Method(s) and Apparatus For Treating Waste

Abstract

The present invention relates to method(s), apparatus and use(s) of apparatus for treating materials such as waste products and by-products of industrial processes e.g. slurries comprising solids and liquids, or, more particularly, slurries comprising solids, oil(s), and water. The invention further relates to method(s), apparatus and use(s) for treating slurry, the apparatus comprising a treatment chamber having a first end configured to receive slurry to be treated and a second end configured to allow egress of solids; at least one heated material conveyor configured to draw material comprising slurry and/or solids through the chamber in a direction from the first end towards the second end; the at least one heated material conveyor being further configured to heat and mix material comprising slurry and/or solids as these are drawn along; a condenser configured to receive vapours from the chamber and condense the vapours into liquid form.

Claims

1. An apparatus for treating slurry, the apparatus comprising: a treatment chamber having a first end configured to receive slurry to be treated and a second end configured to allow egress of solids; at least one heated material conveyor configured to draw material comprising slurry and/or solids through the chamber in a direction from the first end towards the second end; the at least one heated material conveyor being further configured to heat and mix material comprising slurry and/or solids as these are drawn along; a condenser configured to receive vapours from the chamber and condense the vapours into liquid form.

2. The apparatus according to claim 1 in which the treatment chamber is configured to support a vacuum and the apparatus further comprises a vacuum pump, and in which the vacuum pump is configured to provide a vacuum in the treatment chamber of: <1 bar, about 0.25 to about 0.75 bar, about 0.4 bar, about 0.5 bar, 0.25 to 0.75 bar, 0.4 bar, 0.5 bar, <0.5 bar, of about 0.4 to about 0.5 bar, about 0.4 bar, about 0.5 bar.

3-6. (canceled)

7. The apparatus according to claim 1 in which the heated material conveyor comprises twin, intermeshing, hollow flight, thermally-heated screw conveyor(s).

8. (canceled)

9. The apparatus according to claim 1 configured so that the temperature of the vapour(s) exiting the chamber is <100 C., or 50 C. to 100 C., or 60 C. to 100 C., or 60 C. to 80 C., or 50 C., or 55 C., or 60 C., or 65 C., or 70 C., or 75 C., or 80 C., or 85 C., or 90 C., or 95 C.

10. The apparatus according to claim 1 in which the apparatus further comprises a gas circulation unit for drawing vapours and gas through the chamber into the condenser and in which the treatment chamber comprises a gas inlet port and a gas outlet port for flowing gas through the treatment chamber and in which the gas inlet port and gas outlet port are configured so that vapours and gas flow in a direction generally, or substantially, opposite to the direction of movement of slurry and/or solids drawn though the treatment chamber from the first end towards the second end.

11-13. (canceled)

14. The apparatus according to claim 1 configured to support a flow rate of gas of around 0.5 m/s or less.

15. The apparatus according to claim 1 in which the heated material conveyor, or the treatment chamber and material conveyor, is/are inclined at a predetermined angle with respect to the horizontal rising upwardly from the first end to the second end.

16-18. (canceled)

19. The apparatus according to claim 1 in which a solids outlet port is provided at or near the second end of the treatment chamber and in which the solids outlet port comprises a rotary valve.

20. (canceled)

21. The apparatus according to claim 1 comprising a separator configured to receive extracted gas and liquids from the condenser, and to separate these into gas and liquid(s).

22. The apparatus according to claim 1 in which the chamber comprises a slurry inlet port at or near the first end of the treatment chamber and in which the slurry inlet port is configured to receive slurry in a continuous or quasi-continuous manner.

23. (canceled)

24. An apparatus for treating slurry, the apparatus comprising: a treatment chamber having a first end configured to receive slurry to be treated and a second end configured to allow egress of solids; at least one heated screw conveyor assembly comprising at least one thermal, hollow flight screw conveyor; a thermal fluid unit configured to provide thermal fluid to the hollow flights to heat the at least one hollow flight screw conveyor; a condenser configured to receive vapours from the chamber and condense the vapours into liquid form.

25-42. (canceled)

43. The method for treating slurry using the apparatus of claim 1 comprising: introducing slurry into a treatment chamber having a first end configured to receive slurry to be treated and a second end configured to allow egress of solids; using at least one heated material conveyor to heat, mix, and draw material comprising slurry and/or solids through the treatment chamber in a direction from the first end towards the second end; optionally, providing a vacuum in the treatment chamber; evaporating liquid(s) to form vapour(s) from the slurry; extracting vapour(s) from the chamber; condensing extracted vapours into liquid(s); removing solid(s) from the chamber.

44-45. (canceled)

46. The method according to claim 43 comprising: treating slurry in the treatment chamber such that the solids are substantially dry before removal.

47-49. (canceled)

50. The method according to claim 43 comprising controlling the temperature of the vapour(s) exiting the chamber to be <100 C., or 50 C. to 100 C., or 60 C. to 100 C., or 60 C. to 80 C., or 50 C., or 55 C., or 60 C., or 65 C., or 70 C., or 75 C., or 80 C., or 85 C., or 90 C., or 95 C.

51. The method according to claim 43 comprising: drawing gas through the chamber from a gas inlet port to a gas outlet port and into the condenser, and in which gas is drawn through the chamber in a direction generally, or substantially, opposite to the direction of movement of slurry through the treatment chamber from the first end to the second end, optionally in which the gas is air.

52. The method according to claim 51 in which the flow rate of gas through the chamber is about 0.5 m/s or less.

53-55. (canceled)

56. The method according to claims 43 comprising: separating extracted gas and liquid(s) and re-circulating extracted gas into the treatment chamber.

57. (canceled)

58. The method according to claim 43 comprising: selecting, configuring, and controlling one or more parameters from the following: pressure within the treatment chamber; transportation time of slurry and/or solids within the treatment chamber from the an inlet port to an exit port; temperature of incoming slurry; temperature of extracted vapour(s); flow rate of gas through the chamber; temperature of re-circulated gas following a vapour condensing step; temperature of the heated material conveyor; temperature of the solid(s)on egress; temperature of the thermal oil inlet; temperature of thermal oil outlet; rotation of the heated screw conveyors where provided; % of solids by mass of incoming material; rate of ingress of incoming material; moisture level of solid(s) on egress; incline of the chamber; controlling the vacuum to be within a pre-determined value; controlling the level of slurry on ingress so that solid(s) on egress have a desired moisture level, and/or are free from hydrocarbons to a desired level.

