A Hydrodynamic Study of a Fast‐Bed Dual Circulating Fluidized Bed for Chemical Looping Combustion

Abstract

This study explores the use of a dual interconnected circulating fluidized bed (CFB) for chemical looping combustion. This design can enhance gas–solid interactions, but it is difficult to control the solid transfer and circulation rates. With the use of a 1:1 scale cold‐flow model, an investigation determining the hydrodynamic behavior of the dual CFB system has been conducted. The cold‐flow system consists of two identical fast‐bed risers, each with an internal diameter of 100 mm and a height of 7 m. The simplified cold‐flow model is based on the chemical looping Pilot‐Scale Advanced CO2 Capture Technology (PACT) facility at Cranfield. Here, we have determined the minimum fluidization and transport velocities, and we have assessed the solid density profiles, transport capacity, and potential for the dilution by air/N2 leakage into the CO2 stream exiting the fuel reactor. The experimental procedure uses two different bed materials, molochite (ceramic clay) and FE100 (iron particles), and it satisfies the dynamic scaling laws to model the bed inventory within the system. The results indicate that the two fast‐bed risers share similar density and pressure profiles. Stable circulation can be achieved through pneumatic transport. The circulation rate of the system is flexible and can be adjusted by altering the fluidization velocity in the riser and by altering the bed inventory. The gas leakage from the loop seal to the cyclone was found to be sensitive to the bed height and fluidization velocity in the loop seal. However, by maintaining a loop‐seal bed height above 600 mm during operation, the outlet stream remains undiluted.

Transient Cold Flow Simulation of Fast-Fluidized Bed Air Reactor with Hematite as an Oxygen Carrier for Chemical Looping Combustion

“…In addition, its active nature of being easily oxidized and reduced during the reaction is an added benefit. The simulation results are validated with the experimental results performed by Haider et al [22] at Cranfield, UK. For this, FE100 is considered as the OC, and the variations in static pressure at different heights of the air reactor are compared.…”

“…The geometry of the air reactor considered in this simulation is taken to be similar to that in the experimental work of Haider et al [22]. The height of the riser is 7.3 m, with an interior diameter of 0.1 m, while the diameter of the inlet and outlet pipes is 0.04 m. Figures 3a and 3b show the mesh generated on the upper and lower parts of the computational domain.…”

“…This is the initial boundary condition of the simulation. After the bed of OC is formed, the inlet velocity of the air is increased gradually up to 2.50 m/s, which is slightly greater than the minimum fluidization velocity for the particle [22]. This velocity is supposed to lift the particle outside the reactor towards the mixture outlet.…”

“…The geometry of the air reactor is shown in Figure 2. It is a similar geometry to that used in the experimental work performed by Haider et al [22]. The air is chosen as the primary phase and hematite as the secondary phase.…”

“…They found that CuO has a better performance when the ash agglomeration effect is not considered, and Fe 2 O 3 performed better when the ash agglomeration effect was considered. Haider et al [22] experimentally investigated the cold flow performance of a dual circulating fluidized bed system to understand the hydrodynamic behavior of a pilot-scale advanced CO 2 capture technology (PACT) facility at Cranfield, UK. FE100 and molochite were used as the OC.…”