Selective catalytic reduction |


Bringing Direct Injection SCR to European aeroderivatives


EnergyLink International, a Canadian company with extensive expertise in post-combustion air-emissions control for power-drive turbines, is set to launch a new “Direct Injection” selective catalytic reduction (SCR) technology at two peaking power plants and a datacentre in the European Union. The new technology is already installed on eleven aeroderivative open-cycle gas turbines (OCGTs) in the United States, where all turbines require post-combustion SCR to meet strict emissions standards. EnergyLink’s innovation results from a year-long R&D programme and full- scale demonstration unit aimed at delivering a more cost-effective and efficient SCR, with a smaller footprint, fewer materials, and a reduced parasitic load compared to traditional SCR systems


Jeff Wirt Director, Catalyst Systems, EnergyLink International


The idea behind EnergyLink’s patent-pending enhanced SCR system is called “Direct Injection” (DI). The DI innovation replaces the traditional ammonia injection grid (AIG) and standard ammonia vaporisation skid (AVS) by injecting liquid aqueous ammonia directly into the hot exhaust stream at the turbine outlet. This DI technology has been tested and commercialised on one LM6000 and five LM2500 gas turbines in Texas, and the results are shown for the first time in this issue of Modern Power Systems magazine.


Why OCGT SCR now in the EU? Post-combustion SCR behind turbines has not been necessary for EU open-cycle power installations unless situated in an area exceeding two or more health related air quality standards or until the IED 2.0 Industrial Emissions Directive revision, which outlines BAT (Best Available Technique) conclusions for Large Combustion Plants (LCP), becomes law, in July 2026. Cited in an April 2024 European Environmental Bureau (EEB) report, “…a technique can no longer be claimed ‘BAT’ if it is not compatible with climate protection. Hence, the use of fossil fuels in a combustion process with major greenhouse gas (GHG) emissions cannot be BAT any longer.” The EU developments already mentioned, involving EnergyLink in power generation for electricity production or artificial intelligence infrastructure, are implementing BAT by using Hydrotreated Vegetable Oil (HVO) as the fuel source or by constructing the plant to be hydrogen-ready. HVO is a renewable diesel


with the same chemical properties as fossil fuel diesel but emits 90% less CO2


. Another benefit


of HVO is that it can be used in turbines without modification. A drawback of HVO, however, is that it produces higher NOx


emissions than natural


gas. Hydrogen also produces higher levels than natural gas, so SCR technology must be used for hydrogen-powered applications.


The BAT-associated emission levels (BAT-AELs)


from open-cycle gas turbines fuelled by natural gas or HVO, as defined in the 2021 Large Combustion Plant (LCP) directive, are 50 mg/Nm3


for NOx


(milligrams per normal cubic meter). Under the updated Industrial Emissions Directive for LCPs approved in 2024, HVO must meet a limit of 35 mg/Nm3


Environmental Bureau, NOx


. According to the European limits for open-cycle


gas turbines using natural gas are expected to be reduced in the EU to 10–15 mg/Nm3


.


Currently, 100%-hydrogen-fueled LCPs require SCR technology to control NOx


emissions,


although no specific level has been set yet; a new standard for hydrogen-fuelled power plants is expected soon.


In the three European projects involving EnergyLink, the NOx


limits vary along with the


permissible ammonia slip, which indicates the amount of unreacted ammonia (or reagent) that can pass through the SCR catalyst and exit the exhaust stack. As shown in Table 1, the 2021 LCP limits apply in Ireland, while the project in Germany restricts NOx


to the most


stringent legislative level for natural gas with a view to future burning of hydrogen fuel. As


Table 1. HVO-fuelled power plant projects Involving EnergyLink International Gas


turbine size


Project country


Fuel MW


Germany NG (future hydrogen)


Ireland HVO Ireland HVO 62 15 15


Gas turbine emissions, mg/ Nm3


(ppm in


parentheses) at gas


NOX turbine outlet 133 (70.68) 129 (68.55) 135 (71.74) Source: EnergyLink International (2024 and 2025). NOx Limit in mg/Nm3 NOX at stack exit 10 (5.31) 50 (26.57) 50 (26.57)


already noted, hydrogen produces higher NOx levels than natural gas, and in the absence of


a hydrogen-specific NOx limit, the power plant


developer opted for no more than 10 mg/Nm3 of NOx


at the stack exit. Nevertheless, since none of the aeroderivative gas turbines used in these projects can meet the current 50 mg/ Nm3


limit, the pending 35 mg/Nm3 10 mg/Nm3 utilise SCR technology.


While turbine manufacturers have developed methods like DryLowNOx, SoLoNOx, and water injection to lower NOx


emissions, emissions


from gas turbine exhaust when using HVO stay well above the EU’s current and pending limits. According to the EEB, the LCP limits call for additional investments in SCR technology to help comply with the EU’s upcoming stricter BAT standards.


SCR explained


During fossil fuel combustion, NOx forms when N2


reacts with O2 primarily at temperatures


above 2350°Fahrenheit (1290°Celsius). SCR systems remove NOx


NOx and O2 from flue gases produced


by open-cycle gas turbines by injecting ammonia (NH3


) into the exhaust stream before a catalyst. then reacts with NH3


of the catalytic material to produce N2


Chemistry of the SCR process The primary reactions for NOX


4 NH3 + 4 NO + O2  4 N2 8 NH3 + 4 NO2  7 N2


at exhaust stack exit (ppm in parentheses) Ammonia slip 5 (7.18) 3 (4.31) 3 (4.31) limits derived from client specifications 18 | May/June 2026 | www.modernpowersystems.com + 6 H2 + 12 H2 Secondary reactions:


2 NH3 + SO3 + H2O  (NH4 NH3 + SO3 + H2O  NH4


)2 (SO4 HSO4


The primary reactions for CO are: CO + ½ O2


 CO2


Secondary reactions: NO + ½ O2


 NO2 SO2 + ½ O2  SO3 CH4 + 2O2  CO2 + 2H2 O ) O O


on the surface and H2


O. limit for natural gas, they must all limit, or the


are:


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