Compressed Natural Gas (CNG) Storage Solutions: Comprehensive Guide

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There is an escalating demand for compressed natural gas (CNG) due to its role in reducing air pollution and lessening dependence on imported fuels.

Despite the high production levels of CNG, the primary challenge in its widespread adoption is the insufficient number of pipelines for transporting this critical resource.

As the search for alternative energy sources intensifies, the demand for CNG transport and storage systems also surges.

At Advanced Structural Technologies, we specialize in producing large-diameter Type 3 storage and transportation solutions for CNG and other renewable energy types, tailored to various customer needs.

This guide will delve into the different CNG storage options available and their suitable applications, aiding you in finding the perfect energy storage solution for your business needs.

Overview of topics covered:

What is Compressed Natural Gas (CNG)?

Compressed natural gas (CNG) is a clean fuel made by compressing methane to 1% of its usual volume. This eco-friendly fuel, derived from fossil fuels that form under heat and pressure, is not to be confused with LNG, the liquid form of natural gas.

Storing CNG under high pressure enables more efficient transport and storage for various applications, including industrial and residential uses, as well as for vehicles.

Burning CNG results in CO2 and water vapor emissions, reducing carbon monoxide (CO) emissions by 95%, making it the cleanest fossil fuel.

CNG is readily available in the USA and is more economical than coal and gasoline, driving its increased usage as an alternative fuel.

Uses of Compressed Natural Gas

The 1992 Energy Policy Act recognizes CNG as an alternative fuel to reduce carbon emissions, with a goal to enhance air quality through the use of alternative and renewable energy.

Currently, CNG accounts for 30% of the energy consumption in the U.S. 40% of this CNG is used for electricity generation, 30% for residential applications, and the remaining 30% for industrial use.

Future projections show an increase in CNG usage, driven by environmental and health concerns associated with other fuels like petroleum and coal.

Using local resources reduces reliance on imported fuels, making CNG a cheaper and strategically advantageous option, particularly in North America where it is abundantly available.

An emerging market is hydrogen-enriched CNG (HCNG), driven by climate change initiatives, urban air quality concerns, and the need for sustainable energy independence. Hydrogen, known for its quick refueling and lighter system weight, is ideal for high-demand, heavy transport, and remote power applications.

Methods of Natural Gas Transportation

Once extracted from wells, hydrogen and natural gases are treated and transported via pipelines to distributors, who then supply it to customers using pressurized CNG tanks or cylinders.

The limited number of pipelines hampers CNG's adoption as a fuel source, as many consumers are located off the main pipeline grid.

Virtual or mobile pipelines offer an environmentally friendly alternative, transporting CNG by road using high-pressure vessels to areas that cannot be reached by conventional pipelines without causing environmental harm, such as forest clearings in Pennsylvania.

• CNG Refueling Stations: These are specific sites set up by organizations with a fleet of heavy-duty vehicles that use CNG as their primary fuel source.
• Mining Companies: Heavy mining equipment running on CNG can significantly reduce operational costs, with most companies maintaining on-site CNG storage.
• Marine Vessels: Ships and boats also use CNG, and it can be transported by sea to remote consumers.
• Backup Power Systems: CNG can be integrated with systems to provide backup power, especially when paired with hydrogen for a zero-emissions energy solution.

For efficient on-site storage, HCNG requires additional infrastructure to achieve the necessary compression levels. To ensure smooth operation of high-power equipment, users require lightweight tanks for ease of transportation and maximum operational efficiency.

Options for Natural Gas Storage

Compressed natural gas (CNG) is stored in robust, thick-walled pressurized tanks, typically cylindrical in shape with rounded ends for even stress distribution.

CNG tanks are made from various materials such as steel, aluminum, or composite materials, categorized into four types based on the material:

• Type 1
• Type 2
• Type 3
• Type 4

Each type has unique characteristics suited to different applications and requirements.

Type 1 CNG Storage

Type 1 storage tanks, made entirely of steel, are the oldest and heaviest form of CNG storage. These tanks are approximately 0.5 to 1.5 inches thick, making them extremely durable and reliable. With diameters ranging from 11 to 16 inches, Type 1 cylinders are known for their resilience against environmental elements such as heat and scratches.

