Combined Cycle Steam Temperature Control via Segmented De-superheating
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Solution Overview
Problem
The existing steam temperature control systems in combined cycle power plants face challenges such as high minimum flow requirements, erosion of valves, and reduced controllability due to low gas turbine exhaust temperatures and increased plant flexibility, which affect the efficiency and longevity of components like superheaters and manifolds.
Innovation Solution
A system comprising multiple superheaters and re-heaters with inter-stage de-superheaters and attemperating lines, where high and intermediate pressure cooling lines introduce water or steam to control steam temperature, reducing pressure differences across control valves and minimizing flow restrictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If exit-stage de-super-heater is used to control steam temperature, then steam temperature control is achieved, but minimum flow requirement causes unnecessary temperature reduction and performance loss
Solution Approach 1:
The de-super-heating function is segmented into multiple stages: inter-stage de-super-heating before the final super-heater and exit-stage de-super-heating at the HRSG outlet. This allows temperature control to be distributed across different locations, enabling the system to meet steam temperature requirements without imposing excessive minimum flow requirements on a single valve, thereby avoiding unnecessary performance loss.
Solution Approach 2:
Inter-stage de-super-heating is implemented before the steam enters the final super-heater. This preliminary temperature adjustment prevents the need for large temperature reductions at the exit stage, allowing the exit-stage valve to operate with lower flow rates and reducing the negative impact on plant performance during base load and low load operations.
2Temperature
If water is extracted from high pressure economizer for de-super-heating, then steam temperature control is achieved, but high pressure upstream of de-super-heater valve causes erosion
Solution Approach 1:
A high pressure cooling line is introduced as an intermediary pathway to transport water from the high pressure economizer to the inter-stage de-super-heater. This separate cooling line allows water extraction without directly exposing the de-super-heater valve to high pressure conditions, reducing erosion while maintaining temperature control capability.
3Adaptability or versatility
If additional de-super-heater upstream final super-heater is introduced, then plant flexibility is improved, but plant cost increases
Solution Approach 1:
The de-super-heating system is segmented into inter-stage and exit-stage components, with the inter-stage de-super-heater providing the necessary flexibility for plant cycling and load changes. This segmentation allows the system to achieve adaptability without requiring excessive cooling capacity at the exit stage, helping to control overall system cost.
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 maintains low pressure differences across control valves, reduces erosion, and enhances temperature control reliability, allowing for more efficient steam temperature management across varying load conditions without significant increases in plant costs.
Implementation Method 1
a high pressure cooling line connected between an exit end of the high pressure economizer and an entry end of the first super-heater, with a high pressure inter-stage de-super-heater disposed therein to introduce a portion of water that is discharged from the high pressure economizer into the steam that is input into the first super-heater
Implementation Method 2
an intermediate pressure cooling line connected between an exit end of the intermediate pressure economizer and an entry end of the first re-heater, with an intermediate pressure inter-stage de-super-heater disposed therein to introduce a portion of water that is discharged from the intermediate pressure economizer into the steam that is input into the first re-heater
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a combined cycle system, which comprises a gas turbine, a steam turbine and a heat recovery steam generator, wherein the steam discharged from the water separation unit is routed through a high pressure outlet line to the set of super-heaters and discharged from the set of super-heaters through a main outlet line of the heat recovery steam generator to be introduced into the steam turbine, an attemperating line is connected between the high pressure outlet line and the main outlet line of the heat recovery steam generator to introduce a portion of steam that is discharged from the water separation unit into the steam discharged from the set of super-heaters, and that a control valve is disposed in the attemperating line. With the solution of the present invention, pressure difference across control valve for steam temperature remains low in low load or high load application of the combined cycle system.