About Mini Blast Furnace
A Mini Blast Furnace (commonly known as Mandir Bhatti or Shahi Bhatti) is a simple, time-tested and widely used system to produce secondary lead in India and many other countries. It is the most basic of all furnaces and a production system based on this technology has certain distinct characteristics such as:
Low Project Capital Cost
Low Energy Cost ( wooden coke fired)
Easy to install
Easy to operate & maintain
Production of low Antimony Lead (soft lead) at low temperature
Generates high pollution
Description of Mini Blast Furnace
The Furnace itself is a modified blast furnace which consists of a brick lined structure with fire brick oven in the midst and a metal Exo skeletal structure outside. Raw material & fuel (coke) is charged manually through the side metal doors fitted in the brick structure and air is provided from the FD fans provided at the back of the brick structure. Molten metal & slag is tapped at the pits made in front of the brick structure and flue gases are sucked from the top of the brick structure which is provided with a metallic hood.
A typical Double Oven Mini Blast Furnace has the following standard sizes & specifications:
Outside Dimensions of Brick Structure 2400mm L x 1900mm W x 2400mm H
No. of Ovens 2 Nos.
Oven Size
Top Dia 600mm
Bottom Dia 250mm
Depth 650mm
No. of FD Fans 2 Nos. (1 for each oven)
FD Fan Capacity 300cmh at 250mm of WG
No. of Charging Doors 2 Nos. (1 for each oven)
Charging Door Dimensions 1100mm H x 650mm W
Manufacturing Process
Lead to be manufactured from Mini Blast Furnace is usually obtained from scrapped batteries. They are cut open or broken to segregate lead scrap, plastic and other materials from it. Lead scrap in the form of lead powder and plates etc. is charged in the furnace along with a proportionate charge of wooden coke. Thereafter the furnace is manually fired with the help of rags. FD Fan provides the necessary air required for combustion from the back of the furnace. Coke in the oven performs the functions of both, the fuel as well as a reducing agent for obtaining lead from its oxides charged in the form of lead plates & powder.
Temperature of the furnace is maintained at the desired level for approximately 30 minutes, after which molten lead along with slag flows out from the bottom of the oven into the outlet pit. Here slag is separated and molten lead is poured into Ingot Moulds. To maintain this, continuous charge of raw material and coke is maintained in the furnace.
This process leads to generation of flue gases which are toxic in nature and need appropriate and adequate Air Pollution Control System for their treatment.
Process Details for a typical Double Mini Blast Furnace
Raw Material Charged 700-800 kg hr.
Fuel used Wooden Coke
Calorific Value of Fuel used 4000-5000 kCal kg
Fuel Consumed 70-75 kg hr.
Air provided for process 300 cmh
Lead Produced (1st Charge) 300-350 kg hr.
Flue Gas generation 8000-9000 cmh
Advantages and Disadvantages of Mini Blast Furnace
Advantages
No consumables used other than Wooden Coke which is also used as Fuel
Low Power Consumption
Produces low Antimony Lead suitable for soft lead purposes
Pollution can be controlled with minimum fugitive emissions
Easy to install, operate & maintain
Disadvantages
Cannot recover 100% lead in the first operation
Subsequent recovery of lead after first recovery consumes higher coke & manpower.
Equipment cannot be scaled up for higher production capacities.
Various types of lead present in used batteries, plates and paste of lead oxide are charged in the furnace. In addition to these, certain compounds of sulphur are also present in the batteries. When this material is heated in the presence of carbon, lead oxide is converted to lead. This conversion along with burning of fuel generates flue gases and fumes containing dust, dirt, oxides of lead, lead particles and other impurities etc.
Hence, to meet various goals of maintaining employees' health, for factory environments as well as regulatory requirements, it becomes imperative to get high end Air Pollution Control Systems to be installed with the Mini Blast Furnaces.
