Report Requirements (submit electronic and hard copy version) Due Date: 9 AM on May 5, 2014

Transcription

1 Spring 2014 EEC 503 Short Team Project Overall Objective In the team report on the project assigned to you it is expected that you will 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 the pertinent reaction engineering concepts in new situations and suggest quantitative models for at least part 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 (if called upon). 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 have less than 2 weeks to get it done! Report Requirements (submit electronic and hard copy version) Due Date: 9 AM on May 5, 2014 Format Page Limit 1. Objectives (clearly stated, typed) 1 2. Executive Summary (clear summary of work accomplished with conclusions, typed) 2 3. Clear presentation of the work done (typed) 3 to 8 4. Appendices (details, programs, etc.) (need not be typed), (scans of handwritten material suffice). List of projects: PROJECT 1. Conversion of Diluted Sulfur Dioxide to Concentrated Sulfuric Acid. PROJECT 2. Advancing Chemical Looping Combustion (CLC) Processes. PROJECT 3. Carbonation Process for Production of Sodium Bicarbonate. PROJECT 4. Production of Solar and Semiconductor Grade Silicon. PROJECT 5. Pharmaceutical Processing in Micro-Trickle Bed Reactors. PROJECT 6. Absorption of Carbon Dioxide in Amine Solutions. Each student should indicate the preference for each of the projects above (1 being the highest, 6 being the lowest) in an that must be submitted to me and Onkar by Monday, April 21, 6 PM. Also indicate your preferred partner(s). The assignment of a project to each team will be made by prior to the class on Tuesday April 21. Brief project descriptions are attached. 1

2 PROJECT 1. Conversion of Diluted Sulfur Dioxide to Concentrated Sulfuric Acid. One of the key air pollutants in the energy sector 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. 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 from such streams. 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 to explore the following situation: a single porous catalyst particle, which is completely internally wetted, surrounded totally or partially by a liquid film. Consider the gas phase to consist of air, carbon dioxide and sulfur dioxide (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. Illustrate how concentration of sulfuric acid (un-dissociated and dissociated) behaves as a function of time and of model parameters. Is it possible to create concentrated sulfuric acid? What happens to the solubility of sulfur dioxide in the liquid as ph drops and what happens to the catalytic reaction rate? What type of dynamic operation would be needed to maximize the concentration of sulfuric acid? Could that be achieved at reasonable mean reaction rates; that is how high should the catalyst activity and rate constant be? 6. Write and present your findings as per instructions provided. 2

3 PROJECT 2. Advancing Chemical Looping Combustion (CLC) Processes The novel technology of chemical looping combustion (CLC) provides 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 for a methane (or coal) burning power plant. 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. Select the desired carrier for your application. 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) and 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 and oxidized solid carrier are injected and the other in which air and the reduced solid carrier are fed. 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. Present a simplified 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. 7. Write and present your findings as per instructions provided. 3

4 PROJECT 3. 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 a high cost operation (due to high energy requirement for water removal). 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 preferably trona ore, is contacted by carbon dioxide in presence of some water vapor presents an attractive alternative for production of sodium bicarbonate for the dry injection process. Present a multi-scale reaction engineering analysis of the dry carbonation process. 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 reaction pathway 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 crystal growth. Present 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. 7. Write and present your findings as per instructions provided. 4

