The control law of firing rate system of steam drum boiler is examined. Main features of the proposed cascade control system are the presence in the external control loop of the modified PI-control law which includes the functional component of the error signal and the availability at the input of the external control loop of the sum of signal of derivative from the difference between steam flow rate and prescribed value of steam flow rate and the signal of the difference between prescribed value of pressure in header and the current pressure in header.