59. The method according to claim 43 comprising: controlling the temperature of exiting solids to be <100 C., 50 C. to 90 C., 60 C. to 80 C., 50 C., 55 C., 60 C., 65 C., 70 C., 75 C., 80 C., 85 C., 90 C., 95 C.

60. The method according to claim 43 comprising not chemically changing the components of the slurry.

61-64. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

[0067] The present invention will now be described, by way of example only, with reference to the following figures. The same reference numerals refer to the same features throughout the figures.

[0068] FIG. 1 shows a schematic diagram of apparatus according to example embodiment(s) of the invention.

[0069] FIGS. 2A and B show elevation and plan views of a treatment chamber for use in apparatus and method(s) according to example embodiment(s) of the invention, such as the apparatus of FIG. 1 and/or the method(s) of FIGS. 8 and 9.

[0070] FIG. 3 shows a cross-sectional view of the reaction chamber of FIGS. 2A and 2B along line AA.

[0071] FIG. 4 shows a close up plan view of twin intermeshing, self-cleaning, thermally-heated hollow flight screw conveyors in a preferred example embodiment of the invention.

[0072] FIG. 5 shows a schematic perspective view of alternative, intermeshing screw conveyors and dry solids (here sand) at an upper end of a treatment chamber produced just before egress of solids according to an example embodiment of the invention.

[0073] FIG. 6 shows a side elevation (region A) and partially cross-sectional (region B) views of a screw conveyor for use in example embodiment(s) of the invention.

[0074] FIG. 7 shows a schematic, cross-sectional view of a hollow flight, thermally-heated screw conveyor illustrating the path of thermal heating fluid typically in through the central shaft of the screw conveyor and out through the continuous hollow flight of the screw conveyor. Whilst the path of the heating fluid can be opposite to that shown (i.e. in through the flights and out through the central shaft), the arrangement shown may be preferred in certain circumstances as it provides efficient, even heating.

[0075] FIG. 8 shows method steps for use in method(s) for treating materials such as slurries in a further aspect of the invention.

[0076] FIG. 9 shows optional method steps for use in example method(s) of the invention.

[0077] FIGS. 10A to 10D show example experimental conditions and results produced from apparatus and method(s) according to example embodiments of the invention.

[0078] FIGS. 11A to 11G show experimental conditions and results produced from apparatus and method(s) according to further embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0079] A slurry is a mixture of insoluble solids, typically in particulate form, in one or more liquids, examples include cement slurry, bentonite slurry, clay slurry, coal slurry. Other examples of slurries may include two or more immiscible liquids such as one or more oil(s) and water as well as insoluble solid particles. These are particularly difficult to separate into component parts for disposal.

[0080] In fish waste processing macerated salmon may comprise around 28% oil in a slurry of solids, oil(s), and water. The fish oil will evaporate out at around 90 C.

[0081] Treatment of large volumes of slops (e.g. slurries) in oil and gas, and fish processing industries is costly and an environmentally challenging task. The present invention provides method(s) an apparatus for the treatment of oily contaminated drilling slops that can be used at on shore treatment facilities or offshore (rig-based) locations. The apparatus is (relatively) compact and mobile, is easy to operate, has lower energy cost and can handle a wide range of slops, from slightly contaminated to heavy mud e.g. up to 45%-65% solids.

[0082] The types of slurries that can be handled include:

[0083] 10% to 65% (by mass) solids 35% to 90% (by mass) liquid(s).

[0084] Sometimes slurries are referred to by their specific gravity (SG). For example, slurry with 1.52 SG may comprise by weight 31% oil, 36% water, and 33% solids. A slurry with 1.48 SG may comprise 30% oil, 36% water and 34% solids by weight. A slurry with 1.44 SG may comprise 32% oil, 38% water, and 30% solids by weight. Calculation and measurement of specific gravity of slurries may be undertaken by any known method.

[0085] The liquid component may comprise any variation of oil(s) and water.

[0086] The output streams of separated solids, oil(s) and water can be produced to high environmental standards such that water can be discharged to sewage or sea, solids can be sent to landfill, and oil(s) can be re-used as process fuels. The operating temperatures are relatively low (to avoid flashing or cracking of slurry constituents), typically up to around 240 C./250 C./260 C. or even lower, enabling use in hazardous environments (such as rigs).

[0087] Describing an example embodiment in general terms with reference to FIG. 1, apparatus 100 comprises a treatment chamber 20, condenser 30, fan 50, and vacuum pump 60. Whilst these components are preferably provided separately, one or more of these these may be combined together e.g. fan 50 and pump 60 may be combined in a vacuum pump and air (or inert gas) recirculation unit. Treatment chamber 20 comprises a slightly inclined, preferably watertight, preferably stainless steel, chamber with at least one and preferably two (preferably intermeshing) screw conveyors (not shown) 114A, 114B mounted inside it (see FIGS. 3 and 7). Screw conveyors 114A, 114B are shown as screw conveyor assembly 14 in FIG. 1. Both treatment chamber 20 and screw conveyor assembly 14 are double-walled and a thermal heated fluid, e.g. oil 12, is circulated in the intra-wall void. This enables treatment chamber 20 to be heated to a controlled, predetermined temperature. The material to be treated is introduced at one end, preferably a lower first end 20A, of treatment chamber 20 by a pump 10 and slowly drawn upwards toward a raised second end 20B by rotation of screw conveyor assembly 14. A water-cooled condenser 30 is connected to treatment chamber 20 and oil vapour, water vapour, and air are drawn into the condenser either by natural convention currents, or more preferably by fan 50. Liquid condenses out from the mixture of oil vapour, water vapour, and air and the dry air is re-circulated, preferably at low pressure (by the action of the vacuum pump 60) back to treatment chamber 20. At a lower portion of the raised second end 20B of treatment chamber 20, a rotary valve 124 is provided so that solids can exit treatment chamber 20 via outlet port 120 without adversely compromising the desired vacuum inside. Typically rotary valve 124 opens automatically, say 10 times an hour to allow product (e.g. solid(s)) to exit. Rotary valve may also be under manual control.

[0088] In operation, an externally heated thermal fluid 12 is pumped at a predetermined temperature through hollow flights (not shown) of screw conveyor assembly 14 to heat the slurry (and chamber) internally. Preferably, the same thermal fluid 12 is also circulated around optional heating jacket (not shown) of treatment chamber 20 to heat the chamber externally.

