乙醇-水连续精馏装置的工艺设计

《化工原理课程设计》报告

48000吨/年乙醇~水 精馏装置设计

年级 专业 设计者姓名 设计单位

完成日期

年 月 日

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目 录 一、概述 ·············································································································· 4 1.1 设计依据 ································································································ 4 1.2 技术来源 ································································································ 4 1.3 设计任务及要求 ····················································································· 5 二：计算过程 ······································································································· 6 1. 塔型选择 ·································································································· 6 2. 操作条件的确定 ······················································································· 6 2.1 操作压力 ························································································· 6 2.2 进料状态 ························································································· 6 2.3 加热方式 ························································································· 7 2.4 热能利用 ························································································· 7 3. 有关的工艺计算 ······················································································· 7 3.1 最小回流比及操作回流比的确定 ··················································· 8 3.2 塔顶产品产量、釜残液量及加热蒸汽量的计算 ···························· 9 3.3 全凝器冷凝介质的消耗量 ······························································ 9 3.4 热能利用 ······················································································· 10 3.5 理论塔板层数的确定 ···································································· 10 3.6 全塔效率的估算 ··········································································· 11 3.7 实际塔板数NP············································································· 12 4. 精馏塔主题尺寸的计算 ·········································································· 12 4.1 精馏段与提馏段的体积流量 ························································ 12 4.1.1 精馏段 ················································································ 12 4.1.2 提馏段 ················································································ 14 4.2 塔径的计算 ··················································································· 15 4.3 塔高的计算 ··················································································· 17 5. 塔板结构尺寸的确定 ············································································· 18 5.1 塔板尺寸 ······················································································· 18 5.2 弓形降液管 ··················································································· 18 5.2.1 堰高 ···················································································· 19 5.2.2 降液管底隙高度h0 ····························································· 19 5.2.3 进口堰高和受液盘 ····························································· 19 5.3 浮阀数目及排列 ··········································································· 19

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5.3.1 浮阀数目 ············································································ 20 5.3.2 排列 ···················································································· 20 5.3.3 校核 ···················································································· 21 6. 流体力学验算 ························································································· 21 6.1 气体通过浮阀塔板的压力降(单板压降)hp ·································· 21 6.1.1 干板阻力hc ········································································ 21 6.1.2 板上充气液层阻力h1 ························································· 22 6.1.3 由表面张力引起的阻力h················································· 22 6.2 漏液验算 ······················································································· 22 6.3 液泛验算 ······················································································· 22 6.4 雾沫夹带验算 ··············································································· 23 7. 操作性能负荷图 ····················································································· 23 7.1 雾沫夹带上限线 ··········································································· 23 7.2 液泛线 ··························································································· 24 7.3 液体负荷上限线 ··········································································· 24 7.4 漏液线 ··························································································· 24 7.5 液相负荷下限线 ··········································································· 25 7.6 操作性能负荷图 ··········································································· 25 8. 各接管尺寸的确定 ················································································· 27 8.1 进料管 ··························································································· 27 8.2 釜残液出料管 ··············································································· 27 8.3 回流液管 ······················································································· 28 8.4 塔顶上升蒸汽管 ··········································································· 28 8.5 水蒸汽进口管 ··············································································· 29 3

一、概述 乙醇~水是工业上最常见的溶剂，也是非常重要的化工原料之一，是无色、无毒、无致癌性、污染性和腐蚀性小的液体混合物。因其良好的理化性能，而被广泛地应用于化工、日化、医药等行业。近些年来，由于燃料价格的上涨，乙醇燃料越来越有取代传统燃料的趋势，且已在郑州、济南等地的公交、出租车行业内被采用。山东业已推出了推广燃料乙醇的法规。 长期以来，乙醇多以蒸馏法生产，但是由于乙醇~水体系有共沸现象，普通的精馏对于得到高纯度的乙醇来说产量不好。但是由于常用的多为其水溶液，因此，研究和改进乙醇`水体系的精馏设备是非常重要的。 塔设备是最常采用的精馏装置，无论是填料塔还是板式塔都在化工生产过程中得到了广泛的应用，在此我们作板式塔的设计以熟悉单元操作设备的设计流程和应注意的事项是非常必要的。 1.1 设计依据 本设计依据于教科书的设计实例，对所提出的题目进行分析并做出理论计算。 1.2 技术来源 目前，精馏塔的设计方法以严格计算为主，也有一些简化的模型，但是严格计算法对于连续精馏塔是最常采用的，我们此次所做的计算也采用严格计算法。

