Fluidized bed regenerators for Brayton cycles

A recuperator consisting of two fluidized bed regenerators with circulating solid particles is considered for use in a Brayton cycle. These fluidized beds offer the possibility of high temperature operation if ceramic particles are used. Calculations of the efficiency and size of fluidized bed regenerators for typical values of operating parameters were made and compared to a shell and tube recuperator. The calculations indicate that the fluidized beds will be more compact than the shell and tube as well as offering a high temperature operating capability

CFD Simulation of CO2 Sorption in a Circulating Fluidized Bed Using Deactivation Kinetic Model

The Computational Fluid Dynamics (CFD) approach was used to simulate sorption of CO2 using solid sorbents in the riser section of a circulating fluidized bed. The simulation results were compared with the experimental data of Korea Institute for Energy Research (KIER) for continuous CO2 sorption using potassium carbonate in a circulating fluidized bed system

Hydrodynamics in the Gas-Driven Inverse Liquid-Solid Fluidized Bed

A novel reactor named Gas-Driven Inverse Liquid-Solid Fluidized Bed (GDFB for short) was developed in this research. A vertical baffle divides the column into a riser and a downer. Inverse fluidization is driven by the gas and occurs in the downer, where hydrodynamics and their influencing factors were studied. In the solid-baffle system, four fluidization regimes were observed, including the packed bed, semi-fluidized bed, fully-fluidized bed, and circulating bed. Bed expansion ratio was higher for particles with a higher density and a smaller solids loading. Moreover, the average particle velocity was proportional to superficial gas velocity and higher for denser particles. In the meshed-baffle system, the shifted bed was found between the fully-fluidized bed and the circulating bed, and some hydrodynamics differed from that in the solid-baffle system. Considering the similarity and diversity, a solid baffle or a meshed baffle should be selected depending on the needs of chemical processes

Experimental Analysis of Fuel Mixing Patterns in a Fluidized Bed

The mixing pattern of a tracer particle which simulates a fuel particle is studied in a cold 2-dimensional fluidized bed with respect to the influence of fluidization velocity, bed height, tracer particle size and air-distributor pressure drop under conditions typical for bubbling fluidized bed boilers as well as the bottom region of circulating fluidized bed boilers. The results show that for all conditions studied, the tracer particle follows a flow pattern structured into horizontally-aligned vortexes

Modélisation et simulation d'un réacteur à lit fluidisé circulant interne pour le traitement thermique de déchets solides industriels

Modeling of an internally circulating fluidized bed reactor for thermal treatment of industrial solid wastes -- Prediction of gas emission in an internally circulating fluidized bed combustor for treatment of industrial solid wastes -- Parameter analysis and scalled-up considerations for thermal treatment of industrial waste in an internally circulating fluidized bed reactor

Dynamic flowsheet simulation of gas and solids flows in a system of coupled fluidized bed reactors for chemical looping combustion

A novel flowsheet simulation environment is applied to the Chemical Looping Combustion of solid fuels in order to capture dynamic behavior of fluid dynamics inside the system. The process itself is carried out in the majority of cases in a pair of strongly coupled fluidized bed reactors. The plant operated at the TUHH, which is simulated there, comprises a circulating fluidized bed air reactor and a two-stage bubbling bed fuel reactor demonstrated in the Figure. The modelled riser of the circulating fluidized bed system consists of a dense bottom phase and a dilute upper part. The fuel reactors are implemented bubbling bed reactors with a freeboard of elutriated particles and a dense bubbling bed with two phases. The cyclone is modelled according to Muschelknautz. The two loop seals are considered as divided bubbling beds. Please click Additional Files below to see the full abstract

Numerical simulation of a periodic circulating fluidized bed of binary mixture of particles: Budget analysis

Detailed sensitivity numerical studies have shown that the mesh cell-size may have a drastic effect on the modelling of circulating fluidized bed. Typically the cell-size must be of the order of few particle diameters to predict accurately the dynamical behaviour of a fluidized bed. Then the Euler-Euler numerical simulations of industrial processes are generally performed with grids too coarse to allow the prediction of the local segregation effects. A filtered approach is developed where the unknown terms, called sub-grid contributions,have to be modelled. Highly resolved simulations are used to develop the model. They consist of Euler-Euler simulations with grid refinement up to reach a mesh independent solution. Then spatial filters can be applied in order to measure each sub-grid contribution appearing in the theoretical filtered approach. Such kind of numerical simulation is very expensive and is restricted to very simple configurations. In the present study, highly resolved simulations are performed to investigate the sub-grid contributions in case of a binary particle mixture in a periodic circulating gas-solid fluidized bed. A budget analysis is carried out in order to understand and model the effect of sub-grid contribution on the hydrodynamic of polydisperse gas-solid circulating fluidized bed

Ammonia Addition for NOx Reduction in Fluidized Bed Boilers

Ammonia is added to the gases in the combustion chamber of fluidized bed briilers in order to investigate its effect ori the emission of nitrogen oxides. A stationary and a circulating fluidized bed boiler are used. In the sta­tionary fluidized bed boiler an addition corresponding to a (NH3/NOexit-molar ratio of 3 gives a 50% reduction of the NO emission. Larger doses lead to escape of ammonia and other disadvantages. In the circulating fluidized bed boiler no effect from injection of ammonia into the combustion chamber is noted. The ammonia is decomposed. If NH3 is to be used in circulating fluidized bed boilers it should be introduced in the particle-free gas after the particle separator

Particle Population Balances in a Refuse Derived Fuel Fired Circulating Fluidized Bed Combustor

With a population balance model the effects of changes in the operation of a circulating fluidized bed combustor on the bed inventory are simulated. Feeding, discharge and recirculation of solids as well as separation effects in the combustion chamber and in the cyclone are considered. The model predictions are compared with measurements at the refuse-derived fuel incineration plant Neumuenster. The simulation shows that by sieving of the ash withdrawn from the bottom of the combustion chamber and recycling the fine fractions to the bed the non-elutriable fraction of the ash in the bottom zone of the circulating fluidized bed (CF B) can be kept at a low level

Control of particle circulation rate in circulating fluidized bed by a pulsed gas flow

As a coal-fired power generation technology for further improvement of power generation efficiency of coal-fired power generation, exergy regeneration type coal gasification power generation technology (1), a triple-bed circulating fluidized bed (2), has been proposed. The authors analyzed the flow characteristics of the triple-bed circulating fluidized bed, it has the flow characteristics of the riser and downer perform the proposed approach to representation by the equivalent circuit model. The equivalent circuit model of the riser and downer are shown in Figure 1. This equivalent circuit has the nature of the low-pass filter. A combination of the low-pass filter and the pulse voltage is used as a switching power supply. Then, we applied that the pulsed gas supply to the riser combined with a low-pass filter characteristics to control the particle circulation rate of the triple-bed circulating fluidized bed. Figure 2 shows the input output characteristics of the equivalent circuit of the riser/downer inputting a pulse voltage. We used an electric circuit simulator SPICE to calculation of circuit behavior. Circuit constant is to use the value of the reference 3, the input pulse height is set to 80V. When the input pulse width is changed, the output current is changed depending on the pulse width. Moreover, when changing the density of the pulse, the output current is changing depending on the pulse density. This result by giving a pulsed gas supply to the riser, it shows the possibility controlling the particle circulation rate of the triple-bed circulating fluidized bed. Please click Additional Files below to see the full abstract