Search

Highlights • A lab.-scale twin bubbling fluidized-bed CO 2 capture system has been developed. • Two kinds of silica-PEI adsorbents have been evaluated in a continuous way. • The CO 2 removal efficiency of above 80% was achieved. • The dynamic sorption capacity of above 6.0 wt.% was achieved. Abstract In this study, a lab.-scale twin bubbling fluidized-bed system (TBS) has been used continuously to test the performance for CO 2 adsorption of silica-PEI (S.PEI) adsorbents, containing 40 wt.% of PEI, which were supplied by the University of Nottingham (UNOTT). The TBS comprises bubbling-bed adsorption and desorption reactors, a riser for pneumatic conveying of solids from the adsorption to the desorption reactor, and a cyclone for solid-gas separation. The adsorbent prepared using PEI with a molecular mass of 800 (S.PEI-0.8K) was a preliminarily tested for almost 24 h at the given operating conditions by varying the inlet sorbent/CO 2 mass ratio at the adsorber to analyse the CO 2 removal efficiency in the adsorption reactor and the dynamic sorption capacity of the adsorbent. A 180-h continuous test was then carried out by changing various experimental conditions such as the H 2 O concentration, reaction temperature, solid layer height, reaction gas flow rate, and inlet sorbent/CO 2 mass ratio at the adsorber using PEI with a molecular mass of 5000 (S.PEI-5K) adsorbent. In this test, a CO 2 removal efficiency of above 80% and a dynamic sorption capacity greater than 6.0 wt.% were achieved. [ABSTRACT FROM AUTHOR]

Abstract This study aims to optimize the oxy-circulating fluidized bed combustion (oxy-CFBC) process by reducing the amount of flue gas with high-purity carbon dioxide. To achieve this, the stable transition from air mode to oxy mode is tested and validated in a 0.1-MW oxy-CFBC test rig. The results prove that flue gas carbon dioxide separation can achieve 96 vol% (dry) through a stable transition from air mode to oxy mode. Moreover, flue gas production emitted in oxy mode is reduced to one fifth compared to air mode. The proven technologies and oxy-fuel combustion database from this test rig operating experience can be used as empirical operating parameters for the next steps such as demonstration and commercial-scale operation. Highlights • The oxy-circulating fluidized bed combustion (oxy-CFBC) process is optimaized with the flexible flue gas recirculation. • High-purity-CO 2 flue gas is achieved by stable transition from air firing to oxy firing. • 0.1-MW th test results prove that flue gas CO 2 separation achieves 96 vol% (dry). • Optimal operating bed pressure drop conditions derived in oxy-CFBC. [ABSTRACT FROM AUTHOR]

SEWGS (Sorption Enhanced Water Gas Shift) process is one of options for pre-combustion CO 2 capture using dry absorbent and water gas shift catalyst. In this process, the thermodynamic equilibrium in the shift reaction can be enhanced to give more hydrogen yield by adding a CO 2 absorbent into the shift reactor. Total integrated system consists of coal gasifier, hot gas clean-up process (two interconnected fluidized bed desulfurizer), and one loop SEWGS process. In this presentation, continuous operation results of the hot gas clean-up process and one loop SEWGS process using dry absorbents at high temperature and pressure conditions were discussed. Dry absorbents (for desulfurization, CO 2 absorption) were produced by KEPCO RI (Korea Electric Power Corporation Research Institute) by means of spray-drying method. Continuous operation was performed at high pressure (21 bar for gasifier, 20 bar for hot gas clean-up process, and 18 bar for SEWGS process) and reaction temperature was 550 o C for desulfurizer and 236 o C for SEWGS reactor. Totally integrated operation was maintained up to 50 hours. We could get high sulfur capture efficiency (99.6%) in the desulfurizer, high CO conversion (98.9%) and CO 2 capture efficiency (98.0%) in the SEWGS reactor. [ABSTRACT FROM AUTHOR]

This study reports the performance of base-impregnated silica and activated carbons supplied by the University of Nottingham (UNOTT) have been tested in the bubbling fluidized-bed reactor and the two interconnected bubbling fluidized-beds in a continuous system. UNOTT has published several papers with polyethyleneimine (PEI)-silica sorbents using a bubbling fluidized-bed reactor, reporting that the average working capacity was around 8.0 wt.% and the regeneration heat was around 3.3 GJ/tCO 2 based on the cycle tests. In order to verify the performance of this silica adsorbent and to draw comparison with activated carbons that potentially offer have lower regeneration energies, KIER has carried out cycle experiments using a bubbling fluidized bed reactor and also used a continuous CO 2 capture system which consists of a bubbling fluidized-bed-type absorption and regeneration reactors. Further, the sorption characteristics, including equilibrium capacity, kinetics, surface area, pore size distribution, were determined using a volumetric (BET) and a gravimetric (MSB, magnetic suspension balance methods. The sorption mechanism of CO 2 on the sorbent surface was investigated by in situ FT-IR. The optical, physical and chemical characteristics were examined by SEM- EDAX, TGA before and after the sorption - desorption cyclic tests. Particle size distribution of the sorbent was also analyzed by laser diffraction particle size analyzer. [ABSTRACT FROM AUTHOR]

