1 Introduction

Chemical Engineering Principles

Lectures Wednesday Period 6 (12:20 – 13:05) Venue: Sh5 Thursday Period 3 (13:15 – 14:00) Venue: Sh5

Tutorials Thursday Periods 8&9 (14:10 – 15:40) Venue: Sh8/Sh16/Sh19

Assessment

2 Tests 7½% eachAssignment 10%Semester Mark 25%Final Exam (3 hours) 75%

Tests26 Mar Thurs TEST 1: Periods 8&9 LANS6 May Thurs TEST 2: Periods 8&9 TBA

Assignment8 Apr Thurs SUBMIT ASSIGNMENT: PART 112 May Wednes SUBMIT ASSIGNMENT: PART 2

Tutorial Schedule 2010

Date Tutorial / Test / Assignment Venue11 Feb Thurs18 Feb Thurs LECTURE: Periods 8&9 -

Groups 1&2 LANS

25 Feb Thurs LECTURE: Periods 8&9 - Groups 3&4

LANS

4 Mar Thurs TUTORIAL 1: Periods 8&9 - Groups 1&2

LANS

11 Mar Thurs TUTORIAL 1: Periods 8&9 - Groups 3&4

LANS

18 Mar Thurs TUTORIAL 2: Periods 8&9 - Units & Conversions

See tut venues

26 Mar Thurs TEST 1: Periods 8&9 LANS8 Apr Thurs SUBMIT ASSIGNMENT:

PART 115 Apr Thurs22 Apr Thurs29 Apr Thurs TUTORIAL 3: Periods 8&9 -

Mass BalancingSee tut venues

6 May Thurs TEST 2: Periods 8&9 TBA12 May Wednes

SUBMIT ASSIGNMENT: PART 2

13 May Thurs TUTORIAL 4: Periods 8&9 - Energy Balancing

See tut venues

By the end of the course, you should be able to do the following:

Process Flow Sheets: Understand the nature of a processing plant; Unit operations; pictorial representation of a system as a block diagram; generation of Process Flow Diagrams

Basic Engineering Calculations: Convert units; define, calculate and estimate properties of process materials such as fluid density, concentrations, pressure, etc.

Material and Energy Balance Calculations: Draw and label process flowsheets from verbal descriptions; carry-out degree-of-freedom analyses; write and solve mass and energy balance equations for single unit with and without chemical reaction.

Physical Chemistry: Calculate internal energy and enthalpy changes for process fluids undergoing specified changes in temperature, pressure, and phase. Incorporate such calculations into mass and energy balance problems.

Specifically you should be able to:

1. convert a verbal process description into a block diagram and a process flow diagram

2. State if the units in an equation are consistent and homogeneous and convert a quantity expressed in one set of units into its equivalent in any other dimensionally consistent units using conversion factor tables.  Identify the units commonly used to express both mass and weight in SI, cgs and American Engineering units (AES).

3. Calculate process flow rates in mass, molar, and volumetric units given the appropriate process data.

4. Convert between moles, mass and volume; mole fractions and mass fractions; mass fractions (or composition) and mole fractions (or composition). 

5. Convert temperature and pressure among the common scales. Convert a manometer reading or head of a liquid into an equivalent pressure. 

6. Given a description of a steady-state process, draw and label a flowchart, chose a basis of calculation.

7. Determine the limiting and excess reactants in a reaction.

8. Determine unknown flows and compositions by a material balance for single unit for processes without chemical reactions.

9. Perform a material balance on a material flow sheet incorporating a single process unit for reactive processes given extents of reaction and/or yield and selectivity data for the reactions.

10. Single unit energy balances (heat exchangers, reactors and mixers with no chemical reaction, single chemical reaction and multiple chemical reactions)

 Prescribed BookR.M. Felder and R.W.  Rousseau, Elementary Principles of Chemical Engineering, John Wiley & Sons, Third Edition, 1999. Interactive Chemical Process Principles (ICCP), ICCP-CD ROM (accompanies the textbook). 

References: 1. Himmelblau D.M., Basic Principles and

Calculations in Chemical Engineering, Prentice Hall, Sixth Edition (1996).

2. Reklaitis, G. V., Introduction to Material and Energy Balances, John Wiley & Sons Inc., 1983

What is Chemical Engineering?

A ChE is a person who: (1) develops or designs a new process or (2) re-designs, improves, or troubleshoots a process, in order to make or do something as economically, safely, and efficiently as possible.

Chemical engineers turn lower value materials into higher value

products involved with product design and development design processes to manufacture the products involved with process scale-up, development and

optimization perform economic analysis of the production

process operate and control the processes to ensure that the

product quality satisfies the required specification involved with management of the processes involved with product sales and technical service

A “process” is any operation or series of operations which causes a physical or chemical change in a substance or a mixture of substances.

Every chemical process is a collection of units interconnected by streams.

The five most common unit operations are:• reactors • heat exchangers • pumps • mixers and • separators

Reactors are usually the key unit followed by separators.

Examples of separators include:• dryers • filters • absorbers • adsorbers • centrifuges • distillation columns • liquid-liquid extraction • leaching • evaporators • hydrocyclones

Use the difference in physical properties of each of the species to separate mixtures e.g. boiling points,

FLOWCHARTING

Diagrams routinely used by chemical engineers to help design and understand chemical processes. Three principal diagrams are block flow diagram(BFD), process flow diagram (PFD), and the piping and instrument diagram (P&ID).

most useful is the PFD - understanding of the PFD is the central goal of these lectures

Block Flow Diagram

boxes to symbolize unit processes or process units and directed lines to represent material flows.

e.g. a furnace: natural gas is mixed with air and burned while exhaust gas goes out the chimney.

