Description SEPARATING LIQUIDS OR LIQUID AND SOLIDS

[1] This invention relates to an apparatus for separating out a first liquid or solids and a second liquid from a process liquid comprising a mixture of the first liquid or solids and the second liquid and/or a reacting mixture of other liquids, and to a method of operation of such an apparatus.

[2] The invention was originally conceived for use in the production of biodiesel by separating out biodiesel and glycerol from a mixture of biodiesel and glycerol and/or a reacting mixture of base oil and alcohol. However, the invention does have other applications such as the removal of suspended particles, fats or greases from dirty water, and the separation of different polymers from a mixture of those polymers.

[3] Biodiesel is a mix of mono-alkyl esters of long-chain fatty acids derived from biological sources such as vegetable and animal oils that can be used as a fuel as an alternative to petrodiesel in Diesel engines and for other uses. Biodiesel can be made from vegetable and animal oils by a process called transesterification. The base oil is reacted with an alcohol, such as ethanol or, more commonly, methanol, to produce biodiesel (which is less dense than the base oil), glycerol (which is more dense than the base oil) and contaminants, and the biodiesel is separated from the glycerol. It is known that the transesterification process can be improved by increasing the temperature of reaction, by agitating the mixture of base oil and alcohol and by employing a catalyst such as sodium hydroxide.

[4] An aim of the present invention or at least of specific embodiments of it is to provide an improved apparatus for separating out a first liquid or solids (such a glycerol) and a second liquid (such as biodiesel) from a process liquid comprising a mixture of the first liquid or solids and the second liquid and/or a reacting mixture of other liquids (such as base oil and alcohol).

[5] In accordance with a first aspect of the present invention, there is provided such an apparatus, comprising: a vat; an inlet passageway for the process liquid; a hy- drocyclone disposed within the vat, the hydrocyclone having a downwardly-pointing generally-conical wall, an inlet port adjacent the top of the hydrocyclone which is fed by the inlet passageway so that the process liquid is fed tangentially into the hydrocyclone, a lower, downwardly-directed outlet port adjacent the bottom of the hydrocyclone, and an upper, upwardly directed outlet port adjacent the top of the hydrocyclone; a first outlet passageway from the vat adjacent the bottom of the vat; a second outlet passageway from the vat part-way up the vat; and a pump and pipework arranged for recirculating the process liquid from the second outlet passageway to the inlet passageway.

[6] In accordance with a second aspect of the invention, the apparatus of the first aspect of the invention may be operated in a batch production mode comprising the steps of: feeding process liquid into the inlet passageway until the vat is substantially full and the second liquid (for example biodiesel) tends to separate from the first liquid or solids (for example glycerol) in the hydrocyclone (with, in the example, the liquid exiting from the lower outlet port of the hydrocyclone having a higher proportion of glycerol due to its relatively higher density, and the liquid exiting from the upper outlet port of the hydrocyclone having a higher proportion of biodiesel due to its relatively lower density); once the vat is substantially full, recirculating the process liquid from the second outlet passageway via the pump back to the inlet passageway, so as to increase the separation; and once the liquid in the vat is sufficiently separated, ceasing recirculation, and draining the contents of the vat at least through the first outlet passageway.

[7] In the example, if the liquid is drained solely through the first passageway at the bottom of the vat, the liquid that is initially drained will predominantly be glycerol (which may be put in one container); then the draining liquid will change to unreacted base oil and alcohol and/or unseparated biodiesel and glycerol and/or contaminants (which may be put in another container); and then the draining liquid will change to predominantly biodiesel (which may be put in a further container). However, the liquid may also be drained through other passageways, including for example the second passageway.

[8] The apparatus may also have a third outlet passageway from the vat adjacent the top of the vat.

[9] In the batch production mode, the third outlet passageway may or may not be used.

