CO2 Capture Behavior of Shell during Calcination/Carbonation Cycles

The cyclic carbonation performances of shells as CO₂ sorbents were investigated during multiple calcination/carbonation cycles. The carbonation kinetics of the shell and limestone are similar since they both exhibit a fast kinetically controlled reaction regime and a diffusion controlled reaction regime, but their carbonation rates differ between these two regions. Shell achieves the maximum carbonation conversion for carbonation at 680–700 °C. The mactra veneriformis shell and mussel shell exhibit higher carbonation conversions than limestone after several cycles at the same reaction conditions. The carbonation conversion of scallop shell is slightly higher than that of limestone after a series of cycles. The calcined shell appears more porous than calcined limestone, and possesses more pores > 230 nm, which allow large CO₂ diffusion‐carbonation reaction rates and higher conversion due to the increased surface area of the shell. The pores of the shell that are greater than 230 nm do not sinter significantly. The shell has more sodium ions than limestone, which probably leads to an improvement in the cyclic carbonation performance during the multiple calcination/carbonation cycles.     

Effects of Steam Addition during Calcination on Carbonation Behavior in a Calcination/Carbonation Loop

The effects of steam addition during calcination on the carbonation behavior of calcium‐based sorbents in cyclic calcination/carbonation experiments were investigated. Variations in the CaO conversion rate during carbonation were measured to evaluate the influence of operating conditions and particle size on the carbonation reaction in kinetic‐ and diffusion‐controlled reaction regimes. Surface sintering and particle aggregation during cyclic calcination/carbonation affected the sorbent surface area, pore volume, and possibly the pore size, resulting in less sorbent recyclability and a trigger time retard in the fast kinetic‐controlled carbonation. Steam addition during calcination positively affected the recyclability of the sorbents and altered the carbonation behavior.     

Natural Calcium‐Based Sorbents Doped with Sea Salt for Cyclic CO2 Capture

The calcium‐looping process for post‐combustion carbon dioxide capture, an economically and technically feasible method suitable for large‐scale use, has recently gained much attention. However, the capture capacity of calcium‐based sorbents rapidly decreases after only a few cycles. Herein, calcium‐based sorbents with enhanced cyclic CO₂‐capture capacity have been derived from cheap, natural raw materials by using a simple impregnation method. Limestone and shells were used as the calcium‐based raw materials, with sea salt as dopant. Modified limestone had the highest CO₂‐capture capacity after multiple carbonation‐calcination cycles. Sea‐salt‐doped sorbent showed a relatively stable porous surface during cycles, which resulted in a higher CO₂‐capture capacity.     

基于钙基吸收剂循环煅烧/碳酸化反应捕集CO2的试验

利用钙基吸收剂循环煅烧/碳酸化反应(CCCR)吸收CO2是一种新型、廉价、有效的CO2捕集方法.采用热重分析仪研究了吸收剂的矿物组成、颗粒粒径、煅烧温度和碳酸化温度对CCCR快速反应阶段吸收剂循环碳酸化率(XN)的影响.结果表明:吸收剂的碳酸化反应由快速化学反应控制阶段、过渡阶段和缓慢产物层扩散控制阶段组成;白云石具有良好的抗烧结能力,白云石的XN高于石灰石;随着颗粒粒径的增大,吸收剂的XN逐渐降低;当煅烧温度超过950℃时,随着循环反应次数的增加,吸收剂的XN严重降低;吸收剂在725℃碳酸化温度时的XN最高.     

A Two‐Compartment Fluidized Bed Reactor for CO2 Capture by Chemical‐Looping Combustion

Chemical‐looping combustion (CLC) is a combustion method for a gaseous fuel with inherent separation of the greenhouse gas carbon dioxide. A CLC system consists of two reactors, an air reactor and a fuel reactor, and an oxygen carrier circulating between the two reactors. The oxygen carrier transfers the oxygen from the air to the fuel. The flue gas from the fuel reactor consists of carbon dioxide and water, while the flue gas from the air reactor is nitrogen from the air. A two‐compartment fluidized bed CLC system was designed and tested using a flow model in order to find critical design parameters. Gas velocities and slot design were varied, and the solids circulation rate and gas leakage between the reactors were measured. The solids circulation rate was found to be sufficient. The gas leakage was somewhat high but could be reduced by altering the slot design. Finally, a hot laboratory CLC system is presented with an advanced design for the slot and also with the possibility for inert gas addition into the downcomer for solids flow increase.     

Preparation and Application of the Sol-Gel Combustion Synthesis-Made CaO/CaZrO3 Sorbent for Cyclic CO2 Capture Through the Severe Calcination Condition

abstract Calcium looping method has been considered as one of the efficient options to capture CO2 in the combustion flue gas. CaO-based sorbent is the basis for application of calcium looping and shou...     

