In industrial furnaces, boilers, and incinerators, flue gases carry corrosive species—SO₂, HCl, alkali chlorides, and heavy-metal vapors—that attack refractory brick linings. Matching brick grade to flue gas composition maximizes lining life, minimizes downtime, and ensures environmental compliance.
Key Flue Gas Factors
Acidic Components: SO₂, SO₃, and HCl lower pH and form corrosive sulfates/chlorides.
Alkaline Species: KCl, NaCl from biomass or waste feedstock deposit on bricks and flux silica/alumina phases.
Particulate Abrasion: Fly ash and particulates erode brick surfaces under high-velocity flow.
Temperature Profile: Zones range from 800 °C–1,600 °C; each region demands specific chemical and thermal properties.
Brick Grades and Their Chemical Resistance
High-Alumina Bricks (85–95 % Al₂O₃): Excellent resistance to acidic flue gases and siliceous ash. Service up to 1,600 °C with minimal slag penetration. Ideal for mid-zone convection sections.
Magnesia–Chrome (MgO–Cr₂O₃) Bricks: Superior basic-slag resistance; chromium oxide forms self-healing layers against chlorides and sulfates. Recommended for primary combustion chambers handling high Cl/S ratios.
Silicon Carbide (SiC) Bricks: Extremely abrasion-resistant with chemical inertness to most acids and alkalis; service up to 1,400 °C. Best for high-velocity ductwork and particulate-laden flue gas lines.
Insulating Firebricks (IFB): While low-density IFBs (< 1.3 g/cm³) offer thermal insulation, select high-purity alumino-silicate IFBs in back-up layers where chemical exposure is minimal.
Matching Strategy
Analyze Flue Gas Chemistry: Conduct gas sampling and laboratory analysis to quantify SOx, HCl, alkali chloride, and particulate concentrations.
Zone Mapping: Divide duct or furnace into high-temperature (combustion), transition, and cooling zones. Assign brick grades based on local gas chemistry and temperature.
Corrosion Testing: Reference ASTM C724 or IEC slag corrosion data for candidate bricks in simulated flue gas environments.
Thermal and Mechanical Assessment: Ensure chosen bricks also meet thermal shock (ΔT ≥ 1,000 °C) and mechanical strength (CMOR, HMOR) requirements.
Conclusion
Effective flue gas management begins with selecting refractory brick grades tailored to specific chemical compositions and temperature regimes. High-alumina bricks counter acidic sulfur attack; magnesia–chrome bricks resist aggressive chlorides; SiC bricks endure abrasion and alkali exposure. By rigorously analyzing gas chemistries, mapping zones, and validating through corrosion testing, distributors can specify brick linings that deliver extended service life and reliable operation in challenging flue gas environments.
