Apparatus for the treatment of waste water containing fats, oils and grease

Abstract

An apparatus (1) and method for treating contaminated waste water (2). The apparatus comprises a heater (30), a feed apparatus (11, 12, 13, 14), for supplying contaminated waste water (2) to the heater (30) and a centrifuge (50, 60) downstream of the heater (30). A heat exchanger (20) is also provided which has a first channel (22) and a second channel (24). The first channel (22) is connected in a flow path extending between the feed apparatus (11, 12, 13, 14) and the centrifuge (50, 60); and a waste water outlet (9) from the main centrifuge (60) is fluidly coupled to an inlet of the second channel (24) of the heat exchanger (20).

Claims

1. An apparatus for treating contaminated waste water comprising: a heater; a feed apparatus for supplying contaminated waste water to the heater; a main centrifuge provided downstream of the heater; an auxiliary centrifuge provided between the heater and the main centrifuge; the auxiliary centrifuge having a liquid phase outlet that is fluidly coupled to the inlet of the main centrifuge and a solids outlet; a heat exchanger having a first channel and a second channel, wherein the first channel is connected in a flow path extending between the feed apparatus and the main centrifuge; and wherein a waste water outlet from the main centrifuge is fluidly coupled to an inlet of the second channel of the heat exchanger.

2. The apparatus according to claim 1, wherein the first channel of the heat exchanger is provided in a flow path extending between the feed apparatus and the heater.

3. An apparatus according to claim 1, wherein a secondary heater is provided between the auxiliary centrifuge and the main centrifuge.

4. An apparatus according to claim 1, wherein the heater is a main heater, and at least one of the main heater and the secondary heater is a steam heat exchanger.

5. An apparatus according to claim 1, wherein the apparatus further includes a secondary heat exchanger having a first channel and a second channel; and wherein the first channel of the secondary heat exchanger is connected in a flow path between the auxiliary centrifuge and the main centrifuge.

6. An apparatus according to claim 5, wherein the second channel of the secondary heat exchanger is fluidly coupled to the waste water outlet of the main centrifuge.

7. An apparatus according to claim 1, wherein the main centrifuge is a disk-stack-type centrifuge and the auxiliary centrifuge is a decanter-type centrifuge.

8. An apparatus according to claim 1, wherein the or each heat exchanger is a counter-flow heat exchanger.

9. An apparatus according to claim 1, wherein a macerator is provided upstream of the heater.

10. A method of treating contaminated waste water comprising: providing a supply flow of contaminated waste water; heating the supply flow of contaminated waste water in a heater; separating the supply flow of contaminated waste water by conveying the heated supply flow of contaminated waste water to an auxiliary centrifuge configured to separate the supply flow into a heated liquid phase flow and a solids phase flow, and conveying the heated liquid phase flow to a main centrifuge configured to separate the heated liquid phase flow into an output waste water flow, a solids flow, and an oil phase flow; providing a heat exchanger having a first channel and a second channel; conveying the output waste water flow to the second channel of the heat exchanger; and conveying the supply flow of contaminated waste water through the first channel of the heat exchanger before it is conveyed to the main centrifuge.

11. A method according to claim 10, wherein the supply flow of contaminated waste water through the first channel of the heat exchanger is pre-heated in the heat exchanger before being conveyed to the heater.

12. A method according to claim 10, wherein the step of providing a supply flow of contaminated waste water includes removing particle contaminants above a predefined size and/or metallic particles from the supply flow of contaminated waste water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Specific embodiments of the invention will now be described in detail by way of example only and with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic representation of an apparatus according to a first embodiment of the invention;

(3) FIGS. 2a to 2c show schematic views of types of centrifuges used in embodiments of the invention; and

(4) FIGS. 3 to 7 are schematic representations of an apparatus according to further embodiments of the invention.

