| 论文简介 |
Homogenous nucleation or heterogeneous condensation of gaseous alkali salts commonly occurs in biomass-fired power plants, and is mainly responsible for forming fine particles and triggering deposition or corrosion on tubes. This work aims to investigate the influence of surface temperature and exposure time on the initial condensation characteristics of KCl(g) in air atmosphere. It includes both experiment and simulation calculation to qualitatively and quantitatively study the condensation and gas-to-solid conversion of KCl(g) under different temperature gradients. Experiments were carried out in an electrically heated vertical tubular furnace, in which a defined evaporating source of KCl(g) was designed. A sampling probe equipped with a temperature controlled Fe-Cr-Ni alloy condensation surface, was inserted into the furnace to capture KCl(g). For each case, the morphology of condensed salt on the probe surface was analyzed via using Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM-EDS). The results showed significant differences in morphologies of the condensed salts which were respectively observed at the condensation surface temperature of Fe-Cr-Ni alloy of 673.15, 793.15 and 873.15 K. At the same tubular furnace temperature, due to the appearance of dendritic structure, the condensation rate of KCl(g) of 3.28 × 10−6 kg/m2·s at the surface temperature of 793.15 K was greater than that obtained at 673.15 K. The calculation of gas-to-solid conversion found that condensed KCl particles whose diameter is larger than 1 μm could not be formed only relying on the mechanism of nucleation and coagulation, when the gas temperature decreased from 1073.15 K to 673.15/793.15/873.15 K, respectively. The faster the cooling rate is, the smaller the size of formed particles is, and the more the number concentration of ultra-fine particles is. In addition, severe corrosion and cracks of surface material of the condensation surface were clearly observed at 793.15/873.15 K, which may be induced by couple attacks of condensed salts, thermal stress and molecular oxygen. |
(创新港)
