Chang-Keun Yi

Demonstration of inherent CO2 separation and no NOx emission in a 50kW chemical-looping combustor: Continuous reduction and oxidation experiment

Publisher Summary The chapter explains a study that seeks to display a chemical-looping combustion system by a continuous reduction and oxidation experiment in a 50kWth chemical-looping combustor with high CO2 selectivity, no side reaction (carbon deposition and/or hydrogen generation), inherent CO2 separation, and no NOx emission. In this study, NiO/bentonite acts as an oxygen carrier particle in the bed material of the chemical-looping combustion system and CH4 and air are used as reacting gases for reduction and oxidation, respectively. NO, NO2, and N2O concentrations are measured to check whether NOx is formed during oxidation and measured CO2, CO, CH4, H2 concentration to show inherent CO2 separation and no side reaction during reduction. It takes more than 3.5 hour to finish the process. Pressure drop profiles in a system loop are maintained steadily throughout the 3.5 hour run and solid circulation between an oxidizer and a reducer remains smooth and stable. By analysis of gases in the exit stream from the system, the study concluded that inherent CO2 separation and NOx-free combustion are possible in the chemical-looping combustion system.

The effect of fine particles on elutriation of coarse particles in a gas fluidized bed

The effect of fine particles on the elutriation rate of the coarse particles at the gas exit was investigated in a gas-fluidized bed (i.d.: 0.1 m, height: 1.97 m) with sand as bed material. The elutriation rate of the coarse particles increased with the gas velocity and the proportion of fine particles in the bed. It was found to increase nearly proportionally with the upward momentum of the fine particles calculated on bases of unit mass and composition of bed particles at a specified gas velocity. The effect of the fine particles on the elutriation of the coarse particles decreased as the gas velocity increased. The elutriation of the fine particles was not affected by the size distribution of bed particles. An improved correlation to determine the elutriation rate of the coarse particles has been proposed for sand particles.

Development of sorbent manufacturing technology by Agitation Fluidized Bed Granulator (AFBG)

Thousands of ppmv of hydrogen sulfide included in coal gas should be reduced to less than a hundred ppmv in the case of IGCC to prevent a gas turbine from being corroded, and few ppmv to prevent the performance of electrodes from declining in the case of MCFC. In the present paper a laboratory scale AEBG (Agitation Fluidized Bed Granulator) is made and improved. The sorbent for the removal of hydrogen sulfide is produced using an agitation fluidized bed granulator (ZnO 1.5 mole+TiO2 l.0mole+bentonite 5.0 wt%). The techniques for fluidizing fine particles, classified in Geldart C group, in a fluidized bed are developed by installing an agitator blade in a fluidized bed granulator. The fine particles are fluidized and granulated successfully by using the techniques. Statistical, spectral and chaos analyses with granulated sorbent (100-300 Μm) are performed to investigate the hydrodynamics of granulates in a fluidized bed. The average absolute deviation, power spectral density functions, phase space trajectories, and Kolmogorov entropy obtained from pressure fluctuation are plotted as a function of fluidizing velocity. It is shown that the Kolmogorov entropy implying the rate of generation of information can be applied to the control of fluidization regimes.

Simultaneous experiments of sulfidation and regeneration in two pressurized fluidized-bed reactors for hot gas desulfurization of IGCC

Hot Gas Desulfurizarion for IGCC is a new method to efficiently remove H2S in fuel gas with regenerable sorbents at high temperature and high-pressure conditions. The Korea Institute of Energy Research did operation of sulfidation in a desulfurizer and regeneration in a regenerator simultaneously at high pressure and high temperature conditions. The H2S concentration at exit was maintained continuously below 50ppmv at 11,000 ppmv of inlet H2S concentration. The sorbent had little effect on the reducing power in the inlet gas in the range from 11% to 33% of H2. As inlet H2S concentration was increased, H2S concentration in the product gas was also increased linearly. The sorbent was maintained at low sulfur level by the continuous regeneration and the continuous solid circulation at the rate of 1.58× 10−3 kg/s with little mean particle size change.

Simultaneous removal of H2S and COS using Zn-based solid sorbents in the bench-scale continuous hot gas desulfurization system integrated with a coal gasifier

A bench-scale continuous hot gas desulfurization system using Zn-based solid sorbents was developed to remove H2S and COS simultaneously in a 110 Nm3/h of real coal-gasified syngas. The bench-scale unit, which consisted of a fast fluidized-bed type desulfurizer and a bubbling fluidized-bed type regenerator, was integrated with a 3 ton/day-scale coal gasifier installed at the Institute for Advanced Engineering. The solid sorbents, which consisted of 50 wt% of ZnO for sulfides sorption and 50 wt% of supporters for mechanical strength, were manufactured by a spray drying method and supplied by Korea Electric Power Corporation Research Institute. The bench-scale unit was designed to operate at the high temperature of above 500 °C and the high pressure of 19 kgf/cm2 gauge. Integration of the bench-scale unit with a coal gasifier was first performed to investigate the operation stability of the integrated system. And the long-term continuous operation above 30 h was performed to analyze the desulfurization performance of the bench-scale unit. The concentration of both H2S and COS in the syngas was measured by a continuous UV gas analyzer and an online gas chromatograph and that of both H2S and COS after desulfurization was measured by an online gas chromatograph. Through the above 30-h continuous operation, the sulfur removal reached up to 99.9%.

