9th i-CIPEC
September 20-23, 2016 Kyoto, Japan

Thermal Properties of Biocoke for Safety Storage
Ken Ohashi1*, Ken’ichi Sasauchi1, Satoru Mizuno2, Tamio Ida2,
Manabu Fuchihata2 and Takashi Suzuki3
1

Engineering Management Center, CHUGAI RO CO., LTD, Japan
2
Research Institute of Biocoke, Kindai University, Japan3
Department of Comprehensive Engineering, Kindai University Technical College, Japan*Corresponding author: Ken Ohashi (TEL:+81-72-247-2371, FAX:+81-72-247-2304, E-mail:ken.oohashi@n.chugai.co.jp)

ABSTRACT
In order to get out from under global warming, expanding use of renewable energy is proposed in many
countries. Although biomass is one of the renewable energy, it is not common because of its
disadvantage of low transport efficiency from low density. Since Biocoke of which biomass is heatedwith compression has high density and high compressive strength, it is used as substitute of coal coke inseveral types of furnaces or considered as an effective method of volume reduction of gatheredradioactive biomass generated by the Great East Japan Earthquake.
In Japan, Biocoke is determined as designated flammable goods in the same manner of Refuse-derived
fuel, while it is reported that Biocoke is difficult to be ignited because of high density with little porosity.
Although it is very important to know the thermal property while they are stored in other words, in the
low temperature range, it has not investigated enough. So in this study, to investigate the possible
origination of fire accidents, the generated heat from Biocoke made from bark and bark before making to
Biocoke were measured by highly sensitive isothermal calorimeter in the condition of 50 °C, air packed
atmosphere and for 3 days. The exothermic phenomenon which is caused by microbial fermentation wasobserved. Particularly, the sample with water addition appeared the large exothermal peak. In the bothcase with water addition and without water addition, the generated heat from Biocoke is less than thatfrom bark. It is summarised that the storage of Biocoke is safer than that of raw material because
microbial fermentation in the temperature range between 20 and 50 °C is inhibited by 130 °C heated in
the Biocoke manufacturing process. In particular, Biocoke is much safer than raw material when stored
in wet condition such as outdoor without roof.
Keywords: Biocoke, Safety storage, heat by fermentation, Recycled fuel, high sensitivity isothermal calorimeter

1. INTRODUCTION
At the 21st Conference of the Parties of the United Nations Framework Convention on Climate Change(UNFCCC) in Paris (COP21), the Paris Agreement was adopted by consensus by all of the 195
UNFCCC participating member states and the European Union. In this agreement, to keep a global
temperature rise this century well below 2 °C and to drive efforts to limit the temperature increase evenfurther to 1.5 °C above pre-industrial levels was set as main goal [1].
Before and during the Paris conference, countries submitted comprehensive national climate actionplans which is called as Intended Nationally Determined Contributions (INDCs). The outline of Japan’s
INDC [2] is to reduce greenhouse gas (GHG) emissions at the level of 26.0% by fiscal year (FY) 2030
compared to FY 2013 (25.4% reduction compared to FY 2005) (approximately 1.042 billion t-CO2 eq. as2030 emissions). In order to achieve its target, expansion of the use of renewable energy that is solar,
wind power, geothermal, hydropower and biomass is promoted.
Biomass power generation is important as a base-load power because it is capable of stable output that
does not depend on the weather. It is estimated that power generation from biomass will
constitute between 3.7% and 4.6% (between 39.4 and 49.0 billion kWh) of total power generation in FY
2030 (approx. 1065 billion kWh) [2]. For biomass power generation as of November 2014 is 17.7 billion
kWh [3], it is necessary to construct more than twice the power plant in FY 2030. As described above,usage of biomass as energy is required to accomplish Japan’s INDC.

