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1.
A two-dimensional (2D) transient model was developed to simulate the local hydrodynamics of a gas (flue gas)–solid (CaO)–solid (CaCO 3) three-phase fluidized-bed carbonator using the computational fluid dynamic method, where the chemical reaction model was adopted to determine the molar fraction of CO 2 at the exit of carbonator and the partial pressure of CO 2 in the carbonator. This investigation was intended to improve an understanding of the chemical reaction effects of CaO with CO 2 on the CO 2 capture efficiency of combustion flue gases. For this purpose, we had utilized Fluent 6.2 to predict the CO 2 capture efficiency for different operation conditions. The adopted model concerning the reaction rate of CaO with CO 2 is joined into the CFD software. Model simulation results, such as the local time-averaged CO 2 molar fraction and conversion of CaO, were validated by experimental measurements under varied operating conditions, e.g., the fraction of active CaO, chemical reaction temperature, particle size, and cycle number at different locations in a gas–solid–solid three-phase fluidized bed carbonator. Furthermore, the local transient hydrodynamic characteristics, such as gas molar fraction and partial pressure were predicted reasonably by the chemical reaction model adopted for the dynamic behaviors of the gas–solid–solid three-phase fluidized bed carbonator. On the basis of this analysis, capture CO 2 strategies to reduce CO 2 molar fraction in exit of carbonator reactor can be developed in the future. It is concluded that a fluidized bed of CaO can be a suitable reactor to achieve very effective CO 2 capture from combustion flue gases. 相似文献
2.
The CO 2 capture from flue gases by a small fluidized bed reactor was experimentally investigated with limestone. The results showed
that CO 2 in flue gases could be captured by limestone with high efficiency, but the CO 2 capture capacity of limestone decayed with the increasing of carbonation/calcination cycles. From a practical point of view,
coal may be required to provide the heat for CaCO 3 calcination, resulting in some potential effect on the sorbent capacity of CO 2 capture. Experiment results indicated that the variation in the capacity of CO 2 capture by using a limestone/coal ash mixture with a cyclic number was qualitatively similar to the variation of the capacity
of CO 2 capture using limestone only. Cyclic stability of limestone only undergoing the kinetically controlled stage in the carbonation
process had negligible difference with that of the limestone undergoing both the kinetically controlled stage and the product
layer diffusion controlled stage. Based on the experimental data, a model for the high-velocity fluidized bed carbonator that
consists of a dense bed zone and a riser zone was developed. The model predicted that high CO 2 capture efficiencies (>80%) were achievable for a range of reasonable operating conditions by the high-velocity fluidized
bed carbonator in a continuous carbonation and calcination system. 相似文献
3.
A bubbling fluidized bed reactor was used to study CO 2 capture from flue gas by using a potassium-based solid sorbent, sorbKX35 which was manufactured by the Korea Electric Power
Research Institute. A dry sorbent, sorbKX35, consists of K 2CO 3 for absorption and supporters for mechanical strength. To increase initial CO 2 removal, some amount of H 2O was absorbed in the sorbent before injecting simulated flue gas. It was possible to achieve 100% CO 2 removal for more than 10 minutes at 60°C and a residence time of 2 s with H 2O pretreatment. When H 2O pretreatment time was long enough to convert K 2CO 3 of sorbKX35 into K 2CO 3 · 1.5H 2O, CO 2 removal was excellent. The results obtained in this study can be used as basic data for designing and operating a large scale
CO 2 capture process with two fluidized bed reactors.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
4.
Calcium looping processes for capturing CO 2 from large emissions sources are based on the use of CaO particles as sorbent in circulating fluidized‐bed (CFB) reactors. A continuous flow of CaO from an oxyfired calciner is fed into the carbonator and a certain inventory of active CaO is expected to capture the CO 2 in the flue gas. The circulation rate and the inventory of CaO determine the CO 2 capture efficiency. Other parameters such as the average carrying capacity of the CaO circulating particles, the temperature, and the gas velocity must be taken into account. To investigate the effect of these variables on CO 2 capture efficiency, we used a 6.5 m height CFB carbonator connected to a twin CFB calciner. Many stationary operating states were achieved using different operating conditions. The trends of CO 2 capture efficiency measured are compared with those from a simple reactor model. This information may contribute to the future scaling up of the technology. © 2010 American Institute of Chemical Engineers AIChE J, 57: 000–000, 2011 相似文献
5.
