Pressurized fluidized bed

A medium heat (11.2 MJ/m (300 Btu/ft )) gas for iadustrial appHcation has been produced at Westiaghouse Electric s pilot plant ia Waltz Mill, Pennsylvania (50), where lignite is gasified ia a pressurized fluidized bed which uses oxygen and steam. 

Eig. 8. Cost of electricity (COE) comparison where represents capital charges, Hoperation and maintenance charges, and D fuel charges for the reference cycles. A, steam, light water reactor (LWR), uranium B, steam, conventional furnace, scmbber coal C, gas turbine combined cycle, semiclean hquid D, gas turbine, semiclean Hquid, and advanced cycles E, steam atmospheric fluidized bed, coal E, gas turbine (water-cooled) combined low heating value (LHV) gas G, open cycle MHD coal H, steam, pressurized fluidized bed, coal I, closed cycle helium gas turbine, atmospheric fluidized bed (AEB), coal J, metal vapor topping cycle, pressurized fluidized bed (PEB), coal K, gas turbine (water-cooled) combined, semiclean Hquid L, gas turbine... 

In the 1970s commercial fluidized-bed combustors were limited to the atmospheric, bubbling-bed system, called the atmospheric fluidized-bed combustor (AFBC). In the late 1970s the circulating fluidized combustor (CFG) was introduced commercially, and in the 1980s the new commercial unit was the pressurized fluidized-bed combustor (PFBC). 

PressurizedFIuidized-Bed Combustors. By 1983 the pressurized fluidized-bed combustor (PFBC) had been demonstrated to have capacities up to 80 MWt (49). PFBCs operate at pressures of up to 1500 kPa (220 psi) and fluidization velocities of 1—2 m/s. Compared to an AFBC of the same capacity, a PFBC is smaller, exhibits higher combustion efficiencies with less elutfiation of fine particles, and utilizes dolomite, CaCO MgCO, rather than limestone to capture SO2. 

Table 2. Operating Conditions for an Atmospheric Pressure Fluidized-Bed Combustor ...

Beyond the ATS program, the DOE is looking at several new initiatives to work on -with industry. One, Vision 21, aims to virtually eliminate environmental concerns associated with coal and fossil systems while achieving 60 percent efficiency for coal-based plants, 75 percent efficiency for gas-based plants, and 85 percent for coproduction facilities. Two additional fossil cycles have been proposed that can achieve 60 percent efficiency. One incorporates a gasifier and solid oxide fuel into a combined cycle the other adds a pyrolyzer with a pressurized fluidized bed combustor. Also under consideration is the development of a flexible midsize gas turbine. This initiative would reduce the gap between the utility-size turbines and industrial turbines that occurred during the DOE ATS program. 

Once a technique has been established to design a model which simulates the hydrodynamics of a hot (possibly pressurized) fluidized bed, then a series of different sized models can be used to determine the influence of bed size on the performance of commercial beds, see Fig. 20. Model A simulates the behavior of commercial bed A, model B simulates a larger commercial bed B and so forth. Then by comparing models A, B with C we can determine the expected changes in operating characteristics when commercial bed A is replaced by larger beds B and C. 

Figu re 23. Exact and simplified models of a pressurized fluidized bed combustor. 

Glicksman and Farrell (1995) constructed a scale model of the Tidd 70 MWe pressurized fluidized bed combustor. The scale model was fluidized with air at atmospheric pressure and temperature. They used the simplified set of scaling relationships to construct a one-quarter length scale model of a section of the Tidd combustor shown in Fig. 34. Based on the results of Glicksman and McAndrews (1985), the bubble characteristics within a bank of horizontal tubes should be independent of wall effects at locations at least three to five bubble diameters away from the wall. Low density polyurethane beads were used to obtain a close fit with the solid-to-gas density ratio for the combustor as well as the particle sphericity and particle size distribution (Table 6). 

Almstedt, A. E., and Zakkay, V., An Investigation of Fluidized-bed Scaling-capacitance Probe Measurements in a Pressurized Fluidized-bed Combustor and a Cold Model Bed, Chem. Eng. Sci., 45(4) 1071 (1990)... 

Farrell, P. A., Hydrodynamic Scaling and Solids Mixing in Pressurized Fluidized Bed Combustors, Ph.D. Thesis, Massachusetts Institute of Technology (1996)... 

Glicksman, L. R., and Farrell, P., Verification of Simplified Hydrodynamic Scaling Laws for Pressurized Fluidized Beds Part I Bubbling Fluidized... 

Glicksman, L. R., Hyre, M., Torpey, M., and Wheeldon, J., Verification of Simplified Hydrodynamic Scaling Laws for Pressurized Fluidized Beds Part II Circulating Fluidized Beds, Proc. 13th Int. Conf. for Fluidized Bed Combustion, ip. 991 (1995)... 

PFH [Pressurized fluidized-bed hydroretorting] A process for making fuel gas from oil shale. Developed and piloted by the Institute of Gas Technology, Chicago. 

Pressurized fluidized-bed combustion (PFBC) is, as the name implies, operated at above atmospheric pressures. The beds and... 

In this contribution a novel fluidized-bed coating process is introduced to encapsulate heat-sensitive materials with particle sizes below 100 pum. Supercritical carbon dioxide is used as solvent for the coating material as well as carrier fluid for the core material. The behaviour of the high pressure fluidized-bed was investigated for different process parameters and materials. It is shown that the fluidization starts at lower fluid velocities if the pressure is increased and it was possible to fluidized particles with a mean size below 10 xm. The coating of glass beads with stearyl alcohol was carried out and layers with a thickness of 1-8 xm were achieved. 

The experiments were conducted in a laboratory scale device. A schematic view of the high pressure fluidized-bed coating apparatus is shown in Fig. 1. The apparatus consists essentially of three subsections the CO2 supply, the extractor (in which the CO2 becomes saturated with coating) and the high pressure reactor (where the coating takes place). The maximum allowable pressure in the device is 30 MPa at... 

Fig. 1. A schematic view of the high pressure fluidized-bed apparatus.

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