Two-Stage Reheat Steam System for Combined Cycle Power
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Solution Overview
Problem
Conventional combined cycle power generation facilities are limited to one-stage reheat, hindering further improvements in thermal efficiency and output.
Innovation Solution
A combined cycle power generation facility incorporating a gas turbine, heat recovery steam generator, and steam turbines with a two-stage reheat system, utilizing a combustor to further heat steam before introduction to subsequent turbines, and a reheat part in the heat recovery steam generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one-stage reheat is adopted in the heat recovery steam generator, then the device complexity is reduced, but the thermal efficiency and output cannot be improved further
Solution Approach 1:
The reheat process is divided into two separate stages: first reheat in the heat recovery steam generator and second reheat in the combustor. This segmentation allows each stage to operate independently and contribute to thermal efficiency improvement without requiring complete system redesign
Solution Approach 2:
The combustor is introduced as an intermediary device between the heat recovery steam generator and the low-pressure turbine to perform the second reheat. This mediator enables additional thermal processing without modifying the existing heat recovery steam generator configuration
2Temperature
If the temperature of reheat steam is set at the same level as main steam, then the steam turbine performance is optimized, but the number of reheat stages is limited to once
Solution Approach 1:
The first reheat stage in the heat recovery steam generator prepares the steam at an appropriate temperature before it enters the combustor. This preliminary heating enables the second reheat stage to further increase the temperature without requiring excessive energy input in a single stage
Solution Approach 2:
The steam temperature parameter is changed in two sequential steps rather than one large jump. The first reheat raises the temperature partially, then the second reheat in the combustor raises it further, allowing the final temperature to exceed what would be achievable in a single-stage system
3Loss of energy
If two-stage reheat is implemented, then the thermal efficiency and output are improved, but the device complexity increases
Solution Approach 1:
The combustor, which is already part of the gas turbine system, is given an additional function by introducing steam to it for the second reheat process. This multi-functionality approach allows the combustor to serve both its original purpose and the new steam reheating function without adding a completely separate device
Solution Approach 2:
The second reheat process is merged with the existing combustor operation. The steam reheating function is combined with the fuel combustion function in the same device, allowing two functions to be performed in one location and reducing the need for separate dedicated equipment
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
Enhances thermal efficiency and output by allowing two-stage reheat, increasing steam temperature and flow rate, and reducing carbon dioxide emissions per unit output.
Implementation Method 1
a steam generation part which uses a heat quantity of an exhaust gas from the gas turbine to generate steam
Implementation Method 2
a reheat part which reheats steam
Implementation Method 3
a combustor to which steam discharged from the second steam turbine is introduced, and which combusts oxygen and hydrogen to reheat the introduced steam
Implementation Method 4
a condenser which changes steam discharged from the third steam turbine into condensed water
Data Source
Figure 1~2
Figure 3~4
AI summary
A combined cycle power generation facility 1 of an embodiment includes: a gas turbine 10; a heat recovery steam generator 30 including a high-pressure steam generation part 41 which generates steam by using an exhaust gas of the gas turbine 10, and a reheat part 50 which reheats steam; a high-pressure turbine 71 to which the steam from the high-pressure steam generation part 41 is introduced; an intermediate-pressure turbine 72 provided on a downstream side of the high-pressure turbine 71; a reheat steam pipe 63 connecting an outlet of the high-pressure turbine 71 and an inlet of the intermediate-pressure turbine 72 with the reheat part 50 interposed therebetween; a combustor 75 to which steam discharged from the intermediate-pressure turbine 72 is introduced, and which combusts oxygen and hydrogen to reheat the introduced steam; a low-pressure turbine 73 to which steam discharged from the combustor 75 is introduced; and a condenser 74 which changes steam discharged from the low-pressure turbine 73 into condensed water.