초록 ▼

The disclosure is directed to a saturated water spraying system configured to rapidly respond to rapid load changes by implementing a single integrated DCS control block. The integrate DCS control block may include a plurality of process control routines that are necessary to control the operation o

The disclosure is directed to a saturated water spraying system configured to rapidly respond to rapid load changes by implementing a single integrated DCS control block. The integrate DCS control block may include a plurality of process control routines that are necessary to control the operation of the spraying system. For example, upstream and downstream PID control routines may determine and output control variables, and other control routines may be provided as necessary to handle disturbances within a boiler affecting the outlet and spray steam temperatures, and to ensure that the steam temperatures do not fall into the saturation region during operation of the boiler. Because the routines are part of the same control block, the common storage for the control block may be accessed by each of the routines without the necessity of establishing additional communication links for transferring the information as is required when using cascaded function blocks.

대표청구항 ▼

What is claimed is: 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 reg

What is claimed is: 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, the first PID control routine being configured to use an actual outlet steam temperature received at the integrated DCS control block from the first temperature sensor as a first process variable, the first PID control routine being configured to compare the first process variable to a first set point that is equal to a desired outlet steam temperature and to determine a first control variable equal to a post-spray steam temperature that will result in the actual outlet steam temperature being equal to the first set point; the second PID control routine being configured to use an actual post-spray steam temperature received at the integrated DCS control block from the second temperature sensor as a second process variable; the second PID control routine being configured to compare the second process variable to a second set point determined from the first control variable and equal to a desired post-spray steam temperature and to determine a second control variable equal to a control valve position that will result in an amount of saturated water being sprayed into the fluid flow path that will cause the actual post-spray steam temperature to be equal to the second set point; and the second PID control routine being configured to output the second control value to the control valve, 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. 2. A saturated water spraying system according to claim 1, wherein the second PID control routine is configured to set the new second control variable equal to a fully open valve position in response to determining that the original second control variable is equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 3. A saturated water spraying system according to claim 1, wherein the second PID control routine is configured to determine a new second control variable equal to an open valve position providing an amount of saturated water necessary to decrease the actual post-spray steam temperature to an amount that will lower the actual outlet spray temperature to equal the first set point in response to determining that the original second control variable is equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 4. A saturated water spraying system according to claim 1, wherein the integrated DCS control block includes additional control routines configured to determine the second set point based on the value of the first control variable determined by the first PID control routine. 5. 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, the first PID control routine being configured to use an actual outlet steam temperature received at the integrated DCS control block from the first temperature sensor as a first process variable, the first PID control routine being configured to compare the first process variable to a first set point that is equal to a desired outlet steam temperature and to determine a first control variable equal to a post-spray steam temperature that will result in the actual outlet steam temperature being equal to the first set point; the second PID control routine being configured to use an actual post-spray steam temperature received at the integrated DCS control block from the second temperature sensor as a second process variable; the second PID control routine being configured to compare the second process variable to a second set point determined from the first control variable and equal to a desired post-spray steam temperature and to determine a second control variable equal to a control valve position that will result in an amount of saturated water being sprayed into the fluid flow path that will cause the actual post-spray steam temperature to be equal to the second set point; and the second PID control routine being configured to output the second control value to the control valve, wherein the second PID control routine is configured to store the second process variable in storage of the integrated DCS control block, wherein the first PID control routine is configured to determine whether the control valve position of the second control variable that would be calculated by the second PID control routine based on the first control variable and the stored second process 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 values of the first process variable and the first set point, and wherein the first PID control routine is configured to determine a new first control variable for a post-spray steam temperature that will cause the second PID control routine to calculate a second control variable with a control valve position that will cause the actual outlet steam temperature to equal the first set point in response to determining that the post-spray steam temperature of the original first control variable will not cause the actual outlet steam temperature to equal the first set point. 6. A saturated water spraying system according to claim 5, wherein the first PID control routine is configured to set the new first control variable equal to a desired post-spray steam temperature that will cause the second PID control routine to calculate a second control variable equal to a fully open valve position in response to determining that the original first control variable would cause the second PID control routine to calculate a second control variable equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 7. A saturated water spraying system according to claim 5, wherein the first PID control routine is configured to determine a new first control variable equal to a desired post-spray steam temperature that will cause the second PID control routine to calculate a second control variable equal to an open valve position providing an amount of saturated water necessary to decrease the actual post-spray steam temperature to an amount that will lower the actual outlet spray temperature to equal the first set point in response to determining that the original first control variable would cause the second PID control routine to calculate a second control variable equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 8. A saturated water spraying system according to claim 5, wherein the integrated DCS control block includes additional control routines configured to determine the second set point based on the value of the first control variable determined by the first PID control routine. 