SET3041 Group10 Final

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SET3041Energy from Biomass 2009/2010

Major Assignment

Group 10Methanol from woody biomass

Direct gasification of woody biomass via entrained flow reactor

Group 10

Rajeev Baran 1222996 [email protected] Mahesh 1270028 [email protected]

Isabelle Declerck 1278908 [email protected]

Andreas Höllbacher 1229311 [email protected]

Supervisors

Dr.ir. W. de Jong

X. Meng



2

Summary

For the Energy from Biomass course of the Sustainable Energy Technology Master at TU

Delft the production of methanol from woody biomass had to be examined. For this exercise

an entrained flow, downdraft gasifier is considered to gasify torrefied pine wood. The

gasification process is modelled using simple molar and thermodynamic equilibrium methods

which are implemented in Matlab. From the resulting product gas composition the amount of syngas required to meet the demand of 250 kton of methanol production per annum. The

amount of torrefied pinewood required amounts to 1460 kton per year.



3

List of Symbols

SCGP Shell Coal Gasification Process

C Carbon

O2 Oxygen

CO Carbon monoxide

CO2 Carbon dioxideH2 Hydrogen

CH4 Methane

N2 Nitrogen

H2O Water

CH3OH Methanol

H2S Hydrogen sulfide

mw Moisture fraction per mole of dry biomass [-]

m Moisture content of the biomass [%w]

MBio Molar weight of biomass [g/mol]

x1 Molar fraction of carbon monoxide in the product gas [-]

x2 Molar fraction of hydrogen in the product gas [-]

x3 Molar fraction of carbon dioxide in the product gas [-]

x4 Molar fraction of water in the product gas [-]

x5 Molar fraction of methane in the product gas [-]

xg Molar fraction of the oxidizer being fed into the reactor [-]

x Normalized coefficient of atomic hydrogen in biomass [-]

y Normalized coefficient of atomic oxygen in biomass [-]

f H ° Enthalpy of creation [kJ/mol]

T Temperature [K]

Cp Coefficient of thermal expansion [kJ/kgK]



4

Table of Contents

Introduction............................................................................................................................5

1 Methanol Production from Biomass............. ...................................................................6

1.1 Syngas Production ........................................................................................................6

Gasification ....................................................................................................................6

Pre-treatment ..................................................................................................................8Proposed Reactor............................................................................................................9

1.2 Methanol Synthesis.....................................................................................................11

2 Modelling .....................................................................................................................13

2.1 Biomass Gasification ..................................................................................................13

2.2 Methanol Synthesis.....................................................................................................15

3 Calculations and Results ...............................................................................................16

3.1 Determining the performance of the gasification.........................................................16

3.2 Determining Amount of Required Syngas...................................................................17

3.3 Determining the Required Amount of Biomass Feedstock...........................................18

3.4 Determining the Size of the gasification reactor ..........................................................19

3.5 Summary ....................................................................................................................20

4 Conclusion and Recommendations ...............................................................................21

References............................................................................................................................22

Appendix A: Matlab Calculations.........................................................................................23

Appendix B: Matlab Code....................................................................................................24

Appendix C: Matlab Code for Sizing....................................................................................26



5

Introduction

Due to increased concern about the diminishing stocks of fossil fuels and global warming,

increased research is done on the use of biomass. Biomass is available in large quantities and

is the only renewable energy source that is suitable for the production of transportation fuels

and chemicals. Woody biomass is furthermore the most promising among various types of

biomasses, since it has higher carbon content with lower moisture and ash contents than other

biomass. Existing production plants are being converted such that woods or other types of

biomass can be used as feedstock. In the province of Groningen activities are ongoing to

convert a methanol production plant based on natural gas to a plant based on biomass. The

methanol can be produced by direct gasification of biomass leading to syngas which is a

mixture of CO and H2. The direct gasification is done in a pulverized entrained flow gasifier

using steam or oxygen as oxidizer to form the syngas. The syngas is then converted to

methanol.

In this report the calculations are given which are necessary to calculate the amount of

biomass necessary to produce the capacity of the power plant of 250kton/yr of methanol.

First a description will be given concerning the production of syngas out of biomass and a

basic explanation of the steps that have to be followed. In the second chapter the basic

modelling of the syngas and methanol synthesis is elaborated. Then in chapter 3 the actual

calculation and the results are presented. Finally the conclusions and recommendations are

given in the last chapter.

Figure 1: Simplified methanol production process from biomass [9]



6

1 Methanol Production from Biomass

Methanol cannot be produced directly from biomass. As can be seen in figure 1 several

processes have to be performed until the final product is achieved. These can be divided into

the syngas production and the methanol synthesis. In the following two subsections these

processes are treated

1.1 Syngas Production

In order to produce Syngas pre-treated biomass is gasified in a reactor. Therefore the

gasification process, the pre-treatment and a reactor type that could be applied are presented

in the following section.

Gasification

Gasification of biomass occurs during incomplete combustion resulting in the production of

combustible gases. In this case wood is burned to produce syngas consisting of CO and H2

and furthermore traces of methane and tar. Gasification has a high thermodynamic conversion

efficiency of typically 80-85% [3] by converting the organic content of the feed into a fuel gas

mixture. This syngas can then be used to produce methanol. In the following paragraphs a

brief introduction into the different types of reactors and the gasification reactions is given.

The gasifier type depends on the way the products are inserted in the reactor. Three basic

types of gasifiers can be distinguished: downdraft, updraft and crossdraft. The name implies

how the airflow moves through the reactor. For example, in an updraft gasifier, the air is

inserted at the bottom of the reactor where it reacts with the biomass, while the produced

gasses exit at the top (see Figure 2).

