DEPARTMENT OF CHEMICAL ENGINEERING,

UNIVERSITY of ILORIN,

KWARA STATE

LECTURE GUIDE

INDUSTRIAL PROCESS CALCULATIONS

CHE341 - 3 UNITS

2013/2014 SESSION

COURSE: CHE 341 – Industrial Process Calculations

(3 credits /Compulsory)

Lecturer: Dr. ELETTA, Omodele A,A,

B.Sc, MSc. Chemical Eng.(Lagos, ,Ph.D. Environmental Chemistry (Ilorin). Reg. Engr.(COREN),

MNSE MNSChE

Department of Chemical Engineering,

UNIVERSITY OF ILORIN

Kwara State, Nigeria.

E-mail: modeletta@unilorin.edu.ng

Course Content:

Introduction to equipment of chemical plants. Equipment for movement and storage of material.

Heat transfer equipment, mass transfer equipment and equipment for physical processes. The

chemical equation and stoichiometry: limiting reaction, excess reactant, conversion, selectivity

and yield. Material balances. Calculations for steady state systems involving inert recycle, by

pass and purges. Energy balances: Forms of energy and overall energy balance for a chemical

system. Heat capacities. Calculation of enthalpy changes: heat of fusion, vaporization, reaction,

formation and combustion. Solution and mixing. Combined material and energy balances.

Enthalpy concentration charts application and construction.

45h (T) PR CHM212 C

(all are required to bring an original copy of steam tables to this class) Assignment 1: what is chemical engineering. What do you understand by, the unit operations of chemical engineering. Identify any four and write on any one. Course Description:

Consultation Hours: 11.00-1.00 pm Mondays and Wednesdays.

Course Content:

Introduction to equipment of chemical plants; Equipment for movement and storage of material.

Heat transfer equipment, Mass transfer equipment and equipment for physical processes. The

Chemical equation and stoichiometry: limiting reaction, excess reactant, conversion, selectivity

and yield. Material balances. Calculations for steady state systems involving inerts recycle, by

pass and purges. Energy balances: Forms of energy and overall energy balance for a chemical

system. Heat capacities. Calculation of enthalpy changes: heat of fusion, vaporization, reaction,

formation and combustion, solution and mixing. Combined material and energy balances.

Enthalpy concentration charts application and construction.

45h (T) PR CHM212 C

Course Description:

The course is intended to serve as an introduction

to the principles and techniques used in the field

of chemical, petroleum and environmental

engineering. It lays a foundation of relevant

information and skills that can be repeatedly

employed in subsequent courses at higher levels

as well as in professional life.

The course presents systematic problem solving skills ,what material balances are and how to

apply them;what energy balances are and how to apply them. It also presents background

information on units and measurements of physical properties, basic laws about the behaviour of

gas, liquids and solids and some basic mathematical tools.

Course Justification:

Foundations are crucial to the stability and durability

of every building. This statement describes the

importance of the Industrial Process Calculation in the

training of Chemical Engineers. Every Chemical

Engineers should be able to develop a process from

conception to commissioning along with other

professionals . This task will become difficult if not

impossible without the knowledge of basic calculation

procedures that are crucial for equipment design and

sizing which is his sole responsibility in the team.

We are also in the computer age where process

designs are computer aided. However, a good

understanding of the basic principles and procedures of

industrial calculation will enhance the Engineer’s

mastery of the computer aided design softwares as well

as the interpretation of the output from such

computations.

Course Objectives:

The objective of this course as an integral part for the award of B. Eng. Chemical

Engineering is for the student to understand the fundamental principles underlying the

management of materials and energy in a chemical plant. It is also aimed at introducing the unit

operations available for chemical processing.

Course Requirements:

This is a compulsory course for all students studying Engineering In view of this, students

are expected to participate in all the course activities and have minimum of 75% attendance

to be able to write the final examination.

Methods of grading:

No Item Score %

1.

2.

3.

Assignment/ Quiz / Monthly Test

Mid Semester Test

Examination

Total

10

20

70

100

Course Delivery Strategies:

The lecture will be delivered through face-to-face method, lecture guide (lecture note) will be

provided during lectures. Students will be encouraged and required to read around the topics.

The delivery strategies will also be supported by tutorial sessions.