In this study, thermal efficiency of power plant has been evaluated by integrating the KIER-developed dry-sorbent CO 2 capture process (KIERDRY) with a pulverized coal-fired power plant using a commercial simulator, gPROMS. A simple basic KIERDRY model has been developed and connected it to PCPP (Pulverized Coal Power Plant) example in gCCS, a system modelling tool for support of design and operating decisions across the CCS chain. The PCPP capacity of 500 MWe and the KIERDRY capacity of 150 MW (125 tonCO 2 /hr based on captured amount) have been set as a base case. We consider HP steam(307 o C, 31 bar) and IP steam(461 o C, 14∼14.6 bar) as the utility steam of a regenerator in KIERDRY since the steam condition of a regenerator has been set to approximately 14.6∼15 bar, saturated. Totally 5 cases have been evaluated: (1-1) Use HP steam, use condensate to make a process steam, and return to condensate(1 bar); (1-2) Use HP steam and return to 5th feed water heater(12 bar); (2-1) Use IP steam, use condensate to make a process steam, and return to condensate(1 bar); (2-2) Use IP steam and return to 5th feed water heater(12 bar); (2-3) Use IP steam, do additional heat integration by preheating dry sorbents at loop-seal, and return to 5th feed water heater(12 bar). As a result, the condensate generated at the regenerator should be returned to the power plant rather than used to make a process steam, which is supplied as a reactant for the carbonation reaction. Based on several case studies, the reduction of the power output of the PCPP with KIERDRY has been varied from 29.2 MWe(minimum penalty) to 71.7 MWe(maximum penalty). Thus, it can be concluded that the energy penalty of KIERDRY has been significantly reduced by how heat has been integrated with PCPP. [ABSTRACT FROM AUTHOR]

Abstract: Carbon dioxide capture system using dry regenerable K-based sorbents has been developed by Korea Institute of Energy Research (KIER) and Korea Electric Power Research Institute (KEPRI). In late 2009, we installed a 0.5 MWe-scale CO2 capture pilot plant at Hadong coal-fired power plant in Korea. The pilot plant consists of a transport fluidized-bed carbonator for CO2 sorption, cyclones for separating gas and solid, a bubbling fluidized-bed regenerator for sorbent regeneration, and a bubbling fluidized-bed sorbent cooler for sorbent cooling. The footprint of the pilot plant was 6 m x 10 m and the location of that was after Gas Gas Heater of the power plant. Until now, we have performed 100-day operation campaigns to find out the optimum operating conditions and the scale-up factors for 10 MWe-scale capture process. In the operation campaigns, several operating variables such as the moisture content in the flue gas, the solid hold-up in a carbonator, the solid circulation rate between a carbonator and a regenerator, and the reaction temperatures have been changed in order to investigate the effect of those variables on CO2 capture and to derive the scale-up factors. It has been proved that above 80% of CO2 removal for 50-hour continuous operation was possible at the optimum operating conditions. At the same time, we set the small scale unit which consists of two bubbling beds for carbonation and regeneration in order to investigate the effect of the H2O partial pressure in the regenerator on CO2 removal. The CO2 removal in the carbonator increased as the steam mole fraction in the fluidization gas of the regenerator increased, although the content of H2O, which is a product component in the regenerator, increased. We proved that the K2CO3 1.5H2O has been formed in the regenerator by the XRD analysis and TGA analysis of the regenerated sorbent. The formation of K2CO3 1.5H2O makes the carbonation reaction more active so that the CO2 removal increased. It is also verified that high-concentrated CO2 can be recovered when 100% of H2O has been introduced as a steam phase to the regenerator. Thus, we also install the steam injection line to the regenerator in the 0.5 MWe-scale pilot plant. During 100-day operation campaign, we also tested high-concentrated CO2 recovery by introducing 100% of H2O as a steam phase to the regenerator. [Copyright &y& Elsevier]

Abstract: The mass produced K2CO3/Al2O3 sorbents were tested for their CO2 sorption capacity by a 2000Nm3/h (0.5MW) CO2 capture pilot plant, which was built for unit 3 of Hadong thermal power station in 2010. After the commissioning, CO2 capture pilot plant was tested with the flue gas from the power station for 60days. To assess the effect of SO x in the flue gas of coal-fired power plant on the sorbent, the new and used K2CO3/Al2O3 sorbents were analyzed by FE-SEM, IC, EPMA, XRD and XPS. The results show that SO x of 10–40ppm in flue gas was reacted with K2CO3, but not with any other support materials, and formed K2SO4. And also, it is proved that the formed K2SO4 was quite stable in the range of 180–550°C. [Copyright &y& Elsevier]

