Initial Bed Temperature Research Articles

The investigation of the coal ignition temperature and ignition characteristics in an oxygen-enriched FBR

Oxygen-enriched circulating fluidized bed (CFB) technology is considered as one of the low carbon emission power generation technologies. By recycling the flue gas into the furnace, the CO2 concentration in the exhaust gas can reach over 90%. The coal ignition temperature and ignition characteristics are important factors for boiler design and for choosing the feeding temperature during the transition from air-firing to oxy-firing. The ignition and combustion processes of five types of coal under four different atmospheres (air, O2 27%, O2 40%, O2 53%) were measured in a laboratory scale fluidized bed reactor (FBR) with an under-bed preheat system. Using thermocouples and a gas analyzer, the changes in bed temperature and the concentrations of different components, such as O2, CO2 and CO, in flue gas were directly measured to determine the coal ignition temperature, TiF. It was found that TiF decreases with increasing O2 concentration. At lower bed temperatures, two-stage ignition processes were observed in certain ranges of initial bed temperature and oxygen concentration. The influence of initial bed temperature on volatile release and the SO2 emission in the ignition processes were also discussed.

우라늄 베드 초기온도 및 헬륨농도의 수소 흡장 영향

우라늄 베드 초기온도 및 헬륨농도의 수소 흡장 영향

Experimental and numerical investigation of the cryogenic hydrogen storage processes over MOF-5

The processes of hydrogen charging to and discharging from a 3-L cryogenic tank have been studied experimentally and numerically. This study investigated the impacts of factors such as mass flow rate, outlet opening time, bed density, and heating power on the hydrogen charging and discharging processes. For charging, it was found that the flow-through cooling technique could remove the adsorption heat in the process, but some issues such as channeling phenomenon and large thermal mass of the system need to be addressed. Low initial bed temperature is beneficial for hydrogen storage in terms of the efficiency of charging operation. When the bed density of metal organic framework-5 (MOF-5) is increased from 164 kg/m3 to 174 kg/m3, the total storage of hydrogen within the tank increases accordingly. It is found that pressure is the major factor that determines the storage of hydrogen, which increases significantly with the pressure within the tank. For discharging, high pressure in the storage tank can be used to release hydrogen for a certain period of time without heating. However, in order to maintain the desired hydrogen discharge rate, a heat source is eventually needed. This heat must be supplied in order to desorb the additional hydrogen from the system. To deal with the channeling phenomenon in the charging process, cyclic charging was tested and adopted.

Direct Delivery of Hydrogen Isotopes from a DU Hydride Bed

A tritium plant for nuclear fusion power plants consists of an SDS (Storage and Delivery System), an ISS (Hydrogen Isotope Separation System), a TEP (Tokamak Exhaust Processing system), and an ANS (tritium plant Analytical System). Korea has been developing an SDS. The main purpose of this tritium storage and delivery system is to store and supply the D-T gas needed for DT plasma operation and to provide the necessary infrastructure for short- and long-term storage of large amounts of tritium. We have been developing tritium storage beds for the SDS.The primary role of the metal hydride beds in the SDS is to store and supply D-T fuel during DT plasma operation. ZrCo and depleted uranium (DU) have been extensively studied. Compared to the use of ZrCo, which is disproportionate at temperatures of higher than 350°C, DU hydride can be heated up to very high temperatures sufficient to pump hydrogen isotopes without using gas compressors. Our experimental apparatus used to test the experimental DU bed consists of a tank that stores and measures the hydrogen, and a DU bed used for the hydriding/dehydriding of hydrogen. Our DU bed is a horizontal double-cylinder type with sintered metal filters. The bed is composed of primary and secondary vessels. The primary vessel contains a DU, and a vacuum layer is formed between the primary and secondary vessels. In this study, we present our recent experimental results on the direct delivery of hydrogen isotopes from a DU hydride bed. We also present the effect of the initial bed temperature and impurity gas on the hydriding rates.

