ROTAMIX® Advanced SNCR
Rotamix technology is the Nalco Mobotec next-generation, Advanced Selective Non-Catalytic Reduction (SNCR) system. Our extensive combustion experience and world class design team allowed us to develop a superior SNCR injection strategy relative to competitive technologies.
Rotamix penetrates deeper into the furnace than conventional SNCR systems. The turbulent air injection and mixing provided by Rotamix enables higher chemical utilization. The benefit is a result of more effective mixing of chemical reagents with combustion products in the furnace, reducing reagent cost by increasing chemical efficiency.
Because annual chemical costs are typically the largest consideration for an SNCR system, the core design principle of the Rotamix system is to optimize reaction location and maximize mixing to increase chemical utilization. Our patented Rotamix air injection technology increases reagent penetration with air boosted nozzles, to increase chemical efficiency and reduce reagent costs.
The Rotamix system adapts to load and temperature changes in the furnace, and can preferentially introduce chemicals where the temperature is most favorable for NOx reduction. This is accomplished through advanced feedback-control algorithms and on-site tuning, using the controls built into the Rotamix system to adjust the quantities of chemicals added. This technique reduces chemical consumption considerably by increasing the efficiency of reactivity. In fact, Nalco Mobotec Rotamix SNCR technology can decrease recurring chemical usage by up to 50 percent compared with other SNCR systems.
Urea is typically the preferred SNCR chemical reagent because it vaporizes more slowly than water and has a broader reaction window than ammonia. In SNCR design, the goal is to expose all urea to as much of the flue gas as possible at temperatures between 1600°F and 2100°F. Above this temperature range, urea reacts to form NOx; below this range, ammonia slip can cause operational problems.
Nalco Mobotec has designed many advanced SNCR systems. Our design prohibits issues that plague other SNCR systems: corrosion near injectors, ammonium bisulfate buildup in air heater, and reduced boiler efficiency from water spray.
Rotamix Advanced SNCR Solutions:
-Two redundant air systems that drastically reduce chances of corrosion caused by urea dripping on boiler tubes
-Advanced reagent feed control algorithms that minimize scenarios where ammonia slip would cause air heater fouling
-Less water usage reduces the impact on boiler efficiency
The Chemical Reaction of Urea, Water and Pollutants
Urea is mixed with water and injected into the furnace as a droplet. The droplet heats up quickly and the water begins to vaporize. When most of the water is vaporized, the urea itself vaporizes (or sublimates) to a gas phase and then decomposes thermally into HNCO and NH3, both of which are NOx reduction agents. Relative to ammonia alone, urea is a superior SNCR chemical on large and hot units because the urea vaporizes only after most of the water has vaporized. This delays the NOx reduction chemistry to allow for more mixing and cooler flue gas before becoming chemically reactive. Note that urea can be injected into temperatures exceeding 2000ºF due to the time delay for mixing. The result is efficient introduction of chemicals directly into a well distributed, rotating flue gas mixture. The cooling effect of the Rotamix high-velocity jets further extends the maximum temperature of SNCR injection.
A properly designed system that implements a high degree of mixing can inject urea well upstream of the appropriate temperature window. Sufficient water and air promote superior mixing, making urea chemically available to reduce NOx within a broader injection window.
At each Rotamix injection point, the Rotamix air transports urea into the furnace and mixes thoroughly with the combustion products before the urea itself fully vaporizes. The Rotamix system has several parameters that can be adjusted in order to maximize the system performance which include droplet size, urea dilution, boosted air, and lance injection angle. Nalco Mobotec models each system to minimize the number of injection locations while maintaining maximum NOx reduction. NOx can be further lowered by installing a small induct catalyst system in the backpass, thereby reducing NOx to levels comparable with SCR systems.
Nalco Mobotec solutions offer modular technology deployment to meet current and future NOx requirements.