Understanding Process Conditions

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Prof. Adnan Alamer

Chemical Engineering Dept., KFUPM.

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CHE 425CHE 425

Engineering Economics andEngineering Economics andDesign PrinciplesDesign Principles


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CHAPTER 4CHAPTER 4

Understanding ProcessUnderstanding Process

ConditionsConditions


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The ability to make an economicThe ability to make an economic

analysis of a chemical processanalysis of a chemical process

based on a PFD is not proofbased on a PFD is not proof

that the process willthat the process will

actually work.actually work.


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PURPOSE OF CHAPTER 4PURPOSE OF CHAPTER 4

Analyze reasons for selecting specific conditions:Analyze reasons for selecting specific conditions:

TemperaturesTemperatures

PressuresPressures

CompositionsCompositions

Analyze process conditions that require special considerationAnalyze process conditions that require special consideration


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CONDITIONS OF SPECIAL CONCERNCONDITIONS OF SPECIAL CONCERN

It is easier to adjust T and/or P of a stream than to changeIt is easier to adjust T and/or P of a stream than to change

composition.composition.

The following conditions do not cause severe difficultiesThe following conditions do not cause severe difficulties

Temperatures between 40Temperatures between 40 -- 260 C260 C

Pressures between 1Pressures between 1 -- 10 bar10 bar

Conditions outside the above favored temperature and pressureConditions outside the above favored temperature and pressure

ranges are identified asranges are identified as conditions of special concernconditions of special concern


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PRESSUREPRESSURE

Above 10 bar

Below 1 bar

Large equipment

Special construction material

Increase in cost

Favorable condition

Thicker walled expensive equipment

Safety issue

1- 10 bar


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A decision to operate outsideA decision to operate outside

the pressure range of 1the pressure range of 1--1010

bar must be justifiedbar must be justified

PRESSURE (cont.)PRESSURE (cont.)


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TEMPERATURETEMPERATURE (cont.)


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TEMPERATURETEMPERATURE (cont.)


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A decision to operate aboveA decision to operate above400 C must be justified400 C must be justified

TEMPERATURE (cont.)TEMPERATURE (cont.)


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Require

refrigeration

Okay

Requirespecial

heaters

4040 -- 260 C260 C Above 260 CAbove 260 CBelow 40 CBelow 40 C


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T < 40T < 40 CCRefrigerationRefrigeration

Use as much Cooling Water as PossibleUse as much Cooling Water as Possible

OperatingOperating Costs(TableCosts(Table 3.4)3.4) Cooling WaterCooling Water $0.16/ GJ$0.16/ GJ

Refrigerated WaterRefrigerated Water $20.60/ GJ$20.60/ GJ

CW RW


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Do we ever operate outside these limits?

Tables 4.1Tables 4.14.34.3 Reactors and SeparatorsReactors and Separators

Table 4.4Table 4.4

Other EquipmentOther Equipment

DME ProcessDME Processpretty much inside limitspretty much inside limits


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REASONS FOR OPERATING AT CONDITIONS OF SPECIALREASONS FOR OPERATING AT CONDITIONS OF SPECIAL

CONCERNCONCERN

Favorable equilibrium conversionFavorable equilibrium conversion

Increase in reaction ratesIncrease in reaction rates

Maintain a gas phaseMaintain a gas phase

Improve selectivityImprove selectivity

0

ac tE

R T

reactionk k e

=


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Table 4.1Table 4.1


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Table 4.1 (cont.)Table 4.1 (cont.)


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Table 4.2Table 4.2


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Table 4.3Table 4.3


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Table 4.4Table 4.4


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Example 4.2Example 4.2


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Example 4.2 (cont.)Example 4.2 (cont.)


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Process Conditions Matrix (PCM)Process Conditions Matrix (PCM)


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Process Conditions Matrix (PCM) (cont.)Process Conditions Matrix (PCM) (cont.)


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Evaluation of Reactor R-101 Three conditions of concernThree conditions of concern

High TemperatureHigh Temperature High PressureHigh Pressure

NonNon--stoichiometricstoichiometric Feed ConditionsFeed Conditions


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Additional Information about toluene HDA reaction


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Reactor Analysis


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Thermodynamic Consideration High temperature concernHigh temperature concern

Fig 4.1 implies theFig 4.1 implies the rxnrxn is exothermicis exothermic For exothermicFor exothermic rxnrxn, as T ,, as T , XeqXeq

Decrease inDecrease in XeqXeqis undesirableis undesirableUse of high T cannot be justified fromUse of high T cannot be justified from

thermodynamic point of viewthermodynamic point of view


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Thermodynamic Consideration (cont.) High pressure concernHigh pressure concern

RxnRxn stoichiometrystoichiometry shows that there areshows that there areequal number of reactant and productequal number of reactant and product

moles in the HDAmoles in the HDA rxnrxn..

Thus, no effect of pressure onThus, no effect of pressure on XeqXeq

No reason to use high P fromNo reason to use high P from

thermodynamic point of viewthermodynamic point of view


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Example 4.3


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Example 4.3 (cont.)


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Example 4.4


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Conclusions

T < 40T < 40CCRefrigerationRefrigeration

T > 250T > 250CCFired Heater or FurnaceFired Heater or Furnace

T > 400T > 400CCM.O.C. IssuesM.O.C. Issues

P < 1P < 1 atmatmVacuum and Large EquipmentVacuum and Large Equipment

P > 10P > 10 atmatmCostCost


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1 atm

10 atm

Requires

Fired

Heater

Requires

Special

M.O.C.

Requires

Refriger-

ation

Wall Thickness Increases

Vacuum Large Equipment

40 C 250 C 400 C

SUMMARYSUMMARY

Documents

Understanding Process Conditions