LECTURES

Week 1 and 2 : Introduction to Chemical Engineering Calculations

Objective: Students will be able to identify and distinguish various equipment available for

chemical processing and understand the fundamentals of Industrial calculations,

Description: The course outline will be introduced with emphasis on the objectives and delivery

strategies. Introduction to Chemical Engineering Unit Operations and auxiliary

facilities (Equipment for movement and storage of material, Heat transfer

equipment, Mass transfer equipment and equipment for physical processes).

Chemical Engineering Process flow charts and process symbols The basic

equation of process industries( Units and dimensions, the mole units, methods of

analysis and measurements, basis, physical and chemical properties of compounds

and mixtures and techniques of problem solving, Limiting reaction, excess reactant,

conversion, selectivity and yield).

Week 3: The Chemical Equation and Stoichiometry.

Objective: This is to intimate students with various situations of chemicals under various

reaction mechanisms.

Description: Limiting reaction, excess reactant, conversion, selectivity and yield.

Week 4 - 7: Material balances.

Objectives: This is to introduce students to quantitative combination of reactants to form

products.

Description: Calculations for steady state systems involving inerts recycle, by pass and purges.

Student will also be assessed on the topics covered so far through a short Monthly

Quiz.

Week 8 - 11 : Energy Balances

Objectives: This is to introduce students to the energy transformations that accompany the

quantitative combination of reactants to form products.

Description: Forms of energy and overall energy balance for a chemical system. Heat

capacities. Calculation of enthalpy changes, heat of fusion, vaporization, reaction,

formation and combustion, solution and mixing.

Week 12: Test

Objective: This is to assess the students mastery of the topic covered so far.

Description: Students will be tested on all the topics taken so far. This is to serve as a

preparation for the final examination at the end of the semester

Week 13 : Combined Material and Energy Balances.

Objective : This is to integrate the concept of materials and energy balances.

Description: Enthalpy concentration charts application and construction.

Week 14 - 15: Revision/ Tutorial Exercises

Objectives: This is meant to revise the whole course again before examination.

Description: A general overview of the course will be made. Students are expected to seek

explanation on any difficult concept or topic treated during the course.

LIST OF BOOKS FOR FURTHER READING:

1 Felder R.M and Rousseau R.W. (2005) Elementary Principles of Chemical Processes, Wiley

Series in Chemical Engineering. 3rd

edition

2 McCabe,W. L., Smith,J.C. and Harriott, P.(1993) .Unit Operations of Chemical

Engineering. Fifth Edition. McGraw Hill Co. Singapore.

3 Coulson, J.M. and Richardson, J.F., Backhurst,J.R. and Harker, J.H. (2001 ) Chemical

Engineering Volume 1, Sixth Edition, Butterworth Heinmann Inc. Oxford.

3 Himmeblau, D.M. (1996 ) Supplementary problems for Basic principles and

Calculations in Chemical Engineering,Sixth Edition, Prentice Hall Inc. ,Englewood

Cliffs,New Jersey

4 Himmeblau, D.M. and Riggs, J.B. (1989 ) Basic principles and Calculations in

Chemical Engineering, Fifth Edition. Prentice Hall Inc. ,Englewood Cliffs,New Jersey.

LECTURES

MODULE 1

INTRODUCTION TO CHEMICAL ENGINEERING PROCESS

CALCULATIONS

1.1 Some Basic Information about Chemical Engineering

(a) What is Chemical Engineering?

Chemical Engineering has to do with industrial processes in which raw materials are

changed or separated into useful products. The chemical engineer must develop, design, and

engineer both the complete process and the equipment used; choose the proper raw materials;

operate the plants efficiently, safely and economically; and see to it that products meet the

requirements of the customers. The Chemical Engineering profession encompasses a wide

variety of activities and is engaged in resolving problems that occur in industry, government

and academia. Problems encountered by chemical engineers are found in design, operation,

control, troubleshooting and even politics; the latter is because of environmental and

economic concerns.

Figure 1: Defining Chemical Engineering Pictorially

(b) What do Chemical Engineers do for a living?

