Investigation of Factors Affecting Carbon Dioxide Absorption

Computers and Mathematics in Automation and Materials Science

Investigation of Factors Affecting Carbon Dioxide Absorption

STEVEN GARCIA1, HYE JEONG LEE2, PAA KWASI ADUSEI3, SEYED ZAHRAEI1, GBEKELOLUWA OGUNTIMEIN2, *

1Department of Industrial and System Engineering, 2Department of Civil Engineering, 3Department of Electrical and Computer Engineering Morgan State University

1700 East Cold Spring Lane, Baltimore, MD, 21251 UNITED STATES of AMERICA.

stgar3@morgan.edu, hylee1@morgan.edu, paadu1@morgan.edu, sezah1@morgan.edu, gbeke.oguntimein@morgan.edu*

Abstract: Carbon dioxide is a trace gas in the atmosphere. A molecule with unique chemical and physical properties, it is produced by both natural and anthropogenic processes. However, over the past several decades, the increase in its atmospheric concentration has affected the climate due to increasing human activities. A greenhouse gas, carbon dioxide traps the thermal radiation from the sun, warming the air. This warming effect has produced various weather anomalies such as powerful tropical storms, droughts, and floods with economic and health consequences. To reduce the carbon dioxide concentration in the atmosphere, carbon sequestration methods have been developed to capture carbon dioxide. There are biological, physical, and chemical scrubbing methods. However, this paper will focus on chemical scrubbing. A carbon dioxide scrubber was built and a factorial experiment was designed using three factors. An Analysis of Variance (ANOVA) was performed on the data and two factors and a 2-way factor interaction were determined to significantly affect carbon dioxide absorption.

Key-Words: carbon dioxide sequestration, fossil fuels, global warming, carbon dioxide absorption, carbon scrubber

1 Introduction

1.1 Chemical and Physical Properties

carbon dioxide or dry ice can exist at temperatures below -78.5?C and pressures above one atmosphere [3].

Carbon dioxide is a trace gas. It comprises 0.36% of the atmosphere by volume. It is composed of one carbon atom covalently bonded to two oxygen atoms therefore, the geometry is linear. The carbon atom is at the centre of the molecule. Thus, it is electrophilic [2]. The molecular formula for carbon dioxide is CO2, it dissolves in water. For example, when it dissolves in water, carbonic acid is formed. The reaction is illustrated in Equation 1 [3].

CO2 (g) + H2O(aq) H2CO3 (aq.)

(1)

According to Shakashiri [3] the solubility of carbon dioxide is about 90 cm3 of CO2 per 100 mL of water. At atmospheric pressure and any temperature, carbon dioxide does not exist as a liquid. In order to create liquid carbon dioxide, the temperature needs to be 20?C and the pressure needs to be 30 atmospheres. Figure 1 shows the pressuretemperature phase diagram for carbon dioxide. Solid

Figure 1: Pressure-Temperature Phase Diagram for Carbon Dioxide

1.2 Production

*To whom correspondence

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Carbon dioxide is produced both naturally and by humans. Natural processes that produce carbon dioxide include ocean release, plant and animal respiration, soil decomposition, and volcanoes [4]. Figure 2, shows the natural sources of carbon dioxide. Ocean release accounts for 42.84% of carbon dioxide production. Plant and animal respiration and soil decomposition produce 28.56% of the carbon dioxide, respectively. Volcanic eruptions only produce 0.03% of the carbon dioxide.

Combustion of coal produces 43% of carbon dioxide emissions. One ton of coal produces about 2.5 tons of carbon dioxide. Oil produces 36% of the carbon dioxide emissions when combusted and natural gas produces 20% of the carbon dioxide emissions [4]. In 2011, emission of carbon dioxide worldwide was 33.2 billion tons. Heating, electricity generation, transportation, and industry were the main sectors that produced carbon dioxide emissions.

Figure 2: Natural Sources of Carbon Dioxide Humans emit more carbon dioxide into the atmosphere than any other source [4]. Figure 3 shows the carbon dioxide emissions from human sources. Combustion of fossil fuels such as coal for example, has contributed 87% of all the carbon dioxide emissions produced by humans [4]. Clearing forests and changing land use contributed 9% of carbon dioxide emissions and industrial processes contributed 4% of carbon dioxide emissions.

Figure 3: Carbon Dioxide Emissions from Human Sources

The largest contribution of carbon dioxide emissions comes from heat and electricity generation [4]. Figure 4 shows the fossil fuel combustions sources of carbon dioxide. The three most commonly burned fossil fuels are coal, natural gas, and oil.