Chemical looping combustion (CLC) is a flameless two-step fuel combustion that produces a pure CO 2 stream, ready for compression and sequestration. The process is composed of two interconnected fluidized bed reactors. The air reactor which is a conventional circulating fluidized bed and the fuel reactor which is a bubbling fluidized bed. The basic principle is to avoid the direct contact of air and fuel during the combustion by introducing a highly-reactive metal particle, referred to as oxygen carrier, to transport oxygen from the air to the fuel. In the process, the products from combustion are kept separated from the rest of the flue gases namely nitrogen and excess oxygen. This process eliminates the energy intensive step to separate the CO 2 from nitrogen-rich flue gas that reduce the thermal efficiency.Fundamental knowledge of multiphase reactive fluid dynamic behavior of the gas-solid flow is essential for the optimization and operation of a chemical looping combustor.Our recent thorough literature review shows that multiphase CFD-based models have not been adapted to chemical looping combustion processes in the open literature. In this study, we have developed the reaction kinetics model of the fuel reactor and implemented the kinetic model into a multiphase hydrodynamic model, MFIX, developed earlier at the National Energy Technology Laboratory. Simulated fuel reactor flows revealed high weight fraction of unburned methane fuel in the flue gas along with CO 2 and H 2O. This behavior implies high fuel loss at the exit of the reactor and indicates the necessity to increase the residence time, say by decreasing the fuel flow rate, or to recirculate the unburned methane after condensing and removing CO 2. 相似文献
6.
The Canadian regulations on carbon dioxide emissions from power plants aim to lower the emissions from coal-fired units down to those of natural gas combined cycle (NGCC) units. Since coal is significantly more carbon intensive than natural gas, coal-fired plants must operate at higher net efficiencies and implement carbon capture to meet the new regulations. Calcium looping (CaL) is a promising post-combustion carbon capture (PCC) technology that, unlike other capture processes, generates additional power. By capturing carbon dioxide at elevated temperatures, the energy penalty that carbon capture technologies inherently impose on power plant efficiencies is significantly reduced. In this work, the CO 2 capture performance of a calcium-based sorbent is determined via thermogravimetric analysis under relatively high carbonation and low calcination temperatures. The results are used in an aspenONE™ simulation of a CaL process applied to a pressurized fluidized bed combustion (PFBC) system at thermodynamic equilibrium. The combustion of both natural gas and coal are considered for sorbent calcination in the CaL process. A sensitivity analysis on several process parameters, including sorbent feed rate and carbonator operating pressure, is undertaken. The energy penalty associated with the capture process ranges from 6.8–11.8 percentage points depending on fuel selection and operating conditions. The use of natural gas results in lower energy penalties and solids circulation rates, while operating the carbonator at 202 kPa(a) results in the lowest penalties and drops the solids circulations rates to below 1000 kg/s. 相似文献
7.
To demonstrate process feasibility of in situ CO 2 capture from combustion of fossil fuels using Ca-based sorbent looping technology, a flexible atmospheric dual fluidized bed combustion system has been constructed. Both reactors have an ID of 100 mm and can be operated at up to 1000 °C at atmospheric pressure. This paper presents preliminary results for a variety of operating conditions, including sorbent looping rate, flue gas stream volume, CaO/CO 2 ratio and combustion mode for supplying heat to the sorbent regenerator, including oxy-fuel combustion of biomass and coal with flue gas recirculation to achieve high-concentration CO 2 in the off-gas. It is the authors' belief that this study is the first demonstration of this technology using a pilot-scale dual fluidized bed system, with continuous sorbent looping for in situ CO 2 capture, albeit at atmospheric pressure. A multi-cycle test was conducted and a high CO 2 capture efficiency (> 90%) was achieved for the first several cycles, which decreased to a still acceptable level (> 75%) even after more than 25 cycles. The cyclic sorbent was sampled on-line and showed general agreement with the features observed using a lab-scale thermogravimetric analysis (TGA) apparatus. CO 2 capture efficiency decreased with increasing number of sorbent looping cycles as expected, and sorbent attrition was found to be another significant factor to be limiting sorbent performance. 相似文献
8.
