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Title: CO{sub 2} capture from flue gases using three Ca-based sorbents in a fluidized bed reactor

Abstract

Abstract: Experiments of CO{sub 2} capture and sorbent regeneration characteristics of limestone, dolomite, and CaO/Ca{sub 1}2Al{sub 14}O{sub 3}3 at high temperature were investigated in a thermogravimetric analyzer (TGA) and a fluidized bed reactor. The effect of reactivity decay of limestone, dolomite, and CaO/Ca{sub 12}Al{sub 14}O{sub 3}3 sorbents on CO{sub 2} capture and sorbent regeneration processes was studied. The experimental results indicated that the operation time of high efficient CO{sub 2} capture stage declined continuously with increasing of the cyclic number due to the loss of the sorbent activity, and the final CO{sub 2} capture efficiency would remain nearly constant, due to the sorbent already reaching the final residual capture capacity. After the CO{sub 2} capture step, the Ca-based sorbents need to be regenerated to be used for a subsequent cycle, and the multiple calcination processes of Ca-based sorbent under different calcination conditions are studied and discussed. Reactivity loss of limestone, dolomite and CaO/Ca{sub 12}Al{sub 14}O{sub 3}3 sorbents from a fluidized bed reactor at both mild and severe calcination conditions was compared with the TGA data. At mild calcination conditions, TGA results of sorbent reactivity loss were similar to the experimental results of fluidized bed reactor for three sorbents at 850more » degrees C calcination temperature, and this indicated that TGA experimental results can be used as a reference to predict sorbent reactivity loss behavior in fluidized bed reactor. At severe calcination condition, sorbent reactivity loss behavior for limestone and dolomite from TGA compare well with the result from a fluidized bed reactor.« less

Authors:
; ;  [1]
  1. Tsinghua University, Beijing (China). Dept. of Thermal Engineering
Publication Date:
OSTI Identifier:
21197791
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Environmental Engineering (New York); Journal Volume: 135; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; CAPTURE; CARBON DIOXIDE; FLUE GAS; ADSORBENTS; FLUIDIZED BED REACTORS; REGENERATION; LIMESTONE; DOLOMITE; CALCIUM OXIDES; ALUMINIUM OXIDES; THERMAL GRAVIMETRIC ANALYSIS; CALCINATION; REACTIVITY

