CRH Isolation Valve Control for Reheater Overheating
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Solution Overview
Problem
In combined cycle power plants, unbalanced gas turbine outputs can lead to insufficient cooling of reheaters, causing their temperatures to exceed safe limits due to inadequate discharge steam flow rates, especially when one unit's gas turbine output is reduced, resulting in cooling insufficiency and potential overheating.
Innovation Solution
A plant control apparatus that adjusts the CRH isolation valve to proportionally divide the discharge steam flow rate between units based on the flow rate ratio of main steam from each unit, ensuring sufficient cooling by controlling the valve opening degree to maintain a stable steam flow ratio, thereby preventing overheating of reheaters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If unbalanced gas turbine outputs occur and one unit's gas turbine output is reduced, then the discharge steam flow rate for cooling the reheater becomes insufficient, but allowing this unbalanced operation enables flexible plant operation and adapts to varying power demands
Solution Approach 1:
The control apparatus continuously monitors the actual discharge steam flow rate and compares it with the required flow rate for proper reheater cooling. Based on this feedback, the system automatically adjusts the CRH isolation valve opening degree to maintain sufficient cooling capacity even during unbalanced gas turbine operations
Solution Approach 2:
The system dynamically adjusts the CRH isolation valve opening degree in real-time based on the actual operating conditions of each gas turbine unit. The control apparatus calculates the required discharge steam flow rate according to the current gas turbine output and modifies the valve position accordingly, enabling adaptive response to changing operational demands
2Reliability
If the discharge steam flow rate is increased to ensure sufficient reheater cooling, then reheater temperature safety is improved, but this reduces the adaptability to unbalanced output conditions and may cause steam waste
Solution Approach 1:
The control apparatus changes the opening degree parameter of the CRH isolation valve based on the actual gas turbine output and required discharge steam flow rate. By dynamically adjusting this parameter, the system optimizes the discharge steam flow rate to match actual cooling needs, preventing both insufficient cooling and excessive steam waste
Solution Approach 2:
Instead of maintaining maximum discharge steam flow rate, the system applies partial action by adjusting the valve opening to provide only the necessary flow rate required for proper reheater cooling under current operating conditions. This avoids excessive steam waste while ensuring adequate cooling protection
3Reliability
If the CRH isolation valve opening degree is adjusted to control discharge steam flow rate, then reheater cooling is improved, but the system complexity increases due to additional control mechanisms
Solution Approach 1:
The control apparatus performs multiple functions: it monitors gas turbine output, calculates required discharge steam flow rate, determines optimal CRH isolation valve opening degree, and executes real-time control. By consolidating these functions in a single control system, the patent reduces overall system complexity while maintaining effective reheater cooling
Solution Approach 2:
The control apparatus automatically calculates the required discharge steam flow rate based on real-time gas turbine output measurements and autonomously determines the appropriate CRH isolation valve opening degree. This self-service capability eliminates the need for manual intervention and complex external control systems, reducing overall system complexity
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 effectively secures a sufficient discharge steam flow rate for reheaters, preventing overheating and ensuring efficient operation even during unbalanced output conditions by directly controlling the flow rate ratio of discharge steam, thus maintaining optimal reheater temperatures.
Implementation Method 1
the heat recovery steam generator incorporates a heat exchanger such as a superheater or a reheater
Implementation Method 2
A role of the reheater is to generate reheat steam by heat-exchanging discharge steam which is exhaust of a high pressure steam turbine with gas turbine exhaust gas
Implementation Method 3
the reheater itself is cooled by the discharge steam passing through the inside. As a result, a temperature of the reheaters is settled, that is, balanced near a temperature of the reheat steam that passes through the inside
Implementation Method 4
a plant control apparatus that adjusts the CRH isolation valve to proportionally divide the discharge steam flow rate between units based on the flow rate ratio of main steam from each unit
Data Source
AI summary
In one embodiment, a combined cycle power plant includes first and second superheaters to generate first and second main steams, first and second reheaters to heat first and second discharge steams to generate first and second reheat steams, and a steam turbine to be supplied with the merged first and second reheat steams. The plant further includes a first valve to adjust a flow rate of the first discharge or reheat steam, and a second valve to adjust a flow rate of the second discharge or reheat steam. A plant control apparatus includes a determination module to determine a target opening degree of the second valve by using flow rates of the first and second main steams, and a controller to compare the determined target opening degree with a valve opening degree of the second valve and to control the second valve based on a comparison result.