Design and performance analysis of mechanical vapor recompression salt fractionation evaporation crystallization system

doi:10.16085/j.issn.1000-6613.2021-1619

Abstract

Abstract:

Multi-component high salinity wastewater treatment by salt fractionation crystallization technology can realize resource utilization of wastewater. The solubility of sodium sulfate and sodium chloride varies with temperature. To solve the above issue, mechanical vapor recompression(MVR) salt fractionation evaporation crystallization system was proposed. The proposed system was based on a falling film evaporator as a pre-evaporator, combined with two forced circulation evaporators, which can separate sodium sulfate and sodium chloride from wastewater by crystallization and recover condensate. After designing the specific process flow, mathematical model of the proposed system was established according to balance relationship of mass and energy and validated by experimental data. Taking mixed solution with sodium sulfate concentration of 5% and sodium chloride concentration of 8% at atmospheric pressure as an example, the model was calculated by Matlab software. A five-effect evaporation salt separation system was introduced as a contradistinction system. Based on energy and exergy analysis, the results showed that MVR salt fractionation evaporation crystallization system was much more energy-efficient. Its coefficient of performance (COP) was 93.5%, higher than that of the contradistinction system. Its unit energy consumption was 77.6%, lower than that of the contradistinction system. Meanwhile, MVR salt fractionation evaporation crystallization system had higher thermodynamic perfectibility. Its exergy efficiency was 70.4%, higher than that of the contradistinction system, and exergy loss was 33.6%, lower than that of the contradistinction system.

Key words: mechanical vapor recompression(MVR), salt fractionation, crystallization, waste water, mathematical modeling, energy consumption analysis, exergy analysis

摘要：

利用分质提盐蒸发结晶方法处理多组分高含盐废水，可实现废水的资源化利用。本文根据废水中硫酸钠和氯化钠的溶解度随温度的变化关系，提出了机械蒸汽再压缩（MVR）分质提盐蒸发结晶系统，以降膜蒸发器作为系统的预蒸发器，与两效强制循环蒸发器联用，同时对冷凝水加以回收，使废水中硫酸钠和氯化钠分别结晶。首先设计了系统的具体工艺流程，依据质量和能量平衡关系建立系统及其设备的数学模型并进行模型验证。随后对常压下硫酸钠质量分数为5%、氯化钠质量分数为8%的混合溶液蒸发结晶过程进行实例计算，并将其与传统五效蒸发分盐系统进行性能对比。综合能量分析与?分析结果表明，MVR分质提盐蒸发结晶系统的节能程度更高，同一工况下相较于传统五效蒸发分盐系统，效能系数（COP）提高了93.5%，单位能耗则降低了77.6%；?效率提高了70.4%，?损失则降低了33.6%，表明MVR分质提盐蒸发结晶系统在实现废水中硫酸钠和氯化钠结晶回收利用的同时系统热力学完善度和节能性更大。

关键词: 机械蒸汽再压缩, 分质提盐, 结晶, 废水, 数学模拟, 能量分析, ?分析

CLC Number:

X703

JIANG Hua, ZHANG Zihui, GONG Wuqi, CHANG Yueyong. Design and performance analysis of mechanical vapor recompression salt fractionation evaporation crystallization system[J]. Chemical Industry and Engineering Progress, 2022, 41(7): 3947-3956.

姜华, 张子惠, 宫武旗, 常越勇. MVR分质提盐蒸发结晶系统设计及性能分析[J]. 化工进展, 2022, 41(7): 3947-3956.

Figures/Tables 9

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参数	文献［33］数据	计算数据	误差/%
原料液温度/℃	40	40	—
进料流量/kg·h^-1	11500	11500	—
进料质量分数/%	16	16	—
出料质量分数/%	20	20	—
蒸发温度/℃	84.1	84.1	—
蒸发量/kg·h^-1	7718	7718	—
蒸发器传热温差/℃	5	5	—
压缩温升/℃	10.1	10.1	—
蒸发器总换热面积/m²	483.2	495.8	-2.6
蒸发器总换热量/kW	5224.5	5363.3	-2.7
压缩机总功率/kW	208.4	178.0	14.6
压缩机压比	1.5	1.47	2.0

