Btech.project. TiO2 production

PRODUCTION OF ACETYLENE FROM CALCIUM CARBIDE

CONTENTS

CHAPTER 1

Introduction about the product……………………………………………..……….2

CHAPTER 2

Market Survey……………………………………………………………………..…6

Worldwide & Domestic Production………………………………………..…7

Past Supply and Present Demand…………………………………………..…8

Projected Demand……………………………………………………………..9

Pricing Demand……………………………………………………………..…9

CHAPTER 3

Literature Survey.………………………………………………………..……………9

CHAPTER 4

Product properties & uses…....……………………………………………………..12

CHAPTER 5

Different manufacturing processes……………………..….…………………...…..15

5.1. Chemical Reaction Process………………………..….……………….………15

5.2 Thermal Cracking Process…………………………..……………..…………..16

CHAPTER 6

Selection of process with suitable

justification…………………………………..…20

CHAPTER 7

Detailed description of selected process with flow diagram……………………………………………………………………………….21

7.1.Acetylene Reactor………………………………………………………….….21

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Heat Exchanger……………………………………………………….…….….21

Low pressure drier…………………………………………………….…….…..22

Purifier…………………………………………………………………….…... 22

Ammonia Scrubber………………………………………………………….…..22

Acetylene Compressor……………………………………………………….….22

. High Pressure drier………………………………………………………….…..23

Filling Manifold…………………………………………………...………….…23

CHAPTER 8

Mass Balance………………………………………………………………...…….….…24

8.1 Material Balance across generator……………………………………………..….24

Material Balance across Condensor and pressure drier…………………….….…26

Material Balance across Purifier+ High pressure drier+ scrubber………………..26

Overall Material Balance……………………………………………………...….29

CHAPTER 9

Energy Balance……………………………………………………………………….…..30

9.1 Assumptions………………………………………………………………….………..30

CHAPTER 10

Design of Major Equipments……………………………………………………….……34

Design of Reactor………………………………………………………….……..34

Design of Heat Exchanger………………………………………………….…….36

Design of Scrubber………………………………………………………..………41

Design of compressor……………………………………………………..………43

CHAPTER 11

Economic Evaluation…………………………………………………………………..…53

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Estimation of Capital Investment Costs…………………….……………………53

Direct Costs………………………………………….……….……………..53

Indirect Costs……………………………………………….………...…….55

Fixed Capital Investment………………………………….………………..56

Working Capital Investment…………………………….…………….……56

Total Capital Investment……………………………….……………...……56

Estimation of Total Product Cost…………………………………………………57

Manufacturing Cost…………………………………………………………57

General Expenses……………………………………………………………59

Gross Earnings/Income…………………………………………………………….60

Rate of Return……………………………………………………………………..61

Payback Period…………………………………………………………………….61

CHAPTER 12

Plant Location……………………………………………………………………..………..62

Factors Affecting Plant Location…………………………………………..………62

Raw Materials………………………………………………………….…….62

Marketing Area…………………………………………………………..…..62

Transportation Facilities……………………………………………...….…..62

Utilities (Services)……………………………………………………..….…63

Environment Impact and Disposal………………………………………..…63

Climate…………………………………………………………………..…...63

Taxation and Legal Restrictions…………………………….……………….63

Flood and Fire Protection………………………………….………………...63

Plant Location Inferences…………………………………….……………….…...64

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CHAPTER 13

Plant Layout…………………………………………………………………………….…65

Some Principles…………………………………………………………..………..66

Main Factors………………………………………………………………………66

Costs………………………………………………………………………..66

Storage……………………………………………………………..………66

Process Requirements………………………………………………………66

Operations…………………………………………………………………..66

Floor Space…………………………………………………………………66

Safety……………………………………………………………………….66

Plant Expansion……………………………………………………………..67

By-product Storage…………………………………………………………67

CHAPTER 14

Safety & Environmental issues…………………………………………………………….68

General Considerations…………………………………………………………….68

Hazard Identification……………….………………………………………………68

First-aid Measures…………………………………………………………………..69

Firefighting Measures………………………………………………………………69

Accidental Release Measures………………………………………………………69

Exposure Controls………………………………………………………………….70

CHAPTER 15

Effective use of By-product…………………………………………………..……………71

REFERENCES……………....…………………………………………………...………..72

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Chapter 1

INTRODUCTION

Acetylene is a compound with primary elements carbon and hydrogen. It is expressed by the symbol C2H2 and on weight basis; it consists of twelve parts of carbon to one part of hydrogen. It is the simplest alkynes and is known by the systematic name ethyne. It is an unsaturated compound with two carbon atoms bonded together in a triple bond. Due to its synthetic formation, it is the most pure and richest hydrocarbon containing 92.5% of carbon.

At atmospheric pressures and temperatures, it is a colorless gas with weight slightly less than that of air. Acetylene of maximum possible purity is odorless and burns in air with an intensely hot, luminous and smoky flame. In the annals of scientific discoveries, acetylene occupies an almost unique position and its properties had been centre of much scientific interest.

Discovery of Acetylene.

Although, acetylene was first observed by English chemist Edmund Davy in 1836, Weichler announced the discovery of preparation of acetylene from calcium carbide in 1862. He found that at very high temperatures carbon acted upon the alloys of zinc and calcium and that carbide of calcium was produced. He also found out that the gas had the property of being decomposed by water resulting in the formation of acetylene and calcium hydrate.

Edmund Davy’s Discovery in 1836

The original production and recognition of Acetylene as differing from other gaseous compounds was one result of the researches and experiments made by the chemist, Edmund Davy, to ascertain and determine the properties of the Monad and Dyad metals. On his attempt to obtain potassium, he strongly heated a mixture of calcinated tartar and charcoal in a large iron bottle, which produced a black substance that readily decomposed water and yielded a gas. On examination, this gas proved to be a new compound of carbon and hydrogen. This gas was found to be highly flammable and when kindled in contact with air burnt with a bright flame even denser than olefin gas. If the supply of air was limited the combustion of gas was accompanied with a copious decomposition of carbon. When this gas was brought in contact with chlorine gas, instant

explosion took place accompanied by a large red flame and deposition of much carbon. He then named the gas as “klumene”.

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Quet’s Discovery in 1858.

By the action of induction spark upon alcoholic potash for an hour, Quet obtained nearly a liter of gas which gave a red precipitate with ammoniacal cuprous chloride. This substance when dried with vacuum over sulphuric acid or heated on water bath turned brown and detonated with development of light when heated to a temperature over 120C. He also found that when this compound was gently heated with hydrochloricacid, liberated a gas which had the property of burning with a bright flame and of forming carbon dioxide. When vapors of alcohol was passed through a red-hot porcelain tube and bubbled with ammoniacal cuprous chloride, the same gas was produced.

Vogel and Reischauer’s Discovery in 1858.

Vogel and Reischauer noticed that a precipitate was formed on bubbling coal gas through a neutral silver nitrate solution, and that the precipitate would explode on heating. The years 1858-1859 marked the discovery of the formation of metal acetylides.

Berthelot’s first research on Acetylene in 1859.

In the year 1859, French chemist Berthelot, while conducting researchesin the field of hydro-carbon compounds, discovered that when a stream of hydrogen was passed through an electric arc between two carbon electrodes was converted into rich hydro-carbon gas, which on analysis gave a chemical relationship to the organic radical Acetyl, and he therefore named the compound “Acetylene”.

Berthelot’s second research on Acetylene in 1862.

Berthelot in 1862 showed that an intense induction of spark split up methane, with the formation of acetylene and hydrogen.

2CH4------->C2H2+3H2

In the same year, he discovered the direct synthesis of acetylene from itselements.

Wohler’s Discovery in 1860.

German chemist Wohler found out that a mixture composed of an alloy of zinc and calcium and carbon when fused together at a high temperature was converted into a substance, which on being decomposed with water gave off Acetylene gas. Wohler was thus recognized for producing calcium carbide and of having discovered a means whereby acetylene could be produced synthetically upon a

comparatively large scale.

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Chapter 2

MARKET SURVEY

The market survey is based on certain parameters for the selection of process. These parameters were chosen keeping in mind the wide use of acetylene, its production process, the current worldwide production & consumption, domestic consumption, future demand, market price and factors which contribute to market price.

The market survey is carried out in three broad areas:

Past Supply and present demand.

Projected demand

Pricing and distribution

Worldwide and Domestic Production

Global production and consumption of acetylene in 2011 were both almost 28 million metric

tons. Global capacity utilization was 67% in 2011. Acetylene consumption is estimated to have

increased by 3.2% in 2011. Average global utilization rates are expected to increase gradually

after 2011. Production of vinyl chloride monomer, butanediol, chloroprene rubber, welding and

cutting is the major use of acetylene, accounting for large portion of total global consumption.

Acetylene Consumption Pattern

CR

Oxy-acet

VCM

BD

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2.2 Past Supply and Present Demand

Acetylene is an organic gas of the alkaline group and has a very high calorific value. It is, hence principally used in Oxy-Acetylene welding.

The demand for acetylene is met through local production. Few medium and few small scale plants produce acetylene for sale; while lots of automotive repairs and metal/mechanical workshops often generate acetylene with improvised equipment and containers for instantaneous uses. Generating acetylene gas is a simple process; pressure filling it into metallic cylinders for storage and prolonged use requires some capital investment.

The lion’s share of acetylene production plants are attributed to small metal/mechanical and auto workshops which use them for improvised production of acetylene since the quantity produced for the market by many major plants is not sufficient.

To illustrate the demand volume for acetylene gas from another perspective, another approach can be applied here. The basic raw material for the production of acetylene gas is Calcium Carbide. From 1997 to 2006, an average of 536,465 kg of calcium carbide was being produced annually.

The underlying reason for presenting the data regarding the production of calcium carbide is not merely to show the magnitude but to relate the fact that in the case of the improvised production of acetylene gas by workshopsfor own use, all that is generated is not put to use and that most of it is wasted since they do not have the facility to store and preserve acetylene gas generated as such. Calcium carbide may also be converted to Calcium Cyanamid (lime nitrogen) which is used as fertilizer. Since there are few fertilizer manufacturing factory in the country to convert calcium carbide into lime nitrogen, it can be argued that the total imported calcium carbide is destined for the production of acetylene.

The present demand for acetylene is large but industrial supply for acetylene is inadequate and there is quite a big gap between demand and supply.

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2.3 Projected Demand

To establish forecasted demand for acetylene gas, identification of consumers of the product is vital. Mechanical, metallurgical, polymer industries and auto mechanical workshops are the major consumers of acetylene gas. The level of demand is expected to steadily increase with increased activity in these workshops as a result of economic growth

2.4 Pricing and Distribution

Present market price of acetylene is INR 165/m3.

Present market price of calcium carbide is INR 32/kg.

Distribution can best take place by setting up own distribution centers at selected locations, preferably where mechanical and auto mechanical workshops abound. One may also sell through the agency of businessmen already established in existing distribution channels for access to the regions.

Some acetylene producing plants in India:

Chemix Speciality Gases, Bengaluru. Parag Gasses, Pune.

Axcel Gases, Faridabad.

Hindustan Industrial Gases, New Delhi


Chapter 3

LITERATURE SURVEY

The production of acetylene by calcium carbide is one of the oldest and most versatile processes. The raw material for the production process is calcium carbide which is an electric arc product. The process of production is based on the reaction of calcium carbide with water. Calcium carbide reacts with water to form acetylene and calcium hydroxide.

