Recent developments in aqueous ammonia-based post-combustion CO2 capture technologies

Aqueous ammonia(NH3) is a promising alternative solvent for the capture of industrial CO_2 emissions, given its high chemical stability and CO_2 removal capacity, and low material costs and regeneration energy. NH3 also has potential for capturing multiple flue gas components, including NOx, SOxand CO_2, and producing value-added chemicals. However, its high volatility and low reactivity towards CO_2 limit its economic viability. Considerable efforts have been made to advance aqueous NH3-based post-combustion capture technologies in the last few years: in particular, General Electric's chilled NH3 process, CSIRO's mild-temperature aqueous NH3 process and SRI International's mixed-salts(NH3 and potassium carbonate) technology. Here, we review these research activities and other developments in the field, and outline future research needed to further improve aqueous NH3-based CO_2 capture technologies.

Influence of Operating Parameters on NO_(x)and SO_(2)Emissions in Circulating Fluidized Bed with Post-Combustion

Post-combustion technology of circulating fluidized bed can largely reduce the emission of nitrogen oxides(NOx)in the process of combustion and succeed in meeting the ultra-low NO_(x)standard for some fuels like Shenmu coal.Exploring the potential of synergistic control of the emissions of NO_(x)and sulphur dioxide(SO_(2))under post-combustion technology has become a direction that needs further study.The experiments were conducted on a 0.1 MW(thermal)circulating fluidized bed(CFB)test platform,composed of a CFB main combustor and post-combustion chamber(PCC).The paper focuses on the effects of air distribution ratio and temperature in CFB and limestone addition on NO_(x)and SO_(2)emissions.The experimental results showed that compared with traditional CFB combustion,post-combustion technology can reduce NO_(x)emission largely,but lead to a slight increase in SO_(2)emission.The higher SO_(2)emissions at post-combustion can lead to less NO_(x)emission.With the decrease inλ_(CFB),NO_(x)emission first decreased and then increased;by contrast,SO_(2)emission withλ_(CFB)first increased and then decreased.Under post-combustion,whenλ_(CFB)was 0.9,NO_(x)emission was the minimum,while the SO_(2)emission was the largest.Combustion temperature and limestone addition has less adverse effects on NO_(x)emission under post-combustion,compared with traditional CFB combustion.Limestone injection into the furnace is applicable under post-combustion,and the sulfur removal efficiency under post-combustion is very high,almost equivalent to that under traditional combustion.

Review of post-combustion carbon dioxide capture technologies using activated carbon

Carbon dioxide(CO2) is the largest anthropogenic greenhouse gas(GHG) on the planet contributing to the global warming. Currently, there are three capture technologies of trapping CO2 from the flue gas and they are pre-combustion, post-combustion and oxy-fuel combustion. Among these, the post-combustion is widely popular as it can be retrofitted for a short to medium term without encountering any significant technology risks or changes.Activated carbon is widely used as a universal separation medium with series of advantages compared to the first generation capture processes based on amine-based scrubbing which are inherently energy intensive. The goal of this review is to elucidate the three CO2 capture technologies with a focus on the use of activated carbon(AC) as an adsorbent for post-combustion anthropogenic CO2 flue gas capture prior to emission to atmosphere. Furthermore, this coherent review summarizes the recent ongoing research on the preparation of activated carbon from various sources to provide a profound understanding on the current progress to highlight the challenges of the CO2 mitigation efforts along with the mathematical modeling of CO2 capture. AC is widely seen as a universal adsorbent due to its unique properties such as high surface area and porous texture. Other applications of AC in the removal of contaminants from flue gas, heavy metal and organic compounds, as a catalyst and catalyst support and in the electronics and electroplating industry are also discussed in this study.

Integrated adsorption and absorption process for post-combustion CO_(2) capture

This study explored the feasibility of integrating an adsorption and solvent scrubbing process for postcombustion CO_(2) capture from a coal-fired power plant.This integrated process has two stages:the first is a vacuum swing adsorption(VSA)process using activated carbon as the adsorbent,and the second stage is a solvent scrubber/stripper system using monoethanolamine (30 wt-%) as the solvent.The results showed that the adsorption process could enrich CO_(2) in the flue gas from 12 to 50 mol-% with a CO_(2) recovery of >90%,and the concentrated CO_(2) stream fed to the solvent scrubber had a significantly lower volumetric flowrate.The increased CO_(2) concentration and reduced feed flow to the absorption section resulted in significant reduction in the diameter of the solvent absorber,bringing the size of the absorber from uneconomically large to readily achievable domain.In addition,the VSA process could also remove most of the oxygen initially existed in the feed gas,alleviating the downstream corrosion and degradation problems in the absorption section.The findings in this work will reduce the technical risks associated with the state-of-the art solvent absorption technology for CO_(2) capture and thus accelerate the deployment of such technologies to reduce carbon emissions.