[0089] Thermal fluid 12 (although different heating arrangements may be used) is circulated through screw conveyor assembly 14 as will be explained later. At the same time, a partial vacuum is applied to the apparatus to reduce the pressure in the chamber to a desired level, typically about 0.5 bar or thereabouts. Preferably the desired temperature of slurry within the chamber is typically less than that required to crack or chemically change the materials to be treated and preferably also less than the flashpoint of the expected hydrocarbon content of the slurry given the prevailing pressure in the chamber.

[0090] Material to be treated, e.g. slurry, the flow of which is indicated by arrows 70, is introduced into treatment chamber 20 at inlet port 25 and drawn up, mixed, and internally heated by the action of the screw conveyor assembly 14. The heat and reduced pressure in the treatment chamber result in more efficient and effective vaporisation of the oil(s) and water from the solids within the slurry. The resultant vapour(s) 90 are drawn off, by small circulation currents of gas, preferably air, circulated by means of fan 50, and are drawn into the condenser 30. The vapour(s) 90 are returned to liquid form by the drop in temperature in condenser 30 and are collected in a collecting tank 45 by gravity. The resulting fluid can be further processed, e.g. by separation under gravity or by settling action, to separate the oil(s) and water. Meanwhile, the now dry air 80 is preferably recirculated back to treatment chamber 20, and solid(s) 130 are discharged via rotary valve 124 into solids holding bin 125.

[0091] In more detail now, FIG. 1 shows a schematic overview of treatment apparatus 100 according to one example embodiment of the invention. Treatment apparatus 100 comprises an inlet pump 10, a treatment chamber 20, condenser 30, optional separator 40, fan unit 50 (also known as a blower) and optional but preferable vacuum pump 60 and indeed a means to ensure a gas/air flow (e.g. a fan 50) is optional but preferable. Inlet pump 10 is connected to an inlet port 25 of treatment chamber 20 by an inlet duct 24. Material to be processed e.g. slurry 70 comprising liquids e.g. oil(s) and water, and solids, is pumped along material inlet duct 24 from inlet pump 10 into treatment chamber 20 via inlet port 25 at a first end 20A of treatment chamber 20. Optional temperature gauge 15 measures the temperature T1 of incoming material to be treated within inlet duct 24. For example, pump 10 may comprise a 1 inch vane pump for thinner (runnier) materials (e.g. <20% solids by weight). Alternatively, for example a 2.5 inch displacement pump can be used, capable of pumping material up to 70% solids by weight.

[0092] Treatment chamber 20 is typically elongate and may be, for example, 1 to 5 m in length or even longer and 0.2 to 3 m in diameter. Since material (slurry 70) is drawn along the chamber, as will be described later, the length of this journey (and the time it takes) is in part determined by the length of the chamber (or at least an operable part, e.g. a treatment zone, of the chamber). Thus, varying the length of the chamber provides a way of varying the treatment process as does varying the speed of drawing slurry along, and the temperature and pressure conditions within chamber 20. Different input materials will typically require different treatment process conditions. It is envisaged that, where the exact content of material to be treated is not known, the treatment chamber and treatment process conditions may be varied on the fly during processing until optimal conditions are achieved. Any poorly treated initial material can be re-mixed with further incoming material to be re-inputted into the treatment chamber once appropriate conditions are established.

[0093] The material to be treated typically comprises slurries i.e. mixture(s) of liquids and insoluble solids such as oil(s), solids, and water. Examples include drilling mud(s), drilling cuttings and macerated fish processing waste. The treatment comprises separation of solids from liquids so that the solids are substantially dry and/or substantially free from oil(s), i.e. the hydrocarbon component is reduced to a desired level, preferably without any cracking or chemical changes of the components. Where oil(s) are involved this means the temperature and other process conditions are preferably carefully controlled for safety reasons, for example, maintaining the conditions below the expected flashpoint of materials for the temperature and pressure conditions is desirable.

[0094] The treatment chamber 20 is preferably configured to contain liquids such as slurries e.g. by being a watertight container. Preferably this water tightness extends to the entire treatment chamber, and the inlet and outlet ports of the treatment chamber 20 and associated ducts and pipework, although in one embodiment only a lower portion of treatment chamber 20 may be designed to be watertight. Preferably the treatment chamber 20 is also airtight, so that it will support at least a small desired vacuum.

[0095] Supported within treatment chamber 20 is a material conveyor assembly 14 comprising at least one, but preferably comprising at least two twin screw conveyors (not shown). One or more alternative material conveyors may be used, but preferably twin screw conveyors and more preferably, intermeshed twin screw conveyors, even more preferably hollow flight, thermal, intermeshing twin screw conveyors, even more preferably self-cleaning, hollow flight, thermal, intermeshing twin screw conveyors are used (as will be described in more detail later). Thermal means heated by thermal methods e.g. circulation of thermal fluid.

[0096] A gearbox 18 driven by a motor 17 drives the material conveyor assembly 14 to transport material e.g. slurry from inlet port 25 towards an outlet port 120. The flow of slurry from the inlet port 25 towards an outlet port 120 for solids is indicated by arrows 70. Where two twin screw conveyors (not shown) are used, centrelines 16 in FIG. 1 illustrate their general location and general orientation within treatment chamber 20. Treatment chamber 20 is preferably double-walled to form an optional heated jacket and has an optional intra-wall volume (not shown) that may be heated via thermal oil 12. Heated thermal oil 12 is circulated via thermal oil inlet 21 and thermal oil outlet 22 within the external jacket (not shown) of treatment chamber 20. This provides external, even heat to the internal volume of chamber 20. An optional inert gas inlet system 57 (e.g. for nitrogen gas) may also be provided for providing inert gas (instead of air) for circulation in the chamber. Nevertheless, it is preferred to carry out the process in air, preferably under a slight vacuum.

[0097] Where one or more hollow flight screw conveyor(s) (not shown) are used, thermal oil may be circulated within the hollow flights to heat the external surfaces of the flights of the screw conveyor(s) that are in contact with material being treated. This results in internal heating of the slurry, whilst it is being mixed and drawn along by screw conveyor assembly 14. Furthermore, this internal heating is substantially even over the outer surface of the screw conveyor 14 and is relatively slow changing (and therefore gentle). Alternative methods and arrangements for providing internal heat to the material (preferably screw) conveyor assembly may be envisaged so as to provide internal heating and mixing of the slurry as is drawn along by the material conveyor assembly.