DESCRIPTION OF AN EMBODIMENT

(5) FIG. 1 shows a plan view of an apparatus 1 for treating waste water according to a first embodiment of the invention. The apparatus 1 provides a cost effective arrangement for extracting contaminants such as fats, oil and grease (FOG) from waste water. The apparatus 1 includes a storage apparatus 10 holding contaminated water 2 including FOG; a pump 11, a metal removal apparatus 12, a macerator 14, a heat exchanger 20, a heater 30, a holding tank 40, a first centrifuge 50, a second centrifuge 60, and an oil storage tank 70. It will be appreciated that the metal removal apparatus 12 and macerator 14 are optional and can be omitted from the apparatus and/or replaced with a filter. It will be appreciated that the metal removal apparatus 12 and macerator 14 may be used in any of the embodiments described herein.

(6) The contaminated waste water is pumped by the pump 11 through the metal removal apparatus 12 which detects and removes metallic particles 13 in order to prevent damage to the downstream equipment.

(7) The waste is then fed through a macerator 14 which reduces the particles to below a predefined maximum size. The maximum size is determined by the maximum permissible particle size which can be handled by the downstream decanter-type centrifuge 50 (explained in more detail below). In a preferred arrangement, a macerator 14 is provided which reduces the average particle size to below the allowable tolerance of the decanting centrifuge, typically below 5 mm, this allows a heat exchanger 20 having a higher heat transfer coefficient to be used. This also ensures that downstream equipment, such as the centrifuges, is not damaged.

(8) The waste water is then fed through a first channel 22 of the heat exchanger 20 (the operation of which will be explained in more detail below) in which the material is preheated. It is then fed to the heater 30, which raises the material temperature to between 50° C. and 98° C. Since the material has been pre-heated by the economiser heat exchanger, less energy is required by the heater in heating the material up to the desired elevated processing temperature.

(9) From the heater 30, in this embodiment the waste water flow is conveyed to the holding tank 40. The holding tank 40 is a stirred tank, and the waste water is continuously stirred at the elevated temperature allowing additional time for the debinding of the material. The material is conveyed from the tank 40 to the first (auxiliary) centrifuge 50. The holding tank may not be necessary in all applications, and when no holding tank is provided the material is conveyed directly from the heat exchanger 20 to the first centrifuge. It will be appreciated that a holding tank 40 may be used in any of the embodiments described herein.

(10) The first centrifuge 50 is a decanter-type centrifuge. The first centrifuge 50 separates the material into low moisture content solid flow 4 and a liquid phase flow 3 having a low solids content. A typical decanter-type centrifuge (shown in FIG. 2a) includes a horizontal spinning bowl 56, and an auger type screw 58, comprising a helical blade 58a mounted on a shaft 58b which provided within the bowl 56 such that there is a small clearance between the distal extremes of the screw blade 58a and the surface of the bowl 56. The centrifuge 50 includes an inlet 52, a first outlet 53 at a first end of the bowl, and a second outlet 54 at the opposite end of the bowl. Inflow material is fed from the inlet 52 through the shaft 58b into the bowl 56 which rotates at approximately 3000 rpm. The screw 58 is rotated at a slightly lower speed to that of the bowl 56, typically a differential in the range 15-100 rpm. This causes the screw 58 to convey the solids away from the lighter liquid phases. Thus, the solids are discharged from the first outlet 53 and the liquid phases flow is discharged from the second outlet 54. It has been found that the solids are discharged with moisture content typically in the range 10-20%, and the liquid phases are discharged with very low solids content. The decanter-type centrifuge 50 has an operating temperature of approximately 60° C.

