Case Study Batch Reaction Lesson 1

8/12/2019 Case Study Batch Reaction Lesson 1

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Thermal Safety Case Study- Lesson 1This case study shows through an example of a batchreaction how to systematically assess the thermal risk

related to runaway reactions.It was prepared by R.Perrayon and P.Lerena based onthe knowledge of the Swiss Safety Institute (Basel,Switzerland)

Lesson 1 is a step by step procedure to allow a

preliminary evaluation of both severity and probabilityusing simple experimental techniques (SCREENING).


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Summary of lessons

What is risk?

Traditionally the risk is defined as the product of theseverityof a possible incident times its probabilityofoccurrence. Hence the risk assessment requires theevaluation of both the severity and probability.

The following lessons are a guide to a systematicevaluation of the risks of a chemical process.

Lesson 1 is a step by step procedure to allow apreliminary evaluation of both severity andprobability using simple experimental techniques(SCREENING).

Lesson 2 expands the study through the use of moredata if the conclusion of the previous SCREENING isthat the thermal risks of the process are high.

Lesson 3 summarizes the results obtained in theprevious lessons through the construction of aCOOLING FAILURE SCENARIO and the assessmentof its CRITICALITY.

Lesson 4 analyzes the operating conditions requiredto mantain the process under thermal control as wellas the measures that should be taken to prevent anincident from occuring.


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Case study :Batch reaction

Lesson 1

The following is a short descriptionof an actual manufacturingprocedure for the substitution ofpara-chloro-nitrobenzene:

A quantity of 1-chloro-4-nitrobenzene ischarged in a reactor with ammonia

(27% by weight in water).The autoclave is then heated in about 3hours to 195C and maintained at this

temperature for 5 hours. The pressurefinally reaches 41-42 atms.After this time, the reaction mass iscolled down to room temperature.

Cl NO2

H2N

2 NH3

NH4ClNO2

Reaction scheme

+

+


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Process data

Charge

Compound Mass kmol Molar ratio(kg)

1-Chloro-4-

nitro-benzene 423 2.7 1Ammonia 27% 2024 32.1 12

(pure NH3)

Total 2447

Reactor data

Stage Reaction mass Approximate(kg) volume (m3)

Initial 2447* 2.6

Final 2447* 2.6

*In a batch process, the initial and final

reaction mass are the same.

Lesson 1

The results of lesson 1

should be summarized inrisk analysis forms 1 and 2.

Using these forms fill in theheadings and the BATCH

SIZE section of form 1 forthe process data shownopposite.


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Case study : Batch reaction Thermal Data of ReactionBASIC DATA FOR RISK ANALYSIS FORM 1

Product: Batch reaction Ident No:

Location: Case study Proc. dated:Author of risk analysis: ( Your name ) Date: ( actual date )

DESCRIPTION OF SYNTHESIS REACTION (USE ONE SHEET PER STEP)

BATCH SIZE 2.7 kmolat the start 2.6 m3 2447 kg

at the end 2.6 m3

2447 kg

Case study : Batch reaction Thermal StabilityBASIC DATA FOR RISK ANALYSIS FORM 0h

Product: Batch reaction Ident No:Location: Case study Proc. dated:Author of risk analysis: ( Your name ) Date: ( actual date )

CHARACTERISTIC DATA OF DECOMPOSITION REACTIONS(USE SEVERAL SHEETS IF NECESSARY)

Lesson 1Use risk analysis forms 1 and 2 to summarize the results

Case study : Batch reaction Thermal Data of ReactionBASIC DATA FOR RISK ANALYSIS FORM 1


DESCRIPTION OF SYNTHESIS REACTION (USE ONE SHEET PER STEP)

BATCH SIZE 2.7 kmolat the start 2.6 m3 2447 kgat the end 2.6 m3 2447 kg

Case study : Batch reaction Thermal StabilityBASIC DATA FOR RISK ANALYSIS FORM 0h


CHARACTERISTIC DATA OF DECOMPOSITION REACTIONS(USE SEVERAL SHEETS IF NECESSARY)



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Lesson 1Assessment of severity

Lesson 1

In order to obtain a preliminaryevaluation (SCREENING) of the

severity of the chemical processunder study, one shoulddetermine the following data:

Heat of the desired

reactionHeat of thedecomposition reactionSpecific heat capacity ofthe reaction mixture


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Lesson 1

In order to evaluate the heat of the desired

reaction and the heat of the decompositionreaction two thermograms were supplied by

the thermal safety laboratory.