Dynamic modelling and simulation of a post-combustion CO_(2) capture process for coal-fired power plants

Solvent-based post-combustion capture technologies have great potential for CO_(2)mitigation in traditional coal-fired power plants.Modelling and simulation provide a low-cost opportunity to evaluate performances and guide flexible operation.Composed by a series of partial differential equations,first-principle post-combustion capture models are computationally expensive,which limits their use in real time process simulation and control.In this study,we propose a first-principle approach to develop the basic structure of a reduced-order model and then the dominant factor is used to fit properties and simplify the chemical and physical process,based on which a universal and hybrid post-combustion capture model is established.Model output at steady state and trend at dynamic state are validated using experimental data obtained from the literature.Then,impacts of liquidto-gas ratio,reboiler power,desorber pressure,tower height and their combination on the absorption and desorption effects are analyzed.Results indicate that tower height should be designed in conjunction with the flue gas flow,and the gas-liquid ratio can be optimized to reduce the reboiler power under a certain capture target.

Advancement and new perspectives of using formulated reactive amine blends for post-combustion carbon dioxide (CO_(2)) capture technologies

Chemical absorption using amine-based solvents have proven to be the most studied,as well as the most reliable and efficient technology for capturing carbon dioxide(CO_(2))from exhaust gas streams and synthesis gas in all combustion and industrial processes.The application of single amine-based solvents especially the very reactive monoethanolamine(MEA)is associated with a parasitic energy demand for solvent regeneration.Since regeneration energy accounts for up to threeequarters of the plant operating cost,efforts in its reduction have prompted the idea of using blended amine solvents.This review paper highlights the success achieved in blending amine solvents and the recent and future technologies aimed at increasing the overall volumetric mass transfer coefficient,absorption rate,cyclic capacity and greatly minimizing both degradation and the energy for solvent regeneration.The importance of amine biodegradability(BOD)and low ecotoxicity as well as low amine volatility is also highlighted.Costs and energy penalty indices that influences the capital and operating costs of CO_(2) capture process was also highlighted.A new experimental method for simultaneously estimating amine cost,degradation rate,regeneration energy and reclaiming energy is also proposed in this review paper.

Post-combustion slipstream CO_(2)-capture test facility at Jiangyou Power Plant, Sichuan, China: performance of a membrane separation module under dynamic power-plant operations

Membrane-based separation technologies have the potential to lower the cost of post-combustion CO_(2) capture from power-plant flue gases through reduced energy and capital costs relative to conventional solvent approaches.Studies have shown promise under controlled conditions,but there is a need for data on performance and reliability under field conditions.Coal-fired power plants in China operate in a dynamic manner,with increases and decreases in output causing changes in flue-gas composition.In this paper,we describe the first field test of a membrane-based post-combustion CO_(2)-capture system connected to a dynamically operating power plant in China.We report the performance of a Membrane Technology Research,Inc.(MTR)Polaris^(TM) membrane-based capture system over a range of plant operating loads ranging from 54%to 84%and conducted an operational stability test over a 168-h period during which the power plant was operating at an average load of 55%,but ramped as high as 79%and as low as 55%.Our results confirm the ability of a membrane capture system to operate effectively over a wide range of host-plant operating conditions,but also identity several issues related to plant integration,system control and resilience in the face of host-plant upsets that require attention as membrane separation systems move towards commercial use.

The CO_2 absorption and desorption performance of the triethylenetetramine + N,N-diethylethanolamine + H_2O system

Post-combustion CO_2 capture(PCC) process faces significant challenge of high regeneration energy consumption.Biphasic absorbent is a promising alternative candidate which could significantly reduce the regeneration energy consumption because only the CO_2-concentrated phase should be regenerated. In this work, aqueous solutions of triethylenetetramine(TETA) and N,N-diethylethanolamine(DEEA) are found to be efficient biphasic absorbents of CO_2. The effects of the solvent composition, total amine concentration, and temperature on the absorption behavior, as well as the effect of temperature on the desorption behavior of TETA–DEEA–H2 O system were investigated. An aqueous solution of 1 mol·L-1 TETA and 4 mol·L-1 DEEA spontaneously separates into two liquid phases after a certain amount of CO_2 is absorbed and it shows high CO_2 absorption/desorption performance.About 99.4% of the absorbed CO_2 is found in the lower phase, which corresponds to a CO_2 absorption capacity of 3.44 mol·kg-1. The appropriate absorption and desorption temperatures are found to be 30 °C and 90 °C,respectively. The thermal analysis indicates that the heat of absorption of the 1 mol·L-1 TETA and 4 mol·L-1 DEEA solution is-84.38 kJ·(mol CO_2)-1 which is 6.92 kJ·(mol CO_2)-1 less than that of aqueous MEA. The reaction heat, sensible heat, and the vaporization heat of the TETA–DEEA–H2 O system are lower than that of the aqueous MEA, while its CO_2 capacity is higher. Thus the TETA–DEEA–H2 O system is potentially a better absorbent for the post-combustion CO_2 capture process.