Abstract: Korea Institute of Energy Research (KIER) and Korea Electric Power Research Institute (KEPRI) have developed the carbon dioxide (CO2) capture system using dry regenerable sorbents since 2002. The principle of the CO2 capture with regenerable solid sorbents is the reversible reaction between potassium carbonate and potassium bicarbonate in a thermal-swing process. Based on this reaction, we developed a bench scale unit (BSU) which treated 100 Nm3/h of flue gas in late 2006. The BSU consisted of a transport fluidized-bed carbonator, cyclones, a loop-seal, and a bubbling fluidized-bed regenerator. We have tested the BSU facility using a slip stream of the real flue gas from a coal-fired circulating fluidized bed combustor located at KIER in order to check the performance of CO2 removal, the stability of operation. The results showed that more than 80% of CO2 removal had been maintained during more than 50 hour continuous operation and its maximum reached at the 85% level. Those results indicated that the CO2 capture system using solid sorbents developed here could be applied to coal-fired power plant. In the meanwhile, we set the small scale unit which consists of two bubbling beds for carbonation and regeneration in order to investigate the effect of several operating variables on the CO2 removal. The performance of the small scale unit was investigated through the continuous operation with solid circulation under the same experimental conditions as the BSU facility. The CO2 removal of the small scale unit was reached at the 83% level with the inlet CO2 concentration of 10 vol.%. The CO2 removal increased as the water vapor content in the inlet flue gas stream, regeneration temperature, and solid circulation rate increased while it decreased as the gas velocity of the carbonator and carbonation temperature increased. It was found that the performance of the CO2 removal was very sensitive to the water vapor content in the inlet gas stream and the gas velocity of the carbonator (gas-solid contact time in the carbonator). The construction of 0.5 MW scale pilot plant based on the results of BSU at KIER has been finished in late 2009 at the Hadong Coal-Fired Power Plant, Korea Southern Power Company. The overall performance of pilot plant showed very promising and its CO2 capture performance reached at the 85% level. A 10 MW scale CO2 capture plant next development step after 0.5 MWe at the Hadong Coal-Fired Power Plant will be started to construct at the same site in late 2011. [Copyright &y& Elsevier]

Abstract: Korea Institute of Energy Research (KIER) and Korea Electric Power Research Institute (KEPRI) have been developing a CO2 capture technology using dry sorbents. The CO2 removal in dry sorbent CO2 capture system consists of two reactors for carbonation and regeneration. We used dry sorbent manufactured by spray-drying method contains potassium carbonate, which was supplied by KEPRI in order to investigate the sorbent performance in continuous operation mode with solid circulation between a fast fluidized bed type carbonation reactor (13.5 m tall pipe of 0.075 m i.d.) and a bubbling fluidized bed type regeneration reactor (2 m tall bed of 0.25 m i.d.). We used the real flue gas from 2MW coal-fired circulating fluidized bed combustor to check possibility of deactivation of dry sorbent by contaminants such as SO x and NO x in the real flue gas for the 100 Nm3/hr of flue gas treatment facility. The residence time of the dry sorbents was about 3 seconds and 15 minutes in the carbonation reactor and the regeneration reactor, respectively. The CO2 removal during 2 hrs in the whole experiments and the average CO2 removal was above 70%. From the experiment, it was revealed that the removal of heat of sorption in the carbonation reactor was important to increase CO2 removal. During the experiments continuous and smooth operation were accomplished with solid circulation between two reactors. These results indicate that CO2 capture process using potassium carbonate solid sorbent is applicable for CO2 capture in the coal-fired flue gas. [Copyright &y& Elsevier]

CO2 capture from flue gas using a sodium-based solid sorbent was investigated in a bubbling fluidized-bed reactor. Carbonation and regeneration temperature on CO2 removal was determined. The extent of the chemical reactivity after carbonation or regeneration was characterized via 13C NMR. In addition, the physical properties of the sorbent such as pore size, pore volume, and surface area after carbonation or regeneration were measured by gas adsorption method (BET). With water vapor pretreatment, near complete CO2 removal was initially achieved and maintained for about 1–2min at 50°C with 2s gas residence time, while without proper water vapor pretreatment CO2 removal abruptly decreased from the beginning. Carbonation was effective at the lower temperature over the 50–70°C temperature range, while regeneration more effective at the higher temperature over the 135–300°C temperature range. To maintain the initial 90% CO2 removal, it would be necessary to keep the regeneration temperature higher than about 135°C. The results obtained in this study can be used as basic data for designing and operating a large scale CO2 capture process with two fluidized-bed reactors. [Copyright &y& Elsevier]

