Turboexpander Speed Control Without Geared Transmission Losses
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Solution Overview
Problem
In sub-ambient temperature refrigeration systems, the inefficiency of turboexpanders due to constrained speed by complex geared transmissions leads to irreversible losses, limiting operational efficiency during varying conditions.
Innovation Solution
A method and system where a turboexpander's speed is controlled through electromagnetic braking, maintaining optimal efficiency by adjusting the rotor speed based on enthalpy drop and flow rate, eliminating the need for geared transmissions and enhancing efficiency across normal and turndown conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a geared transmission is used to couple the turboexpander to the generator, then the generator can operate at line frequency (60 Hz), but the turboexpander speed is constrained and irreversible losses occur
Solution Approach 1:
The patent replaces the mechanical geared transmission system with an electromagnetic braking system. The generator operates as a variable speed generator coupled directly to the turboexpander, eliminating the need for mechanical gears. The electromagnetic brake provides the necessary speed control and synchronization with the electrical grid without the energy losses inherent in mechanical transmission.
Solution Approach 2:
The patent changes the operating parameters of the generator from fixed line frequency operation to variable speed operation. The generator can now operate at any speed determined by the turboexpander's optimal efficiency point, and the electromagnetic braking system adjusts the speed dynamically to match grid requirements without mechanical transmission losses.
2Reliability
If the turboexpander is constrained to operate at fixed speed, then the generator can supply power to the grid, but the turboexpander cannot operate at optimal efficiency during varying conditions
Solution Approach 1:
The patent makes the turboexpander-speed system dynamic by eliminating the fixed speed constraint imposed by geared transmissions. The variable speed generator coupled with electromagnetic braking allows the turboexpander to operate at any speed, enabling it to track its optimal efficiency point across varying operating conditions while still providing reliable electrical power to the grid.
Solution Approach 2:
The patent implements a control system that uses feedback to maintain optimal turboexpander operation. The system monitors operating conditions and adjusts the electromagnetic braking force to keep the turboexpander at its optimal efficiency speed, ensuring both grid reliability and maximum productivity across varying conditions.
3Ease of operation
If complex geared transmissions are used to couple the turboexpander to the generator, then the generator can operate at standard speeds, but the device complexity increases
Solution Approach 1:
The patent extracts and removes the complex geared transmission system from the coupling between the turboexpander and generator. By using direct coupling with a variable speed generator and electromagnetic braking, the patent eliminates the intermediate mechanical transmission components, thereby reducing device complexity while maintaining ease of operation.
4Adaptability or versatility
If the turboexpander operates during turndown conditions, then the plant can operate at reduced capacity, but the turboexpander efficiency decreases due to speed constraints
Solution Approach 1:
The patent enables the turboexpander to dynamically adjust its speed to maintain optimal efficiency during turndown conditions. The variable speed generator and electromagnetic braking system allow the turboexpander to operate efficiently across the full range of plant capacities, from full load to reduced capacity operations, eliminating the efficiency losses that occur with fixed-speed operation.
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 optimizes turboexpander efficiency by dynamically adjusting speed to match operational conditions, reducing energy losses and maintaining line-matching electrical power output for grid integration.
Implementation Method 1
The compressed process stream is expanded within a turboexpander having an impeller that is driven by the process stream with performance of work, thereby producing an exhaust stream
Implementation Method 2
Electrical power is generated in a generator having a rotor coupled to the impeller so that the generator is driven by the work of expansion
Implementation Method 3
The speed of the rotor of the generator is controlled and therefore, the speed of the turboexpander is also controlled through electromagnetic braking of the rotor
Data Source
AI summary
The present invention provides a method and apparatus for generating refrigeration in a process operating at sub-ambient temperatures in which the refrigeration is generated by a turboexpander. The turboexpander is coupled to a generator controlled so that its speed is maintained at a setpoint through electromagnetic braking and its power output is maintained at line matching voltage and frequency. The speed control of the generator therefore, also controls the speed of the turboexpander. The setpoint is calculated to be equal to a product of an operational efficiency parameter, U/Co, and a square root of twice the enthalpy drop in the flow passing through the turboexpander divided by a product of pi and a diameter of an impeller employed within the turboexpander.