Chemical engineers work in numerous areas besides petroleum refining and the chemical

and petrochemical industries because their background and experience are easily portable

and found useful. Other industries where chemical engineers are involved include: Drugs

and pharmaceutics, Microelectronics, Biotechnology, Explosives and fireworks, Fats and

Oil, Fertilizer and agrochemicals, Food and beverages, Leather tanning and finishing, Lime

and cement, Metallurgical and metal products, Paints, vanishes and pigments, Plastics

materials and synthetic resins, Rubber products, Soap and toiletries, Glass and ceramics,

Wood, pulp, paper and board e.t.c.

© What is a Chemical Process

a combination of process equipment designed to efficiently convert raw materials into

finished or intermediate products

the essential operations that involve chemical reactions

almost all that is required in handling fluid mixtures

examples: petroleum refinery, food products plant, pharmaceutical production plant,

microchip manufacturing facility, paper mill

(d) What is a Process Unit?

a part of a chemical process which accomplishes some physical or chemical change (may

involve single or multiple pieces of equipment, depending on local terminology)

examples: distillation train, continuous-flow catalytic reactor, heat transfer units,

evaporator operations, flash vaporization unit

(e) What is a Unit Operation?

a part of a process unit that can be analyzed independently (sometimes)

examples: fluid flow, heat transfer, distillation, crystallization, chemical reaction

1.2 Dimensions and Units

(a) Dimensions

mental concepts used to distinguish between opposing sense perceptions

length (L), mass (m), time (t), temperature (T), amount of substance (n)

fundamental dimensions - a base set from which all others can be derived

Example. What are the dimensions of mass flux (mass flow rate per unit area perpendicular

to the flow)?

GA

dm

dt

1 dimensions are

m

L t2

(b) Units

scales used to quantify dimensions in a standard way

SI system is now almost universally accepted

the American engineering system (based on British standards) is still used

extensively in the U.S.

( c) Systems of Units

The system of units has the following components:

Base units are units for the dimensions of mass, length, time, temperature, electrical

current, and light intensity

Multiple Units are defined as multiples or fractions of base units such as minutes, hours

etc. eg 5 years instead of (5x12x365x24x60x60)

Derived units are obtained by multiplying and dividing base or multiple units (cm2, ft/min,

kg-m/s2, etc.).

(i) The base SI ((Système Internationale d'Unités)) units

the ampere for electrical current and the candela for luminous

the kelvin for temperature,

meter (m) for length,

the kilogram (kg) for mass, bn

and the second (s) for time.

(ii) CGS system is almost identical to SI, the principal difference being that grams (g) and

centimeters (cm) are used instead of kilograms and meters as the base units of mass and length.

(iii) American Engineering System

foot (ft) for length,

the pound-mass (lbm) for mass,

and the second (s) for time.

For More Information check conversion factors on pages. 1-4 through

1-20 of Perry's Chemical Engineers' Handbook. ( the handbook is a

must for chemical engineering students)

Table 1 SI and CGS Units

1.3 Process Variables

(a) Density and Related Quantities

Average density m

V

Point density

lim

V

m

VV

Note: V is a volume that is very small compared to the size of the system, but large enough to

contain a very large number of molecules.

Note: If the density is constant over a region of space, then the point density is equal to the

average density at all points.

Units of density (kg/m3, g/cm

3, lb/ft

3, etc.)

Related quantities molar density (n/V = /M)

specific volume (V/m = 1/)

molar volume (V/n = M/)

(b)Specific gravity is defined as the ratio of the actual density of a solid (or liquid) to the density

of a reference substance (usually liquid water at 4 oC, 1 atm, where = 1.000 g/cm

3).

© What is air? Composition of clean, dry air (average molecular weight of air = 29.0):

Species Volume % = Mole %

N2 78.09

O2 20.95

Ar 0.93

CO2 0.03

100.00

+ Traces of Ne, He, CH4, Kr, H2, Xe, O3, etc.

Note: Air almost always contains significant amounts of water vapor (humidity), as well as

some particulates and other pollutants (e.g., NO). Amounts depend on local conditions.

Combustion air - taken as 79.0 % "atmospheric N2" + 21.0 % O2

(d) Molecular Weight and Amount of Substance

The molecular weight of a compound is the sum of the atomic weights of the atoms that

constitute a molecule of the compound .A gram-mole (g-mole, or mol in SI units) of a species is

the amount of that species whose mass in grams is numerically equal to its molecular weight.