CO2 reaction characteristics of dry sorbents in fluidized reactors

Publisher Summary The purpose of this chapter is to identify chemical characteristics of dry sorbents in a bubbling fluidized reactor and in a fast fluidized reactor. They consist of a gas feeding part, a main reactor, effluent gas treatment part, and a gas analyzer. The general feature of the system includes a fast fluidized reactor, a mixing zone in the lower part of the fast fluidized reactor, a cyclone, a standpipe, and a bubbling fluidized reactor. One of the advanced concepts for capturing CO2 is an absorption process with dry regenerable sorbents. For the fluidized-bed CO2 capture process, sorbent should have high chemical reactivity and high attrition resistance. Also, it should be regenerable over multicycle use or continuous solid circulation mode between carbonation and regeneration. Pure sodium bicarbonate and a spray-dried sorbent were used to examine the characteristics of CO2 reaction in a flue gas condition. Effects of several variables such as gas velocity, temperature, and H2O concentration on sorbent activity were examined in both the type of reactors in addition with solid concentration and gas velocity.

Performance analysis of K-based KEP-CO2P1 solid sorbents in a bench-scale continuous dry-sorbent CO2 capture process

Korea Institute of Energy Research (KIER) and Korea Electric Power Corporation Research Institute (KEPCORI) have been developing a CO2 capture technology using dry sorbents. In this study, KEP-CO2P1, a potassium-based dry sorbent manufactured by a spray-drying method, was used. We employed a bench-scale dry-sorbent CO2 capture fluidized-bed process capable of capturing 0.5 ton CO2/day at most. We investigated the sorbent performance in continuous operation mode with solid circulation between a fast fluidized-bed-type carbonator and a bubbling fluidized-bed-type regenerator. We used a slip stream of a real flue gas from 2MWe coal-fired circulating fluidized-bed (CFB) power facilities installed at KIER. Throughout more than 50 hours of continuous operation, the temperature of the carbonator was maintained around 70-80 °C using a jacket-type heat exchanger, while that of the regenerator was kept above 180 °C using an electric furnace. The differential pressure of both the carbonator and regenerator was maintained at a stable level. The maximum CO2 removal was greater than 90%, and the average CO2 removal was about 83% during 50 hours of continuous operation.

Axial voidage profile in a cold model circulating fluidized bed

The axial voidage profile was measured in a cold model circulating fluidized bed (0.38 m in diameter and 9.1 m in height) of sand particles as bed materials. Voidage in the riser column increases along the height above the distributor plate with increasing the gas velocity. However, it decreases with an increase in solid circulation rate in the bed. Model correlations to predict the solid circulation rale and the axial voidage profile in the bed are proposed.

Simulation of a bubbling fluidized bed process for capturing CO2 from flue gas

We simulated a bubbling bed process capturing CO2 from flue gas. It applied for a laboratory scale process to investigate effects of operating parameters on capture efficiency. The adsorber temperature had a stronger effect than the regenerator temperature. The effect of regenerator temperature was minor for high adsorber temperature. The effect of regenerator temperature decreased to level off for the temperature >250 °C. The capture efficiency was rather dominated by the adsorption reaction than the regeneration reaction. The effect of gas velocity was as appreciable as that of adsorber temperature. The capture efficiency increased with the solids circulation rate since it was ruled by the molar ratio of K to CO2 for solids circulation smaller than the minimum required one (Gs, min). However, it leveled off for solids circulation rate >Gs, min. As the ratio of adsorber solids inventory to the total solids inventory (xw1) increased, the capture efficiency increased until xw1=0.705, but decreased for xw1>0.705 because the regeneration time decreased too small. It revealed that the regeneration reaction was faster than the adsorption reaction. Increase of total solids inventory is a good way to get further increase in capture efficiency.

Solids circulation rate and static bed height in a riser of a circulating fluidized bed

Solids circulation rate and static bed height in the riser of a circulating fluidized bed (CFB) process, which consisted of a riser and two bubbling-beds, were investigated and discussed at ambient temperature and pressure. Three kinds of powder (FCC catalyst, glass bead, plastic powder) were used as bed materials. The static bed height in the riser increased with the solids circulation rate. However, it decreased with an increase of gas velocity. The effect of gas velocity diminished as the gas velocity increased. The riser static bed height could be used to estimate the solids circulation rate in reasonable accuracy. A correlation on static bed height in the riser, relating to the solids circulation rate, was proposed for the present experimental ranges.