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Journal of Science (JOS) 179 Vol. 2, No. 4, 2012, ISSN 2324-9854Copyright © World Science Publisher, United Stateswww.worldsciencepublisher.org

HYSYS Simulation of a Sulfuric Acid Plant and OptimizationApproach of Annual Profit

1 Niaz Bahar Chowdhury, 1 Zahid Hasan and 1 A. H. M. Biplob

1Chemical Engineering Department, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh

Email: [email protected]

Abstract – Sulfuric acid is a basic chemical used intensively all over the world. One can determine the prosperity of anation by measuring the annual use of sulfuric acid of that country. Also sulfuric acid is a very important basicchemical, widely used in different industrial sector. The main purpose of the study is to simulate and optimize the

annual profit 98.4% sulfuric acid plant by Aspen HYSYS 3.2. In this project, a simplified sulfuric acid production process is simulated and optimized. In order to simulate this process some process operational data of the Sulfuric Acid plant of WATA CHEMICALS LIMITED are used. The optimization criterion of the process is to maximize the annual profit. This study will be helpful for the entrepreneurs who are interested to build a sulfuric acid plant. Also this studywill be very helpful for the plant operators to run the factory efficiently by minimizing the process system requirement.

Keywords – Sulfuric Acid, Converters, Aspen HYSYS, Annual Profit, Optimization

1. Introduction

Aspen HYSYS is a market-leading processmodeling tool for conceptual design, optimization,

business planning, asset management, and performance monitoring for oil & gas production, gas processing, petroleum refining, and air separat ionindustries. Aspen HYSYS is a core element of AspenTech's aspen ONE® Engineering applications. It hasvast importance for chemical engineers to simulate a

process. This project contains a simplified simulationof a sulfuric acid production plant which alsosimulates an optimized annual profit. Sulfuric acid isone of the most widely used and important technical

products. It is employed in the manufacture offertilizers, leather and tin plate, in the refining of

petroleum, and in the dyeing of fabrics [1]

2. Methodology and Simulation

Simulation is done by Aspen HYSYS 3.2. Procedureis described below [2] .

2.1. Components

The components used in this simulation are LiquidSulfur, Oxygen, Nitrogen, Sulfur Dioxide, SulfurTrioxide, Sulfuric Acid, and Water

2.2. Reaction involved

The reactions involved in this simulation are

S+ O 2 = SO 2,

2 SO 2+ O 2 = 2 SO 3,SO 3+ H 2O = H 2SO 4

2.3. Fluid Package

In order to simulate the process as accuratelyas possible COM thermo is selected as advancedthermodynamics databank. In model phaseselection NRTL was selected for liquid phaseand Peng-Robinson was selected for vapor

phase .

2.4. Process Condition

The process conditions of this simulation isdescribed below

2.4.1. Streams

The conditions of the prime streams are

Table1. Stream Conditions

Condition

Pure

LiquidSulfur

Moist Air(65%RH)

DMWater

Product

Temperature 105.0 30.0 30.0 75.0

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Niaz Bahar Chowdhury, et al ., JOS, Vol. 2, No. 4, pp. 179-182, 2012 180

( ° C)Pressure

(atm) 2.0 2.5 1.0 1.0

Flow rate(kmole/hr) 25.0 257.2 30 29.8

2.4.2. Converters

The conditions of various converters used in thissimulation are

PassNumber

Inlettemperature

( C)

Out lettemperature

( C)Conversion

(%)

1st 410.0 616.8 74.02nd 438.0 489.7 70.83rd 4th

432.0427.0

444.1435.8

56.693.9

2.5. Unit Operations

The unit operations used in this simulation is

a. One Waste Heat Boiler b. Three Interbed Coolersc. Three Coolersd. One Circulation Tanke. Two Splittersf. One Drying Tower

2.6. Unit Process

The unit process used in this simulation is

a. One Waste Heat Boiler b. Three Interbed Coolersc. Three Coolersd. One Circulation Tanke. Two Splittersf. One Drying Tower

3. Process Description

Type Moist air is dried in the drying tower using

98% sulfuric acid. The resulting dry air, along withliquid sulfur, is fed to a sulfur burner to producesulfur di oxide.

Figure1. Drying Tower and Sulfur Burner

The sulfur dioxide is converted to sulfur trioxide by passing through 4 converter beds. The sulfurdioxide from the sulfur burner is passed through awaste heat boiler to lower the temperature beforeentering the 1 st converter bed.