Experimental investigation on reflooding of debris beds

In case of a severe accident, continuous unavailability of cooling water to the core may result in over heating of the fuel elements and the loss of core integrity. Under such conditions a structure of heated particles of different sizes and shapes (debris) may be formed by fragmentation of core material inside the reactor pressure vessel (RPV). To avoid any damage to the RPV the reflooding is of great importance in order to establish long-term coolability.In the framework of an GRS R&D project and the SARNET network, specific experimental investigations on the coolability of debris beds with different bed contents (e.g. mono-/polydispersed bed of stainless steel balls with 6/3/2mm in diameter, irregularly shaped particles from PREMIX experiments – KIT) and various initial bed temperatures at ambient pressure (1bar) were carried out at IKE using the DEBRIS test facility and the small DEBRIS test set-up. In both experimental configurations the particles are volumetrically heated by an electromagnetic induction coil to predefined temperatures and then flooded with subcooled water from top (top-flooding) or from bottom (bottom-flooding). Depending on the flooding situation the cooling down (quenching) behaviour of the beds varies significantly due to the change of co- and counter-current liquid–vapour flow and respective heat transfer between solid and generated two-phase flow.This paper presents the main experimental results of systematic quenching studies at IKE. Furthermore, some representative results of benchmark experiments performed by IKE and IRSN (PRELUDE test facility) in the frame of the SARNET joint work are demonstrated. Finally, exemplary comparisons between experimental data and numerical results of simulations with IKE’s code MEWA-2D are shown.

Combustion of Municipal Solid Waste in a Pilot Scale Fluidized Bed Combustor

Combustion study of municipal solid waste combustion in a pilot scale fluidized bed combustor had been carried out. The work was aimed at demonstrating sustainable combustion of municipal solid waste by employing operating parameters gained from previous studies. The primary and secondary air factor used were AF = 0.8 and AF = 0.6 respectively. The fluidization number was 5Umf and both in-bed and freeboard region temperature distributions were monitored continuously. Results on the combustion studies revealed that the initial bed temperature could be sustained due to high thermal capacity of sand but later dropped due to problem related to the mixing of bulky and heterogeneous components of municipal solid waste and sand.

Heat and mass transfer studies in a batch fluidized bed dryer using Geldart group D particles

The drying behavior at low temperatures has been studied with four different uniformly sized particles and three different binary mixtures at different dilutions ranging from 10 to 40 % with an interval of 10 % varying parameters such as air velocity, initial moisture content, initial bed height and temperature. Falling rate period one and two were observed and correlations were developed to predict the drying rate in falling rate periods one and two. Correlations were also developed to predict the average moisture content by considering the effect of various parameters for uniformly sized particles and binary mixture of solids. The heat and mass transfer coefficients have been found for different conditions and compared. Comparison of experimental and predicted average moisture contents for uniformly sized particles and for various binary mixtures has been made and the predicted average moisture content has been found to be in good agreement with experimental average moisture content.

Performance of polyethyleneimine–silica adsorbent for post-combustion CO2 capture in a bubbling fluidized bed

The high performance of polyethyleneimine (PEI)-based solid adsorbent for CO2 capture has been well recognized in thermogravimetric analysis (TGA) and small-scale fixed bed reactors through the measurements of their equilibrium capacities but has not been really demonstrated on larger scales towards practical utilization. In the present study, a laboratory-scale bubbling fluidized bed reactor loaded with a few kg adsorbent is used to evaluate the adsorption performance of PEI–silica adsorbent under different working conditions including with/without the presence of moisture, different gas–solid contact times, initial bed temperatures, and CO2 partial pressures. The adsorption capacities have shown a clear degradation tendency under dry condition. However, they can be stabilized at a high level of 10.6–11.1% w/w over 60 cycles if moisture (ca. 8.8 vol%) is present in the gas flow during adsorption and desorption. Breakthrough capacities can be stabilized at the level of 7.6–8.2% w/w with the gas–solid contact time of 13 s. The adsorption capacities for the simulated flue gases containing 5% CO2 are only slightly lower than those for the simulated flue gases containing 15% CO2, indicating that the PEI–silica adsorbent is suitable for CO2 capture from flue gases of both coal-fired and natural gas-fired combined cycle power plants. The exothermal heat of adsorption is estimated by the energy balance in the fluidized bed reactor and found to be close (within 10%) to the measured value by TG-DSC. The regeneration heat for the as-prepared PEI–silica adsorbent is found to be 2360 kJ/kgCO2 assuming 75% recovery of sensible heat which is well below the values of 3900–4500 kJ/kgCO2 for a typical MEA scrubbing process with 90% recovery of sensible heat.

