Final Project Aai Final

1

A

PROJECT REPORT

ON

Production of Sulphuric Acid from DCDA Process

SUBMITTED BY:

AKSHAY AGARWAL (Roll No. 1104351003)

ANURAG VERMA (Roll No. 1104341009)

ISHA SHUKLA (Roll No. 1104351015)

Report Submission Date:

Submitted in

Partial fulfillment of the requirements for the awarding of degree of

BACHELOR OF TECHNOLOGY IN

CHEMICAL ENGINEERING

Submitted To

UTTAR PRADESH TECHNICAL UNIVERSITY, LUCKNOW

UNDER THE EXPERT GUIDANCE OF:

Er. PRADEEP YADAV

DEPARTMENT OF CHEMICAL ENGINEERING

BUNDELKHAND INSTITUTE OF ENGINEERING AND TECHNOLOGY

JHANSI-284128

SESSION 2014-15

2

CERTIFICATE

This is certified that Akshay Agarwal, Anurag Verma and Isha Shukla have carried out this

project entitled Production of Sulphuric Acid from DCDA Process for the award of

Bachelor of Technology from Uttar Pradesh Technical University, Lucknow under my

supervision. The project embodies result of original work and studies carried out by student

themselves and the contents of the project do not form the basis for the award of any other

degree to the candidates or to anybody else.

Er. A.D. Hiwarikar Er. Pradeep Yadav

Head of the department Assistant Professor

BIET, Jhansi BIET, Jhansi

Date:

3

ACKNOWLEDGEMENT

For the successful accomplishment of our project, we would like to thank The Almighty for His

blessings. A special thanks to our project guide Er. Pradeep Yadav whose help, stimulating

suggestions and encouragement, helped us to coordinate our project especially in writing this

report. We rather find words short to express our gratitude to him. His involvement and personal

interest has enabled us to accomplish this project work successfully.

We are highly thankful to Er. A.D. Hiwarikar, Er. Sudeep Yadav, Er.Ravindra Kumar , Er.

S.K.Srivastava, Er. Ajitesh Mehra and Er. Neeraj Singh, Department of Chemical

Engineering, B.I.E.T. Jhansi for their full cooperation in providing necessary facilities,

environment needed for the work.

Finally we wish to express our modest and sincere regards to our parents and friends for their

intensive support and encouragement for this project work.

4

ABSTRACT

The project includes the detailed designing of a four stage adiabatic catalytic bed reactor for a

sulphuric acid plant of capacity 1000 TPD (tons per day). The feed is at 1 atm and 4100 C. There

are two main processes for manufacturing of sulphuric acid namely the chamber process and the

contact process. The pioneer sulphuric acid manufacturing plants, adopted the chamber process

but at the beginning of the twentieth century with technological advancements, the contact

process gained popularity as the conversion achieved was much higher than that achieved

through chamber process. Chamber process produced sulphuric acid of concentration less than

80 %.The major disadvantage includes the limitations in throughput, quality and concentration of

the acid produced. All known new plants uses the contact process although some older chamber

process plants may still be in use.

The contact process has been gradually modified to use double absorption (also called double

catalyst), which increases yield and reduces stack emission of unconverted SO2. Conversions

using single absorption contact process were typically about 97-98 percent. While in the current

double absorption flow process, achievable conversions are as high as 99.7 percent.

The project mainly comprise of the basic parts of the sulphuric acid manufacturing plant, the

equipments and the catalyst used, flow of materials in and out of the equipments, their material

and energy balances, heat duty of the heat exchangers, weight of the catalyst required and

pollution control.

.

5

TABLE OF CONTENTS

1. List of Tables6

2. List of Figures...7

3. Notations...8

4. Introduction.....10

5. Literature Review....11

6. Uses and Applications.12

7. Sulphuric Acid- World Market....13

8. Status of Existing Sulphuric Acid Plants In India...14

9. The Contact Process........16

10. Available Technologies for Pollution Control........20

11. Material Balance........23

12. Energy Balance.......30

13. Weight of Catalyst......42

14. Summary Sheet.......55

15. Conclusion..57

16. References.......58

17. Appendix.....59

6

1. LIST OF TABLES

Table 1: Capacity wise number of sulphuric acid plants in India.

Table 2: Combustion Chamber Material Balance.

Table 3: Material Balance on First Three Catalytic Beds.

Table 4: Material Balance on Fourth Catalytic Bed.

Table 5: Heat Capacity equation constants for incoming gas mixture.

Table 6: Heat Capacity equation constants for outgoing gas mixture.






Table12: Heat Capacity equation constants for outgoing gas mixture.

Table 13: Calculations of First Catalytic Bed.

Table 14: Rate Calculations of First Catalytic Bed.

Table 15: Calculations of Second Catalytic Bed.

Table 16: Rate Calculations of Second Catalytic Bed.

Table 17: Calculations of Third Catalytic Bed.

Table 18: Rate Calculations of Third Catalytic Bed.

Table 19: Calculations of Fourth Catalytic Bed.

Table 20: Rate Calculations of Fourth Catalytic Bed.

Table 21: Table for mole fractions expressed in terms of conversion.

Table 22: Mole percent of gases entering the converter.

7

2. LIST OF FIGURES

Figure 1: Structure of H2SO4 molecule.

Figure 2: Pie Chart showing Global Consumption of Sulphuric Acid.

Figure 3: Sulfuric acid- structure of the world production capacity by region, 2012.

Figure 4: Double Absorption Contact Process.

Figure 5: Four Stage Catalytic Reactor for Contact Process.

Figure 6: Activity of cesium based catalyst in comparison with conventional catalyst.

Figure 7: Combustion Chamber Balance

Figure 8: Material balance over first three catalytic beds.

Figure 9: Primary absorption tower material balance.

Figure 10: Fourth catalytic bed material balance.

Figure 11: Final absorption tower material balance

Figure 12: Enthalpy balance over first catalytic bed.

Figure 14: Enthalpy balance over third catalytic bed.

Figure 15: Enthalpy balance over fourth catalytic bed

Figure 16: Plot of 1/-RA versus XA for first bed

Figure 17: Plot of 1/-RA versus XA for second bed

Figure 18: Plot of 1/-RA versus XA for third bed

Figure 19: Plot of 1/-RA versus XA for fourth bed

8

3. NOTATIONS

HR Sum of enthalpies of all materials entering the reaction process

relative to the reference state for the standard heat of reaction at

298 K and 101.32 kPa.

H298 Standard heat of reaction at 298 K and 101.32 kPa.

q Net energy or heat added to the system.

HP Sum of enthalpies of all leaving materials referred to the standard

reference state at 298 K

HRT Standard heat of reaction at temperature T (K)

[ (ni Hf) ]products Standard heat of formation of products.

[ (ni Hf )]reactants Standard heat of formation of reactants.

T Temperature expressed in K

k1 Rate of forward reaction expressed in gmol/s-(gm cat)-atm3/2

k2 Rate of backward reaction expressed in gmol/s-(gm cat)-atm

NA Number of moles at conversion XA.

NA0 Initial number of moles.

Superficial mass velocity.

Fluid density

Superficial velocity in axial direction.

Reaction rate expressed in pseudo homogeneous form (i.e. number

of moles transformed per unit time per unit of total reactor volume)

Enthalpy change for the reaction at the indicated conditions.

Bulk density of the catalyst (total mass of catalyst / total volume of

9

reactor)

=

Global reaction rate per unit mass of catalyst.

PA Partial pressure of A

Po Total pressure.

yA Mole fraction of A

Stoichiometric coefficient for reactant A (negative for reactants)

10

4. INTRODUCTION

Sulfuric acid is a highly corrosive strong mineral acid with the molecular formula H2SO4 and

structure shown in the figure below:

Figure 1: Structure of H2SO4 molecule.

