CNG Cascade Pressure Reduction with Knock-Out Vessels
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Solution Overview
Problem
Conventional pressure reduction systems for compressed natural gas (CNG) require pre-heating and use restrictive pressure regulators, leading to maintenance issues and inadequate dew point management, especially when dealing with high levels of heavy hydrocarbons and water vapor.
Innovation Solution
A non-thermal pressure reduction system that uses pressure reduction stages with knock-out vessels and control valves to gradually depressurize CNG without pre-heating, maintaining pressure within a specific range to prevent liquid dropout, eliminating the need for pressure regulators and heaters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If conventional pressure regulators with orifices are used to restrict CNG flow, then pressure reduction is achieved, but temperature of CNG decreases causing water and liquid hydrocarbons to condense
Solution Approach 1:
The pressure reduction process is divided into multiple sequential stages, each with its own pressure regulator and heating system. The first stage reduces pressure from initial high pressure to an intermediate level, the second stage further reduces to a lower intermediate level, and the third stage achieves final usable pressure. This segmentation allows progressive pressure reduction with intermediate heating opportunities at each stage to prevent condensation.
2Reliability
If heating systems are added to prevent liquid dropout, then dew point management is improved, but device complexity and maintenance requirements increase
Solution Approach 1:
Heating is applied as a preliminary action before each pressure reduction stage to prevent condensation from occurring in the first place. The heating systems are positioned upstream of each pressure regulator, proactively raising the CNG temperature above its dew point before the pressure drop occurs, thereby preventing liquid dropout rather than addressing it afterward.
Solution Approach 2:
The system incorporates feedback mechanisms where the outcome of each pressure reduction stage (temperature and pressure measurements) informs the operation of subsequent stages. This allows the multi-stage system to dynamically adjust heating and pressure reduction parameters to maintain optimal operation and prevent condensation throughout the process.
3Device complexity
If single-stage pressure reduction is used, then system simplicity is maintained, but temperature drop causes water and hydrocarbon condensation
Solution Approach 1:
The pressure reduction process is divided into multiple sequential stages, each with its own pressure regulator and heating system. The first stage reduces pressure from initial high pressure to an intermediate level, the second stage further reduces to a lower intermediate level, and the third stage achieves final usable pressure. This segmentation allows progressive pressure reduction with intermediate heating opportunities at each stage to prevent condensation.
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 effectively controls liquid dropout and maintains safe pressure levels for CNG, reducing operational challenges and equipment issues, while allowing for efficient pressure reduction without the need for heating systems.
Implementation Method 1
Control valves and pressure sensors are used to maintain the gas pressure within a pre-designed range of within the knock-out bottles in each pressure reduction stage
Implementation Method 2
Liquid dropout are controlled using knock-out vessels or bottles in each pressure reduction stage, where any liquid dropout is collected in the knock-out bottle
Implementation Method 3
a pressure sensor for monitoring the pressure within the knock-out bottle
Data Source
AI summary
A system and method for reducing the pressure of a pressurized gas is provided, the system including a pressure reduction stage, the pressure reduction stage including: a knock-out bottle; a control valve connected to a gas stream inlet and configured to introduce a gas stream at an initial pressure level into the knock-out bottle; an output connected to a gas stream outlet; and a pressure sensor for monitoring the pressure within the knock-out bottle and changing the operational state of the control valve to maintain the pressure inside the knock-out bottle within a pressure range. More than one pressure reduction stage may be implemented in series to provide a more gradual step down in the gas pressure.