查温度组成图得:加料板为88℃,塔底为130.4℃。
tm??88?130.4?/2?109.2℃
3.平均分子量Mm
加料板:yF?0.930,xF?0.728(查相平衡图)
MVF,m?0.930?78.11??1?0.930??112.61?80.52kg/kmol MLF,m?0.728?78.11??1?0.728??112.61?87.49kg/kmol
塔底: xW?0.01149,yW?0.050。(查相平衡图)
MVW,m?0.050?78.11??1?0.050??112.61?110.9kg/kmol MLW,m?0.01149?78.11??1?0.01149??112.61?112.2kg/kmol
提馏段:MV,m??80.52?110.9?/2?95.71kg/kmol
ML,m??87.49?112.2?/2?99.84kg/kmol
4.平均密度ρm 1)液相平均密度ρL,m
进料板:ρLF,A?912.13?1.1886t?912.13?1.1886?88?807.5kg/m
3ρLF,B?1124.4?1.0657t?1124.4?1.0657?88?1030.6kg/m3 1ρLF,m?aAa0.650.35?B???ρLF,m?873.7kg/m3 ρLF,AρLF,B807.51030.63塔底:?LW,A?912.13?1.1886t?912.13?1.1886?130.4?757.1kg/m
?LW,B?1124.4?1.0657t?1124.4?1.0657?130.4?985.4kg/m3
1?LW,m?aA?LW,A?aB?LW,B?0.0020.998???LW,m?984.8kg/m3 757.1985.43提馏段:?L,m??873.7?984.8?/2?929.2kg/m 2)汽相平均密度ρV,m
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?V,m?pmMV,mRTm?115.8?95.71?3.488kg/m3
8.314??273?109.2?5.液体的平均表面张力σm
进料板:σF,A?20.20mN/m;σF,B?25.34mN/m(88℃)
?σAσBσF,m???σx?σxBA?AB?20.20?25.34???????21.38mN/m ??F?20.20?0.272?25.34?0.728?塔底:?W,A?15.4mN/m;?W,B?20.5mN/m(130.4℃)
?W,m?????A?B15.4?20.5???????20.42mN/m
??AxB??BxA?W?15.4?0.98851?20.5?0.01149?精馏段:?m??21.38?20.42?/2?20.90mN/m 6.液体的平均粘度μL,m
查化工原理附录有:
加料板:μLF,m?0.28?0.728?0.41?0.272?0.315mPa?s 塔 底:?LW,m?0.2?0.01149?0.27?0.98851?0.269mPa?s 提馏段:?L,m??0.315?0.269?/2?0.292mPa?s (二)提馏段的汽液负荷计算
汽相摩尔流率
V??V??1?q?F?V??R?1?D?1.499?159.40?238.94kmol/h
汽相体积流量Vs?VMV,m3600?V,m3?238.94?95.71?1.821m3/s
3600?3.4883汽相体积流量Vh?1.821m/s?6556m/h 液相回流摩尔流率
L??L?qF?RD?qF?0.499?159.40?1?216.78?296.32kmol/h
液相体积流量Ls?LML,m3600?L,m?3296.32?99.84?0.00884m3/s
3600?929.23液相体积流量Lh?0.00884m/s?31.82m/h
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3再沸器的热负荷Q?V?r?238.94?35.3?10/3600?2343kW
??(忽略温度压力对汽化潜热的影响) (三)塔和塔板主要工艺结构尺寸的计算 1.塔径
1)初选塔板间距HT?500mm及板上液层高度hL?60mm,则:
HT?hL?0.5?0.06?0.44m
2)按Smith法求取允许的空塔气速umax(即泛点气速uF)
?Ls???L??????Vs???V?0.5?0.00884??929.2???????1.821??3.488?0.5?0.0792
查Smith通用关联图得C20?0.0948
???负荷因子C?C20???20?泛点气速:
0.2?20.90??0.0948???20?0.2?0.0956
umax?C3)操作气速
??L??V?/?V?0.0956?929.2?3.488?/3.488?1.557m/s
取u?0.7umax?1.090m/s 4)精馏段的塔径
D?4Vs/?u?4?1.821/3.14?1.090?1.458m
为加工方便,圆整取D?1600mm,即上下塔段直径保持一致,此时提馏段的操作气速u?0.906m/s。
2.塔板工艺结构尺寸的设计与计算 1)溢流装置
采用单溢流型的平顶弓形溢流堰、弓形降液管、平形受液盘,且不设进口内堰。 ①溢流堰长(出口堰长)lw
取lw?0.7D?0.7?1.6?1.12m
堰上溢流强度Lh/lw?31.82/1.12?28.41m/?m?h??100~130m/?m?h?,满足筛
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板塔的堰上溢流强度要求。 ②出口堰高hw
hw?hL?how
对平直堰how?0.00284E?Lh/lw?2/3
2.5由lw/D?0.7及Lh/lw ?31.82/1.122.5?23.97,查化工原理图得E?1.08,于是:
how?0.00284?1.08?31.82/1.12?2/3?0.0286m?0.006m(满足要求)
hw?hL?how?0.06?0.0286?0.0314m
③降液管的宽度Wd和降液管的面积Af
由lw/D?0.7,查化原下P147图11-16得Wd/D?0.14,Af/AT?0.09,即:
Wd?0.224m,AT?0.785D2?2.01m2,Af?0.181m2。
液体在降液管内的停留时间
??AfHT/Ls?0.181?0.5/0.00884?10.24s?5s(满足要求)
④降液管的底隙高度ho
液体通过降液管底隙的流速一般为0.07~0.25m/s,取液体通过降液管底隙的流速
??0.08m/s,则有: uoho?Ls0.00884??0.0987m(ho不宜小于0.02~0.025m,本结果满足要求) ?1.12?0.08lwuo2)塔板布置
①边缘区宽度Wc与安定区宽度Ws
与精馏段同,即Wc?60mm,Ws?100mm ②开孔区面积
与精馏段同,即Aa?1.304m 3)开孔数n和开孔率υ
亦与精馏段同,即n?6711孔
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每层塔板的开孔率υ?0.907?t/do?2?0.907?0.101(υ应在5~15%,故满足要求) 23每层塔板的开孔面积Ao??Aa?0.101?1.304?0.132m2 气体通过筛孔的孔速uo?Vs/Ao?1.821/0.132?13.80m/s 4)提馏段的塔高Z2
Z2??Np2?1?HT??14?1??0.5?6.5m
(四)塔板上的流体力学验算 1.气体通过筛板压降hp和Δpp的验算
hp?hc?hl?hσ
1)气体通过干板的压降hc
?u???13.80?3.488hc?0.051?o?V?0.051??0.0570m ?C?0.8929.2???o?L式中孔流系数Co由do/δ?5/3?1.67查图得出,Co?0.8 2)气体通过板上液层的压降hl
22hl?β?hw?how??βhL?0.6?0.06?0.036m
式中充气系数β的求取如下:
气体通过有效流通截面积的气速ua,对单流型塔板有:
ua?Vs1.821??0.996m/s
AT?Af2.01?0.181动能因子Fa?ua?V?0.9963.488?1.860
查化原图11-12得β?0.60(一般可近似取β?0.5~0.6)。 3)气体克服液体表面张力产生的压降hσ
4?4?20.90?10?3h????0.00183m
?Lgdo929.2?9.81?0.005- 25 -