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1.3 设计任务及要求 原料：乙醇~水溶液，年产量48000吨 乙醇含量：35%(质量分数)，原料液温度：45℃ 设计要求：塔顶的乙醇含量不小于90%(质量分数) 塔底的乙醇含量不大于0.5%(质量分数) 表1 乙醇~水溶液体系的平衡数据 液相中乙醇的汽相中乙醇的液相中乙醇的汽相中乙醇的含量(摩尔分数) 含量(摩尔分数) 含量(摩尔分数) 含量(摩尔分数) 0.0 0.0 0.40 0.614 0.004 0.053 0.45 0.635 0.01 0.11 0.50 0.657 0.02 0.175 0.55 0.678 0.04 0.273 0.60 0.698 0.06 0.34 0.65 0.725 0.08 0.392 0.70 0.755 0.10 0.43 0.75 0.785 0.14 0.482 0.80 0.82 0.18 0.513 0.85 0.855 0.20 0.525 0.894 0.894 0.25 0.551 0.90 0.898 0.30 0.575 0.95 0.942 0.35 0.595 1.0 1.0 5

二：计算过程 1. 塔型选择 根据生产任务，若按年工作日300天，每天开动设备24小时计算，产品流量为6667kg/h，由于产品粘度较小，流量较大，为减少造价，降低生产过程中压降和塔板液面落差的影响，提高生产效率，选用浮阀塔。 2. 操作条件的确定 2.1 操作压力 由于乙醇~水体系对温度的依赖性不强，常压下为液态，为降低塔的操作费用，操作压力选为常压 其中塔顶压力为1.01325105Pa 塔底压力[1.01325105N(265~530)]Pa 2.2 进料状态 虽然进料方式有多种，但是饱和液体进料时进料温度不受季节、气温变化和前段工序波动的影响，塔的操作比较容易控制；此外，饱和液体进料时精馏段和提馏段的塔径相同，无论是设计计算还是实际加工制造这样的精馏塔都比较容易，为此，本次设计中采取饱和液体进料 6

2.3 加热方式 精馏塔的设计中多在塔底加一个再沸器以采用间接蒸汽加热以保证塔内有足够的热量供应；由于乙醇~水体系中，乙醇是轻组分，水由塔底排出，且水的比热较大，故可采用直接水蒸气加热，这时只需在塔底安装一个鼓泡管，于是可省去一个再沸器，并且可以利用压力较底的蒸汽进行加热，无论是设备费用还是操作费用都可以降低。 2.4 热能利用 精馏过程的原理是多次部分冷凝和多次部分汽化。因此热效率较低，通常进入再沸器的能量只有5%左右可以被有效利用。虽然塔顶蒸汽冷凝可以放出大量热量，但是由于其位能较低，不可能直接用作为塔底的热源。为此，我们拟采用塔釜残液对原料液进行加热。 3. 有关的工艺计算 由于精馏过程的计算均以摩尔分数为准，需先把设计要求中的质量分数转化为摩尔分数。 原料液的摩尔组成： x3CH2OHfnCHnCH3CH2OHn35/46H2O35/4665/180.1740 同理可求得：xD0.7790,xW0.0002 原料液的平均摩尔质量： MfxfMCH3CH2OH(1xf)MH2O0.174460.826)1822.3kg/kmol 7

同理可求得：MD39.81kg/kmol,MW18.1kg/kmol 45℃下，原料液中H2O971.1kg/m3,CH3CH2OH735kg/m3 由此可查得原料液，塔顶和塔底混合物的沸点，以上计算结果见表2。 表2 原料液、馏出液与釜残液的流量与温度 名称 原料液 馏出液 釜残液 xf/% 35 90 0.5 xf(摩尔分数) 0.1740 0.7790 0.0002 摩尔质量kg/kmol 22.3 39.81 18.1 沸点温度t/℃ 83.83 78.62 99.38 3.1 最小回流比及操作回流比的确定 由于是泡点进料，xqxf0.174，过点e(0.174,0.174)做直线x0.174交平衡线于点d，由点d可读得yq0.516，因此： Rdyq0.7790.516min(1)xy0.769 qxq0.5160.174又过点a(0.779,0.779)作平衡线的切线，切点为g，读得其坐标为xq'0.55,yq'0.678，因此： RDyq'0.7790.678min(2)xyq'xq'0.6780.550.789 8

