Acetic Acid Main

VIT UNIVERSITY (Estd. u/s 3 of UGC Act 1956)

VELLORE – 632 014

SCHOOL OF MECHANICAL AND BUILDING SCIENCES

CHEMICAL ENGINEERING DIVISION

DESIGN PROJECT ON ETHYLENE OXIDE By:ROHIT KUMAR(10BCH0046) SHREY KULSHRESHTHA(10BCH0054) SAMBHAV JOHARI(10BCH0071)

VII Semester B. Tech. Mechanical Engg. Spec. in Chemical Processes

Design Project Record 2012

VIT UNIVERSITY (Estd. u/s 3 of UGC Act 1956)

VELLORE – 632 014 SCHOOL OF MECHANICAL AND BUILDING SCIENCES CHEMICAL ENGINEERING DIVISION

Certified that this is the bonafide record of work done by 1.ABHISHEK RANJAN(09BCH001) 2.ARSHI SAHU(09BCH017) 3.MANISH JAIN(09BCH032) Of Seventh Semester students of B.Tech Mechanical Engineering with Specialization in Chemical Processes during the year 2012.

Project guide Prof. K Rambabu

Acknowledgement

We would like to express our deep gratitude to all those who gave us the possibility to complete this design project. We want to thank the Department of Chemical Engineering of VIT University, Vellore for helping us to commence on this design project. We have furthermore to thank the faculties Prof. David K Daniel, Prof. L.Muruganandam, Prof. Anand Gurumoorthy and Prof. Byron Smith who reviewed us periodically and encouraged us to go ahead with the work. We are deeply indebted to our guide Prof. Rambabu K. who helped us in stimulating suggestions and helped and supported us with all the valuable hints.

Last but not least we wish to avail ourselves of this opportunity, express a sense of gratitude and love to our friends and beloved parents for their manual support, strength, help and for everything.

Preface

This design project includes various aspects of a chemical product development right from the market condition evaluation to the estimation of cost of the plant setup. Chapter 1 deals with the introduction to the product (acetic acid) – its properties both physical and chemical. It also provides the application of acetic acid in various other areas such as manufacture of pharmaceuticals, etc. Chapter 2 contains a study of acetic acid in the global as well as Indian market. The gap between demand and supply is studied and used to set a bar for the production rate for the plant. Chapter 3 has a brief explanation of various available processes for the manufacture of the acetic acid. A comparison is also done between the chosen of the process and the other available processes. The detailed process description is also given for the selected process. Chapter 4 includes material balance over all the equipments used in the plant for a production of 100 TPD of acetic acid. Both component-wise and overall mass flow rate has been provided. The mol%, and wt.% is also provided for each component and the molar flow rate of each is included too. Chapter 5 contains enthalpy balance for all the streams in the plant in and out of each equipment. The utilities requirement are also calculated, stating the amount of cooling water and steam required for daily running of the plant. Chapter 6 contains internal as well as external mechanical design. The number of stages is calculated using McCabe Thiele Method, and then the column design is done along with the plate specifications and then design of skirt support is also done. Chapter 7 provides a cost estimation for the distillation column and also the overall plant cost. The total income and profit is also calculated along with the break even point for the plant. Process flow sheet is also provided at the end along with the material safety data sheet.

TABLE OF CONTENTS Certificate

i

Acknowledgement

ii

Preface

iii

1. Introduction

1

2. Market Analysis

5

3.

9

Process Selection

4. Material Balance

14

5. Energy Balance

17

6. Equipment Design

23

7. Cost Estimation

39

Reference Process Flow Sheet MSDS Sheets

Chapter 1 Introduction 1.1 Basic Properties: Acetic acid has a place in the organic chemical industry that is comparable to sulphuric acid in the inorganic chemical industry. The most commonly known acetic acid is also known as methane carboxylic acid. Its IUPAC name is ethanoic acid. Its molecular formula is CH3COOH and abbreviated as ACOH, with molecular weight of 60.05. A clear, colorless liquid that has a piercingly sharp, pungent (vinegary odour) and is a dangerous vesicant. As the acid of vinegar, acetic acid is as ld as fermented liquors, which sour spontaneously and which are historically recorded prior to 3000BC. It occurs both free and combined in the form of esters of various alcohols in many plants and has also been detected in animal secretions. The term “acetic acid” have been introduced by Libavius (1540-1600AD), and the properties of icy (glacial) acetic acid and common vinegar were recognized. Many (attempts have been made to prepare icy acetic acid from repeated distillation of vinegar during these early studies), but it was normally prepared by dry distillation of copper acetate or similar heavy metals acetates like the production of sulphuric acid from its metallic salts. Later, Lavoisier believed acetic acid made by dry distillation of salts can be distinguished from acetic acid, the hypothetical acid of vinegar. After his death, the identity of acetic and acetous acid was demonstrated by Adet and others. But, final proof was obtained, when Kolbe first prepared acetic acid in 1847. Today, acetic acid is one of the most important industrial organic acids. It is produced mostly synthetically in volume exceeding a billion pounds per year. 1.2 Physical Properties: S.No. 1 2 3 4 5 6 7 8 9 10 11 12

Properties Molar Mass Appearance Solubility in water Melting point Boiling Point Vapor pressure Thermal conductivity Heat of melting Heat of vaporization Specific heat of vapor Density, 20.0ºC Refractive index, nd

13

Specific heat of solid

14 15

Critical pressure Critical temperature

Value -1 60.05 g mol Colourless Liquid Miscible o 16.635 ± .002 C o 118 C log p =7.55716– 1642.54/(233.386+1) 0.158 W/mK at 20ºC 207.1 J/g 394.5 J/g at boiling point 5.029 J/gK at 124ºC 1.04928 g/ml 1.36965 0.837 J/gK at 100K 11.83 mPa.s or cp at 20ºC 10.97 mPa.s or cp at 25ºC 57.856 kPa (571.1 atm) 321.6ºC 1

19 20 21 22 23 24

Magnetic susceptibility Solid Liquid Dielectric constant Solid Liquid surface tension, mN/m or dyne/cm Flash point, open cup Autoignition point Lower limit of flammability Lower limit of flammability Acidity(pKa) Basicity(pKb)

25 26 27 28

Std. Enthalpy of formation ∆fH298 Std. Enthalpy of combustion ∆cH298 o Std. molar entropy S 298 Sp. Heat Capacity

16 17 18

• • • • • • •

32.05 x 10-6 cm3/mol 31.80 x 10-6 cm3/mol 2.665 at -10.0ºC 6.710 at 20.0ºC 27.57 at 20.1ºC 57ºC 465ºC 40ºC 5.4 vol % at 100ºC 4.76 9.198 -483.88 - -483.16 kJ mol -1 -875.5- -874.82 kJ mol -1 -1 158.0 JK mol -1 -1 123.1 JK mol

-1

Though the molecular weight of acetic acid is 60.05, its apparent molecular weight varies with both temperature and the other associating substances present. It is miscible in all proportions with water, ethanol and ether. It is an excellent solvent for organic compounds. A zero dipole moment for unsymmetrical acetic acid structure (is explained by the formation of symmetric dimmers via hydrogen bonding in which the dipole moments cancel). No high dissociation ionic species in acetic acid solution. Possesses relatively low basicity or proton affinity. Has a very strong leveling effect on bases and solvolyzes all strong bases to acetate ion, CH3COO .

