chemical engineering projects can be divided into three types

7/30/2019 Chemical Engineering Projects Can Be Divided Into Three Types

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Chemical engineering projects can be divided into three types, depending on the novelty involved:

1. Modifications, and additions, to existing plant; usually carried out by the plant design group.

2. New production capacity to meet growing sales demand, and the sale of established processes by

contractors. Repetition of existing designs, with only minor design changes.

3. New processes, developed from laboratory research, through pilot plant, to a commercial process.

Even here, most of the unit operations and process equipment will use established designs.

The first step in devising a new process design will be to sketch out a rough block diagram showing the

main stages in the process; and to list the primary function (objective) and the major constraints for


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each stage. Experience should then indicate what types of unit operations and equipment should be

considered.

Stage 1. Raw material storage

Stage 2. Feed preparation

Stage 3. Reactor

Stage 4. Product separation

Stage 5. Purification

Stage 6. Product storage

Ancillary processes

In addition to the main process stages shown in Figure 1.3, provision will have to be made for the supply

of the services (utilities) needed; such as, process water, cooling water, compressed air, steam. Facilitieswill also be needed for maintenance, firefighting, offices and other accommodation, and laboratories;

1.3.1. Continuous and batch processes

Continuous processes are designed to operate 24 hours a day, 7 days a week, throughout the year.

Some down time will be allowed for maintenance and, for some processes, catalyst regeneration. The

plant attainment; that is, the percentage of the available hours in a year that the plant operates, will

usually be 90 to 95%.

Batch processes are designed to operate intermittently. Some, or all, the process units being frequently

shut down and started up.

Continuous processes will usually be more economical for large scale production. Batch processes are

used where some flexibility is wanted in production rate or product specification.


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Batch processes are designed to operate intermittently. Some, or all, the process units being frequently

shut down and started up.

Continuous processes will usually be more economical for large scale production. Batch processes are

used where some flexibility is wanted in production rate or product specification.

Choice of continuous versus batch production

The choice between batch or continuous operation will not be clear cut, but the following rules can be

used as a guide.

Continuous

1. Production rate greater than 5 x106kg/h

2. Single product

3. No severe fouling

4. Good catalyst life

5. Proven processes design

6. Established market

Batch

1. Production rate less than 5 x106kg/h

2. A range of products or product specifications

3. Severe fouling

4. Short catalyst life

5. New product

6. Uncertain design


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Economics


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6.10.4. Rate of return calculations

Cash-flow figures do not show how well the capital invested is being used; two projects

with widely different capital costs may give similar cumulative cash-flow figures. Some

way of measuring the performance of the capital invested is needed. Rate of return (ROR),

which is the ratio of annual profit to investment, is a simple index of the performance

of the money invested. Though basically a simple concept, the calculation of the ROR is

complicated by the fact that the annual profit (net cash flow) will not be constant over

the life of the project. The simplest method is to base the ROR on the average income

over the life of the project and the original investment.


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The rate of return is often calculated for the anticipated best year of the project: the

year in which the net cash flow is greatest. It can also be based on the book value

of the investment, the investment after allowing for depreciation. Simple rate of return

calculations take no account of the time value of money.


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Material Balances

Fundamentals of Material Balances

Material balances are the basis of process design. A material balance taken over the complete process

will determine the quantities of raw materials required and products produced. Balances over individualprocess units set the process stream flows and compositions.

The general conservation equation for any process system can be written as:

Material out =Material in + Generation Consumption- Accumulation

2.18. GENERAL PROCEDURE FOR MATERIAL-BALANCE

The following step-by-step procedure is given as an aid to the efficient solution of material balance

problems. The same general approach can be usefully employed to organize the solution of energy

balance, and other design problems.

Procedure

Step 1. Draw a block diagram of the process. Show each significant step as a block, linked by lines and

arrows to show the stream connections and flow direction.

Step 2. List all the available data. Show on the block diagram the known flows (or quantities) and

stream compositions.

Step 3. List all the information required from the balance.

Step 4. Decide the system boundaries (see Section 2.6).

Step 5. Write out all the chemical reactions involved for the main products and byproducts.

