Method for operating a gas and steam turbine plant and monitoring a liquid level in a plurality of downpipes

A gas and steam turbine plant, comprising:

• a gas turbine;
• a waste heat steam generator connected downstream from the gas turbine on an exhaust gas side;
• and
• a flow medium circuit comprising a plurality of pressure stages,
• wherein a flow medium used to drive a steam turbine is conducted in the flow medium circuit,
• wherein at least one of the pressure stages features an evaporator circuit including a steam collection drum with a plurality of downpipes connected to the steam collection drum and with a plurality of riser pipes connected downstream from the downpipes and connected to the steam collection drum,
• wherein the plurality of flue pipes is heated by the flue gas in the waste heat steam generator,
• wherein a level measurement facility measures the height of the column of liquid formed by the flow medium in the plurality of downpipes, and
• wherein the level measurement facility is connected on a signal side to a monitoring and control facility for the gas and steam turbine plant.