Solvent Absorption Process Research Articles

Assessment of the Potential of Electrochemical Steps in Direct Air Capture through Techno-Economic Analysis.

Direct air capture (DAC) technologies are proposed to reduce the atmospheric CO2 concentration to mitigate climate change and simultaneously provide carbon as a feedstock independent of fossil resources. The currently high energy demand and cost of DAC technologies are challenging and could limit the significance of DAC processes. The present work estimates the potential energy demand and the levelized cost of capture (LCOC) of liquid solvent absorption and solid adsorption DAC processes in the long term. A consistent framework is applied to compare nonelectrochemical to electrochemical DAC processes and estimate the LCOC depending on the electricity price. We determine the equivalent cell voltage needed for the electrochemical steps to achieve comparable or lower energy demand than nonelectrochemical processes. The capital expenses (CapEx) of the electrochemical steps are estimated using analogies to processes that are similar in function. The results are calculated for a range of initial data of CapEx and energy demand to include uncertainties in the data.

Improving the activity of CO2 capturing from flue gas by membrane gas – solvent absorption process

This work is focused on increasing the capturing efficiency of carbon dioxide (CO2) through flue gas purification systems. To maximize the CO2 capture process, many process variables such as temperature, flow rates, absorbent concentrations, and nanoparticles were investigated. This study describes the use of a polypropylene hollow fiber membrane contactor to separate CO2 from nitrogen using different solvents, including Potassium carbonate (K2CO3), N-methyl diethanolamine (MDEA), and monoethanolamine (MEA). Also, the presence of silica nanoparticles and piperazine (PZ) enhances the process performance. On the other hand, the amine and mixed amino absorbents MDEA-PZ and MDEA-MEA were prepared and compared based on the absorption capacity. The optimal order of amine absorbent performance when applied to CO2 membrane absorption is MDEA-MEA followed by MDEA-PZ. At a solute concentration of 9%, MDEA-MEA exhibits the highest CO2 removal efficiency, which is 74.12%. However, at a concentration of 11%, MEA, MDEA-PZ, and MDEA have the highest CO2 removal efficiencies of 80.15%, 75.13%, and 63.12%, respectively.

Total site modeling and optimization for petrochemical low-carbon retrofits using multiple CO2 emission reduction methods

Aiming at the carbon dioxide (CO2) emissions from energy and material flow streams in petrochemical sites, a bi-objective optimization strategy based on retrofit improvements and total site techniques is constructed, which is referred to as the petrochemical CO2 emission reduction comprehensive (Petro-CERC) model. The fossil fuels for heat, steam and power provision, as well as the fossil-fired power importation are condsidered to shift to biomass fuel and renewable power in utilities and process units. A waste heat up-graded utilization system is introduced and adopted to improve the efficiency of heat energy, and a green combined heat and power system based on renewable and sustainable resources is established to reconstruct the conventional utility system. Carbon capture by the organic amine solvent absorption process is also integrated into the bi-objective optimization strategy. The CO2 emission reduction methods were applied individually to a petrochemical site in South China with an annual emission of 3.2 million tons CO2 for the sensitivity analysis. The proposed Petro-CERC model was then performed for the optimization of the combined application of the CO2 emission reduction methods. From the perspective of both carbon neutrality and economy, the optimal value at the trade-off point of CO2 emission is 464 thousand tons CO2/year, and the cost of achieving an 85% reduction of CO2 emission is $44.9 million. Further, the CO2 emission reduction strategies in different petrochemical sites are coupled with four different regions on a national scale according to the matching degree of the three standards of technical feasibility, economic development status and geographical appearance. Consequently, a multi-scenario application based on the four regions is applied in this case, and the feasibility of the CO2 emission reduction methods to achieve the near carbon neutral goal in these scenarios is evaluated.

