The Needs for Carbon Dioxide Capture from Petroleum Industry: A Comparative Study in an Iranian Petrochemical Plant by Using Simulated Process Data

Understanding greenhouse gas capture, utilization, reduction, and storage is essential for solving issues such as global warming and climate change that result from greenhouse gas. Taking advantage of the authors' experience in greenhouse gases, this book discusses an overview of recently developed techniques, methods, and strategies: - Novel techniques and methods on greenhouse gas capture by physical adsorption and separation, chemical structural reconstruction, and biological utilization. - Systemic discussions on greenhouse gas reduction by policy conduction, mitigation strategies, and alternative energy sources. - A comprehensive review of geological storage monitoring technologies.


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behavioural changes. The National Institute for Occupational Safety and Health (NIOSH) air quality standard for the protection of occupational health sets the limit for CO 2 at 10,000 ppm for 10 hours. The Occupational Safety and Health Administration (OSHA) air quality standards for the protection of occupational health set the limit for CO 2 at 5,000 ppm (Webster, 1995).
Human and environmental impacts of solvent-related emissions at a capture and storage of CO 2 facility were estimated by Veltman et al. (2010). They stated that, although carbon dioxide capture is relatively well-studied in terms of power generation efficiency, CO 2 emission reduction, and cost of implementation, but little is known about the potential impacts on human health and the environment. The U.S. Environmental Protection Agency (EPA) has officially declared that CO 2 and other so-called greenhouse gases are dangerous to public health and welfare, paving the way for much stricter emissions standards (EPA, 2009). The 2009 CO 2 emission shows that the Middle East accounted for 3.3% of the total world CO 2 , of which 31% is the share of Iran. Consequently, as shown in Figure 1, the trend of CO 2 emission is progressively increased from 1998 to 2009, which certainly endanger all aspects of life in Iran. The urban environment of Iran is becoming increasingly polluted, with adverse impacts on the health, welfare and productivity of the population. Results indicate that pollution in Tehran, where 20% of Iran's population lives, has well exceeded safe levels (EIA, 2000;Asgari et al., 1998;Masjedi et al., 1998).

CO 2 emission in Iran
Iran is the second-largest producer and exporter in The Organization of the Petroleum Exporting Countries (OPEC), and in 2008 was the fourth-largest exporter of crude oil globally. Iran holds the world's third-largest proven oil reserves and the world's second-largest natural gas reserves. Figure 2 shows the total fuel consumption in Iran. As it is clear in Figure 3, the combustion of fossil energy contributes with about 84 % to the CO 2 emission in Iran.

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The Needs for Carbon Dioxide Capture from Petroleum Industry: A Comparative Study in an Iranian Petrochemical Plant by Using Simulated Process Data

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The main resource of CO 2 emission is fossil fuels that unfortunately now a day are the basic sources to generate energy in industrial-economic systems. On the other hand, energy is a main factor to achieve economic development, which is highly needed for developing countries. In 2009, Iran consists of 527 million metric tones (Mt) of CO 2 emission and is known to be the 9th worst polluter increasing the emissions by 3.2 per cent to 2009, compared with 2008 levels. As shown in Figure 4, the power plant sector with an emission of 28% CO 2 is the largest carbon dioxide emissions source in Iran. Although the consumption of gas has increased in this sector during recent years, still more than 50% of the energy consumption comes from the combustion of heavy fuel oil. The industry sector is the second largest contributor to CO 2 emissions, with about 133 Mt in 2008. The transport sector accounted for 23% of total CO 2 emitted. As Figure 4 shows, the industry sector with about 26% of the total CO 2 emissions was the second major contributor in 2008. The breakdown of the industrial CO 2 emission in Iran ( Figure 5) shows that the petrochemical industry in Iran has more emission contribution in contrast with the other industries such as cement, steel, and gas processing plants. Boilers, process heaters, and other process equipment are the major CO 2 emissions producers in a petrochemical plant. The data presented in Figure 2 through Figure 5 were extracted from different literature; Moradi et al. (2008), Avami and Farahmandpour, (2008), and NIOC (2011). According to the recent study performed by Roshan et al. (2011), the country's temperature annual trend increment would have an increase of maximum 5.72°C to minimum 3.23°C, while considering the most optimistic case, the country's annual temperature would increased by 4.41 °C till 2100. Figure 6 shows the prediction of the total average of temperature annual and seasonal changes from 2025 to 2100 based on the results of an applied scenario for different regions of Iran. According to Figure 7, the highest amount of CO 2 density, which has been forecasted for the year 2100 is 570 ppm. www.intechopen.com

CO 2 capture technologies
As reported by the United Nations Intergovernmental Panel on Climate Changes (UNIPCH) (1995), CO 2 level has risen 30% to nearly 360 ppm from a pre-industrial era level of 280 ppm.

