Air reactors

As is the case with pure bubble columns and gas-operated loop reactors, most bioreactors in technical use are aerated with oxygen or air. Reactors with pure surface aeration, such as roller bottles, shake flasks and small stirred reactors or special reactors with membrane aeration, are exceptions. The latter are used for the cultivation of cells and organisms which are particularly sensitive to shearing (see e. g. [28 - 29]). The influence of gas bubbles in increasing stress has been described in many publications (see e.g. [4, 27, 29, 30]). In principle it can be caused by the following processes ... 

Modem plants operate with o-xylene feedstock loadings of 90-100 g/Nm3 air. Reactor effluent gas is precooled in a gas cooler (3) before... 

Development of the Photo-CREC-Air reactor also involved the characterization of fluid flow patterns in the unit and the assessment of the UV radiation reaching the impregnated mesh. The fluid flow pattern calculation and the fluid flow visualization can be developed using CEX-4.3 software for fluid flow simulation. A plane of symmetry in both the x and y directions can be assumed by simulating the flow patterns in the Venturi section. Hiis enables the sub-division of the reactor s physical volume into 4 quarters. This makes possible the use of smaller cell sizes and an improved convergence (Ibrahim, 2001). 

Ibrahim, H., and de Lasa, H., 2003, Photo-catalytic degradation of air bonre pollutants apparent quantum efficiencies in a novel photo-CREC-air reactor, Chem. Eng. Sci., 58(3-6) 943-949. 

For photocatalytic conversion of model pollutants in air (refer to section 2.10.5), model pollutants such as iso-propanol, acetone, and acetaldehyde are recommended to be used. Acetone and iso-propanol injections of 40, 50, and 60/xl of the liquid pollutant can be employed in the 14.7 L Photo-CREC-Air reactor. For acetaldehyde 30,40, and 50 /xl liquid injections can be used to get the desired initial pollutant concentrations. A gas chromatograph (HP 5890) equipped with a HP-3393A integrator, a TCD and aPoropak Q packed column are adequate to identify and quantify chemical species, including product intermediates and carbon dioxide. Examples of this type of photocatalytic experiments for the photoconversion of model pollutants in air are provided in Chapter VIII. 

The debate still remains regarding which configurations are the most adequate for the photocatalytic reactors to photoconvert air borne pollutants (Ollis and Al-Ekabi, 1993). Several options have been described (Chapter 11) fluidized bed (Brucato et al., 1992 Dibble and Raupp, 1992 Yue et al., 1983 ), annular packed bed (Raupp et al., 1997), coated honeycomb (Sauer and Ollis, 1994 Suzuki et al., 1991 Suzuki, 1993), fixed powder layer (Formenti et al., 1971 Peral and Ollis, 1992) and fiber optic reactor (Peill and Hoffmann, 1995). The Photo-CREC-Air reactor (Ibrahim and de Lasa, 2002) optimizes TiOa-mesh iiradiation and air contacting the supported TiOa. As reported in the upcoming section, this configuration yields model pollutant conversions with high apparent quantum efficiencies. 

APPARENT QUANTUM EFFICIENCY IN PHOTO-CREC-AIR REACTORS... 

The OCs react with the oxygen in the air reactor, while in the fuel reactor different types of fuel can be adopted. The generic reactions that occur during the CLC are listed as follows (Eqs. 5.1-5.4). 

Copper can be present as CuO, CU2O and Cu. Above 1000 °C, it can only be oxidized to CU2O at atmospheric pressure [6]. Because of this thermodynamic equilibrium, this carrier is applicable for the CLOU concept. In this concept, CuO is formed in the air reactor and... 

The chemical looping concept can be accomplished with two main configurations in the first configuration, the solid material is circulating between the fuel reactor and the air reactor, while in the second case the solid material is stationary and the gases are alternatively fed to the reactor by using a gas switching system. 

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. 

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. 

The present facility has been used recently for CLC with solid fuels [39] by changing the fuel feed configuration in order to increase the residence time in the fuel reactor. A carbon stripper is also included to separate the unconverted char and the OC that is transferred in the air reactor. The setup has been also used to scale up a new experimental facility of 100 kWth, which is operated at atmospheric pressure with solid fuels (Figure 5.3). 

A similar facility has been proposed in Ref [40] for 50 kW j combustor with a bubbling fuel reactor and high-velocity riser as air reactor (Figure 5.4). In this case, the solid level in the fuel reactor is controlled by a valve that is connected with an horizontal pipe at the bottom of the reactor where air stream is passing and moving the solids to the air reactor. 

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. 

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). 

Refs. [72, 73] are based on the use of Ni- and Fe-based OCs. In Ref. [72], different GT compressor ratios are investigated in order to optimize the performance of the plant. The maximum temperature of the GT is dictated from the maximum temperature acceptable from the solid material in the air reactor. In the study by Wolf [73], a sensitivity analysis is carried out by using an air reactor temperature of 1000 °C and 1200 °C. By increasing the maximum solid temperature, the efficiency increases from around 49% up to 52.4% with a CO2 capture rate of 100%. In the study by Consonni [72], the maximum solid temperature has been varied from 850 to 1050°C with an electrical efficiency of 43-48% and CO2 capture rate of 100% (Figure 5.26). A supplementary natural gas post-firing has been adopted to improve the combined cycle efficiency up to 52.5% (with reduced CO2 capture rate to 54%) by increasing the maximum turbine inlet temperature (TIT). 

A different approach has been discussed in the studies by Ishida [79] and Naqvi [80] to improve the electrical efficiency of the thermodynamic cycle based on a multi-stage CLC (Figure 5.27). The air from the compressor is fed to an HP air reactor and the HT... 

By increasing the maximum temperature at the air reactor and, thus the TIT of the gas turbine, the electric efficiency increases (about -1-1 percentage points of the net electric efficiency every 100 °C) the lower gain in electric efficiency compared to the natural gas power... 

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