Raymond A. Adomaitis March 7, 2012 To be covered: Class syllabus (http://www.isr.umd.edu/ adomaiti/ench446), grading Team selection (4 members per team) Initial project description Approximate schedule for year Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 1 / 29
What you should know from ENCH444 Flowsheet synthesis, simple material and energy balances, rapid evaluation of design alternatives Shortcut distillation, absorber column, and flash drum calculations Reactor vessel, distillation/absorber column, heat exchanger, pump, and compressor sizing and costing Return on investment, discounted cash flow calculations, project value ChemCAD simulation, detailed designs, elements of process optimization Process utility calculations, heat exchanger networks, pinch design Separation sequences using simplified distillation columns Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 2 / 29
This semester Two major chemical process design projects, both addressing current topics in energy engineering: 1 Design of the ethanol purification section of a fuel-grade ethanol plant Corn is fermented to produce ethanol Focus will be on comparative analysis of alternative separation methods Intended to reinforce basic process design and economic analysis methods 2 Evaluation of shale gas processing systems Appropriate for use in western Maryland Minimize environmental impact of these processing systems Project objectives are less well-defined Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 3 / 29
Project 1 overview 1 Figure From Karuppiah 16. Optimal R, design Peschelof A, bioethanol Grossmannplant I, Martin producing M, Martinson 61.29 M gal W, and per year. Zullo L, Energy optimization for the design of corn-based [Color figureethanol can be viewed plants, in the AIChE online issue, J., 2008 which54 is available 1499-1525. at www.interscience.wiley.com.] Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 4 / 29
Project 1 goals, by week 1 Purification process overall material balance; non-chemcad design of beer and rectification columns (individual projects) 2 ChemCAD design of beer and rectification columns; summary of utilities; basis for economic analysis 3 Design of molecular sieve absorbers as the final step in producing fuel-grade ethanol; operation and regeneration of absorbers 4 Energy integration and economic analysis of complete separation system 5 Analysis of multieffect distillation to reduce energy consumption in the beer and rectification columns 6 Safety issues, final report, group presentation Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 5 / 29
Subproject 1.1 Design basis for the ethanol purification system 60 10 6 gal/yr ethanol plant (see http://www.neo.ne.gov/statshtml/122.htm for representative plant capacities) All calculations are to be done and reported in SI units (m, kg, s, K, etc. with stream compositions given as mole fractions) Overall ethanol recovery: 99.5% (molar) Karuppiah et al. report the fermentor effluent as approximately 11% ethanol and 35% solids by weight. After the mechanical press, we estimate the feed to the beer column to consist of 17% ethanol by weight and the remainder water. The stream is at 1 atm pressure and 30 o C. Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 6 / 29
Subproject 1.1 Design basis, continued For the initial design calculations, assume the entire purification process operates at 1 atm Use the following initial values for column distillate and product stream compositions 1 Beer column distillate 72% ethanol by weight 2 Rectifying column distillate is as close to the azeotrope as possible 3 Absorber effluent is 99.9% ethanol by weight Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 7 / 29
Subproject 1.1 Report (individual assignment) 1 Convert project specifications to SI units 2 Compute an overall material balance for the ethanol and water components, including the molecular sieve absorbers 3 Appropriate shortcut or McCabe-Thiele design of beer column - report reflux ratio, number of trays, feed tray location, condenser and reboiler operating temperatures 4 McCabe-Thiele design of the rectification column, reporting the same quantities 5 Typewritten report summarizing the design basis and preliminary design 6 Validation of VCL usage Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 8 / 29
Binary distillation review Basic assumption: y n and x n are at equilibrium at stage (tray) n of N. A material balance around the top of the column and between stages n and n + 1 gives the top (rectifying, enriching) section operating equation: V n+1 y n+1 = L n x n + Dx D y n+1 = L n x n + D x D V n+1 V n+1 where x D is the distillate concentration of the lower-boiling component. Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 9 / 29
