Focus on Producing All Kinds Of High Quality Refractory Fire Bricks !
Treatment Plan for Refractory Brick Detachment in Hot Blast Stove Lining
Six hot blast stoves in a company’s 640,000-ton calcium carbide production line’s carbon material drying unit have experienced varying degrees of damage to their refractory linings since 2019. During production, refractory bricks have been falling off, severely impacting the stable operation of the hot blast stoves. Furthermore, the loosening of the wall bricks poses a risk of collapse, and the actual service life of the hot blast stoves is far below their design life. This paper analyzes the main factors contributing to the damage to the hot blast stove refractory linings based on actual usage and the locations of the damage, and proposes targeted countermeasures. These measures can prevent further damage to the hot blast stove refractory linings and extend the actual service life of the hot blast stoves.
Refractory Materials for Coke Oven
Main Damaged Parts of the Hot Blast Stove Lining
Structure of the Hot Blast Stove
The hot blast stove consists of a combustion chamber, a baffle wall, and an auxiliary fire bed. The roof is constructed of refractory arch bricks. Its dimensions are: length 5548mm, width 5666mm, height 6400mm. The combustion chamber volume is 60m³, and the auxiliary fire bed volume is 20m³. (See plan and section views of the hot blast stove.)
Parts of Damaged Hot Blast Stove Lining
Damaged, deformed, and collapsed lining above the furnace door. Burned combustion chamber platform; cracked and tilted baffle wall. Cracked, deformed, and tilted gable wall; deformation and collapse of the main wall and arch at the hot blast outlet or inlet; and arch collapse.
Causes of Damage to the Refractory Lining of Hot Blast Stove
Analysis reveals the following main causes of damage to the refractory lining of hot blast stoves:
1. High-Temperature Thermal Stress
The large temperature difference between the inner and outer surfaces of the refractory bricks in the hot blast stove wall generates significant thermal stress. Specifically, the inner surface of the lining experiences substantial compressive stress, while the outer surface experiences significant tensile stress. The expansion force and load on the refractory masonry are concentrated on the inner surface of the inner lining. The temperature changes on the inner surface of the refractory brick lining cause cracking, leading to loosening and detachment, resulting in arch collapse and partition wall collapse.
2. Mechanical Abrasion and Wear
The high-temperature combustion exhaust gas and blast air exert a strong impact and abrasion on the surface of the lining, especially the lower partition wall of the combustion chamber in the hot blast stove. The impact of the high-temperature combustion airflow causes vibration, leading to cracking, detachment, and short circuits in the lower part of the combustion chamber partition wall.
3. Creep Deformation
Creep deformation under high temperature and pressure is the cause of damage to the refractory bricks in hot blast stoves.
4. Inadequate Structural Design
Local damage and deformation lead to gradual deterioration, eventually affecting the entire hot blast stove structure. Wear of the pulverized coal pipes causes pulverized coal to leak into the insulation layer, burning and compressing the refractory bricks, leading to cracks in the load-bearing walls, brick loss and collapse of the arch, and even complete collapse.
5. Improper Operation Exacerbates Damage to the Hot Blast Stove Refractory Layer
(1) The furnace temperature of the hot blast stove consistently exceeds design requirements. The designed furnace temperature is below 850℃, but the actual operating temperature in the carbon material drying section is between 950℃ and 1050℃.
(2) Long-term high negative pressure operation results in excessive thermal stress on the firebreaks, gable walls, and other parts, causing brick cracking and misalignment.
(3) Frequent blast furnace start-up and shutdown cause drastic temperature changes in the refractory masonry, leading to cracks on the inner surface of the wall.
(4) During operation, long-term material return and movement of the drying cylinder impact the inlet flange, causing damage to the hot air outlet wall and arch.
6. Poor masonry quality causes damage to the refractory layer of the hot blast stove.
This is mainly due to large gaps between refractory bricks and insufficient filling of the gaps with refractory mortar during construction.
In response to the above-mentioned damaged parts and factors contributing to the damage to the refractory lining, the following measures are proposed:
(1) Strictly operate the hot blast stove according to the process design requirements. Control the furnace temperature below 850℃, control the air pressure, reduce dryer vibration, and avoid impacting the inlet flange.
(2) During hot blast stove overhauls, use refractory castable to locally reinforce the pulverized coal pipe inlet to prevent pulverized coal from leaking into the insulation interlayer.
(3) During hot blast stove overhauls, use refractory castable and reinforced steel integrally cast ring beams for the arch bearing wall to prevent arch subsidence caused by local damage to the bearing wall.
Hot Blast Stove Lining Repair
The main damaged parts of the hot blast stove lining are above the furnace door, the fire baffle wall, the gable wall, the main wall at the outlet, and the arch ring. Damage is mainly caused by thermal stress, vibrations due to airflow impact, improper operation, and unreasonable local structural design, resulting in overall damage to the hot blast stove lining. By standardizing the operation of the hot blast stove, the furnace temperature is controlled below 850℃ and the air pressure below -30Pa to reduce dryer vibration and avoid impact on the inlet flange.
During major overhauls of the hot blast stove, targeted improvements are made to address structural deficiencies. For example, refractory castable is used for partial reinforcement at the pulverized coal pipe inlet, and the arch-top load-bearing wall is constructed using a ring beam integrally cast with refractory castable and reinforcing steel. This addresses the distribution, bearing, and mitigation of thermal and structural stresses, preventing structural damage caused by concentrated stress release. This also avoids damage to the hot blast stove’s refractory lining, extending its actual service life.
How were refractory materials for coke ovens and hot blast stoves invented and applied?
At that time, Europe did not use a method known as the rudimentary kiln to produce tar from coal. Around 1810, Britain invented a kiln that did not recycle byproducts. Following this, from 1850 to 1900, primarily in Germany, the modern chamber coke oven was invented.
The byproduct-non-recycling kiln used clay bricks, and chamber coke ovens were initially made of clay bricks as well. In the latter half of the 19th century, semi-silica bricks appeared, thus establishing them as the standard material for coke oven refractory bricks. This is because the heating shrinkage characteristics of semi-silica bricks are compatible with those of siliceous bricks and clay bricks, resulting in good volumetric stability at temperature and low manufacturing cost.
Examples of the quality characteristics of semi-silica refractories. The current design of using siliceous refractories in the carbonization chamber of coke ovens began in the early 20th century (1920). Semi-siliceous refractories, with their composition close to the eutectic point of Al2O3-SiO2, exhibit superior thermal strength and dimensional stability compared to silica bricks. General properties of semi-siliceous bricks are described below.
Hot blast stoves, like coke ovens, are indispensable equipment in blast furnace operation. Since Cobb’s invention of the hot blast stove in 1857, the blast furnace and hot blast stove have functioned as a pair of large-scale pieces of equipment. The refractory materials used in these furnaces, from the use of clay bricks to the advent of high-temperature blast in 1960, have remained largely clay-based for a century.
