Closed-loop NPSP Control for Cryogenic Pump Cavitation
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Solution Overview
Problem
In cryogenic liquid transfer systems, maintaining the required Net Positive Suction Pressure (NPSP) is challenging, especially with cryogens like liquid hydrogen, which are susceptible to cavitation issues. Traditional methods of increasing NPSP can lead to unnecessary heating and fluid wastage.
Innovation Solution
A closed-loop NPSP control system that uses temperature and pressure sensors to determine the current NPSP and adjusts it by manipulating a pressure-building valve, ensuring that the target NPSP is maintained without excessive heating or fluid loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure build-up is performed by heating liquid to increase NPSP, then cavitation prevention is improved, but liquid temperature increases causing eventual return to saturation curve and fluid wastage
Solution Approach 1:
The system continuously monitors NPSP through temperature and pressure sensors and uses this feedback to control the pressure-building valve, adjusting pressure build-up dynamically to maintain optimal NPSP without excessive heating. The controller receives real-time data from sensors and manipulates the valve accordingly to prevent cavitation while minimizing temperature rise.
Solution Approach 2:
The system changes the pressure parameter dynamically by adjusting the pressure-building valve based on real-time temperature and pressure measurements. This allows the NPSP to be optimized continuously, maintaining the liquid in a superheated state without reaching the saturation curve, thereby preventing cavitation without causing fluid wastage.
2Reliability
If NPSP is increased beyond minimum required level, then cavitation prevention is improved, but pump flow rate increases causing unpredictable results and downstream process disturbance
Solution Approach 1:
The system uses feedback from temperature and pressure sensors to control the pressure-building valve, dynamically adjusting NPSP to maintain it at the optimal target level. This prevents NPSP from increasing beyond the minimum required, thereby stabilizing pump flow rate while ensuring cavitation prevention.
Solution Approach 2:
The system dynamically adjusts the pressure-building valve based on real-time conditions to maintain NPSP at the optimal target level. This dynamic control ensures that NPSP remains sufficient for cavitation prevention without causing excessive flow rate increases, thereby stabilizing pump performance and downstream process.
3Reliability
If traditional pressure build-up method is used, then NPSP is increased to prevent cavitation, but extra heat transfer causes liquid to warm up faster than normal requiring venting
Solution Approach 1:
The system continuously monitors temperature and pressure to control the pressure-building valve, ensuring that only the necessary amount of pressure build-up is performed. This feedback mechanism prevents excessive heat addition to the liquid, thereby preventing the liquid from warming up faster than normal and eliminating the need for venting.
Solution Approach 2:
The system applies partial pressure build-up only to the extent necessary to achieve the target NPSP, rather than excessive pressure build-up. This controlled approach ensures cavitation prevention while adding minimal heat to the liquid, avoiding the need for subsequent venting and reducing energy loss.
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 system effectively prevents cavitation in cryogenic pumps by maintaining the optimal NPSP, reducing fluid wastage, and minimizing the risk of overheating the cryogenic liquids.
Implementation Method 1
A pressure-building circuit includes a pressure-building valve. A controller is configured to determine a Net Positive Suction Pressure provided to the pump based on measurements from the temperature sensor and the pressure sensor and adjust the determined Net Positive Suction Pressure by manipulation of the pressure-building valve
Implementation Method 2
A temperature sensor and a pressure sensor are configured to measure a temperature and pressure of cryogenic liquid upstream of the pump
Implementation Method 3
A temperature sensor and a pressure sensor are configured to measure a temperature and pressure of cryogenic liquid upstream of the pump
Data Source
AI summary
Systems and methods for reducing cavitation of a pump in a liquid transfer system including a pump and a liquid storage tank. More particularly, systems and methods for maintaining and adjusting Net Positive Suction Pressure (NPSP) are provided to the pump.