TS-64
THE INVESTIGATION OF A NEW DIESEL FUEL PRODUCED FROM WASTE PLASTICS
Valentin A. SOLOIU*, Yoshinobu YOSHIHARA*, Masakatsu HIRAOKA*, Kazuie NISHIWAKI*, Yasuhito MITSUHARA**, Yasufumi NAKANISHI*
ABSTRACT
A new thermal recycling system for the production of alternative fuel from waste plastics is developed, in which plastic waste is melted and mixed with heavy oil A at temperatures around 200 ℃, producing fuels that are suitable for diesel engine generator systems. In experiments, polyethylene (PE), polypropylene (PP), and polystyrene (PS) of weight-average molecular weights (Mw) between 4,000 to 300,000 were used in the production of polymer fuel at mixing ratios of plastic to heavy oil A of between 5% and 40% by mass. Physical properties such as the kinematic viscosity and density of the new polymer fuels were measured, and thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were conducted to investigate the chemical properties. Polymer fuels produced by mixing ratios of 5% PE (MW = 60,000), 25% PP (MW = 1 2,000), 5% PP (MW = 120.000) were tested in a diesel engine and the results showed that the new fuels exhibit performance close to that of heavy oil A.
Key Words: waste plastics, thermal recycling, new fuels, combustion, diesel engine
1. INTRODUCTION
In Japan, commercial plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) account for about 70'/o of all plastic waste [1]. These plastics have a high calorific value, or exergy, nearly equivalent to that of fossil fuels. Therefore, an efficient thermal recycling system may be realized by exploiting the high exergy of waste plastic.
The thermal recycling of plastic waste has been investigated as a means of alternatives to commercial fossile fuels. Liquefaction of waste plastics by thermal cracking has been actively pursued in order to obtain decomposed oil. However, this technique requires high temperatures (over 400 ℃) to sustain thermal decomposition and for subsequent distillation of oil produced [2, 3]. This lead to increases in recycling costs. In addition, gaseous by-products with low ignition temperature are produced in this process, which is a fire hazard.
A new waste plastic thermal recycling system has been investigated. In this system, waste plastic is melted and mixed with heavy oil A at temperatures lower than those required for thermal cracking (below 250 ℃). Therefore, running costs and safety issues are improved in this system in comparison to liquefaction by thermal cracking.
In this study, the physical and chemical properties of the new polymer fuels were measured, and the overall performance of the fuel was evaluated in a practical diesel engine. The combustion and emission characteristics of the new fuel were also investigated.
2. EXPERIMENTAL PROCEDURE AND APPARATUS
In this study, plastics of weight-average molecular weights (Mw) of between 4,000 and 300,000 were mixed with heavy oil A at temperatures lower than 250 ℃. The properties of the plastics used are listed in Table 1. Mixing ratios of plastic to heavy fuel A of 5% to 40% by mass were used. PP of Mw 120,000 and PE of Mw 60,000 were recycled plastic, while all the other materials used in this study were new.
Polymer fuels (mixtures of heavy oil A and plastics) were produced using the apparatus shown in Fig.1. The vessel has a capacity of 2 liters and its temperature can be controlled. Gaseous nitrogen (N2) was supplied to the vessel during the experiment. A stirrer for mixing and a rotation viscometer were fitted to the vessel. The mass of polymer fuel produced in each run was about 1.5 kg, which was used in the investigation of physical and chemical properties. Viscosity and density were measured at temperatures of between 20 ℃ and 250 ℃. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) of the polymer fuels were carried out at temperatures up to 500 ℃.
The polymer fuels to be used in the diesel combustion tests were produced by the facilities shown in Fig. 2. The factory is an integrated system of three major installations, which were identified for development and investigation; the fuel production plant including mixer and auxiliaries, the fuel preparation and engine fuelling plant, and the engine and auxiliaries.
The mixer is equipped with a number of auxiliaries; the electric motor and cycloid gear for rotating the stirrer, and the sludge pot and vacuum pump. The stirrer is rotated at 86 rpm. The mixer is thermally insulated and one batch can produce up to 30 kg of fuel mixture. The mixer operates at atmospheric pressure and at a maximum temperature of 300 ℃. Nitrogen gas is injected in order to prevent explosion. A gear pump extracts the mixture from the mixer at 0.33 l/min through an 80-mesh filter to the mixing tank. The line temperature was set at 150 ℃.
