Selective catalytic reduction | Direct Injection. Standard SCR system


Fresh catalyst Deactivated Fouled


Figure 5. Injection points compared: Direct Injection vs conventional SCR system. Source: EnergyLink International


Temperature (°F)


Figure 3. Graphic of CO catalyst performance for expected turbine exit CO of 100 ppm with stack limit of 6 ppm.


Source: Jeff Wirt, EnergyLink International, and Dan Ott, Environex, Inc, SCR and CO catalyst systems [conference presentation], ProEnergy Services 2024 customer conference, Houston, Texas, United States, 19 November 2024.


EnergyLink’s Direct Injection (DI) EnergyLink International’s DI system introduces ammonia in liquid form to the hot exhaust gas stream in a duct right behind the gas turbine (Figure 5) — termed the Direct Injection duct or Direct Ammonia Injection (DAI) duct. This technology, as already noted, was first tested conceptually by EnergyLink using computational fluid dynamics modeling and physical flow modelling, and then commercially behind an LM6000 and multiple LM2500 turbines in Texas. In EnergyLink’s Direct Injection duct (Figure 6), multiple retractable injection lances and nozzles introduce liquid ammonia into the hot exhaust gas stream immediately after the gas turbine exit.The DI duct is the same diameter as the exhaust diffuser — about 1.8 meters


(6 feet) for an LM6000 turbine. The ammonia injection zone is smaller than that employed in a conventional SCR, occupying only these 1.8 m (6 ft). Conventional SCR designs employ an ammonia injection grid, which is much larger and located considerably downstream of the exhaust inlet. These proprietary retractable lances and nozzles keep the ammonia in liquid form, which is then vaporised by the hot exhaust gases. The lance-nozzle units are easily adjustable in depth and position, allowing the injection of liquid ammonia at multiple locations and various radial distances within the highly turbulent circular inlet (or Direct Injection duct). In both CFD and physical flow modelling, this technology achieved the best percentage root-mean-square (%RMS) ammonia- to-NOx


distribution at the catalyst, along with NOx SCR catalyst CO catalyst AIG


and CO reductions that are comparable to, or better than, those of a conventional SCR system. To evaluate its DI technology outside a laboratory environment, EnergyLink installed a full- scale dual Direct Injection and conventional SCR system behind a ProEnergy Services LM6000PC gas turbine at the Braes Bayou simple-cycle power plant in Richmond, Texas, in 2022. The test criteria included 4.7 mg/Nm3


(2.5 ppmvdc) NOx exit and no more than 9.4 mg/Nm3


ammonia slip (or reagent leakage). For the test rig, EnergyLink used a CORMETECH METEORTM


that reduces NOx (5.0 ppmvdc) multi-emission catalyst , CO, and VOCs within a single


Tempering air system ~30% of exhaust 2 x 100% fans


Exhaust stack


GT Up to 1200°F < 900°F


catalyst layer, replacing the two catalyst beds of traditional SCR systems. According to the catalyst supplier, EnergyLink’s test rig application represented “...one of the first deployments of that catalyst type on a ‘hot’ SCR.” EnergyLink gathered baseline data from the conventional AIG system and then assessed the Direct Injection SCR at full load (47 MW), two- thirds load (32 MW), and half load (25 MW). Since maximum exhaust flow and the shortest residence times in the catalyst bed occur at full load, this condition generally guides catalyst bed design. Test results from field traverse measurements for both the conventional and Direct Injection LM6000 operating at full load are shown in Table 2. Also included in the table are field data from five LM2500XPRESS turbines operating in simple cycle at a datacentre in Texas (Figure 7). EnergyLink’s LM2500 DI systems, installed in April and May 2025, were fully tested in February 2026. Data measurements — NOx


(NO and NO2


T = 300°F at AIG P = +30 in wg


Instrument air


Ammonia vaporiser


Ammonia storage tank 19% aqueous ammonia


Ammonia transfer pumps


2 x 100% pumps Electric


air heaters 3 x 50%


Ammonia FCV


Heated air to vaporiser T = 700 to 800°F at AIG P = +45 to +50 in wg


Dilution air blowers 2 x 100% blowers


Figure 4. Process flow diagram for conventional aqueous ammonia SCR system, simple cycle gas turbine. Source: Dan Ott, Environex, Inc


20 | May/June 2026 | www.modernpowersystems.com ), the NOx -to-


ammonia ratio (%RMS), and ammonia slip — are shown for the installed LM6000 and LM2500 Direct Injection SCRs.


EnergyLink’s LM6000 DI SCR test rig demonstrated that a direct injection system


Injecting ammonia directly into the gas turbine exhaust upstream of the catalyst typically removes between 90% and 95% of NOX


emissions with a single catalyst


bed, and up to 98% with double-bed catalysts, while limiting ammonia slip to less than 9.41 mg/Nm3


(5 ppm).


at the stack


CO oxidation (%)


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