It is a pungent-ethereal, colorless to slightly yellow viscous liquid which is soluble

in water at concentrations. Sometimes, it is dyed dark brown during production to alert people to

its hazards. The historical name of this acid is oil of vitriol. Sulphuric acid is an important

chemical, which has large-scale industrial uses. Its major user is the phosphate fertilizer

industry. Other important applications are in petroleum refining, steel pickling, rayon & staple

fiber, alum, explosives, detergents, plastics and fibers etc. Sulphuric acid industry is very old and

has been continuously adopting the technological developments. The progress made in sulphuric

acid manufacture during recent decades has led to changes in the method and technology of its

manufacture, resulting mainly in the reduction of emissions of sulphur compounds to air and

reduction of harmful waste. [3]

It started with Lead Chamber process followed by contact process with Single

Conversion Single Absorption (SCSA) and now Double Conversion Double Absorption Process

(DCDA). The Sulphuric Acid production through Contact Process is very mature. However,

improvement in conversion and absorption stages are being introduced from time to time to

increase conversion and absorption efficiencies, which also result in reduction in emissions.

Most of the plants use elemental sulphur as raw material and in few cases Copper/ Zinc Smelters

gases are being used to produce Sulphuric Acid. [3]

11

5. LITERATURE REVIEW

Although sulphuric acid is now one of the most widely used chemicals, it was probably little

known before the 16th century. It was prepared by Johann Van Helmont (c.1600) by destructive

distillation of green vitriol (ferrous sulfate) and by burning sulfur. [3]

In the seventeenth century, the German-Dutch chemist Johann Glauber prepared sulfuric acid

by burning sulfur together with saltpeter (potassium nitrate, KNO3), in the presence of steam. As

saltpeter decomposes, it oxidizes the sulfur to SO3, which combines with water to produce

sulfuric acid. In 1736, Joshua Ward, a London pharmacist, used this method to begin the first

large-scale production of sulfuric acid.[3]

In 1746 in Birmingham, John Roebuck adapted this method to produce sulfuric acid in lead-

lined chambers, which were stronger, less expensive, and could be made larger than the

previously used glass containers. Sulfuric acid created by John Roebuck's process approached a

65% concentration. [3]

After several refinements, this method, developed into the so-called the lead chamber

process or "chamber process. Later refinements to the lead chamber process by French

chemist Joseph Louis Gay-Lussac and British chemist John Glover improved concentration to

78%. However, the manufacture of some dyes and other chemical processes require a more

concentrated product. Throughout the 18th century, this could only be made by dry

distilling minerals in a technique similar to the original alchemical processes. Pyrite (iron

disulfide, FeS2) was heated in air to yield iron(II) sulfate, FeSO4, which was oxidized by further

heating in air to form iron(III) sulfate, Fe2(SO4)3, which, when heated to 480 C, decomposed

to iron(III) oxide and sulfur trioxide, which could be passed through water to yield sulfuric acid

in any concentration. However, the expense of this process prevented the large-scale use of

concentrated sulfuric acid.[3]

In 1831, British vinegar merchant Peregrine Phillips patented the contact process, which

was a far more economical process for producing sulfur trioxide and concentrated sulfuric acid.

It was little used until a need for concentrated acid arose, particularly for the manufacture of

synthetic organic dyes. Today, nearly all of the world's sulfuric acid is produced using this

method. In the current flow process, achievable conversions are as high as 99.7 percent.[3]

12

6. USES AND APPLICATIONS

Sulfuric acid is one of the most important compounds made by the chemical industry. It

is used to make, literally, hundreds of compounds needed by almost every industry.

By far the largest amount of sulfuric acid is used to make phosphoric acid, used, in turn,

to make the phosphate fertilizers. It is also used to make ammonium sulfate, which is a

particularly important fertilizer in sulfur-deficient.

It is widely used in the manufacture of chemicals, e.g., in making hydrochloric acid,

nitric acid, sulfate salts, synthetic detergents, dyes and pigments, explosives, and drugs.

It is used in petroleum refining to wash impurities out of gasoline and other refinery

products, and in waste water treatment.

Also widely used in metal processing for example in the manufacture of copper and

the manufacture of zinc and in cleaning the surface of steel sheet, known as pickling.

It is also used to make caprolactam, which is converted into polyamide 6 and in

the manufacture of titanium dioxide, used, for example, as a pigment.

It is used in the production of numerous goods including various cleaning agents,

domestic acidic drain cleaners and electrolytes in lead-acid batteries.[2]

Figure 2: Pie Chart showing Global Consumption of Sulphuric Acid

Global Sulphuric Acid Consumption By End Use Sector in 2013

Fertilizer Production 56%

Other Applications 23%

Manufacture of Chemicals 11%

Agriultural Chemistry 10%

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7. SULPHURIC ACID - WORLD MARKET

The worldwide market for sulphuric acid witnessed stable growth between 2009-2012,

supported by increasing demand from major end-use industries. In 2012, sulphuric acid

production grew by more than 7 million tonnes and exceeded 230.7 million tonnes. Asia

ranks as the leading sulfuric acid manufacturer, accounting for around 45% of the overall

production. China, the US, India, Russia and Morocco are the top five sulfuric acid

manufacturing countries.[6]

Figure 3: Sulfuric acid- structure of the world production capacity by region, 2012

APAC (Uganda) is the major sulphuric acid consumer. In 2012, its consumption volume

surpassed the 106 million mark. The fertilizer industry is the products major end-use sector,

consuming over55% of the overall sulfuric acid output. In 2011, the world foreign trade in

sulphuric acid was valued at more than USD (US dollar) 1.87 billion. Europe is the leading

sulphuric acid exporter, whilst Asia is a market leader in terms of imports. The worldwide

sulphuric acid production is poised to increase in the forthcoming years to go beyond 257.6

million by end-2015. [6]

14

8. STATUS OF EXISTING SULPHURIC ACID PLANTS IN INDIA

In India, there are about 140 Sulphuric Acid Plants (130 Sulphur based & 10 Smelter Gas

based) with Annual Installed Capacity of about 12 Million MT. [6]

Table 1: Capacity wise number of sulphuric acid plants in India

Installed Capacity (MT/Day) Number of Plants %

upto 50 18 12.9

51-100 45 32.1

101-200 40 28.6

201-300 17 12.1

301-500 5 3.6

501-1000 9 6.4

1001- 2000 4 2.9

above 2000 2 1.4

Total 140 100.0

The current annual production of Sulphuric Acid is about 5.5 Million MT, against the

installed capacity of 12 Million MT/Annum from Sulphur based as well as Smelter Gas based

plants. The demand of Sulphuric Acid is fully met by the current production, as the installed

capacity is more than double the demand.

The environmental problems arising due to Sulphuric Acid manufacture include:

Off gases from absorption tower containing oxides of Sulphur (SOx) and acid mist.

Liquid effluent generated through waste heat boiler blow-down, spillage & leakage from

equipment, washing of equipment, cooling tower bleeding etc.

Generation of Solid Waste viz. Sulphur muck & spent catalyst.

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Presently, Gaseous emission limits prescribed by CPCB for Sulphuric Acid Plants are as under:

SO2 : 4.0 Kg/MT of Sulphuric Acid produced (Conc. 100%)

Acid Mist : 50 mg/Nm3

However, due to advancement in process and pollution control technologies, it may be

possible to further reduce & control the emissions of SOx and acid mist. In view of this, CPCB

took up a project to revisit the emission standards. [6]

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9. THE CONTACT PROCESS

Until 1990 there were no plants using the contact process, the more popular process being

used was the chamber process. But, up to mid 1920s there were considerable changes in the

contact process technology, equipments and the catalyst being used. [2]

The primary raw material for producing intermediate product of sulphur dioxide is

elemental sulphur. This can either be made by burning sulphur in an excess of air or by heating

sulphide ores like pyrite in an excess of air. In either case, an excess of air is used so that the

sulphur dioxide produced is already mixed with oxygen for the next stage. [2]

These traditional contact plants can be further subdivided into the double contact double

absorption process (DCDA), which is the type of process now most commonly used in new

plants with intermediate absorption and the older, without intermediate absorption also referred

to as the single contact single absorption process (SCSA). In DCDA Plant, SO3 is removed from

the gas stream after 3rd bed, which shifts the equilibrium and increases the rate of the forward

SO2 to SO3 reaction resulting in higher overall conversion and reduces stack emission of

unconverted SO2.Conversions using single absorption contact process were typically about 97-98

percent. While in the current double absorption flow process, achievable conversions are as high

as 99.7 percent. [2]

6.1 Double Conversion Double Absorption (DCDA) Process

The main steps involved in DCDA process are as below:

Melting solid Sulphur with steam coils, followed by filtration or settling of impurities to

obtain clean sulphur containing less than 10 mg/l of ash.

