TECHNOLOGY Advanced Process Modeling

While designed to solve different challenges, Fuel Tech’s main product lines share several common threads from a process design perspective. Both Air Pollution Control and FUEL CHEM^® applications involve optimizing the injection of the right amount of the right chemical under the right conditions to achieve desired performance levels. The tools used by our engineers to design these systems have grown from our first use of computational engineering software in 1987 to our sophisticated and always expanding suite of process modeling applications today.

Every Fuel Tech product installation has a custom process model supporting it. The model begins with a Computational Fluid Dynamics (CFD) simulation of the conditions under which our product will operate. A CFD model generates predictions of operating temperatures, velocities and other variables from a virtual replication of real-world geometry and operating inputs. For NOxOUT^® and TIFI™ Targeted In-Furnace Injection™ applications, the 3D geometry of the combustor/boiler is generated. For TDI™ Targeted Duct Injection™ applications, it is the back-end ductwork that is modeled. NOxOUT ULTRA^® models reflect the geometry and dynamics of the urea decomposition chamber and its connection to the customer’s ductwork. NOxOUT CASCADE^® models are focused on the distribution of ammonia slip entering a Selective Catalytic Reduction (SCR) catalyst.

Once the base model is generated, it is visualized using our proprietary visualization software. The software is designed to make explicit to the engineer the complex behaviors typical of combustion flows. Fuel Tech engineers can explore their models from any perspective with the software and return to them throughout the process design. Fuel Tech’s visualization software is also used to engage the customer in the design stage and tap into the expertise of their plant’s experts.

Additional modeling is performed for each unit depending on the type of Fuel Tech application. Nitrogen oxide (NOx) reduction applications are analyzed with detailed chemical kinetics modeling (CKM). CKM predicts NOx reduction by simulating relevant chemical reactions along gas temperature profiles derived from the CFD models in the presence of anticipated chemical dosage and key flue gas compositions. In contrast, FUEL CHEM applications are screened for ash composition effects based on fuel and ash sample analyses, but CKM analysis is usually unnecessary. In either case, once a complete understanding of the process conditions is achieved, it is time to optimize a chemical injection strategy.

Fuel Tech has developed its own chemical spray models specific to boiler and duct conditions, and these models have been validated with both laboratory characterizations of our sprays as well as field performance during 20 years of applications. The spray models are coupled to the predicted CFD velocities and temperatures to predict droplet evaporation and subsequent chemical distribution. Fuel Tech engineers use visualization software to reposition sprays dynamically and gauge the effect on desired performance. CFD simulation of the original model with spray injection provides a more precise mapping of chemical performance.

An example of an advanced process modeling sequence is depicted below:

	A typical TIFI or NOxOUT boiler CFD model predicts gas flow characteristics.
	Temperature surfaces are used to identify important zones for chemical injection.
	Injector arrays are screened in a virtual visualization environment.
	Candidate spray solutions are simulated with additional CFD modeling.
	Chemical distribution planes are generated from the CFD model to predict performance.

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