Ch1 Introduction

transcript

PLANT DESIGN AND ECONOMICS FOR

CHEMICAL ENGINEERS

4 Credit-Hour Core Course

INTRODUCTION

CHEMICAL ENGINEERING PLANT DESIGN

PROCESS DESIGN DEVELOPMENT

FLOWSHEET DEVELOPMENT

COMPUTER-AIDED DESIGN

COST ESTIMATION

PROFITABILITY ANALYSIS OF INVESTMENTS

OPTIMUM DESIGN

OPTIMUM ECONOMIC DESIGN

OPTIMUM OPERATION DESIGN

PRACTICAL CONSIDERATION IN DESIGN

ENGINEERING ETHICS IN DESIGN

Contents

INTRODUCTION

In this modern age of industrial competition, a

successful chemical engineer needs more than a

knowledge and understanding of the fundamental

sciences and the related engineering subjects such as

thermodynamics, reaction kinetics, and computer

technology.

Chemical engineering design of new chemical

plants and the expansion or revision of existing

ones require the use of engineering principles

and theories combined with a practical

realization of the limits imposed by industrial

conditions. Development of a new plant or

process from concept evaluation to profitable

reality is often an enormously complex

problem.

INTRODUCTION

A plant-design project moves to completion through a series of stages such as is

shown in the following:

1. Inception

2. Preliminary evaluation of economics and market

3. Development of data necessary for final design

4. Final economic evaluation

5. Detailed engineering design

6. Procurement

7. Erection

8. Startup and trial runs

9. Production

the general term plant design includes all engineering aspects involved in the

development of either a new, modified, or expanded industrial plant. In this

development, the chemical engineer will be making economic evaluations of new

processes, designing individual pieces of equipment for the proposed new venture,

or developing a plant layout for coordination of the overall operation. Because of

these many design duties, the chemical engineer is many times referred to here as a

design engineer.

On the other hand, a chemical engineer

specializing in the economic aspects of the

design is often referred to as a cost engineer. In

many instances, the term process engineering

is used in connection with economic evaluation

and general economic analyses of industrial

processes, while process design refers to the

actual design of the equipment and facilities

necessary for carrying out the process.

The development of a process design, as outlined in Chap. 3,

involves many different steps. The first, of course, must be

the inception of the basic idea. This idea may originate in the

sales department, as a result of a customer request, or to

meet a competing product. It may occur spontaneously to

someone who is acquainted with the aims and needs of a

particular company.

A complete market analysis is made, and samples of

the final product are sent to prospective customers to

determine if the product is satisfactory and if there is

a reasonable sales potential. Capital-cost estimates for

the proposed plant are made. Probable returns on the

required investment are determined, and a complete

cost-and-profit analysis of the process is developed.

Basic Steps in flowsheet synthesis

- Gathering Information and Database creation

• Basic thermo-physical properties for all chemicals considered

• Information about reaction and conditions

• Yield

• Product purity

• Raw materials

• Process bounding (restrictions)

• Utilities

• Environmental Impact and toxicity of components

• Cost of equipment, utilities and sub-products. Chemical prices

Once the process concept has been designed which produces process flowsheet,

the equipment design then has to be performed…..

Distillation

COMPUTER-AIDED DESIGN

Various types of computer programs and techniques are used to carry out the

design of individual pieces of equipment or to develop the strategy for a full

plant design. This application of computer usage in design is designated as

computer-aided design

COST ESTIMATION

The final process-design stage is completed, it, becomes possible to make

accurate cost estimations because detailed equipment specifications and definite

plant-facility information are available. Direct price quotations based on detailed

specifications can then be obtained from various manufacturers. However, as

mentioned earlier, no design project should proceed to the final stages before

costs are considered, and cost estimates should be made throughout all the early

stages of the design when complete specifications are not available.

Evaluation of costs in the preliminary design phases

is sometimes called “guesstimation” but the

appropriate designation is predesign cost estimation.

Such estimates should be capable of providing a basis

for company management to decide if further capital

should be invested in the project.

COST ESTIMATION

In finalising the process and equipment design, several stages of economic analysis could be conducted …

First step;

EP 1 = Revenue – Cost of Raw Material

Second Step (after mass balance developed)

EP 2 = Revenue – Cost of Raw Material - Utility

Third Step (after equipments designed)

EP 3 = Revenue – Cost of Raw Material – Utility – Annualised Cost of Equipment

The economics analysis continues with other costs (manpower, insurance etc) ….

with profitability analysis conducted at the end to assess project viability ……

Pay back time,

Return on Investment

Internal Rate of Return

Cost Estimation

A major function of the directors of a manufacturing firm is to maximize the long-

term profit to the owners or the stockholders. A decision to invest in fixed facilities

carries with it the burden of continuing interest, insurance, taxes, depreciation,

manufacturing costs, etc., and also reduces the fluidity of the company’s future

actions. Capital-investment decisions, therefore, must be made with great care.

