Advanced Process Modeling
Both Air Pollution Control and Chemical Technologies 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 to Support It
A custom process model is used to simulate 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. ULTRA™ models reflect the geometry and dynamics of the urea decomposition chamber and its connection to the customer’s ductwork. NOxOUT CASCADE®, and ASCR™ Advanced SCR 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 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.
Chemical Kinetics Modeling
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, TIFI® 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. |
Experimental Modeling
We specialize in experimental (physical) modeling of air pollution control equipment. Scale models of 1:4 to 1:18 have been built for testing at our North Carolina flow lab for installations in Europe, North America and Asia. Our focus continues to be the delivery of the most accurate and innovative solutions for our customers.
Innovative techniques are used in scale flow modeling to improve performance in flow critical equipment. Our flow models are constructed quickly and accurately using CNC cut steel as a skeleton, while clear plastic is tested using the latest in flow analysis equipment.
Our experimental model studies combined with Computational Fluid Dynamics (CFD) modeling allow for insightful understanding of existing flow situations and effective design of corrective devices such as turning vanes, ash screens, injection systems and static mixers for each unique project. Typical optimization projects reduce system pressure losses, improve temperature, velocity, gas species and ash distributions and prevent in-duct ash and dust fallout, all of which translate to customer savings.
The combination of unique construction techniques, state-of-the-art technology and years of experience enables model studies to be performed in half the time required by our competitors, thereby providing our customers with the confidence and guarantees needed to proceed with construction or retrofitting.
Electrostatic Precipitators
Electrostatic precipitators (ESP) rely on electrostatic attraction to collect particles from a flow stream. As such, they are quite versatile and can be operated with up to 99% efficiency in a wide variety of operating conditions. However, to achieve such high efficiency, several ESP variables must be considered. Specifically, temperature, flow and dust distributions must be uniform to each of the compartments formed by the precipitator plates and dust fallout in the ductwork and re-entrainment from the hoppers must also be taken into consideration.
By combining computational and experimental modeling to predict fluid behavior in new and existing ESP installations, such flow problems can be found, analyzed and prevented. Corrective flow devices can then be designed, tested and optimized to ensure that flow characteristics meet industry standards such as those set by the Institute of Clean Air Companies (ICAC) Technical standard EP-7.
Selective Catalytic Reactors
Selective catalytic reactors use ceramic catalyst to react NO2 and NO3 with ammonia to produce harmless N2 and H2O. NOx emissions have been identified as the main source of smog, ground level ozone and acid rain. The reduction of NOx emissions is beneficial to the environment as well as to general public health.
Selective catalytic reactors are modeled to ensure that the catalyst is effective and catalyst life is extended for as long as possible. Proper mixing of flue gas and good flow and velocity profile are required to prevent ammonia slip (unreacted ammonia in flue gas) and ensure that NOx emissions are minimized. Fuel Tech engineers are highly experienced in the operation of SCRs and the design of ammonia injection systems and work closely with leading catalyst manufacturers to achieve the best possible flow solution.
Fabric Filter
Fabric filter baghouses remove particulates from an air stream through physical exclusion. Even distribution of flow to baghouse compartments and good flow profiles at the bottom of the bags are important to ensure even efficient removal of dust and the prevention of premature wear of the filter fabric.
The design of flow optimization devices requires consideration of dust fallout, dust distribution to baghouse compartments, hopper re-entrainment and protection of the fabric filters. Modeling of baghouses can be used to predict and solve problem areas of wear and particulate fallout in baghouse systems while reducing overall pressure losses. Fuel Tech designs corrective flow devices to conform to industry baghouse performance standards such as those set by the Institute of Clean Air Companies (ICAC) Technical Standard F-7 to ensure optimum baghouse performance.
Flue Gas Desulphurization
Flue gas desulphurization (FGD) wet scrubber systems and dry absorber systems remove SO2 from flue gas by reaction of the acidic SO2 gas with an alkaline reactant to produce an easily collectable by-product. Essential to the efficient operation of an FGD is good mixing of the flue gas stream with the scrubber reactant as well as residence time within the reactor. Nozzle placement, flow optimization devices and mixers are some of the tools used to correct inefficient flow situations in an FGD system.
Using CFD and experimental modeling, poor FGD performance can be improved, and even prevented, while solving other problems associated with wet scrubber systems such as:
- Inlet duct liquid pullback
- Mist eliminator performance
- Excessive pressure losses
- Fan inlet flow distribution
- Spray coverage
- Liquid collection
Virtual Vantage®
Fuel Tech has been using CFD modeling to simulate its core product technology since 1987. Since that time our major development effort has been to bring advanced simulation out of research and into the everyday design environment.
In 1994, Fuel Tech collaborated with Argonne National Laboratory to implement virtual reality and supercomputing techniques to solve practical engineering problems. Fuel Tech provided expertise in CFD techniques and Argonne applied the latest visualization and computational methods. The result was Fuel Tech’s first application for modeling and visualizing spray injection inside a boiler environment.
Today, Fuel Tech uses proprietary visualization software to show our engineering designs in an immersive, interactive way. Our engineers recognize the information contained in their simulation datasets more rapidly and with greater precision.
Group visualization sessions in our stereovision projection laboratory in Warrenville, Illinois allow for enhanced design creativity and further risk management. Our designers and sales personnel can now communicate visually what they have discovered to customers more easily and generate more complete understanding of our recommendations. Customer engagement and feedback on what they see in the virtual environment enriches the design process and further increases quality.
