STUDIES ON INITIATION, GROWTH AND SINTERING IN THE FORMATION OF UTILITY BOILER DEPOSITS

Coal ash deposits and their associated problems still constitute one of the principal limitations for pulverized coal utility boiler design. The objective of this study is to gain a better fundamental understanding of the formation of boiler deposits formed in the use of pulverized coal. Three laboratory-scale devices were utilized to investigate the mechanisms of the initiation, growth and sintering processes involved in the formation of boiler deposits. Sticking apparatus investigations were conducted to study deposit initiation by comparing the adhesion behavior of the ash drops on four types of steel-based heat exchanger materials under the conditions found in a utility boiler and an entrained slagging gasifier. In addition, the adhesion behavior of the ash drops on a reduced steel surface were investigated. All the ash drops used in this investigation were produced from bituminous coals.;The development of deposit strength by fly ash sintering was investigated to provide an insight into the process of sintering occurring in the deposit mass. The investigation was accomplished by measuring the physical and chemical changes of the sintered products as a function of temperature. Additional parameters studied were the composition, time and atmosphere.;The combined use of these three techniques to evaluate deposit initiation, growth and sintering established a preliminary hypothesis to explain the mechanisms of utility boiler deposit formation.;A vertical externally-heated tube furnace was used as an accelerated test to study the deposits formed from nine coals, ranging from high-rank bituminous coals to low-rank subbituminous and lignite coals, under conditions simulating a utility boiler. Synthetic coals prepared from known minerals dispersed in a copolymer (polyester-styrene-divinyl benzene) were also tested to obtain a clearer understanding of the behavior of the minerals in coals during the deposit formation process.