Figure 4: Fossil Fuel Combustion Sources of Carbon Dioxide Emissions

When natural environments are transformed into areas for human use, such as residential developments, this is termed land use change. Over a period of 150 years, from 1850 to 2000, the amount of carbon dioxide released as a result of land use changes was estimated to be 396-690 billion tons of carbon dioxide to the atmosphere, or about 28-40% of total anthropogenic carbon dioxide emissions. In 2011, land use changes contributed 3.3 billion tons of carbon dioxide emissions [4].

Deforestation was the main contributing factor to the increase in emissions. It has had a great impact on the emissions of greenhouse gasses. When forests are removed for timber or converted in to other human areas such as farms, there is a large influx of greenhouse gasses that is released.

Various industrial processes, by way of chemical reactions that are used in certain production processes, generate a large amount of carbon dioxide emissions. In 2011, industrial processes produced 1.7 billion tons of emissions. Direct emissions come from fossil fuel combustion and some come indirectly from electricity consumption. Of all the industrial processes, the production of cement generates the most emissions. The chemical reaction needed to produce cement, by heating calcium oxide, is a major contributor of carbon dioxide emissions. In fact, 1000 kg of cement produces nearly 900 kg of carbon dioxide [4].

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2. Environmental, Economic, and Health Impacts of CO2 Emissions

Carbon dioxide emission is changing the climate. Climate change is defined by the Intergovernmental Panel on Climate Change (IPCC) as a change in the state of the climate that can be identified (e.g. using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. It refers to any change in climate over time, whether due to natural variability or as a result of human activity [5].

According to the National Oceanic & Atmospheric Administration, the parts per million by volume concentration of carbon dioxide has increased by over 26% over the past 50 years as illustrated in Figure 5 [6]. Carbon dioxide is a greenhouse gas. An increase in the atmospheric concentration of carbon dioxide produces the greenhouse effect which traps solar thermal radiation in the atmosphere. This effect, which many scientists believe is warming the globe,

Figure 5: Carbon Dioxide Emissions Data

has caused an increase in the global average surface temperature, an increase in the global average sea level, and a decrease in Northern Hemisphere snow cover illustrated in Figure 6 [5].

Global warming is also causing various weather anomalies such as more powerful tropical storms. According to the National Wildlife Federation, tropical storms are more likely to bring "higher wind speeds; more precipitation; and bigger storm surge in the coming decades [7].

These anomalies have generated a lot of destruction. Thus, climate change also has an economic impact. According to the Natural Resources Defense Council, In 2011, an unprecedented 14 disastrous weather events resulted in an estimated $53 billion in damage ?- not including health costs. [8].

Figure 6: Temperature, Sea Level, and Snow Cover Trends from 1961-1990

There is also health effects associated with global warming. For example, Harmful Algae Blooms (HABs), such as the Blue Green algae, are becoming more prevalent. These blooms contain algae that produce toxins that can cause harm to humans and pets. Fish that consume these HABs are eaten by other fish that are then consumed by humans. According to the Natural Resources Defense Council nearly 20 percent of foodborne disease outbreaks in the United States may result from seafood consumption, with as many as half of those the result of naturally occurring algal toxins[9]. Global warming is having a large impact on the proliferation and toxicity of these HABs. Some of the changes include warming temperatures and changing sunlight conditions that can alter species interaction and ecological processes and "changing rainfall that washes nutrients, sediments, and contaminants into waterways [9].

3. Carbon Sequestration

In order to reduce the atmospheric concentration of carbon dioxide, carbon sequestration methods have been developed to capture carbon dioxide. Carbon sequestration methods include biological, physical,

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and chemical. However, chemical carbon sequestration known as scrubbing will be the focus of this paper.

3.1 Chemical Scrubbing

A carbon dioxide scrubber is a device which removes CO2 by absorption from flue gas of fossilfuel-fired power plants or from air. The most dominant CO2 scrubbing method is using a liquid solvent such as aqueous ammonia and monoethanolamine (MEA) to bind with and separate CO2 from the other gas components. The general process using a liquid solvent is as follows: the gases released from the combustion of fossil fuels are collected and chilled. The CO2 is then absorbed into the solvent, forming a new compound. The new compound separates from the other gases moves into a new chamber and is reheated. By heating, the CO2 is then separated from the solution in a reverse chemical reaction and stored. The solvent is reused by sending it back to the beginning of the cycle. Other CO2 scrubbing methods include adsorption, using selectively permeable membrane, and condensing CO2 for separation by cooling the flue gases [10].

