Press Room - Coal combustion modeling with STAR-CD

RWE Innogy owns and operates a number of coal-fired stations. To help it select fuels that can be burnt safely, economically and without exceeding emissions limits, it also has a 0.5 MW Combustion Test Facility (CTF). To help extend our computer modeling ability, we have been validating STAR-CD predictions against CTF measurements.
The CTF is a refractory-lined rectangular furnace with a single burner that is usually a scaled down version of an actual power station burner. It provides a much better defined environment than is possible with an operating furnace, and it is simpler to model because it has only the one burner; a typical power station furnace may have 48 individual burners.

Coal combustion is a particularly challenging application of CFD. Apart from the need to represent the processes directly linked with coal combustion, it is necessary to use a Lagrangian approach to track the coal particles, and the main gas phase solution is a turbulent, variable density reacting flow. Radiation is the main heat transfer mechanism, and both particle radiation and gas absorption and scattering have to be included. A further issue is the difficulty of obtaining detailed, accurate measurements that can be used to validate any CFD predictions.

We have modeled two completely different burners, designed for coals with different combustion properties.
We have validated predictions against cold flow measurements, wall heat fluxes during combustion and predictions from simpler design methods. We have started validating the CFD predictions against temperature distributions obtained from digital analysis of optical measurements. We are also testing the idea of using a detailed char combustion model to post-process the CFD results. This should give us a more realistic modeling of the final stages of char burnout, which is crucial for accurate prediction of overall coal burnout.

We are interested in CFD for coal combustion because it has the potential to increase our understanding of CTF tests, and therefore increase the value of such tests. It also has the potential to guide us in fuel selection and boiler operation. We certainly do not claim to have solved all the problems with this CFD application, but we do think that we are making progress!

For further information, please contact:

peter.stephenson@rweinnogy.com