The average molecular weight (or mean molecular weight) of a mixture, is the ratio of the mass

of a sample of the mixture to the number of moles of all species in the sample. If yi is the mole

fraction of the ith component of the mixture and Mi is the molecular weight of this component

,then

Example 1

Example 2 :Calculate the average molecular weight of air (1) from its approximate molar

composition of 79% N2, 21% 02 .

Solution

(e) Concentrations

Concentration means the quantity of some solute per fixed amount of solvent, or

solution, in a mixture of two or more components; for example

molar concentration = moles of component per unit volume of solution

mass concentration = mass of component per unit volume of solution

parts per million = moles (or mass) of component per million moles (or mass

units) of mixture. It is the mass ratios (usual for liquids) or mole ratios (usual for

gases) and signify how many parts (grams, moles) of the species are present per

million parts (grams, moles) of the mixture.

Other methods of expressing concentration are molarity (g-mole/litre) and

normality (equivalents /litre)

(f) Basis

1.4 Introduction to Equipment of Chemical Plants

(a) Fluid Flow Equipment

(i) Pumps

A device used to propel a liquid or slurry from one location to another usually through a

pipe or tube. The primary means of transfer of energy to the fluid that causes flow are

gravity, displacement, centrifugal force, electromagnetic force, transfer of momentum,

mechanical impulse, and a combination of these energy-transfer mechanisms. Gravity

and centrifugal force are the most common energy-transfer mechanisms in use.

(ii) Fans and Blower

Blowers are also used to supply draft air to boilers and furnaces. Fans are used to move

large volumes of air or gas through ducts, supplying air for drying, conveying material

suspended in the gas stream, removing fumes, condensing towers and other high flow,

low-pressure applications.

(iii) Compressors

A device that raises the pressure of a gas. Compressors are used to handle large volumes

of gas at pressure increases from 10.32 kPa (1.5lbg/in2) to several hundred kPa (lbg/in

2).

Compressors can be divided into two major categories: Continuous-flow compressors ( a.

Centrifugal compressors b. Axial flow compressors) and Positive displacement

compressors ( a. Rotary compressors b. Reciprocating compressors)

Pump

Valve

(b) Heat Transfer and its Applications

(i) Heat Exchangers

A process unit through which two fluid streams at different temperatures flow on

opposite sides of a metal barrier. Heat is transferred from the stream at the higher

temperature through the barrier to the other stream.

(ii) Condensers

A process unit in which an entering gas is cooled and /or compressed, causing one or

more of the gas components to liquefy. Uncondensed gases and liquid condensate leave

the condenser as separate streams.

(iii) Boilers

A process unit in which tubes pass through a combustion furnace. Boiler feed water is fed

into the tubes and heat transferred from the hot combustion products through the tube

walls converts the feed water to steam.

(iv) Evaporator

A process unit in which a pure liquid, liquid mixture, or solvent in a solution is

vaporized.

( c) Separation / Mass transfer and its Applications

(i) Distillation

A process in which a mixture of two or more species is fed to either a vertical column that

contains a series of vertically spaced horizontal plates, or solid packing through which fluid

can flow. Liquid mixtures of the feed components flow down the column and vapour

mixtures flow up. Interphase contact, partial condensation of the vapour and partial

vapourization of the liquid all take place throughout the column. The vapour flowing up the

column becomes progressively richer in the more volatile component of the feed., and the

liquid flowing down becomes richer in the less volatile components. The vapour leaving the

top of the column is condensed: part of the condensate is taken off as the overhead product

and the rest is recycled to the column as reflux, becoming the liquid stream that flows down

the column. The liquid leaving the bottom of the column is partially vapourized: the vapour

is recycled to the column as boil-up, becoming the vapour stream that flows up the column,

and the residual liquid is taken off as bottom product.

(ii) Leaching

Leaching is concerned with the extraction of a soluble constituent from a solid by means of

a solvent. The separation usually involves selective dissolution, with or without diffusion,

but in the extreme case of simple washing, it consists merely of the displacement of one

interstitial liquid by another with which it is miscible. The insoluble solid may be massive

and porous; more often it is particulate and the particles may be openly porous, cellular with

selectively permeable cell walls, or surface-activated. Leaching Equipment includes batch

and continuous percolators, Bollman-type Extractor, rotocel extractor e.t.c

(iii) Extraction

Extraction is a process for separating components in solution by their distribution between

two immiscible liquid phases. In this process, a liquid mixture of two species ( the solute and

the feed carrier) is contacted in a mixer with a third liquid (the solvent) that is immiscible or

nearly immiscible with the feed carrier. When the liquids are contacted, solute transfers from

the feed carrier to the solvent. The combined mixture is then allowed to settle into two phases

that are then separated by gravity in a decanter. Such a process can also be simply referred to

as liquid extraction or solvent extraction.