Carbon capture and storage (CCS) technologies are a cornerstone for reducing CO 2 emissions from energy and energy-intensive industries. Among the various CCS technologies, solid sorbent looping systems are considered to be potentially promising solutions for reducing CO 2 capture energy penalty. We present an evaluation module for a carbonator with sorbent looping cycle to calculate the carbonation efficiency. The module incorporates a simple sorbent activity model, and the solid/gas balances are constructed by assuming simple reactor mixing quality. By conducting simulations, we examine the variation in the carbonation efficiencies as a function of the sorbent looping operation factors and discuss an optimum operating strategy. 相似文献
9.
The calcium-looping process is a promising technique for CO 2 capture from coal-fired power plants and for reducing GHG emissions from the power generation sector. This paper presents a calculation model of the carbonator, the key reactor of the Ca-looping process, where CO 2 is captured as a result of its reaction with CaO. The model presented is based on the Kunii–Levenspiel theory for circulating fluidized bed and on the recent findings on the properties of CaO as a CO 2 sorbent, while taking into account the effects of coal ash and sulfur species.This model can be used for process optimization and for the prediction of the performance of power plants based on the Ca-looping process. Also presented in this paper are the results of a sensitivity analysis of the primary parameters that influence the performance of the carbonator. These results confirm the feasibility of the Ca-looping process with reactors of reasonable size for industrial applications and highlight the importance of the properties of the Ca-based sorbent as they highly affect the carbonator's performance. 相似文献
10.
The sulfation reaction rate of CaO particles in three reactors comprising a post‐combustion calcium looping system is discussed: a combustion chamber generating flue gases, a carbonator reactor to capture CO 2 and SO 2, and an oxy‐fired calciner to regenerate the CO 2 sorbent. Due to its strong impact on the pore size distribution of CaO particles, the number of carbonation/calcination cycles arises as a new important variable to understand sulfation phenomena. Sulfation patterns change as a result of particle cycling, becoming more homogeneous with higher number of cycles. Experimental results from thermogravimetric tests demonstrate that high sulfation rates can be measured under all conditions tested, indicating that the calcium looping systems will be extremely efficient in SO 2 capture. 相似文献
11.
CO 2 capture systems based on the carbonation/calcination loop have gained rapid interest due to promising carbonator CO 2 capture efficiency, low sorbent cost and no flue gases treatment is required before entering the system. These features together result in a competitively low cost CO 2 capture system. Among the key variables that influence the performance of these systems and their integration with power plants, the carbonation conversion of the sorbent and the heat requirement at calciner are the most relevant. Both variables are mainly influenced by CaO/CO 2 ratio and make-up flow of solids. New sorbents are under development to reduce the decay of their carbonation conversion with cycles. The aim of this study is to assess the competitiveness of new limestones with enhanced sorption behaviour applied to carbonation/calcination cycle integrated with a power plant, compared to raw limestone. The existence of an upper limit for the maximum average capture capacity of CaO has been considered. Above this limit, improving sorbent capture capacity does not lead to the corresponding increase in capture efficiency and, thus, reduction of CO 2 avoided cost is not observed. Simulations calculate the maximum price for enhanced sorbents to achieve a reduction in CO 2 removal cost under different process conditions (solid circulation and make-up flow). The present study may be used as an assessment tool of new sorbents to understand what prices would be competitive compare with raw limestone in the CO 2 looping capture systems. 相似文献
12.
There is increasing interest in CO 2 looping cycles that involve the repeated calcination and carbonation of the sorbent as a way to capture CO 2 from flue gases during the carbonation step and the generation of a pure stream of CO 2 in the oxyfired calcination step. In particular, attrition of the material in these interconnected fluidized bed reactors is a problem of general concern. Attrition of limestone derived materials has been studied in fluidized bed systems by numerous authors. In this work, we have investigated the attrition of two limestones used in a system of two interconnected circulating fluidized bed reactors operating in continuous mode as carbonation and calciner reactors. We observed a rapid initial attrition of both limestones during the calcination step which was then followed by a highly stable period (up to 140 h of added circulation for one of the limestones) during which particle size changes were negligible. This is consistent with previous observations of attrition in other systems that employ these materials. However, a comparison of the attrition model constants with the data reported in the literature showed the two limestones to be particularly fragile during the initial calcination and the first few hours of circulation. Thus, a careful choice of limestone based on its attrition properties must be taken into account in designing future carbonate looping systems. 相似文献
13.