9. A method for maintaining a steam temperature in a boiler having superheated steam flowing along a flow path through a heat exchanger and on to a turbine with an outlet steam temperature at the outlet of the heat exchanger, wherein saturated water is sprayed into the steam flow path before the steam enters the heat exchanger with the steam having a post-spray steam temperature after the saturated water is sprayed into the steam flow path, and wherein the boiler includes a control valve for regulating the amount of saturated water sprayed into the steam flow path, comprising: measuring the actual outlet steam temperature; inputting the actual outlet steam temperature to a first proportional integral derivative (PID) control routine of an integrated distributed control system (DCS) control block as a first process variable; storing the first process variable in storage of the integrated DCS control block; at the first PID control routine comparing the first process variable to a first set point that is equal to a desired outlet steam temperature and determining a first control variable equal to a post-spray steam temperature that will result in the actual outlet steam temperature being equal to the first set point; measuring the actual post-spray steam temperature; inputting the actual post-spray steam temperature to a second PID control routine of the integrated DCS control block as a second process variable; at the second PID control routine comparing the second process variable to a second set point determined from the first control variable and equal to a desired post-spray steam temperature and determining a second control variable equal to a control valve position that will result in an amount of saturated water being sprayed into the fluid flow path that will cause the actual post-spray steam temperature to be equal to the second set point; at the second PID control routine determining 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; outputting the second control value from the second PID control routine of the integrated DCS control block to the control valve in response to determining that the control valve position of the original second control variable will cause the actual outlet steam temperature to equal the first set point; at the second PID control routine determining a new second control variable for a control valve position that will cause the actual outlet steam temperature to equal the first set point and outputting the new second control variable to the control valve instead of the original second control variable 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. 10. A method according to claim 9, comprising setting the new second control variable equal to a fully open valve position in response to determining that the original second control variable is equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 11. A method according to claim 9, comprising determining a new second control variable equal to an open valve position providing an amount of saturated water necessary to decrease the actual post-spray steam temperature to an amount that will lower the actual outlet spray temperature to equal the first set point in response to determining that the original second control variable is equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 12. A method according to claim 9, wherein the integrated DCS control block includes additional control routines, the method comprising at the additional control routines determining the second set point based on the value of the first control variable determined by the first PID control routine. 13. A method for maintaining a steam temperature in a boiler having superheated steam flowing along a flow path through a heat exchanger and on to a turbine with an outlet steam temperature at the outlet of the heat exchanger, wherein saturated water is sprayed into the steam flow path before the steam enters the heat exchanger with the steam having a post-spray steam temperature after the saturated water is sprayed into the steam flow path, and wherein the boiler includes a control valve for regulating the amount of saturated water sprayed into the steam flow path, comprising: measuring the actual outlet steam temperature; inputting the actual outlet steam temperature to a first proportional integral derivative (PID) control routine of an integrated distributed control system (DCS) control block as a first process variable; at the first PID control routine comparing the first process variable to a first set point that is equal to a desired outlet steam temperature and determining a first control variable equal to a post-spray steam temperature that will result in the actual outlet steam temperature being equal to the first set point; measuring the actual post-spray steam temperature; inputting the actual post-spray steam temperature to a second PID control routine of the integrated DCS control block as a second process variable; at the second PID control routine storing the second process variable in storage of the integrated DCS control block; at the second PID control routine comparing the second process variable to a second set point determined from the first control variable and equal to a desired post-spray steam temperature and determining a second control variable equal to a control valve position that will result in an amount of saturated water being sprayed into the fluid flow path that will cause the actual post-spray steam temperature to be equal to the second set point; outputting the second control value from the second PID control routine of the integrated DCS control block to the control valve; at the first PID control routine determining whether the control valve position of the second control variable that would be calculated by the second PID control routine based on the first control variable and the stored second process 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 values of the first process variable and the first set point; and at the first PID control routine determining a new first control variable for a post-spray steam temperature that will cause the second PID control routine to calculate a second control variable with a control valve position that will cause the actual outlet steam temperature to equal the first set point in response to determining that the post-spray steam temperature of the original first control variable will not cause the actual outlet steam temperature to equal the first set point. 14. A method according to claim 13, comprising setting the new first control variable equal to a desired post-spray steam temperature that will cause the second PID control routine to calculate a second control variable equal to a fully open valve position in response to determining that the original first control variable would cause the second PID control routine to calculate a second control variable equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 15. A method according to claim 13, comprising determining a new first control variable equal to a desired post-spray steam temperature that will cause the second PID control routine to calculate a second control variable equal to an open valve position providing an amount of saturated water necessary to decrease the actual post-spray steam temperature to an amount that will lower the actual outlet spray temperature to equal the first set point in response to determining that the original first control variable would cause the second PID control routine to calculate a second control variable equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 16. A method according to claim 13, wherein the integrated DCS control block includes additional control routines, the method comprising at the additional control routines determining the second set point based on the value of the first control variable determined by the first PID control routine. 