At the time of Delivery
1. Lead smelting
A.Mini blast furnace
B.Rotary furnace
2. Refining pots for refining and alloying.
3. Ball mills for lead oxide.
4. Fugitive emission control system.
5. Continous casting machines with ingot and jumbo ingot moulds
6. Battery cutting machines
7. Battery crushing and hydro sepration.
8. Sewage and effluent treatment plant
About Rotary Furnace
The Rotary Melting Furnace is a very flexible and universal equipment used for recycling many non-ferrous metals. It is the major lead production technology used in India and many other countries for Secondary Lead Production. A lead production system based on this technology has certain distinct characteristics such as:
Equipment scalable for installing higher capacities
Recovers all lead in one production cycle
Plates & powder from scrap battery as well as slag from Mini Blast Furnace can be used as raw material
Requires addition of certain consumables
Can be fired with various fuels
Generates high Pollution both as Flue Gases & Fugitive Emissions
Description of Rotary Furnace
It is a Rotary kiln in the form of a metallic cylinder with conical sides on both ends. Mild steel plate is used for construction of this shell and its thickness varies depending upon the capacity of the equipment. This shell is rotated on its own axis at 1-2 rpm. For this purposes tyres (also called riding rings) are fitted on the shell. These are fabricated from MS squares or flats, machined for a smooth finish. These tyres ride on steel rollers which are again machined finely. These rollers are fitted on a robust MS structural frame and driven by a gear & motor arrangement. The shell is lined inside with insulation and fire bricks of suitable Alumina content.
Conical ends of the furnace are open on both sides. The furnace is charged with Raw material along with additives from the front end. This side is provided with a movable door on which a burner is mounted. The burner can be a conventional one or a fully automatic one depending upon the fuel used. At the other end, an exhaust block lined with refractory bricks is provided. A tapping hole is provided in the center of the shell from where molten metal & slag are discharged. Flue gases generated are sucked from the exhaust block side of the furnace.
A typical 3.0 TpB Rotary Furnace has the following standard sizes & specifications :
Outside dimensions of the Rotary
Shell dia : 2075mm
Shell length : 2500mm
Total length : 4500mm
Charging dia : 450mm
Exhaust side dia : 450mm
Refractory thickness : 200mm
Fuel : Furnace Oil
Burner : Model 4 A
FD Fan capacity : 1250 cmh at 1000mm of WG
Gear Box in drive : 8, 1:40
Ratio Motor in drive : 15.0 HP x 960 RPM
Structure used for base : ISMC 250 x 80
Manufacturing Process
Lead to be manufactured from Rotary Furnace can be obtained directly from scrapped batteries or as slag from Mini Blast Furnace. In case of former, batteries are cut open or broken to segregate lead scrap, plastic and other materials from them; lead scrap in the form of lead powder/ plates etc. is charged in the furnace along with a proportionate charge of additives. In the case of latter, slag produced from Mini Blast Furnaces is charged into the Rotary Furnace, again with proportionate additives.
This process is a batch type process. After filling the required quantity of raw material (either manually or mechanically), the lid of the furnace at the front is closed. The burner attached to the moving door is then fired. Complete mass of lead raw.
Material along with additive chemicals is heated at high temperature inside the furnace. After some time, molten lead is collected at the bottom of the furnace by puncturing the central opening of the Rotary Furnace. Lead is collected either directly into Jumbo Ingot Moulds or in receiving channels from which they are poured into Jumbo Ingot Moulds.
After draining the Furnace of the first batch, production of next batch is undertaken and the Furnace is again charged with raw material. After three such batches, one batch of slag collected in Rotary Furnace is executed.
This process leads to generation of flue gases which are toxic in nature and need appropriate and adequate Air Pollution Control System for their treatment. The steps of Charging and Tapping of Rotary Furnace also lead to generation of Fugitive Emissions which need to be captured at source and treated to maintain ambient air standards at workplace.
Process Details of a typical 3.0 TpB Rotary Furnace
Raw Material Charged3000 kgs/ Batch
Total additive chemicals charged:400-500 kgs/ Batch
Rotational speed1-2 RPM
Fuel usedFurnace Oil
Calorific value of fuel used8600 kCal/ kg.
Fuel consumed30-40 lt/ hr.
Air provided for process1250 cmh
Lead produced9000-10000 kg/day (for Raw Material feed of 12-15 T
raw material being lead powder and plates)
Flue gas generation15000 cmh
Section View of Rotary Furnace
Advantages and Disadvantages of Rotary Furnace
Advantages
Recovers 100% lead in the first operation.
Slag produced is lead free.
Equipment can be scaled up for higher production capacities.
Disadvantages
Many chemicals are required for operation.
High power consumption.
Difficult to produce low Antimony lead suitable for soft lead purposes.
Fugitive Emissions need to be captured in addition to flue gases.
Need skilled operators and careful maintenance.
