**4. Materials and methods**

#### **4.1 Physicochemical analysis of oyster shells**

The seashells of oyster, hard-shelled mussel, clam, and seashell from Tong Young province around South Sea in Korea were used as a main material. Salts and other organic substances were removed by washing and drying the waste seashells. Limestone from Danyang and Jungsun province in Korea was adapted for comparison of physicochemical properties of oyster shells. All the materials were crushed 2 times by Jaw crusher and Ball mill after drying enough. The physical and chemical characteristics of the waste oyster shells were analyzed by ICP (ICPS-7500 Shimadzu, Japan), SEM (JEOL superprobe JSM-5400, USA), XRD (SIMENS, Deutsche), and BET surface area (Micromeritics Co., USA). ICP was applied to analyze the atomic properties of the materials. SEM was used to observe the microtissue of the surface of wasted shells. Surface area of the sorbents was measured by BET technique

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 307

In order to check hydration rate, the crushed seashell sieved with the degree of 6 mesh was adapted to calcination reaction. It was added 900 ml water of 25°C to Dewar flask. And a mixer was set to 400 rpm [EPRI, 1988]. After feeding of CaO (100 g), the data system was

As shown in Fig. 3, the reactor used to study the calcination reaction of oyster shells was made of 15 mm ID x 450 mm L quartz glass tube which is corrosion-resistant at high temperatures. The reactor was installed inside a tubular furnace insulated with ceramic wool to reduce heat loss from the inside to the outside and to maintain a constant and uniform temperature inside the electric furnace. The samples were injected where the temperature gradient of the measured reactor temperature was constant and the desired operating temperature was reached, and the flow rates were maintained constant at 2 ℓ/min, 3 ℓ/min, and 4 ℓ/min (1 atm). In addition, the temperature (700 ∼ 1000°C) and flow rate were varied to study the effect of calcination temperature on the BET specific surface

continuously operated to check the temperature variation in every 5 seconds.

area, and the experimental conditions are given in Table 4.

1. Air compressor 8. Porous quartz disk

7. Quartz reactor 14. Gas sampling system

3. Mass flow controller 10. Furnace 4. Mixing chamber 11. Thermocouple 5. Flowmeter 12. Mist eliminator 6. Three way valve 13. Condensor

2. Two way valve 9. Waste shell/Alkali absorbent

Fig. 3. Schematic diagram of the calcination apparatus.

after pretreating to remove vapor in vacuum 1x10-3 and 180°C for 2 hours. The crystal state of shell sorbent and the products before and after reaction was assured by X-ray diffractometer under the condition of 30 kV and 20 mA in the ranges of 10-70 degrees.

#### **4.2 Hydration of oyster shells**

Hydration apparatus was manufactured in order to investigate the effects of properties of calcination sorbent and hydration condition on the reactivity of the hydrated lime [EPRI, 1988]. The reactivity of calcined waste shell was compared with that of imported lime samples. Also, hydration state according to initial temperature was conformed. These were conducted by measuring the reactivity of quicklime. The samples were placed in a stirred vacuum flask containing deionized water and the temperature was measured at time intervals. Rate of heat release was a measure of reactivity. The faster temperature increases the faster the slaking rate. This method can be used in flasker design, to improve slaker performance, to evaluate and compare different limes, or test incoming lime shipments for quality control purposes.

It was calculated for the hydration speed to measure the hydrated reaction using the device of Fig.2 with calcinated shell sorbents suggested by EPRI(1988), respectively. This device was designed to react under same temperature according to the change of hydration condition and was consisted of Dewar flask wrapped dual rubber plate and a mixer made with teflon. K-type thermocouple (1/8″, 30 cm) and a thermoscope were installed on the upper side of flask and conformed the variation of inner temperature.

Fig. 2. Experimental apparatus for measuring the hydration rate of absorbents [EPRI, 1988].

after pretreating to remove vapor in vacuum 1x10-3 and 180°C for 2 hours. The crystal state of shell sorbent and the products before and after reaction was assured by X-ray diffractometer under the condition of 30 kV and 20 mA in the ranges of 10-70 degrees.

