Raymond A. Adomaitis March 7, 2012 Class syllabus (http ...adomaiti/ench446/2012ProjectPart1.pdf ·...

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 drumcalculations

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 processoptimization

Process utility calculations, heat exchanger networks, pinchdesign

Separation sequences using simplified distillation columns


This semester

Two major chemical process design projects, both addressingcurrent topics in energy engineering:

1 Design of the ethanol purification section of a fuel-gradeethanol plant

Corn is fermented to produce ethanolFocus will be on comparative analysis of alternative separationmethodsIntended to reinforce basic process design and economicanalysis methods

2 Evaluation of shale gas processing systems

Appropriate for use in western MarylandMinimize environmental impact of these processing systemsProject objectives are less well-defined


Project 1 overview 1/23/12 10:31 PM

Page 1 of 1http://onlinelibrary.wiley.com.proxy-um.researchport.umd.edu/store…ftp.pdf?v=1&t=gxs9wa54&s=51c71c759be6d67b37bbdcc457f7660141281af1

portation costs or energy requirements for these preprocesses.The cost of all these is assumed to be built into the price ofcorn that is used as feed. The numerical data used in theoptimization and the cost analysis can be obtained from theauthors.

We use as case study a plant producing 61.29 M gal ofethanol a year, operating 360 days per year. The corn feedrate is taken to be 18 kg/s. The ethanol produced is 2.78 gal/bu of corn (1 bu 5 56 lb). On optimizing the energy inputinto the plant without any heat integration or structuralchanges to the distillation columns, a solution of 79,003 kW(or 38,038 BTU/gal of ethanol produced) is obtained as theenergy required to be input into the plant using steam as theutility. This design corresponds to the case when the me-chanical press is placed before the beer column and is shownin Figure 16. Also, note that the corn grit adsorber bed isused together with the molecular sieves. The productioncost for this design is found to be $1.34/gal ethanol andincludes the costs for the process equipment, steam andcooling water costs and other miscellaneous costs. The mis-cellaneous costs include corn cost, electricity cost, generaland administrative expenses, employee salaries, cost ofchemicals, and maintenance costs. Cost estimation for mostof the equipment was done using data from http://www.matche.com/EquipCost/index.htm (as of 10/26/2006)with some adjustments. To calculate the production cost, itwas necessary to predict the annualized capital investment

cost, for which a number of correlations were used for theequipment costing.

Using the flowrates, temperatures, and compositions of thestreams pertaining to various process units in the design, weperform heat integration and are able to reduce the total(steam) energy consumption in the plant to 64,957 kW(equivalently 31,276 BTU/gal of ethanol produced). Onreplacing the distillations columns with multieffect columns(3 columns for the beer column; 2 columns for the rectifica-tion column), and performing an overall heat integration forthe plant, we obtain a design that requires only 45,519 kW(or 21,916 BTU/gal ethanol). The multieffect column struc-tures for the beer column and the rectification column appearin Figures 17a, b, respectively. In these figures, the termsLP, IP, and HP stand for Low Pressure, Intermediate Pres-sure, and High Pressure, respectively.

The energy reduction in the system is shown in Figures18a, b with the help of T–Q diagrams8 for the beer columnand the rectification column.

The overall T–Q curve on using multieffect columnsshows the possibility of further heat integration in the plantand appears in Figure 19. On reducing the reflux ratios in thebeer columns to 1.0, and in the rectification column to 1.5,and using the same combination of multieffect columns andheat integration in the plant, the calculated energy consump-tion reduces to 35,880 kW (equivalent to 17,276 BTU/galethanol produced), which corresponds to a production cost of

Figure 16. Optimal design of bioethanol plant producing 61.29 M gal per year.[Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

AIChE Journal June 2008 Vol. 54, No. 6 Published on behalf of the AIChE DOI 10.1002/aic 1521

From Karuppiah R, Peschel A, Grossmann I, Martin M, Martinson W, and Zullo L, Energy optimization for thedesign of corn-based ethanol plants, AIChE J., 2008 54 1499-1525.


Project 1 goals, by week

1 Purification process overall material balance; non-ChemCADdesign of beer and rectification columns (individual projects)

2 ChemCAD design of beer and rectification columns; summaryof utilities; basis for economic analysis

3 Design of molecular sieve absorbers as the final step inproducing fuel-grade ethanol; operation and regeneration ofabsorbers

4 Energy integration and economic analysis of completeseparation system

5 Analysis of multieffect distillation to reduce energyconsumption in the beer and rectification columns

6 Safety issues, final report, group presentation


Subproject 1.1

Design basis for the ethanol purification system

60× 106 gal/yr ethanol plant (seehttp://www.neo.ne.gov/statshtml/122.htm for representativeplant 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 approximately11% ethanol and 35% solids by weight.