In stationary carbide to water type acetylene reactor, acetylene is produced by reaction of calcium carbide with water. Adequate quantity ofwater is held in the reactor shell to which calcium carbide is fed from top.The following reaction takes place:-

CaC2+2H2O = C2H2 + Ca(OH)2 + 27,000 Calories

The generated acetylene gas occupies the free volume inside the reactor shell overthe water level and pressure of gas goes up till it reaches the set pressure level when by action of the pressure controller carbide feed motor is cut-off. If the acetylene gas is taken out from the reactor, the pressure inside the reactor shell willgo down and by action of the pressure controller carbide feed motor will start and feed further carbide through the screw feed mechanism from the hopper into the shell and further acetylene shall be generated. Thus the process shall continue till the carbide filled in the hopper under operation is exhausted. At that stage change over takes place and second hopper which was filled with carbide when first hopperwas under operation now starts feeding carbide into the reactor shell and first hopper is filled with carbide.

As the process of acetylene generation is exothermic, there is a temperature rise of the reactor. The reactor temperature cannot be allowed to go high because acetylene can catch fire. Moreover, generation of acetylene is optimum at a particular temperature around 60ºC. Hence it is necessary to keep the reactor temperature around this temperature. This is done automatically by the temperature controller which is preset at a temperature of 60ºC. Since the reactor has a tendency of increased temperature, the temperature controller acts on the water inlet valve and opens the valve to bringin fresh process water which reduces temperature of the reactor and thus the reactor temperature is kept at about a particular predetermined set point.

With inlet of fresh water to bring down the reactor temperature the water level inside the reactor goes up and this water level is maintained between a high and low set point by pneumatically operated level controller. Slurry discharge valve is made to open automatically by the level controller to discharge some quantity of slurry to lower the water level inside the reactor when the water level tends to rise above the maximum level. As soon as the level of water goes down the slurry

discharge valve automatically closes. Thus only minimum quantity of slurry is discharged at a time. Water inside the reactor absorbs certain quantity of acetyleneand hence this water already saturated with acetylene should not be discharged continuously or in large volume but should be retained inside the reactor and thus prevent loss of acetylene with the slurry.

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The Agitator is continuously driven when the carbide feed motor is running. However, when the reactor is in dormant state and there is no carbide feed, there is a tendency of the slurry to settle down and jam the agitator. A timer controlled electric motor drive keeps the agitator under operation when the reactor is in dormant state. Thus slurry is always keptmixed with water without sedimentation. Agitator is a very important part of the reactor as it keeps the carbide and water intimately mixed for total reaction of the carbide and thus prevents loss of carbide in the form of solids with the slurry.

Passage of acetylene gas from the reactor to the carbide chamber (hopper) under filling is kept shut off by hydraulically operated shut off device which operates automatically when the carbide in the hopper is exhausted and screw feed motor is stopped.

The generated acetylene passes from the reactor chamber through wet type flash back arrestors and then reaches heat exchanger where the temperature of gas is lowered by cooling water and part of the moisture in the acetylene gasis taken out in the form of water by condensation. Gas then passes through lowpressure dryer filled with calcium chloride to remove further quantities of moisture from acetylene gas before the gas reaches purifying chamber. Gas then passed into purifying chamber with optimum quantity of moisture in the gas (gas is not completely dry). Purifying chamber is filled with purifying chemicals to remove Phosphorus and Sulphur compounds from the gas and if necessary to remove acidic fumes also. Thereafter gas passes to water filled scrubber where acetylene gas is washed with water to remove particles of purifying chemicals which may be carried over with the gas from purifying chamber. The wet gas then enters suction of acetylene compressor, compressed and passed to high pressure dryer filled with mechanical devices and chemicals to remove lube oil vapour and moisture from the gas. Gas after passing through the high pressure dryer is arrested by back pressure valve on the pipeline leading to the cylinder filling manifold.


Chapter 4PHYSICAL PROPERTIES AND USES

At atmospheric temperatures and pressures, acetylene is a colorless gasthat is slightly lighter than air. Acetylene of 100% purity is odorless, but acetylene of ordinary commercial purity has a distinctive, garlic-like odor.

Acetylene burns in air with an intensely hot, luminous, and smoky flame. The ignition temperatures of acetylene and mixtures of acetylene with air or acetylene with oxygen will vary according to composition, pressure, water vaporcontent, and initial temperature. As a typical example, mixtures containing 30% acetylene by volume with air at atmospheric pressure can be ignited at approximately 581°F (305°C). The flammable limits of mixtures of acetylene with air and acetylene with oxygen will depend on the initial pressure, temperature, and water vapor content. In air at atmospheric pressure, the upperlimit of flammability is approximately 82% acetylene in air. The lower limit is 2.5% acetylene in air. Acetylene can be liquefied and solidified with relative ease, but both liquid and solid acetylene are unstable.

Mixtures of gaseous acetylene with air or oxygen in certain proportions can explode if ignited. Gaseous acetylene under pressure may also decompose with explosive force under certain conditions at low pressure, but experience indicates that 15 psig (103 kPa) is generally acceptable as a safe pressure limit Generation, distribution through hoseor pipe, or use of acetylene at pressures in excess of 15 psig (103 kPa) for welding and allied purposes is prohibited.

Commercial acetylene is generally considered a nontoxic gas that has been shown in experiments to have no chronic harmful effects even in high concentrations. In fact, it has been used as an anesthetic. Like most other gases, acetylene is a simple asphyxiant if present in such high concentrations that the lungs are deprived of their required supply of oxygen. In such cases, asphyxiation will result. It should be noted, however, that the lower flammable limit of acetylene in air will be reached well before asphyxiation can occur, and the danger of explosion is reached before any other health hazard is present.


Table 4.1: Physical Properties and Constants

U.S UnitsSI UnitsInternational SymbolC2H2C2H2Molecular weight26.0426.04Vapor pressure at 70°F635 psig4378 kPaDensity of the gas at 32°F and 10.07314 lb/ft1.176 kg/matm

Specific gravity of the gas at0.9060.90632°F and 1 atm (air=1)

Specific volume of the gas at14.7 ft3/lb

0.918 m3/kg70°F and 1 atm

Specific gravity of liquid at -0.6130.613112°F(-80°F)

Density of liquid at 70°F

24.0 lb/ft3

384 kg/m3

Boiling point at 10 psig(69 kpa)

-103.4°F-75.2°CMelting point at 10 psig(69kpa)-116°F-82.2°FCritical temperature96.8°F36.0°CCritical pressure907 psia6254 Kpa,absCritical density14.4 lb/ft3

231 kg/m3

Triple point-116°F at 17.7 psia-82.2°C at 122 Kpa,absLatent heat of vaporization at264 Btu/lb614KJ/Kgtriple point

Latent heat of fusion at -114.7°F41.56 Btu/lb96.67 Kj/kgSpecific heat of gas at 60°F and 1

atm

Cp0.383 Btu/(lb)(°F)1.60 KJ/(Kg)(°C)Cv0.304 Btu/(lb)(°F)1.27KJ/(Kg)(°C)Ratio of specific heats1.261.26Solubility in water,vol/vol at 32°F1.71.7and 1 atm

Solubility in water,vol/vol at 60°F1.11.1


USES OF ACETYLENE

It is mainly used with oxygen to produce oxy-acetylene flame which is used in high temperature welding.

Another important use of acetylene is as a raw material in the productionof chemicals such as Chloroprene, Neoprene, trichloroethylene, vinyl chloride, acrylonitrile, acetic acid, 1-4 butanediol and polyvinylpyrolidone.

Small amounts of acetylene are used for lighting purposes in buoys and beacons. Acetylene is also used to ripen fruits and to mature trees and flowers. Other uses of acetylene include manufacture of plastics, synthetic rubbers, modern drugs and organic compounds like westrosol. In the past acetylene was used as an anaesthetic.

A new application is the conversion of acetylene to ethylene for use in making a variety of polyethylene plastics. Acetylene is a combustible gas mainly used in automatic lubrification for glass bottle production moulding. Acetylene is the fuel gas in atomic absorption spectrophotometry (AAS).


Chapter 5

Different Manufacturing Processes

There are two basic conversion processes used to make acetylene. One is a chemical reaction process, which occurs at normal temperatures. The other is a thermal cracking process, which occurs at extremely high temperatures.

Here are typical sequences of operations used to convert various raw materials into acetylene by each of the two basic processes.

5.1 Chemical Reaction Process

Acetylene may be generated by the chemical reaction between calcium carbide and water. This reaction produces a considerable amount of heat, which must be removed to prevent the acetylene gas from exploding. There are several variations of this process in which either calcium carbide is added to water or water is added to calcium carbide. Both of these variations are called wet processes because an excess amount of water is used to absorb the heat of the reaction. A third variation, called a dry process, uses only a limited amount of water, which then evaporates as it absorbs the heat.

The two principal methods of generating acetylene from calcium carbide are

Batch carbide-to-water method

Wet method

Wet method takes place in a cylindrical water shell surmounted by housing witha hopper and a feed. One kilogram of water is used per kilogram of calcium carbide. The heat of the reaction is 6.2MJ per cubic feet of acetylene. Temperature is kept below 150c and pressure below 204Kpa.

The first variation is most commonly used and it is described below:

Most high-capacity acetylene reactors use a rotating screw conveyor to feed calcium carbide granules into the reaction chamber, which has been filled to a certain level with


water. The granules measure about 0.08 in x 0.25 in (2 mm x 6 mm), which provides the right amount of exposed surfaces to allow a completereaction. The feed rate is determined by the desired rate of gas flow and is controlled by a pressure switch in the chamber. If too much gas is being produced at one time, the pressure switch opens and cuts back the feed rate.

To ensure a complete reaction, the solution of calcium carbide granules and water is constantly agitated by a set of rotating paddles inside the reaction chamber. This also prevents any granules from floating on the surface where they could over-heat and ignite the acetylene

The acetylene gas bubbles to the surface and is drawn off under low pressure. As it leaves the reaction chamber, the gas is cooled by a spray of water. This water spray also adds water to the reaction chamber to keep thereaction going as new calcium carbide is added. After the gas is cooled, it passes through a flash arrester, which prevents any accidental ignition from equipment downstream of the chamber.

As the calcium carbide reacts with the water, it forms a slurry of calcium carbonate, which sinks to the bottom of the chamber. Periodically the reaction must be stopped to remove the built-up slurry. The slurry is drained from the chamber and pumped into a holding pond, where the calcium carbonate settles out and the water is drawn off. The thickened calcium carbonate is then dried and sold for use as an industrial waste water treatment agent, acid neutralizer, or soil conditioner for road construction.

Thermal Cracking Process

Acetylene may also be generated by raising the temperature of various hydrocarbons to the point where their atomic bonds break, or crack, in what is known as a thermal cracking process. After the hydrocarbon atoms break apart, they can be made to rebound to form different materials than the original raw materials. This process is widely used to convert oil or natural gas to a variety of chemicals. It is manufactured by partial oxidation of natural gas or hydrocarbon feed.

There are several variations of this process depending on the raw materials used and the method for raising the temperature. Some cracking processes use an electric arc to heat the raw materials,

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while others use a combustion chamber that burns part of the hydrocarbons to provide a flame. Some acetylene is generated as a coproduct of the steam cracking process used to make ethylene. The most common process uses a combustion chamber to heat and burn natural gas as described below:

Natural gas, which is mostly methane, is heated to about 1,200° F (650° C). Preheating the gas will cause it to self-ignite once it reaches the burner and requires less oxygen for combustion. The heated gas passes through a narrow pipe, called a venturi, where oxygen is injected and mixed with the hot gas. The mixture of hot gas and oxygen passes through a diffuser, which slows its velocity to the desired speed. This is critical. If the velocity is toohigh, the incoming gas will blow out the flame in the burner. If the velocityis too low, the flame can flash back and ignite the gas before it reaches the burner.

