ZA200201662B

ZA200201662B - Apparatus and method for sea bed excavation.

Info

Publication number: ZA200201662B
Application number: ZA200201662A
Authority: ZA
Inventors: Richard Lane; Phil Brown
Original assignee: Psl Technology Ltd; Richard Lane
Priority date: 1999-08-21
Filing date: 2002-02-27
Publication date: 2003-08-27
Also published as: GB9919801D0; WO2001014649A1; AU6852700A

Description

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1 Apparatus and Method for Sea Bed Excavation 2 3 The present invention relates to improved method and 4 apparatus for enabling the extraction of sediment and other particulate materials from the sea bed. 6 . 7 In this specification, references to the sea bed should 8 be construed broadly, and as such should be deemed to ; 9 include river beds, lake beds and the like.

11 There are various applications, motivated by both 12 environmental and commercial considerations where it may 13 be beneficial to excavate an underwater sea bed.

For 14 example, diamonds occur in certain rock and sediment formations lying below the surface of the sea bed.

This 16 is the case on the southern west coast of Africa, where 17 typically the highest concentrations of diamond deposits 18 lie between approximately 0.3 metres and (0.8 metres below 19 the gravel layer surface.

Apparatus is required for extracting the top layer, preferably to a depth of 21 approximately one metre, to allow the diamonds tc be 22 mined.

. - a WO 01/14649 2 PCT/GB00/03208 1 Another application lies in the dredging of harbours or 2 ports where the constant use of oil-based fuels to power 3 marine craft leads to the polluting of the sea bed; 4 creating the desire to provide a means for the periodic lifting and filtering or other cleaning of the sea bed 6 material. A yet further application that is envisaged in 7 consequence to growing environmental concerns relates to 8 the extraction of drill cuttings in the vicinity of off- 9 shore drilling sites. 11 The present invention is not limited to these 12 applications but finds utility in any situation where it 13 might be advantageous to excavate the sea bed. Usually, 14 this will alsc involve the raising of the sea bed particles or other matter to the surface where would be ’ 16 positioned a ship or boat housing the means for 17 performing some operation such as cleaning or separating - 18 the matter, for example. 19

In the art there are provided diverse means for 21 excavating sea beds. One such means that is used in 22 fairly loosely compacted sea beds involves the use of one 23 or more suction units that are dragged by an overhead 24 ship across the sea floor. Suction is provided by pumping apparatus located on the ship. However this 26 technique is associated with a number of disadvantages, 27 including the relative low efficiency of employing 28 suction as a sole means to encourage the dislodging and 29 uplifting of sea bed material. Movement of the suction means in loosely defined linear paths also leads to poor 31 surface coverage of the entire sea bed; there inevitably 32 being gaps between the linear paths and inconsistencies 33 in the depth of penetration of the apparatus. Dragging 34 heavy equipment across the sea bed may also lead toc the il . 1 inadvertent damage of pipelines or other sub sea 2 structures. 3 4 It is an object of the present invention therefore to provide an improvement to this technique, and moreover to 6 offer a systematic method for removing the sediment top 7 layer of a sea bed with improved sea bed coverage at a 8 consistent depth. 9

According to the present invention there is provided 11 apparatus for use on a sea bed, the apparatus comprising 12 a chamber defining a volume of sea water located above an 13 area to be excavated, wherein the apparatus further 14 comprises agitation means located within the chamber for agitating the sea bed in the said area and one or more 16 suction means for receiving sediment or other sea bed ) 17 material agitated by said agitation means. 18 - 19 Preferably the chamber is substantially open at a lower part thereof. 21 22 Alternatively the chamber is partially closed at a lower 23 part thereof by a flexible membrane and securing means, 24 wherein the flexible membrane defines an enclosed passageway between the chamber and the sea bed. 26 27 The suction means may communicate with one or more rigid 28 or flexible delivery risers for conveying the sea bed 29 material to a vessel or platform located on the sea surface. Typically the vessel or platform would be 31 provided with pumping equipment for generating suction in 32 the suction means.

