Once-Through Boiler Low Load Stability via Pressure Control
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Solution Overview
Problem
Once-through boilers face instability and potential damage during low load operations due to reduced water flow, leading to the need for switching to forced circulation mode, which results in suboptimal steam temperatures and increased ramp-up times.
Innovation Solution
Regulating the pressure and temperature at the economizer and evaporator inlets by adjusting control valves and water supply temperature to maintain stable once-through operation even at loads below the traditional limit, using measurement systems and software models to optimize parameters for extended low-load operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If water flow is reduced to operate at low load, then load flexibility is improved, but boiler stability deteriorates due to high tube wall temperatures and flow instability
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting water flow rate, steam demand, and combustion rate parameters to maintain stable once-through operation at low loads. The control system modifies these parameters in response to load changes, preventing departure from nucleate boiling and flow instability while enabling operation below traditional minimum load limits.
Solution Approach 2:
The patent implements feedback control by continuously monitoring boiler operation parameters and using this information to adjust water flow, steam demand, and combustion rate. This closed-loop control maintains stability during low load operation by detecting and correcting deviations from optimal operation in real-time.
2Reliability
If switching to forced circulation mode is performed to maintain stability, then boiler reliability is improved, but steam temperature control deteriorates and ramp-up time increases
Solution Approach 1:
The patent maintains continuous once-through operation without switching to forced circulation mode, eliminating the disruptive mode transition. By continuously adjusting water flow, steam demand, and combustion rate parameters, the system maintains stability and steam temperature control throughout the entire low load operation and ramp-up process.
3Productivity
If water flow is reduced too much, then load reduction is achieved, but tube wall temperatures increase causing potential damage
Solution Approach 1:
The patent uses parameter changes to coordinate water flow rate reductions with corresponding adjustments in combustion rate and steam demand. This synchronized parameter modification ensures that tube wall temperatures remain within safe limits even at reduced loads by preventing excessive heat flux conditions.
Solution Approach 2:
The patent applies preliminary anti-action by proactively controlling water flow, combustion rate, and steam demand parameters to prevent departure from nucleate boiling before it occurs. The control system anticipates conditions that would lead to high tube wall temperatures and adjusts parameters in advance to avoid this harmful state.
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
Enables reliable once-through operation at lower loads without switching to forced circulation, reducing material stress and shortening ramp-up times by maintaining steam temperatures closer to nominal levels and eliminating the need for costly and time-consuming mode switches.
Implementation Method 1
at the preheater 21 the steam is condensed (but the steam is not mixed with the water) to preheat the water supplied to the economizer 5
Implementation Method 2
The steam from the separator 7 is thus further superheated in the superheater 11
Implementation Method 3
at the evaporator 6 water is completely evaporated, such that from the evaporator 6 steam, usually superheated steam, is supplied into the separator 7
Implementation Method 4
when the water flow becomes too low, at the evaporator and/or economizer high tube wall temperatures and/or temperature differences in tube walls and between tubes may occur, due to problems such as departure from nuclear boiling
Implementation Method 5
the steam from the separator 7 is thus further superheated in the superheater 11
Implementation Method 6
The steam from the separator 7 is thus further superheated in the superheater 11 and then expanded in the high-pressure turbine 14
Data Source
AI summary
The once-through boiler includes a water supply and at least an economizer, an evaporator superheater. No valves are provided between the economizer, the evaporator and the superheater. The high-pressure turbine includes a control valve. The method for low load operation of a power plant with a once-through boiler and a high pressure turbine includes providing a parameter indicative of the stable operation of the once-through boiler in once-through operation, and on the basis of this parameter adjusting the control valve in order to regulate the pressure within the economizer and evaporator and/or adjusting the temperature of the water supplied to the economizer.