Patent ID: 7668623
Filing Date: 2010-02-23
Classification: G05D

Abstract:
1. A saturated water spraying system for maintaining a steam temperature in a boiler having superheated steam flowing along a flow path to a turbine, the system comprising: a heat exchanger having an inlet and an outlet disposed along the steam flow path; a control valve for regulating an amount of saturated water sprayed into the steam flow path at a point before the steam enters the heat exchanger; a first temperature sensor disposed proximate the outlet of the heat exchanger and configured to measure an outlet steam temperature of the steam at the outlet of the heat exchanger; a second temperature sensor disposed between the point at which the saturated water is sprayed into the steam flow path and the inlet of the heat exchanger and configured to measure a post-spray steam temperature of the steam after the saturated water is sprayed into the steam flow path; and an integrated distributed control system (DCS) control block operatively connected to the first temperature sensor, the second temperature sensor and the control valve, the integrated DCS control block having a first proportional integral derivative (PID) control routine and a second PID control routine, wherein the first PID control routine is configured to store the first process variable in storage of the integrated DCS control block, wherein the second PID control routine is configured to determine whether the control valve position of the second control variable will cause an amount of saturated water to be sprayed into the steam flow path that will cause the actual outlet steam temperature to equal the first set point based on the stored value of the first process variable and the first set point, wherein the second PID control routine is configured to determine a new second control variable for a control valve position that will cause the actual outlet steam temperature to equal the first set point in response to determining that the control valve position of the original second control variable will not cause the actual outlet steam temperature to equal the first set point, and wherein the second PID control routine is configured to output the new second control variable to the control valve instead of the original second control variable.