Blast Furnace Refractoriness

Blast furnace is shaft furnace which applies blasted hot air to support coke combustion and to make molten iron ore reduce into metal iron, it is continuous iron smelting thermal equipment works at high temperature and reductive atmosphere. Blast furnace is divided into furnace throat, furnace shaft, furnace waist, furnace bosh, furnace hearth and furnace bottom.

Furnace throat is the part where constantly suffers furnace charge direct impact and friction, so high density high alumina bricks are usually used here, to prolong their service life, anti-wearing cast steel protection plate is used to protect them.

Furnace shaft upper and middle parts temperature is only 400~800 ℃, there is no slag formation and almost no slag corrosion, the main damages are furnace charge impacting, ascending dust abrasion, alkali and zinc gases corrosion, carbon deposition. So fireclay bricks are usually used at furnace shaft upper and middle parts. But with the development of long life blast furnace, high grade refractories with better wearing resistance and stripping resistance, such as high alumina bricks and sillimanite bricks are used here.

At furnace shaft lower part, temperature is high, large amount of furnace cinder is formed, accompanied with descending charge friction, ascending furnace dusts washing and alkali vapors corrosion. So premium clay bricks, high alumina bricks, even Si3N4 bonded SiC bricks or Sialon bonded corundum bricks which have excellent slag resistance, alkali resistance, high temperature strength and abrasion resistance are used here. Clay bricks and high alumina bricks are mainly used in small capacity blast furnaces, while SiC products and Sialon bonded corundum bricks are mainly used in large capacity blast furnaces.

At furnace waist, temperature raises to 1400~1600℃, large amount of molten slag is formed here, slag corrosion is very severe, K, Na vapors corrosion is also very severe, dust containing ascending hot air also has great washing and corrosion to furnace lining, coke and other materials also has friction to furnace lining. Under the co-action of up mentioned factors, refractory materials suffers more severe damage. Earlier, fireclay bricks and high alumina bricks are usually used at furnace waist part, especially in small capacity blast furnace. For large capacity blast furnaces, silicon nitride bonded silicon carbide bricks, reaction bonded SiC bricks are often adopted, Sialon bonded corundum bricks are also gradually used. For middle and small blast furnaces, the ratio of alumina carbon bricks is also increasing, i.e., alumina carbon bricks or even micro-pore alumina carbon bricks are applied in middle and small blast furnaces.

At furnace bosh, temperature ascends to 1600~1650℃, sla

g viscosity continually decreases, and its corrosion to furnace lining aggregates. What’s more, air current washing ,furnace charge friction, alkali vapors corrosion, carbon deposition and atmosphere fluctuation all aggregate furnace lining damages, so the quality of refractory products should be further improved. Earlier, high alumina bricks and corundum bricks are usually used at furnace bosh, but now silicon carbide bricks are most often used.

Furnace hearth upper part adjacent to tuyere zone temperature is about 1700~2000 ℃, furnace bottom temperature is about 1450~1500℃. In furnace hearth, coke burns and generates very high temperature, so this part has the severest molten corrosion to furnace lining. Furnace hearth part tuyere adopts sillimanite bricks, corundum castable and graphite packing, now SiC refractory materials are more and more popularly used. Iron spout is usually built by Al2O3-SiC-C bricks or carbon blocks.

Furnace bottom refractory lining mainly suffers molten iron permeation and corrosion damage. Graphite bricks and micro pore carbon bricks with high density, good thermal conductivity and good corrosion resistance are used at furnace bottom. Ceramic cup, i.e., the working lining between furnace bottom and furnace hearth iron liquid containing part built by Sialon bonded corundum bricks, corundum mullite bricks and synthesized  mullite bricks, is developed and has better performance.

Blast furnace tuyere zone temperature is above  2000℃, there also suffers great thermal stress, such s friction and other physical damage, alkali, zinc, carbon deposition and other chemical corrosion, air current and molten materials impact damages. Earlier, fireclay bricks or sillimanite bricks are usually used at tuyere zone, in recent years, SiC products and Sialon boned corundum products which have very good alkali corrosion resistance, high mechanical strength are used at this part.