Figure 2: Types of gasifiers [1]

The type of gasifier chosen depends on the fuel, its size, its moisture content and its ash

content. In this case the downdraft reactor is the best option as it has a low sensitivity to

charcoal, dust and tar content of the fuel [1].

During gasification four processes can be distinguished for the fuel particles that flow through

the reactor. In each of these processes different chemical and thermal reactions take place.



7

Although there is an overlap of these processes, the processes can be distinguished as drying,

pyrolysis, combustion and reduction (see figure 3).

Figure 3: Different processes in a downdraft gasifier [1]

For this assignment an entrained flow gasifier has to be applied. This type of gasifier is the

most successful gasifier developed after 1950 and can be used with any type of fuel, such as

natural gas or biomass. In an entrained-flow gasifier, pulverized feed is fed into a pneumatic-

flow reactor along with a relative amount of oxygen, steam or oxygen and steam. The high

temperatures caused by the added oxygen remove oils and tars almost completely.

The main combustion reactions present are:

2 2C+Ο CO= Eq. 1

2 2 22H +O =2H O Eq. 2

The temperature in the combustion zone rises to around 1450ºC . This is necessary as a

minimum temperature of 1300ºC is needed to crack hydrocarbons.

In the reaction zone, the products of partial combustion pass through the charcoal bed where

the reduction reactions occur. The temperature in the reduction zone is around 800-1000 ºC.

The reduction reactions are:

2C+CΟ 2CO= Eq. 3

2 2C+H O CO+H= Eq. 4

2 2 2CO+H O CO +H= Eq. 5

2 4C+2H CH= Eq. 6

2 2 2CΟ +H CO+H O= Eq. 7



8

Equation 5 is a combination of the first two reactions (eq. 3, the Boudouard reaction and eq. 4,

the water-gas shift reaction) and is called the CO shift reaction. Equation 6 represents the

formation of methane or the methanation reaction. Together with the fifth equation they are

the major reactions occurring in the gasification process.

In the pyrolysis zone H2O, CO2 and other volatile products like tar are given off at

temperatures between 200 and 500 ºC. The downdraft gasifier leaves less tar behind, becausethe material has to move through the combustion zone and is partially broken down.

In the drying zone, as the name already implies, the wood is dried. The wood entering the

gasifiers has a moisture content that is not favourable. During the woods transit through the

drying zone, the moisture content is lowered.

Pre-treatment

As most biomass types are not suitable for direct use in entrained flow gasifiers, pre-treatment

is necessary. The applied woody biomass is the most used type of renewable energy source

today, especially in developing countries. The advantage of using woody biomass as a

feedstock is that it does not conflict with conventional agriculture, such as the use of food

crops, to produce energy. However, the fibrous structure of fresh biomass makes it very

difficult to reduce its particle size to micrometer scale which is necessary in an entrained flow

gasifier, see Figure 4. Hence torrefaction, a thermal treatment of biomass, is one possible way

of pre-treatment.

Torrefaction destroys the fibrous structure of the biomass in the absence of oxygen, at

temperatures of 200-300 ºC . This leads to a greatly improved size reduction behaviour. After

torrefaction the torrefied wood can be ground down to 100 µm particles. The advantage of the

small particle size is that the fuel resembles coal and is hydrophilic, such that minimum

modifications to existing storage and transport systems have to be made. Furthermore this

also leads to complete fuel conversion in the gasifier.

For the calculations in this report the chosen biomass is pine wood torrefied at 230 ºC for 3

hours. The chemical composition of this material is 51.5 wt% carbon, 0.05wt% nitrogen,

6.2wt% hydrogen and 42.2 wt% oxygen [2]. This was chosen because of the high energy

recovery percentage after torrefaction of 97.41% and a low moisture content of 1.4%.

Experiments have shown that torrefied wood also results in an even lower fraction of molten

particles. This might be due to the reduction of the silicon content upon torrefaction [4].



9

Figure 4: Power consumption pulverisation wood vs. torrefied wood [4]

Proposed Reactor

The reactor process that suits the required conditions best is the Shell Coal Gasification

Process (SCGP) which is shown in Figure 5. This reactor was developed with coal as

feedstock. The coal is first ground in a milling and drying unit to a size below 90µm. Then it

is fed into pressurized lock-hoppers and mixed near the outlet nozzle of the burner with a

mixture of oxygen and steam [5]. The resulting entrained flow is then fed into the reactor.These type of reactors operate at temperatures of about 1200-1400°C and 20-40bar. The

residence time of the product are typically around 0.5 to 4 seconds before the product gas

leaves the reactor at the top and the tar and ashes leave through an opening in the bottom of

the reactor. The gas produced consists roughly of 2/3 CO and 1/3 H2. The hot gas is quenched

to 900°C and afterwards it enters the syngas cooler at a temperature of 280°C . Here the gas is

also filtered to remove any solids.



10

Figure 5: Shell coal gasification process [5]



11

1.2 Methanol Synthesis

After gasification the syngas can be used as a feedstock for the production of methanol.

Methanol can be made out of almost all organic materials and can be used as a transportation

fuel in combustion engines. This leads to a CO2 neutral fuel. The process for the production of

methanol from syngas is the same as for the production from natural gas.

To produce methanol the syngas should be first cleaned of tar and dust and should be cooled.