A linear temperature ramp from 23C to 450C

was used in both measurements (scan rate4Cmin-1).

The overall potential thermogram shows an

endothermic signal (fusion of the product) and

two overlapping exothermic signals. The firstsignal equals a potential of +30 kJkg-1 and the

second ones a total potential of -750 kJkg-1.

A sample of the reaction mixture after

completing the desired reaction (final reactionmixture thermogram) shows, excepted the

endotherm, only one peak of -500 kJ

kg

-1

. Thisenergy is in the same temperature range of thesecond exothermic peak of the overall potential

thermogram.

Overall potential thermogram:

Quantitative differential thermal analysis of amixture of the starting materials.

Final reaction mixture thermogram:

Quantitative differential thermal analysis of thefinal reaction mixture.

-0.6

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-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400

-500 kJkg-1

+30 kJkg-1

Heat release rate (Wg-1)

scan rate: 4Cmin-1 Temperature (C)

Heat release rate ( Wg-1)

-1

-0.5

0

0.5

1

1.5

2

50 100 150 200 250 300 350

-750 kJkg-1

+30 kJkg-1

Temperature (C)scan rate: 4Cmin-1

Baselines


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Answer this question:According to the results ofexperimentalmeasurements, what is the

heat of the desiredreaction?(Units should be kJkg-1)





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-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400

-500 kJkg-1

+30 kJkg-1




-1

-0.5

0

0.5

1

1.5

2

50 100 150 200 250 300 350

-750 kJkg-1

+30 kJkg-1


Baselines


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Answer this question:According to the results of

experimentalmeasurements, what is the

heat of the desiredreaction?(Units should be kJkg-1)

Right answer:The heat of the desired

reaction is250 kJkg-1





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-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400

-500 kJkg-1

+30 kJkg-1




-1

-0.5

0

0.5

1

1.5

2

50 100 150 200 250 300 350

-750 kJkg-1

+30 kJkg-1


Baselines


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Answer this question:According to the results ofexperimentalmeasurements, what is the

heat of the decompositionreaction?(Units should be kJkg-1)





-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400

-500 kJkg-1

+30 kJkg-1




-1

-0.5

0

0.5

1

1.5

2

50 100 150 200 250 300 350

-750 kJkg-1

+30 kJkg-1


Baselines


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Answer this question:According to the results of

experimentalmeasurements, what is the

heat of the decompositionreaction?(Units should be kJkg-1)

Right answer:The heat of the

decomposition reaction is500 kJkg-1





-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400

-500 kJkg-1

+30 kJkg-1




-1

-0.5

0

0.5

1

1.5

2

50 100 150 200 250 300 350

-750 kJkg-1

+30 kJkg-1


Baselines


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Lesson 1

In a preliminary evaluation(SCREENING) of the severity of

the chemical process under studythe following data are alreadyknown:

Heat of the desired reactionQR = 250 kJkg-1

Heat of the decompositionreaction

QD = 500 kJkg-1

These results are summarized in

the risk analysis forms 1 and 2.


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Case study : Batch reaction Thermal Data of Reaction

BASIC DATA FOR RISK ANALYSIS FORM 1

POTENTIAL

Heat of reaction Specific heat capacity Adiabatic Temperature Rise(Ratio QR/ Cp)

QR = 250 kJ/kg Cp = kJ/kg/K Tad = C

Highest theoretical attainable temperature in case adiabatic conditions occur: C

Total gas evolution: l/kg l/batchSource of data:

Consequences of allowing adiabatic reaction (Check appropriate boxes)

Harmless temperature rise Boiling (Bp = C) Gas release

Critical temperature rise Decomposition Pressure build up

Other :




