Coal Chemical Looping - Research Paper Example

? Coal Chemical Looping Coal Chemical Looping The increasing demand for energy across the globe has been stimulated by the growth in populations and the development of businesses which seek to satisfy their objectives of expansion by seeking cost-efficient sources of power. In addition to this observation, the rising threat to the environment which is posed by issues such as the rise in pollution and emissions of greenhouse gases in the atmosphere have made the invention of new technologies and investment in innovations a move that is pivotal for future success. As it has been reported that the global demand for energy is likely to be fulfilled by the exploitation and utilization of fossil fuels in decades to come, the need for developing effective systems for the capture and storage of CO2 has become indispensible (Yue 2010). While, the significance of this observation is undeniable the present systems and frameworks which are utilized extensively in the industry are inadequate and do not support the advancement of certain aims and objectives that are associated with the development of suitable technologies. As noted by Yue (2010), present solutions for solving the issue are marked by the absence of cost-efficiency, capture efficiency and conversion efficiency which is an alarming scenario for both researchers and analysts alike. This observation proposes that the technology of chemical looping combustion (CLC) and its related processes have emerged as an innovation which presents numerous prospects and opportunities for the development of energy and power-related technologies by minimizing the risks, limitations and drawbacks that are associated with the solutions that are currently and presently available within the industry. Numerous studies and researches have established that the CLC technology boosts of impressive efficiency rates for the purpose of producing electricity and hydrogen in scenarios where the system of gasification is associated and integrated within the chemical looping technology (Yue 2010). Since the inception of the innovation, empirical studies have also been able to establish the types of suitable components that should be installed within an effective CLC system to maximize desired outcomes. This aspect involves the selection of solid fuels that can be used in chemical looping in addition with the oxygen carriers which have the potential to enhance the oxidation process. Even though, these observations have revealed the possibility of utilizing an extensive range of carbonaceous fuels and carriers, the scope of this paper focuses on the process of coal chemical looping such as the coal-direct looping process and the process of syngas chemical looping. Furthermore, the paper also explores the practical applications of chemical looping combustion in organizations such as General Electric and Alstom. In conclusion the research examines the advantages, challenges and limitations that are associated with the process of coal chemical looping in the light of recent researches and studies. The application of chemical looping combustion (CLC) processes is a revolutionary advancement and innovation in the industry, as stated by Yue (2010): Chemical-looping combustion (CLC) is a new alternative to conventional combustion that prevents the CO2 from being mixed in the combustion gases. This is accomplished by preventing the air-N2 to be present in the part of the reactor system where the oxidation of the fuel takes place. (p. 527) The introduction and subsequent incorporation of chemical looping techniques and strategies was impelled by the absence of frameworks that could be applied for the separation and conversion of chemicals during the occurrence of various product-related procedures (Fan 2011). While, this observation is reflective of the traditional demands and needs which initially required the launch of chemical looping techniques, contemporary applications of chemical looping essentially aim to fulfill the need of establishing a modern, optimized and effective reaction scheme for the purpose of reducing the loss of energy that is characteristic of the functioning of a system which converts both energy and chemicals (Fan 2011). Fan (2011) understands that chemical looping techniques have since undergone a drastic change to enhance their outcomes and applications in the industry. This view essentially highlights the fact that researchers and developers fully understand the need to reduce the emissions of CO2 due to the increased risk which the environment currently faces because of the release of the chemical compound. To achieve this aim, the process of chemical looping has been modified and altered so that the conversion of carbonaceous fuels such as coal-derived syngas and natural gas can be made proficient and efficient. The current applications of chemical looping involve the use of either coal or the syngas which is