所以，RminRmin(2)0.789 可取操作回流比R1(R/Rmin1.27) 3.2 塔顶产品产量、釜残液量及加热蒸汽量的计算 以年工作日为300天，每天开车24小时计，进料量为： F480001033002422.3299kmol/h 由全塔的物料衡算方程可写出： V0FDW y00(蒸汽) D65.85kmol/h V0y0FxfDxDWxW W364.85kmol/h WL'LqFRDqF q1(泡点) V0131.7kmol/h 3.3 全凝器冷凝介质的消耗量 塔顶全凝器的热负荷：QC(R1)D(IVDILD) 可以查得IVD1266kJ/kg,ILD253.9kJ/kg，所以 QC(11)65.8539.81(1266253.9)5.306106kJ/h 取水为冷凝介质，其进出冷凝器的温度分别为25℃和35℃则 平均温度下的比热cpc4.174kJ/kgºC，于是冷凝水用量可求： 6WQCCc5.30610pc(t2t1)4.174(3525)127120kg/h 9

3.4 热能利用 以釜残液对预热原料液，则将原料加热至泡点所需的热量Qf可记为：QfWfcpf(tf2tf1) 其中t45fm83.83264.4ºC 在进出预热器的平均温度以及tfm64.4ºC的情况下可以查得比热cpf4.275kJ/kgºC，所以， 3Q4800010f300244.275(83.8345)1.107106kJ/h 釜残液放出的热量QwWwcpw(tw1tw2) 若将釜残液温度降至t2w55ºC 那么平均温度t55wm99.38277.2ºC 其比热为cpw4.191kJ/kgºC，因此， Qw364.854.191(99.3855)1.228106kJ/h 可知，QwQf，于是理论上可以用釜残液加热原料液至泡点 3.5 理论塔板层数的确定 精馏段操作线方程： yRn1R1xnxDR10.5xn0.39 提馏段操作线方程：

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WWyn1Vxm2.77xm0.0054 0Vxw0q线方程：x0.174 在y~x相图中分别画出上述直线，利用图解法可以求出 NT18块(含塔釜) 其中，精馏段13块，提馏段5块。 3.6 全塔效率的估算 用奥康奈尔法(O'conenell)对全塔效率进行估算： 由相平衡方程式yx1(1)x可得y(x1)x(y1) 根据乙醇~水体系的相平衡数据可以查得： y1xD0.779 x10.741(塔顶第一块板) yf0.516 xf0.174(加料板) xw0.002 yw0.026(塔釜) 因此可以求得： 11.232,f5.06,w13.32 全塔的相对平均挥发度： m31fw31.2325.0613.324.36 全塔的平均温度： ttDtftW78.6283.8399.38m3387.30ºC

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在温度tm下查得H2O0.327mPas,CH3CH2OH0.38mPas 因为LxiLi 所以，Lf0.1740.38(10.174)0.3270.336mPas 全塔液体的平均粘度： Lm(LfLDLW)/3(0.3270.380.327)/30.344mPas 全塔效率ET0.49(0.245L)0.491(4.360.344)0.24545% 3.7 实际塔板数NP NPNT/ET18/0.4540块(含塔釜) 其中，精馏段的塔板数为：13/0.4529块 4. 精馏塔主题尺寸的计算 4.1 精馏段与提馏段的体积流量 4.1.1 精馏段 整理精馏段的已知数据列于表3(见下页)，由表中数据可知： 液相平均摩尔质量：MMfM122.338.72230kg/kmol 液相平均温度：ttftD78.62m283.83281.2ºC

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表3 精馏段的已知数据 位置 进料板 塔顶(第一块板) x'f0.35 y1'xD'0.9 质量分数 y'f0.732 x1'0.885 xf0.174 y1xD0.779 摩尔分数 yf0.516 x10.41 MLf22.3 MLf38.7 摩尔质量/kg/kmol MVf32.45 MVl39.81 温度/℃ 83.83 78.62 在平均温度下查得H2O971.1kg/m3,CH3CH2OH735kg/m3 液相平均密度为： 1'xLmx'Lm1 LmCH3CH2OHH2O其中，平均质量分数x'0.350.885Lm20.603 所以，Lm814kg/m3 精馏段的液相负荷LRD65.85kmol/h LM303nL65.858142.43m/h Lm同理可计算出精馏段的汽相负荷。 13

