Steam Generator Feed-Water Density Control
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Solution Overview
Problem
In continuous steam generators, synchronous changes in feed-water mass flow through the evaporator heating surface and heat entry are challenging to achieve, leading to fishtailing of specific enthalpy and large temperature variations, which complicates temperature control and reduces equipment lifetime due to unreliable direct measurement of feed-water mass flow at the evaporator entry.
Innovation Solution
A regulating device adjusts the feed-water mass flow based on setpoint values correlated with steam generator performance, using actual feed-water density at the preheater entry and accounting for mass injection/extraction effects by calculating feed-water mass flow at the evaporator entry, incorporating average and exit densities to ensure precise heat flow balancing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of feed-water mass flow at evaporator entry is implemented, then measurement precision is improved, but device complexity increases and reliability decreases due to technical complexity
Solution Approach 1:
The patent introduces an intermediary measurement approach by measuring feed-water mass flow at the preheater entry (upstream location) rather than directly at the evaporator entry. This intermediary measurement point avoids the technical complexity and reliability issues of direct evaporator entry measurement while still providing the necessary control data through correlation calculations.
Solution Approach 2:
The patent replaces direct mechanical flow measurement at the evaporator entry with a calculation-based approach. By measuring flow at the preheater entry and using heat flow balance calculations, the system substitutes a simpler measurement system with computational methods to achieve the required measurement precision without the complexity of direct evaporator measurement.
2Device complexity
If feed-water mass flow is regulated based on preheater entry measurement, then device complexity is reduced, but manufacturing precision deteriorates due to mass injection/extraction effects in preheater
Solution Approach 1:
The patent implements feedback control by continuously monitoring the feed-water mass flow at the preheater entry and using this information to adjust the feed-water regulation. The heat flow balance calculation provides a feedback mechanism that accounts for mass injection and extraction effects, allowing the system to maintain precise control despite the indirect measurement approach.
Solution Approach 2:
The patent compensates for mass injection and extraction effects by dynamically adjusting calculation parameters in the heat flow balance. By changing the computational approach to account for temperature and density variations in the preheater, the system maintains manufacturing precision despite using a simpler upstream measurement location.
3Stability of the object's composition
If load changes are limited in speed, then fishtailing of specific enthalpy is reduced, but productivity decreases due to lower efficiency
Solution Approach 1:
The patent applies preliminary action by anticipating load changes and adjusting feed-water mass flow in advance through the regulation system. By using the heat flow balance calculation to predict required feed-water adjustments before actual load changes occur, the system prevents fishtailing of specific enthalpy while allowing rapid load changes and maintaining high productivity.
Solution Approach 2:
The patent implements dynamic control by making the feed-water regulation system responsive to real-time operating conditions. The heat flow balance calculation continuously adapts to changing load conditions, enabling the system to maintain specific enthalpy stability during rapid load changes without limiting productivity, as the regulation dynamically adjusts to each operating state.
4Productivity
If rapid load changes are allowed, then productivity is improved, but reliability decreases due to uncontrollable temperature variations and reduced lifetime
Solution Approach 1:
The patent uses feedback control to monitor and regulate feed-water mass flow in response to rapid load changes. The heat flow balance calculation provides continuous feedback that ensures temperature variations remain within safe limits, allowing rapid load changes for high productivity while maintaining reliability and extending equipment lifetime through controlled regulation.
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 solution enables synchronous regulation of feed-water throughflow and heat entry, preventing fishtailing of specific enthalpy and temperature variations, reducing material stresses and extending the steam generator's lifetime by accurately compensating for density changes and heat entry fluctuations.
Implementation Method 1
a preheater, usually referred to as an economizer, connected upstream from the evaporator heating surface and preheated there
Implementation Method 2
the heating of a number of steam generator tubes which together form the gas-tight enclosing wall of the combustion chamber leads to a complete evaporation of a flow medium in the steam generator tubes
Data Source
AI summary
The invention relates to a process for operating a continuous steam generator. The aim of the invention is to provide, with little technical complexity and for any operating state, a synchronous variation of the feed-water mass flow passing through the evaporator heating surface and of the heat input into the evaporator heating surface. To this end, a regulating device for the discharge of feed-water is allocated to a device for adjusting the feed-water mass flow. The control variable of said regulating device is the feed-water mass flow, while its set-point value in relation to the feed-water mass flow depends on the set-point value associated to the power of the steam generator. The actual value of the feed-water density at the entry of the pre-heater is fed to the regulating device for the discharge of feed-water as one of the input values.