Citation Formats

Li, Z.S., Fang, F., and Cai, N.S. CO{sub 2} capture from flue gases using three Ca-based sorbents in a fluidized bed reactor. United States: N. p., 2009. Web. doi:10.1061/(ASCE)EE.1943-7870.0000066.
Li, Z.S., Fang, F., & Cai, N.S. CO{sub 2} capture from flue gases using three Ca-based sorbents in a fluidized bed reactor. United States. doi:10.1061/(ASCE)EE.1943-7870.0000066.
Li, Z.S., Fang, F., and Cai, N.S. 2009. "CO{sub 2} capture from flue gases using three Ca-based sorbents in a fluidized bed reactor". United States. doi:10.1061/(ASCE)EE.1943-7870.0000066.
@article{osti_21197791,
title = {CO{sub 2} capture from flue gases using three Ca-based sorbents in a fluidized bed reactor},
author = {Li, Z.S. and Fang, F. and Cai, N.S.},
abstractNote = {Abstract: Experiments of CO{sub 2} capture and sorbent regeneration characteristics of limestone, dolomite, and CaO/Ca{sub 1}2Al{sub 14}O{sub 3}3 at high temperature were investigated in a thermogravimetric analyzer (TGA) and a fluidized bed reactor. The effect of reactivity decay of limestone, dolomite, and CaO/Ca{sub 12}Al{sub 14}O{sub 3}3 sorbents on CO{sub 2} capture and sorbent regeneration processes was studied. The experimental results indicated that the operation time of high efficient CO{sub 2} capture stage declined continuously with increasing of the cyclic number due to the loss of the sorbent activity, and the final CO{sub 2} capture efficiency would remain nearly constant, due to the sorbent already reaching the final residual capture capacity. After the CO{sub 2} capture step, the Ca-based sorbents need to be regenerated to be used for a subsequent cycle, and the multiple calcination processes of Ca-based sorbent under different calcination conditions are studied and discussed. Reactivity loss of limestone, dolomite and CaO/Ca{sub 12}Al{sub 14}O{sub 3}3 sorbents from a fluidized bed reactor at both mild and severe calcination conditions was compared with the TGA data. At mild calcination conditions, TGA results of sorbent reactivity loss were similar to the experimental results of fluidized bed reactor for three sorbents at 850 degrees C calcination temperature, and this indicated that TGA experimental results can be used as a reference to predict sorbent reactivity loss behavior in fluidized bed reactor. At severe calcination condition, sorbent reactivity loss behavior for limestone and dolomite from TGA compare well with the result from a fluidized bed reactor.},
doi = {10.1061/(ASCE)EE.1943-7870.0000066},
journal = {Journal of Environmental Engineering (New York)},
number = 6,
volume = 135,
place = {United States},
year = 2009,
month = 6
}
  • The cyclic CO{sub 2} capture and CaCO{sub 3} regeneration characteristics in a small fluidized bed reactor were experimentally investigated with limestone and dolomite sorbents. Kinetic rate constants for carbonation and calcination were determined using thermogravimetric analysis (TGA) data. Mathematical models developed to model the Ca-based sorbent multiple cycles of CO{sub 2} capture and calcination in the bubbling fluidized bed reactor agreed with the experimental data. The experimental and simulated results showed that the CO{sub 2} in flue gases could be absorbed efficiently by limestone and dolomite. The time for high-efficiency CO{sub 2} capture decreased with an increasing number of cyclesmore » because of the loss of sorbent activity, and the final CO{sub 2} capture efficiency remained nearly constant as the sorbent reached its final residual capture capacity. In a continuous carbonation and calcination system, corresponding to the sorbent activity loss, the carbonation kinetic rates of sorbent undergoing various cycles are different, and the carbonation kinetic rates of sorbent circulating N times in the carbonation/calcination cycles are also different because of the different residence time of sorbent in the carbonator. Therefore, the average carbonation rate was given based on the mass balance and exit age distribution for sorbent in the carbonator. The CO{sub 2} capture characteristics in a continuous carbonation/calcination system were predicted, taking into consideration the mass balance, sorbent circulation rate, sorbent activity loss, and average carbonation kinetic rate, to give useful information for the reactor design and operation of multiple carbonation/calcination reaction cycles. 27 refs., 15 figs., 1 tab.« less
  • Coal fired utility boilers are the largest anthropogenic source of mercury release to the atmosphere, and mercury abatement legislation is already in place in the USA. The present study aimed to rank low cost mercury sorbents (char and activated carbon from the pyrolysis of scrap tire rubber and two coal fly ashes from UK power plants) against Norit Darco HgTM for mercury retention by using a novel bench-scale reactor. In this scheme, a fixed sorbent bed was tested for mercury capture efficiency from a simulated flue gas stream. Experiments with a gas stream of only mercury and nitrogen showed thatmore » while the coal ashes were the most effective in mercury capture, char from the pyrolysis of scrap tire rubber was as effective as the commercial sorbent Norit Darco HgTM. Tests conducted at 150{sup o}C, with a simulated flue gas mix that included N{sub 2}, NO, NO{sub 2}, CO{sub 2}, O{sub 2}, SO{sub 2} and HCl, showed that all the sorbents captured approximately 100% of the mercury in the gas stream. The introduction of NO and NO{sub 2} was found to significantly improve the mercury capture, possibly by reactions between NOx and the mercury. Since the sorbents' efficiency decreased with increasing test temperature, physical sorption could be the initial step in the mercury capture process. As the sorbents were only exposed to 64 ng of mercury in the gas stream, the mercury loadings on the samples were significantly less than their equilibrium capacities. The larger capacities of the activated carbons due to their more microporous structure were therefore not utilized. Although the sorbents have been characterized by BET surface area analysis and XRD analysis, further analysis is needed in order to obtain a more conclusive correlation of how the characteristics of the different sorbents correlate with the observed variations in mercury capture ability. 34 refs., 8 figs., 6 tabs.« less
  • Both experimental tests and numerical simulations were conducted to investigate the fluidization behavior of a solid CO 2 sorbent with a mean diameter of 100 μm and density of about 480 kg/m, which belongs to Geldart's Group A powder. A carefully designed fluidized bed facility was used to perform a series of experimental tests to study the flow hydrodynamics. Numerical simulations using the two-fluid model indicated that the grid resolution has a significant impact on the bed expansion and bubbling flow behavior. Due to the limited computational resource, no good grid independent results were achieved using the standard models asmore » far as the bed expansion is concerned. In addition, all simulations tended to under-predict the bubble size substantially. Effects of various model settings including both numerical and physical parameters have been investigated with no significant improvement observed. The latest filtered sub-grid drag model was then tested in the numerical simulations. Compared to the standard drag model, the filtered drag model with two markers not only predicted reasonable bed expansion but also yielded realistic bubbling behavior. As a result, a grid sensitivity study was conducted for the filtered sub-grid model and its applicability and limitation were discussed.« less