Waterjetting 7c - higher pressure washing with power

In the last post, on surface cleaning, I showed how the jet from a fan nozzle spread very quickly once the water left the orifice. With this spread the stream got thinner, to the point that, very rapidly the jet broke into droplets. These droplets decelerate very rapidly in the air, and disintegrate into mist which rapidly slows down. That mist has little capacity but to get a surface wet, and thus, within a very short few inches, the jet loses power and the ability to clean.

How can we overcome this? Obviously the jet would work better if it could carry the energy to a greater distance. And the jet that does that (as we know from trips to Disney) is a cylindrical stream. In some parts of the cleaning trade this is known as a zero degree jet, to distinguish it from the fifteen degree or other angular designation of the fan jet nozzles that it is often sold with.

But the problem with a single cylindrical jet is that it has a very narrow point of application. Depending on the standoff from the nozzle to the target this will increase a little as the distance grows, but is still likely to be less than a tenth of an inch. That, by itself, would make cleaning a bridge deck a long and laborious job. But consider that if we spun the jet so that it is tilted out to cover a 15 degree cone, the same angle as the best of the fan jets, the water would travel further. With a good nozzle it is possible to extend the range to 3 ft, rather than the typical 4 inches of a fan jet.


Figure 1. The gain in performance when a fan spray is changed to a rotating cylindrical jet. (initially proposed by Veltrup, these are our numbers).

In both cases the water flows out of the orifice at the same volume and pressure. But with the rotating jet the water is able to carry the energy some 9 times as far. As a result the area covered is 9-times as wide, and the job is carried out faster.

You can also look at it another way. It takes only about 10% of the water and the power to clean the surface with the rotating jet, as opposed to the amount required to clean with the fan jet. This is even though the pump unit and the flow rates are the same in both cases. This is why, when you buy some of the smaller pressure washers, they include a nozzle that has a round orifice and which then oscillates within a holder. Not quite as efficient as a controlled movement, but at least it is a start.

Now, of course, life is never quite as simple as it at first appears. Because the jet is being rotated there is sometimes, if the jet is being spun fast enough, some breakup of the jet because of the speed of rotation. And so, in the above example, too high rotation speed would have a disadvantage. Doug Wright showed this in a paper he presented to the WJTA in 2007.
Figure 2. The effectiveness of a rotating jet, at two speeds and at different distances (Doug Wright 2007 WJTA Conference Houston).

On the other hand because the jet has to make a complete rotation before it comes back to the same point on the coverage width, if the lance is moving too fast relative to that turning speed, then the jet will miss part of the surface that it is supposed to be cleaning.

I can illustrate this with a sort of an example. To make it obvious the rotating jet has enough power to cut into the material that it is being spun, and moved over. If the rotation speed is too slow, relative to the speed that the head is moving over the surface, then the grooves cut into the surface won’t touch one another and small ribs of material are left in the surface. This is not a good thing, either from a cleaning or mining perspective. The material we were cutting in this case was a simulated radioactive waste, that an improved design later went on to extract as a “hot” material in a real world project. These materials tend to be unforgiving if they are not properly cleaned off.


Figure 3. Cutting path into simulant showing the grooves and ribs where the rotation speed is not properly matched to the speed of the head over the surface.

There is another answer, which is becoming more popular for a couple of different reasons. If the pressure of the water is increased, then the jet will remain coherent for a greater distance, at a higher rotation speed. Going to a higher rotation speed, also brings in an additional change in the design of the cleaning head.


Figure 4. Cleaning head concept sectioned to show vacuum capture of the debris through the suction line after the jet has removed the material and washed it into the blue cylinder.

As the pressure increases, so the energy of the water and the debris rebounding from the surface increase. To a point this is good, since once they are away from the surface it is relatively simple, if the cleaning operation is confined within a small space by a covering dome, to attach a vacuum line to the dome, and suck all the water and debris into a recovery line. The surface remains relatively dry, all the water and debris is captured, and the tool can be made small enough, and light enough, that it can be moved either by a man or on the end of a robotically controlled arm. (The arm we designed the head for was over 30-ft long, which means that the forces from the jets had to be quite small).

With the higher pressure also comes the advantage that the amount of water that is required, for example to remove a lead-bearing paint from a surface, is much lower. If the water becomes contaminated by the material being washed off, then not only has the total volume to be collected, which is an expense, but it also must be stored and then properly be disposed of. And that may cost several times the cost of the actual cleaning operation, if the contaminant is particularly nasty. So reducing the volume of the water is particularly useful.

A friend of mine called Andrew Conn came up with the idea, for removing asbestos coatings from buildings, of tailoring the pressure and the flow from the nozzles, so that the amount of water required was just enough that it was absorbed by the asbestos as it was removed. Simplified and reduced the costs of cleanup, where that was a significant part of the overall price.

