ap-4-12.dvi


Acta Polytechnica Vol. 52 No. 4/2012

The Effect of Temperature on the Gasification Process

Marek Baláš1, Martin Lisý1, Ota Štelcl1

1
Brno University of Technology, Faculty of Mechanical Engineering, Energy Institute, Technická 2, 616 69 Brno, Czech
Republic

Correspondence to: balas.m@fme.vutbr.cz

Abstract

Gasification is a technology that uses fuel to produce power and heat. This technology is also suitable for biomass
conversion. Biomass is a renewable energy source that is being developed to diversify the energy mix, so that the Czech
Republic can reduce its dependence on fossil fuels and on raw materials for energy imported from abroad.

During gasification, biomass is converted into a gas that can then be burned in a gas burner, with all the advantages
of gas combustion. Alternatively, it can be used in internal combustion engines. The main task during gasification
is to achieve maximum purity and maximum calorific value of the gas. The main factors are the type of gasifier, the
gasification medium, biomass quality and, last but not least, the gasification mode itself.

This paper describes experiments that investigate the effect of temperature and pressure on gas composition and low

calorific value. The experiments were performed in an atmospheric gasifier in the laboratories of the Energy Institute at

the Faculty of Mechanical Engineering, Brno University of Technology.

Keywords: biomass, gasification, temperature effect.

1 Introduction

Biomass is one of the most significant renewable en-
ergy sources worldwide. Biomass technology has
many advantages, e.g. there is a comparatively low
negative impact on the environment, and it can be
grown on surplus agricultural land that is not suitable
for, or is not required for, food production purposes.

In recent times, renewable energy sources have
covered almost 4 % of power production in the Czech
Republic, and biomass is a major contributor to these
sources.

There are various ways in which biomass can be
used for heat and power production, ranging from
oil esterification, biogas production and biogas uti-
lization to thermal processes such as pyrolysis, com-
bustion and gasification. At the present time, di-
rect combustion is the most widely used method
for producing power from biomass. It is the oldest
method, with well-mastered technologies. However,
low-capacity processing lines are mostly suitable for
heat production from biomass, and not for more de-
sirable power production.

Fuel gasification, with subsequent utilization of
the generated gas in a cogeneration unit, is another
technology for producing power from biomass. Gasi-
fication is a relatively new method that offers many
advantages. Increased efficiency of energy utilization
from biomass, especially power production, is a ma-
jor advantage of the gasification process. Combustion
of the gas that is produced is a more easily controlled

process than combustion of solid biomass. Gasifi-
cation therefore decreases the production of harm-
ful emissions. Higher power production efficiency is
achieved using gas in gas turbines and steam-gas cy-
cles. Gasification also achieves lower heat loss and
better energy production than biogas combustion [1].

Gasification is the thermo-chemical conversion of
organic mass with a limited oxygen supply into a
lower calorific value gas (4–15 MJ/m3n) whose main
components include: CO, CO2, H2, CH4, more com-
plex hydrocarbons, N2 and pollutants. The operating
temperatures are rather high, commonly from 750 up
to 1 000 ◦C. The gas that is produced is then com-
busted in a boiler or in combustion engines (and/or
combustion turbines). The use of air as the gasifi-
cation medium results in a low calorific value of the
gas (4–7 MJ/m3n) due to dilution of the gas with ni-
trogen (more than 50 %). The use of mixtures of air
and oxygen and/or steam as the gasification medium
produces gas of lower calorific value, ranging from
10–15 MJ/m3n [2]. Heat for endothermic reactions
is most commonly produced by partial oxidation of
the gasified material (air or oxygen as the gasifica-
tion medium), or is supplied from external sources.
The main purpose of the gasification process is to
transform as much energy as possible from fuel into
gas [3].

The most monitored characteristics of the gas
that is produced include quality (lower calorific value,
composition), the amount produced by means of gasi-
fication, and also the amount of pollutants in the gas,

7



Acta Polytechnica Vol. 52 No. 4/2012

and their composition. Our study focuses on the ef-
fect of temperature and pressure on the quality and
composition of the gas that is produced.

2 Methodology for
measurements at the

biofluid 100 gasification fluid
generator

The study was performed at the Biofluid 100 stand
(see Figure 1), which is equipped with a stationary
fluidized bed.

Figure 1: Biofluid 100 experimental equipment

Figure 2: Scheme of the Biofluid gasifier

A simplified scheme of the experimental equip-
ment is presented in Figure 2. Fuel is supplied from a
fuel storage tank equipped with a shovel, and is intro-
duced via a dosing screw with a frequency converter
into the reactor. The primary supply of blower com-
pressed air is led into the reactor under the bed, and
secondary and tertiary supplies are located at two
high-rise levels. The energogas that is produced is
stripped of its solid particulate matter in the cyclone.
The output gas is combusted in a burner equipped
with a stabilization burner for natural gas and an in-
dividual air supply. The ash from the reactor can be
removed from the tank located beneath the bed. The
power-based heater for primary air supply is placed
behind the blower to enable the impact of air pre-
heating to be monitored. In recent years, filters for a
study of the efficiency of various gas cleaning meth-
ods have been attached to basic part of stand.

Reactor parameters:
• Capacity (in produced gas) 100 kWt
• Fuel demand (consumption, requirement)
150 kWt

• Wood consumption 40 kg · h−1
• Air flow rate 50 m3n · h−1

The basic fluid generator operation characteris-
tics are described below:
• Operation of the fluid generator – after ig-
nition, the fluid generator is operated in combus-
tion mode, so that its heating is quickit heats up
quickly. After the required gasification temper-
atures are achieved, secondary and tertiary air
is supplied to the generator, and thus the gas is
immediately combusted and consequently heats
up the generator. The air supplies are then shut
off, and the generator is introduced into stable
mode for a specific and preset gasification tem-
perature. A stable mode is achieved when the
amount of fuel that is dosed remains unaltered,
the amount of gasified air is even, and the tem-
perature swings in middle section of the gasi-
fication generator are stable within the narrow
range specified by the gasification temperature.

