Dal-Hee Bae

Effect of temperature on reduction reactivity of oxygen carrier particles in a fixed bed chemical-looping combustor

In a chemical-looping combustor (CLC), gaseous fuel is oxidized by metal oxide particle, e.g. oxygen carrier, in a reduction reactor (combustor), and the greenhouse gas CO2 is separated from the exhaust gases during the combustion. In this study, NiO/bentonite particle was examined on the basis of reduction reactivity, carbon deposition during reduction, and NOx formation during oxidation. Reactivity data for NiO/bentonite particle with methane and air were presented and discussed. During the reduction period, most of the CH4 are converted to CO2 with small formation of CO. Reduction reactivity (duration of reduction) of the NiO/bentonite particle increased with temperature, but at higher temperature, it is somewhat decreased. The NiO/bentonite particle tested showed no agglomeration or breakage up to 900 ‡C, but at 1,000 ‡C, sintering took place and lumps of particles were formed. Solid carbon was deposited on the oxygen carrier during high conversion region of reduction, i.e., during the end of reduction. It was found that the appropriate temperature for the NiO/bentonite particle is 900 ‡C for carbon deposition, reaction rate, and duration of reduction. We observed experimentally that NO, NO2, and N2O gases are not generated during oxidation.

Carbon Deposition Characteristics and Regenerative Ability of Oxygen Carrier Particles for Chemical-Looping Combustion

For gaseous fuel combustion with inherent CO2 capture and low NOx emission, chemical-looping combustion (CLC) may yield great advantages for the savings of energy to CO2 separation and suppressing the effect on the environment. In a chemical-looping combustor, fuel is oxidized by metal oxide medium (oxygen carrier particle) in a reduction reactor. Reduced particles are transported to the oxidation reactor and oxidized by air and recycled to the reduction reactor. The fuel and the air are never mixed, and the gases from the reduction reactor, CO2 and H2O, leave the system as separate streams. The H2O can be easily separated by condensation and pure CO2 is obtained without any loss of energy for separation. In this study, NiO based particles are examined from the viewpoints of reaction kinetics, carbon deposition, and cyclic use (regenerative ability). The purpose of this study is to find appropriate reaction conditions to avoid carbon deposition and achieve high reaction rate (e.g., temperature and maximum carbon deposition-free conversion) and to certify regenerative ability of NiO/bentonite particles. In this study, 5.04% methane was used as fuel and air was used as oxidation gas. The carbon deposition characteristics, reduction kinetics and regenerative ability of oxygen carrier particles were examined by TGA (Thermal Gravimetrical Analyzer).

Drying Efficiency of Indonesian Lignite in a Batch-Circulating Fluidized Bed Dryer

This research explores the production of low-moisture, high-rank coal using a batch-type, laboratory-scale, circulating fluidized bed to dry low-rank Indonesian coal with a high moisture content of 35 wt%. The operation was performed using air as a fluidization gas in a riser (a 4-m-tall pipe with an inner diameter of 0.04 m) at a gas velocity ranging from 2.0 to 2.7 m/s and a riser temperature of 80 to 150°C. The electric heaters were installed in the upper part of a downcomer to prevent the condensation of the evaporated moist- ure. The drying rate of the coal was investigated in terms of the inlet gas temperature, the gas velocity, and the drying time in order to determine the optimum operating conditions. Changes in the moist- ure content of the coal, before and after the experiments, were char- acterized by a proximate analysis, an ultimate analysis, the higher heating value (HHV), the lower heating value (LHV), a particle size analysis, and by the equilibrium moisture content. The results show that 70 to 80 wt% (wet basis, wb) of the total moisture can be reduced when the gas velocity of the riser is 2.0 m/s and the gas temperature is 150°C. In experiments, a simple mathematical model based on the heat and mass balances and a thin-layer drying model were simul- taneously used to predict the drying behavior of coal under the given operating conditions. The results of the model are similar to those of the experiment.

Effects of Bed Insert Geometry and Shape of WGS Catalysts on CO Conversion in a Fluidized Bed Reactor for SEWGS Process

To enhance the performance of SEWGS system by holding the WGS catalyst in a SEWGS reactor using bed inserts, effects of insert geometry and shape of WGS catalysts on CO conversion were measured and investigated. Small scale fluidized bed reactor was used as experimental apparatus and WGS catalyst (particle and tablet) and sand were used as bed materials. The parallel wall type and cross type bed inserts were used to hold the WGS catalysts. The CO conversion with steam/CO ratio was determined based on the exit gas analysis. The measured CO conversion using the bed inserts showed high value comparable to physical mixing cases. Moreover, gas flow direction was confirmed by bed pressure drop measurement for each case. Most of input gas flowed through the catalyst side when we charged tablet type catalyst into the bed insert and this can cause low CO2 capture efficiency because the possibility of contact between input gas and CO2 absorbent is low in this case. New bed insert geometry was proposed based on the results from this study to enhance contact between input gas and WGS catalyst and CO2 absorbent.

A Study of Nitrous Oxide Decomposition over Calcium Oxide

A study of N2O decomposition reaction in a fixed bed a reactor over bed of CaO particles has been conducted. Effects of parameters such as concentration of inlet N2O gas, reacting temperature and content of CO2/ CO gas present in the reacting materials on the decomposition reaction have been investigated. The results showed that the conversion of N2O decomposition was accelerated by the increase of reaction temperature, and the existence of CO, while the rate was hindered by the existence of CO2. Heterogeneous gas solid reaction kinetics was proposed for N2O decomposition and compared with homogeneous reaction kinetics.

