monoethanolamine-based chemical absorption system and then converted to carbon monoxide (CO) by reverse water gas shift reaction using Cu/ZnO/Al2O3 catalyst, thereby resulting in a syngas stream (H2:CO molar ratio=2:1). To reduce energy requirements of the process, we designed a heat exchanger network for meeting minimum energy consumption by maximizing heat recovery from the process streams. Our economic evaluation results show that the integrated strategy results minimum selling price of $19.31 per GJ (FG scenario) and $16.02 per GJ (BFG scenario).

Comparative assessment of advanced power generation and carbon sequestration plants on offshore petroleum platforms

On conventional offshore petroleum platforms, the combined heat and power production (CHP) currently depends on simple cycle gas turbine systems (SCGT) that operate at lower efficiency and increased environmental impact compared to modern onshore thermoelectric plants. Additionally, the reduced space and the limited weight budget on offshore platforms have discouraged operators from integrating more efficient, but also bulkier cogeneration cycles (e.g. combined cycles). In spite of these circumstances, more stringent environmental regulations of offshore oil and gas activities have progressively led to a renewed interest in the integration of advanced cogeneration systems, together with either customary or unconventional carbon capture approaches, to maintain both higher power generation efficiencies and reduced CO2 emissions. Thus, in this paper, it is evidenced how advanced gas turbine concepts are promising technologies for maintaining or even increasing efficiency, while facilitating the capture rate of CO2 produced, either for geological storage or enhanced oil recovery. Despite the profuse research works on onshore applications, advanced cogeneration and carbon capture systems have been barely studied in the context of supplying power to offshore petroleum platforms. Accordingly, the performance of a conventional offshore petroleum production platform (without carbon capture system) is compared to other configurations, based on either an amine-based chemical absorption system or oxyfuel combustion concepts ( S-Graz and Allam cycles) for CO2 capture purposes. Since the original power and heat requirements of the processing platform must remain satisfied, an energy integration analysis is performed to determine the waste heat recovery opportunities. Additionally, the exergy method helps quantifying the most critical components that lead to the largest irreversibility and identifying the thermodynamic potential for enhanced cogeneration plants. As a result, oxyfuel equipped platforms provide a diversified set of advantages, while keeping competitive efficiencies. For instance, advanced systems allow for cutting down ostensibly the atmospheric CO2 emissions compared to the conventional and amine-based power plant configurations of the FPSO.

Combined exergy analysis, energy integration and optimization of syngas and ammonia production plants: A cogeneration and syngas purification perspective

Abstract Modern ammonia production plants are equipped with efficient energy integration networks able to recover an important fraction of the waste heat exergy available throughout the chemical system. However, in order to drive the endothermic reforming reactions at high temperature, as well as the syngas purification and compression processes, additional energy must be supplied by costly non-renewable resources. Moreover, the choice of the carbon capture unit, based on either physical or chemical absorption systems, drastically affects the way in which the waste heat recovery must be performed, and whether one or more energy technologies should or not be integrated (e.g. heat pump). Meanwhile, the selection among various energy resources, e.g. the import of electricity over the autonomous combined heat and power production (CHP), strongly depends on the ratio between the prices of electricity and fuels consumed, as well as on the extent of the energy integration. Accordingly, a simple trial and error approach falls short in efficiently determining the most suitable operating conditions that enable the production plant to run under the minimum operating cost. Thus, by using a systematic methodology, the most suitable utility systems (cooling, refrigeration, and cogeneration) that satisfy the minimum energy requirement (MER) with the lowest energy consumption and operating cost, are selected. Consequently, the conventional plant efficiency is increased about 10% by using a mixed operating mode or autonomous operating mode with combined cycle. Furthermore, reduced cooling (23%) and heating (51%) requirements are expected when physical solvents are used. The lowest exergy consumption corresponds to mixed operating mode by using a physical absorption unit (27.76 GJ/tNH3). Finally, it is found that exergy efficiency drops 24% when the irreversibility in the upstream steps of feedstock obtainment are considered.

