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. [email protected], [email protected], [email protected], [email protected], [email protected]* http://www.soe.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 carbon dioxide or dry ice can exist at temperatures below -78.5°C and pressures above one atmosphere 1.1 Chemical and Physical Properties [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 3 dioxide is about 90 cm of CO2 per 100 mL of water. At atmospheric pressure and any temperature, Figure 1: Pressure-Temperature Phase Diagram for carbon dioxide does not exist as a liquid. In order to Carbon Dioxide create liquid carbon dioxide, the temperature needs to be 20°C and the pressure needs to be 30 1.2 Production atmospheres. Figure 1 shows the pressure- temperature phase diagram for carbon dioxide. Solid
*To whom correspondence
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Carbon dioxide is produced both naturally and by Combustion of coal produces 43% of carbon humans. Natural processes that produce carbon dioxide emissions. One ton of coal produces about dioxide include ocean release, plant and animal 2.5 tons of carbon dioxide. Oil produces 36% of the respiration, soil decomposition, and volcanoes [4]. carbon dioxide emissions when combusted and Figure 2, shows the natural sources of carbon natural gas produces 20% of the carbon dioxide dioxide. Ocean release accounts for 42.84% of emissions [4]. In 2011, emission of carbon dioxide carbon dioxide production. Plant and animal worldwide was 33.2 billion tons. Heating, electricity respiration and soil decomposition produce 28.56% generation, transportation, and industry were the of the carbon dioxide, respectively. Volcanic main sectors that produced carbon dioxide eruptions only produce 0.03% of the carbon dioxide. emissions.
Figure 4: Fossil Fuel Combustion Sources of Carbon Dioxide Emissions Figure 2: Natural Sources of Carbon Dioxide When natural environments are transformed into Humans emit more carbon dioxide into the areas for human use, such as residential atmosphere than any other source [4]. Figure 3 developments, this is termed land use change. Over shows the carbon dioxide emissions from human a period of 150 years, from 1850 to 2000, the sources. Combustion of fossil fuels such as coal for amount of carbon dioxide released as a result of example, has contributed 87% of all the carbon land use changes was estimated to be 396-690 dioxide emissions produced by humans [4]. billion tons of carbon dioxide to the atmosphere, or Clearing forests and changing land use contributed about 28-40% of total anthropogenic carbon dioxide 9% of carbon dioxide emissions and industrial emissions. In 2011, land use changes contributed 3.3 processes contributed 4% of carbon dioxide billion tons of carbon dioxide emissions [4]. emissions. 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 Figure 3: Carbon Dioxide Emissions from Human consumption. Of all the industrial processes, the Sources production of cement generates the most emissions. The chemical reaction needed to produce cement, by The largest contribution of carbon dioxide emissions heating calcium oxide, is a major contributor of comes from heat and electricity generation [4]. carbon dioxide emissions. In fact, 1000 kg of Figure 4 shows the fossil fuel combustions sources cement produces nearly 900 kg of carbon dioxide of carbon dioxide. The three most commonly burned [4]. fossil fuels are coal, natural gas, and oil.
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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 2. Environmental, Economic, and unprecedented 14 disastrous weather events resulted in an estimated $53 billion in damage –- not Health Impacts of CO2 Emissions including health costs. [8]. 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 Figure 6: Temperature, Sea Level, and Snow Cover many scientists believe is warming the globe, 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 Figure 5: Carbon Dioxide Emissions Data those the result of naturally occurring algal toxins[9]. Global warming is having a large impact has caused an increase in the global average surface on the proliferation and toxicity of these HABs. temperature, an increase in the global average sea Some of the changes include warming temperatures level, and a decrease in Northern Hemisphere snow and changing sunlight conditions that can alter cover illustrated in Figure 6 [5]. species interaction and ecological processes and “changing rainfall that washes nutrients, sediments, Global warming is also causing various and contaminants into waterways [9]. weather anomalies such as more powerful tropical storms. According to the National Wildlife 3. Carbon Sequestration Federation, tropical storms are more likely to bring “higher wind speeds; more precipitation; and bigger In order to reduce the atmospheric concentration of storm surge in the coming decades [7]. 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 Figure 7: Flow Sheet for CO2 Capture from sequestration known as scrubbing will be the focus Flue Gases Using Amine-Based System of this paper. According to Rochelle, the theoretical