The maximum capture efficiency of CO2 using a carbonation/calcination cycle of CaO/CaCO3

The use of natural calcium carbonates as regenerable CO₂ sorbents in industrial processes is limited by the rapid decay of the carbonation conversion with the number of cycles carbonation/calcination. However, new processes are emerging to capture CO₂ using these cycles, that can take advantage of the intrinsic benefits of high temperature separations in energy systems. This work presents an analysis of a general carbonation/calcination cycle to capture CO₂, incorporating a fresh feed of sorbent to compensate for the decay in activity during sorbent re-cycling. A general design equation for the maximum CO₂ capture efficiency is obtained by incorporating to the cycle mass balances a simple but realistic equation to estimate the decay in sorbent activity with the number of cycles.     

CFD Modeling of a Carbonation Reactor with a K‐Based Dry Sorbent for CO2 Capture

A 2D CFD simulation of the carbonation reactor is carried out to evaluate the performance of potassium‐based dry sorbent during the CO₂ capture process. A multiscale drag coefficient model is incorporated into the two‐fluid model to take the effects of clusters into account. The influence of several parameters on CO₂ removal is investigated. The results indicate that increasing the reactor height and reducing the gas velocity can lengthen the residence time of particles and enhance the CO₂ removal. The operating pressure has a significant influence on the performance of solid sorbents. A higher pressure will decrease the CO₂ removal efficiency.     

Effect of Empty Fruit Bunch in Calcium Oxide for Cyclic CO2 Capture

Empty fruit bunch (EFB) is utilized to increase the CO₂ capture capacity and cyclic stability of calcium oxide (CaO) prepared from cockle shells (CS). The cyclic reaction of calcination and carbonation reaction was performed in pure N₂ environment and in the presence of CO₂ in N₂, respectively. The EFB in CS modified the pore structural properties, morphology, and composition of the pristine CaO. Higher EFB loading in CS reduced the CaO composition but improved the CO₂ capture capacity and cyclic stability during cyclic CO₂ capture.     

Cyclic calcination/carbonation looping of dolomite modified with acetic acid for CO2 capture

The dolomite modified with acetic acid solution was proposed as a CO₂ sorbent for calcination/carbonation cycles. The carbonation conversions for modified and original dolomites in a twin fixed-bed reactor system with increasing the numbers of cycles were investigated. The carbonation temperature in the range of 630 °C–700 °C is beneficial to the carbonation reaction of modified dolomite. The carbonation conversion for modified dolomite is significantly higher than that for original sorbent at the same reaction conditions with increasing numbers of reaction cycles. The modified dolomite exhibits a carbonation conversion of 0.6 after 20 cycles, while the unmodified sorbent shows a conversion of 0.26 at the same reaction conditions, which is calcined at 920 °C and carbonated at 650 °C. At the high calcination temperature over 920 °C modified dolomite can maintain much higher conversion than unmodified sorbent. The mean grain size of CaO derived from modified dolomite is smaller than that from original sorbent with increasing numbers of reaction cycles. The calcined modified dolomite possesses greater surface area and pore volume than calcined original sorbent during the multiple cycles. The pore volume and pore area distributions for calcined modified dolomite are also superior to those for calcined unmodified sorbent during the looping cycle. The modified dolomite is proved as a new and promising type of regenerable CO₂ sorbent for industrial applications.     

CO2 Adsorption and Desorption for CO2 Enrichment at Low-Concentrations Using Zeolite 13X

Adsorption of CO₂ using zeolite 13X as adsorbent has been studied extensively, but little attention has been paid to CO₂ adsorption at very low concentrations such as in the ambient air. Furthermore, there is almost no information on CO₂ desorption characteristics. In a carbon enrichment for plant stimulation system, ambient CO₂ is enriched from 400 to 1000 ppm to provide an enriched CO₂ stream for plant growth in greenhouses. To provide essential design data, systematic performance tests were carried out to evaluate both the adsorption and desorption capacity, enrichment factor, moisture content, and cyclic performance. It was found that the adsorption capacity and CO₂ concentration in the enriched air are a function of adsorption temperature and the difference of adsorption and desorption temperatures, for a given adsorbent loading at a properly selected gas flow rate.     

