Kago Baitshenyetsi 200665756

Done By Kago Baitshenyetsi

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Kago Baitshenyetsi 200665756

Table of Contents

Simulation of Reactors and Heaters/Coolers Using HYSYS.......................................0

Introduction.................................................................................................................2

Background Information..............................................................................................3

Problem Statement.....................................................................................................4

Mass and Energy Balance..........................................................................................4

Results: Simulation.....................................................................................................9

Discussion of Results................................................................................................18

Conclusion................................................................................................................19

References................................................................................................................20

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Kago Baitshenyetsi 200665756

IntroductionIn the ever increasing economic demand for resources coupled with constantly variable market conditions, Industries and engineers are faced with challenges of economical efficient ways of production to meet the supply. Most major resource companies (such as for oil and Gas) utilise process modelling software’s to give accurate representation of their basic processes. Aspen Hysys software is one of the most prominently used modelling software’s in the world (Process Modelling, 2012). Its process modelling capabilities allows for the designing, planning and performance monitoring of industrial process. According to (Aspen, 2012) An added advantage is that it also allows engineers to analyse the safest and most profitable plant designs subsequently reducing plant operating costs and maximising plant performance.

The aspen HYSYS software uses the property of fluid packages to perform a wide variety of physical property calculations and flash methods. The simulation basis manager is an aspen software property view window that allows the user to create and manipulate fluid packages (Aspentech, 2012). Different fluid Packages are used to predict different environments. For the rigorous treatment of hydrocarbon systems the PRSV fluid property package is mostly adopted (Aspentech, 2012). The PRSV (or Peng Robison Stryjek Vera) is an improved state of equation to the original Peng Robinson or (PR) state equation. The PRSV extents the application of the PR state method to non-ideal systems with more accurate results even at low temperatures (Aspentech, 2004). The state equation is able to execute rigorous perform rigorous three-phase flash calculations for aqueous systems containing H2O, CH3OH or glycols (Aspentech, 2004). This allows good representation often highly non-ideal systems such as production of ethylene oxide however with disadvantage of added computational time. Therefore aims for this assignment where as follows

To simulate the production of ethylene oxide from ethylene and air by means of conversion Reactor

Effect of coupling the reactor to a cooler in the process To investigate the reactant conversion and cooling requirements

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Background InformationManufacture of Ethylene Oxide

Ethylene oxide is commercially manufactured using two basic routes namely; the direct oxidation process and from ethylene chlorohydrin (Bioinformatics, 2012). The chlorohydrin process involves the reaction of ethylene with hypoclorous acid. The mixture is further undergoes dehydroclorination of chlorohydrin by addition of lime (Bioinformatics, 2012). This produces ethylene oxide and calcium chloride. This however process proved not to be economically efficient and was replaced by the direct oxidation process (Bioinformatics 2012). This process is now the dominant production method of almost all the worlds’ ethylene oxide.

The direct oxidation process involves the vapour phase catalytic oxidation of ethylene in the presence of oxygen over a silver based catalyst to produce ethylene oxide (Huang, 1999). This process can be further divided into two categories depending on the primary source of oxidising agent. These types include the air based process where oxygen enriched air is fed directly into the system and the oxygen based process in which high purity oxygen is directly added into the system (Huang, 1999). In this assignment the air based direct oxidation method was used. Figure 1 below illustrates the basic ethylene production process

Figure 1: Ethylene oxide Absorber and Stripper Process (Aspen Hysys 2012)

The drawback of the direct oxidation process is its poor yield or selectivity of ethylene oxide produced per unit of input ethylene consumed in the process. (Robert, 1988) Therefore operating conditions must be prudently controlled to maximize selectivity.

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Problem StatementAn Ethylene oxide is to be produced by the direct oxidation method of ethylene. The air is put to 1 atmosphere pressure and a fixed bed of silver catalyst is used on a carrier. The inlet stream of ethylene and air enters the reactor at temperature of about 200 ºC and which consists of 5 kmol per cent ethylene and 95 kmol per cent air per hour. Given that the exit temperature from the reactor does not exceed 260 ºC and it is possible to convert 50% of the ethylene to the oxide however about 40% of the ethylene is also at the same time converted to water and carbon dioxide.

Process Equations are

For Reaction 1: C2H 4+3O2→2CO2+2H2O

and. ....... Equation 1For Reaction 2: C2H 4+½O2→CH 3CHO

Assume air to be 21 vol %-oxygen and 79 vol%-nitrogen.

