FLOATATION SWITCH

This invention relates to a floatation switch and to a fluid-containment vessel that includes a floatation switch. In particular, but not exclusively, the invention relates to a bio-fuel processor that may be used for making fuel from oils and fats. The invention also relates to other fluid-containment vessels, including for example hydraulic accumulators.

Bio-fuel (diesel) is a diesel-equivalent processed fuel that is derived from biological sources such as vegetable oils and can be used in modern diesel engine vehicles. Bio-fuel consists of alkyl esters that are made by the transesterification of vegetable oils or animal fats. Numerous types of oil can be used. Bio-fuel is biodegradable and non-toxic, and produces significantly fewer emissions than petroleum-based diesel when burned.

Bio-fuel can be produced by mixing methanol with vegetable oil and a catalyst or caustic soda in a bio-fuel processor. Typically, caustic soda (sodium hydroxide) is mixed with methanol to produce sodium methoxide and this liquid is then mixed with the vegetable oil and heated. The vegetable oil reacts with the sodium methoxide, producing bio-fuel and glycerol. The glycerol is allowed to settle, after which the bio-fuel is drawn off and filtered, and optionally washed. The bio-fuel maybe used as fuel, either undiluted or mixed with conventional petroleum-based diesel fuel. One type of bio-fuel processor includes a stainless steel vessel having a mechanical stirrer, a heater, a temperature sensor and a control system for regulating the heater so as to provide a desired reaction temperature, which is typically in the range 70-95 ⁰ C. The ingredients typically comprise 400 parts vegetable oil to 80 parts methanol and one part caustic soda.

While the process is generally quite safe, it is possible to make mistakes which can lead to dangers. In particular, there may be a risk of explosion or of damage to the heater motor if the processor is operated when it is empty or only partially full, or if the proportion of methanol to vegetable oil is too high.

It is an objective of the present invention to provide a bio-fuel processor, and an override system for a bio-fuel processor, which mitigates at least some of the aforesaid disadvantages. Further objectives of the invention are to provide a floatation switch and a fluid-containment vessel that includes a floatation switch that mitigate disadvantages of known devices.

According to the present invention there is provided a floatation switch including a float, a magnet attached to the float, a guide device constructed and arranged to allow, in use, limited vertical movement of the float, and a magnetic sensor for sensing the magnetic field of the magnet when the magnet is in close proximity with the sensor. The invention allows the sensor to be located remotely from the float and the magnet. It is therefore possible to position the sensor outside a fluid-containment vessel, while the float and the magnet are located inside the vessel. This provides the advantage that no electrical connections need to brought into the vessel, and the wall of the vessel can be left intact. This may be of great importance when the fluids in the containment vessel are corrosive or inflammable, or when the strength of the vessel must not be compromised (for example, when it is a pressure vessel). It also eliminates any risk of leakage and avoids the risk of corrosion to wires, sensors or seals.

The float preferably includes a hollow body. Advantageously, the hollow body is evacuated. This ensures that its volume and overall density are substantially unaffected by changes in temperature.

The float may be made of a material having a high magnetic permeability. For example, it maybe made of austenitic stainless steel, which is non-magnetic and has ahigh magnetic permeability. Alternatively, the float may be made of a suitable plastics material. The magnet is preferably located within the hollowbody. The magnet is preferably a permanent magnet, thus avoiding the need for a power supply.

Advantageously, the guide device is constructed and arranged to shield the float from turbulence. This ensures that operation of the float switch in unaffected by currents in the fluid in which it is placed, as may be caused for example by stirring the fluid. Preferably,

the guide device includes an elongate tube having a vent at each end to allow fluid to enter and leave the tube as its level rises and falls.

According to a further aspect of the invention there is provided a fluid-containment vessel including a wall member defining a fluid-containment volume and a floatation switch comprising a float, a magnet attached to the float, and a magnetic sensor, wherein the float and the magnet are located within the fluid-containment volume and the magnetic sensor is located externally of the fluid-containment vessel. Locating the sensor outside the vessel provides the advantages mentioned above.

The vessel is preferably made at least partially of a material having a high magnetic permeability. The vessel may for example be made of austenitic stainless steel, as this material is strong and inert and allows the magnetic field of the magnet to reach the sensor.

Advantageously, a guide device is attached to the wall of the fluid-containment vessel and is constructed and arranged to allow, in use, limited vertical movement of the float within the fluid-containment vessel. Advantageously, the floatation switch is constructed and arranged to detect when the vessel is filled to a predetermined depth with liquid of a predetermined minimum density.