(iv) Absorption

It is a process in which a gas mixture contacts a liquid solvent and a component (or several

components) of the gas dissolves in the liquid. In an absorption column or absorption tower,

the solvent enters the top of a column, flows down, and emerges at the bottom and the gas

enters at the bottom, flows up contacting the liquids and leaves at the top. The inverse

operation, called stripping or desorption, is employed when it is desired to transfer volatile

components from a liquid mixture into a gas. Absorption is usually carried out in vertical,

cylindrical columns or towers in which devices such as plates or packing elements are

placed. The gas and liquid normally flow countercurrently, and the devices serve to provide

the contacting and development of interfacial surface through which mass transfer takes

place.

(v) Adsorption

A process in which a gas or liquid mixture contacts a solid (the adsorbent) and a mixture

components ( the adsorbate ) adheres to the surface of the solid. Unlike absorption, in which

solute molecules diffuse from the bulk of a gas phase to the bulk of a liquid phase, in

adsorption, molecules diffuse from the bulk of the fluid to the surface of the solid adsorbent

forming a distinct adsorbed phase.

(differentiate between absorption and adsorption)

(vi) Drying

Drying refers to the final removal of water, or another solute, and the operation often follows

evaporation, filtration, or crystallisation. The drying of materials is often the final operation

in a manufacturing process, carried out immediately prior to packaging or dispatch. In some

cases, drying is an essential part of the manufacturing process, as for instance in paper

making or in the seasoning of timber.

(vii) Crystallization

A process in which a liquid solution is cooled or solvent is evaporated to an extent that the

solid crystals of solute form. The crystals in the slurry (suspension of solids in a liquid)

leaving the crystallizer may subsequently be separated from the liquid in a filter or

centrifuge.

(d) Operations involving Particulate Solids.

(i) Size Reduction Equipment

(ii) Screening

Screening is a method of separating particles according to size alone. In industrial screening,

the solids are dropped on ,or thrown against a screening surface. The undersize or fines pass

through the screen openings; oversize or tails don nt. A single screen can make but a single

separation into fractions. These are called unsized fractions because either the upper or the

lower limit of the particle size they contain is known, the other limit is unknown. Material

passed through a series of screens of different sizes is separated into sized fractions i.e

fractions in which both the maximum and minimum particle sizes are known. Screening is

occasionally done wet but much more commonly dry.

(iii) Filtration

Filtration is the separation of a fluid-solids mixture involving passage of most of the fluid

through a porous barrier which retains most of the solid particulates contained in the mixture

called the filter cake. Filtration is the term for the unit operation. A filter is a piece of unit-

operations equipment by which filtration is performed. The filter medium or septum is the

barrier that lets the liquid pass while retaining most of the solids; it may be a screen, cloth,

paper, or bed of solids. The liquid that passes through the filter medium is called the filtrate.

(iv) Sedimentation

Sedimentation is the partial separation or concentration of suspended solid particles from a

liquid by gravity settling. This field may be divided into the functional operations of

thickening and clarification. The primary purpose of thickening is to increase the

concentration of suspended solids in a feed stream, while that of clarification is to remove a

relatively small quantity of suspended particles and produce a clear effluent. These two

functions are similar and occur simultaneously, and the terminology merely makes a

distinction between the primary process results desired. Generally, thickener mechanisms are

designed for the heavier-duty requirements imposed by a large quantity of relatively

concentrated pulp, while clarifiers usually will include features that ensure essentially

complete suspended-solids removal, such as greater depth, special provision for coagulation

or flocculation of the feed suspension, and greater overflow-weir length.