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Greenhouse Gases -Capturing, Utilization and Reduction 86 Judkins et al. (1993) believed that in order to avoid major climate changes, human-generated emissions of CO 2 will have to be reduced by as much as 50-80%. As a result, three strategies had proposed for CO 2 emission control: (1) Exploiting the fuels more efficiently. (2) Replacing coal by natural gas. (3) Recovering and sequestering of CO 2 emissions.
By considering the greenhouse gas effects, it is accepted that natural gas is preferable to other fossil fuels such as coal, and oil. Indeed, removal of CO 2 from natural gas is considered as a practical and more convenience step toward reduction of CO 2 emissions. Removals of CO 2 from gaseous streams have been a current procedure in the chemical industry. Because of the increasing trend of energy consumption globally, removal of CO 2 from natural gas is not easy to be achieved; this task, obviously, required an integrated approach based on modern capturing technologies. The choice of a suitable technology ( Figure 8) depends on the characteristics of the flue gas stream, which depend mainly on the chemical or power plant technology. Figure 8 shows the technologies which are currently used for CO 2 capturing.

Fig. 8. CO 2 capture technologies
Chemical solvent absorption is based on reactions between CO 2 and one or more basic absorbents such as aqueous solutions of Monoethanolamine (MEA), Diethanolamine (DEA) and Methyldiethanolamine (MDEA). An advantageous characteristic of absorption is that it can be reversed by sending the CO 2 -rich absorbent to a stripper where the temperature is raised.
In the present study, simulation of a CO 2 capture from fuel gases of one of the petrochemical plants in Iran was performed by using MEA, DEA and MDEA. In this work, a process by using alkanolamines including CO 2 capture from flue gases was simulated and optimized in a petrochemical plant in Iran. The simulation has been conducted using a commercial software. The required data such as the composition of three type of alcanolamines, were derived in the laboratory. This work consists of six important variables as the output of the simulation process; (1) the amount of CO 2 recovery, (2) amine consumption, (3) mechanical and operational characteristics of the absorption column, (4) CO 2 purity in the stripper column effluent, (5) required energy of the stripper, and (6)  In section 3, the applied process in this study for Amine-based CO 2 capture will be described. The results of this work will be presented in Section 4 and discussed in Section 5. Finally, based on different criteria, the selected alkanolamine will be demonstrated.

Amine-based CO 2 capture plant: Process description
Amine process is the best and commonest choice for separation of CO 2 from flue gases. Driving force of this process is the reaction between CO 2 and amine in which CO 2 with high purity is acquired by one stage process. This process starts with cooling flue gases applying a water cooler to lessen some of their impurities such as NO x and SO x to an acceptable value. Then the chilled gas is pressurized with a blower to the absorption column. Temperature ranges at the top and bottom of the column are about 40-45 and 50-60 °C, respectively. Flue gases and the lean amine are contacted, and CO 2 is absorbed in the amine solution through the absorber. Rich amine at the bottom of the column is pumped into a cross heat exchanger, where its temperature reaches to about 100 °C exchanging heat with the effluent fresh amine of stripping column. Then this solution introduced to the top section of the stripping column. Operating temperature at the top and bottom of the column, operating pressure and column pressure gradient are 110 °C, 120 °C, 1.3 bar and 0.17 bar, respectively.
Required energy for stripping column is supplied from saturated steam at 45 psia. The rich solution of amine and steam are contacted in stripper, and CO 2 is separated from amine. The gas stream containing CO 2 and water steam is exhausted from the top of the column to a condenser where its temperature is lowered to 45 °C. Almost the whole steam is condensed in the condenser and recycled to the top of the column. CO 2 is recovered in a flash drum, then dried and finally compressed to an acceptable pressure. The CO 2 -lean solution leaves the reboiler and enters the cross heat exchanger where it is cooled. The solution is then cooled further before it re-enters the absorber.
Packed columns are often employed in the removal of impurities from gas streams and also the removal of volatile components from liquid streams. The dimensionless Robbins correlation factor is actually the Dry Bed Packing Factor issued to calculate the gas and liquid loading factors, which are in turn used to calculate the pressure drop, particularly with newer packing materials. As shown in Table 3 and Table 5, Robbins packing correlation was used as a default correlation. The Height Equivalent to a Theoretical Plate (HETP) relates to packed towers. The value refers to the height of packing that is equivalent to a theoretical plate. As shown in Table 3 and Table 5, Frank correlation was used to determine the equivalent height to theoretical plate.
The entire schematic diagram of the CO 2 absorption process is illustrated in Figure 9. The flow sheet represents a continuous absorption/regeneration cycling process. Note that the reactions of these alkanolamines and CO 2 are mainly occurred by electrochemical reaction in the aqueous solution. Typical reaction mechanism of MEA and CO 2 are as in the following equations.

Results
Three different alkanolamines (MEA, DEA, and MDEA) were used in the simulation investigation of CO 2 capture in this work. Composition and thermal specifications of feed (flue gas and amine), entering the first tray at the bottom of the absorber are presented in Tables 1 and 2 Table 3. Type and amount of packing are selected so that the maximum recovery is obtained using the minimum consumption of amine. Composition of exit gas and rich amine leaving absorption column is presented in Table 4.

