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Show A leading SNCR process that injects stabilized urea to control NOx is the NOxOUT Process, marketed by Nalco Fuel Tech. In the process, NOxOUT-A, a stabilized urea solution, is injected into a furnace and reacts with NOx in the gas phase to produce molecular nitrogen, water, and CO2. Urea + Nitrogen + Oxygen -> Nitrogen + Carbon + Water Oxide Dioxide A dimensionless parameter that describes the reagent flowrate is the normalized stoichiometric ratio (NSR). This ratio is defined as an actual molar ratio of urea to inlet NOx divided by the stoichiometric molar ratio. The reagent utilization is the ratio of NO x reduction and NSR. N alco Fuel Tech expanded the technology by developing chemical injection hardware, widening the applicable temperature range, and process control expertise required for commercial applications. The design of a system is guided by a computational fluid dynamics (CFD) and chemical kinetic (CKM) models, in addition to results from field measurements. These computer models determine the ideal temperature region for chemical reaction and the optimum injection strategy to distribute the reagent. The NOxOUT Process also provides effective load following capabilities through control of reagent concentration, multilevel injection, droplet size and spray patterns, and the introduction of chemicals at selected injector locations. There are substantial benefits gained from the application of the NOxOUT Process compared to first generation NOx control technologies, such as ammonia injection. These benefits are briefly summarized below: • Use of non-toxic, non-hazardous chemicals • Potentially lower capital cost due to the lack of large system compressors and elimination of anhydrous ammonia storage, handling, and safety equipment • Lower operating costs resulting primarily from minimization of gas (steam or compressed air) requirements • Inherently more effective control of spray patterns and chemical distribution for better mixing with the use of liquid rather than gas-based reagents, thereby resulting in better chemical utilization • Chemical enhancers which can be used to improve control of potential by-product generation while reducing NOx over an expanded temperature range There are over 100 commercial applications of the NOxOUT Process in the world and over 200 shortterm test applications. Recently, the NOxOUT Process has been demonstrated at a cement plant operated by Ash Grove Cement in Seattle. CEMENT KILN/CALClNER Ash Grove Cement in Seattle operates a calcinerlkiln that processes about 160 tons of solids per hour to produce -100 tons of clinker. This unit is an energy efficient design that consists of a kiln and a preheaterl precalciner. The preheater tower, as shown in Figure 1, is made up offive cyclones and a calciner. The plant is equipped with an elaborate feed system, a finishing mill, and storage silos. The entire plant is well instrumented and automated. Combustion products flow countercurrent to solid flow. Hot flue gas is generated with a burner firing natural gas or coal at one end of a kiln. Gas flows through a slightly inclined rotating kiln to a calciner. Inside the kiln, lime, silica, and clay undergo reactions to form clinker which is subsequently milled to produce cement. The calciner is at the bottom of a preheater tower and is about 60 feet high and 14 feet in diameter. To further improve fuel efficiency, gas or coal in an amount of 5 to 10% of total heat input is injected into the calciner. Flue gas enters at the bottom of the calciner and flows upwards carrying solids dropped from the bottom of cyclone #4. Solids are calcined and exit to cyclone #5. Solids are separated from the gas, dropped through a bottom chute to the bottom of the calciner, and then flow into the kiln. Flue gas exits cyclone #5 into cyclone #4 and continues upwards to eventually reach cyclone #1. Finely ground solids of limestone, silica, clay and iron mill scale are fed into cyclone #2 and flow downwards through the cyclones. Flue gas enters the bottom of the calciner at about 2100°F and cools to 550°F at the top of cyclone #1. Flue gas then flows through a raw mill, a cyclone, and a baghouse before exiting to the atmosphere. Flue gas is analyzed at several locations: kiln exit, preheater exit, and stack. NOx, CO, and 0 are monitored at the kiln exit while CO and 0 are 2 measured at the preheater exit. At the stack, NOx, SOx, CO, and O2 are measured. Opacity and flue gas flowrate are also measured at the stack. The stack emission limits for the plant are 422 pounds per hour (pph) of NOx, 538 pph of CO, and 40 pph ofS02. Emissions of S02 are well controlled from reactions between lime and S02 to form CaSO in the preheater/calciner and a r~w m~ll. When the raw mill needs servicing, sodIum bIcarbonate is injected before the baghouse to control S02 emissions. Particulates are well controlled by the baghouse indicated by low opacity. NOx, h~wever, .can be higher than the limit when firing WIth gas In the kiln. NOx emission decreases below the limit when fired with coal. However, NOx still may exceed the limit with coal if the kiln needs to operate at higher than typical kiln temperature to process material that is "hard to burn". It was desir- |