超低排放燃煤电站湿法脱硫和湿式电除尘器中硒含量分布及形态演变

Se partitioning and species in WFGD and WESP system of the ultra-low emission coal fired power plant

煤中硒在燃烧后释放到气相中,并吸附于气相中的细颗粒物上,可被燃煤电厂中的湿法脱硫系统(WFGD)和湿式电除尘(WESP)系统捕获,明确Se在湿法脱硫系统及湿式电除尘系统中的迁移规律和形态分布情况至关重要。基于氢化物发生-原子荧光光谱(HG-AFS)方法研究了湿法脱硫系统及湿式电除尘系统中关键位置处的硒含量分布和形态演变规律。研究发现,燃煤烟气中的硒可被湿法脱硫系统脱除,捕获后的硒在脱硫塔内固相和液相中的含量分别为1.07μg/g和0.123mg/L,在强制氧化作用下,超过80%的四价硒被氧化为六价硒。浆液经旋流分离器分离后,大部分硒转移到废水处理中。常规废水处理过程只对四价硒具有较高的脱除效率,但废水中六价硒占比超过77%,使传统三联箱废水处理工艺无法实现硒的高效脱除,造成现有燃煤电站废水中硒难以脱除。湿式电除尘系统冲灰水固相中硒富集明显,含量达13.9μg/g。液相中硒含量为0.0016mg/L,其中四价硒和六价硒占比分别为34.35%和65.65%。加装湿式电除尘可将难以脱除的气相硒转移到固相灰中,实现燃煤烟气中气相硒的深度脱除,估算机组全年湿式电除尘可脱除烟气中颗粒态硒2.9kg。

Se is released to gas phase and combines with fine particles in flue gas after coal combustion which can be captured by the wet desulfurization(WFGD) system and wet electrostatic precipitator(WESP) in flue gas,and it is important to determine the partitioning and species of Se in these systems.Based on hydride generation-atomic fluorescence spectrometry(HG-AFS),the partitioning and species of Se in the key locations of WFGD and WESP were studied.It is found that Se can be removed by WFGD system in flue gas.The concentration of Se in the solid fraction and liquid fraction of desulfurization tower slurry are 1.07 μg/g and 0.123 mg/L,respectively.Over 80% Se in the desulfurization tower is oxidized to Se(VI) under forced oxidation condition.After separated by a hydrocyclone,most Se is transported to effluent treatment process.The predominant Se species in the effluent treatment process is Se(VI),with the proportion exceeds 77%,which accounts for low efficiency in Se removal by traditional three-linked tank technique.Se exhibits a significant enrichment in solid fraction of the flush water from WESP whose concentration is 13.9 μg/g,while 0.001 6 mg/L Se is determined in the liquid fraction where proportions of Se(IV) and Se(VI) are 34.35% and 65.65%,respectively.WESP equipment achieves Se deep removal from flue gas,and transports this part of Se to the solid fraction of ash.It is calculated that with the help of WESP 2.9 kg/yr particle-bound Se is removed.