According to a further aspect of the invention there is provided a bio-fuel processor including a fluid-containment vessel having a wall member defining a fluid-containment volume and a floatation switch comprising a float, a magnet attached to the float, and a magnetic sensor, wherein the float and the magnet are located within the fluid-containment volume and the magnetic sensor is located externally of the fluid-containment vessel.

By providing a float within the vessel it is possible to ensure that the vessel is filled to the correct height and that the density of the fluid is above a predetermined value, indicating that it is safe to operate the processor. If the fluid level is too low or if the density of the fluid is too low (indicating for example that the proportion of methanol in the fluid is too high), the floatation switch is able to detect this. Appropriate corrective action can then be taken to ensure that the processor in not operated in an unsafe condition.

Because the sensor is located entirely outside the vessel, no breach is required in the wall of the vessel and the integrity of the vessel is not compromised. The electrical connections of the sensor are also outside the vessel, avoiding any risk of a spark igniting the contents of the vessel. Only the float is located inside the vessel, which does not give rise to any potential hazard.

Advantageously, the float has an overall density in the range 800-840kg/m ³ , preferably 810- 830kg/m ³ , and more preferably approximately 818kg/m ³ . The float is buoyant.onlyin fluids having a greater density. Methanol has a density of 792kg/m ³ at room temperature (approx, 25°C), reducing to 735kg/m ³ at 85°C, whereas vegetable cooking oil typically has a density of 908kg/m ³ at room temperature and 866kg/m ³ at 85°C. The preferred mixture consisting of 80 parts methanol to 400 parts vegetable oil has a density of 889kg/m ³ at room temperature and 844kg/m ³ at 85°C, whereas a methanol-rich mixture comprising 50 parts methanol to 50 parts vegetable oil has a density of 850kg/m ³ at room temperature and 800kg/m ³ at 85°C. An 80/20 vegetable oil/sodium methanol mix without sodium hydroxide has a density at 90°C of 835kg/m ³ , whereas methoxide containing 3% sodium hydroxide has a density at 20 ⁰ C of 80 lkg/m ³ Therefore a float with the preferred overall density of 818kg/m ³ will float in pure vegetable oil and in an 80/400 methanol/vegetable oil mix both at room temperature and at 85°C, but will sink in pure methanol or in a methanol/vegetable oil mix if the proportion of methanol is too high. For example, in a 50/50 methanol/vegetable oil mix, the float will be buoyant at room temperature but will sink before the mix reaches 85°C, thus allowing the process to be terminated before the temperature rises to a dangerous level.

The float is preferably located so as to detect when the vessel is filled to a predetermined minimum operating level, thus avoiding the risk of operating the processor when the fluid level is too low or the vessel is empty.

Advantageously, the floatation switch is connected to a control device that is constructed and arranged to prevent operation of the processor unless the vessel is filled to a predetermined depth with liquid of a predetermined minimum density. The control device thus automatically prevents unsafe operation.

Advantageously, the bio-fuel processor includes a heater device, wherein the heater device is connected to the control device and is constructed and arranged to be controlled by the control device. This allows the control device to prevent operation of the heater when the vessel is not filled to the correct level with fluid of an appropriate density.

Advantageously, the bio-fuel processor includes a temperature sensor for sensing the temperature of liquid within the fluid-containment volume, wherein the temperature sensor is connected to the control device, which is constructed and arranged to control the heater device according to the sensed temperature.

The control device is preferably constructed and arranged to provide fail-safe operation, for example by preventing operation of the processor if no signal is received from the floatation switch.

Certain embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic side view of a bio-fuel processor according to a first embodiment of the invention;

Figure 2 is a perspective view of a float, comprising part of an override system for the bio- fuel processor;

Figure 3 is a sectional side view showing a floatation switch mounted within the bio-fuel processor; Figure 4 is a sectional front view on line B-B of figure 3, showing the floatation switch within the bio-fuel processor;

Figure 5 is a perspective view of a bio-fuel processor according to a second embodiment of the invention;

Figure 6 is a side view of the second embodiment bio-fuel processor ;

Figure 7 is a plan view of the second embodiment bio-fuel processor;

Figure 8 is a sectional side view of the second embodiment bio-fuel processor;

Figure 9 is a sectional top view at an enlarged scale, showing a floatation switch comprising part of the second embodiment bio-fuel processor;

Figure 10 is a perspective view of a float comprising part of the second embodiment floatation switch; Figure 11 is a side view of the float;

Figure 12 is a sectional side view of the float, and

Figure 13 is a perspective view of a float cage comprising part of the second embodiment floatation switch.

The bio-fuel processor shown in Figure 1 comprises a stainless pressure vessel 2 mounted on support legs 4. The vessel includes a filling vent 6 and an air vent 8 in the upper part of the vessel, and an outlet vent 10 at its lowest point.

