Appendix-A
CHAPTER-1
INTRODUCTION Acetaldehyde (systematically ethanal) is an organic chemical compound with the formula CH3CHO or MeCHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part of their normal metabolism. It is also produced by oxidation of ethanol and is popularly believed to be a cause of hangovers. Pathways of exposure include air, water, land or groundwater that can expose the human subject directly if they inhale, drink, or smoke.
1.1 PHYSICAL PROPERTIES Acetaldehyde is a colorless, mobile liquid having a pungent suffocating odor that is somewhat fruity and pleasant in dilute concentrations. Some physical properties of acetaldehyde are given in Table(1.1), the vapour pressure of acetaldehyde and its aqueous solutions in Table(1.2 & 1.3) and the solubility of acetylene, CO2 and N2 in liquid acetaldehyde in Table(1.4). The freezing points of aqueous solutions of acetaldehyde are as follows: 4.8 wt.% - 2.5 oC; 13.5 wt.% - 7.8 oC; & 31.0 wt.% - 23.0 oC Acetaldehyde is miscible in all proportions with water and most common organic solvents; acetone, benzene, ethyl alcohol, ethyl ether, gasoline, paraldehyde, toluene, xylene, and acetic acid.
1
Appendix-A
Table-1.1: Physical Properties of Acetaldehyde Formula weight
44.052
Melting point, °C
-123.5
Boiling point at 760 mm, °C
20.16
Density, d2o4
0.7730
Vapor density (air = 1)
1.52
Surface tension at 20oC, dyne/cm
21.2
Absolute viscosity at 15 oC ( cgs units)
0.02456
Specific heat, cal/(oC)(g) at 0oC
0.522
at 25°C
0.336
Latent heat of fusion, cal/g
17.6
Latent heat of vaporization, cal/g
139.5
Heat of combustion of liquid at constt.pr. Kcal/mol
279.2
Heat of formation at 273 oK
39.55
Free energy of formation at 273 oK, Kcal/mole
-32.60
Critical temp, C
181 .5
Critical pressure, atm.
63.2
Dissociation constant, Ka, at 0 oC
0.7 10-14
Flash point, closed cup, °C
-38
Ignition temp. in air, oC
165
Explosive limits of mixtures with air, % acetaldehyde by vol.
4-57
2
Appendix-A
Table-1.2: Vapor Pressure of Acetaldehyde Temperature oC
-50
Vapor Pressure mm Hg 19
20
Vapor pressure mm Hg 755
-20
123
20.16
760
0
330
30
1069
5
411
50
3096
10
508
70
3696
15
622
100
3607
Temperature oC
Table-1.3: Vapor Pressure of Aqueous solutions of Acetaldehyde
10
Vapor Pressure mm Hg 4.9
4.9
Vapor pressure mm Hg 74.5
10
10.5
10.5
139.8
20
5.4
5.4
125.2
20
12.9
12.9
295.2
Temperature oC
Temperature oC
Table-1.4: Solubility of Gases in Liquid Acetaldehyde at 760 mmHg (volume of gas [NTP] dissolved in one volume of acetaldehyde) Temperature oC
Acetylene
Carbon Dioxide
-6
27
11
0
17
6.6
12
7.3
2.45
16
5
1.5
3
Nitrogen
0.15
Appendix-A
1.2 USES About 95% of the acetaldehyde produced is used internally by the manufacturers as an intermediate for the production of other organic chemicals.. Table(1.5), gives an idea of the use pattern. Imports and exports of acetaldehyde are negligible. Acetic acid and anhydride are the major derivatives of acetaldehyde (45% in 1970) followed by n-butanol (19%) and 2-ethylhexanol (17%). Twenty percent of the acetaldehyde is consumed in a variety of other products, the most important being pentaerythritol, trimethylolpropane, pyridines, peracetic acid, crotonaldehyde, chloral, 1,3-butylene glycol, and lactic acid. The proportion of acetaldehyde used in the manufacture of acetic acid and acetic anhydride will tend to increase in the near future, and the proportion used in the synthesis of nbutanol and 2-ethylhexanol will decrease. Acetaldehyde is competing with propylene and -olefins as the raw material for the production of n-butanol and higher alcohols (oxo route). Other uses of acetaldehyde include: in the silvering of mirrors; in leather tanning; as a denaturant for alcohol; in fuel mixtures; as a hardener for gelatin fibres; in glue and casein products; as a preservative for fish and fruit; in the paper industry; as a synthetic flavoring agent; and in the manufacture of cosmetics, aniline dyes, plastics and synthetic rubber. Acetaldehyde is also used in the manufacture of disinfectants, drugs, perfumes, explosives, lacquers and varnishes, photographic chemicals, phenolic and urea resins, rubber accelerators and antioxidants, and room air deodorizers; acetaldehyde is a pesticide intermediate.
4
Appendix-A
Table-1.5 Acetaldehyde, United States Uses in 1970 Acetic acid and anhydride
45 %
n-Butanol
19%
2-Ethylhexanol
17%
AH others
19%
The future growth of acetaldehyde will be mainly dictated by the acetic acid and anhydride picture and the growth of the other minor derivatives mentioned above.
1.3 FUTURE TRENDS In the next decade the major change that will occur in the acetaldehyde picture is a decrease in the use of acetaldehyde for the preparation of derivatives that can be manufactured from alternative raw materials. This has already happened in the production of butanol and 2-ethylhexanol in which acetaldehyde raw material has been replaced by propylene and synthesis gas in oxo-type processes. Acetic acid and anhydride are the major outlets for acetaldehyde. Production of these chemicals from alternative processes (like methanol carbonylation or saturated hydrocarbon oxidation) would also have an adverse effect on acetaldehyde consumption in the future. Here again, the energy crisis could accelerate the expansion of some of these processes that are competing with acetaldehyde by-making synthesis gas and carbon monoxide available through coal gasification. Long range, carbon monoxide and hydrogen could become the new building blocks of the organic chemical industry.
5
Appendix-A
1.4 HANDLING In handling acetaldehyde, one has to remember that it is an extremely reactive compound that can be easily oxidized, reduced, or polymerized, and is highly reactive with oxygen. It has to be treated as a volatile, flammable, and toxic material. The following is a list of precautions recommended when handling acetaldehyde: Nitrogen or other inert gases should be used as a blanketing material whenever exposure to air is a possibility Safety goggles should be used Transfers should be made in open-air structures or using suitable gas mask or self-contained breathing equipment . Drums should be stored out-of-doors, avoiding direct exposure to sunlight Acetaldehyde should be-chilled before transferring and a nitrogen blanket should be used.
1.5 SHIPPING AND STORAGE Acetaldehyde is shipped insulated tank trucks, and insulated tank cars. Acetaldehyde in, the liquid state is non-corrosive to most metals, but it can be easily oxidized to acetic acid. Suitable materials of construction are stainless steel and aluminum. Drums coated with phenolic resins have also been used. If a darker color and some iron contamination are not objectionable, carbon steel may be used. Because acetaldehyde is classed as a flammable liquid, it requires a red DOT (Department of Transportation) shipping table. Bulk storage held at low temperature and pressure is recommended over storage in a pressure vessel.
6
Appendix-A
CHAPTER-2
MANUFACTURING PROCESSES The economics of the various processes for the manufacture of acetaldehyde are strongly dependent on the price of the feed stock used. Since 1960 the liquid phase oxidation of ethylene has been the process of choice. However, there is still commercial production by the partial oxidation of ethyl alcohol and the hydration of acetylene. Acetaldehyde is also formed as a co-product in the high temperature oxidation of butane. A recently developed rhodium catalyzed process produces acetaldehyde from synthesis gas as a co-product with ethyl alcohol and acetic acid.
2.1 HYDRATION OF ACETYLENE In this process high pricing acetylene is fed with steam to a rubber lined vertical reactor which contains a catalyst solution of mercury salt (0.5 to 1 wt.%) sulfuric acid (15 to 20 wt.%) ferrous and ferric iron (2 to 4 wt/%) and water. Minute particles of free mercury are suspended in the catalyst solution. The temperature and pressure are controlled at 90 to 95 oC and 1 to 2 atm, respectively. The acetylene conversion per pass is about 55%.
7
Appendix-A
2.2 ETHYLENE OXIDATION PROCESS The process is essentially based on three chemical reactions. C2H4 + 2CuCl2 + H2O Pdo + 2CuCl2 2CuCl + 2HCl + 1/2O2 C2H4 + ½O2
CH3CHO + Pdo + 2HCl PdCl2 + 2CuCl (Pd oxidation) 2CuCl2 + H2O (CuCl oxidation) CH3CHO
(Overall reaction)
In this process, the palladium chloride is required only in very small concentration, and the copper salts are continuously regenerated with oxygen. In this way direct oxidation of ethylene take place. In this process fresh oxygen and ethylene are fed independently to a vertical ceramic lined reactor containing a water solution of catalyst (PdCl 2 and CuCl2). The reactor is operated to 120 to 130 oC and about 3 atm. The heat of vaporization is removed by evaporating acetaldehyde and water from the catalyst solution. The ethylene conversion per pass is 75%.
2.3 OXIDATION OF SATURATED HYDROCARBONS Acetaldehyde is formed as a co-product in the vapor-phase oxidation of saturated hydrocarbon such as butane. Oxidation of butane yields acetaldehyde, formaldehyde, methanol acetone and mixed solvents as major products, other aldehydes, alcohols, ketones, glycols acetals, epoxides and organic acids are formed in smaller concentrations. This is of historic interest unlike the acetylene rout; it has almost no chance to be used as a major process.
8
Appendix-A
2.4 SYNTHESIS GAS PROCESS A rhodium catalyzed process capable by converting synthesis gas directly into acetaldehyde in a single step was reported in 1974. CO + H2
CH3CHO + other products
The process comprises synthesis gas over 5% rhodium on SiO 2 at 300 oC and 2.0 MPa(20 atm). The principle co products are acetaldehyde 24% are acetaldehyde 24% acetic acid 20%, and ethanol 16%. If there is a substantial degree of coal gasification, the interest in the use of synthesis gas as a raw material for acetaldehyde production will increase.
2.5 ETHYL ALCOHOL PROCESSES There are two commercial processes for the production of acetaldehyde from ethyl alcohol. These are vapor phase oxidation of ethanol. Ag CH3CHCH2OH + ½ O2
CH3CHO + H2O
o
550 C In this process a mixture of ethyl alcohol vapors and oxygen are passed over silver catalyst filled in tubes of multi-tubular fixed bed reactor. The reaction is carried out at 550 oC and conversion of ethyl alcohol to acetaldehyde is 50-55% per pass. The second process is vapor phase dehydrogenation of ethanol. Cr and Cu C2H5OH
o
CH3CHO + H2
260 to 290 C
9
Appendix-A
In this process vapors of ethanol are reacted over a chromium copper catalyst at atmospheric pressure and 260 to 290 oC temperature. The alcohol conversion is 30 to 50% depending upon reaction temperature and alcohol flow rate. Out of these processes we have selected “Ethylene Oxidation Process”. Process description is given below.
2.6 PROCESS DESCRIPTION
10
Appendix-A
CHAPTER-3
MATERIAL & ENERGY BALANCE 3.1
MATERIAL BALANCE
BASIS:
1000 Kg/hr production of acetaldehyde
REACTOR-R1 Material entering with stream-8 C2H5OH = 863.26 Kg/hr = 18.766 Kgmol/hr H2O = 45.43 Kg/hr = 2.524 Kgmol/hr O2 = 635.28 Kg/hr = 19.852 Kgmol/hr N2 = 2090.82 = Kg/hr = 74.62 Kgmol/hr Chemical reaction involved is C2H5OH + ½ O2
CH3CHO + H2O
As conversion of C2H5OH is 50% so C2H5OH converted = 9.383 Kgmol/hr C2H5OH unvonverted = 9.383 Kgmol/hr O2 = converted = 9.383/2 = 4.692 Kgmol/hr O2 = unconverted = 15.16 Kgmol/hr
11
Appendix-A
CH3CHO formed = 9.383 Kgmol/hr H2O = formed = 9.383 Kgmol/hr Total water leaving = 2.524 + 9.383 = 11.907 Kgmol/hr So material leaving with strea-9 C2H5OH = 9.383 Kgmol = 431.6 Kg CH3CHO = 9.383 Kgmol = 412.85 Kg H2O = 11.907 Kgmol = 214.33 Kg O2 = 15.16 Kgmol = 485.12 Kg N2 = 74.67 Kgmol = 2090.82 Kg Total material leaving = 3634 Kg/hr Total material entering = 3634 Kg/hr
ABSORBER-A1 In first absorber 95% entering acetaldehyde will be absorbed
10
11
14
9
Material entering with stream-9 CH3CHO
=
422.85 Kg/hr
12
Appendix-A
C2H5OH
=
431.6 Kg/hr
H2O
=
85.33 + 129 = 214.35 Kg/hr
O2
=
485.12 Kg/hr
N2
=
2090.82 Kg/hr
Material with stream-10 CH3CHO
=
20.64 Kg/hr
C2H5OH
=
17.1 Kg/hr
O2
=
485.12 Kg/hr
N2
=
2090.82 Kg/hr
Material entering with stream-11 H2O
=
4064 Kg/hr
CH3OHO
=
20.43 Kg/hr
C2H5OH
=
17 Kg/hr
Material leaving with stream-14 CH3CHO
=
412.6 Kg/hr
C2H5OH
=
431.5 Kg/hr
H2O
=
4278.6 Kg/hr
Total material entering = 7736 Kg/hr Total material leaving = 7736 Kg/hr
13
Appendix-A
DISTILLATION COLUMN-D1
15
14 16
Product Specifications Top product CH3CHO
=
99%
C2H5OH
=
0.8%
H2O
=
0.2%
There should be no CH3CHO in bottoms Material entering with stream-14 CH3CHO
=
412.6 Kg/hr
=
8.05%
C2H5OH
=
431.58 Kg/hr
=
8.4%
H2O
=
4278.6 Kg/hr
=
83.52%
Total
=
5122.78 Kg/hr
So CH3CHO balance 0.0805 (5122.78) = 0.99 (D) D = 416.55 Kg/hr So top product is =