• Rice husk combustion was performed in a circulating fluidized bed system. • The single air-staging combustion can reduce NO concentration. • The single SNCR process increase in the CO emissions. • The combined air-staging and SNCR can reduce NO emissions. • The RHA recovered from secondary cyclone has completely amorphous silica ash. Rice husk ash produced from rice husk combustion consists of mainly amorphous SiO 2 , which has economic applications in industry. However, the combustion technology for rice husk attributes to crystallization of SiO 2 and environmental impacts associated with NOx emission as particulate matter precursors. In this study, the rice husk combustion in the circulating fluidized bed system was conducted to investigate the combustion characteristics, including temperature and pressure profiles, NO emissions combustion efficiency, and rice husk ash properties. The single and combined air-staging and selective non-catalytic reduction (SNCR) process was applied to suppress NO formation and reduce NO concentration, respectively. At air-staging combustion conditions of primary air/secondary air/tertiary air ratio (vol.%) of 60/10/30 for normalized stoichiometric ratio of 1.1, the synergetic effect was observed on the NO and CO emissions reduction compared to single NO reduction technologies. The highest combustion efficiency of 98.88 % was also found while rice husk ash was recovered as a completely amorphous form with low unburned carbon of 2.92 %. The combined air-staging and SNCR process in the circulating fluidized bed combustion of rice husk shows the technical feasibility to recover fully amorphous SiO 2 and reduce NO emission by 65.6 %. [ABSTRACT FROM AUTHOR]

• K-based sorbents with α -Al 2 O 3 shows better performance than that with γ -Al 2 O 3. • CO 2 capture efficiency from 60 to 90 wt.% and the dynamic sorption capacity from 3–7 wt.%. • CO 2 removal efficiency was not varied at the condition above H 2 O/CO 2 mole ratio = 1.5. • About 76% of CO 2 removed in mixing zone, highly dependent on solid hold-up. • All the experimental data were used for designing the 10 MWe-scale CO 2 capture plant. Three kinds of K 2 CO 3 -based solid sorbents was tested in a 0.5 MWe-scale test-bed, integrated with a real coal fired power plant. The test-bed, consisting of a fast fluidized-bed carbonator, a bubbling fluidized-bed regenerator and a bubbling fluidized-bed sorbent cooler, was installed beside a Unit #3 in a Hadong coal-fired power plant. The components of K 2 CO 3 -based solid sorbents were an active reaction component of K 2 CO 3 for CO 2 sorption with the supports including Al 2 O 3 for mechanical strength. Three different solid sorbents were differentiated depending on the amount of an active component (35 wt.% or 40 wt.%) and the different composition of Al 2 O 3 (alpha alumina or gamma alumina). CO 2 capture performance was evaluated in a test-bed at the same operating conditions for three kinds of solid sorbents, which showed better CO 2 capture performance with the solid sorbent with 40 wt.% than that with 35 wt.% one. Better performance with alpha alumina as a support was obtained as compared to that with gamma alumina. Additionally, the effect of water vapor to CO 2 mole ratio in a flue gas, solid hold-up in a mixing zone of a carbonator and the regeneration temperature on the CO 2 capture performance was analyzed. The experimental results in a test-bed was confirmed by analyzing the solid samples of after-carbonation and after-regeneration. The CO 2 capture efficiency in the carbonator was varied from 60 to 90% whereas the dynamic sorption capacity of the sorbents from 3–7 wt.% in relation with the kinds of sorbents and the operating conditions. All the experimental data was used to design the 10 MWe-scale pilot plant beside a Unit #8 in a Hadong coal-fired power plant. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) co-firing is a promising technology for reducing greenhouse gas emissions in coal-fired power plants. Prior to commercialization, an experimental study on coal–NH 3 co-firing in a pilot-scale circulating fluidized bed (CFB) combustion test rig was conducted for technical verification. The comprehensive combustion characteristics, including pollutant emission, combustion efficiency, and ash properties, of NH 3 co-firing with sub-bituminous coal in a CFB combustion test rig and the CO 2 reduction according to NH 3 co-firing ratios under two different injection positions (dense bed zone (DBZ) and wind box (WB) with primary air) were investigated. When NH 3 was injected at the DBZ, NO emissions decreased as the NH 3 co-firing ratio increased and CO emissions increased more rapidly than with only coal-fired combustion. Compared with only coal-fired combustion, a 25.4% NH 3 co-firing ratio at the WB position simultaneously reduced NO and CO concentrations, achieving the highest combustion efficiency without ash-related problems. However, N 2 O emissions increased by > 1.5 times, indicating the formation of N intermediates during NH 3 burning. Therefore, with minor retrofitting, coal–NH 3 co-firing at the WB position is a feasible solution for simultaneously reducing CO 2 , NO, and CO emissions in commercial CFB combustion plants. [Display omitted] • Coal and NH 3 co-firing was performed in a circulating fluidized bed combustion • NH 3 supply at the dense bed zone significantly increased the CO emission • NH 3 supply at the wind box simultaneously reduced NO and CO emissions • Combustion efficiency improved without ash-related problems • Total GHG emissions decreased as NH 3 co-firing ratio increased [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen carrier is applied to supply some O 2 in a biomass OCA-Oxy-CFBC. • CO emissions decrease to 59% when silica sand is replaced with iron ore. • Adding an oxygen carrier achieved an O 2 saving of 4.86% • CO 2 purity increased to 97.4% without reduction of combustion efficiency. A pure oxygen (O 2) supply for oxy-fuel combustion causes excessive power consumption and decreased net plant efficiency. The oxygen carrier-aided oxy-circulating fluidized-bed combustion (OCA-Oxy-CFBC) process can facilitate reduction in the O 2 supply requirement. Moreover, the use of an oxygen carrier, instead of silica sand, as bed materials may improve oxygen transport in the combustor, leading to a reduction in the pure O 2 supply required. This study aimed to investigate the effect of oxygen carrier addition on Oxy-CFBC characteristics, including temperature, pressure, solid suspension density, pollutant emissions, combustion efficiency, and O 2 reduction for stable operation. As an oxygen carrier, iron ore was introduced into the downcomer pipeline using a dedicated hopper during the biomass Oxy-CFBC process under low excess O 2 conditions. Although the O 2 concentration in the flue gas decreased by 1.7 vol%, the CO emissions decreased from 6.8 mg/MJ to 2.8 mg/MJ when the silica sand was replaced with 33 wt% iron ore. Furthermore, the CO 2 purity in the flue gas improved from 94.3 vol% to 95.7–97.4 vol% under a lower equivalence ratio (1.01–1.07) during stable OCA-Oxy-CFBC operation. Consequently, oxygen can be transported and supplied by adding an oxygen carrier during the biomass Oxy-CFBC operation, indicating O 2 savings of 4.86 % for the total amount of O 2 required. [ABSTRACT FROM AUTHOR]