The gas mixture flows into the burner block, which contains more than 100 narrow channels. As the gas flows into each channel, it self-ignites and produces a flame which raises the gas temperature to about 2,730° F (1,500° C). A small amount of oxygen is added in the burner to stabilize the combustion.

The burning gas flows into the reaction space just beyond the burner where the high temperature cause about one-third of the methane to be converted into acetylene, while most of the rest of the methane is burned. The entire combustion process takes only a few milliseconds.

The flaming gas is quickly quenched with water sprays at the point where the conversion to acetylene is the greatest. The cooled gas contains a large amount of carbon monoxide and hydrogen, with lesser amounts of carbon soot, plus carbon dioxide, acetylene, methane, and other gases.

The gas passes through a water scrubber, which removes much of the carbon soot. The gas then passes through a second scrubber where it is sprayed with a solvent known as N-methylpyrrolidinone which absorbs the acetylene, but notthe other gases.

The solvent is pumped into a separation tower where the acetylene is boiled out of the solvent and is drawn off at the top of the tower as a gas,while the solvent is drawn out of the bottom.

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The most important process routes for the production of acetylene are:

Partial Oxidation: Methane, LPG or light gasoline are pyrolized to cracked gases containing acetylene.

Steam Cracker Acetylene: A small amount of acetylene, related to severity of operating conditions is produced in ethylene steam crackers. Electric Arc or Plasma Arc: Cracking of light hydrocarbons is done in an electric arc.Calcium Carbide: Acetylene is generated by the reaction of calcium carbide and water.


Chapter 6SELECTION OF PROCESS WITH JUSTIFICATION

The Production of acetylene from calcium carbide is one of the oldest and mostversatile processes for the production of acetylene. The following are the reasons that would give this process an upper hand compared to other acetylene manufacturing processes:

This is a very economical process.

The raw material used for acetylene production, calcium carbide, is an electric arc product. It is cheap and readily available with 99%purity. Hazardous wastes are not formed during the production process, the byproduct formed during acetylene production, calcium hydroxide can beeasily handled and it is very stable.

In production of acetylene by partial oxidation of methane, hydrocarbon feed is preheated to 1400c whereas in the calcium carbide process, no preheating of feed is required.

Even though the reaction is exothermic, it is controlled using the generator and the heat liberated is used to evaporate the excess water which in turn dilutes the acetylene and reduces its explosive nature.

The production of acetylene by steam cracking is at the cost of ethylene which in itself is a valuable product. The energy demands are extremely high in the electric arc plasma method as the reaction zone temperature is to be maintained at 10, 000k. But, the acetylene generator in calcium carbide process can be easily maintained at 65c.

It is a proven technology and acetylene with purity greater than ninety-nine percent is obtained.


Chapter 7DESCRIPTION OF THE PROCESS

As shown in the flow diagram, the process consists of an acetylene reactor, heat exchanger, low pressure drier, purifier, ammonia scrubber, acetylene compressor and the high pressure drier.

The medium pressure acetylene reactor is stationary carbide to water automatic reactor. Acetylene is generated and as a result of chemical reaction between calcium carbide and water. The by-product is calcium hydroxide or lime slurry which is continuously discharged from the generator. The reaction is:-

CAC2+2H2O-àC2H2+CA(OH)2

The reactor is designed to generate acetylene at a pressure of 7 psig. Acetylene that has passed through the third stage of the compressor shouldnot be allowed to accumulate in large volumes as acetylene in free state above 15 Psig is highly explosive if ignited.

7.1 Acetylene Reactor:

The medium pressure double hopper reactor mainly consists of:-

Horizontal reactor vessel

The reactor can be filled with water upto a maximum level correspondingto high level position. It is provided with two valves to check high and lowlevel positions. The agitator is provided in order to distribute the carbide particles evenly and to keep the temperature of the lime solution uniform.The agitator consists of paddles rotating in clockwise direction driven by a flame proof electric motor mounted externally.

Agitator and its drive unit

The agitator shaft and the motor shaft are coupled with a brass bushing inside the reactor itself. The other end of the reactor shaft is projected outside so as to see the rotation of the shaft during operation. Two manholes are provided at the bottomfor inside cleaning of the vessel.

Carbide hopper, screw feeder and its driver

The calcium carbide initially filled in a charging hopper at the ground level. Then it

is lifted by a chain pulley and the carbide will be transferred to the hopper permanently mounted at the top. The hopper has a capacity of 150 kgs and the recommended size of the carbide is between 5 and 25mm. The hopper can be closed air-tight due to the unique design of the hopper cover. The

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carbide feed system is completely enclosed conventional screw feed. The screw is driven by a flame proof geared motor through a chain pulley drive. The discharge end of the screw feeder is opened or closed by a disc valve, which in turn is operated by a hydraulic cylinder. The disc valve is supposed to be in open position only when the screw feed rotates. This is ensured by a hydraulic system.

The hydraulic oil system consists of an oil gear pump directly coupled to the screw feed motor. The outlet of the pump is branched into two; one connected to the cylinder of the same screw feeder to open the valve and the other is connected to the cylinder of the other screw feeder to close the valve. Oil leaks in the hydraulic system should be avoided to achieve smooth functioning of the system. The oil pressure required to fully open the valve is 100Psig and this is controlled by a bypass oil pump.

The flash-back arrestors

The reactor is provided with two flash-back arrestor to prevent the back flow of the flash/fire. If occurs from the outlet gas header to the reactor. Itis basically a vertically vessel filled by water to about one-third of its capacity. Perforated discs are provided internally to avert the propagation of the flame. Two manual valves are provided to confirm the water level in the vessel.

Safety relief valves, drain system and the allied automatic control system

The reactor vessel is equipped with five safety relief valves. One is fitted on the gas outlet dome, one on each of the flash back arrestors and one on each of the carbide hoppers. The discharge ends of all the relief valves are connected to the main vent header, which in turn let open to the atmosphere. The bottom of the reactor is fitted with an air-operated drain valve which discharges slurry in response to the slurry level in the reactor i.e. the valve opens when the level is high The top of the reactor is fitted with an air-operated water inlet valve which opens in response to the temperature of the slurry in the reactor i.e. the valve is open when the temperature is high but not when the level is also high simultaneously.

7.2 Heat Exchanger

The acetylene gas leaving the acetylene reactor is hot and laden with moisture and other gaseous impurities like hydrogen sulphide, phosphine, ammonia etc. The heat exchanger cools the gas. Cooling water is circulated on the tube side and acetylene gas on the shell side. The condenser is designed to suit any local conditions provided sufficient water flow is maintained.


7.3 Low Pressure Drier

This is vertical cylinder vessel charged with solid anhydrous calcium chloride. This absorbs the moisture in the gas. The purity of the calcium chloride should be minimum 80% on absorption of the moisture. The calcium carbide becomes fluid and is collected at the bottom. This is drained periodically. The gas leaving the drier should not be absolutely dry as further purification depends on the wetness of the gas. Further purification could not be achieved, due to lack of moisture in the gas. Therefore a bypass line is provided. The valve in the bypass line is to be kept slightly open always.

7.4 Purifier

This is a large vessel divided into two sections by wire mesh frame work. The inside of the vessel is coated with chlorinated rubber paint as anti-corrosive measure. Each section of the purifier will be charged with 200kgs of purifying mass. The purifying mass consist of various chemicals like ferric chloride ,mercuric chloride, cupric chloride, manganese dioxide etc. in a keiselghur carrier and mixed in proper proportions. The purifying mass should be reactivated in every 125 working hours by exposing it to atmosphere and the whole charge shall be replaced in three months. The purifying mss absorbs gases like hydrogen sulfide, phosgene etc.

7.5 Ammonia Scrubber

The ammonia scrubber is a packed bed column filled with 25mm ceramicintalox saddles. Gas is sent from the bottom and water is sent from top of the column. Since ammonia has affinity towards water, it gets absorbed by the water. But, acetylene is sparingly soluble, so acetylene gas isn’t lost. The functions of the scrubber are:

Water soluble impurities like ammonia will be removed.

The gas will be little wet to facilitate compression and further drying. It is also to be noted that the gas should not be absolutely dry during the compression.

Acetylene Compressor

The compressor is a 3-stage type. The whole compressor assembly including inter stage cooling pipes and purge bottles are immersed in water filled tank to avoid any

pressurized acetylene to come in contact with air and also to make sure that all components are continuously cooled. The compressor is driven by a 15HP flame proof motor. The assembly also includes an oil pump, driven by the same motor. This pump feeds lubricating oil to the compressor. All the three stages

22


of the compressor are provided with a pressure gauge to monitor the inter-stage pressures. The rating of the pressure gauges are:-

Suction pressure gauge-0-30 psig First stage gauge-0-150 psig

Second stage gauge-0-400 psig Third stage gauge-0-600 psig

Three control devices are incorporated in the compressor system, a low pressure mercoid switch, a high pressure mercoid switch and a back pressure regulator control valve. The low pressure switch prevents the running of the compressor when acetylene is not being supplied in sufficientquantity to the compressor. The high pressure switch is provided to stop the compressor when pressure exceeds the required charging pressure and also to prevent the starting of the compressor again too heavy loads. The back pressure regulator valve is provided to set the charging pressure in theHP drier for effective removal.

Lubrication- Lubrication is achieved by a belt driven oil pump mounted outside the tank and lubrication in the compressor is achieved by a flash system. The oil circuit is provided with a level gauge to monitor the oil level and also with a vent valve to let off air trapping. The V-belts used in the acetylene compressor should be of anti static type.

Trap drain system-The compressor is provided with inter stage traps for

trapping moisture. There is also a trap at the suction of the 1st stage. The drain lines are inter connected in a manner that all stages can be drained

through the first stage trap. While the 1st stage suction trap is empty as it contains acetylene at only about 5 psig the interstage traps are filled with MS Chain pickings to avoid excessive hold-up if any compressed acetylene.

7.7 High Pressure Drier

The high pressure drier consists of three columns. The first column is fitted with MS chain packings to avoid any void and for proper impact separation. The second and third columns are fitted with two capsules each and are fitted with a drain valve to drain off moisture collected at the bottom periodically.

7.8 Filling Manifold

At this stage, the acetylene gas is of more than 99% purity. It is then filled into the cylinders through the gas filling manifold.


Chapter 8

MATERIAL BALANCE

Assumptions for Material Balance:

There is no material loss from any equipment along any flow line by any means There is no accumulation of material in any equipment, Steady state exists.

CaC2 +2H2o èC2H2 +Ca(OH)2

Basis:

C2H2=500,000cm/yr at Pressure = 225 psig and Temperature = 200C with 7200 working hours. (99.8% pure on weight basis)

8.2 Material Balance across Reactor

C2H2+moisturee

CaC2

Reactor

H2O

Slurry(Ca(OH)2+water)

Volumetric flow rate of gas 69m3/hr.