The hot gas leaving the entrained flow gasifier might contain molten particles and fouling of

the heat exchanger surfaces may occur. Therefore, first quenching to 900°C is performed to

avoid ash related fouling. In a CO-shift reactor the ratio CO/H2 can be adjusted by steam

addition via the catalytically enhanced slightly exothermic reaction given below.

2 2 2CO+H O CO +H→ Eq. 8

Furthermore, the syngas should be cleaned of CO2 and H2S. H2S is a catalyst poison and has

to be removed completely. Wood only contains small amounts of sulphur and therefore thiscan be neglected at this moment.

The gas streaming out of the gasifier has a temperature of about 300-500 ºC this has to be

cooled to raise its energy density.

Methanol is produced with the use of a Cu/Zn/Al catalyst for hydrogenation of carbon oxides.

The reactions are exothermic and decrease the molar volume, for this reason the temperature

should be low with high pressure. During methanol production heat is produced that should

be removed to maintain optimum catalyst life and reaction rate [7]. The last step is distillation.

In this step the water that is produced during methanol synthesis is separated from the

methanol.

Conventional methanol reactors are fixed bed reactors using catalyst pellets operating in gasphase. The two most commonly used reactors are the ICI and the Lurgi. They both operate

between temperatures of 200-300°, pressures between 50-100bar and use a copper based

catalyst.

The main reaction for methanol synthesis is:

2 3CO+2H CH OH = Eq. 9

If there is an excess of hydrogen one can add CO2 to the reactor to increase yield using the

following reaction:

2 2 3 2CO +3H CH OH H O= + Eq. 10

The overall reaction becomes:

2 2 3 2CO+CO +5H 2CH OH H O= + Eq. 11

The processes of ICI and Lurgi differ in the heat removal process. ICI uses cold un-reacted

gas that is injected between the catalyst beds. In a Lurgi reactor, the catalyst is loaded into

tubes and the coolant circulates outside the tubes, see Figure 6 [9].



12

Figure 6: ICI reactor (left) and Lurgi reactor (right) [9]



13

2 Modelling

When considering a process such as the production of methanol from biomass it is essential to

be able to make estimates of the system performance. The simple equilibrium methods

described in the following sections have been reported to lead to reasonably accurate results

[6, 8].

2.1 Biomass Gasification

In order to estimate the output of the gasifier a thermodynamic equilibrium model will be

applied. In the previous section some operating conditions are already mentioned. These and

additional assumptions need to be taken into account before setting up the model:

• The used gasifier is a downdraft entrained-flow gasifier, as the equation holds better

for reactors with low tar content.

•

The operating temperature and pressure of biomass to syngas gasifier is 1200°C and20 bar respectively.

• The residence time of the feedstock in the rector is long enough such that it operates

close or at the thermodynamic equilibrium.

• All carbon content is converted into gaseous form.

• Only the main reaction products are taken into account. These are carbon monoxide(CO), carbon dioxide (CO2), hydrogen (H2), methane (CH4), nitrogen (N2), and water

(H2O).

• Ash in the feedstock is assumed to be inert.

• All gaseous products behave as ideal gases.

• The pressure drop inside the gasifier is assumed negligible.

• The process is adiabatic and no external heat source is applied.

• Only the main and overall reactions of the control volume (the gasifier) are used.

Individual processes going on in the different zone of the reactor are inside of the

control volume and do not need to be considered.

The last assumption characterises the reaction and is therefore used for the calculation (see

equation 11). During gasification an amount of reactants enter the reactor and a particular

amount of products exit the reactor. The reactants consist of the biomass, the moisture content

of the biomass and the air used for the gasification. The products are hydrogen, carbon

monoxide, carbon dioxide, water, methane and nitrogen.

The resulting overall gasification reaction is shown in equation 12 and is similar to the

equation set up by Gautam [6] and Babu [8].

2 2 2

1 2 2 3 2 4 2 5 4 2

( 3.76 )

3.76

x y w g

g

CH O m H O x O N

x CO x H x CO x H O x CH x N

+ + +

→ + + + + +Eq. 12

With x yCH O representing the equivalent composition for woody biomass (neglecting the

nitrogen content as it is very low for torrefied wood). The unknowns to be solved for are the

fractions xg, x1, x2, x3, x4 and x5. The moisture content m [wt%] of the wood is taken into

account as:



14

( )

( )18 1

bio

w

M mm

m=

−Eq. 13

With io M being the molar mass of the biomass feedstock.

From the overall gasification reaction (Eq. 12) and the equations of the main chemical

reactions in the reactor (Eq. 5 and Eq. 6) one can now set up the molar and stoichiometricbalances.

From equation 11 one can now set up the molar balances for C, H and O:

1 3 5 1 x x x+ + = Eq. 14

2 4 52 2 2 4w

x m x x x+ = + + Eq. 15

1 3 42 2w g y m x x x x+ + = + + Eq. 16

The stoichiometric equilibrium constants for equations 5 and 6 are:

2 2 2 2

2 2

3 21

1 4

CO H CO H

CO H O CO H O

P P n n x xK

P P n n x x= = = Eq. 17

( )4 4

22

52 2 2 2

2

CH CH tot

tot

H H

P n n xK n

n xP= = = Eq. 18

The key to solve these equations are known values of K1 and K2 from empirical relations

(e.g. dependant on temperature).

