Posts

#1: Does Wood Sink ?

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Yes, it does ! Live wood sinks....try to break a twig from your garden and drop it in a cup of water!  Live wood is heavier than water because it is  water-logged . Dry, dead wood does not sink...but it can be  water-logged  to sink again.  We can  water-log  wood by submerging wood for  many weeks . Or  in a few minutes  by putting wood under high pressure in water. See Pine wood samples in the picture above, all kept for 10 minutes under pressurized water.  The sample "AT" to the right  was in water under the highest pressure (1000 PSI) and  now it sinks.....! NEXT POST

#2: Why bother sinking wood ?

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There is a really good reason to store wood (and other waste plants) in the deep ocean.   Wood is mostly made of carbon dioxide from the atmosphere.  Less than 2% of a plant is made of soil minerals.  So, a plant is a free and efficient CO2 collector .   We use many parts of plants, but some parts are not useful and are thrown away in landfills, burned or left to decay. Due to global warming, more and more waste plants are available. Ocean storage of this waste material will prevent that much CO2 from being returned to the atmosphere. The ocean already stores a vast amount of carbon dioxide- 135 Trillion tonnes!  It is safe to add any extra CO2 from the atmosphere into the deep ocean, where it will be safely stored. Plants have been flowing to the ocean for millions of years, so plant material is a natural part of the ocean.  A single large storm can transport millions of tons of plant biomass into the ocean. For more detailed science and the potential effectiveness of the method, pl

#3: What is P(max) ?

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Now it is getting interesting ! Different kinds of wood sink at different pressures. The graph above shows five types of wood treated for 10 minutes with a range of pressures, as shown in the x-axis. The height of the line, in the y-axis, shows the length of time the samples sank. At a critical pressure, the wood samples sink for a long time, as shown  by the sharp upturn of the graph lines.  We tracked it for a few weeks, and concluded that the samples would stay sunk forever. We called this pressure P(max), because applying more pressure than this is not necessary to sink wood permanently.   We will say more about this in a later post. Actually, even at pressures less than P(max) , the wood samples did sink, but for only a small amount of time. You have to look closely to see this, at the bottom of the graph. There is a better way to view this, and we will describe it in the next blog post. NEXT POST

#4: Is there a P(min) ?

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Now it is getting scientific ! The graph above is the same graph as the last post, but we changed the graph to magnify the small values and shrink the larger values in the y-axis. This type of graph makes it easier to see the changes in the smaller values and is called a semi-log plot. The graph ignores samples that did not sink at all.  Only numbers from sinking samples are plotted.  As described in the previous post, the pressure corresponding to forever sinking is P(max).   But.....there is also a P(min). So, for pine (blue), the first observed sinking is at 1000 PSI and the sample sank for 30 minutes then floated again.  This pressure is P(min) because it is the minimum pressure when sinking happens, for pine.  The first data point for each wood species in the plot above is P(min) for that species.   P(min) is very important, as we will see in the next post. NEXT POST

#5: P(max) vs. P(min) ?

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Now we can look into practical considerations. As we determined, P(max) for any wood species is the pressure needed to sink it permanently. In the real world, pressurized wood can be dropped in water and will sink all the way to the bottom, even the deepest ocean. The pressurization to P(max) can be done on land, or on a boat. But....in the ocean, there is no need to pressurize P(max) to sink wood. Water supplies its own pressure. For example, in the chart above, the P(max) for Pine is 1250 PSI.  This pressure naturally exists at 2500 ft depth.  So, if we bring Pine wood to 2500 feet below the ocean surface, it will simply sink permanently. But wait !   We don't even need to go all the way up to P(max) when we are already in the ocean. We can just go to P(min). Indeed, if we bring pine wood to the depth of 360 ft, corresponding to its P(min) of 150 PSI; it will start to sink.  Once it starts to sink deeper, the pressure will get higher. So it automatically reaches P(max) and is sun

#6: LIVE Video of Sinking !

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We now have live video!  So far, we were doing our tests in the dark - we could only check for sinking after pressure was released and samples were brought out of the pressure tank.  We recently upgraded our equipment to capture live video of the wood samples sinking inside the pressure tank.  We placed 13 species of wood, farm and fruit wastes in the tank and pressurized it. With the help of a small camera and light in the tank, we could see the sinking of the samples as we increased pressure.   The video shown HERE records the exact instant of sinking at P(min).  Most samples sank after a few minutes in 100 PSI. After 5 minutes, we increased the pressure to 200 PSI.  All except balsa wood sank in about a minute, indicating that pressure was more important than time in the sinking process.  Even balsa wood sank at 300 PSI, equivalent to about 680 ft depth in the ocean.   After varying pressures at 100 PSI steps, up to 500 PSI, we released pressure. All samples floated back up, confir

#7: Real World -- large pieces !

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Time for real world test ! So far, we had used small samples about half-inch cube to look at sinking behavior. To investigate practical conditions, we checked the sinking in the pressure tank with a large piece, about 4 x 4 x 4 inches redwood piece.  Previously, small samples had sunk in a minute or two at 200 PSI.  The large sample was allowed to sit at 200 PSI for 15 minutes and then pressure increased to 400 PSI.  After about 6 minutes at 400 PSI, or 1100 ft depth, the large piece sank. We concluded that for large pieces, 800-900 ft depth would be sufficient to reach P(min) Finally, we went to sea on a boat.  We took a redwood log (picture above) about 2 ft diameter and 2 ft tall and sank it in the ocean at 1000 ft for 30 minutes. We did not have the equipment to detect live sinking, but when the log was brought back up to the surface, it sank, confirming we had reached P(min).  After 5 minutes, it floated, indicating that P(max) was not reached.  When working in the ocean, it is mu