Simulated Flue Gas Conditions Research Articles

Evaluation of CO2 adsorption dynamics of polymer/silica supported poly(ethylenimine) hollow fiber sorbents in rapid temperature swing adsorption

Rapid temperature swing adsorption (RTSA) using polymer/silica supported amine hollow fiber sorbents is a new post combustion CO2 capture methodology that facilitates CO2 adsorption under nearly isothermal conditions with improved energy efficiency via heat integration. In this work, the dynamic CO2 adsorption characteristics of polymer/silica supported poly(ethylenimine) hollow fiber sorbents (CA-S-PEI-PI) are evaluated in a bench scale RTSA system. Non-isothermal fibers have breakthrough and pseudo-equilibrium CO2 capacities of 0.67mmol/g and 1.03mmol/g at 35°C, respectively, under humid simulated flue gas conditions (100% R.H.). Prolonged exposure of the fiber sorbents to water vapor enabled the breakthrough and pseudo-equilibrium CO2 capacities to increase by 60% and 43%, respectively. Upon the removal of the heat of adsorption by flowing cooling water in the bores of the fiber sorbents, there is a substantial increase in the CO2 breakthrough capacity, reaching 1.16mmol/g using simulated humid flue gases. The breakthrough capacity is found to increase 5% upon increasing the adsorption temperature from 35°C to at 45°C, suggesting improved mass transfer in the fiber sorbent at the higher temperature. The CO2 adsorption and desorption rates are shown to be very rapid, with CO2 breakthrough occurring in less than 72s and the majority of the adsorbed CO2 desorbing in 5min. Extensive cycling studies demonstrate that the CA-S-PEI-PI sorbents have good dynamic swing capacities, stabilizing over 60 cycles. A newly developed rechargeable post-spinning amine infusion technique provides the feasibility of recovering the CO2 adsorption performance of deactivated CA-S-PEI-PI fiber modules, by allowing for straightforward re-infusion of PEI into the deactivated sorbents. Amine-incorporated hollow fiber sorbents have good potential for practical use as scalable, adsorbing heat-exchangers.

Removal of elemental mercury by clays impregnated with KI and KBr

The removal of elemental mercury (Hg0) by KI and KBr modified clays (KI-clays and KBr-clays) was studied under simulated flue gas conditions. The physicochemical properties of these catalysts were investigated by a variety of characterization methods. The effects of KI and KBr loading, adsorption temperatures and the flue gas components (such as O2, SO2 and H2O (g)) on Hg0 removal efficiency were investigated. A pseudo-second-order model simulation was also introduced to reveal the mechanisms of Hg0 removal. The results showed that the Hg0 removal efficiency for the clays was significantly enhanced by KI or KBr modification, and the KI-clays performed much better than the KBr-clays in terms of Hg0 removal under the same conditions. An increase in KI or KBr loading and adsorption temperatures improved the Hg0 removal efficiency, which indicated that chemisorption occurred. The presence of O2 and SO2 promoted Hg0 removal, whereas the presence of H2O inhibited Hg0 removal by these modified clays. The formation of I2 from the reaction (2KI+1/2O2↔I2+K2O) was considered to be an important step in the chemisorption of Hg0 on the surfaces of the KI-clays. The lower extent of Hg0 removal exhibited by the KBr-clays than by the KI-clays was due to the difficulty of Br2 formation on the surfaces. The pseudo-second-order model was demonstrated to simulate with the removal of Hg0 by KI-clays and KBr-clays well. The KI-clays displayed much a higher of the initial adsorption rate (H) and Hg0 removal capacity (qe) than the KBr-clays under the same conditions, which demonstrated that KI-clays are more active than KBr-clays with respect to Hg0 removal.

