Mechanism & Dynamic Characteristics Of Fouling And Slagging For Coal And Black Liquor Coal-Water Slurry

For a long time, fouling and slagging is one of the international problems which puzzles boiler whereas not found adequate solution. It endangers boiler's security, economical operation and equipment reliability. Mineral substance in coal is the primary cause giving rise to ash deposition. In order to reveal mechanism of fouling and slagging, mineral elements' migration and deposition behaviour at furnace are investigated in this paper. Sodium, ferrumiron, calcium are the important mineral elements causing ash deposition, accordingly, deliberate consideration is made in selecting trial fuels, Xinwen black liquor coal water slurry which contains plenty of sodium and other four fuels are chosen investigation objects. These fuels have good representativeness both in coal quality composition and ash fusing temperature. Consequently, the investigation in this paper is possessed of some general sense.One of the investigation emphases is black liquor coal water slurry' s combustion characteristics and fouling/slagging performance, aim at surveying its industrial application feasibility and potential problems. The results of thermobalance mechanism experiment, trial furnace pilot plant and industrial furnace application test show, black liquor slurry's viscosity is low, with favorable performance of flow and sprayability. It contains some organic constituents such as lignin, sodium-group compound. As a result, black liquor slurry is easy to fire. It have good quality of flameholding, but also its nitrogen oxide, sulfur dioxide, and flue dust contents are far lower than the coal- water slurry and raw coal. Accordingly, black liquor coal water slurry is possessed of notable economic benefits, environmental benefits and amplitude potential application.Yet, the sodium included in black liquor slurry is amiable to bring about fouling and slagging in heat transfer surface. The sintering test result show black liquor slurry is in possession of very predominant sintering performance, its initial sintering temperature is very low, only about 1073K. In the aspects of foul ing and slagging mechanism, a few innovative instruments and methods are employed to investigate the ash deposition mechanism and dynamic processes in detail, such as heat flux probe, particle sampling along the flue travel and electron probe microanalyzer, et al. For example, scanning electron microscope with energy spectrometer is adopted to analyze and compare the feature and mineral element content of the center grains, near wall grains, grains in wall slags and fly ash grains in chimney. The migration and deposition performance of the mineral substance contained in ash particle are looked into. The results indicate that fouling and slagging have direct relation with fuel self- performance. Sodium is the primary cause of the severefouling and slagging condition in the black I iquor coal water slurry-fired boiler. Its contents both the inial layer and who I ly slags are very high, as a result gave rise to silicium distribution in good agreement with aluminium in ash layer, by reacting with sodium most silicium and aluminium form aluminosiIicate, such as nepheline, whose fusing temperature is very low. The ferr urn iron enrichment is not apparent in the deposit initial layer of black liquor slurry. Silicium, aluminium, ferrumiron, calcium is the essential mineral elements causing coal ash deposition. Ferrumiron enrichment phenomenon is very evident in ash deposits. Ferrumiron and calcium plays synergism roles during the formation of slagging likelihood. The findings also show, the fouling mechanism is much different from slagging. The ferrumiron enrichment doesn't appear in the fouling deposits, thereof contents far less than in slagging deposits, whereas sodium and calcium contents higher than in slag deposits, which shows high temperature environment is in favor of ferrumiron deposition, however lower heating surface temperature is favorable to the coagulation of volati le alka I i and alka I ine earth metal vapor.In conclusion, the present slagging judgement mod...