9th i-CIPEC
September 20-23, 2016 Kyoto, JapanOn the other hand, biomass is lower energy density per volume as compared with fossil fuels so there isa problem that transport efficiency is low. Since the efficiency of the steam-power generation, which is
the mainstream of biomass power generation, is improved as the power generation capacity increases, itis needed that the stable large amounts of biomass can be collected for a long time in order of power
plant operation is economically justified. Therefore, the construction of the power plant is required to bein the vicinity of the biomass supply locations.
Biocoke (BIC) which is patented technology [4] is highly densified biomass fuel [5]. It is made fromphotosynthetic biomass in the manner of heating about lower than 200 °C with compressing about
20MPa and cooling with compression into lower than 60 °C. A commercial size plant was installed in2011 in Takatsuki City, Osaka Prefecture [6] and some plants have been installed for 5 years [7-9]. The
density of BIC is over 1200 kg/m3, so its transportation efficiency is higher than before BIC. It isconsidered that the amount of biomass usage increases by BIC technology. Actually BIC is used as
substitute of coal coke in high temperature gasifying and direct melting furnace [10] and cupola furnace[11] as solid fuel, coupled with another advantage that has high compressive strength[12,13].
On the other hand, a lot of radioactively contaminated debris was generated by the Fukushima Daiichi
nuclear disaster that was occurred on March 11, 2011. They are gathered and stored at temporal space.
Because the bulk density of biomass is low, temporal space is filled with and there is no space to be
carried in. So rehabilitation and reconstruction is not progressed smoothly [14]. In this situation, it has
been investigated that gathered biomass is downsized by BIC technology to utilize temporal space
efficiently [15,16].
Now in the Japanese Fire Service Act, BIC is determined as designated flammable goods in the samemanner of Refuse-derived fuel (RDF), straw products and wood wool which will, once having caught
fire, lead to the quick spread of the fire or make it extremely difficult to carry out fire extinguishingactivities. In fact, it is reported that improper storage of RDF and wood chips makes fire accidents [17,18]. The combustion mechanism starting from exothermic phenomenon from 20 to 50 °C by microbial
fermentation was proposed [19]. Although BIC is considered to be difficult to burn because of highdensity with little porosity [20], the exothermic phenomenon of BIC at less than 50 °C have not been
investigated so much. So the thermal property of BIC for safety storage that is very important in the bothcases that are energy use and downsizing mentioned above is investigated in this study.

2. MATERIALS AND METHODS
2-1. Production of BIC
In this study, bark of wood that is also used as
raw material in Takatsuki plant was used to
produce BIC. Bark was dried to about 11%
moisture in the laboratory kept at 25 °C. And it
was cut under 1 mm size particle by cutter mill.
BIC of diameters 4mm was shaped cylindricallyunder the same manufacturing conditions such as
moisture and heating temperature. Loading force
was determined to add the twice loading pressurein the case of over 8mm size BIC [13,21,22]
because highly densified BIC was not produced if
pressed at same pressure in the case of over 8mm
size BIC. Retention time was set linearly with thediameter to see as a simple one-dimensional heattransfer model. Table 1 lists the production Fig. 1 Schematic drawing of BIC of diameter 4mm
conditions, and Fig. 1 shows a schematic drawing producing deviceof BIC of diameter 4mm producing device. Basedon Table 1 and Fig. 1, the production method of BIC starts with measuring the material weight. The
measured material is stuffed into a cylinder and sealed with molds. Then, the top of the mold in thesealed cylinder is applied pressure at the foregoing setting conditions. After putting the top mold under
the setting pressure, the cylinder is enclosed with an electric heating furnace, and a thermocouple isinserted into the cylinder to control the heating temperature. The set cylinder, in this condition, is heated9th i-CIPEC
September 20-23, 2016 Kyoto, Japan
until it reaches production temperature. Afterward, the production temperature is held during thedetermined retention time. After waiting until a prescribed time, the furnace is taken off and the cylinder
is cooled down to less than 30 °C with an electric fan.