Binary distillation review - continued Likewise, a material balance around the bottom of the column and between stages m and m + 1 gives the bottom (stripping) section operating equation: L m x m = V m+1 y m+1 + Bx B y m+1 = L m x m B x B V m+1 V m+1 where x B is the bottoms concentration of the lower-boiling component. Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 10 / 29
Binary distillation review - continued Defining the external reflux ratio r as r = L 0 D = liquid returned to column distillate we can find by constant molal overflow L n V n+1 = Likewise, the external reboil ratio is s = V N+1 B and so by CMO r r + 1 reboiler vapor returned to column = bottoms L m = s + 1 V m+1 s Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 11 / 29
Binary distillation review - continued This gives the top operating line as y n+1 = the bottom operating line and the feed quality q defined by to give r r + 1 x n + x D r + 1 y m+1 = s + 1 x m x B s s h F = qh L,sat F L B L T = qf + (1 q)h V,sat F V B V T = (q 1)F ŷ = q q 1 ˆx z F q 1 Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 12 / 29
MATLAB McCabe-Thiele 1 ethanol water fractionation 100 stage temperature y e 0.8 0.6 0.4 8 7 3 21 4 5 VLE 0.2 enriching 9 stripping 0 0 0.2 0.4 0.6 0.8 1 x e 6 temperature deg. C 95 90 85 80 75 0 2 4 6 8 10 stage Results produced by column.m for r = s = 3 Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 13 / 29
Project 1.1 - my results Assume plant operates 350 days/year, 17% by wt ethanol to beer column, 99.5% (molar) overall ethanol recovery ethanol product ethanol to beer column water to beer column 128.6 mol/s 129.3 mol/s 1614 mol/s F 1743 mol/s x F 0.0742 Mechanical press product stream at 30 o C and 101325 Pa. Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 14 / 29
Project 1.1 - my beer column minimum external reflux 0.5 = generally use 1.1 to 2r min minimum stages: 3 at total reflux y e 0.6 0.5 0.4 0.3 2 ethanol water fractionation 1 0.2 VLE 3 enriching 0.1 4 q 56 stripping 0 0 0.2 0.4 0.6 x e temperature deg. C 100 95 90 stage temperature 85 1 2 3 4 5 6 stage Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 15 / 29
Project 1.1 - my beer column summary r 2 q 1 (preheat feed to bubble point) 4 + partial reboiler + partial condenser n F 2 N T D 269.7 mol/s x D 0.4772 T c 358 K (85 o C) B 1473 mol/s x B 0.00033 T r 373 K (100 o C) Higher reflux ratio to help offset higher-than-expected number of stages relative to literature. Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 16 / 29
Project 1.1 - my rectification column minimum external reflux 2.1 = generally use 1.1 to 2r min minimum stages: 11 at total reflux 1 ethanol water fractionation 100 stage temperature y e 0.8 0.6 16 11 10 123456789 12 14 15 13 17 0.4 VLE 0.2 18 enriching q 20 19 stripping 0 0 0.2 0.4 0.6 0.8 1 x e temperature deg. C 95 90 85 80 75 0 5 10 15 20 stage Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 17 / 29
Project 1.1 - my rectification column summary r 3 q 0 (vapor from beer column condenser) 18 + partial reboiler + partial condenser n F 16 N T D 151.3 mol/s x D 0.85 T c 351 K (78 o C) B 118.3 mol/s x B 0.00034 T r 373 K (100 o C) ethanol recovery: 0.85(151.3 mol/s) 129.3 mol/s = 0.9951 (relax this constraint?) Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 18 / 29
Subproject 1.2 Report (group assignment) 1 Cover page with team number, date, honor pledge, group members, member contributions, and summary of contents 2 ChemCAD design of beer and rectification columns: single page process flowsheet; single page stream summary; single page with summary of both column designs 3 Single page of heating/cooling duties for feed preheat and both reboilers and condensers 4 Single page summarizing economic basis: interest rate, process equipment cost factors, and estimate of steam, cooling, and electricity costs, all for 2012 Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 19 / 29
Subproject 1.3 Objective Design of molecular sieve absorbers as the final step in producing fuel-grade ethanol; operation and regeneration of absorbers Based on Karuppiah, Peschel, Grossmann, Martin, Martinson, and Zullo, Energy optimization for the design of corn-based ethanol plants, AIChE J., 2008 54 1499-1525, we consider a zeolite adsorption process with the following characteristics: 1 Adsorption and regeneration processes take place at 368 K and 101325 Pa 2 Air for drying is available at 303 K and 70% relative humidity 3 The adsorption potential of the zeolite is a dsp = 0.08 kg water/kg zeolite 4 The absorption process vessels are sized such that the saturation time is t s = 360 s Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 20 / 29
Subproject 1.3 For this project, we further assume that 1 We cannot neglect the heat of adsorption during adsorption and desorption processes - for now, assume the heat of adsorption equals the latent heat of vaporization 2 No ethanol is adsorbed 3 Air leaving the absorber vessel during regeneration is at 368 K and 70 % relative humidity 4 We use two process vessels 5 Zeolite density is 1000 kg/m 3 Report (group assignment) 1 Report the size of the process vessels 2 Report the inlet/exit stream compositions and properties during the adsorption and regeneration phases of operation 3 Propose an industrial zeolite for this process and estimate the cost of the absorber material Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 21 / 29