416.55 Kg/hr
Bottom product
4706.2 Kg/hr
=
C2H5OH in top product = 0.008 416.55
H2O in top product
=
3.33 Kg/hr
=
0.002 416.55
14
Appendix-A
= CH3CHO in top product =
0.833 412.00 Kg/hr
Material leaving in bottom product C2H5OH
=
431.58 – 3.33 = 428.25 Kg/hr
H2O
=
4278.6 – 0.833 = 4277.76 Kg
Total material leaving = 5122 Kg/hr Total material entering = 5122 Kg/hr
15
Appendix-A
3.2
ENERGY BALANCE
VAPORIZER
F
G
Separator B
E
Vaporizer A
C
D
Temperature of stream-A
=
25 oC
Mass flow rate
=
503 Kg/hr
Cp of 95% ethyl alcohol
=
0.64 Kcal/KgoC
So heat with stream-A
=
503 0.64 25
=
8048 Kcal/hr.
Similarly, heat ith stream-B
=
27263 Kcal/hr
So, heat with stream-C
=
27263 + 8048
=
35311 Kcal/hr
=
908.7
=
0.73 Kcal/Kg oC
=
Q/mCp
Flow rate of stream-C Cp Temperature of stream-C
16
Appendix-A
=
35311 908.7 0.73
=
53 oC
Stream-G is saturated liquid at 2.3 atm Heat with stream-G
Q
=
227.1 0.92 112
=
23400 Kcal/hr
=
23400 + 35311
=
58711 Kcal/hr
Flow rate of stream-D
=
1135.8 Kg/hr
Temperature of stream-D
=
58711 1135.8 0.78
=
66 oC
Heat with stream-D
=
mCpT
=
at 2.3 atm ethyl alcohol (95%) will be vaporized at 112 oC, so, we have to supply heat to ethyl alcohol in vaporizer.
In vaporizer Sensible heat Q1
=
mCpT
=
1135.8 0.87 (112 – 66)
=
45454.7 Kcal/hr
Latent heat As only 80% ethyl alcohol (95%) is being vaporized so 908.7 Kg/hr of ethyl alcohol will be vaporized. Water vaporized
=
0.05 908.7
=
45.43 Kg/hr
Latent heat of vaporization of water
QH 2O
=
=
22717.5 Kcal/hr
Ethyl alcohol evaporated =
863.2 Kg/hr
17
500 Kcal/hr
Appendix-A
Latent heat of vaporization =
QC2 H5OH
=
175 Kcal/kg
175 863.2 =
Total heat to be supplied = =
151071
45454.7 + 22717.5 + 151071 219243.5
If steam is used at 130 oC latent heat of steam at 130 oC = 519.8 Kcal/kg So, flow rate of steam
=
219243.5/519.8
=
421 Kg/hr
Reactor Standard heat of reaction =
- 43 Kcal/hr
Heat of reaction at given conditions
=
401860 Kcal/hr
So, 401860 Kcal/hr heat should be removed from reactor by cooling water. Inlet temperature of cooling water
=
25 oC
Outlet temperature of cooling water
=
45 oC
Mass flow rate of water =
=
?
m
=
Q Cp T
=
401860 1 20
=
m
20093 Kg/hr
DISTILLATION COLUMN Input =
Output
WFHF + QR = QC + WBHB(l) + + WDHD(l) WF = 256.4595 Kg-mol/hr WB(l) = 246.9015 Kg-mol/hr WD(l) = 9.5412 Kg-mol/hr HF = 3145495 J/Kg-mol. hr HB(l) = 3169709 Kg-mol/hr
18
Appendix-A
HD(l) = 1473400 Kg-mol/hr QC = 111507000 J/hr QR = 1105043000 J/hr Putting in eq. 917196375 J/hr = 917196375 J/hr
19
Appendix-A
REACTOR DESIGN FIXED BED CATALYTIC REACTORS 4.1 INTRODUCTION Fixed-bed catalytic reactors have been aptly characterized as the workhorses of me process industries. For economical production of large amounts of product, they are usually the first choice, particularly for gas-phase reactions. Many catalyzed gaseous reactions are amenable to long catalyst life (1-10 years); and as the time between catalyst change outs increases, annualized replacement costs decline dramatically, largely due to savings in shutdown costs. It is not surprising, therefore, that fixed-bed reactors now dominate the scene in large-scale chemical-product manufacture.
4.2 TYPES OF FIXED BED REACTOR Fixed-bed reactors fall into one of two major categories: Adiabatic or Non-adiabatic. A number of reactor configurations have evolved to fit the unique requirements of specific types of reactions and conditions. Some of the more common ones used for gas-phase reactions are summarized in Table(4.1) and the accompanying illustrations. The table can be used for initial selection of a given reaction system, particularly by comparing it with the known systems indicated.
20
Appendix-A
Table 4.1: Fixed-Bed Reactor Configurations for Gas-Phase Reactions Classification Single adiabatic bed
Radial flow
Adiabatic beds in series with intermediate cooling or heating
Use Moderately exothermic or endothermic nonequilibrium limited Where low AP is essential and useful where change in moles is large High conversion, equilibrium limited reactions
Multi-tabular non-adiabatic
Highly endothermic or exothermic reactions requiring close temperature control to ensure high selectivity
Direct-fired non-adiabatic
Highly endothermic, high temperature reactions
Typical Applications Mild hydrogenation
Styrene from ethylbenzene
SO2 oxidation Catalytic reforming Ammonia synthesis Hydrocracking Styrene from ethylbenzene Many hydrogenations Ethylene oxidation to ethylene oxide, formaldehyde by methanol oxidation, phthalic anhydride production Steam reforming
4.4 SELECTION OF REACTOR TYPE After analyzing different configuration of fixed bed reactors we have concluded that for our system the most suitable reactors is multi tube fixed bed reactor. Because oxidation of ethyl alcohol is highly exothermic reaction, so cooling will be required otherwise the temperature of reactor will rise and due to rise in temperature the catalyst activity and selectivity will be affected and in
21
Appendix-A
turn, the formation of by-products will increase which is direct loss of productions. As reaction temperature is already high 550 oC if we keep the process adiabatic temperature of reactor will rise and the structure of the catalyst will be changed and catalyst will be damaged. For such a situation the best reactor is multi-tube fixed bed reactor
4.5 CONSTRUCTION AND OPERATION OF MULTI-TUBE FIXED BED REACTOR Because of the necessity of removing or adding heat, it may not be possible to use a single large-diameter tube packed with catalyst. In this event the reactor may be built up of a number of tubes encased in a single body, as illustrated in Fig. The energy exchange with the surroundings is obtained by circulating, or perhaps boiling, a fluid in the space between the tubes. If the heat effect is large, each catalyst tube must be small (tubes as small as 1.0-in. diameter have been used) in order to prevent excessive temperatures within the reaction mixture. The problem of deciding how large the tube diameter should be, and thus how many tubes are necessary, to achieve a given production forms an important problem in the design of such reactors. A disadvantage of this method of cooling is that the rate of heat transfer to the fluid surrounding the tubes is about the same all along the tube length, but the major share of the reaction usually takes place near the entrance. For example, in an exothermic reaction the rate will be relatively large at the entrance to the reactor tube owing to the high concentrations of reactants existing there. It will become even higher as the reaction mixture moves a short distance into the tube, because the heat liberated by the high rate of reaction is
22
Appendix-A
greater than that which can be transferred to the cooling fluid. Hence the temperature of the reaction mixture will rise, causing an increase in the rate of reaction. This continues as the mixture moves up the tube, until the disappearance of reactants has a larger effect on the rate than the increase in temperature. Farther along the tube the rate will decrease. The smaller amount of heat can now be removed through the wall with the result that the temperature decreases. This situation leads to a maximum in the curve of Feed Stream
temperature versus reactor-tube length.
Cooling (or Heating) fluid out
Cooling (or Heating) fluid in
Product Stream
23
Appendix-A
Figure-4.1: Multi-tubular fixed bed reactor
4.6 EFFECT OF VARIABLES ON MULTI-TUBE FIXED BED REACTOR 4.6.1 Particle Diameter The overall heat transfer coefficient declines with decrease in particle size in the usual practical range. Redial gradients increase markedly with decrease in particle size. Small size, however, may improve rate or selectivity in some case by making catalyst inner surface more accessible.
4.6.2 Tube Diameter Reducing tube diameter reduces the radial profile. Heat transfer area per unit volume is inversely proportion al to the tube diameter and reaction temperature is affected by a change in this area.
24
Appendix-A
4.6.3 Outside Wall Coefficient Improvement up to the point where this resistance becomes negligible is worthwhile. Boiling liquids are advantageous because of the high heat transfer coefficient.
4.6.4 Heat of Reaction and Activation Energy Accurate values should be used since calculated temp. is sensitive to both of these, particularly to the value of energy of activation. This roust be determined carefully over the range of interests, but calculated results should be obtained based on different activation energies over the probable range of accuracy for the data so that final equipment sizing can be done with a feel for uncertainties.
4.6.5 Particle Thermal Conductivity One of the mechanisms of radial heat transfer in a bed, conduction through the solid packing which must quite logically depend on the thermal conductivity of the bed, can be reasoned to have some dependence on the thermal conductivity of the solid. But since it only affects one of the several mechanisms, the proportionally cannot be direct. Differences in effective conductivity and the wall heat transfer coefficient h between beds of packing having high and low solid conductivity may be in the range of a factor of 2-3. The largest difference will occur at lower Reynolds numbers. Most catalyst carriers have low conductivities, but some such as carbides have high conductivities.
25
Appendix-A
4.7 DESIGN PROCEDURE FOR MULTI TUBE FIXED BED REACTOR To calculate weight of catalyst required
W FAo
X A2
X A1
dX A rA
If space time is know then space time =
Volume of reactor Volumetric flow rate
By the knowledge of bulk density of catalyst and weight of catalyst Calculate volume of reactor Volume of reactor =
weight of catalyst bulk density of catalyst
Decide the dimensions of tube; keeping in mind that Dia of tube > 30 Dia of catalyst particle
Calculate volume of one tube and then number of tubes required
26
Appendix-A
No. of tubes =
Volume of Reactor Volume of one tube
Calculate the shell dia
2π D k k s 1 2 Pt Ds k1 nk 3 k 4 4 NT = 1.223Pt 2
Calculate pressure drop
ΔP 1 ε G α1 ε μ βG L ε Dpρf C1 Dp Calculate heat transfer co-efficient i)
Shell side
1501 0.011tb V0.8 ho = D0.2 ii)
Tube side
d pG 3.50 k μ
h pd iii)
0.7
4.6
e
dp d
Calculate overall heat transfer coefficient
Calculate area required for heat transfer. Calculate area available for heat transfer. Available area should be greater than required area
27
Appendix-A
SPECIFICATION SHEET Identification Item Item No. No. required Function:
Reactor R-1 1
Production of acetaldehyde by air oxidation of ethyl alcohol.
Operation: Continuous Type: Catalytic Multi tube, fixed bed Chemical Reaction: C2H5OH + ½ O2
Catalyst:
CH3CHO + H2O H298 = - 43 Kcal
Silver, coated on alumina Shape: Spherical Size: 1.25 mm
Tube side: Material handled Feed (kg/hr) C2H5OH 86326 H2O 45.44 CH3CHO ----O2 635.28 N2 2090.82 o Temp ( C) 550
Tubes: Product No. 709 (kg/hr) Length 2.438 m 432.58 O. D 63.5 mm 214.35 Pitch 79.37 mm pattern 412.8 Material of construction = copper 484.96 2090.82 550
28
Appendix-A
Shell side Fluid handled = cooling water Temperature 25oC to 45oC
Shell Dia = 2.66 m Material of construction = Carbon steel
Heat transfer area required = 77.67 m2 Overall heat transfer coefficient = 10.77 W/m2 oC
CHAPTER-5
DESIGN OF ABSORBER 5.1 ABSORPTIONS The removal of one or more component from the mixture of gases by using a suitable solvent is second major operation of Chemical Engineering that based on mass transfer. In gas absorption a soluble vapours are more or less absorbed in the solvent from its mixture with inert gas. The 'purpose of such gas scrubbing operations may be any of the following; a)
For Separation of component having the economic value.
b)
As a stage in the preparation of some compound.
c)
For removing of undesired component (pollution).
5.2 TYPES OF ABSORPTION 1)
Physical absorption,
2)
Chemical Absorption.
29
Appendix-A
5.2.1 Physical Absorption In physical absorption mass transfer take place purely by diffusion and physical absorption is governed by the physical equilibria.
5.2.2 Chemical Absorption In this type of absorption as soon as a particular component comes in contact with the absorbing liquid a chemical reaction take place. Then by reducing the concentration of component in the liquid phase, which enhances the rate of diffusion.
5.3 TYPES OF ABSOR5SRS There are two major types of absorbers which are used for absorption purposes: Packed column Plate column
5.4 COMPARISON BETWEEN PACKED AND PLATE COLUMN 1)
The packed column provides continuous contact between vapour and liquid phases while the plate column brings the two phases into contact on stage wise basis.
