Secondary lead smelters recycle lead bearing scrap metal, primarily lead acid car batteries, into elemental lead or lead alloys. Metal from the batteries are remelted in blast or reverb furnaces and then refined in secondary smelters. The batteries contain high amounts of sulfur which oxidizes to SO2 in the furnaces.
An unutilized secondary lead smelting facility was retrofitted with new process equipment to restart operations. Air pollution control equipment was needed to achieve greater than 96% removal of peak loads of up to 4,500 lb/hr of SO2 from the furnace exhaust.
The customer selected an Envitech packed bed scrubber to meet emission requirements. Three combustion sources are combined in a duct header into a forced draft fan. The fan provides motive force through the scrubber.
The first scrubber step is an evaporative quencher to cool the gas to saturation. The quencher is constructed from T316SS and is a low pressure drop Venturi to provide turbulence for rapid quenching with a wide turn-down ratio. A fiber reinforced plastic (FRP) elbow connects the quencher to a 10 foot diameter FRP absorber vessel.
Gas from the quencher passes vertically upward through a packed bed, counter-current to downward flowing recirculated water. Scrubbing water and excess quench water are collected in a common sump and is recirculated to the top of the packed bed and quencher.
A pre-assembled recirculation pump skid with redundant pumps was supplied with the scrubber. Instruments were pre-mounted and pre-wired to a control box on the skid.
A dilute solution of plant-supplied sodium hydroxide is metered into the scrubber recirculation line to neutralize acid gases and is controlled by the recirculation liquid pH. A blowdown stream purges the system of reaction products and is controlled by conductivity. Blowdown liquid is treated by separate oxidation tanks to convert sulfite reaction products to sulfates.
After the packed bed, the gas passes through a chevron style mist eliminator above the packing material to remove water droplets. A wash header below the mist eliminator provides a periodic wash to keep the chevrons clean. Finally, the gas exits the system and is exhausted through a stack.
The scrubber has been operational since 2010 with good result. Below is a summary of design and performance results.
|Flow rate, acfm||60,000|
|Inlet temp, oF||400|
|Peak SO2 load, lb/hr||4,500|
|SO2 removal||> 98%|
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