利用減壓蒸餾設備進行脫硫廢水處理以及其生命週期評估

Abstract

當燃煤電廠發電時，需通過排煙脫硫程序對產生的硫氧化物進行脫硫。此過程產生的脫硫廢水含有高濃度的硫酸鹽、氯化物、硼，和金屬化合物，包括潛在的有毒重金屬。對應於越來越嚴苛的放流水標準，更新穎的脫硫廢水處理技術有其設置必要性。 本研究使用了商用NanoPlus Tech NRS 250型減壓蒸餾裝置 (NRS-250)來處理台灣某燃煤電廠的脫硫廢水。減壓蒸餾是一種低溫，低壓的水分離過程，可以直接將廢水蒸餾並冷凝回收。通過降低操作壓力，真空蒸餾設備可以消耗更少的能量，並在較低的水沸點（35-55 oC）進行蒸餾。在固液分離過程之後，剩餘的殘留固體(以石膏為主體)可以用於回收或後續處置。比較處理前後的重金屬濃度，去除效率高達95％，並且達到大於90％的除硼效率。此外NRS裝置去除了98％的氯化物，氯離子濃度從1,900 mg / L降低到小於25 mg / L，使回收水可以循環至排煙脫硫設備再利用。 本研究使用SimaPro8.5軟體和ReCiPe（H）中點衝擊方法，通過比較原料使用，能資源使用和廢棄物產生，以處理1m3脫硫廢水為功能單位對該設備進行生命週期評估。在生命週期評估結果顯示海洋生態毒性是最重要的衝擊類別，在不同生命週期階段中，NRS設備的使用階段在所有衝擊類別佔有最大影響，其次是製造與廢棄物處置階段，而運輸階段的影響很小。 最後，本研究評估了在印刷電路板工廠中使用NRS設備的經濟效益。其額定處理量為1 CMD廢酸，在五年的服務年限中，NRS-250設備的年收益為新台幣580萬元，淨現值為新台幣1,897萬元。內部投資報酬率 (IRR) 達49％，高於所選擇的折現率（7％），顯示了真空蒸餾進行廢酸處理的經濟可行性。

When a coal-fired power plant produces electricity, the generated sulfur oxides must be desulfurized through the flue-gas desulfurization (FGD) process. This process produces FGD wastewater containing high concentrations of sulfate, chloride, boron, and metal compounds, including potential toxic metals. Vacuum distillation is a low-temperature, low-pressure water separation process that can distill and condense water directly from the raw FGD wastewater. By successfully decreasing the operating pressure, the vacuum distillation equipment can distill water at a lower boiling points of water (between 35-55 oC), which consumes much less energy. After this solid-liquid separation process, much fewer residual solids on a per mass basis, mainly as gypsum, is left for subsequent disposal or recycling. This study used a commercial NanoPlus Tech NRS model 250 vacuum distillation device (NRS) for treating FGD wastewater in a coal-fired power plant in Taiwan. By comparing the concentrations of heavy metals before and after treatment, the removal efficiency of the metals was up to 95%. The distilled water can be successfully recycled with > 90% boron removal efficiency in all scenarios. Furthermore, NRS removed 98% of the chlorides, reducing chloride content from 1,900 mg/L to less than 25 mg/L, and the remaining water could be recycled back to the FGD units. Additionally, a life cycle assessment (LCA) of this device was performed using the software SimaPro8.5 and ReCiPe (H) midpoint method by comparing raw material use, energy use, chemical input, and waste generation. In the LCA, marine ecotoxicity is a significant impact category. The use phase of the NRS device displays the highest impact across all categories, followed by the manufacturing and the disposal phases, while the transportation phase had only a slight effect. For comparison, an economic evaluation for a case study using NRS in a printed circuit board factory was also addressed. The rated capacity was 1 CMD waste acid. The NRS-250 device showed benefits of NTD 5.8 million per year, and revenues of NTD 18.97 million at present value. The internal return rate (IRR) accounts for 49%, showing viability in the application of vacuum distillation in waste acid treatment, as the IRR is higher than the interest rate chosen (r = 7%).