1 The chamber preferably acts as a barrier to contain the 2 agitated material from the sea bed within a volume 3 defined by the chamber. This serves to increase the 4 efficiency of the apparatus in that the disturbed sea bed material is captured in the excavation area such that it 6 is maintained as available for collection by the suction 7 means. 8 9 The agitation means is preferably a device for jetting sea water at the sea bed. It may for example comprise of 11 a hydraulically driven propeller that is adapted to 12 propel sea water within the chamber forcibly toward the 13 sea bed. The propeller would encourage a circular flow 14 of water in a horizontal plane, but other means may also be included, such as vanes, fins, to encourage such : 16 circular flow. 17 - 18 Alternatively, the agitation means comprises mechanical 19 blades or other members adapted to agitate the sea bed by consequence of physically impacting the sea bed. A yet 21 further alternative may be that the agitation m=ans 22 incorporates a sonic or ultrascnic device. 23 24 Preferably the suction means includes one or more inlets for the intake of sea bed material, wherein the or each 26 inlet is disposed toward the perimeter of the chamber. 27 Most preferably, an inlet is provided at each corner of 28 the lower open side of the chamber. 29

The chamber may be further provided with a vent to 31 balance the volume of water in the chamber. The vent may 32 be associated with a valve or plug such that the vent Is 33 kept open in normal operation, but in the event that the 34 apparatus becomes trapped in the sea bed can be closed

’ "a 1 enabling the suction process to be reversed thus freeing 2 the apparatus. Reversal of the suction process may 3 involve the use of the agitation means. 4

Preferably, the chamber has a skirt at the lower edge of 6 its side walls, the skirt being robust and resilient. 7 8 According to a second aspect of the invention there is 9 provided a method of excavating a sea bed comprising the steps of isolating an area of the sea bed; agitating the 11 sea bed in the said area and sucking the agitated sea bed 12 material to a surface vessel or the like. 13 14 Preferably the area is isolated by a physical barrier.

The sea bed may be agitated by inducing high velocity 16 fluid movement inside the isolated area. . 17 18 Preferably the said method is conducted for a first . 19 period of time and then repeated for successive periods in respect of successive areas tc be excavated. 21 22 Most preferably each successive excavation area is 23 adjacent the preceding area such that optimum coverage of 24 the sea bed is performed. 26 In order to better convey the invention embodiments will 27 now be described by way of example only with reference to 28 the accompanying Figures, in which: 29

Fig.l shows a schematic elevation of a subsea 31 diamond mining system; po i. Lo 33 Fig. 2 shows in elevation excavation apparatus in 34 accordance with the invention;

N WO 01/14649 6 PCT/GB00/03208 2 Fig. 3 is a plan view of the excavation apparatus 3 illustrated in Fig. 2; 4

Fig. 4 is a computer generated simulation of the 6 movement of sea water and sea bec material inside 7 the chamber of Figs. 2 and 3; 8 9 Fig. 5 is a plan view of an alternative embodiment of the excavation apparatus illustrated in Fig. 2; 11 and 12 13 Fig. 6 shows in elevation an alternative embodiment 14 of the excavation apparatus in accordance with the invention; : 16 17 With reference firstly to Fig. 1, a sea going vessel 1 is - 18 provided with hoisting equipment 2 for the controlled 19 lowering and raising of excavation apparatus, generally depicted at 3. The vessel may be provided with means for 21 separating diamonds or material including diamonds from 22 other waste material obtained from the sea bed. It 23 should be appreciated that such means are not critical to 24 the present invention; the invention hereto being concerned with the efficient and systematic collection of 26 excavated material from the sea bed. 27 28 The excavation apparatus 3 1s more clearly depicted in 29 Figs. 2 and 3. The apparatus 3 includes a chamber 4 formed substantially as a cube, but with an open lower 31 side. The lower side 35 1s therefore approximately 32 square, and in the example embodiment is dimensioned with 33 sides of 5 metres.

