Once-Through Evaporator Flow Control for Thermal Stress
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Horizontal once-through evaporators in heat recovery steam generators face temperature imbalances and mechanical stresses due to uneven flow distribution across steam generator tubes, which can lead to damage and require complex expansion bends for compensation.
Innovation Solution
An orifice system with baffles arranged in the second steam generator tubes downstream of the flow medium side is introduced to create additional frictional pressure loss, stabilizing the flow and reducing temperature imbalances, eliminating the need for expansion bends.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a horizontal once-through evaporator is used in a heat recovery steam generator, then the manufacturing and assembly costs are reduced and the design is simplified, but temperature imbalances and mechanical stresses occur due to uneven flow distribution across steam generator tubes
Solution Approach 1:
The patent introduces flow control elements (orifices, restrictors, or variable geometry components) into specific steam generator tubes to create localized flow resistance. This local modification equalizes the flow distribution across all tubes by creating controlled pressure drops in specific locations, thereby balancing the temperature and stress distribution throughout the evaporator system while maintaining the simple horizontal design.
2Reliability
If expansion bends are added to compensate for thermal expansion stresses, then the reliability and service life are improved, but the device complexity and manufacturing costs increase
Solution Approach 1:
The patent extracts and eliminates the need for expansion bends by addressing the root cause of thermal expansion stresses - the uneven flow distribution. By implementing flow control elements that equalize flow across all tubes from the beginning, the system prevents excessive temperature differences and thermal expansion stresses, making compensation components like expansion bends unnecessary and thereby reducing device complexity.
Solution Approach 2:
The flow control elements are installed in advance during manufacturing to pre-establish balanced flow distribution. This preliminary action prevents temperature imbalances and thermal expansion stresses before they can occur during operation, eliminating the need for later compensation measures and reducing overall system complexity.
3Productivity
If the frictional pressure loss in steam generator tubes is low, then the flow rate through tubes is high and productivity is improved, but temperature imbalances occur due to geodetic pressure loss dominating over frictional pressure loss
Solution Approach 1:
The patent modifies the flow characteristics by introducing flow control elements that change the frictional pressure loss parameter. These orifices or restrictors increase the frictional pressure loss component relative to the geodetic pressure loss, thereby altering the flow distribution characteristics. This parameter change enables balanced flow distribution across all tubes while maintaining adequate overall flow rates for system productivity.
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 orifice system ensures even temperature distribution and reduces mechanical stresses, extending the service life of the heat recovery steam generator with a simpler and cost-effective design.
Implementation Method 1
an orifice system with a number of orifices arranged in series in each second steam generator tube... which causes such an additional frictional pressure loss
Implementation Method 2
The heat is transferred in a heat recovery steam generator which is connected downstream of the gas turbine and in which a number of heating surfaces for preheating the water, for generating steam and for superheating steam are usually arranged
Implementation Method 3
the heating of steam generator tubes provided as evaporator tubes leads to evaporation of the flow medium in the steam generator tubes in a single pass
Data Source
Figure 1
Figure 2
Figure 3
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 another 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, an opening system (22) is arranged downstream of the second steam generator tubes (14) on the flow medium side.