Nukiyama and Tanasawa correlation is used to measure the mean size of droplet
The iodine removal efficiency for a non-submerged venturi scrubber is calculated from the following expression;
- 2.2 Model for Submerged Self-Priming Venturi Scrubber
The iodine removal efficiency in submerged selfpriming venturi scrubber depends on the droplets in venturi scrubber and bubbles produced in a venturi tank when gas leaves at the outlet of a venturi scrubber. The model for non-submerged venturi scrubber is used to calculate the iodine removal efficiency in droplet, and bubble. The diameter of the bubble is calculated from the following equation
where contact time is given as,
The mass transfer coefficient from bubbles to the surrounding liquid in the water bed is calculated from Equation 6, where Sherwood and Reynolds number is calculated as below,
The iodine removal efficiency for a submerged venturi scrubber in a venturi scrubber is calculated from the following expression;
The outlet concentration or escaped concentration from a venturi scrubber will be an inlet for the water bed. The removal efficiency calculated in the water bed is given as;
The total iodine removal efficiency for a submerged venturi scrubber is calculated from the following expression;
3. EXPERIMENTAL FACILITY
The schematic diagram of the experimental facility to study the iodine removal efficiency in a self-priming venturi scrubber is shown in
. The compressed gas from an air compressor is stored in an air tank. The gas is airfiltered. The gas flow rate is adjusted by a valve. The mass flow rate of gas is measured by a mass flow meter. The direction of gas flow in a venturi scrubber is against gravity. The aqueous solution is prepared by adding 0.5% (w/w) sodium hydroxide (NaOH) and 0.2% (w/w) sodium thiosulphate (Na
) in water. The venturi tank is filled with aqueous solution and is positioned at a certain height to create the requisite hydrostatic head effect. A constant liquid level in a venturi tank is maintained for each run. The liquid introduced into the scrubber is in the form of film. The leaving liquid at the outlet of a venturi scrubber is collected in the venturi tank and is recycled. In iodine injection devices, the iodine is kept in a constant temperature chamber and iodine gas is generated through a sublimation process. The sample of iodine gas is collected at sampling point S
(inlet concentration) and S
(outlet concentration). The concentration of iodine in the sample is measured by using a spectrophotometer. The mesh filter is installed at the downstream of a venturi tank to remove
Experimental setup for Iodine Removal Efficiency Facility for Self-priming Venturi Scrubber
the droplets from gas. When iodine gas I
reacts with NaOH and Na
, the following reaction takes place:
A self-priming venturi scrubber is operated at two different operating conditions: a non-submerged venturi scrubber, and a submerged venturi scrubber. The working of a non-submerged and a submerged venturi scrubber is presented in
. In a non-submerged condition, the venturi scrubber is not immersed in the venturi tank whereas in a submerged condition, the venturi scrubber is immersed in water. The liquid flow rate depends on the hydrostatic head of the venturi tank. If the level of water is higher in a venturi tank, the flow rate of liquid into a venturi scrubber is higher. The leaving water from the outlet is collected in venturi tank and is recirculated-submerged venturi scrubber, only droplets take part in iodine removal efficiency. However, in a submerged venturi scrubber, droplets and bubbles take part in iodine removal efficiency because at the outlet of a venturi scrubber, the droplets are collected in water above it but gas will escape in the form of bubbles.
4. RESULTS AND DISCUSSION
The absorption process is defined as the transfer of a gaseous component from the gas phase to a liquid phase. According to the two film theory, the mass transfer phenomenon has taken place at the gas liquid interface due to the concentration differences between gas and liquid phases
. The absorption process continues as long as
Venturi Scrubber operated at Non-Submerged and Submerged Venturi Scrubber Conditions
the concentration difference exists between liquid and gas phase. The absorption process can be enhanced by increasing the contact time between phases, greater interfacial contact area between phases, and by increasing the turbulence or good mixing of the phases
In this research work, the iodine removal efficiency in a self-priming venturi scrubber is analyzed. The iodine removal efficiency is operated at different gas and liquid volumetric flow rates. The concentration of NaOH and Na
in scrubbing water remains the same. According to the definition of a self-priming venturi scrubber, the injected liquid depends upon the pressure difference between the hydrostatic pressure of the liquid in the tank and the static pressure of the gas in a venturi scrubber
. If we increase the hydrostatic head in the tank, the volumetric flow rate of liquid increases. The liquid is injected into the throat section in the form of film. According to Bernoulli’s principle, the high gas velocity in a throat causes suction of liquid due to low pressure. The high gas kinetic energy scrubbed the aqueous solution into petite droplets. In the throat section, these tiny droplets accelerate while decelerating in the diffuser section.
- 4.1 Liquid Flow Rate
categorized the venturi scrubber into two types based upon the liquid supplied: forced feed, and self-priming. In the force feed method, the liquid is supplied through pumps so that liquid flow rate is independent of the gas flow rate. But, in a self-priming venturi scrubber, the liquid flow rate depends upon the gas flow rate. The liquid supplied into a self-priming venturi scrubber depends on the static pressure of gas at the throat and hydrostatic pressure of the liquid in the want tank. The liquid flow rate is analyzed at different gas flow rates.
depicts that with the increase of throat gas velocity liquid flow rate decreases. It is also observed that the increase of the hydrostatic head in the tank increases the flow rate of liquid.
- 4.2 Effect on Concentration due to Gas Flow Rate
depicts the relation between the gas flow rate and concentration. It the mass flow rate of injected iodine into the loop is fixed, the concentration of iodine is decreased in the venturi scrubber with the increase of gas flow rate.