After the mechanical press, we estimate the feed to the beercolumn to consist of 17% ethanol by weight and the remainderwater. The stream is at 1 atm pressure and 30o C.


Subproject 1.1

Design basis, continued

For the initial design calculations, assume the entirepurification process operates at 1 atm

Use the following initial values for column distillate andproduct stream compositions

1 Beer column distillate ≤ 72% ethanol by weight2 Rectifying column distillate is as close to the azeotrope as

possible3 Absorber effluent is 99.9% ethanol by weight


Subproject 1.1

Report (individual assignment)

1 Convert project specifications to SI units

2 Compute an overall material balance for the ethanol andwater 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, reportingthe same quantities

5 Typewritten report summarizing the design basis andpreliminary design

6 Validation of VCL usage


Binary distillation review

Basic assumption: yn and xn are at equilibrium at stage (tray) n ofN.

A material balance around the top of the column and betweenstages n and n + 1 gives the top (rectifying, enriching) sectionoperating equation:

Vn+1yn+1 = Lnxn + DxD

yn+1 =Ln

Vn+1xn +

D

Vn+1xD

where xD is the distillate concentration of the lower-boilingcomponent.


Binary distillation review - continued

Likewise, a material balance around the bottom of the column andbetween stages m and m + 1 gives the bottom (stripping) sectionoperating equation:

Lmxm = Vm+1ym+1 + BxB

ym+1 =Lm

Vm+1xm −

B

Vm+1xB

where xB is the bottoms concentration of the lower-boilingcomponent.



Defining the external reflux ratio r as

r =L0D

=liquid returned to column

distillate

we can find by constant molal overflow

LnVn+1

=r

r + 1

Likewise, the external reboil ratio is

s =VN+1

B=

reboiler vapor returned to column

bottoms

and so by CMOLm

Vm+1=

s + 1

s



This gives the top operating line as

yn+1 =r

r + 1xn +

xDr + 1

the bottom operating line

ym+1 =s + 1

sxm −

xBs

and the feed quality q defined by

hF = qhL,satF + (1− q)hV ,satF

to give

LB − LT = qF

VB − VT = (q − 1)F

y =q

q − 1x − zF

q − 1


MATLAB McCabe-Thiele

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

xe

y e

ethanol−water fractionation

123456

7

8

9

VLEenrichingstripping

0 2 4 6 8 1075

80

85

90

95

100

stage

tem

pera

ture

deg

. C

stage temperature

Results produced by column.m for r = s = 3


Project 1.1 - my results

Assume plant operates 350 days/year, 17% by wt ethanol to beercolumn, 99.5% (molar) overall ethanol recovery

ethanol product 128.6 mol/s

ethanol to beer column 129.3 mol/swater to beer column 1614 mol/s

F 1743 mol/sxF 0.0742

Mechanical press product stream at 30o C and 101325 Pa.


Project 1.1 - my beer column

minimum external reflux ≈ 0.5 =⇒ generally use 1.1 to 2rmin

minimum stages: 3 at total reflux

0 0.2 0.4 0.60

0.1

0.2

0.3

0.4

0.5

0.6

xe

y e


1

2

3

456

VLEenrichingqstripping

1 2 3 4 5 685

90

95

100

stage

tem

pera

ture

deg

. C

stage temperature


Project 1.1 - my beer column summary

r 2q 1 (preheat feed to bubble point)

NT 4 + partial reboiler + partial condensernF 2

D 269.7 mol/sxD 0.4772Tc 358 K (85o C)

B 1473 mol/sxB 0.00033Tr 373 K (100o C)

Higher reflux ratio to help offset higher-than-expected number ofstages relative to literature.


Project 1.1 - my rectification column

minimum external reflux ≈ 2.1 =⇒ generally use 1.1 to 2rmin

minimum stages: 11 at total reflux

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

xe

y e


123456789101112131415

16

17

18

1920

VLEenrichingqstripping

0 5 10 15 2075

80

85

90

95

100

stage

tem

pera

ture

deg

. C

stage temperature


Project 1.1 - my rectification column summary

r 3q 0 (vapor from beer column condenser)

NT 18 + partial reboiler + partial condensernF 16

D 151.3 mol/sxD 0.85Tc 351 K (78o C)

B 118.3 mol/sxB 0.00034Tr 373 K (100o C)

ethanol recovery:0.85(151.3 mol/s)

129.3 mol/s= 0.9951 (relax this constraint?)


