Simulation and experimental analysis of spray flash regeneration characteristics of CaCl2 solution

doi:10.11949/j.issn.0438-1157.20181274

Abstract

Abstract:

The flue gas emitted by coal-fired power plants contains a large amount of water vapor, and the calcium chloride solution circulating dehumidification technology has a good dehumidification potential. To study the regeneration performance of the CaCl₂ solution after dehumidification, the droplet flashing process was numerically simulated by using Matlab software, and a test bench on regeneration of CaCl₂ solution by spray flash evaporation was set up. The effects of flash pressure, initial solution temperature, concentration, and solution flow rate on the regeneration of CaCl₂ solution were investigated. The results showed the accuracy of the mathematical model. The difference between vapor pressure on the solution surface and the regeneration pressure and the superheat of the solution are the key factors affecting the regeneration efficiency. The concentration of Cl^- in the condensed water after flashing is less than 0.2 mg/L. CaCl₂ solution with a concentration of 35%, a regeneration temperature of 60℃, a regeneration pressure of 10 kPa, and a flow rate of 0.2 m³/h will has a rate of more than 5 kg/h water recovery quality.

Key words: flash-evaporation, regeneration, numerical simulation, solution dehumidification

摘要：

燃煤电厂排放的烟气中含有大量水蒸气，氯化钙溶液循环除湿技术具有较好的除湿潜力。为了研究吸湿后的氯化钙溶液的再生性能，使用Matlab软件对液滴闪蒸过程进行了数值模拟，并搭建了氯化钙溶液喷雾闪蒸试验台。考察了闪蒸压力，溶液初始温度、浓度、溶液流量等因素对氯化钙溶液再生量的影响。试验结果表明了数学模型的准确性；溶液表面蒸气压和再生压力的差值以及溶液过热度是影响再生量的关键因素；闪蒸出口水蒸气经冷凝后Cl^–含量不足0.2 mg/L。浓度为35%的溶液在再生温度为60℃、再生压力为10 kPa、流量为0.2 m³/h的情况下，可以实现5 kg/h以上的水分回收量。

关键词: 闪蒸, 再生, 数值模拟, 溶液除湿

CLC Number:

TK 124

Hao ZHANG, Kai SHEN, Yanhua LAI, Lin CUI, Yong DONG. Simulation and experimental analysis of spray flash regeneration characteristics of CaCl₂ solution[J]. CIESC Journal, 2019, 70(6): 2269-2278.

张昊, 申凯, 赖艳华, 崔琳, 董勇. 氯化钙溶液喷雾闪蒸再生特性模拟及试验分析[J]. 化工学报, 2019, 70(6): 2269-2278.

Figures/Tables 23

Fig.1 Three-phase diagram

Fig.2 Schematic diagram of CaCl2 droplet evaporation model

Fig.3 Simulation process of CaCl2 droplet flash evaporation

Table 1 Main parameters of simulation

Parameter Value
initial droplet temperature T ₀/K	333.15—343.15
initial droplet concentration x ₀/%	30—40
initial droplet diameter D _s(0) /mm	1
flash evaporation pressure P _∞/kPa	5—15
initial environmental temperature T _∞/K	293.15

Fig.4 Variation of droplet temperature with time at different initial temperatures

Fig.5 Variation of droplet diameter with time at different initial temperatures

Fig.6 Variation of evaporation efficiency with time at different initial temperatures

Fig.7 Variation of droplet temperature with time at different initial concentration

Fig.8 Variation of droplet diameter with time at different initial concentration

Fig.9 Variation of evaporation efficiency with time at different initial concentration

Fig.10 Variation of droplet temperature with time at different evaporation pressure

Fig.11 Variation of droplet diameter with time at different evaporation pressure

Fig.12 Variation of evaporation efficiency with time at different evaporation pressure

Fig.13 Experiment system of CaCl2 solution regeneration in flash evaporation

Table 2 Test instruments of experimental system

Experimental parameters	Instrument	Range	Precision
temperature	PT100 temperature sensor	0—150℃	0.1℃
pressure	MIK-P300 pressure sensor	0—20 kPa	0.5%
solution flow	LWGY-MK-DN6 turbine flowmeter	0.1—0.6 m³/h	±1%
solution density[border:border-bottom:solid;]	densitometer[border:border-bottom:solid;]	1200—1300 kg/m³ 1300—1400 kg/m³ 1400—1500 kg/m³	1 kg/m³[border:border-bottom:solid;]

Fig.14 Variation of evaporation quantity at different solution temperatures

Fig.15 Variation of evaporation quantity at different solution concentrations

Fig.16 Variation of evaporation quantity at different evaporation pressures

Fig.17 Variation of evaporation quantity at different soluion degree of superheat

Fig.18 Experimental and simulated evaporation efficiency at different solution temperatures

Fig.19 Experimental and simulated evaporation efficiency at different solution concentrations

Fig.20 Experimental and simulated evaporation efficiency at different evaporation pressures

Table 3 Cl- concentration under different experimental conditions

Solution temperation/K	Solution concentration/%	Cl^- concentration/ (mg/L)
59.86	0.285	0.142
60.69	0.345	0.156
61.10	0.409	0.175
64.57	0.351	0.163
69.24	0.347	0.165

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Simulation and experimental analysis of spray flash regeneration characteristics of CaCl₂ solution

氯化钙溶液喷雾闪蒸再生特性模拟及试验分析

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References 31

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