Performance evaluation of venturi scrubber for the removal of iodine in filtered containment venting system

Accepted Manuscript Title: Performance Evaluation of Venturi Scrubber for the Removal of Iodine in Filtered Containment Venting System Authors: Manisha Bal, Thamatam Tejaswini Reddy, B.C. Meikap PII: DOI: Reference:

S0263-8762(18)30413-1 https://doi.org/10.1016/j.cherd.2018.08.019 CHERD 3313

To appear in: Received date: Revised date: Accepted date:

8-4-2018 14-6-2018 12-8-2018

Please cite this article as: Bal, Manisha, Reddy, Thamatam Tejaswini, Meikap, B.C., Performance Evaluation of Venturi Scrubber for the Removal of Iodine in Filtered Containment Venting System.Chemical Engineering Research and Design https://doi.org/10.1016/j.cherd.2018.08.019 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Performance Evaluation of Venturi Scrubber for the Removal of Iodine in Filtered Containment Venting System

Manisha Bala, Thamatam Tejaswini Reddya, B. C. Meikapa, b* a

Department of Chemical Engineering, Indian Institute of Technology (IIT) Kharagpur,

West Bengal-721302, India. Department of Chemical Engineering, School of Engineering, Howard College, University

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b

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of Kwazulu-Natal, Durban, South Africa

*Address correspondence to B. C. Meikap,

Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, India,

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Tel: +91-3222 283958; Fax: +91-3222 282250, E-mail: [email protected]

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Graphical abstract

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Highlights FCVS is used for nuclear safety purposes.



Present study deals with the removal of radiotoxic iodine using FCVS.



Efficiency increases with increase in gas velocity, liquid rate, iodine concentration.



Improvement of removal efficiency is done using KI as a scrubbing liquid.



Maximum % removal efficiency obtained from the system is 82.32%.

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

Abstract

Filtered containment venting system (FCVS) is an essential technology in nuclear power

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plants for the removal of iodine. A laboratory scale venturi scrubber has been designed,

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developed and fabricated.The maximum removal efficiency of iodine is obtained as 82.32% at 3×10-3 kmol/m3of KI solution, used as the scrubbing liquid for the throat gas velocity of

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18 m/s and liquid flow rate of 0.033 kg/s with iodine inlet concentration of 0.39 kg/m3. A

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semi-empirical model has been developed to predict the removal efficiency of iodine scrubbing using the experimental results and the variables which show the impact on the

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scrubber performance.

Keywords: Scrubbing; Iodine removal; Nuclear safety; FCVS; Venturi scrubber; Pollution

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control.

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Nomenclature FCVS

Filtered containment venting system

KI

Potassium iodide

Go

Gas flow rate (Nm3/s)

2

Liquid flow rate (m3/s)

ug

Relative velocity (cm/s)

Vth

Throat velocity (m/s)

dd

Sauter mean droplet size (SMD; m)

dth

Diameter of the throat (m)

hth

Length of the throat (m)

mL

Liquid mass flow rate (kg/s)

CI2_i

Inlet concentration of iodine (kg/m3)

CI2_o

Outlet concentration of iodine (kg/m3)

CKI

Initial KI concentration (kg/m3)

CI2,Int

Interfacial I2concentration, (ppm)

𝜂iodine eff

Experimental removal efficiency of iodine (%)

ȠI2-KI

Predicted Removal efficiency of iodine with KI as scrubbing liquid(%)

Ƞi2-H2O

Predicted Removal efficiency of iodine with water as scrubbing liquid(%)

µl

Viscosity of liquid (Pa-s)

µg

Viscosity of gas (Pa-s)

DI2

Diffusivity of iodine in water (m2/s)

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Diffusivity of KI in water (m2/s)

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DKI

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Ql

Density of liquid (kg/m3)

ρg

Density of gas (kg/m3)

σ

Surface tension of gas-water interface (N/m)

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ρl

Reg

Reynolds number of gas at the throat

Sc

Schmidt number of the gas

We

Weber number of the gas

i

Mole ratio of I2 component and reagent (KI),dimensionless 3

1. Introduction When a severe accident takes place in a nuclear power plant, the core melts and fission reaction goes out of control, building up pressure in the reactor, releasing fission products with I-131 as one of the major radiotoxic constituent along with Cesium 137 (Hirao et al.,

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2013; Hoevea and Jacobson. 2012). These fission products are highly radioactive and when

released into atmosphere cause adverse effects to environment and human health (Holt et al.,

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2012). Radioactive I-131 which has a half-life of 8 days when inhaled or absorbed from

contaminated air, water or milk cause thyroid cancer in human body (Ravichandran et

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al.,2014). This necessitates the retainment of aerosols and iodine vapours produced in the

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event of core meltdown from the radioactive exhaust gas. Filtered Containment Venting

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System (FCVS) has been suggested to handle severe accidents in NPP (Song et al., 2013). It

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mainly comprises of a venturi scrubber and metallic fibre filter. Although many designs of filtered containment venting system have been reported (OECD report, 2014), improvements

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are needed to prevent the releases of fission products into the environment in a nuclear accident. Therefore, performance of the venturi scrubber should be increased to secure the

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human life.

