Characterization of the Most Penetrating Aerosol through State-of-the-Art Filters in Electrical Steelmaking

CRISTINA GUTIERREZ-CANAS (1), Luisa Marroquin (2), Alfredo Perez (2), Saioa Astarloa (2), Juan Andres Legarreta (1), and Fernando Vergniory (3).

(1) University of the Basque Country, Alameda Urquijo, 48013Bilbao, Spain (2) AIRg, María Díaz de Haro, 48920 Portugalete, Spain (3) ACYMA Chavarri, 4, 48910 Sestao, Spain

     Abstract Number: 538
     Last modified: May 13, 2010

Abstract
For electric steelmaking is a discontinuous process (<1 hour/batch) at a high material rate (about 100-120 tonne steel/batch), emission rate and dynamics are of special concern. The extended use of galvanized scrap, and its physical state (organics, plastics, dirt) address to specific trace pollutants. Emission limits have been set up throughout the world, for pollutants such as PM10 and PM2.5, depending on local polices), for heavy metals –primarily Zn and Pb-, and for dioxins/furans.

Traces characterization presents specific challenges due to the intrinsic temporal variations and to the lack of standard methods validated for such discontinuous processes. Methodology –as described elsewhere- uses near real-time aerosol analyzers, and in parallel cascade impactors as size-resolved sample preseparators for further analysis.

The aim is to demonstrate the relevance of operation dynamics in understanding emission and, therefore, in identifying control technologies. Zinc aerosol occurs significantly within the penetration window of state-of-the art bag filters. It is reasonable assumption for medium- to low-volatile PCDD/F congeners.

Zinc dynamics is strongly linked to that of the furnace itself and to the further cooling. Precursors are related to volatilization and bursting of CO bubbles inside the furnace. Evolution of Zn-aerosol along a chemically-reacting flow under a non-constant cooling rate lead to a high variety of morphologies and agglomeration patterns, which concentrate around 1 micron. Any Zn-specific control must focus on dynamics. That is not the case for PCDD/Fs. Memory effects and de novo synthesis play a decisive role all along the cooling duct. The main question has been to identify the potential filterability of each individual congener, that means acting on the filter temperature to optimize the removal as condensed matter.
Here are presented the results of a 3-year joint project on 12 full-scale furnaces accounting for ~8% of Europe27 melting capacity.