Unit 7 Conventional Technology of Air Pollution Control 大气污染控制的常规技术
The principal means for control of particulate emissions from industrial sources are cyclones，electrostatic precipitators, fabric filters and scrubbers. 控制工业来源的颗粒物的排放的主要方法是利用旋风分离器、静电除尘器、布袋过滤器和洗涤器。
In addition to these conventional devices, granular bed and panel bed filters have been applied to a limited extent and research is being conducted on devices or combinations of conventional devices, such as charged drop let scrubbers.除了以上的常规设备以外，颗粒层过滤器和平板过滤器在一定程度上得到应用，并且正在开展对设备或组合常规设备的研究，例如荷电液滴洗涤器。
Cyclones 旋风分离器
Cyclonic collectors are round conically shaped vessels in which the gas stream enters tangentially and follows a spiral path to the outlet. 旋风分离吸收器是圆锥形的容器，气体流切向进入并且顺着螺旋状的管道到出口。
The spiral motion produces the centrifugal forces that cause the particulate matter to move toward the periphery of the vessel and collect pm the walls and fall to the bottom of the vessel. 这种螺旋运动产生离心力，使颗粒物沿着容器的外围移动被聚集在壁面然后掉落在容器底部。
The centrifugal force is the major force causing separation of the particulate in a cyclone separator.离心力是引起颗粒物在旋风分离器里分离主要作用力。
The cyclonic collectors are generally of two types: the large diameter, lower efficiency cyclones, and the small diameter, lower efficiency cyclones, and the small diameter, multitube high-efficiency units. 旋风分离除尘器大致分为两种致：大径低效分离器和小径多管高效分离器。
The larger cyclones have lower efficiencies especially on particles less than 50 um. 大直径的旋风分离除尘器的效率会比较低特别是对直径小于50微米的颗粒。
However, they have low initial cost and usually operate at pressure drips of 1 to 3 inches of water. 但是，它们的运行成本较低，一般在1到3英寸水柱的压力降下运行。
The multitube cyclones are capable of efficiencies exceeding 90% but the cost is higher and their pressure drop is usually 3 to 5 inches of water. 多管式的旋风分离除尘器效率通常能够达到90%以上，不过它的运行成本就比较高，一般在在3到5英寸水柱的水压降下运行。
They are also more susceptible to plugging and erosion. 它们经常被堵塞和更加容易受到腐蚀。
The large cyclones are often used as a part of the process when the gas stream is heavily laden with part of the product such as in coal dryers, alfalfa dehydrators and milling operations. 大直径的旋风分离除尘器经常用作于当气流里充满产物的一部分时的过程，比如煤干燥器、紫苜宿脱水器、碾磨的运转。
They are widely used in grain elevators, sawmills, asphalt plants and detergent manufacture. 它们被广泛运用于谷物运输、锯木、沥青制造装置和清洁剂的生产中。
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