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Effect of Phosphorus Compounds in the Fouling Behavior of Hydrothermal Carbonization Sewage Sludge via Drop Tube Furnace Experiments
- Author(s)
- 박주창
- Advisor
- 장혜영
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2022-02
- Language
- eng
- Keyword
- 인; 파울링; 하수슬러지 고형연료
- Alternative Abstract
- Phosphorus is a very important factor that greatly affects the ash polluted sediments generated during the combustion of sewage sludge solid fuel. Existing studies have mainly focused on the increase of slag and sinter due to the presence of phosphorus. Therefore, few studies have been conducted on the effect on the temperature reduction of the heat exchanger surface due to fouling and fouling fusion that may occur in the heat exchanger in the combustion boiler. The fouling fusion phenomenon is an important factor to consider for power generation using solid fuel from sewage sludge because the ash generated in the combustion boiler moves and settles on the surface of the heat exchanger to interfere with heat exchange efficiency. In particular, the decrease in the temperature of the heat exchanger surface caused by heat transfer obstruction due to fouling fusion is directly related to the efficiency of the heat exchanger, so it should be considered together with the fouling fusion. Synthetic ash, phosphorus evaporation, and drip pipe experiments were conducted to investigate the mechanism of fouling formation when phosphorus is burned and how fouling fusion affects the heat exchanger surface temperature reduction. Because phosphorus is highly reactive, it preferentially reacts with alkali metals and alkaline earth metals to lower the melting point of ash or promote fouling fusion. On the contrary, when the fouling fused to the surface of the heat exchanger is melted, a large hollow structure is formed, and the decrease in the surface temperature of the heat exchanger is rather alleviated due to the empty space created inside the fouling. The phosphorus content had a major effect on the fouling fusion and also had an effect on the reduction of the surface temperature of the heat exchanger. During the thermochemical transformation process, deposition phenomena cause operational problems in the plant. In the deposited material, inorganic particulates, especially alkaline earths and alkali metals, are mainly responsible for the accumulation of contamination. Alkali metals such as Na and K are vaporized during combustion of coal particles. Contamination is first initiated by a vaporized material that provides a sticky surface that traps colliding particles. On the other hand, as the charcoal particles are decomposed, alkaline earth metals (Mg, Ca) and Fe compounds attached to the precipitation surface are exposed by the inertial force. They can fuse and agglomerate, after which large ash particles can form. Many researchers have found that base to acid ratio, total alkali content, B/A(%Na2O), iron to calcium ratio, and %Na2O ratio in ash. Existing indicators agree well with the experimental results when coal is used, but do not match the experimental results of sewage sludge solid fuel because the phosphorus content is limited to less than 1%. Therefore, it is important to identify the types of inorganic constituents that influence pollution and the growth of particle agglomerates in order to develop suitable pollution indexes for sewage sludge solid fuels and to predict pollution trends. An improved fouling index was developed by introducing the effect of P to the previously known fouling formation mechanism. Based on the results of the previous study, it was found that the formation of phosphates in P2O5, CaO, and MgO can be a major factor in fouling in samples with a high P content. Several other parameters such as the ash deposit temperature, flue gas temperature, initial deformation temperature of ash, %(P2O5+CaO+MgO)/%(SiO2+Al2O3), and ash weight ratio as a correction coefficient are considered in the newly developed fouling index. Based on these results, the existing fouling index was improved. Although additional research is needed on the fouling phenomenon in the actual combustion environment, the newly developed fouling index can be applied to predict the fouling tendency in sewage sludge solid fuel and biomass pre-fired power generation and co-fired power generation.
- Fulltext
- Appears in Collections:
- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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