1.3 Chemical Properties: Acidity The hydrogen center in the carboxyl group (−COOH) in carboxylic acids such as acetic acid can separate from the molecule by ionization: -

+

CH3CO2H → CH3CO2 + H

Reactions with Organic Compounds

2

Acetic acid undergoes the typical chemical reactions of a carboxylic acid. Upon treatment with a standard base, it converts to metal acetate and water. With strong bases (e.g., organolithium reagents), it can be doubly deprotonated to give LiCH2CO2Li. Reduction of acetic acid gives ethanol Reactions with inorganic compounds Acetic acid is mildly corrosive to metals including iron, magnesium, and zinc, forming hydrogen gas and salts called acetates: Mg + 2 CH3COOH → (CH3COO)2Mg + H2 Because aluminium forms a passivating acid-resistant film of aluminium oxide, aluminium tanks are used to transport acetic acid. Metal acetates can also be prepared from acetic acid and an appropriate base, as in the popular "baking soda + vinegar" reaction: NaHCO3 + CH3COOH → CH3COONa + CO2 + H2O 1.4 Applications of Acetic Acid: The various areas where acetic acid has its wide use are: • Over 60% of acetic acid produced goes into polymers derived from either • Vinyl acetate (vinyl esters) or cellulose (cellulose esters). • Most of poly (vinyl acetate) is used in paints and coatings or used for • Making poly (vinyl alcohol) and plastics. • Also, cellulose acetate is used to produce acetate fibres. • Acetic acid and acetate esters are used extensively as solvents and in organic synthesis. • In the production of white lead and chrome yellow pigments, it is used to • Make lead available in a soluble form for further reaction to give basic lead carbonate and lead chromate. • Also used to provide the necessary acidity in the number of processes carried out in an aqueous media. • Used in the mordanting process and in dyeing of wool in textile industry. • Used as a coagulant for rubber latex in manufacture of elastic thread, as a component of photographic stopping and fixing baths and as a laundry sour. • Also used in electroplating, engraving and in the processing of fish glue. • Dilute acetic acid functions either or both as a preservative and flavouring agent in food stuffs such as pickled vegetables, condiments, jellies and confectionery. • RDX - the high explosive cyclotrimethylenetrinitramine is furnished on nitration of hexamethylenetetramine with acetic acid. • Also, lower alkyl esters such as methanol, ethanol, isopropanol and butanol are widely used as solvents for lacquers and adhesives. • Other esters form basis for synthetic flavors for perfumes and bornyl acetate in the manufacture of synthetic camphor.

3

Acetic acid is mainly utilized in the manufacture of the following products: 1. Acetic Anhydride: Acetic Anhydride is a very versatile product. It is a part of the manufacturing of Cellulose Acetate fiber, Plastics, Vinyl Acetate Monomer etc. The pharmaceutical industry uses Acetic Anhydride as a dehydration agent. The Dye industry also uses it for manufacturing Dyes and Dye intermediates. Ordinance factories use it in the manufacture of explosives. Perfumes are also made by the use of Acetic Anhydride. Aspirin, Paracetamol and other antibiotics are also made by using Acetic Anhydride. 2. Vinyl Acetate: Vinyl Acetate is a basic raw material for Poly Vinyl Acetate and Poly Vinyl Alcohol. Vinyl Acetate Monomer is used in the manufacture of latex paint, paper coatings, Adhesives and textile finishing. 3. Cellulose Acetate: Cellulose Acetate is an important constituent of thermoplastics and fibers. The textile industry uses cellulose acetate widely for the production of cellulose acetate fiber. The other uses of Cellulose Acetate are the production of film, plastic sheets and the formulation of liquor. 4. Monochloro Acetic acid: Monochloro Acetic acid [MCA] is used extensively in the manufacture of Herbicides, Preservatives, Bacteriostat and Glycine. Mainly it is used in the manufacture of Carboxy Methyl Cellulose which is a gummy and strong adhesive powder used in drilling for oil. MCA is also used for producing laboratory chemicals like EDTA and 2 4 D Thioglucolic acid. 5. Purified Terepthalic Acid [PTA]: · Acetic acid finds use in the manufacture of PTA as a solvent. PTA is an alternative raw material for polyester fiber manufacture instead of Dimethyl Terepthalate [DMT] 6. Food Additives[VINEGAR]: Acetic acid is widely used in the form of vinegar as a food additive. As vinegar it is used for the preservation of food and also to impart a sour taste to certain preparations.

4

Chapter 2 Market Analysis Chemicals are a part of every aspect of human life, right from the food we eat to the clothes we wear to the cars we drive. Chemical industry contributes significantly to improving the quality of life through breakthrough innovations enabling pure drinking water, faster medical treatment, stronger homes and greener fuels. The chemical industry is critical for the economic development of any country, providing products and enabling technical solutions in virtually all sectors of the economy. Organic chemicals industry is one of the most significant sectors of the chemical industry. It plays a vital developmental role by providing chemicals and intermediates as inputs to other sectors of the industry like paints, adhesives, pharmaceuticals, dye stuffs and intermediates, leather chemicals, pesticides etc. Methanol, acetic acid, formaldehyde, pyridines, phenol, alkyl amines, ethyl acetate and acetic anhydride are the major organic chemicals produced in India. Formaldehyde and acetic acid are important methanol derivatives and are used in numerous industrial applications. Phenol is an aromatic compound and derived from cumene, benzene and propylene derivatives. Alkyl amines are used in the manufacture of surfactants. Pyridine derivatives are used in the manufacture of pharmaceuticals. Ethyl acetate is the ester of ethanol and acetic acid and is manufactured for use as a solvent. Acetic anhydride is widely used as a reagent. Natural gas/ naphtha are mainly used as feedstock for the manufacture of these organic chemicals. Alcohol is also an important feedstock for the industry, with sizable production of acetic acid and entire production of ethyl acetate being based on alcohol. 2.1 Global Scenario: A market study on glacial acetic acid discloses a large gap between its demand and supply. The production of acetic acid is sound globally but recent data shows a decreasing producing capacity of Asia worldwide. Most of Acetic Acid produced in Asia is consumed internally and the excess is being imported due to its cheapness in the process involved.

5

A comparison of the demand and supply chart from the 2008 data supports the fact. With the demand of 60%, Asian producers are able to supply only 57% of it. The rest of the demand is being imported from producers from other continents. A study of world consumption of acetic acid in the year 2009 also reveals similar facts with china being the greatest consumer of acetic acid in the market and united states being the second most consumer.

