Limestone attrition in circulating fluidized-bed combustors (CFBCs) has received limited attention. Although there are a number of early studies on attrition in bubbling-bed systems, most current studies focus on simultaneous calcination and sulfation. However, this subject is increasing in importance as CO 2 looping cycles are proposed. CO 2 looping cycles involve repeatedly calcining the CaCO 3 component of the limestone to drive off a pure stream of CO 2 for storage or sequestration. Here, we have looked at five limestones from across Canada, the United States, and Mexico to determine the extent of their attrition under calcining conditions in fluidized-bed systems. This work shows that attrition varies very significantly from limestone to limestone, and even among different batches. It is clear, therefore, that each limestone will have to be carefully categorized to determine its potential for use in such cycles. Also, since limestones crush differently, even those limestones that are double-sieved may have very different initial size distributions. This will affect the results seen in tests carried out under realistic conditions. This work shows that most of the material loss in multiple calcination/ carbonation cycles is in the first few cycles, and that even a very low level of sulfation can be a very effective means of reducing that material loss.
Objective Human submandibular gland (SMG) stones are associated with inflammation, fibrosis and microcalcifications in the surrounding tissues. However, there is little information about the accompanying cell injury-repair process, apoptosis, and cell proliferation. The purpose of this study was to investigate such an association and its clinical significance. Design of Study Mid-gland paraffin sections of human SMGs (“stone glands”) and normal SMGs (“non-stone glands”) were subjected to stains for general histology (hematoxylin and eosin), fibrosis (Masson’s trichrome), and calcification (alizarin red) and to immunohistochemistry for proliferative activity (Ki-67), and apoptosis (Caspase-3). Tissues were assessed for areas of inflammation, calcium deposition, and fibrosis, and for cycling and apoptotic cells. Results Acini were atrophic and proportionately fewer in lobules with fibrosis in stone glands. Additionally, stone glands had intraluminal calcifications (microliths) in scattered excretory and striated ducts and blood vessel walls. Areas of inflammation and fibrosis were small and uncommon, and calcifications were not seen in non-stone glands. Proliferating and apoptotic cells were common in the main duct of stone glands where ciliated and mucous cell hyperplasia and stratified squamous metaplasia had occurred, uncommon in the main duct of non-stone glands, and uncommon in all other parenchymal elements of both stone and non-stone glands. Conclusion Stone obstruction in the main excretory ducts of SMG resulted in progressive depletion of acini from proximal to distal lobules via calcification, inflammation, fibrosis, and parenchymal cell atrophy, apoptosis and proliferation. Interlobular duct microliths contributed to this depletion by further provoking intralobular inflammation, fibrosis, and acinar atrophy.
Bench-scale and 160 MWe demonstration tests were conducted for petroleum coke and high volatile bituminous coal blends. The bench-scale apparatus was a 100-mm-dia reactor located at the Canada Centre for Mineral and Energy Technology (CANMET), Energy Research Laboratories. The demonstration tests were conducted on the Tennessee Valley Authority’s (TVA) 160 MWe Shawnee Atmospheric Fluidized Bed Combustion (AFBC) Unit located at Paducah, Kentucky. Five and ten percent nominal volatile petroleum cokes were tested in the bench-scale unit. In addition, for the five-percent petroleum coke blends of 25, 50, and 75-percent petroleum coke, with the balance coal, were also examined at the bench scale. Eight start-up tests have been conducted with 50 percent blend of green delayed petroleum coke at the Shawnee AFBC unit. The bench-scale tests revealed that the volatile content in the petroleum coke was the primary factor affecting start-up. The tests showed that the volatile content from the coke and coal ignited at similar times; the char required longer to ignite. Bench-scale tests showed adequate start-up performance with blends up to 75 percent petroleum coke. Cold start-ups were conducted at the Shawnee AFBC Unit with 7 to 10 percent volatile green delayed petroleum coke. In all the start-ups, the operating temperature of 816°C was reached within 15 min of introducing the petroleum coke blend; this is similar to when high volatile bituminous coal was used. One start-up required a longer time because limestone had to be used to generate the bed. Local hot spots (982°C) were noticed in several start-ups for short periods, but subsided when additional air was supplied. Although more difficult to control, TVA routinely starts the Shawnee AFBC Unit with 50 percent shot petroleum coke and 50 percent high volatile bituminous coal.
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