The gaseous pollutant removal process in a venturi scrubber is its absorption from the

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gaseous stream to a liquid stream. Some of the advantages of venturi scrubber which enhances its worth and importance is: it is relatively simple, has no rotating part, easy to

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install and maintain, occupies less space, has compact volume, can handle high-temperature and corrosive gases (Kurella et al., 2017).One of the major advantages of venturi scrubber is that it provides gas absorption and dust collection in a single unit. It effectively removes dust particles of diameter ranging between 0.1 and 300 µm and gaseous pollutants simultaneously. Venturi scrubber consists of 3 sections: a) converging section b) throat section c) diffuser.

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The inlet of the pollutants is through the converging section and outlet of water containing washed away suspended particles and dissolved gases is through diverging section. The main mechanism by which collection happens in venturi scrubber is inertial impaction. The inlet gas stream enter the converging section, and its velocity increases along this section due to decreasing area of cross section and attains its maximum velocity at the throat section. Liquid

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is introduced at the throat section. Entered liquid sheared from the wall, disintegrates into number of tiny droplets due to high velocity in the throat section. Particle and gas removal

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takes place at the throat section by droplet formation. The inlet gas stream then passes through the diverging section where gas decelerates due to increasing cross sectional area.

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Both liquid and gas streams exits through the diverging section (Yung et al., 1977; Pulley

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1997; Bal and Meikap,2017).

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2. Literature review

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Literature survey reveals that adequate researches have been done to improve the performance of venturi scrubber. Johnstone et al. (1954) has reported that removal

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efficiencies of venturi scrubber for SO2 with scrubbing liquid as alkaline solutions were

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proportional to the droplet’s specific surface area; they also concluded that the gas mass transfer coefficient is increased with the liquid injection flow rate. Taheri and Heines (1969)

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determined the gas cleaning performance of a venturi scrubber which had throat dimension of 6 inch wide ×12 inch long × 12 inch deep used by considering the three water injection. Gas cleaning performance was calculated by the two tests: SO2 absorption and collection

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efficiency of controlled sized methylene blue particles. Boll (1973) presented a mathematical model of collection efficiency based on the venturi configuration, operating condition and particle size. Hesketh (1974) has reported that the collection efficiency as penetration was a function of throat area, liquid to gas ratio and pressure drop. Gamisans et al. (2002) have reported a strong effect of the liquid scrubbing flow rate on pollutant removal efficiency. 5

However, Azzopardi et al. (1991) observed the existence of a liquid film on the wall. They reported that all the liquid does not atomize , some of this liquid flows as a film on the wall, which was very close to annular flow in vertical tube. Later, Gamisans et al.(2004) investigated the effect of liquid film on mass transfer inside the venturi scrubber. It is also reveals from the literature survey that the liquid entered the venturi scrubber by two

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methods: forced feed method and the other is self-priming method. In the case of selfpriming venturi scrubber, liquid gets sucked inside the venturi scrubber at the throat section

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due to pressure difference which is basically the difference between the hydrostatic pressure

of liquid and the static pressure of air (Mayinger and Lehner, 1995; Lehner, 1998). Lehner

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(1998) reported very high removal efficiency of aerosols even at low velocity in self-priming

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venturi scrubber. The effect of multistage injection of liquid on removal efficiency was also

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studied and it showed better results than single stage. Depending on high performance

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efficiency, self-priming venturi scrubber was thought to be a key component of filtered containment venting system in nuclear power plants to remove iodine vapours at the time of

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nuclear accident. Ali et al. (2013) have designed a self-priming venturi scrubber for the removal of iodine and tested it in submerged and non-submerged condition. It was reported

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that the submerged condition gave a better efficiency than non-submerged self-priming venturi scrubber in terms of removal efficiency. Later, Gulhane et al. (2015) investigated the

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iodine removal efficiency in a self-priming venturi scrubber in submerged condition using different pH solutions as a scrubbing liquid. It was found that high pH value of liquid

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improved the iodine removal efficiency. Zhou et al. (2016) reported that the outstanding removal efficiency (99%) of iodide vapour in self-priming venturi scrubber by controlling the flow rate of aqueous solution. In the present paper, an attempt has been made to remove molecular iodine from polluted air in a newly designed forced feed venturi scrubber before it enters the environment. A detailed

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parametric study of throat gas velocity, liquid flow rate and inlet concentrations of iodine on iodine removal efficiency has been done in the present study and the removal efficiency has also been enhanced by taking potassium iodide solution as the scrubbing liquid. A semi empirical model has been developed to predict the efficiency of iodine removal using experimental results.