KINETICS AND ABSORPTION RATE OF CO2 INTO PARTIALLY CARBONATED AMMONIA SOLUTIONS

In this research, kinetics and absorption rate of CO₂ were studied using partially carbonated ammonia solutions. A correlation was proposed to calculate CO₂ absorption rate based on two dimensionless parameters: conversion film parameter and carbonation ratio. Absorption rate experiments have been performed employing a laboratory absorption packed column. More than 60 items of experimental data were used for obtaining the correlation parameters. In the experiments, total ammonia concentration range was 30 to 750 (mol · m^?3), carbonation ratio range was 0.22 to 0.785, and CO₂ partial pressure in the gas mixture was 10, 14, or 18 (kPa). A comparison of the predictions indicated that the proposed correlation was more accurate than other correlations reported in the literature.     

Development of a Scalable Method for Manufacturing High‐Temperature CO2 Capture Sorbents

An engineered process for scalable manufacture of a calcium aluminum carbonate CO₂ sorbent with production amounts of about 1000 g per hour has been developed. The process includes mixing and heating, solid‐liquid separation, drying and extrusion, crushing and conveying, and calcined molding steps. The sorbent preparation involves the coprecipitation of Ca²⁺, Al³⁺, and CO₃^2– under alkaline conditions. By adjusting the Ca:Al molar ratio, a series of Ca‐rich materials could be synthesized for use as CO₂ sorbents at 750 °C. A calcium acetate‐derived sorbent exhibited better cyclic stability than sorbents originating from CaCl₂ and Ca(NO₃)₂. The initial sorption capacity increased with CaO concentration. High stability of more than 90 % was maintained by the Ca:Al sorbents after 40 looping tests.     

CO2 capture capacity of CaO in long series of pressure swing sorption cycles

One promising method for the capture of CO₂ from point sources is through the usage of a lime-based sorbent. Lime (CaO) acts as a CO₂ carrier, absorbing CO₂ from the flue gas (carbonation) and releasing it in a separate reactor (calcination) to create a pure stream of CO₂ suitable for sequestration. One of the challenges with this process is the decay in calcium utilization (CO₂ capture capacity) during carbonation/calcination cycling. The reduction in calcium utilization of natural limestone over large numbers of cycles (>250) was studied. Cycling was accomplished using pressure swing CO₂ adsorption in a pressurized thermogravimetric reactor (PTGA). The effect of carbonation pressure on calcium utilization was studied in CO₂ with the reactor operated at 1000 °C. The pressure was cycled between atmospheric pressure for calcination, and 6, 11 or 21 bar for carbonation. Over the first 250 cycles, the calcium utilization reached a near-asymptotic value of 12.5-27.7%, depending on the cycling conditions. Pressure cycling resulted in improved long-term calcium utilization compared to temperature swing or CO₂ partial pressure swing adsorption under similar conditions. An increased rate of de-pressurization caused an increase in calcium utilization, attributed to fracturing of the sorbent particle during the rapid calcination, as observed via SEM analysis.     

Equilibrium Analysis of Cyclic Adsorption Processes: CO2 Working Capacities with NaY

Abstract

The most common application of adsorption is via pressure swing adsorption. In this type of design, the feed and regeneration temperatures are kept approximately equal, whereas the feed pressure is higher than the regeneration pressure. By exploiting the difference in the amount adsorbed at a higher pressure to the amount adsorbed at a lower pressure, a working capacity is realized. Therefore, by examining the expected (ideal) working capacity of an adsorbent, a performance characteristic can be analyzed for a pressure swing adsorption process (PSA). For this work, feed pressures up to 2.0 atm CO₂ and feed temperatures from 20°C to 200°C were investigated. These limits were chosen due to the nature of the target process: CO₂ removal from flue gas.

Carbon dioxide adsorption isotherms were determined in a constant volume system at 23°C, 45°C, 65°C, 104°C, 146°C, and 198°C, for pressures between 0.001 and 2.5 atm CO₂ with NaY zeolite. These data were fit with the temperature dependent form of the Toth isotherm. Henry's Law constants and the heat of adsorption at the limit of zero coverage were also determined using the concentration pulse method. Comparison of the Henry's Law constants derived from the Toth isotherm, and those obtained with the concentration pulse method provided excellent agreement.

By using the Toth isotherm, expected working capacity contour plots were constructed for PSA (Pressure Swing Adsorption), TSA (Temperature Swing Adsorption), and PTSA (Pressure Temperature Swing Adsorption) cycles. The largest expected working capacities were obtained when the bed was operated under a high‐pressure gradient PSA cycle, or a high thermal and pressure gradient PTSA cycle. The results also showed that certain TSA and PSA cycle conditions would result with higher expected working capacities as the feed temperature increases.     