Burning the molten Sulphur with air to produce gas-containing SO2.

Cooling the hot gas in Waste Heat Boiler System to produce superheated or saturated steam

at conditions fixed, as per requirements.

Catalytic oxidation of SO2 to SO3 in three consecutive passes of converter containing V2O5

catalyst with intercooling of gas in between. The exothermic heat of reaction is utilized to

produce steam in Waste Heat Boiler system and to reheat the gases going to pass IV from the

intermediate absorber.[6]

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The process flow sheet is shown below:

Figure 4: Double Absorption Contact Process

6.2 Chemical Reactions

In the manufacture of sulphuric acid from sulphur, the first step is the burning of sulphur in a

furnace to form sulfur dioxide: [1]

S (l) + O2 (g) SO2 (g) H= -298.3 kJ

Following this step, the sulphur dioxide is converted to sulphur trioxide, using a catalyst,

SO2 (g) + O2 (g) SO3 (g) H= -98.3 kJ

The final step is reacting sulphur trioxide with water to form sulphuric acid.

SO3 (g) + H2O (l) H2SO4 (l) H= -130.4 kJ

6.3 Catalyst

A commercial sulphur dioxide- converting catalyst consists of 4-9 wt % vanadium pentaoxide,

V2O5, as the active component, together with alkali metal sulphate promoters. At operating

temperatures the active ingredient is a molten salt held in a porous silica pellet. Normally

V2O 5

18

potassium sulphate is used as a promoter but in recent years also caesium sulphate has been used.

Caesium sulphate lowers the melting point, which means that the catalyst can be used at lower

temperatures. The carrier material is silica in different forms. The lower temperature limit is 410-

430 C for conventional catalysts and 380-390 C for caesium doped catalysts. The upper

temperature limit is 600-650 C above which, catalytic activity can be lost permanently due to

reduction of the internal surface. These catalysts are long lived up to twenty years and are not

subject to poisoning except fluorine. [2]

6.4 Contact Process Equipments

The main equipments being used in the process are

1) Combustion Chamber

2) Converters

3) Absorbers

4) Heat Exchangers

6.4.1 Converters - heart of the contact sulphuric acid plant

The reactor is often the central unit around which a chemical plant is designed. Good

reactor design is thus important for the performance of the plant. The chemical conversion of

sulphur dioxide to sulphur trioxide is designed to maximize the conversion by taking into

consideration that:

1) Equilibrium is an inverse function of temperature and a direct function of oxygen to sulphur

dioxide ratio.

2) Rate of reaction is a direct function of temperature.

3) Gas composition and amount of catalyst affect the rate of conversion and kinetics of the

reaction.

4) Removal of sulphur trioxide formed allows more sulphur dioxide to be converted.

The commercialization of these basic conditions makes possible high overall conversion

by using a multi pass converter wherein, at an entering temperature of 410C to 440C (the

ignition temperature), the major part of conversion takes place (60 to 75 %) in the first catalytic

bed with an exit temperature of 600C or more, depending largely on the concentration of

19

sulphur dioxide in the gas. The successive lowering of temperatures between stages ensures an

overall high conversion. [2]

The converter is usually provided with trays for supporting the catalyst and manholes for

access to it. Converters have usually been made of cast iron and aluminum-coated steel, but

stainless steel is now the preferred material of construction. Pressure drop through the converter

must be minimized to reduce power consumption. All these must be optimized to secure the

maximum yield and profit. [2]

6.5 Additional Data & Specification

Total Pressure = 1 atm

Feed composition (Mole Percent)

SO2 10

O2 11

N2 79

Overall Conversion = 99.8 %. [1]

The four stage catalytic reactor is shown below:

Figure 5: Four Stage Catalytic Reactor for Contact Process

20

10. AVAILABLE TECHNOLOGIES FOR POLLUTION CONTROL

In upcoming plants, following features are considered important:

Selection of 5-stage converter for maximum conversion efficiency.

Use of sulphur filter for minimizing ash content.

Use of Cesium based catalyst in last bed of Converter for maximum conversion efficiency.

Selection of high efficiency mist eliminators ensuring minimum acid mist exhaust.

Use of Waste heat recovery from acid system.

Use of suitable start-up scrubbing system.[6]

10.1Modified Converter

Existing plants are generally based on 4 stage Converter except for very few plants based on

5 stage Converter that has come up recently. 5-stage converter helps in increasing the conversion

efficiency. This minimizes the stack emissions level of SO2. With conventional catalyst the

conversion efficiency can be increased from 99.7% to 99.8%.

(1 kg SO2 instead of 2 Kg SO2 per MT of acid). [6]

10.2 Cesium Based Catalyst

The addition of Cesium Catalyst (CS) to the conventional Alkali-Vanadium Catalyst has

long been known to enhance the low temperature properties of the catalyst. Cesium based

Catalyst offers high activity at low operating temperature. Emissions from existing plants can

roughly be cut in half without increasing catalyst volume. The acid production capacity can be

increased by using higher strength sulphur dioxide gas without increasing SO2 emissions and

plant pressure drop. New acid plants may be designed with low SO2 emission by selecting

different type of Catalysts for different stages. [6]

21

Figure 6: Activity of cesium based catalyst in comparison with conventional catalyst.

10.3Mist Eliminators

Mist is inevitably formed at various points in Sulphuric Acid Plants. If mist is unchecked,

and carried through rest of the plant in the gas stream, it causes corrosion inside the plant and

environmental menace outside it. Mist is distinct from acid spray, which is formed in the towers

by purely physical process of aspiration into the gas stream of liquid droplets. Now a days, Mist

eliminators that are designed to remove virtually any type of mist from any gas stream are

available. Mist eliminators excel at collecting, the very difficult to remove sub micron size mist

particles from gas stream. [6]

10.4 Waste Heat and Heat Recovery System

The waste heat system is completely integrated in DCDA plants. In economizers that cool

the gases from third & fourth bed of converter, heat is utilized for preheating feed water for

WHB System. Heat generated in Sulphur furnace, heats up this feed water and steam is

generated at about 2500C temperatures. This steam is superheated to about 4000 C for cooling the

1st stage out converter gases. This superheated steam can be used for generating power and

saturated steam for process heating. The Heat Recovery System is basically an absorber that

operates at about 2000 C and uses a boiler to remove the absorption heat as low pressure steam

(at upto 10 bar), instead of acid coolers (where heat is wasted). [6]

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10.5 Scrubbing System

In DCDA Sulphuric Acid plants, emission levels of SO2 are higher during start-up or shut down

when SO2 to SO3 conversion is not proper. Also in SCSA Plant, the emission levels of SO2 are

normally high. While in first case, the start-up scrubbers are required to take care of extra SO2

load during unstabilized conditions, start-up & shutdown, in second case, a continuous scrubbing

unit is required to take care of tail gases going out for the stack.[7]

23

11. MATERIAL BALANCE

11.1 Assumptions

1. Complete burning of S in the burner.

2. 99.8% conversion of SO2 toSO3 in the reactor.

3. Overall absorption of SO3 in the process is 100%

4. 40% excess oxygen is provided.