Absorption of Carbon Dioxide in Aqueous Morpholine Solutions

Mass transfer coefficients for CO2 absorption by aqueous 4 M, 5 M, and 6 M morpholine (MOR) solution at 30 °C under carbon loaded conditions are presented. Measurements were performed using a wetted wall column under simulated flue gas conditions for postcoal combustion CO2 capture. Similar to other major amines, it was found that the amine concentration has a positive impact on the overall mass transfer coefficient at lean loading while at rich loading the difference between each concentration is within experimental uncertainty. It was also observed that the viscosity increases more dramatically with amine concentration in MOR than monoethanolamine (MEA) within the studied carbon loading range due to different hydrogen-bond structures. The calculation of physical mass transfer resistance in the liquid film revealed that the reaction resistance dominates at lean loadings while the physical mass transfer takes a large portion at the rich loadings. The rate constant of the pseudo-first-order reaction of MOR...

An enhanced plasma-catalytic method for DeNOx in simulated flue gas at room temperature

A combined adsorption-discharge plasma process was proposed for DeNOx in simulated flue gas at room temperature. The conversion of NOx to N2 could achieve 95% in the process of NOx storage and reduction with NH3 under simulated flue gas conditions.

Activated coke impregnated with cerium chloride used for elemental mercury removal from simulated flue gas

Gas-phase elemental mercury (Hg0) removal by activated coke impregnated with cerium chloride (AICC) was studied under simulated flue gas conditions. Brunauer–Emmett–Teller (BET), X-ray diffractogram (XRD), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) analyses were used to characterize the samples. The effects of CeCl3 loading values, reaction temperatures and individual flue gas components including O2, NO, SO2 and H2O (g) on Hg0 removal efficiency of AICC samples were investigated. Results showed that Hg0 removal efficiency of AC was significantly enhanced by CeCl3. The optimal CeCl3 loading value and reaction temperature was around 6% and 170°C, respectively. Additionally, the experiment results of effects of flue gas components on Hg0 removal efficiencies showed that when O2 was present in the flue gas, NO and SO2 were observed to promote Hg0 oxidation. However, in the absence of O2, SO2 showed an insignificant inhibition on Hg0 removal. Furthermore, when H2O was added into the flue gas, the Hg0 removal capacity had a slight declination. The analyses of XRD and XPS showed that CexOy and C–Cl were generated on the surface of AICC and those active elements had remarkably positive effects on the Hg0 removal. The reaction mechanism indicated that Hg0 oxidation was achieved through two pathways: one was that Hg0 bond with CeO2 and was converted by the catalytic oxidation of valence variable cerium; the other was that Hg0 reacted with C–Cl on the sample and was oxidized favored by chloride presence. And according to Hg 4f XPS analysis, the mercury on the surface of AICC was mainly in the form of mercuric oxide (HgO) and mercuric chloride (HgCl2).

The effects of Cu/HZSM-5 on combined removal of Hg0 and NO from flue gas

The combined removals of Hg0 and NO over zeolite (HZSM-5 was chosen to use) modified by copper (Cu/HZSM-5) catalysts were studied under different simulated flue gas conditions. Compared with HZSM-5, Cu/HZSM-5 showed higher activity and performed a synergetic effect for the Hg0 and NO removal at 250°C. But the excess of copper could cause destruction of the thin pore walls and blocking of internal porosity of the catalyst leading to decrease of the activity. A comparison between Cu/HZSM-5 of different silica to alumina ratios (SiO2/Al2O3 ratio) was also performed. The highest NO and Hg0 conversions were observed over the lowest SiO2/Al2O3 ratio. In addition, the experimental results indicated that there was a synergetic effect between HZSM-5 and copper for the removal of NO and Hg0 by accelerating the intermediate formation (NO2) and by strengthening the adsorption NO and Hg0 on the catalyst surface under the reaction conditions. Moreover, the effects of individual flue gas components on the removals of Hg0 and NO were examined. O2 in the flue gas had a positive effect on both Hg0 and NO removals. However, the presence of H2O and SO2 inhibited both Hg0 and NO removals.