At the selected pressure and temperature density of acetylene gas

=17.29 kg/m3. Mass produced =1196 kg/hr. = 46.0kmol/hr

Conversion = 0.92

Required Pure CaC2=46/.92=50kmol/hr =50*64kg/hr =3214 kg/hr

Required CaC2=50.51kmol/hr (99% pure on mole basis)

24


Pure H2O required =92 kmol/hr

=1656 kg/hr

Ca(OH)2 produced =46kmol/hr

=3496kg/hr

∆Hf(C2H2)= -227480 kj/kmole

∆Hf(Ca(OH)2)=-986090kj/kmol

∆Hf(CaC2)=-59800kj/kmol

∆Hf(H2Oliq)=-285830kj/kmol

∆HR=--215144kj/kmol

Heat produced=-215144*46=-9896624kj/hr Cooling water required=42700 kg/hr.As acetylene is sparingly soluble in water henry’s law will be applied to calculate its mol fraction in water.

From Antonie equation at 650C Psat of water =24 KPa. At 6 psi mol fraction of water

in vapour phase =Psat/P

=24/41.346 = 0.584

Henry’s constant for acetylene =1350 bar

Mol fraction of acetylene in water =(.416*.408)/1350 =1.257*10-4

So it can be assumed all the acetylene being produced is coming into vapour phase. Mole fraction of acetylene in vapour phase = 0.416

Moles of acetylene being produced =46kmol/hr. Total moles in vapour phase =46/.416=110.57kmol

Moles of water in vapour phase =110.57-46=64.58kmol/hr. Total water used =1656+1162.44+42700=45518kg/hr.


Table 8.1 Material Balance Across Reactor

ComponentInput(kg/hr)Output(kg/hr)

CaC2

3214178

H2O455181162(as moisture)C2H2

-----1196

Slurry (water+Ca(OH)2)-----46196Impurties32.6432.64Total4876448764

8.3 Material Balance Across (Heat Exchanger + L.P. Drier)

Cooling water

Gas outlet to drier

Dried gas

C2H2 INPUT=1196kg/hrHEDrier

Output=1196kg/hr

Water outlet

Gas inlet

Moisture input=1162kg/hr

8.3.2 From industrial data

80% of moisture being removed in condenser + L.P.drier

Moisture (out) =232 kg/hr

The saturation pressure of water at 300C is 4.23KPa and the pressure in the low pressure drier is 1 atm. The partial pressure of moisture is 24.01 KPa and at outlet condition, it is 9 KPa . This shows that there is one hundred percent humidity at both

inlet and outlet. Now, by using the CaCl2 data under these conditions:

Pound of moisture removed per pound of CaCl2 is 17.3 lb.

26


The moisture removed =2047.57 lb.

Therefore the amount of CaCl2 required is 118 lb.

Cooling water

m.*4.18*(50-25)=148599

m.=1422kg/hr

Table 8.2

componentsInput (Kg/hr)Output(Kg/hr)

C2H2

11961196

Moisture1162232+(930 absorbed)

impurity32.6432.64

Cooling Water14221422

Total

3182.643182.64

8.4 Material Balance Across PURIFIER+H.P. Drier+Scrubber

C2H2 input=1196kg/hr

Output=1196kg/hr

Moisture input=232kg/hr

Moisture Output =10ppm(hence neglected in acetylene)

Impurity input=32.64kg/hr

Output (as solid slurry) =32.64kg/hr

27


Cacl2 being usedà3 capsules of hold up capacityà4kg

Purifying mass=20gms/cum of gas

=20*5625/1000

=112.5kg

Table 8.3 Material balance across purifier and scrubber

componentInputOutput

C2H2

11961196

Moisture232-------

Impurity32.64------


Table 8.4 Overall Mass Balance:

componentInput(kg/hr)Output(kg/hr)

CaC2

3214178

Impurity32.6432.64

C2H2

----1196

H2O4694045284

Ca(OH)2

-----3496

Total50186.6450186.64


Chapter 9ENERGY BALANCE

9.1 Data:

Heat Capacities: (in KJ/Kmol.K at 25°C)For C2H2

Cp/R = A+BT+CT2+DT-2

A=6.132, B=1.952*10-3, C=0, D=-1.299*105

For CaC2

Cp/R=A+BT+CT2+DT-2

A=8.254, B=1.429*10-3, C=0, D=-1.042*10-5

For Water

Cp/R =A+BT+CT2+DT-2

A=2.712, B=1.25*10-3, C=-0.18*10-6

For Ca(OH)2

Cp/R=A+BT+CT2+DT-2

A=9.597, B=2.637*10-3, D=0

Water (g)

Cp/R=A+BT+CT2+DT-2

A=3.476, B=1.450*10-3, C=0, D=0.121*10-5

Impurities:

For NH3

Cp/R=A+BT+CT2+DT-2

A=3.578, B=3.02*10-3, D=-0.18*105

For H2S

Cp/R=A+BT+CT2+DT-2

A=3.931, B=1.490*10-3, C=0, D=-0.232*105

For PH3

Cp/R=A+BT+CT2+DT-2

A=1.434, B=1.496*10-3, C=0, D=-0.695*105

Enthalpies of Formation of Compounds at 298.15K (KJ/kmole)

Acetylene=227480Ammonia=-461110Calcium Hydroxide=-986090Water (gas) =-241818Water=-285830

30


Calcium Carbide=-59800.

9.2 Assumptions

The following assumptions have been made in order to carry out the energy balances:

There is no energy loss either through conduction, convection or radiation in all pipelines and equipments.

There is no pressure loss in the pipelines and equipments.

There is no accumulation of heat.

The heat capacities of gases are taken assuming ideal gas behaviour.

The basis is taken as 1 hr.

Energy Balance across each equipment

9.3.1 Across Reactor:

Products (338K)

ΔH2

Reactants (298K) Products (298K)

ΔH1

ΔHr = ΔH1 + ΔH2

Reactant Temperature=25°C Temperature of Reactor=60°C Product Temperature=60°C

As it is an exothermic reaction, heat of reaction will be utilized in heating the reactants from 25°C to 60°C, in heating excess water from 25°C to 60°C and in evaporation of water at 60°C.

Q= ΔHr*Molar flow rate (considering conversion)

Q’ = mvapor*λ + mwater*Cp dT +∫298333 CpUnreacted Cac2+Impurities dT ∆H1=Hf

lC2H2+Hf lCa(oh)2-2Hf lH20(L)-Hf lCaC2

=227480-986090+2*241818+59800

=-215144KJ/Kmol

∆Η2=∫298333CpdT

=R∫298333(25.678+3.929*10-3T+0.18*10-6T2-1.092*10-5T-2)dT

=346011KJ/Kmol

ΔHr=-215144+346011

31


=130867KJ/Kmol

Q=46*130867

=6019882KJ

Kmoles of CaC2=4.02Kmole,NH3=0.4335Kmole,PH3=0.0408Kmole,H2S=0.035Kmole

A=0.0272*3.578+2.24*10-3*3.931+2.56*10-3*3.12+0.255*8.257

=34.93 B=7.16*10-3 C=0 D=0.533*105

R*∫298333(2.22+0.755*10-3T-0.272*105T-2)dT = 10665.33KJ m*Cp*(60-25) =

18565*4.18*35=27116181KJ

m*λ=18*64.58*2833=3293035KJ Q’= ∫298333Cp dT + m*Cp* dT + m*λ

=2650+73.13+417832+204771

=6019882KJ.

9.3.2 Across Heat Exchanger

Mass flow rate of cold stream (water) =79 Kmol/hr ∆HWater(l)=∫ ∆ =1903.85*79=150413

Hot streamInlet Temperature=65°COutlet Temperature=30°C∆HC2H2=46*∫ =1597.31*46 =73476Kj

∆HNH3=0.4335*∫ =1322*0.4335 =573Kj

∆HH2S=.035*∫ =1216.92*0.035 =42.6Kj

∆HPH3=.0408*∫ =0.0408*1301 =53

∆HH2O(g)=1181.09*∫ =64.58*1181.09 =76268

∆HHot stream=∆HC2H2+∆HNH3+∆HPH3+∆HH2S+∆HH2O(g)

=4680.11+35.46+2.73+3.33+4857.82

=150413.∆H Cold stream = ∆H Hot stream.

32


9.3.3 Across Compressor

It is a three stage adiabatic compressor

P, T

P1,T1

P2,T2

P3

For optimum energy input

P1=√PP2

P2=√P1P3

P=21.7 psia ,P3=239.7psia P1=√P.√P1P 3P1

2=P*√P1P3 P11.5=21.7*(239.7).5

P1=48.33 psia P2=107.6 psia

For adiabatic compression (T1/T2)=(P1/P2)γ-1/γ

γ for C2H2=1.235

T2/T1=(P/P1)γ-1/γ T1=352.82K.

The pressure ratio remains constant. The gas will be cooled by the intercoolers so exit temperature after every compressor is 303 KPower required=.∗ ∗∗

(

− 1)

()

Power required =39.40 kw Total power required=3*39.40

=118.2kw

Power required for the compressor is 118.2 kW


Chapter 10DESIGN OF EQUIPMENTS

10.1 Design of Reactor

From the given data for acetylene production,

Reactor conversion = 92%Temperature of the reactor = 65°C (338 K)Pressure of the reactor = 7 psig

From the above graph which is obtained from a US patent, Space time = 5.7 hr.

Density of CaC2= 2.2gm/cc = 2220kg/m3

Mass flow rate of CaC2= 1196 kg/hr Vol. flow rate of CaC2= .53m3/hr Vol. of water =

45.51 m3/hr

Vol. of reactor= 46 m3

Now, assuming 30% allowance Vol.= 1.3*46

34


= 59.8 m3 Assuming L/D=1.5Vol. of reactor = ∗ ∗ /4 = 59.8

D=3.7 m. L=5.55 m.

Length of dished sides=1 m. Total length= 5.55+2*1

= 7.55m.

Mechanical design of the reactor

Thickness of shell

tsPDc

2 fJ P

Working pressure P = 1.48 atm

Design pressure = 1.1 x 1.48 = 1.63 atm = 1.63 x 1.01325 x 105 pascals

= 16497.1 pascals f= 950 kgf/cm2= 93163650 pascals

c= corrosion allowance = 2mm J = 0.85

tS164957.1 3.725.84 mm

2 93163650 0.85 (164957.1)

Head Design (Flanged and Shallow)

Material of construction is stainless steel

Permissible stress = 130 N/mm2

P= 200623 pascals.

Crown radius Rc =outer diameter = 3705.84 mm

Knuckle radius R = 0.1 Rc = 0.1*3705.84 = 370.05 mm

Stress identification factor

1

R0.5

1

310 1.541

W

3C

4

R

4


Thickness of head

tn

PR C W

164957 .1 3705.84 1.5415.94 mm

2 931636500.85

2 fJ

Axial stress due to pressure

fap

PD i

164957.1 37123827.01 104 N / m2

4(ts c)

=

4(6 2)

Agitator specifications are:

Impeller Diameter Da = Dt/3= 3.7/3=1.23 m

Impeller Height above Vessel floor, E = Da = 1.23 m

Length of Impeller Blade, L = Da /4 =1.23/4=.305m

Width of Impeller Blade, W = Da /5=.305/4=.076m

No. of Impeller blades= 2

Shape Factors are

S1

= Da/Dt = 1/3

S2

= E/Dt = 1/3

S3

= L/Da = 0.27

S4

= W/Da = 1/5

Tip Velocity = 3 – 6 m/sec

Tip Velocity = 5 m/sec

Tip Velocity = π x Da x N

Speed of Impeller = N = [5/( π x 2.2)] x 60 = 44 RPM

No. of fans mounted on the shaft =2

Distance between the fans=.74m

No.of agitators =2

Distance between the agitators =L/3=5.55/3 = 1.85m.