derived from the coal; the latter essentially serves as the feedstock in the process. According to Fan (2011) each of these processes are marked by the implementation of distinct operations as a consequence of which they are classified under varying classifications. Examples of these processes include; the Coal-Direct Chemical Looping Process and the Syngas Chemical Looping Process (Fan 2011). Fan (2011) states that during chemical looping combustion (CLC) coal-derived syngas must pass through several of stages before an outcome is achieved. As an advanced and highly sophisticated coal oxy-combustion technology chemical looping combustion integrates the utilization of a compound such as metal oxide which fundamentally performs the function of assisting the transportation of O2 to the fuel through the means of combustion air (Ciferno et al. 2009). The characterization of chemical looping combustion (CLC) as a sophisticated and advanced technology can be attributed to its ability to enhance the efficiency of the techniques and strategies which can be applied to generate CO2 that is of considerable purity through the process which requires the combustion of carbonaceous fuels such as gas. According to Siriwardane et al. (2009), the introduction of this technology transcends the discoveries that have been made in the field previously, because this advancement is unique and reflective of completely new applications and concepts that have not been transformed were not transformed into practical solutions previously. As stated previously, chemical looping combustion incorporates the use of metal oxide which plays the role of an oxygen carrier to facilitate the transportation of oxygen that is obtained from air to the carbonaceous fuel (Siriwardane et al. 2009). A distinct characteristic of this technology is that during the process of transportation, any incidence of a direct contact which may occur between the air and fuel does not take place (Siriwardane et al. 2009). The establishment of a comprehensive and effective chemical looping combustion system comprises of a fuel reactor and an air reactor, this distinguishing feature of these reactors is that in the fuel reactor the metal oxide only reacts to a gaseous structure of the fuel while, in an air reactor the metal which has been reduced is regenerated or restored in the form of its original structure that existed before the occurrence of the previous reaction (Siriwardane et al. 2009). In the first stage of chemical looping combustion, coal-derived syngas reacts with metal oxide as a result of which the compound is transformed to metal and this procedure takes place in a reducer. The outcome of this reaction leads to the development of two outputs which can be identified as steam and CO2 and the latter is subsequently detached (Fan 2011). In the second phase of chemical looping combustion, the metal is transported from the reducer and transferred to the combustor. The combustor assists the occurrence of a reaction, in which the air allows the metal oxide to restore and regenerate (Fan 2011). In comparison with conventional methods of combustion, a key benefit that is derived by the initiation of chemical looping combustion is that it hinders the dilution of a concentrated form of CO2 with N2, as a result of this the CO2 which is attained as an outcome of the process is of the purest form and this result is achieved by without the release of significant energy, the presence of which is otherwise mandatory for the process of separation to occur successfully (Siriwardane et al. 2009). Consequently, this phase of the process is followed by the stage which is marked by the recycling of metal oxide once it has been transported to the reducer. Fan (2011) identifies two distinct characteristics of oxidation which determine the heat of oxidation; these features are that of high-pressure and high-temperature. The high-pressure in this case, precisely allows air which is spent from the combustor to propel the turbine which is installed as an integral component of the entire system for the purpose of generating electricity (Fan 2011). Fig 1. The Process of Syngas Chemical Looping (Source: Fan 2011) While, coal and coal-derived syngas are used in several chemical looping processes, Fan (2011) notes that of those strategies and frameworks, the Coal-Direct Chemical Looping Process that was developed by The Ohio State University is highly effective and also commendable as it essentially simplifies prior schemes and proposals for the conversion of coal to present a comprehensive and straightforward solution that addresses some of the challenges and issues of chemical looping combustion which are discussed in subsequent sections. During the course of the Coal-Direct Chemical Looping Process the combustion of coal is conducted by the means of Fe2O3 that also holds similarity to the compound which is incorporated in the process of Syngas Chemical Looping (Fan 2011). In