Extraction of Fume Impurities in a MSW Incineration Plant
The furnace gases exit the boiler and are directed through an air heater, which heats the boiler combustion air increasing the plant efficiency. The fumes then pass through the fume extraction plant, a series of scrubbers and filters.
- Activated carbon scrubbing
This scrubber removes the heavy metals from the gas stream, with the particulates being drawn off at the bottom or passing on to the filtration unit where the are removed
This scrubber removes the nitric gasses (NOx) from the fumes by catalytic reduction. The residue is either removed at the bottom or when passing onto the filtration unit.
This scrubber uses a mixture or slurry of lime and water to remove the sulphur dioxide from the fumes. Gypsum is a useful by-product of this method of scrubbing
Note: Any water and liquid residue collected in the scrubber hoppers are transported to a waste water plant for further treatment.
- Electrostatic precipitation.
This equipment consists of an enclosure through which the combustion gasses flow. It contains a bank of steel collector plates, interspaced with high voltage wires which hang down between the plates and act as electrodes. The fumes pass between the plates and electrodes.
Electric currents are passed through electrodes causing the dust from the flue gas to adhere to the plates. A rapper knocks against the plates dislodging the dust which falls down from the precipitator into a dust hopper where it is collected for safe disposal.
This is a steel rectangular box structure through which the gasses flow. Dust particles are efficiently removed by passing through the fabric filters. These filters are of circular section, open at the bottom and coming to closure at the top in a conical shape. The gas enters at the bottom of the filter and the particles are removed as it passes upwards and through the fabric of the filter. A layer of dust builds up on the inside of the bags known dust cake which aids the recovery of very microscopic particles, increasing the efficiency. To clean the filters the system is isolated and a shaker mechanism vibrates the bags, with the dust falling off being collected in hoppers underneath.