In a recent study, total worldwide production of virgin acetic acid is estimated at 5 Mt/a (million metric tons per year), approximately half of which is produced in the United States. European production stands at approximately 1 Mt/a and is declining, and 0.7 Mt/a is produced in Japan. Another 1.5 Mt are recycled each year, bringing the total world market to 6.5 Mt/a. The two biggest producers of virgin acetic acid are Celanese and BP 6

Chemicals. Other major producers include Millennium Chemicals, Sterling Chemicals, Samsung, Eastman, and Svensk Etanolkemi. Of the total global acetic acid capacity (virgin acid), 44% is in China, followed by 21% for the rest of Asia, 19% in the United States and 6% in Western Europe. These regions make up 90% of total world capacity. 2.2 Indian market: With Asia’s growing contribution to the global chemical industry, India emerges as one of the focus destinations for chemical companies worldwide. With the current size of $108 billion1, the Indian chemical industry accounts for approximately 7% of Indian GDP. The chemicals sector accounts for about 14% in overall index of industrial production (IlP). Share of industry in national exports is around 11%. In terms of volume, India is the third-largest producer of chemicals in Asia, after China and Japan. Despite its large size and significant GDP contribution, India chemicals industry represents only around 3% of global chemicals. Two distinct scenarios for the future of the Indian chemical industry emerge, based on how effectively the Indian industry leverages its strengths and manages challenges. In the base case scenario, with current initiatives of industry & government, the Indian chemical industry could grow at 11% p.a. to reach size of $224 billion by 2017. However, the industry could aspire to grow much more and its growth potential is limited only by its aspirations. In an optimistic scenario, high end–use demand based on increasing per capita consumption, improved export competitiveness and resultant growth impact for each sub-sector of the chemical industry could lead to an overall growth rate greater than 15% p.a. and a size of $ 290 billion by 2017. th

During the XI Five Year Plan period, production of major organic chemicals(including acetic acid) has shown a significant decline due to large volume imports taking place from countries like China, resulting in low operating ratios of ~ 60%. The demand for organic chemicals in India has been increasing at nearly 6.5% during this period and has reached the level of 2.8 million tonnes. The domestic supply has however grown at a slower pace resulting in gradual widening of demand supply gap which was primarily bridged through imports. Domestic production declined at ~ 6% p.a. and imports th grew at a rate of 17-19% p.a. during the XI plan period. Acetic Acid is primarily used for production of purified terephthalic acid (PTA), vinyl acetate monomer (VAM), acetic anhydride and acetate esters. In India, production of acetic acid is th primarily based on alcohol and its demand has grown at 10% during XI Five Year Plan period. At present the consumption is estimated to be 0.6 million tonnes which would reach th nearly 1.0 million tonnes by end of XII Five Year Plan period (2012-2017). The demand growth is primarily driven by end use demand from PTA which is basic raw material for polyester and fiber. There is substantial incremental capacity of PTA, driving demand for acetic acid in this segment. Acetic acid is primarily produced through alcohol or methanol route. Alcohol route in Indian context is gradually becoming unviable due to high prices and limited availability of this feedstock. At present bulk of acetic acid is imported with domestic production accounting for less than 30% of demand. Amongst the six major organic chemicals produced in India Acetic Acid contribute to nearly 2/3rd of Indian basic organic chemical industry. The balance 1/3rd of the organic chemical consumption in the country is accounted for by other wide variety of chemicals. 7

A comparison of import and import volumes of acetic acid in the indian market shows the increasing import of acetic acid at a cheaper rate than the production cost used in indian market.

The above table shows a considerable increase in the import volumes of acetic acid (in metric th 3 tonnes) from the 7 five year plan. The import volume of 340.5 x 10 metric tonnes for the th half of the 11 five year plan period is also comparatively larger than the volume of 389.7 x 3 th 10 metric tonnes in the 10 five year plan. Moreover, the export volumes of acetic acid can also be seen decreasing from the table following the different five year plans. Cheap import has led the chemical manufacturers to reduce their plant capacity utilization. A bar chart of the demand and supply gap in the Indian market shows a constant existing gap. The global demand is also forecasted to reach 11.3 million tons by the year 2015 and hence a great scope for the establishment of a cost-effective process for acetic acid manufacture lies. In this design project we aim to cover the same gap by proposing a low cost process that is mainly used by the manufacturers outside India.

80000 0

Demand And Supply Chart

700000 600000 500000 400000 300000 200000 100000 0

Production Consumpti on

8

Chapter 3 Process Selection The 99.8% pure acetic acid, sold in the name of glacial acetic acid can be manufactured by various processes. Each processes are discussed in detail in the following sections: 3.1 Various available Processes of Synthesis of Acetic Acid: a) By oxidation of Acetaldehyde: Oxidation of acetaldehyde with air or O2 to acetic acid takes place by a radical mechanism with peracetic acid as an intermediate. The acetyl radical, formed in the initiation step, reacts with O2 to make a peroxide radical which leads to the foris mation of peracetic acid. Although peracetic acid is formed by homolysis of the peroxy group, it is assumed that the peacetic acid preferentially reacts with acetaldehyde to give α-hydroethyl peracetate, which then decomposes through a cyclic transition state to two moles of acetic acid. If a redox catalyst is used for the oxidation of acetaldehyde to acetic acid, it not only serves to generate acetyl radicals initiating the oxidation but also accelerate the decomposition of peracetic acid. The resulting acetoxy causes chain branching. The usual catalysts used are solutions of Co and Mn acetates in low concentration (upto 0.5 wt% of the reactant mixture). 2 CH3CHO + O2 → 2 CH3COOH The mechanism of the process can be graphically represented as:

In Hoechst Process, the oxidation is usually done with oxygen, which operates o continuously at 50-70 C in the oxidations towers of stainless steel (bubble columns) o with acetic acid as solvent. Temperatures of atleast 50 C are necessary to achieve an adequate decomposition of peroxide and thus a sufficient rate of oxidation. The heat of reaction is removed by circulating the oxidation mixture through a cooling system. Careful temperature control limits the oxidative decomposition of acetic acid to formic acid, CO2, and small amounts of CO and H2O. Acetic acid selectivity reaches 95-97% (based on CH,CHO).