Finally the last required equation is provided by the energy balance, which accounts for the

sensible and chemical energy that is being fed in and out of the reactor through the biomass

feedstock, the oxidizer flow and the reaction products:

( ) ( )

( ) ( )

( )

2 2 2

2 2

2 2 2 2

4 4 2

1 2298 298

3 4298 298

5298 298

( ) ( 3.76 )

3.76

g g

g g

g g

f biomass w fH O vap g fO fN

T T

fCO pCO fH pH

T T

fCO pCO fH O pH O

T T

fCH pCH g pN

H m H H x H H

x H C dT x H C dT

x H C dT x H C dT

x H C dT x C dT

ω

° ° ° °

−

° °

° °

°

+ + + +

= + + +

+ + + +

+ + +

∫ ∫

∫ ∫

∫ ∫

Eq. 19

Equations 13, 14, 15, 16 , 17 and 18 can now be solved in a numerical computing environment

such as Matlab. With this procedure on can obtain the equilibrium oxidizer input and product

gas output for a given temperature.



15

2.2 Methanol Synthesis

The synthesis of methanol consists of two reactions which use the syngas components

provided by the gasifier. The separate reactions considered are [10]:

2 32CO H CH OH + → Eq. 9

2 2 3 23CO H CH OH H O+ → + Eq. 10

When analysing these two reactions it is assumed that the reaction constant K for both reactions is

the same. This implies that the gases are modelled following the ideal gas law. Therefore, the two

equations can be added to form one chemical equilibrium reaction:

2 2 3 25 2CO CO H CH OH H O+ + → + Eq. 11

This equation can now be applied in a molar balance.



16

3 Calculations and Results

This chapter discusses the calculations and the results. In the first section the general chemical

equilibrium reactions are solved for the gasifier. In the subsequent section the calculations on

the methanol synthesis reaction are performed in order to determine the amount of syngas

needed. The third section deals with determining the amount of biomass feedstock needed,while the fourth section analysis reactor sizing. This chapter ends with an overview of the

results.

3.1 Determining the performance of the gasification

As mentioned in section 2 the biomass gasifier is modeled in MATLAB using equations 13 to

18. These are six equations with six unknowns, namely x1, x2, x3, x4, x5 and xg. Therefore,

provided with the correct input these relations should deliver an acceptable result.

However, solving this system of equations with MATLAB resulted in unsatisfactory results,i.e. some of the fractions of the product gas were negative. This is a direct result of the

empirical relations applied to establish the different coefficients and heating values.

Therefore, the results of Gautam et al. [6] are used. These are shown in figure 7 and table 1.

Figure 7: Results of the equilibrium equation for different temperatures [6]



17

Table 1: gas composition in the reactor at 1200 ◦C

Component Symbol Fraction

H2O m 0.09

O2 xg 0.47

CO x1 0.65

H2 x2 0.33

CO2 x3 0.33H2O x4 0.42

Rewriting equation 14 leads to the amount of methane (x5) produced:

5 1 31 1 0.65 0.33 0.02 x x x= − − = − − =

Therefore, equation 12 becomes:

1.4 0.7 2 2

2 2 2 4

0.09 0.47

0.65 0.33 0.33 0.42 0.02

CH O H O O

CO H CO H O CH

+ +

→ + + + +

3.2 Determining Amount of Required Syngas

The amount of required syngas can be determined by first considering the production of one

ton of methanol3( )tonCH OH m . This amount of methanol needs to be converted to its molar

equivalent3( )tonCH OH

mol in order to determine the amount of syngas required. To achieve this

goal, first the molar mass3CH OH

M of ethanol is determined [10]:

3 4 12 4 1 16 32 / CH OH C H O M M M M g mol= + + = + ⋅ + = Eq. 20

Here C M , H

M and O M represent the molar mass of carbon (C), hydrogen (H) and oxygen (O)

respectively.

The equivalent of 1 ton of methanol in mol produced can now be determined:

3

3

3

6 6( ) 10 1 10

= =3125032

tonCH OH

CH OH

CH OH

mmol mol

M

⋅ ⋅=

Looking at Eq. 11, the ratios r 1 and r 2 between the components are:

2

3

1

5=

2

H

CH OH

xr

x= Eq. 21

2 2

3 3 3

2

1= = =

2

H O COCO

CH OH CH OH CH OH

x x xr

x x x= Eq. 22



18

In these equations the x-values represent the amount of moles of the related component as

stated in Eq. 11. Knowing these ratios, the molar values for the components can be

determined in case of 1 ton of methanol production:

2 3

578125

2 H CH OH

mol mol mol= = Eq. 23

2 2 3

115625

2 H O CO CO CH OH

mol mol mol mol mol= = = = Eq. 24

These values can now be scaled up for the actual methanol production of 250 kton/yr.

3

3 9

( ) 31250 250 10 7.8125 10 / tot CH OH

mol mol yr = ⋅ ⋅ = ⋅ Eq. 25

2

3 9

( ) 78125 250 10 19.531 10 / tot H

mol mol yr = ⋅ ⋅ = ⋅ Eq. 26

2 2

3 9

( ) ( ) ( ) 15625 250 10 3.9063 10 / tot tot tot H O CO CO

mol mol mol mol yr = = = ⋅ ⋅ = ⋅ Eq. 27

( ) 9 919.531 3.9063 2 10 27.344 10 /

tot synmol mol yr = + ⋅ ⋅ = ⋅ Eq. 28

3.3 Determining the Required Amount of Biomass Feedstock

The amount of biomass feedstock required does not only depend on the molar values for the

components of methanol synthesis, as found in the previous section, but also on the molar

fractions found to form one mole of biomass 1.4 0.7CH O . These values were established in

section 3.1 and the associated chemical equilibrium reaction was given by Eq. 12.

