ONCE-THROUGH BOILER DEVICE AND COMBUSTION CONTROL METHOD FOR ONCE-THROUGH BOILER

PROBLEM TO BE SOLVED: To control starting and stopping of a boiler by adopting boiler combustion control using plural position control.SOLUTION: The once-through boiler device and a combustion control method for a once-through boiler includes a flow rate adjusting means 32 capable of continuously adjusting a flow rate of fuel and capable of adjusting it to a flow rate corresponding to each of a plurality of set combustion load factors; a water level control part 20 controlling to one of a plurality of set water levels on the basis of a water level detection result from a water level detection device; a pressure detector 33 having a plurality of set pressure values and detecting whether a vapor pressure is a set pressure value; and a controller 19 controlling the flow rate adjusting means on the basis of the vapor pressure detection result to provide a fuel supply amount to a burner nozzle such that a combustion load factor of the burner nozzle corresponds to the vapor pressure detection result, controlling the fuel load factor of the burner nozzle in steps, and commanding a water level to which control should be carried out on the basis of the vapor pressure detection result to the water level control part.