And speaking of using higher-pressure water, this means that there is no need for the abrasive additive, when cleaning say a ship hull. And that means that there is no need to buy, collect, and dispose of the abrasive during the operation.


Figure 5. Spent cleaning abrasive at a shipyard.

There are other advantages to the use of high pressure water over abrasive when cleaning metal, and I’ll talk about that subject a little next time.

Deepwater Oil Spill - making the connection

The Deepwater Horizon relief well is approaching the point where it will intersect the original well bore. At the moment production is being maintained through the existing riser remnant and overlying cap and LMRP. The latest figures are:

For the first 12 hours on June 29 (midnight to noon), approximately 8,475 barrels of oil were collected and approximately 4,130 barrels of oil and 28.7 million cubic feet of natural gas were flared.

On June 28, total oil recovered was approx. 23,395 barrels:
approx. 16,275 barrels of oil were collected,
approx. 8,175 barrels of oil were flared
and approx. 56.2 million cubic feet of natural gas were flared

As the well continues to descend there will likely be an increased focus on determining exactly where the two wells lie, one to another. This requires a process that pulls the drill string each time, and so progress is likely to be slow as the RW reaches the level at which the entry into the original well will be first tried.
Kent Wells has described the process. But he does not describe how the wells will be connected. And I will make a little more detailed description of a possible way of doing this, that John Wright has used before, at the end of the post.


Note that Kent Wells points out that the ranging runs do not start until the final set of well casing has been set. (And this was completed on June 19th). Once the casing has been set, the procedure calls to drill 275 ft of MD (measured depth), and then pull the drill.


The instrument package is then run into the hole with a Vector Magnetometer, which is mounted on a wire to carry it in and out (known as a wireline). The process of drill and test, using the Magnetometer, continued until the steel casing in the original hole had been detected.


The process is illustrated a little better in the video of the visit to the relief well team:


Once the initial well has been found the procedure changes. Now after the well has drilled down an additional interval (a distance decided by those monitoring progress) instead of pulling the string all the way out and running the wireline in open hole to find the casing, the bit is only retracted to the cased section, and the magnetometer package is wirelined down inside the drill string.

At present they have made two ranging runs, and have found the initial casing, so that then know that they were 55 ft from it, and they have 16 degrees to turn the well through yet to get it parallel to the original. They have decided that this “additional interval” will be 125 ft, and then they will make another ranging run.

But the process is now changed so that in the new run this will be where the instrument is run inside the DP (drill pipe) instead of pulling it to the surface. After making a measurement it is pulled back out on the wireline. And then the drill can advance the hole a little, it then is backed off the bottom, and the magnetometer again is lowered and locates the original casing, this is plotted and the process repeated. Only the wireline was pulled to remove the magnetometer from the well during drilling (to allow mud to the bit to cool it and remove drill cuttings).


Once the RW passes the original well it will be turned to drill parallel with it and drill down its own 10 1/8th inch hole until it reaches a point just above where the 9 7/8th inch casing liner ended at the bottom of the original hole.

With the new well 50 ft above this point, and 5 ft from it, the relief well will be reamed at the bottom using a 12 ¼” reaming bit to widen the well at the bottom.


A 9 7/8” steel liner will then be run into the hole and cemented into place in the relief well, running back up to the 11 7/8” casing that was set at the beginning of the process.

The relief well will then end 50 ft above the bottom of the 9 7/8” liner length in the original well and 5 ft from it. (Remember that there are questions as to whether the oil is flowing up around the outside of the steel tube inside this one, or up the middle of it).

Now what is interesting, and missing from the presentation, is how the connection between the two wells is made. There is also a little discrepancy over where the hole will be reamed and the 9 7/8” casing will be run to. In the animation it is shown as 17,050 ft (above) and in the visit to the rig, at 17,758 ft. (I think, based on looking at the log that that number should be 17,158 ft, for the top of the 7” x 9 7/8” casing, which is the problem length.


So the BP discussion ends with the RW 50 ft above, and 5 ft over from where the problem might be located (at the bottom of the lined well length) where the oil and gas may be seeping up the outside of the production casing and entering the well.

Let’s remember what the well liner and casing look like, down at the bottom of the hole.


So the question is, once the well is at the bottom of the lined section, are they going to:
a) try and drill down into the leaking zone below the last liner section, intersecting this to use the channels created to carry the mud from the RW into the original well.
b) Mill over to the liner segment of the well and through it into the annulus between the production casing and the liner, and try bottom kill from there.
c) Drill further down and over to mill through and access the production casing, and inject the mud into this to kill the well.

