chemical calculations for chemical engineering. problems in material balance, recycle, bypass &...

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Chemical Calculations 1

Hi folks. I’m Ijotika and I am offering you a compilation of solved Chemical Calculations Problems.However, I omitted the solutions for educational purposes (you can ask for it. Like my mentor, I alsohate spoon feeding the student.

Originally, this compilation was a work of 5 person, I and 4 of my classmates. We failed this subject. Idon’t care why they failed. (OMG this is so simple. If you want to know why I also failed, just contact mein my e-mail.) Well, as part of the requirement to complete the unit, we were asked by our professor toresearch and compile these problems with their solution. After we submitted the drafts for her to check,I thought our task was complete. After 3 months of checking the solution (can you imagine that? Sheburned 3 months of our college life waiting for her approval.), she returned the papers noting that wehave to change some of us have the same problems solved. (Take note, when she returned the paper itwas only 10 days before closing the curtain.) So there we were digging again the net hoping to findanother set of problems that will save our grades. It’s not an easy task, but we managed to collect theneeded problems. After so much effort in editing, I managed to print this and pass it to her. She refusedto accept this because we’re late. Indeed, we’re 6 days late but you can’t blame us for it really is atiresome task—searching for problems that we don’t have idea if it really exist, unless we make our ownproblems (that is our last resort.) After so much persuading, she accepted the pile and said that she’llthink about giving our grade. (F*CK! Ka-pasamba mo!) After a couple of weeks, she asked again for ourdrafts for her to check (WHAT THE F*CK)... well to cut this crap short, three of my classmates passed hersubject in the end while I and my best bud didn’t.

The problems here, like I said, are compiled, came from different sources. You can find the referencebooks used at the end of every section. I also provided some definition of every section. I didn’t putextra lecture because I assume that you have acquired that knowledge from your professor.

If you have any questions, suggestions, comments or anything and everything, feel free to contact me @[email protected]. MABUHAY!!!

P.S. I uploaded this document because I want to help you guys that like me suffer/suffers/suffered fromthe wrath of our prof. this is for you guys.

P.P.S. By the way I came from the BICOL UNIVERSITY COLLEGE OF ENGINEERING here in Legaspi City,Albay, Philippines. So if ever you, BU CEngians, came across this page, you already knew which professorI’m talking about.

P.P.P.S. Please excuse my grammar. I am not goooooooooood in English.

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ijotika

user

Sticky Note

sa mga taga-BU: if ever ma-experience nyo rin ang naexperience ko.. just ask for my help and i'll be there... kontakin nyo lang ako sa e-ad ko...

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MATERIAL BALANCE

A material balance is an application of conservation of mass to the analysis ofphysical systems. By accounting for material entering and leaving a system, massflows can be identified which might have been unknown, or difficult to measure withoutthis technique. The exact conservation law used in the analysis of the system dependson the context of the problem but all revolve around mass conservation, i.e.that matter cannot disappear or be created spontaneously.

Therefore, mass balances are used widely in engineering and environmentalanalyses. For example mass balance theory is used to design chemical reactors,analyze alternative processes to produce chemicals as well as in pollution dispersionmodels and other models of physical systems. Closely related and complementaryanalysis techniques include the population balance, energy balance and the somewhatmore complex entropy balance. These techniques are required for thorough design andanalysis of systems such as the refrigeration cycle.

The general form quoted for a mass balance is The mass that enters a systemmust, by conservation of mass, either leave the system or accumulate within thesystem .

Mathematically the mass balance for a system without a chemical reaction is asfollows:

Strictly speaking the above equation holds also for systems with chemicalreactions if the terms in the balance equation are taken to refer to total mass i.e. thesum of all the chemical species of the system. In the absence of a chemical reaction theamount of any chemical species flowing in and out will be the same. This gives rise toan equation for each species in the system. However if this is not the case then themass balance equation must be amended to allow for the generation or depletion(consumption) of each chemical species. Some use one term in this equation to accountfor chemical reactions, which will be negative for depletion and positive for generation.However, the conventional form of this equation is written to account for both a positivegeneration term (i.e. product of reaction) and a negative consumption term (thereactants used to produce the products). Although overall one term will account for thetotal balance on the system, if this balance equation is to be applied to an individual

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species and then the entire process, both terms are necessary. This modified equationcan be used not only for reactive systems, but for population balances such as occurin particle mechanics problems. The amended equation is given below. Note that itsimplifies to the earlier equation in the case that the generation term is zero.

