Ash behavior

Arvelakis, S. Gehrmann, H. Beckmann, M. Koukios, E. G., Effect of leaching on the ash behavior of olive residue during fluidized bed gasification. Biomass and Bioenergy 2002, 22, 55. 

In practice, types of burning equipment, rate of burning, temperature and thickness of the fire bed, distribution of ash-forming minerals in the coal, and viscosity of the molten ash may influence ash behavior more than do the laboratory-determined ash fusibility characteristics. The correlation of the laboratory test with the actual utilization of coal is only approximate, due to the relative homogeneity of the laboratory test sample compared to the heterogeneous mixture of ash that occurs when coal is burned. Conditions that exist during the combustion of coal are so complex that they are impossible to duplicate completely in a small-scale laboratory test. Therefore, the test should be considered only as an empirical one, and the data should be considered qualitative and should not be overinterpreted. 

Valmari T., et al. (1999) Field Study on Ash Behavior during Circulating Fluidized-Bed Combustion of Biomass. 1. Ash Formation, Energy and Fuels 13, 379-389. 

Valmari, T, Lind, T. M, Kauppinen, E.I., Sfiris, G, Nilsson, K. and Maenhaut, W. (1999) Field study on ash behavior during Circulating Fluidized-Bed Combustion of Biomass.2.Ash Deposition and Alkali Vapor Condensation. Energy Fuels,, 390-395. 

Clearly there is a need for improved techniques for predicting the behavior of mineral matter. This paper will provide a statement of the ash deposition problem in pulverized coal fired boilers it will present an assessment of the older, traditional methods for predicting mineral matter behavior and it will address some of the newer techniques that have been suggested as better ways of characterizing coal ash behavior. Additionally some areas of uncertainty will be identified which require the development of better predictive techniques. 

ASTM measurements such as ash fusibility (D1857) have formed the basis for traditional ash behavior predictive techniques. These bench-scale tests provide relative information on a fuel which is used in a comparative fashion with similar data on fuels of known behavior. Unfortunately, these commonly used tests do not always provide sufficient information to permit accurate comparison. 

Reid, W.T., "The Effect of Mineral Matter in Coal on Ash Behavior in Large Boiler Furnaces", Presentation to the ASME Committee on Corrosion and Deposits from Combustion Gases, September 29, 1971. 

In general, ash behavior depends on fuel properties, boiler design, and boiler operation. Industrial practice has led to the development of a wide variety of indices, nearly... 

The most uniquely suited standardized analyses for ash deposition include ash chemistry and ash fusion temperature. The total ash content from proximate analysis and ash composition provide the fuel irrformation that goes into the majority of common empirical indices of ash behavior, along with ash fusion temperature. The ash chemistry analysis typically reports the ash elemental composition on an oxide basis. This does not mean that all of the species exist as oxides in the fuel (which they do not). It is a convenient method of checking the consistency of the data. The sum of the oxides shoirldbe about the same as the total ash content. The analysis is fundamentally an elemental analysis with no distinction of the chemical speciation of the inorganic species. 

A variety of advanced techniques exists for determining the species composition of the fuel, which is vital to improved predictive methods for coal, and especially ash behavior, in boilers. X-ray diffraction, performed on low-temperature ash, is the most widely used technique for qirahtatively identifying the presence of minerals in their crystalline form in concentrations of a few weight percent or greater. Thermal analytical techniques such as differential thermal analysis (DTA) and thermogravi-metric analysis (TGA) have been used as a signature analysis based on changes in physical properties with temperature. 

Skrifvars, B., T. Lauren, R. Korbee, and P. Ljung. 2001. Ash Behavior in a Pulverized Wood Fired Boiler - a Case Study. Proc. Power Production in the 21 Century Impacts of Fuel Quality and Operations. United Engineering Foundation Advanced Combustion Engineering Research Center. Snowbird, UT. Oct 28-Nov 2. 

Addition of fluxing agents to influence the ash behavior is limited. 

The overview provided in this chapter is limited to the relevant investigations and calculations that might be necessary to judge if a coal is suitable or not to a specific gasification process. Special emphasis will be placed on understanding the ash behavior during gasification as it is very different from combustion. 

Stanislowski, J.J. (2012) Coal ash behavior in reducing environments (CABRE) III. U.S. Department of Energy, National Energy Technology Laboratory (NETL), Rep. No. DE-FE0003466. 

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