Nacre-liked material with tough and post-tunable mechanical properties

• A universal fabrication methodology for post-tunable mechanical properties materials. • Wide tunable range without the need for specific functional groups. • Stable and reversible ‘brick and mortar’ structure. • Superior fracture toughness. Biomaterials, often imparted time-dependent mechanical properties, which are promising in fields ranging from sensors to robotics. Here, a facile method was proposed to fabricate post-tunable mechanical properties composites based on hydrogels and ceramic nanofiller. The wide tunable range of Young's modulus (27.3 kPa to 3.5 GPa) and ultimate stress (173 kPa to 102 MPa) can be achieved by combining solvent absorption and evaporation process with platelets reinforcement effect. Additionally, a large fracture toughness (∼32,000 J m - 2 ) is obtained as a result of the nacre-liked “brick and mortar” structure introduced by shear force during fabrication. The superior flexibility and designability of this material were demonstrated via actuators, portable structure, and metamaterials. Above all, this study provides a new thought to fabricate tough materials with post-tunable mechanical properties.

Analysis of a rich vapor compression method for an ammonia-based CO2 capture process and freshwater production using membrane distillation technology

Post-combustion capturing of CO2 through chemical solvent absorption is a promising technique for reducing the CO2 emissions from fossil fuel power plants. However, the energy penalty associated with the absorbent regeneration continues to be a critical challenge in the chemical solvent absorption process. In this study, the operating parameters of ammonia-based CO2 capture were optimized to reduce the energy penalty. This optimized process was considered a base process to which process modifications were added, with the goal of further reducing the energy consumption. These process modifications included absorber inter-cooling and rich vapor compression (RVC) combined with cold solvent split (CSS) processes. The combined RVC and CSS process was compared with the base process and advanced NH3-based CO2 capture processes, such as the rich split process and the inter-heating process. Compared to the base process, the combined process reduced the energy requirements by 20.2%, which was higher than the 11.6% and 8.26% energy reductions obtained via the rich split and inter-heating processes, respectively. The combined process was also compared with MEA-based process modifications. The energy savings from the combined process were higher than those of the MEA-based process modifications. To estimate the trade-offs between the energy savings resulting from the combined process vs. the capital cost of the additional equipment required, the Aspen Capital Cost Estimator (ACCE) was used. The results showed that the combined process saved $0.707 million per year. Furthermore, a membrane distillation (MD) technology was integrated with the CO2 capture unit to produce freshwater. This additional process produced freshwater at a rate of 719.240 m3/day at a feed stream temperature to the MD unit of 35.66 ℃.

Ammonia-based CO2 capture parameters optimization and analysis of lean and rich vapor compression processes

Carbon dioxide (CO2) capture through chemical solvent absorption process is the most favourable and well-proven technique to reduce CO2 emission. However, in this technique, the energy penalty correlated with absorbent regeneration is a critical challenge. To reduce energy consumption, the operating parameters in NH3-based CO2 capture process were optimized. Then flowsheet modifications including rich vapor compression (RVC) and lean vapor compression (LVC) were proposed for the first time in the NH3-based CO2 capture process. Both the LVC and RVC schemes were combined with cold solvent split (CSS) process to further reduce the energy requirements. Moreover, the LVC and RVC processes of this study were also compared with the advanced NH3-based and MEA-based LVC and RVC processes with respect to energy reduction. The optimized process was considered as a base process and it was compared with the modified processes. The RVC and LVC combined with CSS process reduced the reboiler duty by 26.7% and 19%, respectively. These energy savings are much higher than that of 11.6% and 8.26% energy savings of the advanced NH3-based rich split and inter-heating processes, respectively. The total equivalent energy savings of LVC, RVC, LVC with CSS, and RVC with CSS processes in this study were about 6.4%, 18.1%, 3.4%, and 15%, respectively, which are higher than 3.4% and 8.5% energy savings of MEA-based LVC with CSS and RVC with CSS processes, respectively. Furthermore, these combined processes can also avoid the use of a condenser.