9

Besides CO2 and formic acid, the byproducts include methyl acetate, methanol, methyl formate, and formaldehyde, which is separated by distillation. b) By Oxidation of Alkanes and Alkenes: C, to C, hydrocarbons are the favoured feedstocks for the manufacture of acetic acid by oxidative degradation. They can be separated into the following groups and process modifications: 1. n-Butane (Hoechst Celanese, Huls, UCC) Acetic acid can be prepared by uncatalyzed oxidation of n-Butane with oxygen in a o

bubble column at 15-20 bar and 180 C using liquid oxidation products as reaction mixture. A wide range of by-products are formed including Acetaldehyde, acetone, methyl ketone, ethyl acetate, formic acid, propionic acid and butyric acid. Hence the conversion is limited in this process to 2% to prevent the formation of secondary products (about 60% selectivity). C4H10 + 5/2O2

2CH3COOH + H2O

2. n-Butenes (Bayer, with sec-butyl acetate as intermediate; Huls directly) C4H8 + 2O2

2CH3COOH o

In this process, n-Butene is oxidized at 200 C in a liquid phase consisting essentially of crude acetic acid. However the product acetic acid is very dilute and needs to be concentrated. The selectivity in this process reaches 73% at 75% conversion. c) Anaerobic fermentation Species of anaerobic bacteria Species of anaerobic bacteria, including members of the genus Clostridium or Acetobacterium can convert sugars to acetic acid directly, without using ethanol as an intermediate. The overall chemical reaction conducted by these bacteria may be represented as: C6H12O6 → 3 CH3COOH These acetogenic bacteria produce acetic acid from one-carbon compounds, including methanol, carbon monoxide, or a mixture of carbon dioxide and hydrogen: 2 CO2 + 4 H2 → CH3COOH + 2 H2O This ability of Clostridium to utilize sugars directly, or to produce acetic acid from less costly inputs, means that these bacteria could potentially produce acetic acid more efficiently than ethanol-oxidizers like Acetobacter. However, Clostridium bacteria are less acid-tolerant than Acetobacter. Even the most acid-tolerant Clostridium strains can produce vinegar of only a few per cent acetic acid, compared to Acetobacterstrains that can produce vinegar of up to 20% acetic acid. At present,it remains more cost-effective to produce vinegar using Acetobacter than to produce it using Clostridium and then concentrate it. As a result, although acetogenic bacteria have been known since 1940, their industrial use remains confined to a few niche applications. 10

d) Carbonylation of Methanol: The Carbonylation of methanol is mostly done in the presence of rhodium catalyst combined with iodine and is considered as an active catalyst system for the carbonylation. The reaction is as shown: CH3OH + CO → CH3COOH The process involves iodomethane as an intermediate, and occurs in three steps as shown 1. CH3OH + HI → CH3I + H2O 2. CH3I + CO → CH3COI 3. CH3COI + H2O → CH3COOH + HI This process will be discussed in detail in the next section. 3.2 The Selected Process(Cativa Process): Production of Acetic Acid by carbonylation of methanol used to be done by a process named as Monsanto Process where Rhodium catalyst was used as an active catalyst with iodide of metals such as lithium. The process was carried at 50-60 bar pressure and at a temperature of o 150 to 200 C giving a high selectivity of 99% based on the methanol feed. But B.P chemicals came up with a process named as Cativa that used Iridium catalyst with Hydrogen iodide as the active catalyst in the system. This overcame many limitations of the Monsanto process as • • • •

Lower water concentration was obtained in the product compared to Monsanto process. The process now could be carried at a comparatively lesser pressure and temperature. The number of distillation units was reduced. Iridium is cheaper than Rhodium, hence reducing the cost of production to a large extent. o

The cativa Process is carried 30-40 bar pressure and at a temperature of 150-180 C giving a high selectivity of 99% (based on the methanol feed). The reactions are: Main reaction: CH3OH + CO → CH3COOH

∆H= -138kJ/mol

Side Reactions: CH3OH + CO  C2H5COOH CH3COOH + CH3OH  CH3COOCH3 11

3.3 Advantages of selected process over other processes: The selected process has following advantages over other processes: • • • •

•

The selectivity of cativa process is 99% as compared to the 90% of acetaldehyde and even lesser in other processes. The operation is cheaper than other processes. The methanol used as the feed is comparatively cheaper than the feed in other processes. Fermentation process which also seems viable in terms of operation involves a greater upstream and downstream cost for sterilisation of equipment to provide an environment for microbial growth. The liquid phase reaction is easy to control.

3.4 Process Description: The carbonylation process of methanol is carried out in a continuous stirred tank reactor. The methanol(stream 1) and carbon monoxide(stream 2) is fed to the reactor from the bottom as feed. The carbon monoxide is compressed in a compressor to 30 bar before inlet to the reactor to ensure the reaction is occurs in the liquid phase. The reaction is highly exothermic and hence a cooling jacket is provided outside the reactor to ensure that the proper o

temperature of 150 C is maintained in the reactor. The initial heat required to ignite the reaction is mainly through passage of steam through the jacket. As the reaction starts, the heat of reaction is used to continue the reaction and excess heat is removed. The unreacted gases are vented out through a scrubber (stream 7) which also works as a preheater for a part of methanol feed. A part of methanol feed (stream 3) is preheated from o ambient temperature to 60 C as it comes out of the scrubber (stream 5). Another work that is performed by the side stream is the stripping of entrained liquid in the vent gases and it also ensures that the loss of product with these gases is minimal. The vent gases generally exit the o scrubber at 50 C to the atmosphere. The product stream from the CSTR, i.e. stream 6, rich in acetic acid and containing small concentrations of methanol, by-product propionic acid and water is made to pass through the throttling valve to the flash tank where the product is flashed to a reduced pressure of 1 atm. The product from the flash tank is fed to the light end distillation column at a temperature of o 52 C (stream 9). A recycle stream 8 is pumped from the bottom of the flash tank back to the CSTR. In the light end distillation column the feed containing acetic acid, water, propionic acid, methanol and methyl acetate is distilled to separate light ends (methyl acetate and methanol) from the bottom stream 11 containing acetic acid, propionic acid and little concentration of water. The acetic acid is generally 87.6 % by wt. which is further purified in the acid purification unit to obtain the required product. The feed stream 9 enters at a temperature of o o about 52 C and the bottom stream leaves the end column at a temperature of 97 C. 12

o

In the acid purification unit, the stream 11 enters at a temperature of 97 C. The higher boiling component propionic acid is obtained from the bottom of the distillation tower where a o temperature of 123 C is maintained. Glacial Acetic acid (99.8% by wt.) is obtained from the o top of the distillation tower, maintained at 118 C. Enclosed: Process Flow Sheet of the Process.

13

Chapter 4 Material Balance From literature, selectivity to acetic acid(AA) = 99% (based on Methanol). Yield of Acetic Acid = 90% Basis: 100 ton per day of Glacial Acetic Acid (product) It is known that 99.8% acetic acid by weight is to be obtained as the overhead product and the 93.5(wt %) propionic acid is obtained as bottom product with .09(wt%) of acetic acid in it and balance as water. nd

Hence, for 2

Distillation column (Acetic Acid Purification Column)

We have, xD=0.998, xB=0.00085, xF=0.926 (all in wt%) and D= 100 TPD = 4166.67 kg/hr of AA. Taking wt. per hour basis of acetic acid, B = D*(xF-xD)/(xB-xF) = 4166.67*(0.926-.998)/(0.00085-0.926) = 324.27 kg Thus, F = D + B = 4490.94 kg. Hence, the weight and wt. fraction can be arranged in the table as: Compone nts H 2O CH3COO H C 2H 5COO Total

