Once-through evaporator systems

Patent metadata

Field	Value
Publication number	US-11242987-B2
Application number	US-201816194427-A
Country	US
Kind code	B2
Filing date	Nov 19, 2018
Priority date	Dec 8, 2017
Publication date	Feb 8, 2022
Grant date	Feb 8, 2022

Abstract

The present application provides a method of adjusting a feedwater mass flow rate to maintain a constant steam temperature in an evaporator section. The method may include the steps of determining a change in a number of operational parameters, predicting a change in steam temperature based on the number of operational parameters, combining the predicted changes in steam temperature, determining a feedforward signal based on dynamically offsetting the combined predicted changes in steam temperature, and changing the mass flow rate of feedwater based on the feedforward signal.

First claim

We claim:

1. A method, comprising:
determining changes in a plurality of operational parameters of a once-through evaporator section over a time interval during transient conditions;
predicting a change in a steam temperature based on the changes in the plurality of operational parameters;
determining a feedforward signal based on dynamically offsetting the predicted change in the steam temperature; and
changing a feedwater mass flow rate of the once-through evaporator section based on the feedforward signal to maintain a constant steam temperature in the evaporator section during the transient conditions.

2. The method of claim 1 , wherein the plurality of operational parameters comprises a mass flow rate of a combustion gas in contact with the once-through evaporator section.

3. The method of claim 1 , wherein the plurality of operational parameters comprises an enthalpy of a combustion gas at an inlet and/or an outlet of the once-through evaporator section.

4. The method of claim 1 , wherein the plurality of operational parameters comprises an internal heat absorbed by a metal surface in the once-through evaporator section.

5. The method of claim 1 , wherein the plurality of operational parameters comprises an internal heat absorbed by a feedwater in the once-through evaporator section.

6. The method of claim 1 , wherein the plurality of operational parameters comprises an inlet feedwater enthalpy.

7. The method of claim 1 , further comprising applying a dynamic filter to each of the changes in the plurality of operational parameters.

8. The method of claim 1 , further comprising applying lead-lag compensation to the change in the feedwater mass flow rate.

9. The method of claim 1 , wherein the feedforward signal is based on a dynamic heat balance considering heat exchange in the once-through evaporator section to be unbalanced over time.

10. The method of claim 1 , wherein the transient conditions comprise a startup of the once-through evaporator section.

11. The method of claim 1 , wherein the step of predicting the change in steam temperature is based on heat transfer dynamics and a heat transfer ratio relating to heat transfer between a feedwater and an exhaust gas in the once-through evaporator section, wherein the plurality of operational parameters enable the determination of the feedforward signal during the transient conditions.

12. The method of claim 1 , wherein the step of predicting the change in steam temperature is based on a combination of: the changes in the plurality of operational parameters as an unforced response, a forced response based on a desired change in a steam temperature setpoint, a heat transfer ratio, and an incoming feedwater mass flow rate.

13. The method of claim 1 , comprising the step of separately changing the feedwater mass flow rate in each of a plurality of once-through evaporator sections.

14. The method of claim 1 , wherein the transient conditions comprise load changes of the once-through evaporator section.

15. A once-through evaporator system, comprising:
a plurality of once-through evaporator sections; and
each once-through evaporator section of the plurality of once-through evaporator sections comprising an upstream distribution valve and a controller;
wherein, for each once-through evaporator section of the plurality of once-through evaporator sections, the respective controller is configured to:
determine changes in a plurality of operational parameters of the respective once-through evaporator section over a time interval during transient conditions;
predict a change in a steam temperature based on the changes in the plurality of operational parameters;
determine a feedforward signal based on dynamically offsetting the predicted change in the steam temperature; and
provide the respective upstream distribution valve with the feedforward signal to change a feedwater mass flow rate of the respective once-through evaporator section to maintain a constant steam temperature in the respective once-through evaporator section during the transient conditions.

16. The once-through evaporator system of claim 15 , wherein the transient conditions comprise a startup of the once-through evaporator system.

17. The once-through evaporator system of claim 15 , wherein the transient conditions comprise load changes of the once-through evaporator system.

18. A system, comprising:
a controller configured to change a feedwater mass flow rate of a once-through evaporator section based on a feedforward signal to maintain a constant steam temperature in the once-through evaporator section during transient conditions, wherein the feedforward signal is based on a dynamic offset of a predicted change in the steam temperature, the predicted change in the steam temperature is based on changes in a plurality of operational parameters of the once-through evaporator section, and the changes in the plurality of operational parameters are determined over a time interval during the transient conditions.

19. The system of claim 18 , wherein the transient conditions comprise at least a startup of the once-through evaporator section.

20. The system of claim 18 , wherein the predicted change in the steam temperature is based on a combination of: the changes in the plurality of operational parameters as an unforced response, a forced response based on a desired change in a steam temperature setpoint, a heat transfer ratio, and an incoming feedwater mass flow rate.

Assignees

• General Electric Technology Gmbh

Inventors

• Koller Petrus Johannes
• Taylor Alexander

Classifications

• F22B1/1807

  using the exhaust gases of combustion engines · CPC title

• F22B35/10 Primary

  of once-through type · CPC title

• F22B35/18

  Applications of computers to steam-boiler control · CPC title

• G05D23/1934

  each space being provided with one sensor acting on one or more control means · CPC title

• F22B29/06 Primary

  of once-through type, i.e. built-up from tubes receiving water at one end and delivering superheated steam at the other end of the tubes (combined low- and high-pressure boilers of forced-flow type F22B33/16) · CPC title