Optimization of Air Pollution Control Systems with CFD modeling resulted in the innovative Graduated Straightening Grid (GSG) — In this article, the reader will be walked through the development of the GSG which is now part of all new Fuel Tech SCR applications. In many fossil fueled stationary resources such as power plants and steel mills the installation of the new technology has resulted in operational cost savings.
Fuel Tech provides advanced engineering solutions for Air Pollution Control (APC) in power plant utilities. Their NOx reduction technologies are now installed worldwide on over 800 units, providing customers with the most cost effective and environmentally sustainable methods to produce energy and processed materials.
The recently patented Graduated Straightening Grid (GSG) technology, which has been developed with extensive CFD modeling, is capable of dramatically improving upon typical Selective Catalytic Reduction (SCR) unit performance by optimizing flue gas velocity profiles, reagent consumptions, and catalyst lifetimes while minimizing system pressure losses.
In one of the first GSG retrofit applications at Kansas City Power & Light Company’s La Cygne Station Unit 1, the installation of the new technology has resulted in operational cost savings of more than $5 million associated with reduced system pressure drops, reduced build-up of particulate on catalyst layers, less catalyst erosion and longer catalyst lifetime.
The Urge to Reduce Emissions
With the urge to reduce emissions to meet directives in Europe, as well as new rules proposed by the U.S. Environmental Protection Agency (EPA), many fuel resources, including coal, are faced with being expelled from the market due to environmental control costs.
However, environmental rules typically trigger the development of new cost-effective technologies for emission reduction. As a result, one of the foremost applications of Computational Fluid Dynamics (CFD) and Experimental Fluid Dynamics (EFD) modeling over the past ten years has been in the area of optimizing Air Pollution Control (APC) systems used to reduce emissions from fossil fuel fired stationary sources such as power plants and steel mills.
The Selective Catalytic Reduction (SCR) technology was developed in the 1980s in Japan to effectively reduce NOx concentrations in flue gas by the injection of ammonia (N3) reagent and the reaction via a catalyst substrate. This development was critical in helping coal remain in the market as the most cost-effective fuel source.
Despite the relatively developed nature of this technology, there still exist challenges for coal-fired power plants with SCR units that have been difficult for owners and operators to overcome, such as:
- Minimization of the system pressure losses with the aim to reduce fan power consumption and power plant operating costs.
- Achieve optimally distributed concentrations of velocity, NOx, NH3 reagent, and temperature profiles entering the SCR reactor, enabling better reduction efficiencies and lower ammonia usage.
- Ensuring uniform gas velocity vectors at the catalyst in order to reduce the risk of catalyst erosion and consequently extend catalyst life by lessening catalyst wear and deactivation.
- Avoid particulate dropout and ash accumulation in SCR units which increase system pressure losses, unit downtime for cleaning purposes, and reduce catalyst lifetimes.
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