Fee wt% d wt

Botto wt% m wt

0.376 17.83576 1.636 8.3333333

Overhead wt% wt

9.502431 0.2

87.600 4158.828 0.08521 0.494943 4158.3333 100 4747.521 100 580.8542 4166.6667

99.8 100

st

And, for 1 Distillation column (Light End Distillation Column) We have, xD=0.00839, xB=0.926, xF=0.915 (all in wt%) and B= 4490.94 kg D= B*(xB-xF)/(xF-xD) = 4490.94*(0.926-0.915)/( 0.915-0.00839) = 53.139 kg Thus, F= D + B = 4544.079 kg

14

The weight and wt. fraction values can be arranged in the tabular column as: Compone nts CH3OH H 2O CH3COOH CH3COOC H3 C 2H 5COO Total

Fee wt% d wt

Overhead wt% wt

0.006 0.320521 0.217 0.430373

Bottom wt% Wt 0.376

3.325 164.4556

17.83576 84.127 4160.489 0.839 1.661085 87.600 1.152 56.955 12.024 570.8568 100 197.9845 100 100 4945.505 4747.521

Now, as assumed remaining methanol is converted to methyl acetate during the throttling operation. Hence the amount of acetic acid remains constant and can be used to find the moles(and thus the wt.) of methanol to be used. Main Reactions: CH3OH + CO  CH3COOH

Side Reactions:

CH3OH + ½ CO  C2H5COOH CH3OH + CH3COOH  CH3COOCH3

Material balance for the distillation column, Let the moles of methanol taken be x kmol. Also, yield = conversion * selectivity ∴ we have conversion = 90.91%. Taking mole balance on the reactor itself, we have: CH3OH

+

CO

x kmoles of MeOH

+ x kmoles of CO



CH3COOH

 0.9091*x kmoles of AA

Unreacted MeOH = (1-.9091) * x = 0.0909 * x kmoles Hence, this methanol is used in production of methyl acetate in the flash tank during the throttling process. But it is known that we obtain 1000 ppm of methanol from the tank output. Thus, Methanol consumed in flash tank = 0.0909 * x – 0.001 * x = 0.0899 * x kmoles CH3OH

+

CH3COOH

0.0899 * x kmoles of reactants



CH3COOCH3

+

H2O

0.0899 * x kmoles of products

∴ total CH3COOH to light end distillation feed = 0.9091 * x – 0.0899 * x = 0.8192 * x kmoles 15

But, the kmoles of Acetic acid in the flash tank output = 69.28 kmoles Hence, actual methanol requirement = 69.28/0.8192 = 84.57 kmoles Also, total water is produced in propionic acid and methyl acetate reaction. ∴ Total water produced = 0.01* 0.9091 * 84.57 + 0.0899 * 84.57 = 8.37 kmoles Now, taking considerations of 0.5(wt. %) of water in methanol feed we have, ∴ Total water in light end distillation column feed = 9.13 kmoles Assuming carbon monoxide is taken 7.2% in excess than the methanol feed. ∴ moles of carbon monoxide = 107.2% * 84.57 = 90.66 kmoles Similarly, the moles of propionic acid and methyl acetate were also calculated and the value is presented in the table below. From the total moles, moles % = mole of component * 100/ total moles of mixture From the mole %, wt % can be calculated as, wt. % of component i = (mole fraction of i * molar wt. of i)/total wt. of mixture. Hence, obtaining any one values from %wt., wt. or mol. or mol.%, other values could be easily found out and the same is used to calculate the following table. Thus from the calculations, Components

wt%

CSTR Output wt kmol

mol%

Flash tank to DC-1 Feed wt% wt kmol mol%

CH3OH H2O

4.980

248.4213

7.69

8.85

0.006

0.320521

0.01

0.01

CH3COOH

0.555

27.69448

1.52

1.76

3.325

164.4556

9.13

10.52

CH3COOCH3 93.313

4654.45

76.88

88.51

84.127 4160.489 69.28

79.82

11.390 563.2849

7.60

8.76

1.152

0.77

0.89

C2H5COOH Total

1.151

57.41545

0.77

0.89

100

4987.981

86.87 100.00

100

56.955

4945.505 86.79

100.00

Considering overall material balance assuming the reactor, scrubber and flash tank as a complete system we have, Mass of gas in vent = mass of methanol in + mass of carbon monoxide in – mass of feed in light end distillation column ∴ Mass of vent from scrubber = 2724.33 + 2539.43 – 4945.51 = 318.25 kg Also, 20% in excess promoter, i.e. Hydrogen Iodide and Iridium Catalyst is assumed to be used in the reactor. Hence, weight of catalyst = 20% excess of feed methanol = 12981.36 kg = 12.98 tonnes This catalyst is recycled back to the reactor and hence is not required to be fed again and again.

16

Chapter 5 Energy Balance Enthalpy Balance on Streams in and out of the Reactor system: o

Feed in (at a temperature of 30 C): Total Enthalpy of stream 1 in = mass of methanol * Sp. Enthalpy of methanol + mass of water * Sp. Enthalpy of water = 2710.71 * 7536.23 + 13.62 * 15856.6 = 20644518.73 kJ/hr. Total Enthalpy of stream 2 in = mass of CO * Sp. Enthalpy of CO = 2539.43 * 3941.28 = 10008591.85 kJ/hr. Total Enthalpy of recycle stream 7 in = ∑ mass of component i*Sp. Enthalpy of component i The balance is shown in the following tabular column: Components Acetic Acid Propionic Acid Methanol Water

o

Enthalpy(kJ/kg) @30bar &150 C Kg/hr kJ/hr 7698.63 35.73 285207.11 6534.98 7072.02 15349.07

0.49

3340.79

0.00

20.75

1.41

22397.09

Total 42.48 339960.90 ∴ Total Enthalpy of feed in = 20644518.73 + 10008591.85 + 339960.90 = 31004047.435 kJ/hr = 31004.047 MJ/hr o Feed out (at a temperature of 150 C and 30 bar): Total Enthalpy of stream 6 in = ∑ mass of component I * Sp. Enthalpy of component i o Components Enthalpy(kJ/kg) @30bar &150 C Kg/hr kJ/hr 7698.63 Acetic Acid 4654.45 32575354.10 Propionic Acid Methanol Water Total