精馏段的负荷列于表4。 表4 精馏段的汽液相负荷 名称 汽相 液相 平均摩尔质量/kg/kmol 30 36.13 平均密度/kg/m3 814 1.251 体积流量/m3/h 2.43(0.000625m3/s) 3804(1.056m3/s) 4.1.2 提馏段 整理提馏段的已知数据列于表5，采用与精馏段相同的计算方法可以得到提馏段的负荷，结果列于表6。 表5 提馏段的已知数据 位置 塔釜 进料板 x''W0.005 xf0.35 质量分数 y'W0.065 y'f0.732 xW0.002 xf0.174 摩尔分数 yW0.026 yf0.516 MLW18.1 MLf22.3 摩尔质量/kg/kmol MLV18.7 MVf32.45 温度/℃ 99.38 83.83 14

表6 提馏段的汽液相负荷 名称 液相 汽相 平均摩尔质量/kg/kmol 20.2 25.6 平均密度/kg/m3 911 0.816 体积流量/m3/h 8.09(0.00225m3/s) 4132(1.15m3/s) 4.2 塔径的计算 由于精馏段和提馏段的上升蒸汽量相差不大，为便于制造，我们取两段的塔径相等。有以上的计算结果可以知道： 汽塔的平均蒸汽流量： VSJVST)S(V21.0561.1521.103m3/s 汽塔的平均液相流量： L)0.002253S(LSJST20.00067520.00146m/s 汽塔的汽相平均密度： VT1.2510.816VVJ221.0335kg/m3 汽塔的液相平均密度： LJLT911L28142863kg/m3 塔径可以由下面的公式给出： D4VSu 15

由于适宜的空塔气速u(0.6~0.8)umax，因此，需先计算出最大允许气速umax。 uVmaxCL V取塔板间距HT0.4m，板上液层高度h160mm0.06m，那么分离空间： HTh10.40.060.34m 功能参数：(LSV)L0.001468630.0382 SV1.1031.0335从史密斯关联图查得：C200.073，由于CC20(20)0.2，需先求平均表面张力： 全塔平均温度TDTFTW83.8399.38376.2386.5ºC，在此温度下，乙醇的平均摩尔分数为0.7410.1740.00230.307，所以，液体的临界温度： TcxiTic0.307(273243)(10.307)(273342.2)609K 设计要求条件下乙醇~水溶液的表面张力126dyn/m2 平均塔温下乙醇~水溶液的表面张力可以由下面的式子计算： 2cT21.21.2(Tm1TmcT)，2[609(27386.5)1609(27325)]2619.95dyn/cm 所以： C0.073(19.920)0.20.073 16

uLVmaxC0.0738631.0335V1.03352.11m/s u0.72.111.476m/s D41.1031.4760.951m 根据塔径系列尺寸圆整为D1000mm 此时，精馏段的上升蒸汽速度为： u4VSJ41.056JD2121.345m/s 提馏段的上升蒸汽速度为： uT4VSTD21.464m/s 4.3 塔高的计算 塔的高度可以由下式计算： ZHP(N2S)HTSHTHFHW 已知实际塔板数为N40块，板间距HT0.4m由于料液较清洁，无需经常清洗，可取每隔8块板设一个人孔，则人孔的数目S为： S40814个 取人孔两板之间的间距HT0.6m，则塔顶空间HD1.2m，塔底空间HW2.5m，进料板空间高度HF0.5m，那么，全塔高度： Z1.2(4024)0.440.60.52.520.2m 17

5. 塔板结构尺寸的确定 5.1 塔板尺寸 由于塔径大于800mm，所以采用单溢流型分块式塔板。 取无效边缘区宽度WC40mm，破沫区宽度WS70mm， 查得lW705mm 弓形溢流管宽度Wd146mm 弓形降液管面积Af0.0706m2 Af/AT0.0706/0.78540.09 RD/2WC0.50.040.46m xD/2WdWS0.50.1460.070.284m 验算： 液体在精馏段降液管内的停留时间 JAfHTL0.07060.441.8s5s SJ0.000675液体在精馏段降液管内的停留时间 TAfHT0.07060.4LST0.0022512.6s5s 5.2 弓形降液管 18