参数	文献［33］数据	计算数据	误差/%
原料液温度/℃	40	40	—
进料流量/kg·h^-1	11500	11500	—
进料质量分数/%	16	16	—
出料质量分数/%	20	20	—
蒸发温度/℃	84.1	84.1	—
蒸发量/kg·h^-1	7718	7718	—
蒸发器传热温差/℃	5	5	—
压缩温升/℃	10.1	10.1	—
蒸发器总换热面积/m²	483.2	495.8	-2.6
蒸发器总换热量/kW	5224.5	5363.3	-2.7
压缩机总功率/kW	208.4	178.0	14.6
压缩机压比	1.5	1.47	2.0

设计工况	数值
硫酸钠进料质量分数w_a0/%	5
氯化钠进料质量分数w_b0/%	8
原料液量F₀/kg·h^-1	15900
蒸发量W/kg·h^-1	13500
一效降膜蒸发器蒸发温度（预蒸发）/℃	100
二效强制循环蒸发器蒸发温度（析出硫酸钠）/℃	100
三效强制循环蒸发器蒸发温度（析出氯化钠）/℃	60
压缩温升/℃	12

设计工况	数值
硫酸钠进料质量分数w_a0/%	5
氯化钠进料质量分数w_b0/%	8
原料液量F₀/kg·h^-1	15900
蒸发量W/kg·h^-1	13500
一效降膜蒸发器蒸发温度（预蒸发）/℃	100
二效强制循环蒸发器蒸发温度（析出硫酸钠）/℃	100
三效强制循环蒸发器蒸发温度（析出氯化钠）/℃	60
压缩温升/℃	12

系统管段编号	温度/℃	质量分数/%		流量/kg·h^-1	焓值/kJ·kg^-1	?值/kW	比?/kJ·kg^-1	介质类型
系统管段编号	温度/℃	硫酸钠	氯化钠	流量/kg·h^-1	焓值/kJ·kg^-1	?值/kW	比?/kJ·kg^-1	介质类型
1	25	5	8	15900	—	450.9	102.1	溶液
2	100	5	8	15900	—	496.0	112.3
3	101.1	12	19.2	6625	—	133.1	72.3
4	101.1	18	28.8	4416.7	—	84.4	68.8
5	—	—	—	795	—	3.1	13.9	晶体
6	101.1	—	35.1	3621.7	—	66.7	66.3	溶液
7	63.1	—	35.1	3621.7	—	46.8	46.5
8	63.1	—	35.1	4134.9	—	54.2	47.2
9	63.1	—	35.1	513.3	—	2.8	19.8
10	63.1	—	—	1605	—	21.8	48.8	晶浆
11	—	—	—	1091.7	—	19.0	62.7	晶体
12	112	—	—	12631.2	2697	1920.6	547.4	蒸汽
13	112	—	—	10202	2697	1551.3	547.4
14	112	—	—	2429.2	2697	369.4	547.4
15	101.1	—	—	10269	2679.6	1407.1	493.3
16	101.1	—	—	2445	2679.6	335.0	493.3
17	101.1	—	—	12631.2	2679.6	1730.8	493.3
18	139.4	—	—	12631.2	2750.6	1963.8	559.7
19	72	—	—	2218.3	2628.6	204.0	331.1
20	63.1	—	—	2218.3	2611.6	169.9	275.7
21	108.4	—	—	2218.3	2700.2	326.5	529.9
22	112	—	—	10202	469.8	127.5	45.0	凝水
23	112	—	—	2429.2	469.8	30.4	45.0
24	112	—	—	12631.2	469.8	157.9	45.0
25	21.8	—	—	12631.2	91.5	1.1	0.3
26	32.5	—	—	12631.2	136.2	3.9	1.1
27	72	—	—	2218.3	301.4	8.6	14.0
28	38.4	—	—	14849.5	160.9	29.7	7.2
29	38.4	—	—	331.4	160.9	0.7	7.2
30	38.4	—	—	267	160.9	0.5	7.2
31	38.4	—	—	64.4	160.9	0.1	7.2