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Study on the adsorptive removal of indoor C[O.sub.2] of car running in downtown area.

INTRODUCTION

C[O.SUB.2] is one of the most well-known greenhouse gases, and its capture and storage from stack gases have been studied extensively [Kunze and Spliethoff, 2012; Kuramochi et al., 2012]. However, C[O.SUB.2] of indoor space has gained less public interest since its adverse effect on the residents has not been recognized as serious problems. In general, because C[O.SUB.2] is generated during the breathing of residents in indoor spaces, C[O.SUB.2] concentration is apt to be high when the ventilation is not properly carried out. C[O.SUB.2] concentration will be much higher, if there are more passengers in the car. High concentration of C[O.SUB.2] is known to cause various adverse effects like headache, drowsiness, and dizziness for residents [Occupational Safety and Health Administration, 2011]. And, because exposure at even 3,000 ppm of C[O.SUB.2] for a long time may be dangerous, Korean Government made a guideline that C[O.SUB.2] concentration in train or bus should be lower than 3,000 ppm during rush hours [Korean Ministry of Environment, 2008]. C[O.SUB.2] exposure will be more dangerous for drivers. If drivers are exposed to this concentration of C[O.SUB.2] for a long time, it will be a very dangerous condition because the driver will feel sleepiness or headache while driving.

Ventilation is one of the easiest ways to reduce C[O.SUB.2] concentration, but ventilation is not available when the outdoor air is severely polluted. For example, the air quality in downtown area may be seriously polluted by various kinds of air pollutants, then ventilation may cause the inflow of the harmful air pollutants into the car. For example, Los Angeles smog in 1943 was one of the most famous air pollution cases, and similar smog is still often reported in Los Angeles, Denver, or Mexico City. For this reason, many drivers recirculate the indoor air instead of introducing new fresh outdoor air in downtown area. However, in this case, C[O.SUB.2] concentration inside the car can be very high above 3,000 ppm. So, an alternative way to reduce C[O.SUB.2] concentration is needed.

In this study, a feasibility of applying C[O.SUB.2] adsorbent to control indoor C[O.SUB.2] concentration in car was investigated. A small C[O.SUB.2] adsorption system was prepared, and installed inside a car. Physical C[O.SUB.2] adsorbent and chemical adsorbent was loaded in this system, and C[O.SUB.2] concentration change with and without operation of C[O.SUB.2] adsorption system was monitored. Feasibility of C[O.SUB.2] adsorption system for car was tested in this study.

EXPERIMENTAL

Physical C[O.SUB.2] adsorbent is a material which adsorbs ambient C[O.SUB.2] by a relatively weak van der Waals force [Zukal et al., 2011; Cho et al., 2011]. Chemical C[O.SUB.2] adsorbent is a material which quickly reacts with ambient C[O.SUB.2] by a chemical reaction. In this study, commercial 5A zeolite, which is widely known as one of the most effective molecular sieve, was used as physical C[O.SUB.2] adsorbent. Since the pore size of 5A zeolite is around 5 [Angstrom], it can adsorb C[O.SUB.2] molecules, around 3.5 [Angstrom], very effectively. It was baked at 180[degrees]C (356[degrees]F) for 2 h, and cooled down to room temperature prior to use. And, 5A zeolite modified with lithium hydroxide (LiOH) was used as chemical C[O.SUB.2] adsorbent (noted as LiOH-modified 5A zeolite) in this study. It was prepared by mixing LiOH and 5A zeolite with water, and it was pelletized. The prepared pellets were treated at 50[degrees]C (122[degrees]F) for 24 h prior to use.

C[O.SUB.2] adsorption system for car was prepared as presented in Fig. 1. The air flow rate was 3 [m.sup.3]/min (105.9 [ft.sup.3]/min), and amount of loaded C[O.SUB.2] adsorbent was 150 g (0.33 lb). The case was made of transparent acryl resin to check the working of the system. A medium air filter (made of polyethylene terephthalate, 85% of filtration efficiency for 0.26 [micro]m NaCl particle) was installed to the outflow of this system to filter out any particulate matters. The prepared C[O.SUB.2] adsorption system was installed in a sedan car like Fig. 2. The system was installed on the back of head rest area for rear row. The 12V DC power was supplied from the power outlets of the car.

[FIGURE 1 OMITTED]

[FIGURE 2 OMI8TTED]

C[O.SUB.2] adsorption performance of the system was tested by monitoring C[O.SUB.2] concentration change during the running of the car. C[O.SUB.2] concentration was monitored by using a non-dispersive infrared sensor. The calibration curve of the used sensor was made by using a certified C[O.SUB.2] measuring instrument. The car was driven with 3 passengers in downtown area and highway. The average speed was around 30 km/h (18.6 mi/h) in downtown area, and 90 km/h (55.9 mi/h) on highway. Volatile organic compounds (VOCs) like toluene, benzene, or xylene were not monitored here, because VOCs were not our interest in this study.

