EEC 503 Term Project No 2

Transcription

1 Overall Objective EEC 503 Term Project No 2 Spring 2012 In preparing this term paper you are expected to demonstrate: a) resourcefulness in (i) outlining of and focusing on the problem, (ii) using effectively the library, the web and other sources of information, (iii) organization and team effort b) ability to utilize some of the general reaction engineering and transport concepts in new situations and suggest quantitative modes for at least parts of your problem c) ability to present your findings in a concise and clear manner in a written report and in a brief oral presentation. Keep in mind that all engineering projects are open-ended, i.e. given more time and more information a better job can be done. The trick is to do the job well enough without spending all the time doing it! You only have 3 weeks to get it done! Report Requirements Due Date: May 3, 2012 Format Page Limit 1, Objectives (clearly stated) 1 2. Executive Summary (clear summary of work accomplished with conclusions) 2 3. Description of work done 5 to 8 4. Appendices (details, programs, etc.) within reason May 3: Written report (one per group) due. Team oral presentations to be scheduled List of projects to choose from: PROJECT 1. Conversion of Diluted Sulfur Dioxide to Concentrated Sulfuric Acid. PROJECT 2. Advancing Chemical Looping Combustion (CLC) Processes PROJECT 3. Engineering Micro-Algae Growth as a Source of Renewable Energy PROJECT 4. Novel Carbonation Process for Production of Sodium Bicarbonate PROJECT 5. Conversion of waste gas CO, CO 2 and Hydrogen to Useful Chemicals Each team should indicate their preference for the projects above (1 being the highest, 4 being the lowest) in an that must be submitted by Monday, April PM. The assignment of a project to each team will be made by prior to the class on Tuesday April 17. Brief project descriptions are attached. 1

2 PROJECT 1. Conversion of diluted sulfur dioxide to concentrated sulfuric acid. One of the key air pollutants is sulfur dioxide. Many chemical and metallurgical processes produce large volumes of waste gases with small residual concentration of sulfur dioxide. This is also true of coal producing power plants. Air quality regulation standards do not allow venting of such gases to the environment. End of the pipe treatments by absorption or adsorption are available but create liquid or solid waste disposal problems. Converting such dilute streams of sulfur dioxide to concentrated sulfuric acid would create a product that can be sold. Your task is to examine whether such conversion can be achieved in a catalytic reactor. To do this you are expected to: 1. Summarize typically encountered dilute sulfur dioxide exhaust streams and their composition and flow rates. Pick a representative stream to work with. 2. Outline currently available methods for sulfur dioxide capture and/or conversion. 3. Outline the process for catalytic conversion of sulfur dioxide to sulfur trioxide and its absorption by water to sulfuric acid. Consider activated carbon as carrier of possible additional metallic sites to speed up the reaction. 4. Develop a model for the following situation: a single porous catalyst particle, which is completely internally wetted, surrounded by liquid film. Consider the gas phase to consist of air, carbon dioxide and sulfur dioxide only (sulfur trioxide is essentially all in the liquid phase; ignore for now other components in the gas, like NO x, etc.). Assume that the catalytic reaction rate is first order in concentration of dissolved sulfur dioxide (make the rate constant a parameter in your model with some reasonable dependence on temperature). Assume a semi-batch system such that fresh gas is continuously brought into the contact with the catalyst pellet and its surrounding liquid (keep the ratio of liquid to solid as a parameter in your model). Develop the appropriate equations describing mass transfer between gas and liquid film, liquid film and exterior catalyst surface and diffusion and reaction in the catalyst particle. Describe fully any simplifications or assumptions that you need to make in order to solve the model. 5. Solve a simplified model to illustrate how concentration of sulfuric acid (undissociated and dissociated) behaves as a function of time and model parameters. Is it possible to create concentrated sulfuric acid? Is it possible to do it in reasonable contact time? What are the key [parameters determining this? 6. In order to maintain a high average reaction rate, clearly the liquid on and in the catalyst particle must be periodically or continuously replenished. Consider a trickle bed (packed bed with concurrent gas liquid flow and periodic liquid feed and a rotating packed bed with continuous countercurrent gas liquid feed. Briefly describe what are the figures or merits and possible drawbacks for each. What are critical issues that need to be evaluated before implementation? 2