Hydration apparatus was manufactured in order to investigate the effects of properties of calcination sorbent and hydration condition on the reactivity of the hydrated lime [EPRI, 1988]. The reactivity of calcined waste shell was compared with that of imported lime samples. Also, hydration state according to initial temperature was conformed. These were conducted by measuring the reactivity of quicklime. The samples were placed in a stirred vacuum flask containing deionized water and the temperature was measured at time intervals. Rate of heat release was a measure of reactivity. The faster temperature increases the faster the slaking rate. This method can be used in flasker design, to improve slaker performance, to evaluate and compare different limes, or test incoming lime shipments for

It was calculated for the hydration speed to measure the hydrated reaction using the device of Fig.2 with calcinated shell sorbents suggested by EPRI(1988), respectively. This device was designed to react under same temperature according to the change of hydration condition and was consisted of Dewar flask wrapped dual rubber plate and a mixer made with teflon. K-type thermocouple (1/8″, 30 cm) and a thermoscope were installed on the

Fig. 2. Experimental apparatus for measuring the hydration rate of absorbents [EPRI, 1988].

upper side of flask and conformed the variation of inner temperature.

**4.2 Hydration of oyster shells** 

quality control purposes.

In order to check hydration rate, the crushed seashell sieved with the degree of 6 mesh was adapted to calcination reaction. It was added 900 ml water of 25°C to Dewar flask. And a mixer was set to 400 rpm [EPRI, 1988]. After feeding of CaO (100 g), the data system was continuously operated to check the temperature variation in every 5 seconds.

As shown in Fig. 3, the reactor used to study the calcination reaction of oyster shells was made of 15 mm ID x 450 mm L quartz glass tube which is corrosion-resistant at high temperatures. The reactor was installed inside a tubular furnace insulated with ceramic wool to reduce heat loss from the inside to the outside and to maintain a constant and uniform temperature inside the electric furnace. The samples were injected where the temperature gradient of the measured reactor temperature was constant and the desired operating temperature was reached, and the flow rates were maintained constant at 2 ℓ/min, 3 ℓ/min, and 4 ℓ/min (1 atm). In addition, the temperature (700 ∼ 1000°C) and flow rate were varied to study the effect of calcination temperature on the BET specific surface area, and the experimental conditions are given in Table 4.

	-

Fig. 3. Schematic diagram of the calcination apparatus.

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 309

Gas reactivity

Table 5. Experimental variables and conditions.

Fig. 4. Schematic diagram of packed-bed experimental apparatus.

The physicochemical compositions of the waste oyster shells, mussel, clam, seashell, and commercial Jungsun limestone were summarized in Table 6 [Jung et al., 2007, 2005, 2000; Kwon et al., 2003]. To perform XRF (X-ray fluorescence spectroscopic) analysis, samples were powdered after dehydrated in a drying oven at 105.0°C for 24 hours. From the composition analysis, it was found that oyster-shells consist of mostly CaO, some of SiO2,

**5.1 Physicochemical characteristics of oyster shells** 

**5. Results and discussion** 

Experimental variables Conditions

SO2 concentration (ppm) 1800 NOx concentration (ppm) 250 O2 concentration (%) 6 Reaction temperature (℃) 150 Water content (%) 10


Table 4. Pretreating and experimental conditions.

A thermo gravimetric analysis (TGA) was used to analyze the activation energy and calcination rates, and the experimental equipment was composed of a gas supply system, reactor system, and data treatment system. The specimen measurement dish of the analyzer was installed vertically inside the quartz tube reactor in the cylindrical electric furnace whose temperature can be raised up to 1,200°C. About 10 to 20 mg of 40/60 mesh crushed shells was placed on the dish and nitrogen gas was passed at a flow rate of 30 ml/min for 10 minutes through the analyzer to replace air with nitrogen in the reactor. A corrosionresistant stainless pipe was used from the gas mixer to the entrance of the reactor, and the inside pressure of the reactor was maintained a little over the ambient pressure in the entire experiments. When the reaction conditions were stabilized, the reactor was heated to 900°C while nitrogen passed at a flow rate 30 ml/min. The reaction was judged to be completed in case of no further weight change during the heating period. The heating rate of the calcination reaction was 50°C/min over the temperature range of 100 to 600°C and 10°C/min over the range of 600 to 900°C.

