乙醇精馏设计

目 录

设计说明书

一、设计项目背景····················································································································2 二、生产工艺流程····················································································································4 三、生产规模····························································································································5 四、物料衡算结果····················································································································5 五、能量衡算结果····················································································································5 六、设备选型····························································································································6

计算说明书

一、物料衡算····························································································································7 1、每小时生产能力的计算······································································································7 2、生产工艺流程示意图··········································································································7 3、各塔物料衡算······················································································································7 二、能量衡算····························································································································9 三、设备选型(冷凝器2的选型计算)··················································································10 1、水的定性温度····················································································································10 2、按热面积设定···················································································································· 11 3.传热系数···························································································································· 11

设计说明书

设计项目:乙醇精馏车间 产品名称:工业乙醇 产品规格:纯度95% 一、 设计项目背景: 1.乙醇的理化性质

乙醇又称酒精,分子式为CH3CH2OH,相对分子质量46.07。为无色透明、易燃易挥发的液体,有酒的气味和刺激性辛辣味,溶于水、甲醇、乙醚和氯仿,能溶解许多有机化合物和若干无机化合物,具有吸湿性,能与水形成共沸混合物,蒸气与空气形成爆炸性混合物,爆炸极限4.3%-19.0%(体积)。

无水乙醇相对密度0.7893(20/4℃),熔点-117.3℃,沸点78.32℃,折射率1.3614,闪点(闭杯)14℃。

工业乙醇(含乙醇95%)折射率1.3651,表面张力(20℃)22.8mN/m,粘度(20℃)1.41mPa·s,蒸气压(20℃)5.732kPa,比热容(23℃)2.58J/(g·℃),闪点12.8℃,相对密度0.816,沸点78.15℃,凝固点-114℃,自燃点793℃。

2.乙醇的用途

乙醇有相当广泛的用途,是重要的有机溶剂,广泛用于用于溶结树脂,制造涂料。医疗上常用75%(体积分数)的酒精做消毒剂,它可以渗入细菌体内,在一定浓度下能使蛋白质凝固变性而杀灭细菌。因不能杀灭芽孢和病毒,故不能直接用于手术器械的消毒,50%稀醇可用于预防褥瘊,25%~30%稀醇可擦浴,用于高热病人,使体温下降。

除用作燃料,制造饮料和香精外,乙醇也是一种重要的有机化工原料,如用于制造乙醛、乙二烯、乙胺、乙酸乙酯、乙酸、氯乙烷等等,并衍生出染料、涂料、香料、合成橡胶、洗涤剂、农药等产品的许多中间体,其制品多达300种以上,但目前乙醇作为化工产品中间体的用途正在逐步下降,许多产品例如乙醛、

乙酸、乙基乙醇已不再采用乙醇作原料而用其他原料代替。经过专门精制的乙醇也可用于制造饮料。与甲醇类似,乙醇可作能源使用,有的国家已开始单独用乙醇作汽车燃料或掺到汽油(10%以上)中使用以节约汽油

3.乙醇的制备方法

(1) 水合法

以乙烯和水为原料,通过加成反应制取。水合法分为间接水合法和直接水合法两种。

间接水合法也称硫酸酯法,反应分两步进行。先把95-98%的硫酸和50-60%的乙烯按2:1(重量比)在塔式反应器吸收反应,60-80℃、0.78-1.96MPa条件下生成硫酸酯。第二步是将硫酸酯在水解塔中,于80-100℃、0.2-0.29MPa压力下水解而得乙醇,同时生成副产物乙醚。

直接水合法即乙烯直接与水反应生成乙醇,反应一步完成,由乙烯和水在磷酸催化剂存在下高温加压水合制得。

CH2=CH2+H-OH−−−−−→CH3CH2OH

本法流程简单、腐蚀性小,不需特殊钢材,副产乙醚量少,但要求乙烯纯度高,耗电量大。

无论用发酵法或乙烯水合法,制得的乙醇通常都是乙醇和水的共沸物,即浓度为95%的工业乙醇。为获得无水乙醇,可用下列方法进一步脱水:

(1)用生石灰处理工业乙醇,使水转变成氢氧化钙,然后蒸出乙醇,再用金属

钠干燥,这是最老的方法。

(2)共沸精馏脱水是目前工业上常用的方法。 (3)用离子交换剂或分子筛脱水,然后再精馏。 (2)发酵法

发酵法制乙醇是在酿酒的基础上发展起来的,在相当长的历史时期内,曾是生产乙醇的唯一工业方法。发酵法的原料可以是含淀粉的农产品,如谷类、薯类或野生植物果实等;也可用制糖厂的废糖蜜;或者用含纤维素的木屑、植物茎秆等。这些物质经水洗、粉碎后,进行加压蒸煮,使淀粉糊化,再加入适量的水,

∆,加压,催化剂

冷却至60℃左右加入淀粉酶,使淀粉依次水解为麦芽糖和葡萄糖。然后加入酶母菌进行发酵制得乙醇。发酵液中乙醇的质量分数约为6%~10%,并含有其它一些有机杂质,经精馏可得95%的工业乙醇。