RESULTS AND DISCUSSION

3.1 C[O.SUB.2] Concentration Change without C[O.SUB.2] Adsorption System

Fig. 3 shows the change in C[O.SUB.2] concentration without C[O.SUB.2] adsorption system on highway and in downtown area. 3 passengers were in the car during this experiment. On highway, C[O.SUB.2] concentration was constant near 1,000 ppm when the ventilation mode was on, as presented in Fig. 3. There was slight change in C[O.SUB.2] concentration but mostly constant. However, when the recirculation mode was on, C[O.SUB.2] concentration increased drastically up to 2,500 ppm for the initial 10 minutes. In 10 minutes, the C[O.SUB.2] concentration increase rate was significantly decreased, and C[O.SUB.2] concentration was saturated at around 3,000 ppm.

In downtown area, C[O.SUB.2] concentration was also constant near 1,000 ppm when the ventilation mode was on. However, when the recirculation mode was on, C[O.SUB.2] concentration increased constantly up to 4,000 ppm. No saturation in C[O.SUB.2] concentration increase was observed in downtown area. Big difference between highway and downtown is the speed of car. Average speed was around 90 km/h (55.9 mi/h) in highway and around 30 km/h (18.6 mi/h) in downtown area. If there was no inflow of fresh air at recirculation mode, C[O.SUB.2] concentration should keep increasing linearly. However, as presented in Fig. 3, C[O.SUB.2] concentration increasing rate decreased according to the experimental time. It means there is more inflow of fresh air at higher speed.

[FIGURE 3 OMITTED]

3.2 C[O.SUB.2] Concentration Change with C[O.SUB.2] Adsorption System

Fig. 4 shows the change in C[O.SUB.2] concentration with the operation of C[O.SUB.2] adsorption system on highway and in downtown area with recirculation mode on when physical C[O.SUB.2] adsorbent was used. 3 passengers were in the car during this experiment. Slight decrease in C[O.SUB.2] concentration was observed for both cases, though the amount was not that much. On highway, C[O.SUB.2] concentration could be lowered by around 500 ppm after 30 minutes of run. However, in downtown area, C[O.SUB.2] concentration was not lowered even after 30 minutes.

These results showed that physical C[O.SUB.2] adsorbent was not fully effective for C[O.SUB.2] adsorption in car with 3 passengers in downtown area. But, it may be applicable on highway with 1 or 2 passengers to achieve C[O.SUB.2] concentration of 1,000 ppm. The good points with the physical C[O.SUB.2] adsorbent is that it can be regenerated by heating because C[O.SUB.2] adsorb on the adsorbent by weak physical attraction. Since it can be reused more than 5 times by heat treatment, it is relatively more economical.

[FIGURE 4 OMITTED]

The same experiment was carried out with chemical C[O.SUB.2] adsorbent, rather than physical C[O.SUB.2] adsorbent. The result was presented in Fig. 5. C[O.SUB.2] concentration increased for both highway and downtown, but the absolute C[O.SUB.2] concentration was much lower than when the chemical C[O.SUB.2] adsorbent was used. In case of highway, C[O.SUB.2] concentration could be kept lower than 2,100 ppm with the operation of C[O.SUB.2] adsorption system, while it exceeded 2,800 ppm without the operation the system. The maximum difference in C[O.SUB.2] concentration was about 900 ppm. In case of downtown, C[O.SUB.2] concentration did not exceed 2,400 ppm when C[O.SUB.2] adsorption system was turned on. However, it exceeded 4,000 ppm in the absence of C[O.SUB.2] adsorption system. The maximum difference was larger than 1,700 ppm. It was found that chemical C[O.SUB.2] adsorbent can be very effective for controlling C[O.SUB.2] concentration without ventilation. It is expected that C[O.SUB.2] concentration in car can be kept lower than 1,500 ppm by increasing the load of C[O.SUB.2] adsorbent.

From obtained results, it was found that chemical C[O.SUB.2] adsorbent can be used for controlling C[O.SUB.2] in car. It could lower C[O.SUB.2] concentration more quickly and efficiently than physical C[O.SUB.2] adsorbent. If there are fewer passengers in car, it will be much easier to keep C[O.SUB.2] concentration lower than 1,500 ppm. However, the short point with this chemical C[O.SUB.2] adsorbent is that it cannot be regenerated since the chemical reaction between C[O.SUB.2] and adsorbent is thermodynamically irreversible. Single-use of the chemical C[O.SUB.2] adsorbent may not cost-effective to apply for car. However, the feasibility of artificial C[O.SUB.2] control in car could be found through this experiment. Finding of more effective and cheap C[O.SUB.2] adsorbent is the key points for practical use of this system.

