Patent ID: 8176754

Claim:
A process for making mineral fibres comprising providing a preheated combustion air, suspending a powdered carbonaceous fuel in said preheated combustion air and combusting the suspended carbonaceous fuel to form a flame, providing particulate mineral material which has been preheated to at least 700° C., suspending said preheated particulate mineral material in said flame and melting the mineral material in a circulating combustion chamber at an adiabatic flame temperature of at least 1800° C. and thereby forming a mineral melt and hot exhaust gases, separating said hot exhaust gases from said mineral melt and collecting the melt, flowing a stream of said collected melt to a centrifugal fiberising apparatus and forming mineral fibres by centrifugally fiberising the stream of melt, wherein the preheating of the particulate mineral material is carried out by conveying said exhaust gases to a cyclone preheater and contacting said exhaust gases in said cyclone preheater under NOx-reducing conditions with (a) said particulate mineral material which is to be melted and (b) waste bonded mineral wool containing a source of nitrogen, and thereby both reducing NOx in the exhaust gases and preheating said particulate material to at least 700° C., removing the exhaust gases with reduced NOx from said cyclone preheater, and wherein said combustion air is preheated by heat exchange of air with said exhaust gases with reduced NOx removed from the cyclone preheater, and wherein the hot exhaust gases separated from the mineral melt have their temperature reduced from the temperature at the time they are separated from the mineral melt by dilution with at least one of air and liquid ammonia while being conveyed to the cyclone preheater and before contact with the particulate mineral material in the cyclone preheater.