Amine scrubbing for CO2 capture is a wellunderstood and broadly used technology and can be applied to new and existing plants. An amine scrubbing system is made up of two main components: an absorber in which CO2 is removed from a combustion gas and a regenerator (or stripper) in which CO2 is released in a compressed form and the original solvent is recovered as shown in Figure 7. Not only heating required to regenerate the solvent but also compressing the captured CO2 for pipeline transport to a storage site would adversely affect the system performance and cost. In addition, acid gas impurities such as SO2 and NOx can react with MEA, which reduce the CO2 absorption capacity of the solvent [11].

Figure 7: Flow Sheet for CO2 Capture from Flue Gases Using Amine-Based System

According to Rochelle, the theoretical minimum work is 0.11 MWh per ton of CO2 for heating the regenerator to recover the solvent and for compressing CO2 to 150 bar for transport and sequestration. Regarding solvents, MEA is the least expensive amine, but it is prone to oxidative and thermal degradation. Advanced amines such as KS-1, piperazin (PZ), and ethyldiethanolamine are known to be resistant to degradation but more expensive. Solvent degradation due to SO2, NOx, and fly ash would be reduced by efficient upstream equipment. Oxidative degradation can be minimized by additives, and thermal degradation can be minimized by operating stripper at low temperature. Enhanced process configuration such as absorber intercooling, stripper interheating, flashing systems and multi-pressure stripping will reduce energy use but will increase complexity and capital cost. Rochelle expected that the energy use would be reduced to 0.2 MWh per ton of CO2, or about 20% power loss by improving process and solvents, and stated that about 70% to 95% of CO2 removal from flue gas could be achieved within the range of minimum cost. It is the objective of this study to determine the factors affecting carbon dioxide absorption

4. Materials and Method

4.1 Materials

The materials used in assembling the scrubber include two 60 L plastic containers, one 3" plastic ninety, one 2" plastic ninety, one 2' plastic pipe, one Inline mixed air duct fan, 120 V 100 CFM, . Timer, CO2 meter, Air meter, Digital scale, ten pounds. of dry ice pellets, Ascarite II carbon dioxide scrubber supplied by Thomas Scientific, Gloves, Nylon-spandex socks and. Minitab software

Figure 8 shows the constructed carbon dioxide scrubber. Dry ice goes into the right container when needed. The inline mixed air duct fan moves the carbon dioxide gas through the plastic piping which has the carbon scrubber. The scrubber is Ascarite II by Thomas Scientific. It is a solid sodium hydroxide

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compound encased on an inert silica carrier. Once the carbon dioxide gas moves through the carbon scrubber, it enters the left container. Afterwards, it is exhausted into the atmosphere. The left container has been sealed to increase pressure.

Figure 8 Carbon Dioxide Scrubbers.

4.2 Methodology When scrubbing carbon dioxide gas, various factors can influence the amount that gets absorbed. One method to determine which factors have any influence on absorption is to conduct an experiment based on a factorial design [12]. For the carbon dioxide scrubbing experiment, a 23 factorial design was used. The three factors will be time, amount of dry ice, and amount of scrubber. Each factor will have two levels, a "high level" and "low level." For time, the high level is 20 min. and the low level is 10 min. For amount of dry ice, the high level is 40 grams and the low level is 0 grams. Finally, for amount of scrubber, the high level is 125 grams and the low level is 0 grams. The response variable is ppm of carbon dioxide.

Table 1 shows the factors and their combinations:

Table 1: Factors Combinations

The null hypothesis for this experiment is that there is no difference between the amounts of carbon dioxide absorbed, ppm will not change.

4.4 Data Collection Procedure

Based on the factors combinations, dry ice is weighed; CO2 scrubber is weighed and placed in a nylon spandex sock. The sock is placed in the pipe and dry ice is deposited into the left container. The fan is turned on. Absorption data is collected from the CO2 meter.

5. Results and Discussion

Table 2 shows the data that was collected from the CO2 meter over the 16 trial runs.

Table 2: CO2 Data in ppm

According to Table 3, the p-value for the main effects is less than 0.05. Therefore, the null hypothesis is rejected since there was a difference in the amount of carbon dioxide absorbed. . The amount of dry ice factor with a p-value of 0.00 and amount of scrubber factor with a p-value of 0.018 had a significant effect on the response variable, ppm of carbon dioxide.

Table 3 shows the ANOVA results from Minitab.

4.3 Hypothesis

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The two-way interaction between the amount of dry ice and amount of scrubber factors had a significant effect on amount of carbon dioxide absorbed, since its p-value is less than 0.05.

The main effects plot determines which level of the factors is significant. Figure 9 shows that the amount of dry ice factor and the amount of

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scrubber factor had the most significant effect on the carbon dioxide absorption. The time factor did not have a significant effect on carbon dioxide absorption. Therefore, according to the main effects plot, to maximize the carbon dioxide absorption, 0 grams of dry ice has to be used and 125 grams of scrubber needs to be used.