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3. Materials and methods 3.1.Materials

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Solid iodine of 99% purity was procured from Merck Life Science Pvt Ltd. 99% pure potassium iodide (KI) was used as an absorbing solution and scrubbing liquid which was

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supplied from the Merck Specialties Pvt Ltd. KI solution was prepared by mixing of KI and

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distilled water.

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3.2. Methods

A laboratory scale venturi scrubber has been designed, developed and fabricated. Schematic

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diagram of the experimental setup for the removal of iodine is shown in Fig.1. It mainly consists of five parts; feed tank, heater, air compressor, venturi scrubber, and mesh filter.

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Venturi scrubber is vertical column made of perspex (Polymethyl methacrylate) having 0.61

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m height, throat diameter of 0.025 m and 0.05 m length. 0.005 kg of crushed solid iodine was fed into the feed tank (1) and passed to the heater (2). Iodine was heated for 3600 s so that it could completely vaporize. After 3600 s, air was supplied from the air compressor (6) at a

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specific flow rate which was adjusted using the rotameter (5) and thoroughly mixes with iodine vapour in the tank (4). The mixture of air and iodine vapour is introduced at convergent section and is accelerated to its maximum velocity at throat section. Scrubbing liquid (water in this case) was pumped from a storage tank (9) through the valve and injected at the throat section (12) where the iodine vapour collides with the liquid droplets, mainly

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through inertial impaction and capture the iodine vapour. The flow rate of water was controlled by the rotameter (11). The third segment, diffuser is used for deceleration of gas to allow recovery of pressure. The scrubbed air from the venturi enters the mesh filter (15). Mesh filter removes the small amount of iodine vapour left and entrained liquid droplets. Inlet and outlet concentrations of air iodine samples were collected by the impingers and

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aspirant bottles. The experiments are conducted at the different liquid to gas flow rates, at different iodine concentrations. Pictorial view of the experimental set up is shown in the Fig.

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2.The droplet diameter was estimated from the Nukiyama-Tanasawa equation which is given

below.With reference to the work done by Nukiyama and Tanasawa (1938), the equation

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considered well predicts the droplet diameter for water and potassium iodide solution as a

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scrubbing liquid. The accuracy of the equation has already been reported by Nukiyama &

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Tanasawa and has also been used for evaluating venturi scrubber performance by Yung et al. (1977). 50

Q

g

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dd = u + 91.8(Q l )1.5 g

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4.1. Sampling

(1)

Under steady-state operating conditions, iodine samples were collected at source point 8 and

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16.Inlet and outlet samples were collected simultaneously with the help of impingers and

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aspirant bottle at isokinetic conditions (Meikap et al., 2002; Rajmohan et al., 2008; Kurella et al., 2015). Isokinetic sampling was done by maintaining the velocity of the air coming from the sampling probe nozzle to be equal to the velocity of the undisturbed air in the system. In

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the present study, sample is collected at the flow rate 2.18 x10-5-8.05x10-5m3/s from the sampling port which is same as the inlet of the system at different flow rate of gas. Sampling flow rate is calculated by the below formulae at different flow rates of gas. Sampling flow rate =

flowrate of air at inlet of system area of the inlet of system

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× area of sampimg port

(2)

Maintaining iso-kinetic sampling is very essential for correct measurement of samples.Impingers are borosilicate glass tubes designed to capture airborne contaminants by bubbling the sampled air through an absorbing liquid.10 -4 m3(10 -4 m3 of water and 0.002 kg of KI) of the absorbing solution was placed in an impinger. 10

-4

m3of water and 0.002kg of

KI has been chosen based on the target removal of iodine in KI solution. Basically, iodine

Solubility of iodine in the absorbing solution (10

-4

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reacts with potassium iodide to form potassium tri iodide which is highly soluble in water.

m3water and 0.002 kg of KI) at room

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temperature is 10.76 kg/m3 which were reasonably very high to capture iodine in the absorbing solution. Use of more concentrated KI solution may result in loss of KI and in actual operation it may not be economically feasible. Hence an optimum concentration of KI

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i.e. 20 kg/m3, two times higher the solubility values has been chosen and kept in an impinger

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system.Sample was collected for 180 to 600 s, and the aspirant bottle was used to control the

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flow rate of sample collection by operating the valve. The aspirant bottle was filled with water. A pictorial view of sampling procedure is shown in the Fig. 3.Volume of air sampled

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was calculated by subtracting the initial volume of the water in the aspirant bottle and final volume of water in the aspirant bottle. The concentration of the sample is expressed as the

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product of sample concentration (kg/m3) and volume of the impingement solution (m3) that is divided by the volume of the air (m3). Therefore, unit of concentrations are expressed as

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kg/m3.