Discussion
A brief review on the associated problems of CO 2 emission, such as health and environment effects and the increasing trend of its emission, indicate the seriousness of the CO 2 capture in Iran's energy sector. The Iranian industry sector with about 26% of the total CO 2 emissions was the second major contributor in 2008, and the largest source was the petrochemical industry. The progressively increases of the emission along with its negative effects on the environmental impact, makes the capture of this greenhouse gas a very important issue. The observation of the fact that the combustion of fossil energy contributes with about 84 % to the CO 2 emission in Iran, the general acceptance of gas in contrast with coal or oil, and the advantages of developed technologies applied in the Iranian petrochemical industry, make it possible to take advantages of the Amine-based CO 2 capture in Iran. In order to capture CO 2 from flue gas in one of the petrochemical plants in Iran, three different alkanolamines were utilized in this work.
Today, most of the CO 2 used by the chemical industry is extracted from natural wells. As the extraction price is close to that for recovery from fermentation and other industrial processes, it may be that soon CO 2 recovered from electric energy generation could find a large application in the chemical industry.
To be able to compare the amine processes, the same general configuration of the process, feed composition and flow rate was applied for alkanolamine plant. The amount of CO 2 recovery, amine consumption, mechanical and operational characteristics of absorption column, CO 2 purity in stripper column effluent, required energy of stripper and mechanical and operational features of stripper were compared for three types of amines.
The amount of CO 2 recovery for three types of amines is represented in Figure 10. According to this Figure for MDEA is less than 70%. It means that MDEA is weaker than two other amines and cannot be used for one stage processes. The amount of amine consumption for three types of amines is represented in Figure 11. As can be seen MEA process uses much fewer amines than other processes (about one fourth), i.e. this process is superior to other processes considering economic aspects. The low MEA consumption raises the reboiler duty substantially. The required pump power increases even more. Since the reboiler heat duty is the most important key to operating costs, this is a significant handicap (Chapel and Mariz, 1999). Mechanical and operational characteristics of absorption column for three types of amines are almost the same, except to column height. Height of absorption column for MEA plant (30 m) is considerably lower than DEA (43 m) and MDEA (61 m) plants. Since, column diameter for all plants are the same, it can be concluded that MEA plant is better than others considering mechanical aspects. Figure 12 indicates that, CO 2 purity in stripper column effluent is similar to all types of amines (above 97 %). Hence, this parameter could not be used as a criterion for selection of the optimum process.
As it is shown in the Figure 13, required energy of stripper for DEA plant is significantly smaller than other amine plants (about one tenth).  Taking all parameters into account, it can be concluded that the MEA plant is the best choice for separation of CO 2 from fuel gases.
The removal of CO 2 from flue gases using an amine depends on the gas-liquid mass transfer process. The chemical reactions that permit diffusion of CO 2 in the liquid film at the gas-liquid interface enhance the overall rate of mass transfer. Thus, the CO 2 removal efficiency in the absorber is a function of various parameters that affect the gas-liquid equilibrium (e.g., flow rates, temperature, pressure, flue gas composition, CO 2 concentration, alkanolamine concentration and absorber design). Similarly, the conditions and detailed design of the stripping column affect the energy requirements and overall performance of the system. MEA is the most frequently used solvent for CO 2 absorption, and the greatest advantage of MEA is its relatively high loading. Two moles of MEA are needed for each mole of CO 2 absorbed, which represents the maximum equilibrium pickup and fixes the minimum circulation rate of MEA for completely treating a given quantity of acid gas.

Conclusions
In this chapter, the needs for CO 2 capturing were raised by presenting the negative health and environmental impacts of CO 2 emission in Iran. Direct relationship between fossil-fuel consumption and CO 2 emission was demonstrated in this study. Results show that CO 2 emission, especially from petrochemical plant, will have to be efficiently reduced. So, www.intechopen.com The Needs for Carbon Dioxide Capture from Petroleum Industry: A Comparative Study in an Iranian Petrochemical Plant by Using Simulated Process Data 93 chemical absorption technology for CO 2 capture in a petrochemical plant has been selected in this study.
In the present work, CO 2 capture from fuel gases of one of the petrochemical companies in Iran using three alkanolamines (MEA, DEA and MDEA) was simulated and optimized. Specifications of absorber and stripper and composition of exit gas and rich amine leaving absorber were initially reported as simulation results. Then, these alkanolamines were compared considering some parameters such as CO 2 capture amine consumption, mechanical and operational characteristics of absorber and stripper, and CO 2 purity and energy consumption. It was found that, MEA and DEA are capable to recover almost all of CO 2 from flue gases. Amine consumption in an MEA plant is one-fourth of another amine plant where its energy consumption is the same as MDEA plant and ten times larger than DEA plant. Considering mechanical and operational characteristics, it was realized that MEA plant meets economic and aspects better than other amine plants. Finally, taking all parameters into consideration it was deduced that MEA is the best alkanolamine for separation of CO 2 from flue gases in this issue.