WO2006032845A1

WO2006032845A1 - Soil cleaning method and apparatus

Info

Publication number: WO2006032845A1
Application number: PCT/GB2005/003481
Authority: WO
Inventors: John Russell Tippetts; Geoffrey Hugh Priestman
Original assignee: University Of Sheffield
Priority date: 2004-09-23
Filing date: 2005-09-08
Publication date: 2006-03-30
Also published as: GB2418347A; GB0421092D0

Abstract

A soil/sand cleaning reactor (10) comprises one or two cylinders (18, 20) each having a jet (28) directed towards each other or a target. The jets are immersed in water (14) in a tank (12) and a pump (42) is operated in two modes of operation. In one, both cylinders are pumped simultaneously so that streams issuing from the jets (28) collide and sand/soil particles entrained in the flow are scrubbed. In the second mode of operation the cylinders are pumped alternately. Flow from cylinder enters the other, cavitation occurring on exit of the flow from each jet and implosion occurring in the high pressure region of the other jet, such cavitation and implosion effecting scrubbing of the sand/soil particles. Alternatively, there is just one cylinder (18) whose jet is directed at a target (150). In one mode, water pumped out of the cylinder impacts the target, effecting a scrubbing action on the entrained sand/soil, while in a suction mode, bubbles formed adjacent the mouth (32) by the low pressure there cavitates in the diffuser (30), effecting a further scrubbing action.

Description

Soil Cleaning Method and Apparatus

This invention is in the field of soil cleaning and reclamation.

In many areas, soil becomes contaminated with a variety of contaminants. On the whole, contaminants are water insoluble, since water-soluble contaminants generally get washed away, perhaps to contaminate ground water, outside the scope of the present invention. Insoluble_^ contaminants can be removed by using solvents, but frequently solvents cause as much difficulty and environmental damage as the contaminants alone. Consequently, alternative methods are sought, often involving water and means to scrub soil to dislodge oily contaminants adhered to the surface' of soil particles. The contaminants then enter suspension in the water and, later, can separate therefrom in settling tanks.

WO-A-9942218 includes a discussion of the various techniques that exist to remove oil from particulate material and that have been -tried in the past. That patent is primarily concerned with recovery of heavy oil from production sand. The present invention also has application in that field, as well as in soil cleaning.

WO-A-9942218 discloses a complete separation system involving multiple stages in which produced oily sand is fed to first separators in which hot water and steam achieve a first stage of separation. Slop oil and water mixture float off the top of oily sand that is pumped by a jet pump to^' subsequent reactors disposed in series with one another. The oily sand entering a first of these reactors is passed through a jet in the reactor that entrains flow of liquid and oily particles already in the reactor. The jet causes, through the substantial drop in pressure on exit from the jet, immediate vapour bubble formation on the particles. The jet is directed into a tubular chamber in which the bubbles just formed cavitate violently, causing a scrubbing action that strips oil adhered to the particles. Finally the particles impact a target at the exit of the tubular chamber and heavy, relatively non-oily, particles drop to the base of the tank, while lighter, oily particles impinge upwardly to, potentially, be recycled though the scrubbing process. Separated oil floats to the surface, where it is recovered. The non-oily particles are withdrawn by another jet pump at the base of each reactor to be passed to the next reactor and form the entry jet of the next reactor.

It is an object of the present invention to provide a reactor and process which improves the scrubbing process.

In accordance with the invention there is provided a sand/soil cleaning reactor comprising a cylinder having top and bottom ends, the bottom end entering a reaction tank and forming a reverse diffuser disposed adjacent a target against which a jet issuing from the reverse diffuser is directed, and the top end being connected to fluid drive means, whereby the reactor operates in two cycled modes, in a first mode of which, water is pumped out of said cylinder into said reaction tank by said fluid drive means against said target so that the sand/soil is cleaned by virtue of the scrubbing action caused by said sand/soil impacting said target, and in a second mode of which, water in which said sand/soil is entrained is drawn into said cylinder from said reaction tank by said fluid drive means so that the sand/soil is cleaned by virtue of the scrubbing action caused by cavitation of bubbles formed in said reverse diffuser. Preferably, said cylinder is quiescent, whereby lighter-than-water contaminants separated from the sand/soil floats to the surface of the water in the cylinder for subsequent separation.