the first phase of the strategy, coal powder in addition with particles of Fe2O3 is transported to the reducer; consequently, coal is then transformed to or as a gaseous structure as H2 and CO2 through the application of varied contact patterns that can be used to assist the structure of gas and solid (Fan 2011). Fan (2011) states that the gas which is reductive in nature releases the states of Fe and FeO in addition to the production of H2O and CO2, the latter of which is marked by the presence of high concentration patterns. In the second phase of the chemical looping process, the particles of FeO and Fe which have been reduced in the prior stage within the reducer and transported to the oxidizer. During this phase, the reduced particles of the compound and steam react with each other and Fe3O4 oxidizes with hydrogen that has been produced as a result of the reaction between steam and the particles of FeO and Fe in the earlier stage (Fan 2011). Once this stage is executed, the Fe3O4 which has been produced previously departs from the reactor that is responsible for the production of hydrogen and is transported back to the reactor. This phase of the process is identifiable as the event of particle conveying. At this point, the particle of Fe3O4 is transformed back to Fe2O3 which is the form of its original structure as it had been before the occurrence of earlier stages (Fan 2011). As stated previously, the Coal-Direct Chemical Looping Process depicts a framework of coal conversion that is fairly simple in comparison with other complex techniques that are also inefficient due to several reasons. Fan (2011) states that one of the distinguishing and positive features of the Coal-Direct Chemical Looping Process which is also indicative of its efficiency can be judged by the basis of the hydrogen production efficiency of the scheme which is estimated to be 80%. Fig 2. The Process of Coal-Direct Chemical Looping (Source: Fan 2011) Sioshansi (2009) comments that the technology which enhances the hydrogen production efficiency of the coal-direct looping process and the process of syngas chemical looping prefers the integration of an alternative approach to advance the production of H2 that is free of carbon. This chemical looping technique is rooted in the implementation of an oxidation-reduction cycle in which the chemical looping strategy is to incorporate particles that are created from a metal which has a low state of oxidation as a carrier of oxygen. Another chemical looping strategy that is implemented during the course of coal-direct chemical looping and syngas chemical looping is associated with the division of the phase into two reactors. Sioshansi (2009) asserts that by choosing to classify the process into these stages, high purity H2 is achieved by because in one reactor the oxidation of coal is conducted separately while, the other reactor allows the steam to reduce thereby, rendering the separation of gas to occur readily. The aspects of high-pressure and high-temperature can also be highlighted as the positive factors that are related to both coal-direct chemical looping and the process of syngas chemical looping. As these schemes of coal conversion allow the generation of a stream of CO2 which is ready for sequestration at a high pressure, this feature is conducive to the exclusion of extra charges and expenses that maybe incurred otherwise during the stages in which pressurization is setup (Sioshansi 2009). The industry-wide applications of chemical looping processes that are associated with coal and coal-derived syngas has become extensive since, the introduction of the technology. Furthermore, various companies and organizations that have been operating within the industry have also developed and launched their versions of chemical looping processes to meet their requirements of energy. For example, General Electric has invested in a technology, which makes use of either biomass or coal for the purpose of generating power and hydrogen (Dahlquist 2013). Even though, this technology shares certain aspects and features with the instruments, strategies and coal conversion schemes that have been implemented by other organizations, it demands the requirement of placing three fluidized beds that are fundamental to the execution of each reaction that is needed for the completion of this process. In the initial stage of the process, coal is transformed into a state which is not completely gaseous by the means of steam which generates syngas, consequently, the second stage is marked by the transportation of solids such as sulfate into the second reactor where these solids are reduced to via the Fe2O3 compound which is launched into the system through the third reactor (Dahlquist 2013). Another practical application of the use of coal-based chemical looping processes is that of the French multinational company Alstom which has launched a scheme of coal conversion that can be configured in