Two-Stage Natural Gas Compression System
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Solution Overview
Problem
The high capital costs and large, expensive nature of existing gas compression systems make it impractical to establish public natural gas vehicle (NGV) filling stations, limiting the infrastructure for home refueling of NGVs.
Innovation Solution
A two-stage gas compression system comprising a rotary first stage compressor and a liquid piston second stage compressor, driven by a rotary hydraulic pump, which achieves near-isothermal compression using atomized liquid injection and hydraulic liquid cooling, allowing for efficient compression of natural gas from residential line pressures to standard CNG pressures without the need for separate gas coolers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional gas compression systems are used, then gas compression capability is achieved, but system size and cost become prohibitively large for home use
Solution Approach 1:
The compression system is divided into two distinct stages: a first stage compressor handling initial compression and a second stage compressor handling final high-pressure compression. This segmentation allows each component to be optimized for its specific pressure range, reducing overall system size and cost while meeting home refueling requirements.
Solution Approach 2:
The second stage compressor is positioned within the housing of the first stage compressor, creating a nested configuration. This nesting approach maximizes space utilization, reduces the overall footprint of the system, and allows both compressors to share common mounting structures and piping infrastructure.
2Productivity
If single-stage compression is used, then system simplicity is maintained, but compression efficiency and temperature control deteriorate
Solution Approach 1:
The compression process is segmented into two stages with intermediate cooling, allowing temperature control between stages. This segmentation improves overall compression efficiency by reducing the work required for compression while managing heat generation, and the modular design keeps system complexity manageable.
Solution Approach 2:
The system employs periodic reciprocating motion in both compressors, with the second stage compressor operating in sync with the first stage. This periodic action allows for controlled compression cycles with intermediate cooling periods, improving efficiency while maintaining predictable system behavior that simplifies control.
3Speed
If rapid compression is used, then refueling speed is improved, but gas temperature rise and energy loss increase
Solution Approach 1:
The two-stage compression system with intermediate cooling allows rapid overall refueling while managing temperature rise. The first stage compressor rapidly compresses gas to an intermediate pressure, then cooling occurs before the second stage continues compression to final pressure, reducing total energy loss compared to single-stage rapid compression.
Solution Approach 2:
The intermediate cooling system acts as a mediator between the two compression stages, removing heat generated during the first stage compression before the gas enters the second stage compressor. This intermediary cooling process reduces the energy required for the second stage compression while maintaining rapid overall refueling speed.
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 provides an affordable, compact, and efficient home refueling solution for NGVs, reducing costs and spatial requirements while maintaining high efficiency and safety standards, enabling greater market penetration of NGVs and shifting demand from imported oil to domestic natural gas.
Implementation Method 1
a first stage compressor configured to compress the gas to a first pressure level
Implementation Method 2
a second stage compressor configured to compress the gas from the first pressure level to a second pressure level
Implementation Method 3
a hydraulic pump configured to provide pressurized hydraulic fluid for the second stage compressor(s)
Implementation Method 4
achieves near-isothermal compression using atomized liquid injection and hydraulic liquid cooling
Implementation Method 5
hydraulic liquid cooling, allowing for efficient compression of natural gas
Data Source
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AI summary
A refueling system for natural gas users (e.g., natural gas vehicles) includes a two- stage compression system that compresses low-pressure gas in a natural gas supply line to compressed natural gas (CNG) pressure for use by a user. A single motor drives both a first stage rotary compressor and a rotary hydraulic pump that powers a second-stage liquid piston compressor. The motor, first stage compressor, and pump may be co-axially aligned. Booster vessels store compressed gas to augment the system's compressed gas delivery flow rate when desired. The booster vessels may be recharged with compressed gas when the system is not delivering gas to a user. Hydraulic liquid may be pumped into and out of the booster vessels during booster vessel discharge and recharge, respectively, to maintain a desired pressure within the vessels.