Continuous Evaporator Tube Design for Thermal Stress Reduction
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Solution Overview
Problem
Horizontal continuous-flow steam generators face issues with temperature imbalances and mechanical stresses due to uneven flow medium distribution and different thermal expansion in the second evaporator heating surface, which existing designs attempt to address with complex expansion bends.
Innovation Solution
Designing the second steam generator tubes to maintain a minimum mean mass flow density of 180 kg/m² during full-load operation, ensuring the inside diameter is between 20 mm and 40 mm to balance frictional and geodetic pressure losses, thereby stabilizing the flow and reducing temperature differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expansion bends are added to compensate for thermal expansion stresses, then the mechanical stresses are reduced, but the device complexity and manufacturing costs increase
Solution Approach 1:
The patent removes the expansion bends from the tube bundle structure entirely. Instead of adding compensatory elements, the design extracts the problematic component and replaces it with a simplified straight-tube configuration that relies on proper flow distribution to prevent thermal stress issues.
Solution Approach 2:
The patent changes the flow distribution parameters by implementing a specific inlet structure that ensures uniform flow distribution across all tubes in the second evaporator heating surface. This parameter change in flow distribution prevents the thermal expansion differentials that would otherwise require expansion bends.
2Temperature
If the inside diameter of second steam generator tubes is reduced to increase mass flow density, then temperature imbalances are reduced, but frictional pressure losses increase
Solution Approach 1:
The patent optimizes the inside diameter parameter of the second steam generator tubes to a specific range (20-40 mm) that balances two competing effects: increasing mass flow density for uniform temperature distribution while limiting frictional pressure losses. This parameter optimization achieves both goals simultaneously.
Solution Approach 2:
The patent implements a preliminary flow distribution structure at the inlet that pre-distributes the flow medium uniformly across all tubes before they enter the heating section. This preliminary action prevents temperature imbalances from developing, allowing the use of optimized tube diameters without excessive pressure losses.
3Ease of manufacture
If a horizontal design is used for the heat recovery steam generator, then manufacturing and assembly costs are reduced, but uneven flow distribution and temperature imbalances occur
Solution Approach 1:
The patent applies different structural solutions to different locations within the horizontal heat recovery steam generator. The inlet structure is specifically designed with flow distribution elements tailored for horizontal orientation, while the tube arrangement and support structures are optimized for their specific local conditions. This localized optimization maintains temperature uniformity while preserving the manufacturing advantages of horizontal design.
Solution Approach 2:
The patent modifies the flow distribution parameters specifically for horizontal orientation by implementing inlet structures that compensate for gravity-induced flow stratification. The tube spacing, inlet angle, and flow velocity parameters are adjusted to achieve uniform distribution in the horizontal configuration, maintaining temperature uniformity while preserving manufacturing simplicity.
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 design approach eliminates the need for expansion bends, enhances the service life of the heat recovery steam generator by stabilizing the flow and reducing mechanical stresses, while maintaining a simple and cost-effective construction.
Implementation Method 1
the heat contained in the expanded working medium or heating gas from the gas turbine is used to generate steam for the steam turbine. The heat is transferred in a heat recovery steam generator
Implementation Method 2
a first evaporator heating surface, which comprises a number of essentially vertically arranged first steam generator tubes through which flow occurs from bottom to top
Data Source
AI summary
The invention relates to a continuous evaporator (1) for a horizontally constructed waste heat steam generator (2), which comprises a first evaporator heating surface (8) having a plurality of essentially vertically arranged first steam generator tubes (13) through which a flow medium can flow from bottom to top, and a second evaporator heating surface (10) which is mounted downstream of the first evaporator heating surface (8) on the flow medium side. Said second evaporator heating surface comprises a plurality of additional essentially vertically arranged second steam generator tubes (14) through which a flow medium can flow from bottom to top. The aim of the invention is to produce a continuous evaporator which is simple to construct and which has a long service life. As a result, the second steam generator tubes (14) are designed in such a manner that the average mass flow density which can be controlled in the full load operation does not fall below a predetermined minimum mass flow density in the second steam generator tubes (14).