[FIGURE 5 OMITTED]

CONCLUSIONS

Feasibility of applying C[O.SUB.2] adsorbent to control indoor C[O.SUB.2] concentration in car was investigated in this study. A small C[O.SUB.2] adsorption system was prepared, and installed inside a car. Physical C[O.SUB.2] adsorbent and chemical adsorbent was loaded in this system, and C[O.SUB.2] concentration change with and without operation of C[O.SUB.2] adsorption system was monitored. The car was driven in downtown area and on highway with 3 passengers. The ventilation mode was varied as fresh air intake mode and recirculation mode, and it was found that C[O.SUB.2] concentration was lower than 1,000 ppm with fresh air intake mode, while it was higher than 3,000 ppm with recirculation mode. With the operation of C[O.SUB.2] adsorption system in recirculation mode, C[O.SUB.2] concentration could be lowered to 2,300 ppm when chemical C[O.SUB.2] adsorbent was used. However, when physical C[O.SUB.2] adsorbent was used C[O.SUB.2] concentration could be lowered slightly. Physical adsorbent, made of 5A zeolite, was regenerable, but the efficiency of C[O.SUB.2] adsorption was lower, and C[O.SUB.2] capture time was too long. Chemical C[O.SUB.2] adsorbent was non-regenerable, but it could adsorb C[O.SUB.2] very quickly and efficiently. And, no byproduct is expected for physical C[O.SUB.2] adsorbent, but the generation of Li2CO3 is expected when chemical C[O.SUB.2] adsorbent is used. However, this produced [Li.sub.2]C[O.sub.3] is not hazardous. Since this study was for just feasibility check for C[O.SUB.2] adsorption in car, the cycle of adsorbent changing (or cleaning) has not been extensively studied yet. For physical C[O.SUB.2] adsorbent, it was baked at high temperature of 180[degrees]C (356[degrees]F) to remove C[O.SUB.2] adsorbed, and the baked physical C[O.SUB.2] adsorbent was cooled down to room temperature prior to use. This baking work was carried out by using an oven in the lab. And, if this physical C[O.SUB.2] adsorbent can be practically applicable for the car, then a small regeneration kit can be designed. The filter unit is baked by using this kit, and the spare filter unit can be replaced for the used filter unit.

ACKNOWLEDGMENT

This research was supported by the Converging Research Center Program funded by the Ministry of Education, Science and Technology (grant number: 2012K001373).

REFERENCES

Cho, Y., Lee, J.-Y., Kwon, S. -B., Park, D. -S. and Lee, J. -Y., 2011, Adsorption and desorption characteristics of carbon dioxide at low concentration on zeolite 5A and 13X. Journal of Korean Society of Atmospheric Environment, 27:191200.

Korean Ministry of Environment, 2008. Guideline for indoor air quality in public transportations.

Kunze, C. and Spliethoff, H., 2012. Assessment of oxy-fuel, pre- and post-combustion-based carbon capture for future IGCC plants. Applied Energy 94:109-116.

Kuramochi, T., Ramirez, A., Turkenburg, W. and Faaij, A., 2012. Comparative assessment of C[O.SUB.2] capture technologies for carbon-intensive industrial processes. Progress in Energy and Combustion Science 38:87-112. Occupational Safety and Health Administration, Department of Labor, United States, Indoor air quality in commercial and institutional buildings, 2011 OSHA 3430-04: 14.

Zukal, A., Arean, C.O., Delgado, M.R., Nachtigall, P., Pulido, A., Mayerova, J. and Cejka, J., 2011. Combined volumetric, infrared spectroscopic and theoretical investigation of C[O.SUB.2] adsorption on Na-A zeolite. Microporous and Mesoporous

Materials 146: 97-105.

Youngmin Cho, PhD

Member ASHRAE

Woo-Sung Jung, PhD

Fellow ASHRAE

Soon-Bark Kwon, PhD

Fellow ASHRAE

Seung-Woo Hong, PE

Fellow ASHRAE

Duck-Shin Park, PhD

Fellow ASHRAE

Youngmin Cho is a researcher in Eco-Trans.ort Research Division, Korea Railroad Research Institute, Uiwang, Gyeonggi. Soon-Bark Kwon, Duck-Shin .ark, Woo-Sung Jung, and Seung-Woo Hong are researchers the same affiliation.
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Author:Cho, Youngmin; Jung, Woo-Sung; Kwon, Soon-Bark; Hong, Seung-Woo; Park, Duck-Shin
Publication:ASHRAE Transactions
Article Type:Report
Geographic Code:1USA
Date:Jul 1, 2013
Words:2438
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