5. Humidity of entering air is 65% at 300C

11.2 Calculations

Capacity: 1000 TPD H2SO4 plant

Basis: 1 hr of operation

Purity: 98 % pure acid

Reactions:

S (l) + O2 (g) SO2 (g)

SO2 (g) + O2 (g) SO3 (g)

SO3 (g) + H2O (l) H2SO4 (l)

1000 TPD H2SO4 = (1000 x 103)/ 24 = 41,666.67 kg/hr

98% pure acid produced = 41,666.67 x 0.98 = 40,833 kg/hr

No. of moles of acid produced = 40,833.33 / 98 = 416.67 kmol/hr

(Molecular weight of H2SO4=98)

Overall absorption of acid = 100 %

SO3 (g) + H2O (l) H2SO4 (l)

Therefore, by stoichiometry,

SO3 required =416.67 kmol/hr

Overall conversion of SO2 to SO3 = 99.8 %

V2O 5

24

SO2 (g) + O2 (g) SO3 (g)

Let SO2formed be X kmol/hr

0.998 X=416.67

SO2 required =X= 416.67/0.998 = 417.501 kmol/hr

O2 required = 417.501 x 0.5 =208.75 kmol/hr

11.1.1 Combustion Chamber Balance

Figure 7: Combustion Chamber Balance

S (l) + O2 (g) SO2 (g) (Assuming 100 % combustion)

S required = 417.501 kmol/hr =13,360.053 kg/hr

O2 required = 417.501 x 1 = 417.501 kmol/hr

Total O2 required = 417.501 + 208.75 = 626.25 kmol/hr

O2 is taken in 40% excess

O2 in the combustion chamber = 626.25 x 1.4 = 876.75 kmol/hr

(Dry air contains 21% O2)

Dry air in = 876.765/0.21 = 4175.07 kmol/hr

(Molecular weight of air=29)

Dry air in = 4175.07 x 29 = 121076.381 kg/hr

V2O 5

25

Table 2: Combustion Chamber Material Balance

Component Inlet (kmol) Inlet ( kg) Outlet (kmol) Outlet (kg)

S

O2

N2

SO2

Total

417.501

876.75

3298.306

-

4592.557

13,360.032

28,056.00

92,352.568

-

133,768.6

-

459.249

3298.306

417.501

4175.056

-

14,695.968

92,352.568

26,720.064

133,768.6

11.2.2 Overall Balance over First Three Catalytic Beds

Figure 8: Material balance over first three catalytic beds

SO2 (g) + O2 (g) SO3 (g) (Conversion =96.7 %)

SO2 in = 417.501 kmol

O2 in = 459.249 kmol

SO2 reacted = 417.501*0.967=403.723 kmol/hr

O2reacted = 0.5*403.723 = 201.86 kmol/hr

SO3formed = 403.723 kmol/hr

SO2out = SO2 in SO2reacted

26

=417.501 403.723 =13.778 kmol/hr

O2out = O2 in O2reacted

= 459.249 201.86 =257.389 kmol/hr

Table 3: Material Balance on First Three Catalytic Beds

Component Inlet (kmol) Mole % Inlet (kg) Outlet (kmol) Outlet (kg)

SO2

O2

N2

SO3

Total

417.501

459.249

3298.306

-

4,175.056

10 26,720.064 13.778 881.792

11 14,695.968 257.389 8236.448

79 92,352.568 3298.306 92,353.568

- - 403.723 32297.84

100 133,768.6 3973.196 133769.648

After the third stage, 40 % of product goes to economizer and then to the Interpass Absorber.

11.2.3 Primary Absorber

Figure 9: Primary absorption tower material balance

27

(Assuming 100 % absorption)

SO2 in = 0.4*13.778 = 5.5112 kmol/hr

SO3 in = 0.4*403.723 = 161.489 kmol/hr

O2 in = 0.4 * 257.389 = 102.955 kmol/hr

N2 in = 0.4 * 3298.306 = 1319.3224 kmol/hr

SO3 (g) + H2O (l) H2SO4 (l)

H2SO4 formed = 161.489 kmol/hr

(Sulphur dioxide, Oxygen and Nitrogen are recycled from inter pass absorber to the 4th stage of

reactor).

11.2.4 Fourth Catalytic Bed

Figure 10: Fourth catalytic bed material balance

Conversion = 3.1 % (Overall = 99.8 %)

Gases in to the fourth stage of reactor constitute 60 % of product from third stage and gases

recycled from Interpass absorber.

SO2 in = Total SO2out from the 3rd bed = 13.778 kmol/hr

O2 in = Total O2out from the 3rd bed = 257.389 kmol/hr

N2 in = 3298.306 kmol/hr

28

SO3 in = 60% of SO3out from the 3rd bed

= 0.6 * 403.723 = 242.23 kmol/hr

SO2 (g) + O2 (g) SO3 (g) (Overall Conversion =99.8 %)

SO2 reacted upto 4th bed = 99.8 % of SO2 entering the 1st bed

= 0.998 * 417.501 = 416.67 kmol/hr

SO2 out = Initial SO2 Total SO2 reacted

= 417.501 416.67 = 0.831 kmol/hr

Therefore SO2 reacted in the 4th bed

= SO2 in SO2 out =13.778 0.831 = 12.947 kmol/hr

O2 reacted = 12.947 * 0.5= 6.473 kmol/hr

SO3 formed = 12.947 kmol/hr

O2 out = O2 in O2 reacted

=257.389 6.473 = 250.916 kmol/hr

Total SO3 outlet = SO3 inlet from the 3rd bed+ SO3 formed in the 4th bed

= 242.23 + 12.947 = 255.177 kmol/hr

Table 4: Material Balance on Fourth Catalytic Bed

Component Inlet (kmol) Inlet (kg) Outlet (kmol) Outlet (kg)

SO2 13.778 881.792 0.831 53.184

O2 257.389 8,236.448 250.916 8,029.312

N2 3298.306 92,353.568 3298.306 92,353.568

SO3 242.23 19378.4 255.177 20,414.16

Total 3,809.703 120,850.208 3,805.23 120,850.224

29

11.2.5 Final Absorption Tower

Figure 11: Final absorption tower material balance

SO3 in = 255.173 kmol/hr

SO2 in = 0.831 kmol/hr

O2 in = 250.916 kmol/hr

N2 in = 3298.306 kmol/hr

H2SO4 formed = 255.173kmol/hr

Total H2SO4 formed = 255.173 + 161.489=416.662kmol/hr

30

12. ENERGY BALANCE

12.1Theory

12.1.1 Law of Conservation of Energy

Energy can neither be created nor be destroyed; it can only be changed from one form to

another. In simpler words, all energy entering a process is equal to that leaving plus that left in

the process. Energy can appear in many forms. Some of the forms are enthalpy, electrical energy,

chemical energy (in terms of H reaction), kinetic energy, potential energy, work, and heat

inflow.

In many cases in process engineering , which often takes place at constant pressure ,

electrical energy , kinetic energy, potential energy, and work either are not present or can be

neglected. Then only the enthalpy of the materials (at constant pressure), the standard chemical

reaction energy (H) at 25 C, and the heat added or removed must be taken into account in the

energy balance .This is called heat balance. [5]

12.1.2 Heat Balance

The energy or heat coming into a process in the inlet materials plus any net energy added to

the process is equal to the energy leaving in the materials.

Expressed mathematically,

HR + ( H298 ) + q = HP (1)

where, HR is the sum of enthalpies of all materials entering the reaction process relative to the

reference state for the standard heat of reaction at 298 K and 101.32 kPa.

H298 = standard heat of reaction at 298 K and 101.32 kPa.

The reaction contributes heat to the process, so the negative of H298 is taken to be positive

input heat for an exothermic reaction. [5]

q = net energy or heat added to the system.

HP =sum of enthalpies of all leaving materials referred to the standard reference state at 298 K.