Subproject 1.4 Report (group assignment) 1 Revise your absorber design based on the practical constraints identified in your preliminary design calculations (e.g., increase switching time, increase regeneration air flow rate, etc.) 2 Flowsheet of the complete separation system with no energy integration 3 Capital and operating costs for base-case design; report as an annualized cost with a 20 year plant life, 10% interest rate 4 Create a table of energy sources and sinks; develop a rigorous strategy for assessing the maximum reduction possible using energy integration assuming a 10 o C minimum approach temperature 5 Flowsheet and economic analysis of energy-integrated design Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 22 / 29
Subproject 1.5 Report (group assignment) 1 Examine your beer and rectification column designs after energy integration; which has the higher condenser/reboiler energy demands and why? 2 Split the beer column feed stream into two equal flows; send one of the streams to a beer column with design specifications (reflux ratio, total trays, feed tray, etc) exactly the same as your energy-integrated design. 3 Design a new, higher-pressure column for the remaining feed stream such that its condenser temperature 100 o C + T min 4 Re-adjust the two feed stream flows so that Q atm reb = Qhi P cond 5 Compare the new process utility and capital equipment, and annualized costs to your previous optimized design. Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 23 / 29
Project 1 base case (0), energy integrated (1) costs cap 0 25 op 0 cap 1 op 1 20 cost $10 6 15 10 5 0 1 2 3 4 5 6 7 8 9 randomized team number Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 24 / 29
Annualized costs Our plant produces 60 10 6 gal/yr of anhydrous ethanol, currently valued at about $2.25/gal, resulting in R G = $135 10 6 /yr gross revenue so we compute the fractional cost of our separation process by computing the present worth of this annuity over the n = 20 year project life at i = 0.1 interest rate: P RG = R G (1 + i) n 1 i(1 + i) n If P RO is the present worth of the annual operating costs, C F and C W the fixed and working capital investments, Fractional sep cost = 100 C F + C W + P RO P RG Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 25 / 29
Subproject 1.6 Report (individual assignment) Using the information provided by the Safety and Chemical Engineering Education Website (www.sache.org), write a (max. 2 page) report outlining process design changes you can suggest to your group to improve the separation process safety. Be specific and concise. Group activities (no group report due next week) Note that final report and (5 min.) presentation are due in two weeks. Finish overall design by considering 1 Reasonable pressure drops through columns 2 Pumps and control valves 3 Steam production on-site using natural gas; cooling towers for cooling water circuits 4 Product storage Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 26 / 29
Project 1: costs after double-effect distillation 20 18 cap 2 op 2 16 14 cost $10 6 12 10 8 6 4 2 0 1 2 3 4 5 6 7 8 9 10 11 randomized team number Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 27 / 29
Subproject 1 final report Page limit: 10 including title page; not including references and appendices. 1 Title page, including title, team number, members, member contributions, date, project summary 1, honor pledge 2 Process flow diagram 3 Process stream summary 4 Process equipment summary 5 Project assumptions and basis, followed by a concise process description including energy integration strategy, justification for process assumptions/decisions, alternatives considered, etc. 6 Safety and environmental issues 7 Plant layout, geographical location, on-site storage 8 Capital equipment summary 9 Utilities, including on-site steam generation and cooling water 1 Project summary includes total capital cost, operating costs, separation system fractional cost, total fresh energy required/fuel energy produced Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 28 / 29
Subproject 1 group presentation Time limit: 5 minutes with 3 minutes for questions and transitions 1 Use readable text and figures 2 Do not spend time on motivation or the general process flow diagram: concentrate on your specific design choices and novel aspects of your design, such as energy integration 3 Summarize costs on a single slide, similar to project summary 4 Discuss safety and environmental aspects 5 Absorber system operation 6 Plant layout, integration with upstream processes Raymond A. Adomaitis Spring 2012, ENCH446, Project 1 29 / 29