Biomass reactors

The reactors used to convert biomass are simply the conventional reactors, and they are very important in the biomass transformation process. Depending on the origin of material and the desired prodnct, one can obtain varions geometrical configurations of the reactor. The collection or separation is not less important and requires specific equipments and special controls. 

Despite the huge demand for biomass processes, its reactors do not present major innovations and most of them are nsed in the oil and petrochemical processes. The literature presents several systems, bnt most of them are fluidized beds, because they satisfy some important reqnirements, such as, low residence times, high heat, and mass transfer and, in particnlar, the large movement of solid particles in contact with gases or vapors, which improves the decomposition reaction and fast evolution of products (gases or vapors) in the reactor. This rapid evolution goes to phase separation in cyclones and condensers. Cyclones and separation/cooling processes will not be discussed here they have been extensively reported in the literature (Lede, 2000). 

A major problem in these systems is the fluid dynamics. The bubbling system operates in two or more stages in conntercurrent or concurrent movements. Usually, it happens in both cases. 

In the fluidized bed, there are two phases (gas/liquid and solid). The particles are suspended by the gas bubbles and require a minimum speed of fluidization to keep them in suspension. With increasing gas flow, there will be formation of large bubbles and the solid particles are dragged, this affects the flow of gas and its contact with the particles. The yield to liquid products is high, about 70-75%, depending on the original material. 

It is suggested to consult the other systems in the literature, as described in the review of Bridgwater (2011). 

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Biological systems featuring nitrogen treatment seem to achieve higher removal rates for PhCs with respect to other treatments, such as submerged biofilters or fixed biomass reactors [60, 68, 83],... 

In this paper, we provide an overview of the reactor theory as it applies to the dilute acid hydrolysis and an assessment of the recent development in the process technology. While this paper gives an overall review, emphasis is placed on theory and practice of the biomass reactors performing dilute acid saccharification. Issues concerning the future development of this technology are also discussed. 

Understanding the characteristics and behaviour of biofilms vs. suspended biomass reactor systems. What is the role of biofilms or suspended biomass in the bioremediation of MTBE ... 

Gusmao, V.R. Martins, T. H. Chinalia, F.A. Sakamoto, I.K Thiemann, O.H. Varesche, M.B. (2006). BTEX and ethanol removal in horizontal-flow anaerobic immobilized biomass reactor, under denitrifying condition. Process Biochemistry, Vol.41, No.6, pp. 1391-1400... 

Another hydrogenation process utilizes internally generated hydrogen for hydroconversion in a single-stage, noncatalytic, fluidized-bed reactor (41). Biomass is converted in the reactor, which is operated at about 2.1 kPa, 800°C, and residence times of a few minutes with steam-oxygen injection. About 95% carbon conversion is anticipated to produce a medium heat value (MHV) gas which is subjected to the shift reaction, scmbbing, and methanation to form SNG. The cold gas thermal efficiencies are estimated to be about 60%. 

Some of the other research studies have addressed topics such as high soHds biomass digestion (154), utilization of superthermophilic organisms (155), advanced reactor designs (156), landfill gas enhancement (157), and microbiology of the mixed cultures involved in methane fermentation (158). 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

Ultrafast pyrolysis in the vortex reactor is capable of pyrolyzing biomass at high heat-transfer rates on the reactor wall by ablation and has been... 

Loop reactors are particularly suitable as bioreactors to produce, for example, single-cell protein (96). In this process, single yeast or bacteria ceUs feeding on methanol multiply in aqueous culture broths to form high value biomass at 35—40°C, 20 kg/m ceU concentrations, and specific growth rates of... 

Fluidized Bed. This reactor consists of a sand bed on which the biomass is grown. Siace the sand particles are small, a very large biomass can be developed ia a small volume of reactor. Ia order to fluidize the bed, a high recycle is required. 

The fluidized-bed bioreactor (FBBT) (26) increases the capacity of existing plants. Primary effluent is passed upward through the columnar reactor filled with sand or carbon with sufficient velocity to fluidize the bed. An attached biomass develops on the bed particles. Intimate contact between the biomass and waste is provided and improved removals are reported. Oxygen is provided by a deep U-tube reactor. No biomass recirculation is required and a secondary clarifier is not necessary. 

Because of the differences in primary and secondaiy metabolism, a reactor may have a dual-stage fed-batch system. In other words, fed-batch operation optimizes growth with little or no product formation. When sufficient biomass has accumulated, a different fed-batch protocol comes into play. 

The equations that have been developed for design using these pseudo constants are based on steady-state mass balances of the biomass and the waste components around both the reactor of the system and the device used to separate and recycle microorganisms. Thus, the equations that can be derived will be dependent upon the characteristics of the reactor and the separator. It is impossible here to... 

In the fixed-film reactor, the organisms grow on an inert surface that is maintained in the reactor. The inert surface can be gramJar material, proprietary plastic packing, rotating discs, wood slats, mass-transfer packing, or even a sponge-type material. The reacior can be flooded or have a mixed gas-hquid space (Fig. 25-52). The biomass level on the... 

Recently, a new concept in fixed film reac tors that uses an expanded or fluidized bed of particdes as the biomass support medium has been introduced. This reactor type can easily handle both low- and high-strength wastes with most electron acceptors. It will be discussed in detail in a later section. 

The laboratory studies utilized small-scale (1-5-L) reactors. These are satisfactoiy because the reaction rates observed are independent of reac tor size. Several reac tors are operated in parallel on the waste, each at a different BSRT When steady state is reached after several weeks, data on the biomass level (X) in the system and the untreated waste level in the effluent (usually in terms of BOD or COD) are collected. These data can be plotted for equation forms that will yield linear plots on rec tangular coordinates. From the intercepts and the slope or the hnes, it is possible to determine values of the four pseudo constants. Table 25-42 presents some available data from the literature on these pseudo constants. Figure 25-53 illustrates the procedure for their determination from the laboratory studies discussed previously. 

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