Institute of Energy Process Engineering and Fuel Technology > Research > Development of a database for conventional and Oxyfuel combustion systems (standard and alternative fuels including biomass, biological waste and fuels derived from other waste sources)

Development of a database for conventional and Oxyfuel combustion systems (standard and alternative fuels including biomass, biological waste and fuels derived from other waste sources)

In spite of all the new energy conversion technologies and alternative fuel sources, hydrocarbon based fuels will still play an important role in the coming decades. While there is a wide variety of coals offered in the market, there is also an increasing demand and importance for biomass and other fuels derived from waste, or Refuse Derived Fuels (RDF). These fuels possess widely differing compositions and properties, hence their dissimilar behavior during combustion.

Using an unknown fuel could lead to serious problems during the operation of fuel boilers causing unexpected shutdowns. Before the introduction of a new technology or alterations to the boilers are made, a CFD simulation is frequently used in order to gain an insight into possible problems one might encounter.

Both the wide variety of fuels and the need for reliable CFD simulations create the necessity for developing new methods of characterizing solid fuels. The standard methods are not sufficient for this.There are a number of non-standard methods available, such as heated wire mesh, thermogravimetric analysis (TGA), flow reactors, and fluidized bed reactors. However, these methods produce different types of data.

In order to obtain meaningful data, one must develop a uniform and standardized procedure, one that allows for various assumptions and simplifications to be made in order to predict the complicated phenomena of solid fuel combustion.

Here at TU Clausthal, our method of advanced fuel characterization is based on two vertically arranged reactors: the isothermal plug flow reactor (IPFR), and the down-fired 50 kW combustion chamber (DFCC). The goal is to build a solid fuel database with extended characteristics for fouling and slagging, which will form the basis for CFD calculations.

A description of both systems is found in chapter 3.The electrically heated IPFR makes it possible to investigate the combustion of solid fuels in two separate phases: the devolatilisation phase and burnout from the coke produced therein. Carrying out the research in separate experiments gives us deeper insight into the two processes by making it possible to systematically change system parameters, such as temperature, CO2 and O2 concentrations, and water vapor. With this, it is possible to develop new CFD combustion models.

The second system, the DFCC, uses a more realistic procedure in which the fuel is burned in a flame so that devolatilisation and coke combustion occur simultaneously. The DFCC experiments allow the stability of the flame, the ignition behavior, pollutants emissions and the ash deposition to be determined. Data from this system can then be used to create initial CFD models and simulations.

Both assemblies offer different types of data that complement one another. Some of the most important differences between these two systems are the temperature and oxygen profile differences along each system's length (see Figure 2.2.1).



Figure 2.2.1: Comparison between the temperature and oxygen concentration in the
IPFR and the DFCC


The IPFR system maintains a constant temperature and constant oxygen concentration along the length of the reactor, ensuring that the reacting fuel particles experience uniform conditions throughout. The corresponding profiles of the DFCC are very different. In the flame region, the oxygen concentration drops significantly and becomes stable in the post-combustion region. The temperature is high in the flame region and clearly lower in the post-combustion region.

With both systems, it is possible to run experiments in various atmospheres. This allows us to simulate different combustion procedures, for example Oxy-fuel combustion. Together, both systems provide enough information to build an advanced CFD model with which one can perform complex calculations (Figure 2.2.2).


Figure 2.2.2: Experimental and theoretical analysis of combustion plants.

Catntact:Dipl.-Ing. Y. Poyraz











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