Using the resulting chemical reaction from section 3.1 and the molar values for the

components of the syngas, one can determine the required molar value of the biomass

feedstock as follows:

2

1.4 0.7

2

9( ) 9

( )

19.531 1059.18 10 /

0.33

tot

tot

H

CH O

H

molmol mol yr

x

⋅= = = ⋅ Eq. 29

In this equation the result that from 1 mole of biomass feedstock one can produce 0.33 mole

of H 2 is applied. The calculated value represents the number of moles of biomass feedstock

needed on a yearly basis in order to produce the required amount of 250 kton/year methanol.

The equivalent mass of required biomass feedstock can be calculated by considering the

molar mass of the biomass feedstock:

1.4 0.71.4 0.6

12 1.4 1 0.6 16 24.6 /

CH O C H O M M M M

g mol

= + ⋅ + ⋅

= + ⋅ + ⋅ =Eq. 30

1.4 0.7 1.4 0.7 1.4 0.7( )

9= 59.18 10 24.6 1456 /

tot CH O CH O CH Om mol M

kton yr

= ⋅

⋅ ⋅ =

Eq. 31



19

Apart from biomass feedstock, also oxygen and water (steam) are fed into the reactor. For

oxygen the molar value can be calculated as:

1.4 0.7

2

9( )

( )

59.18 10 0.47882 /

365 24 3600 365 24 3600

tot

tot

CH O g

O

mol xmol mol s

⋅ ⋅ ⋅= = =

⋅ ⋅ ⋅ ⋅Eq. 32

The reason for expressing the molar value of the fed O2 in seconds will become clear in the

next section. The mass of the fed O2 can then be determined as follows:

2 2

2

( ) 882 2 1628.2 /

1000 1000

tot O O

O

mol M m kg s

⋅ ⋅ ⋅= = = Eq. 33

The same can be done for the water (steam) being fed into the reactor:

1.4 0.7

2

9( )

( )

59.18 10 0.09168.9 /

365 24 3600 365 24 3600

tot

tot

CH O

H O

mol mmol mol s

⋅ ⋅ ⋅= = =

⋅ ⋅ ⋅ ⋅Eq. 34

( )2 2

2

( ) 168.9 2 1 163.04 /

1000 1000

tot H O H O

H O

mol M m kg s

⋅ ⋅ ⋅ += = =

Now that the molar and mass values of the components being fed into the reactor are known,

the dimensioning of the reactor can be performed.

3.4 Determining the Size of the gasification reactor

The residence time of the reaction products is 0.5 to 4 s, as mentioned in chapter 1. Thevolume of the products per second can be obtained by summing the volume of the initial

products.

The mass flow of the initial products is calculated as follows:

1.4 0.7( )

365 24 3600

tot CH O i

i

mol xm

⋅=

⋅ ⋅ɺ Eq. 35

This can now be converted to a volume flow using

,i U im R T V P

=ɺ Eq. 36

The temperature and pressure used in this equation are the temperature and pressure of the

reactor, so 1473 K and 20 bar.

Equations 35 and 36 results in table 2.



20

Table 2: Mass-flow and volume flow of the gasification products

Component mɺ [mol/s] V ɺ [m3 /s]

CO 1219.8 7.5

H2 619.3 3.8

CO2 619.3 3.8

H2O 788.2 4.8

CH4 93.8 0.6

The total volume flow is then 20.5 m3 /s. For the sizing of the gasification reactor a residence

time of 5 seconds is assumed (this is higher than the actual residence time of max. 4 seconds,

so the reactor is actually oversized). Therefore the volume of the reactor becomes 102.5 m3.

Assuming a cylindrical shape for the reactor with diameter d of 2.5m, the length L becomes

2 2

102.521

0.25 0.25 2.5

V L m

d π π

= = =⋅

3.5 Summary

The final results of the foregoing sections are summarized in table 3.

Table 3: Final results

Mass of biomass needed 1456 [kton/yr]

Mass of syngas created 320 [kton/yr]

Mass of methanol needed 250 [kton/yr]

Pressure in gasifier 20 bar

Temperature in gasifier 1473.15 [K]

Diameter gasifier 2.5 [m]Height gasifier 21 [m]

Volume flow through gasifier 20.5 [m3 /s]

Hokanson [11] states that to produce 500 tons of methanol, 1500 tons of oven dry wood waste

is required. Hence our calculations are a factor two off. However one can assume that

Hokanson, being a professional chemical engineer, investigated the process and additional

processes that improve the production beyond the potential of the empirical data applied in

this exercise.



21

4 Conclusion and Recommendations

With torrefied pine wood as a biomass source, the calculations done in the scope of this

exercise lead to approximately 1460 kton/year of wood to be converted to 250 kton/year of

methanol (for detailed results see table 3). These values are a factor two off, compared to the

results of a professional study performed by US Department of Agriculture [11]. This

discrepancy can be explained by the difference in expertise.

During the short introduction into Energy from Biomass the authors of this paper made their

first experiences with basic chemical modelling techniques such as molar and thermal

balances. These techniques were implemented in Matlab using empirically obtained data from

scientific papers. In the meantime the described reactors were examined.

Overall this exercise has increased the understanding of the production of bio-fuels from

biomass and methanol in particular. However, this exercise has also exposed the dangers

which lie in the use of third-party empirical data, which can lead to conflicting situations.

Therefore it is recommended to mix groups beforehand, such that each group has a person

with a chemical engineering background (or similar).