(11) The liquid phases 3 are then conveyed to a second, main centrifuge 60. The second centrifuge 60 is a disk stack type centrifuge or separator, also known as a conical plate centrifuge. The disk stack type centrifuge 60 separates the material outputted from the first centrifuge into: a solids discharge flow 8, a lighter oil stream 6 and a heavier waste water flow 9. A typical disk stack type centrifuge separates the phases by subjecting the liquid phases to an extremely high centrifugal force, and includes stack plates which provide increased surface settling area to speed up the separation process. A typical disk stack type centrifuge is shown in FIG. 2b. The disk stack centrifuge 60 includes an inlet 62, a first outlet 63 through which the solids discharge flow is discharged, a second outlet 64 for discharging the heavy water 9 and a third outlet 65 for discharging the lighter oil 6. The oil stream 6 has a water content brought down to solubility levels (<1 weight percentage (wt %)) and with almost all trace solids removed. The waste water flow 9 has a raised temperature, typically in the range 80 to 98° C. and is conveyed to a second channel 24 of the heat exchanger 20. The heat exchanger 20 of the embodiment has a counter-current arrangement in which the water waste inlet is provided at the same end as the material flow outlet. It will be appreciated that other heat exchangers having other flow arrangements (parallel-flow or cross-flow) may also be used. As indicated above, the heat recovered from the waste water heats up the material flowing through the first channel 22, which reduces the heating requirement and therefore energy consumption of the heater 30. The waste water exiting from the apparatus 1 has been cooled sufficiently to be discharged into the sewage network.

(12) In another embodiment (not shown), the apparatus includes a single tricanter-type centrifuge 90 (shown in FIG. 2C) instead of the first and second centrifuges as described above. When the tricanter-type centrifuge is used, the material is transferred from the stirring tank into the centrifuge inlet 92. The solids are conveyed by a screw 98 away from the liquid phases, and then discharged from a first outlet 94. The heavier water waste flow is discharged under pressure from a second outlet 93 and conveyed to the second channel of the heat exchange in the same way as described above for the water waste from the second centrifuge in FIG. 1. The lighter oil stream is discharged by gravity through a third outlet 95.

(13) FIG. 3 shows an apparatus 101 according to second embodiment of the invention. This arrangement utilises the same principle of heat recovery as the first embodiment. The apparatus 101 includes a includes a storage tank 110 holding contaminated water 2 including FOG; a pump (not shown), a macerator 114, a filter 116, a heat exchanger 125, a first heater 130, a first centrifuge 150, a second heater 135, a second centrifuge 160, and an oil storage tank 170. As with the above embodiment, the filter 116 and macerator 114 are optional and can be omitted from the apparatus. It will be appreciated that the filter 116 and macerator 114 may be used in any of the embodiments described herein. The arrangement may also include a metal detection/removal apparatus.

(14) In this arrangement a pump (not shown) pumps the contaminated waste water through the macerator and filter to reduce entrained particle size and remove large contaminants to ensure that subsequent downstream equipment, such as the centrifuges, is not damaged. The processed waste water flow 2a then passes first through the first heater 130 which raises the temperature to approximately 95 C. and then into the first (auxiliary) centrifuge 150. As in the previous embodiment, this is a decanter-type centrifuge which separates the contaminated waste water into a low moisture content solid flow 4 and a liquid phase flow 3 having a low solids content. The liquid phase flow 3 is then conveyed through a first channel of the heat exchanger 125, through a second heater 135 and then to the second, main centrifuge 160. The second centrifuge is a disk stack centrifuge (as before), which separates the flow into: a solids discharge flow 8, a lighter oil stream 6 and a heavier waste water flow 9. The waste water flow 9 is conveyed to a second channel of the heat exchanger 125. The cooled waste water exiting the heat exchanger 125 is then collected in a tank 172, from where it can be discharged into the sewage network.

(15) FIG. 4 shows an apparatus 201 according to third embodiment of the invention. The apparatus 201 includes a includes a storage tank 210 holding contaminated water 2 including FOG; a pump (not shown), a macerator 214, a filter 216, a heat exchanger 220, a first heater 230, a first centrifuge 250, a second heater 235, a second centrifuge 260, and an oil storage tank 270. As above, the filter 216 and macerator 214 are optional and can be omitted from the apparatus. It will be appreciated that the filter 216 and macerator 214 may be used in any of the embodiments described herein. The arrangement may also include a metal detection/removal apparatus. The first centrifuge 250 is a decanter type centrifuge and the second centrifuge 260 is a disk-stack type centrifuge.

