Determining natural gas composition in practice Which instrument(s) are typically used to determine the composition of natural gas streams accurately?

Introduction / Context:
Natural gas custody transfer, heating value computation, and emissions reporting require accurate gas composition data. Modern plants rely on instrumental analysis capable of resolving light hydrocarbons and inert/contaminant species at low concentrations with repeatability and speed.

Given Data / Assumptions:

• Stream is a hydrocarbon gas mixture (methane-dominant) possibly containing ethane, propane, nitrogen, carbon dioxide, etc.
• Methods must be suitable for multi-component analysis.
• Industrial practicality and accuracy are important.

Concept / Approach:
Gas chromatography (GC) is the industry workhorse for natural gas analysis, separating components by retention time on a packed or capillary column and quantifying with thermal conductivity or flame ionization detectors. Mass spectrometry can also determine composition by ion mass-to-charge ratios and is used in specialized applications or laboratories. The classical Haldane apparatus is intended for flue gases (O2, CO2, CO) and is not suitable for detailed hydrocarbon speciation in natural gas.

Step-by-Step Solution:

Verification / Alternative check:
Standards for natural gas (e.g., GPA methods) specify GC for composition and calorific value calculations; MS is recognized in analytical labs.

Why Other Options Are Wrong:

• Haldane apparatus: Limited to a few combustion gases, not detailed hydrocarbon breakdown.

Common Pitfalls:
Confusing flue-gas oxygen/CO2 analysis with hydrocarbon speciation requirements for natural gas billing.

Final Answer:
Both (b) and (c)