Air Pollution Control Device for Steel Induction Furnace

About Induction Melting Furnace
 
Induction Melting Furnace is major steel producing technology using scrap & sponge iron (directly reduced iron) as main raw material. This technology contributes significant steelmaking capacity in secondary steel sector in India and abroad. It has
 
Some distinct advantages:
 
1. Low project capital cost
2. Low energy cost
3. Consumes steel scrap which is a major solid waste
4. Environment Friendly, as it produces lower emission than primary blast furnace
5. Uses clean fuel i.e. electrical power
6. Can be set up near source which saves transportation cost of raw material as well as finished goods.
 
Manufacturing Process
 
Induction Furnace Process includes melting of various types of steel scrap in a pot. The energy required for the melting process is provided by electrical induction. The feeding of raw material in the induction furnace is on intermittent basis. As one charge of scrap melts, slag is removed from the molten metal and certain alloys are added to achieve the desired grade of steel. Molten metal is then poured into refractory lined buckets from where it is further poured in different sizes Moulds to get the desired size of steel cast. Ingot/Billet is allowed to cool down and then the product is separated from the Moulds.
 
Flue gases are generated during melting of scrap. The characteristics and volume of these gases mainly depends upon type of scrap used in the furnace, i.e. with the degree of contamination in the scrap. These flue gases need proper treatment for removal of dust particles/gases before being discharged into the atmosphere.
 
Air Pollution
 
Steel scrap comes from various sources and generally has contaminants/coating etc on it. When this scrap is heated contamination/coating etc. disintegrates from steel and comes out either as slag or becomes air borne, thus causing air pollution. The major source of Air Pollution is :
 
1. Dust & Dirt
2. Rust
3. Oil & Grease
4. Paint & Galvanized Iron
5. PVC Coated Steel
 
Capacity Calculation of required Equipment for Air Pollution Control Device:
 
The volumetric capacity of Air Pollution cannot be judged as such, but fair engineering estimation can be made with data like:
 
1. Furnace Capacity
2. Power Rating in KWH
3. Detailed Dimensions of Furnace
4. Air Cooler Arrangement for workers at Furnace Platform
 
Characteristics of Air Pollution Generated In Induction Furnace:
 
1. Pollutants: Dust & Dirt, Metal Oxide & Traces of NO, SO , CO, CO x 2 2
2. Concentration: Average ******0 mg/Nm , Max. ********0 mg/Nm 3
3. Temperature: At Hood: ******0 C, At Bag House : *****0 C
4. Nature of Dust: Non Sticky, Non Abrasive and Non Explosive
 
Control Practices
 
The control practice adopted in controlling air pollution in this industry mainly depends upon following parameters:
 
1. Dust/Gas Concentration at inlet
2. Discharge Standards
3. Temperature of Flue Gases
4. Nature of Pollutant i.e. Dust (Particulate) or Gaseous
5. Nature of Dust i.e. Sticky, Abrasive
6. Nature of Gases i.e. Corrosive, Non Corrosive
7. Control Practices
 
Selection of Technology for Air Pollution Control Device
 
The following technologies are usually adopted for Air Pollution Control System in Induction Furnace industry:
 
a. Bag Filter Type System (Dry)
b. Venturi Scrubber Type System (Wet)
 
About Bag Filter Type System (Dry Process)
 
Working of Equipment Bag Filter Type System
 
1. Suction Hood
 
Feeding of raw material is an intermittent process in Induction Furnace and at the time of completion of every heat, molten metal is tapped with tilting platform of furnace. Hence, it requires a Movable Hood System so as to facilitate slag removal, raw material (bulk) feeding and tilting of platform. Hoods are designed based on crucible diameter and optimum clearance of hood from furnace.
 
2. Spark Arrestor:
 
This is a pre-filtration device. It is used for arresting live particles and medium to large hot particles which can damage & burn bags. Depending upon factors such as Flue Gas Volume, Dust Load & Temperature Profile, this can be a
Gravity Chamber or Cyclone (with multiple tubes). The Spark Arrestor, depending upon actual conditions in any particular unit, can thus be designed based on centrifugal or gravitational forces or combination of both, suitable for that particular unit.
 
