Once-through evaporator systems

A method to control a once-through evaporator system with a plurality of once-through evaporator sections, comprising:

• receiving section temperatures of the plurality of once-through evaporator sections, wherein each of the plurality of once-through evaporator sections comprises an upstream distribution valve, a downstream temperature sensor, and a position controller in communication with each upstream distribution valve, wherein each downstream temperature sensor and a temperature controller are in communication with each position controller;
• determining, via each position controller, a static head prediction and a required pressure drop over each upstream distribution valve to determine a valve stroke of the respective upstream distribution valve;
• providing, via each temperature controller, a flow target to each position controller as a set point, wherein the set point is based on an average of the section temperatures of the plurality of once-through evaporator sections;
• and
• biasing the set point by a dead band based on the average of the section temperatures with respect to an average saturation temperature.

A once-through evaporator system, comprising:

• a plurality of once-through evaporator sections, wherein each of the plurality of once-through evaporator sections comprises an upstream distribution valve and a downstream temperature sensor;
• a water separator with a water separator temperature sensor downstream of the plurality of once-through evaporator sections;
• a position controller in communication with each upstream distribution valve;
• and
• a deadband flow control system comprising a temperature control loop with a temperature controller, wherein each upstream distribution valve is in communication with the deadband flow control system, wherein each downstream temperature sensor of the plurality of once-through evaporator sections is in communication with the temperature controller, wherein the deadband flow control system is configured to sum the output of each downstream temperature sensor of the plurality of once-through evaporator sections and the water separator temperature sensor and compare the sum to a deadband signal to determine a set point for the temperature controller, wherein the deadband flow control system comprises a flow control loop with a flow controller, wherein the deadband flow control system is configured to combine the set point for the temperature controller with a feedforward signal for a flow controller set point.