Carbon Regeneration Kiln

Overview

A carbon regeneration kiln restores the adsorption capacity of activated carbon used to recover gold. As carbon cycles through a gold plant it picks up not only gold but also organic foulants: flotation reagents, oils, humic matter and fine organics from the ore. These block the pores and slowly kill the carbon's ability to adsorb gold. After the gold has been stripped in an elution column and the carbon acid washed to remove carbonate scale, the kiln heats it to 650-750 C in a steam atmosphere. At that temperature the organic foulants volatilise and burn off the pore walls, reopening the internal surface so the carbon adsorbs almost as well as new. Without regeneration a plant would have to buy fresh carbon constantly; the kiln makes the carbon loop closed and economic.

The heart of the machine is an inclined rotating tube. Wet, acid-washed carbon enters the high end, tumbles slowly down through heated zones as the tube turns, and discharges at the low end into a water quench. Steam injected into the tube strips the foulants and prevents the carbon itself from burning in the otherwise oxygen-starved interior. The whole train sits on a sloped frame, is turned by a geared drive, and is run by a PLC that holds each zone at temperature and meters the feed to keep residence time constant.

The kiln tube

The Kiln Tube is where reactivation happens. Its Kiln Tube Shell is a high-nickel alloy such as Incoloy 800, chosen because plain steel scales and creeps at 700 C in a steam atmosphere. Welded inside are Lifting Flights, vanes that lift the carbon bed and cascade it as the tube rotates so every granule sees the hot wall and the steam. The tube rides on two Riding Ring tyres and is turned through a Girth Gear around its body. Where the rotating tube meets the fixed feed and discharge housings, a Gland Seal gland at each end keeps air from leaking in, because oxygen would let the hot carbon burn instead of regenerate.

Drive and support

The Rotary Drive turns the tube at 1-5 rpm. A Servo Motor feeds a reduction gearbox built from a Helical Gear Pair in a Gearbox Housing on Ball Bearing supports with an Oil Seal at the shaft, and the gearbox turns a Drive Pinion that meshes with the girth gear. The tube weight is carried by the Support Frame: a Base Frame set at the kiln slope holds four Support Roller rollers on Trunnion Bearing blocks, and a Thrust Roller pair stops the inclined tube creeping downhill. The slope plus rotation moves the carbon through the tube the way a cement kiln moves clinker.

Heating and steam

The Heating System holds the tube at temperature. Electric kilns ring the tube with banks of Heating Element units inside a Refractory Lining lining, switched by zone through a Zone Contactor and trimmed by a Element Controller against the Zone Thermocouple in each zone; gas-fired kilns use a burner in a heated muffle instead. Reactivation chemistry depends on steam, so the Off-gas System system feeds a Steam Injector into the tube. The volatilised organics leave with the steam and pass through a Off-gas Scrubber and a Condensate Trap, pulled by a Exhaust Fan that also holds the tube at slight negative pressure so leaks draw in rather than blow out.

Feed and discharge

Carbon arrives wet from the acid wash, so the Feed System system drains and meters it. A Feed Hopper buffers the wet carbon, a Feed Screw driven by a Servo Motor dewaters and augers it up, and a Feed Chute drops it into the high end of the tube, with a Feed Sensor confirming flow. At the low end the glowing carbon must be cooled before it touches air, so the Quench and Discharge system runs a Discharge Chute straight into a Quench Tank of water kept cool by a Quench Pump. A Drain Screen then separates the quenched carbon for return to the adsorption circuit.

Control and operation

The Control Panel panel ties it together. Its PLC Controller runs a temperature loop per zone, sets rotation speed and feed rate to fix residence time, and trips on interlocks through a set of Relay outputs, with an LCD Panel for the operator and a Power Supply feeding the loop. Getting regeneration right is a balance: too cool or too short and foulants remain, so adsorption stays poor; too hot or too long and the carbon itself gasifies, raising attrition losses. Operators trend the recovered activity against virgin carbon and tune temperature and feed to hold it near 90-95 percent. A well-run kiln lets a plant cycle the same carbon inventory for months, replacing only the small fraction lost to attrition and fines each pass.