Experimental and modelling study on the release of potassium during biomass combustion

  • Wenhan CAO

Student thesis: Doctoral Thesis

Abstract

Understanding the release mechanism of potassium (K) is crucial in tackling alkali metal-induced ash problems during the combustion process of biomass. This thesis focuses on enhancing the knowledge on the release mechanism of potassium experimentally and developing a model to predict the release profiles of potassium compounds from biomass. In the beginning, the thesis investigated the thermal characteristics of biomass and its major chemical components in a thermogravimetric analyser (TGA). According to the tests, the thermal conversion process of natural biomass and be predicted through the analyses of artificial biomass, which is the mixture of major chemical components. The results illustrate the feasibility to use major chemical components as initial inputs in the biomass combustion model. Biomass combustion experiments were then performed in a high-temperature furnace-balance system (FBS). The results revealed that the final temperature affects the K transition the most. Over 60% of the initial K was lost as the final temperature increased from 30℃ to 1000℃. The heating rate affects the K transition during combustion by influencing the devolatilisation of volatile matter related K and the structural changes of particles. The higher the heating rate, the more release of K. The developed kinetically controlled model was validated and used to estimate the release of different K compounds under different scenarios. The results indicate that KCl is the major compound released at the early stage of combustion, followed by KOH and K₂SO₄. Analysing the reaction path of K reveals that KO and KO₂ are the most critical intermediate species during combustion. The initial concentration of Cl significantly affects the release of major species: KCl, KOH, HCl and K₂SO₄; while the initial concentration of S can affect the release of KOH and K₂SO₄ at high temperatures. The existence of O₂ in the system favours the formation of KO and KO₂, and thus to control the release of major K species.
Date of Award18 May 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorJun Li (Supervisor) & Leo Lue (Supervisor)

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