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MATERIAL BALANCE PROBLEMS WITHOUT REACTION

1. A lacquer plant must deliver 1000 lb of an 8% nitrocellulose solution. They have in stocka 5.5% solution. How much dry nitrocellulose must be dissolved in the solution to fill theorder?1

2. A liquid adhesive, which is used to make laminated boards, consists of a polymerdissolved in a solvent. The amount of polymer in the solution has to be controlled forthis application. When the supplier of the adhesive receives an order for 3000kg of anadhesive solution containing 13% by weight polymer, all it has on hand is (1) 500kg of a10% by weight solution, (2) a very large quantity of a 20 wt% solution, and (3) puresolvent.

Calculate the weight of each of the three stocks that must be blended together to fill theorder. Use all of the 10% by weight solution.2

P (1000lb)N= 0.08S= 0.92

1.00

M (lb) N= 100%

F (lb)N= 0.055S= 0.945

1.00

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3. Hydrogen pre-carbon in the form of core is burned.a. With complete combustion using theoretical air.b. With complete combustion using 50% excess air.c. Using 50% excess air but with10% of the carbon burning to CO only

IN EACH CASE CALCULATE THE GAS ANALYSIS THAT WILL BE FOUND BYTESTING THE FLUE GASES WITH AN ORSAT APPARATUS.3

4. An evaporator is concentrating solutions coming from two different sources. Thesolutions from the first source containing 10% NaCl and 10% NaOH flows at the rate of50 kg/min. the other solution containing 8% NaCl and 12% NaOH flows at the rate of 70kg/min. The two streams are fed directly to the evaporator. If 50% of the total water is tobe evaporated, calculate the composition and the flow rate of the product.4

50% H2O evaporated

Solution 150 kg/min

10% NaOH10% NaCl

? Compositions and flow rate

Solution 270 kg/min8% NaCl12% NaOH

5. The waste acid from a nitrating process contains 30% H2SO4, 35% HNO3 and 35% H2Oby weight. The acid is to be concentrated to contain 39% H2SO4 and 42% HNO3 byaddition of concentrated sulfuric acid containing 98% H2SO4 and concentrated nitricacid containing 72% HNO3 (wt). Calculate the quantities of 3 acids to be mixed to get1000 kg of desired mixed acid.

EVAPORATOR

BLENDINGConcentrated HNO3

72% HNO3

Desired mixed acid1000kg39% H2SO4,

42% HNO3

Concentrated H2SO4

(98%)

Waste acid

30%H2SO4, 35% HNO3

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REFERENCES:

1. David Himmelblau, Basic Principles and Calculations in Chemical Engineering 6th

edition.2. David Himmelblau, Basic Principles and Calculations in Chemical Engineering 6th


edition.4. Wilfredo I. Jose, Introductory Concepts in Chemical Engineering5. K.A. Gavhane, Introduction to Process Calculations

(www.google.com/books)

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MATERIAL BALANCE WITH CHEMICAL REACTION1. A natural gas consisting entirely of Methane (CH4) is burned with an oxygen enriched

air of composition 40% O2 and 60% N2. The Orsat analysis of the product gas isreported by the laboratory is CO2 : 20.2%, O2 : 4.1%, and N2 : 75.7%. Can the reportedanalysis be correct? Show all calculations.1

2. Plants in Europe sometimes use the mineral pyrites (the desired compound in thepyrites is FeS2) as a source of SO2 for the production of sulfite pulping liquor. Pyrite rockcontaining 48% sulfur is burned completely by flash combustion. All of the iron turnsFe3O4 in the cinder (the solid product), and a negligible amount of SO3 occurs in eitherthe cinder or the product gas. The gas from such as furnace is passed through milk oflime (CaO in water) absorbers to produce bisulfate pulping liquor. The exit gas from theabsorber analyzes: 0.07% SO2, 2.9% O2, 96.4% N2. (Refer to the figure)

Calculate the kg of air supplied to the burner per kg of the pyrite burned.2

3FeS2 + 8 O2 Fe3O4 + 6 SO2

CO2= 20.2O2= 4.1N2= 75.7

P

W

H4 100%

A enriched airO2 = 40N2= 60

A enriched airO2 = 40N2= 60

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3. A gas containing 80% CH4 and 20% He is sent through a quartz diffusion tube torecover the Helium. 20% by weight of the original gas is recovered, and its compositionis 50% He. Calculate the composition of the waste gas if 1ooKmol of gas are processedper minute. The initial gas pressure is 120kPa, and the final gas pressure is 115kPa.The barometer reads 740mmHg. The temperature of the process is 22°C.