Preferably, said fluid drive means comprises pneumatic pump means. In said first mode, a space above the water level in the cylinder is pressurised, while in said second mode said space is evacuated.

Preferably, two of said cylinders are disposed in said reaction tank, with their respective reverse diffusers facing one another, and said modes of operation are cycled in each cylinder in-phase, whereby said target for each diffuser comprises the output of the other diffuser, and said impacting of sand/soil issuing from one diffuser is with sand/soil issuing from the other diffuser.

In accordance with a different aspect of the present invention, there is provided a sand/soil cleaning reactor comprising two cylinders having top and bottom ends, the bottom ends of which enter a reaction tank and are formed as jets directed towards one another, and a pump to drive a mixture of water and sand/soil in the cylinders out of the jets and to draw said mixture from the tank into the cylinders through the jets, wherein the reactor is arranged to operate in at least one of two modes of operation: in a first of said modes, the cylinders are pumped alternately in cyclic phases, one cylinder expelling mixture through its jet and the other admitting mixture through its jet, there being minimal change in level of mixture in the reactor tank, whereby cavitation occurs in the mixture between said jets and implosion and resultant scrubbing of said sand/soil occurs inside the jet of said other cylinder; and in a second of said modes, the cylinders are pumped simultaneously in cyclic phases, there being maximal change in level of mixture in the tank between said phases and, during a pressure phase, the streams of mixture exiting each jet impinge on one another, whereby collisions of sand/soil particles between said jets effects scrubbing of them.

Thus two modes of operation are provided. In the alternate flow operation, the water and sand is driven from one jet, though the tank, and into the jet of the other cylinder. Preferably, the jets are arranged so that, in said first mode, they are close enough to one another that the motive power to fill the other cylinder is primarily provided by the stream of mixture from the issuing jet. Preferably, the jets are arranged so that, in said first mode, they are separated from one another so that mixture in the tank is entrained in the flow to said other cylinder. In any event, the drop in pressure of the stream exiting the jet causes vapour bubble formation (cavitation) which, as soon as the stream enters the other jet which is under relatively higher pressure, immediately implode causing scrubbing of the particles adjacent the bubbles.

In the simultaneous mode of operation, when the cylinders are being pumped, the streams issuing from each jet collide with one another and so the particles are scrubbed by a different mechanism of collision between them. -Which scrubbing action is the more effective is a matter to be determined by trial, but it is possible that the two methods have different effects whereby it would be appropriate to employ the simultaneous mode first, followed by the cyclic mode second, or vice versa. Preferably, said pump is a pneumatic pump, arranged to drive air into the top of the cylinders above the mixture level therein, and, to evacuate air therefrom when the cylinders are being refilled. The advantage of pneumatic pumping is that it does not suffer the problems of pumping water. That problem is one of dealing with the entrained particles, if the pumping is from the bottom of the cylinders, or of dealing with the oil trying to separate out of the water if the pumping is from the top of the cylinders. Nevertheless, that method of pumping is feasible (see below) .

In the case of pneumatic pumping, the level of mixture in each cylinder may be arranged to oscillate between a full position and a low position above the level of the jets. Some mixture is preferably retained in the cylinder beneath said low position, which mixture is relatively quiescent, so oil separated from sand/soil particles by said scrubbing has the opportunity to float to the top of the water in the cylinder, a weir being provided near said full position over which said oil can overflow for reclamation.

An oil coalescer may be disposed in the cylinder beneath said weir. And a particle strainer may be disposed in the cylinder beneath the coalescer. The weir may comprise a side cylinder. An exit for overspill from said weir in said side cylinder preferably includes a level controller to prevent air blowing through said exit. The level controller may comprise a STuVA valve.

In either mode of operation, the cylinders are filled each cycle, by evacuation of their top ends and/or by pumping from the jet of the other cylinder, depending on the mode. In each case, most of the water and soil/sand particles entrained in the water, is arranged to fill the or each cylinder, leaving only a residual amount in the reaction tank, preferably enough to keep the jets covered with water. In the cylinder, the water is relatively quiescent, and so oil separated from particles has the opportunity to float to the top of the water in the cylinder. Also, during pumping, although most of the sand/soil particles will gravitate to the bottom of the cylinders and be pumped out of the jets, a good quantity of water is left in the cylinder when the cycle is ended. In other words, each cylinder is never emptied of water, the level of which is arranged to oscillate between a full position and a low position above the level of the jet.

