Condensing Heat Recovery Steam Generator Bypass Stack
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Solution Overview
Problem
Heat recovery steam generators (HRSGs) face limitations in thermal performance due to corrosion concerns with condensation and the presence of sulfur compounds, leading to a trade-off between thermal power and electricity generation, as well as large recirculation loops for warming feedwater above acid dewpoint.
Innovation Solution
A condensing heat recovery steam generator (cHRSG) system with a main stack, bypass stack, primary water circuit, secondary water circuit, and heat recovery device that includes a condensing area and heat pump, allowing for efficient water vapor condensation and latent heat recovery, transferring heat to the primary water circuit and end-user thermal applications without fluid interconnection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If heat recovery is performed in prior art HRSGs, then thermal power is improved, but corrosion occurs due to condensation of acidic components at low temperatures
Solution Approach 1:
The exhaust gas flow is divided into two separate paths: a main stack for the bulk flow and a bypass stack for a fraction of the exhaust gas. This segmentation allows different temperature zones to be created, with the bypass stack maintaining higher temperatures to prevent condensation and corrosion while the main stack can operate at lower temperatures for efficient heat recovery.
Solution Approach 2:
A recirculation loop acts as an intermediary mechanism, taking a portion of exhaust gas from the main stack and redirecting it through the bypass stack. This intermediary flow serves to maintain elevated temperatures in the heat recovery sections, preventing the condensation of acidic components that would cause corrosion, while still enabling effective heat transfer to the working fluid.
2Object-affected harmful factors
If a large recirculation loop is used to warm feedwater above acid dewpoint, then corrosion is prevented, but the approach temperature increases and thermal efficiency decreases
Solution Approach 1:
Different temperature conditions are applied to different sections of the heat recovery system. The bypass stack and its associated heat exchangers operate at higher temperatures specifically where condensation and corrosion risks exist, while other sections can operate at lower temperatures for maximum heat recovery efficiency. This localized temperature control prevents the need for uniformly high temperatures throughout the entire system.
Solution Approach 2:
The heat recovery process is segmented into multiple stages with different temperature levels. The first stage operates at higher temperatures in the bypass stack to prevent corrosion, while subsequent stages can operate at lower temperatures to maximize thermal efficiency. This staged approach allows the system to achieve both corrosion protection and energy efficiency without requiring a large recirculation loop.
3Loss of energy
If trade-off is made between thermal power and electricity generation, then one parameter is improved, but the other deteriorates
Solution Approach 1:
The system incorporates adjustable flow control mechanisms that allow dynamic optimization of the split between the main stack and bypass stack. Depending on whether thermal power or electricity generation is the priority, the recirculation ratio can be adjusted to favor one objective over the other, providing operational flexibility to respond to changing demand conditions and maximize overall system value.
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
The cHRSG enhances thermal performance by maximizing both electricity and thermal production, reducing the size of recirculation loops, and increasing steam generation while handling acid dewpoint issues, achieving improved cost-effectiveness and efficiency in power output.
Implementation Method 1
a heat recovery device for at least partially recovering latent heat contained inside the fraction of exhaust gas circulating in the bypass stack and for transferring said latent heat to the primary water circuit; wherein the heat recovery device includes a condensing area
Implementation Method 2
a first heat exchanger for providing heat exchange between the primary water circuit and the secondary water circuit, so that the primary water circuit and the secondary water circuit are in thermal contact via the first heat exchanger
Data Source
AI summary
A condensing heat recovery steam generator (cHRSG) includes a main stack for an exhaust hot gas main flow, a bypass stack for allowing a fraction of exhaust hot gas to bypass the exhaust hot gas main flow, and a heat pump. The cHRSG includes a primary water circuit, a secondary water circuit, and a tertiary water circuit. The cHRSG additionally includes a feedwater line, a first heat exchanger for providing heat exchange between the feedwater line and the secondary water circuit, and a second heat exchanger for providing heat exchange between the primary water circuit and the tertiary water circuit. In the cHRSG, latent heat is partially recovered from said exhaust hot gas circulating in the bypass stack through the second heat exchanger and additional heat is extracted in the tertiary water circuit by said heat pump, contributing to a preheating performed in a preheater of the primary water circuit.