Cheng Boost® and CLN® steam-injection processes differ from those used in conventional STIG gas turbines. They require precise premixing of steam and fuel, unique positioning of steam –injection hardware, and the use of control logic to meter a precise quantity of steam with particular characteristics at each injection location. 

The Cheng Low NOx (CLN®) is Cheng Power Systems proprietary technology for modifying new and existing combustion turbine emissions control. CLN® boost is for steam injection to increase their efficiency and capacity. The Cheng boost can be used to provide partial steam injection to increase the capacity of combustion turbines regardless of ambient conditions, usually only up to the limits of their existing electrical-side equipment (generators, step-up transformers, switchgear, etc.)  The Cheng-boost system is especially cost-effective when there is an existing source of steam, such as simple-cycle cogeneration plant or a combined-cycle plant.

The CLN® system precisely meters and mixes steam at specified conditions with fuel gas and sends the steam-fuel mixture to specially-designed fuel nozzles. The CLN nozzle design increases the momentum of the fuel jets, but not the fuel flow rate, and the system uses specially designed mixing equipment to homogenize the fuel with the steam. The higher fuel jet momentum of the CLN® system flame enhances the diffusion rate of oxygen towards the flame front. The CLN® system also reduces the nitrogen concentration at the flame front by the counter-diffusion of a water-vapor flux. One of the unique features of the CLN® system is mixing of the steam into the fuel rather than into the combustion air. The benefit of diluting the fuel rather than the air is that the diluents do not oppose the flux of the combustion products. Also, diluting the fuel and increasing the fuel jet momentum causes the flame front to move closer to the fuel jet. As a result, the temperature gradient in the flame increases, which breaks down the fuel faster, and the diffusion rates and concentration gradients of the combustibles increase, which increases the combustion rate. These changes in flame kinetics produce a smaller flame for the same heat release rate with a more uniform temperature distribution, lower peak temperature and shorter residence time for N species, all of which inhibit NOx formation. It is important to note that with the CLN® system and Cheng-Boost system, the simple-cycle combustion turbine operating characteristics are not permanently altered by the modifications and the nominal simple-cycle power output is available without steam injection exactly the same as for an unmodified combustion turbine. Steam can be diverted to or from process requirements as necessary to match process loads or to increase power outputs up to some plant limit, such as gearbox torque, or generator or step-up transformer temperature rise. Some minimum level of CLN® steam is required to maintain any particular emissions level, though the amount of steam used in the CLN® can be reduced to zero, if unmitigated emissions are allowable. The CLN® boost injects steam to augment power production to a particular level, to control emissions to a particular level or to match process steam demand with not to exceed power and emissions level.

The CLN® and Cheng Boost system have proven to be fast to implement, economical to operate, cost-effective and reliable ways to increase the electrical output and to lower the emissions of combustion-turbines that have a small steam supply available. The CLN® system and the Cheng Boot work equally well whether the steam is from a nearby steam electrical generating plant or fired boiler, or from an HRSG operating in simple-cycle cogeneration or combined-cycle mode.

No catalysts, ammonia, urea or other reagents, subsystems, or additional equipment are required. NOx levels as low as 5 ppm on a volumetric dry basis (ppmvd), corrected to 15% O₂, have been achieved with very stable operating characteristics for some combustion turbine hardware, with experiments achieving levels as low as 2 ppmvd corrected to 15% O₂. Unlike conventional steam or water injection for NOx control, CO levels are very low, typically in the range of 1-5 ppmvd, corrected to 15% O₂.  CO levels are often lower when using CLN® than for the unabated combustion turbine. This indicates that the CLN® has enhanced combustion efficiency, which is contrary to the effects of other steam-injection or water injection systems. 

CLN® reverses the traditional approach by using steam as diluent rather than a cooling mechanism. CLN® mixes steam with fuel to reduce NOx and CO as opposed to mixing steam with combustion air which reduces NOx but not CO.