A kinetic theory based hydrodynamic model with experimentally determined sorption rates for reaction of CO 2 with K 2CO 3 solid sorbent is used to design a compact circulating fluidized bed sorption‐regeneration system for CO 2 removal from flue gases. Because of high solids fluxes, the sorber does not require internal or external cooling. The output is verified by computing the granular temperatures, particle viscosities, dispersion, and mass transfer coefficients. These properties agree with reported measurement values except the radial dispersion coefficients, which are much higher due to the larger bed diameter. With the solid sorbent prepared according to published information, the CO 2 removal percentage at the riser top is 69.16%. To improve the CO 2 removal, an effort is needed to develop a better sorbent or to simply lower the inlet gas velocity to operate in a denser mode, leading to a larger system. Also, the effect of temperature rise on the removal efficiency is investigated. © 2010 American Institute of Chemical Engineers AIChE J, 2010 相似文献
14.
Korea Institute of Energy Research (KIER) and Korea Electric Power Corporation Research Institute (KEPCORI) have been developing a CO 2 capture technology using dry sorbents. In this study, KEP-CO2P1, a potassium-based dry sorbent manufactured by a spray-drying method, was used. We employed a bench-scale dry-sorbent CO 2 capture fluidized-bed process capable of capturing 0.5 ton CO 2/day at most. We investigated the sorbent performance in continuous operation mode with solid circulation between a fast fluidized-bed-type carbonator and a bubbling fluidized-bed-type regenerator. We used a slip stream of a real flue gas from 2MWe coal-fired circulating fluidized-bed (CFB) power facilities installed at KIER. Throughout more than 50 hours of continuous operation, the temperature of the carbonator was maintained around 70-80 °C using a jacket-type heat exchanger, while that of the regenerator was kept above 180 °C using an electric furnace. The differential pressure of both the carbonator and regenerator was maintained at a stable level. The maximum CO 2 removal was greater than 90%, and the average CO 2 removal was about 83% during 50 hours of continuous operation. 相似文献
15.
Thermodynamic equilibrium and kinetic reactor models are used to simulate a fluidized bed membrane reactor with in situ or ex situ hydrogen and/or CO 2 removal for production of pure hydrogen by steam methane reforming. In the equilibrium model, the membranes and CO 2 removal are located in separate vessels downstream of the reformer. As the recycle ratio increases, the overall performance approaches that where membranes are located inside the reactor. Whether located in situ or ex situ, hydrogen removal by membranes and CO 2 capture by sorbents both enhance hydrogen production. In the kinetic reactor model, a circulating fluidized bed membrane reformer is coupled with a catalyst/sorbent regenerator. Sorbent enhancement combined with membranes could provide very high hydrogen yields. In addition, since carbonation is exothermic, with its heat of reaction similar in magnitude to the endothermic heat of reaction of the net reforming reactions, sorbent enhancement can provide much of the heat needed in the reformer. The overall heat needed for the process would then be provided in a separate calciner, acting as a sorbent regenerator. While the technology is promising, several practical issues need to be examined. 相似文献
16.
In chemical-looping combustion (CLC) a gaseous fuel is burnt with inherent separation of the greenhouse gas carbon dioxide. The oxygen is transported from the combustion air to the fuel by means of metal oxide particles acting as oxygen carriers. A CLC system can be designed similar to a circulating fluidized bed, but with the addition of a bubbling fluidized bed on the return side. Thus, the system consists of a riser (fast fluidized bed) acting as the air reactor. This is connected to a cyclone, where the particles and the gas from the air reactor are separated. The particles fall down into a second fluidized bed, the fuel reactor, and are via a fluidized pot-seal transported back into the riser. The gas leaving the air reactor consists of nitrogen and unreacted oxygen, while the reaction products, carbon dioxide and water, come out from the fuel reactor. The water can easily be condensed and removed, and the remaining carbon dioxide can be liquefied for subsequent sequestration.The gas leakage between the reactors must be minimized to prevent the carbon dioxide from being diluted with nitrogen, or to prevent carbon dioxide from leaking to the air reactor decreasing the efficiency of carbon dioxide capture. In this system, the possible gas leakages are: (i) from the fuel reactor to the cyclone and to the pot-seal, (ii) from the cyclone down to the fuel reactor, (iii) from the pot-seal to the fuel reactor. These gas leakages were investigated in a scaled cold model. A typical leakage from the fuel reactor was 2%, i.e. a CO 2 capture efficiency of 98%. No leakage was detected from the cyclone to the fuel reactor. Thus, all product gas from the air reactor leaves the system from the cyclone. A typical leakage from the pot-seal into the fuel reactor was 6%, which corresponds to 0.3% of the total air added to the system, and would give a dilution of the CO 2 produced by approximately 6% air. However, this gas leakage can be avoided by using steam, instead of air, to fluidize the whole, or part of, the pot-seal. The disadvantages of diluting the CO 2 are likely to motivate the use of steam. 相似文献
17.