2)
SCALE: For column diameter of less than approximately 3 ft. It is more usual to employ packed towers because of high fabrication cost of small trays. But if the column is very large then the liquid distribution is problem and large volume of packing and its weight is problem.
3)
PRESSURE DROP: Pressure drop in packed column is less than the plate column. In plate column there is additional friction generated as the
30
Appendix-A
vapour passes through the liquid on each tray. If there are large No. of Plates in the tower, this pressure drop may be quite high and the use of packed column could effect considerable saving. 4)
LIQUID HOLD UP: Because of the liquid on each plate there may be a Urge quantity of the liquid in plate column, whereas in a packed tower the liquid flows as a thin film over the packing.
5)
SIZE AND COST: For diameters of less than 3 ft. packed tower require lower fabrication and material costs than plate tower with regard to height, a packed column is usually shorter than the equivalent plate column. From the above consideration packed column is selected as the absorber,
because in our case the diameter of the column is approximately 0.8 meter which is less than 3 ft. As the solubility is infinity so the liquid will absorb as much gases as it remain in contact with gases so packed tower provide more contact. It is easy to operate.
5.5 PACKING The packing is the most important component of the system. The packing provides sufficient area for intimate contact between phases. The efficiency of the packing with respect to both HTU and flow capacity determines to a significance extent the overall size of the tower. The economics of the installation is therefore tied up with packing choice. The packings are divided into those types which are dumped at random into the tower and these which must be stacked by hand. Dumped packing consists of unit 1/4 lo 2 inches in major dimension and are used roost in the smaller columns. The units in stacked packing are 2 to about 8 inches in size, they are used only in the larger towers.
31
Appendix-A
The Principal Requirement of a Tower packing are: 1)
It must be chemically inert to the fluids in the tower.
2)
It must be strong without excessive weight.
3)
It must contain adequate passages for both streams without excessive liquid hold up or pressure drop.
4)
It must provide good contact between liquid and gas.
5)
It must be reasonable in cost. Thus most packing are made of cheap, inert, fairly light materials such as
clay, porcelain, or graphite. Thin-walled metal rings of steel or aluminum are some limes used. Common Packings are: a)
Berl Saddle.
b)
Intalox Saddle.
c)
Rasching rings.
d)
Lessing rings.
e)
Cross-partition rings.
f)
Single spiral ring.
g)
Double - Spiral ring.
h)
Triple - Spiral ring.
5.6 DESIGNING STEPS FOR ABSORPTION COLUMN Determining the approximate dia of the column Selection of column. Selection of packing and material Calculating the size of packing Calculating the actual dia of column
32
Appendix-A
Calculating the flooding velocity a) Finding loading velocity with the knowledge the flooding velocity b) Calculating actual dia of column Finding the no. of transfer units (NoG) Determining the height of packing Determining the height of the column Determining the pressure drop. a 10b g 2F by equation P = ρG
[in. water /ft of packing]
SPECIFICATION SHEET Identification Item: Item No. No. required
Packed Absorption Column A1 01
Function: To absorb acetaldehyde and ethyl alcohol in water. Operation: Continuous Material Handled
Entering gas Kg/hr
Exit gas Kg/hr
CH3CHO C2H5OH
412.8 431.58
20.64 17.1
33
Liquid entering Kg/hr 20.43 17
Liquid leaving Kg/hr 412.6 414.48
Appendix-A
H2O O2 N2
85.35 484.96 2090.82
------484.96 2090.82
4064 -------------
4278.6 -----------
Design Data No. of transfer units = 7 Height of transfer units = 0.2 ft (0.06 m) Height of packing section = 6.44 ft (1.96 m) Total height of column = 15 ft (4.5 m) Inside diameter = 2.62 ft (0.8 m) Flooding velocity = 2.36 m/sec Maximum allowable gas velocity = 1.416 m/sec Pressure drop = 20 mmH2O/m of packing
Internals Size and type = 66 mm, Material of packing: Method of packing: Packing arrangement: Type of packing support: Type of liquid distributor:
intalox saddle Ceramic (wet) float into tower filled with water. dumped gas injection support Weir flow distributor
34
Appendix-A
DESIGN OF DISTILLATION COLUMN In industry it is common practice to separate a liquid mixture by distillating the components, which have lower boiling points when they are in pure condition from those having higher boiling points. This process is accomplished by partial vaporization and subsequent condensation.
6.1 CHOICE BETWEEN PLATE AND PACKED COLUMN Vapour liquid mass transfer operation may be carried either in plate column or packed column. These two types of operations are quite different. A selection scheme considering the factors under four headings. i)
Factors that depend on the system i.e. scale, foaming, fouling factors, corrosive systems, heat evolution, pressure drop, liquid holdup.
ii)
Factors that depend on the fluid flow moment.
iii)
Factors that depends upon the physical characteristics of the column and its internals i.e. maintenance, weight, side stream, size and cost.
iv)
Factors that depend upon mode of operation i.e. batch distillation, continuous distillation, turndown, intermittent distillation.
The relative merits of plate over packed column are as follows: i)
Plate column are designed to handle wide range of liquid flow rates without flooding.
35
Appendix-A
ii)
If a system contains solid contents, it will be handled in plate column, because solid will accumulate in the voids, coating the packing materials and making it ineffective.
iii)
Dispersion difficulties are handled in plate column when flow rate of liquid are low as compared to gases.
iv)
For large column heights, weight of the packed column is more than plate column.
v)
If periodic cleaning is required, man holes will be provided for cleaning. In packed columns packing must be removed before cleaning.
vi)
For non-foaming systems the plate column is preferred.
vii)
Design information for plate column are more readily available and more reliable than that for packed column.
viii) Inter stage cooling can be provide to remove heat of reaction or solution in plate column. ix)
When temperature change is involved, packing may be damaged.
For this particular process, “Acetaldehyde, ethyl alcohol and water system”, I have selected plate column because: i)
System is non-foaming.
ii)
Temperature is high (91o C).
6.2 CHOICE OF PLATE TYPE There are four main tray types, the bubble cap, sieve tray, ballast or valve trays and the counter flow trays. I have selected sieve tray because: i)
They are lighter in weight and less expensive. It is easier and cheaper to install.
ii)
Pressure drop is low as compared to bubble cap trays.
36
Appendix-A
iii)
Peak efficiency is generally high.
iv)
Maintenance cost is reduced due to the ease of cleaning.
6.3 DESIGNING STEPS OF DISTILLATION COLUMN Calculation of Minimum Reflux Ratio Rm. Calculation of optimum reflux ratio. Calculation of theoretical number of stages. Calculation of actual number of stages. Calculation of diameter of the column. Calculation of weeping point. Calculation of pressure drop. Calculation of thickness of the shell. Calculation of the height of the column.
SPECIFICATION SHEET Identification: Item
Distillation column
Item No.
DC1
No. required
1
Tray type
Sieve tray
Function : Recovery of Acetaldehyde Operation: Continuous
37
Appendix-A
Material handled Feed Quantity
Top
256.4595 Kgmol/hr 9.5412 Kgmol/hr
Bottom 246.9015 Kgmol/hr
Composition of 3.66%
98.2%
0
20o C
96 oC
acetaldehyde Temperature
91oC
Design Data No. of trays = 12
hole area/active area = 0.10
Pressure = 1 atm
weir length = 0.5867 m
Height of column = 4.3 m
weir length = 25.4 mm
Diameter of column = 0.762 m
reflux ratio = 3.5:1
Hole size = 3.175mm
tray spacing = 0.3048 m
Tray thickness = 3mm
Down comer area = 4.56912 . 10-2 m2
Flooding = 53 %
Hole area = 0.045576 m2
Active area = 0.34638 m2
CHAPTER-7
DESIGN OF HEAT EXCHANGERS 7.1 INTRODUCTION A heat exchanger is a heat-transfer devise that is used for transfer of internal thermal energy between two or more fluids available at different
38
Appendix-A
temperatures. In most heat exchangers, the fluids are separated by a heattransfer surface, and ideally they do not mix. Heat exchangers are used in the process, power, petroleum, transportation, air conditioning, refrigeration, cryogenic, heat recovery, alternate fuels, and other industries. Common examples of heat exchangers familiar to us in day-to-day use are automobile radiators, condensers, evaporators, air pre-heaters, and oil coolers. In our project a number of heat exchangers are used . Here we will discuss heat exchanger used as Condenser Vaporizer Preheater All of these are shell and tube heat exchangers.
Selection Guide To Heat Exchanger Types
Type
Fixed tube sheet
Floating head or tubesheet (removable and nonremovable bundles) U-tube; U-Bundle
Significant feature
Both tube sheets fixed to shell. One tubesheet “floats” in shell or with shell, tube bundle may or may not be removable from shell, but back cover can be removed to expose tube ends. Only one tube sheet required. Tubes bent in U-shape. Bundle is removable.
Applications best suited Condensers; liquidliquid; gas-gas; gasliquid; cooling and heating, horizontal or vertical, reboiling. High temperature differentials, above about 200 oF extremes; dirty fluids requiring cleaning of inside as well as outside of shell, horizontal or vertical. High temperature differentials, which might require provision for expansion in fixed
39
Limitations
Approximate relative cost in carbon steel construction
Temperature difference at extremes of about 200 o F Due to differential expansion.
1.0
Internal gaskets offer danger of leaking. Corrosiveness of fluids on shell-side floating parts. Usually confined to horizontal units.
1.28
Bends must be carefully made, or mechanical damage and danger of rupture can result. Tube
0.9-1.1
Appendix-A
tube units. Easily cleaned conditions on both tube and shell side.
side velocities can cause erosion of inside of bends. Fluid should be free of suspended particles.
Double pipe
Each tube has own shell forming annular space for shell side fluid. Usually use externally finned tube.
Relatively small transfer area service, or in banks for larger applications. Especially suited for high pressures in tube (greater than 400 psig).
Services suitable for finned tube. Piping-up a large number often requires cost and space.
0.8-1.4
Pipe coil
Pipe coil for submersion in coil-box of water or sprayed with water is simplest type of exchanger.
Condensing, or relatively low heat loads on sensible transfer.
Transfer coefficient is low, requires relatively large space if heat load is high.
0.5-0.7
Plate and frame
Composed of metalformed thin plates separated by gaskets. Compact, easy to clean.
Viscous fluids, corrosive fluids, slurries, high heat transfer.
Not well suited for boiling or condensing; limit 350-500 oF by gaskets. Used for liquidliquid only; not gas-gas.
0.8-1.5
Cross-flow, condensing, heating.
Process corrosion, suspended materials.
0.8-1.5
Compact, concentric plates; no bypassing, high turbulence.
Spiral
7.2 SHELL AND TUBE HEAT EXCHANGER In process industries, shell and tube exchangers are used in great numbers, far more than any other type of exchanger. More than 90% of heat exchangers used in industry are of the shell and tube type. The shell and tube heat exchangers are the “work horses” of industrial process heat transfer. They are the first choice because of well-established procedures for design and manufacture from a wide variety of materials, many years of satisfactory service, and availability of codes and standards for design and fabrication. They are produced in the widest variety of sizes and styles. There is virtually no limit on the operating temperature and pressure.
7.2.1 Classification of Shell and Tube Heat Exchangers There are four basic considerations in choosing a mechanical arrangement that provides for efficient heat transfer between the two fluids while taking care of such practical matters as preventing leakage from one into the other.
40
Appendix-A
1) Consideration for differential thermal expansion of tubes and shell. 2) Means of directing fluid through the tubes. 3) Means of controlling fluid flow through the shell. 4) Consideration for ease of maintenance and servicing. Heat exchangers have been developed with different approaches to these four fundamental design factors. Three principal types of heat exchangers 2) Fixed tube-sheet exchangers 3) U-tube exchangers and 4) Floating head exchangers—satisfy these design requirements.
Design procedure for shell-and-tube heat exchangers
41
Appendix-A
7.3 VAPORIZERS Vaporizers are heat exchangers which are specially designed to supply latent heat of vaporization to the fluid. In some cases it can also preheat the fluid then this section of vaporizers will be called upon preheating zone and the
42
Appendix-A
other section in which latent heat is supplied; is known as vaporization zone but he whole assembly will be called a vaporizer. Vaporizers are called upon to fulfill the multitude of latent-heat services which are not a part of evaporative or distillation process. There are two principal types of tubular vaporizing equipment used in industry: Boilers and Vaporizing Exchangers. Boilers are directly fired tubular apparatus, which primarily convert fuel energy into latent heat of vaporization. Vaporizing Exchangers are unfired and convert latent or sensible heat of one fluid into the latent heat of vaporization of another. If a vaporizing exchanger is used for the evaporation of water or an aqueous solution, it is now fairly conventional to call it an Evaporator, if used to supply the heat requirements at the bottom of a distilling column, whether the vapor formed be steam or not, it is a Re-boiler; when not used for the formation of steam and not a part of a distillation process, a vaporizing exchanger is simply called a vaporizer. So any unfired exchanger in which one fluid undergoes vaporization and which is not a part of an evaporation or distillation process is a vaporizer.