#### **4.3 Analysis of waste oyster shells as a SO2/NOx removal absorbent**

To enhance the physicochemical properties of the waste oyster-shells, pretreating techniques were applied to the samples before SO2/NOx removal test. The goal of pretreating process was to convert the relatively low reactive calcium component (in the form of calcium carbonate) into a form of calcium oxide and calcium hydroxide that readily reacts with acid gases. These processing referred to calcinations and hydration, respectively.

To calculate the sorbents capacity, the SO2/NOx removal experiments were carried out using a fixed-bed reactor system (Jung et al., 2005) under atmospheric pressure at 150.0°C. The fixed-bed quartz reactor (0.025 m in diameter, 0.25 m in height) was placed in a hot air bath and the temperature was controlled by PID type controller with the precision of ± 1.0°C. After the sample put on the reactor (1 g of samples) and the temperature was stabilized in N2 flow, reacting gas containing SO2, O2, and NOx was injected into the reactor using mass flow controllers (MFC, BROOKS instrument inc., Model 5850E, England). At the same time water was also injected to the reactor by syringe pump to keep a steady vapor concentration in the simulated gas. Hygrometer and SO2/NOx analyzer were used to measure the gas concentration and signals from the measuring instrument were recorded at a personal computer with RS-232C interface. Table 5 shows experimental variables and experimental conditions [Jung, 1999; Jung et al, 2005, 2009].

A thermo gravimetric analysis (TGA) was used to analyze the activation energy and calcination rates, and the experimental equipment was composed of a gas supply system, reactor system, and data treatment system. The specimen measurement dish of the analyzer was installed vertically inside the quartz tube reactor in the cylindrical electric furnace whose temperature can be raised up to 1,200°C. About 10 to 20 mg of 40/60 mesh crushed shells was placed on the dish and nitrogen gas was passed at a flow rate of 30 ml/min for 10 minutes through the analyzer to replace air with nitrogen in the reactor. A corrosionresistant stainless pipe was used from the gas mixer to the entrance of the reactor, and the inside pressure of the reactor was maintained a little over the ambient pressure in the entire experiments. When the reaction conditions were stabilized, the reactor was heated to 900°C while nitrogen passed at a flow rate 30 ml/min. The reaction was judged to be completed in case of no further weight change during the heating period. The heating rate of the calcination reaction was 50°C/min over the temperature range of 100 to 600°C and

To enhance the physicochemical properties of the waste oyster-shells, pretreating techniques were applied to the samples before SO2/NOx removal test. The goal of pretreating process was to convert the relatively low reactive calcium component (in the form of calcium carbonate) into a form of calcium oxide and calcium hydroxide that readily reacts with acid

To calculate the sorbents capacity, the SO2/NOx removal experiments were carried out using a fixed-bed reactor system (Jung et al., 2005) under atmospheric pressure at 150.0°C. The fixed-bed quartz reactor (0.025 m in diameter, 0.25 m in height) was placed in a hot air bath and the temperature was controlled by PID type controller with the precision of ± 1.0°C. After the sample put on the reactor (1 g of samples) and the temperature was stabilized in N2 flow, reacting gas containing SO2, O2, and NOx was injected into the reactor using mass flow controllers (MFC, BROOKS instrument inc., Model 5850E, England). At the same time water was also injected to the reactor by syringe pump to keep a steady vapor concentration in the simulated gas. Hygrometer and SO2/NOx analyzer were used to measure the gas concentration and signals from the measuring instrument were recorded at a personal computer with RS-232C interface. Table 5 shows experimental variables and

Pretreating

Table 4. Pretreating and experimental conditions.

10°C/min over the range of 600 to 900°C.

**4.3 Analysis of waste oyster shells as a SO2/NOx removal absorbent** 

gases. These processing referred to calcinations and hydration, respectively.

experimental conditions [Jung, 1999; Jung et al, 2005, 2009].

Experimental variables Conditions

Hydration temperature (℃) 90 Slurrying velocity (rpm) 200 Absorbent drying time (hr) 24

Calcination temperature (℃) 700 ∼ 1000 Hydration time (hr) 24


Table 5. Experimental variables and conditions.

Fig. 4. Schematic diagram of packed-bed experimental apparatus.
