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 g rowing sales demand, and the sale of e stablished 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 o ut a rough block diagram showing the
main stages in the process; and to list the primary function (objective) and the major constraints fo r
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 m ade for the supply of the services (utilities) needed; such as, process water, cooling water, compressed air, steam. Facilities will also be needed for maintenance, firefighting, o ffices 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, w eek, throughout the year. Some down time will be allowed for maintenance and, for some processes, catalyst regene ration. The plant attainment; that is, the percentage of the available hours in a year that t he 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.
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 pro duction 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 6
1. Production rate greater than 5 x10 kg/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
Economics
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 calc ulation 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.
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.
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 mater ials required and products produced. Balances over individual process 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 approximate d. 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.
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.
CATALYST
WATER
FILTER DRYER
REACTOR
PVC
LOSSES 1%
VCM RECOVERY COLUMN RECYCLE VCM
EFFLUENT
STAGE -2 The first system boundary round the filter and dryer. Product 100,000 kg PVC;
Filter Input
and
0.5% water
Dryer
1% Losses
With 1% loss, polymer entering sub-system =
= 101010 kg
PVC loss = 1010 kg The next boundary round the reactor system; the feeds to the reactor can then be calculated.
Water VCM
Recycle
Reactor 90%
101010 kg
conversion
PVC
Catalyst
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 F 1 , 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,
Water VCM
RECOVERY COLUMN
11223 kg Effluent
VCM
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 %
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.
A Cl2
C
CHLORINATION
ETHYLENE
RECYCLE DCE
DCE
PYROLYSIS
B OXYGEN
OXYHYDRO CHLORINATION
RECYCLE HCl
STAGE -1
Consider the section C: C2H4Cl2 99
C2H3Cl + HCl, yields: on DCE 99 %, 62.5
36.5
VCM
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 + 28
73
O2
C2H4Cl2 + H2O, yield on ethylene 95%,
16
99
18
DCE produced: 73 kg HCl Produce 99 kg DCE 59130 kg HCl produce =
H2O produced: =
= 14580 kg.
O2 required: =
= 12960 kg
Ethylene required: =
= 22680 kg
= 80190 kg DCE
95% ethylene converts to DCM.
Ethylene required =
= 23874 kg
Consider the section A: C2H4 + Cl2 28
C2H4Cl2, yield on ethylene 98 %
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
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
1. Fixed capital investment: (using the ratio factor outline) Ref: H.J.Lang, chemical engineering, 54(10);117 (1947);
Components 1. 2. 3. 4. 5. 6. 7. 8. 9.
Cost
Purchased equipment (delivered) E Purchased equipment installation 39% E Instrumentation (installed) 28% E Piping (installed) 31% E Electrical (installed) 10% E Building (including service) 22% E Yard improvement 10% E Service facilities (installed) 55% E Land 6% E
Total direct plant coast
850,00,00,000 331,50,00,000 238,00,00,000 263,50,00,000 85,00,00,000 187,00,00,000 85,00,00,000 467,50,00,000 51,00,00,000 =
Engineering and supervision 32% E
tk tk tk tk tk tk tk tk tk
2558,50,00,000 tk 272,00,00,000 tk
Final fixed Capital investment
=
2830,50,00,000 tk
2. Working capital:
a. Production cost Item 1. 2. 3. 4.
Cost
Raw material Utilities Spare parts Other
1727,00,00,000 1244,00,00,000 500,00,00,000 100,00,00,000 Total
tk tk tk tk
= 3571,00,00,000 tk
b. Employment cost Item
Cost
1. Salaries and wage 2. Cash and non cash benefit
74,00,00,000 tk 22,00,00,000 tk Total =
96,00,00,000 tk
c. Plant over had coast Item 1. 2. 3. 4. 5. 6. 7.
Cost
Maintenance cost and repair Safety and protection Packing Stationeries , stamps Central laboratories Research and development Recreation and others
100,00,00,000 tk 40,00,00,000 tk 50,00,00,000 tk 120,00,00,000 tk 100,00,00,000 tk 50,00,000 tk 50,00,000 tk Total =
Working capital
411,00,00,000 tk
= 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
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
=
= =
21.22 %
x
100
x 100
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
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) Dryer’s 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.
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 vinyl chloride monomer (VCM) using suspension polymerization. The Chisso2 process sequences are illustrated in Figure 1.
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), and maintaining 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 : 60 0C Reaction time (with 85% conversion) : 6 hours Raw Materials: 1) VCM 2) Purified Water 3) Additives
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.
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