7.4 TYPES OF VAPORIZERS Some common types of vaporizers are Vertical vaporizer Indirect fluid heater Tubular low temperature vaporizer Electrical resistance vaporizer Cryogenic vaporizer The commonest type of vaporizer is the ordinary horizontal 1-2 exchanger or one of its modifications, and vaporization may occur in the shell or in the tubes. If steam is the heating medium, the corrosive action of air in the
43
Appendix-A
hot condensate usually makes it advantageous to carry out the vaporization in the shell. In the case of vaporizer, however, operation is often at high pressure, and it is usually too expensive to provide disengagement space in the shell, since the inclusion of disengagement space at high pressures correspondingly increases the shell thickness. For this reason vaporizers are not usually designed for internal disengagement. Instead some external means. Such as an inexpensive welded drum, is connected to the vaporizer where in the entrained liquid is separated from the vapor. When a 1-2 exchanger is used as a vaporizer, it is filled with tubes and cannot be adapted for blow down, since all the feed to a vaporizer is usually of value and a rejection as blow down is prohibitive. If the feed were completely vaporized in the vaporizer, it would emerge as a vapor and any dirt which a was originally present would be left behind on the tube surface over which total vaporization of occurred, fouling it rapidly, If the 1-2 exchanger (vaporization) were over-designed, that is, if it contained too much surface, disengagement would have to occur on the tubes and due to the excess surface the vapor would superheat above its saturation temperature. The feed to a vaporizer should not be vaporized completely. The value of this rule is apparent. If less that 100 percent to the feed is vaporized in 1-2 exchangers, the residual liquid can be counted on to prevent the accumulation of dirt directly on the surface of the heating element. A maximum of about 80 percent vaporization appears to provide favorable operation in 1-2 exchanges, although higher percentages may be obtained in vessels having interval disengagement space.
44
Appendix-A
Forced and Natural – circulation Vaporizer. When liquid is fed to is fed by forced circulation. The circuit consists of a 1-2 exchanger serving as the vaporizer and a disengaging drum from which the un-vaporized liquid is withdrawn and recombined with fresh feed. The generated vapor is removed form the top of the drum. The vaporized may also be connected with a disengaging drum without the use of a reticulating pump. This scheme is natural circulation. It requires that the disengaging drum be elevated above the vaporizer. The advantages of forced circulation or natural circulation are in part economics and a part dictated by space. The forced-circulation arrangement requires the use of a pump with its continuous operating cost and fixed charges. As with forced-circulation evaporators, the rate of feed recirculation can be controlled very closely. If the installation is small, then use of a pump preferable. If a natural-circulation arrangement is used pump and stuffing box problems are eliminated but considerably more headroom must be provided and recirculation rates cannot be controlled so readily. The vaporization of a cold liquid coming from storage, the liquid may not be at its boiling point and may require preheating to the boiling point. Since the shell of a forced-circulation vaporizer is essentially the same as any other 1-2 exchangers, the preheating can be done in the same shell as the vaporization. If the period of performance of a vaporizer is to be measured by a single overall dirt factor, it is necessary to divide the shell surface into two successive zones, one for preheating and one for vaporization. The true temperature difference is the weighted temperature difference for the two zones, and the clean coefficient is the weighted clean coefficient. Vaporizers tend to accumulate dirt, and for his reason higher circulation rates and large dirt factors will often be desirable. Preference should be given to
45
Appendix-A
the use of square pitch and a removable tube bundle. Although it may reduce the possibility of using a 1-2 vaporizing exchanger for other services, the baffle spacing can be increased or staggered form inlet to outlet to reduce the pressure drop of the fluid vaporizing in the shell.
SPECIFICATION SHEET FOR VAPORIZER Identification
Function
Unit
Vaporizer
Item No.
V-1
Type
Forced Circulation
No. of Item
1
To vaporize the alcohol
Operation Continuous Heat duty
905318.7 Btu/hr
Heat transfer area
260.7 ft2
Overall heat transfer coefficient
88 Btu/hr-ft2 oF
Dirt factor
0.003hr-ft2 oF/Btu
46
Appendix-A
Shell side Fluid circulated Ethyl alcohol Flow rates 2501.76 lb/hr Temperature Inlet = 150.8 oF Outlet = 233.6 oF Pressure 44.1 psi Pressure drop 1.3 psi Material of construction Carbon steel Specifications I.D = 17.25 in C = 0.25 in B = 4 in
Tube side Steam 966.7 lb/hr 266o F 39 psi 0.035 psi Carbon steel OD = ¾ in 16 BWG Pitch = 1 in Square arrangement, Length = 8 ft Nt = 166
7.5 CONDENSERS Introduction A condenser is a two-phase flow heat exchanger in which heat is generated from the conversion of vapor into liquid (condensation) and the heat generated is removed from the system by a coolant. Condensers may be classified into two main types: those in which the coolant and condensate stream are separated by a solid surface, usually a tube wall, and those in which the coolant and condensing vapor are brought into direct contact. The direct contact type of condenser may consist of a vapor which is bubbled into a pool of liquid, a liquid which is sprayed into a vapor, or a packed-column in which the liquid flows downwards as a film over a packing material against the upward flow of vapor. Condensers in which the streams are separated may be subdivided into three main types: air-cooled, shell-and-tube, and plate. In the air-cooled type, condensation occurs inside tubes with cooling provided by air blown or sucked across the tubes. Fins with large surface areas are usually provided on the air side to compensate for the low air-side heat transfer coefficients. In shell-and-tube condensers, the condensation may occur
47
Appendix-A
inside or outside the tubes. The orientation of the unit may be vertical or horizontal. In the refrigeration and air-conditioning industry, various types of two-phase flow heat exchangers are used. They are classified according to whether they are coils or shell-and-tube heat exchangers. Evaporator and condenser coils are used when the second fluid is air because of the low heat transfer coefficient on the air side. In the following sections, the basic types of condensers are shown:
Four Condenser Configuration are Possible 1)
Horizontal with condensation is shell side and cooling medium in the tubes.
2)
Horizontal with condensation in tube side cooling medium in shell side.
3)
Vertical with condensation in the shell.
4)
Vertical with condensation in the tubes.
Horizontal shell side and vertical tube side are the most commonly used types of condensers. In this process we have used the normal mechanism for heat transfer in commercial condenser which film wise condensation. Since vapor-liquid heat transfer changes usually occur at constant or really constant pressure in industry, the vaporization or condensation of a single compared normally occurs isothermally. If a mixture of vapors instead of a pure vapor is condensed at constant pressure, the change does not take place isothermally in most instances.
48
Appendix-A
Types of Condensers Steam Turbine Exhaust Condensers Plate Condensers Air-Cooled Condensers Direct Contact Condensers
SPECIFICATION SHEET CONDENSER Identification: Item condenser No. Required = 1 Function: Condense vapors by removing the latent heat of vaporization (95% ethanol) Operation: Continuous Type: 2-4 Horizontal Condenser Shell side condensation Heat Duty = 8951684.54 Btu/hr Tube Side:
Tubes: ¾ in. diam. 16 BWG
Fluid handled cold water
468 tubes each 10 ft long
Flow rate = 248657 lb/hr
4 passes
Pressure = 14.7 psia
15/16 triangular pitch
Temperature = 77 oF to 113 oF
pressure drop = 472 psi
Shell Side:
Shell: 25 in. diam. 2 passes
Fluid handled C2H5OH + H2O
Baffles spacing 20 in.
vapor (95% ethanol vapor)
Pressure drop = 3.12 psi
Flow rate 22267.8 lb/hr Pressure 14.7 psia Temperature 180oF to 178oF
49
Appendix-A
Utilities: Cold water Ud assumed = 100 Btu/hr-ft2-oF
Ud calculated 109 Btu/hr-ft2-oF
Uc calculated = 163 Btu/hr-ft2-oF
Allowed dirt factor = Rd = 0.003
CHAPTER-8
PUMP AND COMPRESSOR SELECTION 8.1 FACTORS AFFECTING CHOICE OF A PUMP Many different factors can influence the final choice of a pump for a particular operation. The following list indicates the major factors that govern pump selection. . 1) The amount of fluid that must be pumped. This factor determines the size of pump (or pumps) necessary. 2) The properties of the fluid. The density and the viscosity; of the fluid influence the power requirement for a given set of operating conditions, corrosive properties of the fluid determine the acceptable materials of construction. If solid particles are suspended in the fluid, this factor dictates the amount of clearance necessary and may eliminate the possibility of using certain types of pumps. 3) The increase in pressure of the fluid due to the work input of the pumps. The head change across the pump is influenced by the inlet and downstream reservoir pressures, the change in vertical height of the
50
Appendix-A
delivery line, and frictional effects. This factor is a major item in determining the power requirements. 4) Type of flow distribution. If nonpulsating flow is required, certain types of pumps, such as simplex reciprocating pumps, may be unsatisfactory. Similarly, if operation is intermittent, a self-priming pump may be desirable, and corrosion difficulties may be increased. 5) Type of power supply. Rotary positive-displacement pumps and centrifugal pumps are readily adaptable for use with electric-motor or internal-combustion-engine drives; reciprocating pumps can be used with steam or gas drives. 6) Cost and mechanical efficiency of the pump.
PUMP P-1 The duty of P-I is to pump ethyl alcohol from 1 atm to 2.3 atm with a flow rare of 1135.8 Kg/hr. for this purpose the best choice is centrifugal pump because the required pressure is not so high.
PUMP P-2 The duty of pump-2 is to pump a mixture of water, ethyl alcohol and acetaldehyde with slight pressure development and the flow late required is 5122.78 Kg/hr. Centrifugal pump is most suitable pump for such a service i.e. high flow rate and low pressure development.
51
Appendix-A
8.2 COMPRESSOR SELECTION Compressor C-1 The duty of compressor is to compress the air from 1 atm to 2.3 atm and to made the air flow with flow rate 2726 Kg/hr/ As compression ratio is less than 5 so, single stage compressor will be sufficient and type of compressor suitable for this situation is “centrifugal compressor”, because our objective is to develop just 2.3 atm pressure with relatively high flow rate.
CHAPTER-9
52
Appendix-A
INSTRUMENTATION AND PROCESS CONTROL Measurement is a fundamental requisite to process control. Either the control can be affected automatically, semi-automatically or manually. The quality of control
obtainable
also
bears
a
relationship
to
the
accuracy,
re-productability and reliability of the measurement methods, which are employed. Therefore, selection of the most effective means of measurements is an important first step in the design and formulation of any process control system.
9.1 TEMPERATURE MEASUREMENT AND CONTROL Temperature measurement is used to control the temperature of outlet and inlet streams in heat exchangers, reactors, etc. Most temperature measurements in the industry are made by means of thermo-couples to facilitate bringing the measurements to centralized location. For local measurements at the equipment bi-metallic or filled system thermometers are used to a lesser extent. Usually, for high measurement accuracy, resistance thermometers are used. All these meters are installed with thermo-wells when used locally. This provides protection against atmosphere and other physical elements.
9.2 PRESSURE MEASUREMENT AND CONTROL
53
Appendix-A
Like temperature pressure is a valuable indication of material state and composition. In fact, these two measurement considered together are the primary evaluating devices of industrial materials. Pumps, compressor and other process equipment associated with pressure changes in the process material are furnished with pressure measuring devices. Thus pressure measurement becomes an indication of energy increase or decrease. Most pressure measurement in industry are elastic element devices, either directly connected for local use or transmission type to centralized location. Most extensively used industrial pressure element is the Bourderi Tube or a Diaphragm or Bellows gauges.
9.3 FLOW MEASUREMENT AND CONTROL Flow-indicator-controllers are used to control the amount of liquid. Also all manually set streams require some flow indication or some easy means for occasional sample measurement. For accounting purposes, feed and product stream are metered. In addition utilities to individual and grouped equipment are also metered. Most flow measures in the industry are/ by Variable Head devices. To a lesser extent Variable Area is used, as are the many available types as special metering situations arise.
9.4
.
CONTROL SCHEMES OF DISTILLATION COLUMN GENERAL CONSIDERATION
9.4.1 Objectives
54
Appendix-A
In distillation column control any of following may be the goals to achieve 1. Over head composition. 2. Bottom composition 3. Constant over head product rate.
.
4. Constant bottom product rate.
9.4.2 Manipulated Variables Any one or any combination of following may be the manipulated variables 1. Steam flow rate to reboiler. 2. Reflux rate. 3. Overhead product withdrawn rate. 4. Bottom product withdrawn rate 5. Water flow rate to condenser.
9.5 LOADS OR DISTURBANCES Following are typical disturbances 1.
Flow rate of feed
2.
Composition of feed.
3.
Temperature of feed.
4.
Pressure drop of steam across reboiler
5.
Inlet temperature of water for condenser.
55
Appendix-A
9.6 CONTROL SCHEME Overhead product rate is fixed and any change in feed rate must be absorbed by changing bottom product rate. The change in product rate is accomplished by direct level control of the reboiler if the stream rate is fixed feed rate increases then vapor rate is approximately constant & the internal reflux flows must increase.
ADVANTAGE Since an increase in feed rate increase reflux rate with vapor rate being approximately constant, then purity of top product increases.
DISADVANTAGE The overhead reflux change depends on the dynamics of level control system that adjusts it.
56
Appendix-A
Figure: Control scheme
CHAPTER-10
HAZOP STUDY 57
Appendix-A
INTRODUCTION A HAZOP survey is one of the most common and widely accepted methods of systematic qualitative hazard analysis. It is used for both new or existing facilities and can be applied to a whole plant, a production unit, or a piece of equipment It uses as its database the usual sort of plant and process information and relies on the judgment of engineering and safety experts in the areas with which they are most familiar. The end result is, therefore
reliable in terms
of engineering and operational expectations, but it is not quantitative and may not consider the consequences of complex sequences of human errors. The objectives of a HAZOP study can be summarized as follows: 1)
To identify (areas of the design that may possess a significant hazard potential.
2)
To identify and study features of the design that influence the probability of a hazardous incident occurring.
3)
To familiarize the study team with the design information available.
4)
To ensure that a systematic study is made of the areas of significant hazard potential.
5)
To identify pertinent design information not currently available to the team.
