Modern production method of nitric acid production may lead to generation of several different gaseous emission components, such as nitrogen oxides (NOx), ammonia NH3 and nitrous oxide N2O. Nitrogen monoxide is an intermediate gaseous product in manufacturing of nitric acid HNO3. NO is formed in a catalytic reaction between ammonia and molecular oxygen O2. But undesirable side reactions may result in formation of nitrogen dioxide NO2 and nitrous oxide N2O. The NO and NO2 emissions can be reduced by use of Selective Catalytic Reduction unit (SCR), which deploys ammonia gas NH3 to limit emissions of NO and NO2. A modern nitric acid plant needs to monitor the emissions of these gases.
By Gasmet Technologies Oy based in Helsinki, FINLAND.
In recent years the number of Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR) plants for De-NOx have increased significantly. Continuous analysis of NOx prior to the de-NOx plant is often required to measure the concentration generated by the combustion process. This may be required to provide feed-forward to the Ammonia/Urea injection system and also to allow the effectiveness of the reduction process to be assessed. Continuous analysis of NOx post-reduction is required to allow the effectiveness of the reduction process to be assessed. It may also be beneficial to monitor NH3 slippage at this stage by calculating from the pre and post NOx levels if excess Ammonia/Urea is being applied.
By Codel International Ltd based in Bakewell, UNITED KINGDOM.
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