富氧燃烧气氛下石灰石煅烧/硫化特性及模型模拟

Characterization and modeling of limestone calcination and sulfation in oxy-fuel combustion atmosphere

利用自制恒温热重装置,模拟循环流化床富氧燃烧气氛,进行了石灰石同时煅烧/硫化实验,并通过对煅烧/硫化产物孔结构以及硫化产物电导率的测量,探讨了硫化反应机理。相比石灰石先煅烧成Ca O再硫化,吸收剂孔隙更容易堵塞且更早进入到产物层扩散控制阶段;产物层扩散控制阶段固态离子扩散率更高,可获得更快的硫化速率和更高的最终钙转化率。烧结会极大影响Ca O的钙转化率,尤其当温度高于950℃时;粒径效应显著,随石灰石颗粒粒径减小最终钙转化率明显提高;SO2浓度提高有助于最终钙利用率的提高。建立了晶粒-微晶粒模型,对不同温度、粒径、SO2浓度条件下石灰石同时煅烧/硫化特性进行了数学模拟,模拟结果与实验结果较为吻合。

The characteristics of simultaneous calcination and sulfation of limestone in the atmosphere simulating circulating fluidized bed oxy-fuel combustion were studied using an experimental system that could measure sample mass changes at a preset temperature. The pore structure and conductivity of samples were measured to study the diffusion mechanism in the product layer. Compared with Ca O that was calcined without SO2, the porosity of Ca O was easier to be blocked up and the process had a shorter duration before transfering into the diffusion control stage when limestone calcination and sulfation occured simultaneously. A higher sulfation rate and higher conversion were observed because of higher diffusibility in the product layer than that of Ca O calcined without SO2. Sintering of Ca O would decrease its sulfation capability, especially when temperature was above 950℃. Particle size was an important factor that determined sulfation of sorbents, and higher sorbent utilization would be obtained for smaller particles. Also, higher SO2 concentration would improve sulfation of sorbents. A grain-micrograin model was set up, and the effects of some factors, such as temperature, sorbent particle size and SO2 concentration were simulated. The calculation results fitted well with the testing.