Simultaneous dry removal of SO 2 and NO x from flue gas has been investigated using a powder-particle fluidized bed. In a process of flue gas desulfurization by use of solid sorbents such as FeO (dust from a steel plant) and CuO, the smaller the particle size of sorbents, the higher the expected SO 2 conversion. In a powder-particle fluidized bed (PPFB), fine particles less than 40 μm in diameter fed into the bed are fluidized with coarse particles. But only the fine particles are entrained from the bed, and their residence time in the bed is remarkably long. The reduction of NOx with NH3 in the fluidized bed is catalyzed by coarse particles or both coarse and fine particles. In this study, PPFB was applied to simultaneous dry SO2/NOx removal process, and several kinds of sorbents or catalysts were evaluated in a PPFB. Using the selected sorbents and catalysts, kinetic measurements were made in the temperature range of 300 to 600°C. SO2 removal efficiencies were affected by reaction temperature, sorbent/S ratio, and static bed height. NOx removal efficiencies in excess of 95% were achieved at NH3/NOx mole ratio of 1.0. When FeO was used as sorbent, SO2 conversion increased with increasing temperature and reached 80% at 600°C. 相似文献
18.
The effect of bed height on CO 2 capture was investigated by carbonation/regeneration cyclic operations using a bubbling fluidized bed reactor. We used a
potassium-based solid sorbent, SorbKX35T5 which was manufactured by the Korea Electric Power Research Institute. The sorbent
consists of 35% K 2CO 3 for absorption and 65% supporters for mechanical strength. We used a fluidized bed reactor with an inner diameter of 0.05
m and a height of 0.8 m which was made of quartz and placed inside of a furnace. The operating temperatures were fixed at
70 °C and 150 °C for carbonation and regeneration, respectively. The carbonation/regeneration cyclic operations were performed
three times at four different L/D (length vs diameter) ratios such as one, two, three, and four. The amount of CO 2 captured was the most when L/D ratio was one, while the period of maintaining 100% CO 2 removal was the longest as 6 minutes when L/D ratio was three. At each cycle, CO 2 sorption capacity (g CO 2/g sorbent) was decreased as L/D ratio was increased. The results obtained in this study can be applied to design and operate
a large scale CO 2 capture process composed of two fluidized bed reactors.
This work was presented at the 7
th
China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008. 相似文献
19.
In this study, the decomposition conditions of limestone particles (0.25-0.50 mm) for CO 2 capture in a steam dilution atmosphere (20-100% steam in CO 2) were investigated by using a continuously operating fluidized bed reactor. The results show that the decomposition conversion of limestone increased with the steam dilution percentage in the CO 2 supply gas. At a bed temperature of 920 °C, the conversions were 72% without steam dilution and 98% with 60% steam dilution. The conversion was 99% with 100% steam dilution at 850 °C of the bed temperature. Steam dilution can decrease not only the decomposition temperature of limestone, but also the residence time required for nearly complete decomposition of CaCO 3. The hydration and carbonation reactivities of the CaO produced were also tested and the results show that both the reactivities increased with the steam dilution percentage for decomposing limestone. 相似文献
20.
A novel sorbent, potassium carbonate impregnated on porous fine alumina, was produced, and its reactive and regenerative properties were evaluated for dry‐type simultaneous removal of SO 2 and NO from flue gas under stack temperatures, by using a powder‐particle fluidized bed (PPFB) with I.D. of 53 mm as the reactor. High removal efficiencies for SO 2 and NO were achieved simultaneously. An apparent beneficial effect of SO 2 on the enhancement of NO removal was found based on a large amount of data. The alumina carrier was successfully regenerated and used repeatedly for the production of fresh sorbent particles. With no ammonia, low temperature, high removal efficiency, and no second waste emission as main characteristics, this dry process can be a competitive technology for pollution control of flue gas from power plants in the future. 相似文献
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