[0098] A gas outlet duct 27 is provided, preferably near the material inlet 25 (e.g. at or near the first end 20A of treatment chamber 20, or a treatment zone within the chamber 20) for extracting vapour(s) and gas 90 from the chamber via a gas outlet port 26. Where the slurry comprises oil(s), solids, and water, and air is used as a circulation medium, the extracted gas 90 will typically comprise air as well as oil vapours and water vapour both evaporated from the slurry being treated in treatment chamber 20. A temperature gauge 28 measures the temperature T2 of the extracted gas and a pressure gauge 29 measures the pressure P2 within gas outlet duct 27. The extracted mixture of gas and vapours 90 is passed into condenser 30. Condenser 30 is cooled by cooling medium e.g. water circulated around condenser 30 via cooling inlet 32 and water outlet 34. A tap 36 controls the flow of cooling water around the condenser. The temperature T3 of the cooling water may also be measured by a temperature gauge (not shown).

[0099] The oil(s) vapour and water vapour components of the extracted gas 90 condense into liquids within the condenser, the air and condensed liquids (typically an oil(s) and water mixture) are passed to separator 40 (this may be a simple T-piece) and the liquid drops out of liquid outlet 44 into a liquid container 45.

[0100] A temperature gauge 42 may be used to measure the temperature T4 of the gas at the exit of the condenser. Fan 50 draws the (now relatively) dry gas 80 from separator 40 and passes this via separator outlet 46 into recirculated gas duct 52. The temperature T5 and pressure P5 of the dry gas (typically air) within recirculated gas duct 52 are preferably measured here e.g. by temperature gauge 48 and pressure gauge 49. The air flow may be very low (e.g. around 0.5 m/second or less), just enough to cause a circulation of low pressure air into chamber 20 and out towards condenser 30 dragging evaporated vapours with it.

[0101] Vacuum pump 60 is connected by a valve 61 and vacuum duct 54 to recirculated gas duct 52 and recirculated gas inlet duct 56 leading to recirculated gas inlet port 58 of treatment chamber 20. Optionally an air and liquid outlet 59 is also provided leading to a drip tray 55 (for any liquid not yet removed). The vacuum pump 60 reduces the pressure within recirculated gas duct 52 and recirculated gas inlet duct 54 and also within the treatment chamber to provide a slight vacuum (e.g. <1 bar, more typically between about 0.25 to about 0.75 bar, and preferably about 0.5 bar or about 0.4 bar). Whilst using a vacuum and a vacuum pump 60 is optional, it is desirable for reasons as explained elsewhere.

[0102] Fan 50, working in combination with vacuum pump 60, circulates recycled warm, dry or at least drier, gas 80 (typically air) through the treatment chamber 20, condenser 30, separator 40 and back into the treatment chamber 20 (via air inlet port 58).

[0103] Material to be treated, typically slurries comprising liquids and insoluble particles, such as, slurries of one or more oils, water and solids (e.g. drilling mud, drill cuttings and water, macerated fish waste etc.), is introduced into the chamber 20 at inlet end 20A via inlet port 25 and is drawn along the chamber towards the dry air inlet 58 and product outlet 120 by the material conveyor assembly 14. Material conveyor 14 can transport solids and liquids along it, and it heats and mixes these as it does so.

[0104] Product outlet 120 is provided at second end 20B of treatment chamber 20 (or at the end of a treatment zone) for receiving treated material (typically now substantially dry solids 130). A valve 124, preferably a rotary valve, allows exit of product usually now substantially dry solids from chamber 20 into a receiving bin 125 whilst maintaining a vacuum within chamber 20. A temperature gauge 123 may be used to measure the temperature T6 of the exiting solids.

[0105] During the travel of material from first end 20A to a second end 20B of treatment chamber 20, the material (e.g. slurry) is internally heated from the heated material conveyor assembly 14 (typically around 85% of heat is provided internally in this way) and optionally externally heated by heat from the external jacket (not shown) (typically up to 15% of heat is provided externally in this way). Oil(s) vapours and water vapour 110 evaporate because of the heat and low pressure and rise out of the material into air flow 80 to be carried back towards the first end 20A of treatment chamber 20 and out via gas outlet port 26. As the material (e.g. slurry) traverses the chamber from inlet first end 20A to second end 20B, it is continually heated and mixed preferably under a vacuum, preferably a slight vacuum of just under 0.5 bar (e.g. 0.4-0.5 bar). The material is progressively dried, preferably very gently, so that substantially all liquid phases evaporate by the time the material reaches the second end 20A of the chamber. Thus, the liquid components (e.g. oil(s) and water) have been removed and the solid component (e.g. dry sand, dry drill cuttings) remains to exit the chamber at outlet port 120.

[0106] The heat (and vacuum) provided to the chamber via internal heating from the screw conveyor and the optional external jacket (not shown) is controlled and is not sufficient to crack or chemically charge the components of the material being treated (e.g. slurry). Rather, the heat is sufficient to cause phase changes from liquid to vapour enabling oil(s) vapours and water vapour to be driven off from the slurry, thereby drying the slurry out as it traverses chamber 20. The slurry must therefore spend sufficient time within the chamber under the right process conditions for this to occur. Preferably the conditions (e.g. of temperature, pressure) are identified at which vapours (e.g. of oil and water) emerge from the slurry are first identified and these conditions are then maintained for a suitable period of time. For example for a slurry of SG 1.55 solids, oils and water, water and oil vapour may first be observed at 50 C. or at around 60 C. at less than atmospheric pressure of around e.g. 0.5 bar (0.5 bar below atmospheric)see FIG. 11C.

[0107] Treatment chamber 20 is preferably configured (as will be described with reference to FIG. 2) so that the slurry (and liquids within it) tends to congregate towards first end 20A, and drier components (the solids) are lifted out of the slurry towards a second end 20B.