3 PROJECT 2. Advancing chemical looping combustion (CLC) processes The novel technology of chemical looping combustion (CLC) is advertised to provide the potential for clean power generation and simultaneous concentrated carbon dioxide sequestration as it has a lower energy penalty due to its inherent separation of CO 2. CLC is a two-step combustion process; fuel and air are not mixed during combustion but are contacted via intermediary oxygen carrier (OC). Metal oxides on or without carrier are suggested as desirable materials. In Europe where this concept is particularly advanced one envisions metal oxides circulating between two fluidized beds; oxidizing the fuel in one bed and being regenerated with air in another bed. Your task is to present a multi-scale analysis of this process and examine its figures or merit and drawbacks, and if, possible, suggest improvements. In order to simplify the problem consider natural gas (methane) to be your fuel and air the source of oxygen. You are expected to: 1. Summarize metal/metal oxide combinations suggested for CLC. Select a typical pilot plant and plant scale of operation. Outline the reactions postulated for interaction of these metals/metal oxides with fuel (methane) and with air. Calculate the thermodynamic equilibrium as function of temperature. 2. Determine the oxygen carrier capacity based on thermodynamic analysis of the best carriers and report it as moles (and kg) of oxygen carried per kilogram of carrier. Outline what is known about the kinetics of the reactions involved on these particles, possible rate limiting steps, and the limits on oxygen utilization. Also indicate whether the particles are attrition prone or not. 3. Develop the following models: i)a single porous particle oxidized with air and show anticipated conversion as a function of time at different temperatures (indicate what your model parameters are); ii) a single porous oxidized particle reduced with fuel (methane) show anticipated conversion as a function of time at different temperatures (indicate what your model parameters are). Make an energy balance for each situation. 4. Develop a simple model for the two fluidized beds, one in which fuel is injected and oxidized solid carrier and the other in which air is fed and the reduced solid carrier. Assume that each fluidized bed behaves as a perfect stirred tank for solids and gas. Show what the solids flow-rate rate must be to maintain in a stable steady state operation. Make an energy as well as mass balance. Report the energy efficiency. 5. Examine the effect of flow pattern on energy efficiency, by assuming that solids are well mixed but gas is in plug flow in each reactor. 6. Ultimately the fate of this technology may depend on our ability to find the solid carrier of enormous oxygen capacity that can withstand many cycles between fluidized beds. Thus assess the possibility of using these carriers in packed beds in which gas will be cycled and not solids. 3

4 PROJECT 3. Engineering Micro-Algae Growth as Source of Renewable Energy Micro-algae are widely recognized as efficient solar energy harvesters and fastest growing photosynthetic organisms. They are possible sources of bio-fuels due to high lipid content (in some strains up to 80%) and are also used in generating high value added compounds (production of pharmaceuticals, food additives, single cell proteins etc.). Since algae are utilizing CO 2 in their growth cycle, they could potentially serve as a renewable, low carbon footprint source of energy. ExxonMobil and other oil giants have invested billions in small bio-companies to use genetic engineering in producing desirable algae strains. However, for their use and scale up to meaningful production levels a science based foundation for design and scale up of the micro-algal growth systems photo-bioreactors (PBRs) is needed. The growth of micro-organisms in PBRs is a very complex function of photosynthetic processes, reactor flow dynamics, and irradiance distribution. Your task is to present a multi-scale reaction engineering analysis of such system and develop a systematic approach to their scale up. You are expected to do the following: 1. Summarize the key elements on micro-algae growth in PBRs. (Look over the thesis of Huping Luo from CREL). Summarize the importance of photosynthesis rate radiation intensity (P-I) curve, flashing frequency, photon transfer models (Beer- Lambert law), and experimental techniques for characterizing micro-algae growth rate and properties. 2. Outline the design of an experimental reactor for algae growth in which light intensity can be varied at will and the light absorption can be properly quantified and carbon dioxide flow controlled. (See thesis by Zhen Xue in CREL for ideas). 3. Develop a model for your experimental reactor and illustrate based on the kinetics proposed by Luo how light cycles can affect productivity. 4. Outline for unknown kinetics how could your experimental reactor be used to obtain rate data as a function of illumination intensity and frequency. 5. Compare the advantages of your suggested experimental reactor to the currently used ones and clearly outlined which variables your reactor can control and assess precisely that others cannot. 6. Based on your findings, suggest what large scale reactors would likely have to look like in order to optimize productivity. 4