Common uses for Type 1 tanks include:

• Bulk Transportation: Ideal for transporting CNG where weight is not a critical concern.
• Stationary Ground Storage: Suitable for permanent storage at CNG fueling stations and industries requiring on-site CNG for machinery or heating.

However, their significant weight limits their use in scenarios where vehicle weight is an issue, and they may crack if their maximum tensile strength isn't properly managed. High-strength vessels are recommended to prevent such issues.

Type 2 CNG Tanks

Type 2 tanks are identified as hoop-wrapped, featuring a steel liner wrapped in composite fibers like fiberglass, carbon fiber, or wire. This structure offers both storage pressure and added safety.

Lighter than Type 1, but still heavier than Type 3 and 4, Type 2 tanks are suitable for applications requiring high-pressure storage, such as:

• Medical Oxygen Storage: In healthcare settings, these tanks offer an economical and high-pressure solution.
• Vehicular Applications: Widely used in personal vehicles that run on CNG.

Despite their benefits, Type 2 tanks are susceptible to corrosion, UV damage, and abrasions and must be stored properly to ensure longevity.

Type 3 CNG Tanks

Type 3 tanks are lighter and stronger, consisting of an aluminum liner fully wrapped in carbon fiber in various winding patterns to enhance strength and safety.

With a standard service pressure of 3,600 psi, and up to 7,500 psi at AST, Inc, Type 3 tanks allow for greater volume capacity and are suitable for:

• Bulk Transportation: Their lightweight design makes them ideal for transporting large volumes of CNG efficiently.
• On-site Storage: Offering high burst pressure resistance, they are perfect for dedicated refueling stations and industrial on-site storage.

While cyclic fatigue is a minor consideration due to the thin metallic walls, maintaining certified service pressure minimizes this risk.

Type 4 CNG Tanks

For more information, visit LNG Storage solution. Additional resources can be found here: What is the best tank to store gasoline in?.

Type 4 tanks are the lightest among the four types, with a polymer liner wrapped in carbon fiber. These tanks are ideal for:

• On-site Storage: Suitable for CNG refueling stations due to their continuous gas dispensing capability.
• Bulk Transportation: Their lightweight makes Type 4 tanks excellent for transporting CNG in larger amounts.

However, they are vulnerable to high temperatures and should be protected from prolonged sun exposure.

Comparing Type 3 and Type 4 CNG Storage Tanks

Both Type 3 and Type 4 vessels are fully wrapped composite tanks used in various CNG applications. They offer different advantages and limitations based on their structural differences.

Dimensions of CNG Storage Tanks

A standard Type 3 tank typically ranges between 20-26 inches in diameter.

Advanced Structural Technologies offers CNG tanks up to 26 inches in diameter, designed for high pressure and large capacity, suitable for both storage and transportation.

Capacity of CNG Storage Tanks

The capacity of CNG storage tanks is often expressed in gasoline gallon equivalents, accommodating different storage needs.

Choosing the Right CNG Storage Solution

Selecting the appropriate CNG storage solution involves considering the following factors:

• Safety: Proper storage and protection from extreme conditions are crucial to prevent gas leaks and ensure safety.
• Intended Application: Different tank types are designed for specific uses, so choose the one that matches your requirements.
• Regulations: Compliance with government regulations and certifications is essential.
• Budget: While Type 3 tanks are more expensive, their reliability and durability often justify the cost.

Large CNG Storage Tanks

Larger tanks provide greater storage capacity, reducing the number of trips required for transportation and saving both time and money.

At AST, Inc, we manufacture some of the largest available tanks, capable of withstanding pressures up to 10,000 psi.

Efficient Gas Transportation

The demand for cleaner and greener fuels like CNG is on the rise. With its domestic availability and minimal environmental impact, CNG is an excellent alternative fuel source.

Contact us for further information and inquiries. We are eager to assist in solving your CNG and alternative energy storage needs.