www.cgg.cvut.cz Interactive educational system for coal combustion modeling in Power Plant boilers Marek Gayer, Pavel Slavík and František Hrdlička Computer Graphics Group Department of Computer Science and Engineering Faculty of Electrical Engineering of CTU in Prague Czech Republic IEEE Region 8 EUROCON 2003, Ljubljana, September 22-24, 2003 Good afternoon and welcome to my presentation of the paper Interactive System for Pulverized Coal Combustion Visualization with Fluid Simulator. This presentation will summarize all the contents of the paper.

Outline of the presentation Brief introduction and motivation to Interactive education Combustion modelling Computation fluid dynamics (CFD) Our system overview and its key parts Fluid simulator Virtual coal particle system Simplified combustion and heat transfer Results reliability testing Visualization and interactivity demonstration Conclusion and future work Well, here is some road map of the presentation. First there would be some introduction and motivation to combustion processes and interactive education. Than there would some basic info about Fluid Flow modeling and Computation Fluid dynamics also called CFD methods. Next I would briefly describe the units of our system: Our Fluid simulator Virtual coal particle system. Simplified combustion and heat transfer After that, implementation and visualization follows. I will talk about our results and their reliability also. Finally, there would be some conclusion and future work information. EUROCON 2003

Interactive education in general Useful for complex cases where only theoretical explanation is ineffective Often used in individual learning and practicing part of education Doing by learning and “what if” concept Motivates students, utilizes creativity Is more effective, attractive and “fun” EUROCON 2003

Introduction and motivation to coal combustion modeling and visualization Both for the ecological and economical reasons Finding optimal boiler configurations To reduce pollution Combustion optimization To find a way for optimal fuel preparation How can visualization help At first, here is some brief introduction and motivation for our research. For both the economical and ecological reasons, researchers and developers are trying to find optimal boiler configurations. For example, they try to reduce pollution or just finds a way for optimal fuel preparation. Visualization can help here in a way of presenting computed data (for example air velocities and temperatures inside boiler) to human readable and easy understandable form. EUROCON 2003

The modelling of fluid flow - CFD Most often: solving complex differential equations (e.g. Navier-Stokes) Fluid simulators for computer graphics (e.g. ACM SIGGRAPH Proceedings) Coal combustion as an CFD application Current solutions and systems: Precise, robust, well-known Slow, complex, no real-time => unsuitable for education Today’s common way for flow modeling inside boilers is Computation Fluid Dynamics. The modeling is based on simulation of physical process by describing the problem by differential equations such are the Navier-Stokes equation. In the computer graphics field, special fluid simulators for various modeling and visualization task are being constructed. Some of them are refered in our paper. A coal combustion system is just an application of this CFD approach. General disadvantage of the current combustion solutions, especially commercially available systems based on the CFD is very slow computation and impossibility to compute and visualize the results interactively in real-time. + - EUROCON 2003

Our system overview Allows dynamic overview of the combustion process Real-time simulation and visualization (2D simplification) Designed on following key parts Fluid simulator Virtual coal particle system (with simplified combustion engine) EUROCON 2003

Our Fluid Simulator Dividing boiler area to grid cell arrays Values updated in each time step Principle of local simulation We have constructed real-time fluid simulator which computes it using simple physical laws. Firstly, we use arrays which divides the area of the boiler in 2D voxels. In each voxel the characteristics such as temperature and velocity are being computed separately. We determine mass fluxes and velocity changes in the boiler for a specified time dt using Newton’s second law and continuity equation. By using principle of local simulation, we are reduce all the calculations on the nearest neighbors of the calculated voxels. Well there are two types of Fluid simulators, one is so called stable and the second is unstable. The stable simulators allow selecting any time step and and voxel sizes. With so called unstable simulators, as is ours Our fluid simulator is fast and real-time on the other hand, is conditionally stable. The stability depends on the size of the voxel, time step and maximum velocity and mass values in the voxels during solution. We must set the size of the voxel and time-step accordingly to conditions in the boiler. Well we do not have so much time to analyze details of our fluid simulator. Please see more detail description of our fluid simulator in the paper. EUROCON 2003