Mass and Energy Balance

Table 1: Inlet Stream Mass flowSubstance Molar flow rate

(kgmole/h)Molar mass (kg/kmol)

Mass flow rate (kg/h)

C2H4 5 28.05 140.3

O2 19.95 32.00 638.4

N2 75.05 28.00 2101.4

H2O 0 18.00 0.0

CH3CHO 0 44.05 0.0

CO2 0 44.00 0.0

total 2880.1

The mass flow rate = molar mass * molar flow rate

= 5 kgmol/h * 28.05 kg/kmol = 140.3 kg/h

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Table 2: Outlet Stream Mass flowSubstance Molar flow rate

(kgmole/h)Molar mass (kg/kmol)

Mass flow rate (kg/h)

C2H4 5-(2.5+2) =0.5 28.05 14.0

O2 19.95-(6+1.25) =12.70 32.00 406.4

N2 75.05 28.00 2101.4

H2O 4 18.00 72.0

CH3CHO 2.5 44.05 110.1

CO2 4 44.00 176.0

total 2880.0

For the First reaction

C2H 4+3O2→2CO2+2H2O

Undergoes 50% conversion

Table 3: Reaction 1 Mass flowSubstance Stoichiometric

CoefficientMole

Consumption or production

(kmol/h)

Molar mass (kg/kmol)

Mass Consumption or

production (kmol/h)

C2H4 1 2.0 28.05 56.10

O2 3 6.0 16.00 96.00

N2 0 0.0 28.00 0.00

H2O 2 4.0 18.00 72.00

CH3CHO 0 0.0 44.05 0.00

CO2 2 4.0 44.00 176.00

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For the Second Reaction

C2H 4+½O2→CH 3CHO

Undergoes 40% conversion

Also yields Carbon dioxide, water and Nitrogen By-products in negligible amounts

Table 4: Reaction 2 Mass flowSubstance Stoichiometric

CoefficientMole Consumption or production (kmol/h)

Molar mass (kg/kmol)

Mass Consumption or production (kmol/h)

C2H4 1.0 2.5 28.05 70.13

O2 0.5 1.25 16.00 20.00

N2 0.0 0 28.00 0.00

H2O 0.0 0 18.00 0.00

CH3CHO 1.0 2.5 44.05 110.13

CO2 0.0 0 44.00 0.00

The mass comsumption= stoichiometric coefficient* mole consumption * Molar mass

= 1.0 * 2.5 kmol/h* 28.05kg/kmol = 70.13 kmol/h

Overall Balance

The overall reaction mass balance was given by addition of the first and second reaction as shown below

2C2H 4+72

02→2CO2+2H 20+CH 3CHO

Table 5: The Total Inlet Mass flow

Substance Molar flow rate Molar mass (kg/kmol)

Mass flow rate

C2H4 5 28 140

O2 19.95 32 638.4

CO2 0 44 0

H20 0 18 0

CH3CHO 0 44 0

N2 75.05 28 2101.4

Sum 2879.8

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Table 6: the total mass flow rate of the reactionSubstance Stoichiometric

CoefficientMole Consumption or production (kmol/h)

Molar mass (kg/kmol)

Mass Consumption or production (kmol/h)

C2H4 2 4.5 28 126

O2 3.5 7.875 32 252

CO2 2 4.5 44 198

H2O 2 4.5 18 81

CH3CHO 1 2.25 44 99

Table 7: the total Outlet Mass flow rateSubstance Molar flow rate

(kgmole/h)Molar mass (kg/kmol)

Mass flow rate (kg/h)

C2H4 5-(2.5+2) =0.5 28.0 14.0

O2 19.95-(6+1.25) =12.705 32.0 386.4

CO2 4.5 28.0 198.0

H2O 4.5 18.0 81.0

N2 75.05 28.0 2102.4

CH3CHO 2.25 44.0 99.0

Sum 2879.8

Energy Calculations

Formulas used for the calculation of Enthalpy

The total energy balance is given by

H ¿−H out+Eduty−∆ H reaction=0 …………………………..………Equation 2

Rearranging the Equation gives

H ¿−H out=−Eduty+∆ H reaction ……………………………………Equation 3

Heat of the reaction is given by

∆ H reaction=∑ n1H reaction …………………………………………..Equation 4

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Where Hout = enthalpy of outlet stream