Percentage removal of iodine have been calculated in each run by the below formula(Kurella

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and Meikap,2016;Raj Mohan and Meikap,2009).

ηiodine effi =

CI2_i −CI2_o CI2_i

× 100

(3)

4.2. Analysis

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Inlet and outlet concentrations of iodine were measured in terms of KI3 concentration using UV Spectrophotometer at 352 nm. For the calibration, 10-4 kg KI was taken in five test tubes and 2.5x10-4 m3, 4x10-4 m3, 5 x10-4 m3, 6x10-4 m3 and 7x10-4 m3 distilled water is added respectively. Excess amount of iodine was added to these test tubes resulting in the formation of potassium tri iodide in different concentrations. This different concentration of KI3 gives

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different absorbance values in the UV spectrophotometer. A graph was plotted using known

concentrations of KI3 and absorbance values. The unknown KI3 concentration of the samples

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collected was obtained from the calibrated curve as shown in Fig.4.

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166

(5)

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5. Results and discussion

127×2×Y

(4)

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Iodine concentration (kg/m3) =

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166∗concentration of sample obtained from UV = 420

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KI concentration required to form measured concentration (UV Test) of KI3 (Y)

In the present study, fresh water is continuously fed at the throat section after1.4x104 s.As the

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solubility of iodine at room temperature and pressure is 0.565 kg/m3, the iodine in the gas enters the venturi scrubber and it can operate almost 1.44x105s to attain the iodine solubility.

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The experiments were run at gas flow rates from 2.93 x 10-3 Nm3/s - 10.76 x 10-3 Nm3/s and liquid flow rates from 8.33 x 10-6m3/s - 33.33 x 10-6m3/s with iodine concentration 0.05–0.39

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kg/m3. In this technique the difference in the iodine concentration in the impingement solution gives the overall removal efficiency. Operating condition of the experiment is shown in the Table 1. 5.1. Effect of Gas Flow Rate on distribution of droplet Size

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Fig.5 depicts the droplet size distribution with changing gas flow rates at different liquid flow rates. It can be seen from the Fig.5 that as the air flow rate is increased, the droplet size gradually reduces, which is very much favourable for high removal efficiency. Calculated average diameter of droplets from equation 1 in the present study is in the range of 250-2000

5.2.Effect of throat gas velocity on the overall removal efficiency

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µm.

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Throat gas velocity is calculated by using the continuity equation (Vinlet Ainlet = Vth Ath ) at

the throat. Since the throat dimension is known i.e. ID = 0.025 mand gas flow rate is 2.93 x 10-3 Nm3/s - 10.76 x 10-3 Nm3/s, it is possible to calculate the throat gas velocity. The trend in

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Fig.6 shows higher removal efficiency at high throat gas velocity which is reported in the

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literature (Pak and Chang, 2006).The liquid entering the venturi scrubber at the throat

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section, is instantly turned into tiny droplets due to high velocity of gas generated due to

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small restricted area between convergent and diffuser section. Due to high relative velocity of

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air in the throat, it directly strikes the droplets and captures it.In the figure, result shows the overall maximum efficiency of 70.13 % is obtained with throat gas velocity of 18 m/s.

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5.3. Effect of liquid mass flow rate on overall removal efficiency

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Fig.7 shows that the overall removal efficiency increases with the liquid flow rate. Increase in liquid flow rate enhances the number of droplets which is responsible for removal operation.

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5.4.Effect of liquid to gas ratio (L/G) on overall removal efficiency Liquid to gas ratio is one of the important parameter which affects the removal efficiency which is shown in the Fig.8. It is indicated that the removal efficiency increases with increasing the liquid to gas ratio (dimensionless). For smaller L/G ratio, the capturing possibility of iodine by the droplets is reduced. This occurs due to non-uniform distribution 11

of droplets or low concentration of droplets and partial channeling of gas stream. For higher L/Gratio, the removal efficiency increases. This increasing trend is observed earlier by Taheri and Sheih (1975). 5.5. Effect of mass flow rate of gas on the overall removal efficiency

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As shown in Fig.9 with increase in gas flow rate, removal efficiency increases. The developed relative velocity of the down flowing liquid droplets and gas improves the

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impaction between the liquid droplets and gas phase which increases the rate of collision and

possibility to get intercepted. So, the greater removal efficiencies are attained at greater velocities of gas. Ali et al. (2013) reported that the maximum removal efficiency of iodine is % at mass flow rate of gas of 0.115 kg/s in submerged self priming venturi

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0.999 ±0.001

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scrubber using 0.5% sodium hydroxide (NaOH) and 0.2% sodium thiosulphate (Na2S2O3)

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solution as scrubbing liquid. Present experimental results shows that the maximum removal

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efficiency of 70.13 % at gas flow rate of 0.0108 kg/s with normal water as scrubbing liquid.