An electric heater 12 is located in the lower part of the vessel 2 and is connected by a power cable 13 to a control system 14. A temperature sensor 15 is also mounted in the lower part of the vessel 2, above the heater 12. The temperature sensor 15 is connected by a line 16 to the control system 14, which in turn is connected to an electrical power supply 17.

A stirrer 18 is mounted within the vessel 2 and connected to a stirrer motor 20 by a vertical shaft 19 that extends through the upper part of the vessel 2. Power is supplied to the stirrer motor 20 through a cable 21.

A floatation switch 22 comprising part of an override system is mounted in the upper part of the vessel 2 and is connected to the control system 14 through a lead 23. In use, the vessel 2 contains a body of liquid 24, comprising a mixture of vegetable oil and methanol.

The normal filling level 26 of the liquid is shown. A small air space 28 is provided in the upper part of the vessel 2, above the liquid 24. The floatation switch 22 is designed to sense the level of the liquid in the vessel and the density of the liquid (that is, it senses whether the liquid density is above a predetermined value).

The floatation switch 22, which is shown in detail in Figures 2 to 4, includes a float 30 that is retained within a cage 32 attached to the side of the vessel, with its upper end

approximately at the required fluid level 26. The cage 32 is square in cross-section and is designed to allow limited vertical movement of the float 30 between the ends of the cage, but prevents rotation of the float. The cage 32 also isolates the float 30 from turbulence in the liquid 24, being entirely closed apart from small openings 36 at each end. The ends are designed to prevent the float 30 escaping from the cage.

The float 30 includes a hollow cylindrical steel body 38 that is closed at each end by a square steel end plate 40. The float is hollow and its interior is evacuated through a vacuum suction nipple 42, so that its volume does not vary with changes in temperature. The square end plates 40 interact with the sides of the cage 32 to prevent rotation of the float. The float 30 is constructed and calibrated to have an overall density (that is, its total mass divided by its total volume) of approximately 818kg/m ³ so that it floats in an 80/400 methanol/oil mixture at the correct processing temperature and pressure.

Mounted within the float 30 is a powerful industrial bar magnet 44, for example of neodymium, which is attached to the upper end plate 40 by a clamp 46. The magnet is mounted so that one pole of the magnet points towards the side wall of the vessel 2. A sensitive magnetic sensor 48 (for example a Hall effect sensor) is attached to the vessel 2 in a position so that when the float 30 is floating in the liquid at the correct level, the sensor is adjacent the magnet. The sensor 48 is able to sense the presence of the magnet through the walls of the float 30 and the stainless steel vessel 2. The sensor 48 is attached to one of the support legs 4 of the vessel 2 and is connected to the control system 14 by a lead 50. The sensor 48 is arranged to send a signal to the control system 14 to indicate the presence of the magnet 44 in the proximity of the sensor.

The sensor 48 is thus arranged to sense when the float 30 is floating at the correct level within the vessel 2. If the magnet is sensed, the sensor 48 sends a "go" signal to the control system 14, which then allows the heater 12 to be activated. If the vessel is empty or if the liquid level is significantly below the correct operating level, the magnet 44 will not be detected. Similarly, if the proportion of methanol in the methanol/oil mixture is too high so that the density of the liquid is below 818kg/m ³ , the float 30 will sink and the sensor 48 will not then detect the magnet 44. In either of these situations, the sensor will not send a

"go" signal to the control system 14, which responds by overriding the manual controls to prevent operation of the heater, thereby reducing any risk of damage or overheating.

If the vessel is filled with very cold methanol, the density of the liquid may be above 81 Okg/m ³ . In this case, the floatation switch may initially allow operation of the processor. However, as the temperature of the methanol rises, its density will decrease and operation of the processor will be terminated before the temperature reaches a dangerous level.

If the sensor is broken or disconnected, the control system will not receive a "go" signal and activation of the manual controls will be prevented. The system is therefore designed to be fail-safe. It should be noted that the sensor 48 is located entirely outside the stainless steel pressure vessel 2. No breach is required in the wall of the pressure vessel and therefore the integrity of the vessel is not compromised. Furthermore, the electrical connections of the sensor are outside the pressure vessel, so avoiding any risk of a spark igniting the contents of the vessel. Only the stainless steel float 30 is located inside the vessel 2 and this does not give rise to any potential hazard.

Another advantage of the external position of the sensor 48 is that it can easily be repositioned to suit any required change in the filing height of fluid within the vessel 2. It is also possible to employ a plurality of floats and sensors, which may have different densities or be located at different positions, to sense different levels and/or densities of fluid. For example, sensors may be provided for indicating when the vessel is full or ³ A, ¹ A or VA full.