二、生产工艺流程:

(1)流程说明:

原料经换热器3由27℃加热到77℃,然后进入精馏塔Ⅰ;从精馏塔Ⅰ顶得到浓度为60%(wt%)的乙醇溶液;塔底液不含乙醇,釜液温度99℃,经换热器3用来加热进料;浓度为60%的乙醇溶液在加热气化 (泡点80℃) 后进入精馏塔Ⅱ,进一步分离为95%的工业乙醇和水。塔底加热介质均为饱和水蒸汽。两个塔均以3:1的回流比操作,回流液温均为泡点(塔Ⅰ为80℃,塔Ⅱ为78℃)。塔顶冷凝器和热交换器2的冷却水进口温度为27℃,出口水温为50℃。 (2)流程图:

乙醇精制车间流程图

三、生产规模:

年生产能力:5000吨/年。 年连续生产工作日:328天/年。

连续生产每小时产量:635.16千克/小时

四、物料衡算结果

五、能量衡算结果

六、设备选型

由计算说明书中的计算结果得到

K计-K选

K选

⨯100%=

761.3-621.0

⨯100%=22.6%属于10%~25%

621.0

则初选设备及格,故可选用: 管子尺寸(碳钢): Φ25⨯2.5 公称面积: 换热管长度: 壳管流通面积: 管子根数: 中心排管数: 管程数: 公称直径: 管外径:

管内径: 管子排列方法:

2

L=4.5m 1

=0.0198m2 n=126 12

Np=2(双层管) DN =0.45m d0=0.025m

di=0.02m 正三角形排列

s=43.5m s

计算说明书

一:物料衡算

1、

每小时生产能力的计算。

(1)、根据设计任务,乙醇的年生产能力为5000吨/年

(2)、全年365日,除去机械维修等,实际连续工作日为328天。 (3)、每昼夜24小时连续生产,则每小时生产能力为: q

5000⨯103kg/吨

=635.16kg/h 产量=

328天⨯24h

2. 生产工艺流程示意图:

乙醇精制车间流程图

3、各塔物料衡算

精馏塔I的进料液的量为qF, 1,进料时含10%乙醇的组成为x F, 1,而精馏塔I回流液的量为qL, 1,馏出液的量为qD, 1,馏出液含60%乙醇的组成为x D, 1,塔底流出液的量为qW, 1;进入精馏塔II的进料量为qF, 2,而精馏塔II回流液的量为qL, 2,馏出液的量为qD, 2,馏出液含95%乙醇的组成为x D, 2,塔底流出液的量为qW, 2

己知:x F, 1 = 0.10,x F, 2 = x D, 1= 0.60,x D, 2= 0.95,R = 3:1,t1 = 27℃,t2 = 5 0℃,

qD, 2

5000⨯103kg

==635.16kg/h 328d⨯24h

根据物料守衡,得

精馏塔Ⅱ qF, 2 x F, 2 = qD, 2 x D, 2

qF, 2 = qD, 2 + qW, 2qL, 2 = R×qD, 2

代入数据: qF, 2×60%=635.16×95%

qF, 2 =635.16 kg/h +qW, 2 qL, 2 =3×635.16 kg/h

得: qF, 2 =1005.67 kg/h=1.006 t/h

qW, 2 =370.51 kg/h=0.371 t/h

qL, 2 =1905.48 kg/h=1.905 t/h

精馏塔Ⅰ: qF, 1 x F, 1=qD, 1 x D, qD, 1=qF, 2 qF, 1=qD, 1+ qW, 1 xD, 1=x F, 2 qL, 1=R×qD, 1

代入数据得: qF, 1=6034.02 kg/h=6.034 t/h qW, 1=5028.35 kg/h=5.028 t/h

1

qL, 1=3×1005.67=3017.01 kg/h=3.017 t/h

(1)总进口谷物浆=635.16 kg/h×0.95×(0.1+0.1+0.8)/0.1=6034.02 kg/h=6.034 t/h

水 =6034.02 kg/h×0.80=4827.22 kg/h 乙 醇=6034.02 kg/h×0.10=603.40 kg/h 有机物=6034.02 kg/h×0.10=603.40 kg/h

(2)精馏塔1中馏出液中乙醇流量不变,还是为603.40 kg/h=0.603 t/h;

水的流量:603.40×0.40/0.60=402.27 kg/h =0.402 t/h

鉴残液中水的流量:4827.22-402.27= 4424.95 kg/h =4.425 t/h; 有机物的流量不变还为:603.40 kg/h =0.603 t/h

(3)精馏塔2中进口组成也就是精馏塔1的馏出液组分组成。 馏出液,即为产品量:635.16 kg/h=0.635 t/h,其中

水流量为635.16 kg/h×0.05=31.76 kg/h=0.032 t/h

鉴残液只含有水,其流量为:402.27-31.76=370.51 kg/h=0.370 t/h

二.能量衡算

原料液:Cp=0.96 kcal/kg⋅︒C; Cp,c=4.174 kcal/kg⋅︒C

1.冷凝器1

(1)乙醇有相变传热

Q1=4×q n,D1×γ=

80℃

4*1005.67kg/h*375.0kcal/kg*4.1868kJ/kcal

=1754.39kJ/s

3600s/h

(2)水的无相变传热

Q1=Wc,1Cp,c(t2-t1)