1.4 The Chemical Equation and Stoichiometry

General chemical reaction: i iA 0

i's are stoichiometric coefficients (+ for products and - for reactants)

Ai's are chemical formulas for products and reactants

Specific chemical reaction: CH4 + 2O2 CO2 + 2H2O

i +2 for water, +1 for CO2, -1 for CH4, and -2 for O2

Stoichiometric ratio of oxygen to methane = 2/1 = 2 mol O2 reacted per mol CH4

reacted

Limiting reactant : reactant that would disappear 1st if reaction proceeds to completion

(as written)

Excess reactant: any other reactant

%( ) ( )

( )excess

n actual n stoichiometric

n stoichiometric

100 %

fractional conversion -- moles reacted divided by moles fed

fractional conversion

moles reacted

moles fedcan range from to

percent conversion fractional conversion

( )0 1

100%

extent of reaction () -- moles produced divided by stoichiometric coefficient

n n ni i

i

i

i

0 (same for every component in reacting system)

(can range from 0 to )

Example 3

1.5 Multiple Reactions, Yield and Selectivity

Example 4

Example 5

Example 6

1.6 Chemical Engineering Process Flow Charts and Process Symbols.

(a) Process Flow-Sheet

The process flow-sheet shows the arrangement of the major pieces of equipment and their

interconnection. It is a description of the nature of the process. The list given below has therefore

been divided into essential items and optional items. The essential items must always be shown,

the optional items add to the usefulness of the flow-sheet but are not always included.

Essential information

1. Stream composition, either: (i) the flow-rate of each individual component, kg/h, which is

preferred, or

(ii) the stream composition as a weight fraction.

2. Total stream flow-rate, kg/h.

3. Stream temperature, degrees Celsius preferred.

4. Nominal operating pressure (the required operating pressure).

Optional information

1. Molar percentages composition.

2. Physical property data, mean values for the stream, such as: (i) density, kg/m3, (ii) viscosity,

mN s/m2.

3. Stream name, a brief, one or two-word, description of the nature of the stream,

4. Stream enthalpy, kJ/h.

(b) Piping and Instrumentation Diagram

The Piping and Instrument diagram (P and I diagram or PID) shows the engineering

details of the equipment, instruments, piping, valves and fittings; and their arrangement. It is

often called the Engineering Flow-sheet or Engineering Line Diagram. It should include:

1. All process equipment identified by an equipment number. The equipment should be

drawn roughly in proportion, and the location of nozzles shown.

2. All pipes, identified by a line number. The pipe size and material of construction should be

shown. The material may be included as part of the line identification number.

3. All valves, control and block valves, with an identification number. The type and size

should be shown. The type may be shown by the symbol used for the valve or included in

the code used for the valve number.

4. Ancillary fittings that are part of the piping system, such as inline sight-glasses, strainers

and steam traps; with an identification number.

5. Pumps, identified by a suitable code number.

6. All control loops and instruments, with an identification number.

Figure 1:Flow-sheet: simplified nitric acid process

( c) List of Process Symbols

MODULE 2

MATERIAL BALANCES.

2.1 Process Classification

2.2 The General Balance Equation

(a) Integral Balance (apply for some fixed period of time, such as 1 hour)

input - output + generation - consumption = accumulation

OR net input + net generation = accumulation

(b) Differential or Rate Balance (apply at any instant of time)

input rate - output rate + rate of generation - rate of consumption = rate of

accumulation

OR net input rate + net rate of generation = rate of accumulation

These mass balance equations:

1. can be applied to total mass or mass of any component

2. can be applied to amount of substance (“number of moles”) instead of mass

3. can write one balance equation for each species

( c) Special cases for mass balances

1. steady-state process implies no accumulation

2. closed system (batch process) implies no input or output

3. no chemical or nuclear reactions implies no generation or consumption of any species

Example 7

Since the process is at steady state, the accumulation term equals zero and since it

is a non reactive system, generation and consumption terms equal zero thereby

reducing the balance equation to input=output

Example 8

SOLUTION: The input and output streams shown on the figure above denote the

initial and final states of this batch process. In addition, since no reactions are

involved, the generation and consumption terms equal zero and the balance can take

the form: initial input = final output

2.3 Material Balance Calculation

(a) Elements of Using Flowcharts

1. Preparing the basic flowchart for a process

draw boxes (or other symbols) for all equipment and arrows indicating all

streams and their directions of flow

standard practice has major flows from left to right

all equipment and all streams should be named or numbered

2. Choosing a basis for calculation

use an amount or rate of one stream, if one is known

if none are known, assume one for a stream of known composition

if mole fractions are known, use a molar basis

write the basis clearly on the flowchart

3. Writing in values of all known stream variables (with units)

flow rates

compositions

temperature and pressure

use a common basis (mass or moles -- convert volumes)

all values should be on the calculational basis you chose

4. Assigning symbols to unknown stream variables.

use as few symbols as possible

make sure mole fractions add to unity

5. Scaling

if needed, change all stream amounts or rates by a proportional amount

remember that compositions should remain unchanged

(b) General Material Balance Procedure

1. prepare a flowchart (see Items 1-4 above)

