Waterjetting 35c - Developing a waste removal shroud - video.

The short videotapes in this segment show the evolution of a combination of a waterjet and a suction line as a way of easily removing soil or sand relatively quickly. It is a subject covered in an earlier post. These video clips show some of the tests that helped us to develop that design.

As mentioned in that earlier post the central tube connects to a vacuum line which removes the loosened debris and water. An earlier series of tests had shown that the suction nozzle had to be within quarter of an inch of the surface for the suction to be most effective. The jets had, therefore, to clear a way for this nozzle by cutting down through the material and pushing it into the mouth of the tube, before the tube arrived.

For the first test a single nozzle (out of the three on the head) was used at relatively low pressure.

Figure 1. Clip showing a single jet cleaning through 2-inches of sand.

However if the jet pressure is raised to cut harder material, then the jet has enough power to wash the material under and past the suction tube so that only a small part of the solid is picked up and the path fills back up with the washed sand.

Figure 2. A higher-pressure cutting jet does not give the debris time to be sucked out of the tank.

If three jets are used, but with the jets directed so that the paths hit each other within the suction zone this stopping each jet going further for a long enough time that the suction can remove both water and debris. 

 Figure 3. A three-jet combination where the jets are held within the shroud, leaving a clean path.

For those unable to see the video the configuration of the jets meant that they met under the shroud as shown.

Figure 4 The jet configuration around the shroud.

When this is combined with a protective (flexible) outer shroud the final result was a tool that removes material without over-spraying into the surrounding sand and destabilizing it. Leaving a clean channel.

Figure 5. Larger head design removing a 2-inch thick layer of sand.

In a subsequent post I will include (when I can find it among the 200-odd hours of material) a video of a similar (though smaller) tool cutting a clean channel into a soft cement, and leaving a clean path behind it, as shown in the earlier post. For those interested the parts for these cleaning heads were assembled from plumbing supplies from our local hardware store at a cost, per head of around a hundred dollars or so. (back in 1995 when we ran the tests).

Waterjetting 22b - Steep seams and shrouds

It was not until we started to move the auger that I described last time, that I realized how heavy and cumbersome it remained. It is true that we could lighten it considerably (and we did in the UK version), but it was still largely a platform mounted device that was relatively easy to move on the surface, but which would be much more difficult to move around in the confined spaces underground.

In this regard it is worth comparing two photographs.

Figure 1. Coal being transported in the pipes at the Hansa hydraulic mine in Germany.

Notice in this first one how the coal is confined, there is no dust, and the tunnel is relatively clean and clear. Contrast this with the typical mining operation where the coal is carried from the working face to at least the main haulage drifts, and often all the way out of the mine using conveyor belts. (The method of transport that would also likely be used in a typical underground auger section).

Figure 2. Conventional belt conveyor carrying coal underground. (Famur )

Note that in the second photo the belt occupies most of the space in the roadway making passage more difficult, and that the coal is openly exposed. The problem that this occasionally generates is that the coal transfers from one belt to another as it moves through the mine by falling off the end of one belt onto the next. This puts dust into the air, and if not properly maintained coal dust can accumulate under the belt and around the support rollers and drives. If not cleaned this can create heat through friction, and can lead to disastrous fires.

Figure 3. Studying a belt fire underground (Office of Mine Safety and Health Research )

Confining the coal, and using the water that mined it as a transport fluid – or at least part of such – has many advantages.

The Russians were aware of this as they developed some of their different mining machines. One of these was a small monitor that could be pushed up a seam, from a lower drift (without the need of a higher one), by adding segments as the unit was jacked forward.

Figure 4. Russian GVD monitor

The monitor could be advanced up the seam, cutting a channel about 3-ft wide, and to the height of the coal. This relatively narrow channel confined the water and the coal produced, so that both ran back down to the drift, where they could be either enclosed in a pipe, or run into an open flume, that would carry the coal away. Once the drive had reached the end of the section, then the two hydraulic cylinders that sat under the monitor could be turned, so that, from a protected section down-slope, the monitor could successively ream out strips on either side of the entry, until the roof collapsed, or the operation holed through to the previous panel.

Figure 5. Schematic showing the sequence of extraction in a) a coal seam with a relatively strong roof b) a seam with a weak roof, where a pillar of coal is left between successive lifts, typically around 30 ft, so as to provide additional support to the roof as the coal is mined out.

Production from these machines averaged about 76 tons/hour from seams that were in the range from 2 to 4 ft thick, this was more than double the production output achieved by more conventional means, with significantly less manpower.

However while there are some conditions where gravity helps to bring the coal and water back together, there are many cases where this is not possible due to other constraints. This is where it becomes necessary to use a shroud to confine the jets, debris and water so that they can be extracted together, often using a vacuum to assist in the process.

Figure 6. Rendition of the combination of three cutting jets rotating around a vacuum tube to slice into material and remove it.

The particular device shown in Figure 6 was developed as a way of remotely slicing into high-level radioactive waste for the Pacific Northwest National Laboratory. The waste is held in underground storage tanks, where the levels are too high for human access. As a result the waste had to be broken into pieces and removed remotely.

The initial problem was that the tanks, though holding perhaps half-a-million gallons of waste, had only small (18-inches or less) ports through which they could be accessed. Thus a relatively small tool was required, yet the mining rate had to exceed 4-cu. ft/minute. The situation required an excavation system on the end of a robotically controlled arm. But the arm would have to be more than 60-ft long (in the end a cousin of the arm used on the Space Shuttle was used). Any mechanical force applied at the end of such an arm would have tremendous leverage on the holding fixture, and a relatively low overall force would have to be found, yet one capable of cutting material perhaps as strong as a weak cement.

