裸露表面揚塵控制研究

Abstract

空氣污染來源可分為二大類：(1) 自然形成、(2) 人為造成，自然污染問題部分來自於風力造成之揚塵現象，因此本研究之重點於有效抑制微粒揚起而懸浮，除了分析揚塵機制外，本實驗也針對灑水控制技術進行探討。目前對於裸露地面揚塵抑制最有效、最經濟之方式為灑水，利用水分子填充於粉塵間孔隙產生液膜，藉液膜的表面張力作用增加微粒間附著力，使微粒不易自表面脫離。本研究以實驗結果及理論模式推估，提出灑水控制技術操作時之需水量及灑水頻率數據，供現場操作參考。 實驗中採用新竹市南寮地區裸露地之地面粉塵，在內徑30cm之風洞系統中進行揚塵測試。測試粉塵利用美國325號標準網除粒徑大於44 mm之微粒，置微粒於烘箱以105℃烘乾後，放入風洞內測試平台，分別對粒徑分佈、揚塵機制、灑水控制技術進行實驗。透過微粒揚起之模式推估，配合MOUDI量測之粒徑分佈結果，證明粉塵表面微粒在流場中揚起，拖曳力產生之旋轉力矩為主要原因，並非剪應力造成之拖曳作用，揚塵風速閥值約在3 ~ 5 m/s。揚起之微粒大多為大顆粒 ( > 22 mm ) ，小顆粒占總揚塵量比例較低。灑水控制技術實驗中，當粉塵單位面積含水量達到 60 ~ 75 g/m2 ，揚塵控制效率可達到 100 % ；若粉塵表面粗糙度高時，揚塵有效控制之需水量也會相對提高。粉塵含水量因蒸發作用隨時間減少，實驗中顯示較高的風速會因強制對流作用而增加蒸發率。當環境溫濕度為 25 ± 2 ℃、60 ± 10 % 狀態，含水率 30 % 的含水量在穩定均勻之風速作用下 ( 0、2、4 m/s ) ，灑水間隔時間在 3.5、2.2、1.8小時之內。

Air pollution may be classified into two broad categories : (1) Natural、(2) Human made. Windblown dust constitutes one of the natural pollution problems. The importance of the study is to control dust reentrained efficiently. This study focuse on the analysis of the mechanism of reentrainment and discusses watering control technique. Watering is the most efficient and economic technology for controling dust reentrainment from unpaved road. Water molecules fill in the space between dust particles and developed into liquid membrane. The surface tension of liquid membrane increases the attractive force between particles, and detachment of particles from the surface becomes difficult. From this study, we could get the information including water quantity for applying in the field. Test dusts were collected from an unpaved road at Nan-Laio area of Hsin-Chu. Test dusts were placed in the wind tunnel system (inner diameter = 30cm) in the laboratory. The test dusts were first sieved using a standard No.325 mesh to remove particles greater than 44 μm. Then the dusts were dried at 105℃ in the oven. Finally, the dried dusts were embedded in an aluminum cell in the working section of the wind tunnel. The experiment includes particle size distribution、the mechanism of the dust reentrainment and watering control technique. Theoretical analysis base on the size measure by MOUDI (Microorifice Uniform Deposit Impactor) showed that the moment caused by fluid drag force on the particles are the major reason in dust reentrainment. The particles pulled off the surface are mostly large particle( > 22 μm ). In the aspect of watering control technique ,when the mass area density of watering is over 60 ~ 75 g/m2, the dust control efficiency is almost 100 %. Results show that evaporation decreases water content decrease with time. The force convection by wind makes water evaporation rate faster. Under temperature of 25 ± 2 ℃、relative humidity of 60 ± 10 %, the watering interval time must be less than 3.5、2.2、1.7 hours at the wind speed of 0、2、4 m/s for an effective dust reentrainment control at the initial water content of 30%.