Abstract
With the development of computing power, the simulation of circulating fluidized bed (CFB) has developed from riser-simplified simulation to riser-only simulation, then to full-loop simulation. This paper compared these three methods based on pilot-scale CFB experiment data to find the scope of application of each method. All these simulations, using the Eulerian–Eulerian two-fluid model with the kinetic theory of granular theory, were conducted to simulate a pilot-scale CFB. The hydrodynamics, such as pressure balance, solids holdup distribution, solids velocity distribution, and instantaneous mass flow rates in the riser or CFB system, were investigated in different simulations. By comparing the results from different methods, it was found that riser-simplified simulation is not sufficient to obtain accurate hydrodynamics, especially in higher solids circulating rates. The riser-only simulation is able to make a reasonable prediction of time-averaged behaviors of gas–solids in most parts of riser but the entrance region. Further, the full-loop simulation can not only predict precise results, but also obtain comprehensive details and instantaneous information in the CFB system.
Highlights
In the Discussion initialization of the full-loop simulation, particles were patched at a height of 4 m, the same as in the Validationin the storage tank
The predicted pressure drop in the bottom of the riser adjusting aeration rates [15]; the other one is a mechanical valve, such as the butterfly valve in the was lower than the experimental data, which is possibly due to the fact that the Gidaspow drag model present work, which controls Gs by the opening degree of the valve
Riser-simplified, riser-only, and full-loop simulations are conducted for a pilot circulating fluidized bed (CFB) under different operating conditions to compare the differences among different methods
Summary
In the top of the riser, through gas–solids separators such as cyclones, particles are separated from the gas downward back to the downcomer, while gas flows out of the system from the top of the cyclones. The riser is usually used as the main reactor, while the downcomer is usually used as a storage device to adjust particles, a heat exchanger, a catalyst regenerator, or as a standpipe to maintain circulation of solids. To optimize the products of the reactor, both excellent design and reasonable operation of the CFB, which are closely related to the gas–solids distribution, solids back-mixing, and residence time distribution, are critical. Extensive experiment and simulation studies focused on the gas–solids flow characteristics of CFB and found plenty of useful results such as solids holdup distribution, velocity distribution, solids back-mixing, and effects of both geometry and operating conditions [1,2,3,4]
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