5.2.1 堰高 采用平直堰，堰高hwh1how 取h160mm,how10mm，则hw601050mm 5.2.2 降液管底隙高度h0 若取精馏段取h015mm，提馏段取为25mm，那么液体通过降液管底隙时的流速为 精馏段： u'LSJ0l0.000675m/s wh00.70.0150.0643提馏段： u'0LSTl0.002250.129m/s wh00.70.025u'0的一般经验数值为0.07~0.25m/s 5.2.3 进口堰高和受液盘 本设计不设置进口堰高和受液盘 5.3 浮阀数目及排列 采用F1型重阀，重量为33g，孔径为39mm。 19

5.3.1 浮阀数目 浮阀数目N4VS20u 0气体通过阀孔时的速度uF0v 取动能因数F11，那么u1101.035510.82m/s，因此 N1.10340.039210.8286个 5.3.2 排列 由于采用分块式塔板，故采用等腰三角形叉排。若同一横排的阀孔中心距t75mm，那么相邻两排间的阀孔中心距t'计为： t'Aa计N tA2[xR2x2a180R2sin1xR] 2[0.2840.4620.28420.462sin10.2841800.46] =0.487m2t'0.487计860.07575.5mm 取t'80mm时画出的阀孔数目只有60个，不能满足要求，取t'65mm画出阀孔的排布图如图1所示，其中t75mm,t'65mm 图中，通道板上可排阀孔41个，弓形板可排阀孔24个，所以总

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阀孔数目为N4124289个 5.3.3 校核 气体通过阀孔时的实际速度：u4VS0d210.38m/s 0N实际动能因数：F010.381.033510.55(在9~12之间) 开孔率： 阀孔面积22塔截面积100%d0N4A100%(0.039)89T40.785413.5% 开孔率在10%~14之间，满足要求。 6. 流体力学验算 6.1 气体通过浮阀塔板的压力降(单板压降)hp 气体通过浮阀塔板的压力降(单板压降)hphch1h 6.1.1 干板阻力hc 浮阀由部分全开转为全部全开时的临界速度为uoc： uoc1.82573.1/1.825V73.1/1.033510.32m/s 因为uocuo10.38m/s 所以hu2010.382c5.34V2Lg5.341.033528639.810.0367m 21

6.1.2 板上充气液层阻力h1 取板上液层充气程度因数0.5，那么： h1hL0.50.060.03m 6.1.3 由表面张力引起的阻力h 由表面张力导致的阻力一般来说都比较小，所以一般情况下可以忽略，所以： hp0.03670.030.667m0.6678639.81564.7Pa 6.2 漏液验算 动能因数F05，相应的气相最小负荷VSmin为： VSmin24d0Nu0min 其中u0minFV5/1.03354.92m/s 所以V23Smin40.0390894.920.523m/s1.103m3/s 可见不会产生过量漏液。 6.3 液泛验算 溢流管内的清液层高度HdhphdhLh 其中，hp0.0667m,hL0.06m 22

所以，Hd0.6670.060.0030.1297m 为防止液泛，通常Hd(HThw)，取校正系数0.5，则有：(HThw)0.5(0.40.05)0.225m 可见，Hd(HThw)，即不会产生液泛。 6.4 雾沫夹带验算 VVSLSZL泛点率=L1.36VKC FAb查得物性系数K1.0，泛点负荷系数CF0.097 ZLD2Wd120.1460.708m AA0.07060.6442m2bT2Af0.78542 所以， 1.1031.0335泛点率=8631.03351.360.001460.70810.0970.644263.4%80% 可见，雾沫夹带在允许的范围之内 7. 操作性能负荷图 7.1 雾沫夹带上限线 取泛点率为80%代入泛点率计算式，有： 23

