Method of operating a gas and steam power plant

A method of operating a power station plant including a gas-turbine group, a waste-heat steam generator and a downstream steam consumer, the exhaust gas from the gas-turbine group releasing heat to the water conducted in counterflow through the waste-heat steam generator, and the steam produced being fed to the steam consumer via at least one steam line, wherein the water is at any temperature and is fed directly into the waste-heat steam generator via at least one water line having an allocated regulating valve for limiting the flow, and wherein the regulating valve is controlled by a regulating device as a function of measuring devices, during the use of fuels having sulfur contents, the regulating valve is controlled based upon the temperature of the exhaust gas at the discharge from the waste-heat steam generator at a temperature measuring device, and during the use of fuels having no or a low sulfur content, the regulating valve is controlled based upon the temperature of the steam in a steam line at a temperature measuring device.