Natural gas, primarily composed of methane, is a widely used fuel source requiring specialized methods for containment and transport. Natural gas can definitively be stored in a tank, which is an established industrial practice. The storage method depends entirely on the intended application and the required volume. The two primary techniques rely on fundamentally different physical principles to maximize the amount of gas held within a given space, allowing for both small-scale and massive energy reserves.
Compressed Natural Gas Storage
Storing natural gas in its gaseous form involves a process called compression, which is the more straightforward approach. This method, known as Compressed Natural Gas (CNG), involves taking the gas and subjecting it to extremely high pressures while keeping it at ambient, or normal, temperatures. Typical storage pressures range from 3,000 to 3,600 pounds per square inch (psi), which is equivalent to 200 to 250 bar of pressure.
This high-pressure containment allows a significant amount of energy to be packed into a manageable volume, though not as densely as the alternative method. The simplicity of CNG infrastructure is a major benefit, as it avoids the complex machinery required for extreme cooling. CNG tanks are essentially robust, thick-walled pressure vessels, which means the initial infrastructure costs are generally lower compared to other storage types.
A drawback of the compression method is that the energy density remains lower than that of liquid fuels. This means a CNG vehicle or storage facility requires a larger or heavier tank to hold the same amount of energy as a liquid fuel tank. The need for thick-walled tanks to safely withstand the immense internal pressure also adds to the weight and material cost of the storage system. Despite these factors, the relative ease of production and the safety benefit of the gas dissipating quickly upon a leak make it a popular storage solution.
Liquefied Natural Gas Storage
The alternative method, Liquefied Natural Gas (LNG), uses extreme temperature reduction to maximize storage. This process involves cooling the natural gas to cryogenic temperatures, specifically around -260°F (-162°C), which causes the gas to condense into a liquid state. The advantage of this liquefaction is a dramatic volume reduction; in liquid form, natural gas occupies only about 1/600th of the space it would take up as a gas at standard atmospheric pressure.
Storing LNG requires highly specialized equipment designed to maintain this frigid temperature. The tanks must be double-walled and heavily insulated to prevent heat transfer from the environment, which would cause the liquid to revert to gas. This vaporization process, known as boil-off, must be managed, often by capturing, re-condensing, or utilizing the gas that escapes the liquid state.
The necessary infrastructure for LNG includes complex liquefaction plants, specialized heat exchangers, and cryogenic pumps, contributing to a significantly higher initial cost compared to CNG storage. However, the gain in energy density is transformative, making it economically feasible to transport vast quantities of natural gas over long distances. The liquid form allows for greater energy content per unit of tank volume, which unlocks global transport and large-scale storage possibilities.
Real-World Uses of Tank Storage
The choice between CNG and LNG tank storage is determined by the logistical needs of the end-user. CNG is deployed in smaller, localized applications where the energy requirement is moderate and the gas can be refilled frequently. This includes use in fleet vehicles such as city buses and delivery trucks, as well as for small industrial operations or emergency backup power.
CNG is also used in a “virtual pipeline” system, transported via high-capacity tube trailers to customers not connected to the main transmission network. LNG is reserved for applications requiring high energy density or long-distance transport. LNG tanks are used for massive stationary storage facilities, often called peak-shaving plants, which help utility grids manage surges in demand.
The most prominent use for LNG is in global shipping, where massive ocean tankers transport the liquefied gas across continents. Because of its greater energy density, LNG is also the preferred fuel for heavy-duty trucks and marine vessels that require high horsepower and extended operating range. These distinct applications demonstrate that both tank storage methods are necessary to meet the varied logistical demands of the modern energy market.