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5.6. Effect of iodine inlet concentration on overall removal efficiency

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Fig.10 indicates that the removal efficiency increases with the iodine inlet concentration. This is due to fact that higher inlet concentration of iodine leads to higher population density. The

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probability of impaction is high between liquid droplets and iodine molecules when the gap between molecules is little, which results in more effective inertial impaction and therefore increases the removal efficiency. Because of this the higher inlet iodine loading continuously

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reduces distance between the molecules, which favours the higher scrubber efficiency for iodine removal.Trend of increasing efficiency with inlet concentration supports the observation reported by Meikap et al. (2002). 6. Correlation development for prediction of removal efficiency with water as a scrubbing liquid

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The parameters that could possibly affect the iodine removal efficiency(ƞI ) of venturi 2

scrubber are throat diameter (dth),throat velocity (Vth), flow rate of liquid (Ql), density of liquid (ρl), density of gas (ρg), viscosity of liquid (µl), viscosity of gas (µg), height of the throat (hth), inlet iodine concentration (CI2 −i), surface tension of gas-water interface (σ),

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droplet diameter (dd), Diffusivity of iodine (DI2 ). ƞI2 = f (Vth , Ql , ρl , ρg , µl , µg , DI2 , dth , hth , CI2 −i , σ, dd )

(6)

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By employing Buckingham’s π theorem, the equation can be written in dimensionless groups as given in below equation 7.

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(7)

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ƞI2 =

2 ρl m ρg Vth dth m µl m hth m DI2−i CI2−i m Ql m ρg Vth dd m 1 2 3 4 5 6 k1 [ρ ] [ µ ] [µ ] [d ] [ µ ] [Q ] [ σ ] 7 g th g g g l

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Where m1, m2, m3, m4, m5, m6, m7 are the coefficients of the correlation and k1 is the constant

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of the correlation. Therefore, the above correlation can be written in the form of known

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dimensionless numbers as given in the below equation 8. ρ

µ

h

Q

ƞI2 = k1 [ρ l ] m1 [Reg ]m2 [µ l ]m3 [dth ]m4 [Sc]m5 [Q l ]m6 [We]m7 g

th

g

(8)

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g

Where, Reg is the Reynolds number of gas at the throat, Sc is the Schmidt number,We is the

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Weber number of the gas. Higher Reynolds number causes higher turbulence inside the venturi scrubber. If the Reg at throat section increases, then the inertial impaction also increases, this affects the removal efficiency of iodine in venturi scrubber. Schmidt number

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defines the effect of diffusivity of iodine in water. Weber number of the gas affects the droplet formation inside the venturi scrubber.The physical significance of the above numbers are as follows: Reynolds No = Inertial Forces/Viscous Force, Schmidt number = Momentum Diffusivity/Molecular Diffusivity & Weber number = Hydrodynamic Forces/Surface Tension Force 13

The dimensionless groups whose values were kept constant were grouped together as constant as they do not vary while operating the scrubber. Therefore the above correlation is simplified to Q

ƞI2 = k[Reg ]m1 [Sc]m2 [Q l ]m3 [We]m4

(9)

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A functional relationship has been developed between the percentage removal of iodine and

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the various dimensionless groups using multiple linear regression analysis and to evaluate the constant and powers of the equation.

Q

ƞI2 −H2o = 1.68[Reg ]0.57 [Sc]−0.09 [Q l ]0.16 [We]−0.023

(10)

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g

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The resulting equation is

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The above equation yielded the least possible error percentage between predicted and

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experimental results and the least standard deviation thereby presenting the best possible

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correlation between iodine removal efficiency and dimensionless groups. The deviation was observed to be ±12 %. A regression coefficient was found as 0.996. Comparison of removal

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efficiency obtained from the model and experiment is shown in Fig.11. Research further investigated that the validation of this developed correlation (Equation 10). Therefore,

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present correlation is validated with the data of Ali et al.(2013) . Correlation is slightly underestimated the value of Ali et al. (2013) because correlation only consider the water as 0.5% sodium hydroxide (NaOH) and 0.2% sodium

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the scrubbing liquid instead of

thiosulphate (Na2S2O3) solution .Validation of correlation with the data of Ali et al. (2013) is shown in the Fig.12. 7. Effect of potassium iodide solution as the scrubbing liquid on the iodine removal efficiency 14

Experiments were conducted in order to observe the enhanced scrubbing efficiency of iodine using potassium iodide solution compared to water as a scrubbing liquid. The experimental condition is shown in Table 2. From Fig.12 it is seen that the iodine removal efficiency increases with increase in concentration of KI in the scrubbing liquid at the same throat gas velocity and at the same