Investigation of Porous Silica Supported Mixed-Amine Sorbents for Post-Combustion CO2 Capture

Prospective post-combustion CO2 capture sorbents were prepared by the immobilization of a low-molecular-weight, branched polyethyleneimine (PEI) and 3-(aminopropyl)triethoxysilane (APTES) within a commercially available porous PQ Corporation CS-2129 silica support to investigate (i) CO2 adsorption properties of the supported mixed-amine (PEI+APTES) sorbents in both pure CO2 environments and simulated flue gas conditions, (ii) their thermal and hydrolytic stability over numerous adsorption and desorption cycles, and (iii) their equilibrium and kinetic adsorption behavior. Initial CO2 adsorption–desorption measurements via thermogravimetric analysis (TGA) were conducted in pure CO2 to measure dry, near-equilibrium CO2 adsorption capacities, together in calculating amine efficiencies, which was recognized in being a meaningful criterion in evaluating sorbent performance for selecting the “most favorable” mixed-amine (PEI+APTES) composition. The as-prepared materials containing various weight ratios of PEI to...

Removal of Gas-Phase Elemental Mercury in Flue Gas by Inorganic Chemically Promoted Natural Mineral Sorbents

A variety of natural mineral sorbents were synthesized and tested on a lab-scale fixed-bed system to evaluate mercury removal efficiencies under a simulated flue gas condition that contains 84% N2, 4% O2, and 12% CO2 in volume fraction. Three types of natural minerals, bentonite (Ben), mordenite (Mor), and attapulgite (Atp), were selected as raw sorbents, and several chemical promoters, such as CuCl2, NaClO3, KBr, and KI, were employed to enhance mercury removal abilities of the raw sorbents. The physical-chemical characteristics of these minerals were analyzed by an X-ray diffractometer (XRD), an accelerated surface area and porosimeter (ASAP) using the N2 isotherm adsorption/desorption method, and X-ray fluorescence (XRF) spectrometry. The mercury concentration was detected continuously using a VM3000 online mercury analyzer. The results showed that CuCl2-impregnated Atp (Cu-Atp) and CuCl2-impregnated Ben (Cu-Ben) presented about 90% average Hg0 removal efficiencies at 120 °C, respectively. In addition, as the temperature increased, the removal efficiencies decreased. Although NaClO3-impregnated Atp showed an average Hg0 removal efficiency more than 90% at 120 °C, its performance was limited by the testing temperature, and that was probably due to the high iron oxide content in Atp. For the KI-impregnated sorbents, high mercury removal efficiencies could be observed, and the efficiencies increased steadily with the temperature increased from 70 to 150 °C. The three natural minerals presented poor adsorption abilities for bromine, which resulted in the disappointing mercury removal efficiencies. Generally, Cu-Atp, Cu-Ben, and KI-impregnated sorbents were promising cost-effective mercury sorbents.

Dynamic measurement of mercury adsorption and oxidation on activated carbon in simulated cement kiln flue gas

Mercury emissions from cement plants are being regulated by environmental agencies in most countries. Both dynamic mercury emissions in cement kiln systems and removal of mercury by sorbent injection require continuous mercury emission monitoring. Dry converters for total mercury measurements are still under development and are investigated in this work. A commercial red brass converter was tested at 180°C and it was found that the red brass chips work in nitrogen atmosphere only, but do not work properly under simulated cement kiln flue gas conditions. Test of the red brass converter using only elemental mercury shows that when HCl is present with either SO2 or NOx the mercury measurement after the converter is unstable and lower than the elemental mercury inlet level. The conclusion is that red brass chips cannot fully reduce oxidized mercury to elemental mercury when simulated cement kiln gas is applied. A sodium sulfite-based converter material was prepared by dry impregnation of sodium sulfite and calcium sulfate powders on zeolite pellets using water glass as binder. The sulfite converter works well at 500°C with less than 10ppmv HCl in the simulated cement kiln flue gas. The 95% response time of the sulfite converter is short and typically within 2min. Dynamic mercury adsorption and oxidation tests on commercial activated carbons Darco Hg and HOK standard were performed at 150°C using simulated cement kiln gas and a fixed bed reactor system. It is shown that the converter and analyzer system is capable of following the transient mercury outlet concentration in a satisfactory way. Suggestions for practical applications of the sulfite converter in both lab and cement plants are presented.