I suppose it depends on what they find at the point where they set the casing at the bottom of the next interval. (I had planned to talk about the bits they planned to use for the milling, but 5 ft is a long way between the two wells to establish a connection, though presumably this was the distance that has been used in the past when wells were killed this way. John Wright has previously done this by attaching a milling bit to a mud motor and drilling over into the casing and down along it. These are illustrations from a brochure of previous jobs:


And the illustration of the milling bit (which can make the cut in only a few seconds).


Incidentally the company is now part of Boots and Coots.

2009 Energy Conference - Renewable fuels

The renewable energies panel was moderated by Michael Schaal of EIA, and again took the form of a panel sitting around a table chatting. The panel each gave a short presentation and that took up most of the time before a short discussion.

Andy Arden of the National Renewable Energy Lab spoke mainly about the production path for ethanol, since the future supply of gasoline is likely to be flat, and ethanol provides therefore the only path to growth. He anticipates that with a 7% growth in use each year, the contribution from this fuel will grow from 2% to 15% of the total. A considerable part of the ultimate expansion in supply is to come from cellulosic ethanol, and the assumption, since companies are now constructing pilot and production plants, is that the techno-economic analyses are now coming up favorable. This is needed given that the target for that milestone is 2012, for it to be cost competitive, and that by 2022 the yield needs to be 21 billion gallons. The enabling bill has set specific targets for production after 2012, and all that is needed (ALL ??) is for the process to become cost effective.

The problem with that goal now is likely to be a lack of available credit, given the financial condition.

In the division of tasks for the National Labs, NREL deals with the thermo and chemical treatment of the biomass, INL and ORNL are responsible for the biomass production (including such examples as poplar). There is a concern however over logistics and an understanding of the issues of both quality and quantity. Because of scale issues in the economics of these plants a 5-mile gathering radius is too small, but as one goes to a larger harvesting radius then the costs of the harvesting, transport and storage also begin to factor into the equation (see the story from Dubuque). The resulting ethanol has to live within a price spread that makes it viable, which is thought to be around $2.50 as an equivalent price to gasoline).


Unfortunately the long-term numbers are not inspiring for ethanol, it is the current “biofuel du jour” mainly because it only “requires only one miracle to work” while some of the alternatives require several. And so there is a need to look beyond ethanol, to those technologies that, usually based on bacteria, will generate other fuels generally through aqueous phase reforming. One that I had not heard much of before was dark algae, which is a form of algae grown in the dark, that feed on sugar. Companies to watch in these areas are Virent, but the challenge will always be in the provision of an adequate feedstock at an acceptable price.

Matthew Hardwick of the Renewable Fuels Association lists 26 cellulosic programs, but things arre changing, since now credit is hard to come by and this is a capital intensive industry. He felt that the EPA models that consider ethanol were too low when it came to judging it against a carbon production standard, and felt that it was less of a polluter than it was painted to be. But there are other constraints, such as water and land use, that are only now becoming evident as plans to scale up production start to be put in place. And in developing the market forward, there is a blend wall that comes into play at 10% of the fuel market. This will hurt the ability to meet the target goals since they require that ethanol surplant gasoline at levels above 10% of the blend. The hope, therefore, is that EPA will change the mix max to 15% with the target of using an E50 by 2015. However once the mix gets to 12% engines will need to be changed to effectively use the new blend.

Denise Bode (who is the voice on the video at the American Clean Skies website, though is now with American Wind Energy) talked about the benefits of the coming growth in Wind Energy. Though did recognize that there are some concerns about transmission to get it where it needs to be.

Bryan Hannegan of EPRI spoke more from the point of view of the utilities, and noted that renewables still have a long way to go to ramp up to the levels of scale of production that are needed. He quoted a fiure of $27 a ton for carbon credit (allowance) that comes in in 2015, as being part of the models that they use for prediction. In their models gas prices float in the $4.95 to $7.95 range. But in looking at a goal of 35% of the national energy coming from renewables by 2050, there are some things that still must happen. Bear in mind that for that much penetration the renewable source must replace some of the existing legacy systems that are well established, and paid for. Without that there is not enough market for the growth.

He sees wind being the initial market penetration, penetrating even into the Tennessee Valley where there isn’t much wind, and a lot of competition. He had some land use and water concerns over biomass, though this will also be a big player by 2050. From the generation stations there will then be the need for transmission and linkage into the coming smart grids and those also are questions not yet answered. The EPRI position is spelled out in a report available on the EPRI website. He noted that just using natural gas as a fall back when the wind does not blow will put too high a demand on dedicated gas turbines, and that just relying on the grid being big enough so that the wind will be blowing somewhere might be a little optimistic. In the end he felt that to meet the carbon goals the country will need to do more than just rely on the renewables.

It was further noted in the discussion that less than half of the country could name a renewable fuel. And we need to avoid complacency over energy supply when business returns to normal.