Printer Friendly

Formation of sulfur-rich melt near the floor tubing of kraft recovery boilers.

Application: In the floor tubes of kraft recovery boilers, 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, and potassium. Model calculations of melting behavior

According to model calculations, the first melting point 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 measurements of the smelt layer adjacent to the floor tubing showed sudden drops in the resistivity, 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.
COPYRIGHT 2002 Paper Industry Management Association
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2002, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Recovery boiler corrosion: summary of peer-reviewed paper
Author:Pulliainen, Martti
Publication:Solutions - for People, Processes and Paper
Date:Feb 1, 2002
Words:302
Previous Article:Comparison of cracking in recovery boiler composite floor and primary air port tubes.
Next Article:Oxygen delignification as a pretreatment for acetosolv pulps bleaching.


Related Articles
Fueling self sufficiency: pathways to change: black liquor and biomass gasification/ combined cycle is key to energy self-sufficiency in the pulp and...
Fireside behavior of black liquors containing boron.
Dust and flue gas chemistry during rapid changes in the operation of black liquor recovery boilers part II--dust composition.
Dust and flue gas chemistry during rapid changes in the operation of black liquor recovery boilers--Part 3: gaseous emissions.
TAPPI Kraft Recovery Short Course.
Susceptibility of composite floor-tube materials to stress corrosion cracking during recovery boiler operations.
TAPPI Kraft Recovery Short Course.
A pulp mill toolkit: new equipment and operating methods can help mills tackle common pulp mill problems.
Corrosion in lower furnace of kraft recovery boilers--in-situ characterization of corrosive environments.
Weyerhaeuser plans upgrade to Springfield plant.

Terms of use | Privacy policy | Copyright © 2020 Farlex, Inc. | Feedback | For webmasters