[0108] One or more temperatures around the apparatus 100 may be measured and used to feedback control to the system, as well as varied depending upon the type of slurry and % solid content being treated. Typically, slurry is at ambient temperature (e.g. 5-25 C. or even 0-35 C.) when it is loaded into the chamber. T2 is the temperature of the gas and vapours discharging from the treatment chamber. This vapour discharge temperature T2 entering the condenser may be around 125 C. In a preferred low temperature, low energy embodiment, T2 is less than 100 C., or 50 C.-100 C., or 60 C.-100 C., or 60 C.-80 C., at 65 C.-75 C. This can be achieved more easily when the system is at less than atmospheric pressure e.g. around 0.5 bar, or 0.4-0.5 bar. The slightly contaminated warm air from the condenser is reintroduced at the second end 20B giving a warm circulation air flow into the chamber. T3 is the cooling water temperature. T4 is the air temperature exiting the condenser. T5 is the air temperature leading back to the chamber (these are usually the same). T6 is the temperature of the discharged solids, and if no internal temperature sensor is provided, may be used as an estimate of the slurry temperatures.

[0109] FIG. 2 shows an example treatment chamber 20 that may be used. Treatment chamber 20 has a central longitudinal axis 142 which is inclined at a small angle to the horizontal 144. Typically the screw conveyor assembly is in line with the chamber so its longitudinal axis is parallel to that of the axis 142 of chamber 20 (although offset downwardly as seen in FIG. 3). Treatment chamber 20 therefore has a lower first end 20A and an upper second end 20B and screw conveyor assembly 14 is also corresponding lower at a first end compared ti its second end. Typically, upper second end 20B of chamber 20 is 5 to 50 cm above lower first end 20A (e.g. as measured at corresponding locations). The magnitude of the difference in height selected will, of course, depend on the length and diameter of the chamber and the length and diameter of the screw conveyor assembly, and the angle .

[0110] Alternatively, the chamber itself may be generally horizontal and the screw conveyor assembly 14 may be at an angle within it so as to be at a predetermined angle with respect to the horizontal.

[0111] In this example, treatment chamber 20 is mounted on frame 140, and variable height mountings 141 are provided at or near each end 20A, 20B, to facilitate variation of inclination angle .

[0112] FIGS. 3 and 4 show respectively cross sectional and plan view of twin hollow thermal screw conveyors 114A, 114B forming a screw conveyor assembly 114 for use in the chamber of FIG. 2.

[0113] A thermally heated screw conveyor assembly 114 (seen in FIG. 3), comprising thermally heated hollow flight, intermeshing twin screw conveyors 114A and 114B, is provided extending from lower first end 20A to upper second end 20B. Although not shown in FIG. 2, the centrelines 16 of screw conveyors 114A and 114B are typically substantially or generally parallel to the centreline e.g. the central longitudinal axis 142 of treatment chamber 20. In other words, screw conveyors 114A and 114B are also at a small angle with respect to the horizontal. This slight inclination and the watertight nature of chamber 20 (or at least a lower portion thereof) means that liquidised slurries are contained in a lower portion of chamber 20 and these will tend under gravity to lie towards the first end 20A. The expected average surface level 200 of such fluidised slurries (which will be generally horizontal at a first end 20A of the chamber) will lie at a small angle to the screw conveyors 114A and 114B. Thus screw conveyors 114A, 114B will rise out of the slurry towards second end 20B. At or near the lower first end 20A of the chamber 20, the screw conveyors 114A, 114B are expected typically to be completely covered in slurry, whilst at or near the upper second end 20B of the chamber 20, the screw conveyors 114A, 114B will lie at least partially or completely above the expected upper surface level 200 of the liquidised slurry near the first end of 20A, and/or indeed above the expected upper surface level of solids near the upper second end 20B. If the chamber is horizontal but only the screw conveyor(s) are at an angle to the horizontal, these will still emerge above the level of drying slurry or solids near the second end 20B, but the first and second ends of the chamber will be at the same level. A motor and gear box are typically provided opposite second end 20B (not shown) to drive the twin screw conveyors 114A, 114B.

[0114] Treatment chamber 20 comprises a slurry inlet port 25, a solids outlet chute 130 and a solids outlet port 120. Chamber 20 comprises a thermal oil inlet 21 and a thermal oil outlet 22 for circulating thermal oil at a predetermined temperature Toil to heat chamber 20 internally via a hollow material conveyor assembly preferably a hollow flight screw conveyor (not shown).

[0115] In FIG. 2, slurry enters under gravity via inlet port 25 and is temporarily held in receiving cavity 145 by weir 146A extending centrally inwards (typically upwards from the floor and alternatively, or in addition, optionally a weir 146B downwards from the roof) of treatment chamber 20. The cavity 145 and weir(s) 146A, 146B may be offset from the centre of the treatment chamber, or indeed in a side chamber, so the incoming slurry does not fall directly on the screw conveyor assembly 114.

[0116] In a preferred embodiment, particularly suitable for less flowable or thicker slurries, downwardly projecting weir 146B (downwardly projecting from the roof of the chamber) may be provided with a generally or substantially horizontal lower bottom edge 147 which terminates just above the level of the screw conveyors 114A, 114B at the first end of the chamber. This bottom edge 147 is shown in FIG. 3 as a dotted line. This downwardly projecting weir 146B functions to hold back slowly flowing thicker slurries from entering and flooding the chamber. Thicker slurries do not equalise levels quickly and not within the timescale of the transport of material e.g. 1 to 5 revolutions per minute. The bottom edge 147 of downwardly projecting weir 146B helps determine and control the level of slurry at the start of the chamber, i.e. typically just above the level of the screw conveyors 114A, 114B at that end of the chamber.

[0117] Treatment chamber 20 preferably has a double-walled construction (not shown) to also allow heating fluid such as thermal oil to flow in the intra-wall volume providing an externally heated jacket to the internal volume of chamber 20. Preferably, thermal oil (not steam) is circulated in the hollow flights of screw conveyors 114A, 114B to provide internal heating of chamber 20 via inlet port 21 and outlet port 22. Optionally, thermal oil is circulated to double walled external jacket of chamber 20 via inlet port 21 and outlet port 22.

[0118] Other ways for heating the internal volume of chamber 20 may be used (e.g. electrical heating) although thermal oil heating is preferred for both internal and external heating for safety reasons, in part because of the dispersed and slowly changing nature of the heat provided, which can be important to avoid localised overheating of hydrocarbons.