Since all physical assets of an industrial facility decrease in value with age, it is

normal practice to make periodic charges against earnings so as to distribute the

first cost of the facility over its expected service life.

This depreciation expense as detailed in Chap. 9,

unlike most other expenses, entails no current outlay

of cash. Thus, in a given accounting period, a firm has

available, in addition to the net profit, additional

funds corresponding to the depreciation expense. This

cash is capital recovery, a partial regeneration of

the first cost of the physical assets.

OPTIMUM DESIGN

In almost every case encountered by a chemical engineer, there are several

alternative methods which can be used for any given process or operation. For

example, formaldehyde can be produced by catalytic dehydrogenation of

methanol, by controlled oxidation of natural gas, or by direct reaction between

CO and H2 under special conditions of catalyst, temperature, and pressure. Each

of these processes contains many possible alternatives involving variables such

as gas-mixture composition, temperature, pressure, and choice of catalyst. It is

the responsibility of the chemical engineer, in this case, to choose the best

process and to incorporate into the design the equipment and methods which

will give the best results.

OPTIMUM ECONOMIC DESIGN

One typical example of an optimum economic design is determining the pipe

diameter to use when pumping a given amount of fluid from one point to another.

Here the same final result (i.e., a set amount of fluid pumped between two given

points) can be accomplished by using an infinite number of different pipe

diameters. However, an economic balance will show that one particular pipe

diameter gives the least total cost.

OPTIMUM OPERATION DESIGN

Many processes require definite conditions of temperature, pressure, contact

time, or other variables if the best results are to be obtained. It is often possible

to make a partial separation of these optimum conditions from direct economic

considerations. In cases of this type, the best design is designated as the

optimum operation design.

An excellent example of an optimum

operation design is the determination of

operating conditions for the catalytic

oxidation of sulfur dioxide to sulfur

trioxide.

PRACTICAL CONSIDERATION IN DESIGN

The chemical engineer must never lose sight of the practical limitations

involved in a design. It may be possible to determine an exact pipe diameter for

an optimum economic design, but this does not mean that this exact size must be

used in the final design. Suppose the optimum diameter were, 3.43 in. (8.71

cm). It would be impractical to have a special pipe fabricated with an inside

diameter of 3.43 in. Instead, the engineer would choose a standard pipe size

which could be purchased at regular market prices. In this case, the

recommended pipe size would probably be a standard 3.5 in.-diameter pipe

having an inside diameter of 3.55 in. (9.02 cm).

System of moral principles

Principles of right and wrong

Principles of conduct governing

behavior of an individual or a group

ENGINEERING ETHICS IN DESIGN

A person’s behavior is always ethical when one:

A. Does what is best for oneself

B. Has good intentions, no matter how things turn

C. Does what is best for everyone

D. Does what is legal

Quick Questions

Ethics in an Engineering Course????

We have been studying engineering, such as design, analysis, and performance

measurement.

Where does ethics fit in?

How Ethics Fits into Engineering

Engineers . . .

Build products such as cell phones, home appliances, heart valves,

bridges, & cars. In general they advance society by building new

technology.

Develop processes, such as the process to convert salt water into

fresh water or the process to recycle bottles. These processes

change how we live and what we can accomplish.

Products and processes have consequences for society:

If the bridge has an inadequate support, it will

If the gas tank is positioned too close to the

bumper, it might explode from a small accident.

If the process for recycling bottles produces too

much pollution, then it is counterproductive.

If the process for refining gas produces too

much toxins, it harms the local community.

Decisions made by engineers

usually have serious

consequences to people --

often to multitudes of people.

Ethics and ethical reasoning

guide decision-making.

Consider the March 11, 2011

8.9 magnitude earthquake

near Sendai, Japan.

The damage to the Fukushima I Nuclear

Power Plant (Fukushima Dai-ichi)

has led people worldwide to rethink the

ethics of nuclear power.

ISSUE #1: HEALTH AND SAFETY

RISKS: Danger to current and future

generations from leakage of radio-

isotopes used in nuclear power.

Plutonium-239 (half-life = 24,110 yrs)

is a particularly toxic radio-isotope.

Normally, 10 half lives are required

before a Pu-239 contaminated area is

considered safe again, in the case of

plutonium, roughly 250,000 years.

So if Pu leaked, -- say, due to an

earthquake -- it would cause a

health risk for roughly 8000

generations!!

Notice the issues that come up in these discussions:

Issues (cont.):

RISKS, FURTHER

CONSIDERATIONS:

a) The possibility of medical science

discovering a cure for cancer

sometime in the current or next

centuries adds uncertainty to the

long-term health risks of leakages of

radio-active isotopes.

Issues (cont.):

RISKS, FURTHER

CONSIDERATIONS:

b) The use of nuclear power may

increase our knowledge of

radioisotopes used for medical

purposes (possible benefit?).

Finally ….. You will develop the construction details for a process plant ….

Thank you

Ch1 Introduction

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