Background Art Conventionally, bitumen, asphalt, tar or other heavy oils of high viscosity have been emulsified by adding water, because they are hard to pipe line transportation. Such emulsion can be used as fuel for an internal combustion engine (Japanese utility model application Kokai publication No. 1984-96351).

By the way, in case of applying an emulsion to the fuel of a diesel engine, it has been known to clarify the emulsion. Namely, a clarifying method of emulsified fuel consisting in a water separator with an emulsion comprising heavy oil and water by evaporating water, and a purifying train with collected heavy oil for eliminating solid impurities is known (Japanese patent application Kokai publication No. 1996-259970).

However, considerable heat energy is required, in order to evaporate water contained by about 30% in the emulsified fuel.

On the other hand, in case of heating an emulsified fuel and supplying to a diesel engine as fuel, the heating temperature thereof exerts a considerable influence on the concentration of particulate matter in the exhaust gas.

In short, if the heating temperature is too low, the emulsified fuel to be injected into a cylinder from a fuel injection atomizer is not atomized sufficiently, increasing the concentration of particulate matter in the exhaust gas.

On the contrary, if the heating temperature is too high, water in the

emulsified fuel remaining in the fuel injection atomizer vaporizes and spouts into the cylinder together with destroyed emulsified fuel. Such phenomenon is often encountered in the exhaust stroke where the pressure in the cylinder is minimal.

The heavy oil spouted into the cylinder during the exhaust stroke is discharged together with exhaust gas without burning completely, so the concentration of particulate matter in the exhaust gas increases.

Disclosure of the Invention The present invention has been made in order to solve such problems, and has an object to provide a pretreatment method of emulsified fuel that can eliminate easily impurities contained in the emulsified fuel, without destroying the emulsified fuel.

Another object of the present invention is to provide a supply method of emulsified fuel capable of controlling the concentration of particulate matter in the exhaust gas.

In order to attain the aforementioned objects, the pretreatment method of emulsified fuel according to the present invention is characterized by that an emulsified fuel which is emulsified by adding water and surface active agent to Orinoco tar is heated to 70 °C to 95 °C and, at the same time, introduced in a centrifugal separator at a flow rate of 0.35 Q to 1.0 Q for eliminating impurities contained in the emulsified fuel.

It should be appreciated that Q is the actual capacity of the centrifugal separator in case of clarifying in the centrifugal separator a heavy oil of 380 cSt in viscosity at 50 °C by heating to 98 °C.

Here, as emulsified fuel, a slurry fuel emulsified by adding a trace of surface active agent to about 70% of Orinoco tar and about 30% of water, namely"Orimulsion" (brand name) is preferable. This Orimulsion is produced and commercialized by PDVSA Bitor Inc., a government enterprise of South

American Venezuela.

The temperature of emulsified fuel supplied to the centrifugal separator is preferably in a range of 70 °C to 95 °C. In case where the temperature of the emulsified fuel is less than 70 °C, it is hard to separate impurities. On the contrary, in case where the temperature of the emulsified fuel exceeds 95 °C, the emulsified fuel becomes unstable, and tends to destroy easily.

On the other hand, the flow rate of the emulsified fuel supplied to the centrifugal separator is preferably in a range of 0.35 Q to 1. 0Q, and more particularly, in a range of 0.35 Q to 0.90Q. It should be appreciated that Q is the actual capacity of the centrifugal separator (standard flow rate determined by the manufacturer of the concerned centrifugal separator) in case of clarifying in the centrifugal separator a heavy oil of 380 cSt in viscosity at 50 °C by heating to 98 °C.

In case where the flow rate of the emulsified fuel supplied to the centrifugal separator is less than 0.35Q, the emulsified fuel stays longer in the centrifugal separator and tends to destroy easily. On the contrary, in case where the flow rate of the emulsified fuel supplied to the centrifugal separator exceeds 1. OQ, as the flow rate increases, the impurities removal efficiency particularly decreases, making the clarifying difficult (See Fig. 2).

Besides, impurities separated from the emulsified fuel by the centrifugal separator are discharged out of the centrifugal separator preferably with a time interval of 1 to 3 hours.

When impurities separated by the centrifugal separator are discharged out of the centrifugal separator, emulsified fuel is discharged with impurities, the discharged emulsified fuel can not be used as fuel for diesel engine.

Consequently, in case where the interval for discharging impurities is less than 1 hour, the quantity of emulsified fuel to be discharged out of the system of

the centrifugal separator together with impurities increases, uneconomically. On the other hand, in case where the interval for discharging impurities exceeds 3 hours, impurities adhere to the inner wall of the centrifugal separator by centrifugal force, impeding the discharge of impurities.

On the other hand, the supply method of emulsified fuel of the present invention is characterized by that an emulsified fuel which is emulsified by adding water and surface active agent to Orinoco tar is heated to 130 °C to 160 °C after clarifying or non-clarifying and supplied as fuel to a diesel engine.

