Mechanisms and kinetics of granulated sewage sludge combustion
Introduction
The development of civilization has resulted in greater waste production. Particularly, increases in municipal sewage sludge production are important because their properties may allow for its use as a valuable energy-efficient fuel. From ecological, economic, and technical viewpoints, sewage sludge is difficult to dispose of, primarily due to bacterial contamination and the possible presence of heavy metals. It should be emphasized that these substances can harm the environment, reducing the possibility of naturally developing or storing them, which are the current disposal methods.
Due to problems regarding the use and application of this waste, which are associated with increasingly restrictive legislation regarding the need for sewage sludge storage in Poland beginning January 1, 2016, and because the waste has a gross calorific value greater than 6 MJ/kg (Regulation of the Economy Minister, 2013), its thermal disposal has become extremely important. A sewage network development plan should be completed for Poland by the end of 2015. This plan will increase the amount of sewage sludge that must be disposed of. The appropriate choice of method for sludge disposal is dictated by its properties. In this paper, an analysis of sewage sludge properties and potential development is presented while stressing the benefits of its thermal use. Additionally, the large amounts of sewage sludge incineration and co-combustion in power plants provide several tangible benefits, such as reductions in the amounts of input material (dried sewage sludge) and the production of electricity or heat. The addition of these wastes also limits the amount of conventional fuel used. Moreover, according to law, sewage sludge is considered as neutral biomass CO2.
Thus, conducting scientific research to identify sewage sludge properties and combustion processes is urgently needed.
Section snippets
Review of the literature regarding sewage sludge characteristics and combustion
Choosing an appropriate method for sludge disposal should depend on the properties of the sludge. The physical, chemical, sanitary, and technological properties of sewage sludge are important and change depending on the type and method of sewage treatment. Because of its unusual properties, sewage sludge is different from coal and biomass. Sewage sludge combustion is different because it includes incineration drying, devolatilization and the combustion of volatiles and char, which contain an
Experimental studies
This paper presents the results of experimental studies aimed at determining the mechanisms and kinetics of fuel combustion in an air stream depending on the thermal conditions and flow (temperature range of 800–900 °C, air flow velocity range of 2.0–3.5 m/s, and fuel sample diameters range from 5 to 10 mm) using a bench test with a total capacity of 8.2 kW (Fig. 4). One interesting element of this research is the need to visualize the sewage sludge combustion process when using a combustion
Conclusions
The Polish energy sector relies on hard and brown coals. However, other biomass or waste fuel solutions are needed, including sewage sludge.
The experimental studies performed for this study resulted in the following conclusions.
- 1.
The statistical analyses of the test results indicated a correlation between the parameters that determined the course of the fuel combustion in the air stream and the designation of the function approximation that describe the process.
- 2.
The process parameter study (the
Acknowledgement
This work was financially supported by the National Science Centre (Poland) based on decision No. DEC-2012/07/B/ST8/03730. This support is gratefully acknowledged.
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