36


Specification Sheet of Reactor

ItemReactor

OperationContinuous , Isothermal

TypeCSTR

Reactor Volume

59.8 m3

Length7.55 m

Design Stress

130 N/mm2

Shell Thickness5.84 mm

Reactor Diameter3.712 m

Design Pressure164957.1 Pa

Impeller diameter1.23mImpeller Height above Vessel floor1.23mLength of impeller blade.305mNo. of fans mounted on shaft2

Distance between fans.74mNo. of agitators2Distance between agitators1.85m

10.2 Design of Heat Exchanger

The heat exchanger is of shell and tube type.The feed solution entering from the reactor is to be cooled using water at from 65℃ to 300C.

Data: Hot FluidFlow rates of the streams entering:

ComponentMass flow rate

Acetylene2634.34lb/hr

Watergas

2559.47lb/hrProcess conditions:

Hot fluid:

Inlet temperature (

Outlet temperature ( ) = 149℉

) = 86℉

37


Physical properties:

Component

C (Btu/lb- )0.0266-h)

Acetylene

0.76℉

( /

Water

2.622

0.0266

C (mean)= .239 Btu/lbmol-℉

(.0266 lb/ft-h.

= ) =

(. 011 + .011) ∗ 2.42/2

Cold FluidThe coolant used is water.

Process conditions:Inlet temperature ( ) = 77℉Outlet temperature ( ) = 122℉

Mass of the coolant used (w) = 3132 lb/h.

Physical properties:

C = 1.0 Btu/lbmol-℉ s = 1= 1.96 lb/ft-h.

Heat balance:

Q= W*C*(

= w*c*(

balance, heat load Q = 140940Btu/h.

From energy −

)

− )

True Temperature Difference:

Hot fluid

Cold fluidDiff.

149

Higher temperature12227

86

Lower temperature779

63

Differences4518

LMTD =() ()

(

)

LMTD = 16.380F

R = 3

S =.125Using graph, = 0.98

∆ = ∗

38


0.98*16.38 = 16℉

Caloric Temperatures:

LMTD = 16℉ ∆∆ = 0.33

value is 0.15 From graph;0.35 86 + 0.35 ∗ (63) = 108.05℉ 77 + 0.35*(45) = 92.75℉

Where, is the correction factor

is the caloric temperature of the hot fluid.

is the caloric temperature of the cold fluid.

Assume overall heat transfer coefficient

= 20

Btu/sq.ft-

Area of the Heat Exchanger (A) =

=

℉

∆

∗ = 440.43

= 0.1963Sq.ft/lin-ft

Tube selection:

3/4in. OD, 16BWG tubes OD of the tubes (do) = 3/4 in ID of the tubes= 0.62 in. Length of the tube = 16 ft

Heat transfer area per tube per unit length = 0.1963 sq.ft.

Number of tubes = ∗ = ∗ .

= 140TEMA P or S, Floating Head type. The nearest tube count from the table 9 Tube count= 124

8 tube passes (n) and 1 shell pass.

¾ in. Tubes arranged in a 1in. square pitch Shell ID (Ds) = 15.25 in.

Corrected heat transfer area = 124*168*0.1963 = 389.45 sq.ft Corrected heat transfer coefficient = 22.6 Btu/sq.ft℉

Hot fluid: Shell side

a) Flow area, as: since the minimum baffle space will give the maximum value of

ho, we assume

The baffle space (B)= ID/5 = 15.25/5 B = 3.05 in.

39


The clearance (C’) =0.25 in.

Flow area is given by as = ID*C’*B/144*PT

15.25*3.05*0.25/144*1 0.08 sq.ft

Mass velocity Gs = W/as 5193/0.08 64912.5 lb/sq.ft-h

At Tc = 50℃

De =.079(from graph).

Re = De*Gs/0.079*64912.5/.0266 192785

From Re vs jH graph, we have jH =311For

and API=40.6

k(c

/k)1/3 = .007 Btu/h-sq.ft-

/ft

= .011

1/3

* s℉

ho = jH* k(c /k)

Let us assume theviscosity correlation factor s = 1.0

∅

∅

Therefore; ho= 29.77 Btu/h-sq.ft-℉

Cold fluid: Tube side

a) Flow area a’t=0.302 in2.

Total flow area is given by at= NT* a’t/144*n =124*0.302/144*8

0.03 sq.ft

Mass velocity Gt = 3132/0.03 104400 lb/sq.ft-h

Re = Ds*Gt/

104400*0.05/1.96 5143.26

From Re vs jH graph, we have jH =270For

/k)1/3

and API=10.5

k(c

= 0.065 Btu/h-sq.ft-

/ft

= 2.7

/k)1/3

* i℉

hi = jH* k(c

hi = 290*i

∅

hio/

∅i = h∅

i/

i*(ID/OD)

∅

33.82*(0.62/.75) 239.73 Btu/h-sq.ft-℉ Let us assume ∅i is 1.0

Hence; hio = 239.73 Btu/h-sq.ft-℉

Pressure Drop Calculations:

Shell side calculations:

40


For Re= 192785 We have f=0.005 s=0.825 N+1=12*L/B=12*16/3.05=63∆Ps= f*Gs

2*Ds*(N+1)/5.22*1010*De*s*∅s

= 0.005*649122*1.27*63/5.22*1010*0.079*0.825*1 =.484psi

Tube side:

For Re=5143.26 We have f=0.003 s= 1.0∆Pt= f*Gt

2*L*n/5.22*1010*Ds*s*∅t

0.003*104002*16*8/5.22*1010*0.05*1 1.6psi

Clean overall coefficient:

Uc = hio*hi/(hio+ho)179.8*29.77/(179.8+29.77) 25.54 Btu/h-sq.ft-℉

Dirt factor;

Rd = (Uc- Ud)/Uc*Ud

(25.54-22.6)/25.54*22.6 0.00509 h-sq.ft-℉/Btu

Specification Sheet of Heat Exchanger

Item

Heat ExchangerType

1-8 shell & tubeOperation

ContinuousLMTD

16°FInlet temp. processing stream

149°FOutlet temp. processing temp.

86 °F

UC

25.54 Btu /hr. ft2.°F

UD

22.6 Btu /hr. ft2.°FNo.of tubes

124Pressure drop shell side

0.484 psiPressure drop tube side

1.6 psi

41


10.3 Design of Scrubber:

Ammonia is to be absorbed using water as a solvent in a packed bed. Packing is25mm ceramic in-tax saddles.Assuming complete removal of ammonia.

The gas composition is

C2H2-à1196 kg/hr , H2O(moisture)-à232 kg/hr Impurity NH3 -à7.395 kg/hrMole fraction of C2H2=0.77

Mole fraction of H2O(moisture)=0.21 Mole fraction of NH3 (g)=0.02

Mass fraction of C2H2=0.03 Mass fraction of H2O(g)=0.16 Mass fraction of NH3=0.01

ρC2H2=1.17 kg/m3 , ΡC2H2=0.6kg/m3 ,ρNh3=0.73kg/m3

ρgas stream=yC2H2*Ρc2h2+yH2O(g)*ΡH2O(g)+yNH3*ρNH3

=1.074 kg/m3

Flow rate of Gas G=0.016 Kmol/sec

Average Molecular Weight of Gas=24.14 kg/kmol Ammonia Removed=7.395 kg/hr = 0.0021 kg/sec Solvent (liquid) flow rate=2 kg/sec (assumed)

Liquid leaving(L’)=2.0021 kg/sec Gas (G)=0.391 kg/sec

L’/G’ * (ρG/ρL)0.5 = 2.0021/0.397 * (1.074/1.500)0.5 =0.167

Assuming pressure drop at 400N/m2/m From figure, ordinate=0.055

For given packing Cf=98 (from table)

G’=((0.055ρG(ρL-ρG)gl)/CfμL0.1J)0.5

G’=(0.055*1.074*(1000-1.074)/98*(1.002*10-3)0.1)0.5 =1.05 kg/m2s

Cross Sectional Area = (0.392/1.05)=0.378m2

Tower Diameter T=(4*0.378/∏)0.5

=0.69 , approx 0.7m

Z= Htog * Ntog

Dilute solution of NH3-H2O follows Henry’s Law. Ntog= ln (y1-mxl/y2-mx2 (1-1/A)

+1/A)/(1-1/A) x2= 1.009 *10-3

A=L/mgm=0.25

A= 2/0.85*0.397 =5.93

Ntog=3.40 & Htog=G/Fga

42


=(0.016/0.378)/0.0182=2.31

Calculation of Fga (Holdup)

L’=2.0021/0.378 kg/m2s =5.29 kg/m2s

ds=0.032 (from table) B=1.508 ds0.376 = 0.41

Фlsw = 5.014*10-5/ds1.56 = 0.010 m3/m3 Фl+w=(2.32*10-6)(737.5*5.29)0.41/0.0322 =

0.067m3/m3

Фlow=фL+w –фlsw = 0.057 m3/m3

H=1404(5.27)0.57(1.002*10-3)0.13/10000.84(3.24*5.290.413-1)(7.12*102/0.073)0.287-

0.262log5.3 =0.779*2.44 = 1.902

Фlo=фlow*H

=0.057*1.902 = 0.108 Фls=4.23*10-3(1.002*10-

3)0.09*(7.12*102)0.55/0.0321.56(1000)0.37

=1.98*10-3 m3/m3

Фwt=фlo+фls

=0.108+1.98*10-3 =0.109 m3/m3

Interfacial area

m= 73,n= 0.0310L’-0.0630 = 0.1 ρ=-0.359

фAW=m(808G’/ρG0.5)nL18 = 73(808*1.05/1.0740.5)0.1(5.29)-0.359 =83.9 m2/m3

a= 83.9*0.0108/0.057 = 15.8Є=0.69 (Table)ЄL=0.69-0.109 = 0.581

FG(0.0472)/9.77*10-10=25.1(0.0472(2.71)/0.002)0.45*(4990)0.5 FG=1.15*10-3

FG*a = 1.15*10-3*15.8 = 0.0182

HTOG=(0.016/0.378)/0.0182 = 2.31 Z=HTOG*NTOG = 2.31*3.40=7.85

Z=8.00m

The height of the scrubber is obtained as 8.00m.


Specification Sheet of Scrubber

Item

Scrubber

Operation

Counter current,Continuous ; Isobaric

Type

Regular Packing

Voidage

.75

Packing type

25 mm ceramic Intalox saddle

Top Diameter

0.7m

Height

8.0m

Pressure Drop

3200N/M2

10.4 Design of Compressor

The hydrogen compressor is a three stage compressor immersed in water so that pure acetylene does not come in contact with air.

The suction pressure and the discharge pressure are known and all other parameters of the compressor are to be calculated.

The parameters of the compressor to be calculated are:

Volumetric Efficiency

Rotation speed of the crank Bore Diameter

Stroke Length

Hydrodynamic Head

Discharge Temperature Gas Horse power Brake Horse power

For first stage of the compressor

Suction Pressure, Ps = 21.7psia

Discharge Pressure, Pd = 48.33psia

Now, due to intake and exhaust losses,

44


P’s = 0.92 * 21.7 = 19.964psiaP’d = 1.08 * 48.33 = 52.19psia

Volumetric Efficiency:

= [ C+ 1 – C ( P’d/ P’s) ^ (1/γ)] Where C = 0.05 & γ = 1.235

= [0.05 + 1 -0.05 (52.14/19.964) ^ (1/1.235) ] = 0.94.

