Liquefied Gas Unloading With Variable-Speed Tank Evacuation
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Solution Overview
Problem
Traditional single stage compressors leave behind valuable product in supply tanks and do not maintain maximum fluid transfer rates due to fixed operating speeds, which are affected by changing pressures and temperatures during liquefied gas offloading.
Innovation Solution
A two-stage compressor system with a variable frequency drive and programmable logic controller that adjusts operating speed based on temperature and pressure, allowing for both single and two-stage operations, including a liquid trap to handle condensation and valves to change modes for efficient liquid transfer and vapor recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single stage compressor operates at fixed speed, then the structure is simple and easy to operate, but the fluid transfer rate cannot be maintained at maximum due to changing pressures and temperatures
Solution Approach 1:
The patent applies a variable frequency drive (VFD) to the compressor motor, enabling the compressor speed to vary dynamically based on real-time pressure and temperature conditions. This transforms the fixed-speed operation into a dynamic system that automatically adjusts to maintain maximum fluid transfer rate throughout the offloading process, directly resolving the contradiction between operational simplicity and productivity.
2Device complexity
If a single stage compressor is used, then the device complexity is low, but the compressor must stop due to low volumetric efficiency or high discharge temperatures leaving valuable product in supply tanks
Solution Approach 1:
The patent employs a two-stage compression process where the compression function is divided into two sequential stages. The first stage compresses the vapor to an intermediate pressure, and the second stage further compresses it to the final discharge pressure. This segmentation allows the system to achieve deeper tank evacuation and higher product recovery without requiring excessive complexity in a single component.
Solution Approach 2:
The two-stage compression process changes the pressure parameters in steps rather than in a single jump. This intermediate pressure stage reduces the discharge temperature and improves volumetric efficiency, allowing the compressor to continue operating until nearly all product is recovered, thus resolving the contradiction between device complexity and quantity of substance recovered.
3Productivity
If a single stage compressor operates, then the initial capacity and efficiency during liquid transfer are high, but the system cannot adapt to changing pressures and temperatures throughout the offloading process
Solution Approach 1:
The patent incorporates pressure and temperature sensors that continuously monitor system conditions and provide feedback to the control system. The variable frequency drive receives this feedback and automatically adjusts the compressor speed to maintain optimal performance throughout the offloading process, enabling the system to adapt to changing pressures and temperatures while preserving high 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 system enables complete evacuation of supply tanks, maximizing fluid transfer rates and reducing unloading times by adapting to changing conditions, thus recovering more product and minimizing costs.
Implementation Method 1
A two-stage compressor, capable of both single stage and two stage operation, is provided for this process
Implementation Method 2
including a liquid trap to handle condensation
Data Source
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AI summary
A liquefied gas unloading and deep evacuation system may more quickly, more efficiently and more completely unload liquefied gases from transport tanks, such as rail cars, into stationary storage tanks or into truck tanks. The system may utilize a two stage compressor, an electric motor, a variable frequency drive, a four way valve, a three way valve, a two way valve, a programmable logic controller based control system and pressure and temperature transmitters. The valving enables deep evacuation of the transport or supply tank to more completely empty the transport tank. The programmable logic controller and variable speed drive may be used to variably control the speed of the two stage compressor so that the system may be running as fast as possible during changes in ambient temperature and/or different stages of offloading the liquefied gases without exceeding the compressor's horsepower limit.