Unisim-Design Simulation and Analysis of a Sulphuric Acid Manufacturing Plant with Double Absorption Process

UniSim-Design Simulation and Analysis of a Sulphuric Acid Manufacturing Plant with Double Absorption Process

Amine Mounaam1,2, Yasser Harmen2,4, Younes Chhiti2,3, Ahmed Souissi1,2, Mohamed Salouhi1 and Mohamed El Khouakhi2 1All Laboratory, Ecole Mohammadia d’Ingénieurs, Mohammed V University, Rabat, Morocco 2Innovation Lab for Operations, Mohammed VI Polytechnic University, Ben Guérir, Morocco 3Ibn Tofail University, Kenitra, Morocco 4Science Engineer Laboratory for Energy (LabSIPE), National School of Applied Sciences, Chouaib Doukkali University, El Jadida, Morocco

[email protected], [email protected]

Keywords: Sulphuric Acid, Modelling, Simulation, UniSim-Design, Chemical Reactions, Double Absorption Process, UniSim-Thermo, Peng-Robinson, NRTL.

Abstract: In the sulphuric acid manufacturing industries, plant modelling and simulation is a challenging task to minimize emissions, maximize production performance and revenue. In this context, this study presents the steady behaviour of a double absorption process of an industrial sulphuric acid plant. The closed-loop process is modelled and simulated using UniSim Design R451 simulator and validated with plant data. The model includes principally: conversion reactor, plug flow reactors, absorbers, heat exchangers, pumps and compressors. The parameters of the converter kinetic were fitted to the real plant data, while the other parameters were estimated using conventional correlations. The results show a good agreement for the complete plant, with an accuracy that exceeds 97 %. Besides the optimization aspects, UniSim Design plant model is also useful for operator training, simulation of diverse scenarios and development of processes digital twin.

1 INTRODUCTION process was introduced to achieve 99.5 % or higher conversion rate, whereas the unreacted SO2 and SO3 Worldwide, sulphuric acid is the most used chemical are released to the environment (Moeller & Winkler, products in the basic chemical industry (Moats et al., 1968). In this context, improving the performance of 2006). Particularly, sulphuric acid plants are very the double contact process to achieve high energy important in the modern processing industry, because efficiency and maximize revenues, and minimize of its various applications; by far, in the phosphate environmental impact remain major challenges (Lee fertilizer industry (Kiss et al., 2010). The industrial et al., 2019). production of sulphuric acid was started with the In such case, two approaches are available: combustion of sulphur in the presence of steam and experimental tests and/or simulation and modelling. natural nitrate. Nowadays, various technologies are In fact, the experimental tests exhibit some available to produce sulphuric acid. The contact drawbacks, such as high cost of materials acquisition process is the most popular (Oni et al., 2018), overall, and maintenance, and validity area of the solution sulphuric acid is produced in two main steps: (1) complexity. In contrast, the main benefits of simulation and model-based control and optimization oxidation of sulphur dioxide SO2 to sulphur trioxide applications for industrial plants can be summarized SO3, and (2) absorption of SO3 by diluted sulphuric acid to form concentrated sulphuric acid. Indeed, the as: minimization of the experimental tests time and contact process has passed through two stages: single cost, high flexibility in the process flowsheet elaboration with the ability to change and replace absorption process, where 97 % of SO2 is oxidized to equipment (Boschert & Rosen, 2016), and also the SO3 and the unoxidized SO2 is emitted to the environment. Next, in 1968, the double contact development of processes digital twin (Parrott &

91 Mounaam, A., Harmen, Y., Chhiti, Y., Souissi, A., Salouhi, M. and El Khouakhi, M. UniSim-Design Simulation and Analysis of a Sulphuric Acid Manufacturing Plant with Double Absorption Process. DOI: 10.5220/0009832300910100 In Proceedings of the 10th International Conference on Simulation and Modeling Methodologies, Technologies and Applications (SIMULTECH 2020), pages 91-100 ISBN: 978-989-758-444-2 Copyright c 2020 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

SIMULTECH 2020 - 10th International Conference on Simulation and Modeling Methodologies, Technologies and Applications