Rotational speed of the crank, Bore Diameter & Length of Stroke

ή = {m * (1/ρ)suc}/ {(π/4) * L * D2 * ( N/60)} -eq.1 U = {2 * L *N} / 60 -eq.2

Assuming that the value of L /D = 1.2 &U = 5m/s (the value of U varies from 2m/s to 6m/s)

The value is obtained from the graph between stroke length, L and crank shaft speed, N.


Therefore, the value of L*N is obtained as

LN = 150 (from eq.2)

Now, from eq.1

0.94 = {1428 * (1/1.54)} / {3600 * π/4 * D2 * 150/60}

From the above equation

D2 = 0.1444 & D = 0.3So,

L = 1.2 * D = 0.448m.

LN = 150; N = 334rpm

Bore diameter is obtained as 0.38m.

Crank rotation speed is obtained as 334rpm.Stroke length is 448mm.Piston speed is 5m/s.

Discharge Temperature:

Td = Ts / (P’s/P’d)^{(γ-1)/γ}

Td = 363K.

Hydrodynamic head in adiabatic process:

H = {1000 * Z * R * Ts * γ/γ-1 * [ (P’d/ P’s)^(γ-1/γ) – 1]} / g

Where, Z is the compressibility factor

Z = Zo + w Z’

Zo = 1 + Bo* (Pr/Tr) & Z’ = B’* (Pr/Tr)

Pr = 1.476/62.4 = 0.024 & Tr = 0.98

Bo = 0.083 – (0.422/Tr^1.6) & B’ = 0.139 – (0.172/Tr^4.2)

Bo = -0.35 and

B’ = -0.048

46


Substituting the above values, Zo = 0.99 and Z’ = -0.001755 Now, the Value of Z

Z = 0.99 – 0.001755 * 0.3 = 0.98.

Therefore, for further calculations, the value of Z is assumed to be 1.

Now, the Hydrodynamic head is given as

H = {1000 * 0.98 * 8.314 * 303 * (1.235/0.235) * ( [52.19/19.968]^0.19 -1)} / (9.81*26.04) The Hydrodynamic head, H is obtained as 10190.2m

Gas Horse Power

GHP = {G * H * g * 0.000001} / {3.6 * ή}

GHP = {1420 * 10190.2 * 9.81 * 0.000001} / {3.6 * 0.94}

GHP = 42.16 KW.

Brake Horse Power:

BHP = {G H P} / ή

Now, from the following graph


ή = 0.85

Therefore, BHP = 42.16 / 0.85

BHP = 49.6 KW.

For the Second Stage of the compressor:

Suction Pressure = 40.33psia

Discharge pressure = 107.66psia

Due to the intake and exhaust losses

P’s = 0.92 * 40.33 = 44.46psia

P’d = 1.08 * 107.66 = 116.27psia


= [C+ 1 – C ( P’d/ P’s) ^ (1/γ)] Where C = 0.05 & γ = 1.235

= [0.05 + 1 -0.05 (116.27/44.46) ^ (1/1.235)] = 0.94.

Rotational speed of the crank, Bore Diameter & Length of stroke

ρsuc = 3.167 kg/m3

ή = {m * (1/ρ)suc}/ {(π/4) * L * D2 * ( N/60)} -eq.1 U = {2 * L *N} / 60 -eq.2

Assuming that the value of

L /D = 1.2

U = 5m/s

So, the value of L*N is obtained as 150.

48



Therefore, from eq.1

D2 = { 1428 * 4 * 60 } / { π * 150 * 0.94 * 3600 * 3.167}

D = 0.26m, L = 0.31m & N = 480rpm.

Bore diameter is obtained as 260mm



Td = Ts / (P’s/P’d)^{(γ-1)/γ}

Td = 363.24K.


H = {1000 * Z * R * Ts * γ/γ-1 * [ (P’d/ P’s)^(γ-1/γ) – 1]} / g

Where, Z is the compressibility factor

Z = Zo + w Z’

Zo = 1 + Bo* (Pr/Tr) & Z’ = B’* (Pr/Tr)

Pr = 0.05 & Tr = 0.98

Bo = 0.083 – (0.422/Tr^1.6) & B’ = 0.139 – (0.172/Tr^4.2)

Bo = -0.352 and

B’ = -0.048

Substituting the above values,

Zo = 0.98 and

Z’ = -0.00244

Therefore,

49


Z = 0.98

Now, the Hydrodynamic head is given as

H = {1000 * 0.98 * 8.314 * 303 * (1.235/0.235) * (([116.17/44.46]^0.19) -1)} / (9.81*26.04) H = 10190m

Gas Horse Power

GHP = {G * H * g * 0.000001} / {3.6 * ή}

GHP = {1420 * 10190 * 9.81 * 0.000001} / {3.6 * 0.94}

GHP = 42.16 KW.

Brake Horse Power:

BHP = {G H P} / ή

Now, from the graph

ή = 0.85

Therefore, BHP = 42.16 / 0.85

BHP = 49.6 KW.

For the third stage of the compressor:

Discharge pressure = 235.7psi

Suction pressure = 107.6psia

Due to the intake and exhaust losses

P’s = 0.92 * 107.6 = 92.99psia

P’d = 1.08 * 235.7 = 254.56psia



= [C+ 1 – C ( P’d/ P’s) ^ (1/γ)] Where C = 0.05 & γ = 1.235

= [0.05 + 1 -0.05 (254.56/98.99) ^ (1/1.235)] = 0.94.

Rotational speed of the crank, Bore Diameter & Stroke Length

ή = {m * (1/ρ)suc}/ {(π/4) * L * D2 * ( N/60)} -eq.1

U = { 2 * L *N } / 60 -eq.2

ρsuc = 7.05 kg/m3

Assuming that the value of

L /D = 1.2

U = 5m/s ( the value of U varies from 2m/s to 6m/s )

Therefore, the value of L*N is obtained as


From eq.1

D2 = { 1428 * 4 * 60 * (1/7.05) } / { π * 150 * 0.94 * 3600 * 0.44}

D = 0.17m, L = 0.26m & N = 576rpm

Bore diameter is obtained as 170mm



Td = Ts / (P’s/P’d)^{(γ-1)/γ}

Td = 362.65K.

51



H = {1000 * Z * R * Ts * γ/γ-1 * [ (P’d/ P’s)^(γ-1/γ) – 1]} / g Where, Z is the compressibility factorZ = Zo + w Z’

Zo = 1 + Bo* (Pr/Tr) & Z’ = B’* (Pr/Tr) Pr = 0.12 & Tr = 0.98Bo = 0.083 – (0.422/Tr^1.6) & B’ = 0.139 – (0.172/Tr^4.2) Bo = -0.352 and B’ = -0.048Substituting the above values, Zo = 0.956 andZ’ = -0.00588

Therefore,

Z = 0.95

Now, the Hydrodynamic Head is given as

H = {1000 * 0.98 * 8.314 * 303 * (1.235/0.235) * (([116.17/44.46]^0.19) -1)} / 9.81H = 30361.07m

Gas Horse Power

GHP = {G * H * g * 0.000001} / {3.6 * ή}

GHP = {1420 * 30361.07 * 9.81 * 0.000001} / {3.6 * 0.94}

GHP = 40 KW.

Brake Horse Power:

BHP = {G H P} / ή

52


Now, from the graph

ή = 0.85

Therefore,

BHP = 40 / 0.85

BHP = 47.05 KW.

Specification Sheet of Compressor

Compressor typeReciprocating typeNon lubricating/lubricatinglubricatingType of gas coolingOilNo. of compression stages3Compressor Brake horse power3882 KWVolumetric efficiency.94Mechanical efficiency.85Ratio of bore diameter to length stroke1.2Speed of piston5 m/sSuction pressure1.47 atmDischarge pressure16.3 atmGas discharge temperature293 K


Chapter 11

ECONOMIC EVALUATION AND FEASIBILITY

Economic analysis is an essential component to implement a project commercially. Pre-construction cost analysis based on equipments, raw material, maintenance, land charges, building charges, labour, marketing and research and development can give a fairly good estimate of the economic performance of plant. This analysis aims to find the initial capital investment, cost of production, the final profit and the minimum time required to recover the invested capital. Hence the accuracy of the estimate can be around + or - 25%.

Cost Estimation

Cost of Acetylene plant of capacity 432000 cum/yr in 2003 was USD 500,000.

Taking, 1$=50 INR

Cost= INR 2,50,00,000.

Chemical Engineering Plant Cost Index:

Cost index in 2003 = 402

Cost index in 2012-2013 = 852

Thus, Present cost of Plant = (original cost) x ((present cost index)/(past cost index))

= (2500000) x (852 / 402) = Rs. 5298507

i.e., Fixed Capital Cost (FCI) for plant with 500000 cum/yr.capacity =

5298507(500000/432000).6= Rs. 5784226

Fixed Capital Cost (FCI) for plant= Rs. 57,84,226

11.1 Estimation of Capital Investment Cost

11.1.1 Direct Costs:

Material and labor involved in actual installation of complete facility (70-85% of fixed-capital investment)

54


A) Equipment + installation + instrumentation + piping + electrical + insulation +

Painting (50-60% of Fixed-capital investment)

Purchased equipment cost (PEC): (15-40% of Fixed-capital investment) Consider purchased equipment cost = 25% of Fixed-capital investment

i.e., PEC = 25% of 5784226= 1446056= Rs. 1446056

Installation, including insulation and painting: (25-55% of purchased equipment cost.) Consider the Installation cost = 40% of Purchased equipment cost 40% of 1446056= 0.40 x 1446056= Rs. 578422

Instrumentation and controls, installed: (6-30% of Purchased equipment cost.) Consider the installation cost = 15% of Purchased equipment cost 15% of 1446056= 0.15 x 1446056 = Rs. 216908

Piping installed: (10-80% of Purchased equipment cost)

Consider the piping cost = 30% of Purchased equipment cost

30% of 1446056 = 0.30 x 1446056

Rs. 433816

Electrical, installed: (10-40% of Purchased equipment cost) Consider Electrical cost = 25% of Purchased equipment cost

25% of 1446056 = 0.25x 1446056 = Rs. 289211

Hence total cost of (1+2+3+4+5) = Rs 2964413 ---(51.2 % of FCI)

Buildings, process and Auxiliary: (10-70% of Purchased equipment cost) Consider Buildings, process and auxiliary cost = 40% of PEC = 40% of 1446056 = 0.40 x 1446056 = Rs 578422

Service facilities and yard improvement: (40-100% of Purchased equipment cost) Consider the cost of service facilities and yard improvement = 65% of PEC

55


= 65% of 1446056= 0.65 x 1446056= Rs. 939936

D. Land: (1-2% of fixed capital investment or 4-8% of Purchased equipment cost) Consider the cost of land = 5% of PEC = 5% of 1446056= 0.05 x 1446056

= Rs. 72302

Thus, Direct cost = Rs. 45550730 ----- (78.7 % of FCI)

11.1.2 Indirect costs:

Expenses which are not directly involved with material and labour of actual installation of complete facility (15-30% of Fixed-capital investment)

A. Engineering and Supervision: (5-30% of direct costs)

Consider the cost of engineering and supervision = 15% of Direct costs i.e., cost of engineering and supervision = 15% of 4555073

= 0.15 x 4555073= Rs. 683260

Construction Expense and Contractor’s fee: (6-30% of direct costs) Consider the construction expense and contractor’s fee = 14% of Direct costs i.e., construction expense and contractor’s fee = 14% of 4555073

= 0.14 x 4555073= Rs. 637710

Contingency: (5-15% of Fixed-capital investment)

Consider the contingency cost = 10% of Fixed-capital investment i.e., Contingency cost = 10% of 4555073= 0.10 x 4555073

= Rs. 455507

Thus,

Indirect Costs = Rs. 17764770 --- (30.7 % of FCI)

56


11.1.3 Fixed Capital Investment:

Fixed capital investment = Direct costs + Indirect costs = (45550730) + (17764770 )

i.e., Fixed capital investment = Rs. 63315500

Working Capital: (10-20% of Fixed-capital investment) Consider the Working Capital = 15% of Fixed-capital investment i.e., Working capital = 15% of 63315500= 0.15 x 6331550

= Rs. 9497320

Total Capital Investment (TCI):

Total capital investment = Fixed capital investment + Working capital = (63315500) + (9497320)

i.e., Total capital investment = Rs. 7, 28, 12,820.

