Institute for Energy Process Engineering and Fuel Technology > Research > Development of burners and combustion systems

Development of burners and combustion systems

Faced with ever increasing energy prices and stricter emission limits coupled with the demand for higher product quality or the need for changing production conditions, interest within the power industry, and other related industries using high temperature processes, in burners and combustion technologies has grown. The development and testing of low-emission burners and energy-efficient combustion technology is the focus of the IEVB; the use of solid and liquid alternative fuels being of the highest interest.The IEVB has a variety of test plants or test rigs available for the development and investigation of combustion processes up to 1 MW. When designing a burner, we are not only concerned about limiting emissions and increasing efficiency, but also with other objectives, such as recovery of precious metals or other rare materials otherwise lost in the combustion process.  A research project that was carried out in the IEVB from 2006 to 2008 in collaboration with national and international companies demonstrates these additional objectives. This project focused on experimental and theoretical studies about recovering metal oxides (R\textsubscript{x}O\textsubscript{y}) by burning a liquid residue containing the metal in question. Necessary procedures were considered in this project to enable the successful recovery of metaloxide by combustion of the liquid residue. These include: fuel preparation, homogenization and dosing system, burner design, selection of a suitable spray nozzle for the fuel, fuel ignition, specific controls with staged air combustion and exhaust gas recirculation to minimize NO\textsubscript{x} emissions, and cooling mechanisms necessary to form the desired crystal structure and grain sizes. The experiments were conducted in two combustion chambers: in a pilot-scale 50 kW down-fired combustion chamber (DFCC, see Figure 2.4.1) and on a semi-industrial scale 500 kW chamber (TBK, Figure 2.4.2). In the first phase, 300 kg of the fluid source material was burned in the 50KW rig. Alltoghether around twenty tons of the source material were burned at the IEVB.


 Figure 2.4.1: Schematic presentation of the 50 kW DFCC





Figure 2.4.2: Schematic presentation of the 0.5 MW pilot swirl combustion chamber



Figure 2.4.3 shows the measured exhaust gas composition and the emissions produced during combustion of the liquid residure in the DFCC. The crystallized metal oxides collected in the CTF filter are shown in Figure 2.4.4.

The recovery rate of the metal oxides was two to three percent of the combusted material. Figure 2.4.5 shows the residual carbon content in the crystallized metal oxide as a function of time in the 500 kW combustion chamber. For further processing of the metal oxides, a carbon content below a given threshold was necessary.



Figure 2.4.3: Exhaust gas concentrations and emissions along the combustion chamber


Figure 2.4.4: Catridge-tissue-lter with crystallized RO



Figure 2.4.5: Residual carbon content in the crystalline RO with carbon content limit


Theoretical studies were performed with commercial CFD software parallel to the experimental investigations, optimizing the burner design and the combustion process. Figure 2.4.6 shows selected results from the theoretical simulations: temperature profile, gas flow profile, and burning fuel droplets in the semi-industrial combustion chamber. The growth of the refractory metal oxide grain size was investigated in further experiments during the project. Crystal growth was controlled by cooling of the exhaust stream by injecting water and air into the crystallization zone (see Figure 2.4.7).

The goal of the project was to form sufficiently large crystals in the crystallization zone that could easily be filtered in the (fabric bag) filters from the exhaust gas stream and then further purified. Figure 2.4.8 shows three different cooling rates of the exhaust in the crystallization zone. Figure 2.4.9 shows SEM images of crystallized metal oxides formed by the three differing cooling rates. Only the coarsest RO crystals, seen on Figure 2.4.9B, were acceptable due to the separation capabilities of the filter.



Figure 2.4.6: CFD modeling A) Temperature prole in the industrial combustion chamber,
B) Gas ow prole in the combustion chamber, C) burning fuel drops
in the combustion chamber



Figure 2.4.7: Crystallization zone with water lance for exhaust cooling









Figure 2.4.8: Three different exhaust gas cooling rates in the crystallization zone

Contact:Dipl.-Ing. Y. Poyraz




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