Accordingly, a layer of separated contaminant forms at the top of each cylinder, at least it does when the contaminant is lighter than water, which is normally the case and is certainly the case with petroleum products.

Petroleum products are the contaminant that is normally experienced in practice. Therefore, preferably, means are provided to extract the separated oil. For this purpose, a valve controlled weir may be provided over which oil can spill.

Valve switching of the pneumatic circuit is preferably conducted fluidically.

Alternatively, said pump may be a water pump, a circuit ^■ comprising the pump, cylinders and interconnecting conduits being filled with mixture, strainers being disposed in said cylinders to keep sand/soil particles from entering the pump.

A reservoir tank is preferably provided to supply said circuit with water and permit oil separated from said mixture to settle out. The scale of the reactor is entirely at the user's discretion. The reactor of the present invention may be a mobile unit capable of being sited on the back of a truck. Alternatively, it may be a fixed construction integrated into a continuous process involving multiple reactors and through-flow of said mixture through the reactor, although this loses some of the flexibility of the design.

Said through-flow may comprise, on the one hand, inflow by addition of new mixture to said tank and, on the other hand, outflow of processed mixture from said tank, wherein said outflow comprises a branch from the base of each cylinder, motive power for at least a portion of the outflow comprising the pump effect of flow of mixture from one jet to the other in said first mode of operation.

In a different aspect, the present invention provides a process for cleaning sand/soil particles of contaminants adhered to the particles, the process comprising the steps of: a) providing a reactor comprising first and second cylinders having top and bottom ends, the bottom ends of which enter a reaction tank and are formed as jets directed towards one another; b) suspending said sand/soil particles in water; c) pumping said water and entrained sand/soil particles from .the first cylinder, out of its jet, into the jet of the second cylinder, drawing water arid sand/soil particles from the tank into the second cylinder in the process, and causing formation of bubbles of vapour, said bubbles cavitating in the jet of said second cylinder; d) switching said pumping to said second cylinder to repeat the process of step c) in reverse; and e) repeating steps c) to d) cyclically as many times as desired to effect separation of said contaminants from said sand/soil particles.

The process preferably includes the further step of: f) emptying said first cylinder to a desired low level, while filling said second cylinder to a desired top level.

Pumping is preferably effected pneumatically by pressurising and, optionally, evacuating said cylinders.

The process may include the further step of: g) collecting lighter-than-water contaminants^• separated from said sand/soil particles from the surface of the water in the cylinders.

In an alternative aspect, the present invention provides a process for cleaning sand/soil particles of contaminants adhered to the particles, the process comprising the steps of: a) providing a reactor comprising first and second cylinders having top and bottom ends, the bottom ends of which enter a reaction tank and are formed as jets directed towards one another; b) suspending said sand/soil particles in water; c) alternately: i) pumping said water and entrained sand/soil particles from each cylinder, out of their respective jet colliding the streams issuing from each jet to effect scrubbing of said sand/soil particles; ii) drawing water and entrained soil/sand particles in the reactor into each cylinder filling the cylinders to a desired top level; and d) repeating step c) as many times as desired to effect separation of said contaminants from said sand/soil particles.

Said pumping may involve emptying both cylinders to a desired low level, and said drawing may involve filling said cylinders to a desired top level.

The process may further comprise the step of: e) collecting lighter-than-water contaminants separated from said sand/soil particles from the surface of the water in the cylinders.

Said pumping and drawing is preferably effected pneumatically by pressurising and evacuating, respectively, both cylinders at said top ends.

There are two beneficial features of the present .invention. One is that minimal water is employed, it being recycled back and forth through the process. The second is that the process can be repeated as many times as is deemed necessary to effect cleaning of the sand/soil. Thus, if the cycles are initially conducted a set number of times, but particles are still contaminated and oil/contaminants are still separating out, the procedure can be prolonged. An advantage of recycling the water back and forth is that, if it is preferred to add heat, (to increase bubble formation and thereby cavitation) the cost of the process can be kept reasonable since only a relatively small amount of water is needed.