The effect of different process configurations on the performance and cost of potassium taurate solvent absorption

The main method of capture of CO2 in industry is the use of solvents for CO2 absorption in post-combustion capture and the benchmark solvent is monoethanolamine (MEA). However, it presents a few disadvantages such as having a high energy requirement while also being corrosive and toxic. Potassium taurate (K-Tau) is a solvent with the potential to replace MEA because it has similar reaction rates, high cyclic loading, degradation resistant and most importantly, low energy requirement.The objective of this study was to compare and evaluate the effect of different process configurations on the reboiler duty for the precipitating potassium solvent absorption process. Utilising a baseline potassium taurate process, different process configurations were developed in Aspen Plus. These include a cold rich bypass (CRB) of the rich solvent stream to the stripper and a solid-liquid separator. The results show that the modified configurations reduce the reboiler duty of the potassium taurate process by approximately 12% through the reduction in sensible heat and vaporization duty.

Recent Progress on the Performance of Different Rate Promoters in Potassium Carbonate Solvents for CO2 Capture

Over recent years our research group has examined the performance of a range of rate promoters in potassium carbonate solvent for carbon dioxide absorption. Promoters including boric acid, potassium glycinate, potassium prolinate, potassium sarcosinate and a thermally stable carbonic anhydrase enzyme have been studied either with the stopped flow technique, a wetted wall column or in the pilot plant located at The University of Melbourne in Australia. The carbonic anhydrase enzyme was shown to have the best promotion performance. However, improvements are required in further improving thermal stability and recycling options in order for the enzyme to be applied in industrial solvent absorption processes. Amino acid salts including potassium sarcosinate, prolinate and glycinate were proven to have high promotion performance at bench scale. Pilot plant results showed that the promotion performance of boric acid was poor, while potassium glycinate was a good rate promoter with an increase in absorption rate of up to 5–6 times when adding 10 wt. % glycinate into 40–45 wt. % potassium carbonate solvent.

Outcomes from pilot plant trials of precipitating potassium carbonate solvent absorption for CO2 capture from a brown coal fired power station in Australia

A precipitating potassium carbonate (K2CO3) based solvent absorption process has been developed for capturing carbon dioxide (CO2) from industrial sources. Demonstration of this process has been completed using real flue gas in a pilot plant located at Hazelwood power station in Victoria, Australia. The pilot plant was designed to capture up to 1tonne per day of CO2 and was operated over a number of campaigns to test the absorption performance of a liquid solvent (30wt% K2CO3), a precipitating solvent (45wt% K2CO3) and a promoted precipitating solvent (promoter with 45wt% K2CO3). The main aim of this study was to collect operational data from the industry based pilot plant absorber in order to validate thermodynamic experiments and further improve simulation models developed from lab-scale precipitating column trials using synthetic feed gas. The performance of the industry based absorber including CO2 capture rate, pressure drop, solvent loadings and temperature profile, has been measured over a range of operating conditions. The CO2 capture rate improved when operating with a lower gas flow rate, higher solvent temperature and when a rate promoter was added to the solvent. The highly concentrated solvent trials created some difficulties with absorber flooding and intermittent operation due to blockages at start-up but minimal issues were encountered once the system was stabilized. Process simulations have been developed to successfully predict the pilot plant performance over a range of operating conditions. Completion of these pilot plant trials has provided confidence in plant operation and will enable an improved full-scale design and costing of this slurry based solvent process to be completed for commercial scale.

Membrane-Cryogenic Post-Combustion Carbon Capture of Flue Gases from NGCC

Membrane gas separation for carbon capture has traditionally been focused on high pressure applications, such as pre-combustion capture and natural gas sweetening. Recently a membrane-cryogenic combined process has been shown to be cost competitive for post-combustion capture from coal fired power stations. Here, the membrane-cryogenic combined process is investigated for application to post-combustion carbon capture from the flue gas of a Natural Gas Combined Cycle (NGCC) process. This process involves a three-membrane process, where the combustion air is used as the sweep gas on the second membrane stage to recycle CO2 through the turbine. This ensures high CO2 recovery and also increases the CO2 partial pressure in the flue gas. The three-CO2-selective membrane process with liquefaction and O2-enrichment was found to have a cost of capture higher than the corresponding process for coal post-combustion capture. This was attributed to the large size and energy duty of the gas handling equipment, especially the feed blower, because of the high gas throughput in the system caused by significant CO2 recycling. In addition, the economics were uncompetitive compared to a modelled solvent absorption processes for NGCC.