1 A twenty inch diameter lift line 6 feeds into the chamber 2 and divides via a manifold into four arms 7, each arm 7 3 terminating with an inlet 8. The line 6 provides =a 4 suction medium for sucking and conveying sea bed material up to the vessel 1. 6 7 Descending through the centre of the chamber is a 8 relatively powerful water driven propeller 9. The 9 propeller 9 is adapted to thrust sea water downwardly anc forcibly onto the sea bed.

The momentum of the propelled 11 sea water is sufficient to agitate the sea bed to such 12 extent as to cause sediment and other particles tc 13 unsettle and travel around the chamber 4. It will be 14 appreciated that the rotary action of the propeller ¢ will cause the sea water and agitated sea bed material tc 16 move in a swirling direction, which will encourage the . 17 sea bed material to migrate to the corners of the chamber 18 4. Accordingly, the suction inlets 8 are ideally located . 19 at these corners for the efficient collection of the sez bed material. 21 22 This may be more clearly demonstrated by Fig. 4 whicx 23 illustrates a simulation of the movement of the seabec 24 material in the chamber 4. The velocity of the material is dependent on its location in relation to both the 26 propeller 9 and the suction inlets 8. Accordingly, 27 material located directly under the propeller 9 and 28 towards the centre of the sides of the chamber 4 is 29 affected least, while the material located towards tne edges of the propeller 9 and adjacent to the suction

~~ 31 inlets 8 is displaced most.

32 33 In an alternative embodiment, the chamber 4 may be 34 provided with means to improve the swirling effect of the s WO 01/14649 8 PCT/GB00/03208 1 propeller 9 to ensure that the seabed within the area of 2 the chamber ¢ is efficiently agitated.

Figure 5 3 illustrates such an alternative embodiment where baffles 4 or directing blades 10 positioned below the propeller 9 are used tc achieve this effect. 6 7 A further embodiment of the chamber 4 may be provided 8 such that a flexible membrane 11 and chain 12 are 9 incorporated on the lower side 5 of the chamber.

Such an embodiment is illustrated in Figure 6. The flexible 11 membrane 11 is employed to define a shallow passageway 13 12 across the sea bed.

The propeller 9 is then used to 13 generate a high velocity water flow across the sea bed. 14 The water flow enters the passageway 13 at the inlet 14 before passing into the suction inlet 8 at the other end. ’ 16 As the water flow passes through the passageway 13 it - 17 carries with it sediment so permitting excavation of the : 18 sea bed.

The chain 12 is employed to weigh down the : 19 flexible membrane 11 and so stop it billowing upwards when the high velocity water flow passes underneath. 21 22 As the sea going vessel 1 passes over the area to be 23 excavated, the apparatus 3 is placed such that the 24 chamber 4 is stationary on the seabed.

The sediment is then agitated by the action of the propeller 9. The 26 suction arms 7 draw the sediment through the inlets 8 to 27 the vessel 1. Agitation of a single area is typically 28 done for 30-45 seconds depending on the nature of the sea 29 bed to allow an appropriate depth to be excavated.

31 Once in the vessel 1 the sediment can be filtered to 32 remove the desired material, such as diamonds, and 33 subsequently returned to the sea bed.

The apparatus is 34 then translocated to a neighbouring section of the sea

1 bed and the process is repeated. The design of the 2 apparatus is such that the entire sea bed can be covered 3 improving the overall efficiency of the process. 4

Although unlikely, it might be possible as a result of 6 the agitation process that the apparatus can sink into 7 the sea bed and can become stuck. Accordingly, the 8 chamber 4 is also provided with a valve (not shown) which 9 is open during normal operation. However, in the event that the apparatus becomes stuck in the sea bed the valve 11 can be closed and the suction process reversed to free 12 the apparatus. Potentially, this may be achieved in twc 13 ways, namely: 1) the suction through the lift line 6 may 14 be replaced by downward flow, or 2) the suction through the lift line may be deactivated and the upward reaction 16 force of the propeller 9 be relied upon. : 17 18 It will be noted from the example embodiments that the . 19 agitation of the sea bed is achieved without causing any direct impacting of the agitation device on the sea bed. 21 This mitigates the possibility of damaging any existing 22 structures that might pre-exist on the sea floor. 23 24 A further advantage of the present invention is that there is provided apparatus with improved 26 capacity/efficiency for excavating a sea bed or the like 27 as a result of improved coverage, higher concentration of 28 material entering the suction arms and deeper penetration 29 of the bed. 31 Further modifications and improvements may be added 32 without departing from the scope of the invention herein 33 intended.