Embodiments of the invention are further described hereinafter by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic- illustration of a system reactor and pump apparatus in accordance with the present invention;

Figure 2 is a further embodiment of the invention; Figure 3 is a detail of a cylinder employed in a preferred apparatus of Figures 1 or 2;

Figure 4 is a schematic diagram of a water-pump driven embodiment of the present invention,-

Figures 5a and b are diagrams showing a level controller for the side cylinder of Figure 3; and

Figure 6 is a schematic illustration of an alternative embodiment of apparatus in accordance with the present invention.

In Figure 1, a reactor 10 comprises a tank 12 including liquid (water) 14 in which solid material such as sand and soil 16 is mixed. The reactor 10 further comprises two cylinders 18,20 which each have a top end

22 and a bottom end 24. Out of each bottom end 24 extends a tube 26 that terminates in each case in a jet 28. The two jets are arranged to face one another. Each jet has a tapering approach 30 and a flared mouth 32.

A pump arrangement 40 is provided comprising an air pump 42 drawing air from an atmosphere connection 44. Air is pumped under pressure through outlet 46 a branch 48 of which leads to a control arrangement 50. The control arrangement 50 comprises a small electric motor 52 rotating a disc 54 having a cut out sector 56 around half its circumference. The branch 48 divides into two control loops 58, 60. Depending upon the position of the cut out 56 of the disc 54, one or other of the control loops 58 is blocked, and the other is open permitting flow of air from the branch 48. In Figure 1, the loop 58 is shown unblocked, so that control flow through branch 48 is able to pass along loop 58 and enter fluidic diverter 64. The main outflow of the pump 42 is through the diverter 64. When the control flow is in the loop 58, the main flow through the diverter 64 is directed to branch 66, leading to the top end 22 of cylinder 20. However, as the disc 54 rotates, there comes a point when it is loop 58 which is blocked and loop 60 connected to branch 48. When this occurs, diverter 40 is switched so that the main flow is to branch 68 leading to the top end 22 of cylinder 18. Consequently, each cylinder 18, 20 is cyclically pressurised and evacuated.

Taking the position shown in Figure 1 as an example, when cylinder 18 is pressurised, a stream of water and sand issues from its jet 28 and enters the other jet, filling the cylinder 20 in the process. The stream exiting mouth 32 of cylinder 18 is suddenly relieved of pressure. This has the effect of inducing dissolved gas in the water 14 to come out of solution, forming small bubbles wherever a nucleus can be found. Of course, soil and sand particles provide many such nuclei, so that many bubbles form. This is the case even if the water 14 is not hot, although, clearly, cavitation occurs more easily when the water is hot. However, when the stream enters the mouth 32 of the other cylinder 20, two effects are felt. The first is that water and particles in the tank 12 are entrained into the stream, thereby increasing its pressure, and secondly the bore of the tube 26 diverges in section, again slowing flow through it and increasing pressure. Consequently, the just formed bubbles all implode and collapse as the gasses go back into solution.

Of course, while the water being at high temperature may assist cavitation in the first place, at this point it slows down the bubble collapse. Since it is the bubble collapse that provides a scrubbing action, dislodging contaminants adhered to particle surfaces, it is debatable whether the best results are obtained with hot water.

In any event, the cylinder 18 gradually empties while the cylinder 20 fills. Indeed, given the entrainment from the tank 14, the cylinder 20 fills at a greater rate than the cylinder 18 empties. Therefore, each cylinder is provided with a drain 70 to ensure that the maximum and minimum levels of the cylinders 18, 20 remain approximately the same.

The speed of rotation of the motor 52 determines the switching rate of the diverter 40. Various other factors, such as the viscosity of the water and entrained particles, the force of the pump 42 and the size of the drains 70, also determine the upper level 72 and lower level 74 of the liquid in the two cylinders 18, 20. In any event, the lower level 74 is not permitted to go beyond the bottom 24 of each cylinder. As a result, the surface and just below it of the liquid in each cylinder is relatively quiescent. Consequently, oil that separates from the particles 16 has an opportunity to coalesce and float at the top of the liquid in each cylinder 18, 20. Each cylinder is therefore provided with a weir exit 76, which is kept full by liquid overflowing when it reaches the top level 72. This will primarily be oily components of the liquid mix, and these are directed to a separation pond (not shown) .

