Abstract:

In order to study the emissions of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs) during the transient and steady conditions of a medical waste incinerator (MWI) in east China, PCDD/Fs distributions and emission rate under different operating conditions of MWI was investigated. Flue gas sampling of MWI was conducted in accordance with operating conditions, start-up 1, start-up 2, start-up 3 and start-up 4 (four samples), 12 h after start-up(after-start 1, after-start 2, two samples) and 24 h after start-up (after-start 3, after-start 4, two samples). The I-TEQ values of flue gas were 1.68 ng I-TEQ·m^-3 at the end of start-up and 2.77 ng I-TEQ·m^-3 at 12 h after start-up, while the I-TEQ values of fly ash was 4.5 ng I-TEQ·g^-1. The average concentrations of the PCDD/Fs emissions at start-up (0.78 ng I-TEQ·m^-3) and after-start (1.5 ng I-TEQ·m^-3) exceeded the emission limit (0.5 ng I-TEQ·m^-3) for MWIs in China. The PCDD/Fs concentrations at 24 h after start-up (after-start 3, after-start 4) were still above the emission limit, which was proved as a "memory emission" effect due to the start-up conditions. The PCDFs/PCDDs ratio ranged from 0.14 to 0.95 at the beginning of start-up and from 5.46 to 6.29 during the after-start process, which meant PCDFs were dominant in the flue gases of MWI. PCDD/Fs congener profiles of flue gas samples during start-up and after-start were characterized by higher chlorinated PCDD/Fs. The PCDD/Fs congener profiles of fly ash samples were similar to flue gases, also mainly dominated by 2,3,4,7,8-PeCDF. PCDD/Fs in particle phase at the beginning of start-up accounted for 50%, while gas phase PCDD/Fs accounted for over 90% at 12 h after start-up. The PCDD/Fs emission rates of flue gas during start-up were much higher than normal conditions. The highest emission rate was 58.1 mg I-TEQ·h^-1, 40 times higher than the normal level. The total PCDD/Fs emission during start-up was 0.785 mg I-TEQ. The start-up of this MWI was approximately three times per year, and the start-ups of MWI accounted for 28% of the whole year's PCDD/Fs emission.

Key words: waste treatment, flue gas, PCDD/Fs, start-up, memory effect, emission characteristics, pollution

摘要：

选择了位于华东地区的某医疗废物焚烧处置设施开展启炉过程与正常工况下烟气和飞灰的二噁英排放特性对比研究。数据显示, 启炉后期烟气中二噁英的浓度达到1.68 ng I-TEQ·m^-3, 在焚烧炉温度稳定以后12 h, 达到2.77 ng I-TEQ·m^-3, 飞灰中二噁英毒性当量水平也达到4.5 ng I-TEQ·g^-1。启炉过程中烟气中气相二噁英所占比例逐渐增加, 从平均占到50%增加到超过90%。启炉过程中烟气二噁英排放速率高于其正常达标时的排放水平, 最高值为58.1 mg I-TEQ·h^-1, 超过正常排放的40倍。一个启炉周期二噁英的排放总量达到0.785 mg I-TEQ, 达标正常工况下二噁英的年排放总量为8.4 mg I-TEQ, 按照平均每年3次启炉来计算, 启炉过程二噁英的排放量占到全年正常排放的28%。

关键词: 废物处理, 烟道气, 二噁英, 启炉, 记忆效应, 排放特性, 污染