Turboexpander-Compressor Inlet Vane Control for Off-Design Efficiency
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Solution Overview
Problem
Conventional turboexpander-compressor systems are limited in optimizing efficiency during off-design conditions due to the inability to fully control the rotating speed of the shaft, as they can only adjust the pressure of the incoming gas, which passively affects the compressor's efficiency.
Innovation Solution
A system with moveable inlet guide vanes at both the expander and compressor, controlled by a controller that adjusts the pressure of the gas input into the compressor to maximize the ratio of shaft speed to enthalpy drop across the expander, using information from sensors to determine and respond to off-design conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If only the pressure of incoming gas is adjusted to control turboexpander operation, then the system can maintain design pressure values, but the shaft rotating speed cannot be fully controlled in off-design conditions, limiting efficiency optimization
Solution Approach 1:
The patent introduces moveable inlet guide vanes at the compressor inlet that can be dynamically adjusted to control the pressure of gas entering the compressor. This dynamic control mechanism allows the system to adapt to varying operating conditions and optimize the ratio of shaft speed to enthalpy drop across the turboexpander in off-design conditions, transforming the static control system into a dynamic one capable of real-time optimization.
Solution Approach 2:
The patent changes the control parameter from only incoming gas pressure to include compressor inlet pressure as well. By adjusting the compressor inlet pressure through moveable inlet guide vanes, the system can independently control both the turboexpander expansion process and the compressor compression process, enabling optimization of the shaft speed to enthalpy drop ratio even when operating away from design conditions.
2Use of energy by moving object
If the compressor impeller is mounted on the same shaft as the expander impeller to transfer mechanical work, then energy recovery is achieved, but the compression passively affects turboexpander efficiency by altering shaft speed, preventing full control
Solution Approach 1:
The patent introduces a new control parameter - compressor inlet pressure - that can be independently adjusted through moveable inlet guide vanes. This additional parameter allows the system to decouple the passive effect of compression on shaft speed from the active control requirements, enabling independent optimization of both energy transfer and shaft speed control.
Solution Approach 2:
The patent implements a control system that monitors the ratio of shaft speed to enthalpy drop across the turboexpander and adjusts the compressor inlet guide vanes accordingly. This feedback mechanism allows the system to actively maintain optimal operating conditions despite the passive coupling between expander and compressor through the common shaft.
3Stress or pressure
If standard moveable input guide vanes are used to control incoming gas pressure, then pressure control is achieved, but the ability to optimize turboexpander efficiency in off-design conditions is limited
Solution Approach 1:
The patent segments the pressure control function into two independent locations: moveable inlet guide vanes at the expander inlet for incoming gas pressure control, and moveable inlet guide vanes at the compressor inlet for compression pressure control. This segmentation allows independent optimization of both pressure control and efficiency, resolving the contradiction between maintaining pressure control and optimizing efficiency in off-design conditions.
Solution Approach 2:
The patent adds compressor inlet pressure as an additional controllable parameter alongside incoming gas pressure. By controlling both pressures independently through respective moveable inlet guide vanes, the system can optimize the shaft speed to enthalpy drop ratio and improve turboexpander efficiency even when operating away from design conditions.
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 allows for optimized turboexpander efficiency by actively controlling the compressor inlet pressure to align the shaft speed and enthalpy drop ratio with predetermined values, even in off-design conditions, enhancing overall system performance.
Implementation Method 1
the moveable inlet guide vanes at the compressor inlet control the pressure of the gas input into the compressor
Implementation Method 2
an incoming gas is expanded. The gas expansion produces mechanical work causing a rotation of an expander impeller
Implementation Method 3
the energy of the rotation of the compressor impeller is used in the compressor to compress the gas flow input at a pressure p3
Data Source
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AI summary
A turboexpander-compressor system (200) includes an expander (210) configured to expand an incoming gas (214), a first set of moveable inlet guide vanes (218) configured to control a pressure of the incoming gas, a compressor (224) configured to compress a gas received from the expander (210), a shaft (230) configured to support and rotate an expander impeller (212) and a compressor impeller (226), a second set of moveable inlet guide vanes (232) attached to the compressor (224) and configured to control a pressure of the gas input into the compressor (224), and a controller (240) configured to acquire information about a rotating speed of the shaft (230), a pressure and a temperature of the incoming gas, a pressure and a temperature of the gas output from the expander (210), and to control the second set of moveable inlet guide vanes (232) to maximize a ratio between the rotating speed of the shaft (230) and a drop of an enthalpy across the expander (210), in off-design conditions.