In Figure 2, an alternative arrangement of reactor 10' is disclosed where two rotary valves A,B control flow of air from the pump 42. Each valve A,B has two alternative positions. The alternative for each valve is shown on the right hand side of Figure 2. Air permanently exits the pump 42 on line 90. With the valves A,B in the rotary positions shown in Figure 2

(left side) , air in line 90 entering valve A through port

2 thereof exits the valve through port 4 and into line

5 94. Line 94 diverges into lines 95.87, going respectively to ports 3 and 4 of valve B. In the position shown in Figure 2, port 4 of valve B is blocked but port 3 is connected to port 2. Port 2 is connected to vent 96 connected to atmosphere.

10 The vacuum side 98 of pump 42 is connected to port 3 of valve A, which leads to port 1 thereof when it is in the position shown in Figure 2. Line 102 from port 1 also branches. One branch 105 leads to port 1 of valve B, which in turn is connected to port 5. Port 5 leads to

15 line 104, which is connected to top end 22 of cylinder 20. The other branch 106 from line 102 leads directly to the top end 22 of cylinder 18.

From the foregoing, it can be seen that pump 42 evacuates both cylinders 18, 20, venting the air

20 extracted to atmosphere. In so doing, water and sand/soil mixture is sucked through each jet 28 into the cylinders 18,20. When the cylinders 18, 20 are full, valve A is switched to the position shown on the right hand side of Figure 2. Then, the high pressure line 90

25 entering valve A at port 2 is instead connected to port 1, so that the high pressure supply flows down 102 and down both branches 106, 104 pressurising both cylinders 18,20.

At the same time, air is drawn into the pump 42

30. through line 98, which leads to port 3 of valve A.

However, this time, port 3 is connected to port 4 so that air can be drawn through lines 94,95 and vent 96 now acting as an intake. Thus, different from the embodiment described above with reference to Figure 1, here both cylinders 18, 20 are filled and pressurised at the same time. The effect of this is that the filling process draws most of the liquid 14^' and sand/soil particles 16 in the tank 12 into the cylinders (although not allowing the level 110 of the water in the tank 12 from falling below the level of the jets 28) . However, when the cylinders 18,20 are pressurised, the streams exiting the jets 28 collide with one another, creating a great deal of turbulence in the tank 12. This leads to substantial mixing, ensuring that particles 16 do not stagnate in one place. However, more importantly, the colliding streams cause particles in different streams to impact against one another and create an alternative scrubbing action. Which scrubbing action, impact or cavitatioh/implosion, is the more effective at separating oily contamination from the particles is a matter of investigation.

However, as described further below, the arrangement in Figure 2 permits both cyclic and simultaneous pressurising of the cylinders 18, 20.

If valve B is now switched to the position shown on the right hand side of Figure 2, then both branches 95 and 105 of the lines 94, 102 respectively are blocked. Instead, line 94 is connected to line 104 via ports 4 and 5 of valve B, and therefore to the cylinder 20. On the other hand, line 102 is connected only to line 106, leading directly to cylinder 18. Accordingly, when both valves A and B are in the position shown on the right hand side of Figure 2, the pump 42 pumps air through valve A down line 102 and 106 into cylinder 18. At the same time, the pump draws air through line 98, ports 3 and 4 of valve A, line 94, ports 4 and 5 of valve B, and through line 104, from the cylinder 22. In this mode of operation, water and soil/sand particles in the cylinder 18 are driven out of its jet 28. Just beyond the mouth thereof, the pressure is substantially reduced so that cavitation occurs. However, the stream is driven into the mouth of the opposing jet of cylinder 20 entraining water and sand particles from the body of the tank 12. Moreover, inside the mouth of the jet of the cylinder 20, as explained above, the bore expands, diffusing flow and increasing the liquid pressure. Consequently, the just formed bubbles implode, creating a scrubbing action.- The increased pressure also causes filling of the cylinder 20, which is being evacuated at the same time through line 104.

An additional vent 120 may be connected to the input of the pump 42. This prevents both excessively high and excessively low pressures developing in the line 98.