A dry sorbent post-combustion CO 2 capture process using a circulating fluidized bed (CFB) was developed to a 10 MWe scale. Particle attrition is a major challenge for many CFBs owing to the loss of particles and increased operating costs. Furthermore, predicting and alleviating the rate of particle attrition in an entire CFB is difficult owing to limited information on attrition in the riser and cyclone. This study experimentally investigated particle attrition in risers and cyclones and the effect of system scale-up using CO 2 adsorbent particles used in a 10 MWe scale CFB. Experiments were conducted in two types of CFBs to measure the attrition rate in the riser and cyclone for 22 and 12 h for each experimental condition. To verify the scaled-up effect, internals were added to the riser to measure the effect of the surface-area-to-volume ratio. Correlations for the attrition rate of CO 2 adsorbent particles in riser and cyclone were proposed, and a model for the scale-up effect was suggested. In the 10 MWe scale system, particle attrition mainly occurred in the cyclone (58.0 %) and riser (37.3 %) according to the calculation, and the calculated overall attrition rate reasonably matched the operational data. Figure: (a) Calculated attrition rate of CO 2 adsorbent particles in the circulating fluidized bed of 10 MWe scale CO 2 capturing process, and (b) effect of cyclone inlet gas velocity on the particle attrition rate in cyclone. [Display omitted] • Particle attrition mainly occur in the cyclone and riser of a CFB. • Attrition rate in cyclone was proportional to the square of the gas velocity. • The top size of fines formed by attrition in riser increased with gas velocity. • Attrition rate in the riser increases by increasing surface area. • Correlation for particle attrition rate in the riser and cyclone are proposed. [ABSTRACT FROM AUTHOR]

Biomass combustion in the oxy-fuel circulating fluidized bed is a promising technology to maximize the negative carbon dioxide emission and reduce pollutants emission in power plants. However, biomass ash related behaviors under oxy-combustion with kaolin additives still lack sufficient information. In this study, kaolin was used as an additive to manage ash problems during oxy-biomass combustion in a 0.1 MW th circulating fluidized bed combustion facility. Kaolin was fed at ratios of kaolin/wood pellet (wt./wt.): 0.21 and 0.25 by separately feeding or pre-mixing, respectively. The sampled ashes were characterized using X-ray fluorescence and X-ray diffraction analysis. Additionally, the potassium capture performance, slagging and fouling indices, attrition characteristics, and strength were also evaluated. The results revealed that potassium capture performance was improved by up to 24% at the ratio of kaolin/wood pellet (0.25) and kalsilite (KAlSiO 4) within ash increased by adsorption on the metakaolin surface of gaseous potassium. The fouling formation decreased from 0.43 without kaolin to 0.07–0.15 with kaolin. In terms of oxy-fuel operation, SO 2 emission was decreased when kaolin used, performing a high CO 2 concentration of over 93 vol% and combustion efficiency of over 99%. • Ash related behaviors under oxy-biomass combustion with kaolin additive were studied. • Effects of different ratios of kaolin were evaluated in a 0.1 MW th Oxy-CFB test rig. • Potassium capture was improved by up 24% at kaolin/wood pellet (wt./wt.): 0.25. • CO 2 in flue gas was produced above 93 vol% with combustion efficiency >99%. • Oxy-biomass combustion in CFBC with kaolin supplement can be operated stably, maximizing the negative CO 2 reduction. [ABSTRACT FROM AUTHOR]

