Case Study
45% NOx Reduction Goal Met by Use of Spray Injectors
Problem:
Faced with a compliance deadline established by the Environmental Protection Agency’s Clean Air Interstate Rule (CAIR), a power plant in the midwestern US needed to find a NOx control system that would reduce emissions by 30 to 50%. Plant personnel requested a proposal from a leading air pollution control equipment company. The recommended solution was a custom system with a US$1,000,000 price tag. Plant personnel decided to explore more options.
Acting on a referral from another power plant in the region, plant personnel contacted Spraying Systems Co. and requested a proposal. The utility provided furnace parameters and geometries and Spraying Systems Co. collected sample temperature readings.
Solution:
Using proprietary gas cooling calculations, drop size data collected in its test labs and decades of experience, Spraying Systems Co. designed a solution:
- Eight air purge injectors installed on three levels
- Each injector equipped with a hydraulic hollow cone nozzle spraying a water/urea mixture perpendicular to the furnace wall
- Injectors to withstand temperatures up to 1750°F (954°C)
- Air purge to keep urea cool enough to prevent vaporization and nozzle clogging
Design Validation:
CFD (Computational Fluid Dynamics) modeling was recommended by Spraying Systems Co. to validate the design and uncover any unforeseen problems caused by the operating conditions in the furnace.
Results:
The CFD study validated the design and no modifications were required. The injectors were constructed and installed in 12 weeks.
- NOx emissions have been reduced by 45%
- Urea carryover is negligible and within acceptable limits
- Nozzles are clog-free and injectors are performing to specification
- The mixing of the urea in the gas stream is adequate and the desired reaction occurs
- The droplets produced by the hollow cone nozzles are evaporating prior to contact with furnace walls, eliminating damage and excess maintenance caused by wetting
- The use of hydraulic nozzles eliminates the need for costly compressed air and helps keep operating costs low
- The Spraying Systems Co. solution was just 1/3 of the cost of another supplier’s, saving the power plant several hundred thousand dollars (US)
- The project was completed several months before the compliance deadline. The power plant earned emission credits that can be sold in the future
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