Fluidised BED INCINERATOR AS PAINT STRIPPING EQUIPMENT

Cleanliness of the hangers is the primary importance in electrostatic painting / coating. Coated hanger prevents the earth continuity of the components being painted. This results in total stoppage of the electrostatic effect. Hence periodic cleaning of the hangers is necessary.

Paint shop operators try to keep hangers clean by either periodic immersion of the coated hangers in strong, heated chemicals or periodic burning of the hangers. Chemical cleaning is often unsuccessful in cleaning powder-coated hanger fully. It is also expensive in operation and leads inevitably to pollution hazards and clean-up problems. Burning of hanger not only causes pollution but also leads to heavy warpage and distortion of the hangers.

Coated hangers when immersed in the heated Fluidised sand bed the paint stripping action takes place at a controlled temperature. The hangers come in contact with hot sand and not the flame. Hence distortion & warpage of hangers is avoided. The fluidizing sand has abrasive action on the paint coat. The paint burns off while the ash is stripped by Fluidised sand. The coating can be removed within 20 to 25 minutes.

WORKING PRINCIPLE OF PAINT STRIPPING EQUIPMENT

See Figure No.11

• F. D. Fan supplies air at high pressure for fluidization of sand.
• Air is heated to desired temperature and supplied to Fluidised chamber where sand is Fluidised.
• To initially heat the sand fast from cold condition, Start-up burner is provided. Once the temperature of sand is reached, the burner cuts off.
• The sand temperature is maintained constant.
• In running condition Air Preheater will heat the air to desired temperature maintaining the temperature of sand.
• The fluid bed chamber has doors at the top to load and unload the hanger trolley.
• Once the temperature is reached, the doors are opened door opening/closing mechanism. Hanger trolley is lowered in the fluid bed with hoist.
• The doors are closed with hanger trolley kept in suspended position hold by hoist.
• The paint gets burned and ash stripped off the hangers.
• The hot air and gases passes through cyclone where solid particles & ash will get separated.
• The gases pass through after burner where the volatiles are incinerated & destroyed completely meeting the environment rules.
• The temperature of gases after ‘After Burner’ is very high (typically 1000° C or more). To recover the heat from these gases Air-Preheater is installed. Heat is transferred from flue gases to process air.
• The gas coming out of air-Preheater is still at high temperature. Further heat is recovered from gas in heat exchanger to generate hot water/steam etc.
• Venturi type scrubber is provided to arrest solid particulate matter from the flue gases. After scrubbing, the gas is suitable for exhaust to atmosphere.
• I.D. Fan sucks the flue gas and exhausts it to atmosphere through chimney / exhaust duct.
• The typical cycle time is around 30 minutes and fresh trolley is kept ready while the first is burned.

See Figure No.12

• The hangers to be stripped are mounted on trolley. The trolley is to be loaded in the fluid bed chamber.
• Doors are provided on the top of fluid bed chamber to load & unload the trolley.
• Motorized hoist mounted on monorail above the fluid bed chamber maneuvers the trolley. The hoist has vertical and horizontal movement.
• Geared motors are provided for both the doors with chain & pulley arrangement to open & close the doors.
• The doors are kept spring loaded in the open position that facilitates easy closing without getting stuck in open position.
• Limit switches are provided for both the doors for open as well as close position to switch the motor off.
• The doors are over lapped to minimize the heat leakage. Interlock is provided to open the top door first and close it last.
• Limit switches are provided for motorized hoists to restrict its horizontal and vertical movement.
• The trolley is kept hanging during paint stripping operation.
• The hot gas is sucked from the periphery of the chamber through internal duct. The exhaust is from side.

• The length of hanger is 1200 mm.
• The hanger trolley holds about 40 hangers and has size of 750 mm x 1500 mm. The total weight is 200 kg.
• The fluid bed size is 1000 mm x 1750 mm x 1800 mm.
• The sand maintained at around 450° C and volatiles are incinerated at about 1000°C.
• Total cycle time is about 30 minutes.
• Start up time from cold condition is about 2 hours.
• The actual fuel consumption is 25 lph in running condition with air Preheater incorporated. The fuel consumption without air Preheater would have been 40 lph. With additional heat recovery in hot water heat exchanger, the effective fuel consumption is only 12 lph.
• The savings compared with other make is 28 lph of HSD which amounts to 28 x 19 = 532 Rs/hr
• The net annual savings is 532 x 7200 = Rs. 38,30,400/-