Abstract
A counter-flow reactor setup was designed to investigate the gas-phase sulfation and homogeneous nucleation of potassium salts. Gaseous KOH and KCl were introduced into the post-flame zone of a laminar flat flame. The hot flame products mixed in the counter-flow with cold N2, with or without addition of SO2. The aerosols formed in the flow were detected through Mie scattering of a 355 nm laser beam. The temperature distribution of the flow was measured by molecular Rayleigh scattering thermometry. From the temperature where nucleation occurred, it was possible to identify the aerosols formed. Depending on the potassium speciation in the inlet and the presence of SO2, they consisted of K2SO4, KCl, or K2CO3, respectively. The experiments showed that KOH was sulphated more readily than KCl, resulting in larger quantities of aerosols. The sulfation process in the counter-flow setup was simulated using a chemical kinetic model including a detailed subset for the Cl/S/K chemistry. Similar to the experimental results, much more potassium sulfate was predicted when seeding KOH compared to seeding KCl. For both KOH and KCl, sulfation was predicted to occur primarily through the reactions among atomic K, O2 and SO2, forming KHSO4 and K2SO4. The higher propensity for sulfation of KOH compared to KCl was mostly attributed to the lower thermal stability of KOH, facilitating formation of atomic K. According to the model, sulfation also happened through SO3, especially for KCl (KCl → KSO3Cl → K2SO4).
Highlights
Biomass, including energy crops [1], agricultural products [2] and industrial biomass waste [3], is considered as a sustainable and carbon neutral energy source
It is commonly combusted in boilers to provide heat and/or power. Biomass such as agricultural residues may contain relatively high concentrations of potassium, chlorine and sulfur. These elements lead to the formation of potassium chloride (KCl), potassium hydroxide (KOH), hydrogen chloride (HCl) and sulfur dioxide (SO2), causing problems of slagging and fouling, corrosion, and emissions of harmful gases and aerosols
The results were interpreted in terms of an updated chemical kinetic model for Cl/S/K interactions to provide a better understanding of the sulfation process
Summary
Biomass, including energy crops [1], agricultural products [2] and industrial biomass waste [3], is considered as a sustainable and carbon neutral energy source. It is commonly combusted in boilers to provide heat and/or power Biomass such as agricultural residues may contain relatively high concentrations of potassium, chlorine and sulfur. One pathway involved the direct reaction between KOH and SO 2 to form KHSO3, with oxidation of sulfite to sulfate as the rate-limiting step, instead of the oxidation of SO 2 to SO3: KOH + SO2(+M) = KHSO3(+M). Another route of K2SO4 formation can be initiated by the reaction of atomic K with. The results were interpreted in terms of an updated chemical kinetic model for Cl/S/K interactions to provide a better understanding of the sulfation process
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