Method for operating a once-through steam generator and steam generator designed for carrying out the method

A method for operating a once-through steam generator with an evaporator, comprising:

• feeding a feeding mass flow of a flow medium using a feed pump to the evaporator and at least partly evaporated there in the evaporator;
• separating evaporated flow medium from non-evaporated flow medium in a separator, the separator connected downstream from the evaporator, the non-evaporated flow medium feeds into to a circulating mass flow of the non-evaporated flow medium using a circulating pump into the evaporator, so that the mass flow referred to as the evaporator mass flow of the flow medium flowing through the evaporator is composed additively of the feeding mass flow and the circulating mass flow,
• wherein in a moderate-load interval the feeding mass flow is decreased with decreasing load and the circulating mass flow is increased, starting from zero, and
• wherein in a low-load interval the feeding mass flow is decreased further with decreasing load, while the circulating mass flow is kept substantially constant, and
• wherein, for the moderate-load interval a minimum value is defined for the evaporator mass flow and, for the low-load interval, the circulating mass flow is substantially kept constant at the halved minimum value.