Example:Produce some product by reacting A and BA + B → Product + C (by-product)

Feed preparation:

Separate reactor output

Separate by-product C and unreacted A and B

Recycle A and B

All processes have a similar input/output structure - raw materials enter a process and are reacted to form products and by-products - products are separated from unreacted feed - usually recycled - product streams purified to yield products that are acceptable to the market place.

Block flow diagrams are illustrated as a set of connected blocks, or process units. Lines with arrows connect the blocks and indicate the direction of the process flow or “stream”. Raw materials always enter (as input) on the left and products leave (as output) on the right.

The Generic Block Flow Process Diagram

Generic Block Flow Diagram has six basic areas; each block may contain several unit operations

1. Reactor Feed Preparation (pre-processing)Reactor feed streams are adjusted to required concentration, temperature (heating), pressure, state, size (grinding) etc.

2. ReactorChemical reactions take place in this block; streams that leave this block contain products, byproducts, and unused reactants

3. Separator Feed PreparationTemperature and pressure of reactor output streams are adjusted to allow effective separation

4. SeparatorSeparation of products, byproducts, waste streams, and unused feed materials by physical processes such as distillation, absorption, extraction

5. RecycleReturns unreacted feed chemicals to the reactor; this block normally contains only pump or compressor and/or heat exchanger

6. Environmental ControlReduces waste emissions from the process and render all non-product streams harmless to the environment; sometimes a single environmental control unit treats the waste from several processes

Summary: Block Flow Diagrams Operations shown by blocks Major flow lines shown with arrows giving

direction of flow Flow goes from left to right whenever possible Light stream (gases) toward top with heavy

stream (liquids and solids) toward bottom Critical information unique to process supplied If lines cross, then the horizontal line is

continuous and the vertical line is broken Simplified material balance provided

Only four kinds of process units are used in block flow diagrams; mixers, reactors, separators, and splitters.

Mixers combine two or more materials (inputs).

One or more chemical reactions take place inside a reactor.

An input stream is separated into two or more outputs by a separator. The outputs from a separator have different chemical compositions from each other and from the input. The change in chemical composition is due to physical operations, not a chemical reaction.

A splitter also separates an input into two of more outputs but now the outputs have the same chemical composition.

Compressors, pumps, heat exchanges, etc. are not part of the BFD.

Generalised Chemical Engineering Process

Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6

Stage 1. Raw material storage Hold several days, or weeks storageStage 2. Feed Preparation Purification and preparation of raw materials, State - liquid or vapour. Size of solid particlesStage 3. Reactor Heart of process. By-products and unwanted compounds also formed,Stage 4. Product separation Products and by-products separated from unreacted material - recycledStage 5. Purification To meet specificationStage 6. Product storage Inventory held to match production with sales

RawMaterial Storage

FeedPreparation

Reaction ProductSeparation

ProductPurification

ProductStorage

Recycle of unreactedMaterial

By-products

Wastes

Block Flow Diagrams (BFDs)

Initial step - convert a word problem into a block diagram. Diagram consists of a series of blocks representing different equipment or unit operations connected by input and output streams. Starting point for developing a PFD.

BFDs gives overview of process unobstructed by the many details related to the process. Each block in the diagram represents a process function and may, in reality, consist of several pieces of equipment.

Conventions and Format for Laying Out a Block Flow Process Diagram1. Operations shown by blocks.2. Major flow lines shown with arrows giving

direction of flow.3. Flow goes from left to right whenever possible.4. Light stream (gases) toward top with heavy stream

(liquids and solids) toward bottom.5. If lines cross, then the horizontal line is continuous

and the vertical line is broken

In-Class ExamplesToluene and hydrogen are converted in a reactor to produce benzene and methane. The reaction does not go to completion, and excess toluene is required. The noncondensable gases are separated and discharged. The benzene product and the unreacted toluene are then separated by distillation. The toluene is then recycled back to the reactor and the benzene removed in the product stream.

The catalytic dehydrogenation of propane is carried out in a continuous packed-bed reactor. One thousand kilograms per hour of pure propane is preheated to a temperature of 670oC before it passes into the reactor. The reactor effluent gas, which includes propane, propylene, methane, and hydrogen, is cooled from 800oC to 110oC and fed to an absorption tower, where the propane and propylene are dissolved in oil. The off gas is release from the top of the absorber. The oil then goes to a stripping tower in which it is heated, releasing the dissolved gases; these gases are recompressed and sent to a distillation column in which the propane and propylene are separated. The propane stream is recycled back to join the feed to the reactor preheater. The product stream from the distillation column contains 98% propylene and the recycle stream is 97% propylene. The stripped oil is recycled to the absorption tower.

Overall objective: To produce C3H6 from C3H8.

Preheater function: Raise temperature of the reactants to raise the reaction rate.

Reactor function: Convert C3H8 to C3H6.

Absorption tower function: Separate the C3H8 and C3H6 in the reactor effluent from the other components.

Stripping tower function: Recover the C3H8 and C3H6 from the solvent.

Distillation column function: Separate the C3H5 from the C3H8.