二氧化碳捕集、运输与储存技术进展及趋势

目前,全球依然是以使用化石燃料为主导趋势,随着全球气候日益变暖,减排CO2成为我们必须关注的问题。详细介绍了CO2捕获及储存技术,并对CO2各相态输送过程可能产生的问题进行了总结。最后总结了CCTS技术未来的发展趋势并对未来需要努力的方面进行了阐述。     

CO2 Absorption and Regeneration Using Amines with Different Degrees of Steric Hindrance

The influence of steric hindrance in amines upon different characteristics in carbon dioxide chemical absorption, namely, absorption rate, carbon dioxide loading, and regeneration degree, has been analyzed. Aqueous solutions of monoethanolamine, 1‐amino‐2‐propanol, and 2‐amino‐2‐methyl‐1‐propanol were used to compare their behavior during carbon dioxide absorption. The presence of one or two methyl groups on the carbon next to the amino group produced changes in the analyzed parameters. In addition, the influences of the gas‐flow rate and amine concentration on the chemical solvent behavior were studied to improve the mass transfer under different experimental conditions.     

Preparation of high surface area CaCO3 by reacting CO2 with aqueous suspensions of Ca(OH)2: Effect of the addition of sodium polyacrylate

High surface area CaCO₃ was produced through the reaction between CO₂ and an aqueous suspension of Ca(OH)₂ with the addition of an additive, sodium polyacrylate. The surface area of CaCO₃ prepared was affected markedly by the amount of additive and the solution pH when adding the additive. The CaCO₃ with the highest surface area (87.7 ± 1.3 m²/g) was obtained under the conditions that the initial Ca(OH)₂ concentration was 2.4 wt.%, the amount of sodium polyacrylate added was 0.2 wt.%, and the solution pH at which the additive was added was in the range of 11.4-11.1. The high surface area CaCO₃ also had a high pore volume. The CaCO₃ was highly reactive toward SO₂, and a conversion of 0.95 was achieved when it was sulfated at 950 °C and 4000 ppm SO₂ in air for 1 min. Prior calcination reduced the reactivity of this high surface area CaCO₃.     

HIGH TEMPERATURE CAPTURE OF CARBON DIOXIDE: CHARACTERISTICS OF THE REVERSIBLE REACTION BETWEEN CaO(s) and CO2(g)

The reversible reaction between CaO(s) and CO₂(g) may ultimately find application in a high temperature process to control CO₂ emissions from advanced power generation processes. At appropriate temperature and pressure combinations, CO₂(g) is removed from the gas phase and captured as CaC₃(s). At higher temperature and/or lower pressure, the reaction is reversed to produce a gas stream having high CO₂(g) concentration suitable for use or ultimate disposal. Both the calcination and carbonation reactions have been studied in an electrobalance reactor as a function of temperature, pressure, and gas composition. Multicycle tests have provided preliminary information on sorbent durability. Solid structural property characteristics have been measured as a supplement to the reaction studies.

Rapid and complete calcination of CaCO₃ can be achieved at temperatures as low as 750°C under one atmosphere of N2. Higher pressure reduces the calcination rate while the presence of CO₂ in the calcination atmosphere requires the use of higher temperature. Mild calcination conditions produce a CaO product which is most reactive during the carbonation phase. Carbonation is characterized by a rapid initial reaction rate followed by an abrupt transition to a quite slow rate. Significant reduction in CO₂ capacity between the first and second carbonation cycles, ranging from 15% under favorable reaction conditions to more than 30% at severe conditions, was found. However, the capacity loss tended to moderate as the number of cycles increased.     

CO2 Capture Using Activated Amino Acid Salt Solutions in a Membrane Contactor

An activated solution based on amino acid salt was proposed as a CO₂ absorbent. Piperazine (PZ) was selected as an activating agent and added into the aqueous glycine salt to form the activated solution. A coupling process, which associated the activated solution with a PP hollow fiber membrane contactor, was set up. An experimental and theoretical analysis for CO₂ capture was performed. The performances of CO₂ capture by the coupling process were evaluated using the PZ activated solution and the non-activated glycine salt solution. A numerical model for the simulation of the hollow fiber membrane gas–liquid mass transfer was developed. Typical parameters such as outlet gas phase CO₂ concentration, capture efficiency, and mass transfer coefficient for the activated solution were determined experimentally. The effects of operation temperature and liquid CO₂-loading on mass transfer coefficient and capture efficiency were discussed in this work. Axial and radial concentration profiles of CO₂ in the fiber lumen and mass transfer flux were simulated by the model. Results show that the performances of the PZ activated glycine salt solution are evidently better than that of the non-activated glycine salt solution in the membrane contactor for CO₂ capture. Elevation of the operation temperatures can enhance the overall mass transfer coefficient. The activated solution can maintain higher capture efficiency especially in the case of high CO₂-loadings. The gas phase CO₂ concentration with the activated solution is lower than that with the non-activated solution whether along axial or radial distances in the fiber lumen. The model simulation is validated with experimental data.