BIOMASS TO METHANOL PROCESS
DESIGN – LESSON SERIES
Lecture 2-1: Problem Statement,
Interpretation & Gasifier Simulation
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LESSON LAYOUT
• Introduction of the problem statement
• Interpretation of the problem statement
• Stoichiometry of Gasification Unit
• Simulation of the Gasification Unit (CHEMCAD®)
• Cloning of Unavailable Components
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PROBLEM STATEMENT
You are required to design a plant for the production of bio-methanol from
biomass through gasification of biomass and methanol synthesis from syngas. The
final methanol product needs to be of at least 99.5% purity. A rough block flow
diagram for the process is given in Figure 1.
Figure 1: Initial BFD for Biomass to Bio-methanol Process
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PROBLEM STATEMENT
The following design data and specifications are provided.
Capacity
500 KTPA
On Stream Factor: 0.8
Biomass
Molecular
Structure
Sucrose
C12H22O11
Gasification
Temperature
T = 1150 °C
Gasifier Syngas
CO2/CO ratio
CO2/CO = 1.1
Methanol
Synthesis
Conditions
T = 553 K
P = 80 bar
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PROBLEM STATEMENT
Furthermore the following specifications are provided.
Gasification Reactor (Stoichiometric Reactor)
Assume that the gasifier is a stoichiometric reactor with 100% biomass conversion. You
are required to find the amount of water required for the reaction and also to provide the
full stoichiometry of the reaction in Chemcad. Your gasifier need to produce gas with the
CO2/CO ratio as specified.
Water Gas Shift Reactor (Equilibrium Reactor)
Assume Water Gas Shift reactor to be an equilibrium reactor at a temperature and
pressure that will improve you H2/CO ratio to be 2 as required by the Methanol Synthesis
reaction.
Methanol Synthesis Reactor: (Kinetic Reactor)
Use a kinetic reactor and the kinetics provided. The rate expression you are given is from
Kuczynski et. al., (1986);
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PROBLEM INTERPRETATION: PROCESS SYNTHESIS
In this problem we will not use overall mass balance process synthesis approach
like we did with DME Synthesis Design. Due to time limitations, we will use a
sequential process synthesis approach.
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PROCESS SYNTHESIS: GASIFIER REACTION STOICHIOMETRY
The gasifier reacts the biomass with water at high temperature to produce a
mixture of CO, CO2 and H2.
The following reaction occurs:
C12H22O11
+
a∙H2O 
b ∙ CO +
c ∙ CO2 +
d ∙ H2
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PROCESS SYNTHESIS: GASIFIER REACTION STOICHIOMETRY
To use this reaction in Chemcad simulation, we need to have the stoichiometry fully
specified, i.e., we need to find coefficients a, b, c & d.
C12H22O11
+
a∙H2O 
b ∙ CO +
c ∙ CO2 +
d ∙ H2
At the same time, we need to make sure that the ratio of CO2/CO is 1.1, as specified.
This means that c/b = 1.1.
This ratio means that for every 1 mole or atom of carbon that goes to making CO, 1.1
moles (atoms) will go to making CO2. Another way of looking at it is that, for every
2.1 carbons that reacts, 1 will form CO and 1.1 will form CO2. Noting that:
Carbon in reactants (2.1)

Carbon in CO2 (1.1) +
Carbon in CO (1)
What if you have 12 carbons in reactants like we have with our biomass (C12H22O11)
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PROCESS SYNTHESIS: GASIFIER REACTION STOICHIOMETRY
What if you have 12 carbons in reactants like we have with our biomass (C12H22O11)
If
2.1 ∙ C 
1 ∙ CO
and
2.1 ∙ C

1. 1 ∙ CO2
Then
12 ∙ C 
b∙ CO
and
12 ∙ C

c∙ CO2
b = (12 × 1) / 2.1 =
5.71
c = (12 × 1.1) / 2.1 = 6.23
Check if c/b = 1.1
6.23/5.71 = 1.09 ≈ 1.1
NB: We have to be very careful with use of significant figures as this will otherwise cause
problems in Chemcad. The atoms may not balance depending on the significant figures used
in Chemcad. For example, if the acceptable error in Chemad is of the order 10-6, you need to
make sure you provide your numbers to that accuracy or better. Here we have rounded off b
and c to 2 decimal places. This already is likely to cause problems, but lets wait and see.
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PROCESS SYNTHESIS: GASIFIER REACTION STOICHIOMETRY
Next we can do the oxygen atom balance to find how much water will be needed,
i.e., we will calculate a. The reaction now looks like this, with a and d unknown:
C12H22O11
+
a∙H2O 
5.71 ∙ CO
+
6.23 ∙ CO2
+
d ∙ H2
Let us balance oxygen in reactants and products:
O in biomass (11) + O in water (a) = O in CO (5.71) + O in CO2 (2 × 6.23)
Therefore:
a
=
5.71 +
(2 × 6.23)
-
11
=
7.17
5.71 ∙ CO
+
6.23 ∙ CO2
Resulting in
C12H22O11
+
7.17∙ H2O