6534.98 7072.02 15349.07

57.42

341098.78

248.42

1597128.46

164.46

2294763.71

5124.74 36808345.05 17

Total Enthalpy of Vent gases out of the scrubber = mass of gases * Sp. Enthalpy of gases = 318.25 * 3941.28 = 1254311.25 kJ/hr For the methanol side stream to the scrubber, Assuming the stream 5 (side stream from scrubber) is entering the reactor at a temperature of o o 60 C and stream 8 (vent gases) is at a temperature of 50 C. Let the mass of methanol transferred to the side stream 3 by m kg. ∴ Heat gained by methanol stream 3 = Heat lost by gases stream 4 ∴ m * Sp. Enthalpy change of methanol stream = mass of vent gases * (Sp. o o Enthalpy of gas at 150 C – Sp. Enthalpy of gas at 50 C) ∴ m = 318.25 * (3909.995 – 3816.51)/(7536.23-7430.636) = 281.74 kg 3 From literature, heat of reaction, ∆H = -138 kJ/mol = -138 x 10 kJ/kmol ∴ Heat required by steam or coil to start the reaction = 138 x 103 * 76.88 (kmoles/hr of acetic acid) = 10609965.598 kJ/hr Making overall Energy Balance on the reactor we have, Energy in + Energy generated = Energy out + Energy Accumulated ∴ Energy Accumulated = Energy in + Energy generated - Energy out = 31004047.435 + 10609965.598 + 38062656.299 = 3551356.734 kJ/hr o Assuming the cooling water is available from the cooling tower at 17 C and leaves the o reactor jacket at 80 C, this cooling water will be used to remove the extra heat accumulated in the reactor. ∴ Heat gained by the cooling water = heat accumulated in the reactor ∴ Mass of cooling water required by the reactor = heat accumulated/(4.18*(80-17)) = 13485.823 kg/hr

18

Enthalpy Balance about the Light End Distillation Column: Total Enthalpy of Feed stream 8 in = ∑ mass of component i*Sp. Enthalpy of component i The balance is shown in the following tabular column: Feed stream 8: o

Components Enthalpy(kJ/kg) @52 C Kg/hr kJ/hr 644.80 Acetic Acid 4160.49 2682673.08 692.89 Propionic Acid 39463.68 56.95 810.77 Methanol 259.87 0.32 461.89 Methyl acetate 563.28 260176.10 2211.05 Water 164.46 363619.70 Total 4945.51 3346192.44 Similarly, the enthalpy balance for the overhead stream 9 and bottom stream 10 is written as: Overhead stream 9: o

Components Enthalpy(kJ/kg) @62 C Kg/hr kJ/hr 666.72 Acetic Acid 1107.47 1.66 838.35 Methanol 360.81 0.43 482.23 Methyl Acetate 195.89 94465.13 Total 197.98 95933.41 Bottom Stream 10: o

Components Enthalpy(kJ/kg) @97 C Kg/hr kJ/hr 747.32 Acetic Acid 4158.83 3107962.08 796.32 Propionic Acid 570.86 454586.49 2399.71 Water 17.84 42800.70 Total 4747.52 3605349.27 Cooling Water Requirement: Amount of cooling water used by the condenser = mass of vapour being condensed * Sp. (assuming reflux ratio same Enthalpy / (Sp. Enthalpy change as distillation column 2) of cooling water) ∴ mass of cooling water required = 5.1 * 197.98 * 301.5 / (4.18 * (25-17)) = 908.91 kg 19

Steam Requirement: Taking overall energy balance over the distillation column we have, Feed Enthalpy + Enthalpy of steam = Overhead Enthalpy + Bottom Enthalpy + Heat Removed by Cooling Water ∴ Total Enthalpy provided by steam = Overhead Enthalpy + Bottom Enthalpy + Heat Removed by Cooling Water - Feed Enthalpy = 95933.41 + 3605349.27 + 304435.27 – 3346192.44 = 659525.51 kJ/hr Assuming 5% loss of energy from the column, Steam should provide energy = (1+5%) of 659525.51 kJ/hr = 1.05 * 659525.51 = 692501.786 kJ/hr o

o

Now, assuming steam enters at 120 C and leaves as saturated liquid at 100 C we get, Mass of steam = Heat Required / Sp. Enthalpy change of steam = 692501.786 / (1.9*(120-100)) = 300.7 kg/hr Enthalpy Balance about the Acetic Acid Purification Column: Total Enthalpy of Feed stream 10 in = ∑ mass of component i*Sp. Enthalpy of component i The balance is shown in the following tabular column: Feed stream 10: Components Enthalpy(kJ/kg) @97oC Kg/hr kJ/hr 747.32 Acetic Acid 4158.83 3107962.08 796.32 Propionic Acid 570.86 454586.49 2399.71 Water 42800.70 17.84 Total 4747.52 3605349.27 Similarly, the enthalpy balance for the overhead stream 12 and bottom stream 11 is written as: Overhead stream 12: o

Components Enthalpy(kJ/kmol) @118 C kmol/hr kJ/hr 3322358.33 47980.18 Acetic Acid 69.24 20737.89 44131.17 Water 0.46 Total 69.71 3343096. 21

20

Bottom Stream 10: o

Componen Enthalpy(kJ/kmol) @123 C kmol/hr kJ/hr ts 48742.8 Acetic Acid 0.01 401.73 4 63883.9 Propionic 7.71 492293.0 3 Acid 45214.0 Water 0.53 623849.1 4 9 Tota 8.24 516543. l 98

Cooling Water Requirement: Amount of cooling water used by the condenser = mass of vapour being condensed * Sp. (assuming reflux ratio same Enthalpy / (Sp. Enthalpy change as distillation column 2) of cooling water) ∴ mass of cooling water required = 5.1 * 69.71 * 240.32 / (4.18 * (25-17)) = 2554.98 kg Steam Requirement: Taking overall energy balance over the distillation column we have, Feed Enthalpy + Enthalpy of steam = Overhead Enthalpy + Bottom Enthalpy + Heat Removed by Cooling Water ∴ Total Enthalpy provided by steam = Overhead Enthalpy + Bottom Enthalpy + Heat Removed by Cooling Water - Feed Enthalpy = 3343096.21 + 516543.98 + 85438.50 - 3605349.27 = 339729.42 kJ/hr Assuming 5% loss of energy from the column, Steam should provide energy = (1+5%) of 339729.42 kJ/hr = 1.05 * 339729.42 = 356715.891 kJ/hr o

o

Now, assuming steam enters at 120 C and leaves as saturated liquid at 100 C we get, Mass of steam = Heat Required / Sp. Enthalpy change of steam = 356715.891 / (1.9*(120-100)) = 9387.26 kg/hr Evaluating Total Steam and Cooling water requirement of Overall Plant: Total Cooling Water required = CW in reactor + CW in DC-1 + CW in DC-2 = 13485.823 + 908.91 + 2554.98 = 16949.713 kg/hr = 406.793 TPD

21

And, Total Steam Required

= Steam in DC-1 + Steam in DC-2 = 300.7 + 9387.26 = 9687.96 kg/hr = 232.51 TPD

22

Chapter 6 Equipment Design 6.1 Number of Stages Calculation (McCabe Thiele Method): From the material balance, we have Feed to the distillation tower = 4158.828 kmol/ hr of acetic acid + 17.83576 kmol / hr of water + 570.8568 kmol/ hr of propionic acid = 4747.521 kmole/ hr Top product from the distillation tower is 99.8 wt% acetic acid. Bottom product from the distillation tower is 98.288 wt% propionic acid . Feed: Flow rate of feed = 4747.521 kmol/ hr. Mol fraction of acetic acid in feed = 4158.828 / 4747.521 = 0.8884 Average molecular weight of feed = 60.91 kg/kmol Distillate: Flow rate of distillate = 4166.6667 kmol/hr Mol fraction of acetic acid = 0.99336 Average molecular weight of distillate = 59.77 kg/kmol . Residue: Flow rate of residue = 580.8542 kmol/hr. Mol fraction of acetic acid = 0.001 Average molecular weight = 70.48 kg/kmol. o