minimum work is 0.11 MWh per ton of CO2 for 3.1 Chemical Scrubbing heating the regenerator to recover the solvent and for compressing CO to 150 bar for A carbon dioxide scrubber is a device which 2 transport and sequestration. Regarding solvents, removes CO2 by absorption from flue gas of fossil- fuel-fired power plants or from air. The most MEA is the least expensive amine, but it is prone to oxidative and thermal degradation. dominant CO2 scrubbing method is using a liquid solvent such as aqueous ammonia and Advanced amines such as KS-1, piperazin (PZ), monoethanolamine (MEA) to bind with and separate and ethyldiethanolamine are known to be CO2 from the other gas components. resistant to degradation but more expensive. The general process using a liquid solvent is as Solvent degradation due to SO2, NOx, and fly follows: the gases released from the combustion of ash would be reduced by efficient upstream fossil fuels are collected and chilled. The CO2 is equipment. Oxidative degradation can be then absorbed into the solvent, forming a new minimized by additives, and thermal compound. The new compound separates from the degradation can be minimized by operating other gases moves into a new chamber and is stripper at low temperature. Enhanced process reheated. By heating, the CO2 is then separated from the solution in a reverse chemical reaction and configuration such as absorber intercooling, stored. The solvent is reused by sending it back to stripper interheating, flashing systems and the beginning of the cycle. Other CO2 scrubbing multi-pressure stripping will reduce energy use methods include adsorption, using selectively but will increase complexity and capital cost. permeable membrane, and condensing CO2 for Rochelle expected that the energy use would be separation by cooling the flue gases [10]. reduced to 0.2 MWh per ton of CO2, or about Amine scrubbing for CO2 capture is a well- 20% power loss by improving process and understood and broadly used technology and can be solvents, and stated that about 70% to 95% of applied to new and existing plants. An amine CO2 removal from flue gas could be achieved scrubbing system is made up of two main within the range of minimum cost. It is the components: an absorber in which CO is removed 2 objective of this study to determine the factors from a combustion gas and a regenerator (or affecting carbon dioxide absorption 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 4. Materials and Method for pipeline transport to a storage site would adversely affect the system performance and cost. In 4.1 Materials addition, acid gas impurities such as SO2 and NOx can react with MEA, which reduce the CO2 The materials used in assembling the scrubber absorption capacity of the solvent [11]. 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 null hypothesis for this experiment is that there the carbon dioxide gas moves through the carbon is no difference between the amounts of carbon scrubber, it enters the left container. Afterwards, it dioxide absorbed, ppm will not change. is exhausted into the atmosphere. The left container has been sealed to increase pressure. 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
Figure 8 Carbon Dioxide Scrubbers. Table 2 shows the data that was collected from the CO2 meter over the 16 trial runs. 4.2 Methodology Table 2: CO2 Data in ppm 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 According to Table 3, the p-value for the main time, the high level is 20 min. and the low level is effects is less than 0.05. Therefore, the null 10 min. For amount of dry ice, the high level is 40 hypothesis is rejected since there was a difference in grams and the low level is 0 grams. Finally, for the amount of carbon dioxide absorbed. . The amount of scrubber, the high level is 125 grams and amount of dry ice factor with a p-value of 0.00 and the low level is 0 grams. The response variable is amount of scrubber factor with a p-value of 0.018 ppm of carbon dioxide. had a significant effect on the response variable, ppm of carbon dioxide.
Table 3 shows the ANOVA results from Minitab. Table 1 shows the factors and their combinations:
Table 1: Factors Combinations
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 4.3 Hypothesis 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 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 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 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
6. Conclusion Figure 14: Surface Plot: Amount of Dry Ice and Time Carbon dioxide, although a trace gas in the atmosphere, is having a huge impact on the world. The level of factors that maximizes carbon dioxide The production of carbon dioxide from fossil fuel, absorption is 0 grams of dry ice and 10 min. Figure land use changes, and industrial processes has 15 shows the surface plot for the amount of scrubber environmental, economic, and health impacts. To and time. 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 References: and Time
[1] Ritter, Michael E. The Physical The levels of factors that maximizes carbon dioxide Environment: an Introduction to Physical absorption is 0 grams of scrubber and 10 min. Geography. 2006. Figure 16 shows the surface plot for the amount of http://www.uwsp.edu/geo/faculty/ritter/geog scrubber and the amount of dry ice. The level of 101/textbook/title_page.html factors that maximizes carbon dioxide absorption is (Accessed 12 December 2013) 125 grams of scrubber and 0 grams of dry ice. [2] Shapley, Patricia. Carbon Dioxide.
University of Illinois, 2012.
http://butane.chem.uiuc.edu/pshapley/GenC hem2/B3/1.html (Accessed 4 December 2013)
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[3] Shakhashiri. 2008. Chemical of the Week: Carbon Dioxide. www.scifun.org. [8] Natural Resources Defense Council. http://scifun.chem.wisc.edu/chemweek/pdf/ Extreme Weather: Impacts of Climate (Accessed 4 December 2013) Change. Extreme Weather, Climate [4] What’s Your Impact? What Are the Main Change. N.p., n.d. Sources of Carbon Dioxide (CO2) http://www.nrdc.org/globalwarming/climate Emissions? N.p., n.d. -change-impacts/ http://www.whatsyourimpact.org/co2- (Accessed 5 December 2013) sources.php [9] Natural Resources Defense Council. Tides (Accessed 7 December 2013) of Trouble: Increased Threats to Human [5] Berstein, Lenny, et al. Climate Change Health and Ecosystems from Harmful Algal 2007: Synthesis Report. Intergovernmental Blooms. 2010. National Resources Defense Panel on Climate Change, 12 Nov. 2007. Council. http://www.ipcc.ch/pdf/assessment- http://www.nrdc.org/health/files/HABs6pgr report/ar4/syr/ar4_syr.pdf _07hr.pdf. (Accessed 10 December 2013) (Accessed 5 December 2013) [6] National Oceanic & Atmospheric [10] Horton, Jennifer. How CO2 Scrubbing Administration (NOAA) – Earth System Works, HowStuffWorks.com. Research Laboratory (ESRL), Trends in
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