However, the third outlet passageway enables the apparatus to be operated, in accordance with a third aspect of the invention, in a continuous mode comprising the steps of: feeding process liquid into the inlet passageway until the vat is substantially full and the second liquid (for example, biodiesel) tends to separate from the first liquid or solids (for example, glycerol) in the hydrocyclone(with, in the example, the liquid exiting from the lower outlet port of the hydrocyclone having a higher proportion of glycerol due to its relatively higher density and the liquid exiting from the upper outlet port of the hydrocyclone having a higher proportion of biodiesel due to its relatively lower density); once the vat is substantially full, recirculating the process liquid from the second outlet passageway via the pump back to the inlet passageway so as to increase the separation; and once the liquid in the vat is sufficiently separated, draining liquid or solids (which, in the example, will be predominantly glycerol) from the first outlet passageway, and draining liquid (which, in the example, will be predominantly biodiesel) from the third outlet passageway, while feeding further process

liquid to the inlet passageway so as to keep the vat topped up.

[10] The apparatus preferably further includes at least one first valve operable to determine whether the liquid that is pumped to the inlet passageway is freshly introduced process liquid and/or process liquid from the second outlet passageway.

[11] The apparatus preferably further includes a second valve operable to allow or block liquid and/or solids exiting the first outlet passageway.

[12] At least one sensor is preferably provided for sensing a parameter indicative of an operating condition of the apparatus and controlling the pump and/or at least one of the valves in dependence thereon. For example, a first such sensor (such as a level switch) is preferably arranged to sense a parameter indicative of whether or not the vat is substantially full and to control the first valve accordingly. Also, a second such sensor (such as an optical transmissivity sensor) is preferably arranged to sense a parameter indicative of whether or not liquid towards the bottom of the vat has a particular property (for example low optical transmissivity indicative of glycerol) and to control the second valve to allow liquid and/or solids to exit from the first outlet passageway when the liquid towards the bottom of the vat is indicated as having the particular property.

[13] The vat may contain various baffles to improve the separation of the process liquid, in particular: a first baffle extending across the vat below the levels of the second outlet passageway and the lower outlet port of the hydrocyclone and above the level of the first outlet passageway, the first baffle being arranged substantially to restrict downward flow of liquid and/or solids past the first baffle; a second baffle disposed in the vat beneath the first baffle, the second baffle being arranged substantially to restrict swirling of liquid and/or solids around the vat beneath the first baffle; a third baffle extending across the vat generally above the hydrocyclone, the upper outlet port of the hydrocyclone exiting above the third baffle, and the third baffle being arranged substantially to restrict upward flow of liquid past the third baffle; and/or a fourth baffle disposed in the vat above the third baffle, the fourth baffle being arranged substantially to restrict swirling of liquid around the vat above the third baffle.

[14] The apparatus preferably further includes a heater, which is preferably thermostatically controlled, for heating the process liquid that is to be fed to the inlet passageway. In the case of biodiesel production, the heater is preferably sufficiently powerful to elevate the liquid passing therethough from the initial temperature of the oil to the desired temperature for the transesterification process on a single pass of the liquid through the heater, although the liquid may make multiple passes through the heater during recirculation.

[15] The apparatus preferably further includes a device for agitating the process liquid that is to be fed to the inlet passageway so as to promote, in the case of biodiesel

production, the transesterification process. An agitating device that has been found to be particularly effective comprises an outer tube and an inner tube through which the process liquid is to be passed, the inner tube being perforated and deformed within the outer tube to produce a plurality of deflectors which, in use, produce cavitation of the process liquid passing through the tubes.

[16] Such an agitating device may be used in other forms of apparatus for separating out a first liquid or solids and a second liquid from a process liquid comprising a mixture of the first liquid or solids and the second liquid and/or a reacting mixture of other liquids. Therefore, in accordance with a fourth aspect of the present invention, there is provided such an apparatus comprising: a vat; an inlet passageway for feeding the process liquid to the vat; and a device for agitating the process liquid that is to be fed to the inlet passageway, the agitating device comprising an outer tube and an inner tube through which the process liquid is to be passed, the inner tube being perforated and deformed within the outer tube to produce a plurality of deflectors which, in use, produce cavitation of the process liquid passing through the tubes.

