36 results
Now showing1 - 10 of 36
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The MP-PIC method for CFD-simulation of biomass gasification in a lab-scale fluidized bed(2021-05); ; ; ; Aim of the project “Multi-scale analysis and optimization of chemical looping gasification of biomass” of the Hamburg University of Technology (TUHH) with the Southeast University (SEU) is the detailed modeling and subsequent optimization of a Chemical Looping Gasification (CLG) process. For this purpose, the process is simulated using the multiphase particle-in-cell (MP-PIC) method, which allows a detailed simulation of even large-scale units with affordable computational efforts. This paper deals with the implementation and validation of the reaction model for the gasification reactions.Publicationtype: Conference Paper119 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influences on the transition from bubbling to turbulent fluidization for Geldart's group B particles(2020-09-20); ; ; A detailed study of parameters influencing the transition from bubbling to turbulent fluidization was done. The transition velocity Uc was determined by pressure fluctuation analysis for different size fractions of sand and ilmenite particles (Geldart's group B). Four different plants (laboratory and pilot scale) were used having diameters ranging from 0.05 m to 0.4 m. The static bed height was varied, resulting in aspect ratios (static bed height/bed diameter) from 1 to 4. The results of Uc show a clear dependency of aspect ratio, bed diameter, temperature and particle size. The diameter of the bed was found to influence the transition velocity especially in small fluidized beds. The static bed height has a significant influence on the transition velocity which has to be considered in scale-up. As a further parameter, the temperature influence was investigated up to 800 °C. No correlation in literature was found to predict satisfactorily the influences of the parameters investigated.Publicationtype: Journal Article77 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Increasing the efficiency of chemical looping combustion of biomass by a dual-stage fuel reactor design to reduce carbon capture costsThis paper analyzes the capabilities of a pilot-scale chemical looping combustion plant firing wood biomass in two stages to efficiently achieve negative carbon dioxide emissions. The utilized in situ gasification-chemical looping combustion (iG-CLC) process isolates the oxygen supply via air from the fuel conversion itself with the help of two separate fluidized bed reactors and an oxygen carrier to supply the necessary oxygen for the combustion. As a result, a relatively pure stream of carbon dioxide and steam is generated. Thus, the process makes capturing carbon emissions more feasible since it eliminates the need for the cost- and energy-intensive separation of the produced gases. A major issue when using biomass in a chemical looping plant is the high amount of the volatiles exiting unconverted. This problem was mitigated by using a two-stage fuel reactor system. Two bubbling fluidized beds were arranged one upon the other. The lower stage, where the fuel is introduced, is used to release the volatiles and partly convert them. The remaining volatiles rise up into the second stage and are further converted to a high degree. A series of experiments were carried out with a 25-kWth pilot plant located at the Hamburg University of Technology. Gas concentrations were continuously measured after both stages of the fuel reactor to see the gradual conversion of the fuel gases. Additionally, carbon slip at the exhaust was measured to show the effectiveness. The experiments with the reactor concept showed promising results since already at a reactor temperature of 850 °C, the total oxygen demand needed to oxidize the combustible component in the exhaust gas was well below 2%. The carbon dioxide (CO2) capture efficiency when using German hardwood slightly decreased to 93–96% compared to 97% for German lignite. In the future, the reactor design must prove that it scales and that the efficiency can be further increased. Nevertheless, firing biomass with a two-stage iG-CLC process might allow a cost-efficient negative carbon dioxide emission while generating heat with relatively high efficiency. Therefore, it might be a sustainable alternative to generate heat in the future.Publicationtype: Journal Article143 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dynamic modelling of reactive fluidized bed systems using the example of the chemical looping combustion process for solid fuelsThe novel open-source flowsheet simulation software DYSSOL was used to simulate effects inside a system of interconnected fluidized bed reactors. The development of the needed models was done exemplary for the Chemical Looping Combustion process for solid and gaseous fuels. In CLC a solid oxygen carrier material is circulated between interconnected fluidized bed reactors. In the simulation, the focus is laid on the prediction of the dynamics of the whole system, especially the process start-up, shut-down and fuel load change. A dynamic model, which can be applied for bubbling beds and circulating fluidized beds was derived. Additionally, a cyclone was introduced for gas-solid separation. Loop seals ensure gas sealing between the reactors and were included into the modeling. Fluid mechanics inside the systems are modeled with empirical and semi-empirical, one-dimensional correlations, to enable fast calculations. These considerations allow real-time simulations of long-term effects in the system. The chemical reactions for gaseous and solid fuel combustions are included in the simulation. This has an effect on the solid oxygen carrier and so the oxidation and reduction of the carrier are regarded. The simulations were validated with experiments on a 25 kWth Chemical Looping Combustion facility at TUHH. The flowsheet models are able to predict the movement of the bed material between the units after operation changes as well as the time frames in which these changes occur. Besides, the gas and solids conversions in the fluidized bed reactors were simulated accurately.Publicationtype: Book Part120 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Syngas, tar and char behavior in chemical looping gasification of sawdust pellet in fluidized bed(2020-06-15); ; ; ; Due to the advantages of high energy density and convenient transportation, the use of pelletized biomass as fuel for power supply has gained interest over recent years. Chemical looping gasification (CLG) integrates the process of gasification and hot gas conditioning, with the objective to obtain syngas with a low tar amount. The work presents some experimental results using sawdust pellet with high-volatile and low-ash content as fuel, and a natural manganese-iron ore as oxygen carrier for CLG in a bubbling fluidized bed. Without the addition of external steam, the syngas, tar, and char collected at different temperatures (750–950 ℃) and oxygen carrier to biomass ratios (0.2–1.2) were investigated to determine the gasification performance of sawdust pellet. Three-phase product distributions during CLG process were