6)
To provide a mechanism for feedback to the client of the study team's detailed comments.
A HAZOP study is conducted in the following steps:
58
Appendix-A
1)
Specify the purpose, objective, and scope of the study. The purpose may he the analysis of a yet to be built plant or a review of the risk of un existing unit. Given the purpose and the circumstances of the study, the objectives listed above can he made more specific. The scope of the study is the boundaries of the physical unit, and also the range of events and variables considered. For example, at one time HAZOP's were mainly focused on fire and explosion endpoints, while now the scope
usually
includes
toxic
release,
offensive
odor,
and
environmental end-points. The initial establishment of purpose, objectives, and scope is very important and should be precisely set down so that it will be clear, now and in the future, what was and was not included in the study. These decisions need to be made by an appropriate level of responsible management. 2)
Select the HAZOP study team. The team leader should be skilled in HAZOP and in interpersonal techniques to facilitate successful group interaction. As many other experts should be included in the team to cover all aspects of design, operation, process chemistry, and safety. The team leader should instruct the team in the HAZOP procedure and should emphasize that the end objective of a HAZOP survey is hazard identification; solutions to problems are a separate effort.
3)
Collect data. Theodore16 has listed the following materials that are usually needed: Process description Process flow sheets Data on the chemical, physical and toxicological properties of all raw materials,, intermediates, and products. Piping and instrument diagrams (P&IDs)
59
Appendix-A
Equipment, piping, and instrument specifications Process control logic diagrams Layout drawings Operating procedures Maintenance procedures Emergency response procedures Safety and training manuals
60
Appendix-A
Table-10.2: HAZOP Guide Words and Meanings Guide Words
Meaning
No
Negation of design intent
Less
Quantitative decrease
More
Quantitative increase
61
Appendix-A
4)
Part of
Qualitative decrease
As well as
Qualitative Increase
Reverse
Logical opposite of the intent
Other than
Complete substitution
Conduct the study. Using the information collected, the unit is divided into study "nodes" and the sequence diagrammed in Figure , is followed for each node. Nodes are points in the process where process parameters (pressure, temperature, composition, etc.) have known and intended values. These values change between nodes as a result of the operation of various pieces of equipment' such as distillation columns, heat exchanges, or pumps. Various forms and work sheets have been developed to help organize the node process parameters and control logic information. When the nodes are identified and the parameters are identified, each
node is studied by applying the specialized guide words to each parameter. These guide words and their meanings are key elements of the HAZOP procedure. They are listed in Table(10.1). Repeated cycling through this process, which considers how and why each parameter might vary from the intended and the consequence, is the substance of the HAZOP study. 5)
Write the report. As much detail about events and their consequence as is uncovered by the study should be recorded. Obviously, if the HAZOP identifies a not improbable sequence of events that would result in a disaster, appropriate follow-up action is needed. Thus,
62
Appendix-A
although risk reduction action is not a part of the HAZOP, the HAZOP may trigger the need for such action. The HAZOP studies are time consuming and expensive. Just getting the P & ID's up to date on an older plant may be a major engineering effort. Still, for processes with significant risk, they are cost effective when balanced against the potential loss of life, property, business, and even the future of the enterprise that may result from a major release.
HAZOP Study of Storage Tank for Ethyl Alcohol A HAZOP study is to be conducted on ethyl alcohol storage tank, as presented by the piping and instrumentation diagram show in fig(10.2). In this scheme, ethyl alcohol is unloaded from tank trucks into a storage tank maintained under a slight positive pressure until it is transferred to the process. Application of the guide words to the storage tank is shown in Table(10.2) along with a listing of consequences that results from process deviation. Some of the consequences identified with these process deviations have raised additional questions that need resolution to determine whether or not a hazard exist.
63
Appendix-A
Ethyl Alcohol Storage Tank
Figure-10.2: Piping and instrumentation diagram
Deviations from operating conditions
What event could cause this deviation
64
Consequences of this deviation on item of Process equipment under indications consideration
Appendix-A
Level: Less
Tank runs dry
Pump cavitates
LIA-1 FICA-1
More
Rupture of discharge line Reagent released
LIA-1,
V-3 open or broken
FICA-1
V-1 open or broken
Reagent released
LIA-1
Tank rupture (busting of
Reagent released
LIA-1
vessel)
Reagent released
LIA-1
Unload too much from
Tank overfills
LIA-1
Tank overfills
LIA-1
column Reverse flow from process Temperature: Less
Temperature of inlet is
Possible vacuum
colder than normal More
Temperature of inlet is
Region released
hotter than normal External fire
Tank fails
CHAPTER-11
65
Appendix-A
ENVIRONMENTAL ASSESSMENT
IMPACT
HEALTH HAZARD INFORMATION Acute Effects: The primary acute (short-term) effect of inhalation exposure to acetaldehyde is irritation of the eyes, skin, and respiratory tract in humans. Erythema, coughing, pulmonary edema, and necrosis may also occur and, at extremely high concentrations, respiratory paralysis and death. Acute inhalation of acetaldehyde resulted in a depressed respiratory rate and elevated blood pressure in experimental animals. Tests involving acute exposure of animals, such as the LC50 and LD50 tests in rats, rabbits, and hamsters, have demonstrated acetaldehyde to have low acute toxicity from inhalation and moderate acute toxicity from oral or dermal exposure.
Chronic Effects (Noncancer) In hamsters, chronic (long-term) inhalation exposure to acetaldehyde has produced changes in the nasal mucosa and trachea, growth retardation, slight anemia, and increased kidney weight.
66
Appendix-A
Symptoms of chronic intoxication of acetaldehyde in humans resemble those of alcoholism. The RfC for acetaldehyde is 0.009 mg/m3 based on degeneration of olfactory epithelium in rats. EPA has medium confidence in the principal studies because appropriate histopathology was performed on an adequate number of animals and a noobserved-adverse-effect level (NOAEL) and a lowest-observed-adverse-effect level (LOAEL) were identified, but the duration was short and only one species was tested; low confidence in the database due to the lack of chronic data establishing NOAELs and due to the lack of reproductive and developmental toxicity data; and, consequently, low confidence in the RfC. EPA has not established an RfD for acetaldehyde
Reproductive/Developmental Effects No information is available on the reproductive or developmental effects of acetaldehyde in humans. Acetaldehyde has been shown, in animals, to cross the placenta to the fetus. Data from animal studies suggest that acetaldehyde may be a potential developmental toxin. In one study, a high incidence of embryonic resorptions was observed in mice injected with acetaldehyde. In rats exposed to acetaldehyde by injection, skeletal malformations, reduced birth weight, and increased postnatal mortality have been reported.
Cancer Risk
67
Appendix-A
Human data regarding the carcinogenic effects of acetaldehyde are inadequate. Only one epidemiology study is available that several limitations including short duration, small number of subjects, and concurrent exposure to other chemicals and cigarettes. An increased incidence of nasal tumors in rats and laryngeal tumors in hamsters has been observed following inhalation exposure to acetaldehyde. EPA has classified acetaldehyde as a Group B2, probable human carcinogen. EPA uses mathematical models, based on human and animal studies, to estimate the probability of a person developing cancer from breathing air containing a specified concentration of a chemical. EPA calculated an inhalation unit risk estimate of 2.2 H 10-6 (m g/m3)-1. EPA estimates that, if an individual were to breathe air containing acetaldehyde at 0.5 m g/m3* over his or her entire lifetime, that person would theoretically have no more than a one-in-amillion increased chance of developing cancer as a direct result of breathing air containing this chemical. Similarly, EPA estimates that breathing air containing 5.0 m g/m3 would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and air containing 50.0 m g/m3 would result in not greater than a one-in-ten thousand increased chance of developing cancer. EPA's Office of Air Quality Planning and Standards, for a hazard ranking under Section 112(g) of the Clean Air Act Amendments, has ranked acetaldehyde in the nonthreshold category. The 1/ED10 value is 0.033 per (mg/kg)/d and this would place it in the low category under Superfund's ranking for carcinogenic hazard.
68
Appendix-A
ATMOSPHERIC PERSISTENCE Acetaldehyde exists in the atmosphere in the gas phase. It also can be formed in the atmosphere as a result of photochemical oxidation of organic pollutants in urban atmospheres. The dominant atmospheric loss process for acetaldehyde is by reaction with the hydroxyl radical. Based on this reaction, the atmospheric half-life and lifetime is estimated to be 15 hours and 22 hours, respectively. The products of this reaction include formaldehyde and peroxyacetyl nitrate (PAN).
CHAPTER-12
COST ESTIMATION An acceptable plant design must present a process that is capable of operating under conditions which will yield a profit.0^ Since, Net profit total income-all expenses It is essential that chemical engineer be aware of the many different types of cost involved in manufacturing processes. Capital must be allocated for direct
69
Appendix-A
plant expenses; such as those for raw materials, labor, and equipment. Besides direct expenses, many other indirect expenses are incurred, and these must be included if a complete analysis of the total cost is to be obtained. Some examples of these indirect expenses are administrative salaries, product distribution costs and cost for interplant communication.
12.1 ESTIMATION OF EQUIPMENT COST Equipment
Cost (Rs.)
Vaporizer V-I
290436
Exchanger E-I
154427
Exchanger E-2
183702
Heater E-3
175501
Heater E-4
279200
Cooler E-5
193459
Pre-heater E-6
61770
Condenser E-7
70890
Condenser E-8
1283730
Re-boiler E-9
938765
Re-boiler E-10
1415840
70
Appendix-A
Distillation Column D-1
7748874
Distillation Column D-2
11069820
Absorber A-1
7431117
Absorber A-2
9085370
12.2 ESTIMATION OF TOTAL CAPITAL INVESTMENT Direct Cost (Rs) Purchased equipment cost
=
Rs. 40382901
Purchased equipment installation = 0.47 40382901 = Rs. 18979963 Instrumentation & Process Control = 0.12 40382901 = Rs. 2277595 Piping (installed) = 0.66 40382901 = Rs. 26652714 Building (Including Services) = 0.18 40382901 = Rs. 7268922 Yard improvements = 0.1 40382901 = Rs. 4038290 Service facilities (installed) = 0.7 40382901 = Rs. 5088245 Land = 0.06 40382901 = Rs. 305294 Total direct plant cost = Rs. 104993924
Indirect Cost Engg & Supervision = 0.33 40382901 = Rs. 13326357 Construction expenses = 0.41 40382901 = Rs. 16556989
71
Appendix-A
Total Indirect Cost = Rs. 29883346 Total Direct & Indirect Cost
= Rs. 134877270
Contractor’s fee = 0.05 134877270 = Rs. 6743863 Contingency = 0.1 134877270 = Rs. 13487727 Fixed Capital Investment = Total direct + indirect cost + contigency + Contractor’s fee = Rs. 155108860 Total Capital Investment = F.C.I + W.C. Now W.C = 0.15 (T.C.I) = 0.15 (155108860 + W.C) W.C = Rs. 27372151 T.C.I = 155108860 + 27372151 = Rs. 182481011
72
Appendix-A
APPENDIX-A A-1) DESIGN CALCULATIONS OF MULTI-TUBULAR FIXED BED REACTOR PRODUCT CH3CHO = 412.8 Kg/hr C2H5OH = 431.58 Kg/hr H2O = 214.35 Kg/hr O2 = 484.96 Kg/hr N2 = 2090.8 Kg/hr
Cooling Water Out
Cooling Water in
73
Appendix-A
Volume of Reactor Volumetric flow rate of feed to reactor = Vo = 63.84 m3/min Space velocity = S = 15 min-1 as we know that S = Vo/V V
where,
V = Volume of reactor.
= Vo/ S = 63.84/15 = 4.256 m3
Weight of Catalyst (Silver Catalyst on Alumina Support of size 1.25 mm is used) volume of reactor = 4.256 m3 porosity = 0.4 so volume of catalyst = 0.6 4.256 = 2.5536 m3 particle Density of catalyst = 2250 Kg/m3 mass of catalyst = 2250 2.553 b = 5746 Kg
Number of Tubes Length of tube = 8 ft = 2.439 m To calculate tube dia As we know that to prevent deviation from plug flow assumption
74
Appendix-A
Dt/Dp > 30 Where
Dt = dia of tube
Dp = dia of particle Let inside dia of tube = 2.204 in = 55.98 mm Dt/Dp = 55.98/1.25 = 44.78 Volume of one tube
which is satisfactory
= /4 Dt2 Lt = 3.14/4 (55.98/1000)2 2.439 = 0.785 0.00313 2.439 = 0.006 m3
As total volume = 4.256 m3 So number of tubes required = 709 tubes
Diameter of Shell To calculate shell dia eq. (from Ludwig)
2 π D K K s 1 2 - Pt D s - K1 nK 3 K 4 4 NT 1.223Pt 2 where
NT = number of tubes = 709
Ds = shell dia = ? PT = pitch
= 1.25 0.1 of tube = 1.25 2.5 = 3.125 in. (76.2 mm)
for this pitch K1 = 1.08
K2 = - 0.9
K3 = 0.69
K4 = - 0.8
n = 1 ( 1 tube pass) By solving above eq. Ds
= 104.72 in.
