Rotary Furnace with Air Pollution Control Device

A V e n t u r e o f C a p t . A n i l K . V e r m a

The matter was conceived and written by Capt. Anil K. Verma.

Rotary Furnace with Air Pollution Control Device

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

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:

Ÿ Equipment scalable for installing higher capacities

Ÿ Recovers all lead in one production cycle

Ÿ Plates & powder from scrap battery as well as slag from Mini Blast Furnace can be used as raw material

Ÿ Requires addition of certain consumables

Ÿ Can be fired with various fuels

Ÿ 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 RotaryShell dia : 2075mmShell length : 2500mmTotal length : 4500mmCharging dia : 450mmExhaust side dia : 450mmRefractory thickness : 200mmFuel : Furnace OilBurner : Model 4 A Make: Wesman with complete assemblyFD Fan capacity : 550 cmh at 44mm of WGGear Box in drive : 8”, 1:40 RatioMotor in drive : 15.0 HP x 960 RPM

Structure used for base : ISMC 250 x 80

Process Details of a typical 3.0 TpB Rotary Furnace

Section View of Rotary Furnace

Raw material charged : 3000 kgs/ BatchTotal additive chemicals charged : 400-500 kgs/ BatchRotational speed : 1-2 RPMFuel used : Furnace OilCalorific value of fuel used : 8600 kCal/ kg.Fuel consumed : 30-40 lt/ hr.Air provided for process : 550 cmh Lead produced : 9000-10000 kg/day (for Raw Material feed of 12-15 TpD; raw material being lead powder and plates)

Flue gas generation : 15000 cmh

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.

Air Pollution Control Device for Rotary Furnace

3Dust : Less than 50 mg / Nm

3Lead (Pb) : Less than 10 mg / Nm

o Temperature : 60-90 C

Gases : Traces of NO and SO x 2

Discharge Characteristics required as per Norms

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:

Ÿ Rotary Chamber

Ÿ Gravity Chamber

Ÿ Involute Cyclone

Ÿ Pulse Jet based Bag House Filtration System

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

3Dust : 8000-15000 mg/Nm

o Temperature : 100-120 C

Gases : Traces of NO and SOx 2

Details of Equipments allow with Functions

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.

Rotary Chamber

AdvantagesŸ Recovers 100% lead in the first operation.Ÿ Slag produced is lead free.

Ÿ Equipment can be scaled up for higher production capacities.

DisadvantagesŸ Many chemicals are required for operation.Ÿ High power consumption.Ÿ Difficult to produce low Antimony lead suitable for soft lead purposes.Ÿ Fugitive Emissions need to be captured in addition to flue gases.

Ÿ Need skilled operators and careful maintenance.

Advantages and Disadvantages of Rotary Furnace

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.

ID Fan

The generated gases are passed into atmosphere after treatment through chimney of suitable height and diameter.

Stack (Chimney)

Fugitive Emissions Control Device

Smelting of lead in furnaces involve stages or parts where though pollution is generated, it is not handled by the main Air Pollution Control System, like charging of Rotary Furnace when it is red hot or tapping of lead from Rotary Furnace which lead to generation of fumes.

Systems put in place to capture and treat these fugitive emissions as and when they arise are called Fugitive Emission Control System. Fugitive Emissions generally lead to pollution of work atmosphere and jeopardize the maintenance of ambient air standards at the workplace. Hence, to safeguard employee health, these systems are becoming mandatory world over.

Norms of Ambient Air which the Fugitive Emissions Control System help to meet are

Rotary Furnaces of lower capacities are generally charged manually. But manual charging involves time and labour which

Rotary Loading Device

Parameter Approved Range Time Period PM (size < 2.5 micron) < 40 microgm/ Nm3 Annual Basis PM (size < 10 micron) < 60 microgm/ Nm3 Annual Basis Lead < 0.5 microgm/ Nm3 Annual Basis SO2 < 50 microgm/ Nm3 Annual Basis NO2 < 40 microgm/ Nm3 Annual Basis

It is a low pressure drop device which:

Ÿ Allows large size particles to settle down

Ÿ Cools down temperature of flue gases

Ÿ Used as spark arrestor to entrap live or red hot particles.

Gravity Chamber

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.

Involute Cyclone

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.

Bag Filtration System

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.

Duct & Bends

Time SavingIncreases productionReduces direct human contact with Hot Rotary FurnaceReduces temperature loss during chargingReduction in Flue Gases generated

Distinct benefits of a Rotary Charging System are

Jumbo Ingot Moulds are collection trolleys used for collecting molten lead from Rotary Furnaces. They can be of varying capacities, ranging from 500 Kg. to 1500 Kg. The most prevalent of the same is 500 Kg. Ingot Mould. Due to higher weight of the cast, it is called a Jumbo Ingot Mould.

These moulds have trolley type structure with two unidirectional wheels at the back and one free spin wheel at the front. It is provided with a handle to pull it. They are moved manually or on rails electro-mechanically, varying from unit to unit. They are smoothened on the inside and do not have any sharp folds or edges. They are usually constructed in SG cast iron for longer life and increased strength. We also provide Bucket type moulds to be used with material handing device.

Jumbo Ingot Mould

Shape : Pyramidical Hopper TypeSize – Top : 500mm x 500mm (Inside)Size – Bottom : 350mm x 350mm (Inside)Height : 500mmMoC : SG IronThk : 40mmBack Wheels : 200mm Dia x 50mm Wd

Front Wheel : 150mm Dia x 50mm Wd

Typical parameters for a 500 Kg Jumbo Ingot are

A Wet Scrubber in the Air Pollution Control System is mandatory in India and many parts of the world. Wet Scrubber uses

water to scrub clean the flue gases of any pollutant gases or particles that may remain after Bag Filtration System. The

Scrubber therefore requires a pump, pipeline and a retention tank.

The size of the Scrubber depends upon the capacity of the system being installed. Flue gases are introduced in the body of the

Scrubber from side and as they move up towards the top of the Scrubber which has the outlet, they pass through a spray of

fine water droplets provided by a spray shower provided in the body. This fine spray leads to scrubbing of any pollutant in the

flue gases. Cleaned gases escape through the top opening after passing through a mist eliminator whereas water with

pollutants moves to the bottom of the Scrubber from where it is passed into the tank. One or more chambers of the tank allow

for settling of pollutants which are then periodically cleaned and fresh water is added to make up any loss in quantity of water.

It is then recirculated to the Scrubber.

Wet Scrubber for Air Pollution Control Device

Note: Due to continuous up-gradation in technology, specified & projected values may differ in actual products

slows down the production rate and reduces total output. Hence a mechanized Rotary Loading System is provided for feeding of raw material in Rotary Furnace. This leads to huge savings of time & labour and increase the total output. The Rotary Loader is a device specially designed for transfer of raw material from a Chute of adequate capacity to inside the furnace shell.

Below are the commonly used Rotary Chargers:Vibro type, Forklift type and Tractor fitted charging device.

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