5 PROJECT 4. Production of Solar and Semiconductor Grade Silicon Traditionally semiconductor grade silicon was manufactured by hydrogen reduction of various purified chlorosilanes at high temperature. When trichlorosilane and hydrogen are used in the Siemens decomposer, the thermodynamic yield of silicon is about 30%. It was discovered in the 1980s that on the amberlyst catalyst chlorosilanes can be readily and economically converted to silane. Silane thermally decomposes above C to yield silicon at 100% yield. The challenge is to design a proper reactor type so that useful silicon product is obtained, that is particles close to theoretical density of silicon, which are at least 300 micrometers in diameter. Formation of silicon dust (particles smaller than 10 microns) must be avoided at all costs since it is both useless and potentially harmful (cause of explosions). Consider two reactor types: a) free space reactor, FSR, and b) fluidized bed reactor, FBR. a) In the FSR silane is injected into a heated tubular vessel where it instantly pyrolizes. The formed nuclei of silicon grow further by coagulation and effective collision of agglomerates. What are the maximum size particles that can be obtained? These particles can be fed as seeds to an additional reactor in series where silane is added. How many reactors in series would be needed to get an average product size of 300 microns? b) In a fluidized bed reactor (FBR) silane is injected into the bed of existing silicon seed particles of initial size of 100 microns. Silane reacts both to from nuclei that coalesce and grow by coagulation and also deposits silicon by CVD reaction on the existing particles. In addition these large silicon particles scavenge the fines formed by growth of nuclei from homogeneous nucleation. How large can now the seed particles grow? How can elutriation of fines and their capture by existing silicon particles accomplished. Study and update as needed the doctoral theses of Steven Lai and Yubo Yang (both done at Washington University Chem. Eng. Department) and present the updated models for the two reactors. Assume you want to generate 1000 kg/year of pure silicon. 5

6 PROJECT 5. Pharmaceutical Processing in Micro-trickle Bed Reactors Pharmaceuticals are traditionally made in batch operations. Recently there is a trend to conduct a number of catalytic oxidations and hydrogenations continuously in monoliths and/or trickle beds. Trickle beds, packed beds with small catalyst particles through which gas and liquid reactants flow concurrently, have been used for decades in petrochemical processing and production of bulk and specialty chemicals. The key issues are the flow regimes, flow pattern of the two phases, liquid-solid contacting and how these vary with the change of equipment scale and operating conditions. In all of the processes used in trickle beds so far inertial and viscous forces were important. At very small velocities of creeping flow, surface tension forces and gas-liquid and liquid solid interfacial forces play an increased role. 1. You task is to review the currently available knowledge on trickle beds ( e.g. recent review by Dudukovic, Kuzeljevic and Combest in Ullman s Encyclopedia of Chemical Processing and Ph. D. thesis by Kuzeljevic and Combest at EECE Dept. at Washington University) and present a summary as to how one would proceed to scaleup a trickle bed for classical application. 2. Then review a few selected papers on micro-trickle beds ( some will be provided to you by Onkar and me) and report how you would revise your suggestions for experimentation with trickle beds for scale-up of much smaller scale pharmaceutical production rates. You can pick a specific hydrogenation in the pharmaceutical industry for example. 6

7 PROJECT 6. Absorption of Carbon Dioxide in Amine Solutions Traditionally, regenerative carbon dioxide absorption from gas streams was performed by absorption in various amine solutions. Consider a 1000MW coal bring power plant and report the typical molar flow rate, composition and temperature of the exit gas stream for conventional combustion of coal with excess air. Select the recommended amine solution for absorption of CO Determine the effect of temperature on rate of absorption of carbon dioxide. 2. Determine the reaction regime and select the best reactor type for it and determine the reactor size needed for 50%, 90% and 99% removal of carbon dioxide. 3. At what temperature can you do the regeneration and how effective can it be what is the residual carbon dioxide content in the amine solution. 4. Present the energy balance for the absorption solvent regeneration operation. 5. Now consider oxy combustion, where coal is burned by pure oxygen in excess of carbon dioxide to control the combustion temperature, in the same 1000 MW power plant. Report the typical molar flow rate, composition and temperature of this exit gas stream. How do you propose to recover carbon dioxide from this stream? 6. Reality is much more complicated since you need to limit the emissions of mercury, sulfur dioxide and nitric oxides etc. from the exhaust gases. List the compounds and elements whose emissions are limited by EPA. Report whether their elimination by current technologies is done before attempts on CO 2 recovery or after? What would your suggestion be? 7