Effect of Solvent Concentration on the Energy Demand of an Absorption-Based Natural Gas Sweetening Plant

The removal of CO2 from natural gas will enhance its energy content, decrease the volume to be transported and –if coupled with storage technology- it will also contribute to the control of CO2 emissions. Amine-based chemical absorption is the most advanced CO2 capture system. Yet, high energy requirement is a major hinder to its wide deployment. Among the possible routes of improvement is the use of novel amines that can achieve the trade-off between robustness and low regeneration energy. In this paper, we have studied the use of MDEA/DEA as solvent for the capture of CO2 from natural gas. The presence of BTEX (Benzene, Toluene, Ethyl Benzene and Xylene) in the raw natural gas was taken into account. AspenHysys v9 was used to simulate the chemical absorption system. The impact of solvent composition on key process variables, the required flow rate to achieve transport specification, required reboiler duty, pumping energy, BTEX incineration energy and amine losses, were studied. The optimal operating point corresponding to the lowest energy requirement was identified and the separate contribution of each process parameter was estimated. The study showed that the optimal amine mass fraction is influenced by the presence of BTEX and that it shifts from 0.5 if BTEX are not present in the sour feed gas to 0.45 if their incineration is taken into account.

New reliable tools to mathematically model chemical reaction systems

There are a variety of chemical reactions and absorption equipment in chemical production plants across the world. Appropriate modelling of chemical reactors and reactive absorption systems is important for simulation, optimization, and scale-up purposes in the process/chemical engineering discipline. In this study, a chemical reactor and a reactive absorption system are modelled through different mathematical methods. The first case includes two unsteady state first-order reactions in series, and the latter system incorporates a first-order reaction and a diffusive mass transfer phenomenon. The concentration distribution for these two different cases is attained using Homotopy Perturbation Method (HPM) and Enhanced Homotopy Perturbation Method (EHPM) as an efficient, straightforward, and precise technique to solve differential equations. The primary approximation is generally selected with some unknown constant parameters, which can be obtained through applying the initial and boundary conditions. The solution is eventually attained in the form of power series. The modelling results obtained from HPM and EHPM are compared to the outputs attained from the available analytical solutions. The comparison implies that EHPM has a higher capability to provide proper solutions for the governing equations of both reaction cases in this study with a reasonable accuracy. EHPM appears suitable in several cases to obtain approximate analytical solutions where the governing transport phenomena equations in various chemical engineering processes lead to complicated differential equations. This research work introduces a systematic and efficient modelling procedure to properly capture important aspects such as reaction progress, concentration distribution, and phase change in complex transport phenomena systems.

Post‐combustion CO2 capture with chemical absorption and hybrid system: current status and challenges

AbstractPost‐combustion CO2 capture from the power and industrial sectors has gained widespread attention due to its ability to retrofit easily with newly installed and existing plants. This state‐of‐the‐art, updated review provides an overview of technical issues in post‐combustion CO2 capture related to process performance, energy requirements for CO2 capture, and inconsistencies in the prediction of CO2 capture cost. Recent updates are presented regarding chemical absorption‐desorption systems, and particularly CO2 absorption and solubility enhancement studies, absorber operation at elevated pressure, recent developments in absorber configuration, and methods for reducing the heat duty of strippers. Furthermore, recently developed post‐combustion hybrid techniques such as the membrane‐absorbent hybrid process, the membrane‐cryogenic hybrid process, the membrane‐adsorption hybrid process, the absorption‐electrolysis hybrid process, and the solar thermal electrochemical process (STEP) are discussed. Finally, we suggest areas for improvement and indicate that there are significant future prospects for post‐combustion CO2 capture. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

Membrane contactors for process intensification of gas absorption into physical solvents: Impact of dean vortices