[0119] The twin screw conveyors 114A, 114B are therefore preferably thermally heated e.g. by thermal oil (for reasons already stated elsewhere) passing through hollow flights to provide heated external surfaces over the flights and, to the furthermost tip of the flights. Heating the flights (preferably substantially over their external surface and preferably evenly to the tip of the flights) assists in ensuring there are no hot or cold spots that may cause inadvertent overheating or overcooling of the material during treatment. This, in turn, assists in preventing adhesion of debris to the flights and reduces risks of exceeding the flashpoint of the materials being treated. The internal heating will be described in more detail in relation to FIG. 7.

[0120] Recirculated air 80 (indicated by arrows 80) enters chamber 20 by air inlet port 80 and travels in a generally opposing direction to the flow of slurry (arrows 70) and solids (arrows 130) through chamber 20. The size, shape and configuration of the various inlet and outlet ports, and the ducts described, may be varied and is limited only by nature, volume and weight of the material volumes being passed through them, and the need for watertight, and/or airtight fixings where described.

[0121] In one or more embodiments the present invention makes use of the relationship between the phase transition points of a substance and ambient pressure. As the pressure is decreased, so does the temperature of the liquid to gas phase transition of the substance. By ensuring a good seal throughout the apparatus and partial vacuum up to around 0.5 bar below atmospheric (e.g. 0.5 bar), lower temperatures may be used more effectively to separate gas/vapour(s) and dry solids, improving energy efficiency.

[0122] One example of a suitable treatment chamber is a hollow screw heat exchanger chamber of diameter of around 1 m and length around 8 m available from Thies GMbH Germany and this may be capable of processing 1000 /hour of slurry. Whilst a cylindrically shaped treatment chamber is preferred, alternative shapes may be used.

[0123] The chamber must have sufficient internal volume to allow the hollow screw conveyor to emerge from material being treated at a second end of the chamber and for gas to flow freely through the chamber preferably from the second end towards the first end. Thus there will preferably be a gap between the outermost periphery of the hollow screw conveyor and an innermost surface of the roof of the treatment chamber.

[0124] The treatment chamber 20 is in fluid communication with the condenser. One or both of the first and second ends 20A, 20B of the chamber may be at the very end walls of the chamber or somewhat inwardly displaced from the end walls of the chamber, in other words a treatment zone between the first and second ends may be smaller than actual dimension between end walls of the treatment chamber.

[0125] Separator 40 may be, for example, a disk stack centrifuge suitable for separating out oil, water, and any solids carried over from treatment chamber 20. Alternatively, separator 40 may comprise a simple T-piece (gas flows on, liquid(s) drop out).

[0126] The fan or blower 50 need not be particularly powerful, just sufficient to gently blow air (or indeed inert gas) around the system. Typical air speeds might be 0.5 to 5 metres per minute or less. Under a partial vacuum, air will not easily circulate and fan 50 ensures a slow, gentle air circulation occurs.

[0127] The temperature of the thermal oil circulating in the hollow flight screw conveyors is typically 150 C.-280 C., more preferably 175 C.-250 C., more preferably 240 C. or 250 C. The vacuum may be less around 0.5 to 1 bar, preferably around 0.4 to 0.5 bar (1 bar being atmospheric pressure e.g. 760 mm Hg). In a preferred lower energy embodiment, the temperature of the oil may be around 200 C. or 180 C.-220 C. or 190 C.-210 C. This is shown over time to deliver a slurry temperature of less than around 100 C. and more typically 50 C.-100 C. or 60 C.-80 C. or, at or around 80 C., the temperature at which water and oil vapours start to emerge from the slurry, under a slight vacuum (less than 1 bar typically 0.4-0.5 bar). In a more preferred, even lower energy embodiment (see FIGS. 11A to 11G), the temperature of the oil may be 130 C.-180 C., or 135 C.-175 C. Examples of this and typical temperatures of gas/vapour(s) extracted (60 C.-80 C.) are shown in FIGS. 11A to 11G.

[0128] During operation, T2, the temperature of extracted air and vapours may rise to around 115 C. depending upon the product. In a preferred lower energy embodiment the temperature of the extracted air and vapour is maintained at around 50 C.-100 C., or more preferably 60 C.-80 C. or around 60 C., or 60 C.-100 C., or at or around 80 C., or 50 C., or 60 C., or 70 C., or 80 C., or 90 C., or 100 C. Following first introduction, the slurry may take about 30 to 60 minutes to pass through (with substantially dry solids exiting at the second end 20B after this time). This will depend on the speed of rotation of the conveyor, temperature of the conveyor (and temperature and pressure in the chamber), level of vacuum etc. To begin with the slurry will tend to accumulate (under gravity at the first end 20A of the treatment chamber). The conveyor will nevertheless try to draw the slurry towards the second end and under optimal conditions succeeding when sufficient liquid has been evaporated and extracted to leave solid(s) behind which are then drawn along.

[0129] Thermal oil can operate up to around 350 C., however, desired temperature range in the chamber (because of the assistance of vacuum in changing the phase transition points of the liquid(s)) is around 200 C. to 280 C. or more preferably around 240 C. to 260 C. Even more preferably in a lower temperature embodiment, the thermal oil may be 180 C.-220 C., or 190 C.-210 C. or around 200 C. or even as low as 130 C.-180 C. (see FIGS. 11A to 11G).

[0130] The rotary valve typically opens around 10 times an hour. The screw conveyors (seen in FIGS. 3 to 7) typically rotate around 2 to 5 times per minute, preferably 2.5 or 5 times per minute, although even slower speeds of 1 or 1.5 times per minute can be used, especially in preferred lower energy embodiments.

[0131] During the transport of the slurry along the rotating screw conveyors 14, 114A, 114B (see FIGS. 2 to 7), an intense heat exchange happens between the screw conveyors and the chamber contents as these are in direct contact with each other. Typically thermal oil will travel up a central shaft of a screw conveyor and back down through the continuous intra-wall volume of the hollow flights (see FIG. 7). Alternatively, thermal fluid e.g. therma oil can be configured to travel firstly up the hollow flights from an inlet and back down the central shaft before exiting The twin screw conveyors 114A 114B may be geared to rotate at slightly different speeds and/or to have certain outer flight profiles, so as to self-clean against one another. The twin screw conveyors 114A, 114B also have variable speed control to provide control over the revolutions per minute.

[0132] Preferably, internal heating is provided via the flights of the screw conveyors, as this is most efficient. Where external heating is provided e.g. a thermal jacket outside the chamber, it is still preferred that approximately 85% of the heat is still derived from internal heating via the screw conveyors. Experiments have shown that, even in a small trial chamber, 80 to 100 litres per hour of slurry can be processed.