31

12.2 Equations for calculating net enthalpy change at catalyst bed[2]

The temperature dependency of the heat capacity is given by the equation

CP = a+bT+cT2 + (2)

HRT = T 298 (ni Cpi) Reactants dT + H298 + 298 T (ni Cpi) Products dT (3)

where, HRT is the standard heat of reaction at temperature T (K)

HRT = H298 + 298T ( (ni Cpi) Products (ni Cpi) Reactants)dT (4)

Enthalpy change, with 298 K as the reference temperature, can be calculated from the formula,

H = HRT H298 = ( ai ni )(T298) + (( bi ni)/2)(T2 2982) + (5)

Similarly, Enthalpy change between T1 K and T2 K, can be calculated from the formula

H = ( ai ni )(T1T2) + (( bi ni)/2)(T12 T22) + (6)

Standard heat of reaction at 298 K (H298 ) from heat of formation is given by

H298 = [ (ni Hf) ]Products [ (ni Hf )]Reactants (7)

where [ (ni Hf) ]products = standard heat of formation of products and

[ (ni Hf )]reactants = standard heat of formation of reactants

Net heat to be removed from the catalytic bed ,

q = HP HR + H298 (8)

12.3 Data given

12.3.1 Inlet and Effluent Temperatures

First stage: Inlet temperature = 410C

Effluent temperature = 602C

Second stage: Inlet temperature = 438C


Third stage: Inlet temperature = 432C

Effluent temperature = 444 C

32

Fourth stage: Inlet temperature = 427C


12.3.2 Heat Capacities[1]

N2= 29.5909 5.14 x 10-3T (9)

O 2=26.0257 + 11.755 x 10-3T (10)

SO 2 = 24.7706 + 62.9481 x 10-3 T (11)

SO 3 = 22.0376 + 121.624 x 10-3 T (12)

where , Heat capacity is expressed in kJ/kmol-K and T is temperature in K.

12.4 Calculations

a = 22.036 24.771 0.5(26.026) = 15.748

b*103 = 121.624 62.948 0.5(11.755) = 52.799

c*106 = 91.867 ( 44.258) 0.5(2.343) = 46.438

d*109 = 24.369 11.122 0.5( 0.562) = 13.258

From equation (7)

H298 = 395720 ( 296810) = 98910 kJ/kmol SO2

Substituting T=298 K in equation (6)

98910 = Ho + ( 15.748*298) + (((52.799 * 103 ) /2)*2982) + (((46.438 * 106 )/3)*2983)

+ (((13.258 * 109 )/4)*2984)

Ho = 96178kJ/kmol SO2 reacted

Substituting the value of Ho in equation (6), we get

HRT = 96178 15.748 T+ (26.4*10-3) T2 (15.48*10-6)T3+ (3.382*10-9)T4 (13)

33

12.4.1 Calculation of Heat Duty Required In Each Bed

First Catalytic Bed

Table 5: Heat Capacity equation constants for incoming gas mixture

Component ni (kmol/hr.) ai aini bi bini*103

SO2 417.501 24.7706 10341.75 62.9481 26280.89

O2 459.249 26.0257 11952.2767 11.7551 5398.518

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 - 22.0376 - 121.624 -

Total 4175.056 - 119893.8697 - 14722.818

Enthalpy of incoming gas mixture at 683K over 298K can be calculated by substituting T=683 in

equation (5),

HR = 119893.8697(683298) + ((14722.818*10-3)/2) (68322982) =48939432.44 kJ/hr

HR = (48939432.44 /3600) = 13594.286 kW

Table 6: Heat Capacity equation constants for outgoing gas mixture


SO2 108.55 24.7706 2688.848 62.9481 6833.016

O2 304.77 26.0257 7931.852 11.7551 3582.6018

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 308.95 22.0376 6808.516 121.624 37575.7348

Total 4020.576 - 115029.0566 - 31034.76286

Enthalpy of outgoing gas mixture at 875K over 298K can be calculated by substituting T=875 in

equation (5),

Hp = 115029.0566(875298) + ((31034.763*10-3)/2)(87522982) =76874549.2 kJ/hr

Hp = (76874549.2 /3600) = 21354.04144 kW

34

Total heat of reaction at 298 K,

H298 = 98910 kJ/kmol SO2 reacted = (417.501 108.55) (98910/3600) = 8488.428 kW

Net enthalpy change, q = HP HR + H298

q = 21354.04144 13594.286 8488.428 = 728.67 kW

Thus, during the reaction, enthalpy equivalent to -728.67 kW is to be removed from the first

catalytic bed in order to maintain the temperature of the outgoing gas mixture at 875K.

Figure 12: Enthalpy balance over first catalytic bed

Second Catalytic Bed



SO2 108.55 24.7706 2688.848 62.9481 6833.016

O2 304.77 26.0257 7931.852 11.7551 3582.6018

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 308.95 22.0376 6808.516 121.624 37575.7348

Total 4020.576 - 115029.0566 - 31034.76286

35


equation (5),

HR = 115029.056(711298) + ((31034.763*10-3)/2) (71122982) =53973356.79 kJ/hr

HR = (53973356.79 /3600) = 14992.599 kW



SO2 31.73 24.7706 785.97 62.9481 1997.343

O2 266.36 26.0257 6932.2054 11.7551 3131.088

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 385.77 22.0376 8501.144 121.624 46918.89

Total 3982.166 - 113819.46 - 35090.7314


equation (5),

Hp = 1153819.46(778298) + ((35090.7314*10-3)/2)(77822982) =60879790.44 kJ/hr

Hp = (60879790.44 /3600) = 16911.053 kW


H298 = 98910 kJ/kmol SO2 reacted

= (108.5531.73) (98910/3600) = 2110.6295 kW


q = 16911.053 14992.599 2110.6295 = 192.1755 kW

Thus, during the reaction, enthalpy equivalent to 192.1755 kW is to be removed from the

second catalytic bed in order to maintain the temperature of the outgoing gas mixture at 778 K.

36

Figure 13: Enthalpy balance over second catalytic bed

Third Catalytic Bed



SO2 31.73 24.7706 785.97 62.9481 1997.343

O2 266.36 26.0257 6932.2054 11.7551 3131.088

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 385.77 22.0376 8501.144 121.624 46918.89

Total 3982.166 - 113819.46 - 35090.7314


equation (5),

HR = 113819.46(705298) + ((35090.7314*10-3)/2) (70522982) =53486906.95 kJ/hr

HR = (53486906.95 /3600) = 14857.474 kW

37



SO2 13.77 24.7706 341.091 62.9481 866.79

O2 257.38 26.0257 6698.494 11.7551 3025.5276

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 403.77 22.0376 8898.1217 121.624 49103.257

Total 39732.226 - 113536.669 - 36038.989


equation (5),

Hp = 113536.669(717298) + ((36038.989*10-3)/2) (71722982) =55235285.03 kJ/hr

Hp = (55235285.03 /3600) = 15343.1347 kW



= (31.7313.77) (98910/3600) = 493.451 kW


q = 15343.1347 14857.474 493.451= 7.7903 kW

Thus, during the reaction, enthalpy equivalent to 7.7903 kW is to be removed from the third

catalytic bed in order to maintain the temperature of the outgoing gas mixture at 717 K.

38

Figure 14: Enthalpy balance over third catalytic bed

Fourth Catalytic Bed



SO2 13.77 24.7706 341.091 62.9481 866.79

O2 257.38 26.0257 6698.494 11.7551 3025.5276

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 242.238 22.0376 5338.344 121.624 29461.9545

Total 39732.226 - 109977.772 - 16397.686

.


equation (5),

HR = 109977.772(700298) + ((16397.686*10-3)/2) (70022982) =47500407.36 kJ/hr

HR = (47500407.36 /3600) = 13194.5576 kW

39

Table12: Heat Capacity equation constants for outgoing gas mixture.


SO2 0.835 24.7706 20.6834 62.9481 52.5616

O2 250.9125 26.0257 6530.1734 11.7551 2949.5015

N2 3298.306 29.5909 97599.843 -5.141 -16956.59

SO3 255.173 22.0376 5623.4 121.624 31035.1609

Total 3805.2265 - 109774.0998 - 17080.634


equation (5),

Hp = 109775.0998(708298) + ((17080.634*10-3)/2)(70822982) =48773723 kJ/hr

Hp = (48773723/3600) = 13548.256 kW



= (13.770.835) (98910/3600) = 355.389 kW


q = 13480.533 13194.5576 355.389= 1.69 kW

Thus, during the reaction, enthalpy equivalent to 1.69 kW is to be removed from the fourth

catalytic bed in order to maintain the temperature of the outgoing gas mixture at 708 K.