Carbon Dioxide Capture and Sequestration by Adsorption on Activated Carbon

Activated Carbon (AC) materials was selected as suitable adsorbent for the carbon dioxide (CO2) capture and a numerical analysis was carried out to study the rate of adsorption of the gas on ACs. A one dimensional mathematical model was proposed based on the Dubinin's Theory of Volume Filling of Micropores, and analyzed along with the unsteady heat transfer. A parametric analysis was carried out to study the effect of various crucial parameters like radius of bed, cooling fluid temperature, initial bed temperature and heat transfer coefficient on the adsorption amount. The results show that lower bed radius was ideal for obtaining high amount of CO2 adsorbed assuming constant packing density. Also, a high heat transfer coefficient up to 100 Wm-2K-1 and low cooling fluid temperature of 283K was necessary for speeding up the process. High initial bed temperature also supports greater adsorption amount under the same conditions.

Quenching Experiments: Coolability of Debris Bed

In the case of a severe accident, continuous unavailability of cooling water to the core will result in overheating and subsequent meltdown of the fuel elements that would eventually result in the loss of fuel integrity. Under such conditions a porous structure, which is made of heat-generating particles of different sizes and shapes, may be formed. The presence of decay heat in such a debris bed poses a critical threat to the reactor pressure vessel (RPV). To avoid any damage to the RPV, the removal of decay heat from the debris bed is of great importance. The debris bed needs to be quenched by water either flooding from the top or flooding from the bottom until continuous cooling is established. To investigate the quenching behavior of the debris bed by means of experiments, the nonnuclear test facility “DEBRIS” has been established at Institut für Kernenergetik und Energiesysteme (IKE). Experimental investigations of quenching behavior for a preheated debris bed, at various initial bed temperatures, are carried out at IKE. In the new quenching tests, the cooling-down behavior of a superheated polydispersed particle bed from stainless steel spheres at different thermohydraulic conditions has been investigated. Numerical investigation with IKE’s MEWA-2D code has also been carried out for the quenching experiments in order to promote better understanding of the experimental results as well as to verify the code’s applicability to the quenching process.

A new configuration for decoking process in series reactors

In the present work, a new configuration for coke burning process in series reactors has been developed based on a pseudo-homogeneous mathematical model. Series reactors are very common in chemical engineering processes such as petrochemical and petroleum industries. Moreover, the catalyst regeneration procedure in this type of reactors is very important and this process should regenerate catalysts completely. It is notable that the conventional configuration has some complications for catalyst regeneration in series reactor. First of all, the dynamic model is validated with industrial data from conventional configuration. Then, the model is used to simulate new configuration of series reactors for regeneration process. The novel configuration suggests that each bed should regenerate separately. According to the model outputs, the new configuration not only leads the coke to burn completely, but also reduces the regeneration time dramatically. Furthermore, this novel system uses considerably less steam and nitrogen than the conventional one. Eventually, the proposed configuration is implemented in domestic petrochemical company for series reactors in acetylene hydrogenation plant. As a result, the regeneration period decreases significantly by 28h. It is noticeable that the measured data from novel configuration and model outputs were in good agreement. Eventually, the effects of various parameters such as air flow rate and initial bed temperature on decoking process have been studied entirely and rigorously. Furthermore, a new regeneration protocol is achieved for the proposed configuration of series reactors.

Biogas Purification Using Cryogenic Packed-Bed Technology

A novel process concept for biogas treatment based on dynamically operated cryogenic packed beds (CPB) has been proposed and studied with numerical simulations. This work describes the CPB concept and investigates the different process steps involved with simulation results. To demonstrate the potential to treat biogas using the proposed process, the performance is compared to vacuum pressure swing adsorption (VPSA) on the basis of several criteria: purity and recovery of the obtained product, bed dimensions, and energy requirements. Simulation results reveal that the purity and recovery of CH4 are higher for the CPB concept, while also the bed capacity is much higher: the productivity (defined as kgCH4 h–1 mpacking–3) is a factor of 8 higher. The recovery is carried out with air and when operated in reversed flow mode, the novel CPB technology requires a 22% lower energy duty (2.9 MJ/kgCH4 vs 3.7 MJ/kgCH4 for the VPSA process). Furthermore, simultaneous deep H2S removal is possible using the proposed concept, although initial bed temperatures as low as −150 °C are required.