Mesoporous amine‐bridged polysilsesquioxane for CO2 capture

AbstractA novel class of amine‐supported sorbents based on amine‐bridged mesoporous polysilsesquioxane was developed via a simple one‐pot sol‐gel process. The new sorbent allows the incorporation of a large amount of active groups without sacrificing surface area or pore volume available for CO2 capture, leading to a CO2 capture capacity of 3.2 mmol g−1 under simulated flue gas conditions. The sorbent is readily regenerated at 100°C and exhibits good stability over repetitive adsorption‐desorption cycling. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd

Carbon Dioxide Capture by Functionalized Solid Amine Sorbents with Simulated Flue Gas Conditions

A novel solid amine sorbent was prepared using KIT-6-type mesoporous silica modified with tetraethylenepentamine (TEPA). Its adsorption behavior toward CO(2) from simulated flue gases is investigated using an adsorption column. The adsorption capacities at temperatures of 303, 313, 333, 343, and 353 K are 2.10, 2.29, 2.58, 2.85, and 2.71 mmol g(-1), respectively. Experimental adsorption isotherms were obtained, and the average isosteric heat of adsorption was 43.8 kJ/mol. The adsorption capacity increases to 3.2 mmol g(-1) when the relative humidity (RH) of the simulated flue gas reaches 37%. The adsorption capacity is inhibited slightly by the presence of SO(2) at concentrations lower than 300 ppm but is not significantly influenced by NO at concentrations up to 400 ppm. The adsorbent is completely regenerated in 10 min at 393 K and a pressure of 5 KPa, with expected consumption energy of about 1.41 MJ kg(-1) CO(2). The adsorption capacity remains almost the same after 10 cycles of adsorption/regeneration with adsorption conditions of 10 vol % CO(2), 100 ppm SO(2), 200 ppm NO, 100% relative humidity, and a temperature of 393 K. The solid amine sorbent, KIT-6(TEPA), performs excellently for CO(2) capture and its separation from flue gas.

Reaction Kinetics of CO2 Carbonation with Mg-Rich Minerals

Due to their low price, wide availability, and stability of the resulting carbonates, Mg-rich minerals are promising materials for carbonating CO(2). Direct carbonation of CO(2) with Mg-rich minerals reported in this research for the first time could be considerably superior to conventional liquid extraction processes from an energy consumption perspective due to its avoidance of the use of a large amount of water with high specific heat capacity and latent heat of vaporization. Kinetic models of the reactions of the direct CO(2) carbonation with Mg-rich minerals and within simulated flue gas environments are important to the scale-up of reactor designs. Unfortunately, such models have not been made available thus far. This research was initiated to fill that gap. Magnesium silicate (Mg(2)SiO(4)), a representative compound in Mg-rich minerals, was used to study CO(2) carbonation reaction kinetics under given simulated flue gas conditions. It was found that the chosen sorbent deactivation model fits well the experimental data collected under given conditions. A reaction order of 1 with respect to CO(2) is obtained from experimental data. The Arrhenius form of CO(2) carbonation with Mg(2)SiO(4) is established based on changes in the rate constants of the chosen deactivation model as a function of temperature.

High efficiency nanocomposite sorbents for CO2 capture based on amine-functionalized mesoporous capsules

A novel high efficiency nanocomposite sorbent for CO2 capture has been developed based on oligomeric amine (polyethylenimine, PEI, and tetraethylenepentamine, TEPA) functionalized mesoporous silica capsules. The newly synthesized sorbents exhibit extraordinary capture capacity up to 7.9 mmol g−1 under simulated flue gas conditions (pre-humidified 10% CO2). The CO2 capture kinetics were found to be fast and reached 90% of the total capacities within the first few minutes. The effects of the mesoporous capsule features such as particle size and shell thickness on CO2 capture capacity were investigated. Larger particle size, higher interior void volume and thinner mesoporous shell thickness all improved the CO2 capacity of the sorbents. PEI impregnated sorbents showed good reversibility and stability during cyclic adsorption–regeneration tests (50 cycles).

