CNG Compression Technology and Equipment 3

Question 1

Before performing maintenance on a CNG compressor, what is the FIRST required safety step?

Accepted Answer

Isolate and de-energize the compressor using lockout/tagout, then vent and verify zero pressure in the system

Answer

Notify customers that the station will be temporarily closed for maintenance

Answer

Don all required personal protective equipment and begin work immediately

Answer

Obtain written authorization from the local fire authority before any maintenance

Question 2

What is the correct method for detecting gas leaks on CNG compressor fittings and connections?

Accepted Answer

Apply an approved leak detection solution or use a calibrated combustible gas detector

Answer

Use an open flame near fittings to detect gas by observing ignition response

Answer

Rely solely on detecting the mercaptan odorant smell to locate leaks

Answer

Pressurize the system to 150% of working pressure and listen for audible hissing

Question 3

What is the purpose of a pressure relief valve (PRV) on a CNG compressor discharge line?

Accepted Answer

Prevent downstream components and storage vessels from overpressurization if the system exceeds safe pressure limits

Answer

Regulate delivery pressure to the dispenser at vehicle fill pressure

Answer

Control the sequential starting order of multiple compression stages

Answer

Equalize pressure between low, medium, and high cascade storage banks automatically

Question 4

What lubricant is recommended for oil-lubricated CNG reciprocating compressors?

Accepted Answer

Manufacturer-approved synthetic oil specifically formulated for natural gas compressor service

Answer

Standard automotive motor oil to reduce operational costs

Answer

Any food-grade lubricant that is chemically inert

Answer

Petroleum-based hydraulic fluid rated for high-pressure applications

Question 5

What operational condition results when CNG compressor piston rings become excessively worn?

Accepted Answer

Gas blow-by past the piston, reducing efficiency and contaminating crankcase oil with compressed gas

Answer

Increased gas flow rate and higher overall compressor output capacity

Answer

Higher final discharge pressure due to an improved compression ratio

Answer

Lower operating temperatures in the compression chamber

Question 6

What is the primary value of continuous vibration monitoring on a CNG compressor?

Accepted Answer

Excessive vibration can indicate bearing failure, shaft misalignment, or valve issues before catastrophic mechanical failure occurs

Answer

Vibration monitoring is required only for compressors rated above 100 horsepower by regulation

Answer

Vibration monitoring is an optional diagnostic tool rarely used in routine CNG station operations

Answer

Vibration analysis is only relevant during initial startup and commissioning, not ongoing operation

Question 7

Under NFPA 52, what ventilation requirement applies to enclosed CNG compressor buildings?

Accepted Answer

Ventilation must prevent natural gas concentrations from exceeding 25% of the lower flammable limit (LFL)

Answer

Natural ventilation through floor-level openings alone is sufficient for all compressor enclosures

Answer

No specific ventilation requirements apply to compressor buildings under current NFPA 52 provisions

Answer

Ventilation must exchange the entire building air volume a minimum of once per hour