In this arrangement, valve A again serves to switch between filling and emptying of the cylinders 18,20 although in this mode of operation, it merely switches pressurisation of the cylinder 18 to cylinder 20 instead. The timing of switching valve A is arranged so that the filling and emptying of the cylinders 18 and 20 is between the desired upper and lower levels 72,74. The arrangement of cylinders 18,20 when they are cyclically filled out-of-phase with respect to one another, is already known for its pumping effect. That is to say, more liquid/solids enters the cylinder being filled than is expelled by the cylinder being emptied, flow being entrained from the surrounding tank. Accordingly, in Figure 2, a branch 112 is taken from the bottom of each cylinder 18,20, joining into outflow 114. The outflow 114 could simply be returned to the tank 12, or could be employed as a means of circulating to a subsequent stage. In a continuous process operation, a proportion of the material in the tank 12 is passed to a subsequent stage for further cleaning. A supply 116 of "fresh" water/contaminated solids is provided to keep the level 110 in the tank 12.

Turning to Figure 3, an arrangement of one cylinder 18' is shown in which a solids strainer 116 is provided to prevent solids in the water from going into the top half of the cylinder 18' . Above the strainer 116 is an oil coalescer 118 that serves to coalesce oil particles floating on the water, so that homogenised oil is formed. A weir 120 permits escape of oil overflowing the weir 120 into a side extraction pipe 130. An air pressure equaliser 132 is provided. An outflow 134 takes the separated oil to a store (not shown) . An outlet 112 is also provided to discharge slurry, either for further processing or to supply the next stage of a continuous process.

In Figures 5a and b, outlet 134' is in the form of an STuVA level controller 140, which is a switched, turn¬ up vortex amplifier. Here, two inputs 142,143 to a vortex chamber 146 are provided. The inputs to the vortex chamber 146 are tangential, and in opposite directions. When equal flow to the two inputs occurs, there is no vortex formation in the chamber 146. Therefore, maximum flow occurs through a central output orifice 134' of the chamber 146. However, should unequal flow occur, then a vortex develops in chamber 146 inhibiting flow from the outlet 134'. In the STuVA controller 140, input 143 is arranged at a different height to input 142. Should the level of over spill from the weir 120 fall to below the level of input 143, the outlet 134 is restricted by the vortex that follows from the uneven input to the chamber 146 through input 142 alone. However, when the level rises above the input 143, outlet 134' is effectively opened.

Although the apparatus of the present invention as described above in connection with embodiments shown in Figures 1 to 3 are driven by compressed air, this is not an essential driving means. It is certainly advantageous, since there is no requirement to physically pump the solids-containing water.

However, in Figure 4 a water-driven reactor 10" is shown. Here, the cylinders 18,20 have strainers 116 near their top ends 22. The entire system is filled with water, and pump 42 ejects flow through line 90 supplying open or closed valves Α^r _rB^r .

During simultaneous operation, pump 42 is supplied from a tank 136 via valves G and D which are open, while valves B' , C and F are closed. The outflow from pump 42 is therefore fed entirely through valve A' to cylinder 18 and, via valve E, which is open, to cylinder 20. When the desired volume of tank 136 has been sufficiently depleted (or tank 12 sufficiently filled - or again, more significantly, all solids in the cylinders 18,20 have been ejected from the respective jets 28), valves A', D and F are closed while valve B^r and C are opened. Pump 42 therefore pumps liquid through valve B' and G to replenish tank 136. The supply to the pump 42 is through valves C and E, which are opened, drawing flow through each cylinder 18,20 from the reactor tank 12, filling the storage tank 136 in the process. It is in the storage tank 136 that oil separated from the particles finally separates out from the water, the strainers 116 preventing solids from contaminating the pump 42.

The out-of-phase cycling mode of operation can also be employed with the arrangement shown in Figure 4. In that, tank 136 is not employed, except finally to receive discharge of the water employed in the process prior to replenishment of the tank 12.- In this arrangement, therefore, valve G is normally closed. Also, valve E is permanently closed, and valve F permanently open. During a first phase of operation, valves B' and C are closed,

-while valves A' and D are open. Liquid is then drawn from cylinder 20 through valves F and D by the pump 42,

^■and discharged through line 90 and valve A^r to cylinder 18.

Of course, in this water-driven arrangement, the reason for cycling the flow from one cylinder 18 to the other 20 is not because one cylinder runs out of water. Rather, the reason is that one cylinder will become loaded with solids. Therefore regular cycling of flow is still required. Accordingly, in a second phase, valves A' and D are closed, while valves B' and C are opened. Liquid is then drawn out of the top 22 of cylinder 18 by the pump 42 through valve C, and discharged through line 90 and valves B' and F into cylinder 20.

