I. Introduction

Blast furnaces are essential facilities for producing pig iron for steelmaking. With the advancement of ironmaking technology in China, blast furnaces have generally intensified their smelting processes. Ordinary domestic carbon bricks can no longer meet the requirement of achieving a furnace campaign life of over 10 years. As a result, large blast furnaces and many small and medium-sized intensified blast furnaces in China have had to import hot-pressed carbon bricks, (ultra-)microporous carbon bricks, and ceramic cups from abroad for constructing furnace bottoms and hearths. Among the various factors affecting blast furnace longevity, the effectiveness of furnace cooling and the quality of refractory materials are two crucial factors that cannot be ignored. Long-term production practice has shown that besides the belly, waist, and lower shaft of the blast furnace, the furnace bottom and hearth are also highly vulnerable areas. Particularly in recent years, with the use of copper cooling staves and highly efficient in-furnace gunning technology in the belly, waist, and lower shaft areas, significant breakthroughs have been achieved in blast furnace longevity. Consequently, the lifespan of the unrepairable furnace bottom and hearth has become the key determinant of a blast furnace's campaign life.

II. Why Choose "Ceramic Cup - Microporous Carbon Brick - Hearth Microporous Carbon Brick, Ultra-microporous Carbon Brick" Composite Lining Structure Technology for Long-lasting Blast Furnaces?

Blast furnace longevity is a systematic engineering project closely related to furnace design, cooling facility configuration and cooling medium, refractory material quality, furnace construction, front operation maintenance, and other factors. However, many ironmaking workers have deeply realized that temperature is the decisive factor for furnace body longevity because:

  • The mechanical properties of all brick linings and cooling wall materials deteriorate rapidly with increasing temperature;
  • The rate of any chemical and physical erosion accelerates with rising temperature;
  • The thermal stress of brick linings and cooling walls increases with temperature rise;
  • The stability and formation rate of the protective "slag-iron shell" inside the furnace lining decreases as the cooling wall temperature rises, reducing its protective effect on the furnace lining due to continuous peeling.

Therefore, the refractory materials of the furnace lining need to possess high thermal conductivity first, controlling the hot surface temperature of the furnace lining in a "thermal equilibrium" state. This is a basic requirement for reducing the above erosion and damage rate and increasing the furnace body's erosion resistance. Specifically, the 1150°C isotherm of molten iron solidification temperature should be controlled either in the molten pool outside the hot surface of the entire furnace bottom and hearth carbon bricks or in a small area within the hot surface, forming a protective "slag-iron shell" of certain thickness. This "slag-iron shell" serves to protect the furnace bottom and hearth lining while greatly reducing the circulating scouring and penetration erosion of molten iron on the furnace bottom and hearth.

Regarding the refractory material damage in blast furnace bottoms and hearths caused by molten iron penetration erosion and circulating scouring, the industry generally believes that in areas where the hearth and furnace bottom contact molten iron, materials should be selected with low porosity and pore diameters < 1μm.