identified under different operating parameters. The increase of reaction temperature enhances the gas production, with decreasing amount of liquid and solid. Also, it has significant influence on the main gases (CO, CO2, H2 and CH4) distributions in the syngas. Meanwhile, more Polycyclic-Aromatic Hydrocarbons (PAHs) are cracked to Mono-Aromatic Hydrocarbons (MAHs) and further decomposition into syngas, which is confirmed by further Gas Chromatography-Mass Spectrometer (GC–MS) analyses. The Mn/Fe-based oxygen carrier also exhibits a beneficial effect on catalytic cracking of PAHs into MAHs. As for the remaining char, a higher temperature is more sensitive to produce the char with more porous structure and brittle texture.Publicationtype: Journal Article109 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Optimization of the spray-drying process for developing aquasolv lignin particles using response surface methodologyParticle size and morphology are of high industrial importance due to the fact that product properties and performance can be affected by this factors. For instance, bulk properties, processability and appearance of the final product are given by particle size and shape. In this regard, the optimization of process parameters for particle development is required when targeting formulation of specific product and/or particular properties. Response surface methodology (RSM) was used to optimize the spray drying process for the development of aquasolv lignin particles with desired particle size and morphology. The inlet drying temperature X1: 180–200 °C, atomization pressure X2: 1.3–1.7 bar and feeding rate X3: 65–75 mL min−1 were kept as independent variables while the optimizing responses were: Yield fine of particles with desired particle size and particle size (D50). The quadratic part of the equation and statistical analysis showed substantial effect of the atomizing pressure and feeding rate on the responses and the optimized conditions validated the model. Optimum processing conditions for spray drying of aquasolv lignin were inlet temperature of 173 °C, 1.8 bar atomization pressure and 62 mL/min feeding rate. With this, desired responses of powder were 66% of yield and particle size of D50 < 30 µm were obtained. The experimental values were found to be in agreement with the predicted values indicating the suitability of the model in predicting the particle size and yield of aquasolv lignin.Publicationtype: Journal Article108 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Continuous fluidized bed drying: Advanced modeling and experimental investigationsFluidized bed drying is a technology which is widely applied in industry for the drying of particulate solids. One of the major advantages of fluidized bed system results from the fact that due to high heat, mass and momentum transfer, and intensive solids, mixing a good temperature control is possible, which allows an effective drying of heat-sensitive materials as, for example, food or pharmaceutical products, which are very often also porous and hygroscopic. A disadvantage of the nearly perfect solids mixing in the fluidized bed is the wide residence time distribution of the solids, that is, some particle will leave the dryer already a few seconds after they have been fed to it, while other particles stay for very long times inside the dryer, which may result in a wide moisture distribution of the solids at the outlet of the dryer. Based on numerous works from the literature, a drying model for continuous fluidized bed drying has been developed and implemented as a module within the framework of the stationary flowsheet simulation program SolidSim, which allows the simulation of the drying process for many different solids, liquids, and gases. In addition to the residence time distribution described by a population model, the influence of particle size distribution and the moisture distribution of the feed material was taken into account. The module computes the humidity and temperature of the gas versus the bed height and the moisture and temperature distribution of the solids by taking into account their distributed properties such as for the residence time distribution, particle size and initial moisture. Additionally, also the drying of mixtures of particles with different types of sorptive behavior and drying kinetics is possible while assuming that no particle segregation occurs. Furthermore, the model has been extended by a simple approach to simulate the drying in an elongated fluidized bed dryer. For the validation of the model, the main operating parameters were varied and compared with experiments. The model can calculate the moisture distribution at the dryer outlet, but due to technical restriction, only the average moisture of the particles was measured and compared with the model prediction.Publicationtype: Book Part129 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fluidization characteristics of cohesive powders in vibrated fluidized bed drying at low vibration frequencies(2019-12-01); ; ; ; Mechanical vibration is often applied in industrial scale fluidized bed dryers for food and pharmaceutical powders to overcome operational problems caused by the cohesiveness of the products. However, the understanding of the process regarding detailed modeling, apparatus design, up-scaling and process optimization is still incomplete. Almost all of the experimental research in the field of vibrating fluidized beds is conducted on a lab-scale. Within the current project, experiments are conducted in a pilot plant scale unit with a cross section of 250 × 500 mm2 and a total height of 3 m. The influence of several process parameters, such as gas velocity, vibration intensity, powder moisture content and bed mass, on the fluidization characteristics of whole milk powder is studied. In order to characterize the lower limit of fluidization from an operational point of view, the velocity of complete fluidization (ucf) is used and quantified. This is defined as the lowest superficial gas velocity at which the entire bed is fully fluidized. It could be observed that an increase in moisture content of the powder results in a significant increase of ucf. The introduction of mechanical vibration into the bed results in the reduction of ucf, the expansion of the bed and the reduction of the bubble volume fraction. This expansion of the suspension phase explains the increase in heat and mass transfer in vibrated fluidized beds, reported in the literature. Adding the effect of vibration intensity to well established correlations allows for the accurate prediction of gas hold-up and bed porosity of fluidized beds of cohesive whole milk powder under mechanical vibration at low vibration frequencies.Publicationtype: Journal Article153 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The MP-PIC Method for CFD-Simulation of Fluidized Beds-Comparison of Two Different Implementations(Curran Associates, Inc., 2019-05); ; ; Publicationtype: Conference Paper21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Drying of Cohesive Powders in a Pilot Plant Scale Vibrated Fluidized Bed(Curran Associates, Inc., 2019-05); ; ; ; Publicationtype: Conference Paper17