Feedwater control for a forced-flow waste-heat steam generator

Patent metadata

Field	Value
Publication number	US-11530812-B2
Application number	US-201917282022-A
Country	US
Kind code	B2
Filing date	Sep 19, 2019
Priority date	Oct 29, 2018
Publication date	Dec 20, 2022
Grant date	Dec 20, 2022

Abstract

A method for operating a forced-flow steam generator constructed as a waste-heat steam generator having a pre-heater, including pre-heater heating surfaces, and having an evaporator including evaporator heating surfaces connected downstream on the flow medium side of the pre-heater heating surfaces. A device for adjusting a feed water mass flow has a set point for the feed water mass flow. During the creation of the set point for the feed water mass flow, a waste-heat flow transferred to a fluid in the evaporator heating surfaces is determined, and mass storage and energy storage in the fluid in the evaporator heating surfaces is detected during non-steady-state plant operation. A behaviour over time of a mass storage in the evaporator is coupled with a behaviour over time of a mass storage in the pre-heater, wherein scaling is carried out with a ratio of the density changes in the evaporator and pre-heater.

First claim

The invention claimed is:

1. A method for operating a once-through steam generator designed as a waste-heat steam generator, with a pre-heater, comprising a number of pre-heater heating surfaces, and with an evaporator, comprising a number of evaporator heating surfaces connected downstream on the flow medium side of the pre-heater heating surfaces, the method comprising:
determining a setpoint value for a feedwater mass flow based on a waste heat flow transferred to a fluid in the evaporator heating surfaces, and
detecting mass storage and energy storage in the fluid in the evaporator heating surfaces during non-steady-state plant operation,
wherein a behavior over time of the mass storage in the evaporator is coupled to a behavior over time of a mass storage in the pre-heater, and
wherein scaling is carried out with a ratio of the changes in density in the evaporator and in the pre-heater.

2. The method as claimed in claim 1 ,
wherein storage terms for mass storage and energy storage are determined from current measured values.

3. The method as claimed in claim 2 ,
wherein the current measured values are pressures and temperatures at the pre-heater input, at the pre-heater output or at the evaporator input and at the evaporator output.

4. The method as claimed in claim 1 ,
wherein a specific enthalpy of the fluid in the evaporator required for the estimation of the energy storage is approximated by the arithmetic mean value of the boiling enthalpy and saturation enthalpy.

5. The method as claimed in claim 4 ,
wherein the boiling enthalpy and the saturation enthalpy are determined by way of at least one pressure measurement either at the evaporator input or at the evaporator output.

6. The method as claimed in claim 5 ,
wherein temporal derivatives of the boiling and saturation enthalpies in the evaporator and also a density of the flow medium in the pre-heater are evaluated.

7. The method as claimed in claim 6 ,
wherein the temporal derivatives are determined by way of first and second differential elements.

8. The method as claimed in claim 7 ,
wherein the first differential element, describing the variation over time of the change in density in the pre-heater for the estimation of the mass storage, is subjected to a gain factor corresponding to the total volume of the flow medium in the evaporator heating surfaces.

9. The method as claimed in claim 7 ,
wherein the first differential element is subjected to a time constant corresponding to substantially half the transit time of the flow medium through the evaporator.

10. The method as claimed in claim 7 ,
wherein the second differential element for the estimation of the energy storage is subjected to a time constant that lies between 5 s and 40 s.

11. A forced-flow waste-heat steam generator, comprising:
a number of evaporator heating surfaces,
a number of pre-heater heating surfaces connected upstream on the flow medium side, and
a device for setting the feedwater mass flow, which can be guided on the basis of a setpoint value for the feedwater mass flow,
wherein the setpoint value is designed on the basis of the method as claimed in claim 1 .

12. The method as claimed in claim 1 ,
wherein during steady-state plant operation, the temperatures and pressures measured at a specific location in the evaporator at different times are the same, such that the temporal derivatives describing the process become zero.

13. The method as claimed in claim 1 ,
wherein during non-steady-state plant operation, changes in the temperatures and pressures measured at a specific location in the evaporator at different times are taken into account.

Assignees

• Siemens Energy Global Gmbh & Co Kg

Inventors

• Brückner Jan
• Schulze Tobias
• Thomas Frank

Classifications

• F22B29/067

  operating at critical or supercritical pressure · CPC title

• F22D5/34 Primary

  Applications of valves · CPC title

• F22B35/12 Primary

  operating at critical or supercritical pressure · CPC title

• F22D5/30 Primary

  responsive to both water level and amount of steam withdrawn or steam pressure · CPC title