Virtual coal particle system Used for both simulation and visualization of the combustion process Virtual particle system approach Simplified combustion and heat transfer computation Movement determination: Aerodynamic resistance Gravity force Virtual Particle system allows intuitive and efficient way for modeling coal combustion. By it’s nature, they are suitable for both the visualization and simulation of the problem. This is advantageous for implementation and visualization speed. For our work, the particle system allows us computation and visualization of mass elements in the boiler. The particles displayed and calculated just do not correspond to the real coal particles in the boiler. Instead of that, they represent some corresponding mass of coal in the voxel under investigation. Therefore we call them virtual particles. They are moved in the boiler space according to aerodynamic resistance and gravity force. EUROCON 2003

Interaction of virtual coal particles t = 0 seconds: T = 343oC (above ignition) O2 concentration = 25% Coal particle Partially burned particle C C C C C t = 0.01 seconds: T = 345oC (increased) O2 concentration = 24% Partially burned coal particles Coal particle transformed to burned ash particle This is just an figure illustrating the interaction of the virtual coal particles during combustion process in the selected time step. The combustion would pass if the temperature is just above ignition. The combustible part of coal particle in selected voxel is being decreased and burned out particles are transformed to ash particle. According to that the oxygen concentrations are being decreased. C C B EUROCON 2003

Results comparison – numerical approach Built-in numerical comparison code Statistically compares the results between our system and FLUENT From 60% to 80% cells are less than 30% different from FLUENT values (temperature, flow directions, ... ) Moreover, we are developing built-in numerical comparison code It is able to statistically compare the results in each of the boiler area between our system and FLUENT and quantify corresponding errors and differences. Preliminary results from the active part of the boiler show that the share of voxels with deflection up to 20% from values obtained from FLUENT varies between 60% and 80% for temperature, flow directions and other values. Well, this is balanced on the interactivity of the system and ability to test many configurations of boiler with immediate response. EUROCON 2003

Sample visualization - cell characteristics This picture is just a sample screen of our system. More detailed features view of features would be on the following movie. Many parameters could be altered during the simulation and thus it allows fast and easy experiment with the system. In the current implementation in ANSI C++, we can use some interactive actions even during the simulation, in real-time, without restarting the whole simulation. Thus, we can move jets and disable/enable/delete/modify their parameters. Other features include tracking of the selected particles. It allows us to monitor its position and characteristics at any time until it leaves the boiler space. Visualization is based on the OpenGL graphics interface. This means that our system is easily and fully portable to other platforms. EUROCON 2003

Sample visualization – coal particles EUROCON 2003

Sample visualization of particle characteristics (particle tracks) This is just a sample visualization of coal particles flowing from jets and coal. Using the particle system concept, we can easily construct particle tracks, which easily shows the dynamics of the process and directions of velocities of the coal particle movement. EUROCON 2003

Sample visualization - statistics Visualize values distribution in boiler Available for all characteristics (about 10 particle and 40 cell) (e.g. for temperature or coal particle diameter distribution) EUROCON 2003

Our interactive combustion system EUROCON 2003

Conclusion and future research Interactive, educational for coal combustion modelling featuring: Fast & simple real-time fluid simulator Particle system with simplified combustion engine Real-time visualization using OpenGL Results reliability tested with FLUENT Designed for education and “preview” design Future research: Precision improvements – further to reality Further testing on real boiler tasks The real-time 3D combustion system experiment Our interactive 2D coal combustion system is based on simple fluid simulator, which allows real-time computation of the airflow. Simulator is very easy to implement and thus can be reusable in various computer graphics tasks relating to air flow simulation and visualization. The speed of the fluid simulator and simplified combustion engine allows real-time visualization of the results (using OpenGL graphics interface). We have tested our system by modeling of a boiler with real dimensions, characteristics and parameters. It can be used for a good preview of the dynamics of combustion processes in a boiler in design and education. Configurations can be tested and modifications made interactively with an immediate response. For future research we would like to perform some precision improvements as well as further testing on real boiler tasks. We would also like to work on an experiment with trying to model 3D combustion system in real-time. EUROCON 2003

Thank you for your attention. ??? Do you have any questions ? EUROCON 2003