[17] In the apparatus of the first or fourth aspect of the invention, the vat together with the pump and/or at least part of the pipework and/or the heater and/or the agitating device are preferably contained within a thermally-insulated housing.

[18] Specific embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

[19] Figure 1 is a schematic sectioned side view of the apparatus of one embodiment of the invention;

[20] Figure 2 is an exploded isometric view of the internal components of a vat of the apparatus of Figure 1 ;

[21] Figure 3 is an assembled isometric view of the internal components of Figure 2, but with half cut away;

[22] Figures 4A & B are a plan view and a side view, respectively, of an internal baffle of the vat;

[23] Figures 5A & B are a plan view and a side view, respectively, of another internal baffle of the vat;

[24] Figure 6 is an isometric view an internal hydrocyclone of the vat;

[25] Figure 7 is an isometric view of an outlet baffle assembly of the vat;

[26] Figures 8A & B are a plan view and a side view, respectively, of a further internal baffle of the vat;

[27] Figures 9A & B are exploded and assembled isometric views of an agitator of the apparatus;

[28] Figure 9C is a sectioned side view, on a larger scale, of the agitator of Figures 9A &

B;

[29] Figure 10 is a schematic block diagram of a modified apparatus; and

[30] Figure 11 is a schematic sectioned side view of a modified vat.

[31] Referring to Figure 1 of the drawings, a separation apparatus 10 comprises a vat 12, an inlet 14 for vegetable oil, an inlet 16 for methanol and catalyst, an outlet 18, a pump 20, a heater 22, an agitator 24, various pipework and valves that will be described in detail later, and a thermally insulated housing 25 for the vat 12, pump 20, heater 22 and agitator 24.

[32] Referring in particular to Figures 1 to 3, the vat 12 has an upright cylindrical side wall 26 which is closed at the top by a circular end wall 28 and at the bottom by an elliptical bottom wall 30 inclined at an angle of about 5 degrees to the horizontal. The interior of the vat is divided by upper and lower baffles 32,34 into an upper section 36 extending over about a quarter of the height of the vat 12, a middle section 38 extending over about a half of the height of the vat 12 and a lower section 40 extending over the remainder of the height of the vat 12. The baffles 32,34 are welded in place to the side wall 26 of the vat 12.

[33] As shown in particular in Figures 5 A & B, the upper baffle 32 is formed from a circular plate 42 which has eight or so small, upwardly-inclined vanes 44 formed around its periphery and pointing anticlockwise around the plate 42 (as viewed from above). The plate 42 also has a central hole 46 and four or so tangential slots 48 and upwardly extending vanes 50 arranged around the hole 46.

[34] As shown in particular in Figures 8 A & B, the lower baffle 34 is formed from a circular plate 52, but slit and seamed at 54 so that the plate 52 is slightly upwardly conical, for example with a conical half angle of about 85 to 87 degrees. The plate 52 also has eight or so small, upwardly-inclined vanes 56 formed around its periphery and pointing anticlockwise around the plate 52 (as viewed from above). Three mounting holes 58 are formed around the centre of the plate 52. The lower baffle 34 has an auxiliary baffle plate 60 (Figure 7) that is generally a quadrant of a circle with an enlarged central portion 62 which is connected to the main plate 52 of the lower baffle 34 by three spacers 64 (Figure X). The central portion 62 has a hole 66 aligned with the centre of the main plate 52. A middle outlet pipe 68 extends radially of the auxiliary baffle plate 60 along the more-anticlockwise edge 70 of its two radial edges from adjacent the hole 66 to beyond the outer edge 72 of the auxiliary baffle plate 60. Half of the pipe 68 is cut away lengthwise over a region 73 from its inner end to a point short of the outer edge 72 of the auxiliary baffle plate 60 so that the concave side of the remaining half of the pipe faces anticlockwise around the plate 60 (as viewed from above). When assembled, the non-halved portion of the pipe 68 protrudes through a hole in the side wall 26 of the vat 12 and is welded to it to form a middle outlet 74 of the vat 12.