22

References

1. Rajvanshi, A., 1968. Biomass Gasification. In D. Yogi Goswami. Alternative

Energy in Agriculture. CRC Press. Ch. 4. pp 83-102.

2. Pach, M., Zanzi, R., Björnbom, E. 2002. Torrefied biomass a substitute for wood

and charcoal. [online] Available at:

http://hem.fyristorg.com/zanzi/paper/zanzi_apisceuVI.pdf [accessed on March 25,

2010]

3. Arkansas Economic Development Commission. An overview of biomass

gasification. [online] Available at:

http://arkansasedc.com/download/media/143168/overview_biomass_gasification.p

df [accessed on March 30, 2010]

4. Drift, A. Van Der, et al. 2004. Entrained flow gasificaton of biomass. ECN

5. Higman, C., Van Der Burgt, M. 2008. Gasification. Amsterdam. Elsevier – Gulf

Professional Printing

6. Gautam, G., Adhikari, S., Bhavnami, S., 2010. Estimation of biomass synthesis

gas composition using equilibrium modelling. Energy & Fuels.7. Hamelinck, C., Faaij, A., 2001. Future prospects for production of methanol and

hydrogen from biomass. Universiteit Utrecht, Utrecht.

8. Babu, B.V., Pratik N.S. 200X. Modelling&Simulation of Biomass Gasifier: Effect

of Oxygen Enrichtment and Steam to Air Ratio. Chemical Engineering Group

Birla Institute of Technology & Science.

9. Beenackers, A., Van Swaaij, W. 1984 Methanol from wood. Solar Energy. 2.

pp349-367

10. Xiuli, Y., 2004. Synthesizing Methanol from Biomass-Derived Syngas. The

University of Hong Kong.

11. Hokanson, A. E., 1977. Methanol from Wood Waste: A technical and economical

study. U. S. Department of Agriculture.



23

Appendix A: Matlab Calculations

The gasification reaction of biomass in its general form is:

2 2 2 1 2 2 3 2 4 2 5 4 2( 3.76 ) 3.76 x y w g gCH O m H O x O N x CO x H x CO x H O x CH x N + + + → + + + + +

From section 2 the following equations hold for the gasification process:

2 2 2 2

2 2

3 21

1 4

CO H CO H

CO H O CO H O

P P n n x xK

P P n n x x= = = [A.1]

( )4 4

22

52 2 2 2

2

CH CH tot

tot

H H

P n n xK n

n xP= = = [A.2]

1 3 5 1 x x x+ + = [A.3]

2 4 52 2 2 4w x m x x x+ = + + [A.4]

1 3 42 2w g y m x x x x+ + = + + [A.5]

( ) ( )

( ) ( )

( )

2 2 2

2 2

2 2 2 2

4 4 2

1 2298 298

3 4298 298

5298 298

( ) ( 3.76 )

3.762

g g

g g

g g

f biomass w fH O vap g fO fN

T T

fCO pCO fH pH

T T

fCO pCO fH O pH O

T T

fCH pCH g pN

H m H H x H H

x H C dT x H C dT

x H C dT x H C dT

z x H C dT x C dT

ω

° ° ° °

−

° °

° °

°

+ + + +

= + + +

+ + + +

+ + + +

∫ ∫

∫ ∫

∫ ∫

[A.6]

These 6 equations have 6 unknowns: x1, x2, x3, x4, x5 and xg. With the solver-function in

MATLAB this system of equations is analyzed. The results are shown in table A.1.

Table A.1: results from Matlab for the system of equations

Fraction Values (first calculations) Value (improved calculations)

x1 1.05 0.98

x2 4.94 0.58

x3 -29.45 -0.29

x4 -60.25 0.0001

x5 29.40 0.13

xg -61.05 -0.14

From table A.1 the results of the first calculation are wrong. First of all, the output of the

system of equations [A.1] – [A.6] are fractions. So, their values should be between 0 and 1.

Second, the fractions shouldn’t be negative, as in the gasifier either gas is formed or not.

After improving the model the results are still unsatisfactory. The order of magnitude of the

results is now correct, but some values are still negative.

As the model still gives wrong results the results of Gautam et al. [6] are used in the further

calculations, see chapter 1.



24

Appendix B: Matlab Code

Function file

function F = myfun(x)

%Knowns ntot=2; %total number of moles in reactor

%normalised coefficient of atomic H, O, N molecule X=1.4; %values should be altered Y=0.7; Z=0;

Mbio=1*12+X*1+Z*14+Y*16; % [g/mol] molecular weight of biomass

Tc=1200; %[°C] T=Tc+273.15; %[K]

%% Feedstock: Torrefied pine Cb=51.5/100; % in %wt

Nb=0.05/100; Hb=6.2/100; Ob=42.2/100; Sb=0/100; m=15/100; %moisture content in %w mw=(Mbio*m)/(18*(1-m)); %number of mole of water vaport, dry basis

%Unknowns: x1=H2, x2=CO, x3=C02, x4=H2O, x5=CH4, xs, xg=number of moles of %oxygen for gasification

%% Specific heat calculation [kJ/kg] %1;n2, 2:co2, 3:h2, 4:co, 5:ch4, 6:h2og

C=[31.2 -1.36e-2 2.68e-5 -1.17e-8; 19.8 7.34e-2 -5.6e-5 1.72e-8; 29.1 -3e-2 4e-6 -8.7e-10; 30.9 -1.29e-2 2.79e-5 -1.23e-8; 19.3 5.21e-2 1.2e-5 -1.13e-8; 32.2 1.92e-3 1.06e-5 -3.6e-9];

