INQU 5021: CHEMICAL ENGINEERING DESIGN ISPRING 2014 SEMESTER: PARTIAL EXAM #1DEPARTMENT OF CHEMICAL ENGINEERINGUPR-MAYAGUEZInstructor: Dr. Moses N. Bogere

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Date out: April 28, 2014Due Date: May 6, 2014 by 4:00 PM (no exceptions)

Instructions: work within your groups. Submit your work with this …rstpage as your cover.

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Problem #1 (50%). Development of PFD and Economic Perfor-mance.Acetaldehyde (CH3CHO) is used primarily as an intermediate chemical for pro-ducing acetic acid, pyridine and pyridine bases, peracetic acid, pentaeythritol,butyrene glycol, and chloral. It is a colorless liquid with a pungent, fruity odor(like many aldehydes). Furthermore, it is a volatile and ‡ammable liquid that ismiscible in water, alcohol, ether, benzene„ gasoline and other common organicsolvents. There are at least two established commercial processes for produc-tion of acetaldehyde: vapor phase oxidation and vapor phase dehydrogenationof ethanol, all over catalysts.(A) Draw sketches or block ‡ow diagrams of two commercial processes for pro-ducing acetaldehyde, one based on oxidation and the other based on dehydro-genation of ethanol. Clearly identify the main process units and associatedreferences.

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(B) It is proposed to produce 100 million kg/yr acetaldehyde via vapor phasedehydrogenation of ethanol. The reactions that take place in the reactor aregiven below.Acetaldehyde:

CH3CH2OH ! CH3CHO + H2

Ethyl acetate:

2 CH3CH2OH ! CH3COOC2H5 + 2 H2

Butanol:2 CH3CH2OH ! CH3(CH2)3OH + H2O

Acetic acid:

CH3CH2OH +H2O ! CH3COOH + 2 H2

It is estimated that the conversion of ethanol to the various reaction productsis 70%. It is also given that the reactor e­uents contain 93% acetaldehyde,4% ethyl acetate, 2% butanol and 1% acetic acid [all on percent kilogram molebasis].(i) On hourly basis (assuming 8160 hours of operation in a year) calculate theamount of ethanol fed to the reactor, and the amounts of product and all othercomponents from the reactions.

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(ii) For the economic data we will assume that the costing of the plant is year2005 (just before the recession of 2008) and this data is to be extrapolated to year2013 (using Chemical Marketing Reporter or Chemical Engineering Magazine,M&S or CEPCI - chemical engineering plant cost indices). Here you may opt towork in British or SI units since some pricing data is in di¤erent units. Obtainpricing information (and references) of raw materials (including catalyst) andproducts, in increments of …ve years (starting 1985) up to year 2005 and thenextrapolate to year 2013. Some pricing data is given in the tables below.

Raw materials: EthanolYear: 1981 1985 1990Ethanol cost ($/lb): 0.27 0.346 0.50Ethanol cost ($/gal): 1.83 2.27 3.36

Raw materials: Ethanol Catalyst 1101 (or equivalent)Year: 1981 1985 1990Catalyst 1101 ($/ft3): 125 175 300

Product and by-products:Acetaldehyde 1981 1985 1990

Price ($/lb): 0.39 0.54 0.88Acetic acid

Price ($/lb): 0.245 0.32 0.45Hydrogen

Price ($/lb): 0.21 0.627 1.04Butanol & Ethyl acetate

Price ($/lb): 0.04 0.12 0.20Sold as fuel*

Price ($/MM Btu**): 4 12 20*sold as fuel stream containing hydrogen, butanol and ethyl acetate (use

natural gas prices).Many of the by-products are nowadays very useful for example ethyl acetate

is used as a solvent in the pharmaceutical industry in its purest form.

Waste stream treatment (if acetic acid, butanol & ethyl acetate are treatedas such):

Year: 1981 1985 1990Organics per ($/yr/lb/day): 32 51 91

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(iii) Based on year 2013 estimate the annual gross margin based on revenues andraw material costs. Since the catalyst to be used can last many years, excludeit from the annual operating costs (it can later be included in other variablecosts such as supplies). Search for information on cost of overall plant.

