Interconnected Fluidized Bed Reactors

The inventory of the system includes the total amount of material that is in the fuel and air reactors (expressed in kg of solid or in kg /MW j) in the loop seals and in the piping units that connect the different components. The solid circulation is selected to ensure the complete fuel conversion. In terms of mass balance of the system, it is possible to identify two important parameters (i) the solid circulation flow rate and (ii) the solid conversion. 

Assuming 1 MW,, of the fuel entering the system and full conversion of the gas, the solid circulation flow rate is calculated as follows  

And AXs is the solid conversion, which is calculated as the difference in solid mass flow rate at the inlet and the outlet of the fuel and air reactors divided per the total solid mass flow rate difference that is achieved in case of complete solid conversion  

The combination of bubbling fluidized bed as fuel reactor and riser as air reactor has been also presented for a 10 kW i unit in other works [36-38]. The 02-depleted air and the OCs are separated in a HT cyclone to avoid the particle going to the other plant components. Two particle seals are also included to prevent gas mixing between the two reactors the first one is placed between the fuel reactor and the air reactor and it can be fluidized with air or steam, the second one at the bottom of the downcomer that connects the cyclone and the fuel reactor. 

A 65 kW unit based on eirculating fluidized bed reactors has been successfully tested from Alstom [47] operated with CaS04 as OC, and the same eonfiguration has been scaled 

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A lOkWfl, prototype has been constructed and tested from IFP-Lyon [53]. Three interconnected fluidized bed reactors are considered (Figure 5.11) one reactor is operated as fuel reactor and two reactors are used as air reactors. The reactors are bubbUng bed reactors. The control system is based on the use of pneumatic non-mechanical valves that allow the solid circulation to be independent of the gas flow rate in the reactors. In 2011, the same facility has been modified to be operated with coal by the addition of a carbon stripper. New analyses have been carried out in order to test the OC activity, the effect of the temperature in the coal conversion and the gasification reaction [54] that occurs in the fuel reactor. 

Differently from the interconnected fluidized bed reactors, the dynamically operated PBRs have to be operated with proper heat management strategies in order to produce hot gas that are suitable for a combined cycle. In a PBR, the maximum solid temperature, and, thus the maximum gas temperature for the thermodynamic cycle, is usually achieved during the oxidation phase (which is always strongly exothermic as shown in Figure 5.15) and the maximum solid temperature increase is caleulated as follows [61] ... 

Solsvik and Jakobsen [140] performed a set of one-dimensional two-fluid model simulations in order to elucidate whether such simple models can be suitable for further simulations of two interconnected fluidized bed reactor units with a dynamic solid flux transferred between these reactor units which collectively is denoting a circulating fluidized bed. Dynamic solid circulation between two fluidized bed units that operate at different conditions (e.g., temperatures and feed compositions) is an inherent requirement for the novel SE-SMR technology operated in fluidized bed reactors. A less computational demanding one-dimensional model to study the performance of interconnected reactor units will be an important contribution to the progress of the commercialization of circulating fluidized bed reactors intended for the SE-SMR technology. 

The simulation results of the one-dimensional model were found to be in fair agreement with the two-dimensional model considering the chemical conversion of the reactor, as is also utilized by the Kunii-Levenspiel type of modeis [85]. Moreover, with extended conductive fluxes, fair temperature profiles can be predicted with the one-dimensional model. On the other hand, the flow pattern, i.e., the phasic fractions and gas phase velocity, were associated with the largest uncertainty in the current model. However, the internal flow details did not have signiflcant influence on the chemical process performance. Thus, the current one-dimensional model was considered to have good potentials for further CEB model developments in order to study interconnected fluidized bed reactors with a dynamic solid flux transferred between the reactor units. 

Figures 1 and 2, respectively, show the old and new processes. The major innovations are use of (1) a spray dryer absorber in place of the wet venturi, absorber, centrifuge, rotary dryer combination (2) a cyclic hot-water reheat system interconnecting thermally the calciner product solids and the effluent gas from the spray dryer absorber and (3) a coal-fired, fluidized-bed reactor for conversion of magnesium sulfite (MgSO ) and sulfate (MgSO ) to MgO and SO gas. Otherwise, the two systems are very similar, utilizing a regenerable absorbent to recover the sulfur material as a usable commercial grade of concentrated sulfuric acid.

Most of the research about chemical looping has been focused on the first configuration, and different reactor concepts have been developed in recent years to make the process feasible as discussed in Ref. [33]. The utilization of solid fuel has been also investigated in recent years and some pilot plants based on interconnected fluidized beds have been built at different sizes [34]. The chemical looping combustor units have been built at different sizes and tested with several OCs. In the second case, the research is at the early stage. 

A10 kWjij continuous reactor of interconnected fluidized beds has been discussed in Ref. [55] for CLC with biomass (Figure 5.12). The prototype is composed of a fast fluidized bed as air reactor, a cyclone and a spout-fluid bed as fuel reactor. In this case, the spout-fluid type reactor is adopted as fuel reactor in order to have a strong solid mixing between the biomass and OC particles and a long residence time. The spout-fluid reactor is designed to have two difl erent compartments. In the first part, the reaction chamber is located where the OC and the biomass are combined to produce exhaust gas and solid species (metal oxide and unconverted fuel), while the second part contains the inner seal that is located at the top and it is used to allow solids movement to the air reactor. The fuel reactor is fluidized by using exhaust gas recirculation (Table 5.2). 

As with conventional CLC, two continuously operated and interconnected fluidized beds are a well-suited reactor configuration for CLPO due to the excellent gas-solid contacting pattern, and several studies have been conducted with this set-up [92,117,119,120]. Additionally, the back-mixing inherent in this reactor configuration results in a uniform oxygen availability as opposed to the temporal variation in the previously discussed batch-fluidized beds (which constitute integral reactors in which the lattice oxygen decreases with time). 

Opposiny-reactants mode. When immobilized with a catalyst or enzyme, the interconnected tortuous pores or the nearly straight pores of a symmetric inorganic membrane provides a relatively well controlled catalytic zone or path for the reactants in comparison with the pellets or beads in a fixed or fluidized bed of catalyst particles. This unique characteristic of a symmetric membrane, in principle, allows a novel reactor to be realized provided the reaction is sufficiently fast. The concept applies to both equilibrium and irreversible reactions and does not utilize the membrane as a separator. Consider a reaction involving two reactants, A and B ... 

The Spherizone circulating reactor has two interconnected zones. In one, the riser, there is fast fluidization while in the other, the downer, features a slower packed bed mode. The two zones can generate different materials and extend the range of PP properties. 

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