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TOLEDO (SPAIN)PRODUCTION OF CLEAN AND HIGH-CALORY POWDER FUEL FROM MIXTURE OF
WASTE PLASTICS AND WASTE BIOMASS USING SUBCRITICAL WATER
T. Sako1, I. Okajima1, Y. Fujimori1, T. Shimizu2 and I. Kimura2
1Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Japan
2Fujimura Tsuusyou Co., Ltd., Yamato-cho, Ichinomiya 491-0931, Japane-mail:ttsako@ipc.shizuoka.ac.jp

Abstract
The mixtures of waste plastics and waste biomass (garbage, agricultural wastes and others) are difficult to treat properly.
These mixtures are mainly incinerated with auxiliary fuel or landfilled. In proposed technique, the refractory waste
mixtures are converted to high-calory and clean powder fuel using subcritical water. The calorific value of the fuel is 2530MJ/kg and almost equal to that of coal. The fuel hardly has sulfur and chlorine atoms and does not produce toxic
effluent gas.

Keywords: Waste plastic, Waste biomass, Powder fuel, Subcritical water

1.Introduction
Utilization of large amount of waste substances such aswaste plastics and waste biomass is very important in
21st century. Environmentally friendly subcritical water
has been studied to convert the wastes to useful fuels orenergy with high efficiency and short reaction time,
where subcritical water is hot and high-pressure water at
100-300oC and 0.1-20MPa. In this presentation, we
explain the production of clean and high-calory powder
fuel from the mixture of waste plastics and garbage insubcritical water.

together completely at 205 oC. The color of the waste
mixture changed black and the slight carbonation
occured on the surface of the mixture.
The heating value of the powder portion was measured
at the treatment temperature of 150-205 oC. The results
are shown in Figure 3. The heating value increased with

2.Materials and Methods
Figure 1 shows the photo of a bench-scale plant for theproduction of powder fuel from waste plastics and waste
biomass using subcritical water. This was a batch-typeapparatus. The reactor was made of SUS 316 with 0.3m3
in inner volume and it had a horizontal agitator inside.
The target waste was the mixture of waste plastics andgarbage. The waste mixture was put in the reactor andhot steam was charged into the reactor for heating andsupplying subcritical water. The waste mixture wasstirred well with 10rpm in subcritical water and hot steam
at around 200oC and 1.6MPa for 30 min. The mixture
was converted to small powder fuel with high calorificvalue. Then the fuel was dried easily and rapidly.

Fig.1 Bench-scale plant for production ofpowder fuel150oC, 0.5MPa

180oC, 1.0MPa

205oC, 1.7MPa

3.Results and Discussion
The waste mixture of plastics and garbage discharged
from a supermarket was treated by subcritical water atvarious temperatures using the plant shown in Figure 1.
Figure 2 shows the appearance of the products. At 150oC,
both plastics and garbage did not decompose much. A
lot of them remained as they were before the treatment.
On the other hand, the waste mixture changed to thepowder fuel with less than 5mm in diameter and mixed

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Fig.2 Temperature dependence of appearance of producttreated by subcritical water at 30min

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6th International Symposium on Feedstock Recycling of Polymeric Materials

the treatment temperature. It was almost the same asthat of coal, when the reaction temperature was around
205oC. This was because the waste plastic dispersed
well at the treatment temperature above the melting
temperature of the plastics. The powder fuel was acomposite fuel with 2-layer structure: the center wasplastic particle and the surrounding was partly
carbonated biomass powder. Furthermore it hardly
contained sulfur, which is converted to toxic sulfur
dioxide in the combustion process.
At the treatment condition of 205oC and 1.7MPa in which
the heating value of the powder fuel was highest, theinfluence of the treatment time on the heating value wasinvestigated. The results are shown in Figure 4. The
heating value was constant at around 28MJ/kg and thepowder changed little in appearance, when the treatment
time changed from 10 to 30 min.
Next the influence of the rotation number was examined
and the results are shown in Figure 5. The heating value
was also constant at around 28MJ/kg, when the rotation
number was changed from 3 to 15 rpm.
The incineration test of the powder fuel produced fromwaste polyethylene and rice straw was carried out using
a biomass boiler shown on the left-hand side in Figure
6.The fuel could burn stably for more than 12 h, asshown on the right-hand side in Figure 6. The
concentrations of toxic substances such as dioxins,
nitrogen oxide, hydrogen chloride and others were below
the regulation values.

Heating value [MJ/kg]

403020100102030

40

Treatment time [min]Fig.4 Treatment time dependence of heating value of powder
fuel produced by subcritical water (205oC, 1.7MPa,10rpm)

Heating value [MJ/kg]

404.Conclusions
Subcritical water is powerful and environmentally friendly
solvent for the utilization of biomass containing a lot ofwater. The proposed technique is expected to work inearthquake disaster areas in East Japan. It can convert
waste plastics and garbage to energy, and it can improvepoor sanitary condition in disaster areas.

30200510

1520

Rotation number [rpm]Fig.5 Dependence of heating value of powder fuel produce
by subcritical water on rotation number of agitator in reacto(205oC, 1.7MPa, 30min)

Acknowledgment
We thanks the support from Ministry of Agriculture,
Forestry and Fisheries of Japan.

Heating value [MJ/kg]

30Coal2520

Completely drying woodCompletely drying garbage

1510140

160
180
200
Reaction temperature [oC]220

Fig.6 Appearance of boiler and combustion state of powder fu

Fig.3 Temperature dependence of heating value of powder
fuel produced by subcritical water (0.5-1.7MPa, 30min)

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