(16) In the apparatus 201, as before, a pump (not shown) pumps the contaminated waste water through the macerator and filter to reduce entrained particle size and remove large contaminants. In this arrangement, the processed waste water flow 2a passes first through a first channel of the heat exchanger 220 and then through a heater 230. The heated waste water flow is then conveyed into the decanter centrifuge 250 where is separated into a low moisture content solid flow 4 and a liquid phase flow 3. This arrangement differs from previous embodiments in that the liquid phase flow 3 exiting the decanter centrifuge 250 is conveyed through the second heater 235 before entering the disk stack centrifuge 260. The second heater 235 raises the temperature of the liquid phase flow to approximately 95° C. which will allow a greater degree of separation between heavy and light liquid phases at a given flowrate.

(17) As before, the disk stack centrifuge separates the flow into: a solids discharge flow 8, a lighter oil stream 6 and a heavier waste water flow 9. The waste water flow 9 is conveyed through a second channel of the heat exchanger 220. The cooled waste water exiting the heat exchanger 220 is then collected in a tank 272, from where it can be discharged into the sewage network.

(18) FIG. 5 shows an apparatus 301 according to fourth embodiment of the invention. The apparatus 301 includes a includes a storage tank 310 holding contaminated water 2 including FOG; a pump (not shown), a macerator 314, a filter 316, a first heat exchanger 320, a first heater 330, a first centrifuge 350, a second heat exchanger 325, a second heater 335, a second centrifuge 360, and an oil storage tank 370. As above, the filter 316 and macerator 314 are optional and can be omitted from the apparatus, and a metal detection/removal apparatus may also be included upstream of the first heat exchanger 320. It will be appreciated that the filter 316 and macerator 314 may be used in any of the embodiments described herein. The first centrifuge 350 is a decanter type centrifuge and the second centrifuge 360 is a disk-stack type centrifuge.

(19) In this arrangement, the processed waste water flow 2a passes through a first channel in the first heat exchanger 320 and then the first heater 330 before being conveyed into the decanter centrifuge 350. The liquid phase outflow 3 from the decanter centrifuge 350 is passed through a first channel of the second heat exchanger 325 which preheats it before it enters the second heater 335. The second heater 335 heats the flow to a temperature of approximately 95° C. which allows for a greater degree of separation between the heavy and light liquid phases.

(20) The disk stack centrifuge 360 separates the flow into: a solids discharge flow 8, a lighter oil stream 6 and a heavier waste water flow 9. The waste water flow 9 is conveyed first through a second channel of the second heat exchanger 325, and then through a second channel of the first heat exchanger 320. The cooled waste water exiting the first heat exchanger 320 is then collected in a tank 372, from where it can be discharged into the sewage network.

(21) This embodiment provides liquid inflow to the disk stack centrifuge with an elevated temperature which is typically in the range of 80 to 98° C. However, the double heat recovery from the waste water flow reduces the energy required by the two heaters 330, 335.

(22) In another embodiment (not show in the figures), an apparatus is provided which is similar to that shown in FIG. 5, but without the second heater, meaning that the liquid phase flow is heated only by the second heat exchanger before being conveyed into the disk stack centrifuge. Since this arrangement includes only one heater it has a lower energy requirement.

(23) FIG. 6 shows an apparatus 401 according to fifth embodiment of the invention. The apparatus 401 includes a storage tank 410 holding contaminated water 2 including FOG; a pump (not shown), a filter 416, a first heat exchanger 420, a first heater 430, a first centrifuge 450, a second heat exchanger 425, a second heater 435, a second centrifuge 460, and an oil storage tank 470. As above, the filter 416 is optional, and the macerator and/or a metal detection/removal apparatus may also be included upstream of the first heat exchanger. It will be appreciated that the filter 416 and the macerator may be used in any of the embodiments described herein. The first centrifuge 450 is a decanter type centrifuge and the second centrifuge 460 is a disk-stack type centrifuge.