75
Appendix-A
= 8.72 ft
=
2.66 meter
=
2.439 m
Shell Height Length of tube
Leaving 20 % spacing above and below So height of shell = 2 (0.2 2.439) + 2.439 = 3.415 m
Pressure Drop ΔP 1 G α1 μ βG L 3 D P f G D P
= porosity = 0.4 DP = particle dia = 1.25 mm = 0.125 cm Lf = feed density = 0.000948 g/cm3 G = mass velocity = 0.0579 g/cm2 Sec = viscosity of feed = 0.000343 g/cm. Sec C1 = 981.46 cm/sec2 For smoth particles α = 180
β = 1.8
L = length = 2.439 m = 243.9 cm Putting values in above eq. gives ΔP = 210.83 gm/cm2 And 1033.074 g/cm2 = 1 atm So ΔP = 0.204 atm
76
Appendix-A
Calculations of Heat Transfer Co-efficients Shell Side For water a simplified equation for heat transfer co-efficient
ho tb
1501 0.011t b V0.8
D0.2
= average water temperature; oF =
25 45 = 35o C = 95o F 2
D = Diameter, in Equivalent diameter = Flow area =
4 flow area heated perimeter
π 2 2 Ds N t Dot 4
Ds = 104.72 in Nt = 709 Dot = 2.5 in Flow area = 5130 in2 Heated perimeter = Nt Dot = 709 2.5 3.14 = 5565 in. De =
4 5130 = 3.68 in 5565
Now to calculate V = velocity of water in fps Mass velocity = G = W/as W = flow rate of water
= 2009.9 Kg/hr = 44237 lb/hrs
flow area = as = 5130 in2 = 35.625 ft2 G = 44257/35.625 = 1242 lb/hr. ft2
77
Appendix-A
Also G = V = density of water = 62.5 lb/ft
so velocity V = G/
3
= 1242/62.5 = 19.87 ft/hr = 0.00552 fps
so
ho
1501 0.011 850.00552 0.8
3.680.2
= 3.691 Btu/ hr. ft2 oF
Tube Side An equation proposed by LEVA to find heat transfer co-efficient inside the tubes filled with catalyst particles.
dpG 3.5 k μ
h pd
0.7
e 4.6
dp d
G = 420 lb/hr. ft2 = 0.0829 lb/hr. ft k = 0.0315 Btu/hr. ft oF Dp = dia of particle = 0.0041 ft D = dia of tube = 0.1836 ft Putting values in above eq.
h p 0.1836 0.0315
0.0041 420 3.5 0.0829
0.7
5.828 hp = 3.5 (8.36) (0.9023) hp = 4.53 Btu/hr. ft2 oF hio = 4.53 4.53
ID OD
=
4.53 2.204 = Btu/hr. ft2 2.5
Dirt Factor Assume dirt factor = 0.003
78
Appendix-A
Over all H.T. Coefficient
1 1 1 RD U D h io h o 1 1 1 0.003 U D 4 3.691 = 0.5273 UD = 1.896 Btu hr. ft2 Area required for Heat Transfer Q = 1519488 Btu/hr LMTD = 515o C = 959o F UD = 1.896 Btu/hr. ft2 A=
θ 1519488 = 835 ft2 = 77.67 m2 U DLMTD 1.896 959
Area Available for Heat Transfer Length of tube = Lt = 2.439 m Outer Dia of tube = Dot = 0.0635 m Surface area of one tube = πDotLt = 3.14 0.0635 2.439 = 0.486 m2 Total surface area available
= 709 0.486 = 344.9 in2
so sufficient area is available for heat transfer.
A-2) DESIGN CALCULATIONS OF ABSORBER-A1 CH3CHO = 20.64 Kg/hr C2H5OH = 17.1 Kg/hr O2 = 484.96 Kg/hr N2 = 2090.82 Kg/hr
79
H2O = 4064 Kg/hr CH3CHO = 20.43 Kg/hr C2H5OH = 17 Kg/hr
Appendix-A
80
Appendix-A
We want to scrub 412.59Kg acetaldehyde and 431.48kg/hr ethyl alcohol. This duty is done by two absorbers .In fist absorber 95% of acetaldehyde is absorbed and about 99.96% of alcohol is absorbed. The solvent used for this purpose is water.
Compositions of Components in Gas Mixture at Enterance Components
Kg
Kg mol
Mol %
CH3CHO
412.8
9.38
8.27
C2H5OH
431.58
9.38
8.27
H2O
85.35
4.78
4.18
O2
484.96
15.15
13.37
N2
2090.82
74.67
65.89
Total
G = 3505
Gm = 113.32
Composition of Components in Liquid Components
Kg
Kg mol
Mol %
H2O
4064
225.7
0.996
CH3CHO
20.43
0.464
0.002
C2H5OH
17
0.37
0.0016
L = 4101.43
Lm = 226.534
Total
Temperature of entering gas = 30 oC Pressure = 1.1 atm Average molecular weight of Gas
= 3505/113.32 = 30.93 Kg/Kg-mol
G
=
PM/RT
(where, R = 0.08205)
81
Appendix-A
G
=
1.1 30.93 = 1.36 g/L = 1.36 Kg/m3 0.08205 303
water = L = 997 Kg/m3
(at 25 oC)
Approximation of column dia Approximate column dia from figure Dia
1 meter = 3.28 ft
When the dia of column less than 3ft or near about 3ft use packed columns. Because it is always economical to use packed column when the dia is about 1 m or less 1 m.
Selection of Packing We have selected ceramic Intalox saddle. Intalox saddle and pall rings are most popular choices. We have selected ceramic intalox saddle because they are most efficient. We have selected the ceramic material of packing because in our system oxygen and water are present and they can cause corrosion and ceramic material will prevent corrosion.
Size of the Packing Now we will find the maximum size of intalox saddle which would be used for this particular dia of the column. Packing size =
1 D 1 1 15 15
=
0.0666 m = 66 mm
Although the efficiency of higher for small packings, it is generally accept that it is economical to use these small sizes in an attempt to improve the performance of a column. It is preferable to use the largest recommended size of a particular type of packing and to increase the packed height to compensate for small loss of efficiency.
82
Appendix-A
Flooding Velocity
L ρG G ρliquid where, L = 4101.43 Kg/hr G = 3505 Kg/hr L = 997 Kg/m3 G = 1.36 Kg/m3
.
Let superficial velocity should be 60% of flooding velocity. Superficial velocity = 0.6 2.36 = 1.416 m/sec Note: This velocity is near the loading velocity. Mass velocity of gas = density velocity = 6932.73 Kg/hr-m2 As flow rate of gas
= 3505 Kg/hr
Mass velocity flow rate of gas/cross sectional area A=
π 2 D 4
=
3505/6932.74 = 0.5055-m2
D2 = 0.64 D = 0.80 m This the actual diameter of column.
Number of Transfer Units (NOG) y1 = mole fraction of acetaldehyde in entering gas = 0.0828 y2 = mole fraction of acetaldehyde in exit gas = 0.0052 As gas is dilute mixture of acetaldehyde. So by Fig-25 of Appendix-B. y1/y2 = 15.945
83
Appendix-A
m
Gm =? Lm
where m = slop of equilibrium curve and it is straight line because system is dilute one. Let
m
m = 1.6
Gm 1.6 113.3 = = 0.8 226.24 Lm
where Lm = optimum liquid flow rate. It has been optimized before the liquid enters the 2nd column. Optimum value for term m
Gm will lie between 0.7 to 0.8 Lm
So by using Fig.25 NOG =
7
Height of Packing(Z) For ceramic intalox saddle:
Gm 0.316 HOG = 1.14 Lm 0.315 Where Gm = gas flow rate, lb moles/hr. ft2 Lm = liquid flow rate, lbmol/hr.ft2 We have, Gm = 113.3 Kgmol/hr Since cross-section area = A = 0.502 m2 Gm = 113.3/0.502 Kg mol/m2hr = 225.69 Kgmol/m2hr Similarly, Lm = 226.24/0.502 Kgmol/m2hr = 450.67 Kgmol/hr. m2 Gm
= 225.69 Kgmol/hr.m2
84
Appendix-A
= 46.15 lbmol/hrft2 Similarly, Lm = 92.15 lbmol/hr.ft2
46.150.316 HOG = 1.14 92.150.315 HOG = 0.92 ft Where HOG = height of a transfer unit Z = HOG NOG Z = 0.92 7 = 6.44 ft Z = 1.96 m Where Z is the height of packing. Allow 2.0 ft for good liquid distribution through the packing from top. Allowance for supports =
(2 ft) (2 sections) = 4 ft
Total packing height required = Z = 6.44 + 2 + 4 = 12.44 ft use 15 ft of packing.
Degree of wetting LP =
Liquid rate Specific are of packing
Liquid rate = 2.27 m3/m2sec And Specific area of packing = 118 m2/m3 LP = 2.27 10-3/118 = 1.92 10-5 m3/m.sec
85
Appendix-A
Pressure Drop p = a.10b g2F/ G A, b = constants obtained from table 5-1. p = pressure drop
= liquid flow rate lb/ft2sec gF = gas flow rate lb/ft2.sec G = gas density lb/ft3 Note: Above equation is applicable for condition near the flooding. The pressure drop is higher than the value predicted by equation given above and account should be taken of this fart where appropriate. From table for 2-in (50mm) ceramic intalox saddles. A = 0.12 B = 0.1 L = 0.464 lb/sec ft2 Similarly, gF = 0.39 lb/sec.ft2
G = 0.084 lb/ft3 P = 0.12 100.10.464 (0.39)2 / 0.084 P = 0.24 in. of water/ft of packing. To convert above P to S.I units by multiplying the value of P by the factor 83.3 to obtain the units of (mm/m) P = 0.24 83.3 = 19.99 20 = 20 mm H2O/m. of packing.
86
Appendix-A
A-3) DESIGN CALCULATIONS OF DISTILLATION COLUMN (DC-1)
TOP PRODUCT CH3CHOH = 98.2 % C2H5OH = 0.75 % H2O = 0.97 %
FEED CH3CHOH = 3.66 % C2H5OH = 3.66 % H2O = 92.69 %
87
Appendix-A
Process Design Temperature of feed = 91o C Temperature of top product = 20o C Temperature of bottom product = 99o C P = 1 atm
Minimum Reflux Ratio
CH3CHO
Feed F Xf 0.0366
Top D Xd 0.982
0
Relative Volatility 10.87
C2H5OH
0.0366
0.0075
0.0377
2.27
H2O
0.9269
0.0097
0.962
1.00
Component
Light key component = CH3CH2OH = B Heavy key component = H2O = C
88
Bottom W Xw
Appendix-A
Lighter than light key component = CH3CHO = A Using underwood equation
α A xfA α B xfB α C xfC 1 q αA θ αB θ αC θ As feed is at its bubble point so q = 1 Bt trial
= 3.5
Using eq. of min. reflux ratio,
α A xfA α B xfB α C xfC R m 1 αA θ αB θ αC θ putting all values Rm = 2.62 No. of plates at total reflux Using Fenske’s equation
X X log X d X s Nm 1 log α BC ave
Nm
log
B
C
C
B
0.0075 0.962 0.0097 0.0377
log2.27
Relative Volatility Method for Plate to Plate Calculations Above feed plate: Ln = RD = 3.5 9.5412 = 33.3942 Kg mol/hr Vn = (R+1) D = 4.5 9.5412 = 429354 Kgmol/hr
Below feed plate: Lm = Ln + F = 33.3942 + 256.4595 = 289.8537 Kgmol/hr Vm = Lm – W = 289.8537 – 246.9015 = 42.9522 Kgmol/hr
Operating lines above feed point:
89
Appendix-A
ym
Ln D X n 1 xd Vn Vn
yn CH3CHO = 0.7778 Xn+1 + 0.2806 yn C2H5OH = 0.7778 Xn+1 + 0.0021 yn H2O = 0.7778 Xn+1 + 0.0028 Operating lines below feed plate:
ym
Lm W X m 1 Xw Vm Vm
ym CH3CHO = 6.748 Xm+1 ym C2H5OH = 6.748 Xm+1 – 0.2167 ym H2O = 6.748 Xm+1 – 5.5269
Starting from top plate:
Componen t
Xd = yt
Yt/
CH3CHO
10.8
0.782
0.90
C2H5OH
7
0.007
H2O
2.27 1.00
Xt = yt Xt yt
X1 = y1 α X1 y1 α
Y1
Y1/
0.8739
0.96
0.20
0.0794
3
0.032
0
0.02
0.0680
5
0.01
0.0939
0.02
7
0.4282
0.009
7
7
0.17
7
0.00
0.07
0
9
5
Y2
X2
Below feed plate
X3
Y8
0.342
------
0.0363
0
0
0.055
------
0.0361
------
0.0370
0.336
------
0.9258
------
0.963
90
Appendix-A
No. of plates = 8 Rebioler acts as one plate, so actual No. of trays = 7 Feed plate = 2 from bottom
Tray Efficiency: Average temperature of column =
20 96 = 58oC 2
Feed viscosity at average temperature = ave = 0.224 Cp (relative volalitoly of key component) ave = 2.27 0.224 = 0.509 from graph (17) of Appendix-B, overall efficiency of column = 60% So, No. of actual trays = location of feed point =
7 = 12 0 .6 2 =3 0 .6
Determination of the Column Diameter Top Conditions Ln = 33.394 Kgmol/hr Vn = 42.9354 Kgmol/hr Average mol. Wt. = 43.73 Kg/Kgmol T = 20o C Liquid density = L = 0.78158 gm/cm3 Vapour density = V = 3.56 10-3 gm/cm3
Bottom Conditions Lm = 289.8537 Kgmol/hr Vm = 42.9522 Kgmol/hr Average mol. wt. = 19.05 Kg/Kgmol T = 96o C Liquid density = L = 0.99178 g/cm3 Vapor density = V = 1.433 10-3 gm/cm3
Because liquid and vapour flow rates are greater at bottom so based upon bottom flow rates.