Hin = enthalpy of inlet stream

∆ H = energy flow of reaction

n1 = no. of mole x conversion factor

The following were calculated using the HYSYS software

Table 6: Determining the Enthalpy for the system

Reaction Enthalpy of

Reaction (Hr)

N1 Energy Flow

(Hrxn)

1 -1323537.8 2 -2647075.6

2 -104999.8 2.5 -262499.5

total -2909575.1

With the obtained Enthalpy values from the HYSYS software, energy balance was performed

using Equation 4: ∆ H reaction=∑ n1H reaction= -1.04999.8 x 2.5 = -262499.5kJ/h

Table 7: Determining the Change Enthalpy of the System

Component Hrxn Eduty Hin - Hout

Enthalpy -2909575.1 -2717000 -192575.1

The overall energy balance where performed using equation 3:

Hin – Hout = -2.909575.1x106 – (-2.717000x106) = - 192575.1 kJ/h

Results: Simulation Question 3

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The following are simulations of the reactor cooling by means of a one sided heat exchanger

Part A

The cooling water flow rate was determined for the reactor when the availed water was at 40 ºC (ΔP of water is 10 kPa)

Figure 2: Process Flow Diagram of Production of Ethylene Oxide

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Figure 3: Material Stream of Ethylene Oxide process

Figure 4: Composition Streams of Ethylene Oxide process

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Figure 5: Energy Stream of Ethylene Oxide process

Part B

The reactor conversions where decreased by 10% and the water coolant outlet temperature was determined when the water flow rate was fixed at 2000 kgmole/h and the water inlet temperature was 40 ºC

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Figure 6: The reduced conversion by 10% for reaction 1

Kago Baitshenyetsi 200665756

Figure 7: Reduced Conversion by 10% for reaction 2

The streams for the system

Figure 8: Material Stream of the Ethylene oxide process

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Figure 9: Composition streams of Ethylene Oxide process

Figure 10: Energy Stream of the Ethylene Oxide Process

Part C

The reactor was now operated at 200 ºC instead of 260 ºC. The water was availed at 95 ºC and outflow was at 105 ºC, an estimate of the water flow rate was determined (i.e. reverse conversion rates of two reactions to original values).

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Figure 11: Material Stream of Ethylene Oxide Process

Figure 12: Composition Stream of Ethylene Oxide Process

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Figure 13: Energy Stream of the Ethylene Oxide Process

Part D

The following are simulations for if the water cooling had failed and what the temperature of the reactor would be.

Figure 14: Process Flow Diagram of production of Ethylene Oxide without the cooler

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Figure 15: Material Stream of the Ethylene Oxide Process

Figure 16: Composition Streams of the Ethylene Oxide Process

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Figure 17: Energy Streams of Ethylene Oxide Process

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Discussion of ResultsFor Part A

Figure 2 show the process flow diagram of the direct oxidation method for the production of Ethylene Oxide. As shown from the figure the basic process involves a conversion reactor to which the feed is input in the presence of air over a silver based catalyst to produce ethylene oxide. The reaction also produces side products carbon dioxide, nitrogen and water. However these are produced in small quantities and can be neglected. The chemical process is shown by Equation 1. Due to the exothermic nature of the process, heat is released into the reactor vessel; therefore a coolant is a critical component of the system.

In this section, a feed consisting of 95% air (i.e. 0.21-oxygen and 0.79-nitrogen) and 5% kgmole of Ethylene was fed in to the reactor at a molar flow rate of 100kmol/h. the reactor temperature was controlled by circulating coolant water at 1 atm pressure through a cooling coil immersed in the catalyst bed. The temperature rise was made sure not to exceed 10°C. The process reaction takes place in two reactions (as shown in Equation 1). The first reaction occurs at 50% conversion of ethylene to Ethylene Oxide. For the second Reaction 40% of the Ethylene is converted to carbon dioxide and water However 10% of the Ethylene in the process does not react. The nitrogen in this process reaction also does not react. For this task the availed water then set to 40°C and a pressure of 10kPa. The determined cooling water flow rate required by the reactor was found to be 3734 kgmole/h

For Part B

Initially before conversion and the molar follow rate was fixed to 200kmol/h, an increase water coolant temperature from 50°C to 53.76°C was observed. The effect of reducing the conversion rate by 10% resulted in lesser yields of ethylene oxide produced. This was accompanied by the decrease in the reactor temperature. This is proved by the increase in the water outlet temperature as shown in figure 6. In addition a fixed flow rate also increases the amount of heat energy absorbed by the coolant fluid thus the rise in coolant exit temperature. The loss in thermal energy by the system to the coolant is also reflected in the small energy stream of the system as shown in figure 8 compared originally to that of Part A