The bio-fuel processor shown in Figures 5 to 13 represents a second embodiment of the invention and comprises a stainless pressure vessel 102 mounted on support legs 104. The vessel 102 includes a filling vent 106 and an air vent 108 in the upper part of the vessel, and an outlet vent 110 at its lowest point. These vents are fitted with valves (not shown) to control the flow of fluid to or from the vessel.

A floatation switch 122 comprising part of an override system is mounted in the upper part of the vessel 102 and is connected to the control system (not shown) through a lead 123. In use, the vessel 102 contains a body of liquid 124, comprising a mixture of vegetable oil

and methanol. The normal filling level 126 of the liquid is shown. A small air space 128 is provided in the upper part of the vessel 102, above the liquid 124. The floatation switch 122 is designed to sense the level of the liquid in the vessel and the density of the liquid (that is, it senses whether the liquid density is above a predetermined value). The floatation switch 122, which is shown in detail in Figures 9 to 13, includes a float 130 that is retained within a cage 132, which is welded to the side of the vessel 102 with its upper end approximately at the required fluid level 126. The cage 132 is square in cross- section and is designed to allow limited vertical movement of the float 130 between the ends of the cage. The cage 132 also helps to isolate the float 130 from turbulence in the liquid 124, being entirely closed apart from small openings 136 at each end. The ends of the cage are provided with inwards-facing tabs 137, which are designed to prevent the float 130 escaping from the cage.

The float 130 includes a hollow cylindrical steel body 138 that is closed at each end by an end plate 140. The float is hollow and its interior is evacuated through a vacuum suction nipple 142, so that its volume does not vary with changes in temperature. The float 130 is constructed to have an overall density (that is, its total mass divided by its total volume) of approximately 818kg/m ³ so that it floats in an 80/400 methanol/oil mixture at the correct processing temperature and pressure.

Mounted within the float 130 is a powerful industrial magnet 144, made for example of neodymium, which is attached to the upper end plate 140. In this embodiment, a ring magnet is used, comprising a flat annulus with one pole located at its inner diameter and the other pole at its outer diameter. The magnetic field is of the magnet is symmetrical about the axis of the cylindrical float and extends radially beyond the cylindrical wall of the float. A sensitive magnetic sensor 148 (for example a Hall effect sensor) is attached to the vessel 102 in a position so that when the float 130 is floating in the liquid at the correct level, the sensor is adjacent the magnet. The sensor 148 is able to sense the presence of the magnet through the walls of the float 130 and the stainless steel vessel 102. The sensor 148 is attached to one of the support legs 104 of the vessel 102 by a retaining bracket 150 and is connected to the control system by the lead 123. The sensor 148 is arranged to send a

signal to the control system to indicate the presence of the magnet 144 in the proximity of the sensor.

The sensor 148 is thus arranged to sense when the float 130 is floating at the correct level within the vessel 102. If the magnet is sensed, the sensor 148 sends a "go" signal to the control system, which then allows the heater to be activated. If the vessel is empty or if the liquid level is significantly below the correct operating level, the magnet 144 will not be detected. Similarly, if the proportion of methanol in the methanol/oil mixture is too high so that the density of the liquid is below 818kg/m ³ , the float 130 will sink and the sensor

148 will not then detect the magnet 144. In either of these situations, the sensor will not send a "go" signal to the control system, which responds by overriding the manual controls to prevent operation of the heater, thereby reducing any risk of damage or overheating.

Operation of the sensor in other situations is similar to that of the first embodiment described above.

A float switch similar to those described above may be used in other applications where it is required to sense the level and/or density of a fluid within a vessel, and is particularly suitable for applications where it is desirable to avoid any breach in the wall of the vessel or the use of electrical components within the vessel. For example, the float switch may be used to detect the fluid level in a high pressure hydraulic accumulator, used in a hydraulic circuit to maintain a constant hydraulic pressure. Typically, a hydraulic accumulator consists of a vertically-mounted cylinder that contains gas at a pressure of typically 200 bar, which presses down on a body of hydraulic fluid. Usually, electrical sensors are used to sense the level of the hydraulic fluid and a diaphragm is provided above the fluid to prevent any risk that a spark could cause an explosion. By using a floatation switch according to the present invention, the risk of a spark could be eliminated so obviating the need for a diaphragm.

Various modifications of the invention are of course possible. For example, the cage may have multiple shells or shields to protect the float from turbulence. The vessel may also be used for containing various other liquids. For example, the vessel may a fuel tank containing aviation fuel, petrol or diesel, or it may contain other liquids such as mercury.