Tref=298; %°K

cpco=C(4, 1)*T+C(4, 2)*0.5*T^2+C(4, 3)/3*T^3+C(4, 4)/4*T^4-(C(4,

1)*Tref+C(4, 2)/2*Tref^2+C(4, 3)/3*Tref^3+C(4, 4)/4*Tref^4); cpco2=C(2, 1)*T+C(2, 2)*0.5*T^2+C(2, 3)/3*T^3+C(2, 4)/4*T^4-(C(2,

1)*Tref+C(2, 2)/2*Tref^2+C(2, 3)/3*Tref^3+C(2, 4)/4*Tref^4); cph2o=C(6, 1)*T+C(6, 2)*0.5*T^2+C(6, 3)/3*T^3+C(6, 4)/4*T^4-(C(6,

1)*Tref+C(6, 2)/2*Tref^2+C(6, 3)/3*Tref^3+C(6, 4)/4*Tref^4); cpch4=C(5, 1)*T+C(5, 2)*0.5*T^2+C(5, 3)/3*T^3+C(5, 4)/4*T^4-(C(5,

1)*Tref+C(5, 2)/2*Tref^2+C(5, 3)/3*Tref^3+C(5, 4)/4*Tref^4); cph2=C(3, 1)*T+C(3, 2)*0.5*T^2+C(3, 3)/3*T^3+C(3, 4)/4*T^4-(C(3,

1)*Tref+C(3, 2)/2*Tref^2+C(3, 3)/3*Tref^3+C(3, 4)/4*Tref^4); cpn2=C(1, 1)*T+C(1, 2)*0.5*T^2+C(1, 3)/3*T^3+C(1, 4)/4*T^4-(C(1,

1)*Tref+C(1, 2)/2*Tref^2+C(1, 3)/3*Tref^3+C(1, 4)/4*Tref^4);

%% Enthalpies [kJ/kg]

%Table 2; species= 1:Ch4, 2:c0, 3c02, 4h20 columns 1:Hf,298 _ 2:a 3:b 4:c

5:d 6:e 7:f 8:g



25

table2=[-74.8 -4.62e-2 1.13e-5 1.32e-8 -6.65e-12 -4.89e2 14.1 -0.223; -110.5 5.62e-3 -1.19e-5 6.38e-9 -1.85e-12 -4.89e2 0.868 -0.0613; -393.5 -1.95e-2 3.12e-5 -2.45e-8 6.95e-12 -4.89e2 5.27 -0.121; -241.8 -8.95e-3 -3.67e-6 5.21e-9 -1.48e-12 0 2.87 -0.0172];

Hfco=table2(2,1); Hfco2=table2(3,1);

Hfh2o=table2(4,1); Hfch4=table2(1,1); Hfh2ow=-241.8; %[kj/mol]

Hvap=-284;

LHV=4.187*(81*Cb+300*Hb-26*(0-Sb)-6*(9*Hb+m)); %m moisture content in%, Cb,

Hb, etc. in %w Hfb=159; %LHV +sum of ni*pi

R=8.314472; %J/molK

F = [(exp(-(x(2)*(Hfco-table2(2,2)*T*log(T)-table2(2,3)*T^2-

table2(2,4)/2*T^3-

table2(2,5)/3*T^4+table2(2,6)/2/T+table2(2,7)+table2(2,8)*T)+...

x(3)*(Hfco2-table2(3,2)*T*log(T)-table2(3,3)*T^2-table2(3,4)/2*T^3-table2(3,5)/3*T^4+table2(3,6)/2/T+table2(3,7)+table2(3,8)*T)+... x(4)*(Hfco-table2(4,2)*T*log(T)-table2(4,3)*T^2-table2(4,4)/2*T^3-

table2(4,5)/3*T^4+table2(4,6)/2/T+table2(4,7)+table2(4,8)*T)))*(x(1).*x(4))

-x(3).*x(2)); exp((-x(2).*(Hfco-table2(2,2)*T*log(T)-table2(2,3)*T^2-

table2(2,4)/2*T^3-

table2(2,5)/3*T^4+table2(2,6)/2/T+table2(2,7)+table2(2,8)*T)+... x(5).*(Hfco-table2(1,2)*T*log(T)-table2(1,3)*T^2-table2(1,4)/2*T^3-

table2(1,5)/3*T^4+table2(1,6)/2/T+table2(1,7)+table2(1,8)*T))/(R*T)).*(x(2)

^2./ntot)-x(5); 1-x(1)-x(3)-x(5); X+2*mw-2.*x(2)-2.*x(4)-4.*x(5); Y+mw+2.*x(6)-x(1)-2.*x(3)-x(4);

Hfb+mw*(Hfh2ow+Hvap)-(x(1).*(Hfco+cpco)+x(2).*(cph2)+x(3).*(Hfco2+cpco2)+x(4).*(Hfh2o+cph2o)+x(5

).*(Hfch4+cpch4)+(Z/2+x(6)*3.76)*cpn2)];

Solver

clc clear all hold off close all

x0 = [1/6; 1/6; 1/6; 1/6; 1/6; 1/6];% Make a starting guess for thesolution options=optimset('Display','iter'); % Option to display output [x,fval] = fsolve(@myfun,x0,options) % Call solver



26

Appendix C: Matlab Code for Sizing

M_C=12; %molar mass [g/mol] M_H=1; M_O=16; M_CH3OH=M_C+M_H*3+M_O+M_H;

m_CH3OH=1*10^3; %[kg] 1 ton methanol required mol_CH3OH=m_CH3OH*10^3/M_CH3OH; %[mol] 1 ton equivalent mol

methanol

%% ratio chemical equilibrium equation %total reaction: CO+CO2+5H2-->2CH3OH+H20 %Again, 1 ton of CH3OH created.