40

Figure 15: Enthalpy balance over fourth catalytic bed

12.4.2 Calculation of Heat Load for Heat Exchangers

Heat load required between first and second catalytic bed:

At the outlet of first catalytic bed:

aini = 115029.0566

bini = 31034.76286* 10-3

First stage outlet temperature = 602C = 875K

Second stage inlet temperature = 438C =711K

Temperature change = 875 K to 711 K

Heat load is calculated by substituting T1=875K and T2=711K in equation (6),

H1 = 115029.056(711875) + ((31034.763*10-3)/2) (71128752) = 22900898.26 kJ/hr

H1 = (22900898.26 /3600) = 6361.36 kW

Heat load required between second and third catalytic bed:

At the outlet of second catalytic bed:

aini = 113819.46

bini = 35090.7314* 10-3

41

Second stage outlet temperature = 498C = 771K

Third stage inlet temperature = 432C =705K



H2 = 113819.46(705711) + ((35090.7314*10-3)/2) (70527112) = 831982.187 kJ/hr

H2 = (831982.187/3600) = 231.106 kW

Heat load required between third and fourth catalytic bed:

At the outlet of third catalytic bed:

aini = 109977.772

bini = 16397.686* 10-3

Third stage outlet temperature = 444 C = 717 K

Fourth stage inlet temperature = 427C =700 K



H3 = 109977.772(700717) + ((16397.686*10-3)/2) (70027172) = 1996876.366 kJ/hr

H3 = (1996876.366 /3600) = 544.68 kW

42

13. WEIGHT OF CATALYST

13.1 Theory and Data[1]

The kinetic data are represented by a rate expression of the form

=122 232

0.5

20.5 (14)

that may be regarded as a degenerate form of typical Hougen-Watson kinetics. The rate constants

are given by

ln 1 = 12.07 31000 (15)

ln 2 = 22.75 53600 (16)

where

T is temperature expressed in K

R is expressed in cal/gmolK

k1 is expressed in gmol/s-(gm cat)-atm3/2

k2 is expressed in gmol/s-(gm cat)-atm

Derived equation for relationship between temperature and conversion:

= + 307.158( )

1 + 0.0248( ) (17)

Where, T is reference temperature and XA is conversion at this temperature.

T0 is initial temperature and XA0 is conversion at initial conditions.

Relationship between number of moles and conversion:[4]

= (1 )

(1 + )

(18)

where

NA is number of moles at conversion XA.

NA0 is initial number of moles.

43

T0/T is temperature correction factor.

Relationship between partial pressure and mole fraction:

PA = yA Po (19)

PA is partial pressure of A and Po is total pressure.

yA is mole fraction of A.

The partial pressures of the various species are numerically equal to their mole fractions since

the total pressure is one atmosphere.

Equation of Plug flow reactor for calculating weight of catalyst:[4]

=

(20)

where,

W is weight of catalyst required.

FA0 is molar flow rate of Sulphur dioxide entering in feed.

13.2 Calculations

13.2.1 First Catalytic Bed

Sample Calculation:

For T = 773 K, T0 = 683 K, XSO2 = 0

773 =683 + 307.158 2

1 + 0.0248 2

2 = 0.3125

2 = 417.501(1 0.3125)

(1 0.05 0.3125)

683

773

2 = 257.633

2 = 417.501 257.633 = 159.868

3 = 159.868

44

2 = 459.249 (159.868 2 ) = 379.315

= 257.633 + 159.868 + 379.315 + 3298.306 = 4095.122

2 = 2 =159.868

4095.122= 0.062

2 = 2 =379.315

4095.122= 0.0926

3 = 3 =159.868

4095.122= 0.0390

Table 13: Calculations of First Catalytic Bed

T(K) XSO2 NSO2 NO2 NSO3 NN2 TOTAL PSO2(atm) PO2(atm) PSO3(atm)

683 0 417.501 459.249 0 3298.306 4175.056 0.099 0.1099 0

688 0.0172 407.674 454.335 9.826 3298.306 4170.143 0.097 0.108 0.0023

725 0.1452 338.649 419.823 78.851 3298.306 4135.63 0.081 0.1015 0.0190

748 0.2252 298.726 399.861 118.77 3298.306 4115.669 0.072 0.0971 0.0288

773 0.3125 257.633 379.315 159.86 3298.306 4095.122 0.062 0.0926 0.0390

793 0.382 226.33 363.664 191.16 3298.306 4079.472 0.055 0.0891 0.0468

798 0.400 218.711 359.854 198.78 3298.306 4075.661 0.053 0.0882 0.0487

823 0.488 181.753 341.375 235.74 3298.306 4057.182 0.044 0.0841 0.0581

848 0.576 146.579 323.788 270.92 3298.306 4039.595 0.036 0.0801 0.0670

856.4 0.606 135.132 318.064 282.36 3298.306 4033.871 0.033 0.0788 0.07

873 0.665 113.026 307.011 304.47 3298.306 4022.819 0.028 0.0763 0.0756

875 0.6726 110.408 305.702 307.09 3298.306 4021.51 0.027 0.0760 0.0763

45

Sample Calculation:

1 = (12.07 31000

(1.987 773)) = 3 104

2 = (22.75 536000

(1.987 773)) = 5.3 106

=((3 104) 0.062 0.0926) ((5.3 106) 0.0390 0.09260.5)

0.0620.5

= 6.71 106

1 = 149047.3

Table 14: Rate Calculations of First Catalytic Bed

k1 k2 (-rA) (kmol/s-kg catalyst) 1/(-rA)

2.09E-05 5.34E-08 7.27E-07 1375530

2.47E-05 7.12E-08 8.41E-07 1188741

7.87E-05 5.26E-07 2.27E-06 439566

1.53E-04 1.65E-06 3.94E-06 253862.4

3.00E-04 5.30E-06 6.71E-06 149047.3

4.98E-04 1.28E-05 9.7E-06 103124.2

5.64E-04 1.58E-05 1.05E-05 94832.17

1.02E-03 4.42E-05 1.47E-05 68182

1.79E-03 1.16E-04 1.57E-05 63794.88

2.14E-03 1.59E-04 1.38E-05 72398.6

3.02E-03 2.88E-04 2.76E-05 362480.6

3.15E-03 3.10E-04 2.98E-05 378674.7

46

Figure 16: Plot of 1/-RA V/S XA for first bed

FA0 = 417.501 kmol/hr = 417.501/3600 kmol/s = 0.1159725kmol/s

W = FA0 * Area under the curve= 0.1159725*250920

Weight of catalyst in first catalyst bed =29103.3 kg

13.2.2 Second Catalytic Bed

Sample Calculation:

For T = 715 K, T0 = 711 K, 2 = 0.672

715 =711 + 307.158 (2 0.672)

1 + 0.0248 (2 0.672)

2 = 0.686

2 = 417.501(1 0.686)

(1 0.05 0.686)

683

715

2 = 129.523

2 = 417.501 129.523 = 287.978

3 = 287.978

2 = 459.249 (287.978 2 ) = 315.26

47

= 129.523 + 287.978 + 315.26 + 3298.306 = 4031.067

2 = 2 =129.523

4031.067= 0.03213

2 = 2 =315.26

4031.067= 0.0782

3 = 3 =287.978

4031.067= 0.0714

Table 15: Calculations of Second Catalytic Bed

T(K) XSO2 NSO2 NO2 NSO3 NN2 TOTAL PSO2(atm.) PO2(atm) PSO3(atm)