Co-combustion Performance of Oil Shale Semi-coke with Corn Stalk

The burn-out characteristics of oil shale semi-coke, corn stalk and their blends were invest-tigated by thermogravimetric analysis, the maximum burning rate, temperature of the maximum burning rate and burnout index were investigated. Batch charges of samples were burnt in a laboratory scale fluidized bed. The effect of particle size, initial bed temperature, air flow rate and different semi-coke percentages on the burnout time was investigated. The results have shown that an increase in bed temperature or air flow rate was associated with a decrease in burnout time. On the contrary, an increase in particle mean size led to an increase in burnout time. The most significant difference occurred with mixtures on the burnout time. The trend is increasing and then decreasing.

Techno-economic evaluation of cryogenic CO 2 capture—A comparison with absorption and membrane technology

Abstract A techno-economic evaluation of a novel cryogenic post-combustion CO 2 capture technology is presented in this work. The process concept is based on the periodic operation of cryogenically cooled packed beds. A process cycle consists of three consecutive steps: a cooling, capture and recovery step. The bed is first cooled down to temperatures below −120 ° C during the cooling step, possibly using cold energy released during the evaporation of LNG. Flue gas is fed to the refrigerated packed bed during the capture step. The flue gas will be cooled down and components as H 2O and CO 2 will condense and desublimate respectively at the packing surface, while permanent gases such as N 2 will pass through the bed without undergoing any phase change. In a final recovery step the stored components will be recovered from the bed by recycling CO 2 for CO 2 recovery and air for H 2O recovery. A basic process design focusing on the CO 2/N 2 separation for a 600 MW coal fired power plant is given in this work and the CO 2 avoidance costs are calculated. The influence of several process parameters is investigated, lower initial bed temperatures and higher CO 2 concentrations in the feed result in more efficient use of the bed volume. The pressure drop over the system plays an important role in the process economics, due to the high flow rates required in the process. The cryogenic concept is compared to two competing technologies: amine absorption and membrane separation. The results show that the preferred technology highly depends on assumptions related to the availability of utilities.

Fixed bed adsorption for the removal of carbon dioxide from nitrogen: Breakthrough behaviour and modelling for heat and mass transfer

Concentration and temperature profiles for CO 2 adsorption from a CO 2–N 2 gas mixture (10% CO 2 by vol in N 2) have been studied in a dynamic adsorption pilot plant unit to better understand the breakthrough behaviour. The scope of the present work is to study the adsorption characteristics and heat effects of this CO 2–N 2 gas mixture and to develop a simple model for the dynamic simulation of non-isothermal adsorption in a fixed bed. Results indicated that adsorption heat effects were significant for this mixture while the breakthrough time obtained with Ceca 13X adsorbent was independent of the initial bed temperature. The cooling step that follows the thermal regeneration of the adsorption bed could be omitted entirely without affecting the adsorption performance. An earlier breakthrough time was observed for a higher feed flow rate of 6.6 SL/min compared to 4 SL/min. Cooling during the adsorption cycle decreased the width of the mass transfer zone and led to a longer breakthrough time. The study also indicated that online measurements of temperature at different locations along the column bed could be used to predict the concentration breakthrough for this CO 2–N 2 gas mixture. The novel two-population model used in this study provided an adequate representation of the temperature and concentration breakthrough profiles within the adsorption column.

Combustion of oil palm stone in a pilot-scale fluidised bed reactor

Biomass is being generated in vast amounts from oil palm plantations particularly in developing countries such as Malaysia, Thailand and Indonesia. Oil palm stone (OPS) is currently considered a waste material and has not previously been considered for energy purposes. The main objective of this study was to investigate the thermochemical conversion of OPS in a pilot-scale fluidised bed combustor. The net heating value of OPS was 24.93 MJ/kg. The effect of primary air flowrate and initial bed temperature were the main parameters investigated. The bed and bed's surface temperature were found to decrease as the primary air flowrate increased. In all tests CO emissions were less than 0.2%. The emissions of SO 2 and HCl ranged from 0.02 ppm to 0.05 ppm, significantly below the permitted levels set by legislation. Stable combustion was observed at a bed temperature of 950 °C. The most abundant elements found in the ash were Al, Ca, Fe, K, Mg, Mn, P, S and Si. However, due to the temperature regime used in the study fouling would not be an issue.

