Steam Injection in Exhaust Gas Recirculation for HRSG
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Solution Overview
Problem
Modern gas and steam turbine plants face challenges in reducing start-up time and emissions due to prolonged heat recovery steam generator (HRSG) heating times, leading to high fuel consumption and efficiency losses, with existing solutions either increasing water or air injection causing efficiency reductions and pressure losses.
Innovation Solution
Implementing an exhaust gas recirculation system with a blower and steam feed in the HRSG, where gas turbine exhaust gases are recirculated upstream of the heating surfaces, mixed with steam from a boiler water expansion tank, to enhance heat transfer and reduce pressure differences, allowing for faster warm-up and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If water or deionized water is injected into the inflow hood of the heat recovery steam generator to reduce exhaust gas temperature, then the exhaust gas temperature is reduced, but water consumption increases and plant efficiency is significantly reduced
Solution Approach 1:
The patent introduces recirculated exhaust gas as an intermediary medium to transfer heat from the high-temperature exhaust gas to the heating surfaces and feed water, avoiding direct water injection and its associated efficiency losses. The recirculated gas acts as a heat carrier that enables temperature control without the energy penalty of evaporative cooling.
Solution Approach 2:
The patent changes the approach from direct temperature reduction via water evaporation to indirect temperature control through exhaust gas recirculation. By altering the mass flow and temperature parameters of the recirculated exhaust gas, the system achieves exhaust gas temperature reduction while maintaining plant efficiency.
2Temperature
If cold additional air is injected into the inflow hood of the heat recovery steam generator to reduce exhaust gas temperature, then the exhaust gas temperature is reduced, but pressure loss on the exhaust gas side increases and plant efficiency is reduced
Solution Approach 1:
The patent uses recirculated exhaust gas as an intermediary to achieve temperature control without introducing cold air that would cause pressure losses. The recirculated gas, being at a similar temperature and composition to the main exhaust flow, avoids the pressure penalties associated with cold air injection while still enabling heat transfer to heating surfaces.
3Loss of time
If exhaust gas recirculation is implemented to reduce start-up time and emissions, then start-up time is reduced and emissions are minimized, but system complexity increases
Solution Approach 1:
The patent makes the exhaust gas recirculation system multi-functional: it serves to reduce start-up time by rapidly heating the HRSG, minimize emissions by enabling faster CO catalyst activation, control exhaust gas temperature, and transfer heat to feed water. This universal application of a single system reduces the need for separate devices for each function.
Solution Approach 2:
The patent combines multiple functions into the exhaust gas recirculation system: temperature control, heat transfer to feed water, start-up time reduction, and emission control. By merging these functions into a single integrated system rather than using separate devices, the overall system complexity is managed more effectively.
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 approach reduces start-up times, increases efficiency by up to 0.55-0.60% points, minimizes emissions, and extends the operating range of the plant, while reducing material costs and maintaining steam production even at low gas turbine outputs.
Implementation Method 1
A blower arranged in the exhaust gas recirculation line compensates (if necessary overcompensates) the comparatively small pressure difference between exhaust gas extraction and exhaust gas addition at the heat recovery steam generator
Implementation Method 2
The addition of steam to the exhaust gas improves the heat transfer of the exhaust gas to the downstream heating surfaces in the heat recovery steam generator
Implementation Method 3
the heat recovery steam generator comprises heating surfaces of a high-pressure section, of a medium-pressure section and of a low-pressure section
Implementation Method 4
improved heat transfer between the exhaust gas and heating surfaces in the heat recovery steam generator
Data Source
AI summary
A power plant having a gas turbine and having a heat recovery steam generator installed downstream of the gas turbine in the direction of flow of an exhaust gas, wherein the heat recovery steam generator includes heating surfaces of a high pressure section, of an intermediate pressure section and of a low pressure section, wherein an exhaust gas recirculation line branches from the heat recovery steam generator downstream of an evaporator in the flow direction of an exhaust gas in the high pressure section and opens again into the heat recovery steam generator upstream of the heating surfaces. A blower is arranged in the exhaust gas recirculation line, with a steam feed opening into the exhaust gas recirculation line downstream of the blower in the direction of flow of a recirculated exhaust gas. A method operates a power plant of this kind.