关键词: 颗粒, 成核, 凝结, 不可溶核, 可溶无机盐, 数值模拟

Abstract:

The surfaces of fine particles that emitted from power generation processes with the direct combustion of biomass and with the co-combustion of biomass and coal usually contain a certain amount of soluble inorganic salt. Based on the classical heterogeneous nucleation theory, an improved model for vapor heterogeneous nucleation on the surfaces of particles containing a spherical insoluble core and soluble inorganic salt was developed, taking into account the embryo growth mechanisms of surface diffusion and direct deposition. Using the numerical simulation method, the nucleation behaviors of four types of particles (insoluble particle and three types of particle containing soluble inorganic salt) were compared and analyzed. The results show that in cases of medium contact angles, the critical free energy of embryo formation and the critical embryo radius of an insoluble particle are the largest, followed by the particles containing KCl, NaCl and CaCl₂, respectively. Under the condition with critical embryo radii, the ratio of water molecule addition rates due to mechanisms of surface diffusion and direct deposition increases slightly at first and then keeps constant with increasing particle radius, and decreases monotonically with increasing contact angle. It is also found that when the contact angle is small, the critical saturation ratio for nucleation of a particle containing soluble inorganic salt is lower than that of the insoluble particle, whereas when the contact angle is larger, the critical saturation for nucleation of particles containing KCl and NaCl exceeds that of insoluble particles successively.

Key words: particle, nucleation, condensation, insoluble core, soluble inorganic salt, numerical simulation