5 PROJECT 4. Novel carbonation process for production of sodium bicarbonate The conventional commercial production of sodium bicarbonate involves the solution process in which soda ash is dissolved in spent liquor from previous reaction and the solution is carbonated with carbon dioxide to precipitate sodium bicarbonate. Crystals of the product are removed from the solution and dried in high cost operation. Then they are purified for food grade use. However, the use of sodium bicarbonate of lesser purity is sufficient in the highly effective dry injection method for capture of sulfur dioxide from exhaust gases of coal burning power plants. A dry carbonation process by which sodium carbonate (soda ash ), or even better trona ore, is contacted by carbon dioxide in presence of some water vapor presents an at reactive alternative for production of sodium bicarbonate for the dry injection process. Your task is to present a multi-scale reaction engineering analysis of the dry carbonation process. You are expected to: 1. Summarize the findings from the open and patent literature on dry carbonation of sodium carbonate (soda ash) and trona. 2. Outline the reactions occurring in the system that contains sodium carbonate and sodium bicarbonate in various crystal forms with and without water in the crystal lattice, and carbon dioxide and water at temperatures when these are likely in the vapor phase. Report the thermodynamic equilibrium conditions and most likely solid compounds as a function of temperature and carbon dioxide partial pressure. Describe the most likely mechanism by which the process proceeds and calculate the heat of reaction of each step in the sequence of reactions. Report whether reactions are endothermic or exothermic. 3. Consider a single spherical particle of soda ash composed of individual crystals exposed to gas containing an inert component e.g. nitrogen, carbon dioxide and water vapor. Postulate a mechanism by which this solid reactant will ultimately change to a particle of sodium bicarbonate. For example, consider the following possibility. Water vapor, by Kelvin effect, can condense in the micro pores between individual crystals of the solid reactant. Solid reactant may now dissolve into the micro pores and in presence of dissolved carbon dioxide react in solution to form the bicarbonate. Once bicarbonate becomes supersaturated it precipitates and its crystals grow. If reactions are exothermic water is ultimately driven off by the heat of reaction and dry product remains. If they are endothermic heat must be provided to drive the reactions and drive of water. 4. Develop a model for the reaction of a single pellet based on the above scenario or based on your own proposed mechanism. Follow the combination of approaches used in modeling gas-solid reactions and gas-liquid reactions followed by nucleation and 5

6 crystal growth. Present how would solid reactant conversion change in time at different temperatures as function of solid particle size, carbon dioxide partial pressure and ratio of original water to solid ratio. 5. Develop a model for a reactor processing the solids with co-current and countercurrent solid and gas feeds and discuss how solids deviation from plug flow affect productivity would. 6. Present the energy balance for the system. 6

7 EEC 503 spring 2012 PROJECT 5. Conversion of waste gas CO, CO 2 and Hydrogen to Useful Chemicals Look up in the recent journal and patent literature where based on carbon-1 chemistry it is suggested that low value exhaust gases can be converted to valuable low molecular weight chemicals after they are transferred to an aqueous solution. It is also suggested that homogeneous catalysts in solution would be readily poisoned due to presence of toxic to catalyst compounds in the waste gases. The same argument is given for not using heterogeneous catalysts. Claims are made that special strains of bacteria have often evolved close to the sources of these waste streams and that these bacteria can function well in bioreactors to generate the desired product at high selectivity. Study two systems. Select a specific product that can be made from CO and hydrogen and another one from Carbon dioxide and hydrogen. Assume that you have a bacterial strain that can indeed produce your product at 100% selectivity and write your stoichiometric equation based on such an assumption. For the reaction to proceed the two gases must dissolve in the liquid and then find the cell and diffuse into the cell and react to create more biomass growth (cell growth or multiplication) and secrete the specific product. Your task is to model the three most frequently used bioreactor types: 1 Stirred Tank 2. Bubble Column 3. Gas Lift loop reactor and find which has the largest reactor volumetric productivity as a function of operating conditions. For each reactor present the model assumptions and governing equations and indicate for gasses of low solubility that you are dealing with what the effect of pressure would be. Your temperature of operation is between 30 and f 50 degrees centigrade. For each reactor type report the dissipated power needed for the predicted volumetric productivities. Indicate which reactor type is most prone to mass transfer limitations and suggest how to overcome them at minimum additional dissipated power. Present the energy balance for the system. Write and present your findings in your final report as per instructions provided. 7