Jet Pump Forced Circulation for Steam Drum Thermal Stress
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Solution Overview
Problem
Heat recovery steam generators experience rapid drum temperature transients during startup, leading to significant thermal stresses that limit operational flexibility and the number of start-up cycles, as the rapid temperature increase causes compressive and tensile stresses in the steam drum, restricting the use of higher pressures and increasing the risk of fatigue damage.
Innovation Solution
Implementing a temporary forced circulation method using a jet pump to create a pressure gradient during start-up, circulating fluid from the evaporator to the steam drum before boiling, thereby reducing the rate of temperature change and thermal stresses by maintaining a lower pressure in the steam drum until the fluid reaches boiling point, after which natural circulation takes over.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If natural circulation is used during startup, then the system is simple to operate, but the drum temperature rises rapidly causing high thermal stresses
Solution Approach 1:
The jet pump is activated before the fluid reaches boiling point to establish forced circulation, pre-conditioning the system to avoid rapid temperature rise. This preliminary forced circulation phase prepares the fluid and system for smoother transition to natural circulation, preventing thermal shock while maintaining operational simplicity.
2Stress or pressure
If the steam drum wall thickness is increased to handle higher pressure, then the drum can operate at higher pressures, but the thermal stresses during startup become greater
Solution Approach 1:
The system changes the circulation mode parameter from natural to forced during startup, which fundamentally alters the temperature rise profile. This parameter change allows thicker drum walls to be used for higher pressure operation while the forced circulation phase mitigates thermal stress by controlling the heating rate, resolving the contradiction between pressure capability and thermal stress resistance.
3Stress or pressure
If forced circulation is implemented during startup, then thermal stresses are reduced allowing higher pressure operation, but the system complexity increases
Solution Approach 1:
The jet pump serves as an intermediary device that temporarily mediates the circulation process during startup. It bridges the gap between the evaporator and steam drum, establishing controlled forced circulation before natural circulation takes over. This intermediary approach adds minimal complexity while enabling higher pressure operation by controlling thermal stress during the critical startup phase.
4Loss of time
If rapid temperature rise is allowed during startup, then the startup time is reduced, but fatigue damage and cracking risk increase
Solution Approach 1:
The jet pump establishes forced circulation before boiling occurs, pre-conditioning the fluid and system to prevent rapid temperature rise. This preliminary action extends startup time slightly but dramatically improves reliability by preventing thermal shock, fatigue damage, and magnetite layer cracking, thereby protecting the drum's structural integrity throughout its operational life.
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 thermal stresses in the steam drum, allows for the use of steam drums with larger wall thickness, enabling operation at higher pressures and increasing the number of start-up cycles, thus enhancing operational flexibility and extending the operational life of heat recovery steam generators.
Implementation Method 1
creating a temporary pressure gradient during start-up of an evaporator system... transporting a fluid from the evaporator to the drum prior to the fluid reaching its boiling point
Implementation Method 2
prior to the fluid reaching its boiling point in the evaporator... after the fluid has reached its boiling point in the evaporator
Implementation Method 3
transporting a fluid from the evaporator to the drum... circulating the fluid through the evaporator system
Data Source
Figure 1
Figure 2
AI summary
An evaporator system (200) comprises an evaporator (202); a drum (204); and a pump (206) that are in fluid communication with each other. The pump (206) is operative to create a temporary pressure gradient during start-up of an evaporator system (200) and transport a fluid from the evaporator to the drum prior to the fluid reaching its boiling point in the evaporator (202). Following the fluid reaching its boiling point in the evaporator (202), the fluid naturally circulates in the evaporator system.