Air Pollution Control Device for Rotary Furnace
Apart from plates and paste of lead oxide from scrap batteries, slag from Mini Blast Furnace is charged in the Rotary Furnace. In addition to these, certain compounds of sulphur are also present in the batteries. When this material is heated in the presence of carbon, lead oxide is converted to lead. This conversion along with burning of fuel generates flue gases and fumes containing dust, dirt, oxides of lead, lead particles and such other impurities etc.
Hence, to meet various goals of maintaining employees' health and factory environments as well as regulatory requirements, it becomes imperative to get high end Air Pollution Control Systems to be installed with the Rotary Furnaces.
Characteristics of Air Pollution generated in Rotary Furnace
Selection of Technology for Air Pollution Control System
Based on the parameters and the standards mentioned, the following technology is adopted for Air Pollution Control System in Rotary Furnace:
Rotary Chamber
Gravity Chamber
Involute Cyclone
Pulse Jet based Bag House Filtration System
Details of Equipments allow with Functions
Rotary Chamber
Rotary Chamber receives very hot gases from Rotary Furnace while cold gases from atmosphere are induced into chamber via specially designed profile. Thus chamber works as an equalizing chamber to reduce the temperature of gases and also where sedimentation of dust particulate matter takes place.
Duct & Bends
Ducts and Bends are required to convey flue gases from point of suction to final top of the chimney and connect various equipments like gravity chamber, cyclone, bag house, ID Fan and chimney. All bends and reducers are aerodynamically designed and have provision of manhole cleaning mechanism.
Gravity Chamber
It is a low pressure drop device which:
Allows large size particles to settle down
Cools down temperature of flue gases
Used as spark arrestor to entrap live or red hot particles.
Involute Cyclone
Cyclone is used to remove medium size particles from flue gases stream. The treated flue gases are discharged from top and dust is collected at bottom.
Bag Filtration System
It is used for final filtration of flue gases to remove fine dust particulate matter using Pulse Jet Technology. Treated gases from all the bags are collected at top of bag house and passed through ID Fan to exhaust the same through chimney. The dust is collected at bottom of hopper and is discharged through Rotary Air Lock Valve.
ID Fan
ID Fan provides necessary driving force to convey flue gases from top of furnace to top of the chimney. The volume sucked overcome the total resistance offered by equipment and duct with the help of fluid horse power provided by ID Fan driven by suitable motor.
Stack (Chimney)
The generated gases are passed into atmosphere after treatment through chimney of suitable height and diameter.
At the time of Delivery
About Lead Refining
Lead recycled from used lead acid batteries or other sources (Secondary Smelting) via the Mini Blast Furnace or Rotary Furnace route, contains lot of contamination and undesired components. On the other hand, Lead required for battery manufacturing is either soft Lead with 99.97% purity or hard Lead of varying Antimony compositions.
In order to make quality of lead suitable for its different uses, different variations of pot melting processes are employed. These include Re-Melting for removal of slag, Refining” for attaining required purity levels and Alloying for producing various alloys of lead.
The equipments used are the same, the consumables and the processes, however, differ.
Description of Melting Pot
The Melting Pot (or Refining Pot or Alloying Pot, as it is variously called), is a mechanical mixing device with a pot and a heating arrangement. The inner pot is made of heavy MS plate with dish end bottom. It is placed within a jacket of refractory bricks, which in turn, are protected by an outer cover of MS plate with reinforcements. The pot is covered at the top with opening for feeding lead ingots and is provided with an electro-mechanical mixer. At the bottom, a heating source, usually an oil fired burner, is provided to heat the pot and to melt the lead.
Once lead melts, impurities are skimmed and removed and any consumables required are added. Lead is then drained from the pot through an outlet pipe and valve.
Capacity of such pots depends upon the requirements of particular units. Standard pot capacities made are from 4.0 TpB to 20.0 TpB. Higher capacity pots are also manufactured as required by any particular establishment.
A typical 10.0 TpB Refining Pot has the following standard sizes and specifications:
Diameter (ID) 1150mm
Height 1250mm (Dish Depth of 200mm)
Flange Width 350mm
Outer Shell Diameter 1900mm
Stirrer MoC & Dia SS-304 & 75mm
Stirrer Motor 5.0 HP x 960 RPM
Outlet Valve Size 40mm
Burner Diesel Fired
Fuel Consumption Range 8-18kg ltr
Melting pots are installed both with and without accessories which may include Ingot Casting Machine, Ball Making Machine (where Ball Mills are installed down the line), Air Pollution Control Systems, Jib Cranes etc.