CO_(2) capture RD&D proceedings in China Huaneng Group

CO_(2) capture is an important carbon management route to mitigate the greenhouse gas emission in power sector.In recent years,China Huaneng Group(CHNG)has paid more attention on CO_(2)capture technology development and launched a series of R&D and demonstration projects.In the area of pre-combustion CO_(2) capture technology,GreenGen project initiated by CHNG is the first integrated gasification combined cycle(IGCC)power plant in China.Located in Tianjin,GreenGen aims at the development,demonstration and promotion of a near-zero emissions power plant.An IGCC plant of 250 MW has successfully passed full-scale trial operation.In the next phase,a pre-combustion CO_(2) capture unit will be integrated into the system.Pre-combustion process based on coal chemical process has been developed with lower costs successfully.Regarding to post-combustion CO_(2) capture(PCC),in 2008,CHNG built a 3,000 tpa CO_(2) capture plant,which was the first CO_(2) capture demonstration plant in China.In 2009,CHNG launched a PCC project in Shanghai with a capture capacity of 120,000 tpa CO_(2).Recently,Huaneng Clean Energy Research Institute(CERI)and Powerspan formed a joint venture,Huaneng-CERI-Powerspan(HCP).HCP has completed the technology qualification program to supply carbon capture technology for the CO_(2)capture Mongstad project.Besides these activities mentioned above,feasibility studies and system design for large scale PCC system,have been undertaken by CERI and its partners from Australia,US and Europe.

Optimal Bidding and Operation of a Power Plant with Solvent-BasedCarbon Capture under a CO2 Allowance Market： A Solution with aReinforcement Learning-Based Sarsa Temporal-Difference Algorithm

In this paper, a reinforcement learning （RL）-based Sarsa temporal-difference （TD） algorithm is applied tosearch for a unified bidding and operation strategy for a coal-fired power plant with monoethanolamine（MEA）-based post-combustion carbon capture under different carbon dioxide （CO2） allowance market con-ditions. The objective of the decision maker for the power plant is to maximize the discounted cumulativeprofit during the power plant lifetime. Two constraints are considered for the objective formulation. Firstly,the tradeoff between the energy-intensive carbon capture and the electricity generation should be made un-der presumed fixed fuel consumption. Secondly, the CO2 allowances purchased from the CO2 allowance mar-ket should be approximately equal to the quantity of COs emission from power generation. Three case stud-ies are demonstrated thereafter. In the first case, we show the convergence of the Sarsa TD algorithm andfind a deterministic optimal bidding and operation strategy. In the second case, compared with the inde-pendently designed operation and bidding strategies discussed in most of the relevant literature, the SarsaTD-based unified bidding and operation strategy with time-varying flexible market-oriented CO2 capturelevels is demonstrated to help the power plant decision maker gain a higher discounted cumulative profit.In the third case, a competitor operating another power plant identical to the preceding plant is consideredunder the same CO2 allowance market. The competitor also has carbon capture facilities but applies a differ-ent strategy to earn profits. The discounted cumulative profits of the two power plants are then compared,thus exhibiting the competitiveness of the power plant that is using the unified bidding and operation strat-egy explored by the Sarsa TD algorithm.

Integration of multi-stage membrane carbon capture processes to coal-fired power plants using highly permeable polymers

Membrane separation systems could be a feasible option as post combustion carbon capture technologies in coal-fired power plants.Recent advancement on membrane materials based on microporous super glassy polymers could improve significantly the capture process but the properties of the materials have to guide the design of the separation stage. In this study an advanced hybrid two-stage membrane process employing one of the most permeable polymer known(PIM-1) is retrofitted to a coal fired power plant and the process is analysed in terms of energy requirement and cost performance. The results are based on the use of an in-house detailed membrane module model implemented in UniSim Design~?, the Honeywell process flowsheet simulator. The study indicates the need for advanced configuration in order for highly permeable membranes to be competitive with more mature technologies in terms of capture cost. The effect of ageing and impurities on the material is also investigated in order to predict the decline in process performance over time and suggest a timeproof design.