711 0.672 110.408 305.702 307.09 3298.306 4021.51 0.027454 0.076017 0.076363

715 0.686 129.523 315.260 287.97 3298.306 4031.067 0.032131 0.078208 0.07144

718 0.696 124.784 312.890 292.71 3298.306 4028.697 0.030974 0.077665 0.072658

723 0.714 116.957 308.977 300.54 3298.306 4024.784 0.029059 0.076769 0.074673

728 0.731 109.22 305.108 308.28 3298.306 4020.915 0.027163 0.07588 0.076669

733 0.748 101.57 301.283 315.93 3298.306 4017.09 0.025284 0.075 0.078647

738 0.766 94.005 297.501 323.49 3298.306 4013.308 0.023423 0.074129 0.080606

743 0.783 86.523 293.760 330.97 3298.306 4009.567 0.021579 0.073265 0.082547

748 0.800 79.124 290.060 338.37 3298.306 4005.868 0.019752 0.072409 0.08447

753 0.818 71.805 286.401 345.69 3298.306 4002.208 0.017941 0.071561 0.086376

758.3 0.836 64.132 282.564 353.36 3298.306 3998.372 0.01604 0.07067 0.088378

763 0.85 57.4009 279.19 360.10 3298.306 3995.006 0.014368 0.069887 0.090138

768 0.87 50.312 275.654 367.18 3298.306 3991.462 0.012605 0.069061 0.091994

771 0.88 46.094 273.545 371.40 3298.306 3989.353 0.011554 0.068569 0.093099

778 0.90 36.355 268.676 381.14 3298.306 3984.483 0.009124 0.067431 0.095658

48

Table 16: Rate Calculations of Second Catalytic Bed


5.16E-05 2.53E-07 6.11585E-07 1635095

5.83E-05 3.13E-07 7.8216E-07 1278512

6.38E-05 3.66E-07 8.36552E-07 1195383

7.42E-05 4.75E-07 9.34367E-07 1070243

8.61E-05 6.14E-07 1.0383E-06 963113

9.96E-05 7.89E-07 1.14852E-06 870687.1

1.15E-04 1.01E-06 1.26386E-06 791225.4

1.33E-04 1.30E-06 1.38501E-06 722018.9

1.53E-04 1.65E-06 1.28608E-06 777554.9

1.75E-04 2.10E-06 1.31821E-06 758606.4

2.03E-04 2.69E-06 1.3143E-06 760864

2.29E-04 3.36E-06 1.25102E-06 799348

2.63E-04 4.42E-06 1.08457E-06 922027.9

2.84E-04 4.85E-06 9.94423E-07 1005608

3.41E-04 6.94E-06 3.92238E-07 2549474

Sample Calculation:

1 = (12.07 31000

(1.987 715)) = 5.828 105

2 = (22.75 536000

(1.987 715)) = 3.1278 107

=((5.828 105) 0.03213 0.0782) ((3.1278 107) 0.0714 0.07820.5)

0.032130.5

= 7.8216 107

49

1 = 1278512

Figure 17: Plot of 1/-RA v/s XA for second bed

FA0 = 110.408kmol/hr = 110.408/3600 kmol/s= 0.036688 kmol/s

W = FA0 * Area under the curve = 0.036688*161430

Weight of catalyst in first catalyst bed = 4950.878 kg

50

13.2.3 Third Catalytic Bed

Table 17: Calculations of Third Catalytic Bed

T(K) XSO2 NSO2 NO2 NSO3 NN2 TOTAL PSO2(atm) PO2(atm) PSO3(atm)

705 0.905 36.355 268.67 381.14 3298.306 3984.483 0.00912 0.0674 0.09565

707 0.912 37.152 269.07 380.34 3298.306 3984.882 0.00932 0.0675 0.09544

708 0.915 35.648 268.32 381.85 3298.306 3984.13 0.00894 0.0673 0.09584

710 0.922 32.652 266.82 384.84 3298.306 3982.632 0.00819 0.0669 0.09663

712 0.929 29.669 265.33 387.83 3298.306 3981.14 0.00745 0.0666 0.09741

714 0.936 26.700 263.84 390.80 3298.306 3979.656 0.00670 0.0662 0.09819

715 0.939 25.221 263.10 392.27 3298.306 3978.916 0.00633 0.0661 0.09859

716 0.943 23.745 262.37 393.75 3298.306 3978.178 0.00596 0.0659 0.09897

717 0.946 22.272 261.63 395.22 3298.306 3977.442 0.0056 0.0657 0.09936

Sample Calculation:

For T = 708 K, T0 = 705 K, 2 = 0.905

708 =705 + 307.158 (2 0.905)

1 + 0.0248 (2 0.905)

2 = 0.915

2 = 417.501(1 0.915)

(1 0.05 0.915)

683

708

2 = 35.648

2 = 417.501 35.648 = 381.85

3 = 381.85

2 = 459.249 (381.85 2 ) = 268.32

= 35.648 + 268.32 + 381.85 + 3298.306 = 3984.13

51

2 = 2 =35.648

3984.13= 0.00894

2 = 2 =268.32

3984.13= 0.0673

3 = 3 =381.85

3984.13= 0.09584

Table 18: Rate Calculations of Third Catalytic Bed


4.27E-05 1.83E-07 2.27E-07 4396699

4.55E-05 2.04E-07 2.44E-07 4094072

4.69E-05 2.15E-07 2.42E-07 4129794

4.99E-05 2.39E-07 2.37E-07 4224889

5.32E-05 2.67E-07 2.28E-07 4383353

5.65E-05 2.96E-07 2.15E-07 4641287

5.83E-05 3.13E-07 2.07E-07 4825010

6.01E-05 3.29E-07 1.98E-07 5053386

6.19E-05 3.47E-07 1.87E-07 5361426

Sample Calculation:

1 = (12.07 31000

(1.987 708)) = 4.69 105

2 = (22.75 536000

(1.987 708)) = 2.15 107

=((4.69 105) 0.00894 0.0673) ((2.15 107) 0.09584 0.06730.5)

0.008940.5

= 2.42 107

1 = 4129794

52

Figure 18: Plot of 1/-RA v/s XA for third bed

FA0 = 36.355kmol/hr = 36.355/3600kmol/s = 0.0100986kmol/s

W = FA0 * Area under the curve= 0.0100986*181425

Weight of catalyst in first catalyst bed = 1832.14kg

13.2.4 Fourth Catalytic Bed

Table 19: Calculations of Fourth Catalytic Bed

T(K) XSO2 NSO2 NO2 NSO3 NN2 Total PSO2(atm) PO2(atm) PSO3(atm)

700 0.946 22.27 261.63 395.22 3298.306 3977.442 0.0056 0.06578 0.099367

701 0.950 21.350 261.17 396.15 3298.306 3976.981 0.005369 0.065671 0.099611

702 0.953 19.851 260.42 397.64 3298.306 3976.231 0.004993 0.065495 0.100007

704 0.960 16.864 258.93 400.63 3298.306 3974.738 0.004243 0.065144 0.100796

705 0.963 15.376 258.18 402.12 3298.306 3973.994 0.003869 0.064969 0.101189

707 0.970 12.409 256.70 405.1 3298.306 3972.51 0.003124 0.06462 0.101974

708 0.97 10.931 255.964 406.57 3298.306 3971.771 0.002752 0.064446 0.102365

53

Sample Calculation:

For T = 704 K, T0 = 700 K, 2 = 0.96

704 =700 + 307.158 (2 0.96)

1 + 0.0248 (2 0.96)

2 = 0.96

2 = 417.501(1 0.96)

(1 0.05 0.96)

683

704

2 = 16.864

2 = 417.501 16.864 = 400.63

3 = 400.63

2 = 459.249 (400.63 2 ) = 258.93

= 16.864 + 258.93 + 400.63 + 3298.306 = 3974.738

2 = 2 =16.864

3974.738 = 0.004243

2 = 2 =258.93

3974.738 = 0.065144

3 = 3 =400.63

3974.738 = 0.100796

Table 20: Rate Calculations of Fourth Catalytic Bed


3.65E-05 1.39E-07 1.32E-07 7557000

3.76E-05 1.47E-07 1.3E-07 7713771

3.89E-05 1.55E-07 1.24E-07 8072529

4.14E-05 1.73E-07 1.07E-07 9315462

4.27E-05 1.83E-07 9.67E-08 10343043

4.55E-05 2.04E-07 6.97E-08 14342480

4.69E-05 2.15E-07 5.19E-08 19276120

54

Sample Calculation:

1 = (12.07 31000

(1.987 704)) = 4.14 105

2 = (22.75 536000

(1.987 704)) = 1.73 107

=((4.14 105)0.004243 0.065144) ((1.73 107) 0.100796 0.0651440.5)

0.0042430.5

= 1.07 107

1 = 9315462

Figure 19: Plot of 1/-RA v/s XA for fourth bed

FA0 = 22.27kmol/hr = 22.27/3600 kmol/s = 6.18611*10-3kmol/s

W = FA0 * Area under the curve = 6.18611*10-3*2474750

Weight of catalyst in first catalyst bed = 15309.078 kg

55

14. SUMMARY SHEET

1. Diameter of converter = 6 m.

2. Heat load for heat exchanger after first bed = -6361.36 kW

3. Heat load for heat exchanger after second bed = -231.106 kW

4. Heat load for heat exchanger after third bed = -554.68 kW

5. Design Pressure for reactor = 0.1114 N/mm2

6. Design Temperature for reactor =610C =883 K

7. Material of Construction =SS 304

14.1 First Catalytic Bed

Inlet temperature = 410C


Conversion = 0.66

Weight of catalyst = 29103.3 kg.