POTENTIAL


QR = 250 kJ/kg Cp = kJ/kg/K Tad = C

Highest theoretical attainable temperature in case adiabatic conditions occur: CTotal gas evolution: l/kg l/batchSource of data:



Critical temperature rise Decomposition Pressure build up

Other :



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Case study : Batch reaction Thermal Stability


Severity:Energy potential of relevant decomposition reactions: 500 kJ/kgSpecific heat capacity of reaction mass: kJ/kg/KAdiabatic temperature rise: CBoiling point of reaction mass (if relevant): CGas evolution: m3/batchKnown decomposition products:

Source of data:Assessment of severity: Low Medium High




Severity:

Energy potential of relevant decomposition reactions: 500 kJ/kgSpecific heat capacity of reaction mass: kJ/kg/KAdiabatic temperature rise: CBoiling point of reaction mass (if relevant): C

Gas evolution: m3/batchKnown decomposition products:Source of data:

Assessment of severity: Low Medium High



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Lesson 1

In a preliminary evaluation(SCREENING) of the severity of

the chemical process under studythe following data are alreadyknown:


Heat of the decompositionreaction

QD = 500 kJkg-1

The next step of lesson 1 is to

estimate the specific heatcapacity of the reactionmixture.




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Example

Estimate of the specific heat capacity of a mixtureof 2000 kg of an organic compound in 2500 kg ofammonia (27% by weight) in aqueous solution.

Table of data

Compound Cp M MCp(kJkg-1K-1) (kg) (kJK-1)

Organiccompound 1.8 2000 3600Ammonia27% by wt. 3.9 2500 9750

Total 4500 13350

Cp Specific heat capacity of the reaction mixture(kJkg-1K-1)

Mi Mass of a compound (kg)Cpi Specific heat capacity of a compound

(kJkg-1K-1)MR Total mass of the reaction mixture (kg)

Cp MiCpi

MR= =

13350

4500= 3.0 kJkg-1K-1

Specific heat capacity calculation

Lesson 1

A rough estimate of the specific heatcapacity of the reaction mixture can beobtained by addition of the heat capacities of

its components.

The table below shows approximate valuesof specific heat capacities for differentcompound classes. The example shows howto calculate the specific heat capacity of a

mixture of 2000 kg of an organic compoundin 2500 kg of ammonia (27% by weight) in

aqueous solution.

Compound Specific heat capacity(kJkg-1K-1)

Organic 1.8Inorganic 1.0

Ammonia 27% 3.9Water 4.2


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Process data

Charge


1-Chloro-4-nitro-benzene 423 2.7 1Ammonia 27% 2024 32.1 12

(pure NH3)

Total 2447

Remember the following approximatevalues of specific heat capacities for

different compound classes:


Organic compounds 1.8(fused or in solution)

Inorganic 1.0Ammonia 27% 3.9Water 4.2

Answer this question:According to process datashown opposite, what is thespecific heat capacity of thereaction mixture?(Units should be kJkg-1K-1)


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Process data

Charge


1-Chloro-4-nitro-benzene 423 2.7 1Ammonia 27% 2024 32.1 12

(pure NH3)

Total 2447

Remember the following approximatevalues of specific heat capacities for

different compound classes:


Organic compounds 1.8(fused or in solution)

Inorganic 1.0Ammonia 27% 3.9Water 4.2

Answer this question:According to process data

shown opposite, what is thespecific heat capacity of thereaction mixture?(Units should be kJkg-1K-1)

Right answer:The specific heat capacityof the reaction mixture is3.5 kJkg-1K-1


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Lesson 1

In a preliminary evaluation(SCREENING) of the severity of the

chemical process under study thefollowing data are already known:


Heat of the decomposition

reactionQD = 500 kJkg-1

Specific heat capacity of thereaction mixture

Cp = 3.5 kJkg-1K-1

These results are summarizedin risk analysis forms 1 and 2.

Remark

The following procedure is suggested for estimating thespecific heat capacity of the reaction mixture.