[0133] The angle of incline a of the chamber (and hence the screw conveyors) can be varied and is typically 2.5 to 10, preferably 2.5 to 5, more preferably 5, to the horizontal. The inclination of the screw conveyor assembly (and typically also the treatment chamber in which it is mounted) is preferably varied to optimise for the type of incoming material. For example, a steeper incline, say of 5 or more to the horizontal, may be useful for wetter slurries with a lower percentage of solids, so that the dwell time in the chamber is longer, whereas a lower incline, say 2.5 to the horizontal may be useful for drier slurries with a higher percentage of solids. Similarly the speed of rotation of the screw conveyor can be varied to increase or decrease the level of agitation and dwell time within the chamber. Preferably the thermal oil is at 240 to 260 C., more preferably 240 to 250 C. and the vapour extract temperature is 140 C. to 150 C., or more preferably 60 C.-150 C., 60 C., 70 C., 80 C., 90 C., 100 C. or 60 C.-100 C., 60 C.-80 C. or around 80 C. (see also FIGS. 11A to 11G).

[0134] Because of the internal thermal heating, heat is distributed evenly over outer surface of the two interlocking, heated, hollow flight screw conveyors. This is desirable as it maintains drying throughout the chamber from first to second ends. The solids should reach the required moisture level just before the discharge chute 132. The degree of moisture in the exiting solids can be controlled by controlling one or more of the input rate of slurry, angle of incline, temperature of the thermal oil, vacuum, airflow and rotation of the screw conveyors, to optimise the process for particular input materials.

[0135] FIG. 5 shows alternative screw conveyors 214A, 214B and solids 130 (here sand) just prior to egress from the chamber via outlet chute 132 and outlet port 120 into a solids collecting bin 125.

[0136] FIG. 6 shows a typical, long (e.g. 3 to 5 m) screw conveyor 114A, 114B in isolation with hollow flights 154. This might be used in a larger machine or for faster flow rates, to assist in ensuring sufficient dwell time drying within treatment chamber 20.

[0137] FIG. 7 shows a cross-sectional view of a screw-conveyor 114A, 114B with a thermal fluid inlet 21 and thermal fluid outlet 22. The screw conveyors preferably are circular in cross-section (see FIG. 3). The thermal fluid is preferably oil. Preferably oil travels in from inlet 21 through a hollow central shaft of screw conveyor 114A, 114B. The inlet of oil is indicated by arrows 112A. In this example embodiment, the central shaft 114 widens into an internal chamber 150 towards a distal end before exiting chamber 150 into a continuous spiral shaped hollow chamber 152 within hollow flights 154. The oil then flows around outside the central shaft and chamber 150, spiraling around the spiral hollow chamber 152 within hollow flights 154 as shown by arrows 112B, taking heat from oil in the central shaft 149 and chamber 150, and providing heat to the surrounding slurry being treated. Preferably the flights are evenly spaced and evenly sized along the length of screw conveyors 114A, 114B. Thus, in one example embodiment, the slurry being treated (see arrows 70 in FIG. 2) is travelling in a generally opposing direction to the overall direction of travel of thermal oil, in the hollow flights 154, back along the chamber from second end 20B to first end 20A. Alternatively, in certain circumstances e.g. when particularly intense heating is needed at the start of the chamber 20, the thermal fluid flow can be configured such that thermal fluid, e.g. oil, may be inputted first into the hollow flights 152 (in a direction opposite to arrows 112B in FIG. 7) to then be transported to the very tips of the hollow flights and the distal end of the hollow flight thermal screw conveyor 114A, 114B then back down through the central chamber 150 in a direction opposite to arrows 112A, before exiting the screw conveyor 114A, 114B at a proximal end.

[0138] In FIG. 8, method steps for a method 200 of treating material such as slurries comprising liquid(s) and insoluble solids, and in particular slurries comprising solids, oil(s) and water, are shown. Method 200 comprises the step 202 of providing a vacuum in a treatment chamber. Step 204 comprises providing a heated material conveyor, preferably a screw conveyor assembly as described elsewhere herein. Next, step 206 comprises introducing slurry into the chamber, preferably continually, or quasi-continually (e.g. in repeated batches). Next, step 208 comprises, heating, mixing and conveying the slurry through the chamber 20. Preferably the heating is internally applied to the slurry in the chamber e.g. by means of a thermally heated material conveyor, preferably a thermally heated screw conveyor as described elsewhere herein. Optionally, external heating (e.g. from an external jacket to chamber 20, and/or recirculating warm gas) may be provided. Next step 210 comprises evaporating liquid(s) from the slurry. Typically, this occurs because of heating and low pressure) but preferably also because of the mixing to distribute heat and bring inner material so the surface of the slurry, so liquids can more easily evaporate.

[0139] The provision of a slight vacuum e.g. <1 bar or 0.25 to 0.75 bar, about 0.4 bar or about 0.5 bar, or preferably 0.4-0.5 bar, assists in evaporation by lowering the ambient pressure, lowering the temperature at which evaporation can occur. Nevertheless, provision of a heating and a vacuum, and evaporation of vapour(s) from the slurry may not be enough to drive the vapours by convection alone towards the condenser. In any case, provision of a small, gentle (low pressure) gas flow (preferably air or inert gas) provides a circulation of vapour(s) out of treatment chamber 20, but also ensures as the gas above the slurry becomes loaded with vapours, it is moved away to be replaced with drier (preferably re-circulated) gas. This replacement of damp air (or gas) with dry air (or gas) provides a beneficial diffusion gradient encouraging further evaporation of liquid(s).

[0140] Step 212 comprises extracting vapours from the treatment chambers 20. Step 214 comprises condensing the oil(s) vapours and water vapour into liquid oil(s) and liquid water. Step 216 comprises removing solids 130 from the treatment chamber 20.

[0141] It will be understood, that the steps of the method may occur in one or more sequences sequentially, or contemporaneously.