Subproject 1.2

Report (group assignment)

1 Cover page with team number, date, honor pledge, groupmembers, member contributions, and summary of contents

2 ChemCAD design of beer and rectification columns: singlepage process flowsheet; single page stream summary; singlepage with summary of both column designs

3 Single page of heating/cooling duties for feed preheat andboth 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


Subproject 1.3

ObjectiveDesign of molecular sieve absorbers as the final step in producingfuel-grade ethanol; operation and regeneration of absorbers

Based on Karuppiah, Peschel, Grossmann, Martin, Martinson, andZullo, Energy optimization for the design of corn-based ethanolplants, AIChE J., 2008 54 1499-1525, we consider a zeoliteadsorption process with the following characteristics:

1 Adsorption and regeneration processes take place at 368 Kand 101325 Pa

2 Air for drying is available at 303 K and 70% relative humidity

3 The adsorption potential of the zeolite is adsp = 0.08 kgwater/kg zeolite

4 The absorption process vessels are sized such that thesaturation time is ts = 360 s


Subproject 1.3

For this project, we further assume that1 We cannot neglect the heat of adsorption during adsorption

and desorption processes - for now, assume the heat ofadsorption equals the latent heat of vaporization

2 No ethanol is adsorbed3 Air leaving the absorber vessel during regeneration is at 368 K

and 70 % relative humidity4 We use two process vessels5 Zeolite density is 1000 kg/m3


1 Report the size of the process vessels2 Report the inlet/exit stream compositions and properties

during the adsorption and regeneration phases of operation3 Propose an industrial zeolite for this process and estimate the

cost of the absorber material


Subproject 1.4


1 Revise your absorber design based on the practical constraintsidentified in your preliminary design calculations (e.g., increaseswitching time, increase regeneration air flow rate, etc.)

2 Flowsheet of the complete separation system with no energyintegration

3 Capital and operating costs for base-case design; report as anannualized cost with a 20 year plant life, 10% interest rate

4 Create a table of energy sources and sinks; develop a rigorousstrategy for assessing the maximum reduction possible usingenergy integration assuming a 10o C minimum approachtemperature

5 Flowsheet and economic analysis of energy-integrated design


Subproject 1.5


1 Examine your beer and rectification column designs afterenergy integration; which has the higher condenser/reboilerenergy demands and why?

2 Split the beer column feed stream into two equal flows; sendone of the streams to a beer column with design specifications(reflux ratio, total trays, feed tray, etc) exactly the same asyour energy-integrated design.

3 Design a new, higher-pressure column for the remaining feedstream such that its condenser temperature ≥ 100o C +∆Tmin

4 Re-adjust the two feed stream flows so that Qatmreb = −Qhi P

cond

5 Compare the new process utility and capital equipment, andannualized costs to your previous optimized design.


Project 1 base case (0), energy integrated (1) costs

1 2 3 4 5 6 7 8 90

5

10

15

20

25

randomized team number

cost

−−

$106

cap0op0cap1op1


Annualized costs

Our plant produces 60× 106 gal/yr of anhydrous ethanol, currentlyvalued at about $2.25/gal, resulting in

RG = $135× 106/yr gross revenue

so we compute the fractional cost of our separation process bycomputing the present worth of this annuity over the n = 20 yearproject life at i = 0.1 interest rate:

PRG= RG

(1 + i)n − 1

i(1 + i)n

If PROis the present worth of the annual operating costs, CF and

CW the fixed and working capital investments,

Fractional sep cost = 100CF + CW + PRO

PRG


Subproject 1.6

Report (individual assignment)Using the information provided by the Safety and ChemicalEngineering Education Website (www.SAChE.org), write a (max. 2page) report outlining process design changes you can suggest toyour group to improve the separation process safety. Be specificand concise.

Group activities (no group report due next week)

Note that final report and (5 min.) presentation are due intwo weeks.

Finish overall design by considering1 Reasonable pressure drops through columns2 Pumps and control valves3 Steam production on-site using natural gas; cooling towers for

cooling water circuits4 Product storage


Project 1: costs after double-effect distillation

1 2 3 4 5 6 7 8 9 10 110

2

4

6

8

10

12

14

16

18

20

randomized team number

cost

−−

$106

cap2op2


Subproject 1 final report

Page limit: 10 including title page; not including references andappendices.

1 Title page, including title, team number, members, membercontributions, date, project summary1, honor pledge

2 Process flow diagram3 Process stream summary4 Process equipment summary5 Project assumptions and basis, followed by a concise process

description including energy integration strategy, justificationfor process assumptions/decisions, alternatives considered, etc.

6 Safety and environmental issues7 Plant layout, geographical location, on-site storage8 Capital equipment summary9 Utilities, including on-site steam generation and cooling water1Project summary includes total capital cost, operating costs, separation

system ”fractional” cost, total fresh energy required/fuel energy producedRaymond 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 flowdiagram: concentrate on your specific design choices andnovel 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 March 7, 2012 Class syllabus (http ...adomaiti/ench446/2012ProjectPart1.pdf ·...

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