SIMULATION OF REACTOR IN CHEMCAD · 04/04/2018 · Brief Overview of Reactor Types in CHEMCAD...

SIMULATION OF REACTOR IN CHEMCAD A g un g A r i Wi bo w o , S.T, M.ScDep t . Of Ch emi ca l Eng i neer ingPo l i t eknik Neg er i Ma l ang

REACTOR IN CHEMCAD

CHEMCAD provides mechanisms for solving a variety of reactor problems, fromsimple stoichiometric reactions to multiple kinetic reactions. The kinetic reactor willalso solve a limited class of catalytic reactions. Within these extremes,homogeneous equilibrium and multicomponent, multiphase free energyminimization calculations are possible

Brief Overview of Reactor Types in CHEMCAD

• Used for single/multiple reactions, this reactor uses user specified conversion or equilibrium ratios

Equilibrium

• The model estimates the extent of these reactions based on Gibbs free energy minimization

Gibbs Free Energy

• Used for accurate modeling, this model uses kinetic rate expressions to simulate a kinetic reactor. Either a PFR or CSTR model can be used

Kinetic

• Used for a single reaction, this reactor uses user specified stoichiometry and extent of reaction

Stoichiometric

Stoichiometric Reactor

The stoichiometric reactor solves the mass and energy balance for a single reaction. Conversion must be fixed

Suppose we are adiabaticallyforming water from oxygen inthe following reaction:

H2+ ½ O2-> H2O

Basis: 1 mole Oxygen andcomplete reaction, feed at 25 Cand 101.3 kPa

Stoichiometric Reactor

Suppose we are adiabaticallyforming water from oxygen inthe following reaction:

H2+ ½ O2-> H2O

Basis: 1 mole Oxygen andcomplete reaction

Equilibrium ReactorSimulates multiple reactions at once and Requires equilibrium data or conversion for eachreaction

Steam reformer in methane to syngasprocess– Reaction 1:CH4 + H2O ←→ 3 H2 + CO

– Reaction 2:CO + H2O ←→CO2 + H2

Feed CH4 : 10 kmol, H2O: 25 kmol, P: 101.3 kPa, Vf: 1

Equilibrium Reactor with specified conversion

Steam reformer in methane to syngasprocess– Reaction 1:CH4 + H2O ←→ 3 H2 + CO

– Reaction 2:CO + H2O ←→CO2 + H2

CH4 conversion = 75%CO conversion = 80%

If you specify the reaction conversion, an equilibrium calculation is not necessary. Heat and material balance are determined strictly from the stoichiometry, heat of reaction, and specified conversion. For the general equilibrium reactor, conversions will be specified on the reaction screens. A conversion specification is not allowed for shift and methanation reactors.

{conversion} = {amount of key reactant in product stream} / {amount of key reactant in reactant stream}

Specify whether the reaction(s) are in series or in parallel.

1. Parallel reactions (default mode)Reactions are solved simultaneously. Reaction conversion for all reactions is based on the feed stream. A typical

parallel reaction scheme is shown:

A + B ←→P

A + C ←→Q

2. Serial ReactionsUse this mode for series reactions, such as:

A + B ←→ C

C + D ←→ P

Steam reformer in methane to syngasprocess– Reaction 1:CH4 + H2O ←→ 3 H2 + CO

CH4 conversion = 75%

Equilibrium Reactor with specified conversion

Steam reformer in methane to syngasprocess

– Reaction 2:CO + H2O ←→CO2 + H2

CO conversion = 80%

Equilibrium Reactor with specified conversion

If you enter a value for temperature delta, the equilibrium equation(s) is solved using the following temperature:

where:

T reactor s defined by the thermal mode selected above.

ΔT is defined either as the Approach delta T value on this screen or the Approach delta T value in the Equilibrium Data screen for specific reactions.

After solving for Keq with this temperature, Keq is used to determine the material balance.

The heat balance is made using T outlet = T reactor. For the general equilibrium reactor, approach temperature will be specified on the reaction screens. Temperature approach for shift and methanation reactors is input on the main EREA screen.

Equilibrium Reactor with specified Temperature

Reaction of C2H5OH+ CH3COOH to produce ethyl ester

C2H5OH+ CH3COOH ←→CH3COOC2H5 + H2O

T reaction 45 C

Feed 12 kmol Ethanol10 kmol Acetic AcidP: 101.3 kPaT: 25 C

Equilibrium Reactor with specified Temperature

Equilibrium Reactor with specified Temperature

Result

Kinetics ReactorThe kinetic reactor model enables you to rate or design plug flow (PFR) and continuous stirred tank reactors (CSTR).

CSTR

• Perfect mixing.

• Uniform temperature, pressure, and composition throughout the reactor.

• Rate of reaction is constant.

PFR

• No axial mixing or axial heat transfer occurs.

• Transit times for all fluid elements through the reactor, from inlet to outlet, are of equal duration.

Kinetics Reactor with specified Volume

Reaction of C2H5OH+ CH3COOH to produce ethyl ester, at adiabatically operated reactor

Volume of Reactor : 6.5 m3

Feed 12 kmol Ethanol10 kmol Acetic AcidP: 101.3 kPaT: 25 C

Kinetic Data

𝑘= 5 𝑒2 𝑥 10^−7

𝑅𝑇 ; E in (kJ)

C2H5OH+ CH3COOH ←→CH3COOC2H5 + H2O

Kinetics Reactor with specified Volume

Kinetics Reactor with specified Conversion

Reaction of C2H5OH+ CH3COOH to produce ethyl ester, at adiabatically operated reactor

Conversion of Acetic Acid : 80%

Feed 12 kmol Ethanol10 kmol Acetic AcidP: 101.3 kPaT: 25 C

Kinetic Data

𝑘= 5 𝑒2 𝑥 10^−7

𝑅𝑇 ; unit of E (kJ)

C2H5OH+ CH3COOH ←→CH3COOC2H5 + H2O

Kinetics Reactor with specified Conversion

Kinetics Reactor with specified Conversion

Result

Problem

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