Oxy-combustion with a circulating fluidized bed (Oxy-CFBC) can facilitate the separation of high CO 2 concentration and reduce emissions by biomass co-firing. This study investigated Oxy-CFBC characteristics such as temperature, solid hold-up, flue gas concentrations including CO 2 , pollutant emissions (SO 2 , NO, and CO), combustion efficiency and ash properties (slagging, fouling index) with increasing input oxygen levels (21–29 vol%), and biomass co-firing ratios (50, 70, and 100 wt% with domestic wood pellet). The possibility of bio-energy carbon capture and storage for negative CO 2 emission was also evaluated using a 0.1 MW th Oxy-CFBC test-rig. The results show that combustion stably achieved with at least 90 vol% CO 2 in the flue gas. Compared to air-firing, oxy-firing (with 24 vol% oxygen) reduced pollutant emissions to 29.4% NO, 31.9% SO 2 and 18.5% CO. Increasing the biomass co-firing from 50 to 100 wt% decreased the NO, SO 2 and CO content from 19.2 mg/MJ to 16.1 mg/MJ, 92.8 mg/MJ to 25.0 mg/MJ, and 7.5 mg/MJ to 5.5 mg/MJ, respectively. In contrast to blends of sub-bituminous coal and lignite, negative CO 2 emission (approximately −647 g/kW th) was predicted for oxy-combustion only biomass. • Oxy-combustion with a 0.1 MW th CFB was operated. • Effect on the various O 2 concentrations and biomass firing ratios investigated. • Stable shift from air-to oxy-fired easily achieved above 90% (dry) CO 2 flue gas. • Oxy-fired NO and SO 2 emissions lower than those of air-fired. • CO 2 negative emission from biomass-only oxy-firing expected (−647 g CO 2 /kW th). [ABSTRACT FROM AUTHOR]

Attrition rate R a,j versus new stirring factor α new. • The new stirring factor α new was a key factor for jet attrition. • The α new fit well the effect of bed height on jet attrition. • The top size of fines formed by attrition increased with α new. • The attrition rate increased linearly with α new. Particle attrition is a major challenge when handling bulk solid materials with fluidized beds due to its ability to cause particle loss. Herein, the particle attrition induced by the gas jets on a perforated plate distributor in a bubbling fluidized bed was investigated for CO 2 adsorbent particles. An attrition tube, which used air as the fluidizing gas, was used as the fluidized bed. At a constant fluidizing velocity, the initial static bed height and orifice gas velocity were considered as variables. It was confirmed that abrasion dominated the particle attrition. The trend indicating the change in the maximum size of the particles (d pm,a) formed by attrition followed that of the attrition rate (i.e., the formation rate of fine particles via attrition). A new stirring factor that combined the model developed by Werther and Xi with the original stirring factor adequately explained the effect of the static bed height on both the attrition rate and d pm,a when the initial static bed height was greater than the length of the orifice gas jet that penetrated the bed. The attrition rate increased linearly with the new stirring factor. However, d pm,a increased exponentially with the new stirring factor. Relationships were successfully proposed to enable the estimation of the attrition rate and d pm,a for the CO 2 adsorbent particles. This study provided the evidence indicating the significance of the effect of bed height on particle attrition induced by the gas jet on the distributor. Moreover, proper models for correlating the attrition rate and the maximum size of the fine particles formed by attrition in the bubbling fluidized bed were provided. [ABSTRACT FROM AUTHOR]

This study aimed to provide a design and operational approach for a loop-seal, which is the heart of a circulating fluidized bed (CFB). Thousands of CFB systems use this non-mechanical valve to optimize performance by controlling the solids circulation rate while preventing gas mixing between reactors. Nevertheless, its design and operating guidance remains unclear because of its intricate flow characteristics, causing confusion in design and operation of the entire CFB. This study experimentally investigated the three most important elements while designing and operating loop-seal: conditions for initiating solids flow, the maximum obtainable solids flow rate, and quantitative control of solids flow rate. Experiments were conducted in a CFB, which simulated 3 MWth chemical looping combustion (CLC) system that is currently being developed. The onset of solids flow occurs when the gas drag force in horizontal passage overcomes the resistance force generated by the bed of particles. The maximum solids circulation rate was determined by solids height in the supply chamber and pressure around CFB loop. A correlation for quantitative control of solids flow in loop-seal was proposed by the relationship between the gas drag force and particle velocity. Finally, operational conditions for the loop-seal in 3 MWth CLC were proposed. Operating conditions of the loop-seal in 3 MWth chemical looping combustion system derived in this study. [Display omitted] • Flow characteristics in loop-seal was analyzed and design factors were confirmed. • Solid flow started after overcoming resistance force by solid in horizontal path. • Particle velocity in horizontal path increased linearly by drag force of gas. • Solid height in standpipe determined the maximum solid circulation rate. • 3 Nm3/hr of Q sup,in was required for solid circulation of 15 kg/s in 3 MWth CLC. [ABSTRACT FROM AUTHOR]

