Answer
When evaluating whether a Flue Gas/Combustion Inert Gas Generator (IGG) or a Nitrogen (N2) Generator is more convenient on a gas carrier, the answer depends entirely on the nature of your cargo trade profile and the chemical requirements of the grades you carry.
For an LPG/Chemical gas tanker that changes grades frequently—especially between Propane and Ammonia—the Nitrogen (N2) Generator is fundamentally more convenient and operationally superior. Conversely, if the vessel stays on a dedicated, long-term propane/butane run, the IGG becomes highly convenient due to lower running costs.
⚖️ Direct Comparison: Operational Convenience
1. Grade Change and Chemical Flexibility
N2 Generator (Winner): Produces high-purity Nitrogen (≥99.5%) with negligible CO2 (<100 ppm). Because it contains no carbon dioxide, you can use it to inert a tank filled with ammonia vapor, or purge a propane tank right before loading ammonia, without any risk of creating Ammonium Carbamate solid crystals.
IGG: Produces inert gas by burning marine oil, creating a composition of roughly 14% CO2, 85% N2, and <1% O2. You cannot inject this gas into ammonia atmospheres. Using an IGG forces you to add an entire intermediate aeration step (purging with dry air to clear out CO2) during grade changes, lengthening your shipyard or port preparation by 24–48 hours.
2. Startup Time and Port Availability
N2 Generator (Winner): Typically utilizes Pressure Swing Adsorption (PSA) or Hollow-Fiber Membrane separation. It is a "push-button" system that provides on-demand, high-purity gas within 10 to 15 minutes of startup. It can easily run in ports or at anchorages where local emissions regulations or terminal rules ban the combustion of heavy fuels or diesel oil on deck.
IGG: Requires a complex combustion setup involving burner parameters, pilot flames, cooling water pumps, and a scrubbing tower to wash out soot and sulfur oxides (SOx). Stabilization takes time, and soot carryover can contaminate cargo tanks if the scrubber or soot separator fails.
3. Dew Point and Cargo Contamination
N2 Generator (Winner): The separation process naturally produces extremely dry gas, consistently achieving dew points of −65∘C to −70∘C. This easily clears the strict commercial charterparty specs for polymer-grade or high-purity propane.
IGG: Relies heavily on a refrigerated gas cooler and a desiccant air dryer system down-line to pull moisture out of the combustion exhaust. The dew point rarely drops below −40∘C to −45∘C, leaving a smaller margin for error.
4. Running and Maintenance Cost (OPEX)
IGG (Winner): While less flexible chemically, running an IGG requires only fuel oil and basic blower power. For large-scale initial tank inerting from a completely gas-free state, the fuel-to-volume ratio makes an IGG significantly cheaper to operate than a large N2 compressor setup.
N2 Generator: Consumes substantial electrical power because feed-air compressors must compress massive volumes of air to high pressures (7 bar to 13 bar) to force it through the membranes or carbon molecular sieves. Maintenance involves expensive periodical replacement of filters, oxygen sensors, and membrane modules.