[35] A hydrocyclone 76 is fitted in the middle section 38 of the vat 12 between the upper baffle 32 and the auxiliary baffle plate 60 of the lower baffle 34. Referring in particular to Figure 6, the hydrocyclone comprises an upper, upright cylindrical shell 78 the upper edge of which abuts the underside of the upper baffle 32. The lower edge of the cylindrical shell 78 joins an upper edge of a downwardly-pointing frusto-conical shell 80. A horizontal pipe 82 joins the cylindrical shell 78 generally tangentially in a clockwise direction (as viewed from above), and the cylindrical shell 78 has a hole aligned with the bore of the pipe 82 to form an inlet port 84 to the hydrocyclone 76. When assembled, the pipe 82 protrudes through a hole in the side wall 26 of the vat 12 and is welded to it to form an inlet 86 of the vat 12. The open, lower end of the conical shell 80 forms a lower, 'more dense', outlet port 88 of the hydrocyclone 76 and joins the hole 66 in the auxiliary baffle plate 60 of the lower baffle 34. A short vertical pipe 90 is fitted in the central hole 46 in the upper baffle 32 (Figures 1-3) and protrudes down into the cylindrical shell 78 of the hydrocyclone 76 to form an upper, 'less dense', outlet port 92 of the hydrocyclone 76.

[36] The upper section 36 of the vat 12 is subdivided generally in half by a generally horizontal baffle 94 which, as shown particularly in Figures 4A & B, is formed by a circular plate 96 which has its edges folded down along eight symmetrical chords 98 of the circle and which also has a central lipped hole 100. The space in the vat 12 above the baffle 94 is subdivided in half by a generally vertical baffle 102, which, as shown in Figures 1 to 3 is formed by a rectangular plate, the lower edge which has, at its centre, a semicircular cutaway 103 and, at its ends, quarter-circular cutaways 105.

[37] Somewhat similarly, the lower section 40 of the vat 12 is subdivided generally in half by a generally horizontal baffle 104 which is similar to the baffle 94 except that it is slit and seamed at 107 (Figure 2) so that the baffle 104 is slightly upwardly conical, for example with a conical half angle of about 85 to 87 degrees. The space in the vat 12 below the baffle 104 is subdivided in half by a generally vertical baffle 106, which, as shown in Figures 1 to 3, is shaped to follow the conical shape of the baffle plate 104 and the inclination of the bottom plate 30. The upper edge of the baffle 106 has, at its centre, a generally-semicircular cutaway 108 and, at its ends, generally-quarter-circular cutaways 110. The lowermost corner of the plate 106 also has a generally- quarter-circular cutaway 112.

[38] The vat 12 is completed with a pipe 114 protruding through a hole in the side wall 26 of the vat 12 in the region of the cutaway 112 in the plate 106 and welded to the side wall 26 to form a lower outlet 116 of the vat 12.

[39] Referring to Figure 1, the heater 22 and agitator 24 are provided in a housing 118 subdivided by a vertical weir 120. An inlet 122 feeds into the bottom of the housing 118 to the left of the weir 120 where an immersion heater 124 is provided. The

immersion heater 124 is controlled by a thermostat (not shown) which senses the temperature of the inlet 122. Referring also to Figures 9A-C, the agitator 24 is formed by an assembly of a longer inner tube 126, a shorter outer tube 128 and a pair of annular end walls 130 that close the ends of the outer tube 128 around the end portions of the inner tube 126. Within the outer tube 128, the inner tube 126 is formed with a series of generally-hyperbolically- shaped scoops 132 each created by cutting arcuate slots in the inner tube 126 and deforming the wall of the inner tube 126 inwardly to one side of each slot. Half of the scoops 132 face one way, and the other half face the opposite way so that the assembly can be fitted either way round. A hole 134 is also formed through the wall of the inner tube 126 adjacent the lesser-deformed end of each scoop 132. Referring back to Figure 1, the agitator 24 is mounted vertically in the right-hand side of the housing 118 with its lower end adjacent the bottom of the housing 118 and its upper end protruding through and welded to the housing 118.