Of course, the same scrubbing action is conducted in the two jets 28 while solids are in the streams exiting jets 28. Also, in this mode of operation, the same pumping occurs,- so that branches 112, 114 are required in order to maintain balance.

Finally, turning to Figure 6, the invention is here shown in its simplest form, comprising a single cylinder 18. The diffuser 30 and its flared mouth 32 are directed towards a target 150. The pump 42 is cycled between suction and pressure. In pressure mode, water- and entrained sand/soil is driven out of the jet 32 against the target 150. The impacts of the sand/soil particles against the target dislodge contaminants adhered to the particles. In suction mode, the low pressure in the venturi formed at the mouth 32 causes bubbles to form, which, on entering the diffuser section 30, immediately implode causing a second scrubbing action. Separated lighter-than-water contaminants float on the water surface both in the cylinder 18 and the tank 12, although, if the suction level is taken right down to the level of the mouth 32, contaminants can also be drawn into the cylinder 18 where they can be separated from the water as described above. This arrangement is simple and can be repeated as a batch process as long as the particles remain contaminated.

Claims

l. A sand/soil cleaning reactor comprising two cylinders having top and bottom ends, the bottom ends of which enter a reaction tank and are formed as jets directed towards one another, and a pump to drive a mixture of water and sand/soil in the cylinders out of the jets and to draw said mixture from the tank into the cylinders through the jets, wherein the reactor is arranged to operate in at least one of two modes of operation: in a first of said modes, the cylinders are pumped alternately- in cyclic phases, one cylinder expelling mixture through its jet and the other admitting mixture through its jet, there being minimal change in level of mixture in the reactor tank, whereby cavitation occurs in the mixture between said jets and implosion and resultant scrubbing of said sand/soil occurs inside the jet of said other cylinder; and in a second of said modes, the cylinders are pumped simultaneously in cyclic phases, there being maximal change in level of mixture in the tank between said phases^' and, during a pressure phase, the streams of mixture exiting each jet impinge on one another, whereby collisions of sand/soil particles between said jets effects scrubbing of them.

2. A reactor as claimed in claim 1, in which the jets are arranged so that, in said first mode, they are close enough to one another that the motive power to fill the other cylinder is primarily provided by the stream of mixture from the issuing jet.

3. A reactor as claimed in claim 2, in which the jets are arranged so that, in said first mode, they are separated from one another so that mixture in the tank is entrained in the flow to said other cylinder.

4. A reactor as claimed in claim 1, 2 or 3, in which said pump is a pneumatic pump, arranged to drive air into the top of the cylinders above the mixture level therein, and, to evacuate air therefrom when the cylinders are being refilled.

5. A reactor as claimed in claim 4, in which the level of mixture in each cylinder is arranged to oscillate between a full position and a low position above the level of the jets.

6. A reactor as claimed in claim 5, in which some mixture is retained in the cylinder beneath said low position, which mixture is relatively quiescent, so oil separated from sand/soil particles by said scrubbing has the opportunity to float to the top of the water in the cylinder, a weir being provided near said full position over which said oil can overflow for reclamation.

7. A reactor as claimed in claim 6, in which an oil coalescer is disposed in the cylinder beneath said weir.

8. A reactor as claimed in claim 7, in which a particle strainer is disposed in said cylinder beneath said coalescer.

■9. A reactor as claimed in claim 6, 7 or 8, in which said weir comprises a side cylinder.

10. A reactor as claimed in claim 9, in which an exit for overspill from said weir in said side cylinder includes a level controller to prevent air blowing through said exit.

11. A reactor as claimed in claim 10, in which said level controller comprises a StuVA valve.

12. A reactor as claimed in claim 1, 2 or 3, in which said pump is a water pump, a circuit comprising the pump, cylinders and interconnecting conduits being filled with mixture, strainers being disposed in said cylinders to keep sand/soil particles from entering the pump.

13. A reactor as . claimed in claim 12, in which a reservoir tank is provided to supply said circuit with water and permit oil separated from said mixture to settle out.

14. A reactor as claimed in any preceding claim, which is a mobile unit capable of being sited on the back of a truck.

15. A reactor as claimed in any of claims 1 to 13, which is a fixed construction integrated into a continuous process involving multiple reactors and through-flow of said mixture through the reactor.