Here, the temperature of the emulsified fuel supplied as fuel to the diesel engine is preferably in a range of 130 °C to 160 °C. In case where the temperature of the emulsified fuel supplied to the diesel engine is less than 130 °C, the emulsified fuel injected into the cylinder from the fuel injection atomizer is not atomized sufficiently, increasing the concentration of particulate matter in the exhaust gas.

On the other hand, in case where the temperature of emulsified fuel supplied to the diesel engine exceeds 160 °C, water in the emulsified fuel remaining in the fuel injection atomizer evaporates and spouts in the cylinder.

Such phenomenon is often encountered in the exhaust stroke where the pressure in the cylinder lowers. As the Orinoco tar spouted into the cylinder with steam during the exhaust stroke is discharged without burning completely, increasing the concentration of particulate matter in the exhaust gas.

Brief Description of the Drawings Fig. 1 is a schematic view of a pretreatment equipment for performing the pretreatment method of emulsified fuel according to the present invention; and Fig. 2 is a graph showing the relation between the solid impurities separation efficiency (%) and the flow rate (Q) of Orimulsion to be supplied to the centrifugal separator.

Best Mode for Carrying out the Invention Now, embodiments of the present invention shall be described using drawings.

As shown in Fig. 1, Orimulsion (brand name) a in an Orimulsion storage tank 1 is pumped up by a first pump 3 and supplied to a first heater 4 through a first filter 2. At this time, a part of iron rust detached from the Orimulsion storage tank 1 or a piping 21 and of solids such as sand contained in the Orimulsion a are caught by the first filter 2.

Orimulsion supplied to the first heater 4 is heated to 70 °C to 95 °C, before supplied to the centrifugal separator 5 with a flow rate of 0.35 Q to 1. 0Q. It should be appreciated that Q is the actual capacity of the centrifugal separator 5 (standard flow rate determined by the manufacturer of the concerned centrifugal separator) in case of clarifying in the centrifugal separator 5 a heavy oil of 380 cSt in viscosity at 50 °C by heating to 98 °C.

The temperature of Orimulsion a is controlled by the quantity of hot water to be supplied to a heating jacket (not shown) of the first heater 4. Whereas, the flow rate of Orimulsion a is controlled by regulating the rotating speed of the first pump 3.22 indicates a piping connecting the first heater 4 and the centrifugal separator 5.

Impurities such as rubbish, gravel or iron rust are eliminated from the Orimulsion a introduced in the centrifugal separator 5 for clarifying. The clarified Orimulsion a'passes through the piping 23 before being stored in an Orimulsion service tank 6.

On the other hand, a diesel engine 11 is started using diesel oil b in a diesel oil service tank 7. When the diesel engine 11 attains a predetermined load, fuel supplied to the diesel engine 11 changed gradually from diesel oil b to the clarified Orimulsion a'.

At this moment, the Orimulsion a'in the emulsified fuel service tank 6 is pumped by a second pump 8, and supplied to a second heater 9. The Orimulsion a'supplied to the second heater 9 is heated to 130 °C to 160 °C, before being supplied as fuel to the diesel engine 11 through a second filter 10 and a piping 24.

The temperature of Orimulsion a'is controlled, for instance, by the quantity of superheated steam to be supplied to a heating jacket (not shown) of the second heater 9.

On the other hand, impurities separated by the centrifugal separator 5 are discharged out of the centrifugal separator 5 every 1 to 3 hours.

In the drawing, 25 indicates a piping connecting the diesel oil service tank 7 and the piping 24. The aforementioned piping 24 is provided with a first flow regulating valve 26 upstream the second pump 8, and the piping 25 is provided with a second flow regulating valve 27.

In the foregoing, a case where a clarified Orimulsion a'from which impurities are eliminated is supplied to the diesel engine 11 has been described; however Orimulsion a can be supplied to the diesel engine 11 without eliminating impurities contained therein.

As mentioned above, according to the pretreatment method of emulsified fuel of the present invention, an emulsified fuel which is emulsified by adding water and surface active agent to Orinoco tar is heated to 70 °C to 95 °C and, at the same time, introduced in a centrifugal separator at a flow rate of 0.35 Q to 1.0 Q for eliminating impurities contained in the emulsified fuel, allowing to eliminate easily impurities contained in the emulsified fuel, without destroying the emulsified fuel.

On the other hand, according to the supply method of emulsified fuel of the present invention, an emulsified fuel which is emulsified by adding water and

surface active agent to Orinoco tar is heated to 130 °C to 160 °C after clarifying or non-clarifying and supplied as fuel to a diesel engine, allowing to atomize the emulsified fuel injected into the cylinder from the fuel injection atomizer and, on the other hand, prevent water of the emulsified fuel remaining in the fuel injection atomizer from evaporating during the exhaust stroke. As a result, the concentration of particulate matter in the exhaust gas discharged from the diesel engine can be limited.

Industrial Applicability The pretreatment method of emulsified fuel having the aforementioned excellent effects can be used effectively for eliminating impurities contained in the emulsified fuel.

On the other hand, the supply method of emulsified fuel can be used effectively for controlling the concentration of particulate matter in the exhaust gas discharged from the diesel engine.