Steam Generator Water Flow Control via Heat Balance
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Solution Overview
Problem
Once-through steam generators, especially those used as waste-heat boilers, face challenges in reliably regulating the supply water mass flow to maintain target specific enthalpy values during changes in load, due to the lack of suitable parameters like firing power, leading to temperature fluctuations and reduced system stability.
Innovation Solution
A predictive mass flow regulation method that accounts for specific temperature and mass flow characteristics of the hot gas, using heat flow balance calculations to determine the required supply water flow, incorporating parameters like current gas turbine power and enthalpy differences, to ensure accurate adaptation to heat input and desired steam state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If predictive mass flow regulation is implemented using heat flow balance calculations, then the regulation reliability of supply water mass flow is improved, but the device complexity increases due to additional measurement and calculation requirements
Solution Approach 1:
The patent introduces a supply water mass flow regulator as an intermediary device that receives target values from a control device and adjusts the actual mass flow accordingly. This mediator bridges the gap between predictive calculations and actual flow control, improving reliability without requiring direct complex integration of all calculation components into the flow measurement system.
Solution Approach 2:
The control device performs predictive calculations of the required supply water mass flow in advance, before the actual evaporation process occurs. By determining target mass flow values beforehand based on heat flow balance calculations and current operating parameters, the system can proactively adjust supply water flow to maintain target specific enthalpy values, improving regulation reliability.
2Stability of the object's composition
If supply water mass flow is regulated to maintain target specific enthalpy values, then temperature stability is improved, but the difficulty of detecting and measuring increases due to the need for precise mass flow measurement
Solution Approach 1:
The patent replaces direct mechanical mass flow measurement at the evaporator inlet with a regulatory system that controls mass flow based on target values. The supply water mass flow regulator uses control signals rather than direct mechanical measurement to achieve precise flow control, thereby maintaining temperature stability while avoiding the measurement difficulties associated with direct inlet flow measurement.
Solution Approach 2:
The system uses feedback from measured specific enthalpy values at the evaporator outlet to adjust the supply water mass flow. By continuously monitoring the actual specific enthalpy and comparing it with target values, the control device can dynamically adjust the target mass flow values to maintain temperature stability, compensating for measurement uncertainties.
3Manufacturing precision
If the supply water flow is changed synchronously with heat input changes, then the specific enthalpy deviation is reduced, but the response time requirement increases
Solution Approach 1:
The control device calculates target supply water mass flow values in advance based on current heat flow input and operating parameters. By determining the required mass flow adjustment before the actual heat input change fully manifests, the system can respond more quickly to load changes while maintaining precise specific enthalpy control, reducing both deviation and response time delays.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables reliable and stable regulation of the supply water flow, maintaining low deviations in specific enthalpy at the evaporator outlet, even in waste-heat boiler operations, by using measurable characteristics to predict and adjust the supply water mass flow effectively.
Implementation Method 1
the heating of a number of steam generator tubes which together form an evaporator heating surface leads to a complete evaporation of a flow medium in the steam generator tubes in one pass
Implementation Method 2
The flow medium—usually water—is generally fed before its evaporation to a preheater, usually also referred to as an economizer, connected upstream on the flow medium side from the evaporator heating surface and preheated there
Data Source
AI summary
A method for operating a once-through steam generator including an evaporator heating surface is provided. A target value for the supply water mass flow is fed to a device for setting the supply water mass flow, which is predefined using the ratio of the heat flow currently being transferred in the evaporator heating surface from the hot gas to the flow medium to a target enthalpy increase predefined with respect to the desired live steam condition of the flow medium in the evaporator heating surface. A forced-flow steam generator used for carrying out the method is also provided. The heat flow transferred from the hot gas to the flow medium is ascertained for this purpose allowing for a specific temperature value characteristic of the current temperature of the hot gas at the evaporator inlet and a specific mass flow value characteristic for the current mass flow of the hot gas.