4. Pyrites ore is used for the production of the sulfuric acid. The pyrites is 80% FeS2 and20% inert materials. The FeS2 is burned with 30% excess air based on the reaction,

4 FeS2 + 11 O2 2 Fe2O3 + 8 SO2Only 90% of the FeS2 follows this reaction. The rest goes as follows:

4 FeS2 + 15O2 2 Fe2O3 + 8 SO3What is the composition of the gases resulting in the combustion?

SO280% FeS2 SO3

20% inert materials O230% excess air N2

Inerts

5. A fed containing A, B and inerts enters a reactor. The reaction taking place is:2A + B C

The product stream leaving the reactor is having the following composition by mole:A=23.08%, B=11.54%, C=46.15, inerts= 19.23%. Find the analysis of feed on molebasis.

Basis: 100 kmol of product stream

Feed

BURNER

REACTORA,B, inerts

Product stream100 kmol

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REFERENCES:


edition.2. David Himmelblau, Supplementary Problems For Basic Principles and Calculations in

Chemical Engineering3. David Himmelblau, Basic Principles and Calculations in Chemical Engineering 6th

edition.4. Wilfredo I. Jose, Introductory Concepts in Chemical Engineering5. K.A. Gavhane, Introduction to Process Calculations

(www.google.com/books)

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RECYCLEIn a reactive process, there is generally some unreacted feed material found in theproduct. In order to reduce cost and increase efficiency, the unreacted material is oftenseparated and reused in a recycle loop.

Recycle may also be used to recover an expensive catalyst, maintain feedconcentration below certain levels, or in a totally closed loop to pump a cooling orheating fluid. Keep in mind that while flow rates of the process effluent, process product,and recycle vary, all three have identical composition.

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RECYCLE PROBLEMS WITHOUT CHEMICAL REACTION

1. Examine the given figure. What is the quantity of the recycle stream in kg/hr?1

C

Crystals carry off 4% H2O

(4 kg H2O per kg total crystals +H2O)

2. Based on the process drawn in the diagram, what is the kg recycle per kg feed if theamount of W waste is 100 kg? The known compositions are inserted on the processdiagram.2

X

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3. A planting plant has a waste stream containing Zn and Ni in quantities in excess of thatallowed to be discharged into the sewer. The proposed processes to be used as a firststep in reducing the concentration of several of the streams are listed in the table, whatis the flow ( ℎ ) of the recycle stream R32 if the feed is 1( ℎ ).3TABLE CONCENTRATION : g/LStream Zn NiF 100 10.0Po 190.1 17.02P2 3.50 2.19R32 4.35 2.36W 0 0D 0.10 1.00

4. A fresh feed (contains 5,000 kg of wet material) with 60% moisture is needed to bedried. To facilitate the operation, a part of dried product contains 5% water is recycledand mixed with the feed. The mixing stream of the recycle and the fresh feed contains30% water. Calculate the water removed and the recycle to feed ratio.4

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(R)

Fresh feed water evaporated (E)

60% moisture 30% water

5,000 kg 5% (P)

5. Sea water is to be desalinized by reverse osmosis using the schemeR

(S ) (B)Seawater Brine waste

1000lb/hr3.1 % Salt (T) x 5.25% salt

(P)

Given the data in the figure, determine; (a) the rate of waste brine removal, (b)the rate of desalinized (potable water) production; (c) the fraction of the brine leavingthe reverse osmosis cell (which acts in essence as a separator) that is recycled.5

REFERENCE:




edition.4. Wilfredo I. Jose, Introductory Concepts in Chemical Engineering5. David Himmelblau, Basic Principles and Calculations in Chemical Engineering 6th

edition.