(24) In this embodiment, the first heat exchanger 420 includes two heat exchangers 420a, 420b arranged in parallel, downstream of the first heater 430 in the flow path. The processed waste water flow 2a is split into two channels and conveyed through first channels in the two heat exchangers 420a, 420b. As before, after the first heat exchanger 420 the processed waste water flow 2a is conveyed to the first heater 430. Similarly, the second heat exchanger 425 includes two heat exchangers 425a, 425b arranged in parallel in the liquid phase 3 flow path between the decanter centrifuge 450 and the second heater 435.

(25) The disk stack centrifuge 460 separates the flow into: a solids discharge flow 8, a lighter oil stream 6 and a heavier waste water flow 9. The waste water flow 9 is conveyed first through a second channel of the second heat exchanger 425a, and then through a second channel of the first heat exchanger 420a. The oil stream flow 6 is conveyed first through a second channel of the second heat exchanger 425b, and then through a second channel of the first heat exchanger 420b. This means that heat is recovered from both the extracted oil and waste water. The double parallel heat exchanger arrangements produce a greater temperature rise, which results in lower energy requirements for both of the heaters 430, 435.

(26) In a further embodiment (not shown) an apparatus is provided which is similar to that shown in FIG. 6, but without the second heater.

(27) FIG. 7 shows an apparatus 501 according to a further embodiment of the invention. The apparatus 501 includes a storage tank 510 holding contaminated water 2 including FOG; a pump (not shown), a macerator 514, a filter 516, a first holding tank, a first heat exchanger 520, a first heater 530, a first centrifuge 550, a second holding tank 545, a second heat exchanger 525 a second heater 535, two second centrifuges 560a and 560b, an oil storage tank 570 and a waste water tank 572. As above, the filter 516 and macerator are optional, and/or a metal detection/removal apparatus may also be included upstream of the first heat exchanger. It will be appreciated that the filter 516 and macerator may be used in any of the embodiments described herein. The first centrifuge 550 is a decanter type centrifuge and the second centrifuges 560a and 560b are disk-stack type centrifuges.

(28) The apparatus 501 is an example layout of the type suited for large-scale operations which can process large quantities of FOG contaminated waste water, such as in a water utilities company.

(29) In the embodiment shown, the storage tank includes a loop circuit having a hot water heater 518. The feedstock stored in the tank 510 can be pumped by the pump 511 around this circuit to recirculate and heat the feedstock. This storage loop circuit may be provided in combination with the other apparatus layouts described previously.

(30) The processed waste water flow 2a is conveyed through the first holding tank 540 in which it is stirred, and from here conveyed to the first heat exchanger 520 and then to the first heater 530. The heated flow is then conveyed to the decanter centrifuge where it is separated into a solids flow 4 and a liquids phase flow 3. The liquids phase flow 3 is conveyed to the second holding (stirring) tank 545 and then to the second heat exchanger 525. It will be appreciated that holding tanks 540 and 545 may be used in any of the embodiments described herein.

(31) The second heater 535 includes two heaters 535a, 555b arranged in parallel upstream of the second heat exchanger 525. After being pre-heated in the second heat exchanger 525, the flow is split into two and conveyed through the two heaters 535a, 535b. Each of the heaters 535a, 555b feeds a respective disk stack centrifuge 560a, 560b. The oil phase outflows 6 from the disk stack centrifuges are conveyed to an oil storage tank 570. The waste water flows 9 from the disk stack centrifuges 560a, 560b are combined to a single channel and conveyed first through a second channel of the second heat exchanger 525, and then through a second channel of the first heat exchanger 520.

(32) It will be appreciated that single heat exchangers may be provided in the arrangement of FIG. 7 and that the oil phase flow may be conveyed through one heat exchanger and the water phase flow may be conveyed through the second heat exchanger. While the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.