Warshaw, 2017). Therefore, several stationary and Based on the previous investigations, a dynamic modelling and simulation studies have been considerable effort has been made to improve the performed to optimize the sulphuric acid performance of the double-absorption contact manufacturing plant. In particular, numerous studies process. Indeed, these studies were based on multi- have been conducted on the steady and dynamic objective optimization, which considers modelling of SO2 oxidation reactors, which focused environmental impact as a main objective such as on the design and operating conditions. For example, sulphuric acid production. In this context, it is Günther et al. (Günther et al., 2012) developed a important to dispose of more powerful and flexible mathematical model to describe the dynamics modelling and simulation solutions, which reflect the oxidation of SO2 to SO3. The results proposed a new experimental plant reality, and resolve the limitations design for zero-emission to the environment. Also, of the existed models. In this study, the closed loop Mann et al. (Gosiewski, 1993) proposed a new of sulphuric acid process is modelled and simulated dynamic simulation based on ordinary differential using UniSim Design R451 simulator and validated equations, which describes the behaviour of a single- with plant data. bed reactor in the contact sulphuric acid plant, thus, several variables have been studied, such as flow start-up and initial fixed-bed reactor temperatures. 2 PROCESS DESCRIPTION Interestingly, the results showed that the model can be used for the qualitative analysis of SO2 oxidation. The simplified bloc-flow diagram of the sulphuric Recently, Sørensen et al. (Sørensen et al., 2015) acid manufacturing process with double absorption is validated a dynamic model of SO2 oxidation using presented in Figure 1. experimental data from a sulphuric acid pilot plant. Firstly, moist air is filtered in an air filter to The results demonstrated that the dynamic simulation eliminate particles contained in the air. To reduce its can efficiently be used to evaluate operating moisture content, the air is dried by absorption in a conditions, equipment sizing with respect to the drying tower using the circulating sulphuric acid environmental impact. H2SO4. The liquid sulphur that has been prepared in In contrast to the previous studies, few studies the melting unit is burned with the dry air in the were conducted for the complete sulphuric acid plant. sulphur burner, which forms the sulphur dioxide SO2. Notably, Kiss et al. (Kiss et al., 2010) presented a The reaction of sulphur combustion is exothermic; complete model of an industrial sulphuric acid plant thus, a waste heat boiler is paced at the outlet of the using gPROMS tool. The results demonstrated that sulphur burner to recover the heat of the sulphur 40% of SOx emissions can be reduced by the combustion and generate the saturated steam. As the optimization of the split fraction or feed flow rates. In optimal required temperature for the sulphur dioxide addition, they developed an excel interface, which SO2 conversion is 420°C, a by-pass of the sulphur simulates the real behaviour of the plant. Also, the burner is mixed with the waste heat boiler outlet to results of Oni et al. (Oni et al., 2018) showed that the regulate the desired temperature. The conversion of process can be operated at different optimal SO into SO is carried out in a converter formed by conditions, and the ideal conditions was 9.5 ppm of 2 3 four catalytic bed. The vanadium oxide V2O5 is used SOx and 70.9 ppm of acid mist and 143.0 M$/y of net as a catalyst to accelerate the SO /SO conversion. In revenue. Likewise, Rahman et al. (Rahman et al., 2 3 order to reach the high desired conversion on SO2, the 2019) developed a new model that offers a cost- gaseous outlet flow of the 1st converter bed passes effective solution to reduce energy demand and limit through an inter-pass heat exchanger to regulate its emissions of aromatic compounds. In addition to the temperature before feeding the 2nd converter bed. above-mentioned study, Chowdhury et al. Between each bed of the four converter beds, heat (Chowdhury et al., 2012) simulated and optimized a exchangers and economizers are used for the same simplified process for the production of sulphuric raison. After passing the three first beds of the acid using Aspen HYSYS simulator. The results converter, the outlet flow of the 3rd bed feeds the first exhibited that the process plant simulation is an absorption tower, in which the SO formed reacts effective approach to optimizing annual profit. On the 3 with the H2O presented in the diluted circulating other hand, various limitations are noted in the H SO 98% to form the concentrated H SO 99%. models mentioned, for example, the non- 2 4 2 4 The outlet gas flow of the first absorption tower consideration of the thermal kinetics of the feeds the 4th bed of the converter where the remained conversion reactions, which is a key step in the SO is converted to SO , before feeding the second sulphuric acid manufacturing plant. 2 3 absorption tower in order to absorb the formed SO3.

