Cold-Weather CNG Storage Using Active Cooling and Composite Tanks
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Solution Overview
Problem
The storage and distribution of compressed natural gas (CNG) are inefficient at low temperatures, leading to reduced fuel transfer and longer filling times, and existing large capacity tanks are heavy, expensive, and inefficient due to the need for thick steel construction to withstand high pressures.
Innovation Solution
A system utilizing large capacity, insulative storage tanks with a double-walled design and an auxiliary electric heater, where the slow fill compressor maintains the temperature and pressure of the gaseous fuel by compressing low-pressure source gas and using a heat exchange apparatus to control temperature, allowing for efficient distribution and reducing the weight and cost of the tanks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If CNG is stored in large capacity tanks at high pressures (3,000-3,600 psi), then storage capacity is improved, but tank weight and manufacturing cost increase due to thick steel construction requirements
Solution Approach 1:
The patent changes the temperature parameter by actively cooling the CNG storage tank to sub-ambient temperatures (below 40°F). This parameter change allows the tank to store the same quantity of CNG at lower pressures, thereby reducing the structural requirements and weight of the tank while maintaining storage capacity.
Solution Approach 2:
The patent employs composite material construction for the storage tank, combining materials with different thermal and mechanical properties. The tank includes insulative material layers and cooling system integration that create a composite structure capable of maintaining low temperatures while withstanding pressure loads, reducing the need for thick steel construction.
2Quantity of substance
If CNG storage tank capacity is increased, then fuel supply is improved, but tank weight and inefficiency increase
Solution Approach 1:
By actively cooling the tank to sub-ambient temperatures, the patent increases the density of stored CNG. This parameter change allows larger quantities of fuel to be stored in the same volume, improving storage efficiency and productivity while maintaining reasonable tank size and weight.
3Temperature
If ambient temperature decreases below 40°F, then cold-weather operation occurs, but pressure in storage tank drops resulting in reduced fuel transfer efficiency
Solution Approach 1:
The patent applies preliminary anti-action by actively cooling the storage tank before and during cold-weather operation. The cooling system preemptively counteracts the ambient temperature drop, maintaining the CNG at optimal temperatures for pressure and transfer efficiency, thereby preventing the harmful effect of pressure loss.
Solution Approach 2:
The patent converts the harmful effect of cold ambient temperatures into a benefit by using the temperature difference as a driving force for the cooling system. The ambient cold air is utilized to cool the tank, and the system recovers heat from the compression process to pre-cool the incoming gas, turning the environmental condition into an asset for maintaining storage efficiency.
4Stress or pressure
If compression is used to maintain pressure in storage tank, then fuel availability is improved, but energy expenditure increases
Solution Approach 1:
The patent converts the heat generated during compression (typically a waste product) into a useful resource by using it to pre-cool the incoming CNG. This heat recovery process reduces the overall energy expenditure of the system, as the compression heat is utilized rather than discarded, offsetting some of the energy required for active cooling and compression operations.
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 achieves efficient cold-weather storage and distribution of CNG with lighter, more economical tanks that maintain optimal temperature and pressure, reducing energy expenditure and manufacturing costs while ensuring precise temperature control and increased storage capacity.
Implementation Method 1
a heat exchange apparatus 14
Implementation Method 2
an auxiliary electric heater 42
Implementation Method 3
large capacity tanks that are insulative
Data Source
AI summary
A system for the cold-weather storage of gaseous fuels includes a gas source having an inlet pressure, a compressor having an inlet and an outlet, the inlet selectively communicating with the gas source and the outlet having a discharge pressure greater than the inlet pressure, a heat exchange apparatus having an inlet and an outlet, the inlet selectively communicating with the compressor so as to receive pressurized gas therefrom, a high-pressure storage tank having an inlet and an outlet, the inlet selectively communicating with the compressor so as to receive pressurized gas therefrom, and a valve assembly for selectively directing the pressurized gas to the heat exchange apparatus and the high-pressure storage tank in dependence upon a temperature within the storage tank.