91
Appendix-A
Vapour load at bottom
QV
Vm = 0.15861 m3/Sec ρ V 3600
Liquid load at bottom
QL
Lm = 1.542 10-3 m3/Sec ρ L 3600
Tray Dynamic i)
Flow Parameter:
L ρ FLV m v Vm ρ L
ii)
0.5
-3 289.8537 1.433 10 = 42.9522 0.99178
0.5
= 0.2565
Capacity Parameter: Assumed tray spacing = 12 in. = 30.48 Cm From Fig (24) of Appendix-B, sieve tray flooding capacity, Csb(20) = 0.028 m/Sec Surface tension of system = = 74.62 dynes/Cm Corrected Csb = Csb(20)
ρ ρV Now Unf = Cbs L ρ V
iii)
20
0.2
= 0.0364 m/Sec
0.5
= 0.7361 m/Sec
Tray Selection We have selected single crossflow sieve tray with segmental down
comer. For this type of tray,
92
Appendix-A
Down comer area = Ad = 0.12 AT Weir length = Lw = 0.77 DT Selected weir height = hw = 1 in. = 25.4 cm Hole size (range 1/8“ to ½”) = 1/8” = 3.175 mm Assumed tray spacing = 12 in.
iv)
Tower Diameter Let flooding = 53% (Correct trial) F* = 0.53 Un* = Unf F* = 0.390133 m/Sec Un* = flooding velocity based upon net area. Net area An = AT – Ad = 0.88 AT AT =
An QV = = 0.461992 m2 * 0.88 0.88Un
AT =
π 2 D = 0.461992 m2 4
D = 0.76715 m = 2.517 ft. Selected D = 2.5 ft. = 0.761963 m AT =
v)
π 2 D = 0.45576 m2 4
Flooding Check Un =
Now
QV QV = = 0.395467 m/Sec 0.88AT An U F = F* n* U n = 0.537
Now following information are available,
93
Appendix-A
Tower area = AT = 0.45576 m2 Net area
= An = 0.88 AT = 0.40107 m2
Active area = Aa = 0.76 AT = 0.34638 m2 Down comer area = Ad = 0.12 AT = 5.46912 10-2 m2 Hole area = Ah = 0.1 AT = 4.5576 10-2 m2
vi)
Calculation of Entrainment At FLV = 0.2565 and F = 53%
From Figure (23) of Appendix-B, fractional entrainment, = 0.0015 since < 0.2, so now process is satisfactory e=
ψL = 8.295 Kg/hr 1- ψ
vii)
Tray Pressure Drop
a)
Hole Velocity Uh =
L = Lm mol. wt.
here,
QV 0.15861 = 0.1 0.45576 Ah
Tray thickness = 3mm = 0.118 in.
[for steel tray]
Hole dia = 1/8” = 3.175 mm Tray thickness/Hole dia =0.9449
4.5576 10 2 Hole area / active area = = 0.1315 0.34638
hole area Now gross % free area = 100% = 10 % tower area From Fig (20) of Appendix-B,
94
Appendix-A
2
1 1.8 C vo Cvo = dry orifice co-efficient
ρ 1 Dry tray pressure drop = Pdry = 5.08 V U 2h ρ C L vo
2
= 0.288 cm since < 0.1, no need of correction factor.
b)
Areated Liquid Drop, ha: Q Fva = V h 0.5 = 0.01733 Aa
From figure (19) of Appendix-B, aeration factor of liquid on tray, Qp = 0.8 Lw = 0.77 DT = 0.5867 m So height of liquid on the weir,
Q How = 6.66 L LW ha
0.67
= Hw = 1 in. = 2.54 cm
= Qp (hw + how) = 0.8 (2.54 + 12435) = 2.13148 cm
ha = height of areated liquid drop
c)
Total Pressure Drop: PT = Pdry + ha = 0.288 + 2.13148 = 2.41948 cm
Estimation of Weep Point L = 0.99178 gm/cm3 = 991.78 Kg/m3
95
Appendix-A
= 74.62 dynes/cm3 = 0.07462 J/N2 dh = 3.175 mm ha = 4.16348 h =
4.14 104 α = 0.98106 cm ρ Ld h
Now
Pdry + h = 1.26906 cm hw + how = 2.04896 inch Hole area / active area = 0.1315
From figure (22) of Appendix-B, the point of intersection is above the relevant line, so no weeping problem.
Down Commer Residence Time Down comer velocity based upon clear liquid, Vd =
L A dρ L L = Lm mol. wt.
Here,
= 5.5917 Kg/hr So, Vd = 0.02828 m/Sec, Residence time =
L = 991.78 Kg/m3
Tray spacing = 10.78 Sec Vd
Which is greater than 3. so, satisfactory.
Calculation of Liquid Gradient a)
Height of Froth hf =
b)
hσ 0.98106 = = 1.6351 2Qp - 1 2(0.8) - 1
Hydraulic Radius: Rh = cross section / wetted perimeter
96
Appendix-A
Df =
L w DT = 0.676925 m 2
So,
Rh =
h f Df = 0.02 m 2h f 100Df
c)
Velocity of aerated mass Uf: for Fva = 0.01733, = 0.59
100Q L = 0.244394 m/sec h f φDf
Uf =
d)
[figure(19) of Appendix-B]
Reynold’s modulus: Reh =
R h Uf ρL μL
mix = 0.6442 Cp = 6.442 10-4 N.S/m2 L = 491.78 Kg/m3 Rh = 0.02 m Uf = 0.244394 m/Sec Reh
=
7525
e)
Friction factor: f = 0.10
f)
Fig (18) of Appendix-B
Calculation of gradient (): =
100fUf2 L w R hg
g 9.81m/Sec2
= 0.14137 cm Now Pdry = 0.288 cm 1/2 Pdry = 0.144 cm Because < ½ Pdry
97
Appendix-A
Its is satisfactory
g)
Height of aerated mass in down comer: Assuming a try clearance 38 mm. between down comer apron. And the try. hda = 13.1 (QL/Ada)2 = 13.1 (1.542 10-3/0.022294)2 hda = 0.06267
[Ada = Lw clearance in m]
So height of liquid in down comer, hdc = PT + hw + how + + hda = 2.41 + 2.54 + 0.12435 + 0.14137 + 0.06267 = 5.28779 cm height of aerated liquid = hdc/Qp = 6.609738 cm Tray spacing = 12” = 30.48 cm ½ Tray spacing = 15.24 cm half of tray spacing > hdc/Qp so process is satisfactory.
Mechanical Design 1)
Shell Thickness Material of construction = Stainless steel 316 Operating Pressure
= 14.7 Psi
Design Pressure
= 25 Psi
Shell thickness is given by
tm
PD C 2fJ P
Where f = max – allowable working stress = 18700 Psi J = weld efficiency factor (max) = 0.8 C = corrosion factor = 0.002 in./year
98
Appendix-A
For 25 year life C = 0.002 25 = 0.05 in Period = 25 year, D = 2.5 ft = 30 in tm
25 30 0.05 = 0.0525 in 20.81.8700 25
for each 20 ft height 1/16” is added tm = 0.0525 + 1/16 = 0.11 in = 3 mm
Tray Specifications Total no. of holes =
=
Total area for holes Area of one hole
0.045576 100 2
0.01265625 2.542
= 5582 2
No. of holes/in of tray
5582/ 2.542 = = 10 0.34638
Now from graph Fig (21) of Appendix-B, Pitch = 2.0 3.175 = 8.89 mm
Height of Distillation Column No. of plates = 12 Tray spacing 1 ft Distance between 12 plates = 12 ft Top clearance = 1 ft Bottom clearance = 1 ft Tray thickness = 3 mm/plate = 0.00983 ft/plate Total thickness of trays = Total height of column
0.118 12 = 0.118 ft 12 = 11 + 1 + 1 + 0.118
99
Appendix-A
= 13.118 ft = 3.998 ft = 4 ft
NOMENCLATURE OF DISTILLATION COLUMN Aa = Active area
(m2)
Ad = down comer area
(m2)
Ah = hole area
(m2)
An = Net area
(m2)
AT = total area
(m2)
Ada = area under down comer apron
(m2)
C = corrosion allowance
(in/year)
Csb(20) = capacity parameter for liquids ( = 20 dynes/cm) Csb = Capacity parameter of liquid D = Diameter of tower
(m)
Df = flow width normal to liquid flow
(m)
Dh = hole diameter
(m)
e = total entrainment
(Kg/sec)
F = feed
(Kgmol/hr)
F* = Design % loading HF = Enthalpy of feed
(J/Kgmol K)
HB(l) = Enthalpy of bottom
(J/Kgmol K)
HD(L) = Enthlpy of the distillate
(J/Kgmol K)
ha = head loss due to created liquid
(cm)
hf = froth height on tray
(cm)
had = had loss due to down comer apron
(cm)
hdc = height of clear liquid in down comer
(cm)
hw = weir height
(cm)
100
Appendix-A
how = height of liquid crest over weir
(cm)
ho = head loss due to bubble formation
(cm)
J = weld efficiency factor L = liquid flow rate
(Kg/hr)
Lw = weir length
(m)
Nm = min. no. of plates P = period
(years)
Pdry = dry pressure drop
(cm)
PT = total pressure drop
(cm)
QL = Liquid flow rate
(Kg/m3)
Qv = Vapour flow rate
(Kg/ m3)
Qc = condenser duty
(J/ m3)
QR = Rebotr duty
(J/hr)
QP = Areatio factor Rh = Hydraluic radius of aerated mass
(m)
Reh = Modified Reynold No. Rm = Min. reflux ration R = operational reflux ratio Tm = thickness of shell
(mm)
Uh = vapour velocity through holes
(m/sec)
Vm = vapour flow rate at bottom
(Kgmol/hr)
WF = mass flow rate of feed
(Kgmol/hr)
WB() = bottoms
(Kg/hr)
W D() = mass flow rate distillate
(Kg/hr)
Unf = flooding velocity based upon net area
(m/sec)
Vd = down comer liquid velocity
(m/sec)
= relative volatility L = density of liquid
(Kg/m3)
101
Appendix-A
v = density of vapor
(Kg/m3)
average = average viscosity of feed
(Cp)
= fractional entrainment factor = relative froth density = surface tension
(J/N2)
= liquid gradient
A-4) DESIGN CALCULATIONS OF VAPORIZER
Steam
966.7 lb/hr
266o F
266o F
150.8o F
233.6o F
2501 lb/hr
Alcohol
Heat Duty Qt = Q1 + Q2 1)=> Preheating Q1
2)=> Vaporization
= mCpT = 1135.8 0.87 (112-66) = 45454.7 Kmol/hr = 180.375.8 Btu/hr
Q2 = Qalcohol + QH2O
102
Appendix-A
Latent heat of vaporization of H2O = 185.32 Kcal/Kg Latent heat of vaporization of alcohol = 500 Kcal/Kg Q2 = 863.2 + 45.43 + 500 Q2 = 182685 Kcal/hr = 724942.5 Btu/hr Qt = Q1 + Q2 = 228140.2 Kcal/hr = 905318.7 Btu/hr
FOR PREHEATING ZONE T1 = 130o C = 266 oF
For steam
T2 = 130o C = 266 oF For process fluid, T1 = 66o C = 150.8 oF T2 = 112o C = 233.6 oF t1 = LMTD =
266 233.6 266 50.8 266 233.6 ln 266 150.8
= 65.27 oF
For Vaporization Zone t2 = 266 – 233.6 = 32.4 oF t, weighted =
Qt Q1 Δt 1
Q2
Δt
2
103
Appendix-A
t, w =
905318.3 180375.8 724942.5 65.28 32.4
t, w = 36 oF assume UD = 95 Btu/hr. oF. ft2 as Qt = UD A t, w A
=
905318.3 95 36
= 264.71 ft2
Exchange Layout 1-2, shell & tube heat exchanger ¾OD, 1 sq. pitch, A = at Nt Lt A = 0.1963 ft Lt = 8 ft. at = 0.1963 A = 0.1963 8 Nt Nt =
264.7 = 168 0.1963 8
Nt = 166
(Nearest count)
So A = 260.68 ft2 UD = 96 Btu/hr. ft2. oF
SPECIFICATIONS Shell Side
Tube Side
17 ¼, C = 0.25”
¾ OD, 1 sqr. Pitch
104
Appendix-A
B = 4 in
16. BWG
Calculations (Tube Side)
0.302 166 = 0.174 ft2 144 2
at =
Ft = m/at = 966.7/0.174 = 5555.74 lbm/hr. ft2 D = (I.D)Tube/2 = 0.62/12 = 0.052 ft R,t = DGt/ t
T = 130o C = 266 oF
= 0.014 Cp = 0.03388 lb/ft hr Re,t =
0.052 5555.74 = 852.7 0.03388
For condensing steam, hio = 1500 Btu/hr. ft2 oF
Shell Side Calculations as =
I.D CB 144Pt
=
17.25 0.25 4 = 0.119 ft2 144 1
Gs = m/as = 2501.76/0.119 = 21023 lb/hr ft2 Res = De Gs/ De = 0.95/12 = 0.079167 ft (for liquid) = 0.25 Cp = 0.25 2.42 = 0.604 lb/hr. ft Re,s =
0.079167 21023 = 2745 0.604
JH = 300 ho = JH (K/De)(C/K)1/3
105
Appendix-A
= 218.2 Btu/hr.ft2 oF U1
= hioho/ho + hio
