Chap.4: Fundamentals of Material Balances

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From Felder and Rousseau
Amirah Hill
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Amirah Hill
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Batch Process The feed (charge) enters the tank all at once. Once the reaction is complete, the product is removed all at once.
Continuous process feed is always flowing in with a high amount of reactant and effluent is always coming out with a high concentration of product. (Product is constantly withdrawn from the rxtr)
Semi-batch process Not continuous nor batch ex. One reactant is added to a vessel and then later, another one is slowly added.
Steady-State A continuous process where process variables like: -flow rate -temperature -pressure, etc... operate at nominally (by name) consistent values
Transient (Unsteady-state) A process with changing process variables. By nature, semi-batch and batch processes are transient while continuous processes could be either or.
General Balance equation Input - Output + Generation - Consumption = Accumulation
Gen. Balance Eqn for Non-reactive system There's no generation or consumption in a non-reactive system so: Input - Output = Accumulation
General Balance eqn for reactive processes Generation and Consumption depend on the balance at hand. If balance is on a total mass or atomic species, there is no generation or consumption since mass is neither created nor destroyed.
Flowchart Using boxes and other symbols to represent process units and lined with arrows to represent input and output.
Scaling Masses and NOT mass fractions of all streams can be multiplied by a common factor and the process would remain balanced. *scaling up/ scaling down
Basis of Calculation An amount (in either mass or moles) of flow rate of one stream or stream component in a process. Usually use 1 or 100.
Degrees of Freedom DOF<0 underspecified and not solvable DOF=0 solution is possible DOF>0 overspecified and not solvable
DOF for non-reactive process +unknowns -material balances (species) -relationships *For multiple units, ensquare each subsystem and do a DOF analysis
Raffinate The phase rich in the diluent (water for example)
Extract Phase rich in the solvent.
Stoichiometric Proportion The ratio of two reactants A and B in a balanced eqn.
Limiting reactant A reactant is limiting is it is present in less than its stoichiometric proportion relative to every other reactant.
Fractional Excess For percentage excess, multiply by 100.
Fractional Conversion
Yield
Selectivity
DOF for Reactive Molecular species balance +No. unknown labeled variables +No. independent chem reactions (cannot mult./add one eqn to get the other) -No. independent molecular species -No.relationships
DOF for Atomic species balance +No. identified/labeled unknowns - No. independent atomic species -No. non-reactive species -No. other relationships
DOF for extent of reaction +No. labeled unknowns +No. independent chemical rxns -No. independent reactive species -No.independent non-reactive species -No. other relationships
Combustion Rxn of a fuel with oxygen to produce CO2 and H2O
Partial/Incomplete Combustion A combustion reaction where CO is formed from a hydrocarbon.
Composition on a Wet Basis Component moles fractions of a gas that contains water.
Composition on a dry basis The component mole fractions of a gas without water.
Stack gas / Flue gas Product gas that leaves a combustion furnace
Theoretical Oxygen Amount of oxygen produced based on the balanced equation
Percent excess air Trick: If 50% excess, then 1.5 (moles air)theo
Excess air The amount of air fed to the reactor that exceeds the theoretical air.
Molecular Weight ( MW ) of air 29.00 (kg air/kmol, lbm air/lb-mole, etc...)
Composition of Air 0.21 mol O2/mol air 0.79 mol N2/mol air
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