Table of data

Compound Cp M MCp

(kJkg-1K-1) (kg) (kJK-1)

1-Chloro-4- 1.8 423 761.4

nitro-benzeneAmmonia 27% 3.9 2024 7893.6

Total 2447 8655

Cp Specific heat capacity of the reactionmixture (kJkg-1K-1)

Mi Mass of a compound (kg)

Cpi Specific heat capacity of a compound(kJkg-1K-1)

MR Total mass of the reaction mixture (kg)

Cp MiCpi

MR= =

8655

2447= 3.5 kJkg-1K-1

Specific heat capacity calculation


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POTENTIAL


QR = 250 kJ/kg Cp = 3.5 kJ/kg/K Tad = C

Highest theoretical attainable temperature in case adiabatic conditions occur:C




Critical temperature rise Decomposition Pressure build up Other :




POTENTIAL


QR = 250 kJ/kg Cp = 3.5 kJ/kg/K Tad = C

Highest theoretical attainable temperature in case adiabatic conditions occur: CTotal gas evolution: l/kg l/batchSource of data:



Critical temperature rise

Decomposition

Pressure build up

Other :



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Lesson 1

In a preliminary evaluation (SCREENING) ofthe severity of the chemical process understudy the following data are already known:


Heat of the decomposition reactionQD = 500 kJkg-1

Specific heat capacity of the reactionmixture

Cp = 3.5 kJkg-1K-1

The adiabatic temperature rise of thedecomposition reaction will bedetermined in the next step oflesson 1.

Lesson 1

The adiabatic temperature rise of a reaction is calculated by

dividing the heat of reaction by the specific heat capacity ofthe reaction mixture.

Example

The adiabatic temperature rise of a high exothermicdecomposition reaction having a heat of reaction of2000 kJkg-1 in a reaction mixture with 2 kJkg-1K-1 specificheat capacity is:

Tad =QR

Cp=

2000

2= 1000 C

Tad adiabatic temperature rise (K orC)

QR heat of reaction (kJkg-1)Cp specific heat capacity (kJkg-1K-1)

Remember

For the process under study, the following data are alreadyknown:

Heat of the desired reaction

QR = 250 kJkg-1


Specific heat capacity of the reaction mixtureCp = 3.5 kJkg-1K-1


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Lesson 1



Example


Tad =QR

Cp=

2000

2= 1000 C

Tad adiabatic temperature rise (K orC)

QR heat of reaction (kJkg-1)Cp specific heat capacity (kJkg-1K-1)

Remember



QR = 250 kJkg

-1



Answer this question:What is the adiabatictemperature rise of thedecomposition reaction?(Units should be K)


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Lesson 1



Example


Tad =QR

Cp=

2000

2= 1000 C

Tad adiabatic temperature rise (K orC)QR heat of reaction (kJkg-1)

Cp specific heat capacity (kJkg-1K-1)

Remember



QR = 250 kJkg

-1



Answer this question:What is the adiabatic

temperature rise of thedecomposition reaction?(Units should be K)

Right answer:The adiabatic temperaturerise of the decompositionreaction is

143 K


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Lesson 1

The adiabatic temperature rise of thedecomposition reaction is a direct measureof the severity of a possible incident.

As a guideline, the following values can beused

Severity Adiabatic temperature rise

HIGH Tad > 200 CMEDIUM 50 C


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Lesson 1

The adiabatic temperature rise of thedecomposition reaction is a direct measureof the severity of a possible incident.

As a guideline, the following values can beused

Severity Adiabatic temperature rise

HIGH Tad > 200 CMEDIUM 50 C


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Lesson 1

The conclusion of theinitial steps of lesson 1is that the severity of apossible incident in theprocess is MEDIUM.

Lesson 1

The severity of a possibleincident in the process isMEDIUM due to the amountof energy which can bereleased by thedecomposition reaction. The

adiabatic temperature rise isa direct measure of thisenergy potential.

Data used for the

assessment of severity aresummarized in risk analysisform 2.