+
d ∙ H2
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PROCESS SYNTHESIS: GASIFIER REACTION STOICHIOMETRY
Next we can do the hydrogen atom balance to find how much hydrogen will be
produced, i.e., we will calculate d. The reaction now looks like this:
C12H22O11
+
7.17 ∙ H2O

5.71 ∙ CO
+
6.23 ∙ CO2
+
Let us balance hydrogen in reactants and products:
H in biomass (22) + H in water (2×7.17) = H in H2 (2 × d)
Therefore:
d
=
(22 + (2×7.17)) / 2 =
18.17
Resulting in
C12H22O11
+
7.17 ∙ H2O 
5.71 ∙ CO
+
6.23 ∙ CO2
+ 18.17 ∙ H2
CHECK! CHECK! RE-CHECK! Again check C, O & H balance!
d ∙ H2
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PROCESS SYNTHESIS: GASIFIER CHEMCAD SIMULATION
Now we have a balanced chemical reaction, we can proceed to simulate the gasifier
in Chemcad as specified in the problem statement.
C12H22O11
+
7.17 ∙ H2O 
5.71 ∙ CO
+
6.23 ∙ CO2
+ 18.17 ∙ H2
We will use a stoichiometric reactor with the reaction as given above and the
specified reaction/outlet temperature.
Important point to note here is that we can see from the stoichiometry that the ratio
of H2/CO is 3.18, which is much higher than the required 2.
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PROCESS SYNTHESIS: GASIFIER CHEMCAD SIMULATION
To start off, let us use 1 kmol/hr of biomass. We will come back to adjust this value
to produce the required capacity once the entire flowsheet is complete. Let us make
the gasifier pressure to be 20 bar.
If we were using overall mass balance process synthesis approach as I prefer in most
cases, the throughput would be calculated from the beginning.
For this approach, we will use mass ratios after we have completed the simulation to
scale our process to the required capacities. We will come back to this in later
lectures.
For 1 kmol/hr biomass, you know from stoichiometry that you will need 7.17
kmol/hr of steam. Let us supply saturated steam at the gasifier pressure of 20 bar.
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PROCESS SYNTHESIS: GASIFIER CHEMCAD SIMULATION
SIMULATION DEMONSTRATION
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CHEMCAD BASICS: CLONING OF COMPONENTS
What if the biomass compound I am dealing with is not available in the Chemcad
Component Database? For example
For any biomass represented as a component that is not available in the Chemcad
Component Database, we can clone the new component using a known component.
For the purposes of this study, we will use sucrose as our original component to use
for cloning.
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CHEMCAD BASICS: CLONING OF COMPONENTS
In the Thermophysical menu, click “Component Database”. On the expanded menu
click “Clone Component”
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CLONING OF COMPONENTS
In the Available Components Tab, search for
sucrose (or the component you want to
clone). Select sucrose and click OK to
continue.
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CLONING OF COMPONENTS
In the Destination Database Tab, and click OK
to continue.
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CLONING OF COMPONENTS
In the View/Edit Component Tab, and click Synonyms to
continue.
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CLONING OF COMPONENTS
In the View/Edit Component Synonyms
Tab, type the standard name of your new
component, in this case “Lignin-H”. Clear
Synonym 1 -8 and leave them empty, you
do not need them.
DO NOT CHANGE THE CAS NUMBER
Click OK to continue.
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CLONING OF COMPONENTS
In the View/Edit Component Tab, and click Formulas to
continue.
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CLONING OF COMPONENTS
In the View/Edit Component Formulas Tab, edit Formula 1 to be that of your new
component, in this case “Lignin-H” which is C22H28O9. Click OK to continue. It
may sound silly, but make sure oxygen is O not zero (0). Check! Check! Re-check!
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CLONING OF COMPONENTS
A notification tab will pop-up to inform you that the molecular weight (MW)
does not match that of Sucrose. That’s alright. Click Update to continue.
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CLONING OF COMPONENTS
In the View/Edit Component Tab, and click Exit to
continue.
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CLONING OF COMPONENTS
A notification tab will pop-up to inform you about the changes you are about to
make. Ensure that the radio button is on the first option (see red arrow below).
Click OK to continue.
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CLONING OF COMPONENTS
A notification tab will pop-up informing you about the re-initialization of
streams. Click YES to reinitialise streams and to continue.
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CLONING OF COMPONENTS
Your new component has now been added and can be accessed just like any of
the other built-in components in the Chemcad Components Database. Go to
Thermophysical menu and Click Select Components
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CLONING OF COMPONENTS
In the Select Components Tab, search for a keyword of your component, in this case
“lignin”. Select you component from the list and add it to the Selected Components.
Done!!!