Study on thermodynamic analysis and energy saving of heat integrated distillation column

doi:10.16085/j.issn.1000-6613.2017-2594

Abstract

Abstract:

In this study, a method of using entropy to analyze the reversibility of internal thermal coupling column was proposed. Taking the ethanol water system as an example, it was proved that the energy saving of the thermal coupling column was superior to the traditional column, and the optimum operating range of the column was determined. Based on the second law of thermodynamics, the thermodynamic efficiency and the entropy increase formula of the thermal coupled column were deduced. Firstly, it was proved theoretically that the thermal coupling column was superior to the traditional column in terms of energy saving, and it was also calculated separately by the experimental data. The results showed that the operable compression ratio of the column was initially reduced to 1.8—2.6 in order to achieve better heat transfer between two columns, and the energy consumption of the overhead column was the smallest when the compression ratio was at 2.2. However, the thermal efficiency of the whole column was the highest when the range of compression ratio was 2.2—2.5. When the compression ratio is 2.5, the entropy increase of the whole column was also better than the average of the entire operating range. Thus, it was considered that the thermal coupling column had higher reversibility and better energy saving effect in this range. Taking the energy consumption, thermodynamic efficiency and entropy increase and other parameters into account, the compression ratio of 2.2 to 2.5 was the best operating range of the column.

Key words: distillation, heat integrated distillation column, thermodynamic analysis, energy-saving

摘要：

提出了一种运用熵法对内部热耦合塔可逆性进行分析的方法。以乙醇-水体系为例证明了热耦合塔相比于传统塔较优的节能优势，并确定了该塔的最佳操作范围。本文根据热力学第二定律，对热耦合塔的热力学效率以及熵增的公式进行推导，从理论上证明了热耦合塔在节能方面优于传统塔，又结合实验数据分别对其进行了详细计算。结果表明：为实现两塔段间较优的传热推动力，将该塔的可操作压缩比初步缩小到1.8~2.6；压缩比为2.2时塔顶塔釜能耗最低；压缩比为2.5时，全塔热力学效率最高；操作压缩比操作范围在2.2~2.5时，全塔的熵增优于全部操作范围内的平均值，认为在该范围内热耦合塔的可逆性更高，节能效果更优。综合考虑能耗、热力学效率及熵增等各项参数，压缩比2.2~2.5为该塔的最佳操作范围。

关键词: 蒸馏, 内部热耦合塔, 热力学分析, 节能

CLC Number:

TQ028.1

Jing FANG, Mengyu DIAO, Chunli LI, Bihan XUAN. Study on thermodynamic analysis and energy saving of heat integrated distillation column[J]. Chemical Industry and Engineering Progress, 2019, 38(02): 834-841.

方静, 刁梦宇, 李春利, 轩碧涵. 内部热耦合塔的热力学分析和节能研究[J]. 化工进展, 2019, 38(02): 834-841.

Figures/Tables 16

塔段

内径

/mm

壁厚

/mm

填料层

高度/mm

填料

类型

填料尺寸

/mm

填料

材质

参数	数值
进料质量组成(乙醇)/%	45
进料流量/L·h^-1	73
进料温度/℃	33
塔顶产品质量纯度(乙醇)/%	89.5
塔釜产品质量纯度(乙醇)/%	2.9
提馏段操作压力/atm	1
精馏段操作压力/atm	1.5～2.6（步长为0.1）

压缩比	冷凝水流量/L·h^-1	上水温度/℃	下水温度/℃
1.5	280	30	73
1.6	296	28	62
1.7	288	32	63
1.8	268	31	63
1.9	253	33	68
2.0	248	34	65
2.1	218	30	65
2.2	205	30	65
2.3	224	37	74
2.4	220	30	68
2.5	237	30	65
2.6	224	31	68

压缩比	蒸汽压力/MPa	蒸汽出口温度/℃	冷却水流量/L·h^-1
1.5	0.21	86.2	39.2
1.6	0.20	90.5	38.0
1.7	0.19	86.3	37.4
1.8	0.18	89.1	34.7
1.9	0.18	85	33.0
2.0	0.17	90	32.2
2.1	0.16	86.5	32.8
2.2	0.15	92.5	30.1
2.3	0.15	90.1	32.5
2.4	0.15	86.2	33.4
2.5	0.15	85.0	32.3
2.6	0.15	84.0	32.8

CDiC及压缩比	η/%	η _inc/%	ΔS/J·kg^-1·K^-1	ΔS _inc/%
CDiC	18.62	—	14.63	—
P _r/P _s=1.8	25.01	34.29	10.71	26.76
P _r/P _s=1.9	24.82	33.30	10.82	26.04
P _r/P _s=2.0	24.72	32.76	11.00	24.81
P _r/P _s=2.1	24.84	33.39	11.05	24.47
P _r/P _s=2.2	24.98	34.17	11.18	23.57
P _r/P _s=2.3	25.17	35.16	11.18	23.55
P _r/P _s=2.4	25.52	37.06	11.24	23.13
P _r/P _s=2.5	26.05	39.92	11.13	23.90
P _r/P _s=2.6	25.92	39.19	11.04	24.52

压缩比

冷凝器节能

分数/%

再沸器节能

分数/%

η/%

Δ

S_inc /%

压缩比

冷凝器节能

分数/%

再沸器节能

分数/%

η/%

Δ

S_inc /%

最佳操作

62.82

27.01

25.43

23.54

全部操作

62.25

25.36

25.23

24.53

a,b	——	待分离物系中不同组成
m ₁	——	冷却水的质量流量， kg/s
m ₂	——	蒸汽冷凝水的质量流量， kg/s
Q_i	——	对应测温点间的换热量， W
Q _c，Q _Reb	——	传统塔的冷凝器、再沸器热负荷， kW
Q _c，Q _Reb'	——	内部热耦合塔的冷凝器、再沸器热负荷，kW
r	——	水的汽化潜热， kJ/kg
S	——	熵值， J/(kg·K)
ΔS	——	熵增
ΔS _inc	——	熵增减少的百分比
T	——	定性温度， K
T ₀	——	环境温度， K
T _cw	——	冷却介质的温度， ℃
Δt′	——		蒸汽与冷凝水的温度差，℃
T _st	——	加热介质的温度， ℃
ΔT_i	——	对应测温点间的温差， ℃
η	——		热力学效率
η _inc	——		热力学效率增加的百分比

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