Figure2. Four Single Pass Converter Beds

Between each of two consecutive converter beds,there is also an interbed cooler for the same purpose.Finally, the outlet gas from the 4 th converter bed is

passed through a cooler.

Figure3 . Absorption Tower and Circulation Tank

This cool gas, containing sulfur trioxide, is fed to anabsorption tower where it reacts with 98% sulfuric acid toform 98.5% sulfuric acid. The stack gas from theabsorption tower consists predominantly of nitrogen. The98.5% sulfuric acid is fed to circulation tank along withdemineralized water and, 97.5% sulfuric acid whichcomes from the drying tower. The resulting concentrationof the sulfuric acid exiting from the circulation tank is98.1%, which is split into two portions. One portion iscooled and recycled back to the absorption tower. Theother portion is also cooled and further split into two

portions; one of which is the final product (98% sulfuricacid) and the other portion is recycled back to the dryingtower [3] . Therefore, the above is a brief description of thesulfuric acid production process simulated by us.

4. Results and Discussion

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The result of this simulation is discussed in thissection

4.1. Optimized Function

The criterion of the optimization is to maximize

the profit. The function used for optimization is:

-

{(Duty1+ Duty2 + Duty3 + Duty4 + Duty5 + Duty6 +Duty7 ) 0.000293 3 }] 24 ( )

300 ( )

Figure4 : Optimization Spreadsheet

4.2. Variables

The optimization variables are temperatures of –a. Cool 1 st Converter Bed Inlet

b. Cool 2 nd Converter Bed Inletc. Cool 3 rd Converter Bed Inlet

d. Cool 4th

Converter Bed Inlete. Absorber Inletf. Cool Recycle 1g. Cool Final Product

Figure5 . Optimization Variables

4.3. Profit Maximization

The window which shows the profit maximization isgiven below

Figure6 . Maximized Profit

4.4. Product Composition

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Figure8 . Product Composition after Optimization

5. Limitations

a. In our simulation, all reactions areconsidered as conversion reactions, thoughthey are actually equilibrium reactions. Thisis done because sufficient data forequilibrium type of reaction in Hysys werenot available.

b. In practice, solid sulfur is the raw materialinput to the process, which is consequentlymelted in a sulfur melter. But, in Hysys,there is no such unit operation as sulfur

melter. As a result, liquid sulfur is directlyfed as the raw material for the process.

c. In practice, one 4-pass converter or two 2- pass converters in series are used to convertsulfur dioxide into sulfur trioxide. But inHysys, there is no provision for 4-pass or 2-

pass converter. So four single pass convertersin series are used in the simulation [4]

d. In Hysys, there is no absorber where reactioncan take place. This type of unit process isneeded to convert sulfur trioxide to sulfuricacid. In absence of that, conversion reactor isused as an absorption tower.

e. In Hysys, there is no circulation tank wheremixing action take place without flashing.This type of unit operation is needed toconvert 98.5% sulfuric acid to 98.1% sulfuric

acid. In absence of that, the unit operationnamed ‘mixer’ is used as a circulation tank.

f. To avoid complexity, all cooling actions aredone by simple coolers instead of shell andtube heat exchanges or air coolers.

7. Conclusion

By doing this simulation project, the main featuresof industrial production of sulfuric acid wererepresented in a Process Flow Diagram. Satisfactoryresults are obtained in optimizing the process,keeping in mind the fact that the profit maximizationis done in a rather simple way. On the whole, usingthis simulation approach will be helpful for the

process plant to opt imize the annual profit.

Acknowledgements

We express our gratitude to Wata Chemicals Limitedfor providing some basic information on Sulfuric acid

plant

References

[1] W. G. Davenport and M. J. King, Sulfuric Acid Manufacture: Analysis, Control and Optimization ,3rd edition, Elsevier, New York, 2006, pp 33-38

[2] www.aspentech.com

[3] George T. Austin, Shreve’s Chemical Process Industries , 5 th Edition, McGraw-Hill, New York,2008, pp 320-345

[4] W. W. Duecker, and J. R. West, The Manufacture ofSulfuric Acid , Reinhold Publishing Corporation, NewYork, 1966, pp 167-178

Vitae

Mr. Niaz Bahar Chowdhury was born inChittagong, Bangladesh. He obtained a B. Sc degreein 2012 in Chemical Engineering department fromBangladesh University of Engineering in Technology.

He worked as a Research Assistant in the abovedepartment. His research interest includes LPG,Process Engineering, Coal Gasification, and ThermalEngineering.

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