2. do the degree of freedom analysis

count the unknowns you wish to calculate

count the equations that are available

see if the numbers of unknowns and equations are equal

3. write material balance equations

4. convert additional relations between variables into equations

5. solve set of equations and write results on flow chart

6. scale the results if answers are needed on a different basis (see Item 5 above)

( c) Multiple-Unit Processes

Parts of a process about which material balances may be written:

1. overall process

2. individual units or pieces of equipment

3. stream junctions (i.e., mixing or splitting points)

4. any combinations of units and stream junctions

Remember -- Write balances first which involve the fewest unknown variables.

(d) Recycle and bypass streams

(i) Recycle -- bringing a process output stream (or part of stream) back to mix with the feed

stream to the same or another unit in the process

(ii) Bypass -- A procedure in which a fraction of the feed to a process unit is diverted around

the unit and combined with the output stream from the unit.

Example 9

Example 10

Example 11

Example 12

2.4 Balance on Reactive Processes

There are three ways to write balance relations for reacting systems:

1. using material balances on molecular species (+ stoichiometry)

2. using material balances on atomic species (no generation terms)

3. using extent of reaction

Example 13

SOLUTION

Example 14

SOLUTION

2.5 Combustion Reaction

a) Theoretical and Excess Air

b) Material Balances on Combustion Reactor

Study Questions:

1. Explain each of the following terms : (i) recycle (ii) Bye pass (iii) Purge.

2. Differentiate between an orsat gas and a stack gas

3. An aqueous solution of sodium hydroxide contains 30.0% NaOH by mass. It is desired to

produce a 12% NaOH solution by diluting a stream of the 30.0% solution with a stream

of pure water. Calculate the ratio (litres H20/kg feed solution) and (kg product solution

/kg feed solution).

4. Fuel for motor vehicles other than gasoline are being eyed because they generate lower

level of pollutant than does gasoline. Compressed propane has been suggested as a source

of economic power for vehicles. Suppose that in a test 20 lb of C3H8 is burned with 400

lb of air to produce 44 lb of C02 and 12 lb of CO. What was the percent excess air?

5. A distillation column separates 10,000kg/hr of a 50% benzene -50% toluene mixture. The

product D recovered from condenser at the top of the column contains 95% benzene, and

the bottom W from the column contains 96% toluene. The vapour V entering the

condenser from the top of the column is 8000kg/hr. A portion of the product from the

condenser is returned to the column as reflux, and the rest is withdrawn for use

elsewhere. Assume that the compositions of the streams at the top of the column V, the

product withdrawn D and the reflux R are identical because the V stream is condensed

completely. Find the ratio of the amount refluxed R to the product withdrawn D

Reading List:

1 Himmeblau4, D.M. (1996). Supplementary problems for Basic principles and

Calculations in Chemical Engineering,Sixth Edition, Prentice Hall Inc. ,Englewood

Cliffs,New Jersey (pp 29 -70)

2 Himmeblau4, D.M. & Riggs, J.B. (1989). Basic principles and Calculations in Chemical

Engineering, Fifth Edition. Prentice Hall Inc. ,Englewood Cliffs,New Jersey.(pp 102-

190) .ISBN 0-13-066572-X

3 Felder4, R.M. & Rousseau,R.W.(2005). .Elemetary Principles of Chemical Processes .

Third Edition . John Wiley & Sons,Inc. New York . (pp 83-186 ) .ISBN 0- 471-68757-X.

4 Felder4, R.M. & Rousseau,R.W.(2005). Elemetary Principles of Chemical Processes .

Third Edition Solution . John Wiley & Sons,Inc. New York . (pp 4:1 – 4:80 )