Controlling boiler drum level

A heat recovery steam generation system, comprising:

• a drum boiler including a steam drum, an evaporator to receive water from the steam drum and a heated gas from a gas turbine, and a riser between the evaporator and the steam drum to direct steam from the evaporator to the steam drum, where the steam drum has a pressure therein due to at least one of water steam in the drum, steam in the drum and a water/steam mixture in the drum, the method;
• and
• a controller configured to predict a transient change in at least one the water level, or water/steam mixture or pressure in the drum in the steam drum based on plant characteristics including steam flow from the steam drum, drum pressure in the steam drum, and one or both of a gas turbine load and a position of a bypass valve configured to control the steam flow from the steam drum to two or more steam flow conduits, and to control a water level in the steam drum by generating a sliding setpoint based on predicting the transient change in the steam drum,
• wherein the controller is configured to generate a first setpoint with a setpoint model that receives as inputs the steam flow, a feedwater temperature of feedwater provided to the steam drum, a gas fuel temperature, and a gas fuel flow, to determine a desired water level in the steam drum based on the steam flow and the drum pressure, and to select one of the sliding setpoint and the first setpoint to control the water level in the steam drum based on comparing the sliding setpoint and the first setpoint to the desired water level.

A heat recovery steam generator (HRSG) plant controller, comprising:

• memory configured to store plant characteristics and a sliding setpoint transfer function;
• and
• a processor configured to predict a transient change in at least one a water level, or water/steam mixture or pressure in a steam drum of the HRSG plant based on the plant characteristics including steam flow from the steam drum, where the steam drum has a pressure therein due to at least one of water steam in the drum, steam in the drum and a water/steam mixture in the drum, the method drum pressure in the steam drum, and one or both of a gas turbine load and a position of a bypass valve configured to control the steam flow from the steam drum to two or more steam flow conduits, and to generate a sliding setpoint to control a water level in the steam drum based on predicting the transient change,
• wherein the memory is configured to store a setpoint model, and
• the processor is configured to generate a first setpoint with the setpoint model that receives as inputs the steam flow, a feedwater temperature of feedwater provided to the steam drum, a gas fuel temperature, and a gas fuel flow,
• the processor is configured to determine a desired water level in the steam drum based on the steam flow and the drum pressure, and
• the processor is configured to select one of the sliding setpoint and the first setpoint to control the water level in the steam drum based on comparing the sliding setpoint and the first setpoint to the desired water level.