Production Process
Melting Processes have been grouped as
Re-Melting Process
Refining Process
Alloying Process
Re-Melting Process
This process is undertaken for value addition to the recycled lead from furnaces. Lead is melted in the pot and major impurities are skimmed from it to make it saleable in the market.
Refining Process
Lead is melted in the pot, additives such as Sulphur, Wooden Powder and Coke Breeze are added and mixed gently followed by dross removal. Thereafter, Tin is added to remove Copper and temperature is increased to 550-6000C. Further, additives such as Sodium Nitrate & Caustic Soda are added to remove Antimony. This process is repeated to get the desired purity of lead.
Alloying Process
Lead is melted in the pot, additives such as Sulphur, Wooden Powder & Coke Breeze are added and mixed gently followed by dross removal. Thereafter, Tin & Antimony are added to the liquid metal to get the desired grade of Lead.
Air Pollution Control Device for Refining Pot
Melting processes lead to generation of air pollution at the following stages
Initial heating and melting generates fumes
Drossing with sulphur, wooden powder and coke breeze generates lot of smoke and dust particles
Further heating for Refining and Alloying with different chemicals generates fumes and dust particles.
Hence, to meet various goals of maintaining employees' health, factory environments as well as regulatory requirements, it becomes imperative to get high end Air Pollution Control Systems to be installed with the Melting Pots.
Air Pollution Control Device for Refining Pot
Dust : 500-600 mg/Nm
Temperature : 60-80C G
Gases : Fumes and Dust
Discharge Characteristics required as per Norms
Dust : Less than 50 mg/Nm
Lead ( Pb) : Less than 10 mg/Nm
Temperature : 50-60 C
Gases : Not Detectable
Selection of Technology for Air Pollution Control
Based on the Parameters and the Standards mentioned, the following technology is adopted for Air Pollution Control System in Melting Pot:
Pulse Jet based Bag House Filtration System
Details of Air Pollution Control Device with functions
Aerodynamically designed suction hoods are provided to capture flue gases generated at source itself.
Duct & Bends
Ducts and bends are required to convey flue gases from point of suction to final top of the chimney and connect various equipments like suction hood, bag house, ID fan and chimney. All bends and reducers are aerodynamically designed and have provision of manhole cleaning mechanism.
Bag Filtration System:
It is used for final filtration of flue gases to remove fine dust particulate matter using Pulse Jet Technology. Treated gases from all the bags are collected at top of bag house and passed through ID Fan to exhaust the same to chimney. The dust is collected at bottom of hopper and is discharged through Rotary Air Lock Valve.
Bag Filtration System
It is used for final filtration of flue gases to remove fine dust particulate matter using Pulse Jet Technology. Treated gases from all the bags are collected at top of bag house and passed through the ID Fan to exhaust the same through chimney. The dust is collected at bottom of hopper and is discharged through Rotary Air Lock Valve.
ID Fan
ID Fan provides necessary driving force to convey flue gases from top of furnace to top of the chimney. The volume sucked overcome the total resistance offered by equipment and duct with the help of fluid horse power provided by ID Fan driven by suitable motor.
Stack (Chimney)
The generated gases are passed to atmosphere after treatment through chimney of suitable height and diameter.
At the time of Delivery
Ingot casting machine
An ingot casting machine (continuous ingot caster) is a chain conveyor based mechanical arrangement which is used for easier handling of molten lead from melting pots. It leads to hassle-free casting of lead into ingots with minimum human contact and keeps this process safe, clean and fast.
It is a custom made device suited for particular capacity required by user. The size of ingot to be casted can also be varied. Further, in special cases, even subdivision of ingots into smaller shapes is possible for suitability of usage.
The output of a melting pot needs to be synchronized with the speed of the conveyor. A rotary distributor drum continuously receives the molten metal and pours it into ingot moulds below it. The ingot moulds are fastened on a chain conveyor that continuously moves in a loop. A robust frame of ms is provided for fitting of this conveyor alongwith sprockets, shafts and geared motor based drive. There is a water jet based cooling arrangement mounted on the frame itself which helps cooling down of the metal in the mould. It is provided with a mechanical knocking arrangement at the end of line for 100% knocking of ingot from the mould.
These can be further supplemented with provision of multiple cooling lines, water re-circulation system, gas burners for drying up moulds, fumes collection hoods and discharge end conveyors.
Note: due to continuous up-gradation in technology, specified & projected values may differ in actual products