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liquid flow rate. Iodine reacts very easily with KI solution to form more water soluble potassium tri-iodide. When iodine is soluble in the KI solution, the following reaction occurs

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KI + I2 = KI3

(11)

I3- anion is the main reason for the solubility of iodine in KI solution.The diffusion rate of I2

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in KI solution is much faster than in normal water. Edgar and Diggs (1916) investigated the

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effect of KI concentration on the iodine diffusion rate in KI solution. They explained that if

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excess amount of KI is present in the solution, then there will no free iodine present, which

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indicates that there is no effect on the diffusion rate of iodine. On the other hand, potassium

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tri iodide (KI3) is largely dissociated into K+ and I3- in the less concentrated KI solution. This dissociation is less in highly concentrated solution due to excess common K ion. Another

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interesting area that had been noticed was that the fluidity of KI solution is very high. There might be an effect of fluidity of different concentrated KI solution on the diffusion rate of

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iodine, although they had faced some difficulty in correlating the diffusion rate of iodine in KI solution with fluidity. Later, Darrall and Oldham (1968) found a straight line when they

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plotted the log of the diffusion rate against the log of the kinematic viscosity. Therefore in order to increase the solubility of iodine, potassium iodide (KI) is added to water and 0.0006 kmol/m3,0.003 kmol/m3concentration of potassium iodide are used as scrubbing liquids. Iodine removal efficiency is highest for 0.003 kmol/m3KI solution at throat gas velocity of 18 m/s.The iodine removal efficiency with normal water is observed as 70.13%. But the iodine removal efficiency increases to 82.32 % with KI solution as a scrubbing liquid. 15

8. Correlation development for prediction of removal efficiency with KI as a scrubbing liquid The iodine removal efficiency for potassium iodide solution as scrubbing liquid (ƞI2 −KI) can be written as (Chang And Rochelle, 1982 ;Bandyopadhyay and Biswas, 2006)

I2 CI2 ,Int

)

(12)

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DKI CKI

ηI2 −KI = ηI2 −H20 × (1 + i D

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Equation 12 siginifies that the ratio of the mass transfer rates of iodine with and without chemical reaction is proportional to the respective removal efficiencies of iodine in the D𝐾𝐼 C𝐾𝐼

venturi scrubber. Where, (1 + i D

I2 CI2 ,Int

) is a factor which describes the enhancement of

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mass transfer considering the film model(Astarita, 1967). The removal efficiency of iodine by

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using water as scrubbing liquid, ηI2 −H2O , is taken from Equation 10 and to predict the

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removal efficiency by using KI solution as scrubbing liquid Equation 12 is employed. “i” is the mole ratio of I2 component and reagent (KI). DKI is diffusivity of KI in water, D I2

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isdiffusivity of I2 in water, CKI is initial KI concentration and CI2,Int

is interfacial I2

concentration. This semi-empirical correlation shown by Equation 12 can be useful to any physicochemical and

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gas-liquid absorption process in reactive systems at the same

hydrodynamical conditions. This equation shows that the iodine removal efficiency of

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scrubber with KI as scrubbing liquid is dependent on the inlet iodine concentration and the initial concentration of KI solution . It is further noticed from the equation that the removal

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efficiency decreases with an increase in the initial iodine concentration, and it increases with an increase in the initial KI solution concentration. Predicted values of removal efficiency of iodine, calculated using semi-emperical correlation has been plotted against the experimental removal efficiency as shown in Fig.14. Predicted values deviated from the experimental values within satisfactory limit of ±17 %. 16

9. Error analysis In the present study, error bar is shown in the Fig. 6-10 and Fig.13 to check the accuracy of the experimental data. Formulas used to determine the error bar are shown below. sample1 +sample2 +sample3 ….

(13)

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Standard deviation = √ Standard error =

(sample1 −avg)2 +(sample2 −avg)2 …. N

(14)

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Average =

Standard deviation

(15)

√N

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10. Conclusions

Present system aims to prevent one of the fission products, iodine, which gets emitted to the

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environment at the time of the nuclear power plant accidents. For serving this purpose, a

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modified venturi scrubber has been developed to remove iodine from the air using normal

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water and KI solution as a scrubbing liquid. From the experimental results, the maximum

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removal efficiency of the iodine is obtained as 70.13% with normal water as a scrubbing liquid at the throat gas velocity of 18 m/s, liquid flow rate of 0.033 kg/s with iodine

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concentration of 0.39 kg/m3.After increasing the concentration of KI in the scrubbing liquid,

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iodine removal efficiency increases due to increased solubility of iodine in KI solution. Using KI solution as a scrubbing liquid, maximum removal efficiency of the iodine is obtained as

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82.32% with 0.003 kmol/m3of KI concentrations in scrubbing liquid for the throat gas velocity of 18 m/s and liquid flow rate of 0.033 kg/s with iodine inlet concentration 0.39 3

kg/m .It is also concluded that iodine removal efficiency is higher for higher gas flow rate,

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higher liquid flow rate and higher inlet concentration of iodine. A correlation has been developed for predicting the removal efficiency of iodine with water as a scrubbing liquid and experimental results are in excellent agreement with this correlation. Experimental results match well with the predicted values with ± 12% deviation. Another semi empirical correlation has been developed for the removal of iodine with KI solution as a scrubbing 17

liquid which is in good agreement with the experimental results. The deviation was within ±

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17%.