1.0335VVSZLVS0.8L1.36LSVKC8631.03351.360.708LSFAb0.0970.6442 整理可得雾沫夹带上限方程为： VS1.44427.8LS 7.2 液泛线 液泛线方程为aV22/3SbcL2SdLS 其中，a1.91105V21.911051.0335LN863860.0309 bHT(10)0.50.4(0.510.5)0.050.15 c0.153l220.15322192.4 wh00.7050.015d(1110)E(0.667)l2/3(10.5)1.020.6673.553 w0.7052代入上式化简后可得：V23S4.856.217L2S114.9L2/S 7.3 液体负荷上限线 取5s，那么 L0.07060.4SmaxAfHT550.00565m3/s 7.4 漏液线 24

取动能因数F05，以限定气体的最小负荷： V25Smin4d0N0.523m3/s V7.5 液相负荷下限线 取h的计算式：2.841.02[LSminow0.006m代入how1000l]2/30.006 w整理可得：LSmin2.1m3/h0.000584m3/s 7.6 操作性能负荷图 由以上各线的方程式，可画出图塔的操作性能负荷图。 根据生产任务规定的气液负荷，可知操作点P(0.00146，1.103)在正常的操作范围内。连接OP作出操作线，由图可知，该塔的雾沫夹带及液相负荷下限，即由漏液所控制。由图可读得： (VS)max1.65m3/s,(V3S)min0.57m/s 所以，塔的操作弹性为1.65/0.572.89 有关该浮阀塔的工艺设计计算结果汇总于表7

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表7 浮阀塔工艺设计计算结果 项目 数值与说明 备注 塔径D,m 1.0 板间距HT,m 0.4 塔板型式 单溢流弓形降液管 分块式塔板 空塔气速u,m/s 1.476 溢流堰长度lW,m 0.705 溢流堰高度hW,m 0.05 板上液层高度hL,m 0.01 降液管底隙高度h0,m 0.025 浮阀数N,个 89 等腰三角形叉排 阀孔气速u0,m/s 10.38 阀孔动能因数F0 5 临界阀孔气速u0c,m/s 10.32 孔心距t,m 0.075 同一横排的孔心距 排间距t',m 0.065 相临二横排的中心线距离 单板压降p,Pa 564.7 液体在降液管内的停留时间41.8 精馏段 ,s 12.6 提馏段 26

降液管内的清液高度Hd,m 0.1297 泛点率，% 63.4 气相负荷上限(VS)max 1.65 雾沫夹带控制 气相负荷下限(VS)min 0.57 漏夜控制 开孔率，% 13.5 操作弹性 2.89 8. 各接管尺寸的确定 8.1 进料管 进料体积流量VFM29922.33Sff911.37.32m/h0.00203m3/s f取适宜的输送速度uf2.0m/s，故 dif4VSfu40.0020320.036m 经圆整选取热轧无缝钢管(YB231-64)，规格：453mm 实际管内流速：u40.00203f0.03921.7m/s 8.2 釜残液出料管 釜残液的体积流量： VMw364.8518.1SWWm3/h0.00191m3/s w958.46.89取适宜的输送速度uW1.5m/s，则

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d计40.001911.50.04m 经圆整选取热轧无缝钢管(YB231-64)，规格：453mm 实际管内流速：u40.00194W0.03921.6m/s 8.3 回流液管 回流液体积流量 VLML66.8539.8133SL/s L7473.51m/h0.000975m利用液体的重力进行回流，取适宜的回流速度uL0.5m/s，那么 d40.000975计0.50.05m 经圆整选取热轧无缝钢管(YB231-64)，规格：573.5mm 实际管内流速：u40.00194W0.03921.6m/s 8.4 塔顶上升蒸汽管 塔顶上升蒸汽的体积流量： V1)65.8539.8133SV(11.3983750m/h1.042m/s 取适宜速度uV2.0m/s，那么 d1.042计4200.258m 经圆整选取热轧无缝钢管(YB231-64)，规格：2735mm

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41.042实际管内流速：uSV0.263219.2m/s 8.5 水蒸汽进口管 通入塔的水蒸气体积流量： V131.718SO0.5973971m3/h1.103m3/s 取适宜速度u02.5m/s，那么 d41.103计250.237m 经圆整选取热轧无缝钢管(YB231-64)，规格：2455mm 实际管内流速：u41.10300.235225.43m/s 参考资料： [1] 华东理工大学化工原理教研室编. 化工过程设备及设计. 广州：华南理工大学出版社. 1996.02 [2] 天津大学化工原理教研室编. 化工原理(下). 天津：天津大学出版社. 1999.04

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