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 non-evaporated flow medium in a separator connected downstream from the evaporator and is fed back to a circulating mass flow of the separated 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 low-load interval the feeding mass flow is increased as a load rises, while the circulating mass flow is kept substantially constant,
• wherein in a moderate-load interval the feeding mass flow is increased further with increasing load and the circulating mass flow is reduced to zero, and
• wherein when necessary in a high load interval the feeding mass flow is increased further with increasing load and the circulating mass flow is kept at zero, 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.

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;
• and
• separating non-evaporated flow medium in a separator connected downstream from the evaporator and is fed back to a circulating mass flow of the separated 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.

A once-through steam generator, comprising:

• an evaporator for evaporating a flow medium,
• a feed pump connected upstream of the evaporator on the flow medium side a feed pump;
• and
• a separator connected downstream of the evaporator for non-evaporated flow medium,
• wherein the separator is connected via a feedback line, into each a circulating pump is connected, to the evaporator inlet, and
• wherein an electronic control regulation unit is provided for the feed pump and the circulating pump which carries out the method steps as claimed in claim 1.