Pilot plant results for a precipitating potassium carbonate solvent absorption process promoted with glycine for enhanced CO2 capture

The absorption performance of a glycine promoted precipitating potassium carbonate (K2CO3) solvent absorption process for carbon dioxide (CO2) capture has been presented using a laboratory scale pilot plant. Glycine has been added as a rate promoter to 40–45wt.% K2CO3 solutions to examine the enhancement of the CO2 absorption process. The laboratory scale pilot plant has been designed to capture 4–10kg/hr of CO2 from an air/CO2 mixture at a feed gas rate of 30–55kg/hr. Performance data of the absorber including pressure drop, holdup and CO2 removal efficiency has been collected from the pilot plant and presented for a range of operating conditions. The addition of glycine was found to improve the CO2 recovery rate by up to 6 times whilst also slightly increasing the pressure drop and holdup measured in the packed absorption column which is likely due to a reduction in the surface tension of the solvent. Additionally, increasing the K2CO3 solvent concentration and operating with a higher CO2 feed gas concentration were found to increase the CO2 recovery results. Finally performance data from the absorber has been used to validate an Aspen Plus simulation of the system.

Analysis of a precipitating solvent absorption process for reducing CO2 emissions from black coal fired power generation

Carbon capture and storage (CCS) is a technology that has the potential to provide deep cuts in CO2 emissions from coal-fired power generation. This paper describes retrofitting the CO2CRC's low cost “UNO MK 3” precipitating potassium carbonate (K2CO3) process to a 335MW (net) black coal-fired subcritical power station, typical of those in Australia.The use of heat integration to reduce the net energy penalty of retrofitting CO2 capture is also studied and the modifications required to the steam cycle for these cases are outlined. Retrofitting the UNO MK 3 process has a smaller energy penalty compared with amine-based processes. Heat integration strategies can reduce this energy penalty by an additional 20%.To further reduce the impact of CO2 capture on the net output of the power station, the option of partial capture of CO2 is also described here. In the partial capture case, the CO2 emissions intensity of the coal-fired power station is equivalent to that of a natural gas combined cycle (NGCC) power station.A detailed cost analysis of various cases of CO2 capture with and without heat integration is also performed. The results suggest that compared to standard amine-based solvent technologies, the UNO MK 3 process can provide up to 50% cost savings in the cost of CO2 avoided. The levelised cost of electricity also reduces by up to 35% using UNO MK 3 compared to commercial amine-based solvent technologies.

CO2 emission reduction from natural gas power stations using a precipitating solvent absorption process

There has been a rapid increase in the use of natural gas for power generation based on gas turbine technology which elevates the importance of carbon dioxide (CO2) capture technology to reduce CO2 emissions from gas turbine based power stations. The low content of CO2 in the gas turbine exhaust results in low rates of CO2 absorption and larger absorption equipment when compared to studies done on coal fired power stations. Furthermore the high oxygen (O2) content in the exhaust gas adversely affects the solvent stability, particularly for the traditional amine based solvents. This paper describes how exhaust gas recirculation (EGR) along with CO2CRC's low cost “UNO MK 3” precipitating potassium carbonate (K2CO3) process can overcome the challenges of CO2 capture from gas turbine power stations. To further bring down the energy requirements of the capture process, heat integration of the UNO MK 3 process with power generation process is carried out. An economic analysis of the various retrofit options is performed.The current study shows that in the case of retrofitting the UNO MK 3 process to a natural gas combined cycle (NGCC), the use of EGR can reduce the energy penalty of CO2 capture by 15%, whilst a reduction of up to 25% can be achieved with the heat integration strategies described.Significantly the study shows that converting an existing open cycle gas turbine (OCGT) to a combined cycle with steam generation along with retrofitting CO2 capture presents a different steam cycle design for the maximum power output from the combined cycle with CO2 capture. Such a conversion actually produces more power and offers an alternative low emission retrofit pathway for gas fired power.Cost analysis shows that inclusion of the UNO MK 3 CO2 capture process with EGR to an existing NGCC is expected to increase the cost of electricity (COE) by 20%. However, retrofit/repowering of an underutilised or peaking OCGT station with the inclusion of CO2 capture can reduce the COE as well as produce low emission power. This is achieved by increasing the load factor and incorporating a purpose built steam generation cycle.