Size of BIC
Diameter(mm)
4.0

Table 1 Production conditions of BIC
Loading
Production
Moisture
WeightForce
Temperature
(%)
(°C)
(g)
(kg)
11
130
0.1
54

Retention
Time
(sec)
75

2.2 Highly sensitive isothermal calorimeter
In order to evaluate the faint heat generation from themicrobial fermentation, a highly sensitive isothermal
calorimeter (2277 Thermal Activity Monitor (TAM),
Thermometric) was used. Fig. 2 shows a schematic drawing ofTAM. TAM that has a thermostatic bath that has been precisely
temperature control (temperature drift over 24 hours of lessthan ±0.0001K) is one of the most sensitive, stable and flexible
microcalorimeter systems for directly measuring this universal
heat signal and, therefore, the quantitative thermodynamic andkinetic observation of any process such as the stability ofvarious materials and material compatibility. It is a uniquemicrocalorimeter system that is completely modular andcombines the highest heat flow sensitivity with unmatchedlong-term temperature stability for measuring many processes
that are undetectable by other techniques.
The sample, which was measured about 0.1 g, was packed
with air into ampule. The bark that was cut and dried at room
temperature, and cylindrical BIC of diameter 4mm were used.
The samples were isothermally kept at 50.0 °C for about 3 days
Fig. 2 Schematic drawing of TAM
and measured the heat flow. The reason why set temperature is
50 °C is because it is known that much of microorganisms are active in the temperature between 40 and
50 °C, and a lot of investigations measured at 50 °C were reported [19]. And the samples to which ionexchanged water was added (20% of the sample’s weight) were measured in order to examine the effectof moisture. The moisture content after water addition is calculated to be 26%. The measured samples arelisted in Table 2.
Table 2 Sample measured in TAM
SampleMoisture
Shape
WeightBark
Powder
11%
BIC from bark
Cylinder0.1g
Bark + water
Powder
26%
BIC from bark+ water
CylinderSize<1mm
φ4×～5.5<1mm
φ4×～5.5

3. RESULTS AND DISCUSSION
3-1. Produced BIC
Pictures of the produced BIC are shown in Fig. 3. All specimens are blackened on all exposed surfaces(top, side, and bottom) which were brown color before produced. The density of BIC was shown in Fig.4.
The density is in the range between 1.38 kg/m3 and 1.41 kg/m3 and its mean is 1.40 kg/m3 with astandard deviation of 0.019 kg/m3. The real density that is defined, as the ratio of the dry specimen mass
to the volume of its solid part is known about 1.50 kg/m3 in the case of bark of wood [23]. The moisture9th i-CIPEC
September 20-23, 2016 Kyoto, Japan
content of BIC is 11% so the calculated real density
is 1.45 kg/m3. The calculated porosity in BIC is lessthan 5% by heated and compressed enough.

Density of BIC / kg・m-3

1.50
1.40
1.30
1.20
1.10
1.00
80

Fig. 3 The photograph of BIC

90

100
110
Weight of BIC / mg

120

Fig. 4 The density of BIC

1000
900
800
700
600
500
400
300
200
100
0

Bark dried at RT
Heat flow / µW・g-1

Heat flow / µW・g-1

3.2 Highly sensitive isothermal calorimeter
The heat flux per 1gram sample without water is shown in Fig.5 and 6. Sample was set into TAM
immediately after the measurement was started. All samples show rapidly exothermic behavior within a
few minutes after the start of measurement and then heat flux decreased. Its peak of the sample withwater addition is higher than without water addition. In the case of bark dried at RT (room temperature)with water addition, second exothermic peak was appeared about 20 hours after the start of measurement
after peak and heat flux decreased gradually.

Bark dried at RT + water

0

24

48
Time / hour72

Fig. 5 Isothermal measurement of powder before
produced into BIC in the TAM (50 °C)

1000
900
800
700
600
500
400
300
200
100
0

BIC from bark
BIC from bark + water

0

24

48
Time / hour72

Fig. 6 Isothermal measurement of BIC
in the TAM (50 °C)