Drier

ReverseOsmosis Cell

40% salt (M)

Desalinized water500 ppm salt

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RECYCLE PROBLEMS WITH CHEMICAL REACTION

1. Boron trichloride (BCl3) gas can be fed into a gas stream and for doping silicon. Thesimplest reaction (not the only one) is

4 BCl3 + Si 3 SiCl4 + 4 B

If all the BCl3 not reacted is recycled, what is the mole ratio of recycle to SiCl4 exiting theseparator? The conversion on one pass through the reactor is 87% and 1 mole per hourof BCl3 is fed to the reactor.1

2. Many chemicals generate emissions of volatile compounds that needed to becontrolled. In the process shown in the accompanying figure, the CO in the exhaust issubstantially reduced by separating it from the reactor effluent and recycling theunreacted CO together with the reactant. Although the product is proprietary, theinformation is provided that the fresh feed stream contains 40% reactant, 50% inert and10% CO, and that on reaction 2 moles of reactant yield 2.5moles of product. Conversionof the reactant to product is 73% on one pass through the reactor and 90% for the over-all process. The recycle stream contains 80% CO and 20% reactant. Calculate the ratioof moles of the recycle stream to moles of the product stream.2

87%REACTOR SEPARATOR

SiCl4

UnreactedBCl3

BCl3SiCl4

BCl31mol/hr

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3. Nitroglycerine, a widely used high explosive, when mixed with wood flour is called“dynamite’. It is made by mixing high-purity glycerine (99.9+% pure) with nitration acid,which contains 50% H2SO4, 43% HNO3 and 7% H2O by weight.The reaction is:

C3H8O3 + 3HNO3 + (N2SO4) C3H5O3(NO2)3 + 3H2O + (H2SO4)

The H2SO4 does not take part in the reaction, but it is present to “catch” the H2Oformed. Conversion of Glycerine is complete in the nitrator, and there are no sidereactions, so all of the Glycerine fed into the nitrator forms into Nitroglycerine. Themixed acid entering the nitrator (stream G) contains 20% excess HNO3 to assure that allthe Glycerine reacts.

After nitration, the mixture of Nitroglycerine and spent acid (HNO3, H2SO4, and H2O)goes to a separator (a settling tank). The Nitroglycerine is insoluble in the spent acidand its density is less, so it rises to the top. It is carefully drawn off as product stream Pand sent to wash tanks for purifications. The spent acid is withdrawn from the bottom ofthe separator and sent to an acid recovery tank, where the HNO3 and H2SO4 areseparated. The H2SO4- H2O mixture is stream W, and is concentrated and sold forindustrial purposes, the recycle stream to the nitrator is a 70% by weight solution ofHNO3 in H2O. In the diagram, product stream P is 96.5% Nitroglycerine and 3.5% H2Oby weight.

To summarize:

Stream F = 50% by weight H2SO4, 43% HNO3, 7% H2OStream G = 20% excess HNO3Stream P = 96.5% by weight Nitroglycerine, 3.5% by weight H2OStream R = 70% by weight HNO3, 30% by weight H2O

a.) If 1x103 kg of Glycerine/hr is fed to the Nitrator, How many kg/hr of Stream F will be theresult?

b.) How many kg/hr are in the recycle stream?

REACTOR SEPARATORX

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c.) How many kg of fresh feed, Stream F are fed per hour?d.) Stream W is how many kg/hr? What is its analysis in weight %?

4. Propane is dehydrogenated to form propylene in a catalyctic reactor:

C3 H8 C3 H6 + H2

The process is to be designed for 85% overall conversion of propane. The reactionproducts are separated into two streams: the first, which contains H2, C3H6 and0.656% of the propane that leaves the reactor, is taken off as product, the secondstream, which contains the balance of unreacted propane and 5% of the propylene inthe product stream, is recycled to the rector. Calculate the composition of the product,the ration (moles recycled/ moles fresh feed) and the single-pass conversion.

Illustration: Basis 100 mole of fresh feed

Fresh Feed A

100 mol C3 H8Reactor1

2

100 + Xr

Yr

Xp

Yp

Zp

Separationunit

Xr

Yr

3

5%

X 85% conversion0.656%Y

Z

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5. Reactors that involve biological materials (bioreactors) use living organisms to producevariety of products. Bioreactors are used for producing ethanol, antibiotics and proteinsfor dietary supplements and medical diagnosis. The overall conversion of theproprietary component in the fresh feed to product is 100% in recycle bioreactor. Theconversion of the proprietary component to product per pass in the reactor is 40%.Determine the amount of recycle and the mass percent of component in the recyclestream if product contains 90% product, and the feed to the reactor contains 3% wt ofcomponent.