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Severity:

Energy potential of relevant decomposition reactions: 500 kJ/kgSpecific heat capacity of reaction mass: 3.5 kJ/kg/KAdiabatic temperature rise: 143 CBoiling point of reaction mass (if relevant): CGas evolution: m3/batchKnown decomposition products:

Source of data:Assessment of severity: Low Medium High




Severity:

Energy potential of relevant decomposition reactions: 500 kJ/kgSpecific heat capacity of reaction mass: 3.5 kJ/kg/KAdiabatic temperature rise: 143 CBoiling point of reaction mass (if relevant): CGas evolution: m3/batchKnown decomposition products:Source of data:




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Lesson 1Rough estimate ofprobability

Lesson 1

The conclusion of the initial

steps of lesson 1 is that theseverity of a possibleincident in the process isMEDIUM.

The next step of lesson 1 isto make a rough assessmentof the probability oftriggering the decomposition

reaction in the event of loss

of control of the desiredreaction.


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Tad, R adiabatic temperaturerise of the desired

reaction (C).

Tmax, R maximum attainabletemperature if thedesired reaction occursunder adiabaticconditions (C).

Lesson 1

To give a rough estimate of theprobability of triggering the

decomposition reaction in theevent of loss of control of thedesired reaction, the followingdata should be determined:

Lesson 1

Use the equation below to calculate the

adiabatic temperature rise of the desiredreaction.

The parameters which are already known aregiven.

Tad, R =QRCp

Tad, R adiabatic temperaturerise of the desiredreaction (K or C)

QR heat of the desiredreaction ( 250 kJkg-1)

Cp specific heat capacity of

the reaction mixture( 3.5 kJkg-1K-1)


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Lesson 1




Tad, R =QRCp






temperature rise of thedesired reaction?(Units should be K)


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Lesson 1




Tad, R =QRCp






temperature rise of thedesired reaction?(Units should be K)

Right answer:The adiabatic temperaturerise of the desired reaction

is71 K


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Lesson 1


maximum attainable temperature if thedesired reaction occurs under adiabaticconditions.


Tmax, R maximum attainabletemperature if thedesired reaction occursunder adiabatic

conditions (C)Tp process temperature

(195C)

Tad, R adiabatic temperaturerise of the desiredreaction ( 71C)

Tmax, R = Tp + Tad, R

Answer this question:What is the maximum

attainable temperature if thedesired reaction runs underadiabatic conditions?

(Units should be C)


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Lesson 1


maximum attainable temperature if thedesired reaction occurs under adiabaticconditions.


Tmax, R maximum attainabletemperature if thedesired reaction occursunder adiabatic

conditions (C)Tp process temperature

(195C)

Tad, R adiabatic temperaturerise of the desiredreaction ( 71C)

Tmax, R = Tp + Tad, R

Answer this question:What is the maximum

attainable temperature if thedesired reaction runs underadiabatic conditions?

(Units should be C)

Right answer:The maximum attainabletemperature if the desired

reaction runs underadiabatic conditions is266C


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Tad, R: adiabatic temperature rise

of the desired reaction (71

C).Tmax, R: maximum attainabletemperature if the desired

reaction occurs under adiabaticconditions (266C).

Lesson 1

To give a rough estimate of theprobability of triggering the

decomposition reaction in theevent of loss of control of thedesired reaction, the followingdata are already known:

These results should besummarized in risk analysisform 1.




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POTENTIAL

Heat of reaction Specific heat capacity Adiabatic Temperature Rise

(Ratio QR/ Cp)

QR = 250 kJ/kg Cp = 3.5 kJ/kg/K Tad = 71 C

Highest theoretical attainable temperature in case adiabatic conditions occur: 266CTotal gas evolution: l/kg l/batch

Source of data:







POTENTIAL



Highest theoretical attainable temperature in case adiabatic conditions occur: 266CTotal gas evolution: l/kg l/batchSource of data:






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Lesson 1

In the event of loss of thermalcontrol of the desired reaction,the temperature will rise until266C.

The next step in making a roughestimate of the probability oftriggering the decomposition

reaction, is to determine if at thistemperature (266C) the

decomposition reaction is activeenough to produce an incident,in a time too short to take

counter-measures.




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Lesson 1

Taking account ofexperimental conditions, one

can assume that if the traceof the decompositionreaction shows anobservable signal at 266C,

then at this temperature this

reaction is active enough toproduce an incident in a timetoo short (minutes) to takecounter- measures.