Cost effective nitrogen oxide (NO x) reduction technology is crucial for industries and power plants owing to the stringent environmental regulations to which industries and power plants must adhere. Herein, the aim was to optimize the operational conditions for NO x reduction in forest biomass using circulating fluidized bed combustion (CFBC) combined with air staging and flue gas recirculation (FGR). The profiles of temperature and solid suspension density in the combustor, NO and CO emissions, fuel-N conversion, slagging and fouling tendencies, and combustion efficiency were comprehensively observed during combustion. The main operating parameters are the FGR ratios, optimal ratios of air staging [Primary air (PA):Secondary air (SA):Tertiary air (TA)] and FGR, and supply height of TA in the combustor. Notably, under the optimal operational conditions (air staging ratio; PA:SA:TA = 70:10:30, FGR ratio; 8%, and TA supply height; 8.1 m), the NO and CO emissions were simultaneously reduced to 25.9% and 18.2%, respectively, compared with that for the base scenario which excluded air staging and FGR. Furthermore, a high combustion efficiency of 99.72% was maintained without any ash-related problems at well-controlled bed temperatures owing to the constant solid circulation afforded by FGR. A thorough analysis of the this literature has been performed to ensure that the commercialization of the combination of air staging and FGR in biomass CFBC plants is feasible, which could be an inexpensive option for NO reduction. [Display omitted] • Investigated the effects of air staging and flue gas recirculation (FGR) on NO reduction. • Air staging and FGR were optimized for circulating fluidized bed combustion. • Simultaneous reduction of 25.9% NO and 18.2% CO was achieved by air staging and FGR. • FGR can solve combustor temperature instability caused by air staging combustion. • A high combustion efficiency of 99.72% was reached without ashes-related issues. [ABSTRACT FROM AUTHOR]

For stable carbon capture utilization and storage, highly-pure CO 2 content and low pollutant emissions must be maintained throughout oxy-coal firing operation; however, studies on combining absorbent addition and oxidant staging combustion to eliminate simultaneous nitrogen oxides (NO, N 2 O) and sulfur dioxide (SO 2) have not been reported. Accordingly, the purpose of this study was to investigate the effects of oxidant staging and limestone addition on the reductions of NO, N 2 O, and SO 2 emissions in an oxy-circulating fluidized bed combustor at 25% and 31% input oxygen. The operating parameters considered in this study were: oxidant compositions; corresponding flow rate ratios; primary, secondary, and tertiary oxidants (PO, SO, and TO, respectively); TO supply heights; and limestone addition. The results revealed that compared to the TO supply heights, increasing TO flow rate was more effective at reducing the nitrogen oxide emissions. Under an optimal flow rate ratio (PO:SO:TO = 70:10:20) and TO height (6.4 m), NO, N 2 O, and SO 2 emissions were ≈7.4, 4.2 and 4.1 mg MJ−1, respectively. The increase in SO 2 emission caused by the application of oxidant staging could be effectively decreased by 60.6% without impacting combustion performance via limestone injection into the combustor; effectively facilitating the production of >86 vol% CO 2. These findings can serve as valuable references for future designs, and the efficient operation of oxy-coal combustion plants constructed at larger scales, thereby ensuring highly-pure CO 2 content and low pollutant emissions. • Explored staging combustion in oxy-circulating fluidized bed on emissions reductions. • Tertiary oxidant (TO) flow rate was more effective at reducing NO, N 2 O emissions. • Optimal ratio, TO height reduced NO, N 2 O, and SO 2 by 7.4, 4.2, and 4.1 mg MJ−1 • Limestone injection decreased SO 2 emissions by 60.6% without impacting performance. • Provides a valuable reference for future designs of oxy-coal combustion plants with the EHE. [ABSTRACT FROM AUTHOR]

[Display omitted] • The working capacity and stability of absorbent were studied for CO 2 capture. • MPS-supported epoxide-functionalization of PEHA absorbent was synthesized. • PO-PEHA/MPS adsorbent exhibited the working capacity of 1.8 mmol g−1 in 20 cycle. • When the adsorption time was reduced, the regeneration heat was 2.86 GJ tCO 2 -1. • Adsorbent that is regenerated in 100% CO 2 , not inert (N 2 , He) conditions was developed. N -functionalized solid adsorbents have been studied for post-combustion CO 2 capture. Most studies have focused only on the adsorption condition of the adsorbents. Few studies have focused on the regeneration condition of adsorbents. Regeneration is required under the condition of 100 % CO 2 for high-purity CO 2 separation. Regeneration under inert conditions such as N 2 or He, not under the condition of 100 % CO 2 regeneration are required additional cost for high-purity CO 2 separation. In this study, a macroporous silica (MPS) support, which combined a high surface area, large porosity and large pore volume, was selected as the support to achieve high CO 2 capture performance. Pentaethylenehexamine (PEHA) was selected because of its high amine content, high adsorption capacity, high thermal stability, and low cost. The epoxide functionalization of PEHA was used to suppress the urea formation under regeneration conditions. The working capacity and cyclic stability of epoxide functionalization of MPS-based PEHA adsorbents were investigated. A working capacity of 1.8 mmol g−1 was maintained by repeating adsorption and desorption experiments 20 times under an adsorption condition of 15 % CO 2 and a desorption condition of 100 % CO 2. Additionally, the stability of the adsorbent under a 100 % CO 2 regeneration condition was confirmed by maintaining the working capacity constant during 20 repeated adsorption and desorption cycle experiments. When the adsorption time was reduced to minimize H 2 O adsorption, the regeneration heat of the adsorbent was 2.86 GJ tCO 2 -1. These results demonstrated that the regeneration ability was excellent under the condition of 100 % CO 2 , which is the actual process application condition. This approach is promising for industrial applications of CO 2 capture technology. [ABSTRACT FROM AUTHOR]