CO2 capture from flue gas using potassium-based dry regenerable sorbents

Abstract Dry regenerable sorbent technology is one of the emerging technologies as a cost-effective and energy-efficient technology for CO 2 capture from flue gas. Six potassium-based dry regenerable sorbents were prepared by spray-drying techniques. Their physical properties and reactivities were tested to evaluate their applicability to a fluidized-bed or fast transport-bed CO 2 capture process. Each sorbents contained 35 wt% of K 2 CO 3 . All sorbents were sufficient with either attrition resistance or reactivity, or both properties. Sorb KT-5 and KZ-5 sorbents satisfied most of the physical requirements for a commercial fluidized-bed reactor process along with good chemical reactivity. These sorbents had a spherical shape, an average size was 134, 121 μm, respectively. The particle size distribution of these two sorbents had the same range of 40–250 μm, and the bulk density of approximately 0.85 g/mL. The attrition index (AI) of Sorb KT-5 and Sorb KZ-5 reached below 3% compared to about 20% for commercial fluidized catalytic cracking (FCC) catalysts. CO 2 sorption capacity of Sorb KT-5 and Sorb KZ-5 was range of 6–10 wt% in the simulated flue gas condition. These sorbents showed almost-complete regeneration at temperatures less than 140 °C.

Gas-Phase Elemental Mercury Removal by CeO2 Impregnated Activated Coke

We have studied gas-phase elemental mercury (Hg0) capture by a CeO2 loaded activated coke (AC) using a laboratory-scale fixed-bed reactor under simulated flue gas conditions. Through systematic inv...

Bromine Chloride as an Oxidant to Improve Elemental Mercury Removal from Coal-Fired Flue Gas

The equilibria and kinetics of the reaction between bromine (Br(2)) and chlorine (Cl(2)) to form bromine chloride (BrCl) at various temperatures were determined. BrCl was employed to oxidize elemental mercury (Hg(0)) under simulated flue gas conditions. The removal of Hg(0) from the gas phase by a homogeneous gas-phase oxidation reaction and the heterogeneous reactions involving flyash were investigated. The second-order gas phase rate constant was determined to be 2.3(+/-0.2) x 10(-17) cm(3).molecules(-1).s(-1) at 373K. The reaction of Hg(0)/BrCl was significantly accelerated in the presence of flyash, and the estimated Hg(0) removal efficiency in the presence of 0.6 ppmv BrCl and 20 g/m(3) flyash was up to 90%. Unexpectedly, the major product was found to be HgCl(2), rather than HgBr(2), indicating that bromine in part acted as the accelerant in Hg(0) oxidation in BrCl/Br(2)/Cl(2) system by facilitating the formation of intermediates. As a result, bromine consumption is much less than if only bromine gas is utilized alone. These results were helpful not only for understanding the mechanism of Hg(0) removal in coal-fired flue gas but also in any atmosphere in which bromine and chlorine species coexist.

Effects of sulfate species on V2O5/TiO2 SCR catalysts in coal and biomass-fired systems

Sulfation occurs when commercial vanadia SCR catalysts are exposed to SO2-laden coal combustion flue gases. Effects of sulfation on the surface chemistry of vanadia/titania catalysts and SCR activity have not been adequately addressed in previously published work. In this work, in situ FTIR spectroscopy and post situ XPS investigations were performed during vanadia/titania catalyst sulfation under simulated coal combustion flue gas conditions. In situ FTIR spectroscopy combined with XPS analyses on fresh and sulfated TiO2, 2% and 5% V2O5/TiO2 indicate that sulfate does not form on vanadia sites but rather on titania sites. FTIR spectroscopy data show that sulfation inhibits NO adsorption in the presence of oxygen, but greatly enhances NH3 adsorption by generating additional Brønsted acid sites while reducing the concentration of Lewis acid sites. Observed increases in the intrinsic NO reduction activity of sulfated vanadia/titania catalysts (relative to fresh catalysts) are consistent with spectroscopy data showing that the sulfation enhances NO reduction activity by increasing the number of active sites without changing the activation energy or site acid strength.