accordance with the specific and precise requirements of the organization, these configurations comprise of three modes which are that of a) the combustion of coal b) the gasification of coal for the production of syngas c) and the gasification of coal for the generation of hydrogen (Dahlquist 2013). Even though, the benefits and advantages that are derived by the execution of chemical looping combustion are widely accepted by researchers, Siriwardane et al. (2009) state that the availability of empirical data, studies and information with regards to the combustion of coal and other solid fuels is highly limited and restricted. This view is reflective of the fact, that there are numerous issues and challenges which still exist in the development of chemical looping processes namely the Coal-Direct Chemical Looping Process and the Syngas Chemical Looping Process which involve the chemical looping combustion of coal-derived syngas and coal using oxygen carriers. The foremost issue which may hinder the extensive application of chemical looping processes that use oxygen carriers has emerged as a consequence of the demands, requirements and conditions that must be met and satisfied before the scheme is implemented by a prospective manufacturer, company or organization. The first condition dictates that the oxygen carrier should be marked by the presence of an adequate rate that can be applied to a range of reactor systems, the second issue is associated with the condition that the carrier must facilitate a desired release of oxygen to assist the carrier interactions between coal and oxygen, additionally, the oxygen carrier must also have a reactivity which is secure, constant and steady enough so that it can be applied to a range of cycles over a period of time (Siriwardane et al. 2009). Apart from these features, an oxygen carrier should also be characterized by the presence of a high resistance to attrition and a minimal degree of reactivity when brought in contact with various contaminants such as ash (Siriwardane et al. 2009). Recent studies and researches which have been conducted to establish the suitability and effectiveness of metal oxide oxygen carriers and solid fuels that can be utilized during the process of chemical looping combustion have revealed beneficial conclusions to enhance the development and application of pertinent schemes, strategies and techniques. Siriwardane et al. (2009) found that with regards to the direct combustion of coal, metal oxides such as Fe2O3, CuO and NiO have the capability of acting as a provider of oxygen. The findings of Leion, Mattisson and Lyngfelt (2008) revealed similar observations regarding the suitability of the application and incorporation of Fe2O3 in the process. The recommendations of the research stated that it is desirable to initiate a process of direct coal combustion when utilizing the suggested metal oxides however, the process of solid circulation and the component which allows the division of ash and metal oxides must be enhanced for the achievement of positive outcomes and successful results (Siriwardane et al. 2009). Commenting on the various other strategies which can be used for the enhancement of the chemical looping combustion, Jin and Ishida (2004) suggest that the natural gas combustors show a minimum degree of reactivity to a coal gas fueled chemical looping combustor. The implications of this finding are fundamental to the development of strategies and techniques for the enhancement chemical looping processes that are based upon coal and coal-derived syngas. References Ciferno, J. P., Fout, T. E., Jones, A. P., & Murphy, J. T. (2009). Capturing carbon from existing coal-fired power plants. Chemical Engineering Progress,105(4), 33. Dahlquist, E. (2013). Technologies for converting biomass to useful energy. Boca Raton: CRC Press. Fan, L. S. (2011). Chemical looping systems for fossil energy conversions. Wiley. com. Jin, H., & Ishida, M. (2004). A new type of coal gas fueled chemical-looping combustion. Fuel, 83(17), 2411-2417. Leion, H., Mattisson, T., & Lyngfelt, A. (2008). Solid fuels in chemical-looping combustion. International Journal of Greenhouse Gas Control, 2(2), 180-193. Sioshansi, F. P. (2009). Generating electricity in a carbon-constrained world. Oxford: Academic. Siriwardane, R., Tian, H., Richards, G., Simonyi, T., & Poston, J. (2009). Chemical-looping combustion of coal with metal oxide oxygen carriers. Energy & Fuels, 23(8), 3885-3892. Yue, G., International Conference on Fluidized Bed Combustion, & International Conference on Fluidized Bed Combustion. (2010). Proceedings of the 20th International Conference on Fluidized Bed Combustion: [the proceedings of the 20th International Conference on Fluidized Bed Combustion (FBC) collect 9 plenary lectures and 175 peer-reviewed technical papers presented in the conference held in Xi'an China in May 18-21,2009]. Berlin, Heidelberg: Springer-Verlag Berlin Heidelberg. Read More