11.2 Estimation of Total Product cost

11.2.1 Manufacturing Cost

Manufacturing Cost = Direct production cost + Fixed charges + Plant overhead cost.

A. Fixed Charges: (10-20% total product cost)

i. Depreciation: (depends on life period, salvage value and method of calculation-about 10% of FCI for machinery and equipment, and 2-3% for Building Value for Buildings)

Consider depreciation = 10% of FCI for machinery and equipment, and 3% for Building Value for Buildings)

57


i.e., Depreciation = (0.10x 1446056) + (0.03x72302) = Rs. 166296

Local Taxes: (1-4% of fixed capital investment) Consider the local taxes = 4% of fixed capital investment i.e. Local Taxes = 0.04 x 6331550= Rs. 253262

Insurances: (0.4-1% of fixed capital investment) Consider the Insurance = 0.6% of fixed capital investment i.e. Insurance = 0.006 x 6331550= Rs. 379893 Rent: (8-12% fixed capital investment )

Consider rent = 10% of fixed capital investment

10% of 6331550= 0.10 x 6331550

633155

Rent = Rs. 633155

Thus, Fixed Charges = Rs 1432606

.

B. Direct Production Cost:

Now we have Fixed charges = 10-20% of total product charges – (given) Consider the Fixed charges = 15% of total product cost

Total product cost = fixed charges/15% Total product cost = 1432606/15% Total product cost= 1432606/0.15 Total product cost (TPC) = Rs. 9550706

i. Raw Materials: (10-50% of total product cost)

Consider the cost of raw materials = 30% of total product cost

58


Raw material cost = 30% of 9550706= 0.30 x 9550706

Raw material cost = Rs. 2865212

Operating Labor (OL): (10-20% of total product cost) Consider the cost of operating labor = 15% of total product cost Operating labor cost = 15% of 9550706= 0.15 x 9550706 Operating labor cost = Rs 1432606

Direct Supervisory and Clerical Labor (DS & CL): (10-25% of OL) Consider the cost for Direct supervisory and clerical labor = 12% of OL Direct supervisory and clerical labor cost = 12% of 1432606 = 0.12 x (1432606)

Direct supervisory and clerical labor cost = Rs. 171912

Utilities: (10-20% of total product cost)

Consider the cost of Utilities = 15% of total product cost

Utilities cost= 15% of 9550706= 0.15 x 9550706

Utilities cost = Rs 14326059

Maintenance and repairs (M & R): (2-10% of fixed capital investment) Consider the maintenance and repair cost = 5% of fixed capital investment i.e. Maintenance and repair cost = 0.05x 6331550= Rs. 316577

Operating Supplies: (10-20% of M & R or 0.5-1% of FCI)

Consider the cost of Operating supplies = 15% of M & R

Operating supplies cost = 15% of 316577= 0.15 x 316577

Operating supplies cost = Rs. 47486

vii. Laboratory Charges: (10-20% of OL) Consider the Laboratory charges = 15% of OL

59


Laboratory charges = 15% of 1432606= 0.15x 1432606

Laboratory charges = Rs. 214890

viii. Patent and Royalties: (2-6% of total product cost)

Consider the cost of Patent and royalties = 5% of total product cost

Patent and Royalties = 5% of 9550706= 0.05 x 9550706

Patent and Royalties cost = Rs. 477535

Thus, Direct Production Cost = Rs. 19852277

C. Plant overhead Costs (50-70% of Operating labor, supervision, and maintenance or 5-15% of total product cost); includes for the following: general plant upkeep and overhead, payroll overhead, packaging, medical services, safety and protection, restaurants, recreation, salvage, laboratories, and storage facilities.

Consider the plant overhead cost = 60% of OL, DS & CL, and M & R Plant overhead cost = 60% of ((1432606) + (171912) + (316577)) Plant overhead cost = 0.60 x ((1432606) + (171912) + (316577)) Plant overhead cost = Rs. 1152657

Thus, Manufacture cost = Direct production cost + Fixed charges + Plantoverhead costs. Manufacture cost = 19852277+1432606+ 1152657

Manufacture cost = Rs. 22437540

11.2.2 General Expenses

General Expenses = Administrative costs + distribution and selling costs + research and

development costs

A. Administrative costs:(40-60% of operating labor)

60


Consider the Administrative costs = 50% of operating labor

Administrative costs = 0.5 x 1432606

Administrative costs = Rs. 716303

Distribution and Selling costs: (2-20% of total product cost); Includes costs forsales offices, salesmen, shipping, and advertising. Consider the Distribution and selling costs = 10% of total product cost Distribution and selling costs = 10% of 9550706 Distribution and selling costs = 0.1 x 9550706 Distribution and Selling costs = Rs. 955070

Research and Development costs: (about 3% of total product cost) Consider the Research and development costs = 3% of total product cost Research and Development costs = 3% of 9550706 Research and development costs = 0.03 x 9550706 Research and Development costs = Rs 286521 Thus, General Expenses = Rs. 1957894

Total Production cost = Manufacture cost + General Expenses

= (22437540) + (1957894)

Total production cost = Rs. 24395434

11.3 Gross Earnings/Income:

Wholesale Selling Price of acetylene per 6 cum = Rs. 800

Total Income = Selling price x Quantity of product manufactured = (800/6)x500000

Total Income = Rs. 66666666

61


Gross income= Total Income – Total Production Cost

(66666666) – (24395434) Gross Income = Rs. 42271232 Let the Tax rate be 40% (common) Taxes = 40% of Gross income

40% of 42271232= 0.4 x 42271232 Taxes = Rs. 16908493 Net Profit = Gross income - Taxes = Gross income x (1- Tax rate) Net profit = 42271232x (1-0.4) = Rs. 25362739.

11.4 Rate of Return:

Rate of return = Net profit x100 /Total Capital Investment

Rate of Return = (25362739) x 100 / 72812820

Rate of Return = 0.3483 x 100 = 34.83%

11.5 Pay Back Period (PBP):

Therefore, PBP (with no interest time) = (Fixed Capital Investment – Depriciation )/ (Avg. profit +Avg. Depreciation)

Let rate of depreciation be 15% annually.

Therefore, PBP = (63315500 - 166296)/ (25362739 + 166296)

= 2.41 years.

62


Chapter 12PLANT LOCATION AND SITE SELECTION

The geographical location of the plant has a profound effect on the profitability of the plant. Many factors must be considered when selectinga suitable plant site.

Factors affecting plant location:

Raw Material Supply

Location with respect to the Marketing Area

Transport Facilities

Availability of Labour

Availability of Utilities: Water, Fuel and Power

Availability of Land

Environmental Impact and Effluent Disposal

Climate

Taxation and Legal Restrictions

Flood and Fire Protection

Local Community Considerations

12.1.1 Raw Materials:

The availability and price of suitable raw materials often determine the site of location of the plant. It is perhaps one of the most important amongst all factors. In this project, calcium carbide and water are the major raw materials. In order to reduce transportation costs, plant shouldbe in proximity to calcium carbide plants. Since, fresh water is also required in large amounts, the location of the plant should not be in a water deficient region and multiple sources of water should be available.

12.1.2 Marketing Area:

The location of markets or intermediate distribution centres affect the

cost of product distribution and the time required for shipping. Proximity to the major markets is an important consideration in the selection of a plant site, because the buyer usually finds it advantageous to purchase from nearby sources. The closer the market, the lesser will be the transportation cost and the easier will be the access to the products by the buyer. Polymer Industries and fabricators would require acetylene in large amounts. So, proximity to these industries and markets ensures easy access for the buyers.

12.1.3 Transportation Facilities:

The transport of materials to and from the plant will be an overriding consideration in site selection. Here the site should be chosen so as to be closed to at least two major forms of transport: road, rail, waterway or a sea port. Road and rail transport is being increasingly used, and is suitable for long-distance transport of bulk chemicals. Air transport is convenient & efficient, so, the proximity of the site to an airport should be considered.

63


12.1.4 Utilities (Services):The process invariably requires large quantities of water for cooling and as raw material; therefore, the plant must be located near a source of water. Process water may also be drawn from a river, from wells or purchased froma local authority but the water has to be clean from impurities. Electrical power is also needed in large quantities and hence, location of the plant near power stations should be considered. A competitive priced fuel should also be looked for near or on the site power generation in emergencies.

12.1.5 Environment Impact & Disposal:

All industrial processes produce waste products & full consideration must be given for their effective disposal. The disposal of effluents should be done following the local waste disposals regulations & also, the appropriate authorities must be consulted during the initial site survey to determine the standards that must be met. Here, the byproduct of calcium hydroxide formed need not be considered as waste as it can be used for number of applications. The calcium hydroxide is stored in slurry tank and is sold to waste water plants.

12.1.6 Climate:

Adverse climate conditions at a site will increase cost. Abnormally low temperatures will require the provision of additional insulation & special heating for equipment & pipe runs. Stronger structures will be needed at locations which are subjected to strong wind or earthquakes. Besides, the effect of humidity and temperatures at the site must be taken into consideration because it affects the economic evaluation of the project.

12.1.7 Taxation and Legal Restrictions:

Capital grants, tax concessions & other inducements are often given by the government to direct renewed investments to preferred locations, such as inareas of high unemployment. The availability of such grants can be an overriding consideration in site selection.

12.1.8 Flood and Fire Protection:

Before choosing the plant site, the regional history of natural events like floods and hurricane damage should be examined. In case of major fire they should be provision for fire assistance from outside the fire department. Since, acetylene is a highly flammable gas, fire safety should be given a great deal of importance.


12.2 Plant Location Inferences

Considering all the factors for plant location, some favourable areas for the location of the plant are:

Calcutta, West Bengal.

New Delhi

Tirunalveli, Tamil Nadu

The key points considered for plant location were

Presence of calcium carbide plants. Investor friendly taxation and grants. Availability of utilities at reasonable costs. Presence of distributors.

These regions are also well connected by all means of transport.


Chapter 13PLANT LAYOUT

It is a plan of planning the optimum arrangement for industrial facilities, buildings, transport facilities, auxiliary facilities, storage facilities and all other services. An efficient plant layout should provide space needed to all these facilities in the most economical way. Ample space for personnel working in the area must be provided with minimum hazards. It is quite possible that the optimum layout might maximize a criterion for elevation in the cost but cost is also an important consideration. In planning the layout, the overall costs of the space and the facilities must be considered with reference to the hazards.

Some Principles that are to be followed in Plant Layout:

Storage of raw materials, intermediates, finished goods and hazardous materials should be located in isolated areas. Enough space must be provided for each piece of equipment, piping andso on. Elevated space must be put to an economical use. Easy handling of materials and equipment should be provided.

Safety and health hazards to the personnel and safety of equipment are to be considered. Transportation facilities such as rail, road and sea are to be taken into account.

