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Incineration, Pyrolysis, and Energy Recovery
Published in Charles R. Rhyner, Leander J. Schwartz, Robert B. Wenger, Mary G. Kohrell, Waste Management and Resource Recovery, 2017
Charles R. Rhyner, Leander J. Schwartz, Robert B. Wenger, Mary G. Kohrell
In contrast to conventional mass burn incinerators that burn wastes on a grate or hearth, fluid-bed combustors burn wastes in a turbulent bed of heated inert materials, such as sand or limestone, kept in suspension by an upward flow of high velocity primary combustion air. Efficient combustion requires a homogeneous fuel. Sludge, wood chips, or other homogeneous combustible waste can be fed into the chamber directly, but municipal solid waste must be processed into refuse-derived fuel (RDF) prior to burning. Heat is transferred to the waste particles by contact and radiation. In the standard design of the fluid-bed reactor, sometimes called the “bubbling fluid-bed” (BFB), the air velocity is 1 to 3 m/s and the bed medium remains in the chamber. A variation of the design, the circulating fluid-bed reactor (CFB), uses air with a velocity of 5 to 10 m/s which continually sweeps bed media and incompletely combusted feedstock from the chamber. This material is separated from the flue gas and reintroduced into the reactor. Secondary combustion air is supplied in the upper part of the chamber. Figure 8.5 depicts the two circulating fluid-bed combustor designs.
Advanced Fossil Fuel Power Systems
Published in D. Yogi Goswami, Frank Kreith, Energy Conversion, 2017
Advantages of CFB boilers include low furnace temperatures (low NOx, no slagging), coarse circulating solids (simple feed systems, handles poor fuels), and long residence time (complete combustion for reduced UBC and CO, good sorbent utilization). In addition to a wide variety of coals, CFB boilers can burn hard-to-burn fuels such as petroleum coke and anthracite as well as opportunity fuels such as waste coals and biomass (or even discarded tires). They also have very good emissions performance with smaller scrubber systems (with selective noncatalytic reduction for NOx in the boiler). Proper fuel analysis is requisite for proper CFB selection and design (for a range of expected feedstock parameters—especially for the ultimate analysis—see Table 13.8).
Particle Characterization and Dynamics
Published in Wen-Ching Yang, Handbook of Fluidization and Fluid-Particle Systems, 2003
Favorable heat transfer is a major reason for the success of CFB reactors in such applications as combustion and calcination. CFB heat transfer has previously been reviewed by Grace (1986b), Glicksman (1988), Leckner (1990), Yu and Jin (1994), Basu and Nag (1996), Glicksman (1997), and Molerus and Wirth (1997). Temperature gradients tend to be small within the riser due to vigorous internal mixing of particles, while the gas and particle temperatures are locally nearly equal, except at the bottom (Grace, 1986; Watanabe et al., 1991). Because of wear caused by particle impacts, heat transfer surfaces are predominantly vertical, and only this case is considered here. Many CFB combustion systems are also equipped with external fluidized bed heat exchangers, cooling solids returning to the bottom of the riser while they are being recirculated in the external loop. However, these operate as bubbling beds exchangers, and the reader is referred to Chapter 3. In this section we consider the case where the bulk solids are hotter than the wall, as in CFB combustion. It is straightforward to change to the case where the transfer is in the opposite direction.
Study on particle cluster behavior in the multistage circulating fluidized bed
Published in Particulate Science and Technology, 2022
Xiaolai Zhang, Gongpeng Wu, Yan He, Xuejun Yu
Gas-solid flow plays a crucial role in industrial applications of circulating fluidized bed (CFB) reactors. Previous results have revealed that solid phase exists as individual particle and particle cluster in gas-solid flow systems (Yin et al. 2019; Wang et al. 2020). Particle cluster, also known as a mesoscale flow structure, is generally defined as the locally dense particle group. Ideally, dispersed particle flow with uniform distributions can provide satisfactory reaction performances in the riser. Cluster formation, however, tends to occur and even dominate under practical operating conditions due to inevitable gas-particle and particle-particle interactions. Typically, particle clusters are observed in the dilute core-annular flow and the dense phase flow (Helland et al. 2007; Wang et al. 2008). On the one hand, inter-particle and particle-wall collisions cause particle kinetic energy losses, promoting the formation of particle clusters (Moran and Glicksman 2003; Lu et al. 2005). On the other hand, gas-particle interactions such as drag force and gas turbulence also exert important impacts on the cluster formation (Eaton and Fessler 1994; McMillan et al. 2013). Compared with the gas-particle contact, the contact efficiency between gas and cluster becomes poor because clusters exhibit large size and small local void fraction. Further, mass and heat transfer processes, depending on hydrodynamics, are inhibited. Thus, it is essential to clarify cluster motion mechanisms for the enhancement of reactor performances and the optimization of scale-up processes.
Development of a circulating fluidized bed partial gasification process for co-production of metallurgical semi-coke and syngas and its integration with power plant for electricity production
Published in International Journal of Coal Preparation and Utilization, 2022
Diyar Tokmurzin, Desmond Adair, Timur Dyussekhanov, Kalkaman Suleymenov, Boris Golman, Berik Aiymbetov
To validate the feasibility of the proposed method, the experiments were conducted in a custom-designed CFB reactor. Figure 1 illustrates a schematic diagram of the experimental setup. The CFB system consisted of a riser, standpipe, loop seal, coal supply system, gas-solid separators, sample withdrawal devices and syngas treatment subsystem. The riser (1) was made of heat-resistant stainless-steel tube with an inner diameter of 150 mm and a height of 5.6 m. The fluidizing air (I) from an air blower (15) was injected into riser through a series of bubble caps fixed on the air distribution plate at the bottom of the riser. Coal from a bunker (4) was introduced into the riser through one of two hoses (13), both of 70 mm in inner diameter. The coal inlets were located at distances of 700 mm and 350 mm from the air distribution plate. The coal flow rate was adjusted with a screw feeder (5).
Circulating fluidized bed reactors – part 01: analyzing the effect of particle modelling parameters in computational particle fluid dynamic (CPFD) simulation with experimental validation
Published in Particulate Science and Technology, 2021
Janitha C. Bandara, Rajan Thapa, Henrik K. Nielsen, Britt M. E Moldestad, Marianne S. Eikeland
Circulating fluidized bed (CFB) is one of the favored technologies in power generation industries due to its distinct advantages of high heat and mass transfer rates, homogeneous reactor temperatures, extended gas-particle contact time, low pollutant emission and fuel flexibility (Li et al. 2004, 2014; Tricomi et al. 2017). Enhanced particle mixing in CFB prevents the generation of hot and cold spots, which is important in gasification and combustion processes as highly exothermic reactions are involved. CFB can be a single/double reactor system as illustrated in Figure 1 or multiple reactor system according to the process requirement. In a single reactor system, the reactor operates at fast fluidization regime in which the particles are carried away with the gas flow, separated with a cyclone and recycled back to the reactor across a proper gas sealing mechanism such as loop seal, L valve, J valve, seal pots, etc. CFB technology is a superior choice to exchange/circulate the same particle phase between different reactors having distinctive reactive environments. Continuous operation, runtime particle regeneration and controlled material handling some other highlights of CFB. However, efficient and safe design of CFB systems require accurate predictions of the gas-particle behavior in wide range of process conditions, where the rate of particle circulation is one of the most important parameters (Klenov, Noskov, and Parahin 2017).