Product Stream

(W)

wastestream

WaterDead cell

(F) 3% (M)

REFERENCE:


edition.2. David Himmelblau, Supplementary Problems for Basic Principles and Calculations in

Chemical Engineering 6th edition.3. David Himmelblau, Basic Principles and Calculations in Chemical Engineering 6th

edition.4. Felder and Rousseau, Elementary Principle of Chemical Processes (Revised Problem)5. David Himmelblau, Basic Principles and Calculations in Chemical Engineering 6th

edition.

CELLSEPARATORBIO-

REACTOR

PRODUCTRECOVER

Y

10% water,90% product

(PS)

component90%water

10%component

MIXER

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BYPASS

Consider a juice concentration process in which the dehydration process runs mostefficiently by removing more water than is desired. A portion of the feed may be directedaround the dehydrator in a bypass loop, to be mixed with unprocessed feed. The figurebelow illustrates a bypass loop.

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BYPASS PROBLEMS WITHOUT CHEMICAL REACTION1. Air at 310K saturated with water vapor is dehumidified by cooling to 285K and by

consequent condensation of water vapor. Air leaving the dehumidifier, saturated at285K is mixed with a part of the original air which is bypassed. The resulting air streamis reheated to 320K. It is desired that the final air contains water vapor not more than0.03kg per kg of dry air. Calculate the mass of dry air (in kg) bypassed per kg of dry airsent through the dehumidifier.1

2. The figure shows a 3-stage separation process. The ratio of P3/D3 is 3, the ratio of P2/D2is 1, and the ratio of A to B in stream P2 is 4:1. Calculate the composition and percent ofeach component in stream E.2

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3. A process needs an air supply which should contain 0.12 kmol / kmol da exactly. 1500m3/ min of air at 25 °C and 101.3 k Pa is to be treated. Part of this air goes to a spraychamber. Where the air picks up water goes out with the humidified air to produce a1850-kg mixture containing 0.12 kmol H2O/ kmol da. What is the water consumption(kg/min)? What is the ratio of the flowmeter readings of the bypass stream and thestream to the water spray?3

m3 bypass

m2 m4 m5 1,850 kg airm1 spray chamber mixer 0.12 kmol H2O/kmol da1500 m3 /min 0.3 kmol H2O/ kmol d.a25°C, 101.kPa

4. In a textile industry, it is desired to make a 24% solution (by mass) of caustic soda fora mercerization process. Due to the very high heat of dissolution of caustic soda inwater, the above solution is prepared by two step process. First, in a dissolution tank,caustic soda is dissolved in the correct quantity of water to produce 50% solution.After complete dissolution and cooling, the solution is taken to dilution tank wheresome more water is added to produce 24% solution. Assuming no evaporation loss indissolution tank, calculate the mass ratio W1/W2.

W2

Solid NaOH

W1 50% NaOH 24% NaOH(P)

Water

DISSOLUTIONTANK

DILUTIONTANK

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REFERENCES:

1. K.A. Gavhane, Introduction to Process Calculations Stoichiometry.2. David Himmelblau, Basic Principles and Calculatons for Chemical Calculations 6th

edition.3. Wilfredo I. Jose, Introductory Concepts in Chemical Engineering.4. K.A. Gavhane, Introduction to Process Calculations Stoichiometry.

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BYPASS PROBLEMS WITH CHEMICAL REACTION1. Perchloric acid (HClO4) can be prepared from Ba(ClO4)2 and HClO4 , as

shown in the diagram below. Sulfuric acid is supplied 20% in excess in reactor1 that converts 80% of the Ba(ClO4)2. 6125lb of the feed is bypassed to thesecond reactor where 10% in excess H2SO4 is supplied and converts 60% ofBa(ClO4)2. Between the adjacent reactors is a stream that contains 63%HClO4 by mole . . The over-all reaction produces 7400 lb HClO4

over the time period. Calculate;2

a. lbmole of waste H2SO4 per lbmole of BaSO4 that exits the separatorb. lb HClO4 in G per lb feedc. over-all conversion of Ba(ClO4)2.