92 UniSim-Design Simulation and Analysis of a Sulphuric Acid Manufacturing Plant with Double Absorption Process

Figure 1: Bloc-flow diagram of the studied process.

The conversion rate of SO2/SO3 is 99.99%, and the Table 1: UniSim Design components list for the sulphuric absorption rate of SO3 absorption in water is around acid process simulation. 99.98%. Also, a sulphuric acid circulation tank is used to feed the drying tower, the first and the final Component name Component formula absorption tower with the circulating sulphuric acid. Oxygen O2 The cold fluid used to cool the sulphur acid in the acid Nitrogen N2 cooler and the product acid cooler is sea water. Boilers at the liquid outlet of the first absorption Water H2 O tower is used to recover the energy produced by the Sulphur liquid S absorption reaction. Sulphur dioxide SO2

Trioxide sulphur SO3 3 PROCESS SIMULATION Sulphuric acid H2SO4 3.2 Fluid-packages 3.1 Components The UniSim-Thermo was selected as advanced In this study, UniSim-Design R451 simulator was thermodynamics in this simulation. The non-random used to perform the simulation of the studied two-liquid model (NRTL) model was selected for the sulphuric acid manufacturing process. liquid phase. It is used to correlates the activity The simulation goes through two principal steps: coefficients of the different components presented in the basis environment configuration and the liquid phase according to their mole fractions. The simulation environment configuration. At the basis Peng-Robinson (PR) model was selected for the environment stage, the necessary components vapor phase. Henry’s Law was selected for the Henry included in the manufacturing process are added, and constant and solubility coefficients estimation of the appropriate fluid-packages must be chosen to gaseous components in sulphuric acid, especially ensure a correct prediction of flow and mixture water and trioxide sulphur. properties according to their temperature and pressure. At the simulation environment stage, material and energy streams are added and configured. Also, the 3.3 Reactions flowsheet of the studied process is elaborated. Finally, As mentioned above in the process description the different reactions that governs the process must be section, four reactions are involved in the acid specified. For the sulphuric acid manufacturing sulphuric manufacturing process: process, all the required components are available in the simulator components library, except the raw solid SO SO (1) sulphur which has been replaced directly by the liquid sulphur. The components used in this simulation are 1 SO O SO (2) represented in the following table: 2

SIMULTECH 2020 - 10th International Conference on Simulation and Modeling Methodologies, Technologies and Applications

SO HO HSO (3) The catalytic conversion of the SO2 to SO3 was simulated by a plug flow reactor with as a kinetic HSO 2HO 2HO SO (4) heterogenous reaction. In 1997, Froment and Bischoff have proposed a kinetic model to estimate The reaction (1) represents the sulphur the rate of this conversion by the following equation combustion within the sulphur burner. The reaction (Anton A. Kiss et al, 2010): (2) describes the conversion of the sulphur dioxide

SO2 to the sulphur trioxide SO3 using V2O5. The P K.P.P.1 reaction (3) represents the sulphur trioxide SO3 (11) K. P .P absorption in water H2O within the two absorption r 1 K .P K .P ² towers, while the reaction (4) represents the sulphuric acid H2SO4 dilution with the water absorbed in the drying tower. All four reactions are exothermic and Where: generate an enormous amount of energy . r : kinetic reaction rate of the reaction (2) (kmol/kg.cat. s); 3.4 Unit Operations Simulation . P : pressure of the component i (atm); . K1 : first rate constant (1/atm1/2); The combustion of the liquid sulphur was simulated . Kp : second rate constant (kmol/lh.cat.atm².s); using an adiabatic conversion reactor. The . K2 : third rate constant (atm-1); combustion is considered complete with full . K3 : third rate constant (atm-1). consumption of liquid sulphur. The mass balance of The rate constants K1, Kp, K2, K3 were calibrated and the sulphur burner is given by the following equation: adjusted using the simulated plant data, and they are given by: N N ν.ξ (5) , , 45501 K exp 15.31 (12) RT H H ξ.H𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 (6) 93943 K exp41.30 (13) H∑ h, N, (7) RT

