Patent ID: 8573520

Claim:
Method of producing pulverized coal, comprising: providing a drying gas heated to a predefined temperature in a hot gas generator; feeding the heated drying gas into a pulverizer; introducing raw coal into the pulverizer, the pulverizer grinding the raw coal into pulverized coal; collecting a mixture of drying gas and pulverized coal from the pulverizer and feeding the mixture to a filter, the filter separating the dried pulverized coal from the drying gas; collecting the dried pulverized coal for further use and feeding the drying gas from the filter to an exhaust line; collecting the drying gas exiting said filter and feeding part of said collected drying gas to a recirculation line for feeding recirculation drying gas to said hot gas generator wherein said step of providing said drying gas comprises feeding a variable flow rate of hot stove waste gas to said hot gas generator through a hot stove waste gas line so as to maximize the amount of hot stove waste gas used as drying gas; a pressure of said drying gas at a pulverizer gas inlet is controlled by regulating a flow rate of said hot stove waste gas through said hot stove waste gas line; and wherein the method comprises a hot stove waste gas operation mode and a first intermediate operating mode and the method switches from said hot stove waste gas operating mode to said first intermediate operating mode if said hot stove waste gas has a concentration of a predetermined component above a first concentration threshold and/or if said hot stove waste gas has a temperature below a first temperature threshold, wherein in the hot stove waste gas operating mode: said recirculation line is shut-off; such that no recirculation drying gas is fed to said hot gas generator; said hot stove waste gas line is open, such that only hot stove waste gas is fed at a variable flow rate to said hot gas generator; said pressure of said drying gas at said pulverizer gas inlet is controlled by a flow rate of said drying gas in said exhaust line and by regulating said flow rate of said hot stove waste gas through said hot stove waste gas line, and in the first intermediate operating mode: said recirculation line is open, such that recirculation drying gas is fed at a variable flow rate to said hot gas generator; said hot stove waste gas line is open, such that hot stove waste gas is fed at a variable flow rate to said hot gas generator; and said pressure of said drying gas at said pulverizer gas inlet is controlled by setting a flow rate of said drying gas in said exhaust line and by regulating said flow rate of said hot stove waste gas through said hot stove waste gas line.