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(iv) Compare the saleable value of the by-products (excluding hydrogen) towaste treatment as a cost. Note that for the by-products to have value ad-ditional separation steps may be needed (requiring additional infrastructure).Can you estimate these?

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(v) Estimate the hourly cost of heating ethanol feed from 30 deg Celsius to thereactor conditions. Document any information about the cost of utilities inyear 2013 for: cooling water (90 deg F supply and 115 deg F maximum return),steam system (15, 50, 75 and 250 psig all saturated using o¤-site boilers).

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(C) Economic potential EP is generally evaluated in stages. The …rst stageEP is

EP = {product value}+{By-products value}-{Raw material costs}

-{Auxiliary material costs}-{Ecological costs}

Processing costs =fEquipment costs/Payback timeg

+fCost of utilitiesg+fAdditional environmental costsg

The economic potential at any stage n is then

EPn = EPI/O - {Processing costs}

For the acetaldehyde production process the EP can be determined as:

EP = EP I/O-{Rxtor costs/payback time}-{cost of sepns}

-{utilities costs}-{additional environ costs}

You can assume that environmental costs are 5-6% of product and by-productsales. It can be assumed also that sales/(all other costs in EP) ratio is 1.7 -3.0. Use this information to determine annual EP after obtaining the salescosts of products and by-products [assume 340 days of manufacture per year].Use sales cost data you compiled earlier for year 2013.

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(D) Develop a "crude" PFD for the acetaldehyde production process based on(some) patented data and product speci…cations below:

Acetaldehyde: 99+ mol% pure, 0.05 mol% ethanolHydrogen gas: 99+ mol% pureAcetic acid: 90+ mol% pureEthyl acetate & other light organics: 90+ mol% puren-butanol: 90+ mol% pure

Based on your design decisions (and based solely on sales value) your PFD maynot include all by-products in their pure form.Investigate any patented catalytic process that will improve selectivity. Show

also its PFD. As you can realize, there are a lot of opportunities for energy inte-gration (even steam generation) for this process. Identify points in the proposedPFD where additional heat exchangers are located. Compare the PFD to oneinvolving a catalytic process in terms of energy integration.

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Problem #2 (50%). Analysis and Cost of Heat Exchanger Network.In the HEN example solved in class and your project, the analysis was made

assuming that ¢min of 20±. First we need to …nd the annual cost of the heat

exchanger and then compare it to the cost when other ¢ values are assumed(in general though we would need to use some optimization tool to get theoptimum pinch point).

In the analysis, use the same heat exchanger network of seven heat exchang-ers given (this is a little bit ambitious or a serious assumption that needs to bechecked!). Use cost data for the hot oil as $3.50 and for the cooling water as$0.45 each per GJ. These costs take into account in‡ation and higher fuel costs.Use an overall heat transfer coe¢cient of 1400 W/m2¢K for each process-processheat exchanger and 900 W/m2¢K for each utilities heat exchanger. The heatexchanger purchase prices will be estimated from Table 7.2. It is assumed thatthe straight-line depreciation for 5 years is used and at which point there willbe no salvage value (means equipment can be thrown away and replaced). Anincome tax rate (ITR) of 39 percent (today’s rate) per year will be used. Usethe objective function given in class for the analysis. Assume that the totalinvestment (TI) in the heat exchanger system is assumed to be seven (7) timesthe total heat exchangers purchase price. The minimum acceptable return oninvestment or rate of return (ROI) is 15 percent per year after income tax.From the objective function of annual cost of operating the HEN:

= (annual cost of heating oil and cooling water)£(1-ITR)+(annual depreciation)£(1-ITR)+£

In the following parts answer the questions and show all the steps involved inobtaining the solution.

(a) Obtain the annual cost for the HEN when ¢min is 20±.

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(b) Obtain the annual cost for the HEN when ¢min is 10±.

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(c) Obtain the annual cost for the HEN when ¢min is 30±.

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(d) Compare the cost of the three networks and discuss which one you wouldchoose.

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(e) How realistic is it to assume that the original number of heat exchangerswould be the same as in parts (b) and (c)?

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