Heat duty required= -728.67 kW

14.2 Second Catalytic Bed



Conversion = 0.85

Weight of catalyst = 4950.878


14.3 Third Catalytic Bed


Effluent temperature = 444 C

Conversion = 0.96

Weight of catalyst = 1832.14 kg


56

14.4 Fourth Catalytic Bed



Conversion = 0.985

Weight of catalyst = 15309.078 kg

Heat duty required = -1.69 kW

57

15. CONCLUSION

The next step to the Contact Process is DCDA or Double Contact Double Absorption. In this

process the product gases (SO2) and (SO3) are passed through absorption towers twice to achieve

further absorption and conversion of SO2 to SO3 and production of higher grade sulfuric acid.

SO2-rich gases enter the catalytic converter, usually a tower with multiple catalyst beds, and are

converted to SO3, achieving the first stage of conversion. The exit gases from this stage contain

both SO2 and SO3 which are passed through intermediate absorption towers where sulfuric acid

is trickled down packed columns and SO3 reacts with water increasing the sulfuric acid

concentration. Though SO2 too passes through the tower it is unreactive and comes out of the

absorption tower.

This stream of gas containing SO2, after necessary cooling is passed through the catalytic

converter bed column again achieving up to 99.8% conversion of SO2 to SO3 and the gases are

again passed through the final absorption column thus resulting not only achieving high

conversion efficiency for SO2 but also enabling production of higher concentration of sulfuric

acid.

The industrial production of sulfuric acid involves proper control of temperatures and flow rates

of the gases as both the conversion efficiency and absorption are dependent on these.

58

16. REFERENCES

[1] Hill, Charles G. (1977). An Introduction to Engineering Kinetics and Reactor Design, Third Edition,

506,507,509-513.

[2] Douglas K. Louie, (2005). Handbook of Sulphuric Acid Manufacturing , Second Edition, 3-3, 3-8, 3-

10, 3-11, 3-14, 3-28, 3-78, 4-5 4-11, 4-58,6-16-3.

[3] Matt King, Michael Moats and William G.I. Davenport (2013). Sulfuric Acid Manufacture (Second

Edition) Analysis, Control and Optimization, 11-14, 19-21, 73-80, 91-99, 229-234, 262-271.

[4] Levenspiel, Octave, (1999). Chemical Reaction Engineering, Third Edition, 208, 209, 212, 394.

[5] Christie John Geankoplis, (2003). Transport Processes and Separation Process Principles (Includes

Unit Operations) Fourth Edition, 22.

[6] Central Pollution Control Board Ministry of Environment and Forests (May 2007). Comprehensive

Industry Document on Sulphuric Acid Plant, 3, 6-7, 10-14, 22, 25-28, 35-36, 38.

[7] Fogler, H.S., 1999. Elements of chemical reaction engineering, Third edition. Prentice Hall, New

York.

[8] Bhatt, B.I., Vora, S.M., 1996. Stoichiometry. Third edition. Mc-Graw Hill, New Delhi.

[9] Austin G.T., Shreve, 1984 Chemical process industries, Fourth edition.Mc-Graw Hill, Singapore.

59

17. APPENDIX (DERIVATIONS)

17.1 Derivation of relationship between equilibrium conversion and temperature.

Reaction taking place in the reactor:

SO2 (g) + O2 (g) SO3 (g)

Rate Equation:

The kinetic data are represented by a rate expression of the form

=122 2 32

0.5

20.5 (21)

that may be regarded as a degenerate form of typical Hougen-Watson kinetics.

At equilibrium, the rate of forward reaction becomes equal to the rate of backward reaction.

=122 2 32

0.5

20.5 = 0 (22)

Therefore at equilibrium,

1 22 = 2 320.5 (23)

The partial pressures of the various species are numerically equal to their mole fractions since

the total pressure is one atmosphere. These mole fractions can be expressed in terms of a single

reaction progress variable-the degree of conversion-as indicated in the following mole table.[8]

V2O 5

60

Table 21: Table for mole fractions expressed in terms of conversion

Component

Initial moles

(kmol/hr) Moles at conversion XA

Mole fraction at fractional

conversion XA

SO2 417.501 417.501 (1 ) 417.501 (1 )

4175.056 208.7505

O2 459.249 459.249 459.249

(417.501 )

2 208.7505

4175.056 208.7505

N2 3298.306 3298.306 3298.306

4175.056 208.7505

SO3 0.0 417.501 417.501

4175.056 208.7505

Total 4175.056 4175.056 208.7505 1.0

At equilibrium,

1 22 = 2 320.5 (24)

1 (417.501 (1 )

4175.056 208.7505 ) (

459.249 208.75054175.056 208.7505

) =

2 (417.501

4175.056 208.7505 ) (

459.249 208.75054175.056 208.7505

)0.5

(25)

61

=12

=(

417.501

4175.056208.7505 )

(417.501 (1)

4175.056208.7505 ) (

459.249208.7505

4175.056208.7505 )

0.5 (26)

=12

=

(1 )

20 2.2

(27)

17.2 Derivation of relationship between conversion and temperature.

The differential form of energy balance equation for one-dimensional, plug flow model, for

adiabatic operation is as follows, [9]

()

= () = () (28)

where,

= = superficial mass velocity, which does not vary along the length of reactor.

= fluid density

= superficial velocity in axial direction.

= reaction rate expressed in pseudo homogeneous form (i.e. number of moles transformed per

unit time per unit of total reactor volume)

= enthalpy change for the reaction at the indicated conditions.

= bulk density of the catalyst (total mass of catalyst / total volume of reactor)

=

= global reaction rate per unit mass of catalyst.

The equation for material balance is as follows:

()

= = (29)

where

= stoichiometric coefficient for reactant A (negative for reactants) = 1 in this case

62

= (1 + )

(30)

= (1 )

(1 + )

(31)

Therefore

()

=

(32)

=

(33)

()

=

() (34)

Table 22: Mole percent of gases entering the converter

Component Inlet Moles

(Percent )

Molecular

Weight

SO2 10 64

O2 11 32

N2 79 28

Average molecular weight of the inlet gas:

Mavg = 0.10*64+ 0.11*32+0.79*28 = 32.04

For the temperature range of interest (875K to 683K), the heat capacity per unit mass is

substantially independent of the conversion level. Hence, we take the heat capacity as constant at

0.250 cal/gm-K.

( ) = ( ) (35)

Diameter of Converter is taken as 6m. [1]

63

() =

=4175.056 32.04

(62)

4

= 4731.1033

m2= 1.314

2

2 = =417.501 103

3600 (6)2

4

= 4.101688

2

Heat of reaction at temperature T = (H) = 24.60 + 1.99 x 10-3T kcal/gmol

for T in degrees Kelvin.

1.314 0.250 ( ) = (24.60 1.99 x 103T) 4.101688( )

= + 307.158( )

1 + 0.0248( ) (36)

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