[40] Still referring to Figure 1, the middle outlet 74 and lower outlet 116 from the vat 12 are connected to a two-to-one valve 136 which can be set to connect, in state A, the middle outlet 74 and, in state B the bottom outlet 116 to an inlet of a two-to-one valve 138. Another inlet of the valve 138 is connected to the inlet 14 for vegetable oil, and the valve 138 can be set to connect, in state A, inlet 14 for vegetable oil and, in state B, the outlet of the valve 136 to an inlet of the pump 20. The inlet 16 for methanol and catalyst is also connected to the inlet of the pump 20 via an on-off valve 140. The outlet of the pump 20 is connected to an inlet of a one-to-two valve 142 which can be set to connect its inlet, in state A, to the outlet 18 of the apparatus 10 and, in state B, to the inlet 112 of the heater 124 and the inlet of an on-off valve 144. The outlet of the agitator 24 is connected to an inlet of an on-off valve 146. The outlets of the two on-off valves 144,146 are connected to the inlet to the vat 12. The valves 144,146 can be used to adjust the proportion of liquid of liquid that passes through the heater 22 and agitator 24 and the proportion of the liquid that bypasses them.

[41] The operation of the apparatus 10 in a batch mode will now be described starting with a state in which: the vat 12 is empty; the pump 20 and heater 22 are switched off; the valve 136 is in state A; the valves 138,142 are in state B; the valves 140,144 are off, and the valve 146 is on. The apparatus 10 is then operated in a filling phase to fill the vat with vegetable oil, methanol and catalyst by switching on the pump, changing the valve 138 to state A and opening the valve 140. The heater 22 is also turned on. Vegetable oil, methanol and catalyst are drawn by the pump 20 from the oil inlet 14 and the methanol and catalyst inlet 16 and fed via the heater 22 and agitator 24 at a pressure of about 1.5 bar (150 kPa) to the inlet 86 of the vat 12. As it passes through the heater, the mixture of oil, methanol and catalyst is heated to a temperature of about 85 to 90 C to promote transesterification, and as the mixture passes through the

agitator 24 it is agitated violently so as to promote further transesterification. In particular, the scoops 132 and holes 134 in the agitator 24 cause cavitation of the mixture. The liquid fed to the inlet 86 of the vat 12 passes through the inlet port 84 of the hydrocyclone 76 and swirls clockwise (as viewed from above) in the hydrocyclone 76. While the vat 12 is starting to fill, all of the liquid falls through the lower outlet port 88 of the hydrocyclone 76 and drains to the bottom of the vat 12. However, once the level of liquid in the vat 12 reaches about the level of the upper baffle 32, the hydrocyclone 76 begins to have its known effect of causing the more dense molecules of the liquid to drain to its lower outlet port 88, while the less dense molecules rise through the upper outlet port 92. With transesterification having begun, the biodiesel therefore tends to exit through the upper port 92 and the glycerol tends to exit through the lower outlet port 88.

[42] Once the vat 12 has filled with liquid, the methanol and catalyst valve 140 is closed and valve 138 is changed from its state A to state B. Accordingly, the liquid in the vat 12 is recirculated taking the path from the middle outlet 74 of the vat 12, via the valves 136,138, the pump 20, the valve 142, and the heater and agitators 22,24 back to the inlet 86 of the vat 12 and the inlet port 84 of the hydrocyclone 76. Because the liquid has previously been heated, the heater 22 will cut in and out under control of its thermostat to keep the liquid up to temperature. During the recirculation phase, further transesterification will occur over time, promoted by the temperature at which the liquid is maintained and the cavitation caused by the agitator 24 and further separation will occur due to further passage through the hydrocyclone 76. Furthermore, it will noted that, during recirculation, the liquid is taken from the middle outlet 74 of the vat 12 where the liquid will be less dense than glycerol but more dense than biodiesel, and will therefore mainly comprise unseparated biodiesel and glycerol, unreacted oil and methanol, or in other words the portion of the liquid that most needs further cavitation and further separation.

