Processes To Produce Calcined Materials

　　Calcining is a heat treatment process used to remove moisture and volatiles from a raw material.

　　Suitable materials for the calcining include uncalcined coal (e.g.. anthracite) and coke (e.g..

　　pitch coke, metallurgical coke and petroleum coke). These raw materials are supplied at the top

　　of the furnace, with the flow through the furnace controlled by the rate of discharge at the

　　bottom of the furnace. Moisture, sulphur and volatiles are released during this process.

　　There are two type of calcining processes: electrical calcining furnace and gas calciner.

　　An electrical calcining furnace applies electrical power for heating. The necessary electrical

　　current is supplied either to the furnace through one carbon electrode arranged in the top of the

　　furnace and one carbon electrode in the bottom, or through two graphite electrodes arranged in

　　the top of the furnace and one carbon furnace lining in the bottom. The material in the furnace

　　will reach temperatures in the range 1200-3000 oC. Ash components in the carbonaceous

　　material are volatilized in the hottest areas of the furnace and radially transferred outwards,

　　where they condense on cooler material or the furnace lining. The ash components will finally

　　be withdrawn together with the calcined material at the bottom of the furnace. All generated

　　gases are burnt off from the top of the furnace.

　　A gas calciner uses all released volatiles from the calcining process as fuel material to reach the

　　required temperature for the heat treatment. The temperature range is 1200-1350 C.

　　In both cases the flaring of the aforementioned off-gases generates emissions of H2O, CO2, NOx

　　and SO

　　x. The calcined materials are normally used as raw material in green paste. They can also

　　be used as carbon raiser for steel production and cast irons.