Fluidized bed start up and operation

Abstract

At start-up, a bed of pellets derived from pulp mill residual liquor is fluidized by feeding preheated air to the bed to initially raise the temperature of the bed to a temperature at which a particulate ligno-cellulosic auxiliary solid fuel may be completely consumed (800.degree.-850.degree. F.) and less than the yield temperature of the heat exchanger, feeding the auxiliary fuel to the fluidized bed, so as to burn the auxiliary fuel within the bed, feeding coolant to the heat exchanger to protect the heat exchanger from thermally induced damage, coordinating the rate of feeding of coolant with the rate of injection of the solid fuel to further increase the temperature of the bed to at least a temperature at which concentrated residual liquor from said mill will be burned while maintaining the temperature of the heat exchange equipment below the yield temperature for the material from which the heat exchanger is constructed and without build up of carbon in the bed, injecting concentrated residual liquor fuel from said pulp mill to the bed thereby to burn said residual liquor in the bed, continuing to inject at least one of said fuels, coordinating the rate of fuel injection to operate the bed at operating temperature while simultaneously maintaining a rate of addition of coolant to the heat exchanger to insure the temperature of the metal of the heat exchanger does not exceed the yield temperature.