%ratio CH3OH:H2O = 2:1 mol_H2O=mol_CH3OH/2; %amount of moles H2O created with 1

ton methanol m_H2O=mol_H2O*(M_H*2+M_O)*10^-3; %[kg] equivalent amount kg component

%ratio H2:CH3OH = 5:2 mol_H2=mol_CH3OH*(5/2); m_H2=(mol_H2*(M_H*2)*10^-3);

%ratio CO:CH3OH = 1:2 mol_CO=mol_CH3OH/2; m_CO=(mol_CO*(M_C+M_O)*10^-3);

%ratio CO2:CH3OH = 1:2 mol_CO2=mol_CH3OH/2; m_CO2=(mol_CO2*(M_C+M_O*2)*10^-3);

%total mol left and right side chem. reaction:

mol_tot_left=mol_H2+mol_CO+mol_CO2; mol_syn=mol_tot_left; mol_tot_right=mol_CH3OH+mol_H2O;

%total mass left and right side chem. reaction m_tot_left=m_H2+m_CO+m_CO2; m_syn=m_tot_left; m_tot_right=m_CH3OH+m_H2O;

%% upscaling to 250 kt/yr k=250*10^3; %from 1 ton to 250kt (per year) mol_CH3OH_tot=mol_CH3OH*k; %amount of mol of component produced to

meet 250 kt/yr methanol production

mol_H2O_tot=mol_H2O*k; %amount of mol of component produced to meet

250 kt/yr methanol production

mol_H2_tot=mol_H2*k; mol_CO_tot=mol_CO*k; mol_CO2_tot=mol_CO2*k; mol_syn_tot=mol_syn*k;

m_H2_tot=m_H2*k; %amount of mass of component produced to meet

250 kt/yr methanol production

m_CO_tot=m_CO*k; m_CO2_tot=m_CO2*k;



27

m_H2O_tot=m_H2O*k;

m_syn_tot=m_syn*k %[kg] syngas needed

%% Continuing with method b (using chem equilibrium) % calculating amount of moles of components needed based on methanol % synthesis and ratios of component when gasifying 1 mole of biomass

x1=0.65; %CO x2=0.33; %H2 x3=0.33; %CO2 x4=0.42; %H2O x5=0.02; %CH4 xg=0.47; %O2 m=0.09; X=1.4; %subscript H Y=0.7; %subscript O Z=0; %subscript N

mol_CH4=(x5/x2)*mol_H2_tot; %no. moles CH4 needed

M_biomass=M_C+M_H*X+M_O*Y; %[g/mol] mol_biomass=mol_H2_tot/x2; %no. moles biomass needed

to obtain 250 kt/yr methanol mol_biomass_s=mol_biomass/(365*24*3600); %[mol/s] m_biomass=mol_biomass*M_biomass/(10^3) %[kg/yr] m_biomass_s=m_biomass/(365*24*3600); %[kg/s]

mol_H2O_s=mol_biomass_s*x4; %[mol/s] m_H2O_s=mol_H2O_s*(M_H*2+M_O)/1000; %[kg/s]

mol_CO_s=mol_biomass_s*x1; %[mol/s]

m_CO_s=mol_CO_s*(M_O+M_C)/1000; %[kg/s]

mol_H2_s=mol_biomass_s*x2; %[mol/s] m_H2_s=mol_H2_s*(M_H*2)/1000; %[kg/s]

mol_CO2_s=mol_biomass_s*x3; %[mol/s]

m_CO2_s=mol_CO2_s*(M_O*2+M_C)/1000; %[kg/s]

mol_CH4_s=mol_biomass_s*x5; %[mol/s]

m_CH4_s=mol_CH4_s*(M_H*4+M_C)/1000; %[kg/s]

%% Reactor sizing method b p_gasifier=2*10^6 %[N/m^2] T_gasifier=1473.15 %[K] R_universal=8.3145; %[J/(K*mol)]

R_CO=R_universal/((M_C+M_O)*10^-3); %[J/(kg*K)]

rho_CO=p_gasifier/(R_CO*T_gasifier);

R_H2=R_universal/((M_H*2)*10^-3); rho_H2=p_gasifier/(R_H2*T_gasifier);

R_CO2=R_universal/((M_C+M_O*2)*10^-3); %[J/(kg*K)] rho_CO2=p_gasifier/(R_CO2*T_gasifier);

R_H2O=R_universal/((M_H*2+M_O)*10^-3); rho_H2O=p_gasifier/(R_H2O*T_gasifier);



R_CH4=R_universal/((M_H*4+M_C)*10^-3); rho_CH4=p_gasifier/(R_CH4*T_gasifier);

V_flow_CO=m_CO_s/rho_CO; %[m^3/s]

V_flow_CH4=m_CH4_s/rho_CH4; V_flow_H2O=m_H2O_s/rho_H2O; %[m^3/s]

V_flow_CO2=m_CO2_s/rho_CO2; %[m^3/s] V_flow_H2=m_H2_s/rho_H2; V_flow=V_flow_CO+V_flow_CH4+V_flow_H2O+V_flow_CO2+V_flow_H2 %[m^3/s]

D_gasifier=2.5 %[m] assumed value!

Look at reference data L_gasifier=5*V_flow*4/(pi*D_gasifier^2) %[m]

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