Physical Absorption of CO<sub>2</sub> Capture: A Review

Removal of CO2 had been one of the main issues facing in worldwide. Intensive researches are still going on to effectively reduce CO2 at low cost. Physical absorption is one of the well-established technologies used to removal CO2 from other gases. The physical absorption process is simple; whereby it contains only one gas liquid contactor and a series of flash tank to regenerate solvent. The CO2 will be absorbed in the physical solvent in the high pressure gas liquid contactor and flashed out in the medium and low pressure flash tank. The advantage of using physical solvent is that the CO2 is absorbed without any chemical reaction involved, thus it can be flashed out easily by reducing the pressure, passing inert gas through the solvent and mild thermal regeneration. The physical absorption is the best operated at high pressure and low temperature as the solubility of CO2 in the solvent is high at the particular condition. Researches carried out currently are focusing on solvent development, absorption and desorption process development and mathematical modeling.

An assessment of different solvent-based capture technologies within an IGCC–CCS power plant

This study evaluates three different solvent absorption processes for the pre-combustion capture of CO2 for a black coal IGCC (Integrated Gasification Combined Cycle) power-plant, with the aim of determining the best solvent process for pre-combustion capture. The three solvent processes are MDEA (mono diethanolamine), hot potassium carbonate and Selexol™. The study involves detailed thermodynamic models of the entrained flow gasifier, synthesis gas processes, CO2 capture process and the gas turbine and steam turbine combined cycle plant.IGCC without capture yielded an efficiency of 45.02%. For the CO2 capture processes at 90% CO2 capture, the power generation efficiencies are almost identical for MDEA and Selexol™ with 36.39% and 36.42%, respectively. The IGCC with the hot potassium carbonate process yielded the highest efficiency with 37.33%. This improvement is attributed to the higher operating temperature of the absorber which allows water vapor in the synthesis gas to be sent to the gas turbine resulting in a greater power production from the gas turbine.A multi-objective optimization is performed by varying different decision variables in the IGCC with the hot potassium carbonate capture process. By optimizing these variables, an efficiency of 39.31% is obtained – a 2% point improvement for 90% capture.

Demonstration of a Concentrated Potassium Carbonate Process for CO2 Capture

A precipitating potassium carbonate (K2CO3)-based solvent absorption process has been developed by the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) for capturing carbon dioxide (CO2) from industrial sources, such as power plant flue gases. Demonstration of this process is underway using both a laboratory-based pilot plant located at The University of Melbourne and an industrial pilot plant located at the Hazelwood Power Station in Victoria, Australia. The laboratory-scale pilot plant has been designed to capture 4–10 kg/h CO2 from an air/CO2 feed gas rate of 30–55 kg/h. The power-station-based pilot plant has been designed to capture up to 1 tonne/day CO2 from the flue gas of a brown-coal-fired power station. In this paper, results from trials using concentrated potassium carbonate (20–40 wt %) solvent are presented for both pilot plants. Performance data (including pressure drop, holdup, solvent loadings, temperature profile, and CO2 removal efficiency) have been collected from ea...