The answer came in the form of the device shown in Figure 6. By placing three cutting jets to rotate around a central tube, connected to a vacuum line, one could cut into the material and break out relatively small pieces, which could be aspirated away with the cutting water. (The requirements were that there would be no water left in the tank for any significant amount of time). Because the bottom of the tank was some 40 or 50 ft below ground level a small, high-pressure (10,000 psi) jet pump was developed by Michael Mann, capable of drawing particles of up to an inch in size into the line, and then projecting them up with sufficient energy to carry them out of the tank.

Figure 7. Basic system conceived to mine high-level radioactive waste and remove it from a storage tank.

While this description of the system makes the tool seem to be relatively simple to build and operate there are a number of features to the design that are fairly critical in order for it to work well, and I will cover some of those next time.

Deepwater Oil Spill - sealing the cap and jet pumps

There has not been much change down on the sea bed where last evening BP were able to put a cap onto the short riser section coming out of the Lower Riser Assembly (LRA) that sits on the Blowout Preventer (BOP) at the top of the well. I have looked in a variety of places for information on steps forward, and did discover that there is a second assembly above the cap, that I had seen, but had not been able to recognize until watching the video on capping available at the Deepwater Response site. It is here that the methanol is sent down to the cap to make sure that no crystals form within the cap. So for those who wish to keep the right names for the right parts, take note.

The cap, drill pipe, LMRP and riser assembly used to cap the well.

And given that I was calling the cap the 7th generation LMRP when it was (as the big 4 on the side of the yellow structure showed) neither, means I need to take my own message to heart. In this post I am going to talk about the seal under the cap.

There are four ports on the top of the cap, that continue to allow the oil that is flowing into the cap to flow back out while the cap was initially positioned, and to reduce the flow up the BP, until the system has been checked out to ensure there are no unforeseen problems. BP only slowly raised the flow rate up the pipe when they first started using the Riser Insertion Tool (RIT) starting out with a flow of around 1,000 barrels/day and then ramping it up, at the time reporting that flow ramped up first to 2,000 bd and then up to 4,000 bd. However they later rescinded the latter number and dropped the maximum flow level to around 2,200 barrels a day. Oil and gas have started flowing up to the drillship at the top of the riser where the oil is separated and stored, and the gas is being flared. (This was taken during the flare from the RIT operation).


However the flow out of the RIT was monitored, and higher rates have now been reported.

On May 25, 2010, at approximately 17:30 CDT, the RITT logged oil collection at a rate of 8,000 barrels of oil per day, as measured by a meter whose calibration was verified by a third-party. Based on observations of the riser, the team estimated that at least 10% of the flow was not being captured by the riser at the time oil collection was logged, increasing the estimate of total flow to 8,800 barrels of oil per day. Factoring in the flow from the kink in the riser, the RITTI Team calculated that the lower bound estimate of the total oil flow is at least 11,000 barrels of oil per day, depending on whether the flow through the kink is primarily gas or oil.

With the full flow now being emitted through the single confluence of the riser and BP flows at the top of the remaining riser section on the BOP, a full estimate of the leak will, no doubt, not be long in being announced.

The high volume of flow means that there need to be cautious progress in capturing all the oil and gas and sending it up the DP. However there is still a little communications conflict, since there were some reports that the taps bypassing the oil/gas would be closed later today, however at 10:43 pm the Enterprise ROV 2 was still showing an open port.


Oil was also leaking out of the bottom of the cap, which is, even when almost all the oil is being recovered, likely to be a good thing in small quantities, somewhat less than this.

From Skandi ROV 2 10:55 pm 4th June (The Skandi Rov 1 has the picture from the other side, also of the bottom of the cap).

Why is this? Well the way in which the Shear was used to cut the end of the riser and BP means that it is likely to be impossible at the present time to get a good strong seal around the chamber between the flow into the cap from the BOP and that out into the BP up to the LMRP.

When a stream enters a chamber through one port, and exits through another, both of relatively small size, then the jet will create a vacuum in the chamber, which pulls fluid from the surroundings into the chamber and carries it, with the jet fluid into the second port. I am going to embed a short video of a commercial down-hole video and am not endorsing anything but the animation shows you how the jet pump works. (And the flow in the Gulf is easier than that shown here ).

Animation of an oil well jet pump. There is a competing design here (shorter video too)

The reason that it is critical in this operation is that the fluid outside the cap is seawater. If the jet pumping action were to become too efficient as all the oil flowed from one passage to the other, then the “jet pump effect” would draw cold seawater into the chamber and the problem of hydrate generation and blocking of the flow path would be back to block the cap, as it did top hat. By not getting all the flow into the second pipe it should be possible to drop the suction in the chamber to the point that a little oil still leaks out (treated with dispersants) but the majority goes up the well. Getting this right should prove an interesting exercise. (But isn’t calculating this what the “best and the brightest” – Dr. Chu’s team - are there to do?)

Flow control is achieved, simplistically, with a valve at the top of the riser on the Enterprise. By adjusting the flow the valve effectively controls the pressure at the top of the riser and thus also at the bottom.

Incidentally in other circumstances jet pumps are neat tools. One of my students developed a high pressure one for use in lifting high-level radioactive waste out of nuclear waste storage tanks (you want to minimize water use, and do this by upping the driving jet pressure). Worked like a charm, when used in the real tanks. They are also used as remote inexpensive pumps in mines, lying in depressions where water can collect. The water collects, a float valve lifts and the jet flows, sucking the water away. As the water disappears, the float drops and the jet switches off.

Oh, and for those who have ideas on how to deal with any part of this problem, the Government is stepping up the ways in which you can get funding. The process goes through the Federal Business Opportunities Webpage where there is a Broad Agency Announcement on the subject. It would be more fruitful to contact them.