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References [1]

Ali,M., Chanqi,Y., Zhongning, S., Halfeng, G., Junlong,W, Khurram, 2013.Iodine Removal Efficiency in Non-Submerged and Submerged SelfPriming Venturi Scrubber. Nuclear Engineering and Technology, 45(2), 203–

[2]

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210. Astarita, G., 1967. Mass Transfer with Chemical Reaction, Elsevier, Amsterdam.

Azzopardi, B.J., Teixeira, S.F.C.F., Govan, A.H. and Bott, T.R., 1991. An

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improved model for pressure drop in Venturi scrubbers. Trans IChem E ,Part B,

Bal, M, Meikap, B. C.,2017. Prediction of hydrodynamic characteristics of a

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Proc Safe Env Prot, 69: 237–245.

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venturi scrubber by using CFD simulation. South African Journal of Chemical

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Eng. 24,222-231.

Bandyopadhyay, A., Biswas, M. N., 2006. SO2 scrubbing in a tapered bubble

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column scrubber.Chemical Engineering Communications, 193(12), 1562-1580. Boll, R.H., 1973. Particle collection and pressure drop in venturi scrubber. Ind.

Chang, C. S., and Rochelle, Gary T., 1982. Mass Transfer Enhanced by

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Eng. Chem. Fundam.12(1), 40-49.

Equilibrium Reactions. Ind. Eng. Chem. Fundam., 21, 379-385.

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Darrall, K. G., and Oldham, G., 1968.The diffusion coefficienct of the tri-iodide ion in aqueous solutions. J. Chem. Soc(A),0,2584-2586.

Edgar, G., and Diggs, S.H., 1916.The diffusion of iodine in potassium iodide solutions. J. Am. Chem. Soc., 38 (2), 253–25.

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Gamisans, X, Sarra, M., Lafuente,F. J., 2004. The role of the liquid film on the mass transfer in venturi-based scrubbers,Chemical Engineering Research and Design, 82(A3) 372–380.

[11]

Gamisans, X., Sarrà, M.,Lafuente, F. J., 2002.Gas pollutants removal in a single- and two-stage ejector–venturi scrubber.Journal of Hazardous Materials,

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90,251–266.

Gulhane, N.P., Landge, A.D., Shukla, D.S., Kale, S.S., 2015. Experimental

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Study of Iodine Removal Efficiency in Self-Priming Venturi Scrubber.Annals of Nuclear Energy, 78, 152–159.

Hesketh, H.E., 1974.Fine particle collection efficiency related to pressure drop,

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scrubbant and particle properties and contact mechanism.Journal of the Air

Hirao Shigekazu Hirao, Hiromi Yamazawa & Takuya Nagae, 2013.Estimation

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Pollution Control Association,24(10), 939-942.

rate of iodine-131 and cesium-137 from the Fukushima Daiichi nuclear power

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plant. Journal of Nuclear Science and Technology, 50(2) 139–147. Holt, M; Campbell, R, J.; Nikitin, M, B., 2012.Fukushima Nuclear

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Disaster.CRS Report for Congress. John E. Ten Hoevea and Mark Z. Jacobson. 2012. Worldwide health effects of

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the Fukushima Daiichi nuclear accident.Energy Environ. Sci., (5), 8743–875.

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Collection in a Venturi Atomizer.Ind. Eng. Chem.46 (8), 1601-1608.

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Kurella, S., Bhukya,P. K., Meikap,B. C.,2017.Removal of H2S pollutant from gasifier syngas by a multistage dual-flow sieve plate column wet scrubber, Journal of Environmental Science and Health, Part A, ,52(6), 515-523,

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Kurella, S, Meikap B. C., 2016.Removal of fly-ash and dust particulate matters from syngas produced by gasification of coal by using a multi-stage dual-flow sieve plate wet scrubber, J. of Environ Sci and Health. Part A.51(10), 870-876.

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Kurella, S.,Balla, M.,Bhukya, P.K., Meikap B. C., 2015. Scrubbing of HCl Gas

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from Synthesis Gas in a Multistage Dual-Flow Sieve Plate Wet Scrubber by

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Working in Self-Priming Mode. Aerosol Science and Technology. 28:5, 389402.

