Indigo Substation, Palm Desert Peaker Plant, and Emissions Intrigue

Indigo Plant / “Substation’ Indigo is a simple cycle peaker plant located out in north palm springs, consisting of 3 power generation units. Its fuel is natural gas, and the generation units themselves are GE Vernova LM6000-PC Aeroderivative Gas Turbines. Each one can output up to 51 MWs, but in total, Indigo outputs 135 MWs nominally. The generation units (seen in yellow) most likely use water injection for NOx reduction, where demineralized water is injected into the combuster through the fuel nozzles. Their flue gas is exhausted into a CO Catalyst (Basically the same kind of catalytic converter used in your car) that converts leftover hydrocarbons an carbon monoxide into water, and carbon dioxide! It then travels into an ammonia injection grid (the pipes pictured on the side), where aqueous ammonia (or possibly DEF) mixed with pressurized air and steam, is injected into the flue gas to aid in emissions, as it helps the SCR catalyst filter out more NOx.

From EPA/452/B-02-001 Section 4: NOx controls: “The AIG consists of a network of pipes or lances connected in parallel, and perforated with several holes or nozzles. The lances are placed in a grid formation across the width and height of the ductwork. The lances and holes are sized to distribute the ammonia uniformly into the flue gas. Multiple injection zones may be utilized to increase the distribution of ammonia”

Once it has gone through the AIG, it will enter the SCR system (Selective Catalytic Reduction), which will convert NOx emissions (Nitrogen Oxides, but 95% of NOX emissions are nitric oxide) into nitrogen, and water!

From Scott Schreeg of SVI-BREMCO: “The most common SCR catalyst is a vanadium-based one. In these catalysts, vanadium and tungsten oxides form a coating that affixes to a titanium surface. These metal oxides are what drive the nitrogen oxide reduction process. For example, one common SCR setup involves vanadium pentoxide (V2O5) and tungsten trioxide (WO3) on a titanium dioxide (TiO2) surface. When ammonia nears the vanadium catalyst, the vanadium pentoxide readily absorbs the ammonia and NO reacts while in the gas phase.”

Finally the exhaust, now cooled and cleaned, is let out into the atmosphere, consisting mostly of water vapor, nitrogen gas, and CO2!

LM-6000-PC Package Arrangement:

GE Vernova LM-6000 PC:

Ammonia Injection Grid (AIG):

Selective Catalytic Reduction (SCR):

I’ll update this and make it more accurate as I find out more stuff, then I’ll split stuff up into separate articles for Indigo itself, and all the cool emissions stuff which really interest me.