- 4.3 Comparison between Non-Submerged and Submerged Venturi Scrubber
Iodine removal efficiency is investigated at nonsubmerged and submerged conditions with the single-unit venturi scrubber in a venturi tank which is as follow:
- 4.3.1 Non-Submerged Venturi Scrubber
In this case, the venturi tank is filled with water in such a way so that the venturi scrubber is not submerged in it. The volumetric flow rate is adjusted by adjusting the height above the liquid in the venturi tank. The liquid flow rate is less, as compared to the submerged venturi scrubber. The iodine gas is absorbed in droplets, which are formed in a venturi scrubber.
- 126.96.36.199 Effect of Gas Flow Rate
depicts the relationship between the iodine removal efficiency at different gas flow rates. It is observed that with the increase of the flow rate of gas, the iodine removal efficiency also increases. At higher gas flow rates, the kinetic energy of gas is higher which disintegrates the liquid into tiny droplets and increases the number of droplets. As a result, the interfacial area of droplets increases which causes the increase of mass transfer of iodine into droplets.
Effect of Liquid Flow Rate on Venturi Scrubber at Different Hydrostatic Head
Effect of Gas Flow Rate on Iodine Concentration in the Venturi Scrubber
Iodine Removal Efficiency for Non-submerged Venturi Scrubber
- 188.8.131.52 Effect of Inlet Concentration
gives the results of iodine removal efficiency at various gas flow rates for different inlet concentrations of I
. The inlet concentration of I
varies from 40 to 300
Removal Efficiency of Iodine at Different Iodine Inlet Concentration (mg/m3)
). The graph shows the increase in iodine removal efficiency with an increase of C
at same gas flow rate. On the other hand, the iodine removal efficiency is increased by an increase of flow rate.
- 4.3.2 Submerged Venturi Scrubber
In this case, the venturi tank is filled with water in such a way that the venturi scrubber is submerged in it. The volumetric flow rate is adjusted by adjusting the height of the liquid above the venturi scrubber in a venturi tank. The iodine gas has two chances to contact with the aqueous solution. The high kinetic energy of the gas disintegrates the liquid into droplets in the throat section. When the gas departs from the venturi scrubber, it passes through the water bed in the form of bubbles. Therefore, the gas interacts with the droplets first in the venturi scrubber and then interacts with the liquid in the form of bubbles through the water bed above the venturi scrubber.
- 184.108.40.206 Effect of Gas Flow Rate
illustrates the relationship between the iodine removal efficiency at different flow rates. It is observed that the iodine removal efficiency increases with the increase of gas flow rate, and it is higher than 0.995. The highest iodine removal efficiency of 0.999±0.001 is achieved. The removal efficiencies are higher as compare to a non-submerged venturi scrubber due to two reasons: firstly, increase of flow rate of liquid and secondly, interaction of gas in the form of bubbles with the surrounding liquid when passing through the water bed.
- 220.127.116.11 Effect of Inlet Concentration
provides the results of iodine removal efficiency at various gas flow rates for different inlet concentrations of I
. With the increase of iodine inlet concentration at the same gas flow rate, the iodine removal efficiencies are almost similar. It is due to the gas rises from the water bed in the form of bubbles. The iodine removal efficiencies increase with increasing gas flow rate.
Iodine Removal Efficiency for Submerged Venturi Scrubber
Iodine Removal Efficiency at Different Iodine Inlet Concentration (mg/m3)
Comparison of Iodine Removal Efficiency between Calculated and Experimental Results
- 4.4 Model Validation
shows that the theoretical model for a nonsubmerged venturi scrubber underpredicts the results, but the results obtained from the submerged venturi scrubber explain and satisfy the results well. The results were underpredicted because no liquid film on the walls had been supposed. As the Gamisans, the results indicate a considerable improvement in the predictions when the scrubbing effect of the liquid film travelling along the venturi tube walls is considered. Another reason is the partition coefficient effect, which is not considered in the model.
In this research, the iodine removal efficiency in a self-priming venturi scrubber is investigated. Liquid introduced into the scrubber is in the form of film. The aqueous solution is prepared by adding 0.5% sodium hydroxide (NaOH) and 0.2% sodium thiosulphate (Na
) in liquid. A self-priming venturi scrubber is operated with a non-submerged venturi scrubber and a submerged venturi scrubber. The following results are concluded from the present work;
1. The iodine removal efficiency of a venturi scrubber increases with the increase of gas flow rate and iodine inlet concentration.
2. A submerged venturi scrubber has higher iodine removal efficiency than the non-submerged venturi scrubber.
3. The highest iodine removal efficiency of 0.999 ±0.001 is attained in the submerged venturi scrubber.
4. The results from a theoretical model based on mass transfer concur well with the submerged venturi scrubber experimental results but underpredicts with non-submerged venturi scrubber.
C concentration (mg m-3)
C'concentration in water bed above venturi scrubber (mg m-3)
r radius (m)
t time (s)
k mass transfer coefficient (m-1)
V Volume (m3)
v velocity (m s-1)
Sh Sherwood number (dimensionless)
Re Reynolds number (dimensionless)
Sc Schmidt number (dimensionless)
d diameter (m)
D diffusion coefficient (m2s-1)
ρ density (kg m-3)
σ surface tension(N m-1)
Q volumetric flow rate (m3h-1)
μ viscosity (Ns m-2)
V' geometry volume (m3)
l length of water bed in venturi tank above the venturi scrubber (m)
N rate of absorption into droplet (kmol s-1)
re removal efficiency
m distribution parameter
The authors admiringly acknowledge the support ofthe present work from College of Nuclear Science andTechnology, Harbin Engineering University.
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