Institute for Energy Process Engineering and Fuel Technology > Research > Slagging and pollution created when burning solid fuels in conventional and Oxyfuel ring

Slagging and pollution created when burning solid fuels in conventional and Oxyfuel ring

Despite much research in recent years, ash deposition problems still represent a major challenge in pulverized fuel combustion. Of large importance to power plant operators is the formation of deposit on the surface of the heat exchanger and on the combustion chamber walls because of the economical and operational impacts. In particular, the change in fuel quality as a result of co-combustion of alternative fuels can significantly affect ash deposition processes. Careless co-combustion of alternative fuels can have negative effects on the stability and functionality of the boiler and at worst can cause unscheduled shutdown. Combustion of solid fuels under oxyfuel conditions can significantly change slagging behavior and pollutant production. Research in the field of ash deposition is still highly needed and a better understanding of the slagging and fouling processes is essential.The goal of this research is to to carry out extensive studies on ash deposition behavior during co-combustion of various alternative fuels (e.g., sawdust, sewage sludge, refuse derived fuel from waste (RDF)) with regular fuels such as coal or lignite. A comprehensive experimental database is being created that contains the chemical properties of fly ash and ash deposition, deposition rates, the physical structure of the ash deposits, and their compressive strength (see research topic 2.2). Our methods include several experimental steps, such as: laboratory tests of target fuels, ash, fly ash, and ash deposits, experimental studies of ash deposition behavior in the combustion chamber during combustion, and investigation of the sintering behavior in a sintering furnace. The focus of this research is to clearly define and reproduce combustion conditions in industrial and pilot scale plants. Conventional p.f. combustion and new technologies, such as oxyfuel or flameless, combustion are studied.The investigated operating conditions cover the typical range of thermal conditions for a modern pulverized coal boiler, such as: deposition surface temperature, exhaust temperature, and particle retention. The chemical and physical deposition patterns and deposition rates are interpreted systematically as a function of the deposition surface temperature, gas temperature, and particle retention.Figures 2.5.1 and 2.5.2 show exemplary results from a project (ash melting behavior and slagging intensity), during which slagging processes were investigated during the co-combustion of sewage sludge, sawdust, and RDF with coal.

 

 

Figure 2.5.1: Effect of co-combustion of sewage sludge with coal on the ash-melting behavior
of the mixed fuel

 

 

Figure 2.5.2: Effect of co-combustion on the mass deposition relative to the deposition
surface during the incineration of sewage sludge with coal

 

Figure 2.5.3 shows pictures of ash deposits that were collected with deposition probes for various surface temperatures during the incineration of a mixture of sewage sludge, sawdust, and coal.

 

 

Figure 2.5.3: Pictures taken during the co-combustion of two alternative fuels (sawdust
and sewage sludge) with a coal on deposition probes with two deposition
areas of differing final temperatures

In addition to experimental studies, CFD-based ash deposition models are being developed by the simulation working group in the IEVB. Figure 2.5.4 shows examples of the predicted ash concentration in a vertical pilot combustion chamber during coal combustion.

 

 

Figure 2.5.4: To develop fuel-specific and process-specic sub-programs for CFD predictions
of industrial processes

Contact:Dipl.-Ing. Y. Poyraz

 

 

 

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