Blast furnace refractories
For many years, blast furnace where lined throughout with high duty firebricks and despite the development of special type of refractories. the use of high duty firebricks still predominates. The life of lining under the condition prevailing inside the furnace, decised the furnace campaign which should not be less than a few years.
Although the thickness of lining depends on the furnace size And on the location of the furnace.
Importance of Refractory Lining in Blast Furnaces
The refractory lining of a blast furnace is essential to its operational life. A blast furnace’s campaign life can be between the time it is blown up and the time it must be repaired, known as a capital repair shutdown; it normally lasts 5 to 7 years. It is a critical period for profitability, and a properly managed lining allows you to achieve a long campaign life. At worst, premature shutdowns will result in a reduction in productivity.
Factors Influencing Refractory Lining
The conditions in which the refractory lining is within the blast furnace are:
1. The carbon monoxide attack: the refractory lining gets corroded due to high levels of carbon monoxide.
2. Alkali Vapors: These are found in coke have ability to corrode.
3. Slag and Volatile Matters: Slag material that would abrade the lining.
4. Solid Raw-Feed Erosion - The solid raw materials have an abrasive effect.
5. Temperature: This coil operates at temperatures as extreme as 2000°C.
6. Molten Metal Contact - this too can degrade the lining
7. Furnace Operation and Design: One of the culprits is poor design or operation of the furnace itself.
Properties of Refractory Materials
Withstand high temperatures while saving its shape and chemical conditions, that's what refractory materials are designed for. Key properties include:
1. Thermal stability: Ability to withstand elevated temperatures without melting or the loss of performance properties.
2. Chemical Stability: Non-attacked by gases, molten metal or slag
3. Characteristic: Has to bear with mechanical loads at high as well low temperatures.
4. Good Heat Resistance: Ability to retain its shape/size when exposed at high temperatures.
5. Porosity: If lower, the porosity gives higher thermal conductivity
6. Bulk Density (BD) - High density is generally a property for strength & conductivity.
7. Refractoriness Under Load (RUL) - Power of refractory bricks to resist strength at high temperatures and in loaded conditions.
8. Creep resistance - Must not deform over time on exposure to high temperatures.
9. Thermal: Variable thermal conductivity may be imposed depending on the application.
Types of Refractory Materials
Different type of Refractories included from different perspectives:
1. Acid Refractories: Silica and Zirconia are example
2. Neutral Refractories: for example, carbon and graphite.
3. Example: magnesia Application for basic refractories
The type of refractory used depends on the characteristics of slag which is formed in furnace.
Section wise Refractory Lining of Blast Furnace
The blast furnace however is different. It consists of a triangularly shaped regions with names: the stack, bosh and hearth. Different refractory lining is required for different zone.
Stack Lining
Where the stack area differs in temperature and leads to an adequate amount of abrasion. On the top - where it is cooler - fire bricks with up to 35-40% alumina are used. Going down, as the temperature becomes higher and used Silica fire bricks with 50-60% alumina. In many applications this is lined with steel armour to prevent erosion by the solid charge.
Bosh Lining
Heat, slag and molten metal in the bosh region. Because of their excellent thermal conductivity and resistance to erosion, carbon blocks are used with a... A backup alumina brick lining could be provided to shield the carbon blocks. It could also be finished by graphitisation (to minimise erosion and enhancing heat-transfer)
Hearth Lining
Carbon blocks are used in the hearth, where slag and molten metal build up due to their high thermal conductivity and breakout resistance. A graphite coating is usually sprayed over the refractory to resist erosion. The entrapment of slag and metal in the joining material, can cause refractory damage so appropriate joint design need to be utilised and use of join material needs minimising.
Carbon lining pros and cons
There are a number of benefits to carbon lining:
1. Extended Campaign Life: Because of ultralow erosion and thermal conductivity.
2. Uncomplicated Cooling Scheme: High thermal conductivity of Carbon makes cooling much easier.
3. Uniform Surface - results in less erosion and better molten metal flow contact.
4. Thin Lining: More usable volume in the furnace.
Yet, there are some cons:-
1. Cost: It has a higher cost as compared to traditional fire bricks because of carbon lining.
2. Susceptible to water damage: The breaking down of the carbon lining can be very rapid if a cooling system were to fail.
For those seeking professional advice from Dutta & Co and high-quality solutions for furnace lining, including Furnace Lining in Kolkata, it is crucial to consult experts who understand the specific requirements and challenges of refractory materials in various furnace environments.