71655 h, C,T .dT (8) K exp 71.74 (14) RT H∑ h, N, (9) 437269 K exp15.31 (15) RT h, C,T .dT (10) The absorption reactions (3) and (4) were Where: simulated using the absorber model integrated in the simulator and based on column theory. The multi- . N , N : inlet and outlet molar flow of the , , stage absorption towers present a series of component i (mol/h); equilibrium and non-equilibrium flash stages. At each . ν : stoichiometric coefficient of the component stage, there can be a mass and heat transfers between i in the reaction (1); the two phases that feed the column in counter . ξ N,. current. The following equations show the mass . H, H : inlet and outlet heat flows (kJ/h); transfer balance between the components i and j in the . H : molar enthalpy of the reaction (1) gas and liquid streams respectively, within an (kJ/mole); absorption tower: . h , h : inlet and outlet molar enthalpy of , , 4 d the component i (kJ/mole); . Q .C N .A (16) π. D dz , . C,: specific heat of the component i (kJ/mole. °C); 4 d . Q .C N .A (17) . T,T,T : reference, inlet and outlet π. D dz , temperature of the sulphur burner, respectively (°C). N . .C,; N N (18) .

94 UniSim-Design Simulation and Analysis of a Sulphuric Acid Manufacturing Plant with Double Absorption Process

Where: . W: actual required power (W); . D: absorber diameter (m); . P,P: inlet and outlet pressure (Pa); . Q ,Q : gas and liquid volumetric flow rates . M : inlet mass flow rate (kg/h); (m3/h); . ρ: fluid density (kg/m3); . C,,C, : component i and component j . H ,H : inlet and outlet heat flow rates (W); concentration in the gas and liquid respectively . Effenciency %: pump efficiency (%). (mole/m3); The compressors used to increase the pressure of . N : molar flow rate of the component i the gas streams were simulated by the centrifugal (mole/m2.h); compressor model based on the isentropic efficiency. . A: specific area (m2/m3); The isentropic ideal power and the actual power . k,k : gas and liquid partial mass transfer required for gas compression is defined as follow: coefficients; . H: Henry coefficient of the component i; 𝑛 P P . P: partial pressure of the component i (Pa); W M. . . 1.F (24) n1 ρ ρ . D: mass diffusivity of the component i.

The simulation of the heat transfer operations W H H (25) within the process was realized using the heat exchanger model presented in the simulator library. W This model is based on the material and energy Effenciency % (26) balance equations. The Log-Mean Temperature W Difference LMTD method is adopted to calculate the Where: heat transfer flow rate W exchanged between the . ρ : gas inlet density (kg/m3); two flows: . n: volume exponent; W U.A.ΔT.F (19). F: correction factor; . Effenciency %: compressor efficiency (%). T T T T ΔT , , , , T T (20) The following table regroups the different ln , , T, T, UniSim-Design equipment models used to perform this simulation: Where: . W : heat transfer flow rate (W); Table 2: UniSim Design equipment models for the studied process simulation. . U: heat transfer coefficient (W/m². K); . A: heat transfer areas (m²); Equipment model Description . F: correction factor. Conversion reactor Sulphur combustion

The pumps used to increase the pressure of liquid Plug flow reactor SO2 conversion streams were simulated using the centrifugal pump Absorber H2O and SO3 absorption model assuming that that fluid is incompressible. The pump simulation is based on the general pump Heat exchanger Heat transfer equation that gives the ideal power required to rise the Cooler Fluids cooling liquid pressure according the inlet and outlet Pump Liquids pumping pressures, flow rate and density: Compressor Gas compression

P P.M Splitter Flows division W (21) ρ Mixer Flows mixing Valve Flows control W H H (22)

W Effenciency % (23) W 4 RESULTS AND DISCUSSION

Where: In order to configurate the basis environment of the . W: ideal required power (W); simulator, the chemical components involved in the