Simulations of Membrane Gas Separation: Chemical Solvent Absorption Hybrid Plants for Pre- and Post-Combustion Carbon Capture

Solvent absorption and membrane gas separation are two carbon capture technologies that show great potential for reducing emissions from stationary sources such as power plants. Here, plants combining chemical solvent absorption and membrane gas separation are considered for post-combustion capture as well as pre-combustion capture. In all ASPEN HYSYS simulations the membrane stage initially concentrates CO2 into either the permeate or the retentate stream, which is then passed to a monoethanolamine (MEA) based solvent absorption process. In particular, post-combustion capture scenarios examined a membrane that is selective for CO2 against N2, while for the pre-combustion scenario a H2-selective membrane was studied. It was found the energy demand of the combined hybrid plant was always more than that of a stand alone MEA solvent process. This was mainly due to the need to generate a pressure driving force upstream of the membrane in the post-combustion scenario or to recompress downstream gas streams in the pre-combustion scenarios. For both scenarios concentrating the CO2 in the feed to the solvent system reduced the absorber column height and diameter, which could represent a CAPEX saving for the hybrid plant, dependent upon the membrane price. The use of a hydrogen selective membrane downstream of an oxygen fired gasifier was identified as the most prospective scenario, as it led to significant reductions in absorber size, for a relatively small membrane area and energy penalty.

Techno-economic Evaluation Methodology and Preliminary Comparison of an Amine-based and Advanced Solid Sorbent-based CO2 Capture Process for NGCC Power Plants

The post combustion capture process using the traditional amine based solvent absorption process is a very mature technology that suffers from a high energy penalty being taken on the power plant and requires significant capital investment that causes us a high increase in the cost of electricity. An advanced solid-based adsorption is discussed in this work as well as a techno-economic evaluation methodology in order to compare the advantages of this novel process to the conventional process. Some indications of the expected technical and economic benefits of the process are also discussed.

Post-combustion Capture of CO2: Results from the Solvent Absorption Capture Plant at Hazelwood Power Station Using Potassium Carbonate Solvent

Post-combustion capture of CO2 from flue gas generated in a 1600 MW brown-coal-fired power station has been demonstrated using a solvent absorption process. The plant, located at International Power’s Hazelwood power station in Victoria’s Latrobe Valley, was designed to capture up to 25 tons/day of CO2 (expandable to 50 tons/day of CO2). The design of the capture plant was based on a proprietary solvent (BASF PuraTreat F). The main focus of this work, however, is to describe the performance of the plant using an unpromoted 30 wt % potassium carbonate (K2CO3) solution. The CO2-capture plant was successfully operated using both BASF PuratTreat F and K2CO3, during which performance data were collected and analyzed. Although the plant only absorbed 20–25% of CO2 from the flue gas when using the potassium carbonate solvent, valuable operating data were collected, which enabled process simulations to be compared to real plant data. Aspen Plus software was used to predict the performance of the plant while operating with potassium carbonate. In general, the model shows a slight difference (within ±5%) compared to the pilot-plant results. This benchmarked model is an important part of the ongoing development of novel precipitating potassium carbonate processes for large-scale post-combustion CO2 capture.

Advanced hydrogen and CO2 capture technology for sour syngas

Abstract A key challenge for future clean power or hydrogen projects via gasification is the need to reduce the overall cost while achieving significant levels of CO 2 capture. The current state of the art technology for capturing CO 2 from sour syngas uses a physical solvent absorption process (acid gas removal–AGR) such as Selexol™ or Rectisol ® to selectively separate H 2 S and CO 2 from the H 2 . These two processes are expensive and require significant utility consumption during operation, which only escalates with increasing levels of CO 2 capture. Importantly, Air Products has developed an alternative option that can achieve a higher level of CO 2 capture than the conventional technologies at significantly lower capital and operating costs. Overall, the system is expected to reduce the cost of CO 2 capture by over 25%. Air Products developed this novel technology by leveraging years of experience in the design and operation of H 2 pressure swing adsorption (PSA) systems in its numerous steam methane reformers. Commercial PSAs typically operate on clean syngas and thus need an upstream AGR unit to operate in a gasification process. Air Products recognized that a H 2 PSA technology adapted to handle sour feedgas (Sour PSA) would enable a new and enhanced improvement to a gasification system. The complete Air Products CO 2 Capture technology (CCT) for sour syngas consists of a Sour PSA unit followed by a low-BTU sour oxycombustion unit and finally a CO 2 purification / compression system.