Step 6. Note any other constraints,

such as: specified stream compositions, azeotropes, phase equilibria, tie substances

Step 7. Note any stream compositions and flows that can be approximated.

Step 8. Check the number of conservation (and other) equations that can be written, and compare with

the number of unknowns. Decide which variables are to be design variables; see Section 2.10.

This step would be used only for complex problems.

Step 9. Decide the basis of the calculation; see Section 2.7.

The order in which the steps are taken may be varied to suit the problem.


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Material balance

Aim is to produce 100,000 kg/hr. The production will complete in two

stages. In the case of 1st stage VCM will obtain. And 2nd stage is the

production of PVC from VCM.

The calculation will start from the second stage to know how much Raw

material is required for the production of 100,000 kg/hr PVC.

The first system boundary round the filter and dryer.

With 1% loss, polymer entering sub-system =

= 101010 kg

FILTER

RECOVERY

COLUMN

RECYCLE VCM

STAGE -2

CATALYST

VCM

WATERREACTOR PVC

EFFLUENT

DRYER

LOSSES 1%

Filter

and

Dryer

Input

Product 100,000

kg PVC;

0.5% water

1% Losses


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PVC loss = 1010 kg

The next boundary round the reactor system; the feeds to the reactor can

then be calculated.

At 90 % conversion, VCM feed =

= 112233 kg

Unreacted VCM = 112233 1010101 = 11223 kg

Catalyst at 1kg / 1000 kg VCM

= 112233 x 1 x 10-3

= 112.23 kg

Let water feed to reactor be F1 , then for 20% VCM

.20 =

F1 =

= 448932 kg

Now consider filter-dryer sub-system again, Water in PVC 5%

= 101010 x .05 = 5050 kg

Now consider the recovery system,

WaterVCM

RecycleCatalyst

101010 kg

PVC

Reactor 90%

conversion

RECOVERY

COLUMNWater

VCM

11223 kg

Effluent

VCM


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With 98% recovery recycle to reactor = .98 x 11223 = 10998.54 kg

= 11000 kg

Composition of effluent

VCM = 11233-11000 = 233 kg

Water = 448932 5050 = 443882 kg

Effluent = 443882 kg + 233 = 444115 kg

Consider reactor VCM feed

Fresh feed Reactor feed

Recycle 11000 kg

Balance round this fresh VCM required

= 112233- 11000 kg

= 101233 kg

Now considering the stage 1 for the calculation of requires raw material to

produce 101250 kg VCM.

The block diagram shows the main steps in the balanced process for the

production of vinyl chloride monomer from ethylene. Each block represents a

reactor and several other processing units. The main reactions are:

Block A, chlorination

C2H4 + Cl2 C2H4Cl2, yield on ethylene 98 %


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Block B, Oxyhydro chlorination

C2H4 + 2HCl +

O2 C2H4Cl2 + H2O, yield on ethylene 95%,

Block C, pyrolysis

C2H4Cl2 C2H3Cl + HCl, yields: on DCE 99 %,

The HCl from the pyrolysis step is recycled to the oxyhydrochlorination step.

The flow of ethylene to the chlorination and oxyhydrochlorination reactors is

adjusted so that the production of HCl is in balance with the requirement.

The conversion in the pyrolysis reactor is limited to 55 %, and the unreacted

dichloroethane (DCE) separated and recycled.

Consider the section C:

C2H4Cl2 C2H3Cl + HCl, yields: on DCE 99 %,

99 62.5 36.5

RECYCLE DCE

B

STAGE -1

VCMDCE PYROLYSIS

CHLORINATION

OXYHYDRO

CHLORINATION

Cl2

ETHYLENE

OXYGEN

AC

RECYCLE HCl


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62.5 kg VCM produced from 99 kg EDC

101250 kg VCM produced from =

= 160380 kg EDC

62.5 kg VCM produced when HCL 36.5 kg

101250 kg VCM produced when HCL =

= 59130 kg

99% DCE converts to VCM

So required DCE =

= 162000 kg

Consider the section B:

C2H4 + 2HCl +

O2 C2H4Cl2 + H2O, yield on ethylene 95%,

28 73 16 99 18

DCE produced:

73 kg HCl Produce 99 kg DCE

59130 kg HCl produce =

= 80190 kg DCE

H2O produced:

=

= 14580 kg.