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removal in a novel spray-cum-bubble column scrubber,Chemical Engineering

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Research and Design, 87(1), 109-118. Rajmohan, B., Reddy, S. N., Meikap, B. C., 2008. Removal of SO2 from Industrial Effluents by a Novel Twin Fluid Air-Assist Atomized Spray Scrubber.Ind. Eng. Chem. Res. 47(20), 7833–7840.

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containment filtered vent under severe accident conditions at wolsongnpp unit

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1.NuclEng and Tech.45 (5),598-604.

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Taheri, M. and Sheih, C. M.1975. Mathematical modelling of atomizing

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Nuclear Installations Nuclear Safety, NEA/CSNI/R, 2014.

Taheri, M.; Haines, G. F., 1969. Optimization of Factors Affecting Scrubber

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scrubbers. AlChE Journal, 21(1), 153-157.

Performance.J. of the Air Pollu.Contl. Assoc.19(6), 427-431. Yung, S.C., Calvert, S, Barbarika, H.F., 1977.Venturi scrubber performance

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model. Env Sci & Tech. 12(4), 456-459. Zhou, Y., Sun, Z., Gu, H., Miao, Z., 2016. Performance of iodide vapours

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[35]

absorption in the venturi scrubber working in self-priming mode. Ann Nucl

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Energy, 87, 426-434.

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List of Figures Figure 1.Schematic diagram of the experimental set up Figure 2. Pictorial view of the experimental set up

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Figure 3.Pictorial view of sampling process Figure 4.Calibration curve of KI3

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Figure 5. Effect of flow rate of gas on droplet size estimated by the Nukiyama Tanasawa equation

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Figure 6. The effect of throat gas velocity on the iodine removal efficiency

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Figure 7. The effect of liquid mass flow rate on the iodine removal efficiency

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Figure 8. The effect of the L/G ratio on theiodineremoval efficiency

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Figure 9. The effect of gas mass flow rate on theiodine removal efficiency Figure 10.The Effect of iodine inlet concentration on the iodineremoval efficiency

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Figure 11. Comparison between the predicted and experimental removal efficiency Figure 12.Validation of developed correlation with Ali et al. data ((2013)

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Figure 13.Enhancement of iodine removal efficiency by adding KI in scrubbing liquid water.

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Figure 14. Comparison between the predicted and experimental removal efficiency

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Figure 1.Schematic diagram of the experimental set up

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Figure 2. Pictorial view of the experimental set up

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Water

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Figure 3.Pictorial view of sampling process

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Figure 4. Calibration curve of KI3

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Figure 5.Effect of flow rate of gas on droplet size estimated by the Nukiyama Tanasawa

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equation

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Figure 6.The effect of throat gas velocity on the iodine removal efficiency

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Figure 7.The effect of liquid mass flow rate on the iodine removal efficiency

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Figure 8.The effect of the L/G ratio on the iodine removal efficiency

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Figure 9.The effect of gas mass flow rate on the iodine removal efficiency

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Figure 10.The Effect of iodine inlet concentration on the iodine removal efficiency

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Figure 11.Comparison between the predicted and experimental removal efficiency

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Figure 12.Validation of developed correlation with Ali et al. data (2013)

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Figure 13.Enhancement of iodine removal efficiency by adding KI in scrubbing liquid water.

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Figure 14.Comparison between the predicted and experimental removal efficiency

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List of the tables Table 1.Operating conditions for performance study(Water as a scrubbing liquid) Values

Ambient temperature (K)

300 ± 1

Inlet temperature of the experimental air (K)

303-305

Pressure drop (Pa)

33.41-372.54

Gas flow rates (Nm3/s)

(2.93,4.9, 6.85, 8.81, 10.76)x10-3

Throat gas velocity(m/s)

6,10,14,18,22

Liquid flow rates (m3/s)

(8.33, 16, 33.33)x10-6

L/G ratio(dimensionless)

(0.77-11.36)x10-3

Scrubbing liquids

Tap Water

Inlet iodine concentrations(kg/m3)

0.05-0.39

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Parameters

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Table 2.Operating conditions for performances study(KI solution as a scrubbing liquid) Values

Ambient temperature (K)

300 ± 1

Inlet temperature of the experimental air ( K )

303-305

Pressure drop (Pa)

33.41-372.54

Gas flow rates (Nm3/s)

(4.9, 6.85, 8.81, 10.76)x10-3

Throat gas velocity (m/s)

10,14,18,22

Liquid flow rates (m3/s)

33.33x10-6

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Parameters

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Scrubbing liquids as KI Solutions of different 0.0006,0.003

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concentrations ( kmol/m3) Inlet iodine concentrations( kg/m3)

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0.39

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