17. An integrated distributed control system (DCS) control block in a saturated water spraying system for maintaining a steam temperature in a boiler having superheated steam flowing along a flow path to a turbine, wherein the system includes 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, and 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, the integrated DCS control block being operatively connected to the first temperature sensor, the second temperature sensor and the control valve, the integrated DCS control block comprising: a first proportional integral derivative (PID) control routine configured to use an actual outlet steam temperature received at the integrated DCS control block from the first temperature sensor as a first process variable, and configured to compare the first process variable to a first set point that is equal to a desired outlet steam temperature and to determine a first control variable equal to a post-spray steam temperature that will result in the actual outlet steam temperature being equal to the first set point; and a second PID control routine configured to use an actual post-spray steam temperature received at the integrated DCS control block from the second temperature sensor as a second process variable, configured to compare the second process variable to a second set point determined from the first control variable and equal to a desired post-spray steam temperature and to determine a second control variable equal to a control valve position that will result in an amount of saturated water being sprayed into the fluid flow path that will cause the actual post-spray steam temperature to be equal to the second set point, and configured to output the second control value to the control valve, 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. 18. An integrated DCS control block according to claim 17, wherein the second PID control routine is configured to set the new second control variable equal to a fully open valve position in response to determining that the original second control variable is equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 19. An integrated DCS control block according to claim 17, wherein the second PID control routine is configured to determine a new second control variable equal to an open valve position providing an amount of saturated water necessary to decrease the actual post-spray steam temperature to an amount that will lower the actual outlet spray temperature to equal the first set point in response to determining that the original second control variable is equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 20. An integrated DCS control block according to claim 17, comprising additional control routines configured to determine the second set point based on the value of the first control variable determined by the first PID control routine. 21. An integrated distributed control system (DCS) control block in a saturated water spraying system for maintaining a steam temperature in a boiler having superheated steam flowing along a flow path to a turbine, wherein the system includes 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, and 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, the integrated DCS control block being operatively connected to the first temperature sensor, the second temperature sensor and the control valve, the integrated DCS control block comprising: a first proportional integral derivative (PID) control routine configured to use an actual outlet steam temperature received at the integrated DCS control block from the first temperature sensor as a first process variable, and configured to compare the first process variable to a first set point that is equal to a desired outlet steam temperature and to determine a first control variable equal to a post-spray steam temperature that will result in the actual outlet steam temperature being equal to the first set point; and a second PID control routine configured to use an actual post-spray steam temperature received at the integrated DCS control block from the second temperature sensor as a second process variable, configured to compare the second process variable to a second set point determined from the first control variable and equal to a desired post-spray steam temperature and to determine a second control variable equal to a control valve position that will result in an amount of saturated water being sprayed into the fluid flow path that will cause the actual post-spray steam temperature to be equal to the second set point, and configured to output the second control value to the control valve, wherein the second PID control routine is configured to store the second process variable in storage of the integrated DCS control block, wherein the first PD control routine is configured to determine whether the control valve position of the second control variable that would be calculated by the second PID control routine based on the first control variable and the stored second process 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 values of the first process variable and the first set point, and wherein the first PID control routine is configured to determine a new first control variable for a post-spray steam temperature that will cause the second PID control routine to calculate a second control variable with a control valve position that will cause the actual outlet steam temperature to equal the first set point in response to determining that the post-spray steam temperature of the original first control variable will not cause the actual outlet steam temperature to equal the first set point. 22. An integrated DCS control block according to claim 21, wherein the first PID control routine is configured to set the new first control variable equal to a desired post-spray steam temperature that will cause the second PID control routine to calculate a second control variable equal to a fully open valve position in response to determining that the original first control variable would cause the second PID control routine to calculate a second control variable equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 23. An integrated DCS control block according to claim 21, wherein the first PID control routine is configured to determine a new first control variable equal to a desired post-spray steam temperature that will cause the second PID control routine to calculate a second control variable equal to an open valve position providing an amount of saturated water necessary to decrease the actual post-spray steam temperature to an amount that will lower the actual outlet spray temperature to equal the first set point in response to determining that the original first control variable would cause the second PID control routine to calculate a second control variable equal to a closed valve position and that the first process variable and the first set point indicate that the actual outlet spray temperature must be lowered to equal the first set point. 24. An integrated DCS control block according to claim 21, comprising additional control routines configured to determine the second set point based on the value of the first control variable determined by the first PID control routine.