O2 required:

=

= 12960 kg

Ethylene required:

=

= 22680 kg


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95% ethylene converts to DCM.

Ethylene required =

= 23874 kg

Consider the section A:

C2H4 + Cl2 C2H4Cl2, yield on ethylene 98 %

28 71 99

DCM produced in this section

= Total DCM required for VCM production DCM produced in section B

= 162000 - 80190

= 81810 kg

Cl2 required :

=

= 58672 kg

Ethylene required:

=

= 23138 kg

98% ethylene converts to DCM.

Ethylene required =

= 23610 kg


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Overall material balance for the 100000 kg/hr PVC production:

Stage 1:

Ethylene required = section A + Section B = 23610 + 23874 = 47484 kg

Chlorine required = section A = 58672 kg

Oxygen required = section B = 12960 kg

Hydrogen Chloride required ( initially) = section B = 59130 kg

Water produced = section B = 14580 kg

Hydrogen Chloride produced ( recycled) = section C = 59130 kg

VCM produced = section C = 101250 kg

Stage 2:

Catalyst required = 112.23 kg

VCM required (initially) = 112233 kg

VCM recycled = 11000 kg

VCM finally required = 112233-11000 = 101233

Water required = 448932 kg

PVC Produced = 100000 kg

Effluent = 444115 kg

Catalyst = 112.23 kg

PVC loss = 1010 kg


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1.Fixed capital investment:(using the ratio factor outline)

Ref: H.J.Lang, chemical engineering, 54(10);117 (1947);

Components Cost

1. Purchased equipment (delivered) E 850,00,00,000 tk2. Purchased equipment installation 39% E 331,50,00,000 tk3. Instrumentation (installed) 28% E 238,00,00,000 tk4. Piping (installed) 31% E 263,50,00,000 tk5. Electrical (installed) 10% E 85,00,00,000 tk6. Building (including service) 22% E 187,00,00,000 tk7. Yard improvement 10% E 85,00,00,000 tk8. Service facilities (installed) 55% E 467,50,00,000 tk9. Land 6% E 51,00,00,000 tk

Total direct plant coast = 2558,50,00,000 tk

Engineering and supervision 32% E 272,00,00,000 tk

Final fixed Capital investment = 2830,50,00,000 tk

2.Working capital:

a. Production costItem Cost

1. Raw material 1727,00,00,000 tk2.

Utilities 1244,00,00,000 tk

3. Spare parts 500,00,00,000 tk4. Other 100,00,00,000 tk

Total = 3571,00,00,000 tk


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b. Employment costItem Cost

1. Salaries and wage 74,00,00,000 tk2. Cash and non cash benefit 22,00,00,000 tk

Total = 96,00,00,000 tk

c. Plant over had coastItem Cost

1. Maintenance cost and repair 100,00,00,000 tk2. Safety and protection 40,00,00,000 tk3. Packing 50,00,00,000 tk4. Stationeries , stamps 120,00,00,000 tk5. Central laboratories 100,00,00,000 tk6. Research and development 50,00,000 tk7. Recreation and others 50,00,000 tk

Total = 411,00,00,000 tk

Working capital = Production cost + Employment cost + over head cost

= (3571,00,00,000 + 96,00,00,000 + 411,00,00,000)tk

= 4078,00,00,000 tk

Total capital investment = Fixed capital + Working capital

= (2830,50,00,000 + 4078,00,00,000) tk

= 6908,50,00,000 tk

Depreciation

Item percentage value of taka

Building 5% 5,00,00,000 tk

Machinery and equipment 12% 108,00,00,000 tk

Total = 113,00,00,000 tk


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1000,00,00,000 taka is taken as a loan from bank under a rate of interest

12% therefore the annual interest becomes 120,00,00,000 tk

Total manufacturing cost = working capital + Depreciation + Bank interest

= (4078,00,00,000 + 113,00,00,000 + 120,00,00,000)tk

= 4311,00,00,000 tk

Profitability:

