Compressor Control via Isentropic Head Coefficient
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Solution Overview
Problem
Plural stage compressors face limitations due to stonewall and surge conditions, particularly when handling low-temperature LNG, which can lead to compressor damage and operational inefficiencies, with existing solutions being either ineffective or costly.
Innovation Solution
A control system that measures inlet temperature and pressure ratios, calculates an isentropic head coefficient, and adjusts the compressor's working conditions by acting on control valves and recycle lines to prevent stonewall conditions, allowing for increased operational range and reduced surcharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor operates at high flow rates, then productivity is improved, but stonewall conditions occur causing harmful effects
Solution Approach 1:
The control system continuously monitors the actual flow rate and head pressure, calculates the head coefficient, and compares it against predetermined thresholds. When stonewall conditions are detected (head coefficient below threshold), the system automatically adjusts the inlet guide vane angle or impeller speed to reduce flow rate and increase head, thereby eliminating stonewall conditions while maintaining optimal operation within safe boundaries.
Solution Approach 2:
The system dynamically changes operational parameters (inlet guide vane angle, impeller speed) based on real-time calculation of the head coefficient. By adjusting these parameters in response to calculated head coefficient values, the compressor can operate at high flow rates when conditions permit while automatically retreating to lower flow rates when stonewall conditions are approached, thus resolving the contradiction between productivity and harmful effects.
2Use of energy by moving object
If the compressor operates at low flow rates, then energy consumption is reduced, but surge conditions occur causing harmful effects
Solution Approach 1:
The control system monitors actual flow rate and head pressure, calculates the head coefficient, and when surge conditions are detected (head coefficient above threshold), automatically increases flow rate by adjusting inlet guide vane angle or impeller speed. This feedback mechanism ensures the compressor maintains sufficient flow rate to prevent surge while minimizing energy consumption by operating at the lowest safe flow rate.
Solution Approach 2:
The system dynamically adjusts operational parameters based on real-time head coefficient calculation. When surge conditions are approached, the system increases flow rate parameters; when safe operating conditions are confirmed, it reduces flow rate to minimize energy consumption. This continuous parameter adjustment resolves the contradiction between energy efficiency and surge prevention.
3Reliability
If a traditional anti-surge control system is used, then surge conditions are prevented, but device complexity increases
Solution Approach 1:
The invention replaces complex mechanical anti-surge systems (multiple valves, bypass lines, pressure regulators) with an electronic control system that calculates the head coefficient and actuates a single control element (inlet guide vane or impeller speed controller). This substitution of mechanical complexity with electronic calculation and control achieves the same surge prevention function with significantly reduced device complexity.
Solution Approach 2:
Instead of using multiple mechanical components to prevent surge, the system uses a single control parameter (inlet guide vane angle or impeller speed) that is dynamically adjusted based on calculated head coefficient. This parameter-based control approach achieves surge prevention with minimal device complexity, as the entire anti-surge function is accomplished through electronic calculation and single-point actuation rather than complex mechanical systems.
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 stonewall and surge conditions, enabling the compressor to operate safely and efficiently across a broader range of conditions, reducing the risk of damage and increasing operational flexibility.
Implementation Method 1
measuring the temperature at the inlet of the compressor
Implementation Method 2
measuring the ratio between the outlet pressure and the inlet pressure of the first stage of the compressor
Implementation Method 3
acting on a control valve mounted in a line supplying the inlet of the first stage of the compressor
Data Source
AI summary
Method for controlling a plural stage compressor comprising at least a first stage (10), a second stage (20) and a first inter-stage line (12) between the first stage (10) and the second stage (20), comprising the steps of:a—measuring the temperature at the inlet of the compressor,b—measuring the ratio between the outlet pressure (Pout) and the inlet pressure (Pin) of the first stage (10) of the compressor,c—calculating a coefficient (ψ) based at least on the value of the inlet temperature (Tin) and on the measured pressure ratio (Pout/Pin),d—if the calculated coefficient (ψ) is in a predetermined range, acting on a control valve (70; 76; 92) mounted in a line (4; 8) supplying the inlet of the first stage (10) of the compressor or in a gas recycle line (74) which opens into the first inter-stage line (12).