The objectives of a plant layout are:

To provide overall simplification of the manufacturing process.

To minimize the cost of the handling material.

To utilize the space effectively.

To account for worker’s convenience as well as safety.

To avoid unnecessary capital investment and

To stimulate effective labour utilization.

An effective plant layout provides the management with numerous advantages and requires layout engineers with balanced personality as well as with sound technical knowledge. Systematic evaluation of the plant layouts can be achieved by operating a pilot plant and then comparing various process parameters. The economic construction and efficient operation of a process unit will depend on how well the plant and equipment specified on the process flow sheet is laid out.

2 Principal factors considered are:

Economic considerations: construction and operating costs

Storage

The process requirements

Convenience of operation

Floor space and Convenience of maintenance

Safety

Future expansion

Byproduct Storage

66


13.2.1 Costs:

The cost of construction can be minimized by adopting a layout that gives the shortest run of connecting pipe between equipment, and the least amount of structural steel work. However, this will not necessarily be the best arrangement for operation and maintenance. Therefore, the layout has to be made in such a way that least expenses are involved and at the same time, the efficiency of the process is not hindered.

13.2.2 Storage:

For any process, storage of raw materials and finished products should be given paramount importance. The raw materials required for the process, calcium carbide and water are stored close to the generator whereas the final product storage is near to the compressor. Storage cabin is provided for the storage of calcium carbide which comes in weatherproofed drums. Purified water is stored in a water tank. Acetylene is stored in cylinders with acetone and the acetylene cylinders are stored in cylinder racks.

13.2.3 Process requirements:

The equipment should be placed according to the process requirement. The generator is placed below ground level so that it becomes easier for loading of calcium carbide. Similarly, the slurry collection tank is placed at even lower level for effective collection of slurry.

13.2.4 Operations:

Equipment that needs to have frequent attention should be located convenient to the control room. Valves, sample points, and instruments should be located at convenient positions and heights. Sufficient workingspace and headroom must be provided to allow easy access to equipment.

13.2.5 Floor space and convenience for maintenance:

The Engineer should follow the rule of practising economy of floor space, consistent with good housekeeping in the plant and with proper considerations given to line flow of materials, access to equipments, space to permit working on parts of equipment that need frequent servicing and safety and comfort of the operators. Heat exchangers need to be located in convenient positions so that the tube bundles can be easily withdrawn for cleaning and tube replacement. Vessels that require frequent replacement

of catalyst or packing should be located in the isolated parts of building. Equipment that requires dismantling for maintenance, such as compressors , should be places under cover.

13.2.6 Safety:

An important consideration that must be taken into account in every aspect of construction is safety. The plant must be constructed in such a way that in case of any catastrophe, suitable safety measures can be adopted in the least amount of time. Since, acetylene is a highly flammable gas, the importance for safety consideration is even more. Water jets are provided near acetylene storage to reduce the temperature of cylinders. In addition to general safety guidelines, the government guidelines should also be met in best possible ways.

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13.2.7 Plant expansion:Plant expansion is a factor that should always be kept in mind. The cost of change must be borne in mind, for the economics of larger units may, in the end, make replacement imperative. Equipment should be located so that it can be conveniently tied in with any future expansion of the process. Space should be left on pipe alleys for future needs.

13.2.8 By-product storage:

Since by product is evolved in the reaction of calcium carbide with water, it is quite important to give due consideration to the process if waste disposal. The calcium hydroxide evolved should not be considered as waste as it is a very useful inorganic compound. It is sold for other uses like sewage treatment, fresh water treatment etc. The use of the calcium hydroxide is determined by itspurity. Calcium hydroxide is stored in lime pits close to the generator.


Chapter 14SAFETY AND ENVIRONMENTAL ISSUES

General Considerations

Acetylene is highly flammable and explosive gas and in air concentrations in the range of 2.5% to 80%, it gets ignited at a minimum temperature of 305°C. It also reacts with certain metals like copper forming metal acetylide which is extremely shock sensitive.

When acetylene is stored in large amounts at pressures greater than 15psig, it may be polymerized leading to severe explosive condition. All piping carrying acetylene gas should be earthed properly since discontinuity in earthing can cause electrostatic charge to build up leading toexplosive conditions. In order to avoid explosive atmosphere in the working area, adequate ventilation should be provided The possibility of accidents due to electrostatic build up is more when therelative humidity of the atmosphere is less than 30%. Therefore, proper care must be taken under these conditions.

The ignition temperature of acetylene-air mixture decreases in the presence of phosgene which is a common impurity in acetylene. So, the purity of acetylene gas must be monitored continuously.

Hazard Identification

Emergency overview:

The gas may catch fire and explode as the contents of the cylinder are under pressure. The gas can also lead to asphyxiation as oxygen content for breathing is reduced. The gas should be kept away from sources of ignition as it is highly flammable. The gas should be kept away from heat (<52°C/125°F)

The routes of entry are by inhalation, dermal contact and by eye contact.

Potential acute health effects:Inhalation: Inhalation of this product may cause dizziness, irregular heartbeat, narcosis, nausea or asphyxiation. Skin: Contact with rapidly expanding gas may cause burns or frostbite.

Ingestion: Since the product is a gas, it will probably be inhaled rather than ingested. Consider first the preventive measures in case of inhalation. Eyes: Contact with rapidly expanding gas may cause burns or frostbite.

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14.3 First Aid Measures

Prompt medical attention is mandatory in all cases of overexposure to this gas. Rescue personnel should wear a self-contained breathing apparatus and be aware of extreme fire and explosion hazard.Inhalation:

In case of inhalation, conscious persons should be assisted to an uncontaminated area and made to inhale fresh air. The person should be kept warmed and calm. Quick removal from the contaminated area is most important consideration. Unconscious persons should be moved to an uncontaminated area, given assisted resuscitation and supplemental oxygen.

Skin Contact

In case of contact, the skin should be flushed immediately with lots of water. Medical attention is needed if symptoms persist.Eye Contact:

Individual in contact with a gas should not wear contact lenses. In case of contact, eyes should be flushed immediately with plenty of water for atleast 20 minutes.

14.4 Fire Fighting Measures

Auto ignition temperature: 304.85°C (580.7°F)

Flammable Limits: Lower: 2.2% ; Upper: 80 to 100% Products of Combustion: carbon dioxide, carbon monoxide

Fire Hazard: Extremely flammable in the presence of open flames, sparks and static discharge. Firefighting media to be used: Dry chemical, CO2, water spray (fog) or foam

In case of fire, the gas should be allowed to burn if flow cannot be shut off immediately. Water should be applied from a safe distance to cool container and protect surrounding area. Gas may accumulate in confined areas. Gas maytravel considerable distance to source of ignition and flash back. Fire-fighters should wear appropriate protective equipment and self-contained breathing apparatus (SCBA) with a full face-piece operated in positive pressure mode.

14.5 Accidental Release Measures

Personal precautions:

All personnel must be evacuated from the affected area and appropriate protective equipment must be used.Environmental Precautions:

The emergency procedures to deal with accidental gas releases should be in place to avoid contamination of the environment. The relevant authorities must be informed if the product has caused any environmental pollution.Methods for cleaning up:

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The emergency personnel must be contacted immediately. The leak should be stopped if there is no risk. Spark proof tools and explosion proof equipments should be used.

14.6 Exposure Controls

Engineering Controls: Only well ventilated areas should be used for gas production.

Personal Protection:

Respiratory - Respirator selection must be based on known or anticipated exposure levels, the hazards of the product and the safe working limits of the selected respirator.

Hands: Suitable gloves should be used.

Eyes: Safety glasses with side shields should be used.

Skin: Appropriate personal protective suit should be used. Fire retardant clothing may be required when using flammable products.


Chapter 15EFFECTIVE USE OF BY-PRODUCT

In the generation of acetylene from calcium carbide, calcium hydroxide is produced as by-product. Calcium hydroxide water mix is commonly referred to as lime slurry or carbide lime. It is important to get rid of calcium hydroxide slurry in the best possible way. Disposing of acetylene generationco-products can be either an asset or an expense to the company. Lime slurry will have to be treated as a waste product if there is lack of market. Asa waste product, it falls under federal, state and local regulations that apply to industrial wastes. Disposing of lime slurry as a waste product would involve permits, adherence to guidelines and unwanted expenses. But, on the other hand, as an industrial product, regulation is less rigorous. Consequently, if the by-product is considered as a waste, the expenses for the company will be more. But, if suitable markets can be found for lime slurry, it will be quite beneficial to the company. Thus by changing lime slurryfrom a waste item to a salable product can sidestep the regulatory thicket.

Some major uses of lime slurry are:

Chemical processing - used in chemical processing plants;

Dehalogenation - employed in production of organic chemicals such as propylene glycol; pH control - neutralization of industrial acids; metallurgical applications - a part of the manufacture of iron, steel, and non-ferrous metals; Pulp and paper production – applied in several phases of paper production; Coke production - recovery of ammonia in coke plants and other processes; Coatings manufacture - pH control and varnish clarification;

Petroleum refitting - sulfur reduction;

Glass manufacture - sand washing and glass compounding; Flue gas desulfurization – cleaning stack gases; De-icing - a component of nonchlorine de-icing salts;

Industrial waste water treatment- used as a precipitator and pH balancer; Sewage and waste treatment – aids in odor, insect, and parasite control; Masonry - a part ofthe manufacture of concrete and brick products; Soil conditioning – incorporation improves soil characteristics; Odor control - controls landfill odor

Fire suppression - use of slurry to subdue underground


REFERENCES

Vivian B. Lewis, “Acetylene: A handbook for the student and

manufacturer”, 1st edition, The Macmillan Company, 1900. pp. 25-101.

F. H. Leeds and W. J. Atkinson Butterfield, “Acetylene: The principles of its

generation and use”, 2nd edition, C. Griffin and Co., 1971. pp 61-85. M. Gopala Rao and Marshall Sittig, “Dryden’s Outlines of Chemical

Technology”, 2nd Ed., East-West press, 2005. pp.65-70.

George. T. Austin, “Shreve’s Chemical Process Industries”, Fifth edition, McGraw Hill Book Company, 2005. pp. 124-127.

George Gilbert Pond, “Calcium Carbide and Acetylene”, Revised edition, Pennsylvania State University, 1909. pp. 28-43.

Compressed Gas Association, “Acetylene”, 12th edition, 2009. pp 10-13.

G.F Thomson, “Acetylene Gas and Calcium Carbide”, 1st edition, Bixteth Press, 1898. pp 27-34, 59-69.

R. H. Perry and Don W. Green, “Perry’s Chemical Engineers’ Hand

Book”, 7th Ed., Mc-Graw Hill International edition, 2002. pp. 3-96, 3-150, 3-211.

Max S. Peters and Klaus Timmerhaus, “Process Plant Design and Economics For Chemical Engineers”, Fifth edition, Mc-Graw Hill Book Company, 2011. pp.52-57

McCabe, Warren L. Smith, “Unit Operations of Chemical Engineering”, Seventh edition, Mc-Graw Hill Book Company, 2005. pp. 836-850.

Robert E. Treybal, “ Mass- transfer Operations”, 3rd Ed. , Mc-Graw Hill Book Company, 1981. pp. 187-200, 300-309.

J. M. Smith, H. C. Van Ness and M. M. Abbot, “Introduction to Chemical engineering Thermodynamics”, 6th Ed., Mc-Graw Hill Book Company, 2001. pp. 116-140.

R.K Rajput, “Thermal Engineering”, Eighth edition, Laxmi Publications, 2010. pp.1202-1341

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