Item Quantity (ton/yr) Price (tk/ton) total sale value(tk)

PVC 8,76,000 ton/yr 70,000 tk/ton 6132,00,00,000 tk

Gross annual earning = Total sale value Total manufacturing cost

= ( 6132,00,00,000 - 4311,00,00,000 ) tk

= 1821,00,00,000 tk

Income Tax:

20% on gross annual earning = 364,20,00,000 tk

Net annual earning or Profit = Gross annual earning Income taxes

= ( 1821,00,00,000 - 364,20,00,000 )tk

= 1456,80,00,000 tk

Rate of return = x100

=

x 100

= 21.22 %


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PVC Resin quality control:

Root Cause analysis of potential defects as shown in figure 3 is the fishbone

diagram that provides a cause-effect diagram for moisture control of PVC

products.

Plan for quality Control

Quality

Categories Moisture Content

Grade A 0.08% max 0.06% min


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Grade B 0.2% max 0.16% min

Grade C 0.4% max 0.32% min

Table 1: Grade 3 differences with different moisture contents.

There are many PVC grade defined based on PSD, Molecular weight, and

moisture contents as well as other factors. This control plan focuses on the

drying process of the PVC manufacturing process. The moisture content in

PVC becomes the key quality factor in this process. Several different grades

of PVC resin based on the content of moisture are listed in table 1. The

outcomes of these different grades are the combination effects of drying

process attributes such as 1) Dryer Functional Capacities 2) Dryers

Temperature 3) Centrifuge Functional Capacities as outlined in figure 3.

Data Collection Plan:

The data collection process is quite straight forward. The dried samples

were collected very 3 hours from the dryer then delivered to the laboratory

for analysis. The samples collected will be divided into 5 sub-groups and

measured using NIR spectroscopy.


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Selection of technology:

There are three main processes can be used for the commercial production

of PVC powders 1) Suspension 2) Emulsion 3) Bulk methods. The PVC

produced by suspension process provides 80% of worldwide support. So, the

process of PVC polymerization will be focused on the suspension method. In

this study, the Chisso Process (reference) is used to produce PVC from vinylchloride monomer (VCM) using suspension polymerization. The Chisso2

process sequences are illustrated in Figure 1.


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PVC Suspension Process:

This process can be divided into 6 different steps from input of raw materials

to the end products:

a) Input Fresh VCM, additives and water into a stirring reactor (1), andmaintaining temperature during the polymerization to control the grade of

the PVC

b) Discharge PVC powder after 85-90% VCM/PVC conversion to a blowdown

tank (2) to flush off VCM gas and recover VCM gas to VCM gas holder (6)

c) PCV slurry containing VCM is fed into the stripping column (3)

continuously, most of the residual VCM will be recovered from this column

d) The slurry will be de-watered with a centrifuge device (4)

e) The slurry will be dried by the proprietary dryer (5). It is then passed to

storage silos.

PVC Process Inputs and Outputs:

Block diagram and process sequences can be seen from figure 1. This figure

also identifies several needed raw materials and equipment for PVC

polymerization. Many more inputs are needed to produce PVC resins.

Inputs:

Capacity of the Reactor: 130 m3

Mixing speed with rotator : 120 r/s

Water Temperature in Jacket : 600C

Reaction time (with 85% conversion) : 6 hours

Raw Materials: 1) VCM

2) Purified Water

3) Additives


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a) PVC additives

b) Initiators

c) Inhibitors

Centrifuge Time: 10 minutes

Drying Time: 2 Hours

Outputs:

PVC powders with different grading.

Process quality defect metrics on moisture contents:

For each grade of PVC resin, the plant applies a defined control plan which

checks all necessary factors that impact on the PVC resin moisture content in

order to guarantee the moisture content of specific grade upon delivery.


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These factors which are regularly controlled for drying purpose are:

Stream pressure that regulates the temperature for drying

Stream flow that regulates the temperature for drying

Centrifuge speed

RPM of dryer

Speed of wet PVC slurry delivered to the dryer

chemical engineering projects can be divided into three types

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