Attrition rate versus static bed height. [Display omitted] • The rate of attrition (RA) by bubbles related with RA by gas jets. • An equation on top size of particles (TSP) formed by attrition was proposed. • Bed heights existed for minimum RA and TSP formed by attrition. Particle attrition induced by bubbles in a bubbling fluidized bed was investigated with CO 2 adsorbent particles (0.128 mm in diameter, 1770 kg/m3 in apparent density). The theoretical relationship between the rate of attrition by gas jets on the perforated plate distributor (R a,j) and the rate of attrition by bubbles (R a,b) in the bed was revealed that the rate constant of attrition by bubbles (K a,b) was the product of the rate constant of attrition by gas jets (C a) and dimensionless particle diameter (d pbc). An attrition tube (0.035 m-i.d.) using the perforated-plate distributor designed for reducing the attrition by gas jets was employed as the fluidized bed, and the air as the fluidizing gas. The mode of attrition by bubbles was identified as abrasion. The rate of attrition by bubbles (R a,b) was linearly proportional to the power given to the bed solids by bubbles. The top size of the fine particles formed by attrition (d pm,ab) increased exponentially with an increase of bed mass and gas velocity. The effects of temperature, pressure, and area of internal surface contacting particle bed on the R a,b and d pm,ab were negligible under the tested condition. Empirical relationships on R a,b and d pm,ab were proposed based on the experimental data. When both jet and bubble attrition were significant, there existed the static bed heights that gave respectively the minimum attrition rate and the minimum of the top size of fine particles formed by attrition. Each optimal static bed heights increased with an increase of the orifice jet velocity of the perforated plate distributor. [ABSTRACT FROM AUTHOR]

The Potassium-based dry sorbent CO 2 capture process can selectively capture CO 2 from flue gas without toxicity. In this study, the optimization of regeneration condition was investigated to pursue economical CO 2 capture process in a circulated fluidized bed reactor as most energy for CO 2 capture is consumed in the sorbent regeneration. One important part for CO 2 capture process is to produce highly concentrated CO 2 during the sorbent regeneration in the conditions of CO 2 rich with a presence of H 2 O, which thermodynamically reduces the sorbent regeneration efficiency at low temperature. This could be overcome by increasing the regeneration temperature although the sorbent regeneration energy increases. The dry sorbent performance in the carbonator was evaluated by changing the temperature, CO 2 and H 2 O concentration in the regenerator, which showed about 88% CO 2 removal efficiency and 5.6 wt% dynamic sorption capacity. The dry sorbent was sampled at each operating condition to confirm the dry sorbent performance, evaluated over CO 2 concentration. The optimal regeneration condition was obtained by considering CO 2 removal efficiency, dynamic sorption capacity and regeneration energy. Finally, the optimal regenerator temperature was determined to be approximately 468 K where the CO 2 capture process in the circulated fluidized bed reactor showed 95% for CO 2 purity. Image 1 • Highest CO 2 removal efficiency was obtained as 88% in a CFB reactor. • Effect of H 2 O during regeneration was negligible on sorbent performance. • Comparable sorbent performance observed even at high concentration CO 2 condition. • Optimal regenerator temperature was determined to be around 468 K. [ABSTRACT FROM AUTHOR]

Dry sorbent CO 2 capture process is a proven technology to remove CO 2 efficiently from flue gas. The current system was used to understand the effect of solid inlet height (H in) and horizontal heat transfer tubes on solid hydrodynamics in the fast fluidized bed (FFB). Also, the ranges of stable hydrodynamic conditions were visually confirmed at the varied H in , gas velocity (U g) and solid circulation rate (G s). The changes in the suspension density (ρ sus) during CO 2 carbonation reaction was experimentally measured and matched to the ρ sus at the specific gas velocity under no reaction bed. It showed that the ρ sus at the initial U g = 1.4 m/s under the reaction mode increased to that at 1.04 m/s along the bed due to the carbonation reaction. Heat transfer coefficients (HTC) were obtained during CO 2 carbonation operation over 80 h, which resulted in CO 2 removal efficiency (85%) and CO 2 purity (96%). Finally, the effect of ρ sus was determined to be the most significant factor on HTCs, ranged from 135 to 215 W/m2∙oC during the carbonation reaction. It indicated that the different local HTCs at different bed heights were observed at the carbonation or no reaction modes due to the exothermic reaction heat. Image 1 • Hydrodynamics in FB reactor during CO 2 carbonation reaction was investigated. • Over 80 h of carbonation reaction was conducted. • Above 84% average CO 2 removal efficiency with 95% CO 2 purity was achieved. • Suspension density and T cw in FB reactor were important factors determining HTC. • Higher HTC was ranged from 135 to 215 W/m2-oC at different conditions. [ABSTRACT FROM AUTHOR]