The feed to the distillation column is cold liquid at 97 C. q= 1+(Cpl(Tb-Tf)/ λ) ∴ q=1.11 Feed line is a line passing through xF and having a slope of 10 and intercept -8.0764 Now, from x-y plot Rmin / (Rmin + 1) = (xD-y`)/(xD-x`) ∴ Rmin =2.734 Takin Optimum reflux ratio as 1.5 times of Rmin, we have R= 1.5*2.734 = 4.1 From the equilibrium curve we obtain, Number of ideal stages, Ni=18 23

Assuming efficiency 80% Number of real stages, Na = 18/0.8 = 21(approx.) 6.2 Internal design estimation: From the McCabe Thiele curve, we get Slope of the bottom operating line = 1.01 Slope of top operating line = 0.809 From the material Balance, Feed =4747.51/60.91= 77.95 kmol/h Top product Vapor rate, V = D*(1+R)=69.71(1+4.1) = 355.521 kmol/h Liquid rate = L = V*Slope of top operating line = 287.616 kmol/hr An overall mass balance gives: Bottom product, B=8.24 kmol/h Slope of the bottom operating line = Lm`/Vm` =1.01 Vm`= Lm`-B Lm`= 1.01Vm` Vm`= 1.01Vm`-B Vm`= 8.24/0.01 = 824 kmole/hr Lm`= 824 + 8.24 = 832.24 kmole/hr Top: ρv= 3.038 kg/m

3

ρl= 934.360 kg/m

3 -3

Surface tension, σT=27*10 Bottom: ρv= 3.119 kg/m

3

ρl= 905.346 kg/m

3 -3

Surface tension, σB =32.3*10 Calculating flooding velocity:

FLV bottom = 1.01 (3.119/905.346) FLV top = 0.809 (3.038/934.360)

1/2

1/2

=0.0512

=0.046 24

Fig: Flooding Velocity, sieve plates (Fig 11.27 from Chemical Process Design by R.K Sinnott) Taking plate spacing as 0.7m, from the above figure, Base K1=0.12 Top K1=0.13 Using correction for surface tension,

We get, -3

0.2

Base K1 = (32.3*10 /0.02) *0.12 =0.132 -3 0.2 Top K1 = (27*10 /0.02) *0.13 =0.136 Calculations of flooding velocity:

1/2

∴ Base uf = 0.132 (905.346-3.119/3.119) =2.248m/s 1/2 ∴ Top uf =0.138 (934.360-3.038/3.038) =2.4162m/s

25

Design for 85 per cent flooding at maximum flow rate ∴ Base uv=2.245*0.85 =1.90825 m/s ∴Top uv =2.4162 *0.85 =2.0537 m/s

Maximum volumetric flow-rate: 3

∴ Base = 824*70.46/3.119*3600 =5.1722 m /s ∴ Top =355.521*59.77/3.038*3600 =1.9429 m3/s

Net area required: 2

∴ Base = 5.1729/1.90825 = 2.71 m

∴ Top = 1.9429/2.0537 = 0.946 m2

As first trial take downcomer area as 12 per cent of total. Column cross-sectioned area: 2 Base =2.71/0.88 =3.0795 m 2 Top =0.946/0.88 =1.075 m Column Diameter : 1/2

Base = (3.0795*4/3.14) =1.98m 1/2 Top = (1.075*4/3.14) =1.17m As column is of uniform diameter, using same diameter above and below feed We take Column diameter =1.98m Liquid flow pattern -2

3

Maximum volumetric liquid rate=832.24*70.48/3600*905.346 =1.79*10 m /s Using the liq flow rate, a single pass tray can be selected (Ref. fig 11.28 R.K. Sinnott) Provisional plate design: Column diameter, Dc =1.98 m 2 Column area, Ac = 3.0795 m 2 Down-comer area, Ad =0.12*0.50 = 0.36954 m , at 12 per cent 2 Net area, An = Ac -Ad=3.0795- 0.36954= 2.70996 m 2 Active area, Aa = Ac -2Ad =3.0795 -2*0.36954= 2.34042 m 2 Hole area, Ah (take 10 per cent Aa as first trial) = 0.234042 m Weir length: the chord/weir length will normally be between 0.6 and 0.85 of the column diamter. Best intial guess would be 0.76 of column ia. Therefore weir length = 0.76*1.98 =1.5048 26

Take ,weir height = 70mm Hole size =5 mm Plate thickness = 5 mm Check for Weeping: Maximum liquid rate=832.24*70.48/3600 =16.29 kg/sec Minimum liquid rate, at 70 per cent turn-down = 0.7*16.29 =11.40 kg/sec Height of liquid crest over the weir

Maximum how at maximum liquid rate =39.22 =39 mm liquid(approx.) Minimum how at minimum liquid rate =31 mm liquid at minimum rate hw +how =70+ 31=101mm

From above figure K2=31 27

Minimum vapour velocity

uh(min) =7.157 m/s Actual minimum vapour velocity =0.7*5.1729/0.234042 =15.47m/s Thus the minimum operating rate will be well above weep point. Plate pressure drop: Dry plate drop Maximum vapour velocity through holes uh =5.1729/0.234042 =22.1m/s From Figure below, for plate thickness/hole diameter= 1, and Ah/Ap = Ah/Aa = 0.1, C0 = 0.84

28

hd=121mm liquid hr = 12.5*103/905.346=13.8mm total plate pressure drop= ht = hd + hr + hw + how = 244mm liquid Downcomer liquid back up: Downcomer pressure loss: The down comer area and plate spacing must be such that the level of the liquid and froth in the down comer is well below the top of the outlet weir on the plate above. If the level rises above the outlet weir the column will flood. Hap =hw-10 = 60 mm Aap=0.60*60*10-3 =0.036

Hdc =41.46mm Hb=0.384 m liquid

0.3840.1 ∴ acceptable

6.3 Plate Design: We are considering sectional construction plates Allowing 125 mm unperforated strip round plate and 125 mm wide calming zone From Figure below, at lw/Dc =1.5048/1.98 = 0.76 o Φ=99 0 angle subtended by the edge of the plate D 180 -99 = 81 -3 mean length, unperforated edge strips =(1.98-125*10 )3.14*(81/180) =2.621m 2 area of unperforated edge strips 125*10-3*2.621=0.327625m mean length of calming zone, approx. = weir length * width of unperforated strip -3 = 1.5048 *125*10 =1.6298 m -3 2 area of calming zones =1.6298*125*10 =0.40785m 2 total area for perforations, Ap =2.34042-0.40785-0.327625=1.604945m Ah/Ap = 0.234042/1.604945= 0.146 From Figure , lp/dh = 2.6; satisfactory, within 2.5 to 4.0.