Molecular simulation on carbon dioxide capture performance for carbons doped with various elements

Among the different types of CO_(2)capture technologies for post-combustion,sorption CO_(2)capture technology with carbon-based sorbents have been extensively explored with the purpose of enhancing their sorption perfor-mance by doping hetero elements due to the rapid reaction kinetics and low costs.Herein,sorption capacity and selectivity for CO_(2)and N 2 on carbon-based sorbents doped with elements such as nitrogen,sulfur,phosphorus,and boron,are evaluated and compared using the grand canonical Monte Carlo(GCMC)method,the universal force field(UFF),and transferable potentials for phase equilibria(TraPPE).The sorption capacities of N-doped porous carbons(PCs)at 50℃were 76.1%,70.7%,50.6%,and 35.7%higher than those of pure PCs,S-doped PCs,P-doped PCs,and B-doped PCs,respectively.Its sorption selectivity at 50℃was approximately 14.0,nearly twice that of pure PCs or other hetero-element-doped PCs.The N-doped PCs showed the largest sorption heat at 50℃among all the PCs,approximately 20.6 kJ·mol^(−1),which was 9.7%−25.5%higher than that of the pure PCs under post-combustion conditions.Additionally,with the product purity of 41.7 vol.%−75.9 vol.%for vacuum pressure swing sorption,and 53.4 vol.%−83.6 vol.%for temperature swing sorption,the latter is more suitable for post-combustion conditions than pressure-swing sorption.

Application of membrane separation technology in postcombustion carbon dioxide capture process

Membrane separation technology is a possible breakthrough in post-combustion carbon dioxide capture process. This review first focuses on the requirements for C02 separation membrane, and then outlines the existing competitive materials, promising preparation methods and processes to achieve desirable CO2 selectivity and permeability. A particular emphasis is addressed on polyimides, poly （ethylene oxide）, mixed-matrix mem- brane, thermally-rearranged polymer, fixed site carrier membrane, ionic liquid membrane and electrodialysis process. The advantages and drawbacks of each of materials and methods are discussed. Research threads and methodology of CO2 separation membrane and the key issue in this area are concluded

Experiment Study on the High-Temperature Thermal Treatment and Ultra-Low NOx Control of Solid Waste Coal Slime in Circulating Fluidized Bed

Coal slime is a kind of solid waste and inferior fuel, which is urgently needed to utilize. In this paper, a high-temperature thermal treatment of coal slime in a circulating fluidized bed(CFB) was attempted to achieve resource utilization. In the experiment, the combustion characteristics of dried coal slime during high-temperature thermal treatment were investigated in a 0.5 MW pilot-scale CFB. The stable fluidized combustion of dried coal slime was realized. When the excess air ratio was closer to 1.0, the furnace temperatures would be uniform. The ignition method of dried coal slime was changed correspondingly while the feeding position changed. However, feeding coal slime to the loop seal was instrumental in decreasing NO_(x) emissions. Moreover, the NO_(x) emissions were tried to further control by the post-combustion technology. Post-combustion technology could significantly reduce NO_(x) emissions below 50 mg·Nm^(-3) while ensuring combustion efficiency. Besides, it was found that there was an optimum excess air ratio in CFB of about 0.9 resulting in minimum NO_(x) emissions of coal slime. The experiment results could well guide the industrial-scale high temperature thermal treatment of coal slime.

Particuology and climate change

The global concern over the greenhouse gas emissions and its effect on global warming and climate change has focused attention on the necessity of carbon dioxide capture and sequestration. There are many processes proposed to capture carbon either before or after combustion and these processes invariably involve investigation and application of traditional particuology. The solids employed are of different sizes, densities, morphologies, and strengths. Their handling, transportation, recirculation, and reactor applications are the essence of ＇particuology＇. Particuology can play an important and vital role in achieving cost-effective removal of carbon and minimize emissions of greenhouse gases. In this paper, the existing and developing carbon capture processes are briefly reviewed and the opportunities for application of particuology are identified. The review was not intended to be exhaustive. It is only in sufficient detail to make connection between particuology and climate change. For immediate and future challenges of reducing global warming and carbon capture and sequestration, innovative reactor design and application of parricuology is imperative. Expertise and innovation in particuology can greatly enhance the speed of development of those technologies and help to achieve cost-effective implementation. Particuology is indeed intimately related to the climate change and global warming.