Figure 9 Main Effects Plot

Figure 10 shows the interaction plot. There is no apparent interaction between any of the factors. However, based on the ANOVA results, the interaction between the amount of dry ice factor and the amount of the scrubber factor was significant. However, they may intersect at some point.

Figure 11: Contour Plot: Amount of Dry Ice and Time

The levels of factors that maximize carbon dioxide absorption is 0 grams of dry ice and 10 min. Figure 12 shows the contour plot for amount of scrubber and time.

Figure 12: Contour Plot: Amount of Scrubber and Time

The levels of factors that maximize carbon dioxide absorption is 0 grams of scrubber and 10 min. Figure 13 shows the contour plot for the amount of dry ice and amount of scrubber.

Figure 10 Interaction Plot

The contour plot shows the regions of the response variable based on the levels of the factors. This can be useful for optimizing the response variable. Figure 11 shows the contour plot for amount of dry ice and time.

Figure 13: Contour Plot: Amount of Scrubber and Amount of Dry Ice

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The surface plot shows the regions of the response variable based on the levels of the factors in three dimensions. Figure 14 shows the surface plot for the amount of dry ice and time.

Figure 16: Surface Plot: Amount of Scrubber and Dry Ice

Figure 14: Surface Plot: Amount of Dry Ice and Time

The level of factors that maximizes carbon dioxide absorption is 0 grams of dry ice and 10 min. Figure 15 shows the surface plot for the amount of scrubber and time.

6. Conclusion

Carbon dioxide, although a trace gas in the atmosphere, is having a huge impact on the world. The production of carbon dioxide from fossil fuel, land use changes, and industrial processes has environmental, economic, and health impacts. To address these issues, carbon dioxide absorption is one of the methods being considered. A carbon dioxide scrubbing device was built and a factorial design experiment was performed to determine the factors that affect carbon dioxide absorption. ANOVA was used to analyze the data. It was determined that two factors, the amount of dry ice and amount of scrubber significantly affected the absorption of carbon dioxide as reflected in the ppm readout of the carbon dioxide meter. Furthermore, the interaction between the above two factors was also shown to significantly affect the absorption of carbon dioxide.

Figure 15: Surface Plot: Amount of Scrubber Ice and Time

The levels of factors that maximizes carbon dioxide absorption is 0 grams of scrubber and 10 min. Figure 16 shows the surface plot for the amount of scrubber and the amount of dry ice. The level of factors that maximizes carbon dioxide absorption is 125 grams of scrubber and 0 grams of dry ice.

References:

[1] Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography. 2006. 101/textbook/title_page.html (Accessed 12 December 2013)

[2] Shapley, Patricia. Carbon Dioxide. University of Illinois, 2012. hem2/B3/1.html (Accessed 4 December 2013)

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[3] Shakhashiri. 2008. Chemical of the Week: Carbon Dioxide. . (Accessed 4 December 2013)

[4] What's Your Impact? What Are the Main Sources of Carbon Dioxide (CO2) Emissions? N.p., n.d. (Accessed 7 December 2013)

[5] Berstein, Lenny, et al. Climate Change 2007: Synthesis Report. Intergovernmental Panel on Climate Change, 12 Nov. 2007. (Accessed 10 December 2013)

[6] National Oceanic & Atmospheric Administration (NOAA) ? Earth System Research Laboratory (ESRL), Trends in Carbon Dioxide Values given are dry air mole fractions expressed in parts per million (ppm). For an ideal gas mixture this is equivalent to parts per million by volume (ppmv).

[7] National Wildlife Federation. Global Warming and Hurricanes. N.p., n.d. (Accessed 2 December 2013)

[8] Natural Resources Defense Council. Extreme Weather: Impacts of Climate Change. Extreme Weather, Climate Change. N.p., n.d. -change-impacts/ (Accessed 5 December 2013)

[9] Natural Resources Defense Council. Tides of Trouble: Increased Threats to Human Health and Ecosystems from Harmful Algal Blooms. 2010. National Resources Defense Council. _07hr.pdf. (Accessed 5 December 2013)

[10] Horton, Jennifer. How CO2 Scrubbing Works, . (Accessed 14 November 2013).

[11] Anand B. Rao and Edward S. Rubin. (2002). A Technical, Economic, and Environmental Assessment of Amine-Based CO2 Capture Technology for Power Plant Greenhouse Gas Control. Environ. Sci. Technol., 36 (20), pp. 4467?4475

[12] Montgomery, Douglas C. Design and Analysis of Experiments. Hoboken, NJ: John Wiley & Sons, 2013. Print.

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