[0142] In FIG. 9 several optional preferred steps are shown. Step 218 comprises maintaining temperature and pressure conditions below the flash points of the materials involved. (The flash point is the temperature/pressure combination at which vapour(s) above a liquid will ignite in the presence of a spark. Step 220 comprises maintaining a dwell time in treatment chamber 20 and/or temperature and/or vacuum conditions sufficient to dry slurry into solids to a desired moisture level e.g. <1% by weight (e.g. of water or hydrocarbons). Step 222 comprises circulating preferably re-circulating gas, preferably air. Step 224 comprises separating condensed liquid(s) from gas. A further optional step comprises separating liquids e.g. oil(s) from water.

[0143] FIGS. 10A to 10D show various experiments conducting using method(s) and apparatus of the invention.

[0144] In FIG. 10A, watery muddy at 8 C. is treated, and in most cases dried, in a treatment chamber 20 such as that shown in FIGS. 1 and 2 with, in this case, twin thermally heated hollow flight screw conveyors and an external jacket. The thermal oil circulating in the hollow flights and external jacket enters inlet ports 21, 21 at 250 C. and exits at the temperatures shown (Toil Out). The air was not recirculated and the air temperature T5 entering the chamber at 20 via air inlet duct 56 was 10 C. The air exit temperature T2 is as shown. The inclination of chamber 20 was 5 degrees (although 2.5 degrees has been tried) and the screw conveyors 114A, 114B were rotated in a self-cleaning manner (at slightly different speeds) at 2.5 revolutions per minute. The slurry flow rate was increased from 10 l/h to 100 l/h. The product (solids 130) at exit via chute 132 and outlet port 120 varied from slightly moist to entirely dry.

[0145] The slightly moist result might be explained by the apparatus warming up.

[0146] FIG. 10B shows brief results from a single run inputting a thick slurry comprising about 65% solids by weight at a high flow rate of 120 l/h. The exiting solids were entirely dry.

[0147] FIG. 10C shows results for a watery slurry after a partial vacuum and a fan to circulate were introduced. A watery slurry was inputted, and an initial thermal oil temperature of 200 C. was used. This was not sufficient a flow rate of 60 l/h and the exiting solids 130 were wet. Once the thermal oil temperature increased to 240 C. (and the exiting oil temperature was above 220 C.), even at a relatively high flow rate of 80 l/h and 100 l/h, the exiting solids were dry.

[0148] FIG. 10D shows results for, firstly, a watery slurry with a thermal oil input temperature Toil-In of 200 C. at 2.5 revolutions per minute. It appears that once the thermal oil heated to 225 C. and the chamber had heated up (e.g. as evidence by exiting air temperature T2 increasing from 130 C. to 160 C.), dry product (solids 130) was produced. After cleaning and pump testing, in a second experiment with a watery slurry of 15%-20% solids by weight a thermal temperature of 240 C. and 1.5 revolutions per minute produced very dry product (solids 130) at 60 l/h and 80 l/h.

[0149] However once the flow rate was increased to 90 l/h then 100 l/h the exiting product (solids 130) was slightly moist, indicating a variation in process conditions may be required. For example the thermal oil input temperature was not able to be maintained at 240 C. (the thermal oil is recirculated, dropping to 238 C. then to 228 C. indicating that the throughput load of slurry, or % of liquid in the slurry may have been less than optimal.

[0150] Following analysis, the oil distillate from similar experiments using the method(s) and/or apparatus of the invention, from drilling mud or cuttings was thought to be (by flash point and boiling point analysis) a mixture of hydrocarbons e.g. a fraction of crude oil distillation such as diesel oil, although a non-smoky flame associated with unsaturated aliphatic hydrocarbons indicated it may be kerosene or diesel oil. The oil distillate may therefore be used as a fuel or for re-use in drilling muds. Further analysis showed that the aqueous distillate was of low conductivity although slightly contaminated by oil. Oil and water could be easily separated by a tilt-plate separator. Exiting solids were predominantly composed of finely ground rock with elemental metals together with about 2.5% oil. These could be disposed to landfill under appropriate license or reused in asphaltic road tarmacadam or lightweight concrete.

[0151] Later results from experiments 3 and 4 (see FIGS. 10C and 10D) provided water samples that have been analysed and found to be pure enough to be fit for disposal to the public sewer in the UK.

[0152] FIGS. 11A to 11D show various experimental results. FIG. 11A shows results for a thick slurry with no vacuum requiring T.sub.oilIn at 210 C. and with (relatively) hot extracted gases at 120 C., but in which good separation was achieved.

[0153] FIG. 11B shows a similar thick slurry in which a reduction in air pressure from 1 atmosphere by 0.1 bar (to 0.9 bar) initially and then 0.5 bar (to 0.5 bar) enabled a reduction in heat into the system. The thermal oil temperature could be reduced from180 C. to 150 C. then 135 C. with good results.

[0154] FIG. 11C shows a repeat of the same conditions of the last stage of Table 6 (FIG. 11B) but with a slightly wetter slurry of specific gravity 1.55. Good results were obtained.

[0155] FIG. 11D shows similar results, although for the slightly wetter slurry of SG 1.35, a T.sub.oilIn of 155 C. to give good separation at higher slurry flow rate of 120 l/h at 1.5 revs/min.

[0156] FIG. 11E shows a thicker slurry at the higher flow rate of 120 l/h, whereas FIG. 11F shows a wetter slurry of SG 1.35 at the higher flow rate of 120 l/h required T.sub.oilIn of 155 C., but could be improved upon. Raising the T.sub.oilIn to 175 C. and lowering the flow rate to 110 l/h improved matters, as shown in FIG. 11G.

[0157] Inclination of screw conveyors and chambers in all these embodiments is 5.

[0158] Variations on the described apparatus and method(s) may be apparent to those skilled in the art from the information contained therein. All such variations are intended to be within the scope of the present invention. For example, although twin (preferably hollow) screw conveyors are described, triple, or more preferably quadruple (or greater numbers) of (preferably hollow) screw conveyors may be used. Preferably these will all lie in the same plane and interact one with another, e.g. conveyor 1 with conveyor 2, conveyor 2 with conveyors 1 and 3, conveyor 3 with conveyors 2 and 4, and conveyor 4 with conveyor 3. Or two twin conveyors may be provided (screw conveyor 1 interacting with conveyor 2, and conveyor 3 interacting with conveyor 4). The exact arrangement of the being selected (along with process conditions) to suit the nature of the slurry being separated and dried. Also whilst co-rotation is preferred (e.g. all screw conveyors, where used, rotate in the same direction, say anti-clockwise), it is envisaged that counter rotating screw conveyors may be used.