95 SIMULTECH 2020 - 10th International Conference on Simulation and Modeling Methodologies, Technologies and Applications

sulphuric acid manufacturing process were defined V. for the dilution and cooling water key streams. (Table 1). In addition, the necessary fluid-packages Figure 3 presents the simulation results of the (PG for the gaseous phase and NRTL for the liquid sulphuric acid concentration within the drying tower. phase) were specified. The four principal reactions The circulating sulphuric acid used for air-drying governing the process (liquid sulphur burning, feeds the column from the top at the concentration of sulphur dioxide conversion, sulphur trioxide 98.6%, and absorbs the water contained in the wet air absorption and sulphuric acid dilution) were also that feeds the column from the bottom. The sulphuric defined with their reaction rates. Next, in the acid is diluted and leaves the drying column at the simulation environment of the simulator, the concentration of 98.33% as shown in the simulation equipment models were inserted, and the global results. It is observed that the dry air entering the flowsheet of the studied process was elaborated column at 25°C leaves at the temperature of 65.8°C, including the gas circuit and the acid circuit. which is justified by the exothermicity of the Figure 2. shows the simulation of the sulphuric sulphuric acid dilution reaction. acid manufacturing plant with double absorption The dry air leaving the drying column is performed under the UniSim-Design R451 simulator. compressed before feeding the sulphur burner. An The key streams used to perform this simulation are adjustment of the compressor energy stream is used summarized in Table III. for the liquid sulphur and in order to maintains the pressure of the dry air at 153 the wet air properties, Table IV. for the operating key kPa. The energy required to increase the air streams of the circulating sulphuric acid, and Table

Figure 2: UniSim-Design simulation of the sulphuric acid manufacturing process with double absorption.

0,9858

Temperature H SO Concentration 64 0,9852 2 4

0,9846

Temperature (°C) Temperature 0,9840 Mass Fraction (% H2SO4) 60 (a) 0,9834 (b)

0,0 0,2 0,4 0,6 0,8 1,0 0,0 0,2 0,4 0,6 0,8 1,0 Stage Position Stage Position Figure 3: Temperature (a) and sulphuric acid concentration (b) variations in the drying tower stages.

96 UniSim-Design Simulation and Analysis of a Sulphuric Acid Manufacturing Plant with Double Absorption Process

Table 3: Liquid sulphur and wet air properties.

Stream Wet air Liquid sulphur Flow rate (m3/h) 540 32 Temperature (°C) 25 130 Pressure (kPa) 101.3 1920

O2 (%) 20.68 0

N2 (%) 78.04 0

H2O (%) 1.28 0 S (%) 0 100

Table 4: Sulphuric acid operating key streams.

Stream Acid 1 Acid 7 + Acid 9 Acid 10 Sulphuric acid in the Sulphuric acid in the first Sulphuric acid in the final Description drying tower absorption tower absorption tower Flow rate (m3/h) 1245 2890 1030

Concentration (%H2SO4) 98.6 98.97 98.6

Table 5: Water operating key streams.

Stream SW PW1 PW3 Process water for the Process water for the Sea water for the Description strong sulphuric acid circulating sulphuric acid sulphuric acid cooling dilution dilution Flow rate (m3/h) 2765 28 3 pressure from 98 kPa to 154 kPa (Figure 4) is combustion is calculated at 25°C as 298190 kJ/mole. estimated by the simulator at 8302 kW, with an A small amount of the SO3 is also produced because adiabatic efficiency of 75% and a polytropic of the high temperature within the sulphur burner. efficiency of 76.52%. The molar composition of the combustion gas is: 9.7% of O2, 79.16% of N2, 10.87% of SO2 and 0.27% 160 of SO3. The hot combustion gas passes through a 150 waste heat boiler to recover a part of the combustion heat and to promote the required temperature of the 140 SO2 conversion. An adjustment of the by-pass

130 fraction at the inlet of the waste heat boiler is used to maintain the desired temperature. 120 As mentioned in the process description section, Pressure (kPa) Pressure the converter is formed by four catalytic bed, and 110 each bed is simulated by a plug flow reactor. The 100 temperature at the inlet of the three first beds is adjusted to 440°C by superheaters and inter-pass heat 90 60 70 80 90 100 110 120 130 140 exchangers, and at 400 °C for the last bed. As Temperature (°C) illustrated in the SO2 conversion-Temperature curve Figure 4: P-T curve of the air compressor. (Figure 5), the four operating lines represents progress of the conversion rate within the four beds The liquid sulphur feeds the sulphur burner at of the converter. The SO2 conversion rate is 130°C and 1920kPa and reacts with the dry air to accompanied with a temperature increase since the conversion reaction is exothermic. Once the form the SO2. The combustion gas mixture produced at the sulphur burner leaves at the temperature of conversion rate riches the equilibrium curve, a 1216 °C with a complete combustion of the liquid cooling step is required to achieve a higher conversion rate. Several conversion stages and inter- sulphur. The reaction heat of liquid sulphur

