Rotary Furnace With Air Pollution Control Device

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