[43] It will be appreciated that filling and recirculation phases, the liquid in the vat 12, particularly in the middle section 38, in the upper section 36 beneath the baffle 94 and in the lower section 40 above the baffle 104 will swirl in a clockwise direction, as viewed from above. The resulting centrifugal force causes the heavier fractions to move to the periphery of the vat 12, where the vanes 44,56 on the baffles 32,34 will tend to divert the heavier fractions from the upper section 36 to the middle section 38 and from the middle section 38 to the lower section 40, respectively. Furthermore, the vanes 50 and slots 48 in the baffle 32 tend to drawn the lighter fractions from the middle section 38 to the upper section 36.

[44] After a period of time, that may be determined empirically, sufficient to convert all, or the required proportion of, the oil to biodiesel, the apparatus is changed to a draining

phase in which the valve 136 is changed to state B and the valve 142 is changed to state A. Accordingly, liquid is drawn from the vat 12, via the valves 136,138, to the pump 20 and then fed via the valve 142 to the outlet 18. The liquid will initially predominantly be glycerol (which may be put in one container); then the liquid will change to unreacted base oil and alcohol, if any, and/or unseparated biodiesel and glycerol, if any, and/or contaminants (which may be put in another container); and then the liquid will change to predominantly biodiesel (which may be put in a further container).

[45] In a modification to the method of operation described above, during the recirculation phase, the valves 144,146 may alternately be opened and closed periodically. When the valve 146 is open and the valve 144 is closed, the full flow will pass through the heater 22 and agitator 24, which will cause a pressure drop in the liquid. However, when the valve 146 is closed and the valve 144 is open, the full flow bypasses the heater 22 and agitator 24 so that there is less pressure drop, and accordingly the liquid will enter the hydrocyclone 76 at a higher speed so as to improve the separation effect.

[46] It will be noted that the heat producing components of the apparatus 10, predominantly the heater 22 and the pump 20 are contained in the same thermally insulated housing 25 as the vat 12 and the pipework used during the recirculation phase so as to reduce heat loss and therefore reduce the power consumption of the heater 22.

[47] The apparatus 10 may also be operated in a continuous or quasi-continuous mode, which may be automatic or semi-automatic by employing sensors and controllable valves and, as shown in Figure 10, and by making a minor modification to the vat 12 to include a pipe 148 protruding through a hole in the side wall 26 of the vat 12 in the region of one of the cutaways 105 in the plate 102 and welded to the side wall 26 to form an upper outlet 150 of the vat 12, as shown in Figures 1 to 3.

[48] Referring to Figure 10, the recirculation loop for the liquid when the apparatus 10 in the recirculation phase is from the middle outlet 74 of the vat, via the selector valve 138 in its state B, the pump 20, the heater 22 and the agitator 24 to the inlet 86 of the vat 12. When in a filling phase, the valve 138 is changed by a control unit 152 to its state A, so that vegetable oil 154 in a container 156 and a mixture 158 of methanol and catalyst in a container 160 are drawn via a mixer valve 162 through the valve 138 to the pump 20 and thence fed via the heater 22 and agitator 24 to the inlet 86 of the vat 20. The mixing valve 162 is adjustable, for example manually, to provide the required ratio of oil 154 to methanol and catalyst mixture 158. When in the draining phase, on/ off valves 164,166 connected to the upper and lower outlets 150,116, respectively, are opened by the control unit 152 so that biodiesel 168 drains from the top of the vat 12 into a collection container 170 and glycerol 172 drains from the bottom of the vat 12 to a collection container 174. The apparatus 10 has a number of sensors which produce

signals to which the control unit 152 responds, including: a temperature sensor 176 which senses the temperature of the pipe leading to the heater 22; an optical trans- missivity sensor 178 which senses when the optical transmissivity of the liquid just below the baffle 104 in the vat 12 is sufficiently low to indicate that the liquid is glycerol, rather than oil or unseparated glycerol and biodiesel; a level switch 180 which senses when the vat 12 is substantially full; an optical transmissivity sensor 182 which senses when the optical transmissivity of the liquid just above the baffle 94 in the vat 12 is sufficiently high to indicate that the liquid is biodiesel, rather than oil or unseparated glycerol and biodiesel; level switches 184,186 which sense when the containers 156,160 are nearly empty; and level switches 188,190 which sense when the containers 170,174 are nearly full.

