- 學位論文
探討石灰石溶解於密閉式流體化床反應系統中和硫酸及草酸之反應
Discussion on Limestone Dissolution and Neutralization Capacity within Sulfate and Oxalate in FLB System
摘要
本文利用流體化石灰石床系統 (Pulsed Limestone Bed, PLB)的設計原理改良以密閉式流體化石灰石床系統(Fluidized Limestone Bed, FLB)，用以探討石灰石的溶解量，界定其在測定與估計石灰石溶解方法上的溶解特性與機制。 第一階段研究主要設計密閉式流體化石灰石床系統(Fluidized Limestone Bed, FLB)與密閉式振盪系統(Vibration System, VS)，目的為瞭解氣體、液體及固體三相在不同擾動與混合特性下對水質變化之影響，比較兩系統與自來水反應後溶液中的pH值、酸度與鹼度以及Ca2+濃度的變化情形。 研究結果發現：反應過程中產生的鹼度部分主要由石灰石溶解所提供，FLB系統隨著反應時間的增加石灰石溶解有較穩定增加的趨勢，VS系統的石灰石溶解則較不穩定 第二階段為藉由FLB系統探討在不同的二氧化碳壓力(PCO2)；酸水溶液性質(硫酸與草酸)；酸水溶液濃度(2.95 mM硫酸與5.76 mM硫酸)的改變條件下，對於溶液反應前後水質變化的影響與石灰石溶解之的關係。 研究結果發現：實驗證明反應過程中產生的鹼度變化可利用In Acid + Out Alk測得，結果將會等同於系統中石灰石的溶解量；於反應系統中加入二氧化碳能有效提高石灰石的溶解能力；在石灰石與酸性溶液反應的中間過程當中將會產生OH-，易產生特定的鹽類沉殿，加入二氧化碳能快速的中和H+與OH-為HCO3-，能緩和石灰石與酸性溶液之間的反應過程；草酸根非常容易與Ca2+形成鹽類沉澱；當溶液中含有能與Ca2+形成沉澱的物質，以反應後的Ca2+濃度來表示在石灰石的溶解程度會產生誤差；在中和反應後發現反應溶液中有多少濃度的酸便會產生多少濃度的Ca2+，且Ca2+與HCO3-濃度維持著一定的比例關係：Ca2+ (mM) = 2 HCO3- (mM)。 第三階段則利用即時監測以及第二階段的結果嘗試建立並預估石灰石溶解反應過程中的變化特性。 研究結果發現：初期PCO2能快速幫助石灰石中和酸水溶液並降低反應時間；在H+主導石灰石溶解時PCO2的影響遠小於H+對於石灰石溶解反應速率， CO2主導石灰石溶解階段時，PCO2越大石灰石溶解反應速率將越快。H+轉為CO2主導石灰石溶解的過度期，此時HCO3-將能緩衝H+與石灰石的反應。
並列摘要
Accelerating limestone dissolution in fluidized limestone bed (FLB), modified from pulsed limestone bed (PLB) (Watten, 1999), within acid (sulfate, oxalate) environments were discussed in this research. The characteristics of acid neutralization and related mechanisms were monitored also. In order to better understanding the phase reaction within limestone particles, carbon dioxide and acid solutions, simple vibration system (VS) were conducted for comparison in the first stage of the experiments. The differences of pH, alkalinity, acidity and calcium concentration between influent and effluent were tested. The results come out that the alkalinity mostly generated from limestone dissolution with the increment of longer reaction time in FLB system while not cleared seen in VS system. Various pressure of carbon dioxide (0, 68 and 136 kPa) applied to the FLB system with sulfate (2.95 and 5.76 mM) and oxalate (5.76 mM) were conducted in the second stage of experiments for comparison of the effects due to the addition of carbon dioxide. The alkalinity generated (influent Acid plus effluent Alkalinity) were identical to the calcium disolved in the sets sulfate tests while more limestone dissolution with higher neutralization capacity and rapid precipitation of calcium oxalate were monitored in the system. The calcium dissolved from limestone (includes precipitated with oxalate) is half the amount of bicarbonate (HCO3-) which is calculated from the alkalinity generated. The characteristics of limestone dissolution were also monitored using the real-time detection of the pH and the ambient pressure in the system. The hydrogen ion (H+) dominated the major surface reaction to the limestone and the present of carbon dioxide plays the role of enhancing limestone dissolution due to further hydrogen ion generated from CO2 dissolved in water.