• Data entry for the gasification process –
the monitored data is continuously recorded by a
computer at time intervals of 10 seconds for each
measurement. The following values are moni-
tored:
• The frequency of the converter of the dosing
screw, for determining the mass flow rate;

• The temperature in various parts of equip-
ment, which is measured by thermocouples;
the positions of the thermocouples are given
in detail in the scheme in Figure 2. There
are 3 thermocouples along the top of the
generator, 1 thermocouple in the cyclone
and 2 thermocouples in the semi-coke pipe.

8



Acta Polytechnica Vol. 52 No. 4/2012

One thermocouple is in the output gas pipe.
One thermocouple measures the tempera-
ture of the primary air supply.

• The pressure difference between the upper
and lower sections of the fluid generator
(fluid bed);

• The pressure difference at the orifice plate,
for determining the gas flow rate;

• The pressure of the generated gas, at the
generator outlet and at the fuel storage
tank.

Other values, e.g. temperature and air moisture,
primary air flow rate and primary air tempera-
ture, have to be recorded manually.

3 Course of the experiments

The main purpose of the experiments was to deter-
mine the dependency of gas quality on pressure and
temperature changes in the gasifier. The quality of
the gas was assessed by analyzing its composition
and its lower calorific value. A device based on in-
frared spectrometry monitored the gas composition
(CO and H2 components) online after the stand had
stabilized. Gas was also sampled into a test-glass at
regular intervals. These gas samples were later an-
alyzed in a gas chromatograph (H2, CO, CO2, CH4
components). Further required parameters for the
samples were set later.

4 Results and discussion

The dependency of the gas composition on the tem-
perature and pressure in the gasification generator
was experimentally monitored. No dependency of gas
composition on fluid bed temperatures (T 101 and
T 102) or on other values was proved. On the con-
trary, the experimental results showed that the tem-
perature in the freeboard section (T 103), where the
chemical balance reactions take place, is the key tem-
perature for gas composition (see Figure 3 through
Figure10). The charts show that an increase in tem-
perature results in an increase in the proportion of
hydrogen and carbon monoxide, and a decrease in
the proportion of carbon dioxide and methane. This
is due to the decreasing speed of the methanizing re-
actions, and the higher probability of reactions of wa-
ter gas (C + H2O → CO + H2). The available equip-
ment places limitations on analyses of dependency on
pressure. While the temperature can be set within a
range of 100 ◦C, the pressure can be regulated only
within the range from ca. 2.5 to 19 kPa. This is a
rather narrow range. However, an increased propor-
tion of methane is seen to be dependent on pressure,
i.e. this dependency contrasts with the temperature
trends.

Figure 3: Chart of the dependency of H2 content on
T 103 temperature

Figure 4: Chart of the dependency of H2 content on
pressure

Figure 5: Chart of the dependency of CO2 content
on T 103 temperature

Figure 6: Chart of the dependency of CO2 content
on pressure

9



Acta Polytechnica Vol. 52 No. 4/2012

Figure 7: Chart of the dependency of CH4 content
on T 103 temperature

Figure 8: Chart of the dependency of CH4 content
on pressure

Figure 9: Chart of the dependency of CO content on
T 103 temperature

Figure 10: Chart of the dependency of CO content
on pressure

Subsequent analyses of the generated gas focused
on its lower calorific value. As Figure 11 shows, an
increase in temperature results in a slight decrease in
the proportion of nitrogen in the gas. Thus, we see
an increase in the proportion the combustible com-
ponent in the gas, and therefore an increase in the
lower calorific value of the gas (see Figure 13). The

dependency on pressure again contrasts with the de-
pendency on temperature (see Figures 12 and 14).

Figure 11: Chart of the dependency of N2 content on
T 103 temperature

Figure 12: Chart of the dependency of N2 content on
pressure

Figure 13: Chart of the dependency of lower calorific
value on T 103 temperature

Figure 14: Chart of the dependency of lower calorific
value on pressure

5 Conclusion

This paper has analyzed the effect of gasification tem-
perature and pressure on the quality of the gas gen-

10



Acta Polytechnica Vol. 52 No. 4/2012

erated from biomass. The results show that the tem-
perature in the fluid bed of a gasification reactor has
no effect whatsoever on the final composition of the
gas. However, T 103, i.e. the temperature in free-
board, has a direct impact on the final composition
of the gas. An increase in temperature results in an
increase in the proportion of CO and H2, a decrease
in the proportion of CH4 and CO2, and an increase
in the lower calorific value of the gas. A change in
pressure has the opposite effect.

Acknowledgement

Financial support from GAČR project No.
101/09/1464 is gratefully acknowledged.

References

[1] Lisý, M., Baláš, M., Moskalik, J., Posṕı̌sil, J.:
Research into biomass and waste gasification
in atmospheric fluidized bed, 2009, Proceed-
ings of the 3rd WSEAS International Conference
on Renewable Energy Sources, RES ’09. ISBN
978-960-474-093-2.

[2] Baláš, M., Lisý, M.: Vliv vodńı páry na proces
zplyňováńı biomasy, Acta Metallurgica Slovaca,
Vol. 11, No. 1, Košice, 2005. ISSN 1335-1532.

[3] Ochrana, L., Skála, Z., Dvořák, P., Kub́ıček, J.,
Najser, J.: Gasification of Solid Waste and
Biomass, VGB PowerTech, 2004, Vol. 84, No. 6,
p. 70–74. ISSN 1435-3199.

11