U of U CHEN 4253 - De Novo Sodium Reactor Design Homework Problem

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CHFEN 4253 Design I 1 Prof. T.A. Ring 1Homework Problem 4 De Novo Sodium Reactor Design Some of the hardest design work a chemical engineer faces is to design something from scratch. It is desired to produce 500 kg/hr Sodium metal from a 50 % wgt sodium hydroxide solution. You must develop a new process to do this. Sodium hydroxide solution can be concentrated to 95% wgt by evaporation and pumped as a melt into a reactor where a reducing agent is added to reduce the NaOH to sodium metal. The difficulty of this problem is to determine which reducing agent will be used from the list; hydrogen, carbon monoxide, carbon black, and natural gas. Please determine the operating conditions for each of these reactions, e.g. Temperature and Pressure needed, as well as the heat requirements for these reactions at the optimal operating conditions. Burning natural gas should provide any heating needs for the process and any cooling should be provided by DowTherm HT, an oil based heat transfer fluid, as cooling water presents a safety hazard, e.g. Na + H2O  ½ H2 + NaOH, (This reaction and the subsequent combustion of Hydrogen is known to knock toilets off the wall in High Schools across America). Often metal producing reactions are performed at high temperature under vacuum. Due to the vacuum seal needed only a metal reaction vessel should be considered with a maximum temperature of operation of 1150ºC for Inconel. You can assume that the reactor volume is 500 ft3 in all cases. With vacuum operation the air leak rate must be accounted for (see Chemical Engineering June 1991, p. 149 attached.) You are to decide which is the “most practical” reaction from the point of view cost, ease of operability and tolerance to known impurities, e.g. those coming from air leaks N2, O2 , etc. and any potentially problematic reaction products. Once the sodium metal is produced it may be in the vapor state at the operating conditions of the reactor. Sodium metal can be removed from the gaseous state by quenching as a liquid metal at temperatures above 97.8ºC, its melting point, and as a solid at temperatures below 97.8ºC. The cooling for the quench may be used for heating the molten 95% NaOH solution to the reaction conditions as a means to improve heat efficiency of the process. Also the gases produced by the reactor after quenching may be useful within the process. They must be highly reducing so that the metal will not be oxidized and may be useful as combustion gasses or recycle. Using thermo-properties decide which is the most practical reduction agent to use and under what conditions of temperature and pressure and select a single “most practical” reducing agent to proceed with as discussed above. Then develop a complete flow sheet with heat recuperation, recycle and minimization of effluents as needed to give the best process you can deliver to the client. Your homework solution should provide a gross profitability analysis for all reductants, a recommendation of which reducing agent you have selected and reasoning as to why this selection and a summary of your design with an attachment that gives all of your calculations.CHFEN 4253 Design I 2 Prof. T.A. Ring 2Data for DowTherm HT can be obtained from the site http://www.dow.com/products_services/index.html. Data for Natural Gas Natural gas composition and pressure: use that available at the sight of your plant. If no data can be found, use the data below: vol% methane 95 ethane 2.0 propane 1.5 butane 0.65 pentane 0.35 nitrogen 0.5 organic sulfur 2 ppm @5 barg Net Heating Value = 907 BTU/SCF Prices (see below) – Please use 2010 Industrial price of $5.54/1,000 ft3) Note the price has gone down recently. Why?CHFEN 4253 Design I 3 Prof. T.A. Ring 3 Dear Design II students For your HW 1 assignment you will need to do some economic analysis of the various processes to decide which reducing agent to use. You can use various price data available in the literature if you would like as long as you cite the references you used. If you are struggling, you will find useful the following Price information: Prices from Chemical Market Reporter 50% NaOH solution $116/short Ton Sodium Metal $2.2/kg Reductants Carbon (Metallurgical Coke) $80/short Ton CO $0.038/kg H2 $0.196/kg Cost of Energy assuming the burning of Natural Gas with net heating value given based upon the composition. Note that CO2 and water do not have heating values. If they are produced by the process they will be sent to the stack and therefore have a zero price. You may also have some trouble getting the thermochemical data for NaOH (l) as most tables contain data for NaOH(s) only. You can get this data (enthalpy, free energy, entropy and heat capacity), and other data that may be needed, using Nist’s ChemWebbook, see http://webbook.nist.gov/chemistry/. Best Wishes Terry A. RingCHFEN 4253 Design I 4 Prof. T.A. Ring 4Data for NaOH solutions in Figure 1.3. Dark line in Figure 1.3 is the BP of mixture. Note, BP of pure NaOH =1390ºC, MP of pure NaOH= 318.4ºC. From Himmelblau, D.M., “Basic Principles &Calculations in ChE., 6th edition. +.CHFEN 4253 Design I 5 Prof. T.A. Ring


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U of U CHEN 4253 - De Novo Sodium Reactor Design Homework Problem

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