大型燃煤锅炉中含Na/Cl/S组分的演变与受热面结渣倾向的数值模拟

Numerical Simulation of Na/Cl/S-containing Species Evolution and Slagging Propensity of Heat Transfer Walls in a Large-scale Pulverized Coal Boiler

提出了一种考虑煤中含Na/S/Cl组分多步释放、气相组分相互作用、气-固反应以及盐蒸气冷凝耦合灰颗粒黏附的结焦模型,以预测炉内受热面气态碱金属组分冷凝行为、受热面结焦风险以及炉膛出口Na/S/Cl组分分布特性。结果表明:炉膛出口气态含Na组分主要以NaO_(2)、NaCl、Na_(2)SO_(4)和NaOH形式存在;最上层燃烧器至分离燃尽风(SOFA)喷口区域、最下层燃烧器至冷灰斗转角区域的水冷壁结焦风险高;炉膛出口区域后屏过热器底部颗粒黏附位置相对集中,炉内辐射式过热器结焦速率远高于气态钠盐冷凝速率,对流受热面颗粒沉积速率约是钠盐蒸气冷凝速率的3~4倍。

A slagging model was proposed,in which the multi-step release of Na/S/Cl-containing species from coal,the interacting reaction among gas-phase components,gas-solid reactions and ash particle sticking coupling with salt-vapor condensation were considered.This model could be used to predict the condensation behavior of gaseous alkali metal components on the heating surface inside furnace,the slagging risk for the heating surface and the distribution characteristics of Na-S-Cl components at the furnace outlet.Results show that gaseous Na-containing components mainly exist as the forms of NaO_(2),NaCl,Na_(2)SO_(4)and NaOH at the furnace outlet.The slagging risk is high for the water wall from the top burner to the separated overfire air(SOFA)nozzle area and the wall from the bottom burner to the ash hopper corner area.The sticked particles are relatively concentrated at the bottom of the rear platen superheater at the furnace outlet.The slagging rate for the radiant superheaters is much higher than the condensation rate of sodium salt in the gas phase.Whereas the deposition rate of ash particles on the convective heating surface is about 3~4 times of the condensation rate of sodium salt vapor.