30

Number of holes -5 2 Area of one hole = 1.964*10 m -5 Number of hole = 0.234042/1.964*10 =11925 Design pressure =1atm=1.01325 bar 0.101325N/mm Design pressure, take as 10 per cent above operating pressure Therefore design pressure =0.101325*1.1 =0.1114575 N/mm Typical design stress =145 N/mm2 Cylindrical section:

3

E = (0.1114575*1.98*10 )/(2*145-0.1114575) = 0.76mm Say 1mm

31

Choosing Domed head and calculating its thickness: 1. Try a standard dish head(torisphere) Crown radius Rc=Di=1.98m Knuckle radius =0.06*1.98=0.1188m Assuming joint efficiency, J=1

Cs=1.77

∴ Thickness of the torispherical head e =

1.346mm 2. Trying standard ellipsoidal head, major to minor axes ratio =2:1

∴ thickness of ellipsoidal head, e = 0.76(Say 1mm)

Hence we have ellipsoidal head as probably the most economical. ∴ Taking same thickness as wall 1 mm. from column design: Height, between tangent lines= 15 m Diameter=1.98m Skirt support, height =3 m 21 sieve plates, equally spaced Material of construction, stainless steel, design stress 145 N/mm2 at design temperature Operating pressure 1.01325 bar Vessel to be fully radiographed (joint factor 1)

32

Design pressure take 10% above operating pressure =1.01325*1.1*1/10=0.1114575N/mm

2

3

Minimum thickness required for pressure loading = (0.1114575*1.98*10 )/(2*145-0.1114575) = 0.76 A much thicker wall will be needed at the column base to withstand the wind and dead weight loads. As a first trial, take minimum thickness as 5mm Approximate weight of cylindrical vessels with domed end is calculated as: For steel vessel, we have, Cv = 1.15(vessels with plates) -3

Dm = 1.98+5*10 =1.985m Hv=15m T=5mm Wv=45.44kN Obtaining weight of plates, 2

2

Plates area=3.14*1.98 /4 =3.078m

Weight of 1 plate =1.2*3.078=3.6936 kN For 21 plates, total weight =21*3.6936=77.56kN ∴ Total wt=45.44+77.56=123kN

Wind loading Dynamic wind pressure=1280N/m

2

-3

Mean diameter=1.98+2(5*10 ) = 1.99 m Loading (per linear metre)=1280*1.99 = 2547.2N/m 2

Bending moment at the bottom tangent line Mx = 2547.2*15 /2 =286560N/m 33

Analysis of stress at the bottom tangent line,

3

2

3

2

σL=0.1114575*1.98*10 /4*5=11.03 N/mm σh=0.1114575*1.98*10 /2*5=22.06 N/mm Dead weight stress calculation,

2

σw=3.9468 N/mm (compressive) Bending stress Output dia, Do=1.98*103+2*5=1990mm

10

Moment of inertia, Iv=1.535*10 mm

σb=18.575 N/mm

4

2

∴ Resultant longitudinal stress=

σz (upwind) = σL-σw+σb =25.6582 N/mm

2

σz (downwind) = σL-σw+σb =-11.4918 N/mm

2

Greatest difference between the principle stresses will be on downside = 2

22.06-(-11.4918)=33.5518 N/mm which is well below allowable design stress 34

Check elastic stability (buckling)

σc = 50.25 N/mm

2

The maximum compressive stress will occur when the vessel is not under pressure 3.9468+18.575 = 22.5218 > 50.25, well below the critical buckling stress. Skirt support : Try a straight cylindrical skirt (θ=90) of plain carbon steel, design stress 135 N/mm2 2

and Young’s modulus 200,000 N/mm at ambient temperature. Maximum dead weight will occur when the vessel is full of water 2

Approximate weight = (3.14*1.98 *15*1000*9.81)/4 = 452.856kN =453 kN ∴ Weight of vessel = 123kN ∴ Total weight = 453+123=576 kN ∴ Wind loading =2.5472*(15+3)2/2 =412.6464 kNm

Taking initial skirt thickness same as bottom thickness 5mm

σbs 35

2

σbs =26.74 N/mm

W(test)=453kN σws(test)=14.54 N/mm

2

W(operating)=123kN σws(operating)=3.946 N/mm

2

Maximum σs(compressive)=26.71+14.54=41.25 N/mm Maximum σs(tensile)=26.71-3.964=22.746 N/mm

2

2

Take J=1 The skirt thickness should be such that under the worst combination of wind and dead-weight loading the following design criteria are not exceeded:

22.746

125

41.25

63.13

Both criteria are satisfied, add 2 mm for corrosion, gives a design thickness of 7mm

36

Base ring and anchor belts: Scheiman gives the following guide rules which can be used for the selection of the anchor bolts: 1. Bolts smaller than 25 mm (1 in.) diameter should not be used. 2. Minimum number of bolts 8. 3. Use multiples of 4 bolts. 4. Bolt pitch should not be less than 600 mm (2 ft). Approximate pitch circle diameter =2.2m Circumference of bolt circle=2200 No of bolts required at minimum bolt spacing=2200 /600=11.51 Closest multiple of 4=12 the bolt area required is given by:

Where, Ab =area of one bolt at the root of the thread, mm2, Nb = number of bolts, 2

fb =maximum allowable bolt stress, N/mm ; typical design value 125 N/mm2 (18,000 psi), Ms = bending (overturning) moment at the base, Nm, W = weight of the vessel, N, Db = bolt circle diameter, m. Ms=412.6464kNm Ab=418mm

2

Bolt root diameter=(418*4/3.14)=23mm 37

The total compressive load on the base ring is given by:

Fb=153.868kN/m Take bearing pressure 5N/mm 3

2

3

Lb=153.86*10 /5*10 =30.7736mm It is not too large so a cylindrical skirt can be used 3

Bolt spacing=3.14*2.2*10 /12=575mm Use M24 bolts (BS 4190:1967) root area = 418 mm

2

Actual width require=Lr+ts+50 =76+7+50=133mm Where Lr =the distance from the edge of the skirt to the outer edge of the ring(from figure 13.30,coulson th

Richardson volume 6( 4 edition)). Ts=skirt thickness actual bearing pressure on base: 3

3

fc` = 153.868*10 /133*10 =1.156 N/mm

2

base ring thickness,

Hence, the thickness of base ring = tb=11.96=12 (approx.)

38

Chapter 7 COST ESTIMATION 7.1 Cost of Distillation tower: Trays towers: The cost of tray towers can be calculated using the following formulae, C = 1.218 [ f1*Cb + N*f2*f3*f4*Cr + Cp1 ], where the constants can be calculated as, 2

Cb= 1.218 exp [ 7.123 + 0.1478 (ln W) + 0.02488 (ln W) + 0.01580 (L/D) ln (Tb / Tp)] Cr= 457.7 exp(0.1739 D) , 2 < D