hydrogen content in the syngas and minimum char and tar.
Results are presented here from the advanced gasification
system that utilizes high temperature steam for a combined
heat and power system.
In Japan major earthquake occurred in the eastern part of
Japan on March 11, 2011 followed by a tsunami that
destroyed significant number of houses, businesses and plants
and caused a major black out in the area. The necessity for
distributed and compact independent power generation was
called for the systems which could be readily moved so that
they can be loaded on trucks to help restore the human
activity as quickly as possible in the effected areas form such
a big disaster.
The problem due to the diffusion of radioactivity from
Fukushima Daiichi Nuclear Power Station have been still
quite serious even in 2 years after, thus the safety of all
nuclear power generation is now reviewed in Japan since
earthquakes frequently occurs in this country. Nuclear power
has been regarded as one of safe and reliable power
generation without emitting CO
2
to the environment (which
causes global warming). However, such image is now wiped
out as a result of this accident. The safer distributed and
compact power generation systems are more favorable now
than ever before.
The importance of woody biomass as the energy is now
considered by far one of the more important energy resources.
One such source that allows power generation technology is
woody biomass. Several combined biomass fueled
cogeneration systems are now in operation in Japan with
demonstrated success but there is little case made for stable
and continuous operation using biomass feed stock. The
generation system with biomass feedstock in a gasifier should
be free from tar and char so that the system is deposition free,
the cost is reasonable and provides profit to plant owners in a
relatively short time duration. Such demand is now increasing
in Japan using biomass resources that are readily available all
over the country because 70% of land is occupied by forests
in the mountains.
Wastes from tree branches and thinning of trees are
constantly produced. They are now mostly used for
composting for mixing with the soil in farming or burned in
large incinerators together with the household garbage.
Trimmed branches of street trees are available in various
cities and towns close to streets or highways. These wastes
cannot be disposed off locally due to the restriction imposed
by the environmental regulations associated with
beautification of areas so that most of the wastes are gathered
to the specific storage places. This paper focuses on utilizing
such trimmed tree branches to useful energy. The
development of a compact and high efficiency gasification
system is discussed here.
Nippon Furnace Company (Japan) and The Maryland
University (USA) have been further examining novel
gasification technology for nearly a decade using ultra high
temperature steam. Steam gasification at high temperatures,
exceeding 1000
o
C, results in of the production of high
calorific syngas without forming tar
1,2,3,4
. Nippon Furnace
Company is now focusing on the advanced gasification
process as a new and novel technology produce electricity
and hot water by incorporating it with a combined heat and
power generation (CHP) plant. A compact demonstration
gasification plant was built to produce syngas and an
absorption chiller type air conditioning unit that was
connected to test the syngas production along with the
gasification plant. A feasibility study of the combined system
was examined. The results obtained are given in the following.
2.
Super High Temperature Steam Gasification
In this technology super high temperature steam at normal
pressure with steam temperatures exceeding 1000
o
C is used
as the gasification agent of low hydrocarbon produced in the
pyrolysis. The tar produced in this gasification process is
minimal as compared to other gasification technologies. Note
that in steam gasification no air is supplied so that the
gasification reaction and therefore contamination of nitrogen
and carbon dioxides is limited in the syngas to minimum level.
In the cooling process of high temperature syngas, extra
steam is condensed in water for easy separation from the
syngas to result in high calorific value of the syngas.
Pyrolysis and reforming proceeds simultaneously in the
gasification reaction so that the system is very compact and
simple
3,4,5,6,7
. In
Figure 1
the basic difference is clarified
between conventional gasification that involves partial
oxidation or dry distillation process and the more advanced
super high temperature steam gasification. The amount of
syngas produced and its heating value is much higher with
steam gasification as compared to ordinary gasification.
Conventional Gasification (Partial Oxidation)
High Temperature Steam (HiTS) Gasification
Solid Fuel
High Temp. Steam
CO
2
SynGas
H
2
O
CO
2
SynGas
Cooling
Heat
Heat
Solid Fuel
CO
2
, N
2
SynGas
CO
2
, N
2
SynGas
Cooling
Heat
Air
Heat
H
2
O
Solid Fuel
Ext. Heat Source
Tar
Pyrolyzed Gas
Char
CO
2
SynGas
Reforming
O
2
Conventional Gasification (Dry Distillation)
Tar, Soot
Heat
3.
Test Facilities and Method
3.1 The Gasification System
A schematic diagram of the demonstration test facility for
biomass gasification and the syngas utilized diesel engine for
power generation or absorption chiller are shown in
Figure 2
.
The steam temperature intensifier (called SI), which can
generate high temperature steam exceeding 1000
o
C, is placed
at upper side of gasifier and is directly connected to the
gasifier. The high temperature steam from SI is fed into the
gasifier with a swirling flow to allow mixing with the
biomass feedstocks. The biomass particles are gasified with
the passage of steam in the gasifier to provide volatile matter
from the biomass. The char gasification occurs on the grate
which is placed in lower section of the gasifier. The fine ash
Figure 1. A schematic diagram of Super High
Temperature Steam (HiTS) Gasification and conventional
gasification
2013 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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