Compressor Outlet Pressure Control via Inlet Temperature Feedback
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Solution Overview
Problem
Plural stage centrifugal compressors used in natural gas supply systems face challenges in avoiding stonewall conditions, which can lead to compressor damage due to low discharge pressure, and existing solutions are either ineffective or costly.
Innovation Solution
A method involving a compressor load controller that measures inlet temperature and pressure ratio, computes a coefficient, and adjusts the outlet pressure set point to prevent stonewall conditions by increasing the pressure over the required outlet pressure, using a pressure regulator and variable diffusor valves to maintain optimal operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the outlet pressure set point is set according to consumer needs, then the compressor operates efficiently for the intended application, but the compressor may enter stonewall conditions causing damage
Solution Approach 1:
The control system continuously monitors the actual outlet pressure and compares it with the calculated safe operating pressure (based on inlet temperature and pressure ratio). When the actual pressure approaches the safe limit, the system automatically adjusts the outlet pressure set point to maintain a safe margin, preventing stonewall conditions while allowing operational flexibility.
Solution Approach 2:
The system dynamically changes the outlet pressure set point parameter based on real-time measurements of inlet temperature and pressure ratio. By calculating a coefficient that represents the safe operating margin and adjusting the set point accordingly, the system adapts to varying operating conditions to prevent stonewall while maintaining efficiency.
2Reliability
If additional compressor units are added to prevent stonewall conditions, then compressor safety is improved, but system complexity and cost increase
Solution Approach 1:
The control system performs self-monitoring and self-adjustment by continuously calculating the safe operating pressure based on inlet conditions and automatically modifying the outlet pressure set point. This self-service capability eliminates the need for additional compressor units or complex mechanical safety devices, maintaining safety while reducing system complexity.
Solution Approach 2:
The invention replaces potential mechanical solutions (such as additional compressor units or physical bypass systems) with a electronic control system that uses sensors, calculations, and automated set point adjustment. This substitution reduces mechanical complexity while maintaining or improving safety.
3Reliability
If the outlet pressure is increased above consumer requirements to avoid stonewall, then compressor safety is maintained, but energy consumption increases
Solution Approach 1:
The system applies partial excess pressure increase only when necessary to maintain the safe operating margin, rather than continuously operating at excessively high pressures. By dynamically adjusting the outlet pressure set point based on real-time conditions, the system uses the minimum necessary pressure increase to prevent stonewall, minimizing energy waste while maintaining safety.
Data Source
Figure 1~2
AI summary
Method for controlling a compressor comprising a last stage (40) and a compressor load controller (90), a set point outlet pressure corresponding to the consumer needed pressure, being given in the load controller (90) comprising the steps of: a- measuring the temperature at the inlet of the last stage (40), b- measuring the ratio between the outlet and inlet pressure of the last stage (40), c- computing a coefficient (Ψ) based on the value of the inlet temperature (Tin) and on the pressure ratio (Pout/Pin), d- if the coefficient (Ψ) is in a predetermined range, changing the set point outlet pressure by a new greater set point outlet pressure until the coefficient (Ψ) computed with the new set point outlet pressure goes out of the predetermined range, and e- adapting the pressure of the fluid coming out of the compressor in a pressure regulator (100) to the consumer needed pressure.