U1
= 74 Btu/hr.ft2 oF
A1
=
Q1 U1t1
= 37 ft2 For vaporization zone (at 112o C for vaps)
= 0.012 Cp = 0.012 2.42 = 0.029 lb/hr. ft
Re,s = DeGs/ =
0.079 21023 0.029
Re,s = 57269 JH = 140 ho
= JH(K/De)(c/K)1/3 = 141.8 Btu/hr.ft2 oF
U2
=
h io ho h io ho
=129.5 Btu hr. ft2 oF Clean surface required for vaporization A2 = Q2/U2(t)2 A2 = 172.78 ft2 Total clean surface required Ac = A1 + A2 = 37 + 172.78 Ac = 209.78 ft2 Weighted clean overall co-efficient Uc,w =
U1A1 U 2A 2 A1 A 2
106
Appendix-A
= 119 Btu/hr. ft2 oF Rd
=
0.003
1/UD = 1/UC + Rd UD
88 Btu/hr ft2 oF
=
(Correct)
PRESSURE DROP CALCULATIONS Tube side Pressure Drop At
Re,t = 8527 f = 0.00028
Specific volume of steam at 39 Psi = 10.854 ft3/lb s=
1 10.854 ftlb 62.5 ftlb 3
3
s = 0.00147 Gt = 5555.7 lb/hr. ft2 Pt = 1/2 = 1/2
fG2tLn 5.22 1010 0.052 0.00147 1
100028 55553742 8 2 5.22 1010 0.052 0.00147 1
Pt = 0.035 Psi
Shell Side Pressure Drop For preheating zone At Re,s = 2745
f = 0.0027
Length of preheating zone = LP = L t
A1 Ac
= 1.41 ft No. of crosses, (N + 1) =
12 1.4 8
107
Appendix-A
= 4.2 s = 0.81 Ds = 17.25/12 = 1.44 ft
f G s2D3 N 1
Ps1 =
5.22 1010 s s
Ps1 = 0.22 Psi For vaporization zone At
Re’,s = 57269
f = 0.0018
Length of vaporization zone) = Lv = L t = 6.6 ft No. of crosses, (N+1)’
= 12
Lv B
= 19.74 outlet liquid = 0.81 62.5 = 50.625 outlet varps = PM/RT
=
44.1 42.3 10.73 693.6
= 0.25
1135.8
soutlet mix =
908.7
62.5 227.1 0.25 50.625
= 0.005 smean =
0.81 0.005
Ps2 =
N 12
= 0.4
fG s2 DsN 12 5.22 1010 De s 1
= 1.08 Psi Ps
=
Ps1 + Ps2
Ps
=
1.3 psi
108
A2 Ac
Appendix-A
A-5) DESIGNING CALCULATIONS OF PRE-HEATER-E6 Design Calculations T2=240 oF
T1=240 oF
Inlet
temp eratu re of the = t1 = 122 oF
process stream Outlet temperature of
the
t1=122 oF
t2=195.8 oF
process
stream
= t2 = 195.8 oF
Inlet temperature of steam
= T1 = 240 oF
Outlet temperature of steam
= T2 = 240 oF
Mass flow rate of process stream
= m = 11281.45 lb/hr
Specific heat capacity of the process stream
= Cp = 0.943 Btu/lb oF
Heat load Q mC p T Q 11281.45x0.943x78.3
Q 785114.46 Btu
Mass flow rate of steam m
m
Q
785114.46 952.1
109
hr
Appendix-A
m 860.33 lb
hr
LMTD Tm
Tm
(T1 t 2 ) (T2 t1 ) (T t ) ln 1 2 (T2 t1 )
(240 195.8) (240 122) (240 195.8) ln (240 122)
Tm 75.72 o F
Since steam is condensing medium therefore R = 0 and FT = 1 so Tm t
Assumed calculations Value of UD assumed U D 195 Btu
hrft 2o F
Heat transfer area A
A
Q U D t
785114.46 195 x75.72
A 53.17 ft 2
Now, let’s take Tube length = 6ft Tube O.D. = ¾ in Area of one tube = πDL = 1.178 ft2 No. of tubes = 46 tubes
110
Appendix-A
From tube count table For 50 tubes shell I.D. = 10 in for one pass Pitch = PT = 1.25 x ¾ = 0.937 in Baffle spacing = B = 5 in
Clearance = 0.187 in
Shell Side Calculations Flow area as
as
IDxC ' B 144 PT
10 x0.187 x5 144 x0.937
a s 0.052 ft 2
Mass velocity Gs
Gs
W as
11281.45 0.052
Gs 216951.52 lb
hrft 2
Reynolds No. Re
Re
DeGs
0.046 x 216951.92 1.2
Re 8316.49
Value of JH from shell side heat transfer curve
111
Appendix-A
JH = 55
Thermal conductivity k = k1x1 + k2x2 + ………….. + knxn k = 0.36 Btu/hrft2 (oF/ft)
Shell side coefficient k Cp JH o De k
1
ho
3
0.36 0.943x1.2 55 o 0.046 0.36 ho
ho
o
632.74 Btu
hrft 2o F
for coefficient correction wall temperature tw ta
hio (ta Ta ) hio hi
t w 215.94 o F
at wall temperature w 0.6354 lb fthr s w
0.14
1.089
corrected coefficient ho
ho
o
112
s
1
3
Appendix-A
ho 688.92 Btu
hrft 2o F
TUBE SIDE CALCULATIONS Flow area at ' 0.302in as
as
N t at ' 144n
50 x0.302 144 x 2
a s 0.046 ft 2
Mass velocity Gt
Gt
W at
860.33 0.046
Gt 18702.82 lb
hrft 2
Reynolds No. Re
Re
D Gt
0.0517 x18702.82 0.029
Re 33342.61
for steam hio 1500 Btu
113
hrft 2o F
Appendix-A
Clean overall coefficient UC
UC
hio ho hio ho
1500 x688.92 1500 688.92
U C 472.09 Btu
hrft 2o F
Design overall coefficient 1 1 Rd U D UC 1 1 0.003 U D 462.09 U D 202 Btu
hrft 2o F
Pressure drop (Shell side) for Re = 8316.49 friction factor for shell side = f = 0.0025 No. of crosses , N+1 = 12L/B = 14.4 = 15 fG s Ds ( N 1) 2
Ps
Ps
5.22 x1010 De s s
0.0025 x216951.92 2 x0.833x15 5.22 x1010 x0.046 x0.89 x1.085
Ps 0.6 psi
Pressure drop (Tube side) for Re = 33342.61 friction factor for tube side = f = 0.00018
114
Appendix-A
2
fG t Ln 1 Ps 2 5.22 x1010 Ds t
Ps
1 0.00018 x18702.82 2 x6 x2 2 5.22 x1010 x0.0517 x0.00098 x1.0
Ps 0.2 psi
A-6) DESIGN CALCULATIONS OF CONDENSER T2 = 178 oF
T1 = 180 oF
t1 = 77 oF
t2 = 113 oF
Inlet temperature of the process stream
= T1 = 180 oF
Outlet temperature of the process stream
= T2 = 178 oF
Inlet temperature of the water
= t1 = 77 oF
Outlet temperature of the water
= t2 = 113 oF
115
Appendix-A
Mass flow rate of the process stream
= m = 22267.8 lb/hr
Enthalapy of saturated vapor (95% Ethanol)
= Hv = 500 Btu/lb
Enthalapy of saturated liquid (95% Ethanol)
= Hl = 98 Btu/lb
Heat Load Q
=
m(Hv – Hl)
Q
=
22267.8 (500 – 98)
Q
=
8951684.54 Btu/hr
Mass flow rate of cooling water
m
Q CpΔt
116
Appendix-A
=
8951684.54 1 36
= 248657.5 lb/hr
LMTD
Tm
Tm
T1 - t 2 - T2 - t1 T - t ln 1 2 T2 - t1
180 - 113t 2 - 178 - 77 180 - 113 ln 178 - 77
= 81 oF Since process is condensing therefore R=0 and FT = 1 so, Tm t
Assumed Calculations Value of UD Assumed UD
=
100 Btu/hr.ft2 oF
Heat Transfer Area
A
Q U DΔt
A
8951684.54 100 81
= 1105 ft2 Assume 4 passes Now, lets take Tube length =
10 ft
Configuration is 2 shell side passes and 4 tube side passes Tube O.D.
=
¾ in.
117
Appendix-A
Area of one tube
=
DL = 2.35 ft2
No. of tubes
=
1105/2.35 = 470
From tube count table For 468 tube shell I.D.
=
25 in for one pass
Pitch
=
1.25 ¼ = 0.937 in.
=
PT
Baffle spacing
= B = 20 in
Clearance = 0.187 in Then Corrected
A = 1099 ft2
Corrected UD
100.5 Btu/hr.ft2 oF
=
Shell Side Calculations Flow Area
as
ID CB 144Pr
= as
25 187 20 144 937
= 0.692 ft2
Mass Velocity
Gs
W as
118
Appendix-A
= Gs
22267.8 0.692
= 32177.74 lb/hr ft2
Loading
G
G
W LN1/3 t
22267.8 10 466 2 / 3
= 37.09 Assumption h = ho = 200
hio = 909.33 Btu/hr.ft2 oF tw
= h ta
h io Tv t a h io h i
= 110 oF
Film Temperature Tf =
Ta t w 2
Physical Properties at tf Thermal conductivity kf = 0.116 Btu/hr-ft-oF Specific gravity sf = 081 lb/hr-ft Viscosity f = 1.45 lb/hr-ft From Figure(6) of Appendix, h = ho calculated = 200 Btu/hr-ft2-oF
119
Appendix-A
Tube Side Calculations Flow Area
a t
= 302 in.
a t
= Ntat/144a
a t
=
468 0.302 144 4
= 0.245 ft2
Mass Velocity Gt
= W/at
Gt
= 248657/0.245 = 1014926 lb/hr-ft2
Water Velocity V
= Gt / 3600 = 1014926 / 7600 62.5 = 4.512 ft/sec
At ta = 95 oF = 1.7 lb/ft-hr I.D of tube = 0.62/12 = 0.0517 ft
Reynold No. Ret
= DGt/ = 0.0517 1014926.5 / 1.7 = Ret = 30865
from figure of (Kerm)
hi = 1100 Btu/hr-ft2-oF hio = hi
I.D = 909.33 hr-ft2-oF O.D
120
Appendix-A
Clean Overall Coefficient
UC
h io h o h io h o
UC
909.33 200 909.33 200
= 163.94 Btu/hr-ft2 oF
Design Overall Coefficient Calculated Allowable dirt factor Rd = 0.003
UD
1 Rd UC = 1/150 + 0.003 = 109.89 Btu/hr-ft2-oF
Pressure Drop (Shell Side) Reynolds No. At
T = 180 oF ap = 0.01 2.42 = 0.0242 De = 0.55/12 = 0.0458 ft2 Res
= DeGs/ = 0.0458 32177.74/0.0242 = 60898
For Res = 60898 Friction factor for shell side f = 0.0015 No. of crosses, N + 1 = 1210/20 = 6 Density = f = 0.085
(by using ideal ged equation)
S = specific gravity = 0.085/82.5 = 0.0012
121
Appendix-A
Ps
fGs2Ds N 1 5.22 1010 Dess =
0.001532177.742 2.08 6 5.22 1010 0.0458 0.0013
= 3.12 psi
Pressure Drop (Tube Side) Reynolds No. Ret
= DG/ = 144930/1.7 = 20865
for Ret = 30865 Friction factor for tube side f = 0.00021 ft2/in.
Pt
fG2tLn 5.22 1010 Dst =
0.00021 110149302 10 4 5.22 1010 1 1
= 2.0 psi
Pr
= 440.12 / 1 = 0.12 psi
PT Pt Pr = 2.8 + 1.98 = 4.72 psi
REFERENCES 1)
Ludwig, E.E, “Applied Process Design”, 3rd ed, vol. 2, Gulf Professional Publishers, 2002.
2)
Ludwig, E.E, “Applied Process Design”, 3rd ed, vol. 3, Gulf Professional Publishers, 2002.
122
Appendix-A
3)
McKetta, J. J., “Encyclopedia of Chemical Processing and Design”, Executive ed, vol. 1, Marcel Dekker Inc, New York, 1976.
4)
Kuppan, T., “Heat Exchanger Design Hand Book, Marcel Dekker Inc., New York, 2000.
5)
Levenspiel, O., “Chemical Reaction Engineering:, 2 nd ed, John Wiley and Sons Inc., 1972.
6)
Peters, M.S. and Timmerhaus, K.D., “Plant Design and Economics for Chemical Engineering”, Fourth ed, McGraw Hill, 1991.
7)
Rase, H.F., “Fixed Bed Reactor Design and Diagnostics, Butterworth Publishers, 1990.
8)
Thomas, J. M., and Thomas, W.T., “Introduction to the Principles of Heterogeneous Catalysis, Acedenic Press, 1967.
9)
Bockhurst, J.F. and Harker, J.H, “Process Plant Design”, Heinemann Educational Books Ltd, 1973.
10) Coulson, J.m., and Richardson, J.F., “Chemical Engineering”, 4 th ed, Vol.2, Butterworth Heminann, 1991. 11) Peacock, D.G., “Coulson & Richardson’s Chemical Engineering”, 3rd ed, vol, Butterworth Heinenann, 1994. 12) Sinnot, R.K., “Coulson and Richardson’s Chemical Engineering”, 2 nd ed, vol 6, Butterword Heinemann, 1993. 13) Kern, D.Q., “Process Heat Transfer”, McGraw Hill Inc., 2000. 14) McCabe, W.L, “Unit Operations of Chemical Engineering”, 5th Ed, McGraw Hill, Inc, 1993.
123
Appendix-A
15) Perry, R.H and D.W. Green (eds): Perry’s Chemical Engineering Handbook, 7th edition, McGraw Hill New York, 1997. 16) www.nist.com 17) www.uspto.gov 18) www.haverstandard.com
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