A.C.Hoffmann-1Introduction英文电子资料.pdf

1 Introduction The subject of this book is centrifugal gas cleaning devices, namely cyclones used as gas-solids separators (for ‘dedusting’) and as gas-liquid separators (for ‘demisting’). 1.1 Some Historical Background The first cyclone patent was granted to John M. Finch of the United States back in 1885 and assigned to the Knickerbocker Company. Although the “dust collector”, as it was then called, contained the essence of today‘s modern cyclones (see Fig. 1.1.1), the dust was allowed to exit out the side of its cylindrical body, rather than out a conical-shaped bottom. It was also a rather complex device and bore little resemblance to today‘s modern cyclones. Still, the idea of using centripetal acceleration for separating particles from a gas stream was quite a radical idea back in the late 1800’s. After all, everyone knows that dust will settle only when the gas stream carrying the dust is quiet and relatively free of motion for a long time. Indeed, a 10-micron dust particle of unit density requires about 5 1 minutes just to settle 1 meter in 2 still air. The beauty of John Finch’s discovery is that he devised a solution to the problem of dust “settling” which was just the opposite of conventional thinking or even common sense at the time of his discovery. Rather than devising a large, quiet settling chamber, he introduced the dust-laden air into a small cylindrical housing in a tangential manner and imparted a significant velocity to the mixture, thereby separating the dust from the air under highly turbulent flow conditions using the principle of centripetal acceleration, rather than gravity. In the area of separations technology the concept embodied in Finch’s discovery has proven to be one of the most elegant, yet practical inventions of the 19th century. It’s a textbook example of the v