湿法烟气脱硫系统对细颗粒脱除性能的实验研究

Performance of removal of fine particles by WFGD system

针对石灰石-石膏法、双碱法、氨法等典型湿法烟气脱硫(WFGD)工艺,在喷淋脱硫塔中实验研究了WFGD系统对细颗粒的脱除作用;采用电称低压冲击器、场发射扫描电镜、X射线衍射仪等对WFGD系统前后烟气中细颗粒的浓度、粒径分布、形态、元素及物相组成进行了测试分析,考察了脱硫剂、液气比对WFGD系统脱除细颗粒性能的影响,并进行了利用蒸汽相变原理促进细颗粒凝结长大并高效脱除的实验研究。结果表明,脱硫剂对WFGD系统脱除细颗粒的性能具有重要影响,由于形成无机盐气溶胶细颗粒,采用CaCO3、NH3.H2O脱硫剂时,WFGD系统对细颗粒的脱除效果明显不及Na2CO3脱硫剂和水洗涤,且颗粒形貌特征及元素组成发生明显变化;除NH3.H2O脱硫剂外,液气比对WFGD系统脱除细颗粒的影响不明显;在脱硫塔进口烟气、塔内脱硫液进口上方添加适量蒸汽建立蒸汽相变所需的过饱和水汽环境可显著促进细颗粒的脱除。

In a spray column scrubber, the removal of fine particles by wet flue gas desulfurization （WFGD） system was investigated experimentally for the typical WFGD process, such as limestonegypsum double-alkali and ammonia-based process. The number concentration and size distribution, morphologies, elemental and phase composition of fine particles before and after desulfurization were measured by using an electrical low pressure impactor （ELPI）, field emission scanning electron microscope/energy dispersive X-ray spectrometry （FESEM-EDS） and X-ray diffraction （XRD）, respectively. The influences of SO2 absorbent and liquid-gas ratio on fine particles removal by the WFGD system were also investigated. Moreover, an experiment was carried out on the removal of fine particles with high efficiency by heterogeneous condensation of water vapor. The results showed that the removal effect of fine particles by the WFGD system was related to the SO2 absorbent employed. When using CaCO3 and NH3 · H2O to remove SO2 from flue gas, the fine particles removal efficiencies were lower than those for Na2CO3 and water, and the morphology and elemental composition of fine particles were changed. This effect could be attributed to the formation of aerosol particles in the limestone and ammoniabased FGD processes. The effect of liquid-to-gas ratio seemed to be relatively weak except for NH3 · H2O as absorbent. The performance of removal of fine particles by the WFGD system could be significantly improved by means of steam addition both in the gas inlet and above the scrubbing solutions inlet of the scrubber, in which the removal efficiency increased with increasing amount of added steam.