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说明石油精馏塔汽—液分布规律(无中段回流)?

答案

参考答案:

原油进入汽化段后,其气相部分进入精馏段。自下而上,由于温度逐板下降引起回流量逐板增大,因而气相负荷也不断增大。到塔顶低一、二层塔板之间,气相负荷达到最大。经过第一板后,气相的负荷显著减小。从塔顶送入的冷回流,经过第一板后变成了热回流(即处于饱和状态),液相回流量有较大幅度的增加,达到最大值。在这以后自上而下,液相回流量逐板减小。每经过一层侧线抽出板,液相负荷均有突然的下降,其减少的量相当于侧线抽出量。到了汽化段,如果进料没有过汽化量,则从精馏段末一层塔板流向汽化段的液相回流量等于零。

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Libraries form a vital part of the world’s systems of communication and education.
They make available knowledge accumulated through the ages. People in all walks of life use library resources in their work. People also turn to libraries to satisfy a desire for knowledge or to obtain material for leisure-time activity. In addition, many people enjoy book discussions, concerts, film programs, lectures, story hours, and a variety of other activities provided by libraries. Libraries also play an important role in preserving a society’s cultural heritage(遗产). The library ranks as one of society’s most useful service institutions.
The contents of libraries have changed so much through the years that the word library itself is, in a sense, inaccurate. The word comes from the Latin word liber, which means book. Today’s libraries house many books, of course. However, they also have a wide variety of other materials that communicate, educate, and entertain. These materials include magazines, manuscripts (手稿), newspapers, and computer documents.
Audio and visual materials include CDs, audiocassette tapes, videotapes, films, maps, paintings, and photographs.
In addition to regular books, a library may have large-type books, books for the blind, and tape recordings of books, called talking books. Librarians keep pace with the changing contents of libraries to serve as many people as possible. Their efforts have turned libraries into multimedia resource centers.
The expansion of library contents greatly increases the library’s ability to communicate and educate. For example, people interested in classical music can listen to CDs and read books on the topic. Students of agriculture can read magazines and watch videotapes on farming methods. Many people use magazines and newspapers to find the most up-to-date material on current events.
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