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Cemex plant to install SNCR

World Cement,

Cemex’s Lyons plant in Colorado is installing Selective Non-Catalytic Reduction (SNCR) technology as part of a settlement agreement with the EPA. The pollution control technology will reduce NOx emissions by approximately 870 – 1200 tpa, bringing the facility into compliance with the Clean Air Act. At an initial cost of US$600 000 for installing SNCR, the system will cost a further US$1.5 million pa.

In an article in World Cement’s April issue, John Kline examines SCR and SNCR systems:

“At present, selective non-catalytic reduction (SNCR) technology is considered the best available control technology for cement plants. In the SNCR process a reducing reagent is injected into the NOx laden gas stream. Reagents are usually ammonia based with aqueous ammonia being the most common. Other reagents include urea and anhydrous ammonia. SNCR reactions occur most effectively in the 800 to 1000 °C temperature range. Above 1000 °C the ammonia compounds can decompose to form NOx. Below 800 °C the reactions are incomplete, leading to increasing ammonia emissions (often called ammonia slip) as the temperature drops.

Designing SNCR systems for modern preheater/precalciner kilns is fairly simple as the temperature profile in the preheater is easy to identify and control. The effectiveness of the system depends primarily on the dispersion of the reagents within the gas stream. Good dispersion allows for NOx reduction at close to the molar ratio between reagent and NOx as long as the NOx reduction is less than 50%.

Designing SNCR systems for long wet and long dry kilns is more problematic. The proper temperature zone for the reactions is usually inside the kiln; therefore the reagents need to be injected into the gas stream inside the rotating kiln. Once the injection point is fixed, there is little opportunity to control the temperature of the kiln gases. Good dispersion of the reagents in the gas stream is also more difficult to achieve in long wet and long dry kilns. Therefore the effectiveness of SNCR in these systems is reduced."

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Edited from various sources by Katherine Guenioui.

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