Experimental investigation of the effect of initial fuel particle shape, size and bed temperature on devolatilization of single wood particle in a hot fluidized bed

Considerable amount of investigation on the subject of devolatilization of wood is found in the open literature. However, a systematic study of the effect of initial particle size and shape, and bed temperature on devolatilization time and char yield of wood in a hot fluidized bed is still missing. This paper attempts to fill this gap through a systematic experimental investigation to determine the devolatilization time and char yield of a typical woody biomass, “ Casuarina equisetifolia” particles of different initial sizes and shapes at various fluidized bed temperatures. Experiments are conducted using 10, 15, 20, and 25 mm Casuarina wood particles of three shapes, namely, cube, cylinder, and sphere at bed temperatures of 1023, 1123, and 1223 K. It is found that the initial wood particle size has the strongest influence on devolatilization time followed by the shape of initial wood particle and the bed temperature. Correlation for devolatilization time ( τ d) as a function of initial wood particle size ( d eq), sphericity ( ϕ), and bed temperature ( T b), is developed using 573 experimental data points exhibiting a correlation coefficient of 0.96 and predictions falling well within a deviation band of ±20%. The predictions of the present correlation are compared with the predictions of the existing correlations in literature for conditions also out of the present study and the deviation is found to be ±30%. Char yield, defined as the ratio of the residual mass at the end of devolatilization process to the initial mass of the wood particle is found to be in the range of 9–14% for all sizes, shapes, and bed temperatures. Char yield does not depict any definite trend with the variation of initial particle size, shape and bed temperature.

A novel process for cryogenic CO2 capture using dynamically operated packed beds—An experimental and numerical study

A novel process concept has been studied for post-combustion CO2 capture from flue gases based on periodic operation of cryogenically cooled packed beds. Using refrigerated packed beds, an effective separation between H2O, CO2 and the permanent gases can be obtained at atmospheric pressures, due to differences in dew and sublimation points. H2O and CO2 will respectively condensate and desublimate onto the packing surface at different locations, while the permanent gases will pass through the bed. In this work the evolution of the axial temperature and concentration profiles during the consecutive capture, recovery and cooling cycles has been investigated in detail by experiments and numerical simulations, elucidating the effect of the initial bed temperature and feed CO2 and H2O concentrations. Furthermore, the required cooling duties were calculated for different CO2 concentrations in the flue gas and initial bed temperatures. The required cold duty to recover >99% CO2 from a flue gas containing 10vol.% CO2 and 1vol. H2O is estimated at 1.8 MJ/kgCO2, where lower CO2 concentrations in the inlet and higher initial bed temperatures result in higher required cooling duties per mass of CO2 captured.

Repetitive control and online optimization of Catofin propane process

The Catofin propane process is an emerging industrial process for propylene production through dehydrogenation of propane. It is composed of multiple adiabatic fixed-bed reactors which undergo cyclic operations where propane dehydrogenation and catalyst regeneration alternate over roughly 10-min period for each. One of the major concerns in the operation of the Catofin process is maintaining the reactor at an optimum condition while overcoming gradual catalyst deactivation. Addressing this issue, an online optimization of the Catofin process combined with a repetitive control has been investigated. The optimizer computes optimum initial bed temperatures for dehydrogenation and optimum air flow rate for regeneration, and the repetitive controller performs cycle-wise feedback action during regeneration to attain the target bed temperatures at the terminal time of the regeneration period. Numerical studies have shown that the proposed online optimizing control system performs satisfactorily coping with the catalyst deactivation and other disturbances.

Mass loss and apparent kinetics of a thermally thick wood particle devolatilizing in a bubbling fluidized bed combustor

This work presents the results of experiments conducted to determine the mass loss characteristics of a cylindrical wood particle undergoing devolatilization under oxidation conditions in a bubbling fluidized bed combustor. Cylindrical wood particles having five different sizes ranging from 10 to 30 mm and aspect ratio ( l/ d = 1) have been used for the study. Experiments were conducted in a lab scale bubbling fluidized bed combustor having silica sand as the inert bed material and air as the fluidizing medium. Total devolatilization time and mass of wood/char at different stages of devolatilization have been measured. Studies have been carried out at three different bed temperatures ( T bed = 750, 850 and 950 °C), two inert bed material sizes (mean size d p = 375 and 550 μm) and two fluidizing velocities ( u = 5 u mf and u = 10 u mf). Devolatilization time is most influenced by the initial wood size and bed temperature. Most of the mass is lost during the first half of the devolatilization process. There was no clear influence of the fluidization velocity and bed particle size on the various parameters studied. The apparent kinetics estimated from the measured mass history show that the activation energy varied narrowly between 15 and 27 kJ/mol and the pre-exponential factor from 0.11 and 0.45 s −1 for the wood sizes considered.