Lesson 1

In the final reaction mixture thermogram,the signal corresponding to thedecomposition reaction is detected at235C.


Quantitative differential thermal analysis of finalreaction mixture.

Remark: This assumption dependson the sensitivity of the measuringinstrument (10 Wkg-1) and the scanrate (4Cmin-1).

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0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400

-500 kJkg-1

+30 kJkg-1



235C Tmax,R=266C


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Lesson 1

A rough estimate indicates that at

the maximum temperatureattainable on loss of control ofthe desired reaction (266C) , thedecomposition reaction will giverise to an incident in a very shorttime (minutes).

This means that in a preliminaryapproximation (SCREENING), theprobability of triggering thedecomposition reaction is HIGH.

Lesson 1

RemarkRemark

Morever, the overlapping signalsof the heat of the desired reactionand the heat of thedecomposition reaction in thefinal reaction mixture thermogramgives a clear evidence that thePROBABILITY of triggering thedecomposition reaction is HIGH.


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Lesson 1

Pressure build up related to thePressure build up related to the

process...process...

The pressure build up caused byuncontrolled heat release of the desiredand decomposition reactions is an

important risk especially in industrialsynthesis reactions performed under

pressure.

To assure a safe design of the process

and the plant including the choice of an

appropriate pressure relief system, it isindispensible to know the maximumpressure that can be reached in the eventof a failure.

We will study it later in lesson3.


Lesson 1Pressure build-up


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Lesson 1

Maximum Temperature forMaximum Temperature for

Technical reasons (MTT)...Technical reasons (MTT)...

In order to complete the consequences ofloss of thermal control of the desired

reaction, we must consider if theMaximum Temperature for Technical

reasons (MTT) could be reached in theevent of a failure.

The Maximum Temperature for Technicalreasons is the temperature at which the

pressure reaches the maximumpermissible value.

In the case under study, the reactor isequipped with a safety valve. The safety

limit of this valve will be attained if thetemperature of the reactor attains 200C.

Lesson 1

Potential at the MaximumPotential at the Maximum

Temperature for TechnicalTemperature for Technical

reasons (MTT)...reasons (MTT)...

As the process temperature is 195C,only 5C of the 71C adiabatictemperature rise of the desiredreaction is needed to reach theMaximum Temperature for Technicalreasons (MTT = 200C).

Consequently, the remaining energypotential of the desired reaction will bestill high at this point.


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Lesson 1

According to the results of apreliminary evaluation of the thermalrisks of the process under study

(SCREENING), the consequences of aloss of thermal control over thesynthesis reaction may lead to acritical situation:

- the Maximum Temperature for

Technical reasons (MTT) will bereached- at this point, the potential of thedesired reaction is still high: thereexists a risk of pressure build up- the decomposition reaction will be

triggered.

The resultsobtained in

lesson 1should be

summarized inrisk analysisforms 1 and 2.


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POTENTIAL



Highest theoretical attainable temperature in case adiabatic conditions occur: 266CTotal gas evolution: l/kg l/batchSource of data:


Harmless temperature rise Overpressure (MTT = 200C) Gas release


Lesson 1Conclusions



POTENTIAL

Heat of reaction Specific heat capacity Adiabatic Temperature Rise

(Ratio QR/ Cp)


Highest theoretical attainable temperature in case adiabatic conditions occur: 266C



Harmless temperature rise Overpressure (MTT = 200C) Gas release


Lesson 1Conclusions


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Severity:

Energy potential of relevant decomposition reactions: 500 kJ/kgSpecific heat capacity of reaction mass: 3.5 kJ/kg/KAdiabatic temperature rise: 143 CMaximum Temperature for Technical reasons (MTT): 200 CGas evolution m3/batchKnown decomposition products:Source of data:


Lesson 1Conclusions



Severity:Energy potential of relevant decomposition reactions: 500 kJ/kgSpecific heat capacity of reaction mass: 3.5 kJ/kg/KAdiabatic temperature rise: 143 CMaximum Temperature for Technical reasons (MTT): 200 CGas evolution m3/batchKnown decomposition products:Source of data:


Lesson 1Conclusions

Documents

Case Study Batch Reaction Lesson 1