A method for calcining mineral rock in a regenerative parallel-flow vertical shaft furnace including the steps of collecting a portion of the gaseous effluent discharged, in preheating mode, from the furnace shaft in a recirculating circuit, forming an oxidizing mixture by mixing the portion collected from the gaseous effluent with concentrated dioxygen from a dioxygen source, and inserting the oxidizing mixture into the top of the shaft in firing mode so as to ensure the combustion of fuel in the presence of oxygen. The gaseous effluent discharged from the furnace having a high concentration of CO.sub.2.

A method for calcining mineral rock in a regenerative parallel-flow vertical shaft furnace including the steps of collecting a portion of the gaseous effluent discharged, in preheating mode, from the furnace shaft in a recirculating circuit, forming an oxidizing mixture by mixing the portion collected from the gaseous effluent with concentrated dioxygen from a dioxygen source, and inserting the oxidizing mixture into the top of the shaft in firing mode so as to ensure the combustion of fuel in the presence of oxygen. The gaseous effluent discharged from the furnace having a high concentration of CO.sub.2.

A shaft furnace for firing carbonate-containing material may include, in a flow direction of the material, a preheating zone, a firing zone, a cooling zone, and a material outlet for discharging the material from the shaft furnace. Burner lances project into the firing zone. At least one burner lance has a first penetration depth into the firing zone and at least one further burner lance has a second penetration depth into the firing zone that is greater than the first penetration depth. A primary air conduit may be configured to convey combustion air and may be connected to at least one burner lance. An oxygen conduit for conveying oxygen into the firing zone may be arranged such that oxygen flows from the oxygen conduit at least one burner lance having the second penetration depth.

A shaft furnace for firing carbonate-containing material may include, in a flow direction of the material, a preheating zone, a firing zone, a cooling zone, and a material outlet for discharging the material from the shaft furnace. Burner lances project into the firing zone. At least one burner lance has a first penetration depth into the firing zone and at least one further burner lance has a second penetration depth into the firing zone that is greater than the first penetration depth. A primary air conduit may be configured to convey combustion air and may be connected to at least one burner lance. An oxygen conduit for conveying oxygen into the firing zone may be arranged such that oxygen flows from the oxygen conduit at least one burner lance having the second penetration depth.

A method can be used to burn and cool material in a parallel flow-counter flow regenerative shaft kiln having two shafts that are operated alternately as a burning shaft and a regenerative shaft. The material flows through a preheating zone, a burning zone, and a cooling zone to a material outlet. Fuel is supplied in or above the preheating zone, and thus fuel is heated in the preheating zone prior to entering the burning zone. Further, a parallel flow-counter flow regenerative shaft kiln for burning and cooling material may have two shafts that can be operated alternately as a burning shaft and a regenerative shaft. Each shaft has, in a flow direction, a preheating zone for preheating material, a burning zone for burning material, and a cooling zone for cooling material. A fuel inlet that admits fuel into each shaft is arranged above or inside the preheating zone.

Methods for increasing the hardness of aggregate include applying a hardener to the aggregate. The hardener may react with a material of the aggregate and/or a material on a surface of the aggregate. For example, an alkali metal silicate, such as lithium polysilicate, or a colloidal silica may chemically react with calcium oxide and/or calcium hydroxide of an aggregate or on an aggregate to create cementitious material, which may at least partially fill pores in the surface of the aggregate, harden an existing microtexture of the aggregate and/or enhance the microtexture of the aggregate. These characteristics may enhance frictional characteristics, the wear characteristics and the durability of the aggregate, and of any structures formed from composite materials that include the aggregate.

Methods for increasing the hardness of aggregate include applying a hardener to the aggregate. The hardener may react with a material of the aggregate and/or a material on a surface of the aggregate. For example, an alkali metal silicate, such as lithium polysilicate, or a colloidal silica may chemically react with calcium oxide and/or calcium hydroxide of an aggregate or on an aggregate to create cementitious material, which may at least partially fill pores in the surface of the aggregate, harden an existing microtexture of the aggregate and/or enhance the microtexture of the aggregate. These characteristics may enhance frictional characteristics, the wear characteristics and the durability of the aggregate, and of any structures formed from composite materials that include the aggregate.

A system for making oxide material may comprise a preheating cyclone stage for receiving a solid carbonate material and operating at a temperature less than a calcination temperature of the solid carbonate material, a calcination cyclone stage for heating the preheated solid carbonate material and operating at a temperature of at least the calcination temperature to convert the preheated solid carbonate material to a solid oxide material and carbon dioxide gas, a cooling cyclone stage for cooling the solid oxide material and operating at a temperature less than the calcination temperature to cool the solid oxide material to ambient temperature, a first recirculating system to extract and recirculate a first gas from an outlet of the calcination cyclone stage to an inlet of the calcination cyclone stage zone, and a second recirculating system to extract and recirculate a second gas from the cooling cyclone stage to the preheating cyclone stage.

A system for making oxide material may comprise a preheating cyclone stage for receiving a solid carbonate material and operating at a temperature less than a calcination temperature of the solid carbonate material, a calcination cyclone stage for heating the preheated solid carbonate material and operating at a temperature of at least the calcination temperature to convert the preheated solid carbonate material to a solid oxide material and carbon dioxide gas, a cooling cyclone stage for cooling the solid oxide material and operating at a temperature less than the calcination temperature to cool the solid oxide material to ambient temperature, a first recirculating system to extract and recirculate a first gas from an outlet of the calcination cyclone stage to an inlet of the calcination cyclone stage zone, and a second recirculating system to extract and recirculate a second gas from the cooling cyclone stage to the preheating cyclone stage.

A system for making oxide material may comprise a preheating cyclone stage for receiving a solid carbonate material and operating at a temperature less than a calcination temperature of the solid carbonate material, a calcination cyclone stage for heating the preheated solid carbonate material and operating at a temperature of at least the calcination temperature to convert the preheated solid carbonate material to a solid oxide material and carbon dioxide gas, a cooling cyclone stage for cooling the solid oxide material and operating at a temperature less than the calcination temperature to cool the solid oxide material to ambient temperature, a first recirculating system to extract and recirculate a first gas from an outlet of the calcination cyclone stage to an inlet of the calcination cyclone stage zone, and a second recirculating system to extract and recirculate a second gas from the cooling cyclone stage to the preheating cyclone stage.