Formation of sulfur-rich melt near the floor tubing of kraft recovery boilers.Application: In the floor tubes of kraft recovery boilers Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor. In the process lignin of the wood, bound in black liquor at this phase, is burned and heat generated. , conditions are conducive to stress-corrosion cracking in composite metal when smelt that is rich in sulfur enters a molten phase.This study is part of a research project on the conditions that favor the formation of stress-corrosion cracks while a recovery boiler is operating. The project includes full-scale probing and measurements, laboratory studies, and theoretical chemical modeling. Here, we concentrate on sulfur-rich melts that can form near floor tubes. Sampling and analysis Smelt bed samples were taken near the floor tubing in two kraft recovery boilers. The inner layers of the samples had higher concentrations of sulfur, chlorine chlorine (klōr`ēn, klôr`–) [Gr.,=green], gaseous chemical element; symbol Cl; at. no. 17; at. wt. 35.453; m.p. −100.98°C;; b.p. −34.6°C;; density 3.2 grams per liter at STP; valence −1, +1, +3, +5, +7. , and potassium potassium (pətăs`ēəm), a metallic chemical element; symbol K [Lat. kalium=alkali]; at. no. 19; at. wt. 39.0983; m.p. 63.25°C;; b.p. 760°C;; sp. gr. .862 at 20°C;; valence +1. . Model calculations of melting behavior According to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. model calculations, the first melting point melting point, temperature at which a substance changes its state from solid to liquid. Under standard atmospheric pressure different pure crystalline solids will each melt at a different specific temperature; thus melting point is a characteristic of a substance and of a carbonate-sulfide mixture falls from 760[degrees]C to 510[degrees]C when chlorine and potassium are present. It decreased to 320[degrees]C when the mixture has polysulfldes. On-line electrical conductivity Not to be confused with electrical conductance, a measure of an object's or circuit's ability to conduct an electric current between two points, which is dependent on the electrical conductivity and the geometric dimensions of the conducting object. measurements of the smelt layer adjacent to the floor tubing showed sudden drops in the resistivity resistivity Electrical resistance of a conductor of unit cross-sectional area and unit length. The resistivity of a conductor depends on its composition and its temperature. , indicating the beginning of the molten phase. Laboratory measurements confirmed that the low resistivity values relate to the molten phase. Conclusions The composition of the smelt bed close to the floor tubes differs considerably from the average composition of the smelt bed because sulfur, chlorine, and potassium become enriched in the layer closest to the floor tubes. The enrichment of these three elements and the formation of a sulfur-rich melt may accelerate stress-corrosion cracking in the composite metal on the floor tubes in some kraft recovery boilers. However, sulfur enrichment varies widely, even within the same boiler. Backman, Hupa, and Kymalainen are researchers with Abo Akademi University, FI-20500 Abo, Finland. Pulliainen is with Savcor Group Ltd. Oy, FI-50100 Mikkeli, Finland. Address correspondence to Backman by email at: rainer.backman@abo.fi. |
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