97 SIMULTECH 2020 - 10th International Conference on Simulation and Modeling Methodologies, Technologies and Applications

402 50 Reactor Temperature SO3 Molar Flow

399 40 mole/h) 3

30 396

20 Temperature(°C)

393 (10 Flow Molar 3 10 SO

390 (a) 0 (b)

0,0 0,2 0,4 0,6 0,8 1,0 0,0 0,2 0,4 0,6 0,8 1,0 Reactor Lenght Reactor Lenght th Figure 5: Temperature (a) and SO3 molar flow (b) variations in the 4 catalytic bed.

0.9930 189,75

) 0.9925 Temperature 4 SO

2 H SO Concentration 0.9920 2 4 189,20

0.9915

0.9910

Temperature (°C) Temperature 188,65

Mass Fraction (% H (% Fraction Mass 0.9905

(a) 0.9900 (b) 188,10

0,0 0,2 0,4 0,6 0,8 1,0 0.0 0.2 0.4 0.6 0.8 1.0 Stage Position Stage Position Figure 6: Temperature (a) and sulphuric acid concentration (b) variations in the first absorption tower. step cooling are necessary. The outlet temperatures The outflow gas of the 3rd bed is cooled and sent are 643°C, 527°C, 462°C and 404°C for the converter to the first absorption tower in order to absorb the SO3 stages, respectively. The SO2 conversion rates in the produced by the SO2 catalytic conversion, then gone three first beds are 63.43%, 89.95%, 96.54% back to the 4th bed in which the remaining SO2 is respectively. converted into SO3. Figure. 6. Shows the temperature and the SO3 mole flow variations along the 4th bed. 100 SO2 Conversion rate The SO2 conversion rate at the last bed achieves Equilibrum curve 99.97%. However, the conversion of the SO2 into SO3 80 is accompanied with a temperature increase due to the heat generated by the reaction as illustrated in Figure 60 6. The molar enthalpy of this reaction is given by the simulator as 98925 kJ/mole.

40 The absorption rate of SO3 is around 99.98% in the first absorption tower and 100% in the second

20 absorption tower. As shown in the simulation results SO2Conversion Rate(%) of the first absorption tower of Figure 7, the

0 absorption of SO3 is an exothermic reaction that generates 97333kJ/mole. The circulating sulphuric 350 400 450 500 550 600 650 700 acid 98.97% feeds the first absorption tower at Temperature (°C) 189°C, and leaves at the concentration and Figure 7: Conversion-Temperature curve of the catalytic temperature of 99.30% and 173°C, respectively. converter. However, it feeds the second absorption tower with a concentration of 98.60% and a temperature of 65°C,

UniSim-Design Simulation and Analysis of a Sulphuric Acid Manufacturing Plant with Double Absorption Process

100 Plant data Plant data 95 Unisim-Design Unisim-Design 100,0 90

75 99,8

70 Conversion Rate (%) 2 65 SO3(%) RateAbsorption SO 60 (a) (b)

55 99,6 1st bed 2nd bed 3rd bed 4th bed 1st tower 2nd tower Figure 8: UniSim Design converter (a) and absorption towers (b) simulation results versus plant data.

600 R² = 0.9989 1200 R² = 0.9991 500 1000 400 800 300 600

200 3 Unisim-Design Flow rate (m /h) Unisim-Design 400 Temperature (°C)

100 200 (a) (b) 0 0 0 100 200 300 400 500 600 0 200 400 600 800 1000 1200 Plant data Plant data

