A method, and an apparatus for executing such method, of making sealed surface fine lightweight aggregate particles comprising the steps of pretreating argillaceous rock particles so as to form fine aggregates; maintaining such fine aggregates as a dense fluidized bed in a fluid bed reactor wherein the fines therein are of variable size ranging from 0. mm to about 9.5 mm and have an even distribution of the various sizes within such range; subjecting the dense fluidized bed to a supply of fuel and hot oxygen gas containing fluidizing and combustion gases, such fuel being introduced at least in part directly into the bed; continuously introducing pretreated fine aggregates to the bed; and continuously removing finished lightweight aggregate particles having sealed surfaces from the reactor.

A method and apparatus for calcining finely divided material such as limestone and dolomite. The apparatus is especially useful for calcining materials having a size of less than 1/4 inch. The apparatus includes a first stage fluidized bed calcining apparatus and a second stage flash calcining apparatus. Raw material is supplied to the fluid bed reactor. The large particles are calcined within this reactor, withdrawn from the reactor and supplied to a cooler. The fines are elutriated with the spent fluidizing gas and supplied to a cyclone separator. The separated fines are supplied to a flash calciner where they are calcined. The separated spent fluidizing gases may be used as combustion gas in the flash calciner. The calcined fines are removed from the flash calciner and supplied to a cyclone separator and from there to a cooler.

An apparatus for calcining raw material such as the raw material used for making Portland cement. The apparatus is used in conjunction with a preheater and a calciner, such as a rotary kiln, and a cooler. The calciner includes a vessel with means for supplying combustion gas to the bottom of the vessel, an outlet at the top of the vessel, for spent combustion gas and calcined material, a burner for producing a combustion zone intermediate the combustion air supply and the calcined material outlet. Raw material can be supplied to the vessel either from above the combustion zone and below the outlet or from below the combustion zone. The combustion air may be supplied from the cooler or a combination of the cooler and the exhaust gases from the clinkerer. The apparatus is primarily designed for using coal as a fuel.

Green petroleum coke is indirectly dried, than calcined in a cylindrical rotary kiln and indirectly cooled utilizing a one-way gas flow in the system. Most of the dust in the vapor from the drying step is directly burned in a steam boiler whose off-gases are used to heat the dryer. Any residual dust in the gas is collected in an electro-filter. This dust together with dust which settles out from the dryer and the kiln is collected and added in controlled amounts to the dried coke before calcining. Hydrocarbons expelled during calcining are partially burned off with a stream of secondary air introduced at the coke exit end of the kiln. Most of the remaining hydrocarbons are burned off before they leave the coke inlet end of the kiln. The calcined coke product contains 0.1% by weight of hydrocarbons. The final off-gas from the process has a residual dust content of less than 100 mg/nm.sup.3.

Green petroleum coke is indirectly dried, then calcined in a cylindric rotary kiln and indirectly cooled utilizing a one-way gas flow in the system. Most of the dust in the vapor from the drying step is directly burned in a steam boiler whose off-gases are used to heat the dryer. Any residual dust in the gas is collected in an electro-filter. This dust together with dust which settles out from the dryer and the kiln is collected and added in controlled amounts to the dried coke before calcining. Hydrocarbons expelled during calcining are partially burned off with a stream of secondary air introduced at the coke exit end of the kiln. Most of the remaining hydrocarbons are burned off before they leave the coke inlet end of the kiln. The calcined coke product contains 0.1% by weight of hydrocarbons. The final off-gas from the process has a residual dust content of less than 100 mg/nm.sup.3.