2. TiCl4 can be formed by reacting Titanium Dioxide with Hydrochloric Acid.1200Kg feed with 64% TiO2, 3% inerts, 20% HCl, and 13%H2O is the initialfeed. 800Kg of it is fed in to unit 1 that removes all the inerts from the originalfeed but unfortunately, also removes 20% of TiO2 from the feed. That is why abypass stream is needed with an amount of 400Kg. The stream leaving unit 1together with the bypass is sent to unit 2 which converts all TiO2 into TiCl4. Aseparator unit isolates the desired product from the rest.3

Required:A. amount of TiCl4 producedB. amount of W and its composition

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PURGEWhen a process uses a recycle loop, there can often be a buildup of some undesiredmaterial within the system. By using a purge, a fraction of the recycle loop material isremoved. This purge fraction is generally only a few percent of the recycle flow rate.

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PURGE PROBLEMS WITHOUT CHEMICAL REACTION1. Caustic soda, among the largest producing product in Chemical Industry, is produced

by electrolysis of common salt, NaCl, using membrane cell electrolyzers. The NaClsolution feed contains 30% by vol. of the solute. The NaOH produced is collected onstorage tanks and the unreacted material containing 25% NaCl is being recycled. Apurge stream is used to separate/remove the Cl2 from the recycle stream. Calculate thefollowing:

a. Recycle stream flow rate/ recycle stream and product rate.b. Purge rate if it contains 40% Cl2 to produce 32.5 mol of NaOH, equivalent to 65% by

vol. in the final product.

2. To save energy, stack gas from a furnace is used to dry ice. The flow sheet and knowndata are shown in the figure below. What is the amount of recycle gas ( in lb mole) per100 lb of P if the concentration of water in the gas stream entering the dryer is 5.20%?

B

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3. One half of the high-pressure steam after being utilized for power generation is sentto the plant as process steam. The other half is returned to the boiler as condensatecarrying 50 ppm solids.

To keep the solid level in the boiler below 1600 ppm solids, a part of the boiler wateris blowdown (purge) continuously. the fresh boiler feed is found to contain 500ppmsolids. if steam produced is free of solids, calculate the weight ratio of feed water tothe blowdown (purge) water.

4. An evaporator is concentrating solutions from the two different sources. The solutionfrom the first source containing 20% NaCl and 15% NaOH, flows at the rate of 40kg/min. The other solution containing 8% NaCl and 12% NaOH flows at the rate of 70kg/min. The two streams are fed directly to the evaporator, in this process, 60% of thewater evaporated. In order to obtain the desired concentration,80% NaOH and 65% ofNaCl were recycled. However, 20% of H2O was mixed on the recycle stream; to avoidthis, purging of H2O must be done. Calculate the composition of NaOH and NaCl in therecycle stream and the product in the evaporator.

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Illustration:

60% H2O40 kg/min20% NaCl15% NaOH

Solution:70 kg/min8% NaCl 80% NaOH12% NaOH 65% NaCl

20% H2O

5. In the production of NH3 from hydrogen and nitrogen, the nitrogen, the NH3 produced iscondensed for the reactor (convertor) product stream and the unreacted material isrecycled. If the feed contains 0.2% Argon (from the nitrogen separation process),calculate the purge rate required to hold the argon in the recycle stream below 5.0%.

R

Purge5% Argon

Feed Liquid0.2% Argon NH 3

CONDENSER

EVAPORATOR

REACTOR

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REFERENCES:

1. K. Sinnott, John Metcalfe Coulson, and John Francis Richardson, ChemicalEngineering Design.



edition.4. Wilfredo I. Jose, Introductory Concepts in Chemical Engineering5. K. Sinnott, John Metcalfe Coulson, and John Francis Richardson, Chemical Engineering

Design.

