DYNAMIC MATRIX CONTROL OF STEAM TEMPERATURE WITH PREVENTION OF SATURATED STEAM ENTRY INTO SUPERHEATER

• US 20120040299A1
• Filed: 02/07/2011
• Published: 02/16/2012
• Est. Priority Date: 08/16/2010
• Status: Active Grant

• Current Assignee: Emerson Process Management Power & Water Solutions Incorporated (Emerson Electric Company)
• Original Assignee: Emerson Process Management Power & Water Solutions Incorporated (Emerson Electric Company)
• Inventors: Beveridge, Robert A., Whalen, Richard J. Jr.
• Granted Patent: US 9,217,565 B2
• Time in Patent Office: Days
• US Class Current: 432/13
• CPC Class Codes: F01K 13/02 Controlling, e.g. stopping or starting
• CPC Class Codes: F22B 35/004 Control systems for steam generators of nuclear power plants
• CPC Class Codes: F22B 35/18 Applications of computers to steam boiler control

Abstract

A technique of controlling a steam generating boiler system using dynamic matrix control includes preventing saturated steam from entering a superheater section. A dynamic matrix control block uses a rate of change of a disturbance variable, a current output steam temperature, and an output steam setpoint as inputs to generate a control signal. A prevention block modifies the control signal based on a saturatec temperature and an intermediate steam temperature. In some embodiments, the control signal is modified based on a threshold and/or an adjustable function g(x). The modified control signal is used to control a field device that, at least in part, affects the intermediate steam and output steam of the boiler system. In some embodiments, the prevention block is included in the dynamic matrix control block.

Claims

1. A method of preventing saturated steam from entering a superheater section of a steam generating boiler system, comprising:

generating, by a dynamic matrix controller, a control signal based on a signal indicative of a rate of changee of a disturbance variable used in the steam generating boiler system;

obtaining a saturated steam temperature and a temperature of intermediate steam, wherein the temperature of the intermediate steam is determined upstream of a location at which a temperature of output steam is determined, the output steam generated by the steam generating boiler system for delivery to a turbine;

determining a magnitude of a difference between the saturated steam temperature and the intermediate steam temperature;

adjusting the control signal based on the magnitude of the difference between the saturated steam temperature and the intermediate steam temperature; and

controlling the temperature of the intermediate steam based on the adjusted control signal.

2. The method of claim 1, further comprising providing the intermediate steam to the superheater section of the steam generating boiler system.

3. The method of claim 1, wherein adjusting the control signal based on the magnitude of the difference between the saturated steam temperature and the intermediate steam temperature comprises adjusting the control signal when the magnitude of the difference between the saturated steam temperature and the intermediate steam temperature is less than a threshold.

4. The method of claim 3, further comprising forgoing adjusting the control signal when the magnitude is greater than or equal to the threshold.

5. The method of claim 1, wherein adjusting the control signal comprises adjusting the control signal further based on an algorithm.

6. The method of claim 1, wherein at least one of:

obtaining the saturated steam temperature and the temperature of the intermediate steam comprises obtaining the saturated steam temperature and the temperature of the intermediate steam by the dynamic matrix controller;

determining the magnitude of the difference between the saturated steam temperature and the intermediate steam temperature comprises determining the magnitude of the difference between the saturated steam temperature and the intermediate steam temperature by the dynamic matrix controller, or

adjusting the control signal based on the magnitude of the difference between the saturated steam temperature and the intermediate steam temperature comprises adjusting the control signal based on the magnitude of the difference between the saturated steam temperature and the intermediate steam temperature by the dynamic matrix controller.

7. The method of claim 1,

further comprising receiving, at a fuzzifier block or unit, the control signal from the dynamic matrix controller, and

wherein adjusting the control signal comprises adjusting, by the fuzzifier block or unit, the control signal.

8. The method of claim 7, wherein adjusting, by the fuzzifier block or unit, the control signal comprises adjusting, by an algorithm included in the fuzzifier block or unit, the control signal.

9. The method of claim 8, further comprising modifying the algorithm included in the fuzzifier block or unit.

10. A fuzzifier unit for use in a steam generating boiler system, comprising:

a first input to receive a signal indicative of a magnitude of a difference between a saturated steam temperature and a temperature of intermediate steam generated by the steam generating boiler system, wherein the temperature of the intermediate steam is determined upstream of a location at which a temperature of output steam is determined, the output steam generated by the steam generating boiler system for delivery to a turbine;

a second input to receive a control signal generated by a dynamic matrix controller, the control signal based on a rate of change of a disturbance variable used in the steam generating boiler system;

adjustment routine that adjusts the control signal received at the second input based on the magnitude of the difference between the saturated steam temperature and the temperature of the intermediate steam; and

an output to provide the adjusted control signal to a field device to control the temperature of the intermediate steam.

11. The fuzzifier unit of claim 10, wherein:

the adjustment routine includes a threshold,

the control signal is adjusted when the magnitude of the difference between the saturated steam temperature and the temperature of intermediate steam is less than the threshold, and

the control signal is not adjusted when the magnitude of the difference between the saturated steam temperature and the temperature of the intermediate steam is greater than or equal to the threshold.

12. The fuzzifier unit of claim 11, wherein the threshold is modifiable.

13. The fuzzifier unit of claim 10, wherein the control signal generated by the dynamic matrix controller is further based on the temperature of the output steam and a setpoint corresponding to the temperature of the output steam.

14. The fuzzifier unit of claim 10, wherein the field device is a spray valve.

15. The fuzzifier unit of claim 10, wherein the intermediate steam is provided to a superheater section of the steam generating boiler system.

16. The fuzzifier unit of claim 15, wherein the superheater section is a final superheater section.

17. The fuzzifier unit of claim 10, wherein the adjustment routine is modifiable.

18. A steam generating boiler system, comprising:

a boiler including a superheater section;

a field device;

a controller system communicatively coupled to the boiler and to the field device; and

a control system communicatively connected to the controller to receive a signal indicative of a disturbance variable used in the steam generating boiler system, the control system including one or more routines that;

generate a control signal based on a rate of change of the disturbance variable, a temperature of output steam generated by the superheater section, and a setpoint corresponding to the output steam; and

modify the control signal based on a difference between a saturated steam temperature and a temperature of intermediate steam provided to the superheater section, and

provide the modified control signal to the field device to control the temperature of the intermediate steam.

19. The steam generating boiler system of claim 18, wherein:

the control system includes a dynamic matrix controller and a saturation prevention unit,

the dynamic matrix controller includes a first routine that generates the control signal and provides the control signal to the saturation prevention unit, and

the saturation prevention unit includes a second routine that receives the control signal from the dynamic matrix controller, modifies the control signal based on the difference between the saturated steam temperature and the temperature of the intermediate steam, and provides the modified control signal to the field device to control the temperature of the intermediate steam.

20. The steam generating boiler system of claim 19, wherein the saturation prevention unit comprises:

an input to receive a signal indicative of atmospheric pressure;

a steam table to determine the saturated steam emperature based on the atmospheric pressure;

a comparator block to determine a magnitude of the difference between the saturated steam temperature and the temperature of the intermediate steam and to provide a signal indicative of the magnitude of the difference between the saturated steam temperature and the temperature of the intermediate steam to a fuzzifier unit; and

the fuzzifier unit including the second routine.

21. The steam generating boiler system of claim 18, wherein the field device is a spray valve.