16. A reactor as claimed in claim 15, in which said through flow comprises, on the one hand, inflow by addition of new mixture to said tank and, on the other hand, outflow of processed mixture from said tank, wherein said outflow comprises a branch from the base of each cylinder, motive power for at least a portion of the outflow comprising the pump effect of flow of mixture from one jet to the other in said first mode of operation.

17. A process for cleaning sand/soil particles of contaminants adhered to the particles, the process comprising the steps of: a) providing a reactor comprising first and second cylinders having top and bottom ends, the bottom ends of which enter a reaction tank and are formed as jets directed towards one another; b) suspending said sand/soil particles in water; c) pumping said water and entrained sand/soil particles from the first cylinder, out of its jet, into the jet of the second cylinder, drawing water and sand/soil particles from the tank into the second cylinder in the process, and causing formation of bubbles of vapour, said bubbles cavitating in the jet of said second cylinder; d) switching said pumping to said second cylinder to repeat the process of step c) in reverse; and e) repeating steps c) to d) cyclically as many times as desired to effect separation of said contaminants from said sand/soil particles.

18. A process as claimed in claim 17, including the further step of: f) emptying said first cylinder to a desired low level, while filling said second cylinder to a desired top level.

19. A process as claimed in claim 18, wherein said pumping is effected pneumatically by pressurising and, optionally, evacuating said cylinders

20. A process as claimed in claim 18 or 19, including the further step of; g) collecting lighter-than-water contaminants separated from said sand/soil particles from the surface of the water in the cylinders.

21. A process for cleaning sand/soil 'particles of contaminants adhered to the particles, the process comprising the steps of: a) providing a reactor comprising first and second .cylinders having top and bottom ends, the bottom ends of which enter a reaction tank and are formed as jets directed towards one another; b) suspending said sand/soil particles in water; c) alternately: i) pumping said water and entrained sand/soil particles from each cylinder, out of their respective jet colliding the streams issuing from each jet to effect scrubbing of said sand/soil particles; ii) drawing water and entrained soil/sand particles in the reactor into each cylinder filling the cylinders to a desired top level; and d) repeating step c) as many times as desired to effect separation of said contaminants from said sand/soil particles.

22. A process as claimed in claim 21, in which, said pumping involves emptying both cylinders to a desired low level, and said drawing involves filling said cylinders to a desired top level.

23. A process as claimed in claim 22, further comprising the step of: e) collecting lighter-than-water contaminants separated from said sand/soil particles from the surface of the water in the cylinders.

24. A process as claimed in claim 21, 22 or 23, wherein said pumping and drawing is effected pneumatically by pressurising and evacuating, respectively, both cylinders at said top ends.

25. A sand/soil cleaning reactor comprising a cylinder having top and bottom ends, the bottom end entering a reaction tank and forming a reverse diffuser disposed adjacent a target against which a jet issuing from the reverse diffuser is directed, and the top end being connected to fluid drive means, whereby the reactor operates in two cycled modes, in a first mode of which, water is pumped out of said cylinder into said reaction tank by said fluid drive means against said target so that the sand/soil is cleaned by virtue of the scrubbing action caused by said sand/soil impacting said target, and in a second mode of which, water in which said sand/soil is entrained is drawn into said cylinder from said reaction tank by said fluid drive means so that the sand/soil is cleaned by virtue of the scrubbing action caused by cavitation of bubbles formed in said reverse diffuser.

26. A reactor as claimed in claim 25, in which said cylinder is quiescent, whereby lighter-than-water contaminants separated from the sand/soil floats to the surface of the water in the cylinder for subsequent separation.

27. A reactor as claimed in claim 25 or 26, in which said fluid drive means comprises pneumatic pump means.

28. A reactor as claimed in claim 27, in which, in said first mode, a space above the water level in the cylinder is pressurised, while in said second mode said space is evacuated.

29. A reactor as claimed in any of claims 25 to 28, in which two of said cylinders are disposed in said reaction tank, with their respective reverse diffusers facing one another, and said modes of operation are cycled in each cylinder in-phase, whereby said target for each diffuser comprises the output of the other diffuser, and said impacting of sand/soil issuing from one diffuser is with sand/soil issuing from the other diffuser.