[49] The operation of the apparatus 10 of Figure 10 in a quasi-automatic mode will now be described starting with a state in which: the vat 12 is empty; the pump 20 and heater 22 are switched off; the valve 138 is in state B; the valves 166 is off; the valve 164 is on; the containers 156,160 are full, and the containers 170,174 are empty. When the apparatus 10 is switched on using the control unit 152, the apparatus 10 initially operates in a filling phase to fill the vat with vegetable oil, methanol and catalyst by switching on the pump 20, and changing the valve 138 to state A. The heater 22 is also enabled under control of the temperature sensor 176. Vegetable oil, methanol and catalyst are drawn by the pump 20 from the containers 156,160 via the mixer valve 162 and valve 138 and fed via the heater 22 and agitator 24 to the inlet 86 of the vat 12. As in the batch mode, as it passes through the heater 22, the mixture of oil and methanol is heated to a temperature of about 85 to 90 C to promote transesterification, and as the mixture passes through the agitator 24 it is agitated violently at a pressure in excess of 1.5 bar (150 kPa) so as to promote further transesterification. As the vat 12 fills, the hydrocyclone 76 starts to have effect, as described previously. As the liquid reaches the level of the sensor 182, and assuming that the liquid has not yet sufficiently separated, the opaqueness of the liquid is sensed by the sensor 182 and the control unit 152 closes the valve 164.

[50] Once the vat 12 has filled with liquid, as sensed by the sensor 180, the valve 138 is changed by the control unit 152 from state A to state B to commence the recirculation phase. During the recirculation phase, further transesterification and separation of the liquid will occur, as described above in connection with the batch mode of operation.

[51] Once the control unit 152 determines from the sensor 178 that glycerol has formed and risen in the bottom of the vat 12 to the level of the sensor 178, the control unit 152 opens the valve 166 so that glycerol 172 drains from the lower outlet 116 of the vat 12 into the container 174. The level of liquid in the vat 12 falls due to the glycerol 172 being drained off, and this is sensed by the control unit 152 from the sensor 180,

whereupon the control unit 152 changes the valve 138 from state B to state A until the level has risen again, to replenish the vat 12 with fresh oil 154 and methanol and catalyst mixture 158. The control unit 152 keeps the valve 166 open until it senses that the glycerol in the bottom of the vat 12 has fallen below the level of the sensor 178, whereupon the valve 166 is closed. Also, once the control unit 152 determines from the sensor 182 that biodiesel has formed and in the top of the vat 12 down to the level of the sensor 182, the control unit 152 opens the valve 164 so that the biodiesel 168 drains through the upper outlet 150 of the vat 12 into the container 170. Again, the control unit 152 keeps the vat 12 topped up using the sensor 180 and valve 138. The control unit 152 keeps the valve 164 open until the sensor 182 senses that the liquid at its level is no longer biodiesel, whereupon the valve 164 is closed. Accordingly, as glycerol 172 and biodiesel 168 are formed and separated, they are drained off into their respective containers 174,170 and the vat is kept topped-up by adding further oil 154 and methanol and catalyst 158 from the containers 156,160, respectively.

[52] The control unit 152 uses the sensors 184,186,188,190 to determine when the containers 156,160 are nearly empty or the containers 170,174 are nearly full and in response raises an alarm and/or to places the apparatus in a waiting state in which the pump 20, heater 22 and valves 164,166 are off and the valve 138 is in its state B.

[53] In the continuous mode of operation, a bypass pipe may be provided for the heater 22 and agitator 24, together with a two-way diverter valve under control of the control unit 152, so as to produce the pulsed bypass effect described above in connection with the batch production mode.

[54] It has been found that the contaminants that arise are drained with the glycerol 172 so that high quality biodiesel 168 is produced and so that the apparatus 10 can be operated for long service periods without cleaning being required.