It is thought that this heat generation is occurred due to a biological activity that is fermentation, whichis active in wet condition and active in the temperature range below 50 °C [19]. The first peak is
appeared in the heating process in other words in the temperature range between 25 and 50 °C. So it isconsidered the fermentation by microorganisms, which is active below 50 °C, results in the first peak andsubsequent decrease is caused that microorganisms become inactive because of too high temperature
atmosphere for them. The second peak which is shown in the case of bark dried at RT with water
addition is caused by fermentation by which microorganisms is active at 50 °C. In this study, sample
was packed with air so the decrease of heat flux after second peak is result from consumption of oxygen
by aerobic fermentation. It is considered that the sample without water addition does not generate heatbecause the moisture of sample is too low to ferment. Since BIC was produced by heating at 130 °C, it isconsidered that almost of microorganisms attached on sample was dead. So the generated heat fromproduced BIC is less than that from raw material.
The amount of generated heat per 1gram sample without water, which is found by graphical integrationin Fig.5 and 6, and max heat flux are listed in Table 3. The integration range is from 0 to 24 hours, from24 to 72hours and from 0 to 72 hours. The generated heat from BIC is decreased to 72%, 71% and 73%
in the range of 0-24hours, 24-72 and 0-72 respectively compared with that from bark. In the case ofwater addition, the generated heat from BIC is decreased to 54%, 24% and 35% in the range of 0-9th i-CIPEC
September 20-23, 2016 Kyoto, Japan
24hours, 24-72 and 0-72 respectively compared with that from bark. The max heat flux of BIC and BIC
with water addition decrease to 87% and 45% respectively compared with that of bark and bark withwater addition.

SampleBark
BIC from bark
Bark + water
BIC from bark+ water

Table 3 Generated heat kept at 50 °C by TAM
From 0 to 24 hrs
From 24 to 72 hrs
From 0 to 72 hrs
J/g-dry
J/g-dry
J/g-dry
0.81
1.44
2.25
0.58
1.26
1.84
24.7
44.9
69.6
13.4
10.9
24.3

Max heat flux
µW/J/g-dry
112
97
3735
1681

The combustion mechanism with the following steps has been proposed [19]. The first step occurred atfrom 20 to 50 °C by fermentation. When the temperature increased to from 60 to 80 °C, mostmicroorganisms died from heating, which greatly inhibited aerobic heat generation. Generated heataccumulated up to 100 °C, after which the water content vaporized and the second stage of the process
occurred. Fatty acid esters are present in plants, and may be oxidized, producing peroxide. The third step,in which cellulose and other organic materials start burning, occurred over 100 °C.
If the amount of generated heat is not enough to go next step, the fire accident does not occur. In thesituation of storage, the fire accident does not occur if the accumulation of heat is less than sum of therelease of heat from surface of pile and endothermic phenomenon such as vaporization of water.
As the results and discussion described above, we can say that storage of BIC is safer than that of raw
materials because both the amount of generated heat and the peak heat flux of BIC is small compared tothose of raw material. In particular, in the wet condition, for example outdoors storage with no-roof
condition, storage of BIC is much safer than that of raw material. It is difficult to decide the safety
standard of the heat flux in storage because the release of heat from surface of pile changes by thestorage condition such as the amount of pile, coefficient of thermal conductivity and specific heat. And
for totally risk assessment for fire accident, it is necessary to study the pyrolyzed flammable gas,spontaneous ignition and so on in addition to the above.

4. CONCLUSIONSThe heat flux of bark and BIC from bark with and without water addition was measured in the conditionof 50 °C isothermally, air packed atmosphere and for 3 days by highly sensitive isothermal calorimeter(TAM), and the results were summarized as follows:
1) All samples show rapidly exothermic behavior within a few minutes after the start of measurement
and then heat flux decreased. It is caused by the fermentation by microorganisms which is active
below 50 °C.
2) The heat flux of bark and BIC with water addition was increased compared to with no water addition.
It is because almost of microorganisms does not work in the moisture condition suitable for producing
BIC that is about 11%.
3) The amount of generated heat and the peak heat flux of BIC are small compared to those of raw
material. It is because almost of microorganisms attached on bark was dead while BIC was producedby heating at 130 °C.
4) It is revealed that the storage of BIC is safer than that of raw material because microbial fermentationin the temperature range between 20 and 50 °C is inhibited by 130 °C heated in the manufacturing
process. In particular, BIC is much safer than raw material when stored outdoor with out roof.

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