Membrane contactors are considered as one of the most promising intensification technologies for gas-liquid absorption processes. For chemical absorption systems, such as flue gas CO2 absorption in amine solutions, the mass transfer resistance is significantly located in the membrane due to the accelerating effect exerted by the reaction in the liquid. For physical absorption systems however, such as CO2 absorption in water for biogas purification, most of the resistance is located within the liquid phase. Process intensification requires an increase of the gas-liquid interfacial area (provided by the membrane) together with increased mass transfer performances in the rate limiting phase, namely the liquid. In the liquid phase, a boundary layer is formed, in which the solute concentration is higher than at the bulk, thus decreasing the driving force for the transfer. This study investigates the use of Dean vortices as a tool to increase mass transfer performance in membrane contactors. These vortices, generated by a helical hollow fiber, are applied to CO2 absorption in water using dense polymeric membranes. A straight hollow fiber with water flowing in the lumen is compared to different helical shaped hollow fibers. Firstly, Dean vortices, calculated by a CFD approach, are successfully compared to the velocity maps experimentally obtained by MRI, a non-invasive spectroscopy. Hydrodynamic simulations are thus validated, offering parametric studies and design optimization perspectives. The experimental results for the mass transfer performances of a hollow fiber under different liquid velocity conditions are further compared to simulations. A parametric study, combining CFD and mass transfer simulations, shows that Dean vortices enable an increase of the mass transfer coefficient by a factor of 3, with a moderate increment in pressure drop or energy expenditure, when compared to the straight fiber. Lastly, the best helical geometry, with maximal CO2 mass transfer at the expense of minimal energy requirement is investigated. For a given application, it is shown that a large process intensification effect is attainable; with the same energy requirement, a 2-fold decrease in the surface area is achieved. The potential of the concept for practical hollow fiber modules design and applications are finally discussed.

Polytetrafluoroethylene Wire Mesh Packing in a Rotating Packed Bed: Mass-Transfer Studies

Polytetrafluoroethylene (PTFE) material, which is well-known for its excellent anticorrosion properties, was used as wire mesh packing in a rotating packed bed (RPB). The effective interfacial area (ae) and the volumetric liquid-side mass-transfer coefficient (kLae) of the RPB with PTFE packing was studied experimentally by a NaOH–CO2 chemical absorption system and an oxygen–water physical desorption system, respectively. Experimental results showed that both ae and kLae increased with decreasing fiber diameter and pore size. As for material, mass-transfer performance of the PTFE packing was lower than that of the stainless steel wire mesh packing but is applicable in some high-corrosion and -viscosity environments. Moreover, correlations for ae and kLae were proposed.

Reactive absorption in packed bed columns in the presence of magnetic nanoparticles and magnetic field: Modeling and simulation

Abstract In this article, the influences of ferrofluid and magnetic field on the reactive absorption in packed-bed contactors have been investigated. Because of importance of carbon dioxide emission as a global concern, absorption of carbon dioxide was chosen to investigate these effects. In this regard, multitube approach was applied to model the contactor. The simulation results were validated against experimental data reported in the literature in the absence of nanoparticles and magnetic field and good agreement was obtained. Moreover, influences of various operating conditions on the contactor performance were investigated. It was found that for 3.4 vol.% of magnetic nanoparticles (MNPs), the local mass-transfer coefficient for the gas phase at the top of the absorption column increases about six times relative to that obtained in the absence of magnetic field and MNP and an increase of 117% in the average Sherwood number value for the gas phase was obtained. Furthermore, it was found that using MNPs and applying a magnetic field simultaneously enhance the performance of industrial chemical absorption systems.

