For unstable bubbles, foam usually disappears quickly at the early stage. As the foam disappears, a very thin bubble layer exists for a long time, though under certain conditions the bubble layer does not occur and the foam disappears. Two different types of foam extinction occur depending on the temperature change in the AMP aqueous solution, which is used for the CO2 absorbent. As the temperature increases from 20℃ to 65℃, we observed that all the bubbles disappear quickly.
The foam decreases linearly with time, and that the decay velocity, dL/dt, increases gradually within a range of 1.8 cm/s to 2.4 cm/s as the temperature increases. However, if the temperature is greater than 65℃, not all the foam disappears and the layer of stabilized foam remains. The foam no longer disappears linearly with time.
If the operating temperature increases, the gas in the foam expands, thereby promoting the extinction of the foam. Liquids that form a gelatinous surface layer at low temperature change into a structureless Newtonian fluid and the foam disappears as the temperature increases. However, for the AMP aqueous solution, preferably, not all the foam disappears and even the bubble layer remains for the entire temperature range. When the operating temperature increases, the energy barrier increases. The energy barrier disturbs the disappearance of the foam. For the AMP aqueous solution that was used in this experiment, the foam decay mechanism changed near 65℃.
when the operating temperature is below 65℃, the energy barrier has no effect. Therefore, the foam decay time decreases linearly. However, the foam decay velocity can no longer be linear as a result of the energy wall when the operating temperature is greater than 65℃. Below 65℃, the decay velocity ranges between 1.8 cm/s to 2.0 cm/s.
At a temperature greater than 65℃, the state of the straight line is no longer apparent. The value of E/τ, which is the ratio of the energy barrier and the reference time, is 0.1207.
Foamability or foaminess refers to the capability of bubbles forming under the same operating conditions and the meaning of foamability is the foam creation degree [19]. For the foamabilty measurement, we kept the gaseous flowrate at 21.26 cm/s and measured the innitial height of the foam under a fixed gas flux. The initial foam height was the maximum height of the bubbles created under the fixed operating conditions such as the velocity of the gas flow and the temperature.
The foamability increased as the operating temperature increased. When the DEA concentration was 10 wt%, the foamability reached the highest value. We assume this result is due to the change in the physical properties of the aqueous DEA solution, and the result implies that the initial height of the foam shows that the foamability depends on physical properties such as the density of the solution, the viscosity, and the surface tension of the aqueous DEA solution.
If the concentration of amine increases, the initial height of the foam increases to a maximum value and then decreases
As the density of mixture increases, the foam stability and foamability decreases. In the case of foam stability, if the density of the mixture increases, the drainage of the liquids that form the foam is accelerated by gravity. Therefore, the created foam is more easily broken down and becomes unstable. In the case of foamability, the gas and the liquid both flowed upward together and formed the bubbles. As density of the mixture increased, the effect of gravity increased. Therefore, the foam was difficult to create. The experimental results also show these phenomena. As the operating temperature increases, the density of the mixture decreases, and the foam stability of the mixture increases. Because the density of the mixture decreases as the concentration of the amine aqueous solution increases.The effect of density on foamability is less than the effect of viscosity or surface tension.
As the viscosity of the amine mixture increases, the foamability decreases. The injected gas and liquid flowed upward together and formed foam. However, with the increase in the viscosity of the aqueous amine solution, the rising of the gas flow became more difficult. That is, if we increased the viscosity of the mixture at a fixed gas velocity, the liquid resistance against the gas flow incereased. Therefore, the amount of liquid that rises with the gas decreases. From these results, we deduce that the foamability decreases with the increase in the viscosity of the mixture. As shown in experimental results, the viscosity of the aqeous amine solution decrease as the operating temperature increases. Moreover, as the concentration of the mixture increases, the viscosity of the aqueous amine solution increases.
Of all the physical properties, surface tension had the greatest influence on foamability. As the surface tension increases, the foam stability decreases. As the operating temperature increases, the surface tension of the aqueous amine solution decreases and the foamability increases. As the concentration of amine in the aqueous amine solution increases, the surface tension decreases and the foamability increases.
At a low amine concentration, the foamability increases as the amine concentration increases because of the decrease in the density and surface tension. However, as amine concentration increases, the effect of viscosity outweighs the effect of density and surface tension, and the foamability decreases.
1) foam stability
2-amino-2-methyl-1-propanol 수용액의 거품 안정화도는 조업 온도에 따라서 거품 소멸 기구가 변한다는 것을 실험을 통해서 알게 되었다. 실험온도가 65℃ 이하일 때에는 거품 소멸 속도는 측정 시간에 대해서 선형적으로 감소하며, 실험 온도가 증가 할수록 더 빠르게 소멸 된다. 그러나 실험 온도가 65℃ 이상일 때에는 모든 거품이 깨지지 않고 안정화된 거품 층이 오랜 시간을 두고 존재 하게 되며, 거품 소멸 속도 역시 도 측정 시간에 대해서 선형적인 모습을 보이지 않는다. 이렇게 실험 온도 증가에 따라서 안정화된 거품 층이 생성되는 이유로는 실험 온도 증가에 따라서 거품 소멸을 방해하는 에너지 장벽 값이 증가하기 때문이다. 이러한 에너지 장벽의 영향을 아래와 같이 나타낼 수 있다.
◁수식 삽입▷(원문을 참조하세요)
65℃ 이하의 조업온도에서는 1.8-2.0(cm/s)의 거품 소멸속도를 얻었고, 65℃ 이상의 조업온도에서 거품소멸을 방해하는 에너지장벽의 값을 얻었으며 그값은 (E/τ) 0.1207이 된다.
일정한 조업 조건하에서 발생될 수 있는 거품의 양을 나타내는 거품 생성도는 조업 온도와 아민 수용액상의 아민의 농도에 따라서 다른 값을 나타내는데, 거품 발생도에 영향을 미치는 물성으로는 밀도, 점도 그리고 표면장력 등이 있으며, 밀도 , 점도, 표면장력 등의 값이 증가 할수록 거품 생성도는 감소하게 된다.
2) foamability
일정한 조업 조건하에서 발생될 수 있는 거품의 양을 나타내는 거품 생성도는 조업 온도와 아민 수용액상의 아민의 농도에 따라서 다른 값을 나타내는데, 거품 발생도에 영향을 미치는 물성으로는 밀도, 점도 그리고 표면장력 등이 있으며, 밀도 , 점도, 표면장력 등의 값이 증가 할수록 거품 생성도는 감소하게 된다.
이러한 거품생성도는 점성력과 관성력을 나타내는 무차원수인 Reynolds number 와 Weber number의 곱으로 나타낼 수 있다.
◁수식 삽입▷(원문을 참조하세요)
위에서 나타낸 것처럼 무차원 foam height h/d는 Reynolds number와 Weber number 로 표현 할 수 있으며, AMP 수용액의 경우 실험 값으로 -4.12와 0.41을 얻었으며, 실험 상수 C는 $1.07 x 10^5$ 이다.