Wh,1=

Q11754.39kJ/s

==18.27kg/s

Cp,c(t2-t1)4.174kJ/kg⋅︒C⨯23︒C

2.冷凝器2

(1)乙醇有相变传热

Q2=4×q n,D2×γ

78℃

4*635.16kg/h*361.1kcal/kg*4.1868kJ/kcal==1066.97kJ/s

3600s/h

(2)水的无相变传热

Q2=Wc,2Cp,c(t2-t1)

Wh,2

Q21066.97kJ/s===11.109kg/s Cp,c(t2-t1)4.174kJ/kg⋅︒C⨯23︒C

三.设备选型(冷凝器2的选型计算)

1. 水的定性温度

12

tm =(27℃+50℃)=38.5℃

38.5℃的水的物理参数:

ρ=992.7kg/m3 Cp =4.174 kJ/kg·℃ λ=63.14×10-2W·m-1·K-1 μ=67.77×10-5Pa·s Pr=4.48

2. 按热面积设定

qv=Wh,2/ρ=11.109kg/s3=0.01119m/s 3992.7kg/m

△T1=78℃-27℃=51℃, △T2=78℃-50℃=28℃

∵△T2/△T1=0.55<2 ∴∆Tm=

取∆T1+∆T21=(51℃+28℃)=39.5℃ 22K1

选= 640.0W·m-2·K-1

根据Q=K选SΔtm

103J/kJ⨯1066.97kJ/s2S选=Q2/k选⋅∆tm==42.2m 640W/m2.︒C⨯39.5︒C

3. 传热系数

从>中查得与S选 相近的取S=43.5m2

得到的参数有:

公称直径:0.45m , 中心管数:12, 管长:4.5m , 管子总数:126 , 管程数:2 ,

管子尺寸(碳钢): Φ25⨯2.5, 管子排列方法:正三角形排列.

∴管内水流通的面积为:

2-3-3π12623.14⨯(25⨯10-2.5⨯2⨯10)1262s'=⨯m=⨯m=0.0198m2

42422

qv0.01119m3/su===0.565m/s 2s'0.0198m

0.02m⨯0.565m/s⨯992.7kg/m3

Re===16552.324 -5μ67.77⨯10Pa.sduρ

0.8n∵Nu=0.023Re⨯Pr且Nu=α.idi,水被加热:n=0.4 λ

∴管内的对流传热膜系数为:

11

63.14⨯10-2w⋅m-2k-1λ0.80.4iαi=0.023Re⨯Pr⨯=0.023⨯16552.324⨯4.48⨯=3137.623w/m2⋅︒C0.02mdi

而95%乙醇的参数如下: 0.80.4

λ=0.17w/m⋅K, ρ=766kg/m3, μ=0.00047Pa⋅s, nC=1.n

g=9.81N/kg, γ=361.1×4.1868×1000J/kg

∴管外的对流传热膜系数为:

gρ2λ3r1/4α0=0.725(2/3)nCdOμ∆t

⎛9.81N/kg⨯(766kg/m)2⨯(0.17W/m.K)3⨯361.1⨯4.1868⨯1000J/kg⎫⎪=0.725 2/3 ⎪(1.)⨯0.025m⨯0.00047Pa.s⨯∆t⎝⎭=3703.775∆t-1/41/4

设∆t=19.80℃

-1/4α0=3703.775⨯(19.8︒C)=1755.813W.m-2.K-1

污垢参数:

自来水,查得Rsi=1.72⨯10W/m⋅k

-42有机化合物气体,查得Rso=0.86⨯10W/m⋅k -42

管壁导热系数λ=50.0m2⋅︒C/W

管壁厚度b=0.0025m

d0d011bdo12.0⨯10-3⨯0.0250.0250.025-4=+RSO++Rsi+=+0.86⨯10++1.72⨯10-4⨯+0.025-0.02K0α0λdmdiαidi1755.8130.023137.623⨯0.0250⨯0.025In0.02

=1.314⨯10-3M.K.W-1

因此K0=761.3w/m2⋅︒C=K

而计 tO-tWt-t∆T=Wi=m 111+RSO+RSiαOαiKO

12

所以∆t计

1+0.86⨯10-4

1755.813=39.5 1761.3

计算得△t计=19.71℃

.80-19.∆t-∆t计⨯100%=⨯100%=0.45%

∴s选=43.5m2符合要求

K=Q/s1066.97*1000

选选⋅∆tm=43.5⨯39.5=621.0W/m2⋅︒C 而K计-K选

K⨯100%=761.3-621.0

0⨯100%=22.6% 选621.

K

所计的计-K选

K⨯100%在10%~25%內

∴K选亦乎合要求

13


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