CNG Compression Technology and Equipment

Question 1

What type of compressor is most commonly used in CNG fueling stations for achieving the high pressures required for vehicle fueling?

Accepted Answer

Reciprocating piston compressor

Answer

Centrifugal compressor

Answer

Axial flow compressor

Answer

Rotary screw compressor

Question 2

What is the standard service pressure for CNG vehicle storage cylinders in the United States?

Accepted Answer

3,600 psi (248 bar)

Answer

1,800 psi (124 bar)

Answer

2,400 psi (165 bar)

Answer

3,000 psi (207 bar)

Question 3

What is the primary purpose of an intercooler between compression stages in a multi-stage CNG compressor?

Accepted Answer

Cool the compressed gas to improve efficiency and protect downstream components

Answer

Lubricate piston rings between stages

Answer

Remove oil contamination from the gas stream

Answer

Regulate final discharge pressure to the storage bank

Question 4

In a multi-stage CNG reciprocating compressor, what happens to the gas at each successive compression stage?

Accepted Answer

Pressure progressively increases as volume decreases at each stage

Answer

Pressure remains constant while only volume decreases

Answer

Pressure alternately increases and decreases between stages

Answer

Pressure only increases significantly in the final stage

Question 5

What is the function of a moisture separator or coalescing filter in a CNG compression system?

Accepted Answer

Remove water vapor and entrained liquids from compressed natural gas

Answer

Separate nitrogen from methane in the gas stream

Answer

Remove particulate matter from inlet gas before compression only

Answer

Filter compressor lubricating oil from the discharge gas stream

Question 6

What material are piston rings and seals in oil-free CNG compressors commonly made from?

Accepted Answer

PTFE (polytetrafluoroethylene) and carbon composites

Answer

Natural rubber compounds

Answer

Lead alloy ring inserts

Answer

Neoprene rubber

Question 7

What is 'cascade storage' in a CNG fast-fill fueling station?

Accepted Answer

Multiple storage vessel banks maintained at different pressure levels to optimize vehicle fill speed and efficiency

Answer

A system where multiple compressors run in a pre-set timed sequence

Answer

An emergency overflow storage system that activates during peak demand periods

Answer

A backup storage system that activates only during compressor failure