Effect of Pressure on Minimum Fluidization Velocity and Transition Velocity to Fast Fluidization of Oxygen Carrier for Chemical Looping Combustor

Effect of Pressure on Minimum Fluidization Velocity and Transition Velocity to Fast Fluidization of Oxygen Carrier for Chemical Looping Combustor JUNGHWAN KIM, DAL-HEE BAE, JEOM-IN BAEK, YEONG-SEONG PARK, HO-JUNG RYU Korea Institute of Energy Research, Daejeon 34129, Korea Korea Electric Power Corporation (KEPCO) Research Institute, Daejeon 34056, Korea Department of Environmental Engineering, Daejeon University, Daejeon 34520, Korea

A comparison of fluidized bed pyrolysis of oil sand from Utah, USA, and Alberta, Canada

Characterization and thermal pyrolysis of oil sand was conducted. The experiment was performed on Circle Cliffs, Utah, U.S.A. and the results were compared with the data from Alberta, Canada. The reaction character identified by TGA was dual mode of vaporization of light hydrocarbon and thermal cracking of high molecular hydrocarbon. The pyrolysis experiment was performed in a 2 kg/h capacity fluidized bed externally heated by electricity. The process variables investigated were a temperature range of 723-923 K, fluidization gas velocity of 1.5-2 times of the minimum fluidization velocity, solid retention time of 15-30 minutes, and average particle size of 435 microns. The results of TGA and elemental analysis of bitumen provided necessary information regarding maximum liquid yield from the pyrolysis prior to pyrolysis experiment. The oil yield was maximum at 823 K. The yield of liquid was not exceeding the weight percent of maltenes in original bitumen. The optimum reaction condition should be fast vaporization of light hydrocarbon and minimizing thermal cracking of high molecular hydrocarbon. To maximize the liquid yield, fast heating and vaporization of oil sand bitumen and then the rapid removal of the vaporized product from the heating zone is recommended, i.e., operation in a fluidized bed reactor.

CO Conversion Characteristics of WGS Catalysts for SEWGS System

Abstract >> Reactivity of commercial WGS catalyst(MDC-7) and four new catalysts(RMC-3, PC-73, PC-67SU, PC-59) manufactured with various compositions by Korea Electric Power Research Institute(KEPCO RI) were compared to select suitable WGS catalyst for SEWGS system. Steam/CO ratio, gas velocity, flow rates of syngas,and temperature were considered as operating variables. As a result, MDC-7 catalyst showed the highest CO conversion and RMC-3 catalyst showed also high CO conversion. Therefore, MDC-7 and RMC-3 catalysts were selected as applicable catalysts. However, PC-73 catalyst showed low CO conversion at low temperature(200℃) but showed good reactivity at high temperature(225~250℃), and therefore, PC-73 catalyst was selected as applicablecatalyst for high temperature operation. Continuous operations up to 24 hours for those three catalysts(MDC-7,RMC-3, PC-73) were conducted to check reactivity decay of catalysts. All three catalysts maintained their originalreactivity. Key words :

Direct Combustion Characteristics of Coal by Oxygen Carrier

>> Direct combustion characteristics of coal and oxygen carrier were measured in the thermogravimetric analyzer using four coals and two different oxygen carriers. The direct combustion efficiency decreased in order of Roto, Kideco, Sunhwa and Hyper coal for both oxygen carriers. Moreover, OCN703-1100 oxygen carrier showed better combustion efficiency than OCN706-1100 oxygen carrier for all four coals. The reduction characteristics of two oxygen carriers for CH4, CO and H2 gases were measured in the thermogravimetric analyzer to investigate why OCN703-1100 oxygen carrier showed better combustion efficiency than OCN706-1100 for all coals. The OCN703-1100 oxygen carrier represented higher reduction rate than OCN706-1100 for all reducing gases. Moreover, the total pore area and the porosity of OCN703-1100 were higher than those of OCN706-1100 oxygen carrier. The total volatile gas and volatile components of four coals were measured in a batch type fluidized bed reactor to investigate why the direct combustion efficiency decreased in order of Roto, Kideco, Sunhwa and Hyper coal for both oxygen carriers. The direct combustion efficiency was proportional to the total amount of (CH4+ CO+H2) produced during devolatilization of coals.

Effect of solid residence time on CO 2 selectivity in a semi-continuous chemical looping combustor

Chemical looping combustion (CLC) is a promising technology for fossil fuel combustion with inherent CO2 capture and sequestration, which is able to mitigate greenhouse gases (GHGs) emission. In this study, to design a 0.5MWth pressurized chemical looping combustor for natural gas and syngas the effects of solid residences time on CO2 selectivity were investigated in a novel semi-continuous CLC reactor using Ni-based oxygen carrier particle. The semi-continuous chemical looping combustor was designed to simulate the fuel reactor of the continuous chemical looping combustor. It consists of an upper hopper, a screw conveyor, a fluidized bed reactor, and a lower hopper. Solid circulation rate (Gs) was controlled by adjusting the rotational speed of the screw conveyor. The measured solid circulation rate increased linearly as the rotational speed of the screw increased and showed almost the same values regardless of temperature and fluidization velocity up to 800°C and 4 Umf, respectively. The solid circulation rate required to achieve 100% CH4 conversion was varied to change Gs-fuel ratio (oxygen carrier feeding rate/fuel feeding rate, kg/Nm3). The measured CO2 selectivity was greater than 98% when the Gs-fuel ratio was higher than 78 kg/Nm3.