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laboratory-scale reactor. The schematic diagram of experimental for studying the removal of CO2 by NaOH solution fine spray is shown in Figure 1. The CO2 and NaOH solution reactor is made of stainless steel with 120 mm inner diameter and 1300 mm height. The artificial flue gases are obtained from the mixture of pure CO2 gas and N2 gas from cylinders. The influent mixture gas and the NaOH solution are heated to the desired operating temperature by electric heaters before fed into the reactor. A thermocouple is placed at each inlet of the flue gas and the NaOH solution and the temperatures are continuously monitored. The CO2 concentration is measured by the CO2 analyzer. Before the sampling gas entering the analyzer, its water vapor due to the evaporation of the NaOH solution must be removed. At first, the sampling gas is induced into the small gas dryer filled with desiccant CaCl2, where the most of water vapor is absorbed. Then, the sampling gas enters into a filter where the left water vapor is absorbed.

B. Spray of NaOH Solution

In order to make CO2 and NaOH solution contact and react thoroughly, two atomizers are placed at the upper part of the reactor and the Sauter mean diameters (SMD) of the NaOH solution spray are 30 μm to 40 μm when the pressure of the pump are 0.69 MPa to 1.11 MPa, and flue gases are fed into the reactor from the bottom of the reactor, thus the fine spray of NaOH solution and flue gas stream are in counter flow pattern.

C. Reaction of CO2 with NaOH Solution

The absorption of CO2 into hydroxide solutions has been widely studied. The stoichiometric equation of CO2 reaction with hydroxide solutions may be written as [10]

the flow rate of NaOH solution is 180 ml/min. the total gas flow rate is 7.6 l/min, the concentration of CO2 at the inlet is 15% (v/v), experiments are carried out at two different initial temperature of 280C and 350C respectively. It can be found that the concentration of NaOH solution plays an important role on the CO2 removal efficiency. When the value of NaOH solution concentration is 2% (w/w), the CO2 removal efficiencies are only 58.9% and 63.2% at the two different initial temperature of 280C and 350C respectively. With the values of concentration of NaOH solution increasing, the CO2 removal efficiency increases to the high level. The maximum value of CO2 removal efficiency is achieved when the concentration of NaOH solution is 10% (w/w) at the temperature of 350C. Whereas, when the concentration of NaOH solution is higher than 10% (w/w), the CO2 removal efficiency is reduced. When the value of the concentration of NaOH solution is 15% (w/w), the CO2 removal efficiency is 90.7% which is lower than the maximum value of 95.4% when the concentration of NaOH solution is 10% (w/w).

TABLE I.

Concentration of NaOH Solution w/w, %

Rate of NaOH Solution ml/min

EXPERIMENTAL PARAMETERS Gas Flow Rate L/min

Concentration

Temperature

of CO2 at the 0

C

Inlet, v/v, %

7

CO2(l) + 2OH → CO32 + Η2Ο. (1)

10095

The reaction rate is normally given by

CO2 removal efficiency, %

90

85

r = k2[CO2][OH ]

80757065605550The second-order rate constant (k2) for the CO2-NaOH system has been correlated as a function of activation energy and ionic strength (IC) [11]:

log(k2) = 11.895 2382/Τ + 0.221ΙC 0.016Ι

III. RESULTS AND DISCUSSIONS

The effects of several operating and design parameters such as concentration of NaOH solution, CO2 inlet concentration, total gas flow rate, NaOH solution flow rate and initial temperature on the CO2 removal efficiency have been studied. Detailed parameters in experiments are given in Table I.

A. Effect of Concentration of NaOH Solution

Figure 2 shows the CO2 removal efficiency under different concentrations of NaOH solution. In these cases,

2

C. (3)

NaOH concentration, % (w/w)

Figure 2. Effect of concentration of NaOH solution on CO2 removal

efficiency

In general, the CO2 removal efficiencies at 350C are higher than that at 280C. The difference of the CO2 removal efficiency between two temperatures is from 1.5% to 4.3% at different concentrations of NaOH solution.

B. Effect of NaOH Solution Flow Rate

The influence of NaOH solution flow rate on the CO2 removal efficiency is investigated. Figure 3 shows the CO2