For Part C

When the reactor was operated at 200°C instead of 260 °C, The mass flow rate attained was 70.4 kgmole/h which is quite less, compared to the original molar flow before the temperature change as in Part A which was 3734kgmole/h. Increase in kinetic velocity of the coolant increases the rate at which heat energy is removed, hence when temperature of system is reduced, thus reduced molar flow rate would be expected. The inlet water was availed at 95 ºC and outflow was at 105 ºC this

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exceeded the boiling point of water, therefor a vapour fraction of the outlet water was realised, as shown in figure 9.

Comparable to Part A where reactor temperature operated at 260°C there was an overall energy stream of the process increase of 19.2% (i.e.−2.909e+006−(−2.717e+006)

−2.717+006¿∗100=19.2), this was primarily due to the increased

water temperature.

For Part D

Figure 12 shows the process flow diagram with the removed cooler to simulate if the water cooler would have failed. The inlet temperature increased from 200°C to an exit temperature of 1029°C. The increase in temperature was due to the exothermic nature of the direct production of ethylene oxide process. Failure of the cooling system would have resulted in severe damage or even explosion in the plant.

For mass and energy balances

Calculation of the enthalpy of reaction was done aid of the HYSYS software. A total of -2909575.1kJ/h was used by the reactor in order for a complete reaction to take place. To determine the change in enthalpy, the Eduty value obtained from the HYSYS

software was substituted in equation 3 and mathematical operation where made to find Hrxn. The change in enthalpy of the system was found to be -192575.1kJ/h. The negative enthalpy value demonstrations that it is an exothermic reaction

Conclusion

The cooling flow rate required by the reactor is when water was availed at 40ºC and at 10 kPa was 3734 kgmole/h

The water coolant outlet temperature when the water flow rate was fixed at 2000 kgmole/h and the water inlet temperature was 40 ºC was found as 53.76°C

The new water flow rate if water was available at 95 ºC and outflow was at 105 ºC was 70.41 kgmole/h

The temperature of the reactor when the cooler would have failed was 1029°C The overall enthalpy of the reaction was -1.927x105 kJ/h

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References1. Aspen HYSYS® - Aspentech. 2012. Aspen HYSYS® - Aspentech. [ONLINE]

Available at: http://www.aspentech.com/hysys/. [Accessed 27 November 2012].

2. Aspentech. 2004. Simulation Basis. [ONLINE] Available at: http://www.ualberta.ca/CMENG/che312/F06ChE416/HysysDocs/AspenHYSYSSimulationBasis.pdf. [Accessed 27 November 2012].

3. Aspentech. 2012. Aspen Hysys Property Packages. [ONLINE] Available at: http://sites.poli.usp.br/d/pqi2408/BestPracticesOptimumSimulationsHYSYSPropertyPackages.pdf. [Accessed 27 November 2012].

4. Bioinformatics. 2012. Manufacture of Ethylene Oxide. [ONLINE] Available at: http://www.sbioinformatics.com/design_thesis/Ethylene_oxide/Ethylene-2520oxide_Methods-2520of-2520Production.pdf. [Accessed 27 November 2012].

5. Huang.J, et al. 1999. Ethylene Oxide Process System. [ONLINE] Available at: http://www.owlnet.rice.edu/~ceng403/gr1599/finalreport3.html. [Accessed 27 November 2012].

6. Process Modelling Using HYSYS with Chemical Industry Focus. 2012. Process Modelling Using HYSYS with Chemical Industry Focus. [ONLINE] Available at: http://www.scribd.com/doc/7207157/Process-Modeling-Using-HYSYS-With-Chemical-Industry-Focus. [Accessed 27 November 2012].

7. Robert. F. Dye. 1988. Patent US4769047 - Process for the production of ethylene oxide - Google Patents. [ONLINE] Available at: http://www.google.co.uk/patents?hl=en&lr=&vid=USPAT4769047&id=EcQ9AAAAEBAJ&oi=fnd&dq=production+process+of+ethylene+oxide+from+ethylene&printsec=abstract#v=onepage&q=production%20process%20of%20ethylene%20oxide%20from%20ethylene&f=false. [Accessed 27 November 2012].

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