Dual fluidized bed (DFB) is a reactor which consists of two fluidized bed units coupled by linking structures such as valve or some similar devices. In recent years, on count ofits advantages in decoupling thermo chemical reaction to realize optimization and products separation, many researchers have conducted investigations on the possibility of appling dual fluidized bed in step conversion and efficient utilization of fuels.However, due to the complex physical structure and internal flow mechanism, the understanding of gas solid flow characteristics in dual fluidzed bed is not sufficient. Especially the mechanism of solids circulation and coupling has not been well studied to meet the requirements of practical applications of dual fluidized bed reactors. Therefore, it is urgent to conduct systematic research on gas solid flow characteristics in dual fluidzed bed to guide the design, operation and optimization of similar devices.
An interacting dual fluidized bed cold model with two same fast fluidized bed units was built in this work. Each fluidized bed unit consists of riser, downcomer, cyclone separator and loop seal valve. With experimental study in a relative wide range of operation parameters, four flow regimes were realized in this work, i.e. turbulent flow, cluster flow, annular flow and suspension flow. The coupling operation experience was also gained in the experimental study. And five coupling patterns are formed based on operation experiments(CF- CF, CF-TF, CF-AF, AF-AF, AF-SF).
By applying symmetrical and non-symmetrial operation conditions, the effects of operatingparameters(solid inventory, riser aeration flow rate, loop seal aeration flow rate) on pressure distribution, pressure difference in bed, solids concentrations distribution and other gas solid flow characteristic parameters were investigated. The full loop pressure balance model was also developed with experimental pressure distribution data. By analyzing the time-series pressure difference data to investigate the solid concentration fluctuation in full height of risers, the influences of operation parameters on fluctuation strength and operation stability of solid concentration was revealed.
Based on related researches about microwave flow rate monitoring, anon-line, real-time, non-intrusive microwave solids flow measurement system which is suitable for applications in dual fluidized bed was developed for the successive dynamic measurement of solids flow. By analyzing the average deviation and coefficient of variation of time-series solid circulation rates, the influences of operation parameters on fluctuation strength and circulation stability of solid interaction between fluidized bed units was revealed.
The three dimensional Eulerian-Eulerian computational fluid dynamic (CFD) model and simulation method for dual fluidized bed simulation were developed based on kinetic theory of granular flow. Then, the physical model of dual fluidized beds were built and three dimensionalfull loop simulation of dual fluidized bed was realized for the first time. Baesd on the full loop simulation, Key gas-solid flow behaviors related to gas-solid circulation behaviors and instalibilty mechanism which are hard to be acquired in experimental study, e.g. the transient flow regime, solid velocity, solids distribution, circulation characteristics, were numerically investigated.