Fuel Blending Installation

The present invention relates to a fuel blending installation.

It is known that the combustion efficiency of certain engines, in particular diesel engines, varies in dependence upon the load conditions. When operating at a high load, the efficiency of burning in a diesel engine such as a marine diesel is sufficiently high to enable the engine to operate satisfactorily from a lower grade fuel having a higher viscosity, herein termed "heavy oil". On the other hand, when operating under low load conditions, the combustion efficiency is considerably lower necessitating the use of higher grade and more expensive fuel such as diesel oil.

In order to minimize running costs, it is known to change between heavy oil and diesel oil, depending on the load conditions. It is also known to provide a third tank containing an intermediate grade produced by mixing these two grades of fuel. For example, the heavy oil may have a viscosity of 3,500 seconds, the diesel oil 30 seconds and the intermediate grade 300 seconds. However, this creates a problem of requiring a further storage area for a third grade of fuel and there is an additional risk of the 300 second blend not producing a perfect mixture and separating out within the storage tank.

The invention is therefore concerned with blending installations which enable two grades of fuel to be blended to provide a grade of intermediate viscosity.

According to the present invention, there is provided a blending installation comprising a circulation pump, a circuit in which fuel is constantly recirculated by the circulation pump, means for introducing into the circuit controlled quantities of fuels of different grades, a throttle device incorporated in the circuit and a feed line, for connecting the circuit to a fuel consuming device such as an internal combustion engine, connected upstream of the throttle device.

By virtue of the fact that the fuel is being constantly recirculated in the closed circuit it is possible to ensure that the different grades do not separate out.

Advantageously, excess fuel is fed back into the circuit from the fuel pumps of the engine, the supply to the engine and the return from the engine being connected into the circuit on opposite sides of a throttle device.

Advantageously, a heater is incorporated in the circuit to ensure that the fuel is at the correct temperature for the internal combustion engine.

Preferably, the blending installation blends high grade and low grade fuel for supplying an internal combustion engine, in which the blending unit comprises pumps connected to respective reservoirs of the fuels and driven in such a manner that the pure high grade fuel is supplied to the engine under operating loads up to a predetermined threshold and above the threshold low grade fuel is blended with the high grade of fuel to increase the proportion of low grade fuel as a function of increasing load.

Whenever high grade and low grade fuels are blended and applied to an engine there is a risk that in the event of a failure in various parts of the blending installation, a fuel of too high a viscosity will be fed to the engine.

Advantageously, the blending installation has connected in parallel therewith a bypass line containing a valve which is arranged to open automatically in response to a failure within the blending installation to provide pure high grade fuel to the internal combustion engine.

The invention will now be described further, by way of example, with reference to the accompanying drawing, which is a block schematic diagram of a blending installation.

Although the invention will herein be described with reference to a marine installation, it will be appreciated that it is equally applicable to other installations, for example to generating sets and diesel powered locomotives.

In a marine installation, it is common to utilise low grade fuel having a viscosity of, say, 3,000 seconds to operate the large slow speed diesels used for propelling the ship. Such engines are designed to be able to cope with the slow burning heavy oil. A ship will often also include diesel engines to drive generators and these are traditionally run on high grade diesel oil from a separate tank. The installation in the accompanying drawings allows the engines to operate on pure diesel oil when the low load conditions so dictate, but also enables the engines to operate with a lower grade blend under high load conditions to allow the running costs to be reduced without the provision of a still further reservoir with fuel of an intermediate grade.

In the accompanying drawing there is shown a diesel engine 10 which may for example be part of a generating set. The fuel for the diesel engine is contained in two reservoirs 12 and 14 which contain diesel oil and heavy oil, respectively. The diesel oil 12 is fed by way of a line 16 containing a metering pump 18 into a recirculation loop generally designated 20. The loop comprises a recirculation pump 22, a static mixer 24, a heater 26, a filter 28, a choke 30 and a second filter 32. A gravity feedline 34 connects the heavy oil reservoir 14 to the recirculation loop 20 in between the choke 30 and the filter 32. A pressure relief valve 36 is connected in parallel with the metering pump 18 and a pressure relief valve 38 is connected in parallel with the circulation pump 22. A supply line 40 for the engine pump is connected upstream of the choke 30 and a return line 42 is connected downstream of the choke 30 in the direction of circulation.

A Bypass line 44 containing a solenoid valve 46 connects the line 16 from the diesel oil reservoir 12 directly to the supply pipe 40 of the engine 10. The solenoid valve 46 is normally closed and only opens in the event of failure in one of the active elements of the recirculation loop 20.

In operation, fuel is supplied from the diesel oil reservoir 12 into the recirculation loop 12 by the metering pump 18 which meters a predetermined amount of fuel into the loop. In the loop, the fuel is constantly recirculated by the circulation pump 22 and reheated by the heater 26 to the correct viscosity. The static mixer 24 ensures proper mixing of the fuels by agitation.

Fuel is taken from the recirculation loop 20 by the supply line 40 of the engine and the fuel not consumed by the engine is returned to the line 42. The purpose of the choke 30 is to ensure a drop in pressure to enable the fuel from the return line 42 to be reintroduced into the recirculation loop 20.

If the amount of fuel taken by the engine from the loop does not exceed the amount metered by the metering pump 18 then only diesel oil enters the recirculation loop and the pressure within the recirculation loop will not drop. Consequently, the neat diesel oil will be supplied to the engine.

As the engine loads increases so does the quantity of fuel consumed by the engine. When the amount of fuel consumed exceeds the amount metered by the metering pump 18 the balance is automatically introduced into the recirculation loop 20 from the heavy oil reservoir 14 through the line 34 by gravity feed assisted by the pressure drop developed by the recirculation pump 22. Consequently, with increasing loads the quantity of fuel taken from the heavy oil reservoir 14 increases, so that as the efficiency of the engine increases with increasing loads so is the viscosity increased to take advantage of the increased efficiency to burn cheaper grade fuel.

In the event of a failure in the electric heater 26, the metering pump 18 or the pump 22, the solenoid valve 46 is activated to bypass the blending unit and feed neat diesel oil to the engine 10. This ensures that fuel of high viscosity or too low a temperature is never supplied to the engine by the recirculation loop 20.

In addition to the elements so far described, the installation includes a diesel oil counter 48 collected downstream of the metering pump to measure the total amount of diesel oil consumed. The pressure relief valves 36 and 38 serve to prevent a pressure build-up in the recirculation loop 20.

A further advantage of the installations described is that without the use of a third reservoir an intermediate grade of fuel is available. Furthermore, because the viscosity is constantly changed with engine loads it is possible always to make use of the cheapest grade of oil appropriate for a given set of operating conditions.

When an engine has been running on cheap grade fuel it is preferable to run the engine on high grade fuel before shutting down in order to flush the system. The described installations facilitates flushing in as much as when the ship enters port its engines will have been reduced from full load and as a result will automatically be operating on higher grade fuel by the time it is desired to shut off the engines.