Question

which of the following statements is correct?
o a. compressed natural gas is compressed and stored at low pressures.
o b. the volume of space required for liquefied natural gas storage tanks is almost twice that required for compressed natural gas tanks for delivering the equivalent mileage range.
o c. because compressed natural gas is a gas, not a liquid, it does not matter whether the container is standing up or lying down.
o d. compressed natural gas cylinders come in two types: heavy and light.

Explanation:

• Option a: Compressed natural gas (CNG) is stored at high pressures (typically 3000 - 3600 psi), not low pressures. So, option a is incorrect.
• Option b: Liquefied natural gas (LNG) has a higher energy - density than CNG. For the equivalent mileage range, the volume of space required for LNG storage tanks is much less (not almost twice) than that for CNG tanks. So, option b is incorrect.
• Option c: Since CNG is a gas, its distribution within the container (whether the container is standing or lying down) does not affect its availability for use in the same way as a liquid. So, option c is correct.
• Option d: CNG cylinders are mainly classified based on materials (e.g., Type 1 - all - steel, Type 2 - steel with composite overwrap, Type 3 - thin - walled aluminum with composite overwrap, Type 4 - all - composite) rather than just “heavy and light”. So, option d is incorrect.

Answer:

C. Because compressed natural gas is a gas, not a liquid, it does not matter whether the container is standing up or lying down.