[55] The biodiesel 168 that is produced by the apparatus 10 can subsequently be treated in known ways, for example by the addition of proprietary wintering agents to lower its waxing point and the addition of proprietary diesel antibiotics to reduce the growth of microorganisms and increase the storage life of the biodiesel.

[56] Figure 11 shows a modification to the vat 12 described above that provides for adjustment of the hydrocyclone 76. Instead of being fixed to the baffle 32, the upper outlet pipe 90 of the hydrocyclone 76 is a sliding fit in the central hole in the baffle 32. The upper end of the pipe 90 is closed, but a number of holes 192 are formed around the top end portion of the pipe 90 to allow liquid to exit from the pipe 90. A shaft 194 extends upwardly from the pipe 90 and is screw-threaded at its upper end 196 passing through a complementarily screw-threaded sealing boss 198 fixed to the top wall 28 of the vat 12. A knob 200 is fitted to the upper end of the shaft 194. Also, an upwardly tapering valve member 202 is provided at the lower outlet port 88 of the hydrocyclone

76. A shaft 204 extends downwardly from the valve member 202 and is screw- threaded at its lower end 206 passing through a complementarily screw-threaded sealing boss 208 fixed to the bottom wall 30 of the vat 12. A knob 210 is fitted to the upper end of the shaft 194. Accordingly, by rotating the knobs 200,210, it is possible to vary the depth by which the upper outlet pipe 90 protrudes into the hydrocyclone and the vary the amount of obturation of the lower outlet port 88 of the hydrocyclone 76 by the valve member 202 so as to adjust the proportions of liquid which exit the hydrocyclone 76 via the upper and lower outlet ports 92,88.

[57] The specific embodiments of the invention that have been described above provide a number of significant advantages over known apparatus for producing biodiesel, including:

• A small footprint and less ancillary equipment;

• The combination of several processes, and elimination of others.

• Reducing the process time.

• Much less energy requirement, reducing heating costs :-

• heating need only run for a short period,

• only a small part of the oil needs to be heated, some 20 litres as opposed to a full tank (1,300 litres in the case of this prototype).

• Efficient conversion due to higher temperature that the kinetic pressure allows.

• Greater conversion efficiency allowing for less methanol/ethanol use, to just over half of traditional methods, resulting in less waste and less pollution.

• Less requirement, or no requirement, for subsequent filtering of the biodiesel. Tests have shown that with some oils, no filtering is required. However, with other oils or operating parameters, the biodiesel may need a final polish, i.e. fine filtering to below 5 microns.

• Elimination of the need for a wash cycle, thus reducing time yet further, also costs, and contaminated waste.

• Use of lower grade oils.

• It can be used for continuous flow, but can also for batch production of fuel.

• The conversion ratio of oil to biodiesel is enhanced by the process, as contaminants that cause reforming are continuously being taken away during the conversion time by the cyclone.

• It provides less chemical handling, as methanol is injected as appropriate.

• It prioritises processing of unprocessed oil.

• Other than the pump and valves, it has no moving parts.

[58] Various modifications and developments may be made to the apparatuses described

above.

[59] For example, the position at which methanol injection takes place may be modified to be between the middle outlet 74 of the vat 12 and the valve 136, and a vortex chamber may be provided to introduce a swirling movement into the recirculating liquid as the methanol is injected. A further vortex chamber may also be added just upstream of the inlet 86 of the vat 12 to cause a swirling movement of the liquid fed to the hydrocyclone 76. An adjustable valve may be provided in the upper pipe 90 of the hydrocyclone 76 to adjust the proportion of liquid exiting the hydrocyclone 76 through the upper outlet port 92.

[60] Although described in detail above for producing biodiesel, the apparatus may be used for other applications such as the removal of suspended particles, fats or greases from dirty water, and the separation of different polymers from a mixture of those polymers.

[61] It should be noted that the embodiments of the invention have been described above purely by way of example and that many other modifications and developments may be made thereto within the scope of the present invention.