Tubular ceramic-supported sol–gel silica-based membranes for flue gas carbon dioxide capture and sequestration

Pure, amine-derivatized and nickel-doped sol–gel silica membranes have been developed on tubular Membralox-type commercial ceramic supports for the purpose of carbon dioxide separation from nitrogen under coal-fired power plant flue gas conditions. An extensive synthetic and permeation test study was carried out in order to optimize membrane CO 2 permeance, CO 2:N 2 separation factor and resistance against densification. Pure silica membranes prepared under optimized conditions exhibited an attractive combination of CO 2 permeance of 2.0 MPU (1 MPU = 1 cm 3(STP) cm −2 min −1 atm −1) and CO 2:N 2 separation factor of 80 with a dry 10:90 (v/v) CO 2:N 2 feed at 25 °C. However, these membranes exhibited flux decline phenomena under prolonged exposure to humidified feeds, especially in the presence of trace SO 2 gas in the feed. Doping the membranes with nickel (II) nitrate salt was effective in retarding densification, as manifested by combined higher permeance and higher separation factor of the doped membrane compared to the pure (undoped) silica membrane after 168 h exposure to simulated flue gas conditions.

Cyclic Carbonation Calcination Studies of Limestone and Dolomite for CO2 Separation From Combustion Flue Gases

Naturally occurring limestone and dolomite samples, originating from different geographical locations, were tested as potential sorbents for carbonation/calcination based CO2 capture from combustion flue gases. Samples have been studied in a thermogravimetric analyzer under simulated flue gas conditions at three calcination temperatures, viz., 750°C, 875°C, and 930°C for four carbonation calcination reaction (CCR) cycles. The dolomite sample exhibited the highest rate of carbonation than the tested limestones. At the third cycle, its CO2 capture capacity per kilogram of the sample was nearly equal to that of Gotland, the highest reacting limestone tested. At the fourth cycle it surpassed Gotland, despite the fact that the CaCO3 content of the Sibbo dolomite was only 2/3 of that of the Gotland. Decay coefficients were calculated by a curve fitting exercise and its value is lowest for the Sibbo dolomite. That means, most probably its capture capacity per kilogram of the sample would remain higher, well beyond the fourth cycle. There was a strong correlation between the calcination temperature, the specific surface area of the calcined samples, and the degree of carbonation. It was observed that the higher the calcination temperature, the lower the sorbent reactivity. The Brunauer–Emmett–Teller measurements and scanning electron microscope images provided quantitative and qualitative evidences to prove this. For a given limestone/dolomite sample, sorbent’s CO2 capture capacity depended on the number of CCR cycles and the calcination temperature. In a CCR loop, if the sorbent is utilized only for a certain small number of cycles (<20), the CO2 capture capacity could be increased by lowering the calcination temperature. According to the equilibrium thermodynamics, the CO2 partial pressure in the calciner should be lowered to lower the calcination temperature. This can be achieved by additional steam supply into the calciner. Steam could then be condensed in an external condenser to single out the CO2 stream from the exit gas mixture of the calciner. A calciner design based on this concept is illustrated.

Removal and recovery of gas-phase element mercury by metal oxide-loaded activated carbon

The reusability of Co 3O 4 (AC-Co), MnO 2 (AC-Mn) and CuCoO 4 (AC-CC) loaded activated carbon (AC) and their element mercury removal efficiency had been studied using a laboratory-scale fixed-bed reactor under simulated flue gas conditions. Tests showed that spent AC-Co could be regenerated through heating at 673 K under N 2 atmosphere and the enrichment regenerated Hg 0 could be collected to eliminate the secondary pollution. Regenerated AC-Mn and AC-CC's Hg 0 removal efficiency decreased greatly due to AC's decomposition and MnO 2's crystal structure variation. Compared with AC and metal oxides, metal oxide-loaded AC had higher Hg 0 capture ability and capacity due to AC huge surface areas and lots of function groups. TGA analysis results showed that AC-Co and AC-Mn's HgO adsorptive capacity at 523 K reached 19.8 mg g −1 and 5.21 mg g −1, respectively. High loading values and adsorption temperatures were beneficial to AC-Co's Hg 0 removal efficiency. However, CuCoO 4 and MnO 2's AC decomposition ability had negative effect on AC-CC and AC-Mn's performance, respectively, especially at high adsorption temperatures and loading values. SO 2 tests showed that AC-CC had higher anti SO 2-poisoning ability than AC-Co and AC-Mn.