Claims

. 3 PCT/GB00/03208 ) v 10 CLAIMS:

1) Apparatus for use on the sea bed comprising a chamber defining a volume of sea water located above an area to be excavated, an agitation means located within the chamber for agitating the sea bed in the said area and one or more suction means, employed to receive sediment or other sea bed material agitated by said agitation means, characterised in that the suction means are disposed towards the perimeter of the chamber.

2) Apparatus for use on the sea bed as claimed in Claim 1 wherein the chamber is substantially open at the lower end thereof. 3) Apparatus for use on the sea bed as claimed in Claim

1 wherein the chamber is partially closed at the lower end thereof by a flexible membrane and securing means, wherein the flexible membrane defines an enclosed passageway between the chamber and the sea bed.

4) Apparatus for use on the sea bed as claimed in any of the preceding claims wherein the suction means may communicate with one or more rigid or flexible delivery risers for conveying the sea bed material to a vessel or platform located on the sea surface.

5) Apparatus for use on the sea bed as claimed in Claim

4 wherein pumping equipment for generating suction in the suction means is located on the vessel or platform.

6) Apparatus for use on the sea bed as claimed in any of the preceding claims wherein the chamber acts as a barrier to contain the agitated material from the sea bed within a volume defined by the chamber so increasing the efficiency of the apparatus.

AMENDED SHEET

™ “~ - PCT/GB00/03208 a» 11

7. Apparatus for use on the sea bed as claimed in any of the preceding claims wherein the agitation means is a device for jetting sea water at the sea bed.

8. Apparatus for use on the sea bed as claimed in Claim 7 wherein the agitation means is a hydraulically driven propeller.

9) Apparatus for use on the sea bed as claimed in Claim 7 and 8 wherein the agitation means employs means for directing the jetting sea water.

10) Apparatus for use on the sea bed as claimed in Claim 9 wherein the means for directing the jetting sea water are one or more directing blades.

11) Apparatus for use on the sea bed as claimed in Claims 1 to 6 wherein the agitation means comprises mechanical blades or other members adapted to agitate the sea bed by consequence of physically impacting the sea bed.

12) Apparatus for use on the sea bed as claimed in Claims 1 to 6 wherein the agitation means is a sonic or ultrasonic device.

13) Apparatus for use on the sea bed as claimed in any of the preceding claims wherein the chamber comprises a vent that moves between an open and closed position so as to balance the volume of water in the chamber.

14) Apparatus for use on the sea bed as claimed in any of the preceding claims wherein the chamber comprises a skirt at the lower edge of its side walls, the skirt being robust and resilient.

15) A method of excavating a sea bed comprising the steps AMENDED SHEET

As . PCT/GB00/03208 Co 12 of:

1. Isolating an area of the sea bed;

2. Agitating the sea bed in the said isolated area so transferring the agitated material to the } 5 perimeter of the isolated area;

3. Sucking the agitated sea bed material from the perimeter of the isolated area to a surface vessel or the like.

16) A method of excavating a sea bed as claimed in Claim whereby the area is isolated by employing a flexible physical barrier.

17) A method of excavating a sea bed as claimed in Claim 15 and 16 whereby the sea bed is agitated by inducing high-velocity fluid movement inside the isolated area. 15 18) A method of excavating a sea bed as claimed in Claims 15 to 17 whereby the said method is conducted for a first period of time and then repeated for successive period in respect of successive areas to be excavated. 19) A method of excavating a sea bed as claimed in Claim 18 whereby each successive excavation area is adjacent to the preceding area such that optimum coverage of the sea bed is performed. 20) An apparatus according to Claim 1, substantially as herein described and illustrated. 21) A method according to Claim 15, substantially as herein described and illustrated. 22) A new apparatus, or a new method of excavating a sea bed, substantially as herein described. AMENDED SHEET