Gas‐phase mass transfer characteristics in a counter airflow shear rotating packed bed

The gas‐phase mass transfer characteristics in a counter airflow shear rotating packed bed (CAS‐RPB) were studied. The gas volumetric mass transfer coefficient (kyae) was characterized with the physical absorption system NH3‐H2O and the effective interfacial area (ae) was determined by the chemical absorption system CO2‐NaOH, and then the gas‐phase mass transfer coefficient (ky) was obtained. The gas‐phase mass transfer characteristics in the CAS‐RPB were compared with those in the rotating packed bed with split packing (SP‐RPB) under the same operating conditions. The experimental results indicated that the kyae, ae, and ky for counter‐rotation of adjacent packing rings in the CAS‐RPB and SP‐RPB were larger than those for co‐rotation, and the kyae, ae, and ky for counter/co‐rotation in the CAS‐RPB were respectively greater compared with those for counter/co‐rotation in the SP‐RPB. This confirmed that the CAS‐RPB can further intensify the gas‐phase mass transfer process compared to the SP‐RPB. Moreover, the correlative expressions for the kyae, ae, and ky in the CAS‐RPB and SP‐RPB were obtained and were in close agreement with the experimental results.

Mass transfer intensification in a rotating packed bed with surface-modified nickel foam packing

This work examined the liquid-side controlled mass transfer process in a rotating packed bed (RPB) equipped with a surface-modified nickel foam packing (SNP), which is a hydrophobic structured packing. The chemical absorption system CO2–NaOH was used to determine the effective interfacial area (a) and the liquid-side mass transfer coefficient (kL). The volumetric liquid-side mass transfer coefficient (kLa) was thus calculated. Effects of rotational speed, liquid flow rate, and gas flow rate on these mass transfer parameters were investigated. Experimental results show that the RPB with SNP possessed a higher a and kL and thus showed better mass transfer performance in comparison to the RPB with the non-modified nickel foam packing (NNP). Moreover, the possible mechanism for the enhancement of mass transfer in the RPB with SNP was also explored by a flow visualization method.

Energy-saving pathway exploration of CCS integrated with solar energy: Literature research and comparative analysis

One of main technical barriers to a large-scale application of carbon capture and storage (CCS) technology is a significant amount of required energy, e.g., regeneration heat of solvent in the chemical absorption system. Thus, energy consumption and corresponding high operation cost become two primary challenges for the promotion of CCS technology. Meanwhile, energy from the solar source in various forms has already been successfully used as an effective alternative supply in the industrial section for drying, heating and even cooling. Thus, integrating solar energy utilization into the CCS process could be a reasonable option for a sustainable development.A comparative analysis of CCS integrated with solar energy was presented in this paper based on the existing researches. The current status on typical configuration structure, feature and energy-efficiency performance of integrating options is reviewed for post-combustion, pre-combustion and oxygen-combustion systems. Based on these typical CO2 capture systems, a theoretical analysis is conducted for an energy-efficient comparison. Then four typical structures of the post-combustion system, which are highlighted in the review, are chosen as comparative objects for energy-saving and techno-economic evaluation. The results show that systems with a solar-assisted thermal energy and power generation have comparative advantages in term of carbon emission intensity, but the economic cost is increased under the current conditions of the equipment price. Compared to that of baseline case, carbon emission intensity of the case integrated with solar Organic Rankine Cycle can be reduced with a maximum decline of 9.73%, meanwhile the levelized costs of electricity increases 0.01USD/kWh correspondingly.

Analysis of hybrid membrane and chemical absorption systems for CO2 capture

Amine-based absorption of CO2 is currently the industry standard technology for capturing CO2 emitted from power plants, refineries and other large chemical plants. However, more recently there have been a number of competing technologies under consideration, including the use of membranes for CO2 separation and purification. We constructed and analyzed two different hybrid configurations combining and connecting chemical absorption with membrane separation. For a particular flue gas which is currently treated with amine-based chemical absorption at a pilot plant we considered and tested how membranes could be integrated to improve the performance of the CO2 capture. In particular we looked at the CO2 removal efficiency and the energy requirements. Sensitivity analysis was performed varying the size of the membranes and the solvent flow rate.