3. Bag Filtration System :
 
It is used for fine filtration of Flue gases to remove dust particulate matter. Dust particles are retained on one side of Bags and clean gases are received on other side. The combined treated gases from all the bags are collected at top of bag house and are passed through to ID Fan. The dust collected on other side of bags is de-dusted through pulse air jet mechanism with high pressure air. The dust is collected at bottom of hopper and is discharged through a Screw Conveyor and Rotary Air Lock Valve. Pulse jet mechanism is carried out through high pressure air with the help of sequencer and solenoid valve.
 
4. ID Fan:
 
ID Fan provides necessary driving force to convey flue gases from suction hood to top of the chimney. The volume sucked overcomes the total resistance offered by equipment and duct with the help of fluid horse power provided by ID Fan driven by suitable motor.
 
5. Stack (Chimney):
 
The generated gases are passed through chimney of suitable height and diameter. The chimneys are provided and based on volume of flue gases, temperature, dispersion desired, composition of gases and legal provisions for height.
 
Advantages & Disadvantages of Bag Filter Type System
 
Advantages:
 
1. Low Power Consumption
2. Dry System, No water pollution
3. No corrosion of metal except normal wear & tear
4. Suitable for dust pollution which are the major cause of pollution in induction furnace
5. Achieves desired characteristic of treated gases even for high dust load, as
    Efficiency of bag filters is very high
6. Low operation & maintenance cost
 
Control Practices
 
1 Large Floor Area
2 Unchecked high temperature can lead to burning of bags.
 
About Venturi Scrubber Type System (Wet Process)
 
Working of Equipment Venturi Scrubber Type System
 
1. Suction Hood:
 
Feeding of raw material is an intermittent process in Induction Furnace and at the time of completion of every heat, molten metal is tapped with tilting platform of furnace. Hence, it requires a Movable Hood System so as to facilitate slag removal, raw material (bulk) feeding and tilting of platform. Hoods are designed based on crucible diameter and optimum clearance of hood from furnace.
 
2. Ducts & Bends:
 
Ducts and Bends are required to convey flue gases from point of suction to the chimney and connect various equipments like Hood, Venturi Scrubber, ID Fan and Chimney. Their sizes are based on flue gases volume & temperature.
 
3. Venturi Scrubber:
 
In Venturi Scrubber the flue gases are passed through a converging section where velocity of the gases becomes very high. The water is sprayed on high velocity gases with high pressure at throat. The particles in the gases become wet. The purpose of throat is to provide the area with highest velocity and wet these particles so that they become heavy and easily removable. The gases are then passed through a diverging section where lot of energy is recovered which was lost in converging section. These gases are then passed through separator where wet dust particles are collected at bottom and clean gases are passed through mist eliminator followed by exit from scrubber.
 
4. ID Fan :
 
ID Fan provides necessary driving force to convey flue gases from suction hood to top of the chimney. The volume sucked overcomes the total resistance offered by equipment and duct with the help of fluid horse power provided by ID Fan driven by suitable motor.
 
5. Stack (Chimney) :
 
The generated gases are passed through chimney of suitable height and diameter. The chimneys are provided and based on volume of flue gases, temperature, dispersion desired, composition of gases and legal provisions for height.
 
Advantages & Disadvantages of Venturi Scrubber Type System
 
Advantages :
 
1 Low Floor Area
2 Can handle high temperature gases
3 Suitable for gas pollution such as SO , NO , etc. 2 x
 
Disadvantages :
 
1 Higher Power Consumption to achieve desired standards
2 Generates Water Pollution
3 Material of Construction is prone to corrosion hence low life cycle
4 Choking of pipe, Nozzle and duct (near scrubber) due to Wet condition
5 Higher operation & maintenance cost
6 Can remove submicron particle only with very high pressure drop leading to still higher power consumption
7 Material of Construction is prone to corrosion hence low life cycle
8 Choking of pipe, Nozzle and duct (near scrubber) due to Wet condition
9 Higher operation & maintenance cost
*0 Can remove submicron particle only with very high pressure drop leading to still higher power consumption
 
Discharge Characteristics as Per Norms
 
1. Dust : Less than **0 mg/ Nm3
2. Ÿ Temp : Less than *****0 C
3. Gases : Traces of SO , NO , Co , Co 2 x 2
4. Suction Efficiency : More than *0%