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PURGE PROBLEMS WITH CHEMICAL REACTION

1. Ethylene dioxide is produced by oxidation of ethylene as per the followingreaction:

C2H4 + ½ O2 C2H4O

Fresh feed containing ethylene and air is mixed with recycle feed andmixed feed enters into a reactor. The proportion of C2H4 : O2 : N2 in mixedfeed is 1:0.5:5.65 (on mole basis) 50% per pass conversion is achieved inthe reactor are feed to the absorber where only all C2H4O formedremoved. The gases from the absorber containing C2H4, O2 and N2 arerecycled each. To avoid built up of N2 in the system, small portions ofrecycle stream is continuously purged based on 100 mol ethylene is mixedfeed, calculate the fresh feed to the process, the purge stream, recycleratio, combined feed ratio and overall conversion of ethylene.

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2. It is proposed to produce ethylene oxide ((CH2)2O) by the oxidation of ethane(C2H6) in the gas phase;

+ (CH2)2O + H2O

The ratio of the air to the C2H6 in the gross feed into the reactor is 10 to 1, andconversion of C2H6 on one pass through the reactor is 18%. The unreactedethane is separated from the reactor products and recycled as shown in thefigure below. What is the ratio of the recycle stream to the feed stream andcalculate the composition of purge stream and the stream exiting the reactor.

REACTOR SEPARATOREthane

airfresh feed

O2N2

C2H6

100% Ethane recycle

WaterPurgeO2N2

Ethylene oxide

Figure3.

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3. Methanol maybe produced by the reaction of CO2 and H2

CO2 + 3H2 CH3OH + H2O

The fresh feed to the process contains CO2 and H2 in stoichiometricproportions, 0.5mol% Inerts(I). The reactor effluent passes to a condenserwhich removes essentially all of theCH3OH and water formed, none of thereactants or inerts. The latter substances are recycled back to the reactor toavoid build-up of the inerts in the system; a purge stream is withdrawn fron therecycle. The feed to the reactor contains 2% inerts and the single passconversion is 60%. Calculate the molar flow rates of the fresh feed, the totalfeed to the reactor and the purge stream for CH3OH production rate of1000mol/hr.

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4. The fresh feed to an ammonia production process contains N2, H2 and 0.125mole %. The feed is combined with the recycle stream and the combinedstream contains: 24.00 mol% nitrogen, 74 mol% hydrogen and 2% inerts, thenit is feed to the reactor, in which 25% single-pass conversion of nitrogen isachieved. The product pass through a condenser in which essentially all theammonia is removed and the remaining gases are recycled. However, toprevent buildup of the inert in the system, a purge stream must be taken off.Calculate the overall conversion of nitrogen, the ratio (moles purge/mole ofgas leaving the condenser) and the ratio (moles fresh feed/moles feed to thereactor).

ILLUSTRATION:

nr (mol ) np (mol) n4 (mol)X4 N2 mol X4 N2 mol X4 N2 mol

X4 H2 mol X4 H2 mol X4 H2 mol(1-X4N2–X4H2) mol I (1–X4N2–X4H2)mol I (1 - X4 N2 -X4 H2)mol I

n0 REACTOR CONDENSER

X0mol N2 24.00% 25% N2 conversion(0.99875–N2)H2 74.00% H2 n1 mol N2 n3 molNH3.00125 I 2.00% I n2 mol H2

n3 mol NH32 mol I

REACTION: N2 + 3 H2 NH3

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5. Carbon monoxide and hydrogen reacts to give methanol: CO+2H2 CH3OH

The conversion of CO entering the reactor is 20%. A feed stream consisting33% CO, 66.5% H2, and 0.5%CH4 is mixed with a recycle stream and sent toa reactor. The methane leaving the reactor is separated and the unconvertedgases are recycled. To prevent the accumulation of CH4 and keep itsconcentration, in the recycle stream at 3%, a portion of the recycle stream isblown off. For 100 moles of fresh feed, determine the following:a. recycle stream (moles),b. purge stream (moles)c. composition of purge (moles) andd. moles of methanol.

Purge (P, mol)

Recycle

100 mol Product

CO, H2, CH4 CH3OH (M, mol)REACTOR SEPARATOR

CO= xCH4= 0.03H2= 0.97-x

CO= xCH4= 0.03H2= 0.97-x

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REFERENCES:

1. Narayanan, B. Lakshnikutty and K.V. Narayanan, Stoichiometry and ProcessCalculations



edition.4. Wilfredo I. Jose, Introductory Concepts in Chemical Engineering.5. Narayanan, B. Lakshnikutty and K.V. Narayanan, Stoichiometry and Process

Calculations