Dynamic Steam Dump Valve Control for Waste Heat Recovery
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The start-up time of the steam turbine in waste heat recovery units is prolonged due to rapid pressure fluctuations in the steam separator, leading to cavitation and potential corrosion, especially when the steam dump valve's set pressure is constant and independent of the diesel engine's output.
Innovation Solution
A control system that dynamically adjusts the set pressure for the steam dump valve based on the current pressure of the main steam in the steam separator, ensuring it remains within a range that prevents cavitation by varying the set pressure according to the output of the internal combustion engine, thereby controlling the degree of opening of the regulating valve to limit pressure fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the degree of opening of the regulating valve is rapidly increased to start the steam turbine, then the start-up time is shortened, but the pressure of main steam fluctuates rapidly causing cavitation in the pump
Solution Approach 1:
The patent applies dynamics by making the set pressure of the steam dump valve variable rather than fixed. The control unit dynamically adjusts the set pressure based on the actual pressure of main steam in the steam separator, allowing the system to adapt to changing operating conditions. This dynamic adjustment enables the steam dump valve to open at appropriate pressure levels during start-up, preventing cavitation while minimizing start-up time.
Solution Approach 2:
The patent implements feedback control where the control unit continuously monitors the actual pressure of main steam in the steam separator and compares it with the set pressure. Based on this feedback, the control unit adjusts the set pressure to optimize the operation of the steam dump valve. This closed-loop control ensures that the regulating valve opens at the right moment to prevent cavitation while achieving quick start-up.
2Loss of energy
If the set pressure of the steam dump valve is set high to prevent steam waste during normal operation, then steam waste is avoided, but the start-up time of the steam turbine becomes long
Solution Approach 1:
The patent resolves this contradiction by making the set pressure dynamic. During normal operation, the set pressure is maintained at a high level to prevent steam waste. During start-up, the control unit dynamically lowers the set pressure based on the actual pressure of main steam, allowing the steam dump valve to open earlier and reducing start-up time. This dynamic adjustment eliminates the need to choose between high set pressure (preventing waste) and low set pressure (reducing start-up time).
Solution Approach 2:
The patent changes the parameter of set pressure from a fixed value to a variable value that adapts to different operating conditions. By changing the set pressure parameter dynamically, the system can optimize performance for both normal operation (preventing steam waste) and start-up (reducing start-up time) without compromise.
3Object-affected harmful factors
If the degree of opening of the regulating valve is limited to prevent cavitation, then cavitation is prevented, but the start-up time of the steam turbine is extended
Solution Approach 1:
The patent applies preliminary action by having the control unit pre-adjust the set pressure of the steam dump valve before the regulating valve opens. By anticipating the need to prevent cavitation, the control unit sets the appropriate pressure threshold in advance, allowing the steam dump valve to be ready to open at the optimal moment. This preliminary preparation enables the regulating valve to open more aggressively without causing cavitation, thus reducing start-up time while preventing cavitation.
Solution Approach 2:
The dynamic adjustment of set pressure allows the system to tolerate higher pressure fluctuations during start-up when the actual pressure is below the dynamically adjusted set pressure, knowing that the steam dump valve will open to prevent cavitation. This dynamic approach is more permissive than a fixed high set pressure, enabling faster start-up while maintaining cavitation prevention.
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 shortens the start-up time of the steam turbine by maintaining the steam separator pressure within an optimal range, preventing cavitation and reducing the risk of corrosion, while ensuring efficient operation by aligning the steam dump valve's set pressure with the engine's output.
Implementation Method 1
a steam separator to which main steam generated by recovering heat from exhaust gas exhausted from an internal combustion engine is guided
Implementation Method 2
a steam turbine that is driven by the main steam guided from the steam separator
Implementation Method 3
a regulating valve that regulates the flow rate of the main steam flowing from the steam separator to the steam turbine
Implementation Method 4
a steam dump valve that is connected to the steam separator... the steam dump valve is opened when the pressure of the main steam output by the output unit is greater than or equal to a set pressure
Implementation Method 5
When the cavitation occurs, the discharge pressure of the pump is lowered by the bubbles generated at the inlet of the pump... This prevents the pressure of water in the steam separator from falling below the saturated vapor pressure at the temperature of the water
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Provided is a waste heat recovery unit (300) including: an exhaust gas economizer (10) generating main steam; a steam separator (20) to which main steam is guided from the exhaust gas economizer (10); a steam turbine (30) driven by the main steam; a governor valve (35) regulating the flow rate of the main steam flowing from the steam separator (20) to the steam turbine (30); a steam dump valve (60) connected to the steam separator (20); a pressure transmitter (27) detecting a first pressure that is the pressure of the main steam in the steam separator (20); and a control unit (90) controlling the steam dump valve (60) so that it is opened when the pressure of the main steam output by the pressure transmitter (27) is greater than or equal to a set pressure. The control unit (90) sets the set pressure, which varies according to the first pressure, to a value greater than or equal to the first pressure and less than or equal to a second pressure obtained by adding a constant pressure to the first pressure.