CNG Cylinders: Types, Benefits, and Safety Guidelines
Compressed natural gas (CNG) is a clean, economical alternative energy source widely used in the automotive and industrial sectors. CNG cylinders are essential for storing and transporting CNG. Their type selection, performance advantages, and safety management directly impact their efficiency and safety. The following provides a detailed explanation of CNG cylinder types, key advantages, and safety guidelines. I. Main Types of CNG Cylinders
CNG cylinders must withstand high pressure (typically 20 MPa, or 200 times atmospheric pressure). Different materials and structures determine their application scenarios.
II. Core Advantages of CNG Cylinders
Compared to traditional fuel storage containers (such as gasoline tanks) or other gas storage methods (such as LNG tanks), CNG cylinders offer significant advantages, particularly in terms of economy, environmental friendliness, and safety:
1. Low Cost and High Performance
Low Fuel Cost: CNG prices are typically 50%-70% of gasoline/diesel, reducing vehicle fuel costs by 30%-40%.
Low Maintenance Cost: CNG combustion leaves no carbon deposits, reducing engine wear and extending the life of components like oil and spark plugs. This reduces annual vehicle maintenance costs by 15%-20%.
Long Cylinder Life: Steel cylinders have a service life of 15 years, while composite cylinders have a service life of 10-12 years, resulting in low amortized costs over long-term use. 2. Environmentally friendly and clean, with low emissions.
CNG's primary component is methane (CH₄), which undergoes a more complete chemical reaction during combustion, significantly reducing pollutant emissions compared to fuel oil:
Reduced harmful gases: Carbon monoxide (CO) emissions are reduced by over 90%, nitrogen oxides (NOx) by 30%-50%, and hydrocarbons (HC) by over 70%.
Reduced greenhouse gases: Per unit energy, CNG combustion emits 15%-20% less carbon dioxide (CO₂) than gasoline, meeting the "dual carbon" environmental protection requirements.
No secondary pollution: Lead-free and sulfur-free, preventing soil and water contamination from fuel leaks. 3. Reliable Safety Performance and Manageable Risks
The design and production of CNG cylinders must comply with strict national standards (such as GB 17258 "Compressed Natural Gas Cylinders for Automobiles" and GB/T 28053 "Wrapped Compressed Natural Gas Cylinders for Automobiles"). Core safety advantages include:
High-Pressure Resistance: Before leaving the factory, they must pass a "hydraulic pressure test" (2.5 times the rated pressure) and a "burst test" (at least 4 times the rated pressure) to ensure they will not rupture under extreme pressures.
Leak-Proof Design: The cylinder mouth is equipped with a dedicated valve (such as a CNG-specific shut-off valve) that provides overcurrent protection and overpressure relief (the safety valve automatically vents in the event of overpressure).
Material Stability: Steel cylinders are resistant to low temperatures and aging, while the composite wrapping layer of the cylinders is UV- and corrosion-resistant, making them suitable for complex environments.
III. Safe Use Guidelines for CNG Cylinders
While CNG cylinders are safe and reliable, their high-pressure storage characteristics necessitate strict adherence to operating regulations to avoid risks such as leaks and explosions caused by improper handling. The following safety requirements are clarified in four areas: daily inspection, filling regulations, usage precautions, and regular testing:
1. Daily Inspection: Avoid "Using with Defects"
Before use (especially vehicle gas cylinders), daily inspections are required, focusing on the following areas:
Appearance Inspection: Inspect the cylinder for scratches, dents, or corrosion (steel cylinders), or for damage or detachment of the wrapping (composite cylinders). If any damage is found, immediately remove from service.
Valves and Pipes: Check that the cylinder valve is tightly closed, and the connecting pipes (high-pressure hoses) are not aged, cracked, or loose. Check that there are no gas leaks at the joints (apply soapy water to ensure no bubbles).
Instrument Display: The CNG pressure gauge on the vehicle's dashboard should display normal pressure (not overpressure or underpressure), and the overpressure indicator should be off (if on, immediately vent and reduce the pressure). 2. Filling Standards: Eliminate Illegal Operations
CNG filling must be performed at a certified filling station, strictly adhering to the following rules:
Pre-filling Verification: The operator must verify the cylinder's expiration date (exceeded cylinders are prohibited from filling), that the cylinder serial number matches the vehicle license, and that there are no expired or discarded cylinders.
Controlling Filling Volume: Fill by weight or volume. Excessive volume is strictly prohibited (keep within 90% of the rated capacity to avoid excessive pressure caused by temperature rise).
Observation During Filling: Strike or bump the cylinder during filling. Smoking and using open flames are prohibited. If leaks are detected, stop filling immediately and vent the system.
Post-filling Inspection: After filling, confirm that the valves are tightly closed, there are no leaks in the piping, and that the pressure gauge indicates a pressure within 20 MPa ± 0.5 MPa. 3. Usage Taboos: Avoid "Dangerous Behaviors"
During daily use, strictly avoid the following hazardous operations:
Avoid impact and exposure to sunlight: Do not expose gas cylinders to high temperatures (such as in the interior accessories area of a car in summer, where temperatures exceeding 60°C can cause a sudden increase in pressure). Do not impact or squeeze gas cylinders.
Avoid unauthorized modification: Do not disassemble or replace gas cylinder valves or piping without authorization, and do not relocate the gas cylinder installation location (modification must be performed by a qualified contractor).
Avoid open flames: Smoking, using lighters, welding, or other open flames within 5 meters of a gas cylinder. In the event of a leak, immediately close the valve and ventilate the area before handling.
Avoid mixing gases: CNG cylinders can only be filled with compressed natural gas. Do not fill them with other gases, such as liquefied petroleum gas (LPG) and hydrogen, to avoid explosions caused by material incompatibility. 4. Regular Inspection: Ensure "Safety and Validity Period"
CNG cylinders must undergo regular inspections in accordance with national standards. Cylinders that have not been inspected within the specified period must not be used. The inspection cycle is as follows:
Steel cylinders (Type I): Initial inspection 3 years after use, then every 2 years thereafter. Cylinders must be scrapped after 15 years of use.
Wrap-around cylinders (Type III): Initial inspection 3 years after use, then every 2 years thereafter. Cylinders must be scrapped after 10 years of use.
Fully composite cylinders (Type IV): Initial inspection 2 years after use, then every 2 years thereafter. Cylinders must be scrapped after 10 years of use.
Inspection items: Includes visual inspection, hydrostatic test, airtightness test, ultrasonic flaw detection (steel cylinders), and wrap integrity test (composite cylinders). Cylinders may only be used after passing these inspections.