200 100,0 R² = 0.9773 180 R² = 0.9897

99,5 160

140 99,0 120 Unisim-Design 100 Pressure (kPa) Unisim-Design 98,5 H2SO4 Concentration (%) 80 (a) (d) 60 98,0 60 80 100 120 140 160 180 200 98,0 98,5 99,0 99,5 100,0 Plant data Plant data Figure 9: Simulation results versus plant data correlation for the flow rates (a), temperatures (b), pressures (c) and sulphuric acid concentrations (d). and leaves the tower at a concentration of 98.67% and the results indicates that the simulations performed the temperature of 82.76°C (after absorbing the SO3 under UniSim Design R451 simulator represent a generated in the 4th catalytic bed). high level of validity to accurately describe the In order to validate the process simulation, the industrial process. simulation results of the SO2 conversion rate within the four catalytic beds of the converter, and the SO3 absorption rate within the two absorption towers were 5 CONCLUSIONS compared to the plant data as shown in Figure 8. In addition, the temperature, pressure, flow rate and In this study, a steady-state simulation of a double sulphuric acid concentration values found in the absorption sulphuric acid plant was conducted using simulation were compared to the real plant Honeywell UniSim-Design R451 simulator. The measurement and have shown a high accuracy simulated process includes gas and acid circuits, with (Figure 9) between 97% and 99%. The comparison of a SO2 conversion rate of 99.9%, and a SO3 absorption

SIMULTECH 2020 - 10th International Conference on Simulation and Modeling Methodologies, Technologies and Applications

rate of 99.98%, and an average of 140 ppm of SO2 gas Parrott, A., & Warshaw, L. (2017). Industry 4.0 and the sent to the atmosphere. The developed model and digital twin. Deloitte University Press. simulation includes the different manufacturing Rahman, R. K., Ibrahim, S., & Raj, A. (2019). Multi- process units: drying tower and air compressors, objective optimization of sulfur recovery units using a detailed reaction mechanism to reduce energy sulphur burner and heat recovery boiler, consumption and destruct feed contaminants. SO2 converter and heat exchangers, first absorption Computers and Chemical Engineering. tower and energy economizers, second absorption Sørensen, P. A., Møllerhøj, M., & Christensen, K. A. tower, acid and water pumps, acid diluter systems, (2015). New dynamic models for simulation of acid cooling systems and acid circulating tank. The industrial SO2 oxidation reactors and wet gas sulfuric results obtained were validated using the real data acid plants. Chemical Engineering Journal extracted from the manufacturing plant under the same operating conditions, and a considerable accuracy of 97% was observed. Thus, the plant modelling and simulation using UniSim Design R451 simulator can be used to efficiently calculate mass and energy balances. Furthermore, it can be used to improve the manufacturing process, test advanced process control methods and develop digital twins to facilitate the digital transformation of industries.

REFERENCES

Boschert, S., & Rosen, R. (2016). Digital twin-the simulation aspect. In Mechatronic Futures: Challenges and Solutions for Mechatronic Systems and Their Designers. Chowdhury, N. B., Hasan, Z., & Biplob, A. H. M. (2012). HYSYS Simulation of a Sulfuric Acid Plant and Optimization Approach of Annual Profit. Journal of Science (JOS). Gosiewski, K. (1993). Dynamic modelling of industrial so2 oxidation reactors part I. model of “hot” and ’cold’start- ups of the plant. Chemical Engineering and Processing. Günther, R., Schöneberger, J. C., Arellano-Garcia, H., Thielert, H., & Wozny, G. (2012). Design and modeling of a new periodical-steady state process for the oxidation of sulfur dioxide in the context of an emission free sulfuric acid plant. In Computer Aided Chemical Engineering. Kiss, A. A., Bildea, C. S., & Grievink, J. (2010). Dynamic modeling and process optimization of an industrial sulfuric acid plant. Chemical Engineering Journal. Lee, J., Cameron, I., & Hassall, M. (2019). Improving process safety: What roles for digitalization and industry 4.0? Process Safety and Environmental Protection. Moats, M., Davenport, W. G., & King, M. J. (2006). Sulfuric Acid Manufacture. In Sulfuric Acid Manufacture. Moeller, W., & Winkler, K. (1968). The double contact process for sulfuric acid production. Journal of the Air Pollution